Professor Feng Zhihui's team from the Frontier Institute of Science and Technology of Xi'an Jiaotong University (XJTU), in collaboration with Associate Researcher Zou Xuan from the Second Affiliated Hospital of XJTU, published an online research paper in Advanced Science titled A Hepatocyte to Stellate Cell Axis Couples Alternate Day Fasting to Liver Fibrosis Resolution via ATG7 S-Nitrosylation.

The study reveals a novel intercellular communication pathway through which alternate-day fasting (ADF) regulates hepatic stellate cell (HSC) activity via hepatocyte eNOS-paracrine nitric oxide (NO). It elucidates the key regulatory role of protein S-nitrosylation modification in liver fibrosis, providing new targets for lifestyle interventions and targeted therapies for liver fibrosis.

Using public single-cell transcriptome datasets, human liver tissue microarrays (170 clinical samples), and gene-knockout mouse models, the research team demonstrated that hepatocytes can also functionally express eNOS.

During the progression of liver fibrosis in humans and mice, hepatocyte eNOS expression is significantly downregulated. Hepatocyte-specific knockout of eNOS exacerbates CCl₄-induced liver injury, fibrosis, and glucose metabolism disorders, whereas endothelial cell-derived eNOS contributes little to this pathological process.

Further research revealed that short-term ADF can specifically upregulate hepatocyte eNOS expression and elevate circulating NO levels. This eNOS upregulation is primarily restricted to the liver, with no such changes observed in the heart, muscle, adipose tissue, and other organs.

Endothelial-specific eNOS knockout mice still respond to ADF and gain metabolic benefits; however, upon hepatocyte-specific eNOS deletion, the protective effects of ADF in ameliorating liver injury and inhibiting fibrosis completely vanish, proving that hepatocyte eNOS is an essential molecule for ADF to exert its hepatoprotective effects.

Building on the team's previous work (Advanced Science, 2022), ADF downregulates the mitochondrial chaperone SDHAF4, inhibits the assembly of mitochondrial complex II (succinate dehydrogenase, SDH), and thereby drives hepatocyte eNOS expression and NO production. In this study, hepatocyte-specific knockout of Sdhaf4 similarly mimicked the protective effects of ADF in alleviating liver fibrosis.

The NO produced by hepatocytes acts as a paracrine signal on HSCs, elevating the level of S-nitrosylation modification of proteins within HSCs. Utilizing quantitative S-nitrosylation proteomics, the team identified the core autophagy protein ATG7 from HSCs. NO mediates the S-nitrosylation of ATG7 at cysteine 184 (Cys184), disrupting the interaction between the ATG7 and ATG5-ATG12 complex, inhibiting autophagic flux within HSCs, and blocking HSC activation.