Disturbed B cell homeostasis of B cells in SLE: Delineation of intrinsic signaling abnormalities

在系统性红斑狼疮（SLE）中发现了许多B细胞稳态的紊乱（浆母细胞增加和记忆B细胞异常），最初归因于B细胞过度活跃。GWAS数据提供了进一步的支持，其中SLE风险基因与BCR信号传导相关（林恩、BLK、BANK 1、PTPN 22等）。与此形成鲜明对比的是，我们的小组发现了异常的BCR信号，特别是在最近被其他人证实的SLE患者的记忆B细胞中。本研究发现蛋白酪氨酸激酶（PTK）磷酸化水平降低，即脾酪氨酸激酶Syk与蛋白丝氨酸激酶Akt参与B细胞的存活，这种失衡与蛋白酪氨酸磷酸酶（PTP）活性增强有关，但尚不清楚这一发现是否是SLE B细胞特有的，还是反映了受调节的激活后或静止记忆B细胞的特征。我们的工作假设是SLE B细胞具有BCR信号传导的内在异常，包括异常的PTK和PTP（即SHP-1和PTEN）活性，其通过Akt依赖性途径与受损的存活调节相互关联，Akt依赖性途径是维持自身反应性记忆B细胞的机制。另外，外在因素，如细胞因子（I型干扰素）是导致这些功能的变化。该项目将解决是否B细胞耐受性在SLE患者的BCR信号通路的遗传预定义的风险分子或减少的BCR激活的SLE B细胞的基础上的信号通路的内在异常的干扰表示后激活状态。在这方面，该项目将描绘的机制，以控制激活和稳定状态的记忆B细胞在系统性红斑狼疮和其他炎症条件（感染，炎症性风湿性疾病）作为对照。本研究将使用对照和SLE B细胞对BCR相关PTK（例如Btk、PI 3 K、PLC-g2、BLNK）、细胞内Ca释放、PTPs（例如SHP-1、PTEN）以及BCR共受体（例如CD 22、CD 19、CD 45）进行全面的磷酸化分析。功能性BCR激活分析将与所研究的SLE患者的遗传BCR风险基因的直接比较相结合。重要的是，除了BCR以外，B细胞活化途径（CD 40或TLR）及其组合将解决减少的SLE B细胞活化是否限于BCR或更一般的特征。进一步研究前（I型干扰素、TNF、IL-1）和抗炎细胞因子（IL-10、IL-35）的能力及其对SLE和对照B细胞中BCR信号传导和Akt依赖性存活的影响。关于生存研究，该项目将分析上述条件下的p-Akt和下游转录因子（即Bim，Bcl-2，Foxo-1）的失衡。该项目将阐明参与B细胞活化和存活的内在因素在SLE中的作用，这些内在因素可能是自身免疫B细胞的分子机制，并将为新的治疗方法提供信息。

A number of disturbances in B cell homeostasis (increased plasmablasts and abnormal memory B cells) have been identified in systemic lupus erythematosus (SLE) and initially ascribed to B cell hyperactivity. Further support has been provided by GWAS data with SLE risk genes linked to BCR signaling (Lyn, BLK, BANK1, PTPN22 etc.). In striking contrast, our group found abnormal BCR signaling in particular in memory B cells from SLE patients confirmed recently by others. Here a diminished phosphorylation of protein tyrosine kinases (PTK), i.e. spleen tyrosine kinase Syk versus protein serine kinase Akt involved in survival of B cells was found. This dysbalance was related to enhanced protein tyrosine phosphatase (PTP) activity while it remains unknown if this finding is specific of SLE B cells or reflect a characteristic of regulated post-activation or quiescent memory B cells. Our working hypothesis is that SLE B cells have intrinsic abnormalities of BCR signaling including abnormal PTK and PTP (i.e. SHP-1 and PTEN) activity that are interconnected with impaired survival regulation by Akt dependent pathways as mechanisms to maintain autoreactive memory B cells. Alternatively, extrinsic factors such as cytokines (type I interferons) are causing these functional changes.The project will address whether B cell tolerance in SLE patients is disturbed by instrinsic abnormalities of BCR signaling pathways based on genetically predefined risk molecules OR diminished BCR activation of SLE B cells represent a post-activation status. In this regard, the project will delineate the mechanisms to control the activatory and steady state of memory B cells in SLE and other inflammatory conditions (infections, inflammatory rheumatic diseases) as controls. The study will undertake comprehensive phosphorylation analyses of BCR associated PTKs (e.g. Btk, PI3K, PLC-g2, BLNK), intracellular Ca release, PTPs (e.g. SHP-1, PTEN), as well as BCR co-receptors (e.g. CD22, CD19, CD45) using control and SLE B cells. Functional BCR activation analyses will be combined with direct comparison with genetic BCR risk genes of the SLE patients studied. Importantly, other than BCR B cell activation pathways (CD40 or TLRs) and combinations thereof will address if the diminished SLE B cell activation is restricted to BCR or a more general characteristic. Further the capacity of pro- (type I interferons, TNF, IL-1) and antiinflamatory cytokines (IL-10, IL-35) and their impact on BCR signaling and Akt dependent survival in SLE and control B cells will be studied. With regard to survival studies, the project will analyze p-Akt under the conditions mentioned above and the downstream dysbalances of transcription factors (i.e. Bim, Bcl-2, Foxo-1). The project will delineate the role of intrinsic factors involved in B cell activation and survival in SLE which candidate as molecular mechanisms of autoimmune B cells and will inform about new therapeutic approaches.