PAI-1 production by reactive astrocytes drives tissue dysfibrinolysis in multiple sclerosis models.

BACKGROUND: In multiple sclerosis (MS), disturbance of the plasminogen activation system (PAS) and blood brain barrier (BBB) disruption are physiopathological processes that might lead to an abnormal fibrin(ogen) extravasation into the parenchyma. Fibrin(ogen) deposits, usually degraded by the PAS, promote an autoimmune response and subsequent demyelination. However, the PAS disruption is not well understood and not fully characterized in this disorder. METHODS: Here, we characterized the expression of PAS actors during different stages of two mouse models of MS (experimental autoimmune encephalomyelitis-EAE), in the central nervous system (CNS) by quantitative RT-PCR, immunohistofluorescence and fluorescent in situ hybridization (FISH). Thanks to constitutive PAI-1 knockout mice (PAI-1 KO) and an immunotherapy using a blocking PAI-1 antibody, we evaluated the role of PAI-1 in EAE models and its impact on physiopathological processes such as fibrin(ogen) deposits, lymphocyte infiltration and demyelination. RESULTS: We report a striking overexpression of PAI-1 in reactive astrocytes during symptomatic phases, in two EAE mouse models of MS. This increase is concomitant with lymphocyte infiltration and fibrin(ogen) deposits in CNS parenchyma. By genetic invalidation of PAI-1 in mice and immunotherapy using a blocking PAI-1 antibody, we demonstrate that abolition of PAI-1 reduces the severity of EAE and occurrence of relapses in two EAE models. These benefits are correlated with a decrease in fibrin(ogen) deposits, infiltration of T4 lymphocytes, reactive astrogliosis, demyelination and axonal damage. CONCLUSION: These results demonstrate that a deleterious overexpression of PAI-1 by reactive astrocytes leads to intra-parenchymal dysfibrinolysis in MS models and anti-PAI-1 strategies could be a new therapeutic perspective for MS.

MRI-based microthrombi detection in stroke with polydopamine iron oxide.

In acute ischemic stroke, even when successful recanalization is obtained, downstream microcirculation may still be obstructed by microvascular thrombosis, which is associated with compromised brain reperfusion and cognitive decline. Identifying these microthrombi through non-invasive methods remains challenging. We developed the PHySIOMIC (Polydopamine Hybridized Self-assembled Iron Oxide Mussel Inspired Clusters), a MRI-based contrast agent that unmasks these microthrombi. In a mouse model of thromboembolic ischemic stroke, our findings demonstrate that the PHySIOMIC generate a distinct hypointense signal on T2*-weighted MRI in the presence of microthrombi, that correlates with the lesion areas observed 24 hours post-stroke. Our microfluidic studies reveal the role of fibrinogen in the protein corona for the thrombosis targeting properties. Finally, we observe the biodegradation and biocompatibility of these particles. This work demonstrates that the PHySIOMIC particles offer an innovative and valuable tool for non-invasive in vivo diagnosis and monitoring of microthrombi, using MRI during ischemic stroke.