Aquaporins in spinal cord injury: the janus face of aquaporin 4

Photobiomodulation reduces spinal cord edema by decreasing the expression of AQP4 in the astrocytes of male spinal cord injury rats via the JAK2/STAT3 signaling pathway

BACKGROUND

Spinal cord swelling commonly occurs following SCI. Previous studies suggest that PBM may reduce inflammation and scar formation after SCI. However, whether PBM can alleviate post-spinal cord injury edema and its underlying mechanisms have not yet been reported. This study aims to investigate the effects of PBM on spinal cord swelling in rats following SCI and explore the underlying mechanisms.

METHODS

A rat model of SCI was established, and the rats received continuous PBM therapy for two weeks. Tissue hydration, motor function, AQP4 expression, and pathological changes in the spinal cord were evaluated at different time points. In vitro, astrocytes were subjected to PBM and treated with either cucurbitacin I or TGN020 following OGD.

RESULTS

The results indicate that PBM reduces tissue swelling in rats with SCI, improves motor function recovery, and inhibits the upregulation of AQP4 and GFAP associated with SCI. In vitro, PBM reduces abnormal activation of the JAK2/STAT3 signaling pathway in astrocytes, leading to decreased AQP4 synthesis and astrocyte activation.

CONCLUSIONS

These findings suggest that PBM reduces spinal cord swelling in rats after injury. This effect is associated with the inhibition of JAK2/STAT3 signaling pathway activation in astrocytes and the reduction in AQP4 expression.

Water channels in the brain and spinal cord-overview of the role of aquaporins in traumatic brain injury and traumatic spinal cord injury

Knowledge about the mechanisms underlying the fluid flow in the brain and spinal cord is essential for discovering the mechanisms implicated in the pathophysiology of central nervous system diseases. During recent years, research has highlighted the complexity of the fluid flow movement in the brain through a glymphatic system and a lymphatic network. Less is known about these pathways in the spinal cord. An important aspect of fluid flow movement through the glymphatic pathway is the role of water channels, especially aquaporin 1 and 4. This review provides an overview of the role of these aquaporins in brain and spinal cord, and give a short introduction to the fluid flow in brain and spinal cord during in the healthy brain and spinal cord as well as during traumatic brain and spinal cord injury. Finally, this review gives an overview of the current knowledge about the role of aquaporins in traumatic brain and spinal cord injury, highlighting some of the complexities and knowledge gaps in the field.

Aquaporin 4 beyond a water channel; participation in motor, sensory, cognitive and psychological performances, a comprehensive review

Aquaporin 4 (AQP4) is a protein highly expressed in the central nervous system (CNS) and peripheral nervous system (PNS) as well as various other organs, whose different sites of action indicate its importance in various functions. AQP4 has a variety of essential roles beyond water homeostasis. In this article, we have for the first time summarized different roles of AQP4 in motor and sensory functions, besides cognitive and psychological performances, and most importantly, possible physiological mechanisms by which AQP4 can exert its effects. Furthermore, we demonstrated that AQP4 participates in pathology of different neurological disorders, various effects depending on the disease type. Since neurological diseases involve a spectrum of dysfunctions and due to the difficulty of obtaining a treatment that can simultaneously affect these deficits, it is therefore suggested that future studies consider the role of this protein in different functional impairments related to neurological disorders simultaneously or separately by targeting AQP4 expression and/or polarity modulation.

The Role of Aquaporins in Spinal Cord Injury

Edema formation following traumatic spinal cord injury (SCI) exacerbates secondary injury, and the severity of edema correlates with worse neurological outcome in human patients. To date, there are no effective treatments to directly resolve edema within the spinal cord. The aquaporin-4 (AQP4) water channel is found on plasma membranes of astrocytic endfeet in direct contact with blood vessels, the glia limitans in contact with the cerebrospinal fluid, and ependyma around the central canal. Local expression at these tissue-fluid interfaces allows AQP4 channels to play an important role in the bidirectional regulation of water homeostasis under normal conditions and following trauma. In this review, we consider the available evidence regarding the potential role of AQP4 in edema after SCI. Although more work remains to be carried out, the overall evidence indicates a critical role for AQP4 channels in edema formation and resolution following SCI and the therapeutic potential of AQP4 modulation in edema resolution and functional recovery. Further work to elucidate the expression and subcellular localization of AQP4 during specific phases after SCI will inform the therapeutic modulation of AQP4 for the optimization of histological and neurological outcomes.

Aquaporin-4 expression and modulation in a rat model of post-traumatic syringomyelia

Aquaporin-4 (AQP4) has been implicated in post-traumatic syringomyelia (PTS), a disease characterised by the formation of fluid-filled cysts in the spinal cord. This study investigated the expression of AQP4 around a mature cyst (syrinx) and the effect of pharmacomodulation of AQP4 on syrinx size. PTS was induced in male Sprague-Dawley rats by computerized spinal cord impact and subarachnoid kaolin injection. Immunofluorescence of AQP4 was carried out on mature syrinx tissue 12 weeks post-surgery. Increased AQP4 expression corresponded to larger, multiloculated cysts (R2 = 0.94), yet no localized changes to AQP4 expression in perivascular regions or the glia limitans were present. In a separate cohort of animals, at 6 weeks post-surgery, an AQP4 agonist (AqF026), antagonist (AqB050), or vehicle was administered daily over 4 days, with MRIs performed before and after the completion of treatment. Histological analysis was performed at 12 weeks post-surgery. Syrinx volume and length were not altered with AQP4 modulation. The correlation between increased AQP4 expression with syrinx area suggests that AQP4 or the glia expressing AQP4 are recruited to regulate water movement. Given this, further investigation should examine AQP4 modulation with dose regimens at earlier time-points after PTS induction, as these may alter the course of syrinx development.

Differences in the localization of AQP1 and expression patterns of AQP isoforms in rat and mouse sciatic nerve and changes in rat AQPs expression after nerve crush injury

In the peripheral nervous system aquaporins (AQPs) have been reported in both peripheral neurons and glial cells. Previously we described the precise localization of AQP1 in the rat sciatic nerve, which is present in both Remak and myelin Schwann cells, and is enriched in the Schmidt-Lanterman incisures. In this work, we found that AQP1 in mouse is only present in Remak cells, showing a different localization between these species. However, after nerve crush injury the level of AQP1 mRNA expression remains constant at all times studied in rat and mouse. We then performed RT-PCR of nine AQP (AQP1-9) isoforms from rat and mouse sciatic nerve, we found that in rat only five AQPs are present (AQP1, AQP4, AQP5, AQP7 and AQP9), whereas in mouse all AQPs except AQP8 are expressed. Then, we studied the expression by RT-PCR of AQPs in rat after nerve crush injury, showing that AQP1, AQP4 and AQP7 expression remain constant at all times studied, while AQP2, AQP5 and AQP9 are upregulated after injury. Therefore, these two closely related rodents show different AQP1 localization and have different AQPs expression patterns in the sciatic nerve, possibly due to a difference in the regulation of these AQPs. The expression of AQP1 in Remak cells supports the involvement of AQP1 in pain perception. Also, in rat the upregulation of AQP2, AQP5 and AQP7 after nerve injury suggests a possible role for these AQPs in promoting regeneration following injury.

