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Diabetic nephropathy: protective factors and a new therapeutic paradigm
Journal of Diabetes and Its Complications xxx (2013) xxx–xxx
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Journal of Diabetes and Its Complications j o u r n a l h o m e p a g e : W W W. J D C J O U R N A L . C O M
Diabetic nephropathy: protective factors and a new therapeutic paradigm☆ Akira Mima ⁎ Department of Nephrology, Graduate School of Medicine, Institute of Health Biosciences, University of Tokushima, Tokushima, Japan
a r t i c l e
i n f o
Article history: Received 4 January 2013 Received in revised form 25 February 2013 Accepted 19 March 2013 Available online xxxx Keywords: Diabetic nephropathy (DN) Insulin Insulin receptor substrate 1 (IRS1) Protein kinase C (PKC) Vascular endothelial growth factor (VEGF) Src homology-2 domain containing phosphatase-1 (SHP-1) Glucagon like peptide-1 (GLP-1) Dipeptidyl peptidase-4 (DPP-4) inhibitors Endostatin Tumstatin Angiopoietins
a b s t r a c t Diabetic nephropathy (DN) is the most common cause of chronic kidney disease (CKD) and its number has been increasing. CKD is a worldwide threat to health but the precise mechanism of this problem is not fully appreciated. It is believed that hyperglycemia is one of the most important metabolic factors in the development of DN. Multiple molecular mechanisms have been proposed to mediate hyperglycemia’s adverse effects on kidney. To identify targets for therapeutic intervention, most studies have focused on understanding how abnormal levels of such metabolities cause DN. However, there have been few reports regarding endogenous renal protective factors. Thus, recognition of the importance of this could be providing a new perspective for understanding the development of DN and a new therapeutic paradigm to combat DN. © 2013 Elsevier Inc. All rights reserved.
1. Introduction
2. Endogenous protective factors
Diabetes nephropathy (DN) is the most important cause of chronic kidney disease (CKD) in the world that often leads to requirements for dialysis or renal replacement therapy. There have been many advances in the management of DN (The Diabetes Control & Complications Trial Research Group, 1993; UK Prospective Diabetes Study (UKPDS) Group, 1998). It is well known that activation of the renin–angiotensin system contributes to the development of DN and angiotensin-converting enzyme inhibitors (ACEI) or AT1 receptor blockers (ARB) could attenuate DN. However, recent studies suggest these drugs delay but cannot stop the progression of DN (Brenner et al., 2001; Lewis et al., 2001). Despite a reasonable understanding of the pathogenesis and pathology of DN, only few studies revealed the importance of endogenous protective factors or the inhibitory effects of hyperglycemia. This review will focus on the evidence supporting the importance of endogenous protective factors that prevent the progression of DN.
2.1. Insulin
☆ The authors declare that they have no conflict of interest. ⁎ Corresponding author. Department of Nephrology, Graduate School of Medicine, Institute of Health Biosciences, University of Tokushima, Tokushima 770-8503, Japan. Tel.: +81 88 633 7184, fax: +81 88 633 9245. E-mail address: [email protected].
Insulin has many vasotropic actions including survival factors for vascular endothelial cells including glomeruli. Hyperglycemia can selectively inhibit insulin’s anti-atherosclerotic or anti-glomerulosclerotic actions, while hyperinsulinemia, as observed in insulinresistant type 2 diabetes, can enhance insulin’s pro-atherosclerotic diseases (Rask-Madsen & King, 2007). Insulin resistance in vascular tissue is associated with endothelial dysfunction, leading to cardiovascular diseases including atherosclerosis and DN in animal models (Mima et al., 2011; Rask-Madsen & King, 2007). However, hyperinsulinemia itself does not affect atherosclerosis (Rask-Madsen et al., 2012). Insulin can stimulate the production of nitric oxide (NO), which results in vasodilatation and inhibit smooth muscle cell growth and migration, and podocyte apoptosis. Impaired insulin’s action has recognized in the endothelial and mesangial cells in diabetic glomeruli, presumably through the activation of protein kinase C (PKC)β2 isoform (Mima et al., 2011). Insulin-induced NO production has been reported to be mediated through insulin receptor-mediated activation of the insulin receptor substrate (IRS)/PI3K/Akt/endothelial NO synthase (eNOS) (Kuboki et al., 2000; Montagnani, Chen, Barr, & Quon, 2001). Rask-Madsen et al. clearly demonstrated the importance of vascular insulin signaling in
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Please cite this article as: Mima, A., Diabetic nephropathy: protective factors and a new therapeutic paradigm, Journal of Diabetes and Its Complications (2013), http://dx.doi.org/10.1016/j.jdiacomp.2013.03.003
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endothelial insulin receptor knock-out mice (Rask-Madsen et al., 2010). In diabetes and insulin resistance states, the IRS1/Akt/eNOS pathway is selectively inhibited, but another major pathway of insulin signaling, mitogen-activated protein kinase (MAPK), is not inhibited (Jiang et al., 1999; Mima et al., 2011). Interestingly, this selective insulin resistance has also been shown in skeletal muscle from obesity and type 2 diabetes patients (Cusi et al., 2000), and in the vasculature, myocardium of Zucker fatty rats, which are the animal models of insulin resistance (He et al., 2006). Insulin-stimulated endothelin-1 (ET-1) expression might be preserved in insulin resistance (Oliver et al., 1991), since ET-1 expression is dependent on nuclear factors fos/ jun downstream of MAPK signaling (Lee et al., 1991). Further, recent studies clearly show that PKCβ specific inhibitor, ruboxistaurin (RBX) improved insulin signaling on NO production in the vasculature, myocardium and glomeruli of streptozotocin-induced STZ rats and Zucker fatty rats (Mima et al., 2011; Naruse et al., 2006). Other reports indicated that PKCβ directly inhibited insulin signaling. That is, phorbol 12-myristate 13-acetate (PMA) inhibits IRS2/PI3K activity (Kuboki et al., 2000) or IRS1 tyrosine phosphorylation (Motley et al., 2002). Mutations of IRS1 decreased insulininduced eNOS activity through IRS1/PI3K/Akt (Federici et al., 2004). Further, we have shown that high glucose inhibited phosphorylation of Akt, eNOS and glycogen synthase kinase (GSK)3α, decreased IRS1 protein expression and increased association with ubiquitination in glomerular endothelial cells (Mima et al., 2011). Studies using mice overexpressing PKCβ2 in endothelial cells (EC-PKCβ2) showed impaired insulin signaling in renal cortex and diabetic EC-PKCβ2 exhibited more albuminuria and increasing extracellular matrix (Mima, Hiraoka-Yamomoto, et al., 2012). Also, overexpression of IRS1 or RBX reversed the inhibitory effects of high glucose (Mima et al., 2011). Thus, inhibition of PKCβ activity or increasing IRS1 activity in glomerular endothelial cell could be a new therapeutic paradigm. Recent study using mice deleted insulin receptor specifically from podocytes showed severe albuminuria, increasing podocyte apoptosis and deposition of components of the basal membrane (Welsh et al., 2010). This finding strongly supports the importance of insulin signaling as a renoprotective factor. 2.2. HO-1 It is reported that heme oxygenase-1 (HO-1), a potent antioxidant enzyme that can interrupt major mechanisms of vascular injury, is normally upregulated in response to inflammation and oxidative stress. Studies using mice deleted HO-1 gene showed increases of monocyte chemoattractant protein-1 (MCP-1) expression and nuclear factor-κB (NF-κB) activation (Seldon et al., 2007; Tracz et al., 2008). Recently, Geraldes et al. showed that insulin significantly increase protein levels of HO-1 and insulin treatment prevented oxidative stress induced-NF-κB and caspase-8 activation and apoptosis via IRS1/PI3K/Akt2/HO-1 pathway in pericytes (Geraldes et al., 2008). Induction of HO-1 improves hyperglycemia, and reduces podocyte apoptosis and glomerular injury (Elmarakby, Faulkner, Baban, Saleh, & Sullivan, 2012; Lee et al., 2009; Ptilovanciv et al., 2013). Therefore, increasing HO-1 activity through improving insulin sensitivity in glomeruli could decrease the risk for DN. 2.3. VEGF-A Vascular endothelial growth factor (VEGF)-A belongs to a family of growth factors that include VEGF-B, -C, -D, and –E, and platelet-derived growth factor (PDGF) (Carmeliet et al., 1996; Ferrara & Gerber, 2001; Gerber et al., 1999). Among them, VEGF-A plays a significant role in angiogenesis and vascular permeability. VEGF-A is one of the most important growth factor that responds
to hypoxia under normal physiological levels (Ferrara, 2004). Activity of VEGF-A is the ability to promote growth of vascular endothelial cells. VEGF-A promotes angiogenesis, inducing confluent microvascular endothelial cells to invade collagen gel (Nicosia, Nicosia, & Smith, 1994). VEGF-A is also a survival factor for endothelial cells (Alon et al., 1995; Gerber, Dixit, & Ferrara, 1998). VEGF-A prevents endothelial cell apoptosis induced by serum starvation and such activity is mediated by PI3K/Akt pathway (Fujio & Walsh, 1999; Gerber, McMurtrey, et al., 1998). VEGF-A also increases the expression of the anti-apoptotic proteins Bcl-2 (Gerber, Dixit, et al., 1998) or survivin (Tran et al., 2002). Further, VEGF-A increased phosphorylation of Akt and eNOS that prevent endothelial cell apoptosis (Mima, Kitada, et al., 2012). Increases in levels of VEGF-A are recognized in podocytes and mesangial cells in DN (Chen & Ziyadeh, 2008). There are several reports regarding inhibition of VEGF-A results in amelioration of proteinuria and reduction in mesangial expansion in the early stage of DN in rodent models (Ku et al., 2008; Sung et al., 2006). In contrast, some groups showed treatment with VEGF-A antibodies did not improve DN in diabetic rats (Schrijvers et al., 2005). Further, several patients treated with anti-VEGF agent showed proteinuria, hypertension, and renal failure (Eremina et al., 2008). Supporting these phenomena, recent studies have suggested that VEGF-A might be a renoprotective factor, since VEGF-A null mice show proteinuria, glomerulosclerosis and renal failure (Eremina et al., 2003). Also, during fetal development, one of the cell types producing the largest amounts of VEGF-A is the podocytes. Different from many other cells, podocytes continue to express VEGF-A when they are fully differentiated, though absolute levels of expression decrease (Sison et al., 2010). Recently, our study showed that diabetes can cause podocyte apoptosis partly due to increased PKCδ/p38MAPK activation and the expression of Src homology-2 domain-containing phosphatase-1 (SHP-1) to cause impairment of VEGF signaling (Mima, Kitada, et al., 2012). Thus, fine balance in the regulation of VEGF-A activity seems to be important for preventing DN. However, further studies will be needed to conclude whether VEGF-A is truly an endogenous protective factor for DN or not.
