The core autophagy protein ATG5 controls the polarity of the Golgi apparatus and insulin secretion of pancreatic beta cells

Pancreatic β-Cells, Diabetes and Autophagy

PURPOSE

Pancreatic β-cells play a critical role in regulating plasma insulin levels and glucose metabolism balance, with their dysfunction being a key factor in the progression of diabetes. This review aims to explore the role of autophagy, a vital cellular self-maintenance process, in preserving pancreatic β-cell functionality and its implications in diabetes pathogenesis.

METHODS

We examine the current literature on the role of autophagy in β-cells, highlighting its function in maintaining cell structure, quantity, and function. The review also discusses the effects of both excessive and insufficient autophagy on β-cell dysfunction and glucose metabolism imbalance. Furthermore, we discuss potential therapeutic agents that modulate the autophagy pathway to influence β-cell function, providing insights into therapeutic strategies for diabetes management.

RESULTS

Autophagy acts as a self-protective mechanism within pancreatic β-cells, clearing damaged organelles and proteins to maintain cellular stability. Abnormal autophagy activity, either overactive or deficient, can disrupt β-cell function and glucose regulation, contributing to diabetes progression.

CONCLUSION

Autophagy plays a pivotal role in maintaining pancreatic β-cell function, and its dysregulation is implicated in the development of diabetes. Targeting the autophagy pathway offers potential therapeutic strategies for diabetes management, with agents that modulate autophagy showing promise in preserving β-cell function.

Crinophagic granules in pancreatic β cells contribute to mouse autoimmune diabetes by diversifying pathogenic epitope repertoire

Autoimmune attack toward pancreatic β cells causes permanent loss of glucose homeostasis in type 1 diabetes (T1D). Insulin secretory granules store and secrete insulin but are also thought to be tissue messengers for T1D. Here, we show that the crinophagic granules (crinosome), a minor set of vesicles formed by fusing lysosomes with the conventional insulin dense-core granules (DCG), are pathogenic in T1D development in mouse models. Pharmacological inhibition of crinosome formation in β cells delays T1D progression without affecting the dominant DCGs. Mechanistically, crinophagy inhibition diminishes the epitope repertoire in pancreatic islets, including cryptic, modified and disease-relevant epitopes derived from insulin. These unconventional insulin epitopes are largely undetectable in the MHC-II epitope repertoire of the thymus, where only canonical insulin epitopes are presented. CD4+ T cells targeting unconventional insulin epitopes display autoreactive phenotypes, unlike tolerized T cells recognizing epitopes presented in the thymus. Thus, the crinophagic pathway emerges as a tissue-intrinsic mechanism that transforms insulin from a signature thymic self-protein to a critical autoantigen by creating a peripheral-thymic mismatch in the epitope repertoire.

Establishment of Pancreatic β-Cell-Specific Gene Knockout System Based on CRISPR-Cas9 Technology With AAV8-Mediated gRNA Delivery

The Cre-loxP system provides valuable resources to analyze the importance of tissue-specific gene knockout (KO), including pancreatic β-cells associated with the pathogenesis of diabetes. However, it is expensive and time consuming to generate transgenic mice harboring floxed genes of interest and cross them with cell-specific Cre expression mice. We establish a βCas9 system with mice expressing Cas9 in pancreatic β-cells and adeno-associated virus 8 (AAV8)-mediated guide RNA (gRNA) delivery based on CRISPR-Cas9 technology to overcome those shortcomings. Interbreeding CAG-loxP-STOP-loxP (LSL)-Cas9 with Ins1-Cre mice generates normal glucose-tolerant βCas9 mice expressing Cas9 with fluorescent reporter EGFP specifically in β-cells. We also show significant β-cell-specific gene KO efficiency with AAV8-mediated delivery of gRNA for EGFP reporter by intraperitoneal injection in the mice. As a proof of concept, we administered AAV8 to βCas9 mice for expressing gRNA for Pdx1, a culprit gene of maturity-onset diabetes of the young 4. As reported previously, we demonstrate that those mice show glucose intolerance with transdifferentiation of Pdx1 KO β-cells into glucagon-expressing cells. We successfully generated a convenient β-cell-specific gene KO system with βCas9 mice and AAV8-mediated gRNA delivery.

ARTICLE HIGHLIGHTS

The Molecular Effects of SGLT2i Empagliflozin on the Autophagy Pathway in Diabetes Mellitus Type 2 and Its Complications

BACKGROUND

Type 2 diabetes mellitus (T2DM), especially hyperglycemia, is associated with increased glucose cell toxicity and oxidative stress that can lead to irreversible damage in the kidney such as diabetic nephropathy (DN). Autophagy plays a key role in the degradation of damaged intracellular proteins in order to maintain intracellular homeostasis and cell integrity. The disturbance of autophagy is involved in the pathogenesis of diabetic nephropathy. We aim to investigate the molecular effect of sodium-glucose transporter 2 inhibitor (SGLT2i) on the expression of ATG5 and its downstream collaborator LC3-II in diabetic nice model. Material and Methods. We used eight weeks old male mice: twenty C57BL/6 wild type (C57BL/6), twenty BTBR ob/ob (DM), and twenty BTBR ob/ob that were treated with empagliflozin (DM+EMPA), FDA approved SGLT2i. Lysate from murine renal cortex was analyzed by Western blot and immunohistochemistry. ATG5, LC3B, and fibronectin expression were analyzed in murine kidney tissues. All mice were sacrificed 13 weeks after the beginning of the experiment.

RESULTS

Histological and Western blot analyses reveal decrease ATG5, LC3-II, and fibronectin levels at renal specimens taken from DM mice. EMPA treatment reduced T2DM mice body weight and blood glucose and increased urine glucose. Further, it upregulated all of the abovementioned proteins.

CONCLUSIONS

Hyperglycemia reduces LC3-II and ATG5 protein levels which contribute to deficiencies in the autophagy process, with development and progression of DN. SGLT2i significantly reduces progression of DN and onset of end-stage renal disease in T2DM patients, probably through its effect on autophagy.