Buddleoside alleviates nonalcoholic steatohepatitis by targeting the AMPK-TFEB signaling pathway

Nonalcoholic steatohepatitis (NASH) is a combination of hepatic steatosis, inflammation, and fibrosis, and it often follows simple hepatic steatosis in nonalcoholic fatty liver disease (NAFLD). However, no pharmacological treatment is currently available for NASH. Given the important role of TFEB (transcription factor EB) in regulating the macroautophagy/autophagy-lysosomal pathway, TFEB is potentially a novel therapeutic target for treatment of NASH, which function can be regulated by AMP-activated protein kinase (AMPK) and MTOR (mechanistic target of rapamycin kinase) complex 1 (MTORC1). Buddleoside (Bud), a natural flavonoid compound, has recently emerged as a promising drug candidate for liver diseases. Here, we shown that Bud treatment alleviated hepatic steatosis, insulin resistance, inflammation, and fibrosis in mice fed a high-fat and high-cholesterol (HFHC) diet. Notably, Bud activated AMPK, inhibited MTORC1, and enhanced TFEB transcriptional activity as well as autophagic flux in vivo and in vitro. Inhibition of AMPK or knockout of hepatic Tfeb abrogated the alleviation effects of Bud on hepatic steatosis, insulin resistance, inflammation, and fibrosis. Mechanistic investigation revealed that Bud bound to the PRKAB1 subunit via Val81, Arg83, and Ser108 residues and activated AMPK, thereby eliciting phosphorylation of RPTOR (regulatory associated protein of MTOR complex 1) and inhibiting the kinase MTORC1, which activated the TFEB-mediated autophagy-lysosomal pathway and further ameliorated HFHC-induced NASH in mice. Altogether, our results indicate that Bud ameliorates NASH by activating hepatic the AMPK-TFEB axis, suggesting that Bud is a potential therapeutic strategy for NASH.Abbreviations: ACAC, acetyl-CoA carboxylase; ADaM, allosteric drug and metabolite; AICAR, 5-aminoimidazole-4-carboxamide1-β-D-ribofuranoside; AKT, AKT serine/threonine kinase; ALP, autophagy-lysosomal pathway; AMPK, AMP-activated protein kinase; Bud, buddleoside; CAMKK2, calcium/calmodulin dependent protein kinase kinase 2; CC, compound C; CETSA, cellular thermal shift assay; C_max, maximum concentration; CQ, chloroquine; DARTS, drug affinity responsive target stability assay; EIF4EBP1, eukaryotic translation factor 4E binding protein 1; GOT1, glutamic-oxaloacetic transaminase 1; GPT, glutamic-pyruvic transaminase; GSK3B, glycogen synthase kinase 3 beta; GTT, glucose-tolerance test; HFD, high fat diet; HFHC, high-fat and high-cholesterol; HOMA-IR, homeostasis model assessment of insulin resistance; IKBKB, inhibitor of nuclear factor kappa B kinase subunit beta; INSR, insulin receptor; ITT, insulin-tolerance test; LDH, lactate dehydrogenase; STK11, serine/threonine kinase 11; MAP1LC3/LC3, microtubule associated protein 1 light chain 3; MTORC1, MTOR complex 1; NAFLD, non-alcoholic fatty liver disease; NASH, non-alcoholic steatohepatitis; ND, normal diet; NFKB, nuclear factor kappa B; PA, palmitic acid; PSR, picrosirius red; RRAG, Ras related GTP binding; RPTOR, regulatory associated protein of MTOR complex 1; RPS6, ribosomal protein S6; RPS6KB, ribosomal protein S6 kinase B; SMAD2, SMAD family member 2; SMAD3, SMAD family member 3; SQSTM1, sequestosome 1; TFEB, transcription factor EB; tfeb-HKO, hepatocyte-specific tfeb knockout; TSC2, TSC complex subunit 2.