Astrocyte response and transforming growth factor-beta localization in acute spinal cord injury

TGF-β/Smad Signalling in Neurogenesis: Implications for Neuropsychiatric Diseases

TGF-β/Smad signalling has been the subject of extensive research due to its role in the cell cycle and carcinogenesis. Modifications to the TGF-β/Smad signalling pathway have been found to produce disparate effects on neurogenesis. We review the current research on canonical and non-canonical TGF-β/Smad signalling pathways and their functions in neurogenesis. We also examine the observed role of neurogenesis in neuropsychiatric disorders and the relationship between TGF-β/Smad signalling and neurogenesis in response to stressors. Overlapping mechanisms of cell proliferation, neurogenesis, and the development of mood disorders in response to stressors suggest that TGF-β/Smad signalling is an important regulator of stress response and is implicated in the behavioural outcomes of mood disorders.

Bone marrow mesenchymal stem cells improve spinal function of spinal cord injury in rats via TGF-β/Smads signaling pathway

Bone marrow mesenchymal stem cells (BMSCs) on the repair of spinal cord injury (SCI) in rats as well as the role of transforming growth factor-β (TGF-β)/Smads signaling pathway in the repair were investigated. Rat BMSCs and astrocyte-spinal cords (ASCs) were isolated and cultured in vitro, and the cell purity was detected by flow cytometry. ASCs were co-cultured with TGF-β1, BMSCs and BMSCs + TGF-β1, respectively, and grouped accordingly, and ASCs cultured conventionally were included into control group. 3-(4,5)-Dimethylthiahiazo(-z-y1)-3,5-diphenyltetrazoliumbromide (MTT) assay was conducted to detect the proliferation ability of ASCs in each group. Western blotting (WB) was utilized to examine the expression of TGF-β/Smads signaling pathway-related proteins [TGF-β1, Smad2 and phosphorylated (p)-Smad2] in ASCs and ASCs co-cultured with BMSCs. A rat model of SCI was established, and BMSCs were injected locally. Then (BBB) score was used to evaluate spinal cord repair, and WB was adopted to detect the expression of TGF-β1, Smad2 and p-Smad2 at the injured site. BMSCs and ASCs isolated in vitro grew well. According to MTT assay results, TGF-β1 significantly promoted the proliferation of ASCs (P<0.05), and co-culture of ASCs and BMSCs remarkably reduced the proliferation of ASCs (P<0.05). The detection of protein expression at the SCI site via WB demonstrated that the expression of TGF-β1, Smad2 and p-Smad2 in SCI group were obviously upregulated compared with those in Sham group at 1 week (P<0.05), and the injection of BMSCs could markedly downregulate the expression (P<0.05). After 3 week, there were no significant differences in the expression of TGF-β1, Smad2 and p-Smad2 among groups (P>0.05). The transplantation of BMSCs can improve the spinal function of SCI rats probably by inhibiting the TGF-β/Smads signaling pathway and reducing the proliferation of ASCs.

Neuronal hyperexcitability and astrocyte activation in spinal dorsal horn of a dermatitis mouse model with cutaneous hypersensitivity

Cleaning products such as soaps, shampoos, and detergents are comprised mainly of surfactants, agents known to cause dermatitis and cutaneous hypersensitivity characterized by itching, stinging, and burning of the skin and scalp. However, the mechanisms underlying surfactant-induced cutaneous hypersensitivity remain unclear. In the present study, we investigated the mechanisms of cutaneous hypersensitivity in mice treated with the detergent sodium dodecyl sulfate (SDS). Repeated SDS application to the skin induced inflammation, xeroderma, and elongation of peripheral nerves into the epidermis. The number of neurons immunopositive for c-Fos, a well known marker of neural activity, was substantially higher (+441%) in spinal dorsal horn (SDH) lamina I-II (but not lamina III-VI) of SDS-treated mice compared to vehicle-treated mice. In vivo extracellular recording revealed enhanced spontaneous (+64%) and non-noxious mechanical stimulation-evoked firing (+139%) of SDH lamina I-II neurons in SDS-treated mice, and stimulation-evoked neuronal firing was sustained (+5333%) even after stimulation. The number of GFAP-positive (activated) astrocytes, but not Iba1-positive microglia, was also elevated (+137%) in SDH lamina I-II of SDS-treated mice compared to vehicle-treated mice. Peripheral nerve elongation and hyperexcitability of afferent or SDH neurons, possible associated with the activation of spinal astrocytes, may underlie cutaneous hypersensitivity induced by surfactants.

RGMa mediates reactive astrogliosis and glial scar formation through TGFβ1/Smad2/3 signaling after stroke

In response to stroke, astrocytes become reactive astrogliosis and are a major component of a glial scar. This results in the formation of both a physical and chemical (production of chondroitin sulfate proteoglycans) barrier, which prevent neurite regeneration that, in turn, interferes with functional recovery. However, the mechanisms of reactive astrogliosis and glial scar formation are poorly understood. In this work, we hypothesized that repulsive guidance molecule a (RGMa) regulate reactive astrogliosis and glial scar formation. We first found that RGMa was strongly expressed by reactive astrocytes in the glial scar in a rat model of middle cerebral artery occlusion/reperfusion. Genetic or pharmacologic inhibition of RGMa in vivo resulted in a strong reduction of reactive astrogliosis and glial scarring as well as in a pronounced improvement in functional recovery. Furthermore, we showed that transforming growth factor β1 (TGFβ1) stimulated RGMa expression through TGFβ1 receptor activin-like kinase 5 (ALK5) in primary cultured astrocytes. Knockdown of RGMa abrogated key steps of reactive astrogliosis and glial scar formation induced by TGFβ1, including cellular hypertrophy, glial fibrillary acidic protein upregulation, cell migration, and CSPGs secretion. Finally, we demonstrated that RGMa co-immunoprecipitated with ALK5 and Smad2/3. TGFβ1-induced ALK5-Smad2/3 interaction and subsequent phosphorylation of Smad2/3 were impaired by RGMa knockdown. Taken together, we identified that after stroke, RGMa promotes reactive astrogliosis and glial scar formation by forming a complex with ALK5 and Smad2/3 to promote ALK5-Smad2/3 interaction to facilitate TGFβ1/Smad2/3 signaling, thereby inhibiting neurological functional recovery. RGMa may be a new therapeutic target for stroke.

"Targeting astrocytes in CNS injury and disease: A translational research approach"

Astrocytes are a major constituent of the central nervous system. These glia play a major role in regulating blood-brain barrier function, the formation and maintenance of synapses, glutamate uptake, and trophic support for surrounding neurons and glia. Therefore, maintaining the proper functioning of these cells is crucial to survival. Astrocyte defects are associated with a wide variety of neuropathological insults, ranging from neurodegenerative diseases to gliomas. Additionally, injury to the CNS causes drastic changes to astrocytes, often leading to a phenomenon known as reactive astrogliosis. This process is important for protecting the surrounding healthy tissue from the spread of injury, while it also inhibits axonal regeneration and plasticity. Here, we discuss the important roles of astrocytes after injury and in disease, as well as potential therapeutic approaches to restore proper astrocyte functioning.

Effectiveness of minocycline and FK506 alone and in combination on enhanced behavioral and biochemical recovery from spinal cord injury in rats

Injury to the spinal cord results in immediate physical damage (primary injury) followed by a prolonged posttraumatic inflammatory disorder (secondary injury). The present study aimed to investigate the neuroprotective effects of minocycline and FK506 (Tacrolimus) individually and in combination on recovery from experimental spinal cord injury (SCI). Young adult male rats were subjected to experimental SCI by weight compression method. Minocycline (50mg/kg) and FK506 (1mg/kg) were administered orally in combination and individually to the SCI group daily for three weeks. During these three weeks, the recovery was measured using behavioral motor parameters (including BBB, Tarlov and other scorings) every other day for 29days after SCI. Thereafter, the animals were sacrificed and the segment of the spinal cord centered at the injury site was removed for the histopathological studies as well as for biochemical analysis of monoamines such as 5-hydroxytryptamine (5-HT) and 5-hydroxy-indolacetic acid (5-HIAA) and some oxidative stress indices, such as thiobarbituric acid-reactive substances (TBARS), total glutathione (GSH) and myeloperoxidase (MPO). All behavioral results indicated that both drugs induced significant recovery from SCI with respect to time. The biochemical and histopathological results supported the behavioral findings, revealing significant recovery in the regeneration of the injured spinal tissues, the monoamine levels, and the oxidative stress indices. Overall, the effects of the tested drugs for SCI recovery were as follows: FK506+minocycline>minocycline>FK506 in all studied parameters. Thus, minocycline and FK506 may prove to be a potential therapy cocktail to treat acute SCI. However, further studies are warranted.