Elevated intraspinal pressure in traumatic spinal cord injury is a promising therapeutic target

The currently recommended management for acute traumatic spinal cord injury aims to reduce the incidence of secondary injury and promote functional recovery. Elevated intraspinal pressure (ISP) likely plays an important role in the processes involved in secondary spinal cord injury, and should not be overlooked. However, the factors and detailed time course contributing to elevated ISP and its impact on pathophysiology after traumatic spinal cord injury have not been reviewed in the literature. Here, we review the etiology and progression of elevated ISP, as well as potential therapeutic measures that target elevated ISP. Elevated ISP is a time-dependent process that is mainly caused by hemorrhage, edema, and blood-spinal cord barrier destruction and peaks at 3 days after traumatic spinal cord injury. Duraplasty and hypertonic saline may be promising treatments for reducing ISP within this time window. Other potential treatments such as decompression, spinal cord incision, hemostasis, and methylprednisolone treatment require further validation.

Reactive Astrocytes in Central Nervous System Injury: Subgroup and Potential Therapy

Traumatic central nervous system (CNS) injury, which includes both traumatic brain injury (TBI) and spinal cord injury (SCI), is associated with irreversible loss of neurological function and high medical care costs. Currently, no effective treatment exists to improve the prognosis of patients. Astrocytes comprise the largest population of glial cells in the CNS and, with the advancements in the field of neurology, are increasingly recognized as having key functions in both the brain and the spinal cord. When stimulated by disease or injury, astrocytes become activated and undergo a series of changes, including alterations in gene expression, hypertrophy, the loss of inherent functions, and the acquisition of new ones. Studies have shown that astrocytes are highly heterogeneous with respect to their gene expression profiles, and this heterogeneity accounts for their observed context-dependent phenotypic diversity. In the inured CNS, activated astrocytes play a dual role both as regulators of neuroinflammation and in scar formation. Identifying the subpopulations of reactive astrocytes that exert beneficial or harmful effects will aid in deciphering the pathological mechanisms underlying CNS injuries and ultimately provide a theoretical basis for the development of effective strategies for the treatment of associated conditions. Following CNS injury, as the disease progresses, astrocyte phenotypes undergo continuous changes. Although current research methods do not allow a comprehensive and accurate classification of astrocyte subpopulations in complex pathological contexts, they can nonetheless aid in understanding the roles of astrocytes in disease. In this review, after a brief introduction to the pathology of CNS injury, we summarize current knowledge regarding astrocyte activation following CNS injury, including: (a) the regulatory factors involved in this process; (b) the functions of different astrocyte subgroups based on the existing classification of astrocytes; and (c) attempts at astrocyte-targeted therapy.

The role of aquaporin 4 (AQP4) in spinal cord injury

Aquaporin-4 (AQP-4) is an aquaporin composed of six helical transmembrane domains and two highly conserved ASN-pro-ALA (NPA) motifs. It is strongly expressed in rodent and human spinal cord tissues and plays a key role in the pathological process after SCI. After SCI, edema, glial scarring, and inflammation can accelerate the progression of injury and lead to deterioration of function. Many studies have reported that AQP-4 plays an important role in SCI. In particular, it plays an important role in secondary pathological processes (spinal cord edema, glial scar formation, and inflammatory response) after SCI. Loss of AQP-4 has been associated with reduced spinal edema and improved prognosis after SCI in mice. In addition, downregulation of AQP-4 reduces glial scar formation and the inflammatory response after SCI. There is a consensus from numerous studies that AQP-4 may be a potential target for SCI therapy, which guides the ongoing investigation for molecular therapy of SCI. Here, we review the structure of AQP-4, its expression in normal and damaged spinal cord, and its role in SCI, as well as discuss the theoretical basis for the treatment of SCI.

The Role of Astrogliosis in Formation of the Syrinx in Spinal Cord Injury

A massive localized trauma to the spinal cord results in complex pathologic events driven by necrosis and vascular damage which in turn leads to hemorrhage and edema. Severe, destructive and very protracted inflammatory response is characterized by infiltration by phagocytic macrophages of a site of injury which is converted into a cavity of injury (COI) surrounded by astroglial reaction mounted by the spinal cord. The tissue response to the spinal cord injury (SCI) has been poorly understood but the final outcome appears to be a mature syrinx filled with the cerebrospinal fluid with related neural tissue loss and permanent neurologic deficits. This paper reviews known pathologic mechanisms involved in the formation of the COI after SCI and discusses the integrative role of reactive astrogliosis in mechanisms involved in the removal of edema after the injury. A large proportion of edema fluid originating from the trauma and then from vasogenic edema related to persistent severe inflammation, may be moved into the COI in an active process involving astrogliosis and specifically over-expressed aquaporins.

Repairing blood-CNS barriers: Future therapeutic approaches for neuropsychiatric disorders

Central nervous system (CNS) drug development faces significant difficulties that translate into high rates of failure and lack of innovation. The pathophysiology of neurological and psychiatric disorders often results in the breakdown of blood-CNS barriers, disturbing the CNS microenvironment and worsening disease progression. Therefore, restoring the integrity of blood-CNS barriers may have a beneficial influence in several CNS disorders and improve treatment outcomes. In this review, pathways that may be modulated to protect blood-CNS barriers from neuroinflammatory and oxidative insults are featured. First, the participation of the brain endothelium and glial cells in disruption processes is discussed. Then, the relevance of regulatory systems is analysed, specifically the hypothalamic-pituitary axis, the renin-angiotensin system, sleep and circadian rhythms, and glutamate neurotransmission. Lastly, compounds of endogenous and exogenous origin that are known to mediate the repair of blood-CNS barriers are presented. We believe that enhancing the protection of blood-CNS barriers is a promising therapeutic strategy to pursue in the future.

Aquaporin 4 is involved in chronic pain but not acute pain

Accumulating evidence has revealed that spinal glia plays an important role in the processing of pain, particularly chronic pain. Aquaporin 4 (AQP4), the predominant water channel exists in astrocytes, has been proved to modulate astrocytic function and thus participate in many diseases of the central nervous system. However, there is still controversy over whether AQP4 is involved in pain modulation. In the present study, we investigated the effects of AQP4 on pain by examining chronic inflammatory pain, neuropathic pain, and thermal, chemical, and mechanical stimuli-induced acute pain in AQP4 knockout mice. In Complete Freund's adjuvant-induced chronic inflammatory pain and spared nerve injury-induced neuropathic pain models, AQP4^-/- mice attenuated pain-related behavioral responses compared with AQP4^+/+ mice, demonstrating that AQP4 deficiency relieved chronic inflammatory pain and neuropathic pain. In the tail-flick and hot-plate tests, two acute pain models of thermal stimuli, no differences in pain-related behaviors were detected between AQP4^+/+ and AQP4^-/- mice. In the formalin and capsaicin tests, two models of chemical stimuli-induced acute pain, no differences in the durations of licking the injected hindpaw were found between AQP4^+/+ and AQP4^-/- mice. In the von Frey hair test, a model of mechanical stimuli-induced acute pain, no significant differences in withdrawal thresholds were found between these two genotypes mice as well. These results indicated that AQP4 deficiency did not affect acute pain induced by thermal, chemical, and mechanical stimuli. Taken together, our findings suggested that AQP4 contributes to chronic pain, but not acute pain.

