Open AccessHigh Glucose Impairs Insulin Signaling in the Glomerulus: An In Vitro and Ex Vivo Approach
Author(s) -
Elias N. Katsoulieris,
Garyfalia I. Drossopoulou,
Eleni S. Kotsopoulou,
Dimitrios Vlahakos,
Elias A. Lianos,
Effie C. Tsilibary
Publication year - 2016
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0158873
Subject(s) - insulin , endocrinology , medicine , insulin receptor , downregulation and upregulation , biology , protein kinase b , signal transduction , tyrosine phosphorylation , apoptosis , phosphorylation , microbiology and biotechnology , insulin resistance , biochemistry , gene
Objective Chronic hyperglycaemia, as seen in type II diabetes, results in both morphological and functional impairments of podocytes in the kidney. We investigated the effects of high glucose (HG) on the insulin signaling pathway, focusing on cell survival and apoptotic markers, in immortalized human glomerular cells (HGEC; podocytes) and isolated glomeruli from healthy rats. Methods and Findings HGEC and isolated glomeruli were cultured for various time intervals under HG concentrations in the presence or absence of insulin. Our findings indicated that exposure of HGEC to HG led to downregulation of all insulin signaling markers tested (IR, p-IR, IRS-1, p-Akt, p-Fox01,03), as well as to increased sensitivity to apoptosis (as seen by increased PARP cleavage, Casp3 activation and DNA fragmentation). Short insulin pulse caused upregulation of insulin signaling markers (IR, p-IR, p-Akt, p-Fox01,03) in a greater extent in normoglycaemic cells compared to hyperglycaemic cells and for the case of p-Akt, in a PI3K-dependent manner. IRS-1 phosphorylation of HG-treated podocytes was negatively regulated, favoring serine versus tyrosine residues. Prolonged insulin treatment caused a significant decrease of IR levels, while alterations in glucose concentrations for various time intervals demonstrated changes of IR, p-IR and p-Akt levels, suggesting that the IR signaling pathway is regulated by glucose levels. Finally, HG exerted similar effects in isolated glomeruli. Conclusions These results suggest that HG compromises the insulin signaling pathway in the glomerulus, promoting a proapoptotic environment, with a possible critical step for this malfunction lying at the level of IRS-1 phosphorylation; thus we herein demonstrate glomerular insulin signaling as another target for investigation for the prevention and/ or treatment of diabetic nephropathy.