HO-1 regulates liver fibrosis in NAFLD through the SIRT1 TGF-β Smad3 pathway

Background and aims

Heme oxygenase 1 (HO-1) has an influential yet insufficiently investigated effect on Sirtuin 1 (SIRT1), a histone deacetylase activated by nicotinamide adenine dinucleotide, which may impact the transforming growth factor-β (TGF-ß)/Smad3 pathway in nonalcoholic fatty liver disease (NAFLD)-related liver fibrosis. This study aimed to elucidate the regulation of NAFLD-related liver fibrosis induced by HO-1 through the SIRT1/TGF-ß/Smad3 pathway.

Methods

HO-1 induction and inhibition were established in C57BL/6J mice fed a methionine- and choline-deficient (MCD) diet. Additionally, wild-type mice were fed either a normal diet or an MCD diet. Hematoxylin and eosin, Masson's trichrome, and Sirius Red staining were used to assess hepatic steatosis, inflammation, and fibrosis. In vitro, plasmid overexpression and small interfering RNA silencing of HO-1 were performed in LX-2 cells. Cell viability was assessed using the Cell Counting Kit-8, and apoptosis was evaluated via terminal deoxynucleotidyl transferase dUTP nick-end labeling and immunofluorescence. Flow cytometry was employed to assess apoptosis and reactive oxygen species production. Western blot and real-time quantitative reverse transcription polymerase chain reaction were used to analyze the mRNA and protein expression of genes related to HO-1, SIRT1, the TGF-ß signaling pathway, and fibrosis.

Results

MCD-fed mice developed significant liver damage, including steatosis, inflammatory infiltration, and pericellular fibrosis. Zinc protoporphyrin treatment exacerbated these conditions. Corroborating these findings, silencing HO-1 in LX-2 cells increased the expression of fibrosis-related genes. Furthermore, HO-1 overexpression not only increased SIRT1 expression but also reduced the activity of key regulatory factors in the TGF-ß signaling pathway, suggesting a potential interaction between HO-1 and the SIRT1/TGF-ß pathway.

Conclusions

The results of this study demonstrate that HO-1 helps reduce hepatic fibrosis associated with NAFLD by modulating the SIRT1/TGF-β/Smad3 signaling pathway. Insights into the interactions between HO-1 and SIRT1 in NAFLD-associated liver fibrosis could facilitate the development of new biomarkers and treatment strategies for liver dysfunction. Ultimately, this deeper understanding could lead to improved quality of life and life expectancy for patients suffering from NAFLD-related hepatic fibrosis.