Axonal regrowth downregulates the synthesis of glial cell line-derived neurotrophic factor in the lesioned rat sciatic nerve

Gene expression profiles of human adipose-derived mesenchymal stem cells dynamically seeded on clinically available processed nerve allografts and collagen nerve guides

It was hypothesized that mesenchymal stem cells (MSCs) could provide necessary trophic factors when seeded onto the surfaces of commonly used nerve graft substitutes. We aimed to determine the gene expression of MSCs when influenced by Avance® Nerve Grafts or NeuraGen® Nerve Guides. Human adipose-derived MSCs were cultured and dynamically seeded onto 30 Avance® Nerve Grafts and 30 NeuraGen® Nerve Guides for 12 hours. At six time points after seeding, quantitative polymerase chain reaction analyses were performed for five samples per group. Neurotrophic [nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF), pleiotrophin (PTN), growth associated protein 43 (GAP43) and brain-derived neurotrophic factor (BDNF)], myelination [peripheral myelin protein 22 (PMP22) and myelin protein zero (MPZ)], angiogenic [platelet endothelial cell adhesion molecule 1 (PECAM1/CD31) and vascular endothelial cell growth factor alpha (VEGFA)], extracellular matrix (ECM) [collagen type alpha I (COL1A1), collagen type alpha III (COL3A1), Fibulin 1 (FBLN1) and laminin subunit beta 2 (LAMB2)] and cell surface marker cluster of differentiation 96 (CD96) gene expression was quantified. Unseeded Avance® Nerve Grafts and NeuraGen® Nerve Guides were used to evaluate the baseline gene expression, and unseeded MSCs provided the baseline gene expression of MSCs. The interaction of MSCs with the Avance® Nerve Grafts led to a short-term upregulation of neurotrophic (NGF, GDNF and BDNF), myelination (PMP22 and MPZ) and angiogenic genes (CD31 and VEGFA) and a long-term upregulation of BDNF, VEGFA and COL1A1. The interaction between MSCs and the NeuraGen® Nerve Guide led to short term upregulation of neurotrophic (NGF, GDNF and BDNF) myelination (PMP22 and MPZ), angiogenic (CD31 and VEGFA), ECM (COL1A1) and cell surface (CD96) genes and long-term upregulation of neurotrophic (GDNF and BDNF), angiogenic (CD31 and VEGFA), ECM genes (COL1A1, COL3A1, and FBLN1) and cell surface (CD96) genes. Analysis demonstrated MSCs seeded onto NeuraGen® Nerve Guides expressed significantly higher levels of neurotrophic (PTN), angiogenic (VEGFA) and ECM (COL3A1, FBLN1) genes in the long term period compared to MSCs seeded onto Avance® Nerve Grafts. Overall, the interaction between human MSCs and both nerve graft substitutes resulted in a significant upregulation of the expression of numerous genes important for nerve regeneration over time. The in vitro interaction of MSCs with the NeuraGen® Nerve Guide was more pronounced, particularly in the long term period (> 14 days after seeding). These results suggest that MSC-seeding has potential to be applied in a clinical setting, which needs to be confirmed in future in vitro and in vivo research.

Delivery of chondroitinase ABC and glial cell line-derived neurotrophic factor from silk fibroin conduits enhances peripheral nerve regeneration

Nerve conduits are a proven strategy for guiding axon regrowth following injury. This study compares degradable silk-trehalose films containing chondroitinase ABC (ChABC) and/or glial cell line-derived neurotrophic factor (GDNF) loaded within a silk fibroin-based nerve conduit in a rat sciatic nerve defect model. Four groups of silk conduits were prepared, with the following silk-trehalose films inserted into the conduit: (a) empty; (b) 1 µg GDNF; (3) 2 U ChABC; and (4) 1 µg GDNF/2 U ChABC. Drug release studies demonstrated 20% recovery of GDNF and ChABC at 6 weeks and 24 h, respectively. Six conduits of each type were implanted into 15 mm sciatic nerve defects in Lewis rats; conduits were explanted for histological analysis at 6 weeks. Tissues stained with Schwann cell S-100 antibody demonstrated an increased density of cells in both GDNF- and ChABC-treated groups compared to empty control conduits (p < 0.05). Conduits loaded with GDNF and ChABC also demonstrated higher levels of neuron-specific PGP 9.5 protein when compared to controls (p < 0.05). In this study we demonstrated a method to enhance Schwann cell migration and proliferation and also foster axonal regeneration when repairing peripheral nerve gap defects. Silk fibroin-based nerve conduits possess favourable mechanical and degradative properties and are further enhanced when loaded with ChABC and GDNF. Copyright © 2014 John Wiley & Sons, Ltd.

