Probes for INSULIN

Abstract

Objective

GPR142 agonists are being pursued as novel diabetes therapies by virtue of their insulin secretagogue effects. But it is undetermined whether GPR142’s functions in pancreatic islets are limited to regulating insulin secretion. The current study expands research on its action.

Methods and Results

We demonstrated by in situ hybridization and immunostaining that GPR142 is expressed not only in β cells but also in a subset of α cells. Stimulation of GPR142 by a selective agonist increased glucagon secretion in both human and mouse islets. More importantly, the GPR142 agonist also potentiated glucagon-like peptide-1 (GLP-1) production and its release from islets through a mechanism that involves upregulation of prohormone convertase 1/3 expression. Strikingly, stimulation of insulin secretion and increase in insulin content via GPR142 engagement requires intact GLP-1 receptor signaling. Furthermore, GPR142 agonist increased β cell proliferation and protected both mouse and human islets against stress-induced apoptosis.

Conclusions

Collectively, we provide here evidence that local GLP-1 release from α cells defines GPR142’s beneficial effects on improving β cell function and mass, and we propose that GPR142 agonism may have translatable and durable efficacy for the treatment of type 2 diabetes.

Obesity is associated with increased risk for fragility fractures. However, the cellular mechanisms are unknown. Using a translational approach combining RNA sequencing and cellular analyses, we investigated bone marrow stromal stem cells (BM-MSCs) of 54 men divided into lean, overweight, and obese groups on the basis of BMI. Compared with BM-MSCs obtained from lean, obese BM-MSCs exhibited a shift of molecular phenotype toward committed adipocytic progenitors and increased expression of metabolic genes involved in glycolytic and oxidoreductase activity. Interestingly, compared with paired samples of peripheral adipose tissue-derived stromal cells (AT-MSCs), insulin signaling of obese BM-MSCs was enhanced and accompanied by increased abundance of insulin receptor positive (IR+) and leptin receptor positive (LEPR+) cells in BM-MSC cultures. Their hyper-activated metabolic state was accompanied by an accelerated senescence phenotype. Our data provide a plausible explanation for the bone fragility in obesity caused by enhanced insulin signaling leading to accelerated metabolic senescence of BM-MSCs.

Abstract

Objectives

Extracts of the hops plant have been shown to reduce weight and insulin resistance in rodents and humans, but elucidation of the mechanisms responsible for these benefits has been hindered by the use of heterogeneous hops-derived mixtures. Because hop extracts are used as flavoring agents for their bitter properties, we hypothesized that bitter taste receptors (Tas2rs) could be mediating their beneficial effects in metabolic disease. Studies have shown that exposure of cultured enteroendocrine cells to bitter tastants can stimulate release of hormones, including glucagon-like peptide 1 (GLP-1). These findings have led to the suggestion that activation of Tas2rs may be of benefit in diabetes, but this tenet has not been tested. Here, we have assessed the ability of a pure derivative of a hops isohumulone with anti-diabetic properties, KDT501, to signal through Tas2rs. We have further used this compound as a tool to systematically assess the impact of bitter taste receptor activation in obesity-diabetes.

Methods

KDT501 was tested in a panel of bitter taste receptor signaling assays. Diet-induced obese mice (DIO) were dosed orally with KDT501 and acute effects on glucose homeostasis determined. A wide range of metabolic parameters were evaluated in DIO mice chronically treated with KDT501 to establish the full impact of activating gut bitter taste signaling.

Results

We show that KDT501 signals through Tas2r108, one of 35 mouse Tas2rs. In DIO mice, acute treatment stimulated GLP-1 secretion and enhanced glucose tolerance. Chronic treatment caused weight and fat mass loss, increased energy expenditure, enhanced glucose tolerance and insulin sensitivity, normalized plasma lipids, and induced broad suppression of inflammatory markers. Chronic KDT501 treatment altered enteroendocrine hormone levels and bile acid homeostasis and stimulated sustained GLP-1 release. Combined treatment with a dipeptidyl peptidase IV inhibitor amplified the incretin-based benefits of this pure isohumulone.

Conclusions

Activation of Tas2r108 in the gut results in a remodeling of enteroendocrine hormone release and bile acid metabolism that ameliorates multiple features of metabolic syndrome. Targeting extraoral bitter taste receptors may be useful in metabolic disease.

Abstract