Oxygen regulates proliferation of neural stem cells through Wnt/β-catenin signalling

Upregulation of Intracellular Zinc Ion Level after Differentiation of the Neural Stem/Progenitor Cells In Vitro with the Changes in Gene Expression of Zinc Transporters

We measured the intracellular zinc ion concentration of murine fetal neural stem/progenitor cells (NSPCs) and that in the differentiated cells. The NSPCs cultured with 1.5 μM Zn2+ proliferated slightly faster than that in the zinc-deficient medium and the intracellular zinc concentration of the NSPCs and that of their differentiated cells (DCs) cultured with 1.5 μM Zn2+ was 1.34-fold and 2.00-fold higher than those in the zinc-deficient medium, respectively. The zinc transporter genes upregulated over the 3.5-fold change were Zip1, Zip4, Zip12, Zip13, ZnT1, ZnT8, and ZnT10 whereas the only downregulated one was Zip8 during the differentiation of NSPCs to DCs. The cell morphologies of both NSPCs and DCs in the low oxygen culture condition consisting of 2%O2 and 5%CO2, the high carbon dioxide condition consisting of 21%O2 and 10%CO2, and the normal condition consisting of 21%O2 and 5%CO2 were essentially the same each other. The expression of Zip4, Zip8, Zip12, and Zip14 was not drastically changed depending on the O2 and CO2 concentrations.

Neonatal brain injury unravels transcriptional and signaling changes underlying the reactivation of cortical progenitors

Germinal activity persists throughout life within the ventricular-subventricular zone (V-SVZ) of the postnatal forebrain due to the presence of neural stem cells (NSCs). Accumulating evidence points to a recruitment for these cells following early brain injuries and suggests their amenability to manipulations. We used chronic hypoxia as a rodent model of early brain injury to investigate the reactivation of cortical progenitors at postnatal times. Our results reveal an increased proliferation and production of glutamatergic progenitors within the dorsal V-SVZ. Fate mapping of V-SVZ NSCs demonstrates their contribution to de novo cortical neurogenesis. Transcriptional analysis of glutamatergic progenitors shows parallel changes in methyltransferase 14 (Mettl14) and Wnt/β-catenin signaling. In agreement, manipulations through genetic and pharmacological activation of Mettl14 and the Wnt/β-catenin pathway, respectively, induce neurogenesis and promote newly-formed cell maturation. Finally, labeling of young adult NSCs demonstrates that pharmacological NSC activation has no adverse effects on the reservoir of V-SVZ NSCs and on their germinal activity.

Mitochondrial leak metabolism induces the Spemann-Mangold Organizer via Hif-1α in Xenopus

An instructive role for metabolism in embryonic patterning is emerging, although a role for mitochondria is poorly defined. We demonstrate that mitochondrial oxidative metabolism establishes the embryonic patterning center, the Spemann-Mangold Organizer, via hypoxia-inducible factor 1α (Hif-1α) in Xenopus. Hypoxia or decoupling ATP production from oxygen consumption expands the Organizer by activating Hif-1α. In addition, oxygen consumption is 20% higher in the Organizer than in the ventral mesoderm, indicating an elevation in mitochondrial respiration. To reconcile increased mitochondrial respiration with activation of Hif-1α, we discovered that the "free" c-subunit ring of the F1Fo ATP synthase creates an inner mitochondrial membrane leak, which decouples ATP production from respiration at the Organizer, driving Hif-1α activation there. Overexpression of either the c-subunit or Hif-1α is sufficient to induce Organizer cell fates even when β-catenin is inhibited. We propose that mitochondrial leak metabolism could be a general mechanism for activating Hif-1α and Wnt signaling.

MMP13 promotes the osteogenic potential of BMP9 by enhancing Wnt/β-catenin signaling via HIF-1α upregulation in mouse embryonic fibroblasts

Bone morphogenetic protein 9 (BMP9) has been validated as one of the most potent osteoinduction factors, but its underlying mechanism remains unclear. As a member of the matrix metalloproteinase (MMP) family, MMP13 may be involved in regulating the lineage-specific differentiation of mouse embryonic fibroblasts (MEFs). The goal of this study was to determine whether MMP13 regulates the osteoinduction potential of BMP9 in MEFs, which are multipotent progenitor cells widely used for stem cell biology research. In vitro and in vivo experiments showed that BMP9-induced osteogenic markers and/or bone were enhanced by exogenous MMP13 in MEFs, but were reduced by MMP13 knockdown or inhibition. The expression of hypoxia inducible factor 1 alpha (HIF-1α) was induced by BMP9, which was enhanced by MMP13. The protein expression of β-catenin and phosphorylation level of glycogen synthase kinase-3 beta (GSK-3β) were increased by BMP9 in MEFs, as was the translocation of β-catenin from the cytoplasm to the nucleus; all these effects of BMP9 were enhanced by MMP13. Furthermore, the MMP13 effects of increasing BMP9-induced β-catenin protein expression and GSK-3β phosphorylation level were partially reversed by HIF-1α knockdown. These results suggest that MMP13 can enhance the osteoinduction potential of BMP9, which may be mediated, at least in part, through the HIF-1α/β-catenin axis. Our findings demonstrate a novel role of MMP13 in the lineage decision of progenitor cells and provide a promising strategy to speed up bone regeneration.

Development of a Stretchable and Water-Resistant Hydrogel with Antibacterial and Antioxidant Dual Functions for Wound Healing in Movable Parts

The treatment of wounds that develop on moving parts of the body, such as joints, is considered a challenge due to poor mechanical matching and secondary injury caused by continuous motion and inflammation. Herein, a stretchable, multifunctional hydrogel dressing utilizing the dual cross-linking of chitosan (CS) and acrylic acid (AA) and modified with caffeic acid (CA) and aloin (Alo) was developed. Mechanical testing demonstrated that the hydrogel possessed excellent stretching capability (of approximately 869%) combined with outstanding adhesion (about 56 kPa), contributing to its compatibility with moving parts and allowing complete coverage of wound sites without limiting joint and organ motion. Bioinformatics analysis confirmed that use of the hydrogel resulted in upregulated expression of multiple genes related to angiogenesis and cell proliferation. Furthermore, antibacterial testing indicated that the dressing suppressed the growth of Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA), providing a better microenvironment for wound healing. An in vivo wound defect model on movable skin verified that the wound healing observed with the hydrogel dressing was superior to that observed with a commercially available dressing. Taken together, the results suggest that a stretchable multifunctional hydrogel dressing represents a promising alternative wound dressing with therapeutic potential for superior healing, especially for moving parts of the body.

