RNA binding protein Pcbp1 maintains mitochondria integrity to promote antibody production and germinal center response[scRNA-seq]
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ABSTRACT: B cells are crucial for adaptive immunity, orchestrating humoral responses by producing antibodies essential for pathogen clearance. Here, we show that Poly(rC) binding protein 1 (Pcbp1), a multifunctional RNA-binding protein, is a key regulator of antibody production in B cells. Pcbp1 deficiency in B cells resulted in significant reductions in IgM expression at steady state and compromised differentiation of germinal center B cells and production of high-affinity antibodies upon immunization. These effects result from compromised mitochondrial integrity in Pcbp1-deficient B cells, including compromised mitochondrial electron transport chain (ETC) complex I and increased mitochondrial ROS production. Blocking mitochondrial ROS production rescued IgM production and improved germinal center responses caused by Pcbp1 deficiency. Mechanistically, Pcbp1 promotes the expression of Fdxr, a critical component of ETC complex I, via binding to its 3’UTR. Overall, our findings reveal a novel role for Pcbp1 in regulating mitochondrial function, protein synthesis, and antibody responses in B cells, providing novel insight into post-transcriptional regulation and mitochondrial functions.
Project description:B cells are crucial for adaptive immunity, orchestrating humoral responses by producing antibodies essential for pathogen clearance. Here, we show that Poly(rC) binding protein 1 (Pcbp1), a multifunctional RNA-binding protein, is a key regulator of antibody production in B cells. Pcbp1 deficiency in B cells resulted in significant reductions in IgM expression at steady state and compromised differentiation of germinal center B cells and production of high-affinity antibodies upon immunization. These effects result from compromised mitochondrial integrity in Pcbp1-deficient B cells, including compromised mitochondrial electron transport chain (ETC) complex I and increased mitochondrial ROS production. Blocking mitochondrial ROS production rescued IgM production and improved germinal center responses caused by Pcbp1 deficiency. Mechanistically, Pcbp1 promotes the expression of Fdxr, a critical component of ETC complex I, via binding to its 3’UTR. Overall, our findings reveal a novel role for Pcbp1 in regulating mitochondrial function, protein synthesis, and antibody responses in B cells, providing novel insight into post-transcriptional regulation and mitochondrial functions.
Project description:Compared with naïve B cells, the B cell receptor (BCR) signal in germinal center (GC) B cells is attenuated; however, the significance of this signaling attenuation has not been well defined. Here, to investigate the role of attenuation of BCR signaling, we employed a Csk mutant mouse model in which Csk-deficiency in GC B cells resulted in augmentation of net BCR signaling with no apparent effect on antigen presentation. We found that Csk is required for GC maintenance and efficient antibody affinity maturation. Mechanistically, ROS-induced apoptosis was exacerbated concomitantly with mitochondrial dysfunction in Csk-deficient GC B cells. Hence, our data suggest that attenuation of the BCR signal restrains hyper-ROS production, thereby protecting GC B cells from apoptosis and contributing to efficient affinity maturation.
Project description:Memory B cells (MBCs) play a critical role in protection against homologous and variant pathogen challenge by either differentiating to plasma cells (PCs) or to germinal center (GCs) B cells. The human MBC compartment contains both switched IgG+ and unswitched IgM+ MBCs and at present the contribution of these MBC subpopulations to protection is incompletely understood. We discovered that intrinsic antigen-affinity thresholds for activation were at least 100-fold higher for IgG+ as compared to IgM+ MBCs and that IgG+ MBCs when challenged responded only to high affinity antigens and differentiated almost exclusively towards PC fates. In contrast, IgM+ MBCs were eliminated by apoptosis by high affinity antigens and responded to low affinity antigens by differentiating towards GC B cell fates. Thus, IgG+ and IgM+ MBCs may play distinct yet complementary roles in response to pathogen challenge to ensure the immediate production of high affinity antibodies to homologous and closely related challenges and the generation of variant-specific MBCs through GC reactions.