Pharmacological Suppression of CNS Scarring by Deferoxamine Reduces Lesion Volume and Increases Regeneration in an In Vitro Model for Astroglial-Fibrotic Scarring and in Rat Spinal Cord Injury In Vivo

Lesion-induced scarring is a major impediment for regeneration of injured axons in the central nervous system (CNS). The collagen-rich glial-fibrous scar contains numerous axon growth inhibitory factors forming a regeneration-barrier for axons. We demonstrated previously that the combination of the iron chelator 2,2’-bipyridine-5,5’-decarboxylic acid (BPY-DCA) and 8-Br-cyclic AMP (cAMP) inhibits scar formation and collagen deposition, leading to enhanced axon regeneration and partial functional recovery after spinal cord injury. While BPY-DCA is not a clinical drug, the clinically approved iron chelator deferoxamine mesylate (DFO) may be a suitable alternative for anti-scarring treatment (AST). In order to prove the scar-suppressing efficacy of DFO we modified a recently published in vitro model for CNS scarring. The model comprises a co-culture system of cerebral astrocytes and meningeal fibroblasts, which form scar-like clusters when stimulated with transforming growth factor-β (TGF-β). We studied the mechanisms of TGF-β-induced CNS scarring and compared the efficiency of different putative pharmacological scar-reducing treatments, including BPY-DCA, DFO and cAMP as well as combinations thereof. We observed modulation of TGF-β-induced scarring at the level of fibroblast proliferation and contraction as well as specific changes in the expression of extracellular matrix molecules and axon growth inhibitory proteins. The individual and combinatorial pharmacological treatments had distinct effects on the cellular and molecular aspects of in vitro scarring. DFO could be identified as a putative anti-scarring treatment for CNS trauma. We subsequently validated this by local application of DFO to a dorsal hemisection in the rat thoracic spinal cord. DFO treatment led to significant reduction of scarring, slightly increased regeneration of corticospinal tract as well as ascending CGRP-positive axons and moderately improved locomotion. We conclude that the in vitro model for CNS scarring is suitable for efficient pre-screening and identification of putative scar-suppressing agents prior to in vivo application and validation, thus saving costs, time and laboratory animals.

Neuroinflammatory contributions to pain after SCI: roles for central glial mechanisms and nociceptor-mediated host defense

Neuropathic pain after spinal cord injury (SCI) is common, often intractable, and can be severely debilitating. A number of mechanisms have been proposed for this pain, which are discussed briefly, along with methods for revealing SCI pain in animal models, such as the recently applied conditioned place preference test. During the last decade, studies of animal models have shown that both central neuroinflammation and behavioral hypersensitivity (indirect reflex measures of pain) persist chronically after SCI. Interventions that reduce neuroinflammation have been found to ameliorate pain-related behavior, such as treatment with agents that inhibit the activation states of microglia and/or astroglia (including IL-10, minocycline, etanercept, propentofylline, ibudilast, licofelone, SP600125, carbenoxolone). Reversal of pain-related behavior has also been shown with disruption by an inhibitor (CR8) and/or genetic deletion of cell cycle-related proteins, deletion of a truncated receptor (trkB.T1) for brain-derived neurotrophic factor (BDNF), or reduction by antisense knockdown or an inhibitor (AMG9810) of the activity of channels (TRPV1 or Nav1.8) important for electrical activity in primary nociceptors. Nociceptor activity is known to drive central neuroinflammation in peripheral injury models, and nociceptors appear to be an integral component of host defense. Thus, emerging results suggest that spinal and systemic effects of SCI can activate nociceptor-mediated host defense responses that interact via neuroinflammatory signaling with complex central consequences of SCI to drive chronic pain. This broader view of SCI-induced neuroinflammation suggests new targets, and additional complications, for efforts to develop effective treatments for neuropathic SCI pain.

Extracellular matrix regulation of inflammation in the healthy and injured spinal cord

Throughout the body, the extracellular matrix (ECM) provides structure and organization to tissues and also helps regulate cell migration and intercellular communication. In the injured spinal cord (or brain), changes in the composition and structure of the ECM undoubtedly contribute to regeneration failure. Less appreciated is how the native and injured ECM influences intraspinal inflammation and, conversely, how neuroinflammation affects the synthesis and deposition of ECM after CNS injury. In all tissues, inflammation can be initiated and propagated by ECM disruption. Molecules of ECM newly liberated by injury or inflammation include hyaluronan fragments, tenascins, and sulfated proteoglycans. These act as "damage-associated molecular patterns" or "alarmins", i.e., endogenous proteins that trigger and subsequently amplify inflammation. Activated inflammatory cells, in turn, further damage the ECM by releasing degradative enzymes including matrix metalloproteinases (MMPs). After spinal cord injury (SCI), destabilization or alteration of the structural and chemical compositions of the ECM affects migration, communication, and survival of all cells - neural and non-neural - that are critical for spinal cord repair. By stabilizing ECM structure or modifying their ability to trigger the degradative effects of inflammation, it may be possible to create an environment that is more conducive to tissue repair and axon plasticity after SCI.

TGF-β1 attenuates spinal neuroinflammation and the excitatory amino acid system in rats with neuropathic pain

Previous studies have reported that the intrathecal (i.t.) administration of transforming growth factor β1 (TGF-β1) prevents and reverses neuropathic pain. However, only limited information is available regarding the possible role and effects of spinal TGF-β1 in neuropathic pain. We aimed to investigate the antinociceptive effects of exogenous TGF-β1 on chronic constriction injury (CCI)-induced neuropathic pain in rats. We demonstrated that sciatic nerve injury caused a downregulation of endogenous TGF-β1 levels on the ipsilateral side of the lumbar spinal dorsal gray matter, and that the i.t. administration of TGF-β1 (.01-10 ng) significantly attenuated CCI-induced thermal hyperalgesia in neuropathic rats. TGF-β1 significantly inhibited CCI-induced spinal neuroinflammation, microglial and astrocytic activation, and upregulation of tumor necrosis factor-α. Moreover, i.t. TGF-β1 significantly attenuated the CCI-induced downregulation of glutamate transporter 1, the glutamate aspartate transporter, and the excitatory amino acid carrier 1 on the ipsilateral side. Furthermore, i.t. TGF-β1 significantly decreased the concentrations of 2 excitatory amino acids, aspartate and glutamate, in the spinal dialysates in CCI rats. In summary, we conclude that the mechanisms of the antinociceptive effects of i.t. TGF-β1 in neuropathy may include attenuation of spinal neuroinflammation, attenuation, or upregulation of glutamate transporter downregulation, and a decrease of spinal extracellular excitatory amino acids.

PERSPECTIVE

Clinically, medical treatment is usually initiated after the onset of intractable pain. Therefore, in the present study, i.t. TGF-β1 was designed to be administered 2 weeks after the establishment of CCI pain. Compared to the continuous TGF-β1 infusion mode, single-dose administration seems more convenient and practical to use.

Grafted bone marrow stromal cells: a contributor to glial repair after spinal cord injury

In the CNS, astrocytes, oligodendrocytes and microglias are involved in not only development but also pathology such as spinal cord injury (SCI). Glial cells play dual roles (negative vs. positive effects) in these processes. After SCI, detrimental effects usually dominate and significantly retard functional recovery, and curbing these effects is critical for promoting neurological improvement. Bone marrow stromal cells (BMSCs) represent a new therapeutic approach for SCI by enabling improved sensory and motor functions in animal models. Although transdifferentiation to spinal neurons was poor, because of their pleiotropic nature, the protective effects of BMSCs are broad and are primarily mediated through modulation of transdifferentiation into host spinal glial components. Transplantation of BMSCs can positively alter the spinal microenvironment and enhance recovery. The objective of this review is to discuss these and other related mechanisms. Since BMSCs transplantation has been applied in other clinical fields, we hope to provide useful clues for the clinical application of BMSCs to treat the SCI in the near future.

