MicroRNAs and Metabolism Crosstalk in Energy Homeostasis

Please cite this article in press as: Dumortier et al., MicroRNAs and Metabolism Crosstalk in Energy Homeostasis, Cell Metabolism (2013), http:// dx.doi.org/10.1016/j.cmet.2013.06.004

Cell Metabolism

Review MicroRNAs and Metabolism Crosstalk in Energy Homeostasis Olivier Dumortier,1,2,3 Charlotte Hinault,1,2,3,4 and Emmanuel Van Obberghen1,2,3,4,* 1INSERM

U1081, Aging and Diabetes team UMR7284 Institute for Research on Cancer and Aging, Nice (IRCAN), 06107 Nice, France 3University of Nice—Sophia Antipolis, 06100 Nice, France 4Clinical Chemistry Laboratory, University Hospital, 06001 Nice Cedex 1, France *Correspondence: [email protected] http://dx.doi.org/10.1016/j.cmet.2013.06.004 2CNRS

In record time, microRNAs (miRNAs) have acquired the respected stature of important natural regulators of global gene expression. Multiple studies have demonstrated that a large number of miRNAs are under the control of various metabolic stimuli, including nutrients, hormones, and cytokines. Conversely, it is now well recognized that miRNAs control metabolism, thereby generating a bidirectional functional link, which perturbs energy homeostasis in case of disconnection in the miRNA-metabolism interplay. A challenging road lies ahead for defining the role of miRNAs in the pathogenesis of diseases such as diabetes and for establishing their usefulness as new medications and clinically reliable biomarkers. Introduction Metabolism could be viewed as a box containing a gamut of finely regulated biochemical processes that convert fuel from food into the energy needed for organisms to develop, grow, and survive. To maintain these complex biological destinies in spite of internal and external perturbations, cells need to produce a constant supply of energy and derive the precursors necessary for synthesis of nucleic acids, proteins, carbohydrates, and lipids. Cell homeostasis is maintained by the intricate orchestration of a multitude of signaling pathways and ‘‘energetic sensors’’ in tissues and organs. For maintaining this energy balance, induction or repression of metabolic pathways must be adapted to satisfy the energetic demands of cells. The metabolic pathways are governed by an integrative network of signaling cascades, and conversely, the cell metabolic profile influences signal transduction by incorporating various metabolic sensors into the constellation of signaling molecules. A new class of small noncoding RNAs, termed microRNAs (miRNAs), has added an additional level of complexity to the control of metabolic homeostasis. miRNAs are short, single-stranded noncoding gene products, typically 20–22 nucleotides long. The mammalian genome codes for several hundred miRNAs that regulate gene expression through modulation of target messenger RNAs (mRNAs). miRNA biogenesis consists of a series of sequential steps that convert primary miRNA transcripts into biologically mature and active miRNAs (Bartel, 2009; Kim et al., 2009). Most miRNAs interact with specific sequences in the 30 UTR of mRNA. In contrast to plants, in which miRNAs are usually fully complementary to their mRNA targets and promote RNA cleavage and degradation, metazoan miRNAs usually exhibit only partial sequence complementarity to their mRNA targets and promote translational repression rather than mRNA cleavage. However, a recent publication reveals that in mammals, miRNAs would predominantly act to decrease target mRNA levels. Indeed, miRNA destabilization of the mRNA target appears to be the chief cause of reduced protein output (Guo et al., 2010). Computational pre-

dictions of miRNA targets estimate that a single miRNA can regulate hundreds of different mRNAs, suggesting that a large proportion of the transcriptome is subjected to miRNA regulation. Hence miRNAs may modulate up to 30% of all human genes. The biological importance of miRNAs is clearly evidenced by the diverse and profound phenotypic sequels upon changes in their expression. These alterations are associated with perturbed development and pathological conditions. Indeed, miRNAs function as major regulators of gene expression in many biological programs including cell lineage differentiation, as well as embryonic and organ development (Dumortier and Van Obberghen, 2012; Poy et al., 2007). Furthermore, studies have demonstrated that a large number of miRNAs are under the control of various important signal-transduction cascades. These miRNAs contribute to the regulation of different signaling pathways via the repression of their target mRNAs, which results in the modulation of signal transduction (Kim et al., 2009). Although the complex mechanisms of action and the multipronged impact of miRNAs on animal development, physiology, and disease have not been fully elucidated, significant progress has been made in deciphering the individual roles of certain miRNAs in specific biological contexts. Furthermore, models of the regulatory network of miRNAs have been proposed (Ebert and Sharp, 2012; Leung and Sharp, 2010; Mendell and Olson, 2012). In this review we summarize recent advances in our understanding of the emerging roles of miRNAs in the control of metabolism in normal and pathological situations. The regulation of miRNA expression by metabolic stimuli, including nutrients, hormones, and cytokines, is addressed. Finally, we briefly discuss extracellular miRNAs and their potential use as biomarkers of disease situations and the possibility of miRNA-targeted therapies. Regulation of miRNA Expression by the Genomic Environment miRNAs are generated following intricate reactions that promote the sequential cleavage, export, and loading of miRNA into Cell Metabolism 18, August 6, 2013 ª2013 Elsevier Inc. 1

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Review silencing complexes. A growing body of evidence suggests that each of these steps is a potential node of regulation and therefore provides expanding level of complexity to miRNA-dependent gene modulation. The precise regulation of all these actors in miRNA biogenesis was recently reviewed and will not be discussed here (Finnegan and Pasquinelli, 2013). Transcription is one of the major regulatory steps in miRNA biosynthesis. The features of miRNA gene promoters are similar to the promoters of protein-coding genes, and miRNA transcription is known to be controlled by transcription factors similar to those of protein-coding genes (Kim et al., 2009). However, depending on their genomic localization miRNAs can be under the influence of their own promoter or of that of their host genes. miRNA genes are categorized as intergenic, intronic, or exonic according to their genomic location. Intronic miRNAs are harvested in the introns of both proteincoding and noncoding annotated genes. Approximately 40% of mammalian miRNAs are located within the introns of protein-coding genes (Kim et al., 2009). These miRNAs can be present as a single miRNA or as a cluster of several miRNAs. Intronic miRNAs can be transcribed from the same promoter as their host genes and processed from the introns of the host-gene transcripts. This relationship sets the stage for a coordinated expression pattern of intronic miRNAs and suggests that their host genes could establish a concerted action between them. One of the best-described examples of coregulation of mRNA and miRNA is the association between miR-483 and IGF-2 (insulin-like growth factor-2), an insulin family member that plays a crucial role in body-growth regulation. A few years ago, miR483 was identified as an intron-derived miRNA contained within the second intron of the Igf-2 gene (Landgraf et al., 2007). More recently, it was demonstrated that both miR-483 and Igf-2 mRNAs are generated from the same primary transcript. Furthermore, Igf-2-derived intronic miR-483 is involved in hepatic metabolism through downregulation of its target Socs-3 (Ma et al., 2011). Another remarkable example of coordination between miRNA and host-gene action concerns the sterol-regulatory element-binding protein (SREBP) transcription factors and their intronic miRNAs mir-33a and miR-33b, which cooperate to reduce cholesterol efflux and increase cholesterol biosynthesis (Najafi-Shoushtari et al., 2010). Most miRNAs are precisely regulated in a tissue- and development-specific manner for the accomplishment of their specialized functions. As mentioned above, the expression pattern of miRNAs depends in part on their host genes. However, intergenic miRNAs occur in the genomic regions distinct from the known functional transcription units. Intergenic miRNAs can be monocistronic or polycistronic and are known to have their own promoters and other regulatory elements. For example, pancreatic islet cell-specific expression of miR-375 is regulated, at least partly, at the transcriptional level (Avnit-Sagi et al., 2009). Indeed, a region in the miR-375 promoter, particularly sensitive to mutation, contains consensus binding sequences for Hnf6 and Insm1, which have been implicated in the development and function of pancreatic islets. Moreover, enhancer boxes are required for full transcriptional activity, suggesting that the miR-375 gene may be regulated by bHLH transcription factors such as Ngn3 and NeuroD1 (Avnit-Sagi et al., 2009). In addition, chromatin immunoprecipitation revealed that NeuroD1 interacts 2 Cell Metabolism 18, August 6, 2013 ª2013 Elsevier Inc.

with conserved sequences both upstream and downstream of the miR-375 gene. Finally, exonic miRNAs, which occur less frequently than intergenic or intronic miRNAs, are encoded by exons of non-protein-coding transcripts, and their transcription appears to be controlled by their host-gene promoter (Rodriguez et al., 2004). Regulation of miRNA Expression by the Metabolic Environment Cytokines Maintaining metabolic homeostasis requires a balanced immune response, which is achieved by extracellular signals, including cytokines. It is anticipated that perturbation of this equilibrium could result in pathological situations. Indeed, increased levels of markers and mediators of inflammation strongly correlate with the occurrence of diabetes. miRNA expression is sensitive to cytokines, and induction or repression of miRNAs in response to inappropriate cytokine stimulation may lead to the disruption of cellular homeostasis. For example, murine and human pancreatic islets exposed in vitro to proinflammatory cytokines display changes in their miRNA expression profiles (Roggli et al., 2010, 2012). Among them, miR-21, miR-34a, miR-146a, and miR-29 family members have been shown to contribute, at least partially, to cytokine-mediated b cell dysfunction occurring during the initial phases of type 1 diabetes (T1D) in nonobese diabetic (NOD) mice. This indicates that proinflammatory cytokines trigger a complex response resulting in modulation of the expression of islet miRNAs, with important consequences for b cell survival. Hormones One of the mechanisms controlling miRNA biogenesis includes hormonal regulation. For instance, estrogens hamper miRNA production by affecting a posttranscriptional event (Yamagata et al., 2009). Specifically, estrogens suppress the levels of a miRNA set including miR-125a and miR-145 in murine and human cells. In vitro, hormone-bound estrogen receptor a inhibits miRNA maturation by associating with the Drosha complex and preventing the conversion of pri-miRNAs into pre-miRNAs. Furthermore, a role for miRNAs in the hormonally regulated expression of estrogen target genes was revealed. Additional studies have suggested that sex steroid hormones exert posttranscriptional control through the regulation of miRNA processing and expression (Cochrane et al., 2012; Klinge, 2009). In some cases, miRNA modulation by hormones can reenforce the hormone-signaling pathway. For example, insulin, a major hormone in the homeostasis of energy and metabolism, was implicated in the regulation of miRNA expression. Indeed, in human skeletal muscle, insulin decreases the expression of 39 miRNAs (Granjon et al., 2009). Their potential target mRNAs code for proteins that appear to be mainly involved in insulin signaling and ubiquitination-mediated proteolysis. Bioinformatic analysis suggests that combinations of different downregulated miRNAs act in concert to regulate gene expression in response to insulin. In addition, impaired regulation of miRNAs by insulin was found in skeletal muscle of type 2 diabetic (T2D) patients. This suggests that in T2D some of these miRNAs might be implicated in insulin resistance and/or be the consequence of it. Further evidence for hormonal modulation of miRNA expression was provided by the demonstration in rodents that