Notch is Not Involved in Physioxia-Mediated Stem Cell Maintenance in Midbrain Neural Stem Cells

Background and Objectives

The physiological oxygen tension in fetal brains (∼3%, physioxia) is beneficial for the maintenance of neural stem cells (NSCs). Sensitivity to oxygen varies between NSCs from different fetal brain regions, with midbrain NSCs showing selective susceptibility. Data on Hif-1α/Notch regulatory interactions as well as our observations that Hif-1α and oxygen affect midbrain NSCs survival and proliferation prompted our investigations on involvement of Notch signalling in physioxia-dependent midbrain NSCs performance.

Methods and Results

Here we found that physioxia (3% O2) compared to normoxia (21% O2) increased proliferation, maintained stemness by suppression of spontaneous differentiation and supported cell cycle progression. Microarray and qRT-PCR analyses identified significant changes of Notch related genes in midbrain NSCs after long-term (13 days), but not after short-term physioxia (48 hours). Consistently, inhibition of Notch signalling with DAPT increased, but its stimulation with Dll4 decreased spontaneous differentiation into neurons solely under normoxic but not under physioxic conditions.

Conclusions

Notch signalling does not influence the fate decision of midbrain NSCs cultured in vitro in physioxia, where other factors like Hif-1α might be involved. Our findings on how physioxia effects in midbrain NSCs are transduced by alternative signalling might, at least in part, explain their selective susceptibility to oxygen.

Hypoxia Induces Early Neurogenesis in Human Fetal Neural Stem Cells by Activating the WNT Pathway

Fetal neural stem cells (FNSCs) present in the human fetal brain differentiate into cells of neuronal and glial lineages. The developing fetus is exposed to lower oxygen concentrations than adults, and this physiological hypoxia may influence the growth and differentiation of the FNSCs. This study aimed to evaluate the effect of hypoxia on the differentiation potential of human FNSCs isolated from the subventricular zone of aborted fetal brains (n = 5). FNSCs were isolated, expanded, and characterized by Nestin and Sox2 expression using immunocytochemistry and flow cytometry, respectively. These FNSCs were exposed to 20% oxygen (normoxia) and 0.2% oxygen (hypoxia) concentrations for 48 h, and hypoxia exposure (n = 5) was validated. Whole transcriptome analyses (Genespring GX13) of FNSCs exposed to hypoxia (Agilent 4 × 44 K human array slides) highlighted that genes associated with neurogenesis were enriched upon exposure to hypoxia. The pathway analysis of these enriched genes (using Metacore) showed the involvement of the WNT signaling pathway. Microarray analyses were validated using neuronal and glial lineage commitment markers, namely, NEUROG1, NEUROG2, ASCL1, DCX, GFAP, OLIG2, and NKX2.2, using qPCR (n = 9). DCX, ASCL1, NGN1, and GFAP protein expression was analyzed by Western blotting (n = 3). This demonstrated upregulation of the neuronal commitment markers upon hypoxia exposure, while no change was observed in astrocytic and oligodendrocyte lineage commitment markers. Increased expression of downstream targets of the WNT signaling pathway, TCF4 and ID2, by qPCR (n = 9) and increased protein expression of CTNNB1 (β-catenin) and ID2 by Western blot (n = 3) indicated its involvement in mediating neuronal differentiation upon exposure to hypoxia.

HIF-1alpha-pathway activation in cholangiocytes of patients with biliary atresia: An immunohistochemical/molecular exploratory study

BACKGROUND

Biliary atresia is a neonatal disease characterized by choledochal obstruction and progressive cholangiopathy requiring liver transplantation in most patients. Hypoxia-ischemia affecting the biliary epithelium may lead to biliary obstruction. We hypothesized that ischemic cholangiopathy involving disruption of the peribiliary vascular plexus could act as a triggering event in biliary atresia pathogenesis.

METHODS

Liver and porta hepatis paraffin-embedded samples of patients with biliary atresia or intrahepatic neonatal cholestasis (controls) were immunohistochemically evaluated for HIF-1alpha-nuclear signals. Frozen histological samples were analyzed for gene expression in molecular profiles associated with hypoxia-ischemia. Prospective clinical-laboratory and histopathological data of biliary atresia patients and controls were reviewed.

RESULTS

Immunohistochemical HIF-1alpha signals localized to cholangiocytes were detected exclusively in liver specimens from biliary atresia patients. In 37.5% of liver specimens, HIF-1alpha signals were observed in biliary structures involving progenitor cell niches and peribiliary vascular plexus. HIF-1alpha signals were also detected in biliary remnants of 81.8% of porta hepatis specimens. Increased gene expression of molecules linked to REDOX status, biliary proliferation, and angiogenesis was identified in biliary atresia liver specimens. In addition, there was a trend towards decreased GSR expression levels in the HIF-1alpha-positive group compared to the HIF-1alpha-negative group.

CONCLUSION

Activation of the HIF-1alpha pathway may be associated with the pathogenesis of biliary atresia, and additional studies are necessary to confirm the significance of this finding. Ischemic cholangiopathy and REDOX status disturbance are putative explanations for HIF-1alpha activation. These findings may give rise to novel lines of clinical and therapeutic investigation in the BA field.

