89th Annual Meeting Abstracts

PURPOSE: The purpose of this study was to utilize novel, fluorescing transgenic and double-transgenic mice (S-100/GFP and S-100/GFPxMyo-GDNF) models to assess the effects of glial cell line-derived neurotrophic factor (GDNF) on Schwann cell (SC) migration in peripheral nerve regeneration post-transection in a 1 cm sciatic nerve graft model.
METHODS: 110 mice were part of four treatment groups, listed A-D: (A) Transgenic S-100/GFP mice, (B) Double Transgenic S-100/GFPxMyo-GDNF mice, (C) Wild-type (WT) fluorescent naïve mice, and (D) Transgenic fluorescent naïve Myo-GDNF mice. Experimental groups A and B underwent proximal sciatic nerve transection and subsequent repair of a 1 cm nerve gap with both (1) fluorescent naïve nerve isograft, and (2) fluorescent naïve processed nerve allograft - via Hudson technique. Experimental groups C and D underwent proximal sciatic nerve transection and subsequent repair of a 1 cm nerve gap with (3) fluorescing S-100/GFP isograft. All experimental groups were analyzed for fifteen weeks post-operatively. At 3, 6, 9, 12, and 15 week time points, animals underwent in-vivo live -serial imaging, using fluorescence microscopy, to evaluate both host SC migration into the graft and the native graft SC migration into the host nerve. At 15 weeks post-operatively, nerves were harvested for histomorphometric and immunohistochemical outcome measures.
RESULTS: At 3, 6, 9, 12 and 15 weeks post-operative time points, SC were able to be qualitatively analyzed in the constitutively expressing S-100/GFP animals migrating into fluorescence naïve grafts using a special fluorescence dissecting microscope. Additionally, the S-100/GFP grafts showed differential migration of SC out of the graft into the host over time. Finally, longitudinal assessment comparing the Myo-GDNF animals to the WT controls showed earlier migration of host SC into the graft, and preliminary histomorphometry supports increased nerve fiber counts and percent nerve when compared to non-Myo-GDNF expressing mice.
CONCLUSION: We suggest that the findings of this investigation are tri-fold: (1), this study establishes the utility of a longitudinal analysis of SC migration over time using a non-invasive in vivo imaging model; (2), we add further evidence to the growing body of literature concerning the role and importance of SC migration in peripheral nerve regeneration following a transection injury; and (3), that constitutive GDNF over-expression leads to more rapid and robust nerve regeneration compared to non-GDNF expressing controls. This data directly applies to a coming paradigm shift in treatment of peripheral nerve injuries. Future treatment modalities could focus on up-regulating endogenous GDNF levels by either direct muscular injection or via novel viral delivery vectors.