Protein Degradome of Spinal Cord Injury: Biomarkers and Potential Therapeutic Targets

Degradomics is a proteomics sub-discipline whose goal is to identify and characterize protease-substrate repertoires. With the aim of deciphering and characterizing key signature breakdown products, degradomics emerged to define encryptic biomarker neoproteins specific to certain disease processes. Remarkable improvements in structural and analytical experimental methodologies as evident in research investigating cellular behavior in neuroscience and cancer have allowed the identification of specific degradomes, increasing our knowledge about proteases and their regulators and substrates along with their implications in health and disease. A physiologic balance between protein synthesis and degradation is sought with the activation of proteolytic enzymes such as calpains, caspases, cathepsins, and matrix metalloproteinases. Proteolysis is essential for development, growth, and regeneration; however, inappropriate and uncontrolled activation of the proteolytic system renders the diseased tissue susceptible to further neurotoxic processes. In this article, we aim to review the protease-substrate repertoires as well as emerging therapeutic interventions in spinal cord injury at the degradomic level. Several protease substrates and their breakdown products, essential for the neuronal structural integrity and functional capacity, have been characterized in neurotrauma including cytoskeletal proteins, neuronal extracellular matrix glycoproteins, cell junction proteins, and ion channels. Therefore, targeting exaggerated protease activity provides a potentially effective therapeutic approach in the management of protease-mediated neurotoxicity in reducing the extent of damage secondary to spinal cord injury.

Altered Waste Disposal System in Aging and Alzheimer's Disease: Focus on Astrocytic Aquaporin-4

Among the diverse cell types included in the general population named glia, astrocytes emerge as being the focus of a growing body of research aimed at characterizing their heterogeneous and complex functions. Alterations of both their morphology and activities have been linked to a variety of neurological diseases. One crucial physiological need satisfied by astrocytes is the cleansing of the cerebral tissue from waste molecules. Several data demonstrate that aquaporin-4 (AQP-4), a protein expressed by astrocytes, is crucially important for facilitating the removal of waste products from the brain. Aquaporins are water channels found in all district of the human organism and the most abundant isoform in the brain is AQP-4. This protein is involved in a myriad of astrocytic activities, including calcium signal transduction, potassium buffering, synaptic plasticity, astrocyte migration, glial scar formation and neuroinflammation. The highest density of AQP-4 is found at the astrocytic domains closest to blood vessels, the endfeet that envelop brain vessels, with low to zero expression in other astrocytic membrane regions. Increased AQP-4 expression and loss of polarization have recently been documented in altered physiological conditions. Here we review the latest findings related to aging and Alzheimer’s disease (AD) on this topic, as well as the available knowledge on pharmacological tools to target AQP-4.

Protective role of astragalus injection in spinal cord ischemia-reperfusion injury in rats

Objectives:

To investigate the neuroprotective effect of Astragalus injection in a spinal cord ischemia-reperfusion (I/R) injury model.

Methods:

A total of 27 Sprague Dawley rats were randomly divided into 3 groups: control group (n=3), I/R group (n=12), and Astragalus injection group (Ast group, n=12). Spinal cord ischemia was induced by occlusion of the abdominal aorta above the right renal artery for 32 min. Animals in the Ast group were administered Astragalus injection (6.42 mL/kg) at 30 min before the induction of ischemia. After reperfusion for 8, 12, 24, or 48 hours, the serum neuron-specific enolase (NSE) concentration was measured by enzyme-linked immunosorbent assay (ELISA) and the aquaporin-4 (AQP4) protein level was detected by western blotting.

Results:

The pathological changes, as assessed by hematoxylin and eosin (HE) staining, were milder in the spinal cords of the Ast group compared to the I/R group. Enzyme-linked immunosorbent assay demonstrated that the NSE concentration of the Ast group was significantly lower than that of the I/R group (p<0.05). However, the NSE concentrations of the I/R and Ast groups were significantly higher than that of the control group (p=0.05). Additionally, the expression of AQP4 in the Ast group was lower than that of the I/R group at each time point.

Conclusion:

These findings indicate that Astragalus injection has a neuroprotective effect in spinal cord I/R injury by decreasing the AQP4 expression.

Aquaporin 4 regulation by ginsenoside Rb1 intervenes with oxygen-glucose deprivation/reoxygenation-induced astrocyte injury

BACKGROUND

Spinal cord ischemia-reperfusion injury (SCII) is a common complication of spinal surgery as well as thoracic and abdominal surgery. Acute cytotoxic edema is the key pathogenic alteration. Therefore, avoiding or decreasing cellular edema has become the major target for SCII treatment.

METHODS

The antiedema activity of ginsenoside Rb1 on aquaporin (AQP) 4, nerve growth factor (NGF), and brain-derived neurotrophic factor expression was detected by western blot and real-time polymerase chain reaction under conditions of oxygen-glucose deprivation/reoxygenation (OGD/R) in a rat astrocyte model in vitro. In addition, the cellular membrane permeability of AQP4 overexpressing cells or AQP4 small interfering RNA-transfected cells was detected.

RESULTS

Ginsenoside Rb1 significantly prevented OGD/R-induced AQP4 downregulation in rat astrocytes. In addition, ginsenoside Rb1 treatment or AQP4 overexpression in rat astrocytes significantly attenuated the OGD/R-induced increase of cellular membrane permeability. Moreover, ginsenoside Rb1 obviously prevented the OGD/R-induced decrease of NGF and BDNT expression in rat astrocytes.

CONCLUSION

These findings demonstrate that ginsenoside Rb1 can relieve spinal cord edema and improve neurological function by increasing AQP4 expression.

The potential roles of aquaporin 4 in amyotrophic lateral sclerosis

Aquaporin 4 (AQP4) is a primary water channel found on astrocytes in the central nervous system (CNS). Besides its function in water and ion homeostasis, AQP4 has also been documented to be involved in a myriad of acute and chronic cerebral pathologies, including autoimmune neurodegenerative diseases. AQP4 has been postulated to be associated with the incidence of a progressive neurodegenerative disorder known as amyotrophic lateral sclerosis (ALS), a disease that targets the motor neurons, causing muscle weakness and eventually paralysis. Raised AQP4 levels were noted in association with vessels surrounded with swollen astrocytic processes as well as in the brainstem, cortex, and gray matter in patients with terminal ALS. AQP4 depolarization may lead to motor neuron degeneration in ALS via GLT-1. Besides, alterations in AQP4 expression in ALS may result in the loss of blood-brain barrier (BBB) integrity. Changes in AQP4 function may also disrupt K⁺ homeostasis and cause connexin dysregulation, the latter of which is associated to ALS disease progression. Furthermore, AQP4 suppression augments recovery in motor function in ALS, a phenomenon thought to be associated to NGF. No therapeutic drug targeting AQP4 has been developed to date. Nevertheless, the plethora of suggestive experimental results underscores the significance of further exploration into this area.