The Oxygen Cascade from Atmosphere to Mitochondria as a Tool to Understand the (Mal)adaptation to Hypoxia

Hypoxia is a life-threatening challenge for about 1% of the world population, as well as a contributor to high morbidity and mortality scores in patients affected by various cardiopulmonary, hematological, and circulatory diseases. However, the adaptation to hypoxia represents a failure for a relevant portion of the cases as the pathways of potential adaptation often conflict with well-being and generate diseases that in certain areas of the world still afflict up to one-third of the populations living at altitude. To help understand the mechanisms of adaptation and maladaptation, this review examines the various steps of the oxygen cascade from the atmosphere to the mitochondria distinguishing the patterns related to physiological (i.e., due to altitude) and pathological (i.e., due to a pre-existing disease) hypoxia. The aim is to assess the ability of humans to adapt to hypoxia in a multidisciplinary approach that correlates the function of genes, molecules, and cells with the physiologic and pathological outcomes. We conclude that, in most cases, it is not hypoxia by itself that generates diseases, but rather the attempts to adapt to the hypoxia condition. This underlies the paradigm shift that when adaptation to hypoxia becomes excessive, it translates into maladaptation.

Autophagy Is Essential for Neural Stem Cell Proliferation Promoted by Hypoxia

Hypoxia as a microenvironment or niche stimulates proliferation of neural stem cells (NSCs). However, the underlying mechanisms remain elusive. Autophagy is a protective mechanism by which recycled cellular components and energy are rapidly supplied to the cell under stress. Whether autophagy mediates the proliferation of NSCs under hypoxia and how hypoxia induces autophagy remain unclear. Here, we report that hypoxia facilitates embryonic NSC proliferation through HIF-1/mTORC1 signaling pathway-mediated autophagy. Initially, we found that hypoxia greatly induced autophagy in NSCs, while inhibition of autophagy severely impeded the proliferation of NSCs in hypoxia conditions. Next, we demonstrated that the hypoxia core regulator HIF-1 was necessary and sufficient for autophagy induction in NSCs. Considering that mTORC1 is a key switch that suppresses autophagy, we subsequently analyzed the effect of HIF-1 on mTORC1 activity. Our results showed that the mTORC1 activity was negatively regulated by HIF-1. Finally, we provided evidence that HIF-1 regulated mTORC1 activity via its downstream target gene BNIP3. The increased expression of BNIP3 under hypoxia enhanced autophagy activity and proliferation of NSCs, which was mediated by repressing the activity of mTORC1. We further illustrated that BNIP3 can interact with Rheb, a canonical activator of mTORC1. Thus, we suppose that the interaction of BNIP3 with Rheb reduces the regulation of Rheb toward mTORC1 activity, which relieves the suppression of mTORC1 on autophagy, thereby promoting the rapid proliferation of NSCs. Altogether, this study identified a new HIF-1/BNIP3-Rheb/mTORC1 signaling axis, which regulates the NSC proliferation under hypoxia through induction of autophagy.

Protective Effects of Early Caffeine Administration in Hyperoxia-Induced Neurotoxicity in the Juvenile Rat

High-risk preterm infants are affected by a higher incidence of cognitive developmental deficits due to the unavoidable risk factor of oxygen toxicity. Caffeine is known to have a protective effect in preventing bronchopulmonary dysplasia associated with improved neurologic outcomes, although very early initiation of therapy is controversial. In this study, we used newborn rats in an oxygen injury model to test the hypothesis that near-birth caffeine administration modulates neuronal maturation and differentiation in the hippocampus of the developing brain. For this purpose, newborn Wistar rats were exposed to 21% or 80% oxygen on the day of birth for 3 or 5 days and treated with vehicle or caffeine (10 mg/kg/48 h). Postnatal exposure to 80% oxygen resulted in a drastic reduction of associated neuronal mediators for radial glia, mitotic/postmitotic neurons, and impaired cell-cycle regulation, predominantly persistent even after recovery to room air until postnatal day 15. Systemic caffeine administration significantly counteracted the effects of oxygen insult on neuronal maturation in the hippocampus. Interestingly, under normoxia, caffeine inhibited the transcription of neuronal mediators of maturing and mature neurons. The early administration of caffeine modulated hyperoxia-induced decreased neurogenesis in the hippocampus and showed neuroprotective properties in the neonatal rat oxygen toxicity model.

Serial Gene Expression Profiling of Neural Stem Cells Shows Transcriptome Switch by Long-Term Physioxia from Metabolic Adaption to Cell Signaling Profile

Oxygen is an essential factor in the cellular microenvironment with pivotal effects on neural development with a particular sensitivity of midbrain neural stem cells (NSCs) to high atmospheric oxygen tension. However, most experiments are still performed at atmospheric O₂ levels (21%, normoxia), whereas mammalian brain tissue is physiologically exposed to substantially lower O₂ tensions around 3% (physioxia). We here performed serial Affymetrix gene array analyses to detect expression changes in mouse fetal NSCs from both midbrain and cortical tissues when kept at physioxia compared to normoxia. We identified more than 400 O₂-regulated genes involved in cellular metabolism, cell proliferation/differentiation, and various signaling pathways. NSCs from both regions showed a low number but high conformity of regulated genes (9 genes in midbrain vs. 34 in cortical NSCs; 8 concordant expression changes) after short-term physioxia (2 days) with metabolic processes and cellular processes being the most prominent GO categories pointing to cellular adaption to lower oxygen levels. Gene expression profiles changed dramatically after long-term physioxia (13 days) with a higher number of regulated genes and more diverse expression patterns when comparing the two NSC types (338 genes in midbrain vs. 121 in cortical NSCs; 75 concordant changes). Most prominently, we observed a reduction of hits in metabolic processes but an increase in biological regulation and signaling pointing to a switch towards signaling processes and stem cell maintenance. Our data may serve as a basis for identifying potential signaling pathways that maintain stem cell characteristics in cortical versus midbrain physioxic stem cell niches.

