CB1 cannabinoid receptor enrichment in the ependymal region of the adult human 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.

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.

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.

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.

Spatial distribution of cannabinoid receptor type 1 (CB1) in normal canine central and peripheral nervous system

The endocannabinoid system is a regulatory pathway consisting of two main types of cannabinoid receptors (CB₁ and CB₂) and their endogenous ligands, the endocannabinoids. The CB₁ receptor is highly expressed in the central and peripheral nervous systems (PNS) in mammalians and is involved in neuromodulatory functions. Since endocannabinoids were shown to be elevated in cerebrospinal fluid of epileptic dogs, knowledge about the species specific CB receptor expression in the nervous system is required. Therefore, we assessed the spatial distribution of CB₁ receptors in the normal canine CNS and PNS. Immunohistochemistry of several regions of the brain, spinal cord and peripheral nerves from a healthy four-week-old puppy, three six-month-old dogs, and one ten-year-old dog revealed strong dot-like immunoreactivity in the neuropil of the cerebral cortex, Cornu Ammonis (CA) and dentate gyrus of the hippocampus, midbrain, cerebellum, medulla oblongata and grey matter of the spinal cord. Dense CB₁ expression was found in fibres of the globus pallidus and substantia nigra surrounding immunonegative neurons. Astrocytes were constantly positive in all examined regions. CB₁ labelled neurons and satellite cells of the dorsal root ganglia, and myelinating Schwann cells in the PNS. These results demonstrate for the first time the spatial distribution of CB₁ receptors in the healthy canine CNS and PNS. These results can be used as a basis for further studies aiming to elucidate the physiological consequences of this particular anatomical and cellular distribution.

Rimonabant, a selective cannabinoid1 receptor antagonist, protects against light-induced retinal degeneration in vitro and in vivo

The endocannabinoid system is involved in some neurodegenerative diseases such as Alzheimer's disease. An endogenous constellation of proteins related to cannabinoid₁ receptor signaling, including free fatty acids, diacylglycerol lipase, and N-acylethanolamine-hydrolyzing acid amidase, are localized in the murine retina. Moreover, the expression levels of endogenous agonists of cannabinoid receptors are changed in the vitreous fluid. However, the role of the endocannabinoid system in the retina, particularly in the light-induced photoreceptor degeneration, remains unknown. Therefore, we investigated involvement of the cannabinoid₁ receptor in light-induced retinal degeneration using in vitro and in vivo models. To evaluate the effect of cannabinoid₁ receptors in light irradiation-induced cell death, the mouse retinal cone-cell line (661W) was treated with a cannabinoid₁ receptor antagonist, rimonabant. Time-dependent changes of expression and localization of retinal cannabinoid₁ receptors were measured using Western blot and immunostaining. Retinal damage was induced in mice by exposure to light, followed by intravitreal injection of rimonabant. Electroretinograms and histologic analyses were performed. Rimonabant suppressed light-induced photoreceptor cell death. Cannabinoid₁ receptor expression was upregulated by light exposure. Treatment with rimonabant improved both a- and b-wave amplitudes and the thickness of the outer nuclear layer. These results suggest that the cannabinoid₁ receptor is involved in light-induced retinal degeneration and it may represent a therapeutic target in the light-induced photoreceptor degeneration related diseases.

Allodynia Lowering Induced by Cannabinoids and Endocannabinoids (ALICE)

Neuropathic pain is a neurological disorder that strongly affects the quality of life of patients. The molecular and cellular mechanisms at the basis of the neuropathic pain establishment still need to be clarified. Among the neuromodulators that play a role in the pathological pain pathways, endocannabinoids could be deeply involved in both neuronal and non-neuronal mechanisms responsible for the appearance of tactile allodynia. Indeed, the function and dysfunction of this complex system in the molecular and cellular mechanisms of chronic pain induction and maintenance have been widely studied over the last two decades. In this review article, we highlighted the possible modulation of the endocannabinoid system in the neuronal, glial and microglial modulation in neuropathic pain treatment.

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.