Aquaporin-4 expression dynamically varies after acute spinal cord injury-induced disruption of blood spinal cord barrier in rats

The blood-spinal cord barrier (BSCB) changes badly after spinal cord injury (SCI), and it is an important pathophysiological basis of SCI secondary damage. Aquaporin-4 (AQP4), one of the transmembrane proteins in spinal cord, has been shown to be closely related to the development of the BSCB and edema. We established a SCI model in rats using a free-falling weight drop device to subsequently investigate AQP4 expression. AQP4 messenger RNA (mRNA) and protein expression and immunoreactivity were detected in spinal cord tissue using reverse transcription-real-time quantitative polymerase chain reaction (RT-qPCR), immunohistochemistry and Western blot analysis. We found the water content and edema of the spinal cord were significantly higher than the control group after SCI, which was related to the growth of BSCB permeability; both reached their peak on the third day after injury. One, 3, 5, 7 days after injury, the immune response and protein expression in the model group increased from 1 to 3 days, with a plateau period from 3 to 5 days and a decline from 5 to 7 days, showing a significant difference compared with the sham group at each time point (P < 0.05), while the RT-qPCR results showed a decline of mRNA just after 3 days. In conclusion, after SCI, the water content of the spinal cord and the BSCB permeability increases, together with the excessive expression of AQP4, which reached a peak on the third day. AQP4 expression is closely relative to the permeability of BSCB and the water content of the spinal cord.

Methods for Assessing Serpins as Neuroprotective Therapeutics

As the systematic work on the pathogenesis of the white matter injury in the spinal cord models progresses, it becomes obvious that a severe and extraordinarily protracted, destructive inflammation follows the initial injury. Appropriate anti-inflammatory therapies of sufficient duration should not only inhibit but also lead to the elimination of this destructive inflammation, thus resulting in neuroprotection of the spinal cord tissue and a greater preservation of the neurologic function. While dexamethasone, a powerful, anti-inflammatory steroid analog administered continuously by subdural infusion for 7 days inhibited severe macrophage infiltration in the cavity of injury, the dose used was remarkably toxic. A 2-week-long infusion of lower doses of dexamethasone resulted in dose-dependent inhibition of macrophage infiltration and was better tolerated by the rats, but it became evident that a much longer duration of subdural administration of a powerful anti-inflammatory drug is required to eliminate myelin-rich, necrotic debris from the cavity and synthetic steroids such as dexamethasone, and methylprednisolone may be too toxic for this application. Therefore, nontoxic but powerful anti-inflammatory compounds are required for neuroprotective treatment of the spinal cord injury (SCI) and also brain trauma and stroke where the massive injury to the white matter occurs. Serpins have been associated with neurological damage. The mammalian serpin neuroserpin (SERPINI1) is reported to act in a protective manner after cerebrospinal infarction. The serine protease, tissue-type plasminogen activator (tPA), and the serpin plasminogen activator inhibitor (PAI-1, SERPINE1) are both upregulated at sites of central nervous system damage. In preliminary studies, subdural infusion of the myxomaviral serpin, Serp-1, resulted in the powerful inhibition of the macrophage infiltration of the cavity of injury, comparable to the inhibition by high dose of dexamethasone that has proven to be unduly toxic. Nontoxic, yet powerful neuroprotective, anti-inflammatory effects of Serp-1 may indicate this serpin protein as a potential attractive compound to treat SCI and similar syndromes involving massive injury to the white matter such as brain trauma and stroke. Novel methods of drug delivery, chronic subdural infusion, and novel analytic methods to measure the effectiveness of the neuroprotective serpin treatments are discussed in this chapter.

Neuropathic Pain After Spinal Cord Injury: Challenges and Research Perspectives

Neuropathic pain is a debilitating consequence of spinal cord injury (SCI) that remains difficult to treat because underlying mechanisms are not yet fully understood. In part, this is due to limitations of evaluating neuropathic pain in animal models in general, and SCI rodents in particular. Though pain in patients is primarily spontaneous, with relatively few patients experiencing evoked pains, animal models of SCI pain have primarily relied upon evoked withdrawals. Greater use of operant tasks for evaluation of the affective dimension of pain in rodents is needed, but these tests have their own limitations such that additional studies of the relationship between evoked withdrawals and operant outcomes are recommended. In preclinical SCI models, enhanced reflex withdrawal or pain responses can arise from pathological changes that occur at any point along the sensory neuraxis. Use of quantitative sensory testing for identification of optimal treatment approach may yield improved identification of treatment options and clinical trial design. Additionally, a better understanding of the differences between mechanisms contributing to at- versus below-level neuropathic pain and neuropathic pain versus spasticity may shed insights into novel treatment options. Finally, the role of patient characteristics such as age and sex in pathogenesis of neuropathic SCI pain remains to be addressed.

Stem Cells from Human Exfoliated Deciduous Teeth Modulate Early Astrocyte Response after Spinal Cord Contusion

The transplantation of stem cells from human exfoliated deciduous teeth (SHED) has been studied as a possible treatment strategy for spinal cord injuries (SCIs) due to its potential for promoting tissue protection and functional recovery. The aim of the present study was to investigate the effects of the early transplantation of SHED on glial scar formation and astrocytic reaction after an experimental model of SCI. Wistar rats were spinalized using the NYU Impactor. Animals were randomly distributed into three groups: control (naive) (animal with no manipulation); SCI (receiving laminectomy followed by SCI and treated with vehicle), and SHED (SCI rat treated with intraspinal SHED transplantation, 1 h after SCI). In vitro investigation demonstrated that SHED were able to express mesenchymal stem cells, vimentin and S100B markers, related with neural progenitor and glial cells, respectively. The acute SHED transplantation promoted functional recovery, measured as from the first week after spinal cord contusion by Basso, Beattie, and Bresnahan scale. Twenty-four and 48 h after lesion, flow cytometry revealed a spinal cord vimentin⁺ cells increment in the SHED group. The increase of vimentin⁺ cells was confirmed by immunofluorescence. Moreover, the bioavailability of astrocytic proteins such as S100B and Kir4.1 shown to be increased in the spinal cord of SHED group, whereas there was a glial scar reduction, as indicated by ELISA and Western blot techniques. The presented results support that SHED act as a neuroprotector agent after transplantation, probably through paracrine signaling to reduce glial scar formation, inducing tissue plasticity and functional recovery.

Effect of combined chondroitinase ABC and hyperbaric oxygen therapy in a rat model of spinal cord injury

The present study aimed to investigate the effect of combined hyperbaric oxygen (HBO) and chondroitinase ABC (ChABC) enzyme therapy in a rat model of spinal cord injury (SCI) and to explore the underlying mechanisms. A total of 48 healthy male Wistar rats were randomly divided into six groups: Sham, SCI, vehicle, HBO, ChABC enzyme and HBO + ChABC. Excluding the sham group, SCI was established in rats by a clip compression injury and rats subsequently received HBO treatment for 2 weeks with or without an intraspinal injection of 0.1 U/µl ChABC. Neuromotor functions were examined using the Basso‑Beattie‑Bresnahan locomotor rating scale and the inclined plane assessment at baseline and for 4 weeks following SCI establishment. Superoxide dismutase (SOD) and malondialdehyde (MDA) levels were also measured, in addition to the expression of glycogen synthase kinase‑3β (GSK3β) and aquaporin 4 (AQP4). Results revealed that combined HBO and ChABC treatment significantly improved neuromotor function compared with the HBO or ChABC treatments alone. HBO and/or ChABC treatment significantly increased SOD and decreased MDA levels, as well as GSK3β expression, compared with the sham and SCI rats. The combined HBO and ChABC treatment significantly inhibited SCI‑induced AQP4 expression, but ChABC alone did not. Functional recovery in the HBO + ChABC group was significantly increased compared with the HBO or ChABC groups. These results indicate that combined HBO and ChABC treatment is more effective in treating SCI than either therapy alone.

