Endothelial-myocardial interactions may be critically important for
ischemia/reperfusion injury.
Tetrahydrobiopterin (BH4) is a required cofactor for
nitric oxide (NO) production by endothelial
NO synthase (eNOS).
Hyperglycemia (HG) leads to significant increases in oxidative stress, oxidizing BH4 to enzymatically incompetent
dihydrobiopterin. How alterations in endothelial BH4 content impact
myocardial ischemia/
reperfusion injury remains elusive. The aim of this study was to examine the effect of endothelial-myocardial interaction on
ischemia/reperfusion injury, with an emphasis on the role of endothelial BH4 content. Langendorff-perfused mouse hearts were treated by
triton X-100 to produce endothelial dysfunction and subsequently subjected to 30 min of
ischemia followed by 2 h of reperfusion. The recovery of left ventricular systolic and diastolic function during reperfusion was impaired in
triton X-100 treated hearts compared with vehicle-treated hearts. Cardiomyocytes (CMs) were co-cultured with endothelial cells (ECs) and subsequently subjected to 2 h of
hypoxia followed by 2 h of reoxygenation. Addition of ECs to CMs at a ratio of 1∶3 significantly increased NO production and decreased
lactate dehydrogenase activity compared with CMs alone. This EC-derived protection was abolished by HG. The addition of 100 µM
sepiapterin (a BH4 precursor) or overexpression of
GTP cyclohydrolase 1 (the rate-limiting
enzyme for BH4 biosynthesis) in ECs by gene trasfer enhanced endothelial BH4 levels, the ratio of eNOS dimer/monomer, eNOS phosphorylation, and NO production and decreased
lactate dehydrogenase activity in the presence of HG. These results demonstrate that increased BH4 content in ECs by either pharmacological or genetic approaches reduces myocardial damage during
hypoxia/reoxygenation in the presence of HG. Maintaining sufficient endothelial BH4 is crucial for cardioprotection against
hypoxia/reoxygenation injury.