Role of complement activation and disruption of the blood-brain barrier in the pathogenesis of multiple system...

Multiple system atrophy (MSA) is a progressive and sporadic neurodegenerative disorder characterized by the histological appearance of glial cytoplasmic inclusions primarily composed of α-synuclein. Recently, complement-mediated neuroinflammation has been proposed as a key factor in the pathogenesis of numerous neurodegenerative disorders. We conducted immunohistochemical/immunofluorescent assays targeting a number of complements to explore the role of complements in MSA pathogenesis using brain samples from deceased patients and controls. Complement deposition was notably increased in the cerebral vasculature and myelin sheath in the MSA brains. Furthermore, fibrinogen leakage resulting from the disruption of the blood-brain barrier (BBB) was observed, along with the presence of C1q-positive microglia clusters surrounding the MSA brain vessels. These immunohistochemical/immunofluorescent findings suggest that complement activation and BBB disruption play critical roles in MSA progression.