膜分子CMTM7调控B-1a细胞的机制及其在细菌感染中的功能研究

CMTM7 is a member of CMTM family, which was firstly reported by our lab in 2003. With support of the Chinese Natural Science foundation, we found that CMTM7 was a novel regulator of Rab5, a protein known to be required for the traffic and signal transduction of EGFR and other receptors. B-1a cells in peritoneal cavity and serum IgM decreased significantly in Cmtm7 knockout mice, while there was no obvious change in B-1b and B-2 cells. B-1a cells and B-2 cells have different phenotypes and functions, and develop from individual progenitors, but they have similar differentiation stages and BCR signal is essential for their development, survival and function. CMTM7 is highly expressed in B cells, why knockout of Cmtm7 only influences B-1a cells, but not B-2 cells? What is the mechanism by which CMTM7 regulates B-1a cells? To answer these questions, we will investigate the influence of CMTM7 on the development, survival and antibody production of B-1a cells; explore the function of CMTM7 during BCR endocytosis, traffic and signaling pathway; clarify its effects on the first line of defense against bacteria with B cell-specific Cmtm7 knockout mice. The implementation of this project will be helpful to understand the mechanism of B-1a cell development and function.

CMTM是本室2003年首次报道的基因家族，CMTM7是其成员之一。在已结题国自然基金资助下，我们发现CMTM7是一个新的Rab5调节分子，参与EGFR等膜受体的转运和信号转导；在Cmtm7全身敲除和B细胞特异性敲除小鼠中，腹腔B-1a细胞比例和绝对数显著下降，血清总IgM明显减少，B-1b和B-2细胞没有明显变化。B-1a和B-2细胞表型、功能各异，起始于不同前体细胞，但二者分化过程相似，BCR信号对其发育、生存和功能至关重要。CMTM7在B细胞中高表达，敲除Cmtm7为什么选择性影响B-1a？其通过什么机制调控B-1a细胞？为回答上述问题，本项目将利用Cmtm7的B细胞特异性敲除小鼠，研究CMTM7对B-1a细胞发育、生存、抗体产生的作用；探索其在BCR内化、转运、信号转导中的功能；明确CMTM7在细菌感染中的效应。其顺利实施，将有助于深入了解B-1a细胞的发育、功能调控机制。

CMTM是课题申请人于2003年在国际上首次报道的新基因家族，在人类，该家族包括9个基因，即CKLF和CMTM1-8。CMTM7是其成员之一，前期结果证明CMTM7对于B-1a细胞的发育及功能至关重要，然而其调控机制尚不明确。.本项目通过构建Cmtm7敲除小鼠，发现敲除Cmtm7后，小鼠各组织B-1a细胞明显减少，进一步通过胎肝移植模型、骨髓移植模型和B细胞特异性敲除Cmtm7的条件敲除小鼠（Cmtm7f/f;CD19-Cre+）证明Cmtm7缺失后B-1a细胞减少是由B细胞内在因素导致，使B-1a细胞发育阻滞于B-1a特异性过渡期细胞（TrB-1a）。利用Cmtm7f/f;CD19-Cre+小鼠构建盲肠结扎穿孔模型，观察到Cmtm7f/f;CD19-Cre+小鼠表现出更高的死亡率，并伴随更严重的炎症反应，Cmtm7的敲除导致B-1a细胞的活化、增殖以及向浆细胞分化受到抑制，针对TD和TI抗原的早期IgM反应减弱，IL-10产生减少，以上结果说明B细胞缺失Cmtm7使小鼠抗感染能力降低。.BCR信号和TLR信号是介导B-1a细胞向浆细胞分化的重要信号，因此我们对CMTM7调控B-1a细胞发育及功能的分子机制进行了深入研究。敲除Cmtm7并不影响BCR信号转导，但能下调p38磷酸化水平，抑制TLR-MyD88-NF-κB信号通路，导致B-1a细胞无法正常调控浆细胞分化相关转录因子的表达。.综上所述，我们证明了CMTM7是调控B-1a细胞发育及功能的关键因子，可能成为急性感染的治疗或预后分析的新靶标，其相关研究发表于International Immunology（2019.10.16, 31(11): 715~728）、European Journal of Immunology（2020, 50(6): 809-821）和Cellular Immunology（2020, 352: 0-104100）。