2.4. Glucagon like peptide-1 and DPP-4 inhibitors GLP-1 is an incretin hormone which can augment glucosedependent insulin release and promote preservation of β cells (Drucker, 2006). Analysis of GLP-1 receptor (GLP-1R) revealed its expression in endothelial cells and kidney (Bullock, Heller, & Habener, 1996; Erdogdu, Nathanson, Sjoholm, Nystrom, & Zhang, 2010). It is reported that GLP-1 has multiple vasotropic actions in addition to its effects to insulin secretion. For example, its analog, exendin-4, has been shown to improve left ventricular function after myocardial infarction or ischemia (Nikolaidis et al., 2004; Nystrom et al., 2004). In endothelial cells, GLP-1 might inhibit the expression of tumor necrosis factor-α (TNF-α) and vascular cell adhesion molecule-1 (VCAM-1) (Kodera et al., 2011; Liu, Dear, Knudsen, & Simpson, 2009). Recently, we have shown that GLP-1 is partly mediating its protective actions via its own receptor by the activation of protein kinase A (PKA). The elevation of cAMP levels increased the phosphorylation at phospho-c-Raf (Ser259) that may inhibit phospho-c-Raf (Ser338)/phospho-Erk1/2 which are activated by Ang II to induce its inflammatory action such as plasminogen activator inhibitor-1 (PAI-1), CD68 and CXCL2 expression. Further, we clearly indicated PKCβ activation induced by hyperglycemia or free fatty acids can inhibit GLP-1’s protective actions and enhance inflammatory effects on the endothelium by two mechanisms; PKCβ enhances Ang II’s action and decreases GLP-1R by its ubiquitination (Mima, Hiraoka-Yamomoto, et al., 2012).
Please cite this article as: Mima, A., Diabetic nephropathy: protective factors and a new therapeutic paradigm, Journal of Diabetes and Its Complications (2013), http://dx.doi.org/10.1016/j.jdiacomp.2013.03.003
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Dipeptidyl peptidase-4 (DPP-4) inhibitors are considered incretin enhancers; these agents increase active incretin levels by preventing their rapid degradation. Like GLP-1 analog, recent studies suggest that DPP-4 inhibitors also have vasotropic actions and the possibility of an actual reduction in cardiovascular diseases and DN (Chrysant & Chrysant, 2012; Liu et al., 2012).
2.5. Activated protein C Activated protein C (APC) functions by inhibiting factors Va and VIIIa and has pro-fibrinolytic function by modifying clot formation and inhibiting PAI-1 (Fulcher, Gardiner, Griffin, & Zimmerman, 1984; Gruber, Mori, del Zoppo, Waxman, & Griffin, 1994). Further, the levels of APC are reduced and thrombomodulin/protein C system is inhibited in diabetic patients (Hafer-Macko, Ivey, Gyure, Sorkin, & Macko, 2002). Isermann et al. reported that APC modulates DN by modulating apoptosis of endothelial cells and podocytes, using thrombomodulin dependent protein C activation knockout mice or mice that express a hyperactivatable protein C overexpression (Bock et al., 2013; Isermann et al., 2007). Also, recent studies have revealed exogenous APC could improve renal function and pathological changes in mice with diabetic nephropathy, suppressing oxidative stress, the expression of fibrogenic cytokines and growth factors (Bock et al., 2013; Gil-Bernabe et al., 2012). However, a 2012 trial supports the decision to withdraw drotrecogin, recombinant form of human APC, because previous meta-analysis study might improperly strengthen positive results and bleeding concerns were recognized in sepsis trial.
2.6. Endostatin and tumstatin Endostatin and tumstatin inhibit proliferation and migration, and cell-cycle arrest of endothelial cell. They also serve as inhibitors of angiogenesis by suppressing diabetes-induced excessive VEGF-A. Although complete inhibition of VEGF-A in DN remains controversial, induction of these drugs significantly decreased inflammatory markers and mesangial expansion in the early phase of DN (Ichinose et al., 2005; Yamamoto et al., 2004). This finding strongly supports effective therapies for DN need to decrease angiogenic response.
Angiotensin II ET-1
2.7. Angiopoietins It is well known that physiological levels of angiopoietin (Ang)-1 are important for maintaining intact glomerular structures. Also, Ang1 enhances endothelial cell survival and stability (Thurston et al., 2000). In contrast, Ang-2, which antagonizes Ang-1’s effect, induces endothelial cell death and vessel regression. Ang-1 was decreased in the glomeruli of diabetic rats, while Ang-2 was increased. Further, recent study shows upregulation of Ang-2 in the glomeruli and decreased Ang-1/Ang-2 ratio accompanied by inflammation (Ichinose et al., 2005; Ichinose et al., 2006; Yamamoto et al., 2004). Increases in the levels of Ang-1 in the glomeruli using adenoviral vector seem to be effective for the treatment of DN (Lee et al., 2007). 2.8. Adiponectin Adiponectin derived from adipose tissues and its signaling mechanisms through the receptors Adipo-R1 and Adipo-R2, including AMP-activated protein kinase (AMPK) and cAMP/PKA pathways have been implicated in the functions of endothelial cells (Kim et al., 2010; Ouedraogo et al., 2006). Adiponectin suppresses inflammation including tumor necrosis factor-α (TNF-α) and NF-κB (Ouchi et al., 2000). Recent studies have indicated that adiponectin prevents in the injured kidney including DN (Nakamaki et al., 2011). However, it is still unclear whether adiponectin will provide significant effects toward human DN. 3. Summary Although good glycemic control may be the best prevention of DN, it develops in spite of treatment of diabetes. Inhibitors of the aldose reductase pathway, advanced glycation end products (AGEs), oxidative stress, PKC, TGFβ-Smads pathway, inflammation, and the reninangiotensin system, for example, should provide useful targets for therapy; however, unfortunately, many clinical trials using agents directly against these targets have not shown to decrease DN. Thus, we proposed the importance of endogenous protective factors, such as insulin, VEGF and GLP-1, and inhibitory effects of hyperglycemia in neutralizing these protective factors during the initiation and progression of DN (Fig. 1).
Hyperglycemia/diabetes/ n-3 fatty acids
Mesangial cell, endothelial cell
Podocyte
PKCα, β activation
PKCδ activation
Inhibition Inhibition of IRS1 of GLP-1R
p38MAPK
PI3K/Akt NO
VEGF
Endothelial dysfunction
Accumulation of ECM, increase of mesangial expansion
3
SHP-1 Inhibition of IRS1?
NF-κB
Inhibition Caspase of VEGF activation
PI3K/Akt
Podocyte apoptosis
Fig. 1. Schematic representation of potential protective factors and biological targets of PKC activation leading to diabetic nephropathy. PKC, protein kinase C; ET-1, endothelin-1; IRS1, insulin receptor substrate1; NO, nitric oxide; VEGF, vascular endothelial growth factor; GLP-1R, glucagon like peptide-1 receptor; p38 MAPK, p38 MAP kinase; SHP-1, Src homology-2 domain-containing phosphatase-1; NF-κB, nuclear factor-κB; ECM, extracellular matrix.
