Functional recovery and regeneration of descending tracts in rats after spinal cord transection in infancy.

STUDY DESIGN: The functional recovery of rats that underwent spinal cord transection in infancy was evaluated by multimodal examination (functional tests, electrophysiologic evaluation, tract-tracing) to determine the basis for the recovery. OBJECTIVES: To determine whether the hind limb function in rats that underwent spinal cord transection in infancy is regained completely, which descending tracts regenerate after the transection, and whether the functional recovery is correlated with axonal reconnection. SUMMARY OF BACKGROUND DATA: It is widely accepted that a newborn rat recovers its hind limb function after spinal cord transection even without any specific treatments. This functional recovery might be attributed to possible regeneration of some descending pathways, although there is a counterargument that well-trained spinal cord reflexes may bring about functional compensation. METHODS: The thoracic spinal cord of infant rats was completely transected at Th10 when they were 2 weeks of age. Multimodal functional tests and electrophysiologic studies were performed 5 weeks later. Some recovered rats (i.e., those able to walk after the transection) underwent spinal cord retransection, with subsequent reevaluation of locomotion and muscle-evoked potentials. At 6 weeks after the initial transection, tract-tracing studies were performed in some animals. RESULTS: A motor performance score detected the functional differences between the control and the recovered rats. Muscle-evoked potentials of hind limbs after electrical stimulation to the brain were recorded in some of the recovered rats, but never in the unrecovered rats. Moreover, the muscle-evoked potentials of the recovered rats disappeared after spinal cord retransection that resulted in loss of voluntary movement. Morphologic studies in two rats provided evidence that reconnection of rubrospinal, vestibulospinal, and reticulospinal tracts had occurred, whereas corticospinal regeneration was not detected. CONCLUSIONS: It can be concluded that the hind limb function of rats that underwent spinal cord transection in infancy was partially regained; that axonal regeneration of the rubrospinal, vestibulospinal, or reticulospinal tracts was demonstrated, whereas the reconnection of the corticospinal tract was not observed; and that the axonal regeneration of these tracts is involved in the functional recovery.

The association of degeneration of the intervertebral disc with 5a/6a polymorphism in the promoter of the human matrix metalloproteinase-3 gene.

It has been suggested that matrix metalloproteinase-3 (MMP-3, stromelysin-1) has an important role in the degeneration of intervertebral discs (IVDs). A human MMP-3 promoter 5A/6A polymorphism was reported to be involved in the regulation of MMP-3 gene expression. We suggest that IVD degeneration is associated with 5A/6A polymorphism. We studied 54 young and 49 elderly Japanese subjects. Degeneration of the lumbar discs was graded using MRI in the younger group and by radiography in the elderly. 5A/6A polymorphism was determined by polymerase-chain reaction-based assays. We found that the 5A5A and 5A6A genotype in the elderly was associated with a significantly larger number of degenerative IVDs than the 6A6A (p < 0.05), but there was no significant difference in the young. In the elderly, the IVD degenerative scores were also distributed more highly in the 5A5A and 5A6A genotypes (p = 0.0029). Our findings indicate that the 5A allele is a possible risk factor for the acceleration of degenerative changes in the lumbar disc in the elderly.

Fibroblast growth factor downregulates expression of a basic helix-loop-helix-type transcription factor, scleraxis, in a chondrocyte-like cell line, TC6.

