Abstract P731: Genetic Knockout of Cd38 Protects Mice Against Ischemic Brain Injury

Abstract

Introduction: CD38 is an ectoenzyme that is present on the cellular membranes of endothelial cells and subtypes of inflammatory cells. We have shown that ischemia/reperfusion (I/R) in the heart triggers CD38 activation that in turns leads to NADPH depletion and endothelial nitric oxide synthase (eNOS) impairment. This cascade results in worsening of ischemic injury secondary to endothelial dysfunction. We hypothesize that a similar paradigm exists in acute ischemic stroke and that loss of CD38 function is protective against cerebral I/R injury. Methods: Middle cerebral artery occlusion (MCAO) was performed for 60 minutes in 15 week-old CD38 knockout mice (KO) n=12 and wild type (WT) mice n=12. Stroke volume was calculated using T2 MRI sequences obtained at 48 hours post MCAO. Percentage of brain infarction volume compensated for swelling (IFV) was calculated by manual segmentation of the stroke area and non-affected cerebral hemisphere. Following brain MRI, H&E staining and immunohistochemistry assessment of superoxide radicals (DHE fluorescence) nitric oxide (NO) (DAF fluorescence), eNOS expression, CD38 expression and microglia activation (Iba1) were performed. (P<0.05) was considered significant in statistical testing. Results: CD38 KO mice had a smaller IFV as % of the normal contralateral hemisphere volume compared to WT (19.6±3 vs 33.5±9, P=0.001). Both western blotting and immunohistology confirmed lack of CD38 expression in CD38 KO mice. CD38 expression was 55% higher in the ipsilateral stroke side compared to the contralateral stroke side in WT mice (P=0.0105). Compared to WT mice, CD38 KO had 45% lower superoxide levels (P<0.001), 50% higher NO levels (P<0.05) and 46% lower Iba-1 expression with more significance in ipsilateral side (P<0.01) than contralateral side (P<0.05). While eNOS expression was 40% lower in WT vs CD38 KO, this did not reach statistical significance. Conclusions: Thus, genetic deletion of CD38 is protective against cerebral ischemia with reduced superoxide production and preserved NO production, likely through the protection conferred against NADPH depletion. These results suggest that inhibition of CD38 could serve as a potent therapeutic approach to protect against acute ischemic stroke and related brain I/R injury.