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Review Metabolic stimuli

miRNA biogenesis & expression

Nutrients Hormones Cytokines

Epigenetic modulators

METABOLISM HOMEOSTASIS

Transcription factors

Biological effects

Signaling molecules

METABOLIC DISEASES

Figure 1. Conceptual Model of the Multipronged Impact of miRNAs on Cell Metabolism Metabolic stimuli (nutrients, hormones, and cytokines) induce changes in miRNA expression and biogenesis that affect these stimuli, generating a bidirectional functional relationship. Altered miRNA levels may cause changes in gene expression through translational suppression or mRNA cleavage, leading to cellular dysfunction favoring the occurrence of metabolic diseases.

pancreatic b cell mass expansion during pregnancy and obesity is related to changes in the expression of several miRNAs, which regulate b cell proliferation and survival (Jacovetti et al., 2012). In isolated islets, activation of the G protein-coupled estrogen receptor GPR30 and the glucagon-like peptide 1 receptor mimics the modulation in miRNA expression observed during gestation and obesity. Blockade of miR338-3p in b cells reproduces changes occurring during b cell mass expansion and results in increased proliferation and survival both in vitro and in vivo. Thus, miR-338-3p is directly regulated by estradiol and functions as an essential downstream effector in the pathway. Nutrients In humans, miRNAs potentially modulate the expression of about one third of mRNAs, and hence are anticipated to affect multiple chief signaling pathways by targeting transcription factors, secreted factors, receptors, and transporters. The plausible importance of miRNAs in metabolism stems from the observation that misexpression of miRNAs occurs in several human metabolic disorders. Given the key role of nutrients in the regulation of metabolism, one could expect that changes in miRNA expression in response to nutrient availability may affect, at least partly, the regulation of cell metabolism. Although multiple studies examined the dietary modulation of miRNA expression in the context of nutrition and cancer prevention (Ross and Davis, 2011), only scant information is available on dietary modulation of miRNAs in relation to metabolism. Nevertheless, evidence is emerging that chief nutrients, such as glucose and lipids, modify the expression of miRNAs in rodents and in humans (Lovis et al., 2008b; Zampetaki et al., 2010). A common method of identifying miRNAs potentially induced by nutrients involves miRNome analyses of animals fed with particular diets. This approach has revealed miRNAs with modified expression

and led the way to their functional analyses. Thus, Carrer et al. (2012) demonstrated that miR-378 and miR-378* (generated from a common hairpin precursor) are upregulated in the liver of mice fed a high-fat diet. Interestingly, genetic disruption of miR-378 and miR-378* in mice confers resistance to highfat-diet-induced obesity. Furthermore, these transgenic mice exhibit enhanced mitochondrial fatty acid metabolism and elevated oxidative capacity in insulin target tissues (Carrer et al., 2012). Taken together, miR-378 and miR-378* appear as integral components of a regulatory circuit controlled by lipids and impacting organismal energy homeostasis. Glucose was also found to regulate miRNA expression. A few years ago our group was the first to show that incubation of freshly isolated rat pancreatic islets or INS-1E insulinoma cells with glucose reduces miR-375 levels. In INS-1E cells, decreased miR-375 expression induced by high glucose concentration occurs concomitantly with increased insulin signaling and with augmented DNA synthesis. This could explain, at least in part, the stimulatory action of glucose on b cell growth. At present, the molecular route leading to this glucose effect on miRNA expression is unknown (El Ouaamari et al., 2008; Keller et al., 2012). Remarkably, our pioneering observation on glucosemediated miRNA expression is not unique to miR-375; similar effects were recently observed for other miRNAs (Garcı´a-Segura et al., 2013). In summary, a growing body of evidence suggests that two major nutrients, glucose and lipids, take advantage of the miRNA machinery to modulate energy metabolism. An urgent challenge for metabolic disorders is to define the molecular mechanisms linking nutrition and miRNA expression and to discover derailment contributing to diseases such as obesity and T2D. miRNA-Induced Regulation of Metabolic Stimuli Cytokines and Hormones Although miRNA expression is regulated by different stimuli, including cytokines and hormones, some miRNAs modulate the secretion and action of these soluble mediators, generating a bidirectional functional link (Figure 1). Actually, most, if not all, molecular components of multiple signaling pathways may be impacted by miRNAs according to computational algorithms for miRNA-mRNA target predictions. However, despite a myriad of theoretically possible interactions, only few have been experimentally validated so far. For example, several miRNAs have been implicated in the regulation of cytokine production and action. Among them, miR-126 and miR-193b affect the synthesis of the adipocyte inflammatory chemokine CCL2 directly by targeting the CCL2 mRNA and indirectly through a network of transcription factors (Arner et al., 2012). Hence, these miRNAs may be important regulators of adipose inflammation through their effects on CCL2 release from human adipocytes and macrophages. Recent findings suggest that hormone-modulated miRNAs play a substantial role in hormone-receptor-mediated gene regulation, generating a feedback loop. Indeed, the expression of some miRNAs modulated by sex-steroid hormones impacts estrogen and progesterone action. Moreover, some miRNAs appear to affect steroid hormone release, although the molecular mechanisms remain to be revealed (Cochrane et al., 2012; Klinge, 2012). Cell Metabolism 18, August 6, 2013 ª2013 Elsevier Inc. 3

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Review A

B

C

Figure 2. Conceptual Views of miRNA Regulation of Insulin Secretion and Action

Lessons from Insulin Secretion and Action We pay particular attention to miRNAs involved in the regulation of insulin secretion and action, because insulin is the master operator of glucose and lipid metabolism. Remarkably, miR375, which is the most abundant miRNA in pancreatic islets, was the first miRNA to be implicated in hormone secretion (Poy et al., 2004). Indeed, forced miR-375 expression in insulinoma cells leads to reduced glucose-stimulated insulin secretion (GSIS) without interfering with glucose action on ATP production and intracellular calcium levels. More specifically, miR-375 directly interacts with the 30 UTR mRNA of myotrophin, involved in insulin-granule fusion with the plasma membrane, and thereby inhibits exocytosis. We found that miR-375 downregulates insulin-gene expression in INS1-E cells by acting on phosphoinositide-dependent kinase-1 (El Ouaamari et al., 2008), which was the second functionally identified miR-375 target. Interestingly, myotrophin is targeted by other miRNAs such as miR-124 and let-7b (Krek et al., 2005), illustrating the notion of convergent action by multiple miRNAs with the same target (Figure 2A). Inversely, a single miRNA such as miR-124a can target different mRNAs to regulate the same cellular process (Figure 2B). Indeed, we reported that miR-124a binds to the 30 UTR mRNA of the forkhead box protein A2 (FoxA2) transcription factor, which is a prime regulator of pancreatic development and of genes involved in glucose metabolism and insulin secretion (Baroukh et al., 2007). Increasing the miR-124a level in MIN6 4 Cell Metabolism 18, August 6, 2013 ª2013 Elsevier Inc.

b cells decreases the Foxa2 protein, reducing its downstream targets, including the ATP-sensitive potassium channel subunits Kir6.2 and Sur-1, which are crucial for insulin release. In addition, miR-124a alters the expression of other components of the insulin exocytosis machinery (Lovis et al., 2008a). Indeed, miR-124a increases the levels of SNAP25, Rab3A, and synapsin-1A and decreases those of Rab27A and rabphilin-3A-like (Noc2). However, so far miR-124a has only been shown to directly interact with the 30 UTR mRNA of Rab27A. miR-9 decreases insulin secretion through its interaction with the mRNA of the Onecut-2 transcription factor, which reduces granuphilin/Slp4 expression (Plaisance et al., 2006), and through Sirt1 (Ramachandran et al., 2011). The impact of miRNAs is not restricted to insulin secretion, but also concerns insulin signaling and actions, which are mediated by a complex, highly integrated network of pathways (Taniguchi et al., 2006). Based on in silico analyses, the majority of miRNAs appear to be able to modulate the protein abundance of key signaling components of the insulin pathway by acting at several levels. However, these interactions need to be validated in the diverse insulin target tissues, which exert specific functions in the organism. miRNAs are detected in various metabolically active tissues including the endocrine pancreas, liver, muscle, and adipose tissue. Some miRNAs display a tissue-specific expression, suggesting a particular function for these miRNAs. As mentioned earlier, miR-375 has

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Review Figure 3. Misexpression of a Single miRNA in One or More Insulin-Sensitive Tissue(s) Leads to Whole-Body Metabolic Dysfunction

