Wnt-3a protein promote neuronal differentiation of neural stem cells derived from adult mouse spinal cord

Regulating Endogenous Neural Stem Cell Activation to Promote Spinal Cord Injury Repair

Spinal cord injury (SCI) affects millions of individuals worldwide. Currently, there is no cure, and treatment options to promote neural recovery are limited. An innovative approach to improve outcomes following SCI involves the recruitment of endogenous populations of neural stem cells (NSCs). NSCs can be isolated from the neuroaxis of the central nervous system (CNS), with brain and spinal cord populations sharing common characteristics (as well as regionally distinct phenotypes). Within the spinal cord, a number of NSC sub-populations have been identified which display unique protein expression profiles and proliferation kinetics. Collectively, the potential for NSCs to impact regenerative medicine strategies hinges on their cardinal properties, including self-renewal and multipotency (the ability to generate de novo neurons, astrocytes, and oligodendrocytes). Accordingly, endogenous NSCs could be harnessed to replace lost cells and promote structural repair following SCI. While studies exploring the efficacy of this approach continue to suggest its potential, many questions remain including those related to heterogeneity within the NSC pool, the interaction of NSCs with their environment, and the identification of factors that can enhance their response. We discuss the current state of knowledge regarding populations of endogenous spinal cord NSCs, their niche, and the factors that regulate their behavior. In an attempt to move towards the goal of enhancing neural repair, we highlight approaches that promote NSC activation following injury including the modulation of the microenvironment and parenchymal cells, pharmaceuticals, and applied electrical stimulation.

Comparison of the differentiation of dental pulp stem cells and periodontal ligament stem cells into neuron-like cells and their effects on focal cerebral ischemia

Recent studies have reported an increasing incidence of ischemic stroke, particularly in younger age groups. Dental pulp stem cells (DPSCs) and periodontal ligament stem cells (PDLSCs) are the most common stem cells acquired from the teeth of adults, even elderly people. However, there are no detailed reports on whether DPSCs or PDLSCs are suitable for the treatment of ischemic stroke. In this study, the in vitro differentiation of DPSCs and PDLSCs into neuron-like cells was evaluated. Then, we established a rat model of cerebral ischemia. DPSCs or PDLSCs were administered to animals, and the therapeutic effects of these two types of cells were investigated. The results showed that PDLSCs had a higher differentiation rate than DPSCs. Immunofluorescence studies showed that the expression of the neuronal differentiation marker Thy-1 was higher in PDLSCs than in DPSCs, and other gene markers of neuronal differentiation showed corresponding trends, which were confirmed by western blot analysis. In this process, the Notch and Wnt signaling pathways were inhibited and activated, respectively. Finally, rats with transient occlusion of the right middle cerebral artery were used as a model to assess the therapeutic effect of PDLSCs and DPSCs on ischemia. The results showed that rats in the PDLSC-treated group emitted significantly greater red fluorescence signal than the DPSC-treated group. PDLSC transplantation promoted the recovery of neurological function more effectively than DPSC transplantation. Hence, PDLSCs represent an autogenous source of adult mesenchymal stem cells with desirable biological properties and may be an ideal candidate for clinical applications.

Potential Effects of MSC-Derived Exosomes in Neuroplasticity in Alzheimer's Disease

Alzheimer’s disease (AD) is the most common type of dementia affecting regions of the central nervous system that exhibit synaptic plasticity and are involved in higher brain functions such as learning and memory. AD is characterized by progressive cognitive dysfunction, memory loss and behavioral disturbances of synaptic plasticity and energy metabolism. Cell therapy has emerged as an alternative treatment of AD. The use of adult stem cells, such as neural stem cells and Mesenchymal Stem Cells (MSCs) from bone marrow and adipose tissue, have the potential to decrease cognitive deficits, possibly by reducing neuronal loss through blocking apoptosis, increasing neurogenesis, synaptogenesis and angiogenesis. These processes are mediated primarily by the secretion of many growth factors, anti-inflammatory proteins, membrane receptors, microRNAs (miRNA) and exosomes. Exosomes encapsulate and transfer several functional molecules like proteins, lipids and regulatory RNA which can modify cell metabolism. In the proteomic characterization of the content of MSC-derived exosomes, more than 730 proteins have been identified, some of which are specific cell type markers and others are involved in the regulation of binding and fusion of exosomes with adjacent cells. Furthermore, some factors were found that promote the recruitment, proliferation and differentiation of other cells like neural stem cells. Moreover, within exosomal cargo, a wide range of miRNAs were found, which can control functions related to neural remodeling as well as angiogenic and neurogenic processes. Taking this into consideration, the use of exosomes could be part of a strategy to promote neuroplasticity, improve cognitive impairment and neural replacement in AD. In this review, we describe how exosomes are involved in AD pathology and discuss the therapeutic potential of MSC-derived exosomes mediated by miRNA and protein cargo.

