SUMOylation of Pdia3 exacerbates proinsulin misfolding and ER stress in pancreatic beta cells

Post-translational modifications: emerging directors of cell-fate decisions during endoplasmic reticulum stress in Arabidopsis thaliana

Homeostasis of the endoplasmic reticulum (ER) is critical for growth, development, and stress responses. Perturbations causing an imbalance in ER proteostasis lead to a potentially lethal condition known as ER stress. In ER stress situations, cell-fate decisions either activate pro-life pathways that reestablish homeostasis or initiate pro-death pathways to prevent further damage to the organism. Understanding the mechanisms underpinning cell-fate decisions in ER stress is critical for crop development and has the potential to enable translation of conserved components to ER stress-related diseases in metazoans. Post-translational modifications (PTMs) of proteins are emerging as key players in cell-fate decisions in situations of imbalanced ER proteostasis. In this review, we address PTMs orchestrating cell-fate decisions in ER stress in plants and provide evidence-based perspectives for where future studies may focus to identify additional PTMs involved in ER stress management.

SUMOylation of ERp44 enhances Ero1α ER retention contributing to the pathogenesis of obesity and insulin resistance

OBJECTIVE

As the only E2 conjugating enzyme for the SUMO system, Ubc9-mediated SUMOylation has been recognized to regulate diverse biological processes, but its impact on adipocytes relevant to obesity and insulin resistance is yet to be elucidated.

METHODS

We established adipocyte-specific Ubc9 deficient mice to explore the effects of Ubc9 on obesity and metabolic disorders induced by high-fat diet (HFD) in adult mice. The molecular targets of SUMOylation were explored by liquid chromatography-mass spectrometry, and the regulatory mechanism of SUMOylation in T2D was analyzed.

RESULTS

Adipocyte-specific depletion of Ubc9 (AdipoQ-Cre-Ubc9^fl/fl, Ubc9^AKO) protected mice from HFD-induced obesity, insulin resistance, and hepatosteatosis. The Ubc9^AKO mice were featured by the reduced HFD-induced endoplasmic reticulum (ER) stress and inflammatory response. Mechanically, over nutrition rendered adipocytes to undergo a SUMOylation turnover characterized by the change of SUMOylation levels and substrates. ERp44 displayed the highest change in terms of SUMOylation levels of substrates involved in ER-related functions. The lack of ERp44 SUMOylation at lysine 76 (K76) located within the thioredoxin (TRX)-like domain by Ubc9 deficiency enhanced its degradation and suppressed its covalent binding to Ero1α, an oxidase that exists in the ER but lacks ER retention motif, thereby alleviating endoplasmic reticulum stress by promoting Ero1α secretion.

CONCLUSIONS

Our data suggest that modulation of ERp44 SUMOylation in adipocytes could be a feasible strategy against obesity and insulin resistance in clinical settings.

Enhanced insulin activity achieved in VDRa/b ablation zebrafish

INTRODUCTION

1α,25-dihydroxyvitamin D3 (1α,25[OH]₂VD₃) is a hormone known for its key roles in calcium absorption and nutrient metabolism. In teleost fishes, 1α,25(OH)₂VD₃ insufficiency causes impaired glucose metabolism and lipid oxidation. However, the cascade and mechanisms of 1α,25(OH)₂VD₃ and the vitamin d receptor (VDR) signaling are unclear.

RESULTS

In this study, two genes (vdra and vdrb) encoding paralogs of VDRs were genetically knocked out in zebrafish. Growth retardation and accumulated visceral adipose tissue have been observed in vdra ^-/-;vdrb ^-/- deficient line. In the liver elevated accumulation of triglycerides and suppressed lipid oxidation were detected. Morover significantly elevated 1α,25(OH)₂VD₃ levels were detected in vdra^-/-;vdrb^-/- zebrafish due to cyp24a1 transcription repression. Furthermore VDRs ablation Enhanced insulin signaling including elevated insulin/insra trancriptional levels, glycolysis, lipogenesis and promoted AKT/mTOR activity.

DISCUSSION

In conclusion, our present studies provides a zebrafish model with an elevated 1α,25(OH)₂VD₃ levels in vivo. The 1α,25(OH)₂VD₃/VDRs signaling promote lipid oxidation activity. However 1α,25(OH)₂VD₃ activity of regulation of glucose homeostasis through Insulin/Insr was independent of nuclear VDRs in teleosts.

One-Step Genotyping Method in loxP-Based Conditional Knockout Mice Generated by CRISPR-Cas9 Technology

With the development of CRISPR-Cas9 gene editing and in vitro fertilization (IVF) technology, we can now easily construct genetically modified mouse strains with indels, especially for loxP-based strategy. However, the general genotyping methods are time-consuming and unreliable given the loxP site is only 34 bp long. Here, based on the tetra primer-paired PCR amplification, we describe an efficient genotyping method which can simultaneously generate the internal control band, wild type (wt)-genotype band, and/or loxP-genotype band through one single PCR amplification. It is easy to interpret the mouse genotypes from the pattern of the bands. Further, the results could also help to exclude the possibility of minor cross-contamination, since the ratio between the bands’ quantity in wt/wt, wt/loxP, and loxP/loxP mice are relatively constant, which makes the genotyping more reliable when it is performed in a large amount.

The Pancreatic ß-cell Response to Secretory Demands and Adaption to Stress

Pancreatic β cells dedicate much of their protein translation capacity to producing insulin to maintain glucose homeostasis. In response to increased secretory demand, β cells can compensate by increasing insulin production capability even in the face of protracted peripheral insulin resistance. The ability to amplify insulin secretion in response to hyperglycemia is a critical facet of β-cell function, and the exact mechanisms by which this occurs have been studied for decades. To adapt to the constant and fast-changing demands for insulin production, β cells use the unfolded protein response of the endoplasmic reticulum. Failure of these compensatory mechanisms contributes to both type 1 and 2 diabetes. Additionally, studies in which β cells are "rested" by reducing endogenous insulin demand have shown promise as a therapeutic strategy that could be applied more broadly. Here, we review recent findings in β cells pertaining to the metabolic amplifying pathway, the unfolded protein response, and potential advances in therapeutics based on β-cell rest.