The ependymal region of the adult human spinal cord differs from other species and shows ependymoma-like features

Ependymal cells: roles in central nervous system infections and therapeutic application

Ependymal cells are arranged along the inner surfaces of the ventricles and the central canal of the spinal cord, providing anatomical, physiological and immunological barriers that maintain cerebrospinal fluid (CSF) homeostasis. Based on this, studies have found that alterations in gene expression, cell junctions, cytokine secretion and metabolic disturbances can lead to dysfunction of ependymal cells, thereby participating in the onset and progression of central nervous system (CNS) infections. Additionally, ependymal cells can exhibit proliferative and regenerative potential as well as secretory functions during CNS injury, contributing to neuroprotection and post-injury recovery. Currently, studies on ependymal cell primarily focus on the basic investigations of their morphology, function and gene expression; however, there is a notable lack of clinical translational studies examining the molecular mechanisms by which ependymal cells are involved in disease onset and progression. This limits our understanding of ependymal cells in CNS infections and the development of therapeutic applications. Therefore, this review will discuss the molecular mechanism underlying the involvement of ependymal cells in CNS infections, and explore their potential for application in clinical treatment modalities.

An analytic model for the flow induced in syringomyelia cavities

A simple two-dimensional fluid-structure-interaction problem, involving viscous oscillatory flow in a channel separated by an elastic membrane from a fluid-filled slender cavity, is analyzed to shed light on the flow dynamics pertaining to syringomyelia, a neurological disorder characterized by the appearance of a large tubular cavity (syrinx) within the spinal cord. The focus is on configurations in which the velocity induced in the cavity, representing the syrinx, is comparable to that found in the channel, representing the subarachnoid space surrounding the spinal cord, both flows being coupled through a linear elastic equation describing the membrane deformation. An asymptotic analysis for small stroke lengths leads to closed-form expressions for the leading-order oscillatory flow, and also for the stationary flow associated with the first-order corrections, the latter involving a steady distribution of transmembrane pressure. The magnitude of the induced flow is found to depend strongly on the frequency, with the result that for channel flow rates of non-sinusoidal waveform, as those found in the spinal canal, higher harmonics can dominate the sloshing motion in the cavity, in agreement with previous in vivo observations. Under some conditions, the cycle-averaged transmembrane pressure, also showing a marked dependence on the frequency, changes sign on increasing the cavity transverse dimension (i.e. orthogonal to the cord axis), underscoring the importance of cavity size in connection with the underlying hydrodynamics. The analytic results presented here can be instrumental in guiding future numerical investigations, needed to clarify the pathogenesis of syringomyelia cavities.

The activation of dormant ependymal cells following spinal cord injury

Ependymal cells, a dormant population of ciliated progenitors found within the central canal of the spinal cord, undergo significant alterations after spinal cord injury (SCI). Understanding the molecular events that induce ependymal cell activation after SCI represents the first step toward controlling the response of the endogenous regenerative machinery in damaged tissues. This response involves the activation of specific signaling pathways in the spinal cord that promotes self-renewal, proliferation, and differentiation. We review our current understanding of the signaling pathways and molecular events that mediate the SCI-induced activation of ependymal cells by focusing on the roles of some cell adhesion molecules, cellular membrane receptors, ion channels (and their crosstalk), and transcription factors. An orchestrated response regulating the expression of receptors and ion channels fine-tunes and coordinates the activation of ependymal cells after SCI or cell transplantation. Understanding the major players in the activation of ependymal cells may help us to understand whether these cells represent a critical source of cells contributing to cellular replacement and tissue regeneration after SCI. A more complete understanding of the role and function of individual signaling pathways in endogenous spinal cord progenitors may foster the development of novel targeted therapies to induce the regeneration of the injured spinal cord.

Persistence of FoxJ1+ Pax6+ Sox2+ ependymal cells throughout life in the human spinal cord

Ependymal cells lining the central canal of the spinal cord play a crucial role in providing a physical barrier and in the circulation of cerebrospinal fluid. These cells express the FOXJ1 and SOX2 transcription factors in mice and are derived from various neural tube populations, including embryonic roof and floor plate cells. They exhibit a dorsal-ventral expression pattern of spinal cord developmental transcription factors (such as MSX1, PAX6, ARX, and FOXA2), resembling an embryonic-like organization. Although this ependymal region is present in young humans, it appears to be lost with age. To re-examine this issue, we collected 17 fresh spinal cords from organ donors aged 37-83 years and performed immunohistochemistry on lightly fixed tissues. We observed cells expressing FOXJ1 in the central region in all cases, which co-expressed SOX2 and PAX6 as well as RFX2 and ARL13B, two proteins involved in ciliogenesis and cilia-mediated sonic hedgehog signaling, respectively. Half of the cases exhibited a lumen and some presented portions of the spinal cord with closed and open central canals. Co-staining of FOXJ1 with other neurodevelopmental transcription factors (ARX, FOXA2, MSX1) and NESTIN revealed heterogeneity of the ependymal cells. Interestingly, three donors aged > 75 years exhibited a fetal-like regionalization of neurodevelopmental transcription factors, with dorsal and ventral ependymal cells expressing MSX1, ARX, and FOXA2. These results provide new evidence for the persistence of ependymal cells expressing neurodevelopmental genes throughout human life and highlight the importance of further investigation of these cells.

