Neurite outgrowth inhibitors in gliotic tissue

Advances and Perspectives in Dental Pulp Stem Cell Based Neuroregeneration Therapies

Human dental pulp stem cells (hDPSCs) are some of the most promising stem cell types for regenerative therapies given their ability to grow in the absence of serum and their realistic possibility to be used in autologous grafts. In this review, we describe the particular advantages of hDPSCs for neuroregenerative cell therapies. We thoroughly discuss the knowledge about their embryonic origin and characteristics of their postnatal niche, as well as the current status of cell culture protocols to maximize their multilineage differentiation potential, highlighting some common issues when assessing neuronal differentiation fates of hDPSCs. We also review the recent progress on neuroprotective and immunomodulatory capacity of hDPSCs and their secreted extracellular vesicles, as well as their combination with scaffold materials to improve their functional integration on the injured central nervous system (CNS) and peripheral nervous system (PNS). Finally, we offer some perspectives on the current and possible future applications of hDPSCs in neuroregenerative cell therapies.

Inhibition of glial proliferation, promotion of axonal growth and myelin production by synthetic glycolipid: A new approach for spinal cord injury treatment

PURPOSE

After spinal cord injury (SCI) a glial scar is generated in the area affected that forms a barrier for axon growth and myelination, preventing functional recovery. Recently, we have described a synthetic glycolipid (IG20) that inhibited proliferation of human glioma cells. We show now that IG20 inhibited the proliferation of astrocytes and microglial cells, the principal cellular components of the glial scar, and promoting axonal outgrowth and myelin production in vitro.

METHODS

Glial cells were inhibited with IG20 (IC50≈10 μM) and studied by RT-PCR, Western Blotting, immunoprecipitation and fluorescence microscopy. Axonal outgrowth in dorsal root ganglia (DRG) and myelin production by oligodendrocytes were analyzed by immunocytochemistry. Adult rats were assayed in spinal cord contusion model and the recovery of treated animals (n = 6) and controls (n = 6) was followed.

RESULTS

The IG20 was localized in the cytosol of glial cells, forming a complex with RhoGDIα, a regulator of RhoGTPases. Treatment of astroglial cultures with IG20 increase the expression of BDNF receptor genes (TrkBT1, TrkB Full). IG20 reduced the astroglial marker GFAP, while increasing production of myelin basic protein in oligodendrocytes and promoted axonal outgrowth from DRG neurons. Local injection of IG20, near a spinal cord contusion, promoted the recovery of lesioned animals analyzed by BBB test (P <  0.05).

CONCLUSIONS

We propose that inhibition of astrocytes and microglia by IG20 could be diminished the glial scar formation, inducing the re-growth and myelination of axons, these elements constitute a new approach for SCI therapy.

Time Course and Characteristics of Astrocyte Activation in the Rat Brain after Injury

OBJECTIVE

After injury to the central nervous system (CNS), glial scar tissue is formed in the process of wound healing. This can be is a clinical problem because it interferes with axonal regeneration and functional recovery. It is known that intracellular proteins, including the glial fibrillary acidic protein (GFAP), nestin, and vimentin increase in the astrocytes after an injury to the CNS. By studying the time course and co-expression pattern of these intracellular proteins, this study will attempt to prove that these proteins are involved in the processes of glial scar formation.

METHODS

Twenty-five male Sprague-Dawley rats were used in this study. Bregma of the cerebral cortex, an area was incised with a sharp blade, and perfusion was performed. The expressions of the intracellular proteins were assayed, while the co-localization of the intermediate filament (GFAP, nestin, and vimentin) and A2B5 were examined.

RESULTS

At 12 hours, the GFAP was expressed in the white matter underlying the lesion, and in the cerebral cortex. Nestin was expressed in the astrocytes in the perilesional area after 3 days, while A2B5 was observed in the edge of the wound at 12 hours post-injury, with its expression reaching a peak at 7 days. Vimentin was detected in the white matter at 12 hours, and in the cortex, reaching a peak at 7 days.

CONCLUSION

In the processes of glial scar formation, nestin, vimentin, and A2B5 were revealed in the astrocytes, and these factors may be involved in the division, proliferation, and transportation of the astrocytes.

Connexin 43 stabilizes astrocytes in a stroke-like milieu to facilitate neuronal recovery

AIM

Connexin 43 (Cx43) is a member of connexin family mainly expressed in astrocytes, which forms gap junctions and hemichannels and maintains the normal shape and function of astrocytes. In this study we investigated the role of Cx43 in astrocytes in facilitating neuronal recovery during ischemic stroke.

METHODS

Primary culture of astrocytes or a mixed culture of astrocytes and cortical neurons was subjected to oxygen glucose deprivation and reperfusion (OGD/R). The expression of Cx43 and Ephrin-A4 in astrocytes was detected using immunocytochemical staining and Western blot assays. Intercellular Ca(2+) concentration was determined with Fluo-4 AM fluorescent staining. Middle cerebral artery occlusion (MCAO) model rats were used for in vivo studies.

RESULTS

OGD/R treatment of cultured astrocytes caused a decrement of Cx43 expression and translocation of Cx43 from cell membrane to cytoplasm, accompanied by cell retraction. Furthermore, OGD/R increased intracellular Ca(2+) concentration, activated CaMKII/CREB pathways and upregulated expression of Ephrin-A4 in the astrocytes. All these changes in OGD/R-treated astrocytes were alleviated by overexpression of Cx43. In the cortical neurons cultured with astrocytes, OGD/R inhibited the neurite growth, whereas overexpression of Cx43 or knockdown of Ephrin-A4 in astrocytes restored the neurite growth. In MCAO model rats, neuronal recovery was found to be correlated with the recuperation of Cx43 and Ephrin-A4 in astrocytes.

