Lifang Ye

Diabetes mellitus has multiple complications including neuropathy and increases cardiovascular events. Paeoniflorin (PF), a monoterpene glycoside, plays an essential role in neuroprotection and ischemic heart disease. In this study, we aimed to investigate the hypothesis that PF protects mice with diabetes mellitus against myocardial ischemic injury, and determine its associated mechanisms. Myocardial infarction (MI) was generated in the streptozotocin-mediated diabetic mice, which were pretreated with either vehicle or PF, respectively. Myocardial infarct size, myocardial enzyme, cardiac function, circulating calcitonin gene-related peptide (CGRP) concentration, histological analysis and the expression of associated molecules were determined and compared among different experimental groups. Compared to diabetic hearts pretreated with vehicle, hearts pretreated with PF exhibited less tissue damage and better CGRP concentration in serum when subjected to myocardial ischemia. Transient receptor potential vanilloid 1(TRPV1) gene knockout attenuated PF-mediated cardioprotection. Moreover, a specific Ca2+/calmodulin-dependent protein kinase (CaMK) inhibitor, KN-93, increased tissue damage and decreased CGRP activity in serum. Meanwhile, pretreated with PF increased the phosphorylation of cAMP response element binding protein (CREB). Taken together, these findings demonstrate that PF protects diabetic mice against MI at least partially via the TRPV1/CaMK/CREB/CGRP signaling pathway.

Transient potential receptor vanilloid 1 (TRPV1) channels, which are expressed on sensory neurons, elicit cardioprotective effects during ischemia reperfusion injury by stimulating the release of neuropeptides, namely calcitonin gene-related peptide (CGRP) and substance P (SP). Recent studies show that TRPV1 channels are also expressed on cardiomyocytes and can exacerbate air pollutant-induced apoptosis. However, whether these channels present on cardiomyocytes directly modulate cell death and survival pathways during hypoxia/reoxygenation (H/R) injury remains unclear. In the present study, we investigated the role of TRPV1 in H/R induced apoptosis of H9C2 cardiomyocytes. We demonstrated that TRPV1 was indeed expressed in H9C2 cells, and activated by H/R injury. Although neuropeptide release caused by TRPV1 activation on sensory neurons elicits a cardioprotective effect, we found that capsaicin (CAP; a TRPV1 agonist) treatment of H9C2 cells paradoxically enhanced the level of apoptosis by increasing intracellular calcium and mitochondrial superoxide levels, attenuating mitochondrial membrane potential, and inhibiting mitochondrial biogenesis (measured by the expression of ATP synthase β). In contrast, treatment of cells with capsazepine (CPZ; a TRPV1 antagonist) or TRPV1 siRNA attenuated H/R induced-apoptosis. Furthermore, CAP and CPZ treatment revealed a similar effect on cell viability and mitochondrial superoxide production in primary cardiomyocytes. Finally, using both CGRP_8–37 (a CGRP receptor antagonist) and RP67580 (a SP receptor antagonist) to exclude the confounding effects of neuropeptides, we confirmed aforementioned detrimental effects as TRPV1^−/− mouse hearts exhibited improved cardiac function during ischemia/reperfusion. In summary, direct activation of TRPV1 in myocytes exacerbates H/R-induced apoptosis, likely through calcium overload and associated mitochondrial dysfunction. Our study provides a novel understanding of the role of myocyte TRPV1 channels in ischemia/reperfusion injury that sharply contrasts with its known extracardiac neuronal effects.