Carcino-Evo-Devo, A Theory of the Evolutionary Role of Hereditary Tumors

A theory of the evolutionary role of hereditary tumors, or the carcino-evo-devo theory, is being developed. The main hypothesis of the theory, the hypothesis of evolution by tumor neofunctionalization, posits that hereditary tumors provided additional cell masses during the evolution of multicellular organisms for the expression of evolutionarily novel genes. The carcino-evo-devo theory has formulated several nontrivial predictions that have been confirmed in the laboratory of the author. It also suggests several nontrivial explanations of biological phenomena previously unexplained by the existing theories or incompletely understood. By considering three major types of biological development-individual, evolutionary, and neoplastic development-within one theoretical framework, the carcino-evo-devo theory has the potential to become a unifying biological theory.

Stem Cell Therapies for Restorative Treatments of Central Nervous System Ischemia-Reperfusion Injury

Ischemic damage to the central nervous system (CNS) is a catastrophic postoperative complication of aortic occlusion subsequent to cardiovascular surgery that can cause brain impairment and sometimes even paraplegia. Over recent years, numerous studies have investigated techniques for protecting and revascularizing the nervous system during intraoperative ischemia; however, owing to a lack of knowledge of the physiological distinctions between the brain and spinal cord, as well as the limited availability of testing techniques and treatments for ischemia-reperfusion injury, the cause of brain and spinal cord ischemia-reperfusion injury remains poorly understood, and no adequate response steps are currently available in the clinic. Given the limited ability of the CNS to repair itself, it is of great clinical value to make full use of the proliferative and differentiation potential of stem cells to repair nerves in degenerated and necrotic regions by stem cell transplantation or mobilization, thereby introducing a novel concept for the treatment of severe CNS ischemia-reperfusion injury. This review summarizes the most recent advances in stem cell therapy for ischemia-reperfusion injury in the brain and spinal cord, aiming to advance basic research and the clinical use of stem cell therapy as a promising treatment for this condition.

Development of the brain ventricular system from a comparative perspective

The brain ventricular system (BVS) consists of brain ventricles and channels filled with cerebrospinal fluid (CSF). Disturbance of CSF flow has been linked to scoliosis and neurodegenerative diseases, including hydrocephalus. This could be due to defects of CSF production by the choroid plexus or impaired CSF movement over the ependyma dependent on motile cilia. Most vertebrates have horizontal body posture. They retain additional evolutionary innovations assisting CSF flow, such as the Reissner fiber. The causes of hydrocephalus have been studied using animal models including rodents (mice, rats, hamsters) and zebrafish. However, the horizontal body posture reduces the effect of gravity on CSF flow, which limits the use of mammalian models for scoliosis. In contrast, fish swim against the current and experience a forward-to-backward mechanical force akin to that caused by gravity in humans. This explains the increased popularity of the zebrafish model for studies of scoliosis. "Slit-ventricle" syndrome is another side of the spectrum of BVS anomalies. It develops because of insufficient inflation of the BVS. Recent advances in zebrafish functional genetics have revealed genes that could regulate the development of the BVS and CSF circulation. This review will describe the BVS of zebrafish, a typical teleost, and vertebrates in general, in comparative perspective. It will illustrate the usefulness of the zebrafish model for developmental studies of the choroid plexus (CP), CSF flow and the BVS.

The Theory of Carcino-Evo-Devo and Its Non-Trivial Predictions

To explain the sources of additional cell masses in the evolution of multicellular organisms, the theory of carcino-evo-devo, or evolution by tumor neofunctionalization, has been developed. The important demand for a new theory in experimental science is the capability to formulate non-trivial predictions which can be experimentally confirmed. Several non-trivial predictions were formulated using carcino-evo-devo theory, four of which are discussed in the present paper: (1) The number of cellular oncogenes should correspond to the number of cell types in the organism. The evolution of oncogenes, tumor suppressor and differentiation gene classes should proceed concurrently. (2) Evolutionarily new and evolving genes should be specifically expressed in tumors (TSEEN genes). (3) Human orthologs of fish TSEEN genes should acquire progressive functions connected with new cell types, tissues and organs. (4) Selection of tumors for new functions in the organism is possible. Evolutionarily novel organs should recapitulate tumor features in their development. As shown in this paper, these predictions have been confirmed by the laboratory of the author. Thus, we have shown that carcino-evo-devo theory has predictive power, fulfilling a fundamental requirement for a new theory.