Please cite this article as: Mima, A., Diabetic nephropathy: protective factors and a new therapeutic paradigm, Journal of Diabetes and Its Complications (2013), http://dx.doi.org/10.1016/j.jdiacomp.2013.03.003
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In summary, new therapeutic approaches targeting these molecules for DN need to decrease hyperglycemia’s toxic effect and to increase the action of protective factors. Acknowledgment Preparation of this publication was supported by grants to A.M. from Grant-in-Aid for Scientific Research (24890148) from Japan Society for the Promotion of Science, Kurozumi Medical Foundation, Mochida Memorial Foundation for Medical and Pharmaceutical Research, Takeda Science Foundation, Japanese Association of Dialysis Physicians (JADP Grant 2012–03) and The Kidney Foundation, Japan (JKF13-1). References Alon, T., Hemo, I., Itin, A., Pe'er, J., Stone, J., & Keshet, E. (1995). Vascular endothelial growth factor acts as a survival factor for newly formed retinal vessels and has implications for retinopathy of prematurity. Nat Med, 1, 1024–1028. Bock, F., Shahzad, K., Wang, H., Stoyanov, S., Wolter, J., Dong, W., et al. (2013). Activated protein C ameliorates diabetic nephropathy by epigenetically inhibiting the redox enzyme p66Shc. Proc Natl Acad Sci U S A, 110, 648–653. Brenner, B. M., Cooper, M. E., de Zeeuw, D., Keane, W. F., Mitch, W. E., Parving, H. H., et al. (2001). Effects of losartan on renal and cardiovascular outcomes in patients with type 2 diabetes and nephropathy. N Engl J Med, 345, 861–869. Bullock, B. P., Heller, R. S., & Habener, J. F. (1996). Tissue distribution of messenger ribonucleic acid encoding the rat glucagon-like peptide-1 receptor. Endocrinology, 137, 2968–2978. Carmeliet, P., Ferreira, V., Breier, G., Pollefeyt, S., Kieckens, L., Gertsenstein, M., et al. (1996). Abnormal blood vessel development and lethality in embryos lacking a single VEGF allele. Nature, 380, 435–439. Chen, S., & Ziyadeh, F. N. (2008). Vascular endothelial growth factor and diabetic nephropathy. Curr Diab Rep, 8, 470–476. Chrysant, S. G., & Chrysant, G. S. (2012). Clinical implications of cardiovascular preventing pleiotropic effects of dipeptidyl peptidase-4 inhibitors. Am J Cardiol, 109, 1681–1685. Cusi, K., Maezono, K., Osman, A., Pendergrass, M., Patti, M. E., Pratipanawatr, T., et al. (2000). Insulin resistance differentially affects the PI 3-kinase- and MAP kinasemediated signaling in human muscle. J Clin Invest, 105, 311–320. Drucker, D. J. (2006). The biology of incretin hormones. Cell Metab, 3, 153–165. Elmarakby, A. A., Faulkner, J., Baban, B., Saleh, M. A., & Sullivan, J. C. (2012). Induction of hemeoxygenase-1 reduces glomerular injury and apoptosis in diabetic spontaneously hypertensive rats. Am J Physiol Renal Physiol, 302, F791–800. Erdogdu, O., Nathanson, D., Sjoholm, A., Nystrom, T., & Zhang, Q. (2010). Exendin-4 stimulates proliferation of human coronary artery endothelial cells through eNOS-, PKA- and PI3K/Akt-dependent pathways and requires GLP-1 receptor. Mol Cell Endocrinol, 325, 26–35. Eremina, V., Jefferson, J. A., Kowalewska, J., Hochster, H., Haas, M., Weisstuch, J., et al. (2008). VEGF inhibition and renal thrombotic microangiopathy. N Eng J Med, 358, 1129–1136. Eremina, V., Sood, M., Haigh, J., Nagy, A., Lajoie, G., Ferrara, N., et al. (2003). Glomerularspecific alterations of VEGF-A expression lead to distinct congenital and acquired renal diseases. J Clin Invest, 111, 707–716. Federici, M., Pandolfi, A., De Filippis, E. A., Pellegrini, G., Menghini, R., Lauro, D., et al. (2004). G972R IRS-1 variant impairs insulin regulation of endothelial nitric oxide synthase in cultured human endothelial cells. Circulation, 109, 399–405. Ferrara, N. (2004). Vascular endothelial growth factor: Basic science and clinical progress. Endocr Rev, 25, 581–611. Ferrara, N., & Gerber, H. P. (2001). The role of vascular endothelial growth factor in angiogenesis. Acta Haematol, 106, 148–156. Fujio, Y., & Walsh, K. (1999). Akt mediates cytoprotection of endothelial cells by vascular endothelial growth factor in an anchorage-dependent manner. J Biol Chem, 274, 16349–16354. Fulcher, C. A., Gardiner, J. E., Griffin, J. H., & Zimmerman, T. S. (1984). Proteolytic inactivation of human factor VIII procoagulant protein by activated human protein C and its analogy with factor V. Blood, 63, 486–489. Geraldes, P., Yagi, K., Ohshiro, Y., He, Z., Maeno, Y., Yamamoto-Hiraoka, J., et al. (2008). Selective regulation of heme oxygenase-1 expression and function by insulin through IRS1/phosphoinositide 3-kinase/Akt-2 pathway. J Biol Chem, 283, 34327–34336. Gerber, H. P., Dixit, V., & Ferrara, N. (1998). Vascular endothelial growth factor induces expression of the antiapoptotic proteins Bcl-2 and A1 in vascular endothelial cells. J Biol Chem, 273, 13313–13316. Gerber, H. P., Hillan, K. J., Ryan, A. M., Kowalski, J., Keller, G. A., Rangell, L., et al. (1999). VEGF is required for growth and survival in neonatal mice. Development, 126, 1149–1159. Gerber, H. P., McMurtrey, A., Kowalski, J., Yan, M., Keyt, B. A., Dixit, V., et al. (1998). Vascular endothelial growth factor regulates endothelial cell survival through the phosphatidylinositol 3'-kinase/Akt signal transduction pathway. Requirement for Flk-1/KDR activation. J Biol Chem, 273, 30336–30343. Gil-Bernabe, P., D'Alessandro-Gabazza, C. N., Toda, M., Boveda Ruiz, D., Miyake, Y., Suzuki, T., et al. (2012). Exogenous activated protein C inhibits the progression of diabetic nephropathy. J Thromb Haemost, 10, 337–346. Gruber, A., Mori, E., del Zoppo, G. J., Waxman, L., & Griffin, J. H. (1994). Alteration of fibrin network by activated protein C. Blood, 83, 2541–2548.
Hafer-Macko, C. E., Ivey, F. M., Gyure, K. A., Sorkin, J. D., & Macko, R. F. (2002). Thrombomodulin deficiency in human diabetic nerve microvasculature. Diabetes, 51, 1957–1963. He, Z., Opland, D. M., Way, K. J., Ueki, K., Bodyak, N., Kang, P. M., et al. (2006). Regulation of vascular endothelial growth factor expression and vascularization in the myocardium by insulin receptor and PI3K/Akt pathways in insulin resistance and ischemia. Arterioscler Thromb Vasc Biol, 26, 787–793. Ichinose, K., Maeshima, Y., Yamamoto, Y., Kinomura, M., Hirokoshi, K., Kitayama, H., et al. (2006). 2-(8-hydroxy-6-methoxy-1-oxo-1 h-2-benzopyran-3-yl) propionic acid, an inhibitor of angiogenesis, ameliorates renal alterations in obese type 2 diabetic mice. Diabetes, 55, 1232–1242. Ichinose, K., Maeshima, Y., Yamamoto, Y., Kitayama, H., Takazawa, Y., Hirokoshi, K., et al. (2005). Antiangiogenic endostatin peptide ameliorates renal alterations in the early stage of a type 1 diabetic nephropathy model. Diabetes, 54, 2891–2903. Isermann, B., Vinnikov, I. A., Madhusudhan, T., Herzog, S., Kashif, M., Blautzik, J., et al. (2007). Activated protein C protects against diabetic nephropathy by inhibiting endothelial and podocyte apoptosis. Nat Med, 13, 1349–1358. Jiang, Z. Y., Lin, Y. W., Clemont, A., Feener, E. P., Hein, K. D., Igarashi, M., et al. (1999). Characterization of selective resistance to insulin signaling in the vasculature of obese Zucker (fa/fa) rats. J Clin Invest, 104, 447–457. Kim, J. E., Song, S. E., Kim, Y. W., Kim, J. Y., Park, S. C., Park, Y. K., et al. (2010). Adiponectin inhibits palmitate-induced apoptosis through suppression of reactive oxygen species in endothelial cells: involvement of cAMP/protein kinase A and AMP-activated protein kinase. Journal of Endocrinology, 207(1), 35–44. Kodera, R., Shikata, K., Kataoka, H. U., Takatsuka, T., Miyamoto, S., Sasaki, M., et al. (2011). Glucagon-like peptide-1 receptor agonist ameliorates renal injury through its anti-inflammatory action without lowering blood glucose level in a rat model of type 1 diabetes. Diabetologia, 54, 965–978. Ku, C. H., White, K. E., Dei Cas, A., Hayward, A., Webster, Z., Bilous, R., et al. (2008). Inducible overexpression of sFlt-1 in podocytes ameliorates glomerulopathy in diabetic mice. Diabetes, 57, 2824–2833. Kuboki, K., Jiang, Z. Y., Takahara, N., Ha, S. W., Igarashi, M., Yamauchi, T., et al. (2000). Regulation of endothelial