CONCLUSION

Cx43 can stabilize astrocytes and facilitate the resistance to the deleterious effects of a stroke-like milieu and promote neuronal recovery.

The expression of CAP1 after traumatic brain injury and its role in astrocyte proliferation

Adenylate cyclase-associated protein 1 (CAP1), a member of cyclase-associated proteins involved in the regulation of actin filaments, was recently reported to play a role in the pathology of sciatic nerves injury. However, the distribution and function of CAP1 in the central nervous system (CNS) remain unclear. To investigate whether CAP1 is involved in CNS injury and repair, we used an acute traumatic brain injury (TBI) model in adult rats. Western blot analysis and immunohistochemistry showed a significant upregulation of CAP1 in ipsilateral peritrauma cortex compared with the contralateral and sham-operated ones. Double immunofluorescence staining showed that CAP1 was co-expressed with glial fibrillary acidic protein (GFAP). In addition, we detected that Ki-67 had colocalization with GFAP and CAP1 after TBI. In vitro, during the process of lipopolysaccharide (LPS)-induced primary astrocyte proliferation, we observed enhanced expression of CAP1. Specially, CAP1-specific siRNA-transfected primary astrocytes show significantly decreased ability for proliferation. Together, all these data indicated that the change of CAP1 protein expression was associated with astrocyte proliferation after the trauma of the central nervous system (CNS).

Astrocyte transplantation for spinal cord injury: current status and perspective

Spinal cord injury (SCI) often causes incurable neurological dysfunction because axonal regeneration in adult spinal cord is rare. Astrocytes are gradually recognized as being necessary for the regeneration after SCI as they promote axonal growth under both physiological and pathophysiological conditions. Heterogeneous populations of astrocytes have been explored for structural and functional restoration. The results range from the early variable and modest effects of immature astrocyte transplantation to the later significant, but controversial, outcomes of glial-restricted precursor (GRP)-derived astrocyte (GDA) transplantation. However, the traditional neuron-centric view and the concerns about the inhibitory roles of astrocytes after SCI, along with the sporadic studies and the lack of a comprehensive review, have led to some confusion over the usefulness of astrocytes in SCI. It is the purpose of the review to discuss the current status of astrocyte transplantation for SCI based on a dialectical view of the context-dependent manner of astrocyte behavior and the time-associated characteristics of glial scarring. Critical issues are then analyzed to reveal the potential direction of future research.

Spatiotemporal patterns and essential role of MSK1 expression after rat spinal cord injury

Mitogen and stress activated protein kinase (MSK1) protein was initially identified as a particularly interesting protein of mitogen activated protein kinase. It was reported to enhance Bad's phosphorylation to protect cell death, suggesting that MSK1 represents a new type of anti-cell death gene. Moreover, recent study has shown that MSK1 is involved in negative feedback pathways that are crucial to prevent uncontrolled inflammation. However, its function and expression in the central nervous system lesion are not been understood very well. In this study, we performed an acute spinal cord injury (SCI) model in adult rats and studied the dynamic changes of MSK1 expression in spinal cord. Western blot and immunohistochemistry analysis revealed that MSK1 was present in normal spinal cord. It gradually decreased, reached a peak at 3 days after SCI, and then increased during the following days. Immunofluorescence double labeling revealed that MSK1 was co-expressed with NeuN and GFAP, respectively. Interesting, after injury, MSK1 expression was decreased predominantly in astrocytes, which highly expressed proliferating cell nuclear antigen, a marker for proliferating cells. In conclusion, this is the first description of MSK1 expression in spinal cord. Our data suggested that MSK1 might play important roles in CNS pathophysiology after SCI.

FOXO3a/p27kip1 expression and essential role after acute spinal cord injury in adult rat

FOXO3a (Forkhead Class box O3a), as an important direct target of the phosphatidylinositol 3-kinase (PI3K)/protein B (Akt) pathway, which regulates the cell survival and the cell-cycle progression. Recent reports showed that FOXO3a could inhibit cell-cycle progression at the G1/S transition by controlling transcription of the cyclin-dependent kinase inhibitor p27(kip1) , which is also a key regulator of the mammalian neurogenesis. To elucidate the expression and role of FOXO3a in nervous system lesion and repair, we performed an acute spinal cord contusion injury (SCI) model in adult rats, which showed a temporal-spatial expression pattern of FOXO3a. Temporally, FOXO3a protein level significantly reduced day 3 after injury, and following FOXO3a down-regulation, p27(kip1) protein and mRNA levels were also decreased after injury. Spatially, decreased levels of FOXO3a and p27(kip1) were predominant in astrocytes, which were regenerating axons and largely proliferated after injury. Furthermore in vitro, Western blot analysis, RT-PCR, and immunofluorescence staining analysis demonstrated the relationship between FOXO3a and p27(kip1) in primary astrocytes. FOXO3a modulated the cell cycle by transcriptional regulation of p27(kip1) in astrocytes. Administration of the PI3K pharmacological inhibitor LY294002 abrogated this effect by regulating FOXO3a and p27(kip1) expression and subcellular localization. These results suggest that decreased levels of FOXO3a and p27(kip1) in spinal cord are involved in axonal regeneration and the proliferation of glial cells after SCI.

