Conditioned Medium of Wnt/β-Catenin Signaling-Activated Olfactory Ensheathing Cells Promotes Synaptogenesis and Neurite Growth In Vitro

Challenges in corneal endothelial cell culture

Corneal endothelial cells (CECs) facilitate the function of maintaining the transparency of the cornea. Damage or dysfunction of CECs can lead to blindness, and the primary treatment is corneal transplantation. However, the shortage of cornea donors is a significant problem worldwide. Thus, cultured CEC therapy has been proposed and found to be a promising approach to overcome the lack of tissue supply. Unfortunately, CECs in humans rarely proliferate in vivo and, therefore, can be extremely challenging to culture in vitro. Several promising cell isolation and culture techniques have been proposed. Multiple factors affecting the success of cell expansion including donor characteristics, preservation and isolation methods, plating density, media preparation, transdifferentiation and biomarkers have been evaluated. However, there is no consensus on standard technique for CEC culture. This review aimed to determine the challenges and investigate potential options that would facilitate the standardization of CEC culture for research and therapeutic application.

Olfactory Ensheathing Cells express both Ghrelin and Ghrelin Receptor in vitro: a new hypothesis in favor of a neurotrophic effect

Olfactory Ensheathing Cells (OECs) are glial cells able to secrete different neurotrophic growth factors and thus promote axonal growth, also acting as a mechanical support. In the olfactory system, during development, they drive the non-myelinated axons of the Olfactory Receptor Neurons (ORNs) towards the Olfactory Bulb (OB). Ghrelin (Ghre), a gut-brain peptide hormone, and its receptor (GHS-R 1a) are expressed in different parts of the central nervous system. In the last few years, this peptide has stimulated particular interest as results show it to be a neuroprotective factor with antioxidant, anti-inflammatory and anti-apoptotic properties. Our previous studies showed that OB mitral cells express Ghre, thus being able to play an important role in regulating food behavior in response to odors. In this study, we investigated the presence of Ghre and GHS-R 1a in primary mouse OECs. The expression of both Ghre and its receptor was assessed by an immunocytochemical technique, Western Blot and Polymerase Chain Reaction (PCR) analysis. Our results demonstrated that OECs are able to express both Ghre and GHS-R 1a and that these proteins are detectable after extensive passages in vitro; in addition, PCR analysis further confirmed these data. Therefore, we can hypothesize that Ghre and GHS-R 1a interact with a reinforcement function, in the peripheral olfactory circuit, providing a neurotrophic support to the synaptic interaction between ORNs and mitral cells.

Characterization of the iPSC-derived conditioned medium that promotes the growth of bovine corneal endothelial cells

Corneal endothelial cells (CECs) maintain corneal transparency and visual acuity. However, the limited proliferative capability of these cells in vitro has prompted researchers to find efficient culturing techniques for them. The aim of our study was to evaluate the use of conditioned medium (CM) obtained from induced pluripotent stem cells (iPSCs) as a source for the effective proliferation of bovine CECs (B-CECs). In our study, the proliferative ability of B-CECs was moderately enhanced when the cells were grown in 25% iPSC conditioned medium (iPSC-CM). Additionally, hexagonal cell morphology was maintained until passage 4, as opposed to the irregular and enlarged shape observed in control corneal endothelial medium (CEM). B-CECs in both the 25% iPSC-CM and CEM groups expressed and Na+-K+-ATPase. The gene expression levels of NIFK, Na+-K+-ATPase, Col4A and Col8A and the percentage of cells entering S and G2 phases were higher in the iPSC-CM group. The number of apoptotic cells also decreased in the iPSC-CM group. In comparison to the control cultures, iPSC-CM facilitated cell migration, and these cells showed better barrier functions after several passages. The mechanism of cell proliferation mediated by iPSC-CM was also investigated, and phosphorylation of Akt was observed in B-CECs after exposure to iPSC-CM and showed sustained phosphorylation induced for up to 180 min in iPSC-CM. Our findings indicate that iPSC-CM may employ PI3-kinase signaling in regulating cell cycle progression, which can lead to enhanced cellular proliferation. Effective component analysis of the CM showed that in the iPSC-CM group, the expression of activin-A was significantly increased. If activin-A is added as a supplement, it could help to maintain the morphology of the cells, similar to that of CM. Hence, we conclude that activin-A is one of the effective components of CM in promoting cell proliferation and maintaining cell morphology.

