GLIS3, a Susceptibility Gene for Type 1 and Type 2 Diabetes, Modulates Pancreatic Beta Cell Apoptosis via Regulation of a Splice Variant of the BH3-Only Protein Bim

Abstract

Mutations in human Gli-similar (GLIS) 3 protein cause neonatal diabetes. The GLIS3 gene region has also been identified as a susceptibility risk locus for both type 1 and type 2 diabetes. GLIS3 plays a role in the generation of pancreatic beta cells and in insulin gene expression, but there is no information on the role of this gene on beta cell viability and/or susceptibility to immune- and metabolic-induced stress. GLIS3 knockdown (KD) in INS-1E cells, primary FACS-purified rat beta cells, and human islet cells decreased expression of MafA, Ins2, and Glut2 and inhibited glucose oxidation and insulin secretion, confirming the role of this transcription factor for the beta cell differentiated phenotype. GLIS3 KD increased beta cell apoptosis basally and sensitized the cells to death induced by pro-inflammatory cytokines (interleukin 1β + interferon-γ) or palmitate, agents that may contribute to beta cell loss in respectively type 1 and 2 diabetes. The increased cell death was due to activation of the intrinsic (mitochondrial) pathway of apoptosis, as indicated by cytochrome c release to the cytosol, Bax translocation to the mitochondria and activation of caspases 9 and 3. Analysis of the pathways implicated in beta cell apoptosis following GLIS3 KD indicated modulation of alternative splicing of the pro-apoptotic BH3-only protein Bim, favouring expression of the pro-death variant BimS via inhibition of the splicing factor SRp55. KD of Bim abrogated the pro-apoptotic effect of GLIS3 loss of function alone or in combination with cytokines or palmitate. The present data suggest that altered expression of the candidate gene GLIS3 may contribute to both type 1 and 2 type diabetes by favouring beta cell apoptosis. This is mediated by alternative splicing of the pro-apoptotic protein Bim and exacerbated formation of the most pro-apoptotic variant BimS.

CTSH regulates β-cell function and disease progression in newly diagnosed type 1 diabetes patients

“…The expressions of Bim, c-Myc, and DP5 are induced by cytokines in β-cells, and Bim and DP5 are regulated, at least in part, through JNK (25)(26)(27). Importantly, knockdown of DP5 or Bim significantly decreases cytokine-induced apoptosis in both human and rodent β-cells (26)(27)(28), and the proapoptotic effects of Bim in β-cells are modulated by two other candidate genes for T1D, namely PTPN2 (26) and GLIS3 (28). These observations suggest that CTSH protects against β-cell apoptosis through inhibition of JNK and p38 signaling and consequent activation of key proapoptotic genes.…”

IL-17A increases the expression of proinflammatory chemokines in human pancreatic islets

“…The rat insulin-producing INS-1E cell line, kindly provided by C. Wollheim (University of Geneva, Switzerland) [25], was maintained in RPMI 1640 GlutaMAX-I medium (Invitrogen) [26].…”

Emerging roles of GLIS3 in neonatal diabetes, type 1 and type 2 diabetes

“…An in vitro study showed that Glis3 knockdown in INS-1 cells increased basal and inflammatory cytokine (IL1β + IFNγ)-or palmitate-induced β cell apoptosis. Reduced GLIS3 expression was found to modulate the alternative splicing of the pro-apoptotic BH3-only protein Bim, promoting the expression of the pro-death variant BimS and β cell death (Nogueira et al 2013). These data suggest that proper GLIS3 expression could be required for β cell survival.…”

“…2). GLIS3 potently controls insulin gene transcription , ZeRuth et al 2013 as well as likely insulin secretion (Kang et al 2009b and β cell survival (Nogueira et al 2013, Dooley et al 2016, which perturbations may underlie all three forms of diabetes. Mutations or deletions in GLIS3 impair the proper expression and/or function of GLIS3 and its direct downstream target NGN3, causing severely abnormal β cell development in utero and marked impairment in insulin production at birth, culminating in permanent neonatal diabetes .…”