Regulation of neural stem cell proliferation and survival by protein arginine methyltransferase 1

Protein arginine methyltransferase 1 (PRMT1), a major type I arginine methyltransferase in mammals, methylates histone and non-histone proteins to regulate various cellular functions, such as transcription, DNA damage response, and signal transduction. PRMT1 is highly expressed in neural stem cells (NSCs) and embryonic brains, suggesting that PRMT1 is essential for early brain development. Although our previous reports have shown that PRMT1 positively regulates oligodendrocyte development, it has not been studied whether PRMT1 regulates NSC proliferation and its survival during development. To examine the role of PRMT1 in NSC activity, we cultured NSCs prepared from embryonic mouse forebrains deficient in PRMT1 specific for NSCs and performed neurosphere assays. We found that the primary neurospheres of PRMT1-deficient NSCs were small and the number of spheres was decreased, compared to those of control NSCs. Primary neurospheres deficient in PRMT1 expressed an increased level of cleaved caspase-3, suggesting that PRMT1 deficiency-induced apoptosis. Furthermore, p53 protein was significantly accumulated in PRMT1-deficient NSCs. In parallel, p53-responsive pro-apoptotic genes including Pmaip1 and Perp were upregulated in PRMT1-deficient NSCs. p53-target p21 mRNA and its protein levels were shown to be upregulated in PRMT1-deficient NSCs. Moreover, the 5-bromo-2′-deoxyuridine (BrdU) incorporation assay showed that the loss of PRMT1 led to cell cycle defects in the embryonic NSCs. In contrast to the above in vitro observations, NSCs normally proliferated and survived in the fetal brains of NSC-specific PRMT1-deficient mice. We also found that Lama1, which encodes the laminin subunit α1, was significantly upregulated in the embryonic brains of PRMT1-deficient mice. These data implicate that extracellular factors provided by neighboring cells in the microenvironment gave a trophic support to NSCs in the PRMT1-deficient brain and recovered NSC activity to maintain brain homeostasis. Our study implies that PRMT1 plays a cell-autonomous role in the survival and proliferation of embryonic NSCs.

Embryonic Stem Cells Lacking DNA Methyltransferases Differentiate into Neural Stem Cells that Are Defective in Self-Renewal

Background and Objectives

DNA methyltransferases (Dnmts) play an important role in regulating DNA methylation during early developmental processes and cellular differentiation. In this study, we aimed to investigate the role of Dnmts in neural differentiation of embryonic stem cells (ESCs) and in maintenance of the resulting neural stem cells (NSCs).

Methods and Results

We used three types of Dnmt knockout (KO) ESCs, including Dnmt1 KO, Dnmt3a/3b double KO (Dnmt3 DKO), and Dnmt1/3a/3b triple KO (Dnmt TKO), to investigate the role of Dnmts in neural differentiation of ESCs. All three types of Dnmt KO ESCs could form neural rosette and differentiate into NSCs in vitro. Interestingly, however, after passage three, Dnmt KO ESC-derived NSCs could not maintain their self-renewal and differentiated into neurons and glial cells.

Conclusions

Taken together, the data suggested that, although deficiency of Dnmts had no effect on the differentiation of ESCs into NSCs, the latter had defective maintenance, thereby indicating that Dnmts are crucial for self-renewal of NSCs.

Supraphysiological Oxygen Levels in Mammalian Cell Culture: Current State and Future Perspectives

Most conventional incubators used in cell culture do not regulate O2 levels, making the headspace O2 concentration ~18%. In contrast, most human tissues are exposed to 2-6% O2 (physioxia) in vivo. Accumulating evidence has shown that such hyperoxic conditions in standard cell culture practices affect a variety of biological processes. In this review, we discuss how supraphysiological O2 levels affect reactive oxygen species (ROS) metabolism and redox homeostasis, gene expression, replicative lifespan, cellular respiration, and mitochondrial dynamics. Furthermore, we present evidence demonstrating how hyperoxic cell culture conditions fail to recapitulate the physiological and pathological behavior of tissues in vivo, including cases of how O2 alters the cellular response to drugs, hormones, and toxicants. We conclude that maintaining physioxia in cell culture is imperative in order to better replicate in vivo-like tissue physiology and pathology, and to avoid artifacts in research involving cell culture.

Hyperoxygenation During Mid-Neurogenesis Accelerates Cortical Development in the Fetal Mouse Brain

Oxygen tension is well-known to affect cortical development. Fetal brain hyperoxygenation during mid-neurogenesis in mice (embryonic stage E14.5. to E16.5) increases brain size evoked through an increase of neuroprecursor cells. Nevertheless, it is unknown whether these effects can lead to persistent morphological changes within the highly orchestrated brain development. To shed light on this, we used our model of controlled fetal brain hyperoxygenation in time-pregnant C57BL/6J mice housed in a chamber with 75% atmospheric oxygen from E14.5 to E16.5 and analyzed the brains from E14.5, E16.5, P0.5, and P3.5 mouse embryos and pups via immunofluorescence staining. Mid-neurogenesis hyperoxygenation led to an acceleration of cortical development by temporal expansion of the cortical plate with increased NeuN+ neuron counts in hyperoxic brains only until birth. More specifically, the number of Ctip2+ cortical layer 5 (L5) neurons was increased at E16.5 and at birth in hyperoxic brains but normalized in the early postnatal stage (P3.5). The absence of cleaved caspase 3 within the extended Ctip2+ L5 cell population largely excluded apoptosis as a major compensatory mechanism. Timed BrdU/EdU analyses likewise rule out a feedback mechanism. The normalization was, on the contrary, accompanied by an increase of active microglia within L5 targeting Ctip2+ neurons without any signs of apoptosis. Together, hyperoxygenation during mid-neurogenesis phase of fetal brain development provoked a specific transient overshoot of cortical L5 neurons leading to an accelerated cortical development without detectable persistent changes. These observations provide insight into cortical and L5 brain development.

Effect of Physiological Oxygen on Primary Human Corneal Endothelial Cell Cultures

Purpose

Primary human corneal endothelial cells (HCEnCs) cultured in room air are exposed to significantly higher O₂ concentrations [O₂] than what is normally present in the eye. We evaluated the growth and metabolism of HCEnCs cultured under physiological [O₂] (2.5%; [O₂]_2.5) and room air ([O₂]_A).

Methods

Primary cultures of HCEnCs from normal donors and donors with Fuchs dystrophy were grown at [O₂]_2.5 and [O₂]_A. Growth and morphology were compared using phase-contrast microscopy, zonula occludens (ZO-1) localization, cell density measurements, and senescence marker staining. CD44 (cell quality) and HIF-1α (hypoxia-inducible factor-1α) levels were evaluated by Western blotting. Cell adaptability to a reversal of [O₂] growth conditions was measured with cell viability assays, and cell metabolism was assessed via oxygen consumption and extracellular acidification rates.

