Cellular source and proinflammatory roles of high-mobility group box 1 in surgically injured rat vocal folds.

Objectives/hypothesis: High-mobility group box 1 (HMGB1) is a chromatin-binding protein located in the cell nucleus. Following injury, immunocompetent cells secrete HMGB1 to the extracellular milieu under the stimulation of proinflammatory cytokines. Extracellular HMGB1 acts a danger signal that instigates the innate immunity and tissue repair. We previously reported HMGB1 in the vocal fold extracellular compartment between day 3 and day 7 following surgical injury. In this study, we further investigated the cell source of HMGB1 and the relationship of proinflammatory cytokine expression and HMGB1 translocation in wounded vocal folds.

Study Design: Prospective animal study.

Methods: Bilateral vocal fold injury was performed on 122 Sprague-Dawley rats. An additional 18 rats served as uninjured controls. Animals were sacrificed at multiple time points up to 4 weeks after surgery. Immunohistochemical costaining was performed to identify the cell source of HMGB1. Cell markers ED1, fibroblast-specific protein 1 (FSP1), and alpha smooth muscle actin (α-SMA) were used to identify macrophages, fibroblasts, and myofibroblasts, respectively. Enzyme-linked immunosorbent assays were performed to measure cytokine levels of interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) in vocal fold tissue.

Results: Costaining of HMGB1 was strong with ED1 and FSP1 but was minimal with α-SMA in injured vocal folds. Compared to uninjured controls, IL-1β and TNF-α expression increased significantly the first 2 days after injury.

Conclusions: Macrophages and fibroblasts were a major cell source of vocal fold HMGB1. Translocation of HMGB1 may be an active response to the early accumulation of IL-1β and TNF-α in the wounded vocal folds.

Level Of Evidence: NA Laryngoscope, 127:E193-E200, 2017.