Changes in Glial cell line-derived neurotrophic factor expression in the rostral and caudal stumps of the transected adult rat spinal cord

A comparative analysis of differentially expressed genes in rostral and caudal regions after spinal cord injury in rats

The initial mechanical damage of a spinal cord injury (SCI) triggers a progressive secondary injury cascade, which is a complicated process integrating multiple systems and cells. It is crucial to explore the molecular and biological process alterations that occur after SCI for therapy development. The differences between the rostral and caudal regions around an SCI lesion have received little attention. Here, we analyzed the differentially expressed genes between rostral and caudal sites after injury to determine the biological processes in these two segments after SCI. We identified a set of differentially expressed genes, including Col3a1, Col1a1, Dcn, Fn1, Kcnk3, and Nrg1, between rostral and caudal regions at different time points following SCI. Functional enrichment analysis indicated that these genes were involved in response to mechanical stimulus, blood vessel development, and brain development. We then chose Col3a1, Col1a1, Dcn, Fn1, Kcnk3, and Nrg1 for quantitative real-time PCR and Fn1 for immunostaining validation. Our results indicate alterations in different biological events enriched in the rostral and caudal lesion areas, providing new insights into the pathology of SCI.

Thermosensitive heparin-poloxamer hydrogels enhance the effects of GDNF on neuronal circuit remodeling and neuroprotection after spinal cord injury

Traumatic spinal cord injury (SCI) results in paraplegia or quadriplegia, and currently, therapeutic interventions for axonal regeneration after SCI are not clinically available. Animal studies have revealed that glial cell-derived neurotrophic factor (GDNF) plays multiple beneficial roles in neuroprotection, glial scarring remodeling, axon regeneration and remyelination in SCI. However, the poor physicochemical stability of GDNF, as well as its limited ability to cross the blood-spinal cord barrier, hampers the development of GDNF as an effective therapeutic intervention in clinical practice. In this study, a novel temperature-sensitive heparin-poloxamer (HP) hydrogel with high GDNF-binding affinity was developed. HP hydrogels showed a supporting scaffold for GDNF when it was injected into the lesion epicenter after SCI. GDNF-HP by orthotopic injection on lesioned spinal cord promoted the beneficial effects of GDNF on neural stem cell proliferation, reactive astrogliosis inhibition, axonal regeneration or plasticity, neuroprotection against cell apoptosis, and body functional recovery. Most interestingly, GDNF demonstrated a bidirectional regulation of autophagy, which inhibited cell apoptosis at different stages of SCI. Furthermore, the HP hydrogel promoted the inhibition of autophagy-induced apoptosis by GDNF in SCI. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2816-2829, 2017.

Combined transplantation of GDAs(BMP) and hr-decorin in spinal cord contusion repair

Following spinal cord injury, astrocyte proliferation and scar formation are the main factors inhibiting the regeneration and growth of spinal cord axons. Recombinant decorin suppresses inflammatory reactions, inhibits glial scar formation, and promotes axonal growth. Rat models of T₈ spinal cord contusion were created with the NYU impactor and these models were subjected to combined transplantation of bone morphogenetic protein-4-induced glial-restricted precursor-derived astrocytes and human recombinant decorin transplantation. At 28 days after spinal cord contusion, double-immunofluorescent histochemistry revealed that combined transplantation inhibited the early inflammatory response in injured rats. Furthermore, brain-derived neurotrophic factor, which was secreted by transplanted cells, protected injured axons. The combined transplantation promoted axonal regeneration and growth of injured motor and sensory neurons by inhibiting astrocyte proliferation and glial scar formation, with astrocytes forming a linear arrangement in the contused spinal cord, thus providing axonal regeneration channels.

BDNF expression with functional improvement in transected spinal cord treated with neural stem cells in adult rats

Neural stem cells (NSC) could promote the repair after spinal cord transection (SCT), the underlying mechanism, however, still keeps to be defined. This study reported that NSC grafts significantly improved sensory and locomotor functions in adult rats with SCT in acute stage after injury. NSC could survive; differentiate towards neurons or glia lineage in vitro and vivo. Biotin dextran amine (BDA) tracing showed that little CST regeneration in the injury site, while SEP was recorded in NSC engrafted rats. Immunohistochemistry and Real time PCR confirmed that engrafted NSC expressed BDNF and increased the level of BDNF mRNA in injured site following transplantation. The present data therefore suggested that the functional recovery following SCT with NSC transplantation was correlated with the expression of BDNF, indicating the usage of BDNF with NSC transplantation in the treatment of SCI following injury.

