Femke Mathot

Chapter 9 158 Figure 6. Proposed mechanism of MSC-seeding on nerve substitutes. The interaction between MSCs and the nerve substitute results in changes in gene expression profiles, leading to production of trophic factors that are involved in Wallerian degeneration and axon regeneration. GF = growth factor ECM components derived from genes like COL1A1, COL3A1, FBLN1 and LAMB2 are essential for creating a pro-regenerative environment in the early stages after nerve injury and facilitate reinnervation in later stages by guiding the growth cone in the right direction (figure 6). 19, 77 Although autografts previously demonstrated a trend of enhanced expression of these ECM markers in vivo compared to unseeded allografts, none of the differences were statistically significant. 72 In the current study, MSCs seeded onto NeuraGen® Nerve Guides demonstrated a U-shaped expression of COL1A1, COL3A1 and FBLN1, corresponding to the described cascade and previous in vitro studies. 73, 78 Considering the absence of detectable RNA levels of unseeded Avance® Nerve Grafts and NeuraGen® Nerve Guides, the influence of the material components of the nerve substitutes on itself on the ECM gene expression is estimated as negligibly small. CD96 is a membrane protein that is involved in the late phase immune response by interfering in adhesive interactions between cells (step 3, figure 6), which potentially explains why its expression remains more or less stable over time. 55 When studying the demonstrated expression curves, some inconsistent expression ratios can be identified. Measures were taken to minimize the vulnerabilities during the obtainment of the mRNA levels like using five replicates per time point, a stable reference gene and experienced researchers. Besides, not all these inconsistent ratios differ significantly from the measures before and after that specific time point. Studying the demonstrated expression