Oligodendrocytes are the central nervous system cells that make and maintain myelin (an insulating membrane that surrounds nerves and facilitates fast nerve impulses). Myelin is indispensable for the proper function of nerves and muscles. It has previously been shown that oligodendrocytes, isolated from myelinated brain tissue and kept in vitro (i.e., in the laboratory), regenerate and have the potential to resynthesize myelin membranes. It has also been shown that during the process of regeneration, oligodendrocytes reenact the sequence of events that lead to myelination during development. Hence these cells constitute a good model to investigate the mechanism of myelin formation. In vitro, a critical requirement for this entire process is the interaction of oligodendrocytes with an adequate substratum (a surface to which the cells can adhere). A horse serum, heparin-binding glycoprotein (a protein with attached sugars) termed GRASP Glycine (a type of amino acid) Rich Adhesion Serum Protein has now been identified, purified, and partially characterized that, in vitro, fosters the adhesion of oligodendrocytes. This adhesion acts as a driving force that propels oligodendrocytes on their path toward differentiation (i.e., myelin formation). The long-term research endeavors are to define the signaling events and single out the molecular players that initiate and propagate the in vitro regeneration/differentiation of oligodendrocytes. It is hypothesized that GRASP binds to a glycoprotein (receptor) on the surface of oligodendrocytes; this binding turns on the machinery that activates the cells to make myelin. Specifically, this research is an attempt to confirm/refute this hypothesis. To this end, it is proposed to: a) identify and isolate GRASP's putative receptor; b) determine the structure (i.e., the sequence of amino acids) of this receptor; obtain the structure of GRASP and define its mode of interaction with oligodendrocytes. The proposed resear ch should advance our understanding of the mechanisms that are operative in the in vitro model. Ultimately, it is hoped to extend these concepts to the in situ system by identifying GRASP's counterpart on nerve cells. This research should further our knowledge of the biology of OLGs and the mechanism of myelin formation.