Restoration of spinal cord injury: From endogenous repairing process to cellular therapy

Spinal cord injury (SCI) disrupts neurological pathways and impacts sensory, motor, and autonomic nerve function. There is no effective treatment for SCI currently. Numerous endogenous cells, including astrocytes, macrophages/microglia, and oligodendrocyte, are involved in the histological healing process following SCI. By interfering with cells during the SCI repair process, some advancements in the therapy of SCI have been realized. Nevertheless, the endogenous cell types engaged in SCI repair and the current difficulties these cells confront in the therapy of SCI are poorly defined, and the mechanisms underlying them are little understood. In order to better understand SCI and create new therapeutic strategies and enhance the clinical translation of SCI repair, we have comprehensively listed the endogenous cells involved in SCI repair and summarized the six most common mechanisms involved in SCI repair, including limiting the inflammatory response, protecting the spared spinal cord, enhancing myelination, facilitating neovascularization, producing neurotrophic factors, and differentiating into neural/colloidal cell lines.

The immune microenvironment and tissue engineering strategies for spinal cord regeneration

Regeneration of neural tissue is limited following spinal cord injury (SCI). Successful regeneration of injured nerves requires the intrinsic regenerative capability of the neurons and a suitable microenvironment. However, the local microenvironment is damaged, including insufficient intraneural vascularization, prolonged immune responses, overactive immune responses, dysregulated bioenergetic metabolism and terminated bioelectrical conduction. Among them, the immune microenvironment formed by immune cells and cytokines plays a dual role in inflammation and regeneration. Few studies have focused on the role of the immune microenvironment in spinal cord regeneration. Here, we summarize those findings involving various immune cells (neutrophils, monocytes, microglia and T lymphocytes) after SCI. The pathological changes that occur in the local microenvironment and the function of immune cells are described. We also summarize and discuss the current strategies for treating SCI with tissue-engineered biomaterials from the perspective of the immune microenvironment.

Corrigendum: Purinergic signaling systems across comparative models of spinal cord injury

[This corrects the article DOI: 10.4103/1673-5374.338993].

Research progress of endogenous neural stem cells in spinal cord injury

Spinal cord injury (SCI) is a severe disabling disease, which mainly manifests as impairments of sensory and motor functions, sexual function, bladder and intestinal functions, respiratory and cardiac functions below the injury plane. In addition, the condition has a profound effect on the mental health of patients, which often results in severe sequelae. Some patients may be paraplegic for life or even die, which places a huge burden on the family and society. There is still no effective treatment for SCI. Studies have confirmed that endogenous neural stem cells (ENSCs), as multipotent neural stem cells, which are located in the ependymal region of the central canal of the adult mammalian spinal cord, are activated after SCI and then differentiate into various nerve cells to promote endogenous repair and regeneration. However, the central canal of the spinal cord is often occluded to varying degrees in adults, and residual ependymal cells cannot be activated and do not proliferate after SCI. Besides, the destruction of the microenvironment after SCI is also an important factor that affects the proliferation and differentiation of ENSCs and spinal cord repair. Therefore, this review describes the role of ENSCs in SCI, in terms of the origin, transformation, treatment, and influencing factors, to provide new ideas for clinical treatment of SCI.

Turning the Curve Into Straight: Phenogenetics of the Spine Morphology and Coordinate Maintenance in the Zebrafish

The vertebral column, or spine, provides mechanical support and determines body axis posture and motion. The most common malformation altering spine morphology and function is adolescent idiopathic scoliosis (AIS), a three-dimensional spinal deformity that affects approximately 4% of the population worldwide. Due to AIS genetic heterogenicity and the lack of suitable animal models for its study, the etiology of this condition remains unclear, thus limiting treatment options. We here review current advances in zebrafish phenogenetics concerning AIS-like models and highlight the recently discovered biological processes leading to spine malformations. First, we focus on gene functions and phenotypes controlling critical aspects of postembryonic aspects that prime in spine architecture development and straightening. Second, we summarize how primary cilia assembly and biomechanical stimulus transduction, cerebrospinal fluid components and flow driven by motile cilia have been implicated in the pathogenesis of AIS-like phenotypes. Third, we highlight the inflammatory responses associated with scoliosis. We finally discuss recent innovations and methodologies for morphometrically characterize and analyze the zebrafish spine. Ongoing phenotyping projects are expected to identify novel and unprecedented postembryonic gene functions controlling spine morphology and mutant models of AIS. Importantly, imaging and gene editing technologies are allowing deep phenotyping studies in the zebrafish, opening new experimental paradigms in the morphometric and three-dimensional assessment of spinal malformations. In the future, fully elucidating the phenogenetic underpinnings of AIS etiology in zebrafish and humans will undoubtedly lead to innovative pharmacological treatments against spinal deformities.

