More than 200,000 patients are treated every year for peripheral nerve injury. Approximately 90% of patients never recover full movement of an injured limb. Slow axon regeneration and/or misdirected axon targeting are most often blamed for these poor functional outcomes. Increased neuronal activity, such as through exercise or electrical stimulation, enhances axon regeneration following peripheral nerve injury. We have shown that brain derived neurotrophic factor (BDNF) expression in the neurons whose axons are regenerating is required for this enhancement, but also that signaling through androgen receptors is required in both males and females. The source of the ligands for these receptors, androgens, is not known, especially in females. We hypothesize that their availability could be altered by the effects of neuronal activity on steroid converting enzymes. By measuring the expression of these enzymes in both neuronal and non-neuronal cells in response to increased neuronal activity, we anticipate that we can identify the sources of androgen that promote enhanced axon regeneration. The targets of androgenic activity required to promote axon regeneration also are poorly known. By evaluating the effects of increased neuronal activity on axon regeneration in mice in which the androgen receptor gene is knocked out in a cell-type specific manner, we will be able to identify the cellular requirements for androgen receptor-mediated enhancement of axon regeneration. In this proposed study, we will use a combination of newly available technologies to investigate these roles. Clinically, androgen therapy is already in use. Knowledge of androgen production and signaling is needed to tailor this potential therapy for peripheral nerve regeneration and could be applied to other neurodegenerative diseases.
More than 200,000 patients are treated every year for peripheral nerve injury. Approximately 90% of patients never recover full movement of an injured limb. To date there is no medical treatment for these individuals. Surgery consists of simply suturing the nerve together with no further treatments to enhance speed or targeting of regenerating axons. The results of the proposed study will inform clinicians about the role androgens play in activity enhanced axon regeneration, taking into account the androgen status of the patient (men, women, children, and aging) and/or implementing androgen therapy with physical therapies may result in efficacious treatment for a diverse population of nerve injury patients.