Correlation of TGN-020 with the analgesic effects via ERK pathway activation after chronic constriction injury

Extracellular regulated protein kinase (ERK) pathway activation in astrocytes and neurons has been reported to be critical for neuropathic pain development after chronic constriction injury. TGN-020 was found to be the most potent aquaporin 4 inhibitor among the agents studied. The present study aimed to assess whether the inhibition of aquaporin 4 had an analgesic effect on neuropathic pain and whether the inhibition of astrocytic activation and ERK pathway was involved in the analgesic effect of TGN-020. We thus found that TGN-020 upregulated the threshold of thermal and mechanical allodynia, downregulated the expression of interleukin-1β, interleukin-6, and tumor necrosis factor-α, attenuated the astrocytic activation and suppressed the activation of mitogen-activated protein kinase pathways in the spinal dorsal horn and dorsal root ganglion. Additionally, TGN-020 suppressed ERK phosphorylation in astrocytes and neurons after injury. The findings suggested that the analgesic effects of TGN-020 in neuropathic pain were mediated mainly by the downregulation of chronic constriction injury-induced astrocytic activation and inflammation, which is via the inhibition of ERK pathway in the spinal dorsal horn and dorsal root ganglion.

Effects of erythropoietin and methylprednisolone on AQP4 expression in astrocytes

Methylprednisolone sodium succinate (MPSS) has been suggested as a treatment for spinal cord injury (SCI), but its use has been limited due to its adverse effects. Erythropoietin (EPO) has been suggested as a promising candidate for limiting SCI in mammals. The aim of the present study was to investigate the effects of EPO in combination with MPSS on astrocytes following ischemic injury in vitro. Astrocytes were isolated from the cerebral cortex of postnatal day 3 Sprague-Dawley rats and cultured in vitro. Astrocyte ischemic injury was induced by oxygen and glucose deprivation for 4 h, and reperfusion was simulated by subsequent culture under normoxic conditions. The effects of EPO and MPSS on the expression of aquaporin-4 (AQP4) were investigated. Ischemic astrocytes were treated with EPO (10 U/ml), MPSS (10 µg/ml), or EPO (10 U/ml) in combination with MPSS (10 µg/ml) during reperfusion. The cell viability of astrocytes was assessed using an MTT assay. The mRNA and protein expression levels of AQP4 were determined using reverse transcription-quantitative polymerase chain reaction and western blot analysis, respectively. The role of the protein kinase C (PKC) signaling pathway in the molecular mechanisms underlying the effects of EPO and MPSS was also investigated. The present results demonstrated that following treatment with EPO and MPSS, the mRNA expression levels of AQP4 were upregulated and cell viability was enhanced. EPO and MPSS effectively inhibited the oxygen and glucose deprivation-mediated downregulation of AQP4 following reperfusion. In addition, the combined treatment with EPO and MPSS exhibited higher AQP4 expression levels and cell viability compared with each treatment alone. Finally, the effects of EPO and MPSS on AQP4 expression were partially reversed by pretreatment with the PKC inhibitor Ro 31–8220. The present study indicated that EPO and MPSS had a synergistic effect on AQP4 expression following reperfusion, and suggest that they may be combined in the treatment of SCI.

Post-spinal cord injury astrocyte-mediated functional recovery in rats after intraspinal injection of the recombinant adenoviral vectors Ad5-VEGF and Ad5-ANG

OBJECTIVE The most actively explored therapeutic strategy for overcoming spinal cord injury (SCI) is the delivery of genes encoding molecules that stimulate regeneration. In a mouse model of amyotrophic lateral sclerosis and in preliminary clinical trials in patients with amyotrophic lateral sclerosis, the combined administration of recombinant adenoviral vectors (Ad5-VEGF+Ad5-ANG) encoding the neurotrophic/angiogenic factors vascular endothelial growth factor ( VEGF) and angiogenin ( ANG) was found to slow the development of neurological deficits. These results suggest that there may be positive effects of this combination of genes in posttraumatic spinal cord regeneration. The objective of the present study was to determine the effects of Ad5-VEGF+Ad5-ANG combination therapy on motor function recovery and reactivity of astrocytes in a rat model of SCI. METHODS Spinal cord injury was induced in adult Wistar rats by the weight-drop method. Rats (n = 51) were divided into 2 groups: the experimental group (Ad5-VEGF+Ad5-ANG) and the control group (Ad5-GFP [green fluorescent protein]). Recovery of motor function was assessed using the Basso, Beattie, and Bresnahan scale. The duration and intensity of infectivity and gene expression from the injected vectors were assessed by immunofluorescent detection of GFP. Reactivity of glial cells was assessed by changes in the number of immunopositive cells expressing glial fibrillary acidic protein (GFAP), S100β, aquaporin 4 (AQP4), oligodendrocyte transcription factor 2, and chondroitin sulfate proteoglycan 4. The level of S100β mRNA expression in the spinal cord was estimated by real-time polymerase chain reaction. RESULTS Partial recovery of motor function was observed 30 days after surgery in both groups. However, Basso, Beattie, and Bresnahan scores were 35.9% higher in the Ad5-VEGF+Ad5-ANG group compared with the control group. Specific GFP signal was observed at distances of up to 5 mm in the rostral and caudal directions from the points of injection. A 1.5 to 2.0-fold increase in the number of GFAP⁺, S100β⁺, and AQP4⁺ cells was observed in the white and gray matter at a distance of up to 5 mm from the center of the lesion site in the caudal and rostral directions. At 30 days after injury, a 2-fold increase in S100β transcripts was observed in the Ad5-VEGF+Ad5-ANG group compared with the control group. CONCLUSIONS Intraspinal injection of recombinant adenoviral vectors encoding VEGF and ANG stimulates functional recovery after traumatic SCI. The increased number of S100β⁺ astrocytes induced by this approach may be a beneficial factor for maintaining the survival and function of neurons. Therefore, gene therapy with Ad5-VEGF+Ad5-ANG vectors is an effective therapeutic method for SCI treatment.

Aquaporins in the Spinal Cord

Aquaporins (AQPs) are water channel proteins robustly expressed in the central nervous system (CNS). A number of previous studies described the cellular expression sites and investigated their major roles and function in the brain and spinal cord. Among thirteen different mammalian AQPs, AQP1 and AQP4 have been mainly studied in the CNS and evidence has been presented that they play important roles in the pathogenesis of CNS injury, edema and multiple diseases such as multiple sclerosis, neuromyelitis optica spectrum disorders, amyotrophic lateral sclerosis, glioblastoma multiforme, Alzheimer's disease and Parkinson's disease. The objective of this review is to highlight the current knowledge about AQPs in the spinal cord and their proposed roles in pathophysiology and pathogenesis related to spinal cord lesions and injury.

