Reversal of hypoxia in murine atherosclerosis prevents necrotic core expansion by enhancing efferocytosis

OBJECTIVE: Advanced murine and human plaques are hypoxic, but it remains whether plaque hypoxia is causally related to atherogenesis. Here, we hypothesis that reversal of hypoxia in atherosclerotic plaques by hyperoxic carbogen gas will prevent atherosclerosis. APPROACH AND Low-density lipoprotein receptor-deficient mice were fed a Western-type exposed to carbogen (95% O2, 5% CO2) or air, and the effect on plaque size, and phenotype was studied. First, the hypoxic marker pimonidazole detected in murine low-density lipoprotein receptor-deficient plaque from plaque initiation onward. Second, the efficacy of breathing minutes, single exposure) was studied. Compared with air, carbogen arterial blood Po2 5-fold in low-density lipoprotein receptor-deficient reduced plaque hypoxia in advanced plaques of the aortic root (-32%) and (-84%). Finally, the effect of repeated carbogen exposure on progression atherosclerosis was studied in low-density lipoprotein receptor- fed a high cholesterol diet for an initial 4 weeks, followed by 4 weeks and carbogen or air (both 90 min/d). Carbogen reduced plaque hypoxia (- necrotic core size (-37%), and TUNEL+ apoptotic cell content (-50%) and efferocytosis of apoptotic cells by MAC3+ macrophages (+36%) in advanced of the aortic root. Plaque size, plasma cholesterol, hematopoiesis, and inflammation were unchanged. In vitro, hypoxia hampered efferocytosis by marrow-derived macrophages, which was dependent on the receptor Mer kinase. CONCLUSIONS: Carbogen restored murine plaque oxygenation and necrotic core expansion by enhancing efferocytosis, likely via Mer kinase. Thus, plaque hypoxia is causally related to necrotic cor