Fibrin-containing Hydrogels Regulate Human Astrocyte State and Neuronal Reprogramming

Astrocytes are key components in reactive gliosis after brain injury, yet defined in vitro models dissecting the influence of extracellular matrix (ECM) components enriched after injury, such as fibrin, on human astrocyte behaviour and function are still missing. Here, we use fibrinogen-derived fibrin and fibrin-alginate-RGD (FAR) 3D hydrogel substrates to examine the influence on human iPSC-derived astrocyte behaviour and their direct conversion into neurons. Astrocytes develop complex morphologies in 3D-FAR hydrogels while are more proliferative and migratory in 3D-Fibrin. Interestingly, gene expression profile analysis revealed different reactive states of astrocytes in 3D-Fibrin and 3D-FAR, which persist over time. The highly inflammatory state in 3D-FAR is largely incompatible with direct neuronal reprogramming hampering the direct conversion even at early stages. Conversely, astrocytes in 3D-Fibrin hydrogels can readily convert into neurons, demonstrating a potent influence of how fibrin is presented on eliciting distinct astrocyte states with great relevance for fate conversion.