Increased intrathecal pressure after traumatic spinal cord injury: an illustrative case presentation and a review of the literature

PURPOSE

Early surgical management after traumatic spinal cord injury (SCI) is nowadays recommended. Since posttraumatic ischemia is an important sequel after SCI, maintenance of an adequate mean arterial pressure (MAP) within the first week remains crucial in order to warrant sufficient spinal cord perfusion. However, the contribution of raised intraparenchymal and consecutively increased intrathecal pressure has not been implemented in treatment strategies.

METHODS

Case report and review of the literature.

RESULTS

Here we report a case of a 54-year old man who experienced a thoracic spinal cord injury after a fall. CT-examination revealed complex fractures of the thoracic spine. The patient underwent prompt surgical intervention. Intraoperatively, fractured parts of the ascending Th5 facet joint were displaced into the spinal cord itself. Upon removal, excessive protruding of medullary tissue was observed over several minutes. This demonstrates the clinical relevance of increased intrathecal pressure in some patients.

CONCLUSION

Monitoring and counteracting raised intrathecal pressure should guide clinical decision-making in the future in order to ensure optimal spinal cord perfusion pressure for every affected individual.

Advance in spinal cord ischemia reperfusion injury: Blood-spinal cord barrier and remote ischemic preconditioning

The blood-spinal cord barrier (BSCB) is the physiological and metabolic substance diffusion barrier between blood circulation and spinal cord tissues. This barrier plays a vital role in maintaining the microenvironment stability of the spinal cord. When the spinal cord is subjected to ischemia/reperfusion (I/R) injury, the structure and function of the BSCB is disrupted, further destroying the spinal cord homeostasis and ultimately leading to neurological deficit. Remote ischemic preconditioning (RIPC) is an approach in which interspersed cycles of preconditioning ischemia is followed by reperfusion to tissues/organs to protect the distant target tissues/organs against subsequent lethal ischemic injuries. RIPC is an innovation of the treatment strategies that protect the organ from I/R injury. In this study, we review the morphological structure and function of the BSCB, the injury mechanism of BSCB resulting from spinal cord I/R, and the effect of RIPC on it.

Aquaporin-4 and spinal cord injury

Edema formation is a major problem following traumatic spinal cord injury (SCI) that acts to exacerbate secondary damage. Severity of edema correlates with reduced neurological outcome in human patients. To date, there are no effective treatments to directly resolve edema within the spinal cord. The aquaporin-4 (AQP4) water channel is found on membranes of astrocytic endfeet in direct contact with blood vessels, the glia limitans in contact with the cerebrospinal fluid and ependyma around the central canal. Being so locally expressed at the interface between fluid and tissue allow AQP4 channels to play an important role in the bidirectional regulation of water homeostasis under normal conditions and following trauma. With the need to better understand the pathophysiology underlying the devastating cellular events in SCI, animal models have become an integral part of exploration. Inevitably, several injury models have been developed (contusion, compression, transection) resulting in difficult interpretation between studies with conflicting results. This is true in the case of understanding the role of AQP4 in the progression and resolution of edema following SCI, whose role is still not completely understood and is highly dependent on the type of edema present (vasogenic vs cytotoxic). Here, we discuss regulation of AQP4 in varying injury models and the effects of potential therapeutic interventions on expression, edema formation and functional recovery. Better understanding of the precise role of AQP4 following a wide range of injuries will help to understand optimal treatment timing following human SCI for prime therapeutic benefit and enhanced neurological outcome.

Peripheral nerve injury induces aquaporin-4 expression and astrocytic enlargement in spinal cord

Aquaporin-4 (AQP4), a water channel protein, is expressed mainly in the perivascular end-feet of astrocytes in the brain and spinal cord. Dysregulation of AQP4 is critically associated with abnormal water transport in the astrocytes. We aimed to examine whether peripheral nerve injury (PNI) could induce the changes of AQP4 expression and astrocytic morphology in the spinal cord. Two different PNI models [partial sciatic nerve transection (PST) and chronic constriction injury (CCI)] were established on the left sciatic nerve in Sprague-Dawley rats, which decreased the pain withdrawal threshold in the ipsilateral hind paws. Both PNI models were associated with a persistent up-regulation of AQP4 in the ipsilateral dorsal horn at the lower lumbar region over 3 weeks, despite an absence of direct injury to the spinal cord. Three-dimensional reconstruction of astrocytes was made and morphometric analysis was done. Up-regulation of AQP4 was accompanied by a significant increase in the length and volume of astrocytic processes and the number of branch points. The most prominent changes were present in the distal processes of the astrocytes and the changes were maintained throughout the whole experimental period. Extravasation of systemically administered tracers Evans Blue and sodium fluorescein was not seen in both models. Taken together, PNI was associated with a long-lasting AQP4 up-regulation and enlargement of astrocytic processes in the spinal cord in rats, both of which were not related to the disruption of blood-spinal cord barrier. The findings could provide novel insights on the understanding of pathophysiology of spinal cords after PNI.

Curcumin improves the integrity of blood-spinal cord barrier after compressive spinal cord injury in rats

Previous studies have shown that curcumin (Cur) can produce potent neuroprotective effects against damage due to spinal cord injury (SCI). However, whether Cur can preserve the function of the blood-spinal cord barrier (BSCB) is unclear. The present study was performed to investigate the mechanism underlying BSCB permeability changes, which were induced by treatment with Cur (75, 150, and 300 mg/kg, i.p.) after compressive SCI in rats. BSCB permeability was evaluated by Evans blue leakage. Motor recovery of rats with SCI was assessed using the Basso, Beattie, and Bresnahan scoring system every day until the 21st days post-injury. The protein levels of heme oxygenase-1 (HO-1), tight junction protein, and inflammatory factors were analyzed by western blots. The expression of the inflammatory factors tumor necrosis factor-α (TNF-α) and nuclear factor-kappaB (NF-κB) mRNA was determined with reverse transcription-polymerase chain reactions. Treatment with Cur (150 and 300 mg/kg) significantly reduced Evans blue leakage into the spinal cord tissue at 24h after SCI. Cur (150 mg/kg) significantly increased HO-1 protein expression. The levels of TNF-α and NF-κB mRNA and protein greatly increased at 24h after SCI, and this increase was significantly attenuated by Cur treatment. ZO-1 and occludin expression was upregulated by Cur (150 mg/kg) treatment after SCI, and this effect was blocked by the HO-1 inhibitor zinc protoporphyrin. Long-term effects of Cur on motor recovery after SCI were observed. Our results indicated that Cur can improve motor function after SCI, which could correlate with improvements in BSCB integrity.

Immunolocalization of Water Channel Proteins AQP1 and AQP4 in Rat Spinal Cord

Aquaporin (AQP) is a water-selective channel protein. In the brain, AQPs play critical roles in the production of cerebrospinal fluid and in edema formation. In contrast, the expression and role of AQPs in spinal cord are unclear. We aimed to investigate the localization of AQP1 and AQP4 in normal rat spinal cord compared with the expression of marker proteins for astrocytes, neurons, and endothelial cells. Immunohistochemistry demonstrated that AQP1 and AQP4 are expressed along all levels of the spinal cord from the cervical to lumbar levels. AQP1 immunolabeling was observed in the dorsal horns in the gray matter, whereas the labeling was weak and mainly seen close to glia limitans in the white matter. AQP1 was co-labeled with marker proteins for unmyelinated neuronal fibers (peripherin) and endothelial cells (RECA-1) of blood vessels that had penetrated through the glia limitans. In contrast, AQP1 did not colocalize with GFAP, an astrocyte marker, at any level of the spinal cord. AQP4 was exclusively localized at the astrocytes, but AQP4 expression in spinal cord exhibited a less polarized and more spatial distribution than that of brain astrocytes. The observed characteristic localization and expression patterns of AQP1 and AQP4 could provide insights toward gaining an understanding of the role of AQPs in the spinal cord.

