The Molecular Mechansims By Which Lipopeptides Of Staphylococcus Epidermidis Protect From Microbial Infection And Regulate Inflammatory Responses In Skin Wounds

As the first barrier of the host, skin is colonized by a diverse collection of microbia. Most of these microbia have benigh relationship with hosts and in some cases provide vital functions that are not evolved by human genome.Therefore, it’s important to investigate how skin commensals benefit the host.Our previous work shows that skin commensal bacterium Staphylococcus epidermidis, a gram-positive bacteria, has important roles in enhancing innate immune defense and regulating inflammatory responses. However, the identity of the molecule from S.epidermidis to rugulate skin immunity and the corresponding molecular mechanisms remain unknown. Here I isolated lipopeptides from S.epidermidis cell culture media and these peptides have a unique structure with heneicosanoic acid (C20H41COOH) binding to Lysine11(LP01) or Asp1(LP78) of a peptide chain(DIISTIGDLVKWIIDTVIIDATE). We further showed that these lipopeptides play important roles in the regulation of innate immunity.Our data show that in vitro LP01(DIISTlGDLVKWIIDTVIIDATE) increased the expression of β-defensin2(hBD2) and hBD3in neonatal human epidermal keratinocytes (NHEKs), leading to increased capacity of cell lysates to inhibit the growth of S.aureus. In vivo LP01induced the expression of mouse β-defensin4(mBD4) to decrease the survival of local S.aureus in skin and systemic S.aureus survival in liver. The induction of beta-defensins by LP01was dependent on TLR2as Tlr2-deficient mice had decreased mBD4. Furthermore, knockdown of CD36decreased the expression of hBD2and hBD3, and p38MAPK inhibitor significantly inhibited the expression of hBDs and p38phosphorylation induced by LP01. We also found that one isomer named LP78) of LP01inhibited poly(I:C)-induced inflammation in vitro and in vivo. poly(I:C) induced p65nuclear translocation to interact with PPARy, thus initiating inflammatory response. LP78induced β-catenin translocation into nucleus to compete with poly(I:C)-induced p65to interact with PPARy, thus inhibiting inflammatory response. The anti-inflammatory effects of LP78was depended on TLR2-CD14/CD36-PKA as LP78did not inhibit inflammation in Tlr2-deficient mice,or lost its capacity to inhibit inflammatory respose after CD14/CD36was knocked down. Furthermore, PKA inhibitor blocked the inhibitory effect of LP78on TLR3-dependent inflammation. The physilogical relevance of LP78in vivo was that LP78reduced excessive inflammatory responses in ulcer wounds, thus promoting wound healing in diabetic mice.In conclution, these findings demonstrate that S.epidermidis has a benign relationship with the host. In one hand S.epidermidis produces lipopeptide to enhance antibacterial defense against bacterial infection via the activation of TLR2/CD36-p38MAPK. On the other hand, the lipopeptide activates TLR2-CD14/36-PKA-β-catenin signal pathway to regulate inflammatory responses, thus promoting wound healing.