850 After skin wounding, noncoding dsRNA coordinates prostaglandins and WNT7b to promote regeneration

Abstract

In a rare example akin to organogenesis in adult mammals, large full-thickness skin wounds in mice and rabbits lead to de novo morphogenesis of hair follicles. It is still not fully understood what controls this process, known as Wound Induced Hair Neogenesis (WIHN). Previously, our group has demonstrated that double stranded RNA (dsRNA) released during wounding is both necessary and sufficient to stimulate WIHN through Toll like receptor 3 (TLR3), coincident with activation of WNT/β-catenin signaling. In other systems, prostaglandin E2 (PGE2) is an important effector of regeneration and has been shown to stimulate the WNT/β-catenin pathway. Our microarray data shows WNT7b is the most potently enriched WNT transcript induced by dsRNA (#187 out of 49,395 transcripts). Thus, we hypothesize that dsRNA and TLR3-mediated damage-sensing stimulate a PG-dependent mechanism to activate the WNT7b/β-catenin pathway, and WIHN. We find that Wnt7b expression is induced by synthetic dsRNA (poly I:C) in both the epidermis of healing mouse skin wounds and cultured normal human epidermal keratinocytes (P < 0.05, N=3). Mice lacking TLR3 and epidermal STAT3 display a marked reduction of Wnt7b expression (P < 0.05, N=8). Supportively, IL-6 rescues WIHN and Wnt7b levels in TLR3 null mice (P < 0.05, N=8). Additionally, we find the amount and kinetics of WNT7b expression induced by poly I:C closely correlated to that of prostaglandin-endoperoxide synthase 2 (PTGS2/COX2), which was also required for WNT7b protein levels based on PTGS2-siRNA treatment of human keratinocytes (P < 0.05, N=3). In vivo results show that the Ptgs2 inhibitor celecoxib reduces dsRNA-induced WIHN (P < 0.05, N=32) and Wnt7b. Exogenous PGE2 can rescue WIHN and Wnt7b (P < 0.05, N=21). Collectively, these results highlight TLR3-mediated damage sensing mechanism as a novel upstream coordinator of prostaglandin and Wnt levels in regeneration.