Perineurial cells coexpress genes encoding interstitial collagens and basement membrane zone components

Perineurial cell cultures were established from the sciatic nerves of adult Wistar rats. Highly enriched cultures were studied with respect to the production of extracellular matrix components under conditions free from the influence of Schwann cells, axons, or the extracellular matrix of peripheral nerves. Indirect immunofluorescence staining revealed the presence of collagen type IV epitopes, and electron microscopy demonstrated patches of basement membrane on the perineurial cell surfaces. Collagenous fibrils with a diameter of 15-20 nm were also observed in the intracellular space. SDS-PAGE of radiolabeled medium proteins showed a pattern of bands suggesting the synthesis and secretion of fibronectin, and type I and IV collagens. Northern hybridizations revealed characteristic polymorphic mRNA transcripts corresponding to fibronectin, laminin B2 chain, as well as to the alpha- chain subunits of type I, III, and IV collagens. Furthermore, in situ hybridizations suggested expression of these genes by cultured perineurial cells without apparent heterogeneity within the cell populations. In situ hybridizations of sciatic nerve tissue from 2-wk- old rats also suggested that perineurial cells express alpha 1(I) and alpha 2(IV) collagen, as well as laminin B2 chain genes in vivo. This profile of matrix gene expression is different from that of Schwann cells, which do not synthesize fibronectin, or that of fibroblastic cells, which do not form a cell surface basement membrane. The capability of perineurial cells to express genes for the basement membrane zone and for interstitial collagens further adds to our understanding of the functional role of perineurial cells in developing and healing peripheral nerve, as well as in certain neoplastic lesions of neural origin, such as von Recklinghausen's neurofibromas.