Spinal NGF induces anti-intrathecal opioid-initiated cardioprotective effect via regulation of TRPV1 expression

Evidences from previous studies confirmed that intrathecal morphine preconditioning (ITMP) reduces the cardiac injury of ischemia-reperfusion (IR) via the central nervous system. However, the molecular mechanism is not fully understood. The breath of central nerve growth factor (NGF) during nociceptive transmission has been well documented, and little is known about the significance of NGF in myocardial injury of IR and intrathecal morphine-induced cardioprotection. To address these questions, we over-expressed or silenced NGF in the spinal cord by using intrathecal injection of lentivirus-NGF or shRNA respectively, accompanied by ITMP in the IR rat model. The levels of NGF and tropomyosin receptor kinase A (Trka) as well as transient receptor potential vanilloid 1 (TRPV1) in the T2-6 spinal cord were evaluated. The results showed that cardiac damage indicators induced by IR, including the increased infarct size, arrhythmia score and serum troponin levels were attenuated after ITMP. However, overexpression of spinal NGF significantly reversed these decreases, as well as reduced the expression and phosphorylation of TRPV1 that was elicited by ITMP. Conversely, silencing of spinal NGF enhanced ITMP-induced cardioprotective effects. Phosphorylation and expression of TRPV1 in the spinal cord were significantly decreased after regional NGF silencing. These findings suggested that the cardioprotective effects of ITMP may implement by mediating through spinal NGF expression, wherein it involves the nociceptor TRPV1. NGF may act as a potential therapeutic target in the development of new agents for the treatment of cardiac injury induced by IR.