Different modifications of phosphorylated Smad3C and Smad3L through TGF-β after spinal cord injury in mice

Transforming growth factor-β (TGF-β) is an anti-inflammatory cytokine and is expressed in the injured spinal cord. TGF-β signals through receptors to activate Smad proteins, which translocate into the nucleus. In the present study, we investigated the chronological alterations and cellular locations of the TGF-β/Smad signaling pathway following spinal cord injury (SCI) in mice. ELISA analysis showed that the concentration of interleukin-6 (IL-6) in injured spinal cords significantly increases immediately after SCI, while the concentration of TGF-β gradually increased after SCI, peaked at 2 days, and then gradually decreased. Immunohistochemical studies revealed that Smad3 was mainly expressed in neurons of the spinal cord. Phosphorylated Smad3 at the C-terminus (p-Smad3C) was stained within the motor neurons in the anterior horn, while phosphorylated Smad3 at the linker regions (p-Smad3L) was expressed in astrocytes within gray matter. These findings suggest that SCI induces gradual increases in TGF-β and induces different activation of p-Smad3C and p-Smad3L. Phosphorylated Smad3C might be involved in neuronal degeneration after SCI, and p-Smad3L may play a role in glial scar formation by astrocytes.

Predifferentiated GABAergic neural precursor transplants for alleviation of dysesthetic central pain following excitotoxic spinal cord injury

Intraspinal quisqualic acid (QUIS) injury induce (i) mechanical and thermal hyperalgesia, (ii) progressive self-injurious overgrooming of the affected dermatome. The latter is thought to resemble painful dysesthesia observed in spinal cord injury (SCI) patients. We have reported previously loss of endogenous GABA immunoreactive (IR) cells in the superficial dorsal horn of QUIS rats 2 weeks post injury. Further histological evaluation showed that GABA-, glycine-, and synaptic vesicular transporter VIAAT-IR persisted but were substantially decreased in the injured spinal cord. In this study, partially differentiated GABA-IR embryonic neural precursor cells (NPCs) were transplanted into the spinal cord of QUIS rats to reverse overgrooming by replenishing lost inhibitory circuitry. Rat E14 NPCs were predifferentiated in 0.1 ng/ml FGF-2 for 4 h prior to transplantation. In vitro immunocytochemistry of transplant cohort showed large population of GABA-IR NPCs that double labeled with nestin but few colocalized with NeuN, indicating partial maturation. Two weeks following QUIS lesion at T12-L1, and following the onset of overgrooming, NPCs were transplanted into the QUIS lesion sites; bovine adrenal fibroblast cells were used as control. Overgrooming was reduced in >55.5% of NPC grafted animals, with inverse relationship between the number of surviving GABA-IR cells and the size of overgrooming. Fibroblast-control animals showed a progressive worsening of overgrooming. At 3 weeks post-transplantation, numerous GABA-, nestin-, and GFAP-IR cells were present in the lesion site. Surviving grafted GABA-IR NPCs were NeuN⁺ and GFAP⁻. These results indicate that partially differentiated NPCs survive and differentiate in vivo into neuronal cells following transplantation into an injured spinal cord. GABA-IR NPC transplants can restore lost dorsal horn inhibitory signaling and are useful in alleviating central pain following SCI.

Transcriptional activation of endothelial cells by TGFβ coincides with acute microvascular plasticity following focal spinal cord ischaemia/reperfusion injury

Microvascular dysfunction, loss of vascular support, ischaemia and sub-acute vascular instability in surviving blood vessels contribute to secondary injury following SCI (spinal cord injury). Neither the precise temporal profile of the cellular dynamics of spinal microvasculature nor the potential molecular effectors regulating this plasticity are well understood. TGFβ (transforming growth factor β) isoforms have been shown to be rapidly increased in response to SCI and CNS (central nervous system) ischaemia, but no data exist regarding their contribution to microvascular dysfunction following SCI. To examine these issues, in the present study we used a model of focal spinal cord ischaemia/reperfusion SCI to examine the cellular response(s) of affected microvessels from 30 min to 14 days post-ischaemia. Spinal endothelial cells were isolated from affected tissue and subjected to focused microarray analysis of TGFβ-responsive/related mRNAs 6 and 24 h post-SCI. Immunohistochemical analyses of histopathology show neuronal disruption/loss and astroglial regression from spinal microvessels by 3 h post-ischaemia, with complete dissolution of functional endfeet (loss of aquaporin-4) by 12 h post-ischaemia. Coincident with this microvascular plasticity, results from microarray analyses show 9 out of 22 TGFβ-responsive mRNAs significantly up-regulated by 6 h post-ischaemia. Of these, serpine 1/PAI-1 (plasminogen-activator inhibitor 1) demonstrated the greatest increase (>40-fold). Furthermore, uPA (urokinase-type plasminogen activator), another member of the PAS (plasminogen activator system), was also significantly increased (>7.5-fold). These results, along with other select up-regulated mRNAs, were confirmed biochemically or immunohistochemically. Taken together, these results implicate TGFβ as a potential molecular effector of the anatomical and functional plasticity of microvessels following SCI.

Pathology dynamics predict spinal cord injury therapeutic success

Secondary injury, the complex cascade of cellular events following spinal cord injury (SCI), is a major source of post-insult neuron death. Experimental work has focused on the details of individual factors or mechanisms that contribute to secondary injury, but little is known about the interactions among factors leading to the overall pathology dynamics that underlie its propagation. Prior hypotheses suggest that the pathology is dominated by interactions, with therapeutic success lying in combinations of neuroprotective treatments. In this study, we provide the first comprehensive, system-level characterization of the entire secondary injury process using a novel relational model methodology that aggregates the findings of approximately 250 experimental studies. Our quantitative examination of the overall pathology dynamics suggests that, while the pathology is initially dominated by "fire-like", rate-dependent interactions, it quickly switches to a "flood-like", accumulation-dependent process with contributing factors being largely independent. Our evaluation of approximately 20,000 potential single and combinatorial treatments indicates this flood-like pathology results in few highly influential factors at clinically realistic treatment time frames, with multi-factor treatments being merely additive rather than synergistic in reducing neuron death. Our findings give new fundamental insight into the understanding of the secondary injury pathology as a whole, provide direction for alternative therapeutic strategies, and suggest that ultimate success in treating SCI lies in the pursuit of pathology dynamics in addition to individually involved factors.

TGF-beta1 and TGF-beta2 expression after traumatic human spinal cord injury

STUDY DESIGN

Immunohistochemical investigation in control and lesioned human spinal cords.

OBJECTIVES

To assess the spatial and temporal expression patterns of transforming growth factor-beta1 and -beta2 (TGF-beta1 and TGF-beta2) in the human spinal cord after traumatic injury.

SETTING

Germany, Aachen, Aachen University Hospital.

METHODS

Sections from human spinal cords from 4 control patients and from 14 patients who died at different time points after traumatic spinal cord injury (SCI) were investigated immunohistochemically.

RESULTS

In control cases, TGF-beta1 was confined to occasional blood vessels, intravascular monocytes and some motoneurons, whereas TGF-beta2 was only found in intravascular monocytes. After traumatic SCI, TGF-beta1 immunoreactivity was dramatically upregulated by 2 days after injury (the earliest survival time investigated) and was detected within neurons, astrocytes and invading macrophages. The staining was most intense over the first weeks after injury but gradually declined by 1 year. TGF-beta2 immunoreactivity was first detected 24 days after injury. It was located in macrophages and astrocytes and remained elevated for up to 1 year. In white matter tracts undergoing Wallerian degeneration, there was no induction of either isoform.

CONCLUSION

The early induction of TGF-beta1 at the point of SCI suggests a role in the acute inflammatory response and formation of the glial scar, while the later induction of TGF-beta2 may indicate a role in the maintenance of the scar. Neither of these TGF-beta isoforms appears to contribute to the astrocytic scar formation in nerve fibre tracts undergoing Wallerian degeneration.

