GDNF Schwann cells in hydrogel scaffolds promote regional axon regeneration, remyelination and functional improvement after spinal cord transection in rats

Abstract

Positively-charged oligo[poly(ethylene glycol)fumarate] (OPF ) is a biodegradable hydrogel used for spinal cord injury repair. We compared scaffolds containing primary Schwann cells (SCs) to scaffolds delivering SCs genetically modified to secrete high concentrations of glial cell-derived neurotrophic factor (GDNF). Multichannel OPF scaffolds loaded with SCs or GDNF-SCs were implanted into transected rat spinal cords for 4 weeks. GDNF-SCs promoted regeneration of more axons into OPF scaffolds (2773.0 ± 396.0) than primary SC OPF scaffolds (1666.0 ± 352.2) (p = 0.0491). This increase was most significant in central and ventral-midline channels of the scaffold. Axonal remyelination was quantitated by stereologic analysis. Increased myelination of regenerating axons was observed in the GDNF-SC group. Myelinating cell and axon complexes were formed by host SCs and not by implanted cells or host oligodendrocytes. Fast Blue retrograde tracing studies determined the rostral-caudal directionality of axonal growth. The number of neurons that projected axons rostrally through the GDNF-SC scaffolds was higher (7929 ± 1670) than in animals with SC OPF scaffolds (1069 ± 241.5) (p < 0.0001). The majority of ascending axons were derived from neurons located more than 15 mm from the scaffold-cord interface, and were identified to be lumbosacral intraspinal motor neurons. Transected animals with GDNF-SC OPF scaffolds partially recovered locomotor function at weeks 3 and 4 following surgery. Copyright © 2017 John Wiley & Sons, Ltd.

Combinatorial tissue engineering partially restores function after spinal cord injury

“…Our primary study focus was to determine the combinatorial or additive effects between the drug and implanted cells, rather than between the drug in empty scaffolds. We have consistently shown than MG‐only scaffolds are capable of supporting a rate of axonal regeneration that is approximately 80% less than that seen with SC‐implanted scaffolds without drug elution (Chen et al, ; Hakim et al, ; Madigan et al, ). The effect of rapamycin on astrocytes, including on astrocyte infiltration into the scaffold and on astroglial scar formation, was also not assessed in the current study, and represents another important limitation in the clarification of mechanisms behind the observed functional improvement.…”

Combinatorial Tissue Engineering Partially Restores Function after Spinal Cord Injury

“…Different types of biomimetic synthetic scaffolds have previously been compared and demonstrated that OPF+ supports the most robust axonal regeneration . Schwann cells produce the extracellular microenvironment that supports regeneration of CNS axons and promote regeneration in OPF+ scaffolds (Chen et al 2017;Olson et al 2009). Fibrosis and a foreign body response to SC-loaded OPF+ scaffolds were identified as a major remaining barrier to axon regeneration and functional recovery (Hakim et al 2015).…”

“…Scores for the left and right hind limbs were then averaged to obtain the overall BBB score for each animal, which was used for statistical analyses. As in previous our previous studies (Chen et al 2017;Hakim et al 2015) any animal with a BBB score greater than 4 (representing slight movement of all three joints of the hind limb) at one week post implantation was considered to have a physiologically incomplete transection and was excluded from further functional analysis. A total of 10 rats distributed across all groups from both cohorts were excluded in this way (Table 1).…”

“…Ten animals from both groups of the second cohort underwent a second surgery 5 weeks after scaffold implantation for Fast Blue (FB) retrograde tracer analysis, as we have previously described Chen et al 2017). The spinal cord was re-exposed at the level of the prior implantation and 0.6 μL of Fast Blue dye was stereotactically injected into the spinal cord with a Hamilton syringe through a second surgical laminectomy at a distance of 5 mm rostral (5 animals/group) or caudal (5 animals/group) to the implanted scaffold.…”

“…Fast Blue (FB)-labeled neurons were quantified as previously described Chen et al 2017) within 30 micron thick longitudinal frozen sections. Labeled neurons in the P1-P3 and S1-S2 ( Fig.…”