Effects of Common Genetic Variants Associated With Type 2 Diabetes and Glycemic Traits on α- and β-Cell Function and Insulin Action in Humans

Abstract Let7b-5p is a member of the Let-7 miRNA family and one of the top expressed miRNAs in human islets that implicated in glucose homeostasis. The levels of Let7b-5p in type 2 diabetes (T2DM) patients or its role in β-cell function is still unclear. In the current study, we measured the serum levels of let7b-5p in Emirati patients with T2DM (with/without complications) and control subjects. Overexpression or silencing of let7b-5p in INS-1 (832/13) cells was performed to investigate the impact on insulin secretion, content, cell viability, apoptosis, and key functional genes. We found that serum levels of let7b-5p are significantly (p<0.05) higher in T2DM-patients or T2DM with complications compared to control subjects. Overexpression of let7b-5p increased insulin content and decreased glucose-stimulated insulin secretion, whereas silencing of let7b-5p reduced insulin content and secretion. Modulation of the expression levels of let7b-5p did not influence cell viability nor apoptosis. Analysis of mRNA and protein expression of hallmark genes in let7b-5p transfected cells revealed a marked dysregulation of Insulin, Pancreatic And Duodenal Homeobox 1 (PDX1), glucokinase (GCK), glucose transporter 2 (GLUT2), and INSR. In conclusion, an appropriate level of let7b-5p is essential to maintain β-cell function and may be regarded as a biomarker for T2DM.

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Imeglimin Amplifies Glucose-Stimulated Insulin Release from Diabetic Islets via a Distinct Mechanism of Action

10.1101/2020.10.20.346841 ◽

2020 ◽

Author(s):

Sophie Hallakou-Bozec ◽

Micheline Kergoat ◽

Pascale Fouqueray ◽

Sébastien Bolze ◽

David E. Moller

Keyword(s):

Type 2 Diabetes ◽

Mode Of Action ◽

Cell Function ◽

Drug Candidate ◽

Β Cell ◽

Nicotinamide Phosphoribosyltransferase ◽

Predominant Component ◽

Cyclic Adp Ribose ◽

Β Cell Function

ABSTRACTPancreatic islet β-cell dysfunction is characterized by defective glucose-stimulated insulin secretion (GSIS) and is a predominant component of the pathophysiology of diabetes. Imeglimin, a novel first-in-class small molecule tetrahydrotriazine drug candidate, improves glycemia and GSIS in preclinical models and clinical trials in patients with type 2 diabetes; however, the mechanism by which it restores β-cell function is unknown. Here, we show that Imeglimin acutely and directly amplifies GSIS in islets isolated from rodents with Type 2 diabetes via a mode of action that is distinct from other known therapeutic approaches. The underlying mechanism involves increases in the cellular nicotinamide adenine dinucleotide (NAD+) pool – potentially via the salvage pathway and induction of nicotinamide phosphoribosyltransferase (NAMPT) along with augmentation of glucose-induced ATP levels. Further, additional results suggest that NAD+ conversion to a second messenger, cyclic ADP ribose (cADPR), via cyclic ADP ribose hydrolase (CD38) is required for Imeglimin’s effects in islets, thus representing a potential link between increased NAD+ and enhanced glucose-induced Ca2+ mobilization which - in turn - is known to drive insulin granule exocytosis. Collectively, these findings implicate a novel mode of action for Imeglimin that explains its ability to effectively restore β-cell function and provides for a new approach to treat patients suffering from Type 2 diabetes.

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