载脂蛋白M通过1－磷酸鞘氨醇受体1途径参与高密度脂蛋白的抗炎作用

Apolipoprotein M (ApoM) is predominantly presented in high-density lipoprotein (HDL) particles, and may contribute to the cholesterol efflux, antioxidative and endothelial protective effects via sphingosine-1-phosphate (S1P). S1P is a bioactive lysophospholipid generated by the sphingosine kinase catalyzed phosphorylation of sphingosine. Plasma S1P is bound to albumin (about 35%) or carried by ApoM (about 65%) in HDL. Many of the biological effects of S1P are mediated by its binding to five specific G protein-coupled receptors (S1PR1-S1PR5) located on the cell surface in an autocrine and/or paracrine manner. Our preliminary study uncovered ApoM mediated antiflammatory effects. We hypothesized that ApoM-S1P binding to S1PR1 specifically is critical for the anti-inflammatory effects of ApoM. As in-vitro study with cultured human umbilical vein cell and human coronary artery endothelial cell and in vivo study with ApoM gene knock-out mice, the present study is to investigate how the interation of ApoM-S1P binding to S1PR1 affect on the anti-inflammatory effects of ApoM. One of the potential mechanisms may relate to its competitive inhibition of albumin-S1P binding to S1P receptors, since the latter has been confirmed to associate with pro-inflammatory responses. Furthermore, we are going to determine that the impact of ApoM-S1P binding to S1PR1 on the activity of NF-κB signaling pathway in the inflammatory response. The outcome of the study could be potentially important and benificial for the development of new clinical provention and for atherosclerosis.

载脂蛋白M（ApoM）主要存在于高密度脂蛋白（HDL）中，它参与HDL的胆固醇逆转运、抗氧化及通过传递1－磷酸鞘氨醇（S1P）来保护血管内皮的功能。在体内，S1P由白蛋白和ApoM 载运，它有5个特异性受体（S1PR1-5）。 本课题组前期研究发现，ApoM具有抗炎作用。因而推测ApoM可能通过竞争性抑制白蛋白载运S1P，并通过S1PR1途径参与HDL的抗炎作用。本研究应用S1P受体的选择性拮抗剂、人脐静脉内皮细胞、人冠状动脉内皮细胞及ApoM基因敲除小鼠进行研究，通过分析激酶磷酸化水平及炎症相关分子表达的变化来明确S1PR1是否特异性结合ApoM-S1P，而不识别白蛋白-S1P；同时明确ApoM竞争性抑制白蛋白载运S1P后是否具有抗炎作用、是否通过S1PR1途径上调24-脱氢胆固醇还原酶的表达，进而抑制核因子κB途径发挥抗炎作用。预期结果可为动脉粥样硬化的预防和治疗研究提供新的靶向。

载脂蛋白M（Apolipoprotein M, ApoM）主要存在于高密度脂蛋白（high-density lipoprotein, HDL）中，它参与HDL的胆固醇逆转运、抗氧化及通过传递1－磷酸鞘氨醇（S1P）来保护血管内皮的功能。在体内，S1P由白蛋白和ApoM载运，它有5个特异性受体（S1PR1-5）。本课题研究了S1PR1是否特异性结合ApoM-S1P，而不识别白蛋白-S1P；同时研究了ApoM竞争性抑制白蛋白载运S1P后是否具有抗炎作用、是否通过S1PR1途径上调24-脱氢胆固醇还原酶（3β-hydroxysterol Δ-24-reductase, DHCR24）的表达，进而抑制核因子κB（nuclear factor kappa B, NF-κB）途径发挥抗炎作用。结果显示人脐静脉内皮细胞主要表达S1PR1，少量表达S1PR2和S1PR3，不表达S1PR4和S1PR5；提示ApoM-S1P可能主要与S1PR1结合；过表达ApoM（竞争性抑制白蛋白载运S1P）后具有显著的抗炎作用；ApoM可显著上调S1PR1及DHCR24的表达，并且显著抑制NF-κB及相关炎症因子的表达，表明ApoM可通过S1PR1途径上调DHCR24的表达，进而抑制NF-κB途径发挥抗炎作用；最后发现ApoM能显著增加小鼠脾脏组织中CD4+ T淋巴细胞的百分数，提高脾脏组织中CD4+/CD8+ T淋巴细胞的比值，抑制LPS介导的小鼠血清TNF-α的增加；并且能显著增加脾脏VE-cadherin的表达，表明ApoM可通过上调VE-cadherin的表达，增加CD4+ T淋巴细胞的储备而发挥抗炎作用。该成果对动脉粥样硬化预防及治疗的研究提供了新的方向和部分研究基础。