TGF-beta1 suppresses T cell infiltration and VP2 puff B mutation enhances apoptosis in acute polioencephalitis induced by Theiler's virus

GDVII and DA strains of Theiler's murine encephalomyelitis virus (TMEV) differ in VP2 puff B. One week after GDVII virus infection, SJL/J mice had large numbers of TUNEL+ apoptotic cells with a relative lack of T cell infiltration in the brain. DA viruses with mutation in puff B induced higher levels of apoptosis than wild-type DA virus, but levels of inflammation in brains were similar between DA and DA virus mutants. The difference in inflammation among TMEVs could be due to TGF-beta1 expression that was seen only in GDVII virus infection and negatively correlated with CD3+ T cell infiltration.

Regeneration of nigrostriatal dopaminergic axons by degradation of chondroitin sulfate is accompanied by elimination of the fibrotic scar and glia limitans in the lesion site

Chondroitin sulfate increases around a lesion site after central nervous system injury and is believed to be an impediment to axonal regeneration, because administration of chondroitinase ABC, a chondroitin sulfate-degrading enzyme, promotes axonal regeneration of central neurons. To examine the physiological role of chondroitin sulfate up-regulation after injury, the nigrostriatal dopaminergic axons were unilaterally transected in mice, and chondroitinase ABC was then injected into the lesion site. In mice transected only, tyrosine hydroxylase-immunoreactive axons did not extend across the lesion at 1 or 2 weeks after the transection. Immunoreactivities of chondroitin sulfate side chains and core protein of NG2 proteoglycan increased in and around the lesion site, and a fibrotic scar containing type IV collagen deposits developed in the lesion center. In contrast, in mice transected and treated with chondroitinase ABC, numerous tyrosine hydroxylase-immunoreactive axons were regenerated across the lesion at 1 and 2 weeks after the transection. In these animals, chondroitin sulfate immunoreactivity remarkably decreased, and immunoreactivity of 2B6 antibody, which recognizes the stub of degraded chondroitin sulfate side chains, was enhanced. Furthermore, the formation of a fibrotic scar and a glia limitans that surrounds the former was completely prevented, although type IV collagen immunoreactivity remained in newly formed blood capillaries around the lesion site. We discuss the question of whether the chondroitin sulfate is acting as a direct inhibitor of axonal regeneration or whether the observed changes are due to a prevention of the fibrotic scar formation and a rearrangement of astrocytic membranes.

End organ effects of high-dose human equivalent methylprednisolone in a spinal cord injury rat model

STUDY DESIGN

Interventional study.

OBJECTIVE

To analyze the histologic effects of high-dose human equivalent methylprednisolone on the pulmonary, cardiac, intestinal, renal, hepatic, and splenic tissues in a spinal cord injury rat model.

SUMMARY OF BACKGROUND DATA

There are numerous investigations of various medical interventions for the treatment of acute spinal cord trauma. Currently, the only generally accepted medical intervention in an acute spinal cord trauma is the intravenous administration of high doses of methylprednisolone. Although it has been nearly 2 decades since the first National Acute Spinal Cord Injury Study investigated the role high-dose steroids might play in the treatment of acute spinal cord trauma, controversy still exists regarding the efficacy of this treatment. To our knowledge, no study has examined the role of high-dose methylprednisolone in organ systems other than the spinal cord in an acute spinal cord injury model at the histologic level. This study attempts to characterize end organ histologic response to human dose equivalent (HDE) intravenous methylprednisolone administration in a rodent model of acute spinal cord injury.

METHODS

A total of 48 Sprague-Dawley rats were divided equally into control and experimental groups. Each group was subdivided into 6 sets of 4 animals each, according to intervals after injury. Groups 1-6 consisted of animals euthanized at 0, 4, 8, 16, 24, and 48 hours after spinal cord injury. Paraplegia after lower thoracic laminectomy was achieved using a standardized Allen weight drop technique. Within 1 hour of injury, experimental animals were treated with HDE methylprednisolone, infused for 23 hours continuously. Liver, kidney, lung, intestine, spleen, and heart were harvested at variable intervals after injury and prepared for histologic examination. These slides were analyzed with microscopic staining techniques and compared in a blinded manner by a qualified pathologist.

RESULTS

Of all the end organs analyzed, the spleens were most affected. Lymphocytic depletion was seen in as little as 4 hours after methylprednisolone infusion and continued until 48 hours. Pulmonary tissues variably showed interstitial congestion and eosinophilic alveolar collections. Intestinal mucosal tissues showed edema and autolyzed mucosa from 16 hours onwards. Cardiac, kidney, and hepatic tissue did not differ significantly from controls.

CONCLUSIONS

Histologically, HDE methylprednisolone caused significant splenic lymphocytic depletion changes in as little as 4 hours. This trend of end organ lymphocytopenia continued to progress until 48 hours. Pulmonary eosinophilic infiltrates were seen from 8 until 24 hours. Intestinal mucosal edema and necrosis were seen in samples at 16 hours throughout 48 hours. This study was designed to evaluate end organ changes seen in an animal model of an acute spinal cord injury treated with HDE methylprednisolone. Study animals were infused with HDE methylprednisolone given according to the National Acute Spinal Cord Injury Study II protocol. The kidney, lung, cardiac, intestinal, splenic, and hepatic tissues from the aforementioned animals were then sectioned and analyzed using histologic staining techniques by a qualified pathologist.

Pro- and anti-inflammatory cytokines regulate the ERK pathway: Implication of the timing for the activation of microglial cells

Pro-inflammatory molecules induce glial activation and the release of potentially detrimental factors capable of generating oxidative damage, such as nitric oxide (NO) and superoxide anion (O2.-). Activated glial cells (astrocytes and microglia) are associated to the inflammatory process in neurodegenerative diseases. A strong inflammatory response could escape endogenous control becoming toxic to neurons and contributing to the course of the disease. We evaluated in a hippocampal cells-microglia co-culture model, if the pro-inflammatory condition induced by lipopolysaccharide + interferon-gamma (LPS+IFN-gamma) promoted damage directly or if damage was secondary to glial activation. In addition, we explored the effect of the anti-inflammatory cytokine transforming growth factor-beta1 (TGF-beta1), and pro-inflammatory cytokines, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) on the regulation of the inflammatory response of microglia. We found that LPS+IFN-gamma-induced damage on hippocampal cultures was dependent on the presence of microglial cells. In hippocampal cultures exposed to LPS+IFN-gamma, TGF-beta1 was induced whereas in microglial cell cultures LPS+IFN-gamma induced the secretion of IL-1beta. TGF-beta1 and IL-1beta but not TNF-alpha decreased the NO production by 70-90%. PD98059, an inhibitor of MAP kinase (MEK), reduced the IFN-gamma-induced NO production by 40%. TGF-beta and IL-1beta reduced the IFN-gamma induced phosphorylation of ERK1,2 by 60% and 40%, respectively. However, the effect of IL-1beta was observed at 30 min and that of TGF-beta1 only after 24 h of exposure. We propose that acting with different timing, TGF-beta1 and IL-1beta can modulate the extracellular signal-regulated kinase ERK1,2, as a common element for different transduction pathways, regulating the amplitude and duration of glial activation in response to LPS+IFN-gamma. Cross-talk among brain cells may be key for the understanding of inflammatory mechanisms involved in pathogenesis of neurodegenerative diseases.

Transforming growth factor-β1 produced by hippocampal cells modulates microglial reactivity in culture

Activated microglia produce superoxide anion (O2-) and nitric oxide (NO), both of which can be neurotoxic. To identify regulatory mechanisms that might modulate over-activation of microglia, we evaluated the inhibition of microglial activation by factors secreted by hippocampal cells. Supernatants from hippocampal cell cultures (Hippocampal-Cm) prevented microglial O2- and NO production. LAP-TGF beta1 was present in the Hippocampal-Cm as shown by immunoblot and a TGF beta1-dependent proliferation-inhibition bioassay. LAP-TGF beta1 and TGFbeta activity increased in hippocampal cultures exposed to proinflammatory conditions (LPS and Interferon-gamma). The inhibition of O2- and NO production by Hippocampal-Cm was mimicked by the addition of recombinant TGF beta1. Treating Hippocampal-Cm with an antibody against TGF beta1 to neutralize its activity eliminated its ability to inhibit O2- and NO production. Our findings suggest that the TGF beta1 secreted by hippocampal cells modulated microglial activity. We propose that in pathological conditions, impairment of this modulatory mechanism could enhance microglia-mediated neurotoxicity.

