High Glucose Impairs Insulin Signaling in the Glomerulus: An In Vitro and Ex Vivo Approach

Abstract

ObjectiveChronic 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 FindingsHGEC 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.ConclusionsThese 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.

Vitamin D3 ameliorates podocyte injury through the nephrin signalling pathway

“…Specifically, CD2AP was reported to interact with both nephrin and PI3K in vivo, stimulating anti-apoptotic Akt signalling in podocytes [12]. Chronic hyperglycaemia disrupts signal transduction pathways involved in glomerular survival [36]. Our previous work [37], as well as work by others [38] demonstrated a decrease of glomerular nephrin expression as an early event in hyperglycaemic conditions.…”

Transcriptomic characterization of culture-associated changes in murine and human precision-cut tissue slices

“…These are the pathways of nuclear transcription factor receptors: peroxisome proliferator-activated receptor (PPAR), liver X receptor (LXR) and retinoid X receptor (RXR) and have a role in cellular metabolism. The inhibition of PPAR signalling in PCTS might be caused by the high concentration of glucose in the culture media (25 mM), as similar concentrations of glucose were reported to inhibit PPAR (Roduit et al 2000;Cheng et al 2013;Domínguez-Avila et al 2016) and to lead to several transcriptional changes in different organs (Katsoulieris et al 2016;Boztepe and Gulec 2018). However, further functional experiments are needed to confirm this hypothesis.…”

FOXO3a accumulation and activation accelerate oxidative stress‐induced podocyte injury

“…Similarly, earlier reports demonstrated that FOXO3a activation is related to podocyte apoptosis under high glucose conditions and in aging kidneys between which oxidative stress is a common feature. 40,41 These findings suggest that FOXO3a is more likely to induce podocyte apoptosis under oxidative stress conditions. However, some studies show that FOXO3a plays a pro-survival role in chronic tubular injury by activating antioxidant genes or autophagy-related genes, 25,26,42 but we did not observe this protective role of FOXO3a in AOPPs-treated podocyte.…”