RNA Profiling of Mouse Ependymal Cells after Spinal Cord Injury Identifies the Oncostatin Pathway as a Potential Key Regulator of Spinal Cord Stem Cell Fate

Ependymal cells reside in the adult spinal cord and display stem cell properties in vitro. They proliferate after spinal cord injury and produce neurons in lower vertebrates but predominantly astrocytes in mammals. The mechanisms underlying this glial-biased differentiation remain ill-defined. We addressed this issue by generating a molecular resource through RNA profiling of ependymal cells before and after injury. We found that these cells activate STAT3 and ERK/MAPK signaling post injury and downregulate cilia-associated genes and FOXJ1, a central transcription factor in ciliogenesis. Conversely, they upregulate 510 genes, seven of them more than 20-fold, namely Crym, Ecm1, Ifi202b, Nupr1, Rbp1, Thbs2 and Osmr—the receptor for oncostatin, a microglia-specific cytokine which too is strongly upregulated after injury. We studied the regulation and role of Osmr using neurospheres derived from the adult spinal cord. We found that oncostatin induced strong Osmr and p-STAT3 expression in these cells which is associated with reduction of proliferation and promotion of astrocytic versus oligodendrocytic differentiation. Microglial cells are apposed to ependymal cells in vivo and co-culture experiments showed that these cells upregulate Osmr in neurosphere cultures. Collectively, these results support the notion that microglial cells and Osmr/Oncostatin pathway may regulate the astrocytic fate of ependymal cells in spinal cord injury.

The Structure of the Spinal Cord Ependymal Region in Adult Humans Is a Distinctive Trait among Mammals

In species that regenerate the injured spinal cord, the ependymal region is a source of new cells and a prominent coordinator of regeneration. In mammals, cells at the ependymal region proliferate in normal conditions and react after injury, but in humans, the central canal is lost in the majority of individuals from early childhood. It is replaced by a structure that does not proliferate after damage and is formed by large accumulations of ependymal cells, strong astrogliosis and perivascular pseudo-rosettes. We inform here of two additional mammals that lose the central canal during their lifetime: the Naked Mole-Rat (NMR, Heterocephalus glaber) and the mutant hyh (hydrocephalus with hop gait) mice. The morphological study of their spinal cords shows that the tissue substituting the central canal is not similar to that found in humans. In both NMR and hyh mice, the central canal is replaced by tissue reminiscent of normal lamina X and may include small groups of ependymal cells in the midline, partially resembling specific domains of the former canal. However, no features of the adult human ependymal remnant are found, suggesting that this structure is a specific human trait. In order to shed some more light on the mechanism of human central canal closure, we provide new data suggesting that canal patency is lost by delamination of the ependymal epithelium, in a process that includes apical polarity loss and the expression of signaling mediators involved in epithelial to mesenchymal transitions.

Plasticity of the Injured Spinal Cord

Complete spinal cord injury (SCI) leads to permanent motor, sensitive and sensory deficits. In humans, there is currently no therapy to promote recovery and the only available treatments include surgical intervention to prevent further damage and symptomatic relief of pain and infections in the acute and chronic phases, respectively. Basically, the spinal cord is classically viewed as a nonregenerative tissue with limited plasticity. Thereby the establishment of the “glial” scar which appears within the SCI is mainly described as a hermetic barrier for axon regeneration. However, recent discoveries have shed new light on the intrinsic functional plasticity and endogenous recovery potential of the spinal cord. In this review, we will address the different aspects that the spinal cord plasticity can take on. Indeed, different experimental paradigms have demonstrated that axonal regrowth can occur even after complete SCI. Moreover, recent articles have demonstrated too that the “glial” scar is in fact composed of several cellular populations and that each of them exerts specific roles after SCI. These recent discoveries underline the underestimation of the plasticity of the spinal cord at cellular and molecular levels. Finally, we will address the modulation of this endogenous spinal cord plasticity and the perspectives of future therapeutic opportunities which can be offered by modulating the injured spinal cord microenvironment.