constitutive nitric oxide synthase gene expression in endothelial cells and in vivo: A specific vascular action of insulin. Circulation, 101, 676–681. Lee, M. E., Dhadly, M. S., Temizer, D. H., Clifford, J. A., Yoshizumi, M., & Quertermous, T. (1991). Regulation of endothelin-1 gene expression by Fos and Jun. J Biol Chem, 266, 19034–19039. Lee, S. C., Han, S. H., Li, J. J., Lee, S. H., Jung, D. S., Kwak, S. J., et al. (2009). Induction of heme oxygenase-1 protects against podocyte apoptosis under diabetic conditions. Kidney Int, 76, 838–848. Lee, S., Kim, W., Moon, S. O., Sung, M. J., Kim, D. H., Kang, K. P., et al. (2007). Renoprotective effect of COMP-angiopoietin-1 in db/db mice with type 2 diabetes. Nephrol Dial Transplant, 22, 396–408. Lewis, E. J., Hunsicker, L. G., Clarke, W. R., Berl, T., Pohl, M. A., Lewis, J. B., et al. (2001). Renoprotective effect of the angiotensin-receptor antagonist irbesartan in patients with nephropathy due to type 2 diabetes. N Engl J Med, 345, 851–860. Liu, H., Dear, A. E., Knudsen, L. B., & Simpson, R. W. (2009). A long-acting glucagon-like peptide-1 analogue attenuates induction of plasminogen activator inhibitor type-1 and vascular adhesion molecules. J Endocrinol, 201, 59–66. Liu, W. J., Xie, S. H., Liu, Y. N., Kim, W., Jin, H. Y., Park, S. K., et al. (2012). Dipeptidyl peptidase IV inhibitor attenuates kidney injury in streptozotocin-induced diabetic rats. J Pharmacol Exp Ther, 340, 248–255. Mima, A., Hiraoka-Yamomoto, J., Li, Q., Kitada, M., Li, C., Geraldes, P., et al. (2012). Protective effects of GLP-1 on glomerular endothelium and its inhibition by PKCbeta activation in diabetes. Diabetes, 61, 2967–2979. Mima, A., Kitada, M., Geraldes, P., Li, Q., Matsumoto, M., Mizutani, K., et al. (2012). Glomerular VEGF resistance induced by PKCdelta/SHP-1 activation and contribution to diabetic nephropathy. FASEB J, 26, 2963–2974. Mima, A., Ohshiro, Y., Kitada, M., Matsumoto, M., Geraldes, P., Li, C., et al. (2011). Glomerular-specific protein kinase C-β-induced insulin receptor substrate-1 dysfunction and insulin resistance in rat models of diabetes and obesity. Kidney International, 79(8), 883–896. Montagnani, M., Chen, H., Barr, V. A., & Quon, M. J. (2001). Insulin-stimulated activation of eNOS is independent of Ca2+ but requires phosphorylation by Akt at Ser(1179). J Biol Chem, 276, 30392–30398. Motley, E. D., Kabir, S. M., Gardner, C. D., Eguchi, K., Frank, G. D., Kuroki, T., et al. (2002). Lysophosphatidylcholine inhibits insulin-induced Akt activation through protein kinase C-alpha in vascular smooth muscle cells. Hypertension, 39, 508–512. Nakamaki, S., Satoh, H., Kudoh, A., Hayashi, Y., Hirai, H., & Watanabe, T. (2011). Adiponectin reduces proteinuria in streptozotocin-induced diabetic Wistar rats. Exp Biol Med, 236, 614–620. Naruse, K., Rask-Madsen, C., Takahara, N., Ha, S. W., Suzuma, K., Way, K. J., et al. (2006). Activation of vascular protein kinase C-beta inhibits Akt-dependent endothelial nitric oxide synthase function in obesity-associated insulin resistance. Diabetes, 55, 691–698. Nicosia, R. F., Nicosia, S. V., & Smith, M. (1994). Vascular endothelial growth factor, platelet-derived growth factor, and insulin-like growth factor-1 promote rat aortic angiogenesis in vitro. Am J Pathol, 145, 1023–1029. Nikolaidis, L. A., Mankad, S., Sokos, G. G., Miske, G., Shah, A., Elahi, D., et al. (2004). Effects of glucagon-like peptide-1 in patients with acute myocardial infarction and left ventricular dysfunction after successful reperfusion. Circulation, 109, 962–965. Nystrom, T., Gutniak, M. K., Zhang, Q., Zhang, F., Holst, J. J., Ahren, B., et al. (2004). Effects of glucagon-like peptide-1 on endothelial function in type 2 diabetes patients with stable coronary artery disease. Am J Physiol Endocrinol Metab, 287, E1209–1215.
Please cite this article as: Mima, A., Diabetic nephropathy: protective factors and a new therapeutic paradigm, Journal of Diabetes and Its Complications (2013), http://dx.doi.org/10.1016/j.jdiacomp.2013.03.003
A. Mima / Journal of Diabetes and Its Complications xxx (2013) xxx–xxx Oliver, F. J., de la Rubia, G., Feener, E. P., Lee, M. E., Loeken, M. R., Shiba, T., et al. (1991). Stimulation of endothelin-1 gene expression by insulin in endothelial cells. J Biol Chem, 266, 23251–23256. Ouchi, N., Kihara, S., Arita, Y., Okamoto, Y., Maeda, K., Kuriyama, H., et al. (2000). Adiponectin, an adipocyte-derived plasma protein, inhibits endothelial NF-kappaB signaling through a cAMP-dependent pathway. Circulation, 102, 1296–1301. Ouedraogo, R., Wu, X.., Xu, S. Q., Fuchsel, L., Motoshima, H., Mahadev, K., et al. (2006). Adiponectin suppression of high-glucose-induced reactive oxygen species in vascular endothelial cells: evidence for involvement of a cAMP signaling pathway. Diabetes, 55(6), 1840–1846. Ptilovanciv, E. O., Fernandes, G. S., Teixeira, L. C., Reis, L. A., Pessoa, E. A., Convento, M. B., et al. (2013). Heme oxygenase 1 improves glucoses metabolism and kidney histological alterations in diabetic rats. Diabetol Metab Syndr, 5, 3. Rask-Madsen, C., Buonomo, E., Li, Q., Park, K., Clermont, A. C., Yerokun, O., et al. (2012). Hyperinsulinemia does not change atherosclerosis development in apolipoprotein E null mice. Arterioscler Thromb Vasc Biol, 32, 1124–1131. Rask-Madsen, C., & King, G. L. (2007). Mechanisms of disease: Endothelial dysfunction in insulin resistance and diabetes. Nat Clin Pract Endocrinol Metab, 3, 46–56. Rask-Madsen, C., Li, Q., Freund, B., Feather, D., Abramov, R., Wu, I. H., et al. (2010). Loss of insulin signaling in vascular endothelial cells accelerates atherosclerosis in apolipoprotein E null mice. Cell Metab, 11, 379–389. Schrijvers, B. F., De Vriese, A. S., Tilton, R. G., Van de Voorde, J., Denner, L., Lameire, N. H., et al. (2005). Inhibition of vascular endothelial growth factor (VEGF) does not affect early renal changes in a rat model of lean type 2 diabetes. Horm Metab Res, 37, 21–25. Seldon, M. P., Silva, G., Pejanovic, N., Larsen, R., Gregoire, I. P., Filipe, J., et al. (2007). Heme oxygenase-1 inhibits the expression of adhesion molecules associated with endothelial cell activation via inhibition of NF-kappaB RelA phosphorylation at serine 276. J Immunol, 179, 7840–7851.
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Sison, K., Eremina, V., Baelde, H., Min, W., Hirashima, M., Fantus, I. G., et al. (2010). Glomerular structure and function require paracrine, not autocrine, VEGF-VEGFR-2 signaling. J Am Soc Nephrol, 21, 1691–1701. Sung, S. H., Ziyadeh, F. N., Wang, A., Pyagay, P. E., Kanwar, Y. S., & Chen, S. (2006). Blockade of vascular endothelial growth factor signaling ameliorates diabetic albuminuria in mice. J Am Soc Nephrol, 17, 3093–3104. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. The Diabetes Control and Complications Trial Research Group. N Engl J Med, 329. (1993)., 977–986. Thurston, G., Rudge, J. S., Ioffe, E., Zhou, H., Ross, L., Croll, S. D., et al. (2000). Angiopoietin-1 protects the adult vasculature against plasma leakage. Nat Med, 6, 460–463. Tracz, M. J., Juncos, J. P., Grande, J. P., Croatt, A. J., Ackerman, A. W., Katusic, Z. S., et al. (2008). Induction of heme oxygenase-1 is a beneficial response in a murine model of venous thrombosis. Am J Pathol, 173, 1882–1890. Tran, J., Master, Z., Yu, J. L., Rak, J., Dumont, D. J., & Kerbel, R. S. (2002). A role for survivin in chemoresistance of endothelial cells mediated by VEGF. Proc Natl Acad Sci U S A, 99, 4349–4354. Effect of intensive blood-glucose control with metformin on complications in overweight patients with type 2 diabetes (UKPDS 34). UK Prospective Diabetes Study (UKPDS) Group. Lancet, 352. (1998), 854–865. Welsh, G. I., Hale, L. J., Eremina, V., Jeansson, M., Maezawa, Y., Lennon, R., et al. (2010). Insulin signaling to the glomerular podocyte is critical for normal kidney function. Cell Metab, 12, 329–340. Yamamoto, Y., Maeshima, Y., Kitayama, H., Kitamura, S., Takazawa, Y., Sugiyama, H., et al. (2004). Tumstatin peptide, an inhibitor of angiogenesis, prevents glomerular hypertrophy in the early stage of diabetic nephropathy. Diabetes, 53, 1831–1840.
