- Email: [email protected]
Angiopoietin-like proteins: Another player in the metabolic field
Journal of Hepatology 44 (2006) 832–834 www.elsevier.com/locate/jhep
Journal Club Special Section Editors: Peter R. Galle, Peter L.M. Jansen, Jean-Pierre Vinel, Francesco Negro
Angiopoietin-like proteins: Another player in the metabolic field Jacob George* Storr Liver Unit, Westmead Millennium Institute, University of Sydney and Department of Gastroenterology and Hepatology, Westmead Hospital, Westmead, Sydney, NSW 2145, Australia
Angiopoietin-related growth factor antagonizes obesity and insulin resistance. Oike Y, Akao M, Yasunaga K, Yamauchi T, Morisada T, Ito Y, Urano T, Kimura Y, Kubota Y, Maekawa H, Miyamoto T, Miyata K, Matsumoto S, Sakai J, Nakagata N, Takeya M, Koseki H, Ogawa Y, Kadowaki T, Suda T. Angiopoietin-related growth factor (AGF), a member of the angiopoietin-like protein (Angptl) family, is secreted predominantly from the liver into the systemic circulation. Here, we show that most (O80%) of the AGF-deficient mice die at about embryonic day 13, whereas the surviving AGF-deficient mice develop marked obesity, lipid accumulation in skeletal muscle and liver, and insulin resistance accompanied by reduced energy expenditure relative to controls. In parallel, mice with targeted activation of AGF show leanness and increased insulin sensitivity resulting from increased energy expenditure. They are also protected from high-fat diet-induced obesity, insulin resistance and nonadipose tissue steatosis. Hepatic overexpression of AGF by adenoviral transduction, which leads to an approximately 2.5-fold increase in serum AGF concentrations, results in a significant (P!0.01) body weight loss and increases insulin sensitivity in mice fed with a high-fat diet. This study establishes AGF as a new hepatocyte-derived circulating factor that counteracts obesity and related insulin resistance. [Abstract reproduced by permission of Nat Med 2005;11(4):400–8]
The last century has witnessed significant advances in medical science that have lead to major inroads in the * Tel.: C61 2 9845 7705; fax: C61 2 9635 7582. E-mail address: [email protected] (J. George).
fight against microbial diseases. Research more recently, has shifted to understanding and combating the morbidity and mortality associated with malignancy, degenerative disorders and now, the metabolic consequences associated with increasing adiposity. The latter, encompassed by the term metabolic syndrome, refers to a collection of diseases linked to visceral obesity and includes insulin resistance and type 2 diabetes, dyslipidemia, hypertension, accelerated atherosclerotic cardiovascular disease and for the hepatologist, non-alcoholic fatty liver disease (NAFLD). From a public health perspective, policies directed towards reduced energy intake, improved nutrient composition and increased physical activity are the cornerstones for disease prevention and treatment. From a pharmacotherapeutic perspective, understanding the cellular and molecular mechanisms, whereby a net positive energy balance leads to visceral adiposity and the metabolic syndrome, are central to the development of novel approaches to combat these disorders. In this respect, the elegant studies by Oike et al. [1] represent another piece in a puzzle of ever increasing complexity. The hormonal networks and their downstream targets that regulate glucose and lipid metabolism have increased exponentially from the days when insulin was the dominant player. The current plethora of regulatory peptides include the adipose derived cytokines (adipokines) leptin, adiponectin, resistin, TNF and IL6, and more recently the angiopoietin-like (Angptl) family of proteins, 1–6 (Angptl1 to Angptl6) [2,3]. Structurally related to angiopoietins, which play a major role in angiogenesis, the Angptl peptides, like the angiopoietins, comprise a coiled-coil domain and a fibrinogen-like domain [3]. Perhaps, because they lack a cystein-based motif in the fibrinogen-like domain, the Angptl proteins fail to bind the angiopoietin TIE receptors, TIE1 and TIE2. Since, the receptors for the Angptl’s are
0168-8278/$32.00 q 2006 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jhep.2006.01.010
J. George / Journal of Hepatology 44 (2006) 832–834