Aquaporin-4 mitigates retrograde degeneration of rubrospinal neurons by facilitating edema clearance and glial scar formation after spinal cord injury in mice

Atrophy of upper motor neurons hampers axonal regeneration and functional recovery following spinal cord injury (SCI). Apart from the severity of primary injury, a series of secondary pathological damages including spinal cord edema and glial scar formation affect the fate of injured upper motor neurons. The aquaporin-4 (AQP4) water channel plays a critical role in water homeostasis and migration of astrocytes in the central nervous system, probably offering a new therapeutic target for protecting against upper motor neuron degeneration after SCI. To test this hypothesis, we examined the effect of AQP4 deficiency on atrophy of rubrospinal neurons after unilateral rubrospinal tract transection at the fourth cervical level in mice. AQP4 gene knockout (AQP4-/-) mice exhibited high extent of spinal cord edema at 72 h after lesion compared with wild-type littermates. AQP4-/- mice showed impairments in astrocyte migration toward the transected site with a greater lesion volume at 1 week after surgery and glial scar formation with a larger cyst volume at 6 weeks. More severe atrophy and loss of axotomized rubrospinal neurons as well as axonal degeneration in the rubrospinal tract rostral to the lesion were observed in AQP4-/- mice at 6 weeks after SCI. AQP4 expression was downregulated at the lesioned spinal segment at 3 days and 1 week after injury, but upregulated at 6 weeks. These results demonstrated that AQP4 not only mitigates spinal cord damage but also ameliorates retrograde degeneration of rubrospinal neurons by promoting edema clearance and glial scar formation after laceration SCI. This finding supports the notion that AQP4 may be a promising therapeutic target for SCI.

The cancer drug tamoxifen: a potential therapeutic treatment for spinal cord injury

Tamoxifen (TMX) is a selective estrogen receptor modulator that can mimic the neuroprotective effects of estrogen but lacks its systemic adverse effects. We found that TMX (1 mg/day) significantly improved the motor recovery of partially paralyzed hind limbs of male adult rats with thoracic spinal cord injury (SCI), thus indicating a translational potential for this cancer medication given its clinical safety and applicability and the lack of currently available treatments for SCI. To shed light on the mechanisms underlying the beneficial effects of TMX for SCI, we used proteomic analyses, Western blots and histological assays, which showed that TMX treatment spared mature oligodendrocytes/increased myelin levels and altered reactive astrocytes, including the upregulation of the water channels aquaporin 4 (AQP4), a novel finding. AQP4 increases in TMX-treated SCI rats were associated with smaller fluid-filled cavities with borders consisting of densely packed AQP4-expressing astrocytes that closely resemble the organization of normal glia limitans externa (in contrast to large cavities in control SCI rats that lacked glia limitans-like borders and contained reactive glial cells). Based on our findings, we propose that TMX is a promising candidate for the therapeutic treatment of SCI and a possible intervention for other neuropathological conditions associated with demyelination and AQP4 dysfunction.

Estrogen mediates neuroprotection and anti-inflammatory effects during EAE through ERα signaling on astrocytes but not through ERβ signaling on astrocytes or neurons

Estrogens can signal through either estrogen receptor α (ERα) or β (ERβ) to ameliorate experimental autoimmune encephalomyelitis (EAE), the most widely used mouse model of multiple sclerosis (MS). Cellular targets of estrogen-mediated neuroprotection are still being elucidated. Previously, we demonstrated that ERα on astrocytes, but not neurons, was critical for ERα ligand-mediated neuroprotection in EAE, including decreased T-cell and macrophage inflammation and decreased axonal loss. Here, we determined whether ERβ on astrocytes or neurons could mediate neuroprotection in EAE, by selectively removing ERβ from either of these cell types using Cre-loxP gene deletion. Our results demonstrated that, even though ERβ ligand treatment was neuroprotective in EAE, this neuroprotection was not mediated through ERβ on either astrocytes or neurons and did not involve a reduction in levels of CNS inflammation. Given the differential neuroprotective and anti-inflammatory effects mediated via ERα versus ERβ on astrocytes, we looked for molecules within astrocytes that were affected by signaling through ERα, but not ERβ. We found that ERα ligand treatment, but not ERβ ligand treatment, decreased expression of the chemokines CCL2 and CCL7 by astrocytes in EAE. Together, our data show that neuroprotection in EAE mediated via ERβ signaling does not require ERβ on either astrocytes or neurons, whereas neuroprotection in EAE mediated via ERα signaling requires ERα on astrocytes and reduces astrocyte expression of proinflammatory chemokines. These findings reveal important cellular differences in the neuroprotective mechanisms of estrogen signaling through ERα and ERβ in EAE.

The effect of cigarette smoke exposure on spinal cord injury in rats

In this study, we examined whether cigarette smoke has neuroprotective or toxic effects on spinal cord injury (SCI). Male Sprague-Dawley rats were included in the study and received either cigarette smoke exposure or fresh air exposure. Twenty-four hours after the last cigarette smoke or fresh air exposure, all rats were injured at thoracic level 12 (T12), using an established static compression model. Our data showed that the cigarette smoke group had higher water content; higher permeability of the blood-spinal cord barrier (BSCB); higher malondialdehyde (MDA) levels, aquaporin-4 (AQP4) and hypoxia-inducible factor 1-alpha (HIF-1α) protein expression, and mRNA levels; and lower glutathione (GSH) levels than the control group values at 12 h, 24 h, and 48 h after SCI. There was no significant difference in these between the cigarette smoke group and the control group at 0 h after SCI. The results of the Basso, Beattie, and Bresnahan (BBB) hindlimb locomotor rating scale showed that rats in the cigarette smoke group had greater dysfunction in hindlimb movement than did rats in control group from 2 to day 6 after SCI. The extent of recovery did not make any difference from day 7 to day 10 after SCI between the cigarette smoke group and the control group. These results suggested that cigarette smoke can reinforce the oxidative stress injury via HIF-1α and AQP4 in the early stage after SCI. It is possible that cigarette smoke exposure does not affect SCI recovery in the long term; however, it can aggravate the edema and deteriorate BSCB disruption via HIF-1α and AQP4 in the early stage after SCI. More studies will be essential to consider this hypothesis and elucidate the mechanisms involved.

Delayed increase of astrocytic aquaporin 4 after juvenile traumatic brain injury: possible role in edema resolution?

