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

• Applicant: Professor Dr. Thomas Dörner
• Subject Area: Rheumatology
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 390780177

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.

• DFG Programme: Research Grants