High glucose induces Drp1-mediated mitochondrial fission via the Orai1 calcium channel to participate in diabetic cardiomyocyte hypertrophy.

Mitochondrial dysfunction and impaired Ca2+ handling are involved in the development of diabetic cardiomyopathy (DCM). Dynamic relative protein 1 (Drp1) regulates mitochondrial fission by changing its level of phosphorylation, and the Orai1 (Ca2+ release-activated calcium channel protein 1) calcium channel is important for the increase in Ca2+ entry into cardiomyocytes. We aimed to explore the mechanism of Drp1 and Orai1 in cardiomyocyte hypertrophy caused by high glucose (HG). We found that Zucker diabetic fat rats induced by administration of a high-fat diet develop cardiac hypertrophy and impaired cardiac function, accompanied by the activation of mitochondrial dynamics and calcium handling pathway-related proteins. Moreover, HG induces cardiomyocyte hypertrophy, accompanied by abnormal mitochondrial morphology and function, and increased Orai1-mediated Ca2+ influx. Mechanistically, the Drp1 inhibitor mitochondrial division inhibitor 1 (Mdivi-1) prevents cardiomyocyte hypertrophy induced by HG by reducing phosphorylation of Drp1 at serine 616 (S616) and increasing phosphorylation at S637. Inhibition of Orai1 with single guide RNA (sgOrai1) or an inhibitor (BTP2) not only suppressed Drp1 activity and calmodulin-binding catalytic subunit A (CnA) and phosphorylated-extracellular signal-regulated kinase (p-ERK1/2) expression but also alleviated mitochondrial dysfunction and cardiomyocyte hypertrophy caused by HG. In addition, the CnA inhibitor cyclosporin A and p-ERK1/2 inhibitor U0126 improved HG-induced cardiomyocyte hypertrophy by promoting and inhibiting phosphorylation of Drp1 at S637 and S616, respectively. In summary, we identified Drp1 as a downstream target of Orai1-mediated Ca2+ entry, via activation by p-ERK1/2-mediated phosphorylation at S616 or CnA-mediated dephosphorylation at S637 in DCM. Thus, the Orai1-Drp1 axis is a novel target for treating DCM.

Effect of BTP2 on agonist-induced vasoconstriction in the mouse aorta in vitro.

BTP2 is a potent inhibitor of store-operated Ca2+ entry (SOCE), which plays a vital role in vasoconstriction. However, the direct effect of BTP2 on the contractile response remains unclear. Here, we investigated the effects and mechanisms of action of BTP2 in the mouse aorta. Isometric tension was measured using a Multi Myograph System with two stainless steel wires. Ca2+ transient was recorded by confocal laser scanning microscope. The results showed that BTP2 markedly suppressed vasoconstriction mediated by SOCE and Ca2+ influx mediated by SOCE. The cumulative concentration of BTP2 had no effect on the baseline of mouse aortic rings, whereas it increased vasoconstriction stimulated by 3 µmol/L Phenylephrine. BTP2 (1 µmol/L) significantly increased vasoconstriction induced by 3 µmol/L Phe or cumulative concentration. BTP2 also promoted noradrenaline-induced aortic contraction. However, Phe- and noradrenaline-induced contraction was not affected by 0.3 or 3 µmol/L BTP2, and BTP2 at 10 µmol/L significantly suppressed aortic contraction. BTP2 inhibited 5-HT-evoked contraction in a concentration-dependent manner. BTP2 at higher concentrations (>3 µmol/L) inhibited CaCl2 -induced and 60 mmol/L K+ -induced contraction with progressive reduction of maximal contraction in a concentration-dependent manner. These results suggest that 1 µmol/L BTP2 increases contraction evoked by α1 adrenoreceptor activation. BTP2 at higher concentrations may inhibit Cav1.2 channels.