739 Hyaluronan controls adipogenesis following skin injury

Abstract

Skin immune defense and repair is a coordinated response to a variety of danger signals and involves the complex interactions of several different cell types. Dermal adipogenesis is a previously unknown but critical event in this process that participates in antimicrobial defense and inflammation. We have previously shown that high-molecular-weight hyaluronan (HMW-HA) undergoes breakdown into small fragments after injury where it can then activate endothelial cells, macrophages and DCs via TLR4. In this study we investigated if HA may also influence adipogenesis and thus regulate the wound repair process. Maturation of 3T3L1 cells into adipocytes was accompanied by increased HMW-HA seen by Gel Electrophoresis and expression of HAS2 mRNA measured by qPCR (p =0.006). Conversely, digestion of HMW-HA by addition of hyaluronidase inhibited differentiation into mature adipocytes as seen by decreased mRNA for zfp521(p=0.02), zfp423(p=0.01) and Adiponectin (p =0.004), as well as decreased accumulation of lipid droplets and enhanced cell proliferation. The inhibition of early adipogenesis was not due to HA fragments since the addition of HA fragments of 6.4kDa, 50kDa, 150kDa and 1000kD had no effect. In vivo, tissue specific expression of hyaluronidase 1 (HYAL1) in mice prior to injury resulted in less mature dermal fat tissue as seen by immunohistochemistry and lower expression of mRNA for C/EBPα (p=0.002) but not Adiponeqtin(p=0.13) or PPARγ(p=0.27). In normal mice, HA immunostaining was lost 3 days following injury coincident with an increase in expression of HAS2 mRNA (p=0.0008) and mRNA for the hyaluronidase KIAA1199 (p=0.01). The loss of HMW-HA in vivo occurred after the expected increase in adipogenesis immediately after injury. Taken together, these results suggest that HA plays a regulatory role during wound repair by controlling dermal adipogenesis. HMW-HA facilitates fat maturation early in the wound repair process, and hyaluronidase action stops this event later in the wound healing process.