Frizzled 1 and Wnt1 as new potential therapeutic targets in the traumatically injured spinal cord

Despite the experimental evidence pointing to a significant role of the Wnt family of proteins in physiological and pathological rodent spinal cord functioning, its potential relevance in the healthy and traumatically injured human spinal cord as well as its therapeutic potential in spinal cord injury (SCI) are still poorly understood. To get further insight into these interesting issues, we first demonstrated by quantitative Real-Time PCR and simple immunohistochemistry that detectable mRNA expression of most Wnt components, as well as protein expression of all known Wnt receptors, can be found in the healthy human spinal cord, supporting its potential involvement in human spinal cord physiology. Moreover, evaluation of Frizzled (Fz) 1 expression by double immunohistochemistry showed that its spatio-temporal and cellular expression pattern in the traumatically injured human spinal cord is equivalent to that observed in a clinically relevant model of rat SCI and suggests its potential involvement in SCI progression/outcome. Accordingly, we found that long-term lentiviral-mediated overexpression of the Fz1 ligand Wnt1 after rat SCI improves motor functional recovery, increases myelin preservation and neuronal survival, and reduces early astroglial reactivity and NG2+ cell accumulation, highlighting the therapeutic potential of Wnt1 in this neuropathological situation.

Ependymal cells in the spinal cord as neuronal progenitors

Ependymal cells are neural progenitors and form part of the central canal of the spinal cord. Therefore, ependymal cells could serve as a potential source of neural progenitors for regenerative medicine applications. Such applications consist of endogenous activation or exogenous transplantation, alone or in combination with pharmacological treatments, to repair spinal cord injuries. This mini review describes the main phenotypical characteristics of ependymal cells from spinal cord and the opportunities offered for spinal cord injury therapeutic application.

BAF45D Downregulation in Spinal Cord Ependymal Cells Following Spinal Cord Injury in Adult Rats and Its Potential Role in the Development of Neuronal Lesions

The endogenous spinal cord ependymal cells (SCECs), which form the central canal (CC), are critically involved in proliferation, differentiation and migration after spinal cord injury (SCI) and represents a repair cell source in treating SCI. Previously, we reported that BAF45D is expressed in the SCECs and the spinal cord neurons in adult mice and knockdown of BAF45D fail to induce expression of PAX6, a neurogenic fate determinant, during early neural differentiation of human embryonic stem cells. However, the effects of SCI on expression of BAF45D have not been reported. The aim of this study is to explore the expression and potential role of BAF45D in rat SCI model. In this study, adult rats were randomly divided into intact, sham, and SCI groups. We first explored expression of BAF45D in the SCECs in intact adult rats. We then explored SCI-induced loss of motor neurons and lesion of neurites in the anterior horns induced by the SCI. We also investigated whether the SCI-induced lesions in SCECs are accompanied by the motor neuron lesions. Finally, we examined the effect of BAF45D knockdown on cell growth in neuro2a cells. Our data showed that BAF45D is expressed in SCECs, neurons, and oligodendrocytes but not astrocytes in the spinal cords of intact adult rats. After SCI, the structure of CC was disrupted and the BAF45D-positive SCEC-derivatives were decreased. During the early stages of SCI, when shape of CC was affected but there was no disruption in circular structure of the SCECs, it was evident that there was a significant reduction in the number of neurites and motor neurons in the anterior horns compared with those of intact rats. In comparison, a complete loss of SCECs accompanied by further loss of motor neurons but not neurites was observed at the later stage. BAF45D knockdown was also found to inhibit cell growth in neuro2a cells. These results highlight the decreased expression of BAF45D in SCI-injured SCECs and the potential role of BAF45D downregulation in development of neuronal lesion after SCI in adult rats.

Historical setting and neuropathology of lathyrism: Insights from the neglected 1944 report by Oliveras de la Riva

Lathyrism is a central motor system disorder recognized since antiquity resulting from prolonged dietary dependence on the grasspea (Lathyrus sativus). The neuropathology underlying the characteristic spastic paraparesis of lathyrism is sketchy. Described here is a landmark but little-known Spanish-language neuropathological study of two patients with lathyrism of recent onset. Due to erroneous interpretations of Filimonov's influential work in 1926, it was assumed that spastic paraparesis of lathyrism was explained by destruction of Betz's pyramidal cells in the motor cortex. Contrary to present understanding, Betz cells and anterior horn cells were preserved, and pathological findings dominated by myelin loss were largely limited to pyramidal tracts in the lumbar cord. Thickening of the adventitia of capillaries and arterioles, together with proliferation of perivascular astrocytes, was found along the length of the spinal cord. Oliveras de la Riva proposed that the segmental spinal pathology arose because distal regions of elongate pyramidal tract axons are distant from their trophic center in the motor cortex, a view not far from the current distal axonopathy concept of lathyrism. In addition, we review the historical circumstances of Filimonov's work in Russia, a summary of the epidemic of lathyrism in Spain following its Civil War (1936-1939), and some historical aspects of the Cajal Institute in Madrid, where Oliveras de la Riva's work was carried out under the supervision of Fernando de Castro, one of Cajal's favorite students.

