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Apoptosis of podocytes is considered critical in the pathogenesis of diabetic nephropathy (DN). Free fatty acids (FFAs) are critically involved in the pathogenesis of diabetes mellitus type 2, in particular the regulation of pancreatic [beta] cell survival. The objectives of this study were to elucidate the role of palmitic acid, palmitoleic, and oleic acid in the regulation of podocyte cell death and endoplasmic reticulum (ER) stress. We show that palmitic acid increases podocyte cell death, both apoptosis and necrosis of podocytes, in a dose and time-dependent fashion. Palmitic acid induces podocyte ER stress, leading to an unfolded protein response as reflected by the induction of the ER chaperone immunoglobulin heavy chain binding protein (BiP) and proapoptotic C/EBP homologous protein (CHOP) transcription factor. Of note, the monounsaturated palmitoleic and oleic acid can attenuate the palmitic acid-induced upregulation of CHOP, thereby preventing cell death. Similarly, gene silencing of CHOP protects against palmitic acid-induced podocyte apoptosis. Our results offer a rationale for interventional studies aimed at testing whether dietary shifting of the FFA balance toward unsaturated FFAs can delay the progression of DN. diabetic nephropathy; apoptosis; endoplasmic reticulum; stress; palmitic acid doi: 10.1152/ajprenal.00196.2010.

Type 2 diabetes is characterized by dyslipidemia with elevated free fatty acids (FFAs). Loss of podocytes is a hallmark of diabetic nephropathy, and podocytes are susceptible to saturated FFAs, which induce endoplasmic reticulum (ER) stress and podocyte death. Genome-wide association studies indicate that expression of acetyl-CoA carboxylase (ACC) 2, a key enzyme of fatty acid oxidation (FAO), is associated with proteinuria in type 2 diabetes. Here, we show that stimulation of FAO by aminoimidazole-4-carboxamide-1β-d-ribofuranoside (AICAR) or by adiponectin, activators of the low-energy sensor AMP-activated protein kinase (AMPK), protects from palmitic acid-induced podocyte death. Conversely, inhibition of carnitine palmitoyltransferase (CPT-1), the rate-limiting enzyme of FAO and downstream target of AMPK, augments palmitic acid toxicity and impedes the protective AICAR effect. Etomoxir blocked the AICAR-induced FAO measured with tritium-labeled palmitic acid. The beneficial effect of AICAR was associated with a reduction of ER stress, and it was markedly reduced in ACC-1/-2 double-silenced podocytes. In conclusion, the stimulation of FAO by modulating the AMPK-ACC-CPT-1 pathway may be part of a protective mechanism against saturated FFAs that drive podocyte death. Further studies are needed to investigate the potentially novel therapeutic implications of these findings. [ABSTRACT FROM AUTHOR]

ATP-binding cassette transporter 1 (ABCA1), the defective transporter in Tangier disease, binds and promotes cellular cholesterol and phospholipid efflux to apolipoprotein I (apoA-I). Based on a high degree of sequence homology between ABCA1 and ABCA7, a transporter of unknown function, we investigated the possibility that ABCA7 might be involved in apolipoprotein binding and lipid efflux. Similarly to cells expressing ABCA1, HEK293 cells overexpressing ABCA7 showed specific binding and cross-linking of lipid-poor apoA-I. ABCA7 expression increased cellular phosphatidylcholine and sphingomyelin efflux to apoA-I in a manner similar to ABCA1 but had no effect on cholesterol efflux. Western analysis showed a high protein level of ABCA7 in mouse spleen, lung, adrenal, and brain but low expression in liver. In contrast to ABCA1, ABCA7 showed moderate basal mRNA and protein levels in macrophages and lymphocytes but no induction by liver X receptor activation. These studies show that ABCA7 has the ability to bind apolipoproteins and promote efflux of cellular phospholipids without cholesterol, and they suggest a possible role of ABCA7 in cellular phospholipid metabolism in peripheral tissues. [ABSTRACT FROM AUTHOR]

Diabetic nephropathy is the most common cause of end-stage renal disease and is associated with a high morbidity and mortality. Early diagnosis is important as tight control of albuminuria and hypertension improves the renal prognosis. Similarly, good control of hyperglycemia is critical, but emphasis should be given on individualization of treatment goals. Once the estimated GFR is < 60 ml/min/1.73 m2 the antidiabetic medication needs to be reviewed and a dose reduction of many drugs is necessary. The risk for hypoglycemia is particularly high for the sulfonylureas glibenclamide and glimepiride and they are contraindicated once the GFR is < 60 ml/min/1.73 m2. Because of the increased risk of lactic acidosis, metformin requires a dose adjustment if the GFR is < 60 ml/min/1.73 m2 and the drug should be stopped once the GFR falls < 45 ml/min/1.73 m2. In addition, metformin needs to be paused if acute renal failure is imminent. Inhibitors of the DPP-4 enzyme can be employed with impaired renal function, but their use usually requires dose adjustments. Prescription of GLP-1 receptor agonists is possible with a moderately impaired renal function but they should be discontinued if the GFR falls < 30/min/1.73 m2. From the new class of SGLT2 inhibitors canagliflozin and empagliflozin can be used in an adjusted dose as long as the GFR is > 45 ml/min/1.73 m2.