This laboratory has had a longstanding interest in the neurobiological functions of proteoglycans. The present proposal focuses on two large nervous tissue-specific chondroitin sulfate proteoglycans, neurocan and phosphacan, that we have recently identified, biochemically characterized, and cloned. It is planned to determine the localization and developmental changes of three hyaluronic acid-binding proteoglycans (versican, aggrecan, and brevican) that are structurally related to neurocan, and to examine the effects of deleting genes for both neurocan and neural cell adhesion molecule ligands (L1 and N-CAM) that this laboratory has previously identified. Because of recent evidence that N-linked oligosaccharides present on both the proteoglycans and their neural cell adhesion molecule ligands mediate or modulate binding, the structural properties of these glycans will be examined following derivatization and specific chemical or enzymatic degradation, in conjunction with electrospray mass spectrometry and collision-induced dissociation. Deletion variants, proteolytic fragments, and recombinant domains of tenascin-C and Ng-CAM/L1 will be tested for their ability to bind to neurocan and phosphacan, attempts will be made to identify short amino acid sequences involved in the binding process using phage-displayed peptide libraries, and rat brain cDNA libraries expressed on the surface of filaments phages will be used to identify potential new ligands. The distinctive properties of each proteoglycan (e.g., relative affinity for different ligands, consequences of developmentally regulated proteolytic processing, modulatory effects of chondroitin sulfate and N-linked oligosaccharides) suggest that neurocan and phosphacan are components of a multidimensional mechanism for the regulation of cell-cell and cell-matrix interactions during nervous tissue histogenesis. These studies may therefore significantly advance understanding of the roles of these extracellular matrix components not only in the normal development of the central nervous system, but also in pathological conditions such as schizophrenia in which demonstrated alterations in the expression of neural cell adhesion molecules may be responsible for abnormalities in hippocampal plasticity.