Harpagide inhibits neuronal apoptosis and promotes axonal regeneration after spinal cord injury in rats by activating the Wnt/β-catenin signaling pathway

The neuronal apoptosis program associated with spinal cord injury (SCI) has a severe impact on spinal cord function, which leads to further secondary and permanent neuronal damage that may cause irreparable damage to the central nervous system. Activation of the Wnt/β-catenin signaling pathway is effective in reducing apoptosis and preventing SCI. Harpagide is one of the main active constituents of the iridoid class of molecules, which have neuroprotective effects after SCI. In this study, we demonstrated that harpagide attenuated neuronal apoptosis via activation of the Wnt/β-catenin signaling pathway. This resulted in a promotion of axonal regeneration and an inhibition of glial scar formation, which ultimately improved functional behavioral recovery after SCI in rats. Specifically, the administration of harpagide after SCI increased the expression levels of β-catenin, c-myc and cyclin D1 proteins in spinal cord neurons, as well as increased the number of motor neurons and reduced the size of the SCI lesion area. In addition, the administration of harpagide after SCI also decreased the protein expression levels as well as the number of cells immuno-stained for the pro-apoptotic proteins Bax and cleaved-caspase 3. The expression level of the anti-apoptotic protein Bcl-2 was also increased. When the Wnt /β-catenin signaling pathway was inhibited, a weakened anti-apoptotic effect of harpagide was observed. Additionally, the application of harpagide led to an increase in NF200 staining and a reduction in GFAP staining in the SCI injury site. In summary, our study suggested that harpagide may be a promising drug for the treatment of SCI.

MicroRNA‑381/Hes1 is a potential therapeutic target for spinal cord injury

The aim of the present study was to investigate whether microRNA‑381 is a potential therapeutic target for spinal cord injury (SCI) and its possible mechanism. Reverse transcription quantitative polymerase chain reaction (qPCR) for mRNA expression was used to analyze the changes of microRNA-381 expression. Cell viability and cell apoptosis were measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry. Caspase‑3 activity was measured using caspase‑3 activity kit, and western blot analysis was used to measure the protein expression of neurogenic locus notch homolog protein 1 (Notch1), notch 1 intracellular domain (NICD) and transcription factor HES-1 (Hes1). The data showed that microRNA‑381 expression of model SCI rats was downregulated compared with that of control rats. Overexpression of microRNA‑381 promoted cell proliferation, and inhibited apoptosis and caspase‑3 and apoptosis regulator BAX (Bax) protein expression in neurocytes. Overexpression of microRNA‑381 also increased Wnt and β‑catenin protein expression, and suppressed the protein expression of Notch1, NICD and Hes1 in neurocytes. Wnt inhibitor, Wnt‑C59 (1 µmol/l), inhibited cell proliferation, promoted apoptosis and caspase‑3 and Bax protein expression, suppressed β‑catenin protein expression and induced Hes1 protein expression in neurocytes following microRNA‑381 overexpression. Notch inhibitor, FLI‑06 (1 µmol/l), promoted cell proliferation, inhibited apoptosis and caspase‑3 and Bax protein expression, and suppressed NICD and Hes1 protein expression in neurocytes following microRNA‑381 overexpression. Thus, this study showed that overexpression of microRNA‑381 promotes cell proliferation of neurocytes in SCI via Hes1 expression, which may be a novel important mechanism for SCI in clinical applications.

A growing field: The regulation of axonal regeneration by Wnt signaling

The canonical Wnt/β-catenin pathway is a highly conserved signaling cascade that plays critical roles during embryogenesis. Wnt ligands regulate axonal extension, growth cone guidance and synaptogenesis throughout the developing central nervous system (CNS). Recently, studies in mammalian and fish model systems have demonstrated that Wnt/β-catenin signaling also promotes axonal regeneration in the adult optic nerve and spinal cord after injury, raising the possibility that Wnt could be developed as a therapeutic strategy. In this review, we summarize experimental evidence that reveals novel roles for Wnt signaling in the injured CNS, and discuss possible mechanisms by which Wnt ligands could overcome molecular barriers inhibiting axonal growth to promote regeneration. A central challenge in the neuroscience field is developing therapeutic strategies that induce robust axonal regeneration. Although adult axons have the capacity to respond to axonal guidance molecules after injury, there are several major obstacles for axonal growth, including extensive neuronal death, glial scars at the injury site, and lack of axonal guidance signals. Research in rodents demonstrated that activation of Wnt/β-catenin signaling in retinal neurons and radial glia induced neuronal survival and axonal growth, but that activation within reactive glia at the injury site promoted proliferation and glial scar formation. Studies in zebrafish spinal cord injury models confirm an axonal regenerative role for Wnt/β-catenin signaling and identified the cell types responsible. Additionally, in vitro and in vivo studies demonstrated that Wnt induces axonal and neurite growth through transcription-dependent effects of its central mediator β-catenin, potentially by inducing regeneration-promoting genes. Canonical Wnt signaling may also function through transcription-independent interactions of β-catenin with cytoskeletal elements, which could stabilize growing axons and control growth cone movement. Therefore, these studies suggest that Wnt-induced pathways responsible for regulating axonal growth during embryogenesis could be repurposed to promote axonal growth after injury.