Effects of methylprednisolone on the neural conduction of the motor evoked potentials in spinal cord injured rats

Methylprednisolone(MP), a glucocorticoid steroid, has an anti-inflammatory action and seems to inhibit the formation of oxygen free radicals produced during lipid peroxidation in a spinal cord injury(SCI). However, the effects of MP on the functional recovery after a SCI is controversial. The present study was conducted to determine the effects of MP on the recovery of neural conduction following a SCI. A SCI was produced using the NYU spinal cord impactor. A behavioral test was conducted to measure neurological disorders, and motor evoked potentials (MEPs) were recorded. According to the behavioral test, using BBB locomotor scaling, MP-treated animals showed improved functional recoveries when compared to saline-treated animals. MEP latencies in the MP-treated group were shortened when compared to those in the control group. Peak amplitudes of MEPs were larger in the MP-treated group than those in the control group. The thresholds of MEPs tended to be lower in the MP-treated group than those in the control group. These results suggest that MP may improve functional recovery after a SCI.

Injury in the spinal cord may produce cell death in the brain

Functional deficits after spinal cord injury have originated not only from the direct physical damage itself, but from the secondary biochemical and pathological changes. Apoptotic cell death has been seen around the periphery of an injured site and has been known to ultimately progress to necrosis and infarction. We have initiated the present study focusing on the role of apoptosis in the secondary injury of the brain after acute spinal cord injury (SCI), and conducted a series of experiments, the study examining the morphological changes in the brain following the spinal injury. Under pentobarbital anesthesia, male Sprague-Dawley rats were subjected to SCI model. Rats were laminectomized and SCI was induced using NYU spinal impactor at T9 segment. The behavioral test was performed. Electrophysiologically, motor evoked potentials (MEPs) were recorded. The animals were subjected to morphological study at 12, 24, 48, 72 h, and 1 week, postoperatively. Locomotor deficits were observed after SCI, and changes in the amplitudes and latencies of the MEPs were observed. The morphological changes were evidenced by terminal TUNEL staining and Calbindin-D(28K) immunohistochemistry. The TUNEL-positive cells were located at the brain motor cortex after SCI. TUNEL-positive cells were seldom found 4 h after injury. In addition, Calbindin-D28K immunoreactive neurons were observed in the motor cortex after injury. These results suggest that apoptosis may play an important role in the pathophysiology of the brain motor cortex following acute spinal cord injury and functions that were deteriorated after SCI may be related to these electrophysiological and morphological changes.

Activation of P2X7 purinoceptor-stimulated TGF-beta 1 mRNA expression involves PKC/MAPK signalling pathway in a rat brain-derived type-2 astrocyte cell line, RBA-2

The present study investigates the receptor and mechanisms involved in ATP-stimulated transforming growth factor-beta 1 (TGF-beta 1) mRNA expression of a type-2 astrocyte cell line, RBA-2. RT-PCR analysis revealed that RBA-2 type-2 astrocytes possess abundant P2X(4) and P2X(7) receptors. ATP and P2X(7) receptor-sensitive agonist, BzATP, both stimulated TGF-beta 1 mRNA expression in a time and dose-dependent manner. The stimulation required a minimum of 500 muM ATP; BzATP was much more potent that ATP, and P2X(7)-selective antagonist, oATP, inhibited the effects. In addition, ATP metabolites ADP, AMP and adenosine were ineffective in stimulation of TGF-beta 1 mRNA expression. Thus, the effect of ATP was mediated through the P2X(7) receptors. To investigate further the mechanisms by which the P2X(7) receptor mediated the TGF-beta 1 mRNA expression, the cells were treated with inhibitors for mitogen-activated kinase (MAPK) or protein kinase C (PKC), PD98059 or GF109203X, respectively. Both PD98059 and GF109203X inhibited the ATP-stimulated TGF-beta 1 mRNA expression. Furthermore, ATP and BzATP stimulated ERK1/2 activation and the activation was inhibited by PKC inhibitors, GF109203X and Gö6976. In conclusion, activation of P2X(7) receptors enhanced TGF-beta 1 mRNA expression and the effect involved PKC/MAPK signalling pathway in RBA-2 type-2 astrocytes.

Role of the bcl-2 gene after contusive spinal cord injury in mice

OBJECTIVE

Apoptosis is indicated to have an important role in the secondary injury mechanisms of acute spinal cord injury (SCI). The proto-oncogene bcl-2 has been demonstrated to prevent apoptotic cell death in a wide variety of cell types. This study examined the recovery of behavioral function and histopathological variables after controlled-impact SCI in human bcl-2 transgenic (TG) mice and control mice.

METHODS

Six bcl-2 TG mice and five control mice were subjected to controlled-impact SCI of moderate severity at T10, with the use of a pneumatic impact device (0.25-mm-deep deformation; impact velocity, 2 m/s). Functional deficits were evaluated at times up to 28 days after SCI, with assessments of hindlimb reflexes and coordinated motor function. The extents of the lesions were histopathologically analyzed and quantified with morphometric measurements.

RESULTS

Both control and bcl-2 TG mice exhibited profound deficits immediately after injury, with subsequent gradual symptomatic recovery. The mean functional scores for the control mice were lower than those for the bcl-2 TG mice, although the Mann-Whitney U test revealed no significant differences. The mean lesion volume for the bcl-2 TG mice (mean +/- standard deviation, 2.9 +/- 1.1 x 10(-2) mm(3)) was significantly lower than that for the control mice (5.1 +/- 0.8 x 10(-2) mm(3); unpaired t test, P = 0.0101). Immunohistological analysis of the spinal cords from the bcl-2 TG mice revealed marked expression of Bcl-2 at the injury site and in adjacent regions.

CONCLUSION

Our results suggest that overexpression of the bcl-2 gene may play a protective role in neuropathological sequelae after SCI.

TGF-beta1 upregulates CX3CR1 expression and inhibits fractalkine-stimulated signaling in rat microglia

Following peripheral nerve transection, CX3CR1 and TGF-beta1 are increased in a time-dependent manner within the injured facial motor nucleus. To explore the relationship between TGF-beta1 and CX3CR1 in the CNS, the effects of TGF-beta1 on CX3CR1 mRNA, protein and fractalkine-dependent stimulation of signal transduction cascades in primary cultures of rat microglia were examined. TGF-beta1 increased steady state levels of CX3CR1 mRNA, 125I-fractalkine binding sites and blunted fractalkine-stimulated ERK1/2 phosphorylation. The half-life of CX3CR1 mRNA was unaltered by TGF-beta1 and two potential Smad binding elements (SBEs) were identified in the rat CX3CR1 promoter. TGF-beta1 may shift fractalkine-dependent signaling away from activation of ERK1/2 towards other pathways and/or may provide a mechanism for microglia to more strongly adhere to neurons.

Differential expression of nerve growth factor transcripts in glia and neurons and their regulation by transforming growth factor-beta1

Nerve growth factor (NGF) influences neuronal development, function, and response to injury. Using reverse transcriptase polymerase chain reaction, we find that mouse and rat cortex and spinal cord, and both neurons and glia in culture, express NGF mRNA. In the mouse, NGF is regulated by at least two promoters that govern synthesis of four different transcripts, A through D, that are all expressed in the mouse tissues and cells examined. In contrast, rat NGF expression varies with tissue and with cell type: transcript C is expressed strongly in brain but weakly in spinal cord, and transcript D is undetectable in rat central nervous system (CNS). In addition to species- and tissue-specific expression, NGF transcripts also exhibit cell type-specific expression: transcripts B, C and D are expressed in rat astrocytes but poorly or not at all in rat neurons, identifying glia as an important source of NGF in rat. NGF increases sharply after injury. TGF-beta1, which also increases immediately after injury, induces NGF mRNA and protein in rat and mouse glia but not in neurons. Furthermore, transcripts A, B and D, but not C, are upregulated by TGF-beta1 in mouse glia, whereas in rat glia, the major responsive transcript is C. Thus, there may be multiple TGF-beta1-responsive elements in the NGF promoters located upstream of exons 1 and 3 that may differ between mouse and rat. Moreover, NGF transcripts are differentially expressed in a species-, cell type-, and inducer-specific manner. These results have implications for the use of mice versus rats as models for the study of NGF regulation following CNS injury.

