Femke Mathot

9 MSC gene expression on nerve substitutes 153 impede axon sprouting by inducing scarring. 51 The time passed after seeding (p=0.014) and the type of nerve substitute (p=0.033) both had a significant effect on the COL1A1 gene expression ratio. Directly after seeding, MSCs on NeuraGen® Nerve Guides (2.468 ± 0.064) had a significant higher COL1A1 expression ratio than MSCs on Avance® Nerve Grafts (1.152 ± 0.332) (p=0.008). Aside from increased COL1A1 expression directly (NeuraGen® Nerve Guide), 14 (Avance® Nerve Graft) and 21 days (NeuraGen® Nerve Guides) after seeding, the COL1A1 expression in the NeuraGen® Nerve Guide group was comparable to the baseline COL1A1 expression of unseeded MSCs. Collagenase type 3 (COL3A1) Just like type 1, collagenase type 3 is a fibril forming collagen and an ECM component in the peripheral nervous system, regulating Schwann cell differentiation and axonal guidance. 51, 52 The COL3A1 gene expression ratio was significantly affected by time after seeding (p<0.001) and the type of nerve substitute (p=0.014). The expression curve of both groups was u-shaped and approximated a ratio of 1 (i.e. comparable to baseline COL3A1 expression), with a significant higher expression ratio of MSCs seeded onto NeuraGen® Nerve Guides after 21 days (1.696 ± 0.132 versus 0.664 ± 0.192, p<0.001). Fibulin-1 (FBLN1) FBLN-1 expression was assessed as it is a component of the perineurium of peripheral nerves and fulfills a axonal guiding and supporting function. 53 Time after seeding (p<0.001) and type of nerve substitute (p=0.002) both significantly affected the FBLN1 expression ratio. When comparing groups over time, the MSCs seeded onto NeuraGen® Nerve Guides had a significant higher FBLN1 expression ratio after 14 (0.760 ± 0.193 versus 0.236 ± 0.079, p=0.037) and 21 days (1.962 ± 0.318 versus 0.340 ± 0.183, p<0.001). The expression in the Avance® Nerve Graft group remained low over time, while the expression in the NeuraGen® Nerve Guide group seemed to arise from 7 days onwards, demonstrating significant upregulation of the baseline FBLN1 expression. Laminin Beta 2 subunit (LAMB2) LAMB2 is a basis laminin protein that is essential in proper synaptogenesis at neuromuscular junctions. 54 There was no significant effect of either the time passed after seeding (p=0.247) nor the type of nerve substitute (p=0.354). No significant differences between groups occurred over time, while the expression in both groups remained lower than the expression in unseeded MSCs. Immunoglobulin expression (Figure 5) Cluster of Differentiation 96 (CD96) CD96 is an immunoglobulin family member that interferes in the adhesive interactions between cells, in the late phase immune response. 55 Only the factor time significantly affected the CD96 expression rate (p=0.011). 21 days after seeding, the expression in MSCs seeded onto NeuraGen® Nerve Guides (2.226 ± 0.443) was significantly higher than the expression