Activation of matrix metalloproteinase (MMP)-2 by membrane type 1-MMP and abnormal immunolocalization of the basement membrane components laminin and type IV collagen in canine spontaneous hemangiosarcomas.

We performed immunohistochemical investigation of the basement membrane (BM) components, namely, type IV collagen and laminin, in 83 canine hemangiosarcomas (HSAs), 22 hemangiomas, and some granulation tissues (GTs). Additionally, we analyzed the expression and activities of matrix metalloproteinase (MMP)-2, MMP-9, and membrane type 1-MMP (MT1-MMP) using the same samples by immunohistochemistry and gelatin zymography to investigate whether MMPs were associated with the BM degradation. In immunohistochemistry for the BM components, many HSAs showed discontinuous linear/negative immunoreactivity in the BM (type IV collagen: 49.4%/14.5%, laminin: 60.3%/10.8%, respectively). In contrast, almost all hemangiomas showed continuous staining in the BM (type IV collagen: 90.9%, laminin: 95.5%, respectively). Interestingly, positive cytoplasmic immunoreactivity for type IV collagen and laminin was observed in 97.6% and 91.6% HSA, respectively. Although MMP-9 immunoreactivity wasn't detected in neoplastic and active angiogenic endothelial cells (ECs), MMP-2 was detected in all ECs of GTs and in neoplastic cells of both vascular tumors. A strong immunoreactivity for MT1-MMP was observed in active angiogenic ECs in GTs and in neoplastic ECs in HSAs. However, almost all hemangiomas showed weak/negative immunoreactivity. In gelatin zymography, significantly strong activity of active MMP-2 was observed in HSAs, similar to that in active angiogenesis in GTs; however, weak/no activity of active MMP-2 was detected in hemangiomas. In canine HSA, neoplastic cells had active MMP-2, possibly activated by MT1-MMP, and discontinuous status of BM might be associated with activity of active MMP-2.