Redox-sensitive high-mobility group box-1 isoforms contribute to liver fibrosis progression and resolution in mice

Background & aims: High-mobility group box-1 (HMGB1) significantly increases and undergoes post-translational modifications (PTMs) in response to liver injury. Since oxidative stress plays a major role in liver fibrosis and induces PTMs in proteins, we hypothesized that redox-sensitive HMGB1 isoforms contribute to liver fibrosis progression and resolution.

Methods: We used ESI-LC-MS (electrospray ionization-liquid chromatography-mass spectrometry) to study PTMs of HMGB1 during fibrosis progression and resolution. Conditional knockout mice were used for functional analyses.

Results: We identified that disulfide ([O]) and sulfonated ([SO₃]) HMGB1 increase during carbon tetrachloride-induced liver fibrosis progression, however, while [O] HMGB1 declines, [SO₃] HMGB1 drops but remains, during fibrosis resolution. Conditional knockout of Hmgb1 revealed that production of [O] and [SO₃] HMGB1 occurs mostly in hepatocytes. Co-injection of [O] HMGB1 worsens carbon tetrachloride-induced liver fibrosis more than co-injection of [H] HMGB1. Conversely, ablation of [O] Hmgb1 in hepatocytes reduces liver fibrosis. Moreover, ablation of the receptor for advanced-glycation end-products (Rage) reveals that the profibrogenic effect of [O] HMGB1 is mediated by RAGE signaling in hepatic stellate cells (HSCs). Notably, injection of [SO₃] HMGB1 accelerates fibrosis resolution due to RAGE-dependent stimulation of HSC apoptosis. Importantly, gene signatures activated by redox-sensitive HMGB1 isoforms in mice, classify patients with fibrosis according to fibrosis and inflammation scores.

Conclusion: Dynamic changes in hepatocyte-derived [O] and [SO₃] HMGB1 signal through RAGE-dependent mechanisms on HSCs to drive their profibrogenic phenotype and fate, contributing to progression and resolution of liver fibrosis.

Impact and implications: Since oxidative stress plays a major role in liver fibrosis and induces post-translational modifications of proteins, we hypothesized that redox-sensitive HMGB1 isoforms contribute to liver fibrosis progression and resolution. This study is significant because a rise in [H] HMGB1 could flag 'patient at risk', the presence of [O] HMGB1 could suggest 'disease in progress or active scarring', while the appearance of [SO₃] HMGB1 could point at 'resolution under way'. The latter could be used as a readout for response to pharmacological intervention with anti-fibrotic agents.