TLR4诱导平滑肌源性泡沫细胞形成的作用和机制研究

Vascular smooth muscle cell (VSMC) is the main source of foam cells in the middle and late stages of atherosclerotic lesions. The mechanism underlying the formation of VSMC foam cell remains to be elucidated. TLR4 has been demonstrated to promote the transformation of macrophages to foam cells. However, the role of TLR4 in VSMC-derived foam cell is still unclear. Reportedly, multiple pro-inflammatory factors downstream of TLR4 participate in lipid accumulation in VSMC, which suggests an involvement of TLR4 in VSMC foam cells. Furthermore, our previous study found that TLR4 activation accelerated the lipid accumulation in VSMC. Herein, we postulate that TLR4 promotes the formation of VSMC-derived foam cell, which may in part through decreasing the ABCA1 expression and impairing reverse cholesterol transport (RCT). In the present study, ApoE-/- mice were used as an atherosclerotic model. The role of TLR4 in VSMC lipid accumulation was assessed via manipulating TLR4 expression using TLR4-/- mice in vivo and genetic approach in vitro. We also test the hypothesis that TLR4 down-regulates the ABCA1 expression through suppressing PPARγ and subsequently impaires RCT , which ultimately accelerates the atherosclerosis. The present study aims to provide further insight into the mechanisms of VSMC foam cells formation, and provide TLR4 as a promising target for therapeutic of atherosclerosis.

血管平滑肌细胞（VSMC）是中晚期动脉粥样硬化病变中泡沫细胞的主要来源，但平滑肌源性泡沫细胞形成的具体机制远未阐明。现已证实TLR4可促进巨噬细胞源性泡沫细胞的形成，但TLR4是否参与VSMC的泡沫样变尚不清楚。研究发现TLR4下游的多个促炎症因子均与VSMC的脂质聚集有关，我们的研究（NSFC资助，30970998）发现活化TLR4可促进VSMC内脂质聚集，据此认为TLR4可促进平滑肌源性泡沫细胞的形成，其机制可能与下调脂质转运体ABCA1表达，干扰胆固醇逆转运（RCT）有关。本项目拟建立ApoE-/-动脉粥样硬化小鼠模型，利用TLR4-/-小鼠和基因工程技术控制TLR4表达，明确TLR4在平滑肌源性泡沫细胞形成中的作用；并探讨TLR4是否通过抑制PPARγ下调ABCA1表达，进而干扰RCT而促进泡沫细胞形成。旨在深入研究平滑肌源性泡沫细胞形成的分子机制，为动脉粥样硬化的防治提供新思路。

血管平滑肌细胞（VSMC）是中晚期动脉粥样硬化病变中泡沫细胞的主要来源，但平滑肌源性泡沫细胞形成的具体机制远未阐明。现已证实 TLR4 可促进巨噬细胞源性泡沫细胞的形成，但 TLR4 是否参与 VSMC 的泡沫样变尚不清楚。三磷酸腺苷-结合盒转运子是调节细胞内脂质沉积的关键基因，但其具体分子机制仍需进一步阐述。我们的研究中使用50 μg/ml oxLDL刺激培养野生型VSMC，活化TLR4信号通路，结果发现ABCA1表达明显下调，VSMC内脂质沉积明显增多。TLR4基因敲除后逆转oxLDL诱导的ABCA1表达下调及VSMC内脂质沉积。进一步研究证实，IL-1R相关激酶1（IRAK1）参与TLR4诱导ABCA1表达下调及VSMC脂质沉积这一过程。我们另一研究证实，oxLDL活化TLR4通路后，过氧化物酶体增殖物激活受体γ （PPARγ）、肝X受体alpha （LXRα）及ABCG1表达明显下调，TLR4基因敲除后同样逆转上述分子表达下调。罗格列酮活化PPARγ表达后，ABCG1表达明显增多，VSMC内脂质沉积明显减少。siRNA沉默PPARγ基因表达后，LXRα及ABCG1表达受抑制，VSMC内脂质沉积明显增多。我们的研究深入地研究平滑肌源性泡沫细胞形成的分子机制，为动脉粥样硬化的防治提供了新思路。