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Journal of Diabetes and Its Complications j o u r n a l h o m e p a g e : W W W. J D C J O U R N A L . C O M
Diabetic nephropathy: protective factors and a new therapeutic paradigm☆ Akira Mima ⁎ Department of Nephrology, Graduate School of Medicine, Institute of Health Biosciences, University of Tokushima, Tokushima, Japan
a r t i c l e
i n f o
Article history: Received 4 January 2013 Received in revised form 25 February 2013 Accepted 19 March 2013 Available online xxxx Keywords: Diabetic nephropathy (DN) Insulin Insulin receptor substrate 1 (IRS1) Protein kinase C (PKC) Vascular endothelial growth factor (VEGF) Src homology-2 domain containing phosphatase-1 (SHP-1) Glucagon like peptide-1 (GLP-1) Dipeptidyl peptidase-4 (DPP-4) inhibitors Endostatin Tumstatin Angiopoietins
a b s t r a c t Diabetic nephropathy (DN) is the most common cause of chronic kidney disease (CKD) and its number has been increasing. CKD is a worldwide threat to health but the precise mechanism of this problem is not fully appreciated. It is believed that hyperglycemia is one of the most important metabolic factors in the development of DN. Multiple molecular mechanisms have been proposed to mediate hyperglycemia’s adverse effects on kidney. To identify targets for therapeutic intervention, most studies have focused on understanding how abnormal levels of such metabolities cause DN. However, there have been few reports regarding endogenous renal protective factors. Thus, recognition of the importance of this could be providing a new perspective for understanding the development of DN and a new therapeutic paradigm to combat DN. © 2013 Elsevier Inc. All rights reserved.
1. Introduction
2. Endogenous protective factors
Diabetes nephropathy (DN) is the most important cause of chronic kidney disease (CKD) in the world that often leads to requirements for dialysis or renal replacement therapy. There have been many advances in the management of DN (The Diabetes Control & Complications Trial Research Group, 1993; UK Prospective Diabetes Study (UKPDS) Group, 1998). It is well known that activation of the renin–angiotensin system contributes to the development of DN and angiotensin-converting enzyme inhibitors (ACEI) or AT1 receptor blockers (ARB) could attenuate DN. However, recent studies suggest these drugs delay but cannot stop the progression of DN (Brenner et al., 2001; Lewis et al., 2001). Despite a reasonable understanding of the pathogenesis and pathology of DN, only few studies revealed the importance of endogenous protective factors or the inhibitory effects of hyperglycemia. This review will focus on the evidence supporting the importance of endogenous protective factors that prevent the progression of DN.
2.1. Insulin
☆ The authors declare that they have no conflict of interest. ⁎ Corresponding author. Department of Nephrology, Graduate School of Medicine, Institute of Health Biosciences, University of Tokushima, Tokushima 770-8503, Japan. Tel.: +81 88 633 7184, fax: +81 88 633 9245. E-mail address: [email protected].
Insulin has many vasotropic actions including survival factors for vascular endothelial cells including glomeruli. Hyperglycemia can selectively inhibit insulin’s anti-atherosclerotic or anti-glomerulosclerotic actions, while hyperinsulinemia, as observed in insulinresistant type 2 diabetes, can enhance insulin’s pro-atherosclerotic diseases (Rask-Madsen & King, 2007). Insulin resistance in vascular tissue is associated with endothelial dysfunction, leading to cardiovascular diseases including atherosclerosis and DN in animal models (Mima et al., 2011; Rask-Madsen & King, 2007). However, hyperinsulinemia itself does not affect atherosclerosis (Rask-Madsen et al., 2012). Insulin can stimulate the production of nitric oxide (NO), which results in vasodilatation and inhibit smooth muscle cell growth and migration, and podocyte apoptosis. Impaired insulin’s action has recognized in the endothelial and mesangial cells in diabetic glomeruli, presumably through the activation of protein kinase C (PKC)β2 isoform (Mima et al., 2011). Insulin-induced NO production has been reported to be mediated through insulin receptor-mediated activation of the insulin receptor substrate (IRS)/PI3K/Akt/endothelial NO synthase (eNOS) (Kuboki et al., 2000; Montagnani, Chen, Barr, & Quon, 2001). Rask-Madsen et al. clearly demonstrated the importance of vascular insulin signaling in
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Please cite this article as: Mima, A., Diabetic nephropathy: protective factors and a new therapeutic paradigm, Journal of Diabetes and Its Complications (2013), http://dx.doi.org/10.1016/j.jdiacomp.2013.03.003
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endothelial insulin receptor knock-out mice (Rask-Madsen et al., 2010). In diabetes and insulin resistance states, the IRS1/Akt/eNOS pathway is selectively inhibited, but another major pathway of insulin signaling, mitogen-activated protein kinase (MAPK), is not inhibited (Jiang et al., 1999; Mima et al., 2011). Interestingly, this selective insulin resistance has also been shown in skeletal muscle from obesity and type 2 diabetes patients (Cusi et al., 2000), and in the vasculature, myocardium of Zucker fatty rats, which are the animal models of insulin resistance (He et al., 2006). Insulin-stimulated endothelin-1 (ET-1) expression might be preserved in insulin resistance (Oliver et al., 1991), since ET-1 expression is dependent on nuclear factors fos/ jun downstream of MAPK signaling (Lee et al., 1991). Further, recent studies clearly show that PKCβ specific inhibitor, ruboxistaurin (RBX) improved insulin signaling on NO production in the vasculature, myocardium and glomeruli of streptozotocin-induced STZ rats and Zucker fatty rats (Mima et al., 2011; Naruse et al., 2006). Other reports indicated that PKCβ directly inhibited insulin signaling. That is, phorbol 12-myristate 13-acetate (PMA) inhibits IRS2/PI3K activity (Kuboki et al., 2000) or IRS1 tyrosine phosphorylation (Motley et al., 2002). Mutations of IRS1 decreased insulininduced eNOS activity through IRS1/PI3K/Akt (Federici et al., 2004). Further, we have shown that high glucose inhibited phosphorylation of Akt, eNOS and glycogen synthase kinase (GSK)3α, decreased IRS1 protein expression and increased association with ubiquitination in glomerular endothelial cells (Mima et al., 2011). Studies using mice overexpressing PKCβ2 in endothelial cells (EC-PKCβ2) showed impaired insulin signaling in renal cortex and diabetic EC-PKCβ2 exhibited more albuminuria and increasing extracellular matrix (Mima, Hiraoka-Yamomoto, et al., 2012). Also, overexpression of IRS1 or RBX reversed the inhibitory effects of high glucose (Mima et al., 2011). Thus, inhibition of PKCβ activity or increasing IRS1 activity in glomerular endothelial cell could be a new therapeutic paradigm. Recent study using mice deleted insulin receptor specifically from podocytes showed severe albuminuria, increasing podocyte apoptosis and deposition of components of the basal membrane (Welsh et al., 2010). This finding strongly supports the importance of insulin signaling as a renoprotective factor. 2.2. HO-1 It is reported that heme oxygenase-1 (HO-1), a potent antioxidant enzyme that can interrupt major mechanisms of vascular injury, is normally upregulated in response to inflammation and oxidative stress. Studies using mice deleted HO-1 gene showed increases of monocyte chemoattractant protein-1 (MCP-1) expression and nuclear factor-κB (NF-κB) activation (Seldon et al., 2007; Tracz et al., 2008). Recently, Geraldes et al. showed that insulin significantly increase protein levels of HO-1 and insulin treatment prevented oxidative stress induced-NF-κB and caspase-8 activation and apoptosis via IRS1/PI3K/Akt2/HO-1 pathway in pericytes (Geraldes et al., 2008). Induction of HO-1 improves hyperglycemia, and reduces podocyte apoptosis and glomerular injury (Elmarakby, Faulkner, Baban, Saleh, & Sullivan, 2012; Lee et al., 2009; Ptilovanciv et al., 2013). Therefore, increasing HO-1 activity through improving insulin sensitivity in glomeruli could decrease the risk for DN. 2.3. VEGF-A Vascular endothelial growth factor (VEGF)-A belongs to a family of growth factors that include VEGF-B, -C, -D, and –E, and platelet-derived growth factor (PDGF) (Carmeliet et al., 1996; Ferrara & Gerber, 2001; Gerber et al., 1999). Among them, VEGF-A plays a significant role in angiogenesis and vascular permeability. VEGF-A is one of the most important growth factor that responds
to hypoxia under normal physiological levels (Ferrara, 2004). Activity of VEGF-A is the ability to promote growth of vascular endothelial cells. VEGF-A promotes angiogenesis, inducing confluent microvascular endothelial cells to invade collagen gel (Nicosia, Nicosia, & Smith, 1994). VEGF-A is also a survival factor for endothelial cells (Alon et al., 1995; Gerber, Dixit, & Ferrara, 1998). VEGF-A prevents endothelial cell apoptosis induced by serum starvation and such activity is mediated by PI3K/Akt pathway (Fujio & Walsh, 1999; Gerber, McMurtrey, et al., 1998). VEGF-A also increases the expression of the anti-apoptotic proteins Bcl-2 (Gerber, Dixit, et al., 1998) or survivin (Tran et al., 2002). Further, VEGF-A increased phosphorylation of Akt and eNOS that prevent endothelial cell apoptosis (Mima, Kitada, et al., 2012). Increases in levels of VEGF-A are recognized in podocytes and mesangial cells in DN (Chen & Ziyadeh, 2008). There are several reports regarding inhibition of VEGF-A results in amelioration of proteinuria and reduction in mesangial expansion in the early stage of DN in rodent models (Ku et al., 2008; Sung et al., 2006). In contrast, some groups showed treatment with VEGF-A antibodies did not improve DN in diabetic rats (Schrijvers et al., 2005). Further, several patients treated with anti-VEGF agent showed proteinuria, hypertension, and renal failure (Eremina et al., 2008). Supporting these phenomena, recent studies have suggested that VEGF-A might be a renoprotective factor, since VEGF-A null mice show proteinuria, glomerulosclerosis and renal failure (Eremina et al., 2003). Also, during fetal development, one of the cell types producing the largest amounts of VEGF-A is the podocytes. Different from many other cells, podocytes continue to express VEGF-A when they are fully differentiated, though absolute levels of expression decrease (Sison et al., 2010). Recently, our study showed that diabetes can cause podocyte apoptosis partly due to increased PKCδ/p38MAPK activation and the expression of Src homology-2 domain-containing phosphatase-1 (SHP-1) to cause impairment of VEGF signaling (Mima, Kitada, et al., 2012). Thus, fine balance in the regulation of VEGF-A activity seems to be important for preventing DN. However, further studies will be needed to conclude whether VEGF-A is truly an endogenous protective factor for DN or not.
