Type IV collagen induces expression of thrombospondin-1 that is mediated by integrin α1β1 in astrocytes

Following brain injury, thrombospondin-1 (TSP-1) is involved in angiogenesis and synaptic recovery. In this study, we used a cold injury-model and found that TSP-1 mRNA was markedly upregulated after brain injury. Immunohistochemistry showed that TSP-1 was upregulated in both the core of the lesion and in the perilesional area of injured brain tissue. Numerous astrocytes immunopositive for glial fibrillary acidic protein (GFAP) were found in the perilesional area, and TSP-1 was also expressed in almost all astrocytes surrounding blood vessels at 4 days after injury. Next, we examined the influence of vascular basement membrane components on TSP-1 expression. When astrocytes were cultured on type IV collagen, TSP-1 was significantly upregulated compared with the expression when cells were grown on laminin, fibronectin, or poly-L-lysine. This increase occurred exclusively when astrocytes were grown on the native form of type IV collagen but not on the heat-denatured form or the non-collagenous 1 domain. Further, integrin a1 and b1 mRNAs were upregulated concomitantly with GFAP mRNA, and integrin a1 protein was localized to the endfeet of astrocytes that surrounded blood vessels in the injured brain. Using function-blocking antibodies, we found that the effect of type IV collagen was attributed to integrin a1b1 in primary astrocytes. Collectively, our results suggest that vascular basement membrane components substantially impact gene expression in astrocytes during brain tissue repair.