Oxidation of HMGB1 Is a Dynamically Regulated Process in Physiological and Pathological Conditions

Abstract

Acute inflammation is a complex biological response of tissues to harmful stimuli, such as pathogens or cell damage, and is essential for immune defense and proper healing. However, unresolved inflammation can lead to chronic disorders, including cancer and fibrosis. The High Mobility Group Box 1 (HMGB1) protein is a Damage-Associated Molecular Pattern (DAMP) molecule that orchestrates key events in inflammation by switching among mutually exclusive redox states. Fully reduced HMGB1 (frHMGB1) supports immune cell recruitment and tissue regeneration, while the isoform containing a disulphide bond (dsHMGB1) promotes secretion of inflammatory mediators by immune cells. Although it has been suggested that the tissue itself determines the redox state of the extracellular space and of released HMGB1, the dynamics of HMGB1 oxidation in health and disease are unknown. In the present work, we analyzed the expression of HMGB1 redox isoforms in different inflammatory conditions in skeletal muscle, from acute injury to muscle wasting, in tumor microenvironment, in spleen, and in liver after drug intoxication. Our results reveal that the redox modulation of HMGB1 is tissue-specific, with high expression of dsHMGB1 in normal spleen and liver and very low in muscle, where it appears after acute damage. Similarly, dsHMGB1 is highly expressed in the tumor microenvironment while it is absent in cachectic muscles from the same tumorbearing mice. These findings emphasize the accurate and dynamic regulation of HMGB1 redox state, with the presence of dsHMGB1 tightly associated with leukocyte infiltration. Accordingly, we identified circulating, infiltrating, and resident leukocytes as reservoirs and transporters of dsHMGB1 in tissue and tumor microenvironment, demonstrating that the redox state of HMGB1 is controlled at both tissue and cell levels. Overall, our data point out that HMGB1 oxidation is a timely and spatially regulated process in physiological and pathological conditions. This precise modulation might play key roles to finetune inflammatory and regenerative processes.

Redox modifications of cysteine residues regulate the cytokine activity of HMGB1

“…The box A domain binds to TLR 4 with high affinity and slow off-rate, while once in close proximity the box B domain binds to MD-2 with low affinity but extremely slow off-rate (He et al 2018 ). Furthermore, recent studies in tissue samples obtained from pathological and physiological conditions underline a close association of disulfide HMGB1 expression with an inflammatory state characterized by the presence of immune cells and identifies leukocytes as reservoirs of disulfide HMGB1 (Ferrara et al 2020 ; Kwak et al 2020 ).…”

HMGB1 augments cognitive impairment in sepsis‐associated encephalopathy by binding to MD‐2 and promoting NLRP3‐induced neuroinflammation

“…Redox forms of HMGB1 are classified as frHMGB1 and dsHMGB1, and dsHMGB1 could bind to MD‐2, which is an extracellular adaptive molecule of signal pathways to elicit the synthesis of signals and the subsequent pro‐inflammatory factors 23,24 . We speculated that HMGB1 in mouse brain tissue might bind to MD‐2 in the form of dsHMGB1 to activate NLRP3 expression.…”

Complement System and Alarmin HMGB1 Crosstalk: For Better or Worse

“…HMGB1 action is finely tuned by its associations and localization, which are modulated by post-translational modifications ( 33 , 34 ). For example, the oxidation state of its cysteines (two in the A-box, one in the B-box) modulates its biological activity in the extracellular environment ( Figures 1 , 3 ) ( 35 ). Only fully reduced HMGB1 and the non-oxidizable HMGB1 mutant 3S, in which three serine residues replace cysteines, induce chemotaxis by binding CXCL12 through the CXCR4 receptor [maintained at the surface by the CXCL12/HMGB1 heterodimer ( 36 )], and recruit stem cells to orchestrate tissue regeneration ( 37 ) ( Figure 3 ).…”