In this study, we constructed an AAV9 vector expressing Fat-1, which was applied to WT and LDLR−/− hamsters to mimic transgene conditions, and then aimed to investigate the impacts of Fat-1 on blood lipids, MAFLD, and atherosclerosis under physiological and/or pathophysiological conditions and explore the possibility that AAV9-based gene therapy of Fat-1 would be considered for the treatment of metabolic disorders. The gene discussed is FAT1; the disease is atherosclerosis.