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Day RT, Cavaglieri RC, Feliers D. Apelin retards the progression of diabetic nephropathy. Am J Physiol Renal Physiol 304: F788-F800, 2013. First published January 9, 2012; doi:10.1152/ajprenal.00306.2012.-Apelin and its receptor APJ have pleiotropic effects in mice and humans and play a protective role in cardiovascular diseases at least partially by inhibiting oxidative stress. Our objective was to study the effect of apelin on the progression of kidney disease in mice with established type 1 diabetes. Ove26 mice with type 1 diabetes received daily subcutaneous injections of apelin for 2 or 14 wk. APJ localizes in the glomeruli and blood vessels of kidneys. Renal APJ expression was reduced in diabetic mice but increased after treatment with apelin. Apelin treatment did not affect glycemia, body weight, or blood pressure in diabetic mice. Whole kidney and glomerular hypertrophy, as well as renal inflammation, including monocyte chemoattractant protein 1 and vascular cell adhesion molecule 1 expression, NF-B activation, and monocyte infiltration, was inhibited after short and long treatment with apelin. Apelin administration significantly reduced albuminuria at 6 mo. Short treatment with apelin was sufficient to reverse the downregulation of the antioxidant enzyme catalase. Expression of angiotensin II and angiotensin type 1 receptor (AT1) in kidneys from diabetic mice treated was not affected by apelin. These findings show for the first time that apelin exerts a protective effect on the diabetic kidney. Short administration is sufficient to reduce kidney and glomerular hypertrophy as well as renal inflammation, but prolonged treatment is required to improve albuminuria. This effect was independent of the activation of the renin angiotensin system but correlated with upregulation of the antioxidant catalase. Apelin may represent a novel tool to treat diabetic nephropathy. diabetes; nephropathy; apelin; inflammation DIABETES IS THE MOST COMMON cause of end-stage renal disease (1) and nephropathy affects 20% of patients with type 1 diabetes (60). Early manifestations of diabetic nephropathy include the development of hyperfiltration and hypertrophy, thickening of the glomerular basement membrane, and mesangial matrix expansion. This is followed by increased urinary albumin excretion, glomerulosclerosis, tubulo-interstitial fibrosis, and end-stage renal failure. Current treatment strategies, including tight glycemic control (7a) and inhibition of the renin angiotensin system (32), slow down progression of diabetic nephropathy but do not reverse the course of diabetic nephropathy. The renin-angiotensin-aldosterone system contributes importantly to the pathogenesis of diabetic nephropathy; thus the role played by recently identified novel modulators of angiotensin actions such as apelin would be of significant interest. However, little is known about the effect of apelin in the kidney.Oxidative stress has been shown to play an important role in the development of diabetic nephropathy (4,22). Oxidative stress is due to...

HIF-2alpha plays a critical role in renal tumorigenesis. HIF-2alpha is stabilized in Von Hippel-Lindau (VHL)-deficient renal cell carcinoma through mechanisms that require ongoing mRNA translation. Mammalian target of Rapamycin (mTOR) functions in two distinct complexes, Raptor-associated mTORC1 and Rictor-associated mTORC2. Rictor-associated mTORC2 complex has been linked to maintaining HIF-2alpha protein in the absence of VHL, however the mechanisms remain to be elucidated. Although Raptor-associated mTORC1 is a known key upstream regulator of mRNA translation, initiation and elongation, the role of mTORC2 in regulating mRNA translation, is not clear. Complex assembly of the mRNA cap protein, eIF4E, with activators (eIF4G) and inhibitors (4E-BP1) are rate-limiting determinants of mRNA translation. Our laboratory has previously demonstrated that reactive oxygen species, mediated by p22phox-based Nox oxidases, are enhanced in VHL-deficient cells and play a role in the activation of Akt on S473, a site phosphorylated by the mTORC2 complex. In this study, we examined the role of Rictor-dependent regulation of HIF-2alpha through eIF4E-dependent mRNA translation and examined the effects of p22phox-based Nox oxidases on TORC2 regulation. We demonstrate for the first time that mTORC2 complex stability and activation is redox sensitive and further defined a novel role for p22phox-based Nox oxidases in eIF4E-dependent mRNA translation through mTORC2. Furthermore, we provide the first evidence that silencing of p22phox reduces HIF-2alpha-dependent gene targeting in vitro and tumor formation in vivo. The clinical relevance of these studies is demonstrated.

Summary We explored molecular events associated with aging-induced matrix changes in the kidney. C57BL6 mice were studied in youth, middle age, and old age. Albuminuria and serum cystatin C level (an index of glomerular filtration) increased with aging. Renal hypertrophy was evident in middle-aged and old mice and was associated with glomerulomegaly and increase in mesangial fraction occupied by extracellular matrix. Content of collagen types I and III and fibronectin was increased with aging; increment in their mRNA varied with the phase of aging. The content of ZEB1 and ZEB2, collagen type I transcription inhibitors, and their binding to the collagen type Iα2 promoter by ChIP assay also showed age-phase-specific changes. Lack of increase in mRNA and data from polysome assay suggested decreased degradation as a potential mechanism for kidney collagen type I accumulation in the middle-aged mice. These changes occurred with increment in TGFβ mRNA and protein and activation of its SMAD3 pathway; SMAD3 binding to the collagen type Iα2 promoter was also increased. TGFβ-regulated microRNAs (miRs) exhibited selective regulation. The renal cortical content of miR-21 and miR-200c, but not miR-192, miR-200a, or miR-200b, was increased with aging. Increased miR-21 and miR-200c contents were associated with reduced expression of their targets, Sprouty-1 and ZEB2, respectively. These data show that aging is associated with complex molecular events in the kidney that are already evident in the middle age and progress to old age. Agephase-specific regulation of matrix protein synthesis occurs and involves matrix protein-specific transcriptional and post-transcriptional mechanisms.

Objective We previously demonstrated that NADPH oxidase 4 (Nox4) mediates increased monocyte priming and chemotaxis under conditions of diabetic metabolic stress (DMS), and emerging data indicate that Group VIA Phospholipase A2 (iPLA2β) also participates in regulating monocyte chemotaxis. Here we examined relationships between iPLA2β expression and Nox4 action in mouse peritoneal macrophages subjected to DMS. Approach and Results Increased iPLA2β expression and activity were observed in macrophages from low density lipoprotein receptor knockout (LDLR−/−) mice that were fed a high fat diet (HFD), and this was associated with time-dependent increases in atherosclerotic lesion size and macrophage content. Incubating macrophages with 30 mM D-glucose (HG), 100 μg/ml LDL, or both (HG+LDL) induced a robust increase in iPLA2β expression and activity and in cell migration in response to monocyte chemoattractant protein-1 (MCP-1). The increases in iPLA2β activity and cell migration were prevented by a bromoenol lactone (BEL) iPLA2β suicide inhibitor or an iPLA2β antisense oligonucleotide. Incubating macrophages under conditions that mimic DMS ex vivo resulted in increased Nox4 expression and activity and H2O2 generation compared to controls. BEL prevented those effects without affecting Nox2 expression. Nox4 inhibition eliminated DMS-induced acceleration of macrophage migration. Lysophosphatidic acid (LPA) restored Nox4 expression, H2O2 generation, and migration to BEL-treated cells, and an LPA receptor antagonist abrogated iPLA2β-mediated increases in Nox4 expression. Conclusions Taken together, these observations identify iPLA2β and LPA derived from its action as critical in regulating macrophage Nox4 activity and migration in the diabetic state in vivo and under similar conditions ex vivo.