Contribution of HMGB1 to keratinocyte inflammation in recessive dystrophic epidermolysis bullosa.

Recessive dystrophic epidermolysis bullosa is an inherited skin disorder characterized by fragile skin, blistering, and chronic wounds. Keratinocytes, the primary cells in the epidermis, are directly affected by persistent injury in recessive dystrophic epidermolysis bullosa, contributing to chronic inflammation. HMGB1 (high mobility group box 1) is elevated in the serum of individuals with recessive dystrophic epidermolysis bullosa. However, its role in keratinocyte inflammation remains unclear. In this study, we report an increase in HMGB1 expression in keratinocytes at chronic wound sites compared with that on matched nonwounded skin from an individual with recessive dystrophic epidermolysis bullosa, suggesting a potential link to the upregulation of local proinflammatory stimuli. Pharmacologic inhibition of HMGB1 using inflachromene reduced lipopolysaccharide-induced secretion of proinflammatory cytokines in keratinocytes, supporting a role for keratinocyte-specific HMGB1 in inflammatory response. Surprisingly, deletion of HMGB1 alone or together with its paralog HMGB2 did not suppress the release of proinflammatory cytokines in response to lipopolysaccharide. Furthermore, inflachromene still reduced the secretion of proinflammatory cytokines in HMGB1- and HMGB2-knockout cells. This unexpected discrepancy between genetic deletion and pharmacologic inhibition points to a more complex role for HMGB1 or off-target effects of the compound. These findings suggest that HMGB1 may contribute to proinflammatory signaling in keratinocytes; however, its exact function needs further investigation.