Injuries to peripheral nerves are common, but recovery from them is very poor. There is currently no non- surgical treatment available. Brain-derived neurotrophic factor (BDNF), and other growth factors, are known to promote axon regeneration following peripheral nerve injury. The objectives of this proposal are to: 1) investigate whether the molecular mechanism by which this effect is achieved is through stabilization of the axonal microtubule-associated protein, Tau in the regenerating axons; and 2) to examine the therapeutic efficacy of two targeted pharmacological agents designed to mimic these cellular effects. Asparagine endopeptidase (AEP), a cysteine protease, is robustly activated in cut peripheral nerves and mediates cleavage of Tau that degrades its stabilizing effect on the axonal cytoskeleton. Because such stabilization is an essential feature of successful axon regeneration after peripheral nerve injury, inhibiting AEP could be an important effect of growth factor signaling after peripheral nerve injury. We hypothesize that Akt, activated by growth factors such as BDNF (or the small molecule BDNF mimetic, 7,8 DHF), phosphorylates AEP and suppresses its enzymatic activity, thereby preventing degradation of Tau, leading to enhanced axon regeneration. We will combine in vitro and in vivo experiments to evaluate critical aspects of this hypothesis in the first two Specific Aims. We have developed a prodrug that elevates oral bioavailability of 7,8-DHF. We also have identified a small allosteric inhibitor of AEP, which blocks Tau cleavage in mice. We will explore the therapeutic efficacy of treatments with the prodrug or/and the AEP inhibitor in promoting axon regeneration and functional recovery in Specific Aim 3. Successful completion of the proposed studies will lead to better understanding of the molecular mechanisms of growth factor-mediated axon regeneration and identification of a novel drug target for treatment of peripheral nerve injury.
There are more than 200,000 new traumatic peripheral nerve injuries and nearly twice as many non-traumatic nerve injuries in the US each year. A very large percentage of these affected indi- viduals never recover any function, and there is no medical (non surgical) treatment for them. The scientific discoveries expected from the experiments in this proposal will represent new knowledge that could be applied to reduce the burdens of disability for these victims.
