Dual Function of Wnt Signaling during Neuronal Differentiation of Mouse Embryonic Stem Cells

Emerging role of tumor microenvironment derived exosomes in therapeutic resistance and metastasis through epithelial-to-mesenchymal transition

The tumor microenvironment (TME) constitutes multiple cell types including cancerous and non-cancerous cells. The intercellular communication between these cells through TME derived exosomes may either enhance or suppress the tumorigenic processes. The tumor-derived exosomes could convert an anti-tumor environment into a pro-tumor environment by inducing the differentiation of stromal cells into tumor-associated cells. The exosomes from tumor-associated stromal cells reciprocally trigger epithelial-to-mesenchymal transition (EMT) in tumor cells, which impose therapeutic resistance and metastasis. It is well known that these exosomes contain the signals of EMT, but how these signals execute chemoresistance and metastasis in tumors remains elusive. Understanding the significance and molecular signatures of exosomes transmitting EMT signals would aid in developing appropriate methods of inhibiting them. In this review, we focus on molecular signatures of exosomes that shuttle between cancer cells and their stromal populations in TME to explicate their impact on therapeutic resistance and metastasis through EMT. Especially Wnt signaling is found to be involved in multiple ways of exosomal transport and hence we decipher the biomolecules of Wnt signaling trafficked through exosomes and their potential in serving as therapeutic targets.

Role of miRNA-mRNA Interaction in Neural Stem Cell Differentiation of Induced Pluripotent Stem Cells

miRNA regulates the expression of protein coding genes and plays a regulatory role in human development and disease. The human iPSCs and their differentiated progenies provide a unique opportunity to identify these miRNA-mediated regulatory mechanisms. To identify miRNA-mRNA regulatory interactions in human nervous system development, well characterized NSCs were differentiated from six validated iPSC lines and analyzed for differentially expressed (DE) miRNome and transcriptome by RNA sequencing. Following the criteria, moderated t statistics, FDR-corrected p-value ≤ 0.05 and fold change-absolute (FC-abs) ≥2.0, 51 miRNAs and 4033 mRNAs were found to be significantly DE between iPSCs and NSCs. The miRNA target prediction analysis identified 513 interactions between 30 miRNA families (mapped to 51 DE miRNAs) and 456 DE mRNAs that were paradoxically oppositely expressed. These 513 interactions were highly enriched in nervous system development functions (154 mRNAs; FDR-adjusted p-value range: 8.06 × 10^-15-1.44 × 10^-4). Furthermore, we have shown that the upregulated miR-10a-5p, miR-30c-5p, miR23-3p, miR130a-3p and miR-17-5p miRNA families were predicted to down-regulate several genes associated with the differentiation of neurons, neurite outgrowth and synapse formation, suggesting their role in promoting the self-renewal of undifferentiated NSCs. This study also provides a comprehensive characterization of iPSC-generated NSCs as dorsal neuroepithelium, important for their potential use in in vitro modeling of human brain development and disease.

The Distinct Role of Tcfs and Lef1 in the Self-Renewal or Differentiation of Mouse Embryonic Stem Cells

Background and Objectives

Tcfs and Lef1 are DNA-binding transcriptional factors in the canonical Wnt signaling pathway. In the absence of β-catenin, Tcfs and Lef1 generally act as transcriptional repressors with co-repressor proteins such as Groucho, CtBP, and HIC-5. However, Tcfs and Lef1 turn into transcriptional activators during the interaction with β-catenin. Therefore, the activity of Tcfs and Lef1 is regulated by β-catenin. However, the intrinsic role of Tcfs and Lef1 has yet to be examined. The purpose of this study was to determine whether Tcfs and Lef1 play differential roles in the regulation of self-renewal and differentiation of mouse ES cells.