Liver Let-7

IR, IRS-2

miR-103/107

Cav1

miR-143

ORP8

miR-802

Hnf1b

let-7, whereas miRNAs acting on downstream molecules are likely to exert more specific effects, as seen with miR-29 (Figure 2B). Indeed, miR-29a/c Skeletal muscle overexpression in primary hepatocytes Let-7 ? and livers from mice decreased the miR-375 Mtpn protein levels of peroxisome proliferator-activated receptor g coactivator-1a (PGC-1a) and glucose-6-phosphatase Endocrine pancreas Cav1 miR-103/107 (G6Pase), thereby reducing glucose production. Conversely, loss of miRmed13 Adipose ssue 29a/c function in primary hepatocytes augments the protein levels of PGC-1a and G6Pase and increases glucose miR-208 production. Interestingly, forced PGC1a expression increases miR-29a/c Heart expression in primary hepatocytes, thus forming a negative feedback regulation loop (Liang et al., 2013). At the organa robust expression in pancreatic islets (Poy et al., 2004), ismal level, miR-29a/c lower fasting glycemia levels by blocking whereas miR-122 is more specific to the liver, and they have hepatic gluconeogenesis through the regulation of downstream respective roles in b cell physiology and hepatic lipid meta- actors of the insulin cascade. bolism, as described below (Esau et al., 2006; Kru¨tzfeldt et al., 2005). Inversely, some miRNAs are ubiquitously ex- miRNA-Induced Regulation of Energy Metabolism pressed and probably have a more general role in several By regulating the expression of important components of tissues, such as for let-7 (Figures 2 and 3). Indeed, the let-7 signaling pathways, miRNAs participate in a wide spectrum of family regulates multiple aspects of glucose metabolism in the biological processes (Figure 1). Because of this, they govern pancreas, liver, and muscle (Frost and Olson, 2011). Further- key aspects of organismal homeostasis, and their aberrant more, let-7 downregulates the phosphatidyl inositol-3-kinase expression eventuates in disease situations. A general con(PI3K) route at multiple sites by interacting with the 30 UTR sensus exists on the role of miRNAs as fine-tuners of metabolic mRNA of insulin receptor (IR), insulin growth factor-1 receptor processes in mammals (Rottiers and Na¨a¨r, 2012). Glucose and (IGF-1R), and insulin receptor substrate-2 (IRS-2) (Zhu et al., lipid homeostasis requires the presence of both insulin and the 2011) (Figure 2). Moreover, Lin28, a RNA-binding protein down- responsive target tissues to generate the appropriate biological regulating let-7, increases the protein abundance of IRS-2 in program. C2C12 myoblasts and of IR and IGF-1R in skeletal muscle. Glucose Metabolism Although the effects of let-7 and Lin28 on the expression of Glucose homeostasis is mainly regulated by the antagonistic individual genes are modest, simultaneous regulation of multi- couple formed by insulin and glucagon, secreted by pancreatic ple components of signaling cascades could explain how this b and a cells, respectively. miRNAs involved in secretion and/ RNA processing pathway coordinately regulates glucose meta- or action of these hormones are destined to impact glucose bolism and insulin action (Zhu et al., 2011) (Figure 2B). Further- metabolism. Although several miRNAs described above directly more, miRNAs can modulate insulin signaling by acting on a interact with components of the insulin secretion machinery, to common target to mediate a convergent action (Figure 2A). the best of our knowledge, none have been directly implicated For instance, in addition to let-7, miR-33a and miR-33b (miR- in glucagon secretion. Obviously, miRNAs critical for the devel33a/b) interact with IRS-2, and miR-126 targets IRS-1 (Da´valos opment of the endocrine pancreas and the establishment of et al., 2011; Ryu et al., 2011). Schematically speaking, multiple the appropriate islet cell mass will potentially exert an indirect miRNAs can have an additive action regulating different targets effect on hormone secretion and glucose homeostasis (Dumort(Figure 2C). Considering that Let-7, miR-33, and miR-29a down- ier and Van Obberghen, 2012). Interestingly, miR-375 knockout regulate IR, IRS, and PI3K, respectively, in hepatocytes and mice suffer from hyperglycemia and glucose intolerance associliver, they could act in concert to decrease insulin action (Da´va- ated with increased gluconeogenesis (Poy et al., 2009). This los et al., 2011; Frost and Olson, 2011; Pandey et al., 2011; Zhu hyperglycemia is thought to be primarily caused by hyperglucaet al., 2011). Finally, miRNAs regulating actors from the top of gonemia resulting from disrupted islet architecture with an inthe insulin cascade generate broad effects, as is the case for crease in a cell number in the islet core rather than increased

IR, IRS2

Let-7

Glucose homeostasis

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Review glucagon secretion per a cell. miR-375 deletion influences not only the a but also the b cell mass by modulating a group of genes governing cell growth and proliferation. To sum up, studies in cultured cells and in animals indicate that miR-375 exerts multiple and distinct effects and participates not only in pancreas development by regulating b and a cell mass, but also in the safeguard of b cell physiology. Additional miRNAs have been implicated in glucose metabolism and metabolic homeostasis in intact animals (Figure 3). The Lin28/let-7 axis regulates glucose metabolism, partially by targeting key insulin signaling components as mentioned above (Zhu et al., 2011). Indeed, muscle-specific Lin28a loss or let-7 overexpression induces insulin resistance and impaired glucose tolerance in mice. Moreover, global and pancreas-specific transgenic mice overexpressing let-7 display impaired glucose tolerance and GSIS (Frost and Olson, 2011). Reduced miR-103/107 expression in mice leads to improved insulin action and glucose homeostasis, whereas forced miR-103/107 expression is sufficient to induce impaired glucose homeostasis coupled to increased gluconeogenesis (Trajkovski et al., 2011). Improvement in insulin action by these miRNAs is attributed in part to caveolin-1 inhibition, which influences IR stabilization in lipid rafts. Mice deficient in the miR-143/145 cluster are protected from insulin resistance following a high-fat diet, whereas transgenic mice with induced hepatic overexpression of miR-143, but not miR-145, suffer from diminished insulin-stimulated Akt activation and glucose metabolism (Jordan et al., 2011). Interestingly, the oxysterol-binding-protein-related protein 8 (ORP8), a regulator of insulin-induced Akt phosphorylation in the liver, was identified as a miR-143 target by quantitative mass spectrometry. Recently, miR-802 was shown to inhibit Hnf1b in the liver, leading to decreased insulin action and impaired glucose tolerance in mice (Kornfeld et al., 2013). A fascinating and unexpected role of the cardiac-specific miR-208 in metabolism was recently revealed (Grueter et al., 2012). Indeed, reduced miR208 expression protects mice from obesity and reduces whole-body insulin action and glucose tolerance. These remarkable data uncover a novel role of the heart in systemic energy homeostasis. A hallmark of the models discussed in this paragraph is that the misexpression of a single miRNA in one or more insulin-sensitive tissue(s) suffices to perturb whole-body glucose homeostasis, indicating that these miRNAs affect major metabolic pathways (Figure 3). Lipid Metabolism Although the liver-specific miR-122 and miR-33a/b are recognized to directly regulate lipid metabolism, a number of other miRNAs are also implicated (Rottiers and Na¨a¨r, 2012). miR-122 was the first miRNA identified as tissue specific and is the most abundant miRNA in the liver. Among several studies, two pioneered in revealing the role of miR-122 in lipid metabolism regulation by in vivo antisense targeting (Esau et al., 2006; Kru¨tzfeldt et al., 2005). Indeed, miR-122 inhibition leads to decreased plasma cholesterol and triglyceride levels associated with altered cholesterol biosynthesis and increased fatty acid oxidation. Although several genes are regulated by miR-122, most of them have not been validated as direct targets. Several groups have highlighted the regulation of lipid homeostasis by the bifunctional SREBF2-miR-33a locus (Rottiers and Na¨a¨r, 2012). 6 Cell Metabolism 18, August 6, 2013 ª2013 Elsevier Inc.

Indeed, the Srebf2 gene encodes both SREBP2, which modulates cholesterogenic gene expression, and miR-33a located within an intronic region of the gene. miR-33b is found in an intronic region of the Srebf1 gene encoding SREBP1a/c, which modulates lipogenic gene expression. Interestingly, miR-33a and miR-33b target components of fatty acid degradation and cholesterol efflux. Therefore, SREBP proteins and miR-33 act in concert with their host genes as crucial regulators of cholesterol and lipid homeostasis. Other miRNAs have been related to lipid metabolism such as miR-370, reported to control the expression of miR-122 and its targets (Iliopoulos et al., 2010). miR-758 is thought to posttranscriptionally modulate the levels of the ABCA1 cholesterol transporter and cholesterol efflux from macrophages (Ramirez et al., 2011). Although the liver is the main tissue for lipid metabolism, adipose tissue likewise plays a crucial role, notably in lipid storage. Numerous miRNAs are involved in white-adipocyte differentiation including miR-103/107, miR-378/378*, miR-143, miR-21, miR-27a, and miR-130 (Hulsmans et al., 2011). In addition, miR-133 was recently shown to participate in brownadipocyte differentiation (Trajkovski et al., 2012). Amino Acid Metabolism Amino acid metabolism is also modulated by miRNAs. For instance, in mammals, miR-29b exerts control on a metabolic pathway of amino acid catabolism. Thus, miR-29b targets the mRNA of the dihydrolipoamide branched chain acyltransferase component of branched-chain keto acid dehydrogenase, which catalyzes the first irreversible step in branched-chain amino acid (BCAA) breakdown (Mersey et al., 2005). Increased miR-29b expression downregulates the rate-limiting step of BCAA degradation with accumulation of BCAA. BCAA homeostasis is crucial given that these amino acids account for up to 20% of the amino acids found in most proteins. Moreover, BCAAs play important roles in the regulation of hormone secretion (e.g., insulin), protein synthesis, and autophagy, notably through the modulation of the mammalian target of rapamycin pathway. miRNAs Mediating a Stress Response Biological systems are characterized by resistance to environmental changes to ensure proper health, but failure in the protective mechanisms will set the stage for exacerbated disease risk (Li et al., 2009). A groundbreaking concept in this context is that miRNAs are instrumental in generating biological robustness. Indeed, it is possible that miRNAs buffer fluctuations in gene expression generated by perturbations inside and/or outside organisms. A trailblazing example showed that in Drosophila, miR-7 is necessary for the proper photoreceptor development in eyes under conditions of temperature fluctuation (Li et al., 2009). Even though biological vigor is usually associated with phenotypic stability, physiological responses to stress such as aging, inflammation, or perturbed nutrient availability also need to be reproducible and robust (Mendell and Olson, 2012). Inappropriate responses often lead to pathological situations such as accelerated aging and diabetes. Aging and Longevity Aging is a complex, naturally occurring process characterized by an evolving homeostatic imbalance due to inapt metabolism, a progressive impairment of the organism to cope with environmental stress, and a growing frailty with increasing risk of