Maternal exposure to prostaglandin E2 modifies expression of Wnt genes in mouse brain - An autism connection

Prostaglandin E₂ (PGE₂) is a lipid signaling molecule important for brain development and function. Various genetic and environmental factors can influence the level of PGE₂ and increase the risk of developing Autism Spectrum Disorder (ASD). We have previously shown that in neuronal cell lines and mouse brain, PGE₂ can interfere with the Wnt canonical pathway, which is essential during early brain development. Higher levels of PGE₂ increased Wnt-dependent motility and proliferation of neuroectodermal stem cells, and modified the expression of Wnt genes previously linked to autism disorders. We also recently established a cross-talk between these two pathways in the prenatal mouse brain lacking PGE₂ producing enzyme (COX^-/-). The current study complements the published data and reveals that PGE₂ signaling also converges with the Wnt canonical pathway in the developing mouse brain after maternal exposure to PGE₂ at the onset of neurogenesis. We found significant changes in the expression level of Wnt-target genes, Mmp7, Wnt2, and Wnt3a, during prenatal and early postnatal stages. Interestingly, we observed variability in the expression level of these genes between genetically-identical pups within the same pregnancy. Furthermore, we found that all the affected genes have been previously associated with disorders of the central nervous system, including autism. We determined that prenatal exposure to PGE₂ affects the Wnt pathway at the level of β-catenin, the major downstream regulator of Wnt-dependent gene transcription. We discuss how these results add new knowledge into the molecular mechanisms by which PGE₂ may interfere with neuronal development during critical periods.

Neuroprotective and regenerative roles of intranasal Wnt-3a administration after focal ischemic stroke in mice

Wnt signaling is a conserved pathway involved in expansion of neural progenitors and lineage specification during development. However, the role of Wnt signaling in the post-stroke brain has not been well-elucidated. We hypothesized that Wnt-3a would play an important role for neurogenesis and brain repair. Adult male mice were subjected to a focal ischemic stroke targeting the sensorimotor cortex. Mice that received Wnt-3a (2 µg/kg/day, 1 h after stroke and once a day for the next 2 days, intranasal delivery) had reduced infarct volume compared to stroke controls. Wnt-3a intranasal treatment of seven days upregulated the expression of brain-derived growth factor (BDNF), increased the proliferation and migration of neuroblasts from the subventricular zone (SVZ), resulting in increased numbers of newly formed neurons and endothelial cells in the peri-infarct zone. Both the molecular and cellular effects of Wnt-3a were blocked by the Wnt specific inhibitors XAV-939 or Dkk-1. In functional assays, Wnt-3a treatment enhanced the local cerebral blood flow (LCBF) in the peri-infarct, as well as improved sensorimotor functions in a battery of behavioral tests. Together, our data demonstrates that the Wnt-3a signaling can act as a dual neuroprotective and regenerative factor for the treatment of ischemic stroke.

Erythropoietin signaling increases neurogenesis and oligodendrogenesis of endogenous neural stem cells following spinal cord injury both in vivo and in vitro

