Extracellular matrix components reflect the dynamics of a healing tympanic membrane perforation--a histochemical study.

Extracellular matrix components have hitherto been sparsely studied in tissue repair processes. In this study, the distribution of hyaluronan (HYA), fibronectin, and five chondroitin sulfate glycosaminoglycans (GAGs) was analysed in healing tympanic membrane (TM) perforations of rats, at different time points, using a HYA-binding protein probe and six monoclonal antibodies (MAbs). Hyaluronan appeared, the first day, around migrating squamous epithelial and inflammatory cells in the perforation borders and close to dilated vessels at the malleus handle. Accumulated HYA persisted in the thickened perforation rim until closure of the perforation, then it slowly disappeared from the healed TM area. Fibronectin immunoreactivity occurred around proliferating cells in the perforation edge and around collagen bundles in the connective tissue. The MAbs for chondroitin sulfate GAGs rendered specific, constant immunostaining patterns throughout the healing process. Unsulfated chondroitin, chondroitin-4-sulfate and chondroitin-6-sulfate were present in small amounts in the connective tissue surrounding collagen fibres and fibroblasts. The staining for native chondroitin and dermatan sulfate was most pronounced in the epithelial layers, in particular the squamous epithelium and its keratin layer, whereas the loose connective tissue was left unstained. After closure of the TM perforations, the immunoreactivity for unsulfated chondroitin, native chondroitin and dermatan sulfate increased in the scar tissue. It is concluded that HYA is abundant in early stages of healing of TM perforations, whereas fibronectin, unsulfated chondroitin, chondroitin-4 and 6-sulfate are constantly present in small amounts during the healing process. Unsulfated chondroitin, native chondroitin and dermatan sulfate increase in the healed TM area.