Ghrelin promotes midbrain neural stem cells differentiation to dopaminergic neurons through Wnt/β-catenin pathway

Ghrelin plays a neuroprotective role in the process of dopaminergic (DAergic) neurons degeneration in Parkinson's disease (PD). However, it still largely unknown whether ghrelin could affect the midbrain neural stem cells (mbNSCs) from which DAergic neurons are originated. In the present study, we observed that ghrelin enhanced mbNSCs proliferation, and promoted neuronal differentiation especially DAergic neuron differentiation both in vitro and ex vivo. The messenger RNA levels of Wnt1, Wnt3a, and glial cell line-derived neurotrophic factor were increased in response to the ghrelin treatment. Results showed that Wnt/β-catenin pathway was relevant to this DAergic neuron differentiation induced by ghrelin. Our finding gave a new evidence that ghrelin may enable clinical therapies for PD by its neurogenesis role.     

Wnt/β‐catenin signalling pathway mediated aberrant hippocampal neurogenesis in kainic acid‐induced epilepsy

Temporal lobe epilepsy is a chronic disorder of nerve system, mainly characterized by hippocampal sclerosis with massive neuronal loss and severe gliosis. Aberrant neurogenesis has been shown in the epileptogenesis process of temporal lobe epilepsy. However, the molecular mechanisms underlying aberrant neurogenesis remain unclear. The roles of Wnt signalling cascade have been well established in neurogenesis during multiple aspects. Here, we used kainic acid‐induced rat epilepsy model to investigate whether Wnt/β‐catenin signalling pathway is involved in the aberrant neurogenesis in temporal lobe epilepsy. Immunostaining and western blotting results showed that the expression levels of β‐catenin, Wnt3a, and cyclin D1, the key regulators in Wnt signalling pathway, were up‐regulated during acute epilepsy induced by the injection of kainic acids, indicating that Wnt signalling pathway was activated in kainic acid‐induced temporal lobe epilepsy. Moreover, BrdU labelling results showed that blockade of the Wnt signalling by knocking down β‐catenin attenuated aberrant neurogenesis induced by kainic acids injection. Altogether, Wnt/β‐catenin signalling pathway mediated hippocampal neurogenesis during epilepsy, which might provide new strategies for clinical treatment of temporal lobe epilepsy. Temporal lobe epilepsy is a chronic disorder of nerve system, mainly characterized by hippocampal sclerosis. Aberrant neurogenesis has been shown to involve in the epileptogenesis process of temporal lobe epilepsy. In the present study, we discovered that Wnt3a/β‐catenin signalling pathway serves as a link between aberrant neurogenesis and underlying remodelling in the hippocampus, leading to temporal lobe epilepsy, which might provide new strategies for clinical treatment of temporal lobe epilepsy.     

Dopaminergic neurotoxicity of S‐ethyl N,N‐dipropylthiocarbamate (EPTC), molinate,and S‐methyl‐N,N‐diethylthiocarbamate (MeDETC) in Caenorhabditis elegans

Epidemiological studies corroborate a correlation between pesticide use and Parkinson's disease (PD). Thiocarbamate and dithiocarbamate pesticides are widely used and produce neurotoxicity in the peripheral nervous system. Recent evidence from rodent studies suggests that these compounds also cause dopaminergic (DAergic) dysfunction and altered protein processing, two hallmarks of PD. However, DAergic neurotoxicity has yet to be documented. We assessed DAergic dysfunction in Caenorhabditis elegans (C. elegans) to investigate the ability of thiocarbamate pesticides to induce DAergic neurodegeneration. Acute treatment with either S‐ethyl N,N‐dipropylthiocarbamate (EPTC), molinate, or a common reactive intermediate of dithiocarbamate and thiocarbamate metabolism, S‐methyl‐N,N‐diethylthiocarbamate (MeDETC), to gradual loss of DAergic cell morphology and structure over the course of 6 days in worms expressing green fluorescent protein (GFP) under a DAergic cell specific promoter. HPLC analysis revealed decreased DA content in the worms immediately following exposure to MeDETC, EPTC, and molinate. In addition, worms treated with the three test compounds showed a drastic loss of DAergic‐dependent behavior over a time course similar to changes in DAergic cell morphology. Alterations in the DAergic system were specific, as loss of cell structure and neurotransmitter content was not observed in cholinergic, glutamatergic, or GABAergic systems. Overall, our data suggest that thiocarbamate pesticides promote neurodegeneration and DAergic cell dysfunction in C. elegans, and may be an environmental risk factor for PD.     