FoxM1 involvement in astrocyte proliferation after spinal cord injury in rats

The Forkhead box M1 (FoxM1) protein is a proliferation-associated transcription factor that plays a key role in controlling both the G1/S and G2/M transitions of the cell cycle and regulates transcription of cell cycle genes, including cyclin-dependent kinase inhibitors p27(kip1) and p21(waf1/cip1). The expression levels of FoxM1 directly correlated with the proliferation index, cancer survival, genomic instability rate, and microvessel density, and inversely correlated with apoptosis. Furthermore, FoxM1 is determined to play a role in tissue repair following injury in the lungs and liver. However, the signaling of FoxM1, involved in its expression and its role in central nervous system lesion and repair is poorly known. In this study, we performed a spinal cord injury (SCI) model in adult Sprague-Dawley rats and investigated the dynamic changes and role of FoxM1 expression in the spinal cord. Western blot analysis revealed that FoxM1 was lowly presented in normal spinal cord. It gradually increased, reached a peak at day 3, and then declined to basal levels at 14 days after spinal cord injury. Immunohistochemistry further confirmed that FoxM1 was expressed at low levels in gray and white matters in normal condition and increased after SCI. Double immunofluorescence staining showed that FoxM1was co-expressed with NeuN (neuronal marker) and GFAP (astrocytic marker), and FoxM1 expression was increased predominantly in astrocytes after injury, which were regenerating axons and largely proliferated after injury. Furthermore, co-immunoprecipitation studies demonstrated increased interactions among FoxM1, Skp2, and p27(kip1) in the spinal cord after injury. Taken together, these results provide new insights into the molecular mechanisms underlying astrocyte proliferation during SCI and suggest that FoxM1 might play crucial roles in CNS pathophysiology after SCI.

Exposure to environmental enrichment prior to a cerebral cortex stab wound attenuates the postlesional astroglia response in rats

Modulation of astroglial components involved in reactive postlesional responses in the rat cerebral cortex was analyzed following exposure to environmental enrichment (EE) condition prior to injury. For this purpose, changes in % immunoreactive (IR) area of GFAP, vimentin, EAAT1 and ezrin were evaluated in the perilesional zone after placing a cortical stab wound in the visual cerebral cortex of adult rats. GFAP-IR postlesional reactive astrocytosis in the perilesional cortex was significantly lower in the animal group exposed to EE during postnatal development. This GFAP-IR reaction seems to be associated with existing astroglia, because neither BrdU- nor endogenous Ki-67-labeled nuclei were found in the perilesional cortex analyzed. Increased ezrin-IR area in the visual cortex of rats exposed to EE condition suggests the formation of new synapses or the enhancement of astroglial involvement in the existing ones. No effects of EE were found on either EAAT1- or vimentin-IR area. Results suggest that exposure to EE conditions prior to injury attenuates the postlesional astroglia GFAP-response in the perilesional cortex of rats. Whether this attenuated postlesional astroglia GFAP-response promotes or not protective effects on the cortical neuropil remains to be explored in futures studies.

KPC1 expression and essential role after acute spinal cord injury in adult rat

KPC1 (Kip1 ubiquitylation-promoting complex 1) is the catalytic subunit of the ubiquitin ligase KPC, which regulates the degradation of the cyclin-dependent kinase inhibitor p27(kip1) at the G1 phase of the cell cycle. To elucidate the expression and role of KPC1 in nervous system lesion and repair, we performed an acute spinal cord contusion injury (SCI) model in adult rats. Western blot analysis showed a significant up-regulation of KPC1 and a concomitant down-regulation of p27(kip1) following spinal injury. Immunohistochemistry and immunofluorescence revealed wide expression of KPC1 in the spinal cord, including expression in neurons and astrocytes. After injury, KPC1 expression was increased predominantly in astrocytes, which highly expressed PCNA, a marker for proliferating cells. Co-immunoprecipitation demonstrated increased interactions between p27(kip1) and KPC1 4 days after injury. To understand whether KPC1 plays a role in astrocyte proliferation, we applied LPS to induce astrocyte proliferation in vitro. Western blot analysis demonstrated that p27(kip1) expression was negatively correlated with KPC1 expression following LPS stimulation. Immunofluorescence analysis showed subcellular localizations of p27(kip1) and KPC1 were also changed following the stimulation of astrocytes with LPS. These results suggest that KPC1 is related to the down-regulation of p27(kip1); this event may be involved in the proliferation of astrocytes after SCI.

A relationship between p27(kip1) and Skp2 after adult brain injury: implications for glial proliferation

S-phase-associated kinase protein-2 (Skp2) is involved in ubiquitination and proteasome-mediated degradation of p27(kip1), which plays an important role in mammalian cell-cycle regulation and neurogenesis in the developing central nervous system. To investigate their expression and function in central nervous system injury and repair, we used a brain-penetrating injury model in adult rats. Western blot analysis showed a significant downregulation of p27(kip1) and a concomitant upregulation of Skp2 following brain injury, and their expression profiles were temporally correlative (r = -0.910, p = 0.037). Immunofluorescence double-labeling revealed that p27(kip1) was highly expressed in neurons (51%), astrocytes (72%), and microglia (76%) in the sham group, while its expression was decreased prominently in microglia (26%) and astrocytes (32%) at 3 days after injury. Meanwhile, Skp2 expression was very low in all cell types in the sham group; however, 3 days after injury, its expression was increased significantly in microglia (51%) and astrocytes (31%) (p < 0.001), and less significantly in neurons (8%) (p = 0.038), and the astrocytes and microglia had proliferated. We also examined the expression profiles of CDK2, threonine-187 phosphorylated p27(kip1), proliferating cell nuclear antigen (PCNA), and Ki67, and their changes correlated with the expression profiles of p27(kip1) and Skp2. Moreover, co-immunoprecipitation data suggested that the protein-protein interactions between p27(kip1) and Skp2 were enhanced after injury. Taken with results of previous reports, we hypothesize the Skp2 is related to the downregulation of p27(kip1) expression after brain injury, and such an event may be associated with glial proliferation, including that of astrocytes and microglia.

