Peter McCaffery - US grants

My long-range goal is to have a successful academic research career in the field of retinoid neurobiology. This area is an extension of my post- doctoral research on the role of retinoic acid (RA) in the development of the retina. My work has provided new tools and techniques which I intend to use to elucidate new facets of retinoid metabolism. The retinoid vitamin A is an essential nutritional supplement required for growth, reproduction and sight. RA, the active metabolite of vitamin A, is increasingly used in the clinical treatment of cancers and skin diseases. Exposure to retinoid homologues may even come from insecticides such as methoprene. Potential hazards exist since RA, in excess, is neurotoxic, particularly in children, and is also one of the most teratogenic substances identified. Its pernicious actions are through the disregulation of the normal patterns of RA metabolism and the central nervous system (CNS) is particularly sensitive. The aim of this proposal is to map the pathways of retinoid metabolism in the developing CNS. I will focus on the development of a single region of the brain, the cerebellum, allowing a straightforward, coherent research program to be developed. The cerebellum is a region of the CNS in which development and function can be disrupted through disturbances in RA metabolism. Accidental exposure of embryos to the acne drug Acutane(R) has shown that human cerebellar development is vulnerable to a disruption in the normal pattern of RA distribution. A high susceptibility to systemically applied retinoic acid indicates that the developing cerebellum is naturally disposed to respond to endogenously synthesized RA. l now propose to investigate the pathways of retinoid metabolism and signal transduction in the developing cerebellum in order to determine how factors that interfere with these processes disrupt development. l will be assisted by several experts at the Shriver Center in the fields of lipid analysis and molecular biology. Initially, l will use both novel and traditional techniques to study RA metabolism during normal cerebellar development, then investigate the developmental changes that result from in-vivo disturbances of such pathways. In order to facilitate future work on cerebellar abnormalities in humans l will also isolate the human homologue of the murine retinoic-acid generating enzyme.

DESCRIPTION (provided by applicant): Numerous clinical reports have associated the use of the acne drug Accutane (Isotretinoin, 1 3-cis retinoic acid, RA) with depression. However, the precise behavioral effects of RA are unknown because few studies have investigated the neurological effects of RA. RA enters the CNS and is a potent transcriptional activator and thus it is highly likely that RA will influence brain function. One of the few areas of the adult brain in which RA function has been investigated is the hippocampus where RA is required for learning and memory. These processes probably require new neuronal birth in the hippocampus and RA may be linked via its influence as a powerful inducer of neural stem cell differentiation. A new hypothesis for the underlying cause of human depression is a decline in the birth of new neurons in the hippocampus. Chronic exposure to RA would be expected to cause exactly that by persistently inducing neuronal differentiation and eventually depleting the neural stem cells that generate neurons. The goal will be to test this hypothesis by investigating the influence of RA on cell division in the hippocampus as measured by 5-bromo deoxy-uridine (BrdU) incorporation into cells double labeled for either neuronal or glial cell markers. This will be correlated with hippocampal dependant and independent behavioral changes in these animals. We predict that treatment with RA will result in a decrease in hippocampal neurogensis in mice and will result in degradation of hippocampal dependant behavior. These studies will lead to future studies on 1) the normal function of RA in hippocampal neurogenesis, 2) the role of neurogenesis in behavior changes and, most importantly 3) the neurological consequences of Accutane treatment.