Vocal fold paralysis (VFP) occurs when the recurrent laryngeal nerve (RLN) is injured, most commonly during surgery of the neck. Bilateral injury to the RLN can result in potentially life-threatening airway obstruction and the need for tracheostomy. The RLN can regenerate some of its axons, but in many patients with paralysis some form of intervention is required to correct the airway obstruction and voice changes. This is most frequently achieved through reinnervation of the laryngeal muscles to restore function. Current practice is to wait 6-24 months before any intervention is performed as spontaneous recovery can occur. This delay before repair allows chronic changes in the nerve distal to the site of injury to occur and results in poor recovery. The overall goal of this proposal is to accelerate recovery after RLN injury and reduce the consequences of prolonged denervation before nerve graft. Previous work has focused mainly on events that occur late in the repair and remodeling process. Little is known about how manipulating events in the early stages of repair can be used to improve recovery. We have recently shown that modifying the type of macrophages accumulating at the graft site early after injury increases Schwann cell migration in the regenerative bridge and improves recovery. Our preliminary data show that when graft is delayed the phenotype of macrophages at the repair site is altered. We hypothesize that changes in the function of senescent Schwann cells (SC) in the distal nerve stump are responsible for this change. In this proposal we will evaluate how macrophage and SC function and gene expression are altered after delayed graft. We will determine gene expression, phagocytosis and migration for both cell types and determine the consequences of these changes on tissue remodeling using a variety of techniques including protein expression, the formation of a polarized microvasculature, axon extension and the number of axons reaching their target. Our preliminary data also demonstrate that an exogenous anti-inflammatory ligand can alter macrophage phenotype and promote axon extension and the formation of neuromuscular junctions. We will then test the neuroprotective ability of this ligand to rescue the changes we have identified in delayed repair and then confirm these changes are mediated by macrophages. Finally, we test the ability of manipulation of macrophage phenotype to accelerate recovery after acute injury using a translational animal model. The ability to accelerate recovery following RLN injury, by intervening intra-operatively, would reduce the consequences of delayed repair and improve recovery for patients with VFP.
This project determines the mechanisms which affect nerve repair when nerve graft is delayed. We will determine how a delay affects alters macrophage and Schwann cell function and subsequent remodeling and identify and verify the importance of up to four potential therapeutic targets for the treatment of recurrent laryngeal nerve injury. We will also test the ability of one target to diminish the consequences of RLN injury and restore normal voice and breathing in patients with laryngeal paralysis.