Endogenous spinal cord stem cells in multiple sclerosis and its animal model

The adult mammalian spinal cord (SC) harbors neural stem cells (NSCs). The SC-NSCs are mostly quiescent during physiological conditions but are quickly activated in traumatic injury models. The SC-NSCs generate mostly glia, but are able to differentiate into neurons when affected by favourable conditions. An example is the inflammatory milieu in the SC of rat EAE, where the SC-NSCs migrate into demyelinated lesions and give rise to both glia and neurons. In MS, cells with progenitor phenotypes accumulate in inflammatory lesions both in brain and SC, but the extent to which these cells contribute to repair remains to be revealed.

RNA Profiling of the Human and Mouse Spinal Cord Stem Cell Niches Reveals an Embryonic-like Regionalization with MSX1+ Roof-Plate-Derived Cells

Anamniotes, rodents, and young humans maintain neural stem cells in the ependymal zone (EZ) around the central canal of the spinal cord, representing a possible endogenous source for repair in mammalian lesions. Cell diversity and genes specific for this region are ill defined. A cellular and molecular resource is provided here for the mouse and human EZ based on RNA profiling, immunostaining, and fluorescent transgenic mice. This uncovered the conserved expression of 1,200 genes including 120 transcription factors. Unexpectedly the EZ maintains an embryonic-like dorsal-ventral pattern of expression of spinal cord developmental transcription factors (ARX, FOXA2, MSX1, and PAX6). In mice, dorsal and ventral EZ cells express Vegfr3 and are derived from the embryonic roof and floor plates. The dorsal EZ expresses a high level of Bmp6 and Gdf10 genes and harbors a subpopulation of radial quiescent cells expressing MSX1 and ID4 transcription factors.

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A molecular resource for the human and mouse spinal cord ependymal zone

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Identification of 120 transcription factors in the human and mouse ependymal zone

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Embryonic-like organization of the adult spinal cord ependymal zone

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Dorsal ependymal cells expressing Msx1 are derived from the embryonic roof plate

Wnt Signaling Alterations in the Human Spinal Cord of Amyotrophic Lateral Sclerosis Cases: Spotlight on Fz2 and Wnt5a

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder with no cure, and elucidation of the mechanisms mediating neuronal death in this neuropathology is crucial to develop effective treatments. It has recently been demonstrated in animal models that the Wnt family of proteins is involved in this neuropathology, although its potential involvement in case of humans is almost unknown. We analyzed the expression of Wnt signaling components in healthy and ALS human spinal cords by quantitative RT-PCR, and we found that most Wnt ligands, modulators, receptors, and co-receptors were expressed in healthy controls. Moreover, we observed clear alterations in the mRNA expression of different components of this family of proteins in human spinal cord tissue from ALS cases. Specifically, we detected a significant increase in the mRNA levels of Wnt3, Wnt4, Fz2, and Fz8, together with several non-significant increases in the mRNA expression of other genes such as Wnt2b, Wnt5a, Fz3, Lrp5, and sFRP3. Based on these observations and on previous reports of studies performed in animal models, we evaluated with immunohistochemistry the protein expression patterns of Fz2 and Fz5 receptors and their main ligand Wnt5a in control samples and ALS cases. No substantial changes were observed in Fz5 protein expression pattern in ALS samples. However, we detected an increase in the amount of Fz2+ astrocytes in the borderline between gray and white matter at the ventral horn in ALS samples. Finally, Wnt5a expression was observed in neurons and astrocytes in both control and ALS samples, although Wnt5a immunolabeling in astroglial cells was significantly increased in ALS spinal cords in the same region where changes in Fz2 were observed. Altogether, these observations strongly suggest that the Wnt family of proteins, and more specifically Fz2 and Wnt5a, might be involved in human ALS pathology.

