Abstract TP140: Loss Of Fibroblasts Aggravates Hemorrhagic Brain Injury By Diminishing Timp2 Secretion

Abstract

Although Col1a1 + fibroblast-like cells have been identified in large blood vessels in the CNS, their function remains largely unknown. To answer this important question, we generated mutant mice (Col1a1-DTR) with ablated fibroblast-like cells by crossing the Col1a1-Cre mice with DTR mice, which contain a loxP-flanked STOP sequence before diphtheria toxin receptor. The Col1a1-DTR mice were grossly normal after diphtheria toxin injection, suggesting that Col1a1 + fibroblast-like cells are dispensable under homeostatic conditions. After hemorrhagic stroke, however, these mice demonstrated exacerbated brain injury, including enhanced blood-brain barrier (BBB) leakage and aggravated injury volume. In addition, the expression of Collagen-1 and PDGFRα, two fibroblast markers, was significantly reduced. These findings highlight a beneficial role of Col1a1 + fibroblast-like cells in hemorrhagic stroke. Consistent with these results, similar results were also observed in vitro. Specifically, fibroblast-conditioned medium (FCM) attenuated endothelial damage (increased TEER and decreased FITC-Dextran leakage) in an in vitro model of hemorrhagic stroke. Subsequent mechanistic study revealed that FCM up-regulated the expression of various tight junction proteins (occludin, ZO-1, and claudin-5) without affecting that of caveolin-1, a key protein in transcytosis. These results indicate that fibroblasts protect BBB via paracellular rather than transcellular mechanism. To further investigate how exactly fibroblasts exert this beneficial role in hemorrhagic stroke, we performed mass spectrometry analysis, and identified TIMP2 (a protein with known BBB-protecting function) in the FCM. Using both pharmacological and genetic approaches, we further showed that ablating TIMP2 abolished the neuroprotective effect of FCM. Altogether, these findings suggest that Col1a1 + fibroblasts secrete TIMP2, which inhibits tight junction protein loss and paracellular leakage, promoting BBB repair and hemorrhagic stroke recovery. These results suggest that fibroblasts and TIMP2 may be targeted in the therapy of stroke.