Virginia Research Day 2021

Graduate Student Research Biomedical

05 The Selective B Cell Lymphoma 6 (BCL6) Inhibitor Decreases Germinal Center (GC) Formation and Reduces Kidney Disease in Lupus Induced Mice

Ashton Shiraz 1,2 ; Eric Panther 3 ; Samuel Dickerson 3 ; Chandler Davis 2 ; Christopher Reilly 1,2,3 Corresponding author: aks2026@vt.edu

1 Biomedical and Veterinary Sciences, Virginia-Maryland College of Veterinary Medicine, Virginia Tech 2 Department of Cellular and Molecular Physiology, Via College of Osteopathic Medicine- Virginia Campus 3 Virginia Polytechnic Institute and State University, Virginia Tech

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the production of multiple autoantibodies and B cell hyperactivity. Perturbations of B cell maturation may permit generation, activation, differentiation, and clonal expansion of B cells that secrete pathogenic autoantibodies, which damage kidneys to cause nephritis. Maturation of antibody responses occurs within germinal centers (GCs). The transcriptional repressor B cell lymphoma 6 (BCL6) regulates a large transcriptional network required for the formation and maintenance of GC during the antibody-mediated response. GCs are the main sites in which B cells undergo both class-switch recombination and somatic hypermutation. Since BCL6 is critical for GC formation, we hypothesized that selective BCL6 inhibitor (BCL6i) would decrease GC formation and reduce kidney disease in the NZB×NZW F1 (NZB/W) female lupus mouse model.

NZB/W mice were treated with a selective BCL6 inhibitor at 30 mg/kg (LD) or 100 mg/kg (HD) body weight (BW) at 20 weeks-of-age for 6 weeks. 2mg/ kg BW Dexamethasone (Dex) and, Methyl Cellulose (MC) were administered daily as positive and negative controls, respectively. Treatment with both concentrations of the BCL6i significantly decreased spleen weight, development of proteinuria, and decreased anti-DNA titers. BCL6i significantly decreased GC formation in the spleen and reduced IgG and C3 in the kidney of both LD and HD treated mice. At the 100 mg/kg BW treated mice, the total number of B cells as well as B cell subsets (immature, mature, and class switched) were decreased in the spleens of NZB/W mice. Additionally, mice treat with Dex had significant decreases in spleen weight, development of proteinuria and formation of GC, and, interestingly, an increase in the number of immature B cells. However, there were no changes in the levels

of IgG and C3 in Dex treated mice. The mature B-cell numbers were significantly decreased in Dex treated mice as compared to the MC, LD, and HD treated mice. Furthermore, the HD and Dex treated mice had a reduced number of class switch B-cells compared to other groups. Moreover, the number of immature B-cells decreased in both LD and HD treated mice as compared to the MC treated mice. There was also a significant increase in the number of CD23 positive B-cells in LD, HD, and Dex treated mice as compared to the MC treated mice. Finally, there were no significant differences in either the total number of bone marrow B-cells nor the follicular B-cells in any treatment groups. Taken together these results provide a strong rationale for BCL6 inhibition as therapeutic approach for lupus nephritis.

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