Dottorato in BIOLOGIA CELLULARE E DELLO SVILUPPO

Titolo della tesi: Role of CD28 in the regulation of IL-17A expression and in the modulation of the metabolic programs regulating pro-inflammatory T cell functions in Multiple Sclerosis

The immunopathogenesis of Multiple Sclerosis (MS) depends on the expansion of specific inflammatory T cell subsets, which are key effectors of tissue damage and demyelination. Several studies have evidenced that Th17 cells and IL-17-producing cells strongly contribute in initiating the autoimmune responses against components of the central nervous system. Therefore, the characterization of the mechanisms and molecules regulating IL-17 production and IL-17 producing cell amplification and functions could represent an important goal of the ongoing research in MS. CD28 is an important costimulatory receptor for T lymphocytes that, in humans, may deliver TCR-independent signal leading to the up-regulation of IL-17A expression in peripheral CD4+ T lymphocytes from MS patients. In this work, we characterized the mechanisms and signalling mediators responsible for CD28-induced IL-17A expression. We found that CD28-mediated up-regulation of IL- 17A was dependent on IL-6- associated STAT3 and RelA/NF-kB transcription factors, which following CD28 stimulation bind specific sequences on the IL-17A promoter, thus inducing its expression. Emerging studies also evidenced that a reprogramming of T cell metabolism regulates specific pro-inflammatory T cell responses and amplifies Th17 cells in MS. Starting from these evidences, we also characterized the involvement of CD28 and associated signalling mediators in the modulation of the metabolic programs regulating pro- inflammatory T cell functions in MS. Our data evidenced that CD28 stimulation up-regulates glycolysis by promoting the increase of c-myc and the glucose transporter, Glut1, in CD4+ T cells from relapsing- remitting (RR) MS patients. CD28-induced increase of glycolysis was required for the up-regulation of pro-inflammatory cytokines, as demonstrated by the strong inhibition exerted by a glycolysis inhibitor. By using specific inhibitory drugs, we also identified phosphatidylinositol 3 kinase (PI3K) as the critical regulator of CD28 proinflammatory and metabolic functions. These data suggest that CD28 may provide TCR- independent signals modulating the metabolic processes associated to specific pro-inflammatory T cell responses in MS.