Germinal center (GC) response ensures the generation of diverse and high-affinity antibodies during the T cell-dependent (TD) immune response. This process is controlled by coordinated transcriptional and posttranscriptional gene regulatory mechanisms. Minor intron splicing is known to be involved in posttranscriptional regulation of gene expression. RNA-binding region (RNP1, RRM) containing 3 (RNPC3) is a minor spliceosome component involved in stabilizing the U11/U12 di-snRNP complex, which is essential for minor intron splicing. However, it remains unclear if RNPC3 and RNPC3-related gene regulatory mechanisms are important for the TD immune response. In this study, we conditionally ablated RNPC3 in activated B cells and showed that the mutant mice had defective antibody generation due to impaired GC B cell response. We demonstrate that RNPC3 deficiency inhibits the proliferation and promotes the apoptosis of activated B cells. Mechanistically, we show that RNPC3 regulates the development of GC B cells in a minor spliceosome-dependent manner by controlling the removal of minor introns from minor intron-containing genes associated with cell proliferation and apoptosis. Our study thus uncovers a previously unappreciated role for RNPC3 in regulating GC B cell response.
© 2025 Wiley‐VCH GmbH.

Myocardial infarction (MI) results in aberrant cardiac metabolism, but no therapeutics have been designed to target cardiac metabolism to enhance heart repair. We engineer a humanized monoclonal antibody against the ectonucleotidase ENPP1 (hENPP1mAb) that targets metabolic crosstalk in the infarcted heart. In mice expressing human ENPP1, systemic administration of hENPP1mAb metabolically reprograms myocytes and non-myocytes and leads to a significant rescue of post-MI heart dysfunction. Using metabolomics, single-nuclear transcriptomics, and cellular respiration studies, we show that the administration of the hENPP1mAb induces organ-wide metabolic and transcriptional reprogramming of the heart that enhances myocyte cellular respiration and decreases cell death and fibrosis in the infarcted heart. Biodistribution and safety studies showed specific organ-wide distribution with the antibody being well tolerated. In humanized animals, with drug clearance kinetics similar to humans, we demonstrate that a single "shot" of the hENPP1mAb after MI is sufficient to rescue cardiac dysfunction.
Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.

Summary The transition from IgM to affinity-matured IgG antibodies is vital for effective humoral immunity. This is facilitated by germinal centers (GCs) through affinity maturation and preferential accumulation of IgG + B cells over IgM + B cells. However, it is not known whether the positive selection of the different immunoglobulin isotypes within GCs varies in its dependency on specific transcriptional mechanisms. Here, we identified IgG1 + GC B cell transcription factor dependency using CRISPR-Cas9 and conditional mouse genetics. We found that MIZ1 was specifically required for IgG1 + GC B cell survival during positive selection, whereas IgM + GC B cells were largely independent. Mechanistically, MIZ1 induced TMBIM4, an ancestral anti-apoptotic protein that regulated inositol trisphosphate receptor mediated Ca 2+ mobilization downstream of IgG1. The MIZ1-TMBIM4 axis prevented mitochondrial dysfunction-induced IgG1 + GC cell death caused by excessive Ca 2+ accumulation. This study uncovers a unique immunoglobulin isotype-specific dependency, on a hitherto unidentified mechanism in GC positive selection.

Naïve B cells become activated and differentiate into antibody-secreting plasma cells (PCs) when encountering antigens. Here, we reveal that the WW domain-containing adapter protein with coiled-coil (Wac), which is important for histone H2B ubiquitination (ubH2B), is essential for PC differentiation. We demonstrate that B cell-specific Wac knockout mice have severely compromised T cell-dependent and -independent antibody responses. PC differentiation is drastically compromised despite undisturbed germinal center B cell response in the mutant mice. We also observe a significant reduction in global ubH2B in Wac-deficient B cells, which is correlated with downregulated expression of some genes critical for cell metabolism. Thus, our findings demonstrate an essential role of Wac-mediated ubH2B in PC differentiation and shed light on the epigenetic mechanisms underlying this process.
© 2023 Federation of European Biochemical Societies.

Plasma cells (PC) are antibody-secreting cells and terminal effectors in humoral responses. PCs differentiate directly from activated B cells in response to T cell-independent (TI) antigens or from germinal center B (GCB) cells in T cell-dependent (TD) antigen-induced humoral responses, both of which pathways are essentially regulated by the transcription factor BLIMP1. The p38 mitogen-activated protein kinase isoforms have already been implicated in B cell development, but the precise role of p38α in B cell differentiation is still largely unknown. Here we show that PC differentiation and antibody responses are severely impaired in mice with B cell-specific deletion of p38α, while B cell development and the GCB cell response are spared. By utilizing a Blimp1 reporter mouse model, we show that p38α-deficiency results in decreased BLIMP1 expression. p38α-driven BLIMP1 up-regulation is required for both TI and TD PCs differentiation. By combining CRISPR/Cas9 screening and other approaches, we identify TCF3, TCF4 and IRF4 as downstream effectors of p38α to control PC differentiation via Blimp1 transcription. This study thus identifies an important signalling pathway underpinning PC differentiation upstream of BLIMP1, and points to a highly specialized and non-redundant role for p38α among p38 isoforms.
© 2022. The Author(s).