Immunohistochemical localization of basement membrane collagens and associated proteins in the murine cochlea

Immunohistochemistry using antibodies specific for each of the basement membrane collagen chains was used to assess the location and composition of basement membranes in the mouse cochlea. The classical chains (COL4A1, 4A2) localized primarily in the osseous spiral lamina and in the capillaries of the spiral ligament. In contrast, the novel collagen chains (4A3, 4A4, and 4A5) localized to the interdental cells of the sulcus, the inner sulcus, the basilar membrane, and the region of type II fibrocytes in the spiral ligament. Antibodies against type 4A5 collagen also heavily stained the stria vascularis. Weak staining in the stria was observed with antibodies against 4A3. Basement membrane-associated proteins were also assessed. The basement membrane in the perineurium of the osseous spiral lamina immunostained using antibodies against laminin, heparan sulfate proteoglycan, and entactin. The basilar membrane contained only fibronectin in association with the novel collagen chains. The capillaries of the spiral ligament and the stria vascularis stained heavily for heparin sulfate proteoglycan and laminin. Generalized staining for laminin was observed in the spiral ligament. These results indicate that an abundance of basement membrane collagen containing extracellular matrix exists in the murine cochlea and that the composition of these matrices are surprisingly varied and tissue specific.