Femke Mathot

Chapter 9 152 Myelin protein zero (MPZ) MPZ is also expressed by Schwann cells and is the main protein of (compact) myelin. Reduced expression of MPZ results in instable myelination, leading to neuropathies and axonal loss. MPZ is therefore pivotal in successful nerve regeneration. 43 The MPZ gene expression ratio was not significantly affected by type of nerve substitute (p=0.936), nor by the time passed after seeding (p=0.650). Compared to the baseline MPZ expression in unseeded MSCs, the expression ratio in both groups was increased both at the beginning (up to 3 days after seeding) and at the end (21 days) of the experiment. There were no significant differences in MPZ expression over time between groups. Angiogenic gene expression (Figure 3) Vascular Endothelial Growth Factor alpha (VEGF-a) Neoangiogenesis occurs from two days onwards after nerve injury and facilitates the delivery of trophic factors at the nerve stump and guides Schwann cells in the right direction. 46-48 Enhanced expression and production of VEGF-A induces local angiogenesis, playing an important role in the peripheral nerve regeneration process. 49 The type of nerve substitute had no significant effect on the VEGF-a expression of seeded MSCs (p=0.107). Time passing did have a significant effect on the VEGF-a expression of seeded MSCs (p<0.001). The VEGF-a expression in both groups was high (4 to 12 fold of the baseline expression) in the first 24 hours after seeding, equal to unseeded MSCs around 3 to 7 days after seeding and then increased again (3 to 8 fold of the baseline expression) up to 21 days after seeding. The VEGF-a expression was significantly higher in the MSCs seeded on NeuraGen® Nerve Guides directly after seeding (11.006 ± 0.33 versus 6.698 ± 1.502, p=0.020) and 21 days after seeding (8.690 ± 2.062 versus 4.118 ± 1.847, p=0.011). Platelet Endothelial Cell Adhesion Molecule (PECAM-1/CD31) CD31 regulates endothelial cell adhesion, being crucial in the process of angiogenesis. 50 The factor time significantly influenced the CD31 expression ratio (p<0.001), but the type of nerve substitute did not have a significant impact (p=0.77). When comparing groups over time, MSCs seeded onto NeuraGen® Nerve Guides had a significant higher CD31 expression ratio compared to MSCs seeded onto Avance® Nerve Grafts directly after seeding (3.016 ± 0.364 versus 1.096 ± 0.13, p=0.025) and 21 days after seeding (2.254 ± 0.815 versus 0.244 ± 0.123, p=0.017). The expression in the NeuraGen® Nerve Guide group was significantly lower than in the Avance® Nerve Graft group 1 day after seeding (p<0.001). With the exception of directly, 1 day and 21 days after seeding, all other time points demonstrated significant downregulation of the baseline CD31 expression of unseeded MSCs. Extracellular matrix gene expression (Figure 4) Collagenase type 1 (COL1A1) The COL1A1 gene encodes for the main component of type 1 collagen. This ECM-component regulates Schwann cell proliferation and differentiation, but overexpression of COL1A1 could