Investigation of clusterin genetic polyorphisms and the effects of circulating microRNAs on plasma clusterin level and cognitive performance in relapsing-remitting multiple sclerosis

Multiple Sclerosis (MS) is a demyelinating, autoimmune, and neurodegenerative chronic disease of the central nervous system. Complex interactions of genetic and environmental factors play an important role in the etiology of MS, the most common clinical form of which is relapsing-remitting MS (RRMS). The prevalence of cognitive impairment, an indicator of progression in MS, ranges from 40% to 70%. Clusterin plays a major role in cell survival and cell death pathways. Single nucleotide polymorphisms (SNP's) in the CLU gene, which encodes clusterin protein, have been associated with many diseases, and there is evidence in the literature suggesting an association between clusterin level in circulation and cognitive performance. MicroRNAs involved in the regulation of gene expression have been associated with the diagnosis and progression of many diseases and they are important foci of biomarker discovery studies. In this thesis, the aim was to investigate the relationships between RRMS risk and the CLU rs11136000 C/T, rs3087554 T/C, rs2279590 C/T, and rs1532278 C/T SNPs, as well as to determine the associations between plasma levels of clusterin and plasma relative expression levels of miR-21-5p and miR-195-5p, which are known to target CLU gene, with disease risk and cognitive impairment. For this purpose, there are two study groups: Group-1 consisted of 310 RRMS patients and 310 healthy controls, while Group-2 consisted of 30 treatment-naïve RRMS patients, 30 injectable disease modifying therapy (DMT)-receiving RRMS patients, and 30 healthy controls. Genotypes of RRMS patients in Group-1 were determined by PCR-RFLP and RT-PCR. Cognitive evaluations of participants in Group-2 were carried out by applying the BICAMS test battery. Plasma relative expressions levels of miR-21-5p and miR-195-5p were determined by qRT-PCR, and plasma clusterin concentrations were analyzed with ELISA. The samples were collected from Ankara City Hospital Neurology Clinic. In this thesis, it was observed that the C allele of the rs3087554 T/C is associated with both RRMS risk and progression. The plasma relative expression levels of miR-21-5p and miR-195-5p were found to have the potential to be biomarkers for the diagnosis of RRMS. Moreover, the findings suggested that miR-21-5p could be a potential therapeutic biomarker. In addition, both miR-21-5p and miR-195-5p are thought to be therapeutic targets of injectable DMT's used in MS. With this thesis, the role of clusterin in MS was evaluated at genotype, phenotype, and cognitive level. The relationship between rs11136000 C/T, rs3087554 T/C, rs2279590 C/T, rs1532278 C/T SNP's, and RRMS risk was investigated for the first time in this thesis. In addition, for the first time in this study, the relationships between plasma clusterin levels, plasma miR-21-5p and miR-195-5p relative expression levels, and cognitive performance of RRMS patients were investigated. With this study, which identifies potential biomarker candidates in plasma for the diagnosis and prognosis of RRMS, will guide the development of biosensors, therapeutic agents, and diagnostic kits. This thesis, which is a product of a multidisciplinary approach, is a study contributing to the field of Biomedical Engineering in the aforementioned aspects.