Fibrinogen triggers intial perivascular fibroblast activation in a mouse model of cortical ischemic stroke
Perivacular fibroblasts (PVFs) in the perivascular space delaminate from blood vessels, expand, express and deposit an excess of collagen I (Col I) and become an integral component of the fibrotic scar after central nervous system (CNS) disease. Here, we show that blood-derived fibrinogen deposition in the perivascular space initially induces PVF activation after photothrombosis, a mouse model of ischemic stroke. Pharmacological fibrinogen depletion reduces PVF activation and their delamination from blood vessels to build up the fibrotic scar. Fibrinogen induces beta1 integrin signaling in PVF to induce Col I expression and secretion. Single-cell RNA sequencing (scRNA-Seq) and genetic approches revealed a contribution of fibrinogen-induced perivascular macrophages to PVF activation. Finally, fibrinogen depletion abrogates PVF-astrocyte signaling and astrocyte lesion border formation, promoting neuronal survival and plasticity. Therefore, we propose that fibrinogen is a critical trigger for PVF activation and fibrotic scar formation, inhibiting neuronal regeneration after stroke. Overall design: C57Bl/6J mice were implanted with subcutaneous pumps filled with saline or Ancrod (2.4 U) 2 days before receiving photothrombotic stroke using rose bengal and a cold light illuminator over 4-mm diameter of the right sensorimotor cortex. After 6 days, the lesion and 1-mm of surrounding spared tissue (not including the corpus callosum) was microdissected and dissociated. No FACS or beads were  used to filter the cells or to enrich for a specific cell type.