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Review disease (Vijg and Campisi, 2008). The first evidence that miRNAs act as aging modulators was gathered in C. elegans (Boehm and Slack, 2005). Studies in mammals suggest that miRNAs have similar roles in this overarching biological phenomenon. Indeed, comparison of miRNA profiles in younger and older mammals reveal that several miRNAs are differentially expressed (SmithVikos and Slack, 2012). These miRNA patterns generally appear to be tissue-specific, which is consistent with the tissue-specific functions of aging signaling pathways. For example, in mice the level of the key miRNA regulatory protein Dicer drops with age in adipose depots together with a declining level of several miRNAs. A similar decrease in Dicer with age occurs in C. elegans and in preadipocytes from elderly humans (Mori et al., 2012). In C. elegans and mice, this reduced Dicer level is prevented by caloric restriction, the most efficacious intervention delaying senescence and the onset of age-associated diseases. Dicer knockdown in cells with resulting decrease in multiple miRNAs impairs the ability of preadipocytes to respond to stress. Moreover the adipose-tissue-specific Dicer knockout mouse is more sensitive to oxidative stress. Thus, miRNA processing in adipose-related tissues plays an important role in aging, stress survival, and longevity (Mori et al., 2012). By contrast, when miRNA expression in the skeletal muscle of young humans was compared with that of older ones, 18 miRNAs were found to be differentially expressed, and let-7b and let-7e were upregulated (Drummond et al., 2011). These let-7 family members repress the cell-cycle regulators CDK6, CDC25A, and CDC34, as well as PAX7, which is important for muscle satellite cell turnover. Significant progress has been made in delineating biochemical and molecular pathways involved in aging. Twenty years ago it was discovered that the insulin/IGF-1 signaling (IIS) pathway influences lifespan (Kenyon et al., 1993). IIS is an evolutionarily conserved cascade that modulates longevity across many species. Multiple miRNAs participating in the regulation of this pathway have been identified. Among them is the miR17-92 cluster, which, along with its paralogous clusters, miR106a-363 and miR-106b-25, decreases with age and regulates cellular senescence (Grillari et al., 2010). These miRNAs target PTEN (phosphatase and tensin homolog), a lipid phosphatase inhibiting PI3K action. It is thought that their repression during aging causes an increase in PTEN levels, which results in attenuation of the IIS pathway. Other miRNAs target components of the IIS pathway. For example, in mouse brain and human fibroblasts, miR-470, miR-669b, and miR-681 suppress expression of the IGF1-R, which results in decreased phosphorylation of Akt and FOXO3. The latter is an important checkpoint of metabolic regulation, associated with human longevity (Pawlikowska et al., 2009). Although numerous miRNAs are differentially expressed during mammalian aging, many fundamental questions regarding their precise role and impact remain. Furthermore, for a grasp of the true influence of miRNAs in the multidimensional process of aging, it is crucial to identify the upstream factors that control the differential expression of these molecules during senescence at the cell, tissue, and organism levels. Inflammation It is widely recognized that chronic low-grade inflammation plays a key role in the initiation, propagation, and development of

metabolic disorders including T2D. Indeed, excessive levels of nutrients, including glucose and lipids, stress the pancreatic islets and insulin-sensitive tissues, leading to the local production and release of cytokines, which promotes inflammation (Donath and Shoelson, 2011). As mentioned above, miRNA expression is sensitive to nutrients and cytokines, and conversely, some miRNAs modulate the secretion and action of cytokines, generating a bidirectional functional link. Indeed, several miRNAs are implicated in the inflammatory process, acting as positive or negative regulators (Hulsmans et al., 2011). During obesity, macrophages progressively infiltrate into the adipose tissue, where they produce inflammatory chemokines, contributing to chronic low-grade inflammation (Donath and Shoelson, 2011). This increased infiltration is a key event in obesity, insulin resistance, and atherogenesis. It has been proposed that miRNAs could be common regulators of these pathogenic processes in adipose and vascular tissues (Hulsmans et al., 2011). According to this view, a common set of miRNAs including let-7, miR-21, miR-34a, and miR-143 appear to display the same functions in the two tissues. However, further progress in functional analysis and the discovery of synergetic actions is required for uncovering causal connections to inflammation. Notwithstanding this, recent studies point to a link between specific miRNAs, inflammation, and T2D. For example, in Asian Indian T2D patients the miR-146a levels in peripheral blood mononuclear cells negatively correlate with insulin resistance, poor glycemic control, and circulating tumor necrosis factor a and interleukin-6 levels (Balasubramanyam et al., 2011). Likewise, miR-146a appears to control the induction of NF-kBresponsive genes. Indeed, in T cells, miR-146a is an important member of the negative feedback loop controlling the induction of NF-kB-responsive genes involved in various aspects of T cell activation (Yang et al., 2012). Another member of the miR-146 family, miR-146b-5p, exerts anti-inflammatory actions during obesity (Hulsmans et al., 2012). Finally, a possible role of miR107, a Toll-like-receptor-regulated miRNA, in modulating the inflammatory process that might lead to T2D has been proposed. Hence, it was suggested that miR-107 may be the link between obesity, inflammation, and insulin resistance (Foley and O’Neill, 2012). Autophagy Autophagy corresponds to autodigestion of cell components and recycling of biological building elements destined for reuse. Autophagic vacuole formation and delivery is an evolutionarily conserved catabolic pathway in which complex cell building blocks are engulfed within vesicles and degraded into small molecules for providing nutritional elements to be utilized again (Kroemer et al., 2010). This critical process allows cells to gain survival advantages under various stress situations due to growth and environmental changes. Recently, Kovaleva et al. (2012) revealed that autophagic flux can be regulated by Dicer. On the flip side, autophagy engages regulation of Dicer and Ago proteins, pointing to a fundamental connection between miRNAs and autophagic flux (Gibbings et al., 2012). In mammals, autophagy induction is initiated by the ULK complex, composed of ULK1, ULK2, ATG13, FIP200, and ATG101 (Kroemer et al., 2010). miRNAs interfere at the most upstream event in autophagosome formation. For instance, miR-20a and miR-106b bind to the ULK1 mRNA and reduce its protein level Cell Metabolism 18, August 6, 2013 ª2013 Elsevier Inc. 7

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Cell Metabolism

Review (Wu et al., 2012). The next step in autophagosome genesis is the vesicle-nucleation step, which is initiated by the beclin-1/class III PI3K complex. Among the members of this complex, beclin-1 is a potential target of numerous miRNAs. For example, miR-30a, miR-376b, and miR-519a bind directly to beclin-1 30 UTR mRNA (Zhai et al., 2013). Interestingly, Beclin-1 lies at the crossroad between autophagy and apoptosis (Kang et al., 2011), suggesting that, depending on the stress response, miRNAs could cross-regulate autophagy and apoptosis. The elongation and enclosure of membranes thought to be critical for autophagosome formation is associated with ubiquitination-like conjugations. Several miRNAs have been identified as regulators of this step. ATG7, required for the initial step in conjugation systems, was recognized as a target of miR-375 (Chang et al., 2012). miR-30a, besides its association with the beclin-1 complex, was implicated in the ATG12-ATG5-ATG16 complex. Other potential regulators of ATG5-ATG12 conjugation include miR-101, miR-181a, miR-374a, and miR-630 (Zhai et al., 2013). The lysosomes are the final destination for autophagosomes, thereby forming the autolysosome, in which cargo is exposed to lysosomal hydrolases that lead to its breakdown. Finally, the resulting macromolecules are transported back into the cytosol through membrane permeases for reuse. Intriguingly, to the best of our knowledge, no miRNAs directly affecting the fusion process have been revealed so far. miRNAs in Diabetes Diabetes itself represents a state of cellular stress induced by hyperglycemia and/or hyperlipidemia. Indeed, diabetes is defined as chronic hyperglycemia due to pancreatic failure in T1D and to a combination of insulin resistance and insufficient insulin secretion in T2D. Given the general role of miRNAs on cells and organisms, the tantalizing hypothesis that their misexpression could be associated with disease situations, including metabolic disorders such as diabetes, emerged very early on. In the previous sections we discussed the impact of a series of miRNAs on insulin secretion and action, which reflects a direct or indirect causal relationship depending on the targets. Here, we briefly review the miRNAs found to be misexpressed in diabetes. It must be stressed that these miRNA alterations could participate in the disease process and/or be the consequence of it. miRNA Misexpression in Diabetes To assess the involvement of miRNAs in diabetes, most research efforts address their expression profile in animal models and, when possible, in diabetic patients. Concerning T1D, NOD mice correspond to a well-characterized spontaneous model closely resembling the human disease. Among several miRNAs differentially expressed in islets from NOD mice, miR-21, miR-34a, and miR-29a/b/c are upregulated (Roggli et al., 2010, 2012). Interestingly, these miRNAs were reported to inhibit different targets involved in b cell death, including the tumor suppressor programmed cell death protein 4 (PDCD4) and the antiapoptotic proteins Mcl1 and Bcl2 (Guay et al., 2012) (Figure 2C). Because T2D is a multicausal and heterogeneous disease, animal models fail to regroup all pathological hallmarks observed in humans. However, the db/db mice deficient in leptin receptor 8 Cell Metabolism 18, August 6, 2013 ª2013 Elsevier Inc.