Results

HCEnCs grown at [O₂]_A and [O₂]_2.5 displayed similar morphologies, ZO-1 localization, CD44 expression, and senescence. Cells from donors with Fuchs dystrophy grew better at [O₂]_2.5 than at [O₂]_A. HIF-1α was undetectable. Cells displayed greater viability at [O₂]_2.5 than at [O₂]_A. HCEnCs showed significantly greater proton leak (P < 0.01), nonmitochondrial oxygen consumption (P < 0.01), and spare capacity (P < 0.05) for oxygen consumption rates, and greater basal glycolysis (P < 0.05) with a decreased glycolytic reserve capacity (P < 0.05) for extracellular acidification rates.

Conclusions

Primary HCEnCs show unique metabolic characteristics at physiologic [O₂]. The effect of [O₂] for optimization of HCEnC culture conditions should be considered.

Translational Relevance

With the advance of cell-based therapeutics for corneal endothelial diseases, [O₂] should be considered an important variable in the optimization of HCEnC culture conditions.

Early Chronic Intermittent Maternal Hyperoxygenation Impairs Cortical Development by Inhibition of Pax6-Positive Apical Progenitor Cell Proliferation

Maternal hyperoxygenation is a feasible, noninvasive method to treat fetal diseases, such as heart hypoplasia, but effects of maternal hyperoxygenation on the developing brain remain poorly understood. Previous studies showed that short-term maternal hyperoxygenation during midneurogenic phase (E14-E16) but not in earlier development (E10-E12) increases oxygen tension and enhances neurogenesis in the developing mouse cortex. We investigated effects of early chronic maternal hyperoxygenation (CMH) as a potential clinical treatment. Pregnant C57BL/6J mice were housed in a chamber at 75% atmospheric oxygen and the brains of E16 fetuses were analyzed using immunohistochemistry. The mitosis marker phH3 showed a significant reduction of proliferation in the dorsolateral cortices of CMH-treated E16 fetuses. Numbers of Tbr2-positive intermediate progenitor cells were unaffected whereas numbers of Pax6-positive apical progenitor cells were significantly reduced in CMH-treated mice. This resulted in altered cortical plate development with fewer Satb2-positive upper layer neurons but more Tbr1-positive neurons corresponding to the deeper layer 6. Thus, maternal hyperoxygenation affects the developing cortex depending on timing and length of applied oxygen. Early CMH causes a severe reduction of neuroprogenitor proliferation likely affecting cortical development. Further studies are needed to investigate the mechanisms underlying these findings and to assess the clinical and neurodevelopmental outcomes of the pups.

Markov chain Monte Carlo for active module identification problem

Background

Integrative network methods are commonly used for interpretation of high-throughput experimental biological data: transcriptomics, proteomics, metabolomics and others. One of the common approaches is finding a connected subnetwork of a global interaction network that best encompasses significant individual changes in the data and represents a so-called active module. Usually methods implementing this approach find a single subnetwork and thus solve a hard classification problem for vertices. This subnetwork inherently contains erroneous vertices, while no instrument is provided to estimate the confidence level of any particular vertex inclusion. To address this issue, in the current study we consider the active module problem as a soft classification problem.

Results

We propose a method to estimate probabilities of each vertex to belong to the active module based on Markov chain Monte Carlo (MCMC) subnetwork sampling. As an example of the performance of our method on real data, we run it on two gene expression datasets. For the first many-replicate expression dataset we show that the proposed approach is consistent with an existing resampling-based method. On the second dataset the jackknife resampling method is inapplicable due to the small number of biological replicates, but the MCMC method can be run and shows high classification performance.

Conclusions

The proposed method allows to estimate the probability that an individual vertex belongs to the active module as well as the false discovery rate (FDR) for a given set of vertices. Given the estimated probabilities, it becomes possible to provide a connected subgraph in a consistent manner for any given FDR level: no vertex can disappear when the FDR level is relaxed. We show, on both simulated and real datasets, that the proposed method has good computational performance and high classification accuracy.

HBO Promotes the Differentiation of Neural Stem Cells via Interactions Between the Wnt3/β-Catenin and BMP2 Signaling Pathways

Hyperbaric oxygen (HBO) therapy may promote neurological recovery from hypoxic-ischemic encephalopathy (HIE). However, the therapeutic effects of HBO and its associated mechanisms remain unknown. The canonical Wnt/β-catenin signaling pathways and bone morphogenetic protein (BMP) play important roles in mammalian nervous system development. The present study examined whether HBO stimulates the differentiation of neural stem cells (NSCs) and its effect on Wnt3/β-catenin and BMP2 signaling pathways. We showed HBO treatment (2 ATA, 60 min) promoted differentiation of NSCs into neurons and oligodendrocytes in vitro. In addition, rat hypoxic-ischemic brain damage (HIBD) tissue extracts also promoted the differentiation of NSCs into neurons and oligodendrocytes, with the advantage of reducing the number of astrocytes. These effects were most pronounced when these two were combined together. In addition, the expression of Wnt3a, BMP2, and β-catenin nuclear proteins were increased after HBO treatment. However, blockade of Wnt/β-catenin or BMP signaling inhibited NSC differentiation and reduced the expression of Wnt3a, BMP2, and β-catenin nuclear proteins. In conclusion, HBO promotes differentiation of NSCs into neurons and oligodendrocytes and reduced the number of astrocytes in vitro possibly through regulation of Wnt3/β-catenin and BMP2 signaling pathways. HBO may serve as a potential therapeutic strategy for treating HIE.

Chondrogenic differentiation potential of adult and fetal equine cell types

OBJECTIVE

To determine the chondrogenic potential of cells derived from interzone tissue, the normal progenitor of articular cartilage during fetal development, compared to that of adult bone marrow-derived and adipose-derived mesenchymal cell isolates. The objective of this study was to compare the chondrogenic potential of fetal musculoskeletal progenitor cells to adult cell types, which are currently used therapeutically to facilitate joint cartilage repair in equine clinical practice. The hypothesis tested was that cells derived from interzone tissue have a chondrogenic potential that exceeds that of adult bone marrow-derived and adipose-derived mesenchymal cell isolates.

