HDAC9 and metabolic disease: Previous studies have demonstrated the efficacy of histone deacetylase (HDAC) inhibitors for the treatment of various metabolic diseases, such as obesity, type 1 and type 2 diabetes mellitus (DM), non-alcoholic fatty liver disease (NAFLD), and even chronic kidney disease (CKD) (Zhang et al., 2019; Christensen et al., 2011; Meier and Wagner, 2014).