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.

Prolonged survival and milder impairment of motor function in the SOD1 ALS mouse model devoid of fibroblast growth factor 2

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by selective motoneuron loss in brain and spinal cord. Mutations in the superoxide dismutase (SOD) 1 gene account for 10-20% of familial ALS patients. The ALS-mouse model over-expressing a mutant human SOD1 (G93A) gene closely mimics human ALS disease. The cause for the selective death of motoneurons is still unclear, but among several pathomechanisms discussed, loss of neurotrophic factors is one possibility. Basic fibroblast growth factor 2 (FGF-2) plays a prominent role in the motor system. In order to evaluate a role of FGF-2 in ALS pathogenesis, double mouse mutants transgenic for the human SOD1 mutation and lacking the endogenous FGF-2 gene were generated. Both heterozygous and homozygous FGF-2 deficient mutant SOD1 mice showed a significant delay in disease onset and less impaired motor performance in comparison to mutant SOD1 mice with normal FGF-2 levels. Survival of the double mouse mutants was significantly prolonged for two weeks. Motoneuron numbers were significantly higher in the double mutants and astrocytosis was diminished at disease endstage. While one would initially have expected that FGF-2 deficiency deteriorates the phenotype of mutant SOD1 animals, our results revealed a protective effect of FGF-2 reduction. In search of the underlying mechanisms, we could show up-regulation of other neurotrophic factors with proven protective effects in the ALS mouse model, ciliary neurotrophic factor (CNTF) and glial derived neurotrophic factor (GDNF) in muscle and spinal cord tissue of double mutant animals.

Activity-dependent increase in neurotrophic factors is associated with an enhanced modulation of spinal reflexes after spinal cord injury

Activity-based therapies such as passive bicycling and step-training on a treadmill contribute to motor recovery after spinal cord injury (SCI), leading to a greater number of steps performed, improved gait kinematics, recovery of phase-dependent modulation of spinal reflexes, and prevention of decrease in muscle mass. Both tasks consist of alternating movements that rhythmically stretch and shorten hindlimb muscles. However, the paralyzed hindlimbs are passively moved by a motorized apparatus during bike-training, whereas locomotor movements during step-training are generated by spinal networks triggered by afferent feedback. Our objective was to compare the task-dependent effect of bike- and step-training after SCI on physiological measures of spinal cord plasticity in relation to changes in levels of neurotrophic factors. Thirty adult female Sprague-Dawley rats underwent complete spinal transection at a low thoracic level (T12). The rats were assigned to one of three groups: bike-training, step-training, or no training. The exercise regimen consisted of 15 min/d, 5 days/week, for 4 weeks, beginning 5 days after SCI. During a terminal experiment, H-reflexes were recorded from interosseus foot muscles following stimulation of the tibial nerve at 0.3, 5, or 10 Hz. The animals were sacrificed and the spinal cords were harvested for Western blot analysis of the expression of neurotrophic factors in the lumbar spinal cord. We provide evidence that bike- and step-training significantly increase the levels of brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and NT-4 in the lumbar enlargement of SCI rats, whereas only step-training increased glial cell-derived neurotrophic factor (GDNF) levels. An increase in neurotrophic factor protein levels that positively correlated with the recovery of H-reflex frequency-dependent depression suggests a role for neurotrophic factors in reflex normalization.

Recombinant DNA vaccine against inhibition of neurite outgrowth promotes functional recovery associated with endogeous NGF expression in spinal cord hemisected adult rats

Axonal regeneration across the site of spinal cord lesion is often aborted in adult mammalian species. The use of DNA vaccine to nullify the inhibitory molecules has been shown to be effective in promoting axonal regeneration in injured spinal cord. The possible molecular mechanisms, however, remain to be elucidated. The present study showed that the administration of recombinant DNA vaccine encoding multiple domains, Nogo-66, Nogo-N, TnR, and MAG, significantly improved hindlimb locomotor functions in rats subjected to ablation of the dorsal halves of the cord. Western blot analysis demonstrated that nerve growth factor (NGF) levels in the spinal cord of immunized rats were significantly upregulated than those of control rats. Immunohistochemistry as well as in situ hybridization confirmed that NGF was expressed in neurons of the spinal cord. These findings indicated that functional recovery in immunized rats could be correlated with endogeous NGF expression in hemisected rat spinal cords.