Cask methylation involved in the injury of insulin secretion function caused by interleukin1-β

The biological functions and pathological mechanisms of CASK in various diseases

Background

As a scaffold protein, calcium/calmodulin-dependent serine protein kinase (CASK) has been extensively studied in a variety of tissues throughout the body. The Cask gene is ubiquitous in several tissues, such as the neurons, islets, heart, kidneys and sperm, and is mostly localised in the cytoplasm adjacent to the basement membrane. CASK binds to a variety of proteins through its domains to exerting its biological activity.

Scope of review

Here, we discuss the role of CASK in multiple tissues throughout the body. The role of different CASK domains in regulating neuronal development, neurotransmitter release and synaptic vesicle secretion was emphasised; the regulatory mechanism of CASK on the function of pancreatic islet β cells was analysed; the role of CASK in cardiac physiology, kidney and sperm development was discussed; and the role of CASK in different tumours was compared. Finally, we clarify the importance of the Cask gene in the body, and how deletion or mutation of the Cask gene can have adverse consequences.

Major conclusions

CASK is a conserved gene with similar roles in various tissues. The function of the Cask gene in the nervous system is mainly involved in the development of the nervous system and the release of neurotransmitters. In the endocrine system, an involvement of CASK has been reported in the process of insulin vesicle transport. CASK is also involved in cardiomyocyte ion channel regulation, kidney and sperm development, and tumour proliferation. CASK is an indispensable gene for the whole body, and CASK mutations can cause foetal malformations or death at birth. In this review, we summarise the biological functions and pathological mechanisms of CASK in various systems, thereby providing a basis for further in-depth studies of CASK functions.

Unraveling the epigenetic fabric of type 2 diabetes mellitus: pathogenic mechanisms and therapeutic implications

Type 2 diabetes mellitus (T2DM) is a rapidly escalating global health concern, with its prevalence projected to increase significantly in the near future. This review delves into the intricate role of epigenetic modifications - including DNA methylation, histone acetylation, and micro-ribonucleic acid (miRNA) expression - in the pathogenesis and progression of T2DM. We critically examine how these epigenetic changes contribute to the onset and exacerbation of T2DM by influencing key pathogenic processes such as obesity, insulin resistance, β-cell dysfunction, cellular senescence, and mitochondrial dysfunction. Furthermore, we explore the involvement of epigenetic dysregulation in T2DM-associated complications, including diabetic retinopathy, atherosclerosis, neuropathy, and cardiomyopathy. This review highlights recent studies that underscore the diagnostic and therapeutic potential of targeting epigenetic modifications in T2DM. We also provide an overview of the impact of lifestyle factors such as exercise and diet on the epigenetic landscape of T2DM, underscoring their relevance in disease management. Our synthesis of the current literature aims to illuminate the complex epigenetic underpinnings of T2DM, offering insights into novel preventative and therapeutic strategies that could revolutionize its management.

The Protective Action of Metformin against Pro-Inflammatory Cytokine-Induced Human Islet Cell Damage and the Mechanisms Involved

Metformin, a drug widely used in type 2 diabetes (T2D), has been shown to protect human β-cells exposed to gluco- and/or lipotoxic conditions and those in islets from T2D donors. We assessed whether metformin could relieve the human β-cell stress induced by pro-inflammatory cytokines (which mediate β-cells damage in type 1 diabetes, T1D) and investigated the underlying mechanisms using shotgun proteomics. Human islets were exposed to 50 U/mL interleukin-1β plus 1000 U/mL interferon-γ for 48 h, with or without 2.4 µg/mL metformin. Glucose-stimulated insulin secretion (GSIS) and caspase 3/7 activity were studied, and a shotgun label free proteomics analysis was performed. Metformin prevented the reduction of GSIS and the activation of caspase 3/7 induced by cytokines. Proteomics analysis identified more than 3000 proteins in human islets. Cytokines alone altered the expression of 244 proteins (145 up- and 99 down-regulated), while, in the presence of metformin, cytokine-exposure modified the expression of 231 proteins (128 up- and 103 downregulated). Among the proteins inversely regulated in the two conditions, we found proteins involved in vesicle motility, defense against oxidative stress (including peroxiredoxins), metabolism, protein synthesis, glycolysis and its regulation, and cytoskeletal proteins. Metformin inhibited pathways linked to inflammation, immune reactions, mammalian target of rapamycin (mTOR) signaling, and cell senescence. Some of the changes were confirmed by Western blot. Therefore, metformin prevented part of the deleterious actions of pro-inflammatory cytokines in human β-cells, which was accompanied by islet proteome modifications. This suggests that metformin, besides use in T2D, might be considered for β-cell protection in other types of diabetes, possibly including early T1D.

Specific Deletion of CASK in Pancreatic β Cells Affects Glucose Homeostasis and Improves Insulin Sensitivity in Obese Mice by Reducing Hyperinsulinemia Running Title: β Cell CASK Deletion Reduces Hyperinsulinemia

Calcium/calmodulin-dependent serine protein kinase (CASK) is involved in the secretion of insulin vesicles in pancreatic β-cells. The present study revealed a new in vivo role of CASK in glucose homeostasis during the progression of type 2 diabetes mellitus (T2DM). A Cre-loxP system was used to specifically delete the Cask gene in mouse β-cells (βCASKKO), and the glucose metabolism was evaluated in βCASKKO mice fed a normal chow diet (ND) or a high-fat diet (HFD). ND-fed mice exhibited impaired insulin secretion in response to glucose stimulation. Transmission electron microscopy showed significantly reduced numbers of insulin granules at or near the cell membrane in the islets of βCASKKO mice. By contrast, HFD-fed βCASKKO mice showed reduced blood glucose and a partial relief of hyperinsulinemia and insulin resistance when compared to HFD-fed wildtype mice. The IRS1/PI3K/AKT signaling pathway was upregulated in the adipose tissue of HFD-βCASKKO mice. These results indicated that knockout of the Cask gene in β cells had a diverse effect on glucose homeostasis: reduced insulin secretion in ND-fed mice, but improves insulin sensitivity in HFD-fed mice. Therefore, CASK appears to function in the insulin secretion and contributes to hyperinsulinemia and insulin resistance during the development of obesity-related T2DM.

Epigenetic Regulation of β Cell Identity and Dysfunction

β cell dysfunction and failure are driving forces of type 2 diabetes mellitus (T2DM) pathogenesis. Investigating the underlying mechanisms of β cell dysfunction may provide novel targets for the development of next generation therapy for T2DM. Epigenetics is the study of gene expression changes that do not involve DNA sequence changes, including DNA methylation, histone modification, and non-coding RNAs. Specific epigenetic signatures at all levels, including DNA methylation, chromatin accessibility, histone modification, and non-coding RNA, define β cell identity during embryonic development, postnatal maturation, and maintain β cell function at homeostatic states. During progression of T2DM, overnutrition, inflammation, and other types of stress collaboratively disrupt the homeostatic epigenetic signatures in β cells. Dysregulated epigenetic signatures, and the associating transcriptional outputs, lead to the dysfunction and eventual loss of β cells. In this review, we will summarize recent discoveries of the establishment and disruption of β cell-specific epigenetic signatures, and discuss the potential implication in therapeutic development.