Piers, T.M.; (2012) Fibrin and fibrinogen pathways in microglia fibrinogen-induced signalling – implications for neurodegeneration. Doctoral thesis , UCL (University College London).

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Abstract

Blood brain barrier dysfunction and breakdown is increasingly implicated in neurodegenerative disease (NDD) pathogenesis. Recently, the blood borne protein fibrinogen and the cleaved form fibrin were shown to be involved in neuroinflammatory pathways in animal models of NDDs, with microglia, the immune cells of the central nervous system playing a central role. Studies have identified binding sites on microglia for fibrinogen and induction of an activated phenotype has been reported. Studies performed here using primary microglial and cerebellar granule cell (CGC) cultures aimed to elucidate the signalling pathways induced in microglia by fibrinogen and fibrin, and specifically how these signals affected neuronal integrity. Fibrin induced microglial death after prolonged exposure with both fibrinogen and fibrin capable of inducing significant release of the pro-inflammatory cytokines TNFα and IL-6. However, this was dependent on culture serum conditions, which also affected iNOS expression after treatment with fibrinogen. Non-apoptotic induction of caspase-3/7 expression in microglia was also proposed after treatment with fibrinogen. Characterisation of the CGCs identified the presence of a population of microglia and development of a microglial depletion technique suggested the observed population was involved in fibrinogen- and fibrin-mediated neuronal death. Further manipulation using pharmacology, microglial depletion and conditioned medium suggested that microglial TNFα release and caspase activation were specifically involved in fibrinogen- and fibrin-mediated neuronal death. Endoplasmic reticulum stress and calcium dyshomeostasis in the form of calpain activation were coupled to the microglial activation pathway as well as being associated with neuronal death after fibrinogen exposure. Neuroprotection from fibrinogen and fibrin treatment was found by coactivating specific metabotropic glutamate receptors on either microglia or neurons. Finally, translation of specific findings to a human phagocyte culture model provides strong support for the induction of the same pathways in humans.

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