currently unknown, these peptides are considered orphan ligands. Expression of Angptl1 and Angptl2 is widespread, including the gastrointestinal tract, ovary and uterus. Angptl3 and Angptl6 (angiopoietin-related growth factor [AGF]) expression is restricted predominantly to liver (though Angptl6 is also expressed in hemopoietic cells), while Angptl4 expression is most abundant in liver and adipose tissue. Angptl3, 4 and 6 are detected in the systemic circulation, suggesting an endocrine function. Angptl peptides, like the angiopoietins, play an important role in angiogenesis, but have additional novel effects on triglyceride and lipid metabolism, and on insulin sensitivity. Thus, Angptl3, a downstream target of the oxysterol receptor LXR, mediates the hypertriglyceridemia seen following treatment with LXR agonists [4]. The mechanism for this effect appears to be via Angptl3mediated reductions in VLDL clearance secondary to the inhibition of lipoprotein lipase (LPL) and direct activation of lipolysis in adipocytes [5,6]. Angptl4, (also called peroxisome proliferator-activated—g angiopoietin-related protein [PGAR] and fasting-induced adipose factor [FIAF]) is a downstream target of peroxisome proliferator-activated receptors (PPARs), including PPARa (important in fatty acid oxidation) and PPARg (involved in modulating insulin sensitivity and adipocyte differentiation) [7,8]. The role of PPARd(b) in modulating Angptl4 transcription remains controversial. Angptl4, like Angptl3, increases circulating triglycerides by inhibition of LPL. Being downstream of PPARg, Angptl4 has beneficial effects on insulin sensitivity [9]. Perhaps the most interesting member of the Angptl family in relation to glucose and lipid homeostasis and insulin sensitivity is Angptl6, the subject of the paper by Oike et al. [1]. Previously cloned in the same laboratory [10], Angptl6, highly expressed in the liver and present in the circulation, promotes angiogenesis and keratinocyte proliferation leading to rapid wound closure. The current manuscript characterises the metabolic actions of Angptl6, using knock-out and knock-in technology. In brief, O80% of Angptl6 K/Kmice die around embryonic day 13, while surviving offspring develop visceral and subcutaneous adiposity, increased adipocyte size, triglyceride accumulation in skeletal muscle, liver and brown adipose tissue (BAT) and an elevation in circulating free fatty acids. The mice exhibited hyperglycemia, hyperinsulinemia and reduced insulin sensitivity. Serum levels of TNF and adiponectin were unaltered, while consistent with the increased adipocyte mass, leptin levels were elevated. Most interestingly, Angptl6 K/K mice had lower rectal temperatures and a concomitant reduction in oxygen consumption without any alteration in food intake, suggesting that adiposity in these mice was secondary to an impairment in adaptive thermogenesis. Molecular evidence for such an effect included
833
a reduction in the mRNA expression of genes involved in stimulating energy expenditure, including PPARa, PPARg and their co-activators PGC-1 and UCPI in BAT and PPARd(b) and UCP3 in skeletal muscle [1]. The expected converse effects were noted in Angptl6transgenic mice generated using the CAG promoter. Despite normal energy intake, these mice were lean with reduced subcutaneous and visceral fat relative to controls. Transgenic mice were more insulin-sensitive despite a lower serum leptin. This effect, in part, could be mediated by a direct effect of increased serum Angptl6 or perhaps be a consequence of the abundant secretion of adiponectin by white adipose tissue (WAT) in the transgenic mice. The postulated mechanisms for the reduction in body weight included improved adaptive thermogenesis in the transgenic animals manifested by an increase in the basal metabolic rate, and increased angiogenesis in skeletal muscle leading to heat dissipation. Genes coding for proteins mediating energy expenditure, including PPARa, PPARg and PGC-1b in BAT and PPARa PPARd(b), PGC-1a and UCP2 in skeletal muscle were upregulated. From a therapeutic perspective, transgene expression reduced adiposity as well as triglyceride accumulation in BAT, liver and skeletal muscle, improved serum lipid profiles and reduced plasma insulin in mice fed a high fat diet. Results of insulin sensitivity tests were not reported. High fat fed wild-type mice injected with an adenovirus construct expressing Angptl6 demonstrated weight loss and improvements in insulin sensitivity, despite a normal food intake. These studies clearly demonstrate a major role for the Angptl peptides and in particular, hepatocyte-derived Angptl6 in the modulation of body weight, adiposity and insulin sensitivity. Increasing energy expenditure in the setting of obesity and reduced physical activity, as seen in a large proportion of adults in economically advantaged societies, would appear to be