Extravasation of fibrinogen and TGF through disrupted BBB is a particular mechanism suggested to directly trigger CSPG synthesis by astrocytes [134]. Reactive astrocytes have important roles in restoring extracellular homeostasis and releasing pro and anti-inflammatory cytokines following

injury, but it is their role in scar formation that directly impacts upon the organization and composition of Selleckchem DZNeP the ECM in regions of CNS injury [126]. The glial scar has crucial healing and protective aspects. Blocking scar synthesis has been found to delay BBB sealing which has consequences for the period in which immune cells infiltrate. This was demonstrated via ganciclovir ablation of reactive astrocytes expressing a HSV-thymidine kinase transgene and resulted in pronounced degeneration and substantial motor deficits [135]. The wound healing role of reactive astrocytes was further evidenced by selective STAT3 deletion, where their reduced migration resulted in markedly increased and detrimental inflammatory cell infiltration [136]. Astrocytes elongate and organize into a barrier via STAT3 and TGF-β/Smad-dependent mechanisms, spatially isolating core damage, inflammation and/or

fibrotic infiltration from spared tissue [137,138]. This orchestrated wound-healing response also depends on astrocyte-meningeal fibroblast interactions, thought to be regulated by OTX015 in vitro ephrin-B2 and EphB2, expressed by astrocytes and meningeal fibroblasts respectively [139]. However, despite the beneficial role of glial scar formation in maintaining homeostasis and sealing-off areas of CNS damage, it is also associated with regeneration failure [140,141]. This has, in part, been attributed to the presence of the dense configuration of reactive astrocytes which form a physical

barrier preventing growth cone advancement, but is also due to the accumulation and persistence of a number of inhibitory ECM molecules, in particular CSPGs [44,142]. These will be discussed in more detail below. In addition to astrocytes, microglia and OPCs contribute to the glial scar. Microglia are the resident Roflumilast immune cells within the CNS, ubiquitously distributed as a quiescent population. Upon injury they proliferate and undergo morphological changes and release cytokines, reactive oxygen species and free radicals and also acquire a phagocytic phenotype [143,144]. OPCs also proliferate following CNS injury and display hypertrophy with extended cell processes. They upregulate expression of the α-receptor for platelet-derived growth factor (PDGF) and CSPGs, particularly NG2 [62,67,145]. A general feature of scarring in all organs across various pathologies is the generation of fibroblast-derived collagenous tissue and ECM proteins [146].