Activation of Wnt/β‐catenin signalling is required for TGF‐β/Smad2/3 signalling during myofibroblast proliferation

Fibrosis in animal models and human diseases is associated with aberrant activation of the Wnt/β‐catenin pathway. Despite extensive research efforts, effective therapies are still not available. Myofibroblasts are major effectors, responsible for extracellular matrix deposition. Inhibiting the proliferation of the myofibroblast is crucial for treatment of fibrosis. Proliferation of myofibroblasts can have many triggering effects that result in fibrosis. In recent years, the Wnt pathway has been studied as an underlying factor as a primary contributor to fibrotic diseases. These efforts notwithstanding, the specific mechanisms by which Wnt‐mediated promotes fibrosis reaction remain obscure. The central role of the transforming growth factor‐β (TGF‐β) and myofibroblast activity in the pathogenesis of fibrosis has become generally accepted. The details of interaction between these two processes are not obvious. The present investigation was conducted to evaluate the level of sustained expression of fibrosis iconic proteins (vimentin, α‐SMA and collagen I) and the TGF‐β signalling pathway that include smad2/3 and its phosphorylated form p‐smad2/3. Detailed analysis of the possible molecular mechanisms mediated by β‐catenin revealed epithelial–mesenchymal transition and additionally demonstrated transitions of fibroblasts to myofibroblast cell forms, along with increased activity of β‐catenin in regulation of the signalling network, which acts to counteract autocrine TGF‐β/smad2/3 signalling. A major outcome of this study is improved insight into the mechanisms by which epithelial and mesenchymal cells activated by TGFβ1‐smad2/3 signalling through Wnt/β‐catenin contribute to lung fibrosis.     

p57 controls adult neural stem cell quiescence and modulates the pace of lifelong neurogenesis

Throughout life, neural stem cells (NSCs) in the adult hippocampus persistently generate new neurons that modify the neural circuitry. Adult NSCs constitute a relatively quiescent cell population but can be activated by extrinsic neurogenic stimuli. However, the molecular mechanism that controls such reversible quiescence and its physiological significance have remained unknown. Here, we show that the cyclin‐dependent kinase inhibitor p57^kip2 (p57) is required for NSC quiescence. In addition, our results suggest that reduction of p57 protein in NSCs contributes to the abrogation of NSC quiescence triggered by extrinsic neurogenic stimuli such as running. Moreover, deletion of p57 in NSCs initially resulted in increased neurogenesis in young adult and aged mice. Long‐term p57 deletion, on the contrary, led to NSC exhaustion and impaired neurogenesis in aged mice. The regulation of NSC quiescence by p57 might thus have important implications for the short‐term (extrinsic stimuli‐dependent) and long‐term (age‐related) modulation of neurogenesis.     

Fibrillar β‐amyloid 1‐42 alters cytokine secretion,cholinergic signalling and neuronal differentiation

Adult neurogenesis is impaired by inflammatory processes, which are linked to altered cholinergic signalling and cognitive decline in Alzheimer's disease. In this study, we investigated how amyloid beta (Aβ)‐evoked inflammatory responses affect the generation of new neurons from human embryonic stem (hES) cells and the role of cholinergic signalling in regulating this process. The hES were cultured as neurospheres and exposed to fibrillar and oligomeric Aβ_1‐42 (Aβf, AβO) or to conditioned medium from human primary microglia activated with either Aβ_1‐42 or lipopolysaccharide. The neurospheres were differentiated for 29 days in vitro and the resulting neuronal or glial phenotypes were thereafter assessed. Secretion of cytokines and the enzymes acetylcholinesterase (AChE), butyrylcholinesterase (BuChE) and choline acetyltransferase (ChAT) involved in cholinergic signalling was measured in medium throughout the differentiation. We report that differentiating neurospheres released various cytokines, and exposure to Aβf, but not AβO, increased the secretion of IL‐6, IL‐1β and IL‐2. Aβf also influenced the levels of AChE, BuChE and ChAT in favour of a low level of acetylcholine. These changes were linked to an altered secretion pattern of cytokines. A different pattern was observed in microglia activated by Aβf, demonstrating decreased secretion of TNF‐α, IL‐1β and IL‐2 relative to untreated cells. Subsequent exposure of differentiating neurospheres to Aβf or to microglia‐conditioned medium decreased neuronal differentiation and increased glial differentiation. We suggest that a basal physiological secretion of cytokines is involved in shaping the differentiation of neurospheres and that Aβf decreases neurogenesis by promoting a microenvironment favouring hypo‐cholinergic signalling and gliogenesis.     

