Grant: Discovery Grants Program - Individual

Understanding the mechanisms underlying the response of neurons of the mature nervous system to stress and injury is the focus of this proposal. We have been studying mechanisms associated with neuronal survival and axonal regeneration in the dorsal root ganglion (DRG) sensory neurons of adult rodents, with particular interest in the role of heat shock proteins as well as the extracellular environment in these processes.DRG neurons and their axons are the primary sensors of our external environment and as such can be exposed to mechanical, thermal, chemical and osmotic stimuli that can potentially be deleterious. Adult sensory neurons, unlike their embryonic or neonatal counterparts or unlike neurons of the CNS, are relatively resistant to a variety of environmental stressors (heat, high glucose, nutrient starvation), and it is of interest to determine if these cells possess different coping mechanisms in this regard. However, in some situations these stimuli can cause axon terminal damage progressing to axonal dieback and potentially neuronal loss. Autophagy is a regulated cellular process for the degradation and recycling of various cellular components. While autophagy in the nervous system has often been considered in the context of neurodegeneration and stress responses, it is becoming clear that healthy neurons also exhibit basal autophagy although the mechanisms regulating this are not fully understood. It has also been suggested that autophagy may be uniquely regulated in neurons compared to other cell types and may be adapted to the local physiology in the axons. In contrast to studies of autophagy in the CNS there are relatively few studies investigating the role of autophagy in peripheral sensory neurons. Autophagy has been linked to neuronal survival, but the influence differs in different neuronal types and experimental contexts. Although increased numbers of autophagosomes have been observed in damaged axons, the role of autophagy in regeneration following injury remains unclear. Understanding how these processes can influence cellular responses to injury and subsequent neurite regrowth is a fundamental question in the nervous system.Our objectives are to investigate the contribution of autophagy to the response of DRG neurons under basal conditions and following experimental interventions?nutrient deprivation and oxidative stress. Preliminary data support the feasibility of the proposed experiments. We will determine whether autophagy has a positive or negative influence on neuronal survival and axonal regeneration by using chemical modulators of autophagy (eg., rapamycin, 3-MA, chloroquine), by overexpression or RNAi to alter expression of proteins known to regulate the process (eg., beclin, mTOR, Ulk1, HMGB1). We will investigate both neuronal survival and axonal regeneration. Obviously if the neurons undergo autophagic or apoptotic cell death, there will be no axonal regeneration. However, axonal dieback in response to local damage is a problem in the mature nervous system, and understanding how to prevent axonal dystrophy and promote axonal recovery and elongation is key to promoting recovery of function.