fulfill minimal criteria justifying their use in miRNA studies. Among several miRNAs described to be altered in this model, miR-34a and miR-146 are upregulated in islets (Lovis et al., 2008b), and miR-29 family members and miR-125a are increased in other insulin target tissues (He et al., 2007; Herrera et al., 2009). Given that T2D is often associated with obesity, several studies were performed in ob/ob mice deficient for leptin or in diet-induced obesity (DIO) mice. For instance, miR-103 and miR-107 expression is altered in the liver and white adipose tissue of ob/ob and DIO mice (Trajkovski et al., 2011). miR-143 and miR-802 are increased in the liver of db/db and DIO mice (Jordan et al., 2011; Kornfeld et al., 2013). To sum up, the expression of a number of miRNAs is dysregulated in diabetic and obese animal models. Concerning human studies, a meager number of reports have appeared because of limitations inherent to tissue accessibility. Gallagher et al. (2010) performed a genome-wide analysis of mRNAs and miRNAs on skeletal muscle from subjects without or with T2D. A list of differentially expressed miRNAs was identified, and several of them are predicted to target molecules relevant to metabolic disease. Additionally, Klo¨ting et al. (2009) compared miRNA expression in omental and subcutaneous adipose tissue of individuals with normal glucose tolerance or newly diagnosed T2D. A significant correlation was found between the expression of several miRNAs and both adiposetissue morphology and key metabolic parameters. More recently, investigation of a specific miRNA set in human islets from nondiabetic and diabetic subjects revealed that miR-21 is significantly increased, whereas miR-375 merely shows a tendency (Bolmeson et al., 2011). This contrasts with another study on the correlation between miR-375 expression and islet amyloid deposition reporting that miR-375 is upregulated in islets of T2D (Zhao et al., 2010). To summarize, although changes in miRNA expression in human diabetes exist, the limited available data do not draw a clear picture. Important pitfalls possibly exist due to the small cohort size, the lack of uniformity in miRNA measurement techniques, and confounding factors related to age, body mass index, and sex differences (Becker and Lockwood, 2013). Extracellular miRNAs as Biomarkers of Diabetes Although a consensus exists on the importance of miRNAs in the cells wherein they are produced (i.e., in situ effects), the demonstration that miRNAs circulate in blood points to ex situ actions. The possibility of miRNAs acting at a distance opens an entirely novel repertoire of biological functions. miRNAs found in blood could originate in organs or tissues and/or be passively released from broken cells following injury, apoptosis, or necrosis (Zernecke et al., 2009). Independently of these two possible scripts, the exported versus passively released miRNAs found in blood could exert a paracrine function by acting on neighboring cells and even extend their action at a distance. For both actions (i.e., paracrine and remote), a certain stability of these molecules is a prerequisite. Indeed, circulating miRNAs appear to be remarkably robust despite the austere conditions to which they are subjected. This is compatible with the fact that circulating miRNAs travel as passengers of several transportation vehicles that offer protection from ribonuclease activity. Although the secretory mechanism of miRNAs remains obscure, different scenarios have been proposed for their carriage. According to one, circulating miRNAs are part of microvesicles or exosomes or

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Review bound to high-density lipoproteins. According to another, a significant portion of circulating miRNAs in plasma are associated with the RNA-binding proteins Ago2 and NPM1 (Turchinovich et al., 2011). An important spin-off provided by the fact that miRNAs are found in biological fluids points to their potential use as biomarkers for disease states and to the possible development of miRNA-based therapeutics. Several groups have revealed an altered profile of circulating miRNAs in various metabolic diseases such as T2D. For example, a plasma miRNA signature for T2D was identified in a cohort of 80 patients (Zampetaki et al., 2010). Among the 12 miRNAs correlated with the disease, miR-126 shows a gradual decrease from normal to impaired glucose tolerance. Previously, miR-126 was found to be highly enriched in endothelial cells for governing the maintenance of vascular integrity, angiogenesis, and vessel repair (Fish et al., 2008; Wang et al., 2008). T2D is one of the major risk factors of cardiovascular disease and is associated to endothelial dysfunction with micro- and macrovascular complications. Generally speaking, cardiovascular diseases cause most of the increased morbidity and mortality of diabetic patients. Although additional validation in large cohorts is needed, loss of endothelial miR-126 in plasma might reflect altered endothelial function, and thus could have a prognostic value for the development of diabetic vascular complications. More recently, Kong et al. (2011) focused on the increased expression of seven diabetes-related circulating miRNAs (miR-9, miR-29a, miR-30d, miR-34a, miR-124a, miR-146a, and miR-375) during the pathogenesis of the disease. Their upregulated expression dovetails with their previously described involvement in the pathogenesis of the disease, in that all of these miRNAs were identified as negative regulators of the expression, production, secretion, or action of insulin (Guay et al., 2012). As mentioned above, in human and mouse pancreatic islets miR-375 displays the most robust expression, and b cells could thus be viewed as a major supplier of blood-borne miR-375. Consequently, the measurement of miR-375 plasma levels could represent an attractive means for estimating b cell mass in insulin-resistant patients before the development of pancreatic failure in order to adapt the treatment. In summary, the discovery that miRNAs are present in a stable form in several body fluids, including blood, suggests that extracellular miRNAs hold promise to serve as novel biomarkers for metabolic disorders and/or their associated complications. The latter aspect would be especially useful for diabetes, for which prognostic markers for complications are missing. The validated use of miRNAs as bona fide disease biomarkers is a ways off, as several key issues need to be addressed, including the following ones: On the technical side, the lack of standardization of the methods for measuring miRNA levels generates limitations for the validation and verification of the profiles obtained by different laboratories and platforms. In addition, the use of miRNAs as biomarkers necessitates the uniformity of preclinical sample preparation, which is too often neglected. Furthermore, at present it remains to be sorted out whether extracellular miRNAs, and particularly the circulating ones, merely reflect the disease and/ or are actively participating in the disease process. Finally, given the pleiotropic actions of most miRNAs, some of which have opposing actions, it must be determined whether aberrant

expression of miRNAs per se should be used as biomarker, or whether a chart of misexpressed miRNAs affecting a particular disease-related biological process would be more informative. miRNAs as Therapeutic Tools The central implication of miRNAs in metabolism and associated disorders combined with the remarkable stability of extracellular miRNAs raises the question of the possibility of miRNA-targeted therapies. miRNA mimics or miRNA inhibitors can be used to elevate or block the activity of miRNAs that drive disease initiation and/or progression. The ability to therapeutically manipulate miRNA expression and the pharmacokinetic and dynamic properties of current mimic and antimiR designs were recently reviewed (Quiat and Olson, 2013) and will be not discussed here. In a groundbreaking publication, Janssen et al. (2013) showed for the first time in humans the ability to therapeutically manipulate miRNA expression and function. Using LNA-miR-122 (Miravirsen) in patients with chronic hepatitis C virus (HCV) infection, they observed prolonged dose-dependent reductions in HCV RNA levels without evidence of viral resistance. This work provides promising expectations that antimiRs could become new medications; however, additional clarification is eagerly awaited, as the exact mechanism by which Miravirsen reduces HCV replication remains elusive. Indeed, the Miravirsen effect is thought to be based on 50 UTR binding of miR-122 and not on a ‘‘classical’’ 30 UTR binding of a predicted target gene. Another key challenge to be resolved concerns the delivery strategy. Evidently, targeting the liver or pancreas demands different requirements than reaching readily accessible sites such as skin and bones. Some strategies are based on systemic approaches including the use of antibody-based delivery agents, nanoparticles, and liposomes to target and/or restore miRNAs in specific cell types (Langer et al., 2012). Interestingly, a recent study demonstrates that miRNAs present in food appear to regulate the expression of target genes in mammals (Zhang et al., 2012). These intriguing results raise questions about food-derived miRNAs and their active role in human health, but they also open unexpected perspectives as an oral delivery strategy. However, to prove the salutary effects of this promising approach, several issues must be solved, including the desired delivery specificity, the possible immune stimulation, and the toxic accumulation in tissues. One of the most attractive strategies of restoring miRNAs in disease is through adenoassociated viruses (AAVs). The availability for numerous different AAV serotypes allows for potential tissue enrichment as a result of the natural tropism of AAV subtypes. For example, administration of AAV6, AAV8, and AAV9 appears to be efficient for genetic manipulation of the pancreas in vivo (Jimenez et al., 2011). However, some tissues remain refractory to transduction with the available serotypes (Daya and Berns, 2008). In addition, the host immune response remains a concern. Thus, although very promising studies are emerging in the field of miRNAs as therapeutic tools, the whole area is in its infancy, and more knowledge is needed on current obstacles ranging from adequate delivery strategies to possible side effects. Conclusions and Future Directions More than a thousand miRNAs have been identified in rodents and humans; however, only the tip of the iceberg is visible with Cell Metabolism 18, August 6, 2013 ª2013 Elsevier Inc. 9