MicroRNA‐140‐5p elevates cerebral protection of dexmedetomidine against hypoxic–ischaemic brain damage via the Wnt/β‐catenin signalling pathway

Hypoxia–ischaemia (HI) remains a major cause of foetal brain damage presented a scarcity of effective therapeutic approaches. Dexmedetomidine (DEX) and microRNA‐140‐5p (miR‐140‐5p) have been highlighted due to its potentially significant role in the treatment of cerebral ischaemia. This study was to investigate the role by which miR‐140‐5p provides cerebral protection using DEX to treat hypoxic–ischaemic brain damage (HIBD) in neonatal rats via the Wnt/β‐catenin signalling pathway. The HIBD rat models were established and allocated into various groups with different treatment plans, and eight SD rats into sham group. The learning and memory ability of the rats was assessed. Apoptosis and pathological changes in the hippocampus CA1 region and expressions of the related genes of the Wnt/β‐catenin signalling pathway as well as the genes responsible of apoptosis were detected. Compared with the sham group, the parameters of weight, length growth, weight ratio between hemispheres, the rate of reaching standard, as well as Bcl‐2 expressions, were all increased. Furthermore, observations of increased levels of cerebral infarction volume, total mortality rate, response times, total response duration, expressions of Wnt1, β‐catenin, TCF‐4, E‐cadherin, apoptosis rate of neurons, and Bax expression were elevated. Following DEX treatment, the symptoms exhibited by HIBD rats were ameliorated. miR‐140‐5p and si‐Wnt1 were noted to attenuate the progression of HIBD. Our study demonstrates that miR‐140‐5p promotes the cerebral protective effects of DEX against HIBD in neonatal rats by targeting the Wnt1 gene through via the negative regulation of the Wnt/β‐catenin signalling pathway.     

Akhirin regulates the proliferation and differentiation of neural stem cells/progenitor cells at neurogenic niches in mouse brain

Specialized microenvironment, or neurogenic niche, in embryonic and postnatal mouse brain plays critical roles during neurogenesis throughout adulthood. The subventricular zone (SVZ) and the dentate gyrus (DG) of hippocampus in the mouse brain are two major neurogenic niches where neurogenesis is directed by numerous regulatory factors. Now, we report Akhirin (AKH), a stem cell maintenance factor in mouse spinal cord, plays a pivotal regulatory role in the SVZ and in the DG. AKH showed specific distribution during development in embryonic and postnatal neurogenic niches. Loss of AKH led to abnormal development of the ventricular zone and the DG along with reduction of cellular proliferation in both regions. In AKH knockout mice (AKH^−/−), quiescent neural stem cells (NSCs) increased, while proliferative NSCs or neural progenitor cells decreased at both neurogenic niches. In vitro NSC culture assay showed increased number of neurospheres and reduced neurogenesis in AKH^−/−. These results indicate that AKH, at the neurogenic niche, exerts dynamic regulatory role on NSC self-renewal, proliferation and differentiation during SVZ and hippocampal neurogenesis.     