Treatment of spinal cord impact injury in the rat with transforming growth factor-beta

To investigate the contribution of cytokines, proinflammatory TNF-alpha and inhibitory TGF-beta, to spinal cord injury (SCI) in a rat model, two studies were performed using adult Sprague-Dawley rats which were injured at T9/T10. In the first study, rats were sacrificed at 1, 6, 24, 96 and 168 h after SCI for immunocytochemistry of coronal sections for the presence of mononuclear phagocytes, astrocytes, TNF-alpha and TGF-beta, among other markers. From intervening frozen sections, RNA was extracted for semiquantitative polymerase chain reaction (RT-PCR) analysis of TNF-alpha and TGF-beta. In the second experiment, rats were treated with intravenous TGF-beta 30 min after injury and sacrificed at 6 and 48 h after injury. Spinal cord sections were immunocytochemically stained and RNA extracted for semiquantitative PCR as mentioned above, as well as quantitation of lesion volume. There were increases in mononuclear phagocytes and astrocytes, as early as 1 h after SCI, with steady progression over 168 h after injury. TNF-alpha and TGF-beta was produced locally by mononuclear phagocytes and astrocytes. There was an 18-h delay in peak mRNA production of TGF-beta compared to TNF-alpha. The treatment of SCI rats with TGF-beta reduced lesion volume by 50% at 48 h and this was associated with decreased accumulation of mononuclear phagocytes in and around the injury site. This reduction of mononuclear phagocyte numbers around the site of trauma would reduce their contribution to secondary injury.

Expression of TGFbeta2 but not TGFbeta1 correlates with the deposition of scar tissue in the lesioned spinal cord

Transforming growth factor-betas (TGFbetas) are implicated in fibrotic pathologies. TGFbeta1 and -beta2 expression is increased around the glial/fibrotic scar in the injured brain. Moreover, local injection of TGFbeta antagonists into cerebral wounds reduces glial scarring. Here, we monitored expression of TGFbeta1 and -beta2 mRNA and protein in the spinal cord after transection of the dorsal funiculi. Levels of TGFbeta1 mRNA were most elevated over the acute inflammatory phase, while TGFbeta2 mRNA levels were raised locally about the wound, particularly in astrocytes and neovascular endothelial cells, over the subacute period of scarring. TGFbeta protein production also increased after injury. Both TGFbeta1 and TGFbeta2 were found in hematogenous inflammatory cells, while TGFbeta1 was also neuron-associated, and high levels of TGFbeta2 were localized to multiple cell types in the wound, including reactive astrocytes, during the period of glial/collagen scar formation. The cellular localization and temporal pattern of expression of TGFbeta after spinal cord injury suggest that TGFbeta1 modulates the inflammatory and neuronal responses, while TGFbeta2 regulates glial/collagen scarring.

Histologic characterization of acute spinal cord injury treated with intravenous methylprednisolone

OBJECTIVE

Many substances have been investigated for attenuation of spinal cord injury after acute trauma; however, pharmacologically only steroid administration has shown clinical benefits. This study attempts to characterize local spinal cord histologic response to human dose equivalent (HDE) intravenous methylprednisolone (MP) administration in a rodent model of acute spinal cord injury.

DESIGN

Forty-eight Sprague-Dawley rats were divided equally into control and experimental groups. Each group was subdivided into eight sets of three animals each, according to postinjury intervals. Paraplegia after lower thoracic laminectomy was achieved using a standardized weight drop technique.

INTERVENTION

Within one hour, experimental animals were treated with HDE MP followed by 23-hour continuous infusion of HDE MP. Spinal cords were harvested at variable intervals postinjury and prepared for histologic/immunohistochemistry examination.

MAIN OUTCOME MEASUREMENTS

Edema, necrosis, and glial fibrillary acidic protein (GFAP) positivity in the specimens from treated/control groups were graded by microscopy and immunohistochemistry staining and compared in a blinded manner by a qualified neuropathologist and senior authors.

RESULTS

Minimal differences were observed between control and MP-treated animals at zero and four hours. At eight hours, increased white matter and medullary edema was evident in control versus MP-treated rats. This trend continued through twelve, sixteen, twenty-four, forty-eight, and seventy-two hours. No difference was observed in the astrocytic response to injury by GFAP immunohistochemistry between the groups.

CONCLUSIONS

Histologically, MP reduces the development of severe edema and preserves spinal cord architecture adjacent to the site of injury. In contrast, MP does not alter the development of spinal cord necrosis or astrocytic response at the zone of injury.

Neuronal, astroglial and microglial cytokine expression after an excitotoxic lesion in the immature rat brain

Cytokines are important intercellular messengers involved in neuron-glia interactions and in the microglial-astroglial crosstalk, modulating the glial response to brain injury and the lesion outcome. In this study, excitotoxic lesions were induced by the injection of N-methyl-D-aspartate in postnatal day 9 rats, and the cytokines interleukin-1 beta (IL-1beta), interleukin-6 (IL-6), tumour necrosis factor alpha (TNFalpha) and transforming growth factor beta 1 (TGF-beta1) analysed by ELISA and/or immunohistochemistry. Moreover, cytokine-expressing glial cells were identified by means of double labelling with glial fibrillary acidic protein or tomato lectin binding. Our results show that both neurons and glia were capable of cytokine expression following different patterns in the excitotoxically damaged area vs. the nondegenerating surrounding grey matter (SGM). Excitotoxically damaged neurons showed upregulation of IL-6 and downregulation of TNFalpha and TGF-beta1 before they degenerated. Moreover, in the SGM, an increased expression of neuronal IL-6, TNFalpha and TGF-beta1 was observed. A subpopulation of microglial cells, located in the SGM and showing IL-1beta and TNFalpha expression, were the earliest glial cells producing cytokines, at 2-10 h postinjection. Later on, cytokine-positive glial cells were found within the excitotoxically damaged area and the adjacent white matter: some reactive astrocytes expressed TNFalpha and IL-6, and microglia/macrophages showed mild IL-1beta and TGF-beta1. Finally, the expression of all cytokines was observed in the glial scar. As discussed, this pattern of cytokine production suggests their implication in the evolution of excitotoxic neuronal damage and the associated glial response.

Thrombomodulin as a new marker of lesion-induced astrogliosis: involvement of thrombin through the G-protein-coupled protease-activated receptor-1

Because injury of the CNS causes an astrogliosis, characterized by cell swelling and proliferation, similar to the effects of the serine protease thrombin on astrocytes, we hypothesized that a high level of thrombin at the site of injury might initially induce an astrocyte reaction and later increase the expression of its specific inhibitor, thrombomodulin. Thrombomodulin could then stabilize the astroglial scar through its adhesive properties. Here, we studied the in vivo injury response of astrocytes in the anterior medullary velum of adult rat by immunostaining and in situ hybridization of thrombomodulin. Thrombomodulin was poorly expressed on astrocytes in normal tissue, increased up to 2 d after injury, and was still highly expressed at 6 d. To check that thrombin had a direct effect on thrombomodulin expression by astrocytes, we used brain cortical astrocyte primary cultures treated with either thrombin or the agonist peptide thrombin receptor-activating peptide-6, known to activate directly the thrombin G-protein-coupled receptor (GPCR) protease-activated receptor-1 (PAR-1). Modification of thrombomodulin expression was studied by Western blotting and quantitative reverse transcription-PCR. There was a dose-dependent increase in thrombomodulin after 48 hr of treatment, with gene expression peaking at 24 hr but falling to control levels by 48 hr. Together, these results show the following: (1) injury increases astrocyte thrombomodulin expression; (2) thrombin might mediate thrombomodulin expression via the specific receptor PAR-1; and (3) serine proteases, their inhibitors, and the new family of GPCR, PARs, are active on astrogliosis.

