Increased hexosamine biosynthetic pathway flux dedifferentiates INS-1E cells and murine islets by an extracellular signal-regulated kinase (ERK)1/2-mediated signal transmission pathway

Abstract

Aims/hypothesis Beta cell failure is caused by loss of cell mass, mostly by apoptosis, but also by simple dysfunction (decline of glucose-stimulated insulin secretion, downregulation of specific gene expression). Apoptosis and dysfunction are caused, at least in part, by lipoglucotoxicity. The mechanisms implicated are oxidative stress, increase in the hexosamine biosynthetic pathway (HBP) flux and endoplasmic reticulum (ER) stress. Oxidative stress plays a role in glucotoxicity-induced beta cell dedifferentiation, while glucotoxicity-induced ER stress has been mostly linked to beta cell apoptosis. We sought to clarify whether ER stress caused by increased HBP flux participates in a dedifferentiating response of beta cells, in the absence of relevant apoptosis. Methods We used INS-1E cells and murine islets. We analysed the unfolded protein response and the expression profile of beta cells by real-time RT-PCR and western blot. The signal transmission pathway elicited by ER stress was investigated by real-time RT-PCR and immunofluorescence. Results Glucosamine and high glucose induced ER stress, but did not decrease cell viability in INS-1E cells. ER stress caused dedifferentiation of beta cells, as shown by downregulation of beta cell markers and of the transcription factor, pancreatic and duodenal homeobox 1. Glucose-stimulated insulin secretion was inhibited. These effects were prevented by the chemical chaperone, 4-phenyl butyric acid. The extracellular signal-regulated kinase (ERK) signal transmission pathway was implicated, since its inhibition prevented the effects induced by glucosamine and high glucose. Conclusions/interpretation Glucotoxic ER stress dedifferentiates beta cells, in the absence of apoptosis, through a transcriptional response. These effects are mediated by the activation of ERK1/2.

Mechanisms of β-cell dedifferentiation in diabetes: recent findings and future research directions

“…The normalization of these alterations in diabetic animals using phlorizin treatment, sulfonylureas or insulin therapy, but not bezafibrate treatment, strongly supports the implication of glucotoxicity rather than lipotoxicity (Jonas et al 1999, Harmon et al 2001, Gaisano et al 2002, Kjorholt et al 2005, Xu et al 2007, Brereton et al 2014. Several pathways downstream of glucotoxicity (Bensellam et al 2012b) have been implicated in the loss of β-cellenriched genes including oxidative stress (Tanaka et al 1999, Kaneto et al 2002b, Harmon et al 2005, Robertson & Harmon 2006, Guo et al 2013, ER stress (Hollien & Weissman 2006, Pirot et al 2007, Lipson et al 2008, Han et al 2009, Szabat et al 2011, Lombardi et al 2012, the hexosamine pathway (Kaneto et al 2001, Yoshikawa et al 2002, inflammation (Nordmann et al 2017) and hypoxia (Puri et al 2013, Sato et al 2014. Downregulation of the β-cell-enriched genes is linked with altered expression of key transcription factors.…”

Natural history of β-cell adaptation and failure in type 2 diabetes

“…Indeed, failure of the adaptive UPR and ER stress in islets can contributes to β-cell dedifferentiation and is linked with abnormalities in the expression of key β-cell genes, such as Pdx1 276 . Similarly, chronic ROS could contribute to dedifferentiation by down regulation of differentiated β-cell markers such as Glut2, Pdx1, and MafA 277 .…”

Transcription Factor Ets1 Regulates Expression of Thioredoxin-Interacting Protein and Inhibits Insulin Secretion in Pancreatic β-Cells

“…Glucotoxic ER stress dedifferentiates β-cells, in the absence of apoptosis, through a transcriptional response. These effects are mediated by the activation of ERK1/2 [6]. Pentose phosphate pathway metabolites also contribute to decreases in insulin gene expression and glucose-stimulated insulin secretion, and these effects depend on the activation of ERK1/2.…”