Eph receptor tyrosine kinases regulate astrocyte cytoskeletal rearrangement and focal adhesion formation

EphA4 null mice have impaired astrocytic gliosis following spinal cord injury. This may be because of altered cytoskeletal regulation and is examined herein using cultured astrocytes from wildtype and EphA4 null mice. Under basal conditions EphA4 null astrocytes appeared relatively normal but following stimuli resulting in cytoskeletal rearrangement, EphA4 null cells responded more slowly. When F-actin stress fibers were collapsed using the Rho kinase inhibitor HA1077, fewer EphA4 null cells showed stress fiber collapse in response to HA1077 and recovered stress fibers more slowly following HA1077 removal. EphA4 null astrocytes were less adherent and had smaller focal adhesions, while activation of Eph receptors with ephrin-A5-Fc increased the numbers of focal adhesions in both wildtype and knockout astrocytes following serum starvation. Using scratch wound assays, EphA4 null astrocytes invading the scratch showed impaired glial fibrillary acidic protein expression, particularly in proliferative cells. Astrocytes did not express Ephexin, a major Eph-interacting Rho guanine exchange factor, but they expressed Vav proteins, with lower levels of phospho-Vav in EphA4 null compared to wildtype astrocytes. This may contribute to the slower cytoskeletal responses generally observed in the EphA4 null astrocytes. Eph receptor signaling therefore regulates astrocyte reactivity through modulation of cytoskeletal responses.

An optimal protocol to analyze the rat spinal cord proteome

Since the function of the spinal cord depends on the proteins found there, better defing the normal Spinal Cord Proteome is an important and challenging task. Although brain and cerebrospinal fluid samples from patients with different central nervous system (CNS) disorders have been studied, a thorough examination of specific spinal cord proteins and the changes induced by injury or associated to conditions such as neurodegeneration, spasticity and neuropathies has yet to be performed. In the present study, we aimed to describe total protein content in the spinal cord of healthy rats, employing different proteomics tools. Accordingly, we have developed a fast, easy, and reproducible sequential protocol for protein extraction from rat spinal cords. We employed conventional two dimensional electrophoresis (2DE) in different pH ranges (eg. 4–7, 3–11 NL) combined with identification by mass spectrometry (MALDI-TOF/TOF), as well as first dimension protein separation combined with Liquid Chromatography Mass Spectrometry/Mass Spectrometry (LC-MS/MS) to maximise the benefits of this technology. The value of these techniques is demonstrated here by the identification of several proteins known to be associated with neuroglial structures, neurotransmission, cell survival and nerve growth in the central nervous system. Furthermore this study identified many spinal proteins that have not previously been described in the literature and which may play an important role as either sensitive biomarkers of dysfunction or of recovery after Spinal Cord Injury.

Nano neurology and the four P's of central nervous system regeneration: preserve, permit, promote, plasticity

True nanomaterials are delivered as a specific structure, or combination of structures, designed to deliver the therapeutic intact, directly to the site, requiring a much lower dose. These materials use very specific and deliberate molecular structures that can interact with neurons or protein structures inside the cells. Until recently, functional recovery of the central nervous system (CNS) was an unattainable goal and nanotechnology was an invisible science. A well-planned treatment spaced over time will produce functional return in the CNS. The four P's of CNS regeneration is a new framework for approaching CNS injury and evidence shows that nanotechnology is currently being used for stroke rehabilitation and, in several clinical trials, the treatment of scar formation blockade in the spinal cord. The four components are preserve, permit, promote, and plasticity.

Hyaluronan-CD44 interaction stimulates Rac1 signaling and PKN gamma kinase activation leading to cytoskeleton function and cell migration in astrocytes

Both hyaluronan [HA, the major glycosaminoglycans in the extracellular matrix (ECM)] and CD44 (a primary HA receptor) are associated with astrocyte activation and tissue repair following central nervous system (CNS) injury. In this study we investigated the question of whether HA-CD44 interaction influences astrocyte signaling and migration. Our data indicated that HA binding to the cultured astrocytes stimulated Rac1 signaling and cytoskeleton-mediated migration. To determine the cellular and molecular basis of these events, we focused on PKN gamma, a Rac1-activated serine/threonine kinase in astrocytes. We determined that HA binding to astrocytes stimulated Rac1-dependent PKN gamma kinase activity which, in turn, up-regulated the phosphorylation of the cytoskeletal protein, cortactin, and attenuated the ability of cortactin to cross-link F-actin. Further analyses indicated that the N-terminal antiparallel coiled-coil (ACC) domains of PKN gamma interacted with Rac1, and transfection of astrocytes with PKN gamma-ACCcDNA inhibited PKN gamma activity. Over-expression of the PKN gamma-ACC domain also functions as a dominant-negative mutant to block HA/CD44-mediated PKN gamma activation of cortactin and astrocyte migration. Taken together, these findings strongly suggest that hyaluronan/CD44 interaction with Rac1-PKN gamma plays a pivotal role in cytoskeleton activation and astrocyte migration. These newly discovered HA/CD44-induced astrocyte function may provide important insight into novel therapeutic treatments for tissue repair following CNS injury.

Gelation under dynamic conditions: a strategy for in vitro cell ordering

Ordered gelation under spin-coating conditions, as reported here, is a suitable method to order cells in biogels. Cell ordering is of great importance for functional repair of central nervous system (CNS) injuries, because therapies must include strategies to bridge chystic gaps and facilitate axon growth towards its target. Organized biocompatible and biodegradable substrates may be used for this purpose, to supply trophic support and provide directional cues for neuronal process outgrowth. Atomic force microscopy (AFM) and low temperature scanning electron microscopy (LTSEM), confirmed that fibrils in kappa-carrageenan/chitosan and fibrin hydrogels prepared under spin-coating conditions, were longitudinally arranged. The cell model was conveniently tested using rat C6 glioma cells. C6 cells were distributed regularly in fibrin gels formed under centrifugal force. The ability of ordered fibrin scaffolds to promote uniform distribution of transplanted cells, was confirmed by fluorescence microscopy.

