Investigating the novel role of sarcospan in modulating immune function in mice
Authors: Mohammadipoor Nazanin , Valera Isela , Rahimi Kahmini Aida , Patel Sonu , Florence Jaelynn , Olateju Bolade , King Khari 
Published: May 2024

Objective: The tetraspanin-like protein sarcospan (SSPN) has been shown to have an important in stabilizing muscle cell membranes and promoting cell adhesion. SSPN has documented expression in immune cells with the highest level of expression in B cells. Examination of SSPN-deficient (SSPN−/−) mice revealed alterations in important immune pathways, which remain uncharacterized. This led us to hypothesize that SSPN may play a role in modulating immune cell development and/or function. Methods: Flow cytometry was used to perform immunophenotyping of spleens obtained from SSPN−/− and WT mice. Cytokine analysis was performed using Luminex to assess cytokines that serve as important signals for immune cell maturation. Hematopoietic stem cells were isolated from red bone marrow and stimulated with phorbol myristate acetate (PMA), a mitogen and polyclonal activator of B cells, to assess whether SSPN deficiency affected their proliferative capacity. To determine whether SSPN plays a role in immunoglobulin isotype switching — antibody isotyping was performed. The presence of immune (antibody-antigen) complexes was investigated in kidney sections obtained from WT and SSPN−/− mice and visualized using biotinylated IgG and IgM antibodies. Autoantigen screening was also performed to assess whether SSPN−/− mice generated abnormal levels of autoantibodies that could be responsible for circulating antibody-antigen complexes. Results: The presence of SSPN on major immune cell types was confirmed using flow cytometry. In addition, flow cytometry analysis showed insignificant baseline differences in the percentage of B cells, T cells, plasmacytoid dendritic cells in SSPN−/− compared to WT spleens. One difference was noted in SSPN−/− females with increased counts of dendritic cells. Spleens in female SSPN−/− mice were found to be slightly larger compared to WT. Levels of B-cell activating factor (BAFF) and B-cell maturation antigen (BCMA) were elevated in SSPN−/− mice, therefore it is expected that SSPN−/− B cells received appropriate signals. Overall B cell proliferation was assessed by CD19+ and appeared unaffected by the absence of SSPN. Subtle increases in IgG1 and IgG2b were detected in SSPN−/− mice, however immunoglobulin isotypes were within normal ranges. SSPN−/− mice were also assessed for signs of dysregulated immune reactivity, evidenced by the presence of immune (antibody-antigen) complexes within filtration units of the kidney. Overall, male SSPN−/− mice were found to have a larger subset of increased IgG autoantibodies compared to male WT mice while female SSPN−/− mice exhibited a larger subset of increased IgM autoantibodies compared to female WT mice. Conclusions: This study examines potentially important functions of SSPN in the immune system. Overall, deletion of SSPN has not been found to affect maturation of major immune cell classes. However, SSPN does appear to influence formation of antigen-antibody complexes in mice, which may contribute to kidney dysfunction. These studies are ongoing and directed toward understanding the role SSPN plays in immune function. FSU Funding, Florida Department of Health, James and Esther King Biomedical Research Program #21K12. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.