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Review regard to their precise roles. An emerging coherent picture of their biological actions suggests that miRNAs are at the core of mechanisms involved in metabolism regulation. Remarkably, the relationship between miRNAs and metabolism appears as a bidirectional link. Indeed, miRNAs impinge on metabolism by interacting with the production and/or signaling of key players involved in metabolic regulation. By the same token, miRNA expression and processing are modulated by major metabolic stimuli such as glucose and hormones. This mutually enriching relationship between miRNAs and metabolism is likely to participate in the complex regulation of homeostasis. Hence, disconnection of this bidirectional interworking is destined to contribute to disease situations. Although the elementary vocabulary of the miRNA language has been decoded, many urgent questions remain to be addressed. A central issue in the miRNA world concerns the assessment of miRNA activity and function, both of which depend on the miRNA targets and on the relative miRNA and target abundancy (Ebert and Sharp, 2012; Leung and Sharp, 2010). The functional identification of miRNA targets is one of the most challenging tasks, because a single miRNA often has hundreds of potential mRNA targets. Conversely, several different miRNAs can combinatorially impact the same mRNA target. It is obvious that the ultimate biological effect of the miRNA will be determined by its own concentration, but in addition by that of its multiple targets. To make the situation even more complex, the biological effect will be affected by the different disappearance rates of the multiple targets. Finally, the arising evidence in mammals for the existence of intracellular miRNA sponges such as ‘‘competing endogenous RNA,’’ and more recently circular RNAs, probably has to be integrated in the assessment of miRNA action (Hansen et al., 2013). When considering the therapeutic potential of miRNAs, it must be kept in mind that by aiming at several targets, some displaying antagonizing effects, miRNAs could exert dual actions. In the context of the miRNA-metabolism crosstalk, an igniting question relates to the impact of circadian rhythms (Kojima et al., 2011). This aspect is particularly relevant considering the fact that feeding (i.e., nutrients) modulates the circadian clock and that the latter regulates metabolism. A second fascinating issue relates to the observation that certain mature miRNAs can re-enter the nucleus, where they function in a noncanonical manner by directly regulating the biogenesis of miRNAs including their own and the function of long-noncoding RNA (Chen et al., 2012). This ‘‘nuclear’’ effect of miRNA has to be taken into account in attempts to evaluate the global biological repertoire of a particular miRNA. A third issue to be examined concerns the significance of extracellular miRNAs. An immediate benefit is their possible use as disease biomarkers, but their biological functions remain to be clarified. The enticing possibility that extracellular miRNAs, and in particular the blood-borne ones, are indeed involved in cell-cell communications would not only make inroads in basic biology, but in addition would show promise for their use as potential therapeutic tools. Since their discovery, miRNAs have received enormous attention, and their biological stature as natural actors in geneexpression regulation is now clearly established. Although important roadblocks exist, novel experimental tools are poised to reveal their possible utility in the treatment of diseases either 10 Cell Metabolism 18, August 6, 2013 ª2013 Elsevier Inc.

as therapeutic means themselves or as targets of therapeutic interventions. Stringent collaborative endeavors are needed for evaluating the miRNAs in the armamentarium of therapeutics for human diseases. ACKNOWLEDGMENTS Our research was supported by INSERM, Universite´ de Nice Sophia Antipolis, Conseil Re´gional PACA and Conseil Ge´ne´ral des Alpes-Maritimes, by the Aviesan/AstraZeneca,‘‘Diabetes and the vessel wall injury’’ program, by the Agence Nationale de la Recherche (ANR), and by the European Foundation for the Study of Diabetes (EFSD/Lilly; European Diabetes Research Programme; 2011). O.D. was supported by grants from Socie´te´ Francophone du Diabe`te, (SFD, 2008) and the Fondation pour la Recherche Me´dicale (2009–2010). We apologize for being unable to discuss all relevant papers due to space limitations. REFERENCES Arner, E., Mejhert, N., Kulyte´, A., Balwierz, P.J., Pachkov, M., Cormont, M., Lorente-Cebria´n, S., Ehrlund, A., Laurencikiene, J., Hede´n, P., et al. (2012). Adipose tissue microRNAs as regulators of CCL2 production in human obesity. Diabetes 61, 1986–1993. Avnit-Sagi, T., Kantorovich, L., Kredo-Russo, S., Hornstein, E., and Walker, M.D. (2009). The promoter of the pri-miR-375 gene directs expression selectively to the endocrine pancreas. PLoS ONE 4, e5033. Balasubramanyam, M., Aravind, S., Gokulakrishnan, K., Prabu, P., Sathishkumar, C., Ranjani, H., and Mohan, V. (2011). Impaired miR-146a expression links subclinical inflammation and insulin resistance in Type 2 diabetes. Mol. Cell. Biochem. 351, 197–205. Baroukh, N., Ravier, M.A., Loder, M.K., Hill, E.V., Bounacer, A., Scharfmann, R., Rutter, G.A., and Van Obberghen, E. (2007). MicroRNA-124a regulates Foxa2 expression and intracellular signaling in pancreatic beta-cell lines. J. Biol. Chem. 282, 19575–19588. Bartel, D.P. (2009). MicroRNAs: target recognition and regulatory functions. Cell 136, 215–233. Becker, N., and Lockwood, C.M. (2013). Pre-analytical variables in miRNA analysis. Clin. Biochem. 46, 861–868. Boehm, M., and Slack, F. (2005). A developmental timing microRNA and its target regulate life span in C. elegans. Science 310, 1954–1957. Bolmeson, C., Esguerra, J.L., Salehi, A., Speidel, D., Eliasson, L., and Cilio, C.M. (2011). Differences in islet-enriched miRNAs in healthy and glucose intolerant human subjects. Biochem. Biophys. Res. Commun. 404, 16–22. Carrer, M., Liu, N., Grueter, C.E., Williams, A.H., Frisard, M.I., Hulver, M.W., Bassel-Duby, R., and Olson, E.N. (2012). Control of mitochondrial metabolism and systemic energy homeostasis by microRNAs 378 and 378*. Proc. Natl. Acad. Sci. USA 109, 15330–15335. Chang, Y., Yan, W., He, X., Zhang, L., Li, C., Huang, H., Nace, G., Geller, D.A., Lin, J., and Tsung, A. (2012). miR-375 inhibits autophagy and reduces viability of hepatocellular carcinoma cells under hypoxic conditions. Gastroenterology 143, 177–187, e8. Chen, X., Liang, H., Zhang, C.Y., and Zen, K. (2012). miRNA regulates noncoding RNA: a noncanonical function model. Trends Biochem. Sci. 37, 457–459. Cochrane, D.R., Spoelstra, N.S., and Richer, J.K. (2012). The role of miRNAs in progesterone action. Mol. Cell. Endocrinol. 357, 50–59. Da´valos, A., Goedeke, L., Smibert, P., Ramı´rez, C.M., Warrier, N.P., Andreo, U., Cirera-Salinas, D., Rayner, K., Suresh, U., Pastor-Pareja, J.C., et al. (2011). miR-33a/b contribute to the regulation of fatty acid metabolism and insulin signaling. Proc. Natl. Acad. Sci. USA 108, 9232–9237. Daya, S., and Berns, K.I. (2008). Gene therapy using adeno-associated virus vectors. Clin. Microbiol. Rev. 21, 583–593. Donath, M.Y., and Shoelson, S.E. (2011). Type 2 diabetes as an inflammatory disease. Nat. Rev. Immunol. 11, 98–107.

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Cell Metabolism

Review Drummond, M.J., McCarthy, J.J., Sinha, M., Spratt, H.M., Volpi, E., Esser, K.A., and Rasmussen, B.B. (2011). Aging and microRNA expression in human skeletal muscle: a microarray and bioinformatics analysis. Physiol. Genomics 43, 595–603. Dumortier, O., and Van Obberghen, E. (2012). MicroRNAs in pancreas development. Diabetes Obes. Metab. 14(Suppl 3 ), 22–28. Ebert, M.S., and Sharp, P.A. (2012). Roles for microRNAs in conferring robustness to biological processes. Cell 149, 515–524. El Ouaamari, A., Baroukh, N., Martens, G.A., Lebrun, P., Pipeleers, D., and Van Obberghen, E. (2008). miR-375 targets 30 -phosphoinositide-dependent protein kinase-1 and regulates glucose-induced biological responses in pancreatic beta-cells. Diabetes 57, 2708–2717. Esau, C., Davis, S., Murray, S.F., Yu, X.X., Pandey, S.K., Pear, M., Watts, L., Booten, S.L., Graham, M., McKay, R., et al. (2006). miR-122 regulation of lipid metabolism revealed by in vivo antisense targeting. Cell Metab. 3, 87–98. Finnegan, E.F., and Pasquinelli, A.E. (2013). MicroRNA biogenesis: regulating the regulators. Crit. Rev. Biochem. Mol. Biol. 48, 51–68. Fish, J.E., Santoro, M.M., Morton, S.U., Yu, S., Yeh, R.F., Wythe, J.D., Ivey, K.N., Bruneau, B.G., Stainier, D.Y., and Srivastava, D. (2008). miR-126 regulates angiogenic signaling and vascular integrity. Dev. Cell 15, 272–284. Foley, N.H., and O’Neill, L.A. (2012). miR-107: a toll-like receptor-regulated miRNA dysregulated in obesity and type II diabetes. J. Leukoc. Biol. 92, 521–527. Frost, R.J., and Olson, E.N. (2011). Control of glucose homeostasis and insulin sensitivity by the Let-7 family of microRNAs. Proc. Natl. Acad. Sci. USA 108, 21075–21080. Gallagher, I.J., Scheele, C., Keller, P., Nielsen, A.R., Remenyi, J., Fischer, C.P., Roder, K., Babraj, J., Wahlestedt, C., Hutvagner, G., et al. (2010). Integration of microRNA changes in vivo identifies novel molecular features of muscle insulin resistance in type 2 diabetes. Genome Med. 2, 9. Garcı´a-Segura, L., Pe´rez-Andrade, M., and Miranda-Rı´os, J. (2013). The emerging role of MicroRNAs in the regulation of gene expression by nutrients. J Nutrigenet. Nutrigenomics 6, 16–31. Gibbings, D., Mostowy, S., Jay, F., Schwab, Y., Cossart, P., and Voinnet, O. (2012). Selective autophagy degrades DICER and AGO2 and regulates miRNA activity. Nat. Cell Biol. 14, 1314–1321. Granjon, A., Gustin, M.P., Rieusset, J., Lefai, E., Meugnier, E., Gu¨ller, I., Cerutti, C., Paultre, C., Disse, E., Rabasa-Lhoret, R., et al. (2009). The microRNA signature in response to insulin reveals its implication in the transcriptional action of insulin in human skeletal muscle and the role of a sterol regulatory elementbinding protein-1c/myocyte enhancer factor 2C pathway. Diabetes 58, 2555–2564. Grillari, J., Hackl, M., and Grillari-Voglauer, R. (2010). miR-17-92 cluster: ups and downs in cancer and aging. Biogerontology 11, 501–506. Grueter, C.E., van Rooij, E., Johnson, B.A., DeLeon, S.M., Sutherland, L.B., Qi, X., Gautron, L., Elmquist, J.K., Bassel-Duby, R., and Olson, E.N. (2012). A cardiac microRNA governs systemic energy homeostasis by regulation of MED13. Cell 149, 671–683. Guay, C., Jacovetti, C., Nesca, V., Motterle, A., Tugay, K., and Regazzi, R. (2012). Emerging roles of non-coding RNAs in pancreatic b-cell function and dysfunction. Diabetes Obes. Metab. 14(Suppl 3 ), 12–21. Guo, H., Ingolia, N.T., Weissman, J.S., and Bartel, D.P. (2010). Mammalian microRNAs predominantly act to decrease target mRNA levels. Nature 466, 835–840. Hansen, T.B., Jensen, T.I., Clausen, B.H., Bramsen, J.B., Finsen, B., Damgaard, C.K., and Kjems, J. (2013). Natural RNA circles function as efficient microRNA sponges. Nature 495, 384–388. He, A., Zhu, L., Gupta, N., Chang, Y., and Fang, F. (2007). Overexpression of micro ribonucleic acid 29, highly up-regulated in diabetic rats, leads to insulin resistance in 3T3-L1 adipocytes. Mol. Endocrinol. 21, 2785–2794. Herrera, B.M., Lockstone, H.E., Taylor, J.M., Wills, Q.F., Kaisaki, P.J., Barrett, A., Camps, C., Fernandez, C., Ragoussis, J., Gauguier, D., et al. (2009). MicroRNA-125a is over-expressed in insulin target tissues in a spontaneous rat model of Type 2 Diabetes. BMC Med. Genomics 2, 54.