Methods and Results

Interestingly, the expression of Tcfs and Lef1 was dynamically altered under various differentiation conditions, such as removal of LIF, EB formation and neuronal differentiation in N2B27 media, suggesting that the function of each Tcf and Lef1 may vary in ES cells. Ectopic expression of Tcf1 or the dominant negative form of Lef1 (Lef1-DN) contributes to ES cells to self-renew in the absence of leukemia inhibitory factor (LIF), whereas ectopic expression of Tcf3, Lef1 or Tcf1-DN did not support ES cells to self-renew. Ectopic expression of either Lef1 or Lef1-DN blocked neuronal differentiation, suggesting that the transient induction of Lef1 was necessary for the initiation and progress of differentiation. ChIP analysis shows that Tcf1 bound to Nanog promoter and ectopic expression of Tcf1 enhanced the transcription of Nanog.

Conclusions

The overall data suggest that Tcf1 plays a critical role in the maintenance of stemness whereas Lef1 is involved in the initiation of differentiation.

Insights into the neuropathology of cerebral ischemia and its mechanisms

Cerebral ischemia is a result of insufficient blood flow to the brain. It leads to limited supply of oxygen and other nutrients to meet metabolic demands. These phenomena lead to brain damage. There are two types of cerebral ischemia: focal and global ischemia. This condition has significant impact on patient’s health and health care system requirements. Animal models such as transient occlusion of the middle cerebral artery and permanent occlusion of extracranial vessels have been established to mimic the conditions of the respective type of cerebral ischemia and to further understand pathophysiological mechanisms of these ischemic conditions. It is important to understand the pathophysiology of cerebral ischemia in order to identify therapeutic strategies for prevention and treatment. Here, we review the neuropathologies that are caused by cerebral ischemia and discuss the mechanisms that occur in cerebral ischemia such as reduction of cerebral blood flow, hippocampal damage, white matter lesions, neuronal cell death, cholinergic dysfunction, excitotoxicity, calcium overload, cytotoxic oedema, a decline in adenosine triphosphate (ATP), malfunctioning of Na+/K+-ATPase, and the blood-brain barrier breakdown. Altogether, the information provided can be used to guide therapeutic strategies for cerebral ischemia.

Wnt/β-Catenin Signaling in Neural Stem Cell Homeostasis and Neurological Diseases

Neural stem/progenitor cells (NSCs) maintain the ability of self-renewal and differentiation and compose the complex nervous system. Wnt signaling is thought to control the balance of NSC proliferation and differentiation via the transcriptional coactivator β-catenin during brain development and adult tissue homeostasis. Disruption of Wnt signaling may result in developmental defects and neurological diseases. Here, we summarize recent findings of the roles of Wnt/β-catenin signaling components in NSC homeostasis for the regulation of functional brain circuits. We also suggest that the potential role of Wnt/β-catenin signaling might lead to new therapeutic strategies for neurological diseases, including, but not limited to, spinal cord injury, Alzheimer's disease, Parkinson's disease, and depression.

MicroRNA Profiling During Neural Differentiation of Induced Pluripotent Stem Cells

MicroRNAs (miRNA) play an essential role in the regulation of gene expression and influence signaling networks responsible for several cellular processes like differentiation of pluripotent stem cells. Despite several studies on the neurogenesis process, no global analysis of microRNA expression during differentiation of induced pluripotent stem cells (iPSC) to neuronal stem cells (NSC) has been done. Therefore, we compared the profile of microRNA expression in iPSC lines and in NSC lines derived from them, using microarray-based analysis. Two different protocols for NSC formation were used: Direct and two-step via neural rosette formation. We confirmed the new associations of previously described miRNAs in regulation of NSC differentiation from iPSC. We discovered upregulation of miR-10 family, miR-30 family and miR-9 family and downregulation of miR-302 and miR-515 family expression. Moreover, we showed that miR-10 family play a crucial role in the negative regulation of genes expression belonging to signaling pathways involved in neural differentiation: WNT signaling pathway, focal adhesion, and signaling pathways regulating pluripotency of stem cells.