Scleraxis is a basic helix-loop-helix-type transcription factor that is expressed in sclerotome. Fibroblast growth factor (FGF) is one of the cytokines produced by the cells in skeletal tissues and is a potent modulator of skeletogenesis. The aim of this study was to examine the effects of FGF on the expression of scleraxis in chondrocyte-like cells, TC6. In these cells, scleraxis mRNA was constitutively expressed as a 1 .2 kb message at a high level in contrast to its low levels of expression in fibroblast-like cells or osteoblast-like cells. Upon treatment with FGF, scleraxis mRNA level was decreased within 12 h. This effect was at its nadir at 24 h and the scleraxis mRNA level returned to its base line level by 48 h. The FGF effect was maximal at 1 ng/ml. FGF effects on scleraxis were blocked by actinomycin D but not by cycloheximide, suggesting the involvement of transcriptional events that do not require new protein synthesis. The FGF effects on scleraxis were blocked by genistein, suggesting the involvement of tyrosine kinase in the post-receptor signaling. TGFbeta treatment of TC6 cells enhanced scleraxis mRNA expression; however, combination of the saturation doses of FGF and TGFbeta resulted in suppression of scleraxis mRNA level. BMP2 also suppressed scleraxis mRNA expression in TC6 cells and no further suppression was observed in combination with FGF. These results indicate that scleraxis is expressed in chondrocyte-like TC6 cells and it is one of the targets of FGF action in these cells.

Messenger RNA expression of the genes encoding receptors for bone morphogenetic protein (BMP) and transforming growth factor-ß (TGF-ß) in the cells from the posterior longitudinal ligament in cervical spine.

Posterior longitudinal ligament (PLL) in cervical spine is one of the sites of ossification in idiopathic hyperostotic diseases. Although the mechanism of the pathological triggering of the disease has not yet been clarified, the cells in PLL have been reported to express osteotropic cytokines such as BMP-2 and TGF-ß. However, it has not been known whether the cells in PLL express receptors for these cytokines. We examined the expression of the messenger RNAs of the genes encoding receptors for BMP-2/4 and TGF-ß in the PLL cells. Tissues from three OPLL (ossification of the posterior longitudinal ligament) patients who underwent anterior decompression surgery with removal of the ossified PLL were dissected microscopically and were subjected to explant cultures; the cells outgrown from the explants were examined. Type I BMP receptor (BMPR) mRNA was expressed at moderate levels in the cells derived from both ossifying PLL tissues as well as nonossifying adjacent fibrous tissues. Type II TGF-ß receptor (TßR) mRNA and α1(I) collagen mRNA were also constitutively expressed in these PLL cells from either regions. Treatment with BMP-2 enhanced the expression of BMPR mRNA in five out of ten of the cell cultures, suggesting that functional BMP receptors were expressed in at least a part of the PLL cells. The BMP-2 effect on BMPR was specific since no such enhancement was observed with regard to the levels of TßR mRNA in all of the ten cultures. These results indicated for the first time that mRNAs of the genes encoding receptors for BMP-2/4 and TGF-ß were expressed in the cells derived from human PLL cells.

Fibroblast growth factor enhances expression of TGFß-stimulated-clone-22 gene in osteoblast-like cells.

Transforming growth factor-ß1 (TGFß1)-stimulated clone 22 (TSC-22) is a primary response gene isolated by subtractive screening of genes expressed in murine osteoblastic cells treated with TGFß1, which is one of the cytokines abundantly stored in bone. Fibroblast growth factor (FGF) is also stored in bone matrix and acts as a potent autocrine/paracrine modulator of osteoblastic function. In this report, we investigated FGF effects on the expression of TSC-22 gene in a murine osteoblast-like cell line, MC3T3E-1. Treatment with recombinant basic FGF enhanced TSC-22 mRNA level in these cells within 1 h. This effect peaked at 2 h with several fold enhancement, after which the mRNA abundance returned to the basal level by 24 h. The FGF effect was dose-dependent, starting at 0.2 ng/ml, peaking at 2 ng/ml, and then declining at 20 ng/ml. The FGF effect on TSC-22 mRNA was blocked by actinomycin D, indicating the involvement of transcriptional events. The FGF enhancement of TSC-22 mRNA expression was partially blocked by genistein. Additive effect was observed upon contreatment with saturating concentrations of FGF and TGFß, suggesting the presence of at least two independent pathways for the two cytokines in the regulation of TSC-22 gene expression. These results indicate that the TSC-22 gene is one of the targets of FGF action in osteoblasts.