Germline ablation of dermatan-4O-sulfotransferase1 reduces regeneration after mouse spinal cord injury.

Chondroitin/dermatan sulfate proteoglycans (CSPGs/DSPGs) are major components of the extracellular matrix. Their expression is generally upregulated after injuries to the adult mammalian central nervous system, which is known for its low ability to restore function after injury. Several studies support the view that CSPGs inhibit regeneration after injury, whereas the functions of DSPGs in injury paradigms are less certain. To characterize the functions of DSPGs in the presence of CSPGs, we studied young adult dermatan-4O-sulfotransferase1-deficient (Chst14(-/-)) mice, which express chondroitin sulfates (CSs), but not dermatan sulfates (DSs), to characterize the functional outcome after severe compression injury of the spinal cord. In comparison to their wild-type (Chst14(+/+)) littermates, regeneration was reduced in Chst14(-/-) mice. No differences between genotypes were seen in the size of spinal cords, numbers of microglia and astrocytes neither in intact nor injured spinal cords after injury. Monoaminergic innervation and re-innervation of the spinal cord caudal to the lesion site as well as expression levels of glial fibrillary acidic protein (GFAP) and myelin basic protein (MBP) were similar in both genotypes, independent of whether they were injured and examined 6weeks after injury or not injured. These results suggest that, in contrast to CSPGs, DSPGs, being the products of Chst14 enzymatic activity, promote regeneration after injury of the adult mouse central nervous system.

Tegaserod, a small compound mimetic of polysialic acid, promotes functional recovery after spinal cord injury in mice.

In a previous study, we have shown that the small organic compound tegaserod, a drug approved for clinical application in an unrelated condition, is a mimic of the regeneration-beneficial glycan polysialic acid (PSA) in a mouse model of femoral nerve injury. Several independent observations have shown positive effects of PSA and its mimetic peptides in different paradigms of injury of the central and peripheral mammalian nervous systems. Since small organic compounds generally have advantages over metabolically rapidly degraded glycans and the proteolytically vulnerable mimetic peptides, a screen for a small PSA mimetic compound was successfully carried out, and the identified molecule proved to be beneficial in neurite outgrowth in vitro, independent of its originally described function as a 5-HT4 receptor agonist. In the present study, a mouse spinal cord compression device was used to elicit severe compression injury. We show that tegaserod promotes hindlimb motor function at 6 weeks after spinal cord injury compared to the control group receiving vehicle only. Immunohistology of the spinal cord rostral and caudal to the lesion site showed increased numbers of neurons, and a reduced area and intensity of glial fibrillary acidic protein immunoreactivity. Quantification of regrowth/sprouting of axons immunoreactive for tyrosine hydroxylase and serotonin showed increased axonal density rostral and caudal to the injury site in the ventral horns of mice treated with tegaserod. The combined observations suggest that tegaserod has the potential for treatment of spinal cord injuries in higher vertebrates.

Transgenic overexpression of the cell adhesion molecule L1 in neurons facilitates recovery after mouse spinal cord injury.

It has been shown that the X-chromosome-linked neural cell adhesion molecule L1 plays a beneficial role in regeneration after spinal cord injury (SCI) in young adult rodents when applied in various molecular and cellular forms. In an attempt to further characterize the multiple functions of L1 after severe SCI we analyzed locomotor functions and measured axonal regrowth/sprouting and sparing, glial scarring, and synaptic remodeling at 6 weeks after severe spinal cord compression injury at the T7-9 levels of L1-deficient mice (L1-/y) and their wild-type (L1+/y) littermates, as well as mice that overexpress L1 under the control of the neuron-specific Thy-1 promoter (L1tg) and their wild-type littermates (L1+/+). No differences were found in the locomotor scale score and single frame motion analysis between L1-/y and L1+/y mice during 6 weeks after SCI, most likely due to the very low expression of L1 in the adult spinal cord of wild-type mice. L1tg mice, however, showed better locomotor recovery than their L1+/+ littermates, being associated with enhanced numbers of catecholaminergic axons in the lumbar spinal cord, but not of cholinergic, GABAergic or glutamatergic terminals around motoneuron cell bodies in the lumbar spinal cord. Additionally, no difference between L1tg and L1+/+ mice was detectable in dieback of corticospinal tract axons. Neuronal L1 overexpression did not influence the size of the glial fibrillary acidic protein-immunoreactive astrocytic scar 6 weeks after injury. We conclude that neuronal overexpression of L1 improves functional recovery from SCI by increasing catecholaminergic axonal regrowth/sprouting and/or sparing of severed axons without affecting the glial scar size.

Down-regulation of the axonal polysialic acid-neural cell adhesion molecule expression coincides with the onset of myelination in the human fetal forebrain.

The polysialic acid (PSA) modification of neural cell adhesion molecule, which reduces neural cell adhesion molecule (NCAM) - mediated cell adhesion, is involved in several developmental processes, such as cell migration, axonal growth, path finding, and synaptic plasticity. It has been suggested that PSA-NCAM expression may inhibit myelination. To clarify the relationship between myelination and the expression of PSA-NCAM we systematically investigated its expression in the human forebrain from embryonic stage to midgestation (19-24 gestation weeks, gw). Immunofluorescence on cryosections showed that PSA-NCAM is expressed at the earliest stage studied (5.5 gw) in the primordial plexiform layer of the telencephalon, which mainly consists of neuronal processes. At midgestation, cortical axonal tracts in the emerging white matter were PSA-NCAM+, but they were not yet myelinated, based on the lack of myelin basic protein (MBP) immunoreaction. To follow the progression of myelination we developed organotypic slice cultures that included the subventricular and intermediate zones of the fetal forebrain. In freshly prepared slices, similar to cryosections, axonal tracts were PSA-NCAM+ but did not express MBP. After 5 days in culture there was a dramatic increase in MBP expression around the axons of the intermediate zone, which suggested the onset of myelination. Simultaneously with MBP up-regulation PSA-NCAM expression in axons was completely lost, as demonstrated both with immunofluorescence and Western blot analysis. These results support the idea that in the human fetal forebrain axonal PSA-NCAM expression is inversely related to primary myelination.

GRO-alpha and CXCR2 in the human fetal brain and multiple sclerosis lesions.

Chemokines, small proinflammatory cytokines, are involved in migration of inflammatory cells, but also have a role in normal central nervous system development. One chemokine, growth-related oncogene-alpha (GRO-alpha) and its receptor CXCR2, are involved in proliferation and migration of oligodendrocyte progenitors in rats. Here we studied the regional and cell type-specific expression of GRO-alpha and CXCR2 in the human telencephalon at midgestation, the time that oligodendrocytes are being generated in the human brain. Our results showed that both GRO-alpha and CXCR2 are predominately expressed by oligodendrocyte progenitors and activated microglial cells in the highly proliferative subventricular zone. This cellular and regional localization suggests that GRO-alpha/CXCR2 may play a role in human oligodendrocyte proliferation and subsequent migration. We also studied the expression of GRO-alpha and CXCR2 in brain sections of multiple sclerosis (MS) patients. Consistent with their role in the inflammatory process of MS, both GRO-alpha and CXCR2 were expressed in activated microglia localized on the border of MS lesions. However, neither GRO-alpha nor CXCR2 were present in early oligodendrocyte progenitors, a finding that may partially explain why remyelination is not more efficient in MS.