Nano neuro knitting: peptide nanofiber scaffold for brain repair and axon regeneration with functional return of vision

Nanotechnology is often associated with materials fabrication, microelectronics, and microfluidics. Until now, the use of nanotechnology and molecular self assembly in biomedicine to repair injured brain structures has not been explored. To achieve axonal regeneration after injury in the CNS, several formidable barriers must be overcome, such as scar tissue formation after tissue injury, gaps in nervous tissue formed during phagocytosis of dying cells after injury, and the failure of many adult neurons to initiate axonal extension. Using the mammalian visual system as a model, we report that a designed self-assembling peptide nanofiber scaffold creates a permissive environment for axons not only to regenerate through the site of an acute injury but also to knit the brain tissue together. In experiments using a severed optic tract in the hamster, we show that regenerated axons reconnect to target tissues with sufficient density to promote functional return of vision, as evidenced by visually elicited orienting behavior. The peptide nanofiber scaffold not only represents a previously undiscovered nanobiomedical technology for tissue repair and restoration but also raises the possibility of effective treatment of CNS and other tissue or organ trauma.

Regeneration of lesioned entorhino-hippocampal axons in vitro by combined degradation of inhibitory proteoglycans and blockade of Nogo-66/NgR signaling

Damaged axons do not regenerate after axotomy in the adult mammalian central nervous system (CNS). This may be due to local inhibitory factors at the site of injury, such as overexpression of chondroitin sulfate (CS) proteoglycans (CSPG), and the presence of myelin-associated inhibitors (MAI). To overcome CSPG- or myelin-induced inhibition, strategies based on extrinsic and intrinsic treatments have been developed. For example, NEP1-40 is a synthetic peptide that promotes axonal regeneration by blocking Nogo-66/NgR interaction and chondroitinase ABC (ChABC), which degrades CS, thereby also promoting axon regrowth. Here, we examined whether the combination of these complementary strategies facilitates regeneration of the lesioned entorhino-hippocampal pathway (EHP) in slice cultures. In this model, overexpressed CSPG and MAI impaired axon regrowth, which mimics regeneration failure in vivo. Both CS cleavage with ChABC and NEP1-40 strongly facilitated the regrowth of entorhinal axons after axotomy, permitting the re-establishment of synaptic contacts with target cells. However, the combined treatment did not improve the regeneration induced by ChABC alone, and the delayed treatment of ChABC, but not NEP1-40, had a less pronounced effect on axonal regrowth compared with acute treatment. These results provide insight into the development of new assays and strategies to enhance axon regeneration in injured cortical connections.

Role of Rho GTPase in astrocyte morphology and migratory response during in vitro wound healing

Small Rho GTPases are key regulators of the cytoskeleton in a great variety of cells. Rho function mediates morphological changes as well as locomotor activity. Using astrocyte cultures established from neonatal mice we investigated the role of Rho in process formation during astrocyte stellation. Using a scratch-wound model, we examined the impact of Rho on a variety of morphological and functional variables such as stellation and migratory activity during wound healing. C3 proteins are widely used to study cellular Rho functions. In addition, C3 derived from Clostridium botulinum (C3bot) is considered selectively to promote neuronal regeneration. Because the latter requires a balanced activity of neurones and glial cells, the effects of C3 protein on glial cells such as astrocytes have to be considered carefully. Low nanomolar concentrations of C3 proteins significantly promoted process outgrowth and increased process branching. Besides enzymatic inactivation of Rho by ADP-ribosylation, changes in protein levels of the various Rho GTPases may also contribute to the observed effects. Furthermore, incubation of scratch-wounded astrocyte cultures with C3bot accelerated wound healing. By inhibiting the Rho downstream effector ROCK with the selective inhibitor Y27632 we were able to demonstrate that the accelerated wound closure resulted from both enhanced polarized process formation and increased migratory activity of astrocytes into the lesion site. These results suggest that Rho negatively regulates astrocytic process growth and migratory responses after injury and that its inactivation by C3bot in nanomolar concentrations promotes astrocyte migration.

Cell cycle inhibition provides neuroprotection and reduces glial proliferation and scar formation after traumatic brain injury

Traumatic brain injury (TBI) causes neuronal apoptosis, inflammation, and reactive astrogliosis, which contribute to secondary tissue loss, impaired regeneration, and associated functional disabilities. Here, we show that up-regulation of cell cycle components is associated with caspase-mediated neuronal apoptosis and glial proliferation after TBI in rats. In primary neuronal and astrocyte cultures, cell cycle inhibition (including the cyclin-dependent kinase inhibitors flavopiridol, roscovitine, and olomoucine) reduced up-regulation of cell cycle proteins, limited neuronal cell death after etoposide-induced DNA damage, and attenuated astrocyte proliferation. After TBI in rats, flavopiridol reduced cyclin D1 expression in neurons and glia in ipsilateral cortex and hippocampus. Treatment also decreased neuronal cell death and lesion volume, reduced astroglial scar formation and microglial activation, and improved motor and cognitive recovery. The ability of cell cycle inhibition to decrease both neuronal cell death and reactive gliosis after experimental TBI suggests that this treatment approach may be useful clinically.

