The adult central nervous system is virtually incapable of structural repair or regeneration. CNS axons seldom regenerate and neurogenesis is absent in the mature CNS. Thus, once lost or damaged, be it by trauma, ischemia or neurodegenerative disease, neurons must either be replaced or induced to regrow. Axonal outgrowth is a complex process which can be influenced by many factors including both intrinsic neuronal features as well as cellular and molecular environmental characteristics. The latter includes both stimulatory and inhibitory cues such as trophic factors, components of the extracellular matrix, and cell surface molecules. L1 is a neuronal cell adhesion molecule which has been strongly implicated in neurite extension and guidance. Laboratory work has suggested a role for this molecule in promoting survival of CNS adrenal medullary transplants in experimental models of Parkinson's disease, while clinical genetic studies have linked a defect in the L1 gene to the syndrome of X- linked hydrocephalus. Studies of this molecule have largely been limited to experiments with the purified protein or antibody studies. Further studies of the molecule in a cellular membrane environment are essential to the better characterization of the molecule with potential application towards axonal regeneration and CNS grafting. The Phase I goals of this proposal are to transfect the human L1 gene into various cells (including fibroblasts and oligodendoglia) and to assess the ability of the transfected cells to support neurite outgrowth in vitro. This will be accomplished by the use of several neurite outgrowth assays which will assess a range of neuronal populations and ages, thus providing a comprehensive evaluation of the molecule's neurotropic potential. In Phase II of the project, L1-transfected fibroblasts will be transplanted into the rat brain using several experimental paradigms (fibroblasts alone and fibroblasts in conjunction with both adrenal and nigral grafts in an animal model of Parkinson's disease) to assess the effect of L1 on transplant survival and function. Additionally, rat models of demyelinating disorders and a compression model will be used to evaluate the natural biologic response to these insults. This program offers a perfect educational opportunity for Dr. HIavin. It combines a firm foundation in fundamental molecular biology and tissue culture techniques during the first phase of the proposal with more practical application to animal models of Parkinson's disease and traumatic nervous system injury in the second portion. These studies will not only broaden our understanding of the processes involved in neural outgrowth and regeneration, particularly with regard to transplantation, but also offers the potential therapeutic application of cell adhesion molecules in the treatment of neural disorders, especially in the context of CNS transplantation for neurodegenerative disorders. This will complement Dr. Hlavin's clinical training as a neurosurgeon ideally by enabling her to be well versed in the basic scientific principles of neural regeneration and transplantation which can be then be developed towards practical application in patients with neuronal damage or dysfunction.