Silencing long non‐coding RNA MEG3 accelerates tibia fraction healing by regulating the Wnt/β‐catenin signalling pathway

As fracture healing is related to gene expression, fracture healing is prospected to be implicated in long non‐coding RNAs (lncRNAs). This study focuses on the effects of epigenetic silencing of long non‐coding RNA maternally expressed gene 3 (lncRNA MEG3) on fracture healing by regulating the Wnt/β‐catenin signalling pathway. Genes expressed in fracture were screened using bioinformatics and the subcellular location of MEG3 was determined using FISH. Next, we successfully established tibia fracture (TF) models of C57BL/6J and Col2a1‐ICAT mice and the effect of silencing lncRNA MEG3 on fracture healing was detected after TF mice were treated with phosphate buffer saline (PBS), MEG3 siRNA and scramble siRNA. X‐ray imaging, Safranin‐O/fast green and haematoxylin‐eosin (HE) staining and histomorphometrical and biomechanical analysis were adopted to observe and to detect the fracture healing conditions. Additionally, the positive expression of collagen II and osteocalcin was examined using immunohistochemistry. At last, in the in vitro experiment, the relationship of MEG3 and the Wnt/β‐catenin signalling pathway in fraction healing was investigated. MEG3 was located in the cell nucleus. In addition, it was found that MEG3 and the Wnt/β‐catenin signalling pathway were associated with fraction healing. Moreover, silencing MEG3 was proved to elevate callus area and maximum bending load and to furthermore enhance the recanalization of bone marrow cavity. Finally, MEG3 knockdown elevated levels of Col10a1, Runx2, Osterix, Osteocalcin, Wnt10b and β‐catenin/β‐catenin whereas it reduced p‐GSK‐3β/GSK‐3β levels. Taken together, our data supported that epigenetic silencing of lncRNA MEG3 could promote the tibia fracture healing by activating the Wnt/β‐catenin signalling pathway.     

Axin2‐mTurquoise2: A novel reporter mouse model for the detection of canonical Wnt signalling

The canonical Wnt signalling pathway has been implicated in organogenesis and self‐renewal of essentially all stem cell systems. In vivo reporter systems are crucial to assess the role of Wnt signalling in the biology and pathology of stem cell systems. We set out to develop a Turquoise (TQ) fluorescent protein based Wnt reporter. We used a CRISPR‐Cas9 approach to insert a TQ fluorescent protein encoding gene into the general Wnt target gene Axin2, thereby establishing a Wnt reporter mouse similar to previously generated Wnt reporter mice but with the mTurquoise2 gene instead of E. coli‐β‐galactosidase (LacZ). The use of mTurquoise2 is especially important in organ systems in which cells need to a be alive for further experimentation such as in vitro activation or transplantation studies. We here report successful generation of Axin2‐TQ mice and show that cells from these mice faithfully respond to Wnt signals. High Wnt signals were detected in the intestinal crypts, a classical Wnt signalling site in vivo, and by flow cytometry in the thymus. These mice are an improved tool to further elucidate the role of Wnt signalling in vivo.     

Members of the CIP4 family of proteins participate in the regulation of platelet‐derived growth factor receptor‐β‐dependent actin reorganization and migration

Background information. The F‐BAR {Fes/CIP4 [Cdc42 (cell division cycle 42)‐interacting protein 4] homology and BAR (Bin/amphiphysin/Rvs)} proteins have emerged as important co‐ordinators of signalling pathways that regulate actin assembly and membrane dynamics. The presence of the F‐BAR domain is the hallmark of this family of proteins and the CIP4 (Cdc42‐interacting protein 4) was one of the first identified vertebrate F‐BAR proteins. There are three human CIP4 paralogues, namely CIP4, FBP17 (formin‐binding protein 17) and Toca‐1 (transducer of Cdc42‐dependent actin assembly 1). The CIP4‐like proteins have been implicated in Cdc42‐dependent actin reorganization and in regulation of membrane deformation events visible as tubulation of lipid bilayers. Results. We performed side‐by‐side analyses of the three CIP4 paralogues. We found that the three CIP4‐like proteins vary in their effectiveness to catalyse membrane tubulation and actin reorganization. Moreover, we show that the CIP4‐dependent membrane tubulation is enhanced in the presence of activated Cdc42. Some F‐BAR members have been shown to have a role in the endocytosis of the EGF (epidermal growth factor) receptor and this prompted us to study the involvement of the CIP4‐like proteins in signalling of the PDGFRβ [PDGF (platelet‐derived growth factor) β‐receptor]. We found that knock‐down of CIP4‐like proteins resulted in a prolonged formation of PDGF‐induced dorsal ruffles, as well as an increased PDGF‐dependent cell migration. This was most likely a consequence of a sustained PDGFRβ activation caused by delayed internalization of the receptor in the cells treated with siRNA (small interfering RNA) specific for the CIP4‐like proteins. Conclusions. Our findings show that CIP4‐like proteins induced membrane tubulation downstream of Cdc42 and that they have important roles in PDGF‐dependent actin reorganization and cell migration by regulating internalization and activity of the PDGFRβ. Moreover, the results suggest an important role for the CIP4‐like proteins in the regulation of the activity of the PDGFRβ.     

