Activation of Hypoxia Response in Endothelial Cells Contributes to Ischemic Cardioprotection

Abstract

Small-molecule inhibition of hypoxia-inducible factor prolyl 4-hydroxylases (HIF-P4Hs) is being explored for the treatment of anemia. Previous studies have suggested that HIF-P4H-2 inhibition may also protect the heart from an ischemic insult. Hif-p4h-2^gt/gt mice, which have 76 to 93% knockdown of Hif-p4h-2 mRNA in endothelial cells, fibroblasts, and cardiomyocytes and normoxic stabilization of Hif-α, were subjected to ligation of the left anterior descending coronary artery (LAD). Hif-p4h-2 deficiency resulted in increased survival, better-preserved left ventricle (LV) systolic function, and a smaller infarct size. Surprisingly, a significantly larger area of the LV remained perfused during LAD ligation in Hif-p4h-2^gt/gt hearts than in wild-type hearts. However, no difference was observed in collateral vessels, while the size of capillaries, but not their number, was significantly greater in Hif-p4h-2^gt/gt hearts than in wild-type hearts. Hif-p4h-2^gt/gt mice showed increased cardiac expression of endothelial Hif target genes for Tie-2, apelin, APJ, and endothelial nitric oxide (NO) synthase (eNOS) and increased serum NO concentrations. Remarkably, blockage of Tie-2 signaling was sufficient to normalize cardiac apelin and APJ expression and resulted in reversal of the enlarged-capillary phenotype and ischemic cardioprotection in Hif-p4h-2^gt/gt hearts. Activation of the hypoxia response by HIF-P4H-2 inhibition in endothelial cells appears to be a major determinant of ischemic cardioprotection and justifies the exploration of systemic small-molecule HIF-P4H-2 inhibitors for ischemic heart disease.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.00432-13.

ACKNOWLEDGMENTS

We thank T. Aatsinki, M. Arbelius, E. Lehtimäki, and K. Salo for their excellent technical assistance and L. Eklund for helpful discussions.

We thank the Core Facilities for Imaging and Physiological Analysis of Transgenic Animals at Biocenter Oulu, University of Oulu (cofunded by Biocenter Finland). This study was supported by Academy of Finland grants 120156, 140765, and 218129 (P.K.), 218044 and 263731 (R.K.), 200471, and 202469, by Center of Excellence 2012-2017 grant 251314 (J.M.), by the S. Jusélius Foundation (P.K., R.K., and J.M.), by the Finnish Foundation for Cardiovascular Research (R.K.), and by FibroGen, Inc. (J.M.).