Cells in the adult human spinal cord ependymal region do not proliferate after injury

In vertebrates that regenerate the injured spinal cord, cells at the ependymal region proliferate and coordinate the formation of bridges between the lesion stumps. In mammals, these cells also proliferate profusely around the central canal after spinal cord injury, although their actual contribution to repair is controversial. In humans, however, the central canal disappears from early childhood in the majority of individuals, being replaced by astrocyte gliosis, ependymocyte clusters, and perivascular pseudo-rosettes. In this human ependymal remnant, cells do not proliferate under normal conditions, but it is not known if they do after a lesion. Here, we studied the human ependymal remnant after traumatic spinal cord injury using samples from 21 individuals with survival times ranging from days to months post-injury. With three different monoclonal antibodies raised against two different proliferation markers (Ki67 and MCM2), we found that the ependymal remnant in adult humans does not proliferate after injury at any time or distance from the lesion. Our results seriously challenge the view of the spinal cord ependymal region as a neurogenic niche in adult humans and suggest that it would not be involved in cell replacement after a lesion. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Foxj1a is expressed in ependymal precursors, controls central canal position and is activated in new ependymal cells during regeneration in zebrafish

Zebrafish are able to regenerate the spinal cord and recover motor and sensory functions upon severe injury, through the activation of cells located at the ependymal canal. Here, we show that cells surrounding the ependymal canal in the adult zebrafish spinal cord express Foxj1a. We demonstrate that ependymal cells express Foxj1a from their birth in the embryonic neural tube and that Foxj1a activity is required for the final positioning of the ependymal canal. We also show that in response to spinal cord injury, Foxj1a ependymal cells actively proliferate and contribute to the restoration of the spinal cord structure. Finally, this study reveals that Foxj1a expression in the injured spinal cord is regulated by regulatory elements activated during regeneration. These data establish Foxj1a as a pan-ependymal marker in development, homeostasis and regeneration and may help identify the signals that enable this progenitor population to replace lost cells after spinal cord injury.

Laser-Capture Microdissection for the Analysis of Rat and Human Spinal Cord Ependyma by qPCR

In the last few decades many efforts have been dedicated to decipher the nature and regenerative potential of neurogenic niches and endogenous stem cells after damage of the central nervous system. In the spinal cord, it has been largely focused on the ependymal region, which hosts neural precursors/stem cells (NSC) in rodents but differs between species and ages. In the current chapter, we detail our protocol to study the gene expression profile of this region using fresh frozen blocks of rat and human post-mortem spinal cords. We describe how to prepare and process those tissues, how to identify and dissect the ependymal region using Laser-Capture Microdissection (LCMD), and how to isolate and amplify RNA with different integrity states to finally obtain enough material for performing gene expression assays using Taqman^® Low Density Arrays. LCMD technique maintains tissue integrity allowing for subsequent analysis without manipulation steps that may alter molecular properties of cells and the eventual loss of delicate cell types in comparison with other approaches that require previous disaggregation of the tissue and cell manipulation before isolation.

Ependymal cell contribution to scar formation after spinal cord injury is minimal, local and dependent on direct ependymal injury

Ependyma have been proposed as adult neural stem cells that provide the majority of newly proliferated scar-forming astrocytes that protect tissue and function after spinal cord injury (SCI). This proposal was based on small, midline stab SCI. Here, we tested the generality of this proposal by using a genetic knock-in cell fate mapping strategy in different murine SCI models. After large crush injuries across the entire spinal cord, ependyma-derived progeny remained local, did not migrate and contributed few cells of any kind and less than 2%, if any, of the total newly proliferated and molecularly confirmed scar-forming astrocytes. Stab injuries that were near to but did not directly damage ependyma, contained no ependyma-derived cells. Our findings show that ependymal contribution of progeny after SCI is minimal, local and dependent on direct ependymal injury, indicating that ependyma are not a major source of endogenous neural stem cells or neuroprotective astrocytes after SCI.

Growth Hormone (GH) and Rehabilitation Promoted Distal Innervation in a Child Affected by Caudal Regression Syndrome

Caudal regression syndrome (CRS) is a malformation occurring during the fetal period and mainly characterized by an incomplete development of the spinal cord (SC), which is often accompanied by other developmental anomalies. We studied a 9-month old child with CRS who presented interruption of the SC at the L2–L3 level, sacral agenesis, a lack of innervation of the inferior limbs (flaccid paraplegia), and neurogenic bladder and bowel. Given the known positive effects of growth hormone (GH) on neural stem cells (NSCs), we treated him with GH and rehabilitation, trying to induce recovery from the aforementioned sequelae. The Gross Motor Function Test (GMFM)-88 test score was 12.31%. After a blood analysis, GH treatment (0.3 mg/day, 5 days/week, during 3 months and then 15 days without GH) and rehabilitation commenced. This protocol was followed for 5 years, the last GH dose being 1 mg/day. Blood analysis and physical exams were performed every 3 months initially and then every 6 months. Six months after commencing the treatment the GMFM-88 score increased to 39.48%. Responses to sensitive stimuli appeared in most of the territories explored; 18 months later sensitive innervation was complete and the patient moved all muscles over the knees and controlled his sphincters. Three years later he began to walk with crutches, there was plantar flexion, and the GMFM-88 score was 78.48%. In summary, GH plus rehabilitation may be useful for innervating distal areas below the level of the incomplete spinal cord in CRS. It is likely that GH acted on the ependymal SC NSCs, as the hormone does in the neurogenic niches of the brain, and rehabilitation helped to achieve practically full functionality.

