Characterizing neurodegeneration, neuroinflammation and immunological status through multimodal strategies in type 1 diabetes mellitus and relapsing-remitting multiple sclerosis
Type 1 diabetes mellitus (T1DM) and Multiple sclerosis (MS) are chronic organ-specific diseases caused by immune system dysfunction. The study of T1DM and MS has gained increasing attention because of their high prevalence, progressive nature, impact on patients' daily lives, the lifelong management these conditions require, and the increased co-occurrence of both pathologies. Nevertheless, despite advances in the availability of therapeutic options, the mechanisms driving their progression are still not fully understood. In fact, both autoimmune illnesses have more aetiologic and pathologic similarities than one might anticipate, including systemic dysregulations, central nervous system (CNS)-specific components of neuroinflammation and axonal damage, or the presence of cognitive impairment, among others. Moreover, although both conditions manifest immune-mediated tissue destruction, the precise inflammatory-immune profiles and regulatory mechanisms underlying these processes remain unexplored. Thus, while MS is recognized primarily for its neuroinflammatory effects and its neurodegeneration markers are relatively well characterized by neuroimaging and biochemical approaches, increasing evidence suggests that T1DM may also be associated with CNS alterations in addition to peripheral neuropathy, so deeper investigations into CNS involvement are still needed. This knowledge could be crucial for identifying biomarkers, assessing cognitive impairment, and improving early detection and therapeutic strategies for neurological and associated complications in those diseases. Given the importance of conducting a comprehensive comparative analysis, this thesis is structured into three distinct but interconnected studies to ensure clarity and an in-depth investigation of T1DM and MS. Each study focuses on a key aspect of disease pathophysiology, neurodegeneration, systemic inflammation and immunity, and molecular mechanisms, as detailed in the following sections. The first study, which focused on neurodegeneration, employed a cross-sectional design in which T1DM and MS patients were compared with healthy controls (HCs). Comprehensive assessments included clinical and neuropsychological evaluations, alongside advanced neuroimaging techniques such as whole-brain and regional grey matter volumetry and optical coherence tomography (OCT) for retinal nerve fibre layer (RNFL) thickness. Serum neurofilament light chain (sNfL) and glial fibrillary acidic protein (GFAP) were also measured. Both patient groups exhibited cognitive and mood disturbances and significantly elevated sNfL levels, indicative of early neurodegeneration, compared with controls. While MS patients presented with significant thalamic atrophy and retinal thinning, these structural changes were initially absent in early T1DM patients. However, longer-duration T1DM patients presented increased sNfL and a trend towards retinal thinning, suggesting progressive neurodegenerative processes. Notably, impaired cognitive processing speed was associated with increased sNfL, retinal thinning, and reduced thalamic volume, particularly in MS, underscoring shared neurodegenerative features and the importance of early biomarkers in both autoimmune diseases. The second study examines systemic immune alterations by analysing serum cytokines and immune cell subpopulations through flow cytometry and mRNA expression, characterizing the distinct and overlapping immune profiles and inflammatory dysregulations present in T1DM and MS. This study investigates the impact of systemic inflammation on disease progression and identifies potential immunological targets for therapy. Systemic inflammatory mediator profiles revealed a reactive status in the T1DM group, whereas the MS group exhibited a quiescent status, likely due to immunotherapy. Notably, the proinflammatory analysis revealed elevated IL-2Ra levels in both groups, whereas the IL-12 levels differed between the T1DM and MS groups. Regarding the anti-inflammatory cytokine profile, the T1DM group presented increased IL-13, IL-4, and IL-1ra levels, whereas no significant changes were observed in the MS group. Analysis of immune cell populations revealed no differences in T-cell populations between groups. However, a distinct upregulation of Th1 and Th17 subpopulations was observed in T1DM and MS patients, respectively. These findings suggest that cytokine expression patterns in PBMCs play crucial roles in immune cell differentiation, potentially contributing to disease-specific immune responses in patients with T1DM and MS. The third study explored shared and disease-specific molecular mechanisms in T1DM and MS using label-free quantitative proteomics analysis of PBMCs. A total of 2,476 differentially expressed proteins were identified, with this analysis highlighting 15 dysregulated proteins common to both autoimmune conditions compared with controls. These shared proteins are involved in key biological processes, including immune system regulation; neurological disorders; signal transduction; and nucleotide, protein, and RNA metabolism. Notably, despite their common involvement, T1DM and MS patients presented distinct expression patterns of these proteins, suggesting overlapping yet disease-specific immune responses, neurological complications, and disruptions in autophagy. Importantly, CSTB, RSP21, and TTR, among other proteins, have emerged as potentially key proteins involved in the development of T1DM or MS. Proteomic analysis revealed key signalling pathways involved in disease regulation and progression, which may aid in identifying novel therapeutic targets. Together, these findings underscore the shared and distinct molecular mechanisms underlying neuroinflammation and immune dysregulation in T1DM and MS, which contribute to neurological complications. Identifying key molecules involved in disease progression may provide critical insights into early pathological changes and facilitate the development of targeted therapeutic strategies. The observed immune-mediated neurological impact highlights the necessity of integrating systemic and CNS-specific biomarkers to improve early detection and intervention. A comprehensive, multidisciplinary approach contributes to refining personalized treatment strategies and identifying novel therapeutic targets. Further research into the interplay between immune responses and neurodegeneration in autoimmune diseases is crucial to unravelling their complex pathophysiology and mitigating long-term neurological consequences.
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