Localization of transforming growth factor-beta1 and receptor mRNA after experimental spinal cord injury

Transforming growth factor-beta1 (TGFbeta1) is a cytokine/growth factor found within the pathological central nervous system. TGFbeta1 has been shown to inhibit the release of cytotoxic molecules from microglia and macrophages, decrease astrocyte proliferation, and promote neuron survival. Because of the relevance of these actions to spinal cord injury, we examined TGFbeta1 and its receptors betaRI and betaRII mRNA levels and localization within the contused rat spinal cord using in situ hybridization. At the lesion site, TGFbeta1 mRNA peaked at 7 days postinjury and declined thereafter. Temporal and spatial localization of the betaRI and betaRII receptor mRNA closely mimicked that for TGFbeta1 in the epicenter. TGFbeta1, betaRI, and betaRII mRNAs also were elevated rostral and caudal to the injury, especially in regions known to contain activated microglia and degenerating axon profiles. Immunohistochemical staining of nearby sections confirmed that the highest levels of TGFbeta1 and receptor mRNA corresponded to regions filled with activated microglia and macrophages. The similar expression pattern of TGFbeta1, betaRI, and betaRII mRNA within the injured spinal cord suggests a local site of action. Since TGFbeta1 can act as an immunosuppressant as well as a stimulant for growth factors and neurite sprouting, it likely plays an important role, both temporally and spatially, in orchestrating postinjury events within the spinal cord.

Carbon filaments direct the growth of postlesional plastic axons after spinal cord injury

The effect of implantation of carbon filaments and fetal tissues on the axonal regeneration following contusion injury in a rat model was investigated by in situ immunofluorescence. Female Sprague-Dawley rats were subjected to severe contusion injury to the spinal cord at T9-T10. All animals were divided into 5 groups (N = 5/group): normal controls. surgical controls, with carbon filament implants, with fetal tissue implants and with implants consisting of fetal tissue cocultured with carbon filaments. After a 10-week survival period, the astroglial response was assessed by immunoreactive glial fibrillary acidic protein and the neuro-axonal profile by immunoreactive phosphorylated and nonphosphorylated neurofilament proteins. The contusion injury resulted in: (a) dramatically increased immunoreactivity of glial fibrillary acidic protein indicating injury-associated reactive astrogliosis, (b) increase in immunoreactive phosphorylated neurofilament protein indicating upregulated phosphorylation of neurofilament protein, (c) with no change in the highly differentiated nonphosphorylated neurofilament protein which normally occur in the nonregenerating mature neurons. Implantation of fetal tissues alone following contusion injury did not show any appreciable change with regard to the immunoreactivities for the glial and neuronal markers studied, compared to the injury controls. However, the implantation of carbon filaments alone or together with fetal tissues directed the growth of glial fibrillary acidic protein-positive astroglia and phosphoneurofilament-positive neurites along the carbon fibers, with no effect on nonphosphoneurofilament protein. In conclusion, implantation of carbon filaments appears to be critical for facilitating the attachment of astroglia forming a substrate and scaffolding that can further support and direct the growth of postlesional plastic axons across the lesion. In addition, carbon filament prostheses in combination with fetal tissue implants provides an improved combinational approach to promote regrowth of injured neurons following injury.

The effect of surgical trauma on rat tunica albuginea

PURPOSE

Increased TGF-beta1 protein expression in tunica albuginea has been found to be associated with Peyronie's disease. The present study is designed to investigate whether surgical trauma induces TGF-beta up-regulation and histological changes in rat penis.

MATERIALS AND METHODS

Thirty-two adult male Sprague-Dawley rats were divided into two groups. The first group (n=24) underwent incision and suture repair of the tunica albuginea of the penis. The second group (n=8) received sham surgery (incision of the penile skin and underlying fascia) as the control group. The trauma-induced group was divided into four subgroups in which the rats were euthanized at 6 hours (n=6), 1 day (n=6), 3 days (n=6), and 8 weeks (n=6). Two sham-operated (control) animals were also euthanized at each of the above time points. All tunical tissues from the trauma-induced and sham-operated rats were collected and examined histologically using Trichrome and Hart elastic fiber stain. Electron microscopy was used to study the ultrastructural changes of both trauma induced and control specimens. Western blotting technique was performed to study TGF-beta protein expression in both experimental and sham-operated groups.

RESULTS

Tissue edema and hemorrhage between collagen bundles are noted in the experimental groups after 6 hours, 1 day and 3 days. At 8 weeks the most prominent changes observed were inflammatory cellular infiltration and disorganization of the collagen bundles. In the control group the tunica albuginea retains normal wavy regular appearance in all rats. This histological analysis is similar to the reported description of histological features of the acute phase of Peyronie's disease. Electron microscopy showed packed collagen bundles in the trauma-induced group with normal appearing elastic fibers. No abnormal change was detected in the control group. Immunoblot results revealed remarkable TGF-beta1 protein expression in 1, 5, 3, and 0 rats of trauma induced subgroups after 6 hours, 1 day, 3 days, and 8 weeks respectively. No TGF-beta1 protein expression in any rats in the control group was detected. No significant TGF-beta2 or TGF-beta3 protein expression was observed either in the trauma induced group or in the control group.

CONCLUSION

Trauma can induce histological changes similar to the acute phase of Peyronie's disease but not the overt picture of the chronic phase of Peyronie's disease. It can also result in an early but transient up-regulation of TGF-beta1 protein expression in the rat penis. We conclude that surgical incisional trauma does not result in Peyronie's disease-like changes in the tunica.

Inflammation in traumatic brain injury: role of cytokines and chemokines

A traumatic injury to the adult mammalian central nervous system (CNS), such as a stab wound lesion, results in reactive astrogliosis and the migration of hematogenous cells into the damaged neural tissue. The roles of cytokines and growth factors released locally by the damaged endogenous cells are recognized in controlling the cellular changes that occur following CNS injury. However, the role of chemokines, a novel class of chemoattractant cytokines, is only recently being studied in regulating inflammatory cell invasion in the injured/diseased CNS (1). The mRNAs for several chemokines have been shown to be upregulated in experimental allergic encephalomyelitis (EAE), an inflammatory demyelinating disease of the CNS, but chemokine expression in traumatic brain injury has not been studied in detail. Astrocytes have been demonstrated to participate in numerous processes that occur following injury to the CNS. In particular, astrocytic expression of cytokines and growth factors in the injured CNS has been well reviewed (2). Recently a few studies have detected the presence of chemokines in astrocytes following traumatic brain injury (3,4). These studies have suggested that chemokines may represent a promising target for future therapy of inflammatory conditions. This review summarizes the events that occur in traumatic brain injury and discusses the roles of resident and non-resident cells in the expression of growth factors, cytokines and chemokines in the injured CNS.

In vivo Bcl-2 oncogene neuronal expression in the rat spinal cord

STUDY DESIGN

An acute mechanical rat spinal cord injury model was used to investigate in vivo Bcl-2 oncogene overexpression in neuronal tissue.

OBJECTIVES

To introduce the Bcl-2 oncogene in vivo by a recombinant adenovirus vector into rat spinal cord tissue, and to investigate any potential protective effect on neural tissue in the zone of injury in a rat spinal cord model.

SUMMARY OF BACKGROUND DATA

The Bcl-2 oncogene inhibits apoptotic and necrotic neural cell death in vitro by regulating an antioxidant pathway at sites of free radical generation. Thus, overexpression of the Bcl-2 oncogene may have a role in limiting the secondary injury cascade of spinal cord injury through its regulation of antioxidants.

METHODS

After confirmation of Bcl-2 gene expression in vitro and in vivo in the rat spinal cord, a weight-drop spinal cord injury model was performed on seven rats with prior Bcl-2 inoculation, and on seven rats with prior B-gal inoculation (controls).

RESULTS

In vivo Bcl-2 expression was documented by immunostaining. After spinal cord harvest, quantification of percentage preserved tissue at the spinal cord injury site suggested that Bcl-2 overexpression confers neuroprotection.

CONCLUSIONS

In vivo Bcl-2 oncogene overexpression was successfully induced in neuronal tissue. After Bcl-2 oncogene expression in the rat spinal cord, the zone of microscopic injury was diminished. Further investigation of the Bcl-2 oncogene for potentially enhancing neuronal survival after spinal cord injury appears indicated.

