Schizophrenia patients have a greater rate of premature death from cardiovascular disease compared with the general population. Although the higher incidence of cardiovascular disease in schizophrenia patients is due to increased cardiovascular disease risk factors, new evidence suggests genetic susceptibility in this patient group may account for the greater risk of cardiovascular disease. Therefore, it is pertinent to identify mechanistic relationships that could act as a pathophysiological link between schizophrenia and cardiovascular disease. Human clinical studies highlighted the link between a genetic variant of Neurogranin (Ng, 7.6 kDa), a calmodulin (CaM)-binding protein, thought to be exclusively expressed in the brain, and a risk of developing schizophrenia. Interestingly, we recently discovered that deletion of Ng in mice also resulted in significant cardiac dysfunction; it was associated with decreased ejection fraction and fractional shortening as well as perivascular fibrosis. Ng ?/? mice also show decreased plasma nitric oxide (NO) levels, indicative of endothelial cell dysfunction, similar to the endothelial NO synthase (eNOS) dysfunction observed in schizophrenic patients. Our preliminary studies also demonstrated that Ng is highly expressed in the endothelium and significantly up-regulated in response to laminar flow, a known inducer of NO production. Thus, we hypothesize that Ng mediates Ca2+-dependent eNOS activity in the endothelium and that defects in Ng signaling increases vascular resistance resulting in cardiac fibrosis, hypertrophy, and eventually cardiac failure. To test this hypothesis, AIM1 will determine the mechanistic role of Ng in eNOS signaling using in vitro approaches. We will test whether altered Ng expression using knockout (Ng siRNA and Ng CRISPR/Cas9 knockout) and overexpression (Lentivirus-oNg and Lentivirus-dnNg) affect eNOS expression and the sensitivity of eNOS to inflammation.
AIM2 will also determine the effect of Ng deletion on cardiovascular function in mice. We will conduct flow-mediated vasodilation and angiotensin II infusion to test the susceptibility of Ng-mediated vascular resistance and cardiac failure. The results of these aims will discover a novel Ng-eNOS mechanism in the endothelium that contributes to cardiac dysfunction. Moreover, these results will contribute to our goal of establishing clinical interventions between cardiovascular disease and schizophrenia and to positively impact treatment strategies for cardiovascular disease.
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