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Objective: Disruption of B cell homeostasis and subsequent dominance of effector B cell subsets are critical for the development of systemic lupus erythematosus (SLE). Revealing the key intrinsic regulators involved in the homeostatic control of B cells has important therapeutic value for SLE. This study was undertaken to determine the regulatory role of the transcription factor Pbx1 in B cell homeostasis and lupus pathogenesis. Methods: We constructed mice with B cell–specific deletion of Pbx1. T cell–dependent and T cell–independent humoral responses were induced by intraperitoneal injection of nitrophenyl‐containing hapten (NP) conjugated to keyhole limpet hemocyanin or NP‐Ficoll. The regulatory effects of Pbx1 on autoimmunity were observed in a Bm12‐induced lupus murine model. We investigated mechanisms of Pbx1 using RNA sequencing, the cleavage under targets and tagmentation assay, and chromatin immunoprecipitation–quantitative polymerase chain reaction assay. We transduced B cells from SLE patients with plasmids that overexpressed PBX1 to explore the in vitro therapeutic efficacy of PBX1. Results: Pbx1 was specifically down‐regulated in autoimmune B cells and negatively correlated with disease activity. The deficiency of Pbx1 in B cells resulted in excessive humoral responses following immunization. In the Bm12‐induced lupus model, mice with B cell–specific Pbx1 deficiency displayed enhancements in germinal center responses, plasma cell differentiation, and autoantibody production. Pbx1‐deficient B cells had increased survival and proliferative advantages after activation. Pbx1 regulated genetic programs by directly targeting critical components of the proliferation and apoptosis pathways. In SLE patients, PBX1 expression was negatively correlated with effector B cell expansion; when PBX1 expression was enforced, the survival and proliferative capacity of SLE B cells were attenuated. Conclusion: Our study reveals the regulatory function and mechanism of Pbx1 in adjusting B cell homeostasis and highlights Pbx1 as a therapeutic target in SLE. [ABSTRACT FROM AUTHOR]

Human Phenotype Ontology (HPO)-based approaches have gained popularity in recent times as a tool for genomic diagnostics of rare diseases. However, these approaches do not make full use of the available information on disease and patient phenotypes. We present a new method called Phen2Disease, which utilizes the bidirectional maximum matching semantic similarity between two phenotype sets of patients and diseases to prioritize diseases and genes. Our comprehensive experiments have been conducted on six real data cohorts with 2051 cases (Cohort 1, n  = 384; Cohort 2, n  = 281; Cohort 3, n  = 185; Cohort 4, n  = 784; Cohort 5, n  = 208; and Cohort 6, n  = 209) and two simulated data cohorts with 1000 cases. The results of the experiments showed that Phen2Disease outperforms the three state-of-the-art methods when only phenotype information and HPO knowledge base are used, particularly in cohorts with fewer average numbers of HPO terms. We also observed that patients with higher information content scores have more specific information, leading to more accurate predictions. Moreover, Phen2Disease provides high interpretability with ranked diseases and patient HPO terms presented. Our method provides a novel approach to utilizing phenotype data for genomic diagnostics of rare diseases, with potential for clinical impact. Phen2Disease is freely available on GitHub at https://github.com/ZhuLab-Fudan/Phen2Disease. [ABSTRACT FROM AUTHOR]

Objective: Emerging evidence indicates that a distinct CD11c+T‐bet+ B cell subset, termed age/autoimmune‐associated B cells (ABCs), is the major pathogenic autoantibody producer in lupus. Human lupus is associated with significant metabolic alterations, but how ABCs orchestrate their typical transcription factors and metabolic programs to meet specific functional requirements is unclear. We undertook this study to characterize the metabolism of ABCs and to identify the regulators of their metabolic pathways in an effort to develop new therapies for ABC‐mediated autoimmunity. Methods: We developed a T‐bet–tdTomato reporter mouse strain to trace live T‐bet+ B cells and adoptively transferred CD4+ T cells from bm12 mice to induce lupus. We next sorted CD11c+tdTomato+ B cells and conducted RNA sequencing and an extracellular flux assay. A metabolic restriction to constrain ABC formation was tested in human and mouse B cells. We used a bm12‐induced lupus mouse model to conduct the metabolic intervention. Results: ABCs exhibited a hypermetabolic state with enhanced glycolytic capacity. The increased glycolytic rate in ABCs was promoted by interferon‐γ (IFNγ) signaling. T‐bet, a downstream transcription factor of IFNγ, regulated the gene program of the glycolysis pathway in ABCs by repressing the expression of Bcl6. Functionally, glycolysis restriction could impair ABC formation. The engagement of glycolysis promoted survival and terminal differentiation of antibody‐secreting cells. Administration of a glycolysis inhibitor ameliorated ABC accumulation and autoantibody production in the lupus‐induced bm12 mouse model. Conclusion: T‐bet can couple immune signals and metabolic programming to establish pathogenic ABC formation and functional capacities. Modulation of ABCs favored a metabolic program that could be a novel therapeutic approach for lupus. [ABSTRACT FROM AUTHOR]

Objective: Increased Toll‐like receptor 7 (TLR‐7) signaling leading to the production of type I interferon (IFN) is an important contributor to human systemic lupus erythematosus (SLE). Protein kinase C and casein kinase substrate in neurons 1 (PACSIN1), a molecule that regulates synaptic vesicle recycling, has been linked to TLR‐7/TLR‐9–mediated type I IFN production in humans and mice, but the underlying mechanism is unknown. We undertook this study to explore the pathogenicity and underlying mechanism of a de novo PACSIN1 missense variant identified in a child with SLE. Methods: PACSIN1 Q59K de novo and null variants were introduced into a human plasmacytoid dendritic cell line and into mice using CRISPR/Cas9 editing. The effects of the variants on TLR‐7/TLR‐9 signaling in human and mouse cells, as well as PACSIN1 messenger RNA and IFN signature in SLE patients, were assessed using real‐time polymerase chain reaction and flow cytometry. Mechanisms were investigated using luciferase reporter assays, RNA interference, coimmunoprecipitation, and immunofluorescence. Results: We established that PACSIN1 forms a trimolecular complex with tumor necrosis factor receptor–associated factor 4 (TRAF4) and TRAF6 that is important for the regulation of type I IFN. The Q59K mutation in PACSIN1 augments binding to neural Wiskott‐Aldrich syndrome protein while it decreases binding to TRAF4, leading to unrestrained TRAF6‐mediated activation of type I IFN. Intriguingly, PACSIN1 Q59K increased TLR‐7 but not TLR‐9 signaling in human cells, leading to elevated expression of IFNβ and IFN‐inducible genes. Untreated SLE patients had high PACSIN1 expression in peripheral blood cells that correlated positively with IFN‐related genes. Introduction of the Pacsin1 Q59K mutation into mice caused increased surface TLR‐7 and TRAIL expression in B cells. Conclusion: PACSIN1 Q59K increases IFNβ activity through the impairment of TRAF4‐mediated inhibition of TLR‐7 signaling, possibly contributing to SLE risk. [ABSTRACT FROM AUTHOR]