Fibroblast growth factor 21 (FGF21) promoter methylation drives the progression of chronic hepatitis B by mediating oxidative stress and inflammatory immunity

Hepatitis B virus (HBV) infection can cause liver damage through oxidative stress (OS) and immune-inflammatory responses. This study aims to explore the clinical significance of fibroblast growth factor 21 (FGF21) in the development and progression of chronic hepatitis B (CHB). A total of 336 participants were recruited, including 320 CHB patients and 16 healthy controls. The expression of FGF21, immune cytokines, and OS-related molecules in peripheral blood mononuclear cells (PBMCs) was detected using real-time quantitative polymerase chain reaction. The methylation level of the FGF21 gene promoter in PBMCs was detected using TaqMan probe-based quantitative methylation-specific PCR. The expression level of FGF21 in the peripheral blood of CHB patients was higher than that of HC, but the methylation level of the FGF21 promoter was lower than that of HC, especially in patients during the immune activation phase. The mRNA expression levels of CXCR3 and CCL5 in PBMCs of CHB patients during the immune activation and reactivation phases were higher than those in other clinical stages. Single-cell analysis revealed that CXCR3 and CCL5 expression in the immune tolerance and immune activation phases with high HBsAg expression was closely related to T lymphocytes (T cells) and natural killer cells (NK cells) and was highly expressed in CD4 and CD8 T cells and NK cells. In addition, the mRNA expression levels of Nrf2 and GPX4 in the reactivation phase were higher than those in other clinical stages. The mRNA expression level and methylation level of FGF21 in PBMCs of CHB patients were correlated with the viral load, immune inflammation, and OS levels during the antiviral treatment course of CHB. The methylation level of the FGF21 promoter has the potential to become a non-invasive biomarker for monitoring the progress of antiviral treatment in CHB. IMPORTANCE This study conducted an in-depth exploration of the application of methylation detection technology, analyzing its value and driving mechanism in the oxidative stress and immune-inflammatory balance during the course of chronic hepatitis B. The study analyzed the methylation patterns of the FGF21 promoter and the expression levels of its receptor FGFR1, as well as the expression levels of chemokines CXCR3, CCL5, and oxidative stress factors GPX4 and Nrf2 in the immune tolerance period, immune clearance period, immune control period, and reactivation period of chronic hepatitis B. It clarified the association between these molecules and the FGF21/FGFR1 axis and revealed the synergistic or antagonistic mechanisms of these molecules in the oxidative stress and inflammatory vicious cycle. At the same time, this study also explored the value of FGF21 promoter methylation in disease diagnosis and prognosis, providing a theoretical basis for evaluating the antiviral treatment effect and disease progression of chronic hepatitis B.