Project description:CD4 T cell help is critical for both the generation and maintenance of germinal centers, and T follicular helper (TFH) cells are the CD4 T cell subset required for this process. SAP (SH2D1A) expression in CD4 T cells is essential for germinal center development. However, SAP-deficient mice have only a moderate defect in TFH differentiation as defined by common TFH surface markers. CXCR5+ TFH cells are found within the germinal center as well as along the boundary regions of T/B cell zones. Here we show that germinal center associated T cells (GC TFH) can be identified by their co-expression of CXCR5 and the GL7 epitope, allowing for phenotypic and functional analysis of TFH and GC TFH populations. Here we show GC TFH are a functionally discrete subset of further polarized TFH cells, with enhanced B cell help capacity and a specialized ability to produce IL-4 in a TH2-independent manner. Strikingly, SAP-deficient mice have an absence of the GC TFH subset and SAP- TFH are defective in IL-4 and IL-21 production. We further demonstrate that SLAM (Slamf1, CD150), a surface receptor that utilizes SAP signaling, is specifically required for IL-4 production by GC TFH. GC TFH cells require IL-4 and IL-21 production for optimal help to B cells. These data illustrate complexities of SAP-dependent SLAM family receptor signaling, revealing a prominent role for SLAM receptor ligation in IL-4 production by germinal center CD4 T cells but not in TFH and GC TFH differentiation. Analysis of in vivo polyclonal GC Tfh vs Tfh vs Non-Tfh eight days after LCMV viral infection. Analysis of in vivo follicular helper CD4 T cells (CXCR5high GL7low), versus germinal center follicular helper CD4 T cells (CXCR5hi GL7hi), versus non-follicular helper CD4 T cells (CXCR5low) eight days after viral infection.
Project description:The NLRP3 inflammasome is linked to sterile and pathogen-dependent inflammation, and its dysregulation underlies many chronic diseases. Mitochondria have been implicated as regulators of NLRP3 inflammasome through multiple mechanisms including generation of mitochondrial ROS. Here we report that mitochondrial electron transport chain (ETC) complexes I, II, III and V inhibitors all prevent NLRP3 inflammasome activation. Ectopic expression of Saccharomyces cerevisiae NADH dehydrogenase (NDI1) or Ciona intestinalis alternative oxidase (AOX), which can respectively complement the functional loss of mitochondrial complex I or III, without generation of ROS, rescued NLRP3 inflammasome activation in the absence of endogenous mitochondrial complex I or complex III function. Metabolomics revealed phosphocreatine (PCr), which can sustain ATP levels, as a common metabolite that is diminished by mitochondrial ETC inhibitors. PCr depletion decreased ATP levels and NLRP3 inflammasome activation. Thus, mitochondrial ETC sustains NLRP3 inflammasome activation through PCr-dependent generation of ATP but a ROS independent mechanism.
Project description:The Germinal center is a dynamic microenvironment wherein B cells expressing high affinity antibody variants produced by hypermutation are selected for clonal expansion by limiting numbers of T follicular helper cells. Although a great deal is known about the mechanisms that control B cell selection in the germinal center, far less is understood about the clonal behavior of the T follicular helper cells that regulate this process. Here we report on the dynamic behavior of clones of T follicular helper cells during the germinal center reaction. We find that like germinal center B cells, T follicular helper cells undergo antigen dependent selection during the germinal center reaction resulting in differential proliferative expansion and contraction. Increasing the amount of antigen presented in the germinal center leads to increased T follicular cell division. Competition between T follicular helper cell clones is mediated by T cell receptor affinity for peptide-MHC ligand. Higher affinity T cells expanding preferentially in the germinal center show increased expression of genes downstream of the T cell receptor, genes required for metabolic reprogramming, cell division and cytokine production. These dynamic changes lead to dramatic remodeling of the functional T follicular cell repertoire during the germinal center reaction.
Project description:Transcriptional profiling of Ramos germinal center B cells, comparing untreated cells to cells treated with etoposide, and untreated cells to cells treated with anti-IgM. Both treatments, engagement of the B-cell receptor with anti-IgM and induction of DNA double-strand breaks with etoposide, result in phosphorylation and cytoplasmic sequestration of CRTC2, and cause downregulation of known CRTC2 target gene TCL1. The goal of these experiments was to determine what other genes are downregulated by both of these CRTC2-inactivating treatments, and to compare this list to the list of genes whose promoters were occupied by CRTC2 in our ChIP-on-chip assay. Untreated samples vs. etoposide-treated samples, untreated samples vs. anti-IgM-treated samples. Each comparison was done in biological triplicate plus dye swap.
Project description:While reactive oxygen species (ROS) have long been known to drive aging and neurodegenera-tion, their persistent depletion below basal levels also disrupts organismal function. Cells counter-act loss of basal ROS via the reductive stress response, but the identity and biochemical activity of ROS sensed by this pathway remain unknown. Here, we show that the reductive stress E3 ligase CUL2FEM1B specifically acts at mitochondrial TOM complexes, where it is regulated by ROS that are produced as byproducts of complex III of the electron transport chain (ETC) during oxidative phosphorylation. By modulating localized CUL2FEM1B activity, ROS tune protein import into mitochondria and thereby control the abundance of the rate-limiting ETC complex IV. As complex III yields most ROS when the ETC outpaces metabolic demands or oxygen availability, our findings identify basal ROS as sentinels of mitochondrial activity that help cells adjust their ETC to fluctuating environments, as required for cell differentiation and survival.