Although cathepsins are widely expressed in nearly all liver cells that possess lysosomes37 and their expression in hepatic stellate cells (HSCs) is elevated during HSC activation, according to a previous study40, we found that cathepsin B and D were predominantly expressed in macrophages in healthy and NAFLD mouse livers (Supplementary Fig. 5a-b). Here, CTSS is linked to metabolic dysfunction-associated steatotic liver disease.