Brain PDGFRβ ⁺ cells exhibit diverse reactive phenotypes after stroke without requiring KLF4

Ischemic stroke triggers a cascade of molecular and cellular processes leading to fibrotic scar formation, entailing activation of brain platelet-derived growth factor receptor (PDGFR)β ⁺ cells. Krüppel-like factor (KLF)4 plays an important role in regulating the activation of peripheral PDGFRβ ⁺ perivascular cells in response to hypoxia/ischemia. Herein, we aimed to characterize the spatiotemporal responses of brain PDGFRβ ⁺ cells while assessing the contribution of KLF4. This was achieved using transgenic mice that enable tracking or conditionally depleting KLF4 in PDGFRβ ⁺ cells, which were subjected to experimental ischemic stroke. Next, we employed point pattern analysis (PPA) and topological data analysis (TDA) to quantitatively characterize cell phenotypic changes and spatial distribution over injury progression after ischemic stroke. We show that brain PDGFRβ ⁺ cells rapidly become reactive and early localize to regions prone to irreversible damage. We report the emergence of parenchymal PDGFRβ ⁺ cells, which cannot be causally linked to proliferation or vascular detachment. Moreover, our analysis reveals that KLF4 is barely expressed in brain PDGFRβ ⁺ cells under normal conditions, and that its expression is slightly induced in reactive cells in the injured brain. Notably, specific attenuation of KLF4 induced expression in PDGFRβ ⁺ cells does not affect cell reactivity and spatiotemporal distribution, nor scar formation and injury severity. These observations suggest that in contrast with the periphery, KLF4 is not implicated in regulating the responses of brain PDGFRβ ⁺ cells. Our results indicate that the reactivity of brain PDGFRβ ⁺ cells after stroke is spatiotemporally diverse, evolve over injury progression, and is distinct from peripheral perivascular cells.