Redox homeostasis and cell cycle activation mediate beta-cell mass expansion in aged, diabetes-prone mice under metabolic stress conditions: Role of thioredoxin-interacting protein (TXNIP)

Comprehensive analysis of endoplasmic reticulum stress-related mechanisms in type 2 diabetes mellitus

BACKGROUND

The endoplasmic reticulum (ER) is closely related to a wide range of cellular functions and is a key component to maintain and restore metabolic health. Type 2 diabetes mellitus (T2DM) is a serious threat to human health, but the ER stress (ERS)-related mechanisms in T2DM have not been fully elucidated.

AIM

To identify potential ERS-related mechanisms and crucial biomarkers in T2DM.

METHODS

We conducted gene set enrichment analysis (GSEA) and gene set variation analysis (GSVA) in myoblast and myotube form GSE166502, and obtained the differentially expressed genes (DEGs). After intersecting with ERS-related genes, we obtained ERS-related DEGs. Finally, functional analyses, immune infiltration, and several networks were established.

RESULTS

Through GSEA and GSVA, we identified several metabolic and immune-related pathways. We obtained 227 ERS-related DEGs and constructed several important networks that help to understand the mechanisms and treatment of T2DM. Finally, memory CD4⁺ T cells accounted for the largest proportion of immune cells.

CONCLUSION

This study revealed ERS-related mechanisms in T2DM, which might contribute to new ideas and insights into the mechanisms and treatment of T2DM.

TXNIP Exacerbates the Senescence and Aging-Related Dysfunction of β Cells by Inducing Cell Cycle Arrest Through p38-p16/p21-CDK-Rb Pathway

Aims: Thioredoxin-interacting protein (TXNIP) is a crucial molecular promoter of oxidative stress and has been identified to be associated with cellular senescence. It is an important mediator of β cell insulin secretion and has effects on β cell mass. However, its role in β cell senescence is unclear. The present study was designed to investigate the effects and mechanisms of TXNIP on the senescence and aging- and diet-related dysfunction of β cells. Methods: Human pancreatic paraffin tissues and serum samples from different ages were collected to detect TXNIP expression. TXNIP^-/- and C57BL/6J mice were fed either a normal chow diet (NCD) or a high-fat diet (HFD) until 5, 11, 14, or 20 months. The recapitulation experiment was conducted with TXNIP protein injection. MIN6 cells were transfected with LV-TXNIP and LV-siTXNIP. The biochemical indexes, ageing-related markers, cell cycle proteins, and pathways were examined both in vivo and in vitro. Results: TXNIP expression showed an age-related increase in β cells and serum samples from humans. TXNIP significantly impaired glucose metabolism and insulin secretion in an age-dependent manner. TXNIP aggravated age-related and obesity-induced structural failure, oxidative stress, decreased proliferation, increased apoptosis in β cells, and induced the cell cycle arrest. TXNIP interacted with p38 mitogen-activated protein kinase (p38MAPK) and modulated the p16/p21-CDK-Rb axis to accelerate β cell senescence. Innovation and Conclusions: The present study demonstrated that TXNIP may exacerbate pancreatic β cell senescence and age-related dysfunction by inducing cell cycle arrest through the p38-p16/p21-CDK-Rb pathway, in natural and pathological states. Antioxid. Redox Signal. 38, 480-495.

miR-146a-5p/TXNIP axis attenuates intestinal ischemia-reperfusion injury by inhibiting autophagy via the PRKAA/mTOR signaling pathway

Autophagy is being increasingly recognized as an important regulator of intestinal ischemia-reperfusion(I/R)injury, but its exact role is still debated. Emerging evidence suggests that miR-146a-5p is involved in the initiation and development of I/R injury, but its role in intestinal I/R injury remains unclear. The present study generated an intestinal I/R mouse model and an oxygen glucose deprivation/reoxygenation (OGD/R) Caco-2 cell model and found that autophagy was increased and contributed to the intestinal injury and cell death induced by I/R and OGD/R. In addition, in both I/R and OGD/R models, the miR-146a-5p expression level was decreased and accompanied by an increase in TXNIP expression. By transfecting cells with an miR-146a-5p inhibitor or mimic, we observed that miR-146a-5p inhibits autophagy during OGD/R by targeting TXNIP; this was confirmed by the dual luciferase reporter gene assay. Additionally, through overexpression and knockdown cell lines, we established that TXNIP regulates autophagy during intestinal I/R via the PRKAA/mTOR pathway. The interaction between TXNIP and p-PRKAA was verified by immunofluorescence co-localization and immunoprecipitation assays. Moreover, we confirmed that TXNIP is indispensable for miR-146a-5p-mediated cell protection. Finally, we observed that miR-146a-5p overexpression inhibits autophagy and attenuates intestinal I/R injury via the PRKAA/mTOR pathway by targeting TXNIP in vivo. In conclusion, this study highlights the role of miR-146a-5p in regulating autophagy by targeting TXNIP, suggesting that miR-146a-5p may be a novel drug target for intestinal I/R therapy.

Reduced Liver Autophagy in High-Fat Diet Induced Liver Steatosis in New Zealand Obese Mice

Non-alcoholic fatty liver disease (NAFLD), as a consequence of overnutrition caused by high-calorie diets, results in obesity and disturbed lipid homeostasis leading to hepatic lipid droplet formation. Lipid droplets can impair hepatocellular function; therefore, it is of utmost importance to degrade these cellular structures. This requires the normal function of the autophagic-lysosomal system and the ubiquitin-proteasomal system. We demonstrated in NZO mice, a polygenic model of obesity, which were compared to C57BL/6J (B6) mice, that a high-fat diet leads to obesity and accumulation of lipid droplets in the liver. This was accompanied by a loss of autophagy efficiency whereas the activity of lysosomal proteases and the 20S proteasome remained unaffected. The disturbance of cellular protein homeostasis was further demonstrated by the accumulation of 3-nitrotyrosine and 4-hydroxynonenal modified proteins, which are normally prone to degradation. Therefore, we conclude that fat accumulation in the liver due to a high-fat diet is associated with a failure of autophagy and leads to the disturbance of proteostasis. This might further contribute to lipid droplet stabilization and accumulation.