Erythropoietin (Epo) promotes functional recovery following spinal cord injury (SCI); however, the exact underlying mechanisms are yet to be determined. Although endogenous neural stem cells (NSCs) in the adult spinal cord are a therapeutic target in SCI models, the effect of Epo on this NSC population remains unknown. The present study investigated the effects of Epo on endogenous NSCs in the adult spinal cord both in vitro and in vivo. For the in vivo analyses, normal rats (Normal) and SCI contusion model rats (SCI) received either recombinant human Epo or saline treatment for 7 days (5,000 U/kg), and spinal cords were subsequently analyzed at 2, 8, and 14 days. For in vitro analyses, NSCs harvested from adult rat spinal cords were exposed to Epo (10 U/ml). A significant increase in β-tubulin⁺ new neurons (P<0.01) was observed at all three time points and O4⁺ new oligodendrocytes (P<0.05) at days 8 and 14 in the SCI+Epo group compared with the SCI+Saline group. This was concomitant with a prolonged activation of Epo signaling; however, no effect on NSCs proliferation was observed. Similar results were also obtained in vitro. Motor functional recovery was also noted at days 8 and 14 only in the Epo-treated SCI rats. Although the expression of Epo and EpoR significantly increased in Normal+Epo rats compared with Normal+Saline rats (P<0.05), the cell numbers and phenotype were comparable between the two groups. To the best of the author's knowledge, this is the first study to demonstrate that Epo signaling promotes both neurogenesis and oligodendrogenesis following SCI and that these may represent the underlying mechanisms for the functional recovery and therapeutic effects of Epo following SCI.

Effects of acupuncture on cortical expression of Wnt3a, β-catenin and Sox2 in a rat model of traumatic brain injury

OBJECTIVE

To observe the effects of acupuncture treatment on the expression of Wnt/β-catenin signalling pathway-related genes (Wnt3a, β-catenin and Sox2) in the injured cerebral cortex of rats with traumatic brain injury (TBI).

METHODS

A controlled impact model of TBI was established using Feeney's free-drop method. Seventy-eight Sprague-Dawley rats were randomly divided into the following three groups: a normal group (n=18) that was left untreated; a model group (n=30) that received no treatment after TBI; and an acupuncture group (n=30) that received acupuncture (at LI4, GV20, GV26 and GV16) after TBI. Rats in each group were randomly and equally divided into 3-day, 7-day and 14-day subgroups according to the duration of therapy. Real-time fluorescence quantitative PCR (RT-qPCR) was used to measure mRNA expression of Wnt3a, β-catenin and Sox2. Western blots were performed to determine the expression levels of WNT3a, β-Catenin and SOX2.

RESULTS

Wnt3a mRNA was upregulated in the 7-day and 14-day acupuncture subgroups compared with the corresponding model subgroups (p<0.05). β-catenin expression was significantly increased in the 7-day and 14-day acupuncture subgroups compared with the corresponding model subgroups (p<0.01). In the 3-day and 7-day acupuncture subgroups, Sox2 expression was significantly higher than that in the normal and model groups (p<0.01 each). The levels of WNT3a, β-catenin and SOX2 were generally consistent with the corresponding mRNA levels.

CONCLUSIONS

Acupuncture exerts a regulatory effect on the Wnt/β-catenin signalling pathway, which may in turn influence the proliferation and differentiation of endogenous neural stem cells.

Apoptosis in glioma-bearing rats after neural stem cell transplantation

Abnormal activation of the Ras/Raf/Mek/Erk signaling cascade plays an important role in glioma. Inhibition of this aberrant activity could effectively hinder glioma cell proliferation and promote cell apoptosis. To investigate the mechanism of glioblastoma treatment by neural stem cell transplantation with respect to the Ras/Raf/Mek/Erk pathway, C6 glioma cells were prepared in suspension and then infused into the rat brain to establish a glioblastoma model. Neural stem cells isolated from fetal rats were then injected into the brain of this glioblastoma model. Results showed that Raf-1, Erk and Bcl-2 protein expression significantly increased, while Caspase-3 protein expression decreased. After transplantation of neural stem cells, Raf-1, Erk and Bcl-2 protein expression significantly decreased, while Caspase-3 protein expression significantly increased. Our findings indicate that transplantation of neural stem cells may promote apoptosis of glioma cells by inhibiting Ras/Raf/Mek/Erk signaling, and thus may represent a novel treatment approach for glioblastoma.