Melatonin Inhibits Neural Cell Apoptosis and Promotes Locomotor Recovery via Activation of the Wnt/β-Catenin Signaling Pathway After Spinal Cord Injury

The spinal cord is highly sensitive to spinal cord injury (SCI) by external mechanical damage, resulting in irreversible neurological damage. Activation of the Wnt/β-catenin signaling pathway can effectively reduce apoptosis and protect against SCI. Melatonin, an indoleamine originally isolated from bovine pineal tissue, exerts neuroprotective effects after SCI through activation of the Wnt/β-catenin signaling pathway. In this study, we demonstrated that melatonin exhibited neuroprotective effects on neuronal apoptosis and supported functional recovery in a rat SCI model by activating the Wnt/β-catenin signaling pathway. We found that melatonin administration after SCI significantly upregulated the expression of low-density lipoprotein receptor related protein 6 phosphorylation (p-LRP-6), lymphoid enhancer factor-1 (LEF-1) and β-catenin protein in the spinal cord. Melatonin enhanced motor neuronal survival in the spinal cord ventral horn and improved the locomotor functions of rats after SCI. Melatonin administration after SCI also reduced the expression levels of Bax and cleaved caspase-3 in the spinal cord and the proportion of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) positive cells, but increased the expression level of Bcl-2. These results suggest that melatonin attenuated SCI by activating the Wnt/β-catenin signaling pathway.

Lentiviral Modulation of Wnt/β-Catenin Signaling Affects In Vivo LTP

Wnt signaling is involved in hippocampal development and synaptogenesis. Numerous recent studies have been focused on the role of Wnt ligands in the regulation of synaptic plasticity. Inhibitors and activators of canonical Wnt signaling were demonstrated to decrease or increase, respectively, in vitro long-term potentiation (LTP) maintenance in hippocampal slices (Chen et al. in J Biol Chem 281:11910-11916, 2006; Vargas et al. in J Neurosci 34:2191-2202, 2014, Vargas et al. in Exp Neurol 264:14-25, 2015). Using lentiviral approach to down- and up-regulate the canonical Wnt signaling, we explored whether Wnt/β-catenin signaling is critical for the in vivo LTP. Chronic suppression of Wnt signaling induced an impairment of in vivo LTP expression 14 days after lentiviral suspension injection, while overexpression of Wnt3 was associated with a transient enhancement of in vivo LTP magnitude. Both effects were related to the early phase LTP and did not affect LTP maintenance. A loss-of-function study demonstrated decreased initial paired pulse facilitation ratio, β-catenin, and phGSK-3β levels. A gain-of-function study revealed not only an increase in PSD-95, β-catenin, and Cyclin D1 protein levels, but also a reduced phGSK-3β level and enhanced GSK-3β kinase activity. These results suggest a presynaptic dysfunction predominantly underlying LTP impairment while postsynaptic modifications are primarily involved in transient LTP amplification. This study is the first demonstration of the involvement of Wnt/β-catenin signaling in synaptic plasticity regulation in an in vivo LTP model.

N-cadherin regulates beta-catenin signal and its misexpression perturbs commissural axon projection in the developing chicken spinal cord

N-cadherin is a calcium-sensitive cell adhesion molecule that plays an important role in the formation of the neural circuit and the development of the nervous system. In the present study, we investigated the function of N-cadherin in cell-cell connection in vitro with HEK293T cells, and in commissural axon projections in the developing chicken spinal cord using in ovo electroporation. Cell-cell connections increased with N-cadherin overexpression in HEK293T cells, while cell contacts disappeared after co-transfection with an N-cadherin-shRNA plasmid. The knockdown of N-cadherin caused the accumulation of β-catenin in the nucleus, supporting the notion that N-cadherin regulates β-catenin signaling in vitro. Furthermore, N-cadherin misexpression perturbed commissural axon projections in the spinal cord. The overexpression of N-cadherin reduced the number of axons that projected alongside the contralateral margin of the floor plate, and formed intermediate longitudinal commissural axons. In contrast, the knockdown of N-cadherin perturbed commissural axon projections significantly, affecting the projections alongside the contralateral margin of the floor plate, but did not affect intermediate longitudinal commissural axons. Taken together, these findings suggest that N-cadherin regulates commissural axon projections in the developing chicken spinal cord.