Traumatic brain injury (TBI) is one of the leading causes of death and disability in children and adolescents. The neuropathological sequelae that result from TBI are a complex cascade of events including edema formation, which occurs more frequently in the pediatric than the adult population. This developmental difference in the response to injury may be related to higher water content in the young brain and also to molecular mechanisms regulating water homeostasis. Aquaporins (AQPs) provide a unique opportunity to examine the mechanisms underlying water mobility, which remain poorly understood in the juvenile post-traumatic edema process. We examined the spatiotemporal expression pattern of principal brain AQPs (AQP1, AQP4, and AQP9) after juvenile TBI (jTBI) related to edema formation and resolution observed using magnetic resonance imaging (MRI). Using a controlled cortical impact in post-natal 17 day-old rats as a model of jTBI, neuroimaging analysis showed a global decrease in water mobility (apparent diffusion coefficient, ADC) and an increase in edema (T2-values) at 1 day post-injury, which normalized by 3 days. Immunohistochemical analysis of AQP4 in perivascular astrocyte endfeet was increased in the lesion at 3 and 7days post-injury as edema resolved. In contrast, AQP1 levels distant from the injury site were increased at 7, 30, and 60 days within septal neurons but did not correlate with changes in edema formation. Group differences were not observed for AQP9. Overall, our observations confirm that astrocyticAQP4 plays a more central role than AQP1 or AQP9 during the edema process in the young brain.

Vascular Pathology as a Potential Therapeutic Target in SCI

Acute traumatic spinal cord injury (SCI) is characterized by a progressive secondary degeneration which exacerbates the loss of penumbral tissue and neurological function. Here, we first provide an overview of the known pathophysiological mechanisms involving injured microvasculature and molecular regulators that contribute to the loss and dysfunction of existing and new blood vessels. We also highlight the differences between traumatic and ischemic injuries which may yield clues as to the more devastating nature of traumatic injuries, possibly involving toxicity associated with hemorrhage. We also discuss known species differences with implications for choosing models, their relevance and utility to translate new treatments towards the clinic. Throughout this review, we highlight the potential opportunities and proof-of-concept experimental studies for targeting therapies to endothelial cell-specific responses. Lastly, we comment on the need for vascular mechanisms to be included in drug development and non-invasive diagnostics such as serum and cerebrospinal fluid biomarkers and imaging of spinal cord pathology.

Development of a Novel Ligand, [C]TGN-020, for Aquaporin 4 Positron Emission Tomography Imaging

Aquaporin 4 (AQP4), the most abundant isozyme of the water specific membrane transporter aquaporin family, has now been implicated to play a significant role in the pathogenesis of various disease processes of the nervous system from epilepsy to Alzheimer’s disease. Considering its clinical relevance, it is highly desirable to develop a noninvasive method for the quantitative analysis of AQP distribution in humans under clinical settings. Currently, the method of choice for such diagnostic examinations continues to be positron emission tomography (PET). Here, we report the successful development of a PET ligand for AQP4 imaging based on TGN-020, a potent AQP4 inhibitor developed previously in our laboratory. Utilizing [¹¹C]-TGN-020, PET images were successfully generated in wild type and AQP4 null mice, providing a basis for future evaluation regarding its suitability for clinical studies.

Expression of water channel aquaporin-4 during experimental syringomyelia

Object

Aquaporins (aqp) are protein channels providing water transport across cell membranes. The main member of this family expressed in the CNS is aqp-4. The pattern and amount of expression of this channel suggest a dominant role in bulk water movement into the nervous tissue. It has also been shown to play a role in several water balance disorders in the CNS. In this study, the authors investigated the possible role of aqp-4 in syringomyelia.

Methods

Twenty-five male Wistar-Hannover rats were divided into experimental (20 rats) and control (5 rats) groups. Syringomyelia was induced in the experimental group by kaolin injection into the cisterna magna. Eight weeks later, the animals were killed, and their spinal cords were removed. Central canal dilations were noted in all experimental animals. Immunohistochemistry and Western blot analysis were performed to evaluate aqp-4 expression.

Results

Both groups demonstrated positive immunoreactive signals to aqp-4. Western blot analysis revealed a slight decrease in the mean aqp-4 value in the experimental group; however, the difference did not reach statistical significance (p > 0.05). Immunohistochemical analysis showed a similar pattern and intensity of aqp-4 staining in both groups.

Conclusions

The results of this study indicate that aqp-4 most likely does not play a major role in chronic syringomyelia. Its slight downregulation during the initial stage of syrinx formation is possibly a compensatory mechanism. This effect is not present during the late stage of syringomyelia, and aqp-4 is most likely not involved in the pathophysiology of syrinx cavity formation.

Amiloride improves locomotor recovery after spinal cord injury

Amiloride is a drug approved by the United States Food and Drug Administration, which has shown neuroprotective effects in different neuropathological conditions, including brain injury or brain ischemia, but has not been tested in spinal cord injury (SCI). We tested amiloride's therapeutic potential in a clinically relevant rat model of contusion SCI inflicted at the thoracic segment T10. Rats receiving daily administration of amiloride from 24 h to 35 days after SCI exhibited a significant improvement in hindlimb locomotor ability at 21, 28, and 35 days after injury, when compared to vehicle-treated SCI rats. Rats receiving amiloride treatment also exhibited a significant increase in myelin oligodendrocyte glycoprotein (MOG) levels 35 days after SCI at the site of injury (T10) when compared to vehicle-treated controls, which indicated a partial reverse in the decrease of MOG observed with injury. Our data indicate that higher levels of MOG correlate with improved locomotor recovery after SCI, and that this may explain the beneficial effects of amiloride after SCI. Given that amiloride treatment after SCI caused a significant preservation of myelin levels, and improved locomotor recovery, it should be considered as a possible therapeutic intervention after SCI.

Expression and function of aquaporins in peripheral nervous system

The expression and role of the aquaporin (AQP) family water channels in the peripheral nervous system was less investigated. Since 2004, however, significant progress has been made in the immunolocalization, regulation and function of AQPs in the peripheral nervous system. These studies showed selective localization of three AQPs (AQP1, AQP2, and AQP4) in dorsal root ganglion neurons, enteric neurons and glial cells, periodontal Ruffini endings, trigeminal ganglion neurons and vomeronasal sensory neurons. Functional characterization in transgenic knockout mouse model revealed important role of AQP1 in pain perception. This review will summarize the progress in this field and discuss possible involvement of AQPs in peripheral neuropathies and their potential as novel drug targets.

2-Methoxyestradiol inhibits the up-regulation of AQP4 and AQP1 expression after spinal cord injury

The study investigated the mechanism of the up-regulation of aquaporin-4 (AQP4) and aquaporin-1 (AQP1) expression induced by spinal cord injury (SCI). Using adult rat spinal cord injury model, it was found that up-regulation of hypoxia inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), AQP4, and AQP1 in response to spinal cord injury was greatly antagonized by 2-methoxyestradiol (2ME2), which can post-transcriptionally inhibit the expression of HIF-1α. VEGF alone significantly increased the extravasation of Evans blue and up-regulated the levels of AQP4 protein expression in the injured spinal cord issue, but the levels of AQP1 expression were not significantly changed. Taken together, our results suggest that expression of AQP4 and AQP1 is correlated with up-regulation of HIF-1α after SCI through the mechanisms that were dependent and independent of the VEGF signaling pathway, respectively. And the inhibitor of HIF-1α is a novel promising therapeutic agent for human SCI-induced edema in the future.