Corticospinal regeneration into lumbar grey matter correlates with locomotor recovery after complete spinal cord transection and repair with peripheral nerve grafts, fibroblast growth factor 1, fibrin glue, and spinal fusion

Knowledge of which tracts are essential for the recovery of locomotor function in rats after repair is unknown. To assess the mechanism of recovery, we examined the correlation between functional recovery and axonal regeneration. All rats underwent complete cord transection and repair with peripheral nerves, fibroblast growth factor 1, fibrin glue, and spinal fixation. Repaired rats recovered both motor-evoked potentials recorded at the lumbar level and locomotor function. Cord retransection rostral to the repair abolished the recovery, indicating improvement was due to long tract regeneration. To determine which long tracts correlated with recovery, a novel technique of simultaneous bidirectional axonal tracing and immunohistochemical examination of axonal type was used to quantitate the regeneration of corticospinal, rubrospinal, reticulospinal, vestibulospinal, raphespinal, propriospinal, serotonergic, and calcitonin gene-related peptide containing axons. Multiple linear regression analysis revealed recovery of function correlated only with regeneration of corticospinal axons into the gray matter of the lumbar spinal cord (R = 0.977, p < 0.02). For the first time, we show that regeneration of the corticospinal tract into the lumbar gray matter is a mechanism of functional locomotor recovery after complete cord transection and repair.

Selective estrogen receptor modulators protect hippocampal neurons from kainic acid excitotoxicity: differences with the effect of estradiol

Neuroprotective effects of estradiol are well characterized in animal experimental models. However, in humans, the outcome of estrogen treatment for cognitive function and neurological diseases is very controversial. Selective estrogen receptor modulators (SERMs) may represent an alternative to estrogen for the treatment or the prevention of neurodegenerative disorders. SERMs interact with the estrogen receptors and have tissue-specific effects distinct from those of estradiol, acting as estrogen agonists in some tissues and as antagonists in others. In this study we have assessed the effect of tamoxifen, raloxifene, lasofoxifene (CP-336,156), bazedoxifene (TSE-424), and 17beta-estradiol on the hippocampus of adult ovariectomized rats, after the administration of the excitotoxin kainic acid. Administration of kainic acid induced the expression of vimentin in reactive astroglia and a significant neuronal loss in the hilus. SERMs did not affect vimentin immunoreactivity in the hilus, while 17beta-estradiol significantly reduced the surface density of vimentin immunoreactive profiles. Estradiol, tamoxifen (0.4-2 mg/kg), raloxifene (0.4-2 mg/kg), and bazedoxifene (2 mg/kg) prevented neuronal loss in the hilus after the administration of kainic acid. Lasofoxifene (0.4-2 mg/kg) was not neuroprotective. These findings indicate that SERMs present different dose-dependent neuroprotective effects. Furthermore, the mechanisms of neuroprotection by SERMs and estradiol are not identical, because SERMs do not significantly affect reactive gliosis while neuroprotection by estradiol is associated with a strong down-regulation of reactive astroglia.

Basic Fibroblast Growth Factor Promotes Neuronal Survival but Not Behavioral Recovery in the Transected and Schwann Cell Implanted Rat Thoracic Spinal Cord

It was investigated whether the addition of basic fibroblast growth factor (FGF-2) enhances the efficacy of a Schwann cell (SC) bridge to repair the transected spinal cord by assessing tissue sparing and neuronal survival near the graft-cord interfaces, axonal regeneration and myelination in the graft, and behavioral recovery up to 12 weeks post-grafting. Experimental animals received a bridge of SCs within fibrin containing 1 microg of FGF-2; control animals received a SC implant without FGF-2. Sparing of tissue in a 2.5-mm-long segment near the graft-cord borders was 69% in the rostral and 52% in the caudal cord at 6 weeks post-grafting, not significantly different from the control group. With FGF-2, survival of NeuN-positive cells was increased in the rostral cord: 24.4%, 20.4%, and 17.2% of the number of positive cells in the uninjured cord compared to 13.5%, 9.1%, and 8.9% in controls at 3, 6, and 12 weeks post-grafting, respectively. Similarly, in the caudal cord, survival of NeuN-positive cells was increased with FGF-2: 19.3%, 16.8%, and 14.5% compared to 10.8%, 5.6%, and 6.1% in controls. The staining intensity of glial fibrillary acidic protein was significantly higher at the interfaces of both cord stumps at 3 weeks with SC/FGF-2 grafts; chondroitin sulfate proteoglycan (CS-56) staining was more intense in the rostral cord but only at 6 weeks. Blood vessels in the FGF-2 grafts were larger and less regular in shape than those in control grafts. Axonal growth into the bridge was not improved by the addition of FGF-2. Retrogradely traced neurons were not found rostral to the implant, indicating that axons had not grown a few mm into the caudal spinal tissue. Recovery of hind limb function was similar in both groups. Despite the neuroprotective effects of FGF-2, improved effects on axonal regeneration and functional recovery were not observed.

Macroglia distribution in the developing and adult inferior colliculus

Macroglia distribution in the developing and adult gerbil inferior colliculus (IC) was investigated using two oligodendrocytic [myelin-associated-glycoprotein (MAG) and oligodendrocyte-specific molecule (Rip)] and two astrocytic [glial fibrillary acidic protein (GFAP) and S100] markers and immunohistochemistry. There was a spatio-temporal pattern of myelin marker expression starting in the ventral area of the IC and continuing to the dorsal part of the nucleus. Myelination, as revealed by MAG and Rip markers, starts in the IC during the second postnatal week. The intensity of myelination increased between stages P15 and P21 and extended to the whole IC. The appearance of myelin proteins in the IC may suggest a possible axonal outgrowth inhibition by oligodendrocytes in this structure. A differential pattern of staining was obtained with S100 and GFAP antibodies. Astrocytes identified as S100 immunoreactive cells were observed in the IC by birth and the staining was localized to their cell body and processes. S100 positive cells were homogeneously distributed within the IC nucleus. S100 pattern of staining remained the same in stages P7, P15 and P21. In adult IC, S100 positive cell processes were in contact with neuronal cell bodies, other S100 positive cells and blood vessels. Quantitative analysis showed an increase in the density of positive cells during the first postnatal week and a decrease then after through to adulthood. Unlike S100, GFAP immunoreactivity showed a different pattern of staining. At birth GFAP positive astrocytes were observed along the collicular brain midline and around the IC nucleus delimiting its boundaries. The GFAP pattern of labelling remained the same during development and in the adult. This data suggests the presence of two astrocytes subtypes with different locations in the IC nucleus. The GFAP positive astrocytes were located along the edge of the nucleus, while the S100 positive ones displayed a homogeneous distribution across the nucleus.

