Acetylcholinesterase and Neuroregeneration

Most victims of spinal cord injury (SCI) are between the ages of 16 and 45 and often require costly supportive care and suffer drastic reduction in the quality of life for many decades. In SCI involving the white matter, the centrally projecting axons of the dorsal root ganglion (DRG) which convey somatosensory information from the limbs and trunk are severed. Regeneration and formations of functional synaptic contacts of these fibers is essential for the restoration of sensory perception from the trunk and limbs. Studies from our laboratory and others have identified a novel, neurite growth promoting function of the enzyme acetylcholinesterase (AChE) which is present throughout the life of these neurons and in their immediate environment. AChE is well known for its presence at cholinergic synapses to hydrolyze and terminate the action of the neurotransmitter acetylcholine (ACh). However it is present in DRG neurons though there are no synapses at DRG suggesting a non-synaptic function of AChE in DRG. Cell culture studies have shown that the level of AChE expression in DRG neurons is substratum sensitive and inhibition of AChE impairs neurite growth in these neurons. AChE can function as a neuronal growth factor as it shares aminoacid sequence homology with cell adhesion molecules which are known to promote neurite growth. Based on these findings and our preliminary results we propose to investigate AChE's role as a neurite growth factor in DRG neurons in dissociated neuronal and implant ganglia cultures since cell culture methods allow us to readily analyze and manipulate the immediate environment of the neuron and determine the direct response of neurons to trophic factors. The experiments in the specific aims are designed to address (1) Does AChE promote neurite growth in DRG independent of its catalytic function? (2) if so, does AChE promote neurite gowth by promoting cell adhesion to substratum or extracellular matrix? (3) Does AChE's effect on neurite growth is mediated by its carbohydrates? These studies will enable us to understand how AChE stimulates regeneration in DRG neurons and will help me extend these studies to SCI models. Knowledge of the mechanism of action of a ubiquitous neurotrophic factor which is readily available in adult CNS neurons, cerebrospinal fluid, macrophages and erythrocytes will help in developing strategies to promote growth and thus accelerate functional recovery following spinal cord injury.