Theodore, Keith

Abstract Iron-sulfur (Fe-S) clusters are cofactors essential for the activity of numerous enzymes including DNA polymerases, helicases, and glycosylases. They are synthesized in the mitochondria as Fe-S intermediates and are exported to the cytoplasm for maturation by the mitochondrial transporter ABCB7. Here, we demonstrate that ABCB7 is required for bone marrow B cell development, proliferation, and class switch recombination, but is dispensable for peripheral B cell homeostasis in mice. Conditional deletion of ABCB7 using Mb1-cre resulted in a severe block in bone marrow B cell development at the pro-B cell stage. The loss of ABCB7 did not alter expression of transcription factors required for B cell specification or commitment. While increased intracellular iron was observed in ABCB7-deficient pro-B cells, this did not lead to increased cellular or mitochondrial reactive oxygen species, ferroptosis, or apoptosis. Interestingly, loss of ABCB7 led to replication-induced DNA damage in pro-B cells, independent of VDJ recombination, and these cells had evidence of slowed DNA replication. Interestingly, ABCB7 appeared to be dispensable for splenic B cell homeostasis, as CD23-cre ABCB7 cKO mice had normal splenic B cell populations. However, stimulated ABCB7-deficient splenic B cells from CD23-cre ABCB7 cKO mice had a striking loss of proliferation and a defect in class switching. Thus, ABCB7 is essential for early B cell development, proliferation, and class switch recombination. Supported by 1R21 AI157328-01 to V.S.S., T32AI007425 to M.J.L.

Abstract Inflammatory bowel disorders (IBD) including ulcerative colitis (UC) and Crohn’s disease (CD) affect between 1–3 million people in the United States with prevalence on the rise. Patients present with symptoms including diarrhea, abdominal cramps, and weight loss. Many factors are implicated in pathogenesis, including host immune response. Identification of molecules that regulate IBD is critical in understanding pathogenesis. ST8Sia6 is a sialic acid transferase that adds terminal a2,8 disialic acids to cell surface glycoproteins, and we have found that ST8Sia6 knockout (KO) mice exhibit increased spontaneous small bowel lamina propria CD4 TH1 polarization, increased inflammatory cytokine production, and decreased IgA class switching of Peyer’s patch B cells, indicative of inflammation. Additionally, adult ST8Sia6 KO mice have shortened small bowels, likely due to baseline inflammation. These mice do not exhibit obvious baseline symptoms, but ST8Sia6 KO mice exhibit increased weight loss and decreased survival when challenged with dextran sodium sulfate (DSS)-induced colitis, which was also enhanced when co-housed with wildtype (WT) mice and after antibiotic treatment. These DSS-challenged ST8Sia6 KO mice exhibit increased histological damage and immune infiltration of the gut as compared to WT controls. The accelerated DSS-colitis is also observed when ST8Sia6-deficient bone marrow is transplanted into WT recipients, indicating that the effect is mediated specifically by immune cells. This data demonstrates a role for ST8Sia6 in regulating the host immune response to inflammatory bowel disorders, and further elucidating this role will aid in developing a mechanistic understanding of IBD pathogenesis. Supported by grants from NIH R01 CA243545