STUDY DESIGN

In vitro study.

ANIMALS

Six young adult horses (15-17 months of age) and 6 equine fetuses aged 45-46 days of gestation.

METHODS

Three-dimensional pellet cultures were established under chondrogenic conditions with fresh, primary cells isolated from adult (articular cartilage, bone marrow, adipose, dermis) and fetal (interzone, skeletal anlagen cartilage, dermis) tissues. Cellular morphology, pellet architecture, and proteoglycan synthesis were assessed in the pellet cultures. Steady state levels of ACAN (aggrecan core protein), COL2A1 (collagen type II), and COL1A1 (collagen type I) messenger RNA (mRNA) were compared among these cell types as pellet cultures and monolayer cultures.

RESULTS

Adult articular chondrocytes, fetal interzone cells, and fetal anlage cells generated the largest pellets under these chondrogenic culture conditions. Pellets derived from adult articular chondrocytes and fetal anlage cells had the highest scores on a neocartilage grading scale. Fetal anlage and adult articular chondrocyte pellets had low steady-state levels of COL1A mRNA but high COL2A1 expression. Anlage chondrocyte pellets also had the highest expression of ACAN.

CONCLUSION

Adult articular chondrocytes, fetal interzone cells, and fetal anlage chondrocytes exhibited the highest chondrogenic potential. In this study, adult adipose-derived cells exhibited very limited chondrogenesis, and bone marrow-derived cells had limited and variable chondrogenic potential.

CLINICAL SIGNIFICANCE

Additional investigation of the high chondrogenic potential of fetal interzone cells and anlage chondrocytes to advance cell-based therapies in diarthrodial joints is warranted.

Chronic mild hypoxia promotes hippocampal neurogenesis involving Notch1 signaling in epileptic rats

Cognitive impairment is one of the most common and disabling co-morbidities of epilepsy. It is therefore imperative to find novel treatment approaches to rescue cognitive function among epilepsy patients. Adult neurogenesis is strongly implicated in cognitive function, and mild hypoxia is known to promote the proliferation and differentiation of both embryonic and adult neural stem cells (NSCs). In the present study, we investigated the effect of mild hypoxia on cognitive function and hippocampal neurogenesis of rats with pilocarpine-induced chronic epilepsy. Chronic epilepsy induced marked spatial learning and memory deficits in the Morris water maze that were rescued by consecutively 28 days mild hypoxia exposure (6 h/d at 3000 m altitude equivalent) during the chronic phase. Moreover, mild hypoxia reversed the suppression of hippocampal neurogenesis and the downregulation of NT-3 and BDNF expression in hippocampus and cortex of epileptic rats. Mild hypoxia in vitro also promoted hippocampus-derived NSC proliferation and neuronal differentiation. In addition, mild hypoxia enhanced Notch1 and Hes1 expression, suggesting that Notch1 signaling may be involved in neuroprotection of hypoxia. Our data may help to pave the way for identifying new therapeutic targets for rescuing cognition conflicts in epileptic patients by using hypoxia to promote hippocampus neurogenesis.

Possible Role of PHD Inhibitors as Hypoxia-Mimicking Agents in the Maintenance of Neural Stem Cells' Self-Renewal Properties

Hypoxia is the most critical factor for maintaining stemness. During embryonic development, neural stem cells (NSCs) reside in hypoxic niches, and different levels of oxygen pressure and time of hypoxia exposure play important roles in the development of NSCs. Such hypoxic niches exist in adult brain tissue, where the neural precursors originate. Hypoxia-inducible factors (HIFs) are key transcription heterodimers consisting of regulatory α-subunits (HIF-1α, HIF-2α, HIF-3α) and a constitutive β-subunit (HIF-β). Regulation of downstream targets determines the fate of NSCs. In turn, the stability of HIFs-α is regulated by prolyl hydroxylases (PHDs), whose activity is principally modulated by PHD substrates like oxygen (O₂), α-ketoglutarate (α-KG), and the co-factors ascorbate (ASC) and ferrous iron (Fe²⁺). It follows that the transcriptional activity of HIFs is actually determined by the contents of O₂, α-KG, ASC, and Fe²⁺. In normoxia, HIFs-α are rapidly degraded via the ubiquitin-proteasome pathway, in which PHDs, activated by O₂, lead to hydroxylation of HIFs-α at residues 402 and 564, followed by recognition by the tumor suppressor protein von Hippel–Lindau (pVHL) as an E3 ligase and ubiquitin labeling. Conversely, in hypoxia, the activity of PHDs is inhibited by low O₂ levels and HIFs-α can thus be stabilized. Hence, suppression of PHD activity in normoxic conditions, mimicking the effect of hypoxia, might be beneficial for preserving the stemness of NSCs, and it is clinically relevant as a therapeutic approach for enhancing the number of NSCs in vitro and for cerebral ischemia injury in vivo. This study will review the putative role of PHD inhibitors on the self-renewal of NSCs.

Lithium chloride promotes proliferation of neural stem cells in vitro, possibly by triggering the Wnt signaling pathway

The objective of this study was to clarify the relationship between the effect and associated mechanisms of lithium chloride on neural stem cells (NSCs) and the Wnt signaling pathway. The expression of key molecules proteins related to the Wnt signaling pathway in the proliferation and differentiation of control NSCs and lithium chloride-treated NSCs was detected by Western blot analysis. Flow cytometry analysis was applied to study the cell cycle dynamics of control NSCs and NSCs treated with lithium chloride. The therapeutic concentrations of lithium chloride stimulated NSC proliferation. β-catenin expression gradually decreased, while Gsk-3β expression gradually increased (P < 0.01). Furthermore, NSCs treated with lithium chloride showed significantly enhanced β-catenin expression and inhibited Gsk-3β expression in a dose-dependent manner. NSCs in the G0/G1-phases were activated with an increased therapeutic concentration of lithium chloride, while NSCs in the S-phase, as well as G2/M-phases, were arrested (P < 0.01). These data confirm that the proliferation of NSCs is remarkably promoted through changes of cell dynamics after treatment with lithium chloride. Our results provide insight into the effects of lithium chloride in promoting the proliferation abilities of NSCs in vitro and preventing the cells from differentiating, which is potentially mediated by activation of the Wnt signaling pathway.