Hulsmans, M., De Keyzer, D., and Holvoet, P. (2011). MicroRNAs regulating oxidative stress and inflammation in relation to obesity and atherosclerosis. FASEB J. 25, 2515–2527. Hulsmans, M., Van Dooren, E., Mathieu, C., and Holvoet, P. (2012). Decrease of miR-146b-5p in monocytes during obesity is associated with loss of the antiinflammatory but not insulin signaling action of adiponectin. PLoS ONE 7, e32794. Iliopoulos, D., Drosatos, K., Hiyama, Y., Goldberg, I.J., and Zannis, V.I. (2010). MicroRNA-370 controls the expression of microRNA-122 and Cpt1alpha and affects lipid metabolism. J. Lipid Res. 51, 1513–1523. Jacovetti, C., Abderrahmani, A., Parnaud, G., Jonas, J.C., Peyot, M.L., Cornu, M., Laybutt, R., Meugnier, E., Rome, S., Thorens, B., et al. (2012). MicroRNAs contribute to compensatory b cell expansion during pregnancy and obesity. J. Clin. Invest. 122, 3541–3551. Janssen, H.L., Reesink, H.W., Lawitz, E.J., Zeuzem, S., Rodriguez-Torres, M., Patel, K., van der Meer, A.J., Patick, A.K., Chen, A., Zhou, Y., et al. (2013). Treatment of HCV infection by targeting microRNA. N. Engl. J. Med. 368, 1685–1694. Jimenez, V., Ayuso, E., Mallol, C., Agudo, J., Casellas, A., Obach, M., Mun˜oz, S., Salavert, A., and Bosch, F. (2011). In vivo genetic engineering of murine pancreatic beta cells mediated by single-stranded adeno-associated viral vectors of serotypes 6, 8 and 9. Diabetologia 54, 1075–1086. Jordan, S.D., Kru¨ger, M., Willmes, D.M., Redemann, N., Wunderlich, F.T., Bro¨nneke, H.S., Merkwirth, C., Kashkar, H., Olkkonen, V.M., Bo¨ttger, T., et al. (2011). Obesity-induced overexpression of miRNA-143 inhibits insulinstimulated AKT activation and impairs glucose metabolism. Nat. Cell Biol. 13, 434–446. Kang, R., Zeh, H.J., Lotze, M.T., and Tang, D. (2011). The Beclin 1 network regulates autophagy and apoptosis. Cell Death Differ. 18, 571–580. Keller, D.M., Clark, E.A., and Goodman, R.H. (2012). Regulation of microRNA375 by cAMP in pancreatic b-cells. Mol. Endocrinol. 26, 989–999. Kenyon, C., Chang, J., Gensch, E., Rudner, A., and Tabtiang, R. (1993). A C. elegans mutant that lives twice as long as wild type. Nature 366, 461–464. Kim, V.N., Han, J., and Siomi, M.C. (2009). Biogenesis of small RNAs in animals. Nat. Rev. Mol. Cell Biol. 10, 126–139. Klinge, C.M. (2009). Estrogen Regulation of MicroRNA Expression. Curr. Genomics 10, 169–183. Klinge, C.M. (2012). miRNAs and estrogen action. Trends Endocrinol. Metab. 23, 223–233. Klo¨ting, N., Berthold, S., Kovacs, P., Scho¨n, M.R., Fasshauer, M., Ruschke, K., Stumvoll, M., and Blu¨her, M. (2009). MicroRNA expression in human omental and subcutaneous adipose tissue. PLoS ONE 4, e4699. Kojima, S., Shingle, D.L., and Green, C.B. (2011). Post-transcriptional control of circadian rhythms. J. Cell Sci. 124, 311–320. Kong, L., Zhu, J., Han, W., Jiang, X., Xu, M., Zhao, Y., Dong, Q., Pang, Z., Guan, Q., Gao, L., et al. (2011). Significance of serum microRNAs in pre-diabetes and newly diagnosed type 2 diabetes: a clinical study. Acta Diabetol. 48, 61–69. Kornfeld, J.W., Baitzel, C., Ko¨nner, A.C., Nicholls, H.T., Vogt, M.C., Herrmanns, K., Scheja, L., Haumaitre, C., Wolf, A.M., Knippschild, U., et al. (2013). Obesity-induced overexpression of miR-802 impairs glucose metabolism through silencing of Hnf1b. Nature 494, 111–115. Kovaleva, V., Mora, R., Park, Y.J., Plass, C., Chiramel, A.I., Bartenschlager, R., Do¨hner, H., Stilgenbauer, S., Pscherer, A., Lichter, P., and Seiffert, M. (2012). miRNA-130a targets ATG2B and DICER1 to inhibit autophagy and trigger killing of chronic lymphocytic leukemia cells. Cancer Res. 72, 1763–1772. Krek, A., Gru¨n, D., Poy, M.N., Wolf, R., Rosenberg, L., Epstein, E.J., MacMenamin, P., da Piedade, I., Gunsalus, K.C., Stoffel, M., and Rajewsky, N. (2005). Combinatorial microRNA target predictions. Nat. Genet. 37, 495–500. Kroemer, G., Marin˜o, G., and Levine, B. (2010). Autophagy and the integrated stress response. Mol. Cell 40, 280–293.

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Review Kru¨tzfeldt, J., Rajewsky, N., Braich, R., Rajeev, K.G., Tuschl, T., Manoharan, M., and Stoffel, M. (2005). Silencing of microRNAs in vivo with ‘antagomirs’. Nature 438, 685–689. Landgraf, P., Rusu, M., Sheridan, R., Sewer, A., Iovino, N., Aravin, A., Pfeffer, S., Rice, A., Kamphorst, A.O., Landthaler, M., et al. (2007). A mammalian microRNA expression atlas based on small RNA library sequencing. Cell 129, 1401–1414. Langer, C., Ru¨cker, F.G., Buske, C., Do¨hner, H., and Kuchenbauer, F. (2012). Targeted therapies through microRNAs: pulp or fiction? Ther. Adv. Hematol. 3, 97–104. Leung, A.K., and Sharp, P.A. (2010). MicroRNA functions in stress responses. Mol. Cell 40, 205–215. Li, X., Cassidy, J.J., Reinke, C.A., Fischboeck, S., and Carthew, R.W. (2009). A microRNA imparts robustness against environmental fluctuation during development. Cell 137, 273–282. Liang, J., Liu, C., Qiao, A., Cui, Y., Zhang, H., Cui, A., Zhang, S., Yang, Y., Xiao, X., Chen, Y., et al. (2013). MicroRNA-29a-c decrease fasting blood glucose levels by negatively regulating hepatic gluconeogenesis. J. Hepatol. 58, 535–542. Lovis, P., Gattesco, S., and Regazzi, R. (2008a). Regulation of the expression of components of the exocytotic machinery of insulin-secreting cells by microRNAs. Biol. Chem. 389, 305–312. Lovis, P., Roggli, E., Laybutt, D.R., Gattesco, S., Yang, J.Y., Widmann, C., Abderrahmani, A., and Regazzi, R. (2008b). Alterations in microRNA expression contribute to fatty acid-induced pancreatic beta-cell dysfunction. Diabetes 57, 2728–2736. Ma, N., Wang, X., Qiao, Y., Li, F., Hui, Y., Zou, C., Jin, J., Lv, G., Peng, Y., Wang, L., et al. (2011). Coexpression of an intronic microRNA and its host gene reveals a potential role for miR-483-5p as an IGF2 partner. Mol. Cell. Endocrinol. 333, 96–101.

