Temporal and spatial patterns of endogenous danger signal expression after wound healing and in response to lymphedema

Abstract

While acute tissue injury potently induces endogenous danger signal expression, the role of these molecules in chronic wound healing and lymphedema is undefined. The purpose of this study was to determine the spatial and temporal expression patterns of the endogenous danger signals high-mobility group box 1 (HMGB1) and heat shock protein (HSP)70 during wound healing and chronic lymphatic fluid stasis. In a surgical mouse tail model of tissue injury and lymphedema, HMGB1 and HSP70 expression occurred along a spatial gradient relative to the site of injury, with peak expression at the wound and greater than twofold reduced expression within 5 mm (P < 0.05). Expression primarily occurred in cells native to injured tissue. In particular, HMGB1 was highly expressed by lymphatic endothelial cells (>40% positivity; twofold increase in chronic inflammation, P < 0.001). We found similar findings using a peritoneal inflammation model. Interestingly, upregulation of HMGB1 (2.2-fold), HSP70 (1.4-fold), and nuclear factor (NF)-κβ activation persisted at least 6 wk postoperatively only in lymphedematous tissues. Similarly, we found upregulation of endogenous danger signals in soft tissue of the arm after axillary lymphadenectomy in a mouse model and in matched biopsy samples obtained from patients with secondary lymphedema comparing normal to lymphedematous arms (2.4-fold increased HMGB1, 1.9-fold increased HSP70; P < 0.01). Finally, HMGB1 blockade significantly reduced inflammatory lymphangiogenesis within inflamed draining lymph nodes (35% reduction, P < 0.01). In conclusion, HMGB1 and HSP70 are expressed along spatial gradients and upregulated in chronic lymphatic fluid stasis. Furthermore, acute expression of endogenous danger signals may play a role in inflammatory lymphangiogenesis.