Involvement of follistatin-like 3 in preeclampsia

INTRODUCTION

Preeclampsia is a main cause of maternal and perinatal mortality and morbidity. The expression of follistatin-like 3 (FSTL3) is enhanced in maternal serum and placenta of preeclamptic women. However, whether FSTL3 is involved in the pathophysiologic of preeclampsia has not been clarified yet.

METHOD

Trophoblast cell lines Swan71 and JAR cells were cultured and siRNA was used to silence FSTL3. The expression of FSTL3 was determined by Western blotting. The matrigel-coated transwell and wound healing assays were used to assess invasion and migration, cell proliferation and apoptosis were detected by CCK-8 and flow cytometric analysis, respectively. Oil red O staining was used to detect the lipid storage in trophoblast.

RESULTS

Hypoxia culture significantly enhanced the expression of FSTL3 by trophoblast. Down-regulation of FSTL3 significantly suppressed the proliferation, migration, invasion and lipid storage but increased apoptosis of trophoblast.

DISCUSSION

Aberrant expression of FSTL3 in preeclampsia led to the dysfunction of trophoblast, indicating its involvement in the pathogenesis of preeclampsia.

Retinoic Acid Is Required for Neural Stem and Progenitor Cell Proliferation in the Adult Hippocampus

Neural stem and precursor cell (NSPC) proliferation in the rodent adult hippocampus is essential to maintain stem cell populations and produce new neurons. Retinoic acid (RA) signaling is implicated in regulation of adult hippocampal neurogenesis, but its exact role in control of NSPC behavior has not been examined. We show RA signaling in all hippocampal NSPC subtypes and that inhibition of RA synthesis or signaling significantly decreases NSPC proliferation via abrogation of cell-cycle kinetics and cell-cycle regulators. RA signaling controls NSPC proliferation through hypoxia inducible factor-1α (HIF1α), where stabilization of HIF1α concurrent with disruption of RA signaling can prevent NSPC defects. These studies demonstrate a cell-autonomous role for RA signaling in hippocampal NSPCs that substantially broadens RA's function beyond its well-described role in neuronal differentiation.

Chemical compound-based direct reprogramming for future clinical applications

Recent studies have revealed that a combination of chemical compounds enables direct reprogramming from one somatic cell type into another without the use of transgenes by regulating cellular signaling pathways and epigenetic modifications. The generation of induced pluripotent stem (iPS) cells generally requires virus vector-mediated expression of multiple transcription factors, which might disrupt genomic integrity and proper cell functions. The direct reprogramming is a promising alternative to rapidly prepare different cell types by bypassing the pluripotent state. Because the strategy also depends on forced expression of exogenous lineage-specific transcription factors, the direct reprogramming in a chemical compound-based manner is an ideal approach to further reduce the risk for tumorigenesis. So far, a number of reported research efforts have revealed that combinations of chemical compounds and cell-type specific medium transdifferentiate somatic cells into desired cell types including neuronal cells, glial cells, neural stem cells, brown adipocytes, cardiomyocytes, somatic progenitor cells, and pluripotent stem cells. These desired cells rapidly converted from patient-derived autologous fibroblasts can be applied for their own transplantation therapy to avoid immune rejection. However, complete chemical compound-induced conversions remain challenging particularly in adult human-derived fibroblasts compared with mouse embryonic fibroblasts (MEFs). This review summarizes up-to-date progress in each specific cell type and discusses prospects for future clinical application toward cell transplantation therapy.

Notch signaling molecule is involved in the invasion of MiaPaCa2 cells induced by CoCl2 via regulating epithelial‑mesenchymal transition

Pancreatic cancer exhibits a high mortality rate resulting from metastasis and there is currently no effective treatment strategy. Hypoxia serves an important role in cancer cells, where cellular metabolic rate is high. The underlying mechanisms that trigger hypoxia and the invasion of pancreatic cancer cells remain unknown. Investigation of the importance of hypoxia in the invasion of pancreatic cancer cells for potential, novel treatment strategies is of primary concern. Cell Counting Kit-8 assay, invasion assay, western blotting and reverse transcription-quantitative polymerase chain reaction were used to investigate invasion and epithelial mesenchymal transition (EMT) and the expression of Notch1 in MiaPaCa2 cells treated with cobalt II chloride (CoCl₂). Hypoxia-inducible factor 1α (HIF-1α) small interfering (si)RNA and Notch1 inhibitor N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT) were also selected to investigate these mechanisms. Data indicated that CoCl₂ increased the invasion ability and altered EMT in MiaPaCa2 cells. CoCl₂ regulated the expression of HIF-1α and Notch1 in MiaPaCa2 cells. In addition, HIF-1α siRNA inhibited the effects of CoCl₂ on the expression of Notch1 and decreased Snail, EMT and invasion in MiaPaCa2 cells. DAPT increased the expression of epithelial-cadherin and decreased the content of neural-cadherin, Snail and invasion in MiaPaCa2 cells in the presence or absence of CoCl₂. CoCl₂ promoted invasion by stimulating the expression of HIF-1α and regulating the expression of Notch1 and EMT in MiaPaCa2 cells. Targeting the Notch1 signaling molecule may be a novel treatment strategy for the prevention and treatment of pancreatic cancer.