Glycogen Synthase Kinase-3β Regulates Equilibrium Between Neurogenesis and Gliogenesis in Rat Model of Parkinson’s Disease: a Crosstalk with Wnt and Notch Signaling

Neurogenesis involves generation of functional newborn neurons from neural stem cells (NSCs). Insufficient formation or accelerated degeneration of newborn neurons may contribute to the severity of motor/nonmotor symptoms of Parkinson’s disease (PD). However, the functional role of adult neurogenesis in PD is yet not explored and whether glycogen synthase kinase-3β (GSK-3β) affects multiple steps of adult neurogenesis in PD is still unknown. We investigated the possible underlying molecular mechanism of impaired adult neurogenesis associated with PD. Herein, we show that single intra-medial forebrain bundle (MFB) injection of 6-hydroxydopamine (6-OHDA) efficiently induced long-term activation of GSK-3β and reduced NSC self-renewal, proliferation, neuronal migration, and neuronal differentiation accompanied with increased astrogenesis in subventricular zone (SVZ) and hippocampal dentate gyrus (DG). Indeed, 6-OHDA also delayed maturation of neuroblasts in the DG as witnessed by their reduced dendritic length and arborization. Using a pharmacological approach to inhibit GSK-3β activation by specific inhibitor SB216763, we show that GSK-3β inhibition enhances radial glial cells, NSC proliferation, self-renewal in the SVZ, and the subgranular zone (SGZ) in the rat PD model. Pharmacological inhibition of GSK-3β activity enhances neuroblast population in SVZ and SGZ and promotes migration of neuroblasts towards the rostral migratory stream and lesioned striatum from dorsal SVZ and lateral SVZ, respectively, in PD model. GSK-3β inhibition enhances dendritic arborization and survival of granular neurons and stimulates NSC differentiation towards the neuronal phenotype in DG of PD model. The aforementioned effects of GSK-3β involve a crosstalk between Wnt/β-catenin and Notch signaling pathways that are known to regulate NSC dynamics.     

Methylation‐reprogrammed Wnt/β‐catenin signalling mediated prenatal hypoxia‐induced brain injury in foetal and offspring rats

Prenatal hypoxia (PH) is a common pregnancy complication, harmful to brain development. This study investigated whether and how PH affected Wnt pathway in the brain. Pregnant rats were exposed to hypoxia (10.5% O₂) or normoxia (21% O₂; Control). Foetal brain weight and body weight were decreased in the PH group, the ratio of brain weight to body weight was increased significantly. Prenatal hypoxia increased mRNA expression of Wnt3a, Wnt7a, Wnt7b and Fzd4, but not Lrp6. Activated β‐catenin protein and Fosl1 expression were also significantly up‐regulated. Increased Hif1a expression was found in the PH group associated with the higher Wnt signalling. Among 5 members of the Sfrp family, Sfrp4 was down‐regulated. In the methylation‐regulating genes, higher mRNA expressions of Dnmt1 and Dnmt3b were found in the PH group. Sodium bisulphite and sequencing revealed hyper‐methylation in the promoter region of Sfrp4 gene in the foetal brain, accounting for its decreased expression and contributing to the activation of the Wnt‐Catenin signalling. The study of PC12 cells treated with 5‐aza further approved that decreased methylation could result in the higher Sfrp4 expression. In the offspring hippocampus, protein levels of Hif1a and mRNA expression of Sfrp4 were unchanged, whereas Wnt signal pathway was inhibited. The data demonstrated that PH activated the Wnt pathway in the foetal brain, related to the hyper‐methylation of Sfrp4 as well as Hif1a signalling. Activated Wnt signalling might play acute protective roles to the foetal brain in response to hypoxia, also would result in disadvantageous influence on the offspring in long‐term.