Quiat, D., and Olson, E.N. (2013). MicroRNAs in cardiovascular disease: from pathogenesis to prevention and treatment. J. Clin. Invest. 123, 11–18. Ramachandran, D., Roy, U., Garg, S., Ghosh, S., Pathak, S., and Kolthur-Seetharam, U. (2011). Sirt1 and mir-9 expression is regulated during glucose-stimulated insulin secretion in pancreatic b-islets. FEBS J. 278, 1167–1174. Ramirez, C.M., Da´valos, A., Goedeke, L., Salerno, A.G., Warrier, N., CireraSalinas, D., Sua´rez, Y., and Ferna´ndez-Hernando, C. (2011). MicroRNA-758 regulates cholesterol efflux through posttranscriptional repression of ATPbinding cassette transporter A1. Arterioscler. Thromb. Vasc. Biol. 31, 2707– 2714. Rodriguez, A., Griffiths-Jones, S., Ashurst, J.L., and Bradley, A. (2004). Identification of mammalian microRNA host genes and transcription units. Genome Res. 14(10A), 1902–1910. Roggli, E., Britan, A., Gattesco, S., Lin-Marq, N., Abderrahmani, A., Meda, P., and Regazzi, R. (2010). Involvement of microRNAs in the cytotoxic effects exerted by proinflammatory cytokines on pancreatic beta-cells. Diabetes 59, 978–986. Roggli, E., Gattesco, S., Caille, D., Briet, C., Boitard, C., Meda, P., and Regazzi, R. (2012). Changes in microRNA expression contribute to pancreatic b-cell dysfunction in prediabetic NOD mice. Diabetes 61, 1742–1751. Ross, S.A., and Davis, C.D. (2011). MicroRNA, nutrition, and cancer prevention. Adv. Nutr. 2, 472–485. Rottiers, V., and Na¨a¨r, A.M. (2012). MicroRNAs in metabolism and metabolic disorders. Nat. Rev. Mol. Cell Biol. 13, 239–250. Ryu, H.S., Park, S.Y., Ma, D., Zhang, J., and Lee, W. (2011). The induction of microRNA targeting IRS-1 is involved in the development of insulin resistance under conditions of mitochondrial dysfunction in hepatocytes. PLoS ONE 6, e17343. Smith-Vikos, T., and Slack, F.J. (2012). MicroRNAs and their roles in aging. J. Cell Sci. 125, 7–17.

Mendell, J.T., and Olson, E.N. (2012). MicroRNAs in stress signaling and human disease. Cell 148, 1172–1187.

Taniguchi, C.M., Emanuelli, B., and Kahn, C.R. (2006). Critical nodes in signalling pathways: insights into insulin action. Nat. Rev. Mol. Cell Biol. 7, 85–96.

Mersey, B.D., Jin, P., and Danner, D.J. (2005). Human microRNA (miR29b) expression controls the amount of branched chain alpha-ketoacid dehydrogenase complex in a cell. Hum. Mol. Genet. 14, 3371–3377.

Trajkovski, M., Hausser, J., Soutschek, J., Bhat, B., Akin, A., Zavolan, M., Heim, M.H., and Stoffel, M. (2011). MicroRNAs 103 and 107 regulate insulin sensitivity. Nature 474, 649–653.

Mori, M.A., Raghavan, P., Thomou, T., Boucher, J., Robida-Stubbs, S., Macotela, Y., Russell, S.J., Kirkland, J.L., Blackwell, T.K., and Kahn, C.R. (2012). Role of microRNA processing in adipose tissue in stress defense and longevity. Cell Metab. 16, 336–347.

Trajkovski, M., Ahmed, K., Esau, C.C., and Stoffel, M. (2012). MyomiR-133 regulates brown fat differentiation through Prdm16. Nat. Cell Biol. 14, 1330– 1335.

Najafi-Shoushtari, S.H., Kristo, F., Li, Y., Shioda, T., Cohen, D.E., Gerszten, R.E., and Na¨a¨r, A.M. (2010). MicroRNA-33 and the SREBP host genes cooperate to control cholesterol homeostasis. Science 328, 1566–1569. Pandey, A.K., Verma, G., Vig, S., Srivastava, S., Srivastava, A.K., and Datta, M. (2011). miR-29a levels are elevated in the db/db mice liver and its overexpression leads to attenuation of insulin action on PEPCK gene expression in HepG2 cells. Mol. Cell. Endocrinol. 332, 125–133. Pawlikowska, L., Hu, D., Huntsman, S., Sung, A., Chu, C., Chen, J., Joyner, A.H., Schork, N.J., Hsueh, W.C., Reiner, A.P., et al.; Study of Osteoporotic Fractures. (2009). Association of common genetic variation in the insulin/ IGF1 signaling pathway with human longevity. Aging Cell 8, 460–472. Plaisance, V., Abderrahmani, A., Perret-Menoud, V., Jacquemin, P., Lemaigre, F., and Regazzi, R. (2006). MicroRNA-9 controls the expression of Granuphilin/ Slp4 and the secretory response of insulin-producing cells. J. Biol. Chem. 281, 26932–26942.

Turchinovich, A., Weiz, L., Langheinz, A., and Burwinkel, B. (2011). Characterization of extracellular circulating microRNA. Nucleic Acids Res. 39, 7223– 7233. Vijg, J., and Campisi, J. (2008). Puzzles, promises and a cure for ageing. Nature 454, 1065–1071. Wang, S., Aurora, A.B., Johnson, B.A., Qi, X., McAnally, J., Hill, J.A., Richardson, J.A., Bassel-Duby, R., and Olson, E.N. (2008). The endothelial-specific microRNA miR-126 governs vascular integrity and angiogenesis. Dev. Cell 15, 261–271. Wu, H., Wang, F., Hu, S., Yin, C., Li, X., Zhao, S., Wang, J., and Yan, X. (2012). MiR-20a and miR-106b negatively regulate autophagy induced by leucine deprivation via suppression of ULK1 expression in C2C12 myoblasts. Cell. Signal. 24, 2179–2186. Yamagata, K., Fujiyama, S., Ito, S., Ueda, T., Murata, T., Naitou, M., Takeyama, K., Minami, Y., O’Malley, B.W., and Kato, S. (2009). Maturation of microRNA is hormonally regulated by a nuclear receptor. Mol. Cell 36, 340–347.

Poy, M.N., Eliasson, L., Krutzfeldt, J., Kuwajima, S., Ma, X., Macdonald, P.E., Pfeffer, S., Tuschl, T., Rajewsky, N., Rorsman, P., and Stoffel, M. (2004). A pancreatic islet-specific microRNA regulates insulin secretion. Nature 432, 226–230.

Yang, L., Boldin, M.P., Yu, Y., Liu, C.S., Ea, C.K., Ramakrishnan, P., Taganov, K.D., Zhao, J.L., and Baltimore, D. (2012). miR-146a controls the resolution of T cell responses in mice. J. Exp. Med. 209, 1655–1670.

Poy, M.N., Spranger, M., and Stoffel, M. (2007). microRNAs and the regulation of glucose and lipid metabolism. Diabetes Obes. Metab. 9(Suppl 2 ), 67–73.

Zampetaki, A., Kiechl, S., Drozdov, I., Willeit, P., Mayr, U., Prokopi, M., Mayr, A., Weger, S., Oberhollenzer, F., Bonora, E., et al. (2010). Plasma microRNA profiling reveals loss of endothelial miR-126 and other microRNAs in type 2 diabetes. Circ. Res. 107, 810–817.

Poy, M.N., Hausser, J., Trajkovski, M., Braun, M., Collins, S., Rorsman, P., Zavolan, M., and Stoffel, M. (2009). miR-375 maintains normal pancreatic alpha- and beta-cell mass. Proc. Natl. Acad. Sci. USA 106, 5813–5818.

12 Cell Metabolism 18, August 6, 2013 ª2013 Elsevier Inc.

Zernecke, A., Bidzhekov, K., Noels, H., Shagdarsuren, E., Gan, L., Denecke, B., Hristov, M., Ko¨ppel, T., Jahantigh, M.N., Lutgens, E., et al. (2009). Delivery

Please cite this article in press as: Dumortier et al., MicroRNAs and Metabolism Crosstalk in Energy Homeostasis, Cell Metabolism (2013), http:// dx.doi.org/10.1016/j.cmet.2013.06.004

Cell Metabolism

Review of microRNA-126 by apoptotic bodies induces CXCL12-dependent vascular protection. Sci. Signal. 2, ra81. Zhai, H., Fesler, A., and Ju, J. (2013). MicroRNA: a third dimension in autophagy. Cell Cycle 12, 246–250. Zhang, L., Hou, D., Chen, X., Li, D., Zhu, L., Zhang, Y., Li, J., Bian, Z., Liang, X., Cai, X., et al. (2012). Exogenous plant MIR168a specifically targets mammalian LDLRAP1: evidence of cross-kingdom regulation by microRNA. Cell Res. 22, 107–126.

Zhao, H., Guan, J., Lee, H.M., Sui, Y., He, L., Siu, J.J., Tse, P.P., Tong, P.C., Lai, F.M., and Chan, J.C. (2010). Up-regulated pancreatic tissue microRNA375 associates with human type 2 diabetes through beta-cell deficit and islet amyloid deposition. Pancreas 39, 843–846. Zhu, H., Shyh-Chang, N., Segre`, A.V., Shinoda, G., Shah, S.P., Einhorn, W.S., Takeuchi, A., Engreitz, J.M., Hagan, J.P., Kharas, M.G., et al.; DIAGRAM Consortium; MAGIC Investigators. (2011). The Lin28/let-7 axis regulates glucose metabolism. Cell 147, 81–94.

Cell Metabolism 18, August 6, 2013 ª2013 Elsevier Inc. 13