Motor cortex activation is preserved in patients with chronic hemiplegic stroke

Many central nervous system conditions that cause weakness, including many strokes, injure corticospinal tract but leave motor cortex intact. Little is known about the functional properties of surviving cortical regions in this setting, in part because many studies have used probes reliant on the corticospinal tract. We hypothesized that many features of motor cortex function would be preserved when assessed independent of the stroke-affected corticospinal tract. Functional MRI was used to study 11 patients with chronic hemiplegia after unilateral stroke that spared regions of motor cortex. Activation in stroke-affected hemisphere was evaluated using 3 probes independent of affected corticospinal tract: passive finger movement, a hand-related visuomotor stimulus, and tapping by the nonstroke index finger. The site and magnitude of cortical activation were similar when comparing the stroke hemisphere to findings in 19 control subjects. Patients activated each of 8 cortical regions with similar frequency as compared to controls, generally with a smaller activation volume. In some cases, clinical measures correlated with the size or the site of stroke hemisphere activation. The results suggest that, despite stroke producing contralateral hemiplegia, surviving regions of motor cortex actively participate in the same proprioceptive, visuomotor, and bilateral movement control processes seen in control subjects.

Experimental models of partial lesion of rat spinal cord to investigate neurodegeneration, glial activation, and behavior impairments

The article demonstrates two experimental models of spinal cord partial injury in rats: a contuse model promoted by the NYU impactor system and a partial hemitransection model achieved by a stereotaxic-positioned adjustable wire knife. By means of a defined impact weight (10 g) and a digital optical potentiometer linked to a computer, the impactor transferred and registered a moderate or a severe contusion to the rat spinal cord at a low thoracic level after dropping the weight from distances of 25 mm and 50 mm, respectively, to the dorsal surface of the exposed dura spinal cord. Impact curve was calculated and the parameters of the trauma, like impact velocity, cord compression distance and cord compression rates were obtained in order to demonstrate trauma severity. To promote partial hemitransection, rats were positioned in a spinal cord unit of a stereotaxic apparatus and lesion was made with the adjustable wire knife spatially oriented. By means of a computerized infrared motion sensor-home cage activity monitor and a noncomputerized evaluation of motor behavior using the inclined plane and the motor score of Tarlov tests, behavior was analyzed in an acute period postlesion. Rats were sacrificed and spinal cords were processed for routine staining to show neurons and for GFAP and OX42 immunohistochemistry to demonstrate glial cells. The tissue labelings were quantified using computer assisted stereology by means of an optical disector and microdensitometric image analysis by means of quantification of gray values of discriminated profiles. While partial hemitransection model favored a more accurate control of the lesion location, the contuse model allowed us to perform different degrees of lesion severity. A close correlation between behavioral impairment and severity of trauma was seen in the rats submitted to spinal cord contusion. The stereologic lesion index showed a correlation between severity of trauma and tissue damage by 7 days and demonstrated a time-dependent secondary degeneration after moderate but not after severe spinal cord contusion from 7 to 30 days after injury. Long-lasting activations of astrocytes and microglia seen by persisted increases in the specific mean gray values of immunoreactivities were also found in all levels of the white and gray matters of the partial hemitransected spinal cord until 3 months postinjury which can be related to wound/repair events and paracrine trophic support to spinal cord remaining neurons. The results showed that controlled partial lesions may provide an important toll to study trophism and plasticity in the spinal cord.

Vaccinia virus complement control protein enhances functional recovery after traumatic brain injury

Inflammation is a major contributor to the neuropathological consequences of traumatic brain injury (TBI). Previous studies have shown that proinflammatory complement activation fragments are present in the injured brain within the first 24 h after trauma. To investigate whether complement activation within the injured brain leads to the neuropathology and subsequent functional impairment associated with TBI, we examined what effect administration of a complement inhibitor, the vaccinia virus complement control protein (VCP), would have on spatial learning and memory in brain injured rats, as measured using the Morris Water Maze (MWM) procedure. Animals were subjected to a lateral fluid percussion brain injury of moderate severity and, 15 min later, received a 10-microL injection of either full-length VCP, a truncated version of VCP (VCPt), which lacks the complement inhibitory activity but retains the heparin binding activity of VCP, or saline directly into the cortex. Results of such intervention indicated that, at 2 weeks postinjury, both VCP and VCPt treatment attenuated impairments in spatial memory, but not neuropathological damage, as compared to the saline treated controls. These results were surprising and suggest that the neuroprotective effects following administration of VCP after acute brain injury are mediated by mechanisms other than complement inhibition. Potential mechanisms are discussed.