a particularly attractive modality for combating obesity and insulin resistance. Further, the dual role of Angptl6, in stimulating energy expenditure and heat dissipation (through its angiogenic properties), renders this protein and any future agonists, particularly appealing. Despite their obvious potential, several unanswered questions remain, including the nature of and reasons for the differences between the O80% of Angptl6 knock-out mice that die in utero and their surviving litter mates that have normal vasculogenesis. Likewise, while mRNA expression studies of genes involved in energy expenditure are suggestive, analysis of protein expression would have been useful. The reasons for the elevations in UCP2 mRNA in both Angptl6 knock-out and transgenic mice in skeletal muscle are unclear. To fully realise their therapeutic potential, future studies need to identify the cognate receptors of the
834
J. George / Journal of Hepatology 44 (2006) 832–834
Angptl peptides, their tissue distribution and downstream signalling pathways. Further, the relationship of Angptl6 protein in serum and/or human tissues to the presence or absence of obesity and insulin resistance needs to be addressed. Knowledge of the key regulators of Angptl6 expression is unknown, particularly in relation to nutrient intake. Identifying the positive and negative transcriptional regulators of Angptl6 would be an important area for future study. In the realms of hepatology, improvements in obesity and insulin sensitivity following high fat feeding to Angptl6 over-expressing mice resulted in reductions in hepatic triglyceride deposition. If such findings are translated to humans, Angptl6 agonists would be expected to result in improvements in and the consequences of both alcoholic and non-alcoholic fatty liver diseases. More intriguing would be the effects of Angptl6 modulation on hepatic fibrogenesis given that transgene expression in keratinocytes was associated with accelerated wound closure [10]. The interplay between Angptl6 and other adipokines with a demonstrated role in fibrogenesis and lipid homeostasis, including leptin and adiponectin remains a fertile area for study. Like all interesting observations, the discovery of Angptl peptides has raised many questions. It points yet once again, however, to the increasing complexity (and perhaps redundancy) of the networks that regulate metabolic homeostasis. Unravelling these mysteries should lead to important therapeutic advances and clinical applications for the angiopoietin-like peptides and their agonists.
References [1] Oike Y, Akao M, Yasunaga K, Yamauchi T, Morisada T, Ito Y, et al. Angiopoietin-related growth factor antagonizes obesity and insulin resistance. Nat Med 2005;11:400–408. [2] Pittas AG, Joseph NA, Greenberg AS. Adipocytokines and insulin resistance. J Clin Endocrinol Metab 2004;89:447–452. [3] Oike Y, Akao M, Kubota Y, Suda T. Angiopoietin-like proteins: potential new targets for metabolic syndrome therapy. Trends Mol Med 2005;11:473–479. [4] Inaba T, Matsuda M, Shimamura M, Takei N, Terasaka N, Ando Y, et al. Angiopoietin-like protein 3 mediates hypertriglyceridemia induced by the liver X receptor. J Biol Chem 2003;278:21344–21351. [5] Shimizugawa T, Ono M, Shimamura M, Yoshida K, Ando Y, Koishi R, et al. ANGPTL3 decreases very low density lipoprotein triglyceride clearance by inhibition of lipoprotein lipase. J Biol Chem 2002;277:33742–33748. [6] Shimamura M, Matsuda M, Kobayashi S, Ando Y, Ono M, Koishi R, et al. Angiopoietin-like protein 3, a hepatic secretory factor, activates lipolysis in adipocytes. Biochem Biophys Res Commun 2003;301: 604–609. [7] Yoon JC, Chickering TW, Rosen ED, Dussault B, Qin Y, Soukas A, et al. Peroxisome proliferator-activated receptor gamma target gene encoding a novel angiopoietin-related protein associated with adipose differentiation. Mol Cell Biol 2000;20:5343–5349. [8] Kersten S, Mandard S, Tan NS, Escher P, Metzger D, Chambon P, et al. Characterization of the fasting-induced adipose factor FIAF, a novel peroxisome proliferator-activated receptor target gene. J Biol Chem 2000;275:28488–28493. [9] Xu A, Lam MC, Chan KW, Wang Y, Zhang J, Hoo RL, et al. Angiopoietin-like protein 4 decreases blood glucose and improves glucose tolerance but induces hyperlipidemia and hepatic steatosis in mice. Proc Natl Acad Sci USA 2005;102:6086–6091. [10] Oike Y, Yasunaga K, Ito Y, Matsumoto S, Maekawa H, Morisada T, et al. Angiopoietin-related growth factor (AGF) promotes epidermal proliferation, remodeling, and regeneration. Proc Natl Acad Sci USA 2003;100:9494–9499.