The Human Central Canal of the Spinal Cord: A Comprehensive Review of its Anatomy, Embryology, Molecular Development, Variants, and Pathology

The human central canal of the spinal cord is often overlooked. However, with advancements in imaging quality, this structure can be visualized in more detail than ever before. Therefore, a timely review of this part of the cord seemed warranted. Using standard search engines, a literature review was performed for the development, anatomy, and pathology involving the central canal. Clinicians who treat patients with issues near the spine or interpret imaging of the spinal cord should be familiar with the morphology and variants of the central canal.

A Review of Stem Cell Therapy for Spinal Cord Injury: Large Animal Models and the Frontier in Humans

OBJECTIVE

To review the literature of spinal cord injury and stem cell therapy for large animal models and incorporate those results into an understanding of stem cell therapy for human cord injury.

METHODS

Review of the literature.

RESULTS

Eleven canine studies were identified and 3 sub-human primate studies were identified showing variable results.

CONCLUSIONS

Stem cell therapy is a promising therapeutic option for patients with spinal cord injury; however, the technology has many un-answered questions and further research is needed.

Wnts Are Expressed in the Ependymal Region of the Adult Spinal Cord

The Wnt family of proteins plays key roles during central nervous system development and in several physiological processes during adulthood. Recently, experimental evidence has linked Wnt-related genes to regulation and maintenance of stem cells in the adult neurogenic niches. In the spinal cord, the ependymal cells surrounding the central canal form one of those niches, but little is known about their Wnt expression patterns. Using microdissection followed by TaqMan® low-density arrays, we show here that the ependymal regions of young, mature rats and adult humans express several Wnt-related genes, including ligands, conventional and non-conventional receptors, co-receptors, and soluble inhibitors. We found 13 genes shared between rats and humans, 4 exclusively expressed in rats and 9 expressed only in humans. Also, we observed a reduction with age on spontaneous proliferation of ependymal cells in rats paralleled by a decrease in the expression of Fzd1, Fzd8, and Fzd9. Our results suggest a role for Wnts in the regulation of the adult spinal cord neurogenic niche and provide new data on the specific differences in this region between humans and rodents.

Spinal cord reconstitution with homologous neural grafts enables robust corticospinal regeneration

The corticospinal tract (CST) is the most important motor system in humans, yet robust regeneration of this projection after spinal cord injury (SCI) has not been accomplished. In murine models of SCI, we report robust corticospinal axon regeneration, functional synapse formation and improved skilled forelimb function after grafting multipotent neural progenitor cells into sites of SCI. Corticospinal regeneration requires grafts to be driven toward caudalized (spinal cord), rather than rostralized, fates. Fully mature caudalized neural grafts also support corticospinal regeneration. Moreover, corticospinal axons can emerge from neural grafts and regenerate beyond the lesion, a process that is potentially related to the attenuation of the glial scar. Rat corticospinal axons also regenerate into human donor grafts of caudal spinal cord identity. Collectively, these findings indicate that spinal cord 'replacement' with homologous neural stem cells enables robust regeneration of the corticospinal projection within and beyond spinal cord lesion sites, achieving a major unmet goal of SCI research and offering new possibilities for clinical translation.

CB1 cannabinoid receptor enrichment in the ependymal region of the adult human spinal cord

Cannabinoids are involved in the regulation of neural stem cell biology and their receptors are expressed in the neurogenic niches of adult rodents. In the spinal cord of rats and mice, neural stem cells can be found in the ependymal region, surrounding the central canal, but there is evidence that this region is largely different in adult humans: lacks a patent canal and presents perivascular pseudorosettes, typically found in low grade ependymomas. Using Laser Capture Microdissection, Taqman gene expression assays and immunohistochemistry, we have studied the expression of endocannabinoid system components (receptors and enzymes) at the human spinal cord ependymal region. We observe that ependymal region is enriched in CB₁ cannabinoid receptor, due to high CB₁ expression in GFAP+ astrocytic domains. However, in human spinal cord levels that retain central canal patency we found ependymal cells with high CB₁ expression, equivalent to the CB₁^HIGH cell subpopulation described in rodents. Our results support the existence of ependymal CB₁^HIGH cells across species, and may encourage further studies on this subpopulation, although only in cases when central canal is patent. In the adult human ependyma, which usually shows central canal absence, CB₁ may play a different role by modulating astrocyte functions.