Deficiency of Transient Receptor Potential Vanilloid 1 Receptor Attenuates Lipopolysaccharide-Mediated Inflammatory Responses in Murine Macrophages

• Main Authors: Hsu-Wen Tseng, 曾栩文
• Other Authors: Tzong-Shyuan Lee
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/41723058478284269866

碩士 === 國立陽明大學 === 生理學研究所 === 96 === Abstract Transient receptor potential vanilloid 1 (TRPV1) is a calcium channel activated by numerous noxious stimuli including capsaicin, heat (>43℃), protons, arachidonic acid metabolites and inflammatory mediators. TRPV1 is widely distributed over body and mediates various cell functions. Recent studies suggested that TRPV1 might positively or negatively regulate lipopolysaccharide (LPS)–induced inflammation; however, the exactly role of TRPV1 in inflammation is not fully understood. It is well established that macrophages play dominant roles in innate immune responses, and toll-like receptor (TLR) 4–mediated signaling transduction contributes largely to the inflammatory responses evoked by LPS. The mitogen-activated protein kinase (MAPK) and nuclear factor-kappaB (NF-kappaB) pathways are responsible for the expression of many inflammation-associated genes. Therefore, the aims of this study were to investigate the possibility that TRPV1 could regulate LPS-mediated inflammatory responses in macrophages, and the involvement of TRPV1 in TLR4 signaling pathway. To explore the hypothesis, bone marrow-derived macrophages harvested from wild type (WT) and TRPV1 knock out (TRPV1-/-) mice were used as cell models. The LPS-induced elevation of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), inducible nitric oxide synthase (iNOS) and subsequent product nitric oxide (NO) were attenuated in TRPV1-/- macrophages. Compared with WT macrophages, the phosphorylation of inhibitor of NF-kappaB (IkappaB), translocation of NF-kappaB and activation of MAP kinase were reduced in LPS-treated TRPV1-/- macrophages. Based on the results of immunoprecipitation, deficiency of TRPV1 in macrophages impaired the LPS-triggered immune-complex formation of myeloid differentiation protein 88 (MyD88), TLR4, IL-1 receptor-associated kinase (IRAK) and IkappaB kinases (IKK) that are important in TLR4 signaling pathway. Furthermore, the association between TRPV1, TLR4 and CD14 was observed in WT macrophages at basal condition and the interaction was increased within 5 minutes after LPS administration. In conclusion, TRPV1 might participate in the TLR4: CD14 complex formation and maintain the LPS-mediated inflammatory responses through TLR4 signaling pathway.