Insights into the Molecular Mechanisms of Lithium on Cardioprotection in Social Stress(2/2)

Background: Cardiovascular disease is the leading cause resulting in the excessive and premature deaths in patients with bipolar disorder. Recently, our research findings are in line with the literature suggesting that sympathetic nervous over-activity following social stress plays an important role in the pathogenesis of cardiovascular disease in patients with bipolar disorder. In addition, our laboratory studies found that inhibition of histone deacetylases (HDACs) can attenuate angiotensin-II-dependent cardiac fibrosis and heart failure. In particular, emerging data has suggested that lithium may provide neuroprotective effects via its actions on regulation of HDACs. However, little is known about whether lithium can attenuate cardiac fibrosis and heart failure via its inhibitory actions on sympathetic nervous activation, angiotensin-II stimulation, and epigenetic dysregulation following the social stress. In our preliminary study, we found that lithium can attenuate autonomic nervous dysregulation in patients with bipolar disorder. Moreover, lithium at therapeutic concentration can reduce the migration ability and HDAC3 expression in human cardiac fibroblasts. Accordingly, the aims of this proposed study are to determine whether lithium at therapeutic level can reduce cardiac fibrogenesis in both human cardiac fibroblast and social stressed rat through its inhibitory action on sympathetic nerve and angiotensin-II activation in the first year experiment, and whether the mechanism for anti-fibrotic action of lithium in social stress model is via its therapeutic action on Class I HDACs in the second year experiment. Methods: In the first year experiment, cell proliferation assay, MTS proliferation assay, and cell migration assay will be performed in human cardiac fibroblasts treated with LiCl at 0.1 mM, 0.3 mM (mimics the low therapeutic concentration for bipolar disorder), and 1 mM (mimics the high therapeutic concentration for bipolar disorder) for 24 hours with or without angiotensin-II 100 nM. In addition, LiCl at therapeutic dosage (1 mmol/kg per day) or saline (i.e. control group) will be administrated for 4 weeks in social stress rat model. Electrocardiogram and echocardiography will be conducted to study the autonomic nervous activity and cardiac function in control and LiCl-treated rats. Picro-Sirius red staining will be applied to evaluate the extent of cardiac fibrosis. In the second year experiment, luminescence assay will be used to measure Class I HDAC activity in human cardiac fibroblasts treated with LiCl at 0.1 mM, 0.3 mM, and 1 mM for 24 hours with or without angiotensin-II 100 nM. Western blot analysis will be conducted to determine the expression levels of Class I HDACs and proteins involved in signal transduction cascades regulated by HDACs. In addition, calcium imaging experiment will be performed to assess the intracellular calcium signaling. Last, microRNAs targeting Class I HDACs will be transfected into human cardiac fibroblasts to confirm the role of Class I HDACs in anti-fibrotic actions of lithium. Significance: By utilizing social stress model which is with translational relevance to the pathogenesis of cardiovascular disease in bipolar disorder, this proposed study will provide the molecular evidence for future development of high-value therapy in bipolar disorder patients who are at a high risk of cardiovascular disease.