2.4. Glucagon like peptide-1 and DPP-4 inhibitors GLP-1 is an incretin hormone which can augment glucosedependent insulin release and promote preservation of β cells (Drucker, 2006). Analysis of GLP-1 receptor (GLP-1R) revealed its expression in endothelial cells and kidney (Bullock, Heller, & Habener, 1996; Erdogdu, Nathanson, Sjoholm, Nystrom, & Zhang, 2010). It is reported that GLP-1 has multiple vasotropic actions in addition to its effects to insulin secretion. For example, its analog, exendin-4, has been shown to improve left ventricular function after myocardial infarction or ischemia (Nikolaidis et al., 2004; Nystrom et al., 2004). In endothelial cells, GLP-1 might inhibit the expression of tumor necrosis factor-α (TNF-α) and vascular cell adhesion molecule-1 (VCAM-1) (Kodera et al., 2011; Liu, Dear, Knudsen, & Simpson, 2009). Recently, we have shown that GLP-1 is partly mediating its protective actions via its own receptor by the activation of protein kinase A (PKA). The elevation of cAMP levels increased the phosphorylation at phospho-c-Raf (Ser259) that may inhibit phospho-c-Raf (Ser338)/phospho-Erk1/2 which are activated by Ang II to induce its inflammatory action such as plasminogen activator inhibitor-1 (PAI-1), CD68 and CXCL2 expression. Further, we clearly indicated PKCβ activation induced by hyperglycemia or free fatty acids can inhibit GLP-1’s protective actions and enhance inflammatory effects on the endothelium by two mechanisms; PKCβ enhances Ang II’s action and decreases GLP-1R by its ubiquitination (Mima, Hiraoka-Yamomoto, et al., 2012).
Please cite this article as: Mima, A., Diabetic nephropathy: protective factors and a new therapeutic paradigm, Journal of Diabetes and Its Complications (2013), http://dx.doi.org/10.1016/j.jdiacomp.2013.03.003
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Dipeptidyl peptidase-4 (DPP-4) inhibitors are considered incretin enhancers; these agents increase active incretin levels by preventing their rapid degradation. Like GLP-1 analog, recent studies suggest that DPP-4 inhibitors also have vasotropic actions and the possibility of an actual reduction in cardiovascular diseases and DN (Chrysant & Chrysant, 2012; Liu et al., 2012).
2.5. Activated protein C Activated protein C (APC) functions by inhibiting factors Va and VIIIa and has pro-fibrinolytic function by modifying clot formation and inhibiting PAI-1 (Fulcher, Gardiner, Griffin, & Zimmerman, 1984; Gruber, Mori, del Zoppo, Waxman, & Griffin, 1994). Further, the levels of APC are reduced and thrombomodulin/protein C system is inhibited in diabetic patients (Hafer-Macko, Ivey, Gyure, Sorkin, & Macko, 2002). Isermann et al. reported that APC modulates DN by modulating apoptosis of endothelial cells and podocytes, using thrombomodulin dependent protein C activation knockout mice or mice that express a hyperactivatable protein C overexpression (Bock et al., 2013; Isermann et al., 2007). Also, recent studies have revealed exogenous APC could improve renal function and pathological changes in mice with diabetic nephropathy, suppressing oxidative stress, the expression of fibrogenic cytokines and growth factors (Bock et al., 2013; Gil-Bernabe et al., 2012). However, a 2012 trial supports the decision to withdraw drotrecogin, recombinant form of human APC, because previous meta-analysis study might improperly strengthen positive results and bleeding concerns were recognized in sepsis trial.
2.6. Endostatin and tumstatin Endostatin and tumstatin inhibit proliferation and migration, and cell-cycle arrest of endothelial cell. They also serve as inhibitors of angiogenesis by suppressing diabetes-induced excessive VEGF-A. Although complete inhibition of VEGF-A in DN remains controversial, induction of these drugs significantly decreased inflammatory markers and mesangial expansion in the early phase of DN (Ichinose et al., 2005; Yamamoto et al., 2004). This finding strongly supports effective therapies for DN need to decrease angiogenic response.
Angiotensin II ET-1
2.7. Angiopoietins It is well known that physiological levels of angiopoietin (Ang)-1 are important for maintaining intact glomerular structures. Also, Ang1 enhances endothelial cell survival and stability (Thurston et al., 2000). In contrast, Ang-2, which antagonizes Ang-1’s effect, induces endothelial cell death and vessel regression. Ang-1 was decreased in the glomeruli of diabetic rats, while Ang-2 was increased. Further, recent study shows upregulation of Ang-2 in the glomeruli and decreased Ang-1/Ang-2 ratio accompanied by inflammation (Ichinose et al., 2005; Ichinose et al., 2006; Yamamoto et al., 2004). Increases in the levels of Ang-1 in the glomeruli using adenoviral vector seem to be effective for the treatment of DN (Lee et al., 2007). 2.8. Adiponectin Adiponectin derived from adipose tissues and its signaling mechanisms through the receptors Adipo-R1 and Adipo-R2, including AMP-activated protein kinase (AMPK) and cAMP/PKA pathways have been implicated in the functions of endothelial cells (Kim et al., 2010; Ouedraogo et al., 2006). Adiponectin suppresses inflammation including tumor necrosis factor-α (TNF-α) and NF-κB (Ouchi et al., 2000). Recent studies have indicated that adiponectin prevents in the injured kidney including DN (Nakamaki et al., 2011). However, it is still unclear whether adiponectin will provide significant effects toward human DN. 3. Summary Although good glycemic control may be the best prevention of DN, it develops in spite of treatment of diabetes. Inhibitors of the aldose reductase pathway, advanced glycation end products (AGEs), oxidative stress, PKC, TGFβ-Smads pathway, inflammation, and the reninangiotensin system, for example, should provide useful targets for therapy; however, unfortunately, many clinical trials using agents directly against these targets have not shown to decrease DN. Thus, we proposed the importance of endogenous protective factors, such as insulin, VEGF and GLP-1, and inhibitory effects of hyperglycemia in neutralizing these protective factors during the initiation and progression of DN (Fig. 1).
Hyperglycemia/diabetes/ n-3 fatty acids
Mesangial cell, endothelial cell
Podocyte
PKCα, β activation
PKCδ activation
Inhibition Inhibition of IRS1 of GLP-1R
p38MAPK
PI3K/Akt NO
VEGF
Endothelial dysfunction
Accumulation of ECM, increase of mesangial expansion
3
SHP-1 Inhibition of IRS1?
NF-κB
Inhibition Caspase of VEGF activation
PI3K/Akt
Podocyte apoptosis
Fig. 1. Schematic representation of potential protective factors and biological targets of PKC activation leading to diabetic nephropathy. PKC, protein kinase C; ET-1, endothelin-1; IRS1, insulin receptor substrate1; NO, nitric oxide; VEGF, vascular endothelial growth factor; GLP-1R, glucagon like peptide-1 receptor; p38 MAPK, p38 MAP kinase; SHP-1, Src homology-2 domain-containing phosphatase-1; NF-κB, nuclear factor-κB; ECM, extracellular matrix.