Journal Club Special Section Editors: Peter R. Galle, Peter L.M. Jansen, Jean-Pierre Vinel, Francesco Negro
Angiopoietin-like proteins: Another player in the metabolic field Jacob George* Storr Liver Unit, Westmead Millennium Institute, University of Sydney and Department of Gastroenterology and Hepatology, Westmead Hospital, Westmead, Sydney, NSW 2145, Australia
Angiopoietin-related growth factor antagonizes obesity and insulin resistance. Oike Y, Akao M, Yasunaga K, Yamauchi T, Morisada T, Ito Y, Urano T, Kimura Y, Kubota Y, Maekawa H, Miyamoto T, Miyata K, Matsumoto S, Sakai J, Nakagata N, Takeya M, Koseki H, Ogawa Y, Kadowaki T, Suda T. Angiopoietin-related growth factor (AGF), a member of the angiopoietin-like protein (Angptl) family, is secreted predominantly from the liver into the systemic circulation. Here, we show that most (O80%) of the AGF-deficient mice die at about embryonic day 13, whereas the surviving AGF-deficient mice develop marked obesity, lipid accumulation in skeletal muscle and liver, and insulin resistance accompanied by reduced energy expenditure relative to controls. In parallel, mice with targeted activation of AGF show leanness and increased insulin sensitivity resulting from increased energy expenditure. They are also protected from high-fat diet-induced obesity, insulin resistance and nonadipose tissue steatosis. Hepatic overexpression of AGF by adenoviral transduction, which leads to an approximately 2.5-fold increase in serum AGF concentrations, results in a significant (P!0.01) body weight loss and increases insulin sensitivity in mice fed with a high-fat diet. This study establishes AGF as a new hepatocyte-derived circulating factor that counteracts obesity and related insulin resistance. [Abstract reproduced by permission of Nat Med 2005;11(4):400–8]
The last century has witnessed significant advances in medical science that have lead to major inroads in the * Tel.: C61 2 9845 7705; fax: C61 2 9635 7582. E-mail address: [email protected] (J. George).
fight against microbial diseases. Research more recently, has shifted to understanding and combating the morbidity and mortality associated with malignancy, degenerative disorders and now, the metabolic consequences associated with increasing adiposity. The latter, encompassed by the term metabolic syndrome, refers to a collection of diseases linked to visceral obesity and includes insulin resistance and type 2 diabetes, dyslipidemia, hypertension, accelerated atherosclerotic cardiovascular disease and for the hepatologist, non-alcoholic fatty liver disease (NAFLD). From a public health perspective, policies directed towards reduced energy intake, improved nutrient composition and increased physical activity are the cornerstones for disease prevention and treatment. From a pharmacotherapeutic perspective, understanding the cellular and molecular mechanisms, whereby a net positive energy balance leads to visceral adiposity and the metabolic syndrome, are central to the development of novel approaches to combat these disorders. In this respect, the elegant studies by Oike et al. [1] represent another piece in a puzzle of ever increasing complexity. The hormonal networks and their downstream targets that regulate glucose and lipid metabolism have increased exponentially from the days when insulin was the dominant player. The current plethora of regulatory peptides include the adipose derived cytokines (adipokines) leptin, adiponectin, resistin, TNF and IL6, and more recently the angiopoietin-like (Angptl) family of proteins, 1–6 (Angptl1 to Angptl6) [2,3]. Structurally related to angiopoietins, which play a major role in angiogenesis, the Angptl peptides, like the angiopoietins, comprise a coiled-coil domain and a fibrinogen-like domain [3]. Perhaps, because they lack a cystein-based motif in the fibrinogen-like domain, the Angptl proteins fail to bind the angiopoietin TIE receptors, TIE1 and TIE2. Since, the receptors for the Angptl’s are
0168-8278/$32.00 q 2006 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jhep.2006.01.010
J. George / Journal of Hepatology 44 (2006) 832–834
