As the most prevalent liver disease globally, nonalcoholic fatty liver disease (NAFLD) encompasses a diverse range of pathological states from steatosis to steatohepatitis, even progressing to fibrosis and cirrhosis. NAFLD has the characteristics of hepatic steatosis and insulin resistance, and exhibits a close relationship with conditions such as obesity and diabetes (Younossi et al., 2019). NAFLD occurs in about 25% global population, with the lowest rates in African countries, while South America and Middle East are reporting the highest incidences (Younossi et al., 2016). Lifestyle maintenance is the primary approach for NAFLD management (Kim and Park, 2019), underscoring the dire need for pharmacotherapy. However, a healthy lifestyle takes a strong mind to hold. Due to the complex pathogenesis and difficulties in diagnosis of NAFLD, there are no approved pharmacotherapies currently. Lipid and glucose metabolism disorder was proven as the major hallmark and the critical pathological process of NAFLD (Chao et al., 2019). Thus, the exploration of active molecules modulating lipid and glucose metabolism might become the pharmacological medication for NAFLD.

Coptidis rhizome is the rhizome of Coptis chinensis Franch., Coptis deltoidea C. Y. Cheng et Hsiao, and Coptis teeta Wall., and it has been used for metabolic diseases, especially diabetes in China for thousands of years (Li et al., 2004). Since the 1980s, berberine (BBR) has been accepted as the main active ingredient of Coptidis rhizome to exert hypoglycemic and hypolipidemic effects (Yin et al., 2002). BBR is an isoquinoline alkaloid naturally extracted from Coptidis rhizome and it exhibits therapeutic effects on hepatic steatosis, dyslipidemia, diabetes, etc. (Chang et al., 2015). In addition, BBR has various beneficial impacts on NAFLD confirmed in patients with NAFLD, high-fat, high-sucrose diet fed C57BL/6 mice and palmitate-treated HepG2 cells (Sun et al., 2018; Yan et al., 2015). Therefore, BBR is recognized as a promising pharmacological intervention in NAFLD. Currently, a phase IV clinical trial of BBR (NCT03198572) has been initiated to treat NAFLD and nonalcoholic steatohepatitis (NASH) (Yan et al., 2020). Feng and Wang et al. have comprehensively studied the mechanisms of NAFLD abnormality improvements by BBR at the molecular level (Feng et al., 2019; Wang et al., 2021c). However, its direct targets and the related downstream pathways have not well identified yet, which has markedly restricted BBR's further clinical utility.

Aldo-keto reductase 1B10 (AKR1B10) operates as an NADPH-dependent reductase for the reduction of aldehydes, ketones and quinones (Endo et al., 2021). It was highly expressed in the hepatic samples from the patients afflicted with NAFLD, steatosis (Bitter et al., 2015), steatohepatitis (Starmann et al., 2012), fibrosis (Govaere et al., 2020), even hepatocellular carcinoma (HCC) (DiStefano and Davis, 2019). Accumulating evidence suggests that AKR1B10 may be a consistent marker for diagnosing NAFLD-related diseases (Kanno et al., 2019; Pettinelli et al., 2018), indicating that AKR1B10 might be a suitable target for controlling NAFLD-related diseases.

Recently, click chemistry has been widely used to identify the molecular targets of natural medicines, including artemisinin, glycyrrhetinic acid (Wang et al., 2015; Zhang et al., 2019). Through click chemistry, Yi & Zeng groups identified that BBR directly targets NEK7 and actin and subsequently exerts its strong pharmacological effects (Yi et al., 2017; Zeng et al., 2021). Herein, by using click chemistry-proteomics and RNA sequencing, we proved that the major alkaloid of Coptidis rhizome, BBR, inhibited hepatic steatosis, promoted insulin sensitivity and TG lowering effects, etc, by regulating the PPAR pathway through targeting AKR1B10 protein. In the current study, target identification of BBR helps to elucidate the mechanism of other active natural compounds and establish new treatments for NAFLD.