Piezo1 channel activation mimics high glucose as a stimulator of insulin release

Glucose and hypotonicity induced cell swelling stimulate insulin release from pancreatic β-cells but the mechanisms are poorly understood. Recently, Piezo1 was identified as a mechanically-activated nonselective Ca2+ permeable cationic channel in a range of mammalian cells. As cell swelling induced insulin release could be through stimulation of Ca2+ permeable stretch activated channels, we hypothesised a role for Piezo1 in cell swelling induced insulin release. Two rat β-cell lines (INS-1 and BRIN-BD11) and freshly-isolated mouse pancreatic islets were studied. Intracellular Ca2+ measurements were performed using the fura-2 Ca2+ indicator dye and ionic current was recorded by whole cell patch-clamp. Piezo1 agonist Yoda1, a competitive antagonist of Yoda1 (Dooku1) and an inactive analogue of Yoda1 (2e) were used as chemical probes. Piezo1 mRNA and insulin secretion were measured by RT-PCR and ELISA respectively. Piezo1 mRNA was detected in both β-cell lines and mouse islets. Yoda1 evoked Ca2+ entry was inhibited by Yoda1 antagonist Dooku1 as well as other Piezo1 inhibitors gadolinium and ruthenium red, and not mimicked by 2e. Yoda1, but not 2e, stimulated Dooku1-sensitive insulin release from β-cells and pancreatic islets. Hypotonicity and high glucose increased intracellular Ca2+ and enhanced Yoda1 Ca2+ influx responses. Yoda1 and hypotonicity induced insulin release were significantly inhibited by Piezo1 specific siRNA. Pancreatic islets from mice with haploinsufficiency of Piezo1 released less insulin upon exposure to Yoda1. The data show that Piezo1 channel agonist induces insulin release from β-cell lines and mouse pancreatic islets suggesting a role for Piezo1 in cell swelling induced insulin release. Hence Piezo1 agonists have the potential to be used as enhancers of insulin release

Receptor tyrosine kinase inhibitors cause dysfunction in adult rat cardiac fibroblasts in vitro.

The anti-cancer receptor tyrosine kinase inhibitors include known cardiotoxins: a component of this toxicity may be mediated by effects on cardiac fibroblasts (CFs). We hypothesised that imatinib mesylate (imatinib) and sunitinib malate (sunitinib) cause significant dysfunction in adult CFs. Following in vitro treatments with imatinib or sunitinib, adult rat CF viability was assessed by fluorescein diacetate assay, proliferation measured by bromodeoxyuridine nuclear incorporation and changes to the expression of CF secretome components determined by real time quantitative RT-PCR. Imatinib and sunitinib significantly reduced cell viability over 48 h, with EC50 values of 11.0 μM (imatinib) and 4.5 μM (sunitinib) respectively. Imatinib reduced CF proliferation from 35.5 ± 3.2% in control to 23.0 ± 5.5% (3 μM; p < 0.001) and to 9.4 ± 2.5% (10 μM; p < 0.001), whereas sunitinib reduced proliferation to 22.9 ± 3.1% (1 μM; p < 0.001) and to 15 ± 1.0% (3 μM; p < 0.001). Further, 10 μM imatinib increased mRNA expression of TGFB1 7-fold, (p < 0.01), IL6 6-fold (p < 0.01), and IL1B 7-fold (p < 0.05) and reduced PDGFD 15-fold (p < 0.01); whereas sunitinib specifically reduced IL1B mRNA expression 17-fold (p < 0.01). Overall, these findings show tyrosine kinase inhibitors cause significant dysfunction in CFs. These data point to an important role for the PDGF pathway in governing CF functions, including survival and proliferation

Novel mitochondrial complex I inhibitors restore glucose-handling abilities of high-fat fed mice

Metformin is the main drug of choice for treating type 2 diabetes, yet the therapeutic regimens and side effects of the compound are all undesirable and can lead to reduced compliance. The aim of this study was to elucidate the mechanism of action of two novel compounds which improved glucose handling and weight gain in mice on a high-fat diet. Wildtype C57Bl/6 male mice were fed on a high-fat diet and treated with novel, anti-diabetic compounds. Both compounds restored the glucose handling ability of these mice. At a cellular level, these compounds achieve this by inhibiting complex I activity in mitochondria, leading to AMP-activated protein kinase activation and subsequent increased glucose uptake by the cells, as measured in the mouse C2C12 muscle cell line. Based on the inhibition of NADH dehydrogenase (IC50 27µmolL−1), one of these compounds is close to a thousand fold more potent than metformin. There are no indications of off target effects. The compounds have the potential to have a greater anti-diabetic effect at a lower dose than metformin and may represent a new anti-diabetic compound class. The mechanism of action appears not to be as an insulin sensitizer but rather as an insulin substitute