Pja2 Inhibits Wnt/β-catenin Signaling by Reducing the Level of TCF/LEF1

Ubiquitination of proteins plays an essential role in various cellular processes, including protein degradation, DNA repair, and cell signaling pathways. Previous studies have shown that protein ubiquitination is implicated in regulating pluripotency as well as fate determination of stem cells. To identify how protein ubiquitination affects differentiation of embryonic stem cells, we analyzed microarray data, which are available in the public domain, of E3 ligases and deubiquitinases whose levels changed during stem cell differentiation. Expression of pja2, a member of the RING-type E3 ligase family, was up-regulated during differentiation of stem cells. Wnt/β-catenin signaling is one of the most important signaling pathways for regulation of the self-renewal and differentiation of embryonic stem cells. Pja2 was shown to bind to TCF/LEF1, which are transcriptional factors for Wnt/β-catenin signaling, and regulate protein levels by ubiquitination, leading to down-regulation of Wnt signaling activity. Based on these results, we suggest that E3 ligase Pja2 regulates stem cell differentiation by controlling the level of TCF/LEF1 by ubiquitination.

Newt cells secrete extracellular vesicles with therapeutic bioactivity in mammalian cardiomyocytes

Newts can regenerate amputated limbs and cardiac tissue, unlike mammals which lack broad regenerative capacity. Several signaling pathways involved in cell proliferation, differentiation and survival during newt tissue regeneration have been elucidated, however the factors that coordinate signaling between cells, as well as the conservation of these factors in other animals, are not well defined. Here we report that media conditioned by newt limb explant cells (A1 cells) protect mammalian cardiomyocytes from oxidative stress-induced apoptosis. The cytoprotective effect of A1-conditioned media was negated by exposing A1 cells to GW4869, which suppresses the generation of extracellular vesicles (EVs). A1-EVs are similar in diameter (~100–150 nm), structure, and share several membrane surface and cargo proteins with mammalian exosomes. However, isolated A1-EVs contain significantly higher levels of both RNA and protein per particle than mammalian EVs. Additionally, numerous cargo RNAs and proteins are unique to A1-EVs. Of particular note, A1-EVs contain numerous mRNAs encoding nuclear receptors, membrane ligands, as well as transcription factors. Mammalian cardiomyocytes treated with A1-EVs showed increased expression of genes in the PI3K/AKT pathway, a pivotal player in survival signaling. We conclude that newt cells secrete EVs with diverse, distinctive RNA and protein contents. Despite ~300 million years of evolutionary divergence between newts and mammals, newt EVs confer cytoprotective effects on mammalian cardiomyocytes.

Fine Tuning of Canonical Wnt Stimulation Enhances Differentiation of Pluripotent Stem Cells Independent of β-Catenin-Mediated T-Cell Factor Signaling

The canonical Wnt/β-catenin pathway is crucial for early embryonic patterning, tissue homeostasis, and regeneration. While canonical Wnt/β-catenin stimulation has been used extensively to modulate pluripotency and differentiation of pluripotent stem cells (PSCs), the mechanism of these two seemingly opposing roles has not been fully characterized and is currently largely attributed to activation of nuclear Wnt target genes. Here, we show that low levels of Wnt stimulation via ectopic expression of Wnt1 or administration of glycogen synthase kinase-3 inhibitor CHIR99021 significantly increases PSC differentiation into neurons, cardiomyocytes and early endodermal intermediates. Our data indicate that enhanced differentiation outcomes are not mediated through activation of traditional Wnt target genes but by β-catenin's secondary role as a binding partner of membrane bound cadherins ultimately leading to the activation of developmental genes. In summary, fine-tuning of Wnt signaling to subthreshold levels for detectable nuclear β-catenin function appears to act as a switch to enhance differentiation of PSCs into multiple lineages. Our observations highlight a mechanism by which Wnt/β-catenin signaling can achieve dosage dependent dual roles in regulating self-renewal and differentiation. Stem Cells 2018;36:822-833.

