Martinez, Kodi

Abstract Introduction Generation of T cells requires dynamic epigenetic alteration of histones to control gene expression at each developmental stage. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) facilitate addition or removal of various acyl groups from lysine residues, including acetylation (KAc) and crotonylation (KCr). The Class I deacetylases HDAC1, HDAC2, and HDAC3 have been shown to have 3 functions: adaptor, decrotonylase, and deacetylase activity. The relative importance of each function in T cells is not known. Genetic knockout of HDAC3 in mice using CD2icre results in a severe block in T cell development and spontaneous development of severe colitis. Our lab determined that HDAC3 is required for three different aspects of this process: CD4+CD8 + (DP) cell survival, positive selection, and CD4+ lineage commitment. We generated a novel mouse model with CD2icre-mediated deletion of endogenous HDAC3 and linked re-expression of HDAC3 “VRPP” mutant mice, which maintained adaptor function but lacks enzymatic activity. Strikingly, these mice do not develop spontaneous colitis even up to one year of age. Methods We used flow cytometry to assess T cell development and maturation in the thymus, spleen, mLN, and colon of HDAC3 cKO vs. HDAC3 VRPP mice. CUT&RUN was utilized to determine differences in H3K9Ac, H3K27Ac, and H3K18Cr across CD8 and CD4 lineage genes. H&E was utilized to assess structural changes in thymus and colon. Results Similar to CD2icre HDAC3 cKO mice, HDAC3 VRPP mice have a block in positive selection due to failure to down regulate RORγt and decreased DP cell survival due to increased expression of P2RX7. Although fewer T cells are produced in HDAC3 VRPP mice, CD4+ lineage commitment is restored, likely mitigating the development of spontaneous colitis. Conclusion Our results demonstrate that HDAC3 enzymatic activity is necessary for several aspects of T cell development, while HDAC3 adaptor function is sufficient to restore CD4+ lineage commitment. Funding Source NIAID RO1 AI150100, T32 AI170478 Topic Categories Hematopoiesis and Immune System Development (HEM)

Abstract Introduction The mitochondrial transporter ABCB7 is essential for exporting iron-sulfur (Fe-S) clusters, a function known to be critical in B cells. This study was conducted to investigate the broader, previously unknown roles of ABCB7 in regulating the overall lymphocyte development and homeostasis. Methods The study utilized conditional knockout (cKO) mouse models (CD2-iCre and Mb1-Cre) to create a specific deficiency of ABCB7 in certain immune populations. To determine if the observed effects were due to ABCB7 deletion in myeloid cells, two further models (CD2i-Cre ABCB7 cKO/C/EBPα and CD2-iCre LSL TMT ABCB7 cKO) were developed. The effects of blocking the cytokine G-CSF were also examined to understand its role in the observed myelopoiesis. Results ABCB7 deficiency was found to dramatically impair erythropoiesis while simultaneously driving emergency myelopoiesis. We confirmed that the myeloid expansion was not a direct result of ABCB7 loss in myeloid cells. A significant autoimmune phenotype also developed, characterized by hyperactivated T cells and a sharp decrease in peripheral regulatory T cells (Tregs). This Treg instability was linked to decreased thymic expression of key stability genes (like CD28 and PD-1) and reduced O-GlcNAc modification in T cells, a process crucial for maintaining Treg lineage. Conclusion The findings establish ABCB7 as a pivotal regulator of hematopoietic balance, linking mitochondrial function to both myeloid expansion and Treg stability. Funding Source T32AI170478 Topic Categories Hematopoiesis and Immune System Development (HEM)