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Background Pro‐NTs (precursor of neurotrophins) and their receptor p75 are potential targets for preventing microvascular dysfunction induced by myocardial ischemia–reperfusion injury ( IRI ). p75ECD (ectodomain of neurotrophin receptor p75) may physiologically produce neurocytoprotective effects by scavenging pro‐ NT s. We therefore hypothesized that p75 ECD may have a cardioprotective effect on IRI through microvascular mechanisms. Methods and Results Myocardial IRI was induced in Sprague‐Dawley rats by occluding the left main coronary arteries for 45 minutes before a subsequent relaxation. Compared with the ischemia–reperfusion group, an intravenous injection of p75 ECD (3 mg/kg) 5 minutes before reperfusion reduced the myocardial infarct area at 24 hours after reperfusion (by triphenyltetrazolium chloride, 44.9±3.9% versus 34.6±5.7%, P NT s expression at 24 hours and 28 days after reperfusion (by Western blotting). A simulative IRI model using rat microvascular pericytes was established in vitro by hypoxia–reoxygenation (2/6 hours) combined with pro‐ NT s treatment (3 nmol/L) at R. p75 ECD (3 μg/mL) given at R improved pericyte survival (by methyl thiazolyl tetrazolium assay) and attenuated apoptosis (by terminal deoxynucleotidyl transferase‐mediated dUTP‐biotin nick‐end labeling). In the reperfused hearts and hypoxia–reoxygenation +pro‐ NT s‐injured pericytes, p75 ECD inhibited the expression of p‐JNK (phospho of c‐Jun N‐terminal kinase)/caspase‐3 (by Western blotting). SP 600125, an inhibitor of JNK , did not enhance the p75 ECD ‐induced infarct‐sparing effects and pericyte protection. Conclusions p75 ECD may attenuate myocardial IRI via pro‐ NT s reduction‐induced inhibition of p‐ JNK /caspase‐3 pathway of microvascular pericytes in rats.

Cx43 has been documented to be involved in ischemic preconditioning (IPC). However, the participation of Cx43-formed hemichannels in IPC and the potential underlying mechanisms remain unclear. The present study focused on cardiomyocytes' volume regulation during IPC to investigate the role of hemichannels in the IPC-induced cardioprotection. In the study, mice cardiomyocytes were respectively treated with a hemichannel blocker, octanol or 18a-Glycyrrhizic acid (18a-GA), and a Cx43-silenced lentivirus. They were subsequently cultured in hypotonic solution to simulate ischemic reperfusion (SIR) and systemic ischemic preconditioning (SIP). Cell morphology and volumetric (area) change were detected by inverted microscopy at 30 min following the addition of hypotonic solution. Cardiomyocyte mortality was assessed by trypan blue stain assay. The analyses revealed that regardless of the treatments, hypotonic solution aggravated cell edema: Compared with the initial condition (the moment before the solution addition, 0 min), the volumetric area increased significantly 30 min later (for hypotonic+DMSO, 5,050±1,511 vs. 3,464±723 µm(2); for hypotonic+scramble lentiviral vector, 5,517±1,128 vs. 2,331±536 µm(2); P0.05 for all). Notably, results indicated that the SIP group had lower mortality rates compared with its SIR counterpart; the hypotonic+octanol, hypotonic+18a-GA, and hypotonic+Cx43-silenced group showed markedly-declined mortality when compared with their respective control groups (respectively, 35.70±1.02, 30.76±2.20 vs. 53.58±2.14%; 30.89±2.37 vs. 54.12±2.55%; P