Screening the human druggable genome identifies ABHD17B as an anti-fibrotic target in hepatic stellate cells

Abstract

Background & Aims: Chronic liver injury leads to activation of hepatic stellate cells (HSCs), which transdifferentiate into HSC myofibroblasts and produce the extracellular matrix (ECM) that forms the fibrotic scar. While the progression of fibrosis is understood to be the cause of end stage liver disease, there are currently no approved therapies directed at interfering with the activity of HSC myofibroblasts. Methods: We performed a high-throughput small interfering RNA (siRNA) screen in primary human HSC myofibroblasts targeting RNAs from >9,500 genes to identify those that promote the fibrotic phenotype of HSCs. The screen identified ABHD17B (Abhydrolase domain containing 17B, depalmitoylase), which was evaluated through loss-of -function studies in multiple primary human HSC lines. Structural analysis was performed to identify key amino acids in the hydrolase pocket of ABHD17B, and depalmitoylase inhibitors were evaluated. Protein partners were identified by mass spectrometry (MS), and Abhd17b-/- mice were challenged with carbon tetrachloride (CCl4) as a model of chronic liver injury. Results: Depletion of ABHD17B promotes the inactivation of HSCs, characterized by reduced COL1A1 and ACTA2 expression and accumulation of lipid droplets. RNA-seq and MS analysis also indicated a broader impact on ECM production and cytoskeletal organization. Mice deficient in Abhd17b are viable, demonstrate normal liver histology, and are protected from fibrosis in the setting of in vivo liver injury. While ABHD17B is a depalmitoylase, inhibiting this function alone is not sufficient to affect the fibrotic activity of HSCs. Conclusions: ABHD17B promotes fibrosis through pathways independent of depalmitoylation that include regulating expression of COL1A1 and other ECM genes and interacting with proteins involved in cytoskeletal organization, contractility, and adhesion. Targeting ABHD17B may have potential as an antifibrotic therapy.