NeuronRead, an open source semi-automated tool for morphometric analysis of phase contrast and fluorescence neuronal images

Neurons are specialized cells of the Central Nervous System whose function is intricately related to the neuritic network they develop to transmit information. Morphological evaluation of this network and other neuronal structures is required to establish relationships between neuronal morphology and function, and may allow monitoring physiological and pathophysiologic alterations. Fluorescence-based microphotographs are the most widely used in cellular bioimaging, but phase contrast (PhC) microphotographs are easier to obtain, more affordable, and do not require invasive, complicated and disruptive techniques. Despite the various freeware tools available for fluorescence-based images analysis, few exist that can tackle the more elusive and harder-to-analyze PhC images. To surpass this, an interactive semi-automated image processing workflow was developed to easily extract relevant information (e.g. total neuritic length, average cell body area) from both PhC and fluorescence neuronal images. This workflow, named 'NeuronRead', was developed in the form of an ImageJ macro. Its robustness and adaptability were tested and validated on rat cortical primary neurons under control and differentiation inhibitory conditions. Validation included a comparison to manual determinations and to a golden standard freeware tool for fluorescence image analysis. NeuronRead was subsequently applied to PhC images of neurons at distinct differentiation days and exposed or not to DAPT, a pharmacological inhibitor of the γ-secretase enzyme, which cleaves the well-known Alzheimer's amyloid precursor protein (APP) and the Notch receptor. Data obtained confirms a neuritogenic regulatory role for γ-secretase products and validates NeuronRead as a time- and cost-effective useful monitoring tool.

Identification of molecular markers distinguishing adult neural stem cells in the subventricular and subcallosal zones

Neural stem cells (NSCs) in the adult subventricular zone (SVZ) are regionally specified and have distinct molecular gene expression signatures. Recently, we identified the subcallosal zone (SCZ) as a novel brain region where adult NSCs maintain and spontaneously produce neuroblasts. In an attempt to isolate genes specifically expressed in the SCZ or SVZ, microarray analyses of their differentially expressing transcripts were done. The comparison between neurospheres generated from SVZ and SCZ revealed differential expression >1.5-fold in two groups in only 83 genes, representing <0.03% of the genes examined, suggesting that these two populations are largely similar. The differential expression patterns SCZ and SVZ genes were confirmed by RT-PCR and Western blots. The selective expressions of two genes (CRBP1, HMGA1) in SVZ-NSCs were further confirmed by immunohistochemistry. These molecular markers could be useful for further molecular and cellular characterization of NSCs.

An Overview of Neural Differentiation Potential of Human Adipose Derived Stem Cells

There is wide interest in application of adult stem cells due to easy to obtain with a minimal patient discomfort, capable of producing cell numbers in large quantities and their immunocompatible properties without restriction by ethical concerns. Among these stem cells, multipotent mesenchymal stem cells (MSCs) from human adipose tissue are considered as an ideal source for various regenerative medicine. In spite of mesodermal origin of human adipose-derived stem cells (hADSCs), these cells have differentiation potential toward mesodermal and non-mesodermal lineages. Up to now, several studies have shown that hADSCs can undergo transdifferentiation and produce cells outside of their lineage, especially into neural cells when they are transferred to a specific cell environment. The purpose of this literature review is to provide an overview of the existing state of knowledge of the differentiation potential of hADSCs, specifically their ability to give rise to neuronal cells. The following review discusses different protocols considered for differentiation of hADSCs to neural cells, the neural markers that are used in each procedure and possible mechanisms that are involved in this differentiation.

How Wnt Signaling Builds the Brain: Bridging Development and Disease

Wnt/β-catenin signaling plays a crucial role throughout all stages of brain development and remains important in the adult brain. Accordingly, many neurological disorders have been linked to Wnt signaling. Defects in Wnt signaling during neural development can give rise to birth defects or lead to neurological dysfunction later in life. Developmental signaling events can also be hijacked in the adult and result in disease. Moreover, knowledge about the physiological role of Wnt signaling in the brain might lead to new therapeutic strategies for neurological diseases. Especially, the important role for Wnt signaling in neural differentiation of pluripotent stem cells has received much attention as this might provide a cure for neurodegenerative disorders. In this review, we summarize the versatile role of Wnt/β-catenin signaling during neural development and discuss some recent studies linking Wnt signaling to neurological disorders.