Regulation of plasma cell homeostasis and antibody secretion through modulation of autophagy and endoplasmic reticulum stress by Trk-fused-gene (TFG)

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Antibodies (Ab) are secreted by plasma blasts and plasma cells that are generated in secondary lymphatic organs. Endoplasmic reticulum (ER) quality control and autophagy are essential for plasma cell differentiation and maintenance, Ab assembly and secretion. We have previously demonstrated that TFG (Tropomyosin receptor kinase fused gene), a scaffold protein that is up-regulated in plasma cells, prevents ER stress and supports autophagy flux in CH12 B cells. Proteomic analyses of CH12 B cells suggest a role for TFG in the regulation of intracellular transport, mitochondrial metabolism and JCHAIN abundance. We therefore hypothesize that TFG is important for plasma cell homeostasis in vivo. To test this hypothesis, we have generated mice carrying a floxed tfg allele (tfgfl/fl) that were crossed to mb1-Cre mice (TFG_BKO). Preliminary data from non-immunized tfgB mice show reduced plasma cell numbers. Serum IgM and IgG were reduced while IgA was not. However, there is no dimeric serum IgA in tfgB mice in steady state and IgA in feces is strongly diminished. In this project we will extend these preliminary data by eliciting T cell dependent and independent immunity and explore the IgM, IgG and IgA responses in TFG_BKO mice. Owing to the effects of TFG on JCHAIN and IgA we will specifically analyze B cell and plasma cell subsets in spleen, bone marrow as well as gut associated lymphoid tissue (GALT) in depth, along with resolution of GALT structure. To explore the TFG-dependent JCHAIN amount, JCHAIN will be quantified in plasma cell subsets of TFG_BKO mice in steady state, after immunization and in overexpression experiments. Furthermore, we will resolve Ig assembly and homeostasis. The effect of tfg-deletion on ER homeostasis, autophagy and metabolic signaling will be determined in primary activated B cells from tfgB mice. Elucidation of the role of TFG in B cells and plasma cells will help to understand the cell biology of plasma cells that is required to support antibody synthesis and humoral immunity.