Chordin-like protein 1 promotes neuronal differentiation by inhibiting bone morphogenetic protein-4 in neural stem cells

In the present study, the effects of chordin‑like protein 1 (CHRDL1) overexpression, together with bone morphogenetic protein‑4 (BMP‑4) treatment, on the differentiation of rat spinal cord‑derived neural stem cells (NSCs) was investigated. Adult rat spinal cord‑derived NSCs were cultured in serum‑free medium. The recombined eukaryotic expression vector pSecTag2/Hygro B‑CHRDL1 was transfected into adult rat spinal cord‑derived NSCs using a lipid‑based transfection reagent and protein expression was assessed by western blot analysis. Differentiation of transfected NSCs following BMP‑4 treatment was determined by immunocytochemistry. The percentage of microtubule‑associated protein‑2 (MAP‑2)‑positive cells in the BMP‑4‑treated (B) group was found to be significantly lower compared with that in the non‑transfected control (N) group. The percentage of MAP‑2‑positive cells in the pSecTag2/Hygro B‑CHRDL1‑transfected, BMP‑4‑treated group was identified to be significantly higher compared with that in group B, however, no significant difference was observed between group N and the transfected, non‑BMP‑4‑treated control group. The current study indicates that CHRDL1 protein antagonizes BMP‑4 activity and induces spinal cord‑derived NSCs to differentiate into neurons.

Differential expression of Wnts after spinal cord contusion injury in adult rats

BACKGROUND

Spinal cord injury is a major cause of disability that has no clinically accepted treatment. Functional decline following spinal cord injury is caused by mechanical damage, secondary cell death, reactive gliosis and a poor regenerative capacity of damaged axons. Wnt proteins are a family of secreted glycoproteins that play key roles in different developmental processes although little is known of the expression patterns and functions of Wnts in the adult central nervous system in normal or diseased states.

FINDINGS

Using qRT-PCR analysis, we demonstrate that mRNA encoding most Wnt ligands and soluble inhibitors are constitutively expressed in the healthy adult spinal cord. Strikingly, contusion spinal cord injury induced a time-dependent increase in Wnt mRNA expression from 6 hours until 28 days post-injury, and a narrow peak in the expression of soluble Wnt inhibitors between 1 and 3 days post-injury. These results are consistent with the increase in the migration shift, from day 1 to 7, of the intracellular Wnt signalling component, Dishevelled-3. Moreover, after an initial decrease by 1 day, we also found an increase in phosphorylation of the Wnt co-receptor, low-density lipoprotein receptor-related protein 6, and an increase in active β-catenin protein, both of which suffer a dramatic change, from a homogeneous expression pattern in the grey matter to a disorganized injury-induced pattern.

CONCLUSIONS

Our results suggest a role for Wnts in spinal cord homeostasis and injury. We demonstrate that after injury Wnt signalling is activated via the Wnt/β-catenin and possibly other pathways. These findings provide an important foundation to further address the function of individual Wnt proteins in vivo and the pathophysiology of spinal cord injury.

Endogenous Wnt signaling maintains neural progenitor cell potency

Wnt signaling regulates neural stem cell (NSC) function and development throughout an individual's lifetime. Intriguingly, adult hippocampal progenitors (AHPs) produce several Wnts, and the intracellular machinery necessary to respond to them, creating the potential for an active autocrine-signaling loop within this stem cell niche. However, the standard luciferase-based Wnt assay failed to detect this signaling loop. This assay is inherently less temporally sensitive to activity among a population of unsynchronized proliferating cells because it relies on the rapidly degrading reporter luciferase. We circumvented this limitation using a promoter assay that employs green fluorescent protein (GFP), as a relatively long-lived reporter of canonical Wnt activity. We found that at baseline, AHPs secreted functional Wnt that self-stimulates low-level canonical Wnt signaling. Elimination baseline Wnt activity, via application of an extracellular Wnt antagonist promoted neurogenesis, based on a combination of unbiased gene expression analysis and cell-fate analysis. A detailed clonal analysis of progenitors transduced with specific intracellular antagonists of canonical signaling, either Axin or truncated cadherin (beta-catenin sequestering), revealed that loss of baseline signaling depletes the population of multipotent precursors, thereby driving an increasing fraction to assume a committed cell fate (i.e., unipotent progenitors). Similarly, baseline Wnt signaling repressed differentiation of human NSCs. Although the specific Wnts produced by neural precursors vary with age and between species, their effects remain remarkably consistent. In sum, this study establishes that autonomous Wnt signaling is a conserved feature of the neurogenic niche that preserves the delicate balance between NSC maintenance and differentiation.