Please cite this article as: Mima, A., Diabetic nephropathy: protective factors and a new therapeutic paradigm, Journal of Diabetes and Its Complications (2013), http://dx.doi.org/10.1016/j.jdiacomp.2013.03.003
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In summary, new therapeutic approaches targeting these molecules for DN need to decrease hyperglycemia’s toxic effect and to increase the action of protective factors. Acknowledgment Preparation of this publication was supported by grants to A.M. from Grant-in-Aid for Scientific Research (24890148) from Japan Society for the Promotion of Science, Kurozumi Medical Foundation, Mochida Memorial Foundation for Medical and Pharmaceutical Research, Takeda Science Foundation, Japanese Association of Dialysis Physicians (JADP Grant 2012–03) and The Kidney Foundation, Japan (JKF13-1). References Alon, T., Hemo, I., Itin, A., Pe'er, J., Stone, J., & Keshet, E. (1995). Vascular endothelial growth factor acts as a survival factor for newly formed retinal vessels and has implications for retinopathy of prematurity. Nat Med, 1, 1024–1028. Bock, F., Shahzad, K., Wang, H., Stoyanov, S., Wolter, J., Dong, W., et al. (2013). Activated protein C ameliorates diabetic nephropathy by epigenetically inhibiting the redox enzyme p66Shc. Proc Natl Acad Sci U S A, 110, 648–653. Brenner, B. M., Cooper, M. E., de Zeeuw, D., Keane, W. F., Mitch, W. E., Parving, H. H., et al. (2001). Effects of losartan on renal and cardiovascular outcomes in patients with type 2 diabetes and nephropathy. N Engl J Med, 345, 861–869. Bullock, B. P., Heller, R. S., & Habener, J. F. (1996). Tissue distribution of messenger ribonucleic acid encoding the rat glucagon-like peptide-1 receptor. Endocrinology, 137, 2968–2978. Carmeliet, P., Ferreira, V., Breier, G., Pollefeyt, S., Kieckens, L., Gertsenstein, M., et al. (1996). Abnormal blood vessel development and lethality in embryos lacking a single VEGF allele. Nature, 380, 435–439. Chen, S., & Ziyadeh, F. N. (2008). Vascular endothelial growth factor and diabetic nephropathy. Curr Diab Rep, 8, 470–476. Chrysant, S. G., & Chrysant, G. S. (2012). Clinical implications of cardiovascular preventing pleiotropic effects of dipeptidyl peptidase-4 inhibitors. Am J Cardiol, 109, 1681–1685. Cusi, K., Maezono, K., Osman, A., Pendergrass, M., Patti, M. E., Pratipanawatr, T., et al. (2000). Insulin resistance differentially affects the PI 3-kinase- and MAP kinasemediated signaling in human muscle. J Clin Invest, 105, 311–320. Drucker, D. J. (2006). The biology of incretin hormones. Cell Metab, 3, 153–165. Elmarakby, A. A., Faulkner, J., Baban, B., Saleh, M. A., & Sullivan, J. C. (2012). Induction of hemeoxygenase-1 reduces glomerular injury and apoptosis in diabetic spontaneously hypertensive rats. Am J Physiol Renal Physiol, 302, F791–800. Erdogdu, O., Nathanson, D., Sjoholm, A., Nystrom, T., & Zhang, Q. (2010). Exendin-4 stimulates proliferation of human coronary artery endothelial cells through eNOS-, PKA- and PI3K/Akt-dependent pathways and requires GLP-1 receptor. Mol Cell Endocrinol, 325, 26–35. Eremina, V., Jefferson, J. A., Kowalewska, J., Hochster, H., Haas, M., Weisstuch, J., et al. (2008). VEGF inhibition and renal thrombotic microangiopathy. N Eng J Med, 358, 1129–1136. Eremina, V., Sood, M., Haigh, J., Nagy, A., Lajoie, G., Ferrara, N., et al. (2003). Glomerularspecific alterations of VEGF-A expression lead to distinct congenital and acquired renal diseases. J Clin Invest, 111, 707–716. Federici, M., Pandolfi, A., De Filippis, E. A., Pellegrini, G., Menghini, R., Lauro, D., et al. (2004). G972R IRS-1 variant impairs insulin regulation of endothelial nitric oxide synthase in cultured human endothelial cells. Circulation, 109, 399–405. Ferrara, N. (2004). Vascular endothelial growth factor: Basic science and clinical progress. Endocr Rev, 25, 581–611. Ferrara, N., & Gerber, H. P. (2001). The role of vascular endothelial growth factor in angiogenesis. Acta Haematol, 106, 148–156. Fujio, Y., & Walsh, K. (1999). Akt mediates cytoprotection of endothelial cells by vascular endothelial growth factor in an anchorage-dependent manner. J Biol Chem, 274, 16349–16354. Fulcher, C. A., Gardiner, J. E., Griffin, J. H., & Zimmerman, T. S. (1984). Proteolytic inactivation of human factor VIII procoagulant protein by activated human protein C and its analogy with factor V. Blood, 63, 486–489. Geraldes, P., Yagi, K., Ohshiro, Y., He, Z., Maeno, Y., Yamamoto-Hiraoka, J., et al. (2008). Selective regulation of heme oxygenase-1 expression and function by insulin through IRS1/phosphoinositide 3-kinase/Akt-2 pathway. J Biol Chem, 283, 34327–34336. Gerber, H. P., Dixit, V., & Ferrara, N. (1998). Vascular endothelial growth factor induces expression of the antiapoptotic proteins Bcl-2 and A1 in vascular endothelial cells. J Biol Chem, 273, 13313–13316. Gerber, H. P., Hillan, K. J., Ryan, A. M., Kowalski, J., Keller, G. A., Rangell, L., et al. (1999). VEGF is required for growth and survival in neonatal mice. Development, 126, 1149–1159. Gerber, H. P., McMurtrey, A., Kowalski, J., Yan, M., Keyt, B. A., Dixit, V., et al. (1998). Vascular endothelial growth factor regulates endothelial cell survival through the phosphatidylinositol 3'-kinase/Akt signal transduction pathway. Requirement for Flk-1/KDR activation. J Biol Chem, 273, 30336–30343. Gil-Bernabe, P., D'Alessandro-Gabazza, C. N., Toda, M., Boveda Ruiz, D., Miyake, Y., Suzuki, T., et al. (2012). Exogenous activated protein C inhibits the progression of diabetic nephropathy. J Thromb Haemost, 10, 337–346. Gruber, A., Mori, E., del Zoppo, G. J., Waxman, L., & Griffin, J. H. (1994). Alteration of fibrin network by activated protein C. Blood, 83, 2541–2548.
Hafer-Macko, C. E., Ivey, F. M., Gyure, K. A., Sorkin, J. D., & Macko, R. F. (2002). Thrombomodulin deficiency in human diabetic nerve microvasculature. Diabetes, 51, 1957–1963. He, Z., Opland, D. M., Way, K. J., Ueki, K., Bodyak, N., Kang, P. M., et al. (2006). Regulation of vascular endothelial growth factor expression and vascularization in the myocardium by insulin receptor and PI3K/Akt pathways in insulin resistance and ischemia. Arterioscler Thromb Vasc Biol, 26, 787–793. Ichinose, K., Maeshima, Y., Yamamoto, Y., Kinomura, M., Hirokoshi, K., Kitayama, H., et al. (2006). 2-(8-hydroxy-6-methoxy-1-oxo-1 h-2-benzopyran-3-yl) propionic acid, an inhibitor of angiogenesis, ameliorates renal alterations in obese type 2 diabetic mice. Diabetes, 55, 1232–1242. Ichinose, K., Maeshima, Y., Yamamoto, Y., Kitayama, H., Takazawa, Y., Hirokoshi, K., et al. (2005). Antiangiogenic endostatin peptide ameliorates renal alterations in the early stage of a type 1 diabetic nephropathy model. Diabetes, 54, 2891–2903. Isermann, B., Vinnikov, I. A., Madhusudhan, T., Herzog, S., Kashif, M., Blautzik, J., et al. (2007). Activated protein C protects against diabetic nephropathy by inhibiting endothelial and podocyte apoptosis. Nat Med, 13, 1349–1358. Jiang, Z. Y., Lin, Y. W., Clemont, A., Feener, E. P., Hein, K. D., Igarashi, M., et al. (1999). Characterization of selective resistance to insulin signaling in the vasculature of obese Zucker (fa/fa) rats. J Clin Invest, 104, 447–457. Kim, J. E., Song, S. E., Kim, Y. W., Kim, J. Y., Park, S. C., Park, Y. K., et al. (2010). Adiponectin inhibits palmitate-induced apoptosis through suppression of reactive oxygen species in endothelial cells: involvement of cAMP/protein kinase A and AMP-activated protein kinase. Journal of Endocrinology, 207(1), 35–44. Kodera, R., Shikata, K., Kataoka, H. U., Takatsuka, T., Miyamoto, S., Sasaki, M., et al. (2011). Glucagon-like peptide-1 receptor agonist ameliorates renal injury through its anti-inflammatory action without lowering blood glucose level in a rat model of type 1 diabetes. Diabetologia, 54, 965–978. Ku, C. H., White, K. E., Dei Cas, A., Hayward, A., Webster, Z., Bilous, R., et al. (2008). Inducible overexpression of sFlt-1 in podocytes ameliorates glomerulopathy in diabetic mice. Diabetes, 57, 2824–2833. Kuboki, K., Jiang, Z. Y., Takahara, N., Ha, S. W., Igarashi, M., Yamauchi, T., et al. (2000). Regulation of endothelial constitutive nitric oxide synthase gene expression in endothelial cells and in vivo: A specific vascular action