Recent thymic emigrants (RTEs) are newly generated T cells that need to undergo post-thymic maturation to gain functional competency and enter the long-lived naïve T cell pool. The mechanism of T cell maturation remains incompletely understood. Previously, we demonstrated that the transcriptional repressor NKAP is required for T cell maturation. As NKAP associates with histone deacetylase 3 (HDAC3), we examined whether HDAC3 is also required for T cell maturation. While thymic populations are similar in CD4-cre HDAC3 conditional knockout (cKO) mice compared to wild-type (WT) mice, however, the peripheral numbers of CD4+ and CD8+ T cells are dramatically decreased. In the periphery, the majority of HDAC3-deficient naïve T cells are RTEs, indicating a block in T cell maturation. CD55 upregulation during T cell maturation is substantially decreased in HDAC3-deficient T cells. Consistent with a block in functional maturation, HDAC3-deficient peripheral T cells have a defect in TNF licensing after TCR/CD28 stimulation. CD4-cre HDAC3 cKO mice do not have a defect in intrathymic migration, thymic egress, T cell survival or homeostasis. In the periphery, similar to immature NKAP-deficient peripheral T cells, HDAC3-deficient peripheral T cells were bound by IgM and complement proteins, leading to the elimination of these cells. In addition, HDAC3-deficient T cells display decreases in the sialic acid modifications on the cell surface that recruit natural IgM to initiate the classical complement pathway. Therefore, HDAC3 is required for T cell maturation.

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To generate functional peripheral T cells, proper gene regulation during T cell development is critical. Here, we found that histone deacetylase 3 (HDAC3) is required for T cell development. T cell development in CD2-icre HDAC3 conditional knockout mice (HDAC3-cKO) was blocked at positive selection, resulting in few CD4 and CD8 T cells, and could not be rescued by a TCR-transgene. These SP thymocytes failed to upregulate Bcl-2, leading to increased apoptosis. HDAC3-cKO mice failed to downregulate RORγt during positive selection, and phenocopied the block in positive selection in RORγt-transgenic mice. In the absence of HDAC3, the RORC promoter was hyperacetylated. In the periphery, the few CD4 T cells present were skewed towards RORγt+ IL-17-producing Th17 cells, leading to inflammatory bowel disease. Positive selection of CD8SP thymocytes was restored in RORγt-KO Bcl-xl-transgenic HDAC3-cKO mice, demonstrating that HDAC3 is required at positive selection to down-regulate RORγt.

BackgroundAutosomal recessive polycystic kidney disease (ARPKD) and autosomal dominant polycystic kidney disease (ADPKD) are genetically distinct, with ADPKD usually caused by the genes PKD1 or PKD2 (encoding polycystin-1 and polycystin-2, respectively) and ARPKD caused by PKHD1 (encoding fibrocystin/polyductin [FPC]). Primary cilia have been considered central to PKD pathogenesis due to protein localization and common cystic phenotypes in syndromic ciliopathies, but their relevance is questioned in the simple PKDs. ARPKD’s mild phenotype in murine models versus in humans has hampered investigating its pathogenesis.MethodsTo study the interaction between Pkhd1 and Pkd1, including dosage effects on the phenotype, we generated digenic mouse and rat models and characterized and compared digenic, monogenic, and wild-type phenotypes.ResultsThe genetic interaction was synergistic in both species, with digenic animals exhibiting phenotypes of rapidly progressive PKD and early lethality resembling classic ARPKD. Genetic interaction between Pkhd1 and Pkd1 depended on dosage in the digenic murine models, with no significant enhancement of the monogenic phenotype until a threshold of reduced expression at the second locus was breached. Pkhd1 loss did not alter expression, maturation, or localization of the ADPKD polycystin proteins, with no interaction detected between the ARPKD FPC protein and polycystins. RNA-seq analysis in the digenic and monogenic mouse models highlighted the ciliary compartment as a common dysregulated target, with enhanced ciliary expression and length changes in the digenic models.ConclusionsThese data indicate that FPC and the polycystins work independently, with separate disease-causing thresholds; however, a combined protein threshold triggers the synergistic, cystogenic response because of enhanced dysregulation of primary cilia. These insights into pathogenesis highlight possible common therapeutic targets.