currently unknown, these peptides are considered orphan ligands. Expression of Angptl1 and Angptl2 is widespread, including the gastrointestinal tract, ovary and uterus. Angptl3 and Angptl6 (angiopoietin-related growth factor [AGF]) expression is restricted predominantly to liver (though Angptl6 is also expressed in hemopoietic cells), while Angptl4 expression is most abundant in liver and adipose tissue. Angptl3, 4 and 6 are detected in the systemic circulation, suggesting an endocrine function. Angptl peptides, like the angiopoietins, play an important role in angiogenesis, but have additional novel effects on triglyceride and lipid metabolism, and on insulin sensitivity. Thus, Angptl3, a downstream target of the oxysterol receptor LXR, mediates the hypertriglyceridemia seen following treatment with LXR agonists [4]. The mechanism for this effect appears to be via Angptl3mediated reductions in VLDL clearance secondary to the inhibition of lipoprotein lipase (LPL) and direct activation of lipolysis in adipocytes [5,6]. Angptl4, (also called peroxisome proliferator-activated—g angiopoietin-related protein [PGAR] and fasting-induced adipose factor [FIAF]) is a downstream target of peroxisome proliferator-activated receptors (PPARs), including PPARa (important in fatty acid oxidation) and PPARg (involved in modulating insulin sensitivity and adipocyte differentiation) [7,8]. The role of PPARd(b) in modulating Angptl4 transcription remains controversial. Angptl4, like Angptl3, increases circulating triglycerides by inhibition of LPL. Being downstream of PPARg, Angptl4 has beneficial effects on insulin sensitivity [9]. Perhaps the most interesting member of the Angptl family in relation to glucose and lipid homeostasis and insulin sensitivity is Angptl6, the subject of the paper by Oike et al. [1]. Previously cloned in the same laboratory [10], Angptl6, highly expressed in the liver and present in the circulation, promotes angiogenesis and keratinocyte proliferation leading to rapid wound closure. The current manuscript characterises the metabolic actions of Angptl6, using knock-out and knock-in technology. In brief, O80% of Angptl6 K/Kmice die around embryonic day 13, while surviving offspring develop visceral and subcutaneous adiposity, increased adipocyte size, triglyceride accumulation in skeletal muscle, liver and brown adipose tissue (BAT) and an elevation in circulating free fatty acids. The mice exhibited hyperglycemia, hyperinsulinemia and reduced insulin sensitivity. Serum levels of TNF and adiponectin were unaltered, while consistent with the increased adipocyte mass, leptin levels were elevated. Most interestingly, Angptl6 K/K mice had lower rectal temperatures and a concomitant reduction in oxygen consumption without any alteration in food intake, suggesting that adiposity in these mice was secondary to an impairment in adaptive thermogenesis. Molecular evidence for such an effect included
833
a reduction in the mRNA expression of genes involved in stimulating energy expenditure, including PPARa, PPARg and their co-activators PGC-1 and UCPI in BAT and PPARd(b) and UCP3 in skeletal muscle [1]. The expected converse effects were noted in Angptl6transgenic mice generated using the CAG promoter. Despite normal energy intake, these mice were lean with reduced subcutaneous and visceral fat relative to controls. Transgenic mice were more insulin-sensitive despite a lower serum leptin. This effect, in part, could be mediated by a direct effect of increased serum Angptl6 or perhaps be a consequence of the abundant secretion of adiponectin by white adipose tissue (WAT) in the transgenic mice. The postulated mechanisms for the reduction in body weight included improved adaptive thermogenesis in the transgenic animals manifested by an increase in the basal metabolic rate, and increased angiogenesis in skeletal muscle leading to heat dissipation. Genes coding for proteins mediating energy expenditure, including PPARa, PPARg and PGC-1b in BAT and PPARa PPARd(b), PGC-1a and UCP2 in skeletal muscle were upregulated. From a therapeutic perspective, transgene expression reduced adiposity as well as triglyceride accumulation in BAT, liver and skeletal muscle, improved serum lipid profiles and reduced plasma insulin in mice fed a high fat diet. Results of insulin sensitivity tests were not reported. High fat fed wild-type mice injected with an adenovirus construct expressing Angptl6 demonstrated weight loss and improvements in insulin sensitivity, despite a normal food intake. These studies clearly demonstrate a major role for the Angptl peptides and in particular, hepatocyte-derived Angptl6 in the modulation of body weight, adiposity and insulin sensitivity. Increasing energy expenditure in the setting of obesity and reduced physical activity, as seen in a large proportion of adults in economically advantaged societies, would appear to be a particularly attractive modality for combating obesity