Proteomic comparison of biomaterial implants for regeneration of peripheral nerve tissue

Abstract

Tissue regenerates resulting from the healing of transected peripheral nerve differ in morphological and electrophysiological properties based on the biomaterial implant used to bridge the interneural wound gap. At gap lengths >/=10 mm, impermeable silicone tubes promote little to no nerve regenerate unlike its porous, degradable collagen alternative. This study assayed rat sciatic nerve wounds treated with silicone and collagen tubes at a 14-day time point for concentration differences in transforming growth factor beta 1, 2, 3 (TGF [beta]1, [beta]2, and [beta]3) and alpha smooth muscle actin ([aipha] SMA) to measure disparities in proteins associated with wound healing that may determine nonregenerative from regenerative outcomes. Transected nerves treated with silicone or collagen tubes were compared on a "whole wound" basis to determine differences in protein expression over the entire tissue and on a "per segment" basis to determine local differences in protein expression over ~2-4 mm regions of tissue. Immunofluorescent comparisons of wounds were performed on cross sections taken along the length of the nerve. In each cross section, a region of interest (ROI) was defined from the periphery of the regenerate tissue to -65 gm radially inwards where presence of a contractile capsule was reported by earlier investigators and also observed in this study. A 200% increase in whole wound TGF [beta]3 levels in the collagen compared to the silicone treatment group was determined by immunoblot (p=0.0026). A 30-50% increase in whole wound TGF [beta]1 levels was found in the silicone compared to the collagen treatment group, which was statistically significant by only one of the two assays used (enzyme-linked immunosorbent assay; p=0.0021).

(cont.) There was no significant difference in TGF [beta]2 levels between treatment groups. Whole wound expression of a SMA was 440% greater in the silicone treatment group than in the collagen treatment group by immunoblot measurement. Immunofluorescent measurement indicated that a SMA expression in the ROI was 160% greater in silicone than in collagen treated wounds, with significant differences in the nerve stumps (proximal, p=.0243; distal, p=.0021). Proteomic comparisons suggest that collagen tubes are more effective at promoting nerve regenerate than silicone tubes due to heightened levels of TGF 03, less [alpha] SMA expression, and possibly decreased levels of TGF p1 at early stages of wound healing. Trends in protein differences observed in nerve wounds treated with regenerative versus nonregenerative devices are consistent with differences observed in wounds in the early fetal versus adult healing stages. Results from this study support early fetal regeneration as a model for induced regeneration in the peripheral nerve.