Translation Attenuation through eIF2α Phosphorylation Prevents Oxidative Stress and Maintains the Differentiated State in β Cells

Abstract

SUMMARY Accumulation of unfolded protein within the endoplasmic reticulum (ER) lumen attenuates mRNA translation through activation of the protein kinase PERK and subsequent phosphorylation of eukaryotic initiation factor 2 on Ser51 of the alpha subunit (eIF2α). Genetic disruption of the PERK/eIF2α pathway in humans and mice produces severe pancreatic beta cell deficiency and post-natal lethality. To elucidate the role of eIF2α phosphorylation in beta cells, we have rescued the lethality of homozygous eIF2α Ser51Ala mice by expression of a loxP-flanked wild-type eIF2α transgene. Beta cell-specific transgene deletion to prevent eIF2α phosphorylation caused a severe diabetic phenotype due to heightened, unregulated proinsulin translation, defective intracellular trafficking of secretory and plasma membrane proteins, increased oxidative damage, reduced expression of stress response and beta cell-specific genes, and apoptosis. However, glucose intolerance and beta cell death in these mice were attenuated by antioxidant treatment. We conclude that phosphorylation of eIF2α coordinately attenuates mRNA translation, prevents oxidative stress, and optimizes ER protein folding to support insulin production in the beta cell. These findings that show increased proinsulin synthesis causes oxidative stress leading to beta cell failure may reflect events in the beta cell loss associated with insulin resistance in type 2 diabetes.

Autophagy deficiency in beta cells leads to compromised unfolded protein response and progression from obesity to diabetes in mice

“…Our results are consistent with recent reports showing increased ROS damage in beta cells with genetic deficiency of UPR [13] or autophagy-deficient kidney cells [33]. However, NAC and Ebselen both failed to suppress the increased death rate of autophagy-deficient beta islet cells after PA treatment, suggesting a possible contribution from other pathways.…”

“…1a, b), suggesting that basal UPR is compromised in autophagy-deficient beta cells. Expression of genes related to protection against ER stress, such as Sod1, Sod2, Ho1, Gpx1, Gpx2, Ucp2, Ppargc1b and Pparg [13], was also significantly downregulated in autophagydeficient beta cells (p<0.05-0.001; Fig. 1c).…”

“…Dysfunctional mitochondria or ER in autophagydeficient cells may produce more ROS and, further, may not be able to cope with increased stress such as metabolic load [24]. Nitrotyrosine staining showed increased accumulation of peroxynitrite-modified tyrosine residues, reflecting ROS damage to proteins [13] in beta cells from Atg7 Δβ-cell -ob/ob mice compared with Atg7 F/F -ob/ob or Atg7 Δβ-cell -ob/w mice (Fig. 5g).…”

“…cDNA was synthesised using Superscript II (Invitrogen) and oligo(dT) [12][13][14][15][16][17][18] primer. Expression of UPR-related genes, antioxidant genes and p85α and p85β subunits of phosphoinositide 3-kinase (PI3K) was examined by real-time RT-PCR analysis using specific primers (electronic supplementary material [ESM] Table 1) [13].…”

C/EBP homologous protein contributes to cytokine-induced pro-inflammatory responses and apoptosis in β-cells

“…eIF2a phosphorylation and reduced rate of protein translation are considered as protective mechanisms preventing oxidative stress and apoptosis during ER stress. 38 Thus, by inducing GADD34, CHOP may promote eIF2a dephosphorylation and sustained protein synthesis, leading to apoptosis. 39 In this study, CHOP KD prevented GADD34 overexpression, but did not decrease eIF2a phosphorylation.…”