LB926 Hyaluronic acids (HAs) molecular size-dependent biological functions on UVB-induced DAMPs-mediated keratinocyte inflammation

Abstract

Physiologic responses mediated by hyaluronic acid (HAs) depend on their molecular weights and binding receptors, TLR4 and CD44. Low molecular weight HA (LMW-HA) induces inflammation, while high molecular weight HA (HMW-HA) works as an anti-inflammation factor. UVB-induced epidermal inflammation is usually initiated by endogenous molecules released from damaged cells upon skin tissue injury, called damaged-associated molecular patterns (DAMPs). Calprotectin, a typical DAMP, usually causes severe skin inflammation through activating TLR4 pathways. Since both LMW-HA and HMW-HA have inhibitory functions on TLR-mediated macrophage inflammation, HAs are assumed to suppress UVBinduced Calprotectin-mediated skin inflammations. In this study, ultra-LMW-HA, uLMW-HA (0.8 kDa) and HMW-HA (1200kDa), are utilized in the evaluation of UVB-irradiated keratinocyte inflammation. Calprotectin and proinflammatory cytokines secretion were demonstrated on UVB-irradiated keratinocytes. Results showed increased amounts of IL-6 and IL-8 in the medium after irradiation. Under HAs treatments on UVB-irradiated keratinocytes, IL-6 secretion showed a nearly 20% reduction(p<0.05), which indicates the anti-UVB-induced inflammatory effect of uLMW-HA and HMW-HA. Additionally, we treated the calprotectintreated keratinocytes with HAs since it was clear that UVB up-regulated Calprotectin secretion. Results showed suppressive effects of HAs on IL-6 secretion, and HMW-HA presented more substantial inhibitory effect compared to uLMW-HA. Furthermore, TLR4 downstream protein, TRAF6 expression was down-regulated in uLMW-HA-treated conditions, which supported uLMW-HA's blocking effects on Calprotectin/TLR4 signal. It is firmly believed that understanding the detailed molecular mechanisms of natural skin response to HAs will be helpful in guiding future HA-containing formulations designs.