Schwann cells genetically modified to secrete human BDNF promote enhanced axonal regrowth across transected adult rat spinal cord

Abstract

The infusion of BDNF and NT-3 into Schwann cell (SC) grafts promotes regeneration of brainstem neurones into the grafts placed in adult rat spinal cord transected at T8 (Xu et al., 1995b). Here, we compared normal SCs with SCs genetically modified to secrete human BDNF, grafted as trails 5 mm long in the cord distal to a transection site and also deposited in the transection site, for their ability to stimulate supraspinal axonal regeneration beyond the injury. SCs were infected with the replication-deficient retroviral vector pL(hBDNF)RNL encoding the human preproBDNF cDNA. The amounts of BDNF secreted (as detected by ELISA) were 23 and 5 ng/24 h per 106 cells for infected and normal SCs, respectively. Biological activity of the secreted BDNF was confirmed by retinal ganglion cell bioassay. The adult rat spinal cord was transected at T8. The use of Hoechst prelabelled SCs demonstrated that trails were maintained for a month. In controls, no SCs were grafted. One month after grafting, axons were present in SC trails. More 5-HT-positive and some DbetaH-positive fibres were observed in the infected vs. normal SC trails. When Fast Blue was injected 5 mm below the transection site (at the end of the trail), as many as 135 retrogradely labelled neurones could be found in the brainstem, mostly in the reticular and raphe nuclei (normal SCs, up to 22, mostly in vestibular nuclei). Numerous neurones were labelled in the ventral hypothalamus (normal SCs, 0). Also, following Fast Blue injection, a mean of 138 labelled cells was present in dorsal root ganglia (normal SCs, 46) and spinal cord (39 vs. 32) rostral to the transection. No labelled spinal neurones rostral to the transection were seen when SCs were not transplanted. Thus, the transplantation of SCs secreting increased amounts of BDNF improved the regenerative response across a transection site in the thoracic cord. Moreover, the enhanced regeneration observed with infected SCs may be specific as the largest response was from neurones known to express trkB.

Freeze-dried poly(d,l-lactic acid) macroporous guidance scaffolds impregnated with brain-derived neurotrophic factor in the transected adult rat thoracic spinal cord

“…Axons were present in BDNF-foam at 2 weeks after implantation, whereas at this time point control foam was lacking axons. Previously, BDNF has been shown to promote axonal regeneration into and from intraspinal grafts [18,25,27,[40][41][42]. Clearly, the more rapid growth of axons into the BDNF containing foam may have resulted from the axonal growth-promoting properties of BDNF.…”

“…Following grafting into the transected spinal cord, a SC bridge contained in a polymer tubular scaffold promotes regeneration and myelination of damaged axons [22,23]. Combining a SC graft with a neuroprotective agent [24] or growth factors [25][26][27] enhances the overall axonal growth response. In the abovementioned studies, the SC bridge was contained within a non-degradable polyacrylnitril/polyvinylchloride (PAN/PVC) scaffold.…”

“…For this study, foams (diameter 2.6 mm; same as adult rat thoracic spinal cord) were made with or without incorporation of the neurotrophic factor, brain-derived neurotrophic factor (BDNF). BDNF was chosen in combination with the foam because of its effects on cell survival [36][37][38][39] and axonal regeneration [18,27,[40][41][42]. Following implantation, we have evaluated the effects of the foams on tissue sparing, neuronal survival, axonal regeneration, and behavioral improvements of the hindlimbs in the transected adult rat thoracic spinal cord.…”

Transplantation strategies to promote repair of the injured spinal cord

“…When the two neurotrophins were infused into the space between the SC bridge and the channel wall for 14 days (and the animals maintained for a month), there were twice as many myelinated axons on the bridge, there were three times as many responding spinal cord neurons, and brainstem neurons were responsive; when a tracer was placed inside the bridge, there was labeling of a mean of 92 neurons in the brainstem. In other experiments [25], SCs were transduced with a human prepro BDNF cDNA that was introduced by means of a retrovirus. This paradigm differed somewhat from the one described above, in that the spinal cord was transected and the SCs (transduced or untreated) were deposited in the distal stump to create a 5 mm-long trail, as well as in the transection site.…”

Setting the stage for functional repair of spinal cord injuries: a cast of thousands

“…253 Both types of cells have been genetically modified prior to transplantation to deliver growth factors at the lesion site. 245,254,255 OECs have been reported to integrate more successfully with astrocytes, 256 and to induce less glial scarring 257 than SCs, but may themselves express inhibitory molecules (such as Nogo or proteoglycans, discussed in 'Stimulating axonal growth in the injured spinal cord' above) after transplantation. 258 Few experiments have directly compared SC-and OEC-transplantation in the same injury.…”