and insulin resistance. Further, the dual role of Angptl6, in stimulating energy expenditure and heat dissipation (through its angiogenic properties), renders this protein and any future agonists, particularly appealing. Despite their obvious potential, several unanswered questions remain, including the nature of and reasons for the differences between the O80% of Angptl6 knock-out mice that die in utero and their surviving litter mates that have normal vasculogenesis. Likewise, while mRNA expression studies of genes involved in energy expenditure are suggestive, analysis of protein expression would have been useful. The reasons for the elevations in UCP2 mRNA in both Angptl6 knock-out and transgenic mice in skeletal muscle are unclear. To fully realise their therapeutic potential, future studies need to identify the cognate receptors of the
834
J. George / Journal of Hepatology 44 (2006) 832–834
Angptl peptides, their tissue distribution and downstream signalling pathways. Further, the relationship of Angptl6 protein in serum and/or human tissues to the presence or absence of obesity and insulin resistance needs to be addressed. Knowledge of the key regulators of Angptl6 expression is unknown, particularly in relation to nutrient intake. Identifying the positive and negative transcriptional regulators of Angptl6 would be an important area for future study. In the realms of hepatology, improvements in obesity and insulin sensitivity following high fat feeding to Angptl6 over-expressing mice resulted in reductions in hepatic triglyceride deposition. If such findings are translated to humans, Angptl6 agonists would be expected to result in improvements in and the consequences of both alcoholic and non-alcoholic fatty liver diseases. More intriguing would be the effects of Angptl6 modulation on hepatic fibrogenesis given that transgene expression in keratinocytes was associated with accelerated wound closure [10]. The interplay between Angptl6 and other adipokines with a demonstrated role in fibrogenesis and lipid homeostasis, including leptin and adiponectin remains a fertile area for study. Like all interesting observations, the discovery of Angptl peptides has raised many questions. It points yet once again, however, to the increasing complexity (and perhaps redundancy) of the networks that regulate metabolic homeostasis. Unravelling these mysteries should lead to important therapeutic advances and clinical applications for the angiopoietin-like peptides and their agonists.
References [1] Oike Y, Akao M, Yasunaga K, Yamauchi T, Morisada T, Ito Y, et al. Angiopoietin-related growth factor antagonizes obesity and insulin resistance. Nat Med 2005;11:400–408. [2] Pittas AG, Joseph NA, Greenberg AS. Adipocytokines and insulin resistance. J Clin Endocrinol Metab 2004;89:447–452. [3] Oike Y, Akao M, Kubota Y, Suda T. Angiopoietin-like proteins: potential new targets for metabolic syndrome therapy. Trends Mol Med 2005;11:473–479. [4] Inaba T, Matsuda M, Shimamura M, Takei N, Terasaka N, Ando Y, et al. Angiopoietin-like protein 3 mediates hypertriglyceridemia induced by the liver X receptor. J Biol Chem 2003;278:21344–21351. [5] Shimizugawa T, Ono M, Shimamura M, Yoshida K, Ando Y, Koishi R, et al. ANGPTL3 decreases very low density lipoprotein triglyceride clearance by inhibition of lipoprotein lipase. J Biol Chem 2002;277:33742–33748. [6] Shimamura M, Matsuda M, Kobayashi S, Ando Y, Ono M, Koishi R, et al. Angiopoietin-like protein 3, a hepatic secretory factor, activates lipolysis in adipocytes. Biochem Biophys Res Commun 2003;301: 604–609. [7] Yoon JC, Chickering TW, Rosen ED, Dussault B, Qin Y, Soukas A, et al. Peroxisome proliferator-activated receptor gamma target gene encoding a novel angiopoietin-related protein associated with adipose differentiation. Mol Cell Biol 2000;20:5343–5349. [8] Kersten S, Mandard S, Tan NS, Escher P, Metzger D, Chambon P, et al. Characterization of the fasting-induced adipose factor FIAF, a novel peroxisome proliferator-activated receptor target gene. J Biol Chem 2000;275:28488–28493. [9] Xu A, Lam MC, Chan KW, Wang Y, Zhang J, Hoo RL, et al. Angiopoietin-like protein 4 decreases blood glucose and improves glucose tolerance but induces hyperlipidemia and hepatic steatosis in mice. Proc Natl Acad Sci USA 2005;102:6086–6091. [10] Oike Y, Yasunaga K, Ito Y, Matsumoto S, Maekawa H, Morisada T, et al. Angiopoietin-related growth factor (AGF) promotes epidermal proliferation, remodeling, and regeneration. Proc Natl Acad Sci USA 2003;100:9494–9499.