Central and peripheral nerve regeneration by transplantation of Schwann cells and transdifferentiated bone marrow stromal cells

In contrast to the peripheral nervous system (PNS), little structural and functional regeneration of the central nervous system (CNS) occurs spontaneously following injury in adult mammals. The inability of the CNS to regenerate is mainly attributed to its own inhibitorial environment such as glial scar formation and the myelin sheath of oligodendrocytes. Therefore, one of the strategies to promote axonal regeneration of the CNS is to experimentally modify the environment to be similar to that of the PNS. Schwann cells are the myelinating glial cells in the PNS, and are known to play a key role in Wallerian degeneration and subsequent regeneration. Central nervous system regeneration can be elicited by Schwann cell transplantation, which provides a suitable environment for regeneration. The underlying cellular mechanism of regeneration is based upon the cooperative interactions between axons and Schwann cells involving the production of neurotrophic factors and other related molecules. Furthermore, tight and gap junctional contact between the axon and Schwann cell also mediates the molecular interaction and linking. In this review, the role of the Schwann cell during the regeneration of the sciatic (representing the PNS) and optic (representing the CNS) nerves is explained. In addition, the possibility of optic nerve reconstruction by an artificial graft of Schwann cells is also described. Finally, the application of cells not of neuronal lineage, such as bone marrow stromal cells (MSCs), in nerve regeneration is proposed. Marrow stromal cells are known as multipotential stem cells that, under specific conditions, differentiate into several kinds of cells. The strategy to transdifferentiate MSCs into the cells with a Schwann cell phenotype and the induction of sciatic and optic nerve regeneration are described.

Modulation of astrocyte proliferation by cyclin-dependent kinase inhibitor p27(Kip1)

We previously demonstrated that type 1 astrocytes exhibited homotypic cell contact-dependent inhibition of proliferation with increased expression of cyclin-dependent kinase inhibitor p27(Kip1). Here, we investigated the functional role of p27 in contact-dependent inhibition of astrocytes and reactive gliosis in vitro and in vivo. An increase in the number of proliferating cells was detected in high-density cultures of astrocytes derived from mice carrying a targeted deletion in the p27 gene compared to astrocytes from wild-type mice. Overexpression of p27 by adenovirus vectors inhibited astrocyte proliferation, which was accompanied by downregulation of cyclin A. In a gliosis model in vitro, a transient decrease in the p27 level and an increase in the proliferation rate were observed. Astrocyte proliferation following cortical injury lasted longer in p27-deficient mice than in wild-type mice. Forced expression of p27 in both in vitro and in vivo models of gliosis effectively suppressed astrocyte proliferation. In summary, we demonstrated that p27 contributed to the cell contact-dependent inhibition of astrocyte proliferation and to the cessation of proliferation in reactive astrocytosis. p27 may be used to modulate reactive astrocytosis.

White matter extracellular matrix chondroitin sulfate/dermatan sulfate proteoglycans in multiple sclerosis

Extracellular matrix (ECM) alterations in the central nervous system (CNS) of multiple sclerosis (MS) patients result from blood-brain barrier breakdown, release and activation of proteases, and synthesis of ECM components. To elucidate their potential pathophysiologic roles, we analyzed expression of major CNS ECM proteoglycans (PGs) in MS and control CNS tissues. In active MS plaque edges, 3 CNS lecticans (versican, aggrecan, and neurocan) and dermatan sulfate PG were increased in association with astrocytosis; in active plaque centers they were decreased in the ECM and accumulated in foamy macrophages, suggesting that these ECM PGs are injured and phagocytosed along with myelin. In inactive lesions they were diminished and in normal-appearing white matter they showed heretofore-unappreciated abnormal heterogeneous aggregation. Phosphacan, an ECM PG abundant in both gray and white matter, was less markedly altered. Since in development the spaciotemporal expression of ECM PGs influences neurite outgrowth, cell migration, axon guidance, and myelination, these data suggest that 1) enhanced white matter lectican and dermatan sulfate PG expression in the pro-inflammatory milieu of expanding lesion edges contributes to their sharp boundaries and the failure of neuronal ingrowth; 2) decreases in plaque centers may preclude regeneration and repair; and 3) diffuse ECM PG damage relates to axon degeneration outside of overt lesions. Thus, ECM PG alterations are specific, temporally dynamic, and widespread in MS patients and may play critical roles in lesion pathogenesis and CNS dysfunction.

Solid human embryonic spinal cord xenografts in acute and chronic spinal cord cavities: a morphological and functional study

While therapeutic spinal cord grafting procedures are of interest in the chronic spinal cord injury stage, previous experimental grafting studies, including human spinal cord tissue, have mainly focused on the acute stage. Therefore, solid human embryonic spinal cord grafts were implanted in acute or chronic spinal cord aspiration cavities of immunodeficient rats to compare the morphological and locomotor outcome to that of lesion alone cases. Locomotor function was assessed using the Basso, Beattie, and Bresnahan open-field locomotor rating scale up to 6 months, while the morphological evaluation of graft survival, growth, and integration was performed at 6 weeks or 6 months after implantation. Graft survival was 94% in both lesion models, while graft growth was enhanced in the chronic compared to the acute cavity group. Human specific Thy-1 and neurofilament immunoreactive fibers were observed up to 7 mm into host white matter, while aminergic fibers were observed up to 1 mm into the grafts. Abundant calcitonin gene-related peptide immunoreactive fibers in the grafts in the absence both of immunoreactive cell bodies and colocalized human-specific neurofilament immunoreactivity, suggested host fiber ingrowth. At 6 months, the grafted cases presented less central canal deformation and lower glial fibrillary acidic protein immunoreactivity at the host cavity border compared to that of the nongrafted cases. The strong compensatory regain of locomotor function after unilateral spinal cord lesions was not affected by the human spinal cord grafts. In conclusion, solid human embryonic spinal cord tissue transplanted to a cavity in the adult injured spinal cord results in beneficial morphological effects in both the acute and chronic spinal cord lesion.