A Study of T-Cell Activation RhoGTPase Activating Protein (TAGAP) in Rheumatoid Arthritis

Abstract

Rheumatoid Arthritis (RA) is an autoimmune disorder which is associated with swelling and inflammation in the synovial membrane of joints leading to bone and joint damage. Etiology of this disorder still needs a comprehensive understanding however the relationship among different factors of genetics and environment is supposed to lead towards the occurrence of this disease with 65% involvement of inheritance and the rest being attributed to the environment. Approximately one percent of the global population which usually comprises the adults and is mostly from the developed states is affected by this disorder whereas Pakistan’s prevalence for this disease is reported to be around 0.1-0.5%. Several studies in the past have identified and named a range of variants and loci which are found connected with RA incidence in inhabitants of diverse populations. The T-cell Activation RhoGTPase Activating Protein (TAGAP) is one such gene which is considered meticulously significant in RA and other autoimmune disorders because of its involvement in T cells activation. Considering the SNP association studies, so far three TAGAP gene polymorphisms have been reported to have significant association with RA in different populations of Europe and they are rs212389, rs182429 and rs394581. Present study was aimed to carry out both in-vitro and in-vivo investigations on different aspects of the TAGAP gene including the association of its SNPs with RA in Pakistani population, kinetics of its expression in this disease and computational analysis of its missense SNPs to identify the deleterious mutations which could lead to the malfunctioning of this gene. A SNP association study on Pakistani RA patients (n=186) and healthy controls (n=185) was carried out through Taqman SNP genotyping assays. The results showed that the TAGAP polymorphism rs182429 is associated with Rheumatoid Arthritis (P=0.0014) under recessive genetic model while no association was found for the other SNP rs212389. Investigating TAGAP expression in cia mice model showed descending pattern in spleen and lymph nodes (P<0.01) while the disease affected paws depicted an increase in the gene expression. This altered expression reflects the movement of leukocytes towards the antigen presentation sites and then to the disease site with the progression of the immune response. Kinetics of the TAGAP mRNA expression analysis revealed notably higher levels of TAGAP in RA patients from both European and Pakistani population (P<0.05). IFNγ was also found significantly higher in RA patients (P<0.05) but no correlation was detected between TAGAP and IFNγ. The in silico approach to analyze missense SNPs in TAGAP revealed three highly damaging non-synonymous missense SNPs which might affect the protein’s structure and/or function. These are Glycine to Glutamic Acid at site 120, Glycine to Tryptophan at site 141 and Valine to Methionine at site 151. It can be stated that this project will help in exploring therapeutic strategies for RA hence will contribute in the management of the disease and that would be a great benefit for upcoming generations.