TACR1 and digestive system neoplasm: Moreover, upon cholestatic liver injury, serum SP level and SP/NK-1R expression in the liver are up-regulated, leading to SP/NK-1R pathway hyperactivation, which promotes liver fibrosis by mediating cell aging in hepatic stellate cells and cholangiocytes as well as enhancing the biliary secretion of TGF-β1 (18).