miR-344-5p Modulates Cholesterol-Induced β-Cell Apoptosis and Dysfunction Through Regulating Caveolin-1 Expression

MicroRNA regulation of islet and enteroendocrine peptides: Physiology and therapeutic implications for type 2 diabetes

The pathogenesis of type 2 diabetes (T2D) is associated with dysregulation of glucoregulatory hormones, including both islet and enteroendocrine peptides. Microribonucleic acids (miRNAs) are short noncoding RNA sequences which post transcriptionally inhibit protein synthesis by binding to complementary messenger RNA (mRNA). Essential for normal cell activities, including proliferation and apoptosis, dysregulation of these noncoding RNA molecules have been linked to several diseases, including diabetes, where alterations in miRNA expression within pancreatic islets have been observed. This may occur as a compensatory mechanism to maintain beta-cell mass/function (e.g., downregulation of miR-7), or conversely, lead to further beta-cell demise and disease progression (e.g., upregulation of miR-187). Thus, targeting miRNAs has potential for novel diagnostic and therapeutic applications in T2D. This is reinforced by the success seen to date with miRNA-based therapeutics for other conditions currently in clinical trials. In this review, differential expression of miRNAs in human islets associated with T2D will be discussed along with further consideration of their effects on the production and secretion of islet and incretin hormones. This analysis further unravels the therapeutic potential of miRNAs and offers insights into novel strategies for T2D management.

Irisin alters D-galactose-induced apoptosis by increasing caveolin-1 expression in C2C12 myoblasts and skeletal muscle fibroblasts

Muscle atrophy and skeletal muscle fibrosis are significant pathological manifestations of primary sarcopenia. The regulation of C2C12 myoblast and skeletal muscle fibroblast apoptosis is associated with these pathological changes. Previous studies have indicated that irisin, the cleaved form of fibronectin type III domain-containing protein 5 (FNDC5), can alleviate primary sarcopenia. However, the mechanisms of the effect of irisin in age-related apoptosis remain unknown. Our present research aimed to explore the effect of irisin and the underlying mechanism of D-galactose (D-gal)-induced apoptosis in skeletal muscle fibroblasts and C2C12 myoblasts. We found the opposite effects of D-gal on C2C12 myoblasts and fibroblasts. We also found that irisin suppressed C2C12 cell apoptosis and promoted fibroblast apoptosis. Mechanistically, irisin altered D-gal-induced apoptosis by increasing caveolin-1 expression. Taken together, these findings further demonstrated that irisin is a potential agent that can treat aged-relative muscle atrophy and fibrosis.

Caveolin-1 deficiency alleviates palmitate-induced intracellular lipid accumulation and inflammation in pancreatic β cells

Lipotoxicity-induced pancreatic β cell damage is a strong predictor of type 2 diabetes mellitus (T2DM). Our previous work showed that Caveolin-1 (Cav-1) depletion decreased β-cell apoptosis and improved β-cell viability. Further microarray analysis indicated significant changes in the expression of genes related to fatty acid metabolism and inflammation. The objective of this study was to explore the role of Cav-1 in intracellular lipid accumulation and inflammation in β cells under lipotoxic conditions. Here, we established a β-cell-specific Cav-1 knockout (β-Cav-1 KO) mouse model and a CAV-1 depleted β cell line (NIT-1). We found that Cav-1 silencing significantly reduced palmitate (PA)-induced intracellular triglyceride (TG) accumulation and decreased proinflammatory factor expression in both the mouse and cell models. Further mechanistic investigation revealed that amelioration of lipid metabolism was achieved through the downregulation of lipogenic markers (SREBP-1c, FAS and ACC) and upregulation of a fatty acid oxidation marker (CPT-1). Meanwhile, decrease of inflammatory cytokines (IL-6, TNF-α, and IL-1β) secretion was found with the involvement of the IKKβ/NF-κB signaling pathways. Our findings suggest that Cav-1 is of considerable importance in regulating lipotoxicity-induced β-cell intracellular lipid accumulation and inflammation.

Micro-RNA Implications in Type-1 Diabetes Mellitus: A Review of Literature

Type-1 diabetes mellitus (T1DM) is one of the most well-defined and complex metabolic disorders, characterized by hyperglycemia, with a constantly increasing incidence in children and adolescents. While current knowledge regarding the molecules related to the pathogenesis and diagnosis of T1DM is vast, the discovery of new molecules, such as micro ribonucleic acids (micro-RNAs, miRNAs), as well as their interactions with T1DM, has spurred novel prospects in the diagnosis of the disease. This review aims at summarizing current knowledge regarding miRNAs' biosynthesis and action pathways and their role as gene expression regulators in T1DM. MiRNAs follow a complex biosynthesis pathway, including cleaving and transport from nucleus to cytoplasm. After assembly of their final form, they inhibit translation or cause messenger RNA (mRNA) degradation, resulting in the obstruction of protein synthesis. Many studies have reported miRNA involvement in T1DM pathogenesis, mainly through interference with pancreatic b-cell function, insulin production and secretion. They are also found to contribute to β-cell destruction, as they aid in the production of autoreactive agents. Due to their elevated accumulation in various biological specimens, as well as their involvement in T1DM pathogenesis, their role as biomarkers in early preclinical T1DM diagnosis is widely hypothesized, with future studies concerning their diagnostic value deemed a necessity.