Abstract Atherosclerosis is the underlying cause of great majority of cardiovascular diseases (CVD) and poses a great threat to public health. Activation of thermogenic adipocytes reduces cholesterol levels and protects against atherosclerosis in animal models. Lower thermogenic adipocyte activity in dyslipidemic patients has been characterized by high plasma triglycerides (TG), low plasma high density lipoprotein cholesterol (HDL-C) concentration and lower uncoupling protein 1 (UCP1) expression. These findings in mice and humans underscore the importance of inducers of the thermogenic adipocyte program as potential therapeutic targets for the treatment of dyslipidemia and CVD. Our published and preliminary data demonstrate that follistatin (Fst) plays an important role not only in adipocyte browning but also in lipoprotein metabolism to regulate TG, total cholesterol (TC), and HDL-C levels. In this proposal, we will test our central hypothesis that Fst-induced adipose browning protects against the development of atherosclerosis. We will test our hypothesis under these Specific Aims: Aim 1: We will determine the role of Fst in adipose browning, lipoprotein metabolism and development of atherosclerosis. We will determine the effects of Fst tissue and systemic overexpression using mouse low density lipoprotein receptor (LDLR)-deficient WT and adipose-specific transgenic (FstAdQTg ) mice, and adeno-associated virus 1 (AAV1)-FST344 injected LDLR-/- mice respectively to determine the role of Fst on i) adipose browning, plasma lipoprotein, TG, and TC levels, ii) tissue (adipose, aorta, and liver), plasma metabolites and iii) gene expression during diet-induced development of dyslipidemia and atherosclerosis. Effect of transient loss of Fst on browning, lipoprotein metabolism and atherosclerosis progression will be analyzed in mPCSK9 injected Fstfl/fl / CreAdQ mice. Aim 2: We will determine the molecular mechanisms by which Fst confer the pro-browning and anti-atherogenic effects. We will test whether arginase 1 (Arg 1)/beta-adrenergic receptor (β-AR)/ p38MAPK/FGF21 signaling pathway confer Fst-induced pro-browning and antiatherogenic action in the three animal models. We will utilize gene aortic lesion and gene metabolite correlation dataset obtained from system genetics approach of atherosclerosis hybrid mouse diversity panel (HMDP) to identify key Fst-regulated genes and metabolites. We will perform comprehensive RNA-sequence analysis, and tissue and plasma metabolite analysis combined with pharmacological inhibition studies to identify novel genes and metabolites involved during Fst-induced adipose browning and its anti-atherogenic actions. Our proposed studies will provide significant novel insights into the pro-browning and anti-atherogenic role of Fst and identify key molecular targets involved in favorably altering lipoprotein metabolism and the development of atherosclerosis. Inhibition of atherosclerosis development by using Fst protein/peptid...