Abstract

Background: Metabolic dysfunction associated steatohepatitis (MASH) involves immune mechanisms and the contribution of adaptive immunity to disease progression has been increasingly recognized. B cells, with their ability to modulate inflammation, are key players in inflammatory diseases. However, their precise role and underlying mechanisms in MASH pathogenesis remain unclear. Therefore, our research aims to investigate the mechanisms driving B cell activation and their pro-inflammatory activity in MASH.

Methods: We established a mouse model of MASH by feeding mice a high-fat, high-carbohydrate diet to closely resemble human MASH. We focused on studying the secretome of B cells by employing Isoplexis single-cell B cell secretome analysis specifically on intrahepatic B cells from mice with MASH and healthy controls. To understand the phenotypic landscape of liver B cells during MASH, single-cell RNA sequencing was used to characterize their transcriptional profiles. Metabolic adaptations of B cells during MASH were explored using Seahorse XF assays and targeted metabolomics. To investigate the role of B cell antigen-specific responses in MASH, B cell receptor restricted mice fed the MASH-inducing diet were utilized.

Results: Our investigation revealed a notable accumulation of pro-inflammatory B cells in the livers of MASH patients and mice fed a high-fat, high-carbohydrate diet. Single-cell B cell secretome analysis uncovered a proteomic landscape reflecting their pro-inflammatory function. Additionally, single-cell RNA sequencing identified a population of immature B cells that diminished during MASH, indicating altered maturation. We hypothesized that metabolic regulation might be involved due to these changes. Seahorse XF assays showed that B cells in MASH rely on increased oxidative phosphorylation (OXPHOS) rather than glycolysis for energy during immune activation. Importantly, we found that OXPHOS-dependent ATP production is fueled by pyruvate oxidation. Inhibiting pyruvate oxidation in MASH B cells completely abolished their pro-inflammatory potential, dependent on B cell receptor signaling. B cell receptor-restricted mice, recognizing an irrelevant antigen, displayed improved disease outcomes with enhanced fatty acid β-oxidation, decreased steatosis, and reduced fibrosis. Additionally, disease amelioration was accompanied by systemic decreases in IgG antibody isotypes, previously correlated with MASH severity in humans.

Conclusion: Our study highlights the pro-inflammatory role of B cells in MASH, driven by metabolic adaptations and antigen-specific responses. Understanding the factors regulating B cell metabolism during inflammation could open avenues for selectively targeting their pathogenic activity in MASH.