Conditional over-expression of heme-oxygenase 1 in myelomonocytic cells reduces AngII-induced hypertension and vascular inflammation in mice

Abstract Background Systemic arterial Hypertension is one of the most important risk factor responsible for morbidity and mortality world-wide. Angiotensin II (Ang II), a potent vasoconstrictor and key player in the renin-angiotensin-aldosterone system (RAAS) is responsible for vascular dysfunction, inflammation, and tissue damage. Heme oxygenase-1 (HO-1) overexpression may confer antioxidant and anti-inflammatory properties in Ang II-induced hypertension through its action on heme catabolism, generating carbon monoxide (CO), ferritin and biliverdin/bilirubin by the action of biliverdin reductase A (BLVRA). Methods and results Male 9–12-weeks-old HO-1indxLySMCre/wt and LySMCre/wt mice were infused with AngII (1mgAngII/Day/Kg) for 7 days to induce hypertension and compared to sham treatment. Blood pressure monitoring by tail-cuff method, and endothelium-dependent vasodilator studies via organ chamber system using acetylcholine (ACh) in isolated aortic segments (~4 mm), revealed that overexpression of HO-1 in myeloid cells resulted in decreased systolic blood pressure and improved endothelial function in AngII-infused HO-1indxLySMCre/wt mice compared to controls. Concurrently, increased BLVRA expression in liver tissue and elevated plasma bilirubin levels were detected by transcriptome analysis and high-performance liquid chromatography, respectively. These results were supported by a reduction in the expression of inducible cytokines and cell adhesion molecules (CAMs) in the aorta, assessed using qPCR. Bone marrow transplant experiments demonstrated that bone marrow from LysMcre mice in HO-1indxLySMCre/wt mice abrogated the protective effect of HO-1, resulting in endothelial damage and increased blood pressure, potentially due to decreased liver BLVRA expression and the accumulation of bone marrow-derived cells in the vessel wall in response to AngII. Additionally, adeno-associated viral vector (AAV) transfection targeting specifically BLVRA activity in liver lead to an increase in blood pressure values and worse endothelium relaxation, in parallel with higher oxidative stress and the blood neutrophils concentration, as assessed in whole blood by using oxidative burst method and blood count system respectively. Conclusion The overexpression of HO-1 in myeloid cells confers anti-inflammatory protection in AngII-induced arterial hypertension in mice. Myeloid cells bone marrow-derived overexpressing HO-1 regulate the differentiation and infiltration of pro-inflammatory immune cells in the vasculature. BLVRA expression and bilirubin levels downstream of HO-1 play a critical role in protecting against vascular damage by reducing leukocyte infiltration.