Simvastatin inhibits neural cell apoptosis and promotes locomotor recovery via activation of Wnt/β-catenin signaling pathway after spinal cord injury

Statins exhibit neuroprotective effects after spinal cord injury (SCI). However, the molecular mechanism underlying these effects remains unknown. This study demonstrates that the hydroxymethylglutaryl coenzyme A reductase inhibitor simvastatin (Simv) exhibits neuroprotective effects on neuronal apoptosis and supports functional recovery in a rat SCI model by activating the Wnt/β‐catenin signaling pathway. In specific, Simv administration after SCI significantly up‐regulated the expression of low density lipoprotein receptor‐related protein 6 phosphorylation and β‐catenin protein, increased the mRNA expression of lymphoid enhancer factor‐1 and T‐cell factor‐1, and suppressed the expression of β‐catenin phosphorylation in the spinal cord neurons. Simv enhanced motor neuronal survival in the spinal cord anterior horn and decreased the lesion of spinal cord tissues after SCI. Simv administration after SCI also evidently reduced the expression levels of Bax, active caspase‐3, and active caspase‐9 in the spinal cord neurons and the proportion of transferase UTP nick end labeling (TUNEL)‐positive neuron cells, but increased the expression level of Bcl‐2 in the spinal cord neurons. However, the anti‐apoptotic effects of Simv were reduced in cultured spinal cord nerve cells when the Wnt/β‐catenin signaling pathway was suppressed in the lipopolysaccharide‐induced model. Furthermore, the Basso, Beattie, and Bresnahan scores indicated that Simv treatment significantly improved the locomotor functions of rats after SCI. This study is the first to report that Simv exerts neuroprotective effects by reducing neuronal apoptosis, and promoting functional and pathological recovery after SCI by activating the Wnt/β‐catenin signaling pathway.

We verified the neuroprotective properties associated with simvastatin following spinal cord injury (SCI). Simvastatin reduced neuronal apoptosis, improved the functional and pathological recovery via activating Wnt/β‐catenin signal pathway, however, the anti‐apoptosis effects of simvastatin were reversed following suppressing Wnt/β‐catenin signaling pathway in primary spinal cord neurons. The significant findings may provide clinical therapeutic value of simvastatin for treating SCI.

Methylprednisolone promotes recovery of neurological function after spinal cord injury: association with Wnt/β-catenin signaling pathway activation

Some studies have indicated that the Wnt/β-catenin signaling pathway is activated following spinal cord injury, and expression levels of specific proteins, including low-density lipoprotein receptor related protein-6 phosphorylation, β-catenin, and glycogen synthase kinase-3β, are significantly altered. We hypothesized that methylprednisolone treatment contributes to functional recovery after spinal cord injury by inhibiting apoptosis and activating the Wnt/β-catenin signaling pathway. In the current study, 30 mg/kg methylprednisolone was injected into rats with spinal cord injury immediately post-injury and at 1 and 2 days post-injury. Basso, Beattie, and Bresnahan scores showed that methylprednisolone treatment significantly promoted locomotor functional recovery between 2 and 6 weeks post-injury. The number of surviving motor neurons increased, whereas the lesion size significantly decreased following methylprednisolone treatment at 7 days post-injury. Additionally, caspase-3, caspase-9, and Bax protein expression levels and the number of apoptotic cells were reduced at 3 and 7 days post-injury, while Bcl-2 levels at 7 days post-injury were higher in methylprednisolone-treated rats compared with saline-treated rats. At 3 and 7 days post-injury, methylprednisolone up-regulated expression and activation of the Wnt/β-catenin signaling pathway, including low-density lipoprotein receptor related protein-6 phosphorylation, β-catenin, and glycogen synthase kinase-3β phosphorylation. These results indicate that methylprednisolone-induced neuroprotection may correlate with activation of the Wnt/β-catenin signaling pathway.