Cyp2c44 gene disruption is associated with increased hematopoietic stem cells: implication in chronic hypoxia-induced pulmonary hypertension.

We have recently demonstrated that disruption of the murine cytochrome P-450 2c44 gene (Cyp2c44) exacerbates chronic hypoxia-induced pulmonary artery remodeling and hypertension in mice. Subsequently, we serendipitously found that Cyp2c44 gene disruption also increases hematopoietic stem cell (HSC) numbers in bone marrow and blood. Therefore, the objective of the present study was to investigate whether CYP2C44-derived eicosanoids regulate HSC proliferation/cell growth and whether increased HSCs contribute to chronic hypoxia-induced remodeling of pulmonary arteries in Cyp2c44 knockout mice. Our findings demonstrated that lack of CYP2C44 epoxygenase, which catalyzed the oxidation of arachidonic acid to epoxyeicosatrienoic (EETs) and hydroxyeicosatetraenoic (HETE) acids, increases the numbers of 1) HSCs (CD34(+), CD117(+), and CD133(+)), 2) proangiogenic (CD34(+)CD133(+) and CD34(+)CD117(+)CD133(+)) cells, and 3) immunogenic/inflammatory (CD34(+)CD11b(+), CD133(+)CD11b(+), F4/80(+), CD11b(+), and F4/80(+)CD11b(+)) macrophages in bone marrow and blood compared with wild-type mice. Among the various CYP2C44-derived arachidonic acids, only 15-HETE decreased CD117(+) cell numbers when applied to bone marrow cell cultures. Interestingly, CD133(+) and von Willebrand factor-positive cells, which are derived from proangiogenic stem cells, are increased in the bone marrow, blood, and lungs of mice exposed to chronic hypoxia and in remodeled and occluded pulmonary arteries of CYP2C44-deficient mice. In conclusion, our results demonstrate that CYP2C44-derived 15-HETE plays a critical role in downregulating HSC proliferation and growth, because disruption of the Cyp2c44 gene increased HSCs that potentially contribute to chronic hypoxia-induced pulmonary arterial remodeling and occlusion.NEW & NOTEWORTHY This study demonstrates that cytochrome P-450 2C44 plays a critical role in controlling the phenotype of hematopoietic stem cells and that when this enzyme is knocked out, stem cells are differentiated. These stem cells give rise to increased circulating monocytes and macrophages and contribute to the pathogenesis of chronic hypoxia-induced pulmonary artery remodeling and hypertension.