Tissue engineering strategies for reinnervation of the larynx.

Objectives. Injury to the recurrent laryngeal nerve (RLN) results in synkinesis and a dysfunctional larynx. Novel nerve repair techniques might enhance the speed of RLN regeneration and encourage accurate muscle reinnervation. Our first approach has been to apply neurotrophins (NT) to the site of repair using artificial nerve conduits. Currently we are investigating whether adult stem cells can be differentiated to provide a source of Schwann cells for future cell-based therapies. Method. In a pig model, the phrenic nerve was anastomosed with the RLN abductor branch(1 )and repaired using poly-hydroxybutyrate wrap-around conduits either untreated or impregnated with NT-3 (500 ng/mL). Markers of nerve regeneration (neurofilament) and muscle denervation/reinnervation (NCAM) were assessed to determine the efficiency of repair. Stem cells were isolated from adipose tissue and treated with glial growth factors for 2 weeks before phenotypic characterisation. Results. Compared with controls, NT-3 treated animals showed significantly elevated levels of neurofilament protein in the distal nerve segment at 2 months (n = 5, P <0.01). Injury increased the number of denervated, NCAM positive abductor muscle fibres from 1.3 +/- 0.68% to 33.9 +/- 5.8% at 2 months and 3.7 +/- 2.3% at 4 months. NT-3 did not significantly reduce these numbers. Differentiated adipose derived stem cells adopted a bi-polar morphology similar to Schwann cells and expressed S100 and GFAP glial proteins. Conclusions. NT-3 treatment promotes early nerve regeneration but is insufficient to enhance long-term muscle reinnervation. Differentiated adipose derived stem cells may represent a novel source of Schwann cells for future RLN repair studies. Reference 1 Kingham P.J., Birchall M.A., Burt R., et al. (2005) Reinnervation of laryngeal muscles: a study of changes in myosin heavy chain expression. Muscle Nerve. 32(6), 761--766.