The Role of Vascular Matrix Metalloproteinase-2 and Heme Oxygenase-2 in Mediating the Response to Hypoxia

Systemic hypoxia frequently occurs in patients with cardiopulmonary diseases. Maintenance of vascular reactivity and endothelial viability is essential to preserving oxygen delivery in these patients. The role of matrix metalloproteinase-2 (MMP-2) and heme oxygenase-2 (HO-2) in the vascular response to hypoxia were investigated. In the first part of the thesis, the role of MMP-2 in regulating systemic arterial contraction after prolonged hypoxia was investigated. MMP-2 inhibition with cyclic peptide CTTHWGFTLC (CTT) reduced phenylephrine (PE)-induced contraction in aortae and mesenteric arteries harvested from rats exposed to hypoxia for 7 d. Responses to PE were reduced in MMP-2-/- mice exposed to hypoxia for 7 d compared to wild-type controls. CTT reduced contraction induced by big endothelin-1 (big ET-1) in aortae harvested from rats exposed to hypoxia. Increased contraction to big ET-1 after hypoxia was observed in wild-type controls, but not MMP-2-/- mice. Rat aortic MMP-2 and MT1-MMP protein levels and MMP activity were increased after 7 d of hypoxia. Rat aortic MMP-2 and MT1-MMP mRNA levels were increased in the deep medial vascular smooth muscle. These results suggest that hypoxic induction of MMP-2 activity potentiates contraction in systemic conduit and resistance arteries through proteolytic activation of big ET-1. The second part of the thesis investigated oxygen regulation of HO-2 protein and whether it plays a role in preserving endothelial cell viability during hypoxia. HO-2, but not HO-1, protein level was maintained during hypoxia in human endothelial cells through enhanced translation of HO-2 transcripts. Inhibition of HO-2 expression increased the production of reactive oxygen species, decreased mitochondrial membrane potential, and enhanced apoptotic cell death and activated caspases during hypoxia, but not during normoxia. These data indicate that HO-2 is translationally regulated and important in maintaining endothelial viability and function during hypoxia. In summary, the thesis demonstrates the importance of MMP-2 and HO-2 in preserving vascular function during prolonged systemic hypoxia. These enzymatic pathways may, therefore, represent novel therapeutic targets that may be exploited to ameliorate the effects of hypoxia in patients with cardiopulmonary disease.Ph