ROLE OF THE PRKCA GENE AND OF MICRORNAS IN THE SUSCEPTIBILITY TO MULTIPLE SCLEROSIS

Multiple sclerosis (MS) is a multifactorial neurological disorder characterized by chronic inflammation, demyelination, and axonal damage, probably caused by an altered immune response against myelin antigens. Despite extensive studies, the genetic and environmental determinants of MS are still poorly understood. In this thesis, we analyzed the role of the PRKCA gene that encodes the protein kinase C alpha, and has been involved in MS both by linkage and association studies in different populations (Finns, Canadians, and UK population), as well as the possible involvement of microRNAs (miRNAs) in the pathogenesis of MS. As far as PRKCA is concerned, a case-control association study performed on the Italian population allowed us to identify two association signals in the PRKCA gene: a protective allele mapping in the promoter region (P=0.033; OR=0.12, 95% CI=0.015-0.94) and a risk haplotype, partially overlapping the predisposing haplotypes observed both in Finns and Canadians within PRKCA intron 3 (P=7.4*10-4; OR=1.57, 95% CI=1.24-1.99). We identified and characterized, both in vitro and in vivo, the functional variants underlying these association signals, and demonstrated that higher PRKCA expression levels play a protective role towards MS predisposition. Moreover, we describe here for the first time so-far unknown PRKCA transcript isoforms, which are differentially expressed in MS cases and controls, and eventually lead to the synthesis of aberrant proteins, potentially dangerous for the cells. Furthermore, we characterized the MIR634 gene, mapping within the PRKCA locus, and demonstrated its involvement in the regulation of PRKCA expression. As far as miRNAs are concerned, we monitored the differential expression of several immunity-related miRNAs in peripheral blood mononuclear cells of MS patients and healthy controls, and identified miR-155 as the most upregulated miRNA in MS cases (fold change=3.30; P=0.013). Interestingly, this miRNA was previously reported to be up-regulated also in MS brain lesions. The role of miR-155 in MS susceptibility was also investigated by genotyping four single nucleotide polymorphisms mapping in the miR-155 genomic region. A three-SNP haplotype resulted associated with the disease status (P=0.035; OR=1.36, 95% CI=1.05-1.77), suggesting that this locus strongly deserves further investigations. In conclusion, this thesis work points to a possible role of post-transcriptional regulation mechanisms in the pathogenesis of MS, particularly supporting the uprising hypothesis that in MS a dysregulation of the splicing may play a pivotal role in MS.