Characterisation of fibrinogen deposition and its associations with neuronal loss and microglial alterations in the multiple sclerosis motor cortex

Thesis

In multiple sclerosis (MS), a chronic inflammatory and demyelinating disease of the central nervous system (CNS), neurodegeneration underlies the gradual accrual of irreversible disability. A key mechanism of this neurodegenerative process is the establishment of persistent low-grade inflammation in the CNS. Fibrinogen, a plasma protein that is part of the acute phase reaction and is integral to the clotting cascade has been demonstrated to trigger microglial inflammatory responses by binding to the CD11b/CD18 receptor. Previous work has demonstrated fibrinogen to be negatively associated with neuronal density in layer 5 of the motor cortex. However, the mechanisms of this, and specific neuronal vulnerabilities, are currently unknown.

This thesis extensively characterises the deposition of fibrinogen in a large cohort of postmortem MS cases. We show that fibrinogen is extremely spatially heterogenous, and that deposition type is crucial to pathological outcomes. By using novel image analysis methods, we have shown that fibrinogen is associated with reduced neuronal density across, with the strongest effects in intermediate sized neurons (91-150μm² cell body). Microglial-targeted laser-capture microdissection and proteomics provided insight into the microglial response to fibrinogen in the MS motor cortex, suggesting a shift towards glycolysis, alongside a specific reduction in inhibitory synaptic components (GAD1, GABRB2), as well as the key integrin adaptor kindlin3, and synapse loss-associated protein. Kindlin3 was validated within microglia/macrophages, with positive cells demonstrated to have an altered morphology with shorter, branches in high fibrinogen cases. Finally, we confirmed at the local scale that fibrinogen variability robustly negatively associates with neuronal density.

Collectively these results demonstrate that the deleterious effects of fibrinogen are present at small scales within cases, and that microglia show a significant phenotypic change which may underlie this. This highlights the crucial need to investigate neurodegenerative processes within microenvironments, and to consider vascular pathology as an essential contributor to this.

Authors: Crane, MG

• DOI: 10.5287/ora-6qke01mvb
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: pathology; multiple sclerosis; neurodegeneration; neuroscience; motor cortex; neuropathology; fibrinogen; microglia
• Subjects: Pathology; Neurosciences