of insulin. Circulation, 101, 676–681. Lee, M. E., Dhadly, M. S., Temizer, D. H., Clifford, J. A., Yoshizumi, M., & Quertermous, T. (1991). Regulation of endothelin-1 gene expression by Fos and Jun. J Biol Chem, 266, 19034–19039. Lee, S. C., Han, S. H., Li, J. J., Lee, S. H., Jung, D. S., Kwak, S. J., et al. (2009). Induction of heme oxygenase-1 protects against podocyte apoptosis under diabetic conditions. Kidney Int, 76, 838–848. Lee, S., Kim, W., Moon, S. O., Sung, M. J., Kim, D. H., Kang, K. P., et al. (2007). Renoprotective effect of COMP-angiopoietin-1 in db/db mice with type 2 diabetes. Nephrol Dial Transplant, 22, 396–408. Lewis, E. J., Hunsicker, L. G., Clarke, W. R., Berl, T., Pohl, M. A., Lewis, J. B., et al. (2001). Renoprotective effect of the angiotensin-receptor antagonist irbesartan in patients with nephropathy due to type 2 diabetes. N Engl J Med, 345, 851–860. Liu, H., Dear, A. E., Knudsen, L. B., & Simpson, R. W. (2009). A long-acting glucagon-like peptide-1 analogue attenuates induction of plasminogen activator inhibitor type-1 and vascular adhesion molecules. J Endocrinol, 201, 59–66. Liu, W. J., Xie, S. H., Liu, Y. N., Kim, W., Jin, H. Y., Park, S. K., et al. (2012). Dipeptidyl peptidase IV inhibitor attenuates kidney injury in streptozotocin-induced diabetic rats. J Pharmacol Exp Ther, 340, 248–255. Mima, A., Hiraoka-Yamomoto, J., Li, Q., Kitada, M., Li, C., Geraldes, P., et al. (2012). Protective effects of GLP-1 on glomerular endothelium and its inhibition by PKCbeta activation in diabetes. Diabetes, 61, 2967–2979. Mima, A., Kitada, M., Geraldes, P., Li, Q., Matsumoto, M., Mizutani, K., et al. (2012). Glomerular VEGF resistance induced by PKCdelta/SHP-1 activation and contribution to diabetic nephropathy. FASEB J, 26, 2963–2974. Mima, A., Ohshiro, Y., Kitada, M., Matsumoto, M., Geraldes, P., Li, C., et al. (2011). Glomerular-specific protein kinase C-β-induced insulin receptor substrate-1 dysfunction and insulin resistance in rat models of diabetes and obesity. Kidney International, 79(8), 883–896. Montagnani, M., Chen, H., Barr, V. A., & Quon, M. J. (2001). Insulin-stimulated activation of eNOS is independent of Ca2+ but requires phosphorylation by Akt at Ser(1179). J Biol Chem, 276, 30392–30398. Motley, E. D., Kabir, S. M., Gardner, C. D., Eguchi, K., Frank, G. D., Kuroki, T., et al. (2002). Lysophosphatidylcholine inhibits insulin-induced Akt activation through protein kinase C-alpha in vascular smooth muscle cells. Hypertension, 39, 508–512. Nakamaki, S., Satoh, H., Kudoh, A., Hayashi, Y., Hirai, H., & Watanabe, T. (2011). Adiponectin reduces proteinuria in streptozotocin-induced diabetic Wistar rats. Exp Biol Med, 236, 614–620. Naruse, K., Rask-Madsen, C., Takahara, N., Ha, S. W., Suzuma, K., Way, K. J., et al. (2006). Activation of vascular protein kinase C-beta inhibits Akt-dependent endothelial nitric oxide synthase function in obesity-associated insulin resistance. Diabetes, 55, 691–698. Nicosia, R. F., Nicosia, S. V., & Smith, M. (1994). Vascular endothelial growth factor, platelet-derived growth factor, and insulin-like growth factor-1 promote rat aortic angiogenesis in vitro. Am J Pathol, 145, 1023–1029. Nikolaidis, L. A., Mankad, S., Sokos, G. G., Miske, G., Shah, A., Elahi, D., et al. (2004). Effects of glucagon-like peptide-1 in patients with acute myocardial infarction and left ventricular dysfunction after successful reperfusion. Circulation, 109, 962–965. Nystrom, T., Gutniak, M. K., Zhang, Q., Zhang, F., Holst, J. J., Ahren, B., et al. (2004). Effects of glucagon-like peptide-1 on endothelial function in type 2 diabetes patients with stable coronary artery disease. Am J Physiol Endocrinol Metab, 287, E1209–1215.
Please cite this article as: Mima, A., Diabetic nephropathy: protective factors and a new therapeutic paradigm, Journal of Diabetes and Its Complications (2013), http://dx.doi.org/10.1016/j.jdiacomp.2013.03.003
A. Mima / Journal of Diabetes and Its Complications xxx (2013) xxx–xxx Oliver, F. J., de la Rubia, G., Feener, E. P., Lee, M. E., Loeken, M. R., Shiba, T., et al. (1991). Stimulation of endothelin-1 gene expression by insulin in endothelial cells. J Biol Chem, 266, 23251–23256. Ouchi, N., Kihara, S., Arita, Y., Okamoto, Y., Maeda, K., Kuriyama, H., et al. (2000). Adiponectin, an adipocyte-derived plasma protein, inhibits endothelial NF-kappaB signaling through a cAMP-dependent pathway. Circulation, 102, 1296–1301. Ouedraogo, R., Wu, X.., Xu, S. Q., Fuchsel, L., Motoshima, H., Mahadev, K., et al. (2006). Adiponectin suppression of high-glucose-induced reactive oxygen species in vascular endothelial cells: evidence for involvement of a cAMP signaling pathway. Diabetes, 55(6), 1840–1846. Ptilovanciv, E. O., Fernandes, G. S., Teixeira, L. C., Reis, L. A., Pessoa, E. A., Convento, M. B., et al. (2013). Heme oxygenase 1 improves glucoses metabolism and kidney histological alterations in diabetic rats. Diabetol Metab Syndr, 5, 3. Rask-Madsen, C., Buonomo, E., Li, Q., Park, K., Clermont, A. C., Yerokun, O., et al. (2012). Hyperinsulinemia does not change atherosclerosis development in apolipoprotein E null mice. Arterioscler Thromb Vasc Biol, 32, 1124–1131. Rask-Madsen, C., & King, G. L. (2007). Mechanisms of disease: Endothelial dysfunction in insulin resistance and diabetes. Nat Clin Pract Endocrinol Metab, 3, 46–56. Rask-Madsen, C., Li, Q., Freund, B., Feather, D., Abramov, R., Wu, I. H., et al. (2010). Loss of insulin signaling in vascular endothelial cells accelerates atherosclerosis in apolipoprotein E null mice. Cell Metab, 11, 379–389. Schrijvers, B. F., De Vriese, A. S., Tilton, R. G., Van de Voorde, J., Denner, L., Lameire, N. H., et al. (2005). Inhibition of vascular endothelial growth factor (VEGF) does not affect early renal changes in a rat model of lean type 2 diabetes. Horm Metab Res, 37, 21–25. Seldon, M. P., Silva, G., Pejanovic, N., Larsen, R., Gregoire, I. P., Filipe, J., et al. (2007). Heme oxygenase-1 inhibits the expression of adhesion molecules associated with endothelial cell activation via inhibition of NF-kappaB RelA phosphorylation at serine 276. J Immunol, 179, 7840–7851.
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Sison, K., Eremina, V., Baelde, H., Min, W., Hirashima, M., Fantus, I. G., et al. (2010). Glomerular structure and function require paracrine, not autocrine, VEGF-VEGFR-2 signaling. J Am Soc Nephrol, 21, 1691–1701. Sung, S. H., Ziyadeh, F. N., Wang, A., Pyagay, P. E., Kanwar, Y. S., & Chen, S. (2006). Blockade of vascular endothelial growth factor signaling ameliorates diabetic albuminuria in mice. J Am Soc Nephrol, 17, 3093–3104. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. The Diabetes Control and Complications Trial Research Group. N Engl J Med, 329. (1993)., 977–986. Thurston, G., Rudge, J. S., Ioffe, E., Zhou, H., Ross, L., Croll, S. D., et al. (2000). Angiopoietin-1 protects the adult vasculature against plasma leakage. Nat Med, 6, 460–463. Tracz, M. J., Juncos, J. P., Grande, J. P., Croatt, A. J., Ackerman, A. W., Katusic, Z. S., et al. (2008). Induction of heme oxygenase-1 is a beneficial response in a murine model of venous thrombosis. Am J Pathol, 173, 1882–1890. Tran, J., Master, Z., Yu, J. L., Rak, J., Dumont, D. J., & Kerbel, R. S. (2002). A role for survivin in chemoresistance of endothelial cells mediated by VEGF. Proc Natl Acad Sci U S A, 99, 4349–4354. Effect of intensive blood-glucose control with metformin on complications in overweight patients with type 2 diabetes (UKPDS 34). UK Prospective Diabetes Study (UKPDS) Group. Lancet, 352. (1998), 854–865. Welsh, G. I., Hale, L. J., Eremina, V., Jeansson, M., Maezawa, Y., Lennon, R., et al. (2010). Insulin signaling to the glomerular podocyte is critical for normal kidney function. Cell Metab, 12, 329–340. Yamamoto, Y., Maeshima, Y., Kitayama, H., Kitamura, S., Takazawa, Y., Sugiyama, H., et al. (2004). Tumstatin peptide, an inhibitor of angiogenesis, prevents glomerular hypertrophy in the early stage of diabetic nephropathy. Diabetes, 53, 1831–1840.
Please cite this article as: Mima, A., Diabetic nephropathy: protective factors and a new therapeutic paradigm, Journal of Diabetes and Its Complications (2013), http://dx.doi.org/10.1016/j.jdiacomp.2013.03.003