The overall goal of our research is to understand the interaction of signal transduction cascades which mediate neuronal development and survival. Both neurotrophins and neuronal activity induce the transcription of genes crucial for neuronal survival. However, the mechanisms by which these pathways interact to modulate gene expression are unclear. Recent results indicate that cross-talk exists between neurotrophin- and activity- induced cascades. Olfactory receptor neurons (ORNs) are used as a model for these studies: they depend upon both activity and neurotrophins (brain-derived neurotrophic factor, BDNF) for survival ORNs are continually replaced during life from a maintained population of precursors, providing us with an excellent opportunity to study neurogenesis Our data show that both odorants and neurotrophins activate the Ras-MAPK cascade and induce CREB phosphorylation. Odorants increase cAMP, cGMP, inositol phosphates, and intracellular calcium levels. Therefore, any of these pathways may interact with the neurotrophin-induced cascade. We hypothesize that odorant-induced signals modulate neurotrophin-activated cascades to influence neuronal survival. Primary cultures of ORNs in which odorant and neurotrophin signaling is preserved, and genetic models in which activity of neurotrophin signal transduction is interrupted, are utilized in this proposal.
In Aim 1, we will use primary cultures and activators/inhibitors of odorant-induced signaling pathways to characterize the interactions of odorant and BDNF-activated cascades. We will determine dose-response curves and time courses for CREB activation by odorants and BDNF; define the role of the odorant-induced cAMP pathway in CREB activation; and identify the role of other odorant-induced signaling pathways in CREB activation.
In Aim 2, we will define the steps in the Ras-MAPK pathway through which odorant-activated cascades interact with the neurotrophin pathway.
In Aim 3, we will determine which signaling paths are important to ORN survival. Odorants may activate multiple pathways, but not all may be relevant to survival. Genetic models in which either activity (OCNC1 null mice) or BDNF signaling (BDNF null mice) is interrupted are used to define the physiological role of these pathways in survival. Understanding these mechanisms is essential to our ability to manipulate that process.
