| Popis: |
Over two million individuals worldwide are affected with the devastating autoimmune disease, multiple sclerosis (MS), and as of yet, there is no cure. MS is primarily diagnosed in young adults aged 20-40, resulting in a substantial socioeconomic burden of $40,000 per patient per year. Heightened pro-inflammatory Th1 and Th17 cell responses drive demyelination and disability in MS patients, whereas beneficial Th2 and regulatory T cell responses are deficient. Thus, it would be therapeutically beneficial to suppress inflammatory and promote regulatory Th cell responses in MS patients. Epigenetic modifications, such as acetylation and methylation, are essential to control Th cell responses. Interestingly, pan-methylation reaction inhibitors suppress Th cell proliferation and cytokine production, as well as disease severity in the MS model, experimental autoimmune encephalomyelitis (EAE). However, the principal methyltransferase behind these effects has not yet been identified. Protein arginine methyltransferase 5 (PRMT5) is a Type II arginine methyltransferase, that catalyzes symmetric dimethylation of arginine residues on histones and other proteins. PRMT5 is a well-known cancer driver, but its role in Th cells requires further study. In my dissertation work, I used mouse and human in vitro cell culture as well as in vivo mouse models to analyze the impact of PRMT5 expression in Th cell responses and autoimmunity. We found that PRMT5 protein expression was upregulated after mouse naive and memory and human memory Th1 and Th2 cell activation, suggesting that PRMT5 may play an important role in T cell proliferation. We collaborated with the Drug Development Institute at OSU in the development and testing of novel PRMT5-selective inhibitors, CMP5 and HLCL65. PRMT5 inhibitors suppressed Th cell proliferation, more potently affecting inflammatory Th1 cell proliferation compared with beneficial Th2 cells. Finally, treatment with HLCL65 prevented EAE disease development and suppressed established EAE disease. These data supported an essential role for PRMT5 in Th cell expansion and EAE autoimmunity, thus we further explored upstream PRMT5 regulators as well as downstream PRMT5 targets. Our data support a model in which PRMT5 is upregulated in a NF-¿B, mTOR and MYC-dependent manner after initial naive Th cell activation, followed by PRMT5 downregulation as naive Th cells reach a resting, memory state in a miRNA dependent manner. Subsequent reactivation of memory Th cells induces rapid loss of Prmt5-targeting miRNAs leading to rapid upregulation of PRMT5 protein in a post-transcriptional manner. Finally, we developed an inducible Th cell specific PRMT5 knockout mouse model, that had no overt phenotype or changes in basal immune cell populations. We validated that PRMT5 drove Th cell proliferation and we observed that PRMT5 deficiency suppressed symmetric dimethylation of arginine, as well as expression of MYC and Cyclin D1 (CCND1). Overall, these data provide insight to the molecular mechanisms contributing to autoimmunity, and support the therapeutic potential of targeting PRMT5 in T cell-mediated autoimmune diseases, such as MS. |