VEGF mRNA induction correlates with changes in the vascular architecture upon spinal cord damage in the rat

The multiple cellular and molecular processes induced by injury to the central nervous system (CNS) are still poorly understood. In the present study, we investigated the response of the vasculature and the expression of mRNA for the angiogenic vascular endothelial growth factor (VEGF) following X-irradiation of the spinal cord in the newborn and following traumatic spinal cord injury in the adult rat. Both lesion models induced changes in the density and the distribution pattern of blood vessels: while X-irradiation led to a permanent local increase in vascular density in the fibre tracts of the exposed segments, a transient local sprouting of vessels was induced upon traumatic spinal cord injury. In situ hybridization showed that an increase of VEGF mRNA anticipated and overlapped with the vascular responses in both lesion models. In addition to the temporal correlation of VEGF expression and vascular sprouting, there was a clear correlation in the spatial distribution patterns. Following X-irradiation, the expression of VEGF mRNA was restricted to the fibre tracts, precisely the areas where the changes in the vasculature were observed later on. Upon transection in the adult animal, VEGF was mainly detectable at the border of the lesion area, where the transient increase in vascular density could be observed. Interestingly, according to the type of lesion applied, astrocytes (X-irradiation) or inflammatory cells (presumably microglial cells or macrophages; traumatic lesion) are the cellular sources of VEGF mRNA. Our results strongly indicate that VEGF is crucially involved in mediating vascular changes following different types of injury in the CNS.

TGF-beta in the central nervous system: potential roles in ischemic injury and neurodegenerative diseases

The Transforming Growth Factor-betas (TGF-beta) are a group of multifunctional proteins whose cellular sites of production and action are widely distributed throughout the body, including the central nervous system (CNS). Within the CNS, various isoforms of TGF-beta are produced by both glial and neural cells. When evaluated in either cell culture or in vivo models, the various isoforms of TGF-beta have been shown to have potent effects on the proliferation, function, or survival of both neurons and all three glial cell types, astrocytes, microglia and oligodendrocytes. TGF-beta has also been shown to play a role in several forms of acute CNS pathology including ischemia, excitotoxicity and several forms of neurodegenerative diseases including multiple sclerosis, Parkinson's disease, AIDS dementia and Alzheimer's disease.

Altered immunoreactivity for glial fibrillary acidic protein in astrocytes within 1 h after cervical spinal cord injury

One hour after a C2 spinal cord hemisection, there are changes in astrocyte morphology and increased glial fibrillary acidic protein immunoreactivity (GFAP IR) near the site of the lesion. Astrocytes adjacent to the lesion display thick, richly branched processes within 1/2 segment rostral and caudal to the level of hemisection. Astrocytes are also enlarged and immunoreactive in gray matter regions of the spinal cord as far caudal as C4 and rostrally to C1. Sham-operated controls, undergoing a laminectomy and durotomy at C2, but not spinal cord hemisection, also exhibit a strong astroglial reaction within 1 h from C1 to C4. However, controls undergoing only a C2 laminectomy do not demonstrate alterations in GFAP IR compared to non-operated controls. The results of this investigation suggest that spinal cord astrocytes are extremely sensitive to both major as well as minor alterations of their microenvironment. Rapid changes in astroglial morphology, as detected by altered GFAP IR, may play a role in changes in neuronal function following spinal cord injury.

Local changes in vascular architecture following partial spinal cord lesion in the rat

Lesions of the CNS induce a complex cascade of tissue reactions. The purpose of this study was to determine the response of the vasculature to partial spinal cord transection. Adult rat spinal cords were lesioned and then examined during acute, subacute, and chronic periods for the presence of endothelial cells and blood vessels at the lesion site. The association of endothelial cells and astrocytes was examined immunohistochemically (RECA-1 and glial fibrillary associated protein, respectively). During the first 48 h following an incision lesion of the dorsal spinal cord, the vasculature was significantly decreased, concurrently with the tissue loss due to primary and secondary degeneration. Subsequently, at 4 days postlesion, vasculature repair processes were evidenced by a significant increase in the number of vessels present at the lesion center. Blood vessels even formed in areas densely packed with macrophages and tissue debris. After 1 week, the number of blood vessels declined in the lesion center and at the place of the forming caverns. These results show significant initial attempts at repair of the vasculature which do not, however, lead to the restoration of a compact tissue and cannot prevent the subsequent formation of caverns.

Chemokine expression in rat stab wound brain injury

A traumatic injury to the adult mammalian central nervous system (CNS) results in reactive astrogliosis and the migration of hematogenous cells into the damaged neural tissue. Chemokines, a novel class of chemoattractant cytokines, are now being recognized as mediators of the inflammatory changes that occur following injury. The expression of MCP-1 (macrophage chemotactic peptide-1), a member of the beta family of chemokines, has recently been demonstrated in trauma in the rat brain (Berman et al.: J Immunol 156:3017-3023, 1996). Using a stab wound model for mechanical injury, we studied the expression of two other beta chemokines: RANTES (Regulated on Activation, Normal T cell Expressed and Secreted) and MIP-1 beta (macrophage inflammatory protein-1 beta) in the rat brain. The stab wound injury was characterized by widespread gliosis and infiltration of hematogenous cells. Immunohistochemical staining revealed the presence of RANTES and MIP-1 beta in the injured brain. RANTES and MIP-1 beta were both diffusely expressed in the necrotic tissue and were detected as early as 1 day post-injury (dpi). Double-labeling studies showed that MIP-1 beta, but not RANTES, was expressed by reactive astrocytes near the lesion site. In addition, MIP-1 beta staining was also detected on macrophages at the site of injury. The initial expression of the chemokines closely correlated with the appearance of inflammatory cells in the injured CNS, suggesting that RANTES and MIP-1 beta may play a role in the inflammatory events of traumatic brain injury. This study also demonstrates for the first time MIP-1 beta expression in reactive astrocytes following trauma to the rat CNS.

Endogenous endothelin-1 initiates astrocytic growth after spinal cord injury

We developed a rat spinal cord injury model and investigated whether endogenous endothelin (ET)-1 plays a role in astrocytic growth after injury. Immunohistochemical study showed that the number of immature astrocytes (ACs) exhibiting strong reactivity to the monoclonal antibody, RC1, markedly increased 24 h after the injury. Injection of a potent nonselective ET receptor antagonist, SB209670, into the lesion sites significantly inhibited the appearance of RC1-positive cells 24 h after the injury. In conjunction with this result, the increase in immunostaining density of 5-bromo-2'-deoxyuridine in the spinal cord 24 h after the injury was inhibited by the injection of SB209670. The tissue content of ET-1-LI was significantly increased 12 and 24 h after the injury. These results suggest that endogenous ET-1 is involved in astrocytic growth after spinal cord injury.

Effects of exogenous transforming growth factor-beta 1 on spinal cord injury in rats

This study was undertaken to examine the effect of transforming growth factor-beta 1 (TGF-beta 1) administered into the subarachnoid space after spinal cord injury (SCI) on the increased production of inducible-nitric oxide synthase (i-NOS) in the injured spinal cord in rats. The expression of i-NOS mRNA after SCI was remarkably down-regulated by TGF-beta 1 in vivo. Rats treated with TGF-beta 1 showed a better outcome regarding hindlimb motor dysfunction in the first 5 days after injury compared to the saline-treated rats. However, the final outcome was not better and fibrous scar formation in the injured spinal cord was more evident, which was demonstrated as increased immunoreactivity of fibronectin in the later stage after SCI. These results provide evidence of both positive and negative contributions of TGF-beta 1 to the pathology associated with SCI.

Roles of nitric oxide in compression injury of rat spinal cord

Nitric oxide (NO) was measured directly after spinal cord injury (SCI) in rats by an ESR spin-trapping technique using Fe2+ and diethyldithiocarbamate (DETC). The levels of NO and lipid peroxides expressed as thiobarbituric acid reactive substances (TBARS) were increased by SCI in the injured region and the adjacent central region. Pretreatment with 30 mg/kg of NG-nitro-L-arginine methylester (L-NAME), an inhibitor of NO synthase, accelerated increases of the TBARS level and myeloperoxidase (MPO) activity in the injured tissue and caused deterioration of hind limb motor function after SCI, suggesting that NO formation by constitutive NO synthase (c-NOS) has a protective effect against cellular damage resulting from ischemia-reperfusion after SCI. Though c-NOS mRNA expression was not altered after SCI, inducible NO synthase (i-NOS) mRNA expression increased to a maximum of 24 h after SCI with progress of motor dysfunction. Intravenous injection of L-NAME (0.1 mg/kg) 6, 24, 48, and 72 h after SCI reduced the motor disturbance. These results indicate that NO induced by i-NOS may be neurotoxic in the subacute phase after SCI.