Injury-induced accumulation of glial cell line-derived neurotrophic factor in the rostral part of the injured rat spinal cord

The spinal cord of a 7-week-old female Wistar rat was hemi-transected at thoracic position 10 with a razor blade, and changes in glial cell line-derived neurotrophic factor (GDNF) protein and mRNA expression levels in the spinal cord were examined. GDNF protein and mRNA expression levels were evaluated by enzyme immunoassay and reverse transcription polymerase chain reaction, respectively. Although GDNF is distributed in the healthy spinal cord from 150 to 400 pg/g tissue in a regionally dependent manner, hemi-transection (left side) of the spinal cord caused a rapid increase in GDNF content in the ipsilateral rostral but not in the caudal part of the spinal cord. On the other hand, injury-induced GDNF mRNA was distributed limitedly in both rostral and caudal stumps. These observations suggest the possibility that increased GDNF in the rostral part is responsible for the accumulation of GDNF that may be constitutively transported from the rostral to caudal side within the spinal cord. Although such local increase of endogenous GDNF protein may not be sufficient for nerve regeneration and locomotor improvement, it may play a physiological role in supporting spinal neurons including motoneurons.

Alginate-matrigel microencapsulated schwann cells for inducible secretion of glial cell line derived neurotrophic factor

Controlled expression of glial cell line derived neurotrophic factor (Gdnf) can be integrated in the development of a system for repair of injured peripheral nerves. This delivery strategy was demonstrated via inducible Gdnf from microencapsulated cells in barium alginate. The Schwann cell line RT4-D6P2T was initially modified utilizing an ecdysone-based stable transfection system to produce RT4-Gdnf cells. During construct preparation, it was found that C6 cells (where Gdnf cDNA was isolated) make three Gdnf transcript variants. Additionally, the importance of 5' untranslated region to drive biologically-functional Gdnf synthesis was shown. Encapsulation of RT4-Gdnf in 1% alginate was then performed. It was determined that cells were able to survive at least 1 month in vitro using starting densities of 20, 200 and 2000 cells/capsule and barium ion concentrations of 10, 50, 100 and 200 mM. Most importantly, encapsulated cells secreted exogenous Gdnf upon ponasterone A induction. Mixture of basement membrane extract Matrigel to alginate promoted increased proliferation, cell spreading and Gdnf release. Finally, compression tests showed that cell-loaded microcapsules fractured at 75% diameter compression with 38 kPa of stress. Regulated Gdnf release from these microcapsules in vivo may potentially aid in the regeneration of damaged nerves.

Neuroprotective effect of sonic hedgehog up-regulated in Schwann cells following sciatic nerve injury

The physiological roles of sonic hedgehog (Shh) have been intensively characterized in development of various organs. However, their functions in adult tissues have not been fully elucidated. We investigated the expression and the potential function of Shh in crush-injured adult rat sciatic nerves. The Shh expression was up-regulated in Schwann cells adjacent to the injured site. The time-course analyses of various neurotrophic factors revealed the up-regulation of Shh mRNA followed by that of brain-derived neurotrophic factor (BDNF) mRNA. The continuous administration of cyclopamine, a hedgehog signal inhibitor, to the injured site suppressed the increase of BDNF expression and deteriorated the survival of motor neurons in lumbar spinal cord. Treatment of exogenous Shh in cultured Schwann cells enhanced the BDNF expression. The BDNF promoter activity (exon I and II) was increased in IMS32 cells co-transfected with Shh and its receptor Smoothened. These findings imply that the up-regulated expression of Shh in Schwann cells may play an important role in injured motor neurons through the induction of BDNF.

Stimulation of production of glial cell line-derived neurotrophic factor and nitric oxide by lipopolysaccharide with different dose-responsiveness in cultured rat macrophages

To understand the molecular basis of inflammation-induced neurotrophic influences, we investigated the effects of lipopolysaccharide (LPS) on production of glial cell line-derived neurotrophic factor (GDNF) in the injured rat spinal cord or in cultured rat macrophages in comparison with the effects on synthesis/secretion of inducible nitric oxide synthase (iNOS) and nitric oxide (NO). We found that GDNF mRNA expression lasted longer than that of iNOS mRNA in the injured spinal cord after injection of the high-dose LPS that had improved locomotor function, suggesting that the GDNF expression and its balance with NO generation were critical for injury regeneration. Therefore, we next investigated the effects of LPS on cultured macrophages. Levels of iNOS mRNA and secreted NO were enhanced by LPS at lower concentrations (10 ng/mL and above), whereas mRNA expression and secretion of GDNF were elevated only at higher concentrations (100 ng/mL and above). The culture medium of macrophages treated with 10 ng/mL of LPS was actually neurotoxic against cultured cortical neurons, whereas that conditioned at 1000 ng/mL was not. These observations suggest that neurotoxicity partly based on NO is induced by a lower degree of inflammation, whereas neurotrophic effects based on GDNF are manifested at a higher degree of inflammatory activity.