? Neurotrophins, such as nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF), are a family of proteins that have been established to play critical roles in vertebrate nervous system. Alterations in neurotrophin levels have been implicated in neurodegenerative disorders, as well as psychiatric disorders such as depression and substance abuse. While there has been significant advances recently in delineating the downstream signal transduction events in the neurotrophin system, less has been established about the sequence of events involved in neurotrophin receptor trafficking upon activation by ligands. Trk neurotrophin receptor, the key mediator of neurotrophin's biological responses (survival, differentiation, synaptic plasticity), has been shown to be undergo rapid endocytosis upon activation by neurotrophin, and is subsequently sorted to a variety of endocytic pathways. In addition, we have recently shown that small molecules can activate a population of intracellular Trk receptors in the absence on neurotrophins. The hypothesis of this research proposal is that there are highly specialized biochemical mechanisms that regulate trafficking of activated Trk receptors to these different intracellular pathways which are critical determinants of the biological responses of neurotrophins. Preliminary studies suggest the existence of specialized mechanisms of endocytic regulation that appears to be mediated by novel protein interactions. The studies proposed in this application are designed to establish quantitative trafficking assays that will be used to characterize specific proteins that mediate these sorting mechanisms, and examine the functional consequences of these sorting proteins on the neurotrophin system.
The Specific Aims of the proposed studies are 1) to map the endocytic fate of activated Trk neurotrophin receptors from initial internalization to postendocytic pathways (recycling, degradative), 2) identify and elucidate the functional role of candidate sorting molecules obtained from a live cell imaging assay and a yeast two hybrid screen which interact with a defined Trk receptor domain, and 3) examine the membrane pathway used by Trk receptors activated by small molecules in the absence of neurotrophins. Understanding these sorting mechanisms to these pathways has broad relevance to fundamental molecular mechanisms of neurotrophin receptor regulation, and will inform clinical research efforts to utilize the neurotrophin system for the treatment of neurodegenerative and psychiatric disorders. ? ? The candidate is a psychiatrist with a longstanding interest in neuroscience and behavior. The career development of the candidate will be provided by two outstanding mentors: Fred Maxfield for membrane trafficking expertise, and Jack Barchas for overall development as a physician-scientist. The long term goal of this award is to provide the candidate the opportunity to gain expertise in membrane trafficking and ensure optimal flexibility and adaptability in the development of his program of funded research into basic molecular, neural mechanisms that are relevant to neuropsychiatric disorders. ? ?
