Expression of Thrombin-Cleaved Osteopontin and Integrin α9 and β1 Signaling Pathway Molecules in Chronic Subdural Hematomas

Chronic subdural hematoma (CSDH) is considered to be an inflammatory and angiogenic disease. Osteopontin is an extracellular matrix protein. Osteopontin is cleaved by thrombin, resulting in N-half osteopontin, which is more prominent in integrin signal transduction. We examined the expression of N-half osteopontin in the CSDH fluid and the expression of integrin α9 and β1 and the downstream components of the angiogenic signaling pathways in the outer membrane of CSDHs. Twenty samples of CSDH fluid and 8 samples of CSDH outer membrane were included. The concentrations of N-half osteopontin in the CSDH fluid were measured using ELISA kits. The expression of integrin α9 and β1, vinculin, talin-1, focal adhesion kinase (FAK), paxillin, α-actin, Src and β-actin was examined by western blot analysis. The expression of integrin α9 and β1, FAK and paxillin was also examined by immunohistochemistry. We investigated whether CSDH fluid could activate FAK in cultured endothelial cells in vitro. The concentration of N-half osteopontin in CSDH fluid was significantly higher than that in the serum. Western blot analysis revealed above-mentioned molecules. In addition, integrin α9 and β1, FAK and paxillin were localized in the endothelial cells of vessels within the CSDH outer membrane. FAK was significantly phosphorylated immediately after treatment with CSDH fluid. Our data suggest that N-half osteopontin in CSDH fluid promotes neovascularization in endothelial cells through integrins α9 and β1. The N-half osteopontin and integrin signaling pathway might be a useful therapeutic target for treating the growth of refractory CSDH.