The effect of Fibulin-5 on early brain injury after subarachnoid hemorrhage in mice

Early brain injury (EBI) is an important cause that determines outcomes after aneurysmal subarachnoid hemorrhage (SAH). Our recent clinical study reported that a high concentration of plasma fibulin-5 (FBLN5), one of matricellular proteins, was associated with poor outcomes after SAH. The aim of this study was to investigate whether and how FBLN5 was associated with EBI during an acute phase of SAH in mice. C57BL/6 male mice underwent sham or filament perforation SAH modeling, and vehicle or four dosages (0.001, 0.01, 0.1, and 1 μg) of short or long recombinant FBLN5 (rFBLN5) were randomly administrated by an intracerebroventricular injection. Neurobehavioral test, measurements of brain water content, immunohistochemical staining, and Western blotting were performed to evaluate EBI 24 h after SAH. Short rFBLN5 had no significant effects on EBI, but administration of long rFBLN5 containing an arginine-glycine-aspartic acid motif improved neurobehavior functions depending on the dosages, without affecting brain edema. Administration of long rFBLN5 also reduced cleaved caspase-3-dependent neuronal apoptosis, associated with the inhibition of post-SAH upregulation of transforming growth factor-β1, but no significant changes in the expression level of Smad 2/3, mitogen-activated protein kinases, and another matricellular protein tenascin-C. Although further research is required to clarify the detailed mechanism, this study demonstrated for the first time that FBLN5 played a protective role against neuronal apoptosis in an acute phase of experimental SAH.