The oncoprotein TBX3 is controlling severity in experimental arthritis

Abstract Background Development of autoimmune diseases is the result of a complex interplay between hereditary and environmental factors, with multiple genes contributing to the pathogenesis in human disease and in experimental models for disease. The T-box protein 3 is a transcriptional repressor essential during early embryonic development, in the formation of bone and additional organ systems, and in tumorigenesis. Methods With the aim to find novel genes important for autoimmune inflammation, we have performed genetic studies of collagen-induced arthritis (CIA), a mouse experimental model for rheumatoid arthritis. Results We showed that a small genetic fragment on mouse chromosome 5, including Tbx3 and three additional protein-coding genes, is linked to severe arthritis and high titers of anti-collagen antibodies. Gene expression studies have revealed differential expression of Tbx3 in B cells, where low expression was accompanied by a higher B cell response upon B cell receptor stimulation in vitro. Furthermore, we showed that serum TBX3 levels rise concomitantly with increasing severity of CIA. Conclusions From these results, we suggest that TBX3 is a novel factor important for the regulation of gene transcription in the immune system and that genetic polymorphisms, resulting in lower expression of Tbx3, are contributing to a more severe form of CIA and high titers of autoantibodies. We also propose TBX3 as a putative diagnostic biomarker for rheumatoid arthritis

A transcriptional regulator controlling severity in experimental arthritis

Background: Susceptibility to Rheumatoid Arthritis (RA) is dependent on complex interactions among genetic and environmental factors. Protein candidates and their role in pathways leading to chronic inflammation of the joints, in addition to their potential as drug targets, can be revealed with the help of experimental models for disease (1). From the results of functional genetic studies, we have recently shown that the T-box gene, TBX3, is a candidate gene in Collagen Induced Arthritis (CIA), an experimental model for RA (2). TBX3 encodes a transcriptional regulator involved in differentiation of several organs, including bone, during embryonic development. It has, in addition, been demonstrated important in oncogenesis (3). Our studies suggest that TBX3 has a role in B-cell activation and is important for the severity of disease in the CIA model (2). Objectives: The objective of this project is to understand the role for the transcriptional regulator TBX3 in development of RA. Methods: Bioinformatics based comparative studies of mouse and human alleles in the regulatory region of TBX3. CRISPR/Cas9-introduced deletions and base modifications in human B-cell lines. Activation of genetically modified B-cells in vitro, followed by analyses of proliferative response and antibody production. Results: Studies of CIA development in mice with single nucleotide polymorphisms (SNPs) in the regulatory region of Tbx3 revealed a significant difference in severity of arthritis. In line with this, the anti-collagen type II antibody titers were shown substantially higher in mice with more severe arthritis, even before onset of disease. In addition, preliminary data shows that the proliferative response to Type II collagen upon re-challenge of lymph node cells in vitro is higher in these mice, suggesting a more active response to the disease-inducing antigen. Because the TBX3 gene is conserved between mouse and human, we are investigating whether similar genetic variations are found in the regulatory region of the human TBX3 gene and whether the putative genetic variation would lead to a distinct B-cell phenotype upon activation in vitro. Conclusion: We suggest that the oncoprotein TBX3 is a novel candidate contributing to disease severity in experimental arthritis. Investigations of genetic variation in the TBX3 gene and its role in the activation of human B-cells will reveal whether this protein is a candidate for influencing also development of RA

Analysis of polymorphisms in the mediator complex subunit 13-like (Med13L) gene in the context of immune function and development of experimental arthritis

The Mediator complex subunit 13-like (MED13L) protein is part of the multi-protein mediator complex and plays an important role in gene transcription. Polymorphisms in the MED13L gene have been linked to congenital heart anomalies and intellectual disabilities. Despite recent evidence of indirect links of MED13L to cytokine release and inflammation, impact of genetic variations in MED13L on immune cells remains unexplored. The B10.RIII and RIIIS/J mouse strains vary in susceptibility to induced experimental autoimmune disease models. From sequencing data of the two mouse strains, we identified six polymorphisms in the coding regions of Med13l. By using congenic mice, we studied the effect of these polymorphisms on immune cell development and function along with susceptibility to collagen-induced arthritis, an animal model for Rheumatoid Arthritis (RA). Combining in vivo disease data, in vitro functional data, and computational analysis of the reported non-synonymous polymorphisms, we report that genetic polymorphisms in Med13l do not affect the immune phenotype in these mice and are predicted to be non-disease associated. © The Author(s) 2018This work was supported by The Danish Rheumatism Association, The AP Møller Research grant for Medical Science, and The Oticon foundation.</p