Inhibition of DRG-TRPV1 upregulation in myocardial ischemia contributes to exogenous cardioprotection.

Myocardium ischemia-reperfusion injury (IRI) is the major cause of postoperative cardiac dysfunction. While intrathecal morphine preconditioning (ITMP) can reduce IRI in animals, the molecular processes underlying IRI and ITMP remain elusive. Transient receptor potential vanilloid type 1 (TRPV1) is highly expressed in cardiac sensory neurons and has a crucial role in detecting myocardial ischemia. This study aimed to determine the role of up-regulated dorsal root ganglion (DRG)-TRPV1 in IRI and whether its inhibition contributes to ITMP-induced cardioprotection. Animal model of IRI was established by left coronary artery occlusion (30 min) and reperfusion (2 h) in rats. Intrathecal intubation was prepared for morphine preconditioning, TRPV1-shRNA or selective TRPV1 antagonist administration. After IRI, both protein and phosphorylation levels of TRPV1 were significantly increased, and the immunofluorescence intensity of TRPV1 was increased and colocalized with μ-opioid receptors in DRG. Intrathecal pre-administration of either TRPV1-shRNA or TRPV1 antagonist significantly reduced myocardial injury and the upregulation of TRPV1 in DRG induced by IRI. Simultaneously, ITMP significantly suppressed TRPV1 protein expression and phosphorylation in DRG, as well as the heart infarct size and arrhythmia score caused by IRI. The suppression of TRPV1 elevation and activation by ITMP were reversed by intrathecal injection of the selective μ receptor antagonist. Furthermore, IRI elevated DRG cAMP, while intrathecal administration of the selective cAMP-PKA inhibitor reduced myocardial injury. Finally, we showed that activation of opioid receptor by morphine inhibited PKA activator-induced TRPV1 channel activity at the cellular level. These findings suggest that the elevation and activation of TRPV1 in DRG during myocardial ischemia-reperfusion might be responsible for cardiac injury. ITMP exerts cardioprotection by inhibiting DRG-TRPV1 activity via modulation cAMP. Therefore, inhibition of TRPV1 upregulation in DRG might be used as a novel therapeutic mechanism for myocardium ischemia-reperfusion injury.