Akt activation and augmented fibronectin production in hyperhexosemia

Abstract

Dysmetabolic state in diabetes may lead to augmented synthesis of extracellular matrix (ECM) proteins. In the endothelial cells, we have previously demonstrated that glucose-induced fibronectin (FN) production and that of its splice variant, EDB+FN, is regulated by protein kinase B (PKB, also known as Akt). In this study, we investigated the role of Akt1 in ECM protein production in the organs affected by chronic diabetic complications. We studied Akt1/PKBα knockout mice and wild-type control littermates. To avoid confounding effects of systemic insulin, we used 30% galactose feeding to induce hyperhexosemia for 8 wk starting at 6 wk of age. We investigated FN mRNA, EDB+FN mRNA, and transforming growth factor (TGF)-β mRNA expression, Akt phosphorylation, Akt kinase activity, and NF-κB and AP-1 activation in the retina, heart, and kidney. Renal and cardiac tissues were histologically examined. Galactose feeding caused significant upregulation of FN, EDB+FN, and TGF-β in all tissues. FN protein levels paralleled mRNA. Such upregulation were prevented in Akt1-deficient galactose-fed mice. Galactose feeding caused ECM protein deposition in the glomeruli and in the myocardium, which was prevented in the Akt knockout mice. NF-κB and AP-1 activation was pronounced in galactose-fed wild-type mice and prevented in the galactose-fed Akt1/PKBα-deficient group. In the retina and kidney, Ser473 was the predominant site for Akt phosphorylation, whereas in the heart it was Thr308. Parallel experiment in streptozotocin-induced diabetic animals showed similar results. The data from this study indicate that hyperhexosemia-induced Akt/PKB activation may be an important mechanism leading to NF-κB and AP-1 activation and increased ECM protein synthesis in the organs affected by chronic diabetic complications.

Regulation of cardiomyocyte hypertrophy in diabetes at the transcriptional level

“…We have previously demonstrated that, in endothelial cells, hyperglycemia-induced protein kinase C and mitogen-activated protein kinase, as well as protein kinase B activation, may enhance the activity of p300 (30). All such pathways have been demonstrated in the heart of diabetic animals and may potentially contribute to p300 activation (12,23,49). This study supports the notion that p300 may represent a common final pathway upon which several signaling mechanisms may converge.…”

DNA-Free Recombinant SV40 Capsids Protect Mice from Acute Renal Failure by Inducing Stress Response, Survival Pathway and Apoptotic Arrest

“…Mice kidneys: Proteins were extracted from frozen mouse kidneys using RIPA [43] For microscopy, kidneys were fixed in 4% formaldehyde. Paraffin-embedded kidney sections were dewaxed, rehydrated and stained.…”

The role of EMT in renal fibrosis

“…These contrasting findings highlight the complex nature of miRNA research. Other miRNA that have been implicated in contributing to fibrogenesis in DN are miR-216a and miR-217 (Kato et al 2009;Xin et al 2007), miR-377 that regulates fibronectin expression (Wang et al 2008) and studies have shown TGF-β1-induced EMT is associated with upregulation of miR-21 (Zavadil et al 2007;Lan et al unpublished data). We have recently observed that miR-21 expression was significantly upregulated in a mouse model of obstructive nephropathy and was also upregulated by TGF-β/Smad3 signalling pathway.…”