Mechanisms of Receptor Mediated Neuronal Survival

              Nerve cells, both in the brain and in the peripheral nervous system, require specific growth factors for their survival and development into fully functional neurons. These growth factors act on specific neurons by binding to specialized regions on the cell surface, called receptors, which are capable of transmitting information from the outside of the cell to the inner cellular apparatus. This proposal will investigate the properties of a specific receptor, the nerve growth factor receptor, which is critically involved in regulating the growth and development of a subgroup of neurons in the brain, the forebrain cholinergic neurons . These cells are of particular clinical significance as they undergo degeneration during aging, and in Alzheimer’s disease. Furthermore, treatment of these dying neurons with nerve growth factor (NGF), in a rat model, can partially rever se the cell degeneration, and may improve memory. Therefore, further study of the interactions of nerve growth factor with its specific receptor may yield critical information not only on the normal mechanism s whi ch regulate nerve cell survival, but may have eventual clinical significance in the understanding and treatment of Alzheimer’s disease.                 NGF mediates its action by binding to specific, high affinity receptors on the cell surface. The high affinity receptor is a multimolecular complex of the low affinity re ceptor protein which binds directly to NGF, and an effector protein of larg er molecular mas s. The intera ct ion of NGF with the low affinity receptor in the absence of the other molecular species le ads to no detectable functional responses, indicating that the effector protein i s required for signal tran sduc tion . In this proposal, we identify this effector protein in the brain , and outline a method for purifying the protein to homogeneity. Specifically we plan to purify this protein in sufficient quantity to allow the mole c ular cloning of the gene encoding this protein, by two related technique s: (1) determining the amino acid sequence of the protein , which will allow us to clone the cDNA en coding this protein by polymerase chain reaction technology and (2) developing specific antibodies to this protein, to allow us to identify this protein from an expression library.           Once we have isolated the genetic sequence encoding this protein, we will investigate where this protein is expressed in the peripheral and central nervous systems. In addition , we plan to reconstitute the functional high affinity receptor by coexpressing this protein with the previously cloned and characterized low affinity receptor protein, using the techniques of gene transfer.            The identification and molecular cloning of this protein will allow us to address several fundamental questions concerning neuronal degeneration, particularly in regard to the mechanisms promoting the course of Alzheimer’s disease, and potentially in it s treatment . Several long term goal of this project include: (1) determining if this protein is underexpressed, or expressed in an abnormal form in Alzheimer ‘ s disease . Either of these findings could , in part , account for the degeneration of basal forebra in cholinergic neurons in this disease; (2) defining if this protein can act as a signal tran sducer for other growth factors which have putative functional significance in t his region of the brain, including brain derived neurotrophic factor and neurotrophin 3; and (3) localizing the critical regions of thi s protein which are required for its appropriate interaction with nerve growth factor , and the structural features required to transmit its signal intracellularly.