Comparative Response of Brain to Chronic Hypoxia and Hyperoxia

Two antithetic terms, hypoxia and hyperoxia, i.e., insufficient and excess oxygen availability with respect to needs, are thought to trigger opposite responses in cells and tissues. This review aims at summarizing the molecular and cellular mechanisms underlying hypoxia and hyperoxia in brain and cerebral tissue, a context that may prove to be useful for characterizing not only several clinically relevant aspects, but also aspects related to the evolution of oxygen transport and use by the tissues. While the response to acute hypoxia/hyperoxia presumably recruits only a minor portion of the potentially involved cell machinery, focusing into chronic conditions, instead, enables to take into consideration a wider range of potential responses to oxygen-linked stress, spanning from metabolic to genic. We will examine how various brain subsystems, including energetic metabolism, oxygen sensing, recruitment of pro-survival pathways as protein kinase B (Akt), mitogen-activated protein kinases (MAPK), neurotrophins (BDNF), erythropoietin (Epo) and its receptors (EpoR), neuroglobin (Ngb), nitric oxide (NO), carbon monoxide (CO), deal with chronic hypoxia and hyperoxia to end-up with the final outcomes, oxidative stress and brain damage. A more complex than expected pattern results, which emphasizes the delicate balance between the severity of the stress imposed by hypoxia and hyperoxia and the recruitment of molecular and cellular defense patterns. While for certain functions the expectation that hypoxia and hyperoxia should cause opposite responses is actually met, for others it is not, and both emerge as dangerous treatments.

Hypoxia-regulated human periodontal ligament cells via Wnt/β-catenin signaling pathway

BACKGROUND

The aim of this study is to investigate the effects of hypoxia on the proliferation, morphology, migration ability, hypoxia inducible factor (HIF) 1 (HIF-1) expression, and the relationship with Wnt/β-catenin signaling of human periodontal ligament cells (hPDLCs) in vitro.

METHODS

hPDLCs (4th passage) cultured by the tissue culture method were randomly assigned to slight (5% O2), severe hypoxia (1% O2) groups, and the control (21% O2) group, respectively. From 1st to 7th day, the optical density values were detected, and the growth curve was described. Wound healing assay was done to observe the migration ability of hPDLCs under various O2 conditions. Then reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) was used to detect the expression of cementum-related genes and Wnt signaling pathway-related genes. Further, RT-qPCR, Western blot, and immunofluorescence staining method were constructed to show HIF expressions under different O2 concentrations in hPDLCs.

RESULTS

The growth rate of hPDLCs decreased with the reduction of O2 content by degree, and the morphology of hPDLCs changed in different O2 contents. Besides, hPDLCs migrate faster in 21% and 5% O2 than in 1% O2, and both the expressions of cementum-related genes and Wnt signaling pathway-related genes were raised under hypoxic conditions. In addition, with the reduction of O2 concentration, the messenger RNA and protein level expression of HIF were all increased, and HIF was gradually transported from cytoplasm into the nucleus and in 1% O2 concentration, it was mainly expressed in the nucleus.

CONCLUSION

This finding demonstrated that hypoxia was capable of suppressing the proliferation and migration ability, changing the morphology of hPDLCs, and stabilizing HIF-1α against degradation and promoting its translocation to the nucleus. Meanwhile, hypoxia may regulate hPDLCs proliferation and cementogenic differentiation via Wnt/β-catenin signaling pathway, which may potentially provide a novel insight into the etiology and treatment of periodontal diseases.

Hypoxia regulates CD44 expression via hypoxia-inducible factor-1α in human gastric cancer cells

Hypoxia induces proliferation and invasion in cancer cells via hypoxia-inducible factor (HIF)-1α. The cell adhesion molecule cluster of differentiation (CD) 44 has been associated with increased cell invasion and metastasis. Whether hypoxia regulates the expression of CD44 in gastric cancer cells remains to be established. In the current study, the effects of hypoxia on HIF-1α and CD44 expression levels in human gastric cell lines SGC-7901 and BGC-823 were evaluated. The cells were cultured in 1% O₂ for 1 week and then treated with 20 nM rapamycin for 72 h. Cell viability was evaluated using the Cell Counting kit-8 assay, and cell invasion was detected by the Transwell invasion assay. The protein and messenger (m) RNA expression levels of HIF-1α and CD44 were detected using western blotting and reverse transcription-quantitative polymerase chain reaction, respectively. The results revealed that cell viability and invasion increased under hypoxic conditions, but decreased following rapamycin treatment in SGC-7901 and BGC-823 cells. Hypoxia also increased the protein and mRNA expression levels of HIF-1α and CD44 in these two cell lines. However, this hypoxia-induced increase in HIF-1α and CD44 protein and mRNA expression levels was inhibited by rapamycin. These findings suggest that hypoxia induced the proliferation and invasion of SGC-7901 and BGC-823 cells. Furthermore, CD44 expression levels were potentially associated with HIF-1α expression levels. Therefore, in gastric cancer cells, hypoxia may regulate CD44 expression via HIF-1α in order to promote cell proliferation and invasion.

Does Renal Repair Recapitulate Kidney Development?

Over a decade ago, it was proposed that the regulation of tubular repair in the kidney might involve the recapitulation of developmental pathways. Although the kidney cannot generate new nephrons after birth, suggesting a low level of regenerative competence, the tubular epithelial cells of the nephrons can proliferate to repair the damage after AKI. However, the debate continues over whether this repair involves a persistent progenitor population or any mature epithelial cell remaining after injury. Recent reports have highlighted the expression of Sox9, a transcription factor critical for normal kidney development, during postnatal epithelial repair in the kidney. Indeed, the proliferative response of the epithelium involves expression of several pathways previously described as being involved in kidney development. In some instances, these pathways are also apparently involved in the maladaptive responses observed after repeated injury. Whether development and repair in the kidney are the same processes or we are misinterpreting the similar expression of genes under different circumstances remains unknown. Here, we review the evidence for this link, concluding that such parallels in expression may more correctly represent the use of the same pathways in a distinct context, likely triggered by similar stressors.

Neurotrophic Factor-α1: A Key Wnt-β-Catenin Dependent Anti-Proliferation Factor and ERK-Sox9 Activated Inducer of Embryonic Neural Stem Cell Differentiation to Astrocytes in Neurodevelopment

Embryonic neurodevelopment involves inhibition of proliferation of multipotent neural stem cells (NSCs) followed by differentiation into neurons, astrocytes and oligodendrocytes to form the brain. We have identified a new neurotrophic factor, NF-α1, which inhibits proliferation and promotes differentiation of NSC/progenitors derived from E13.5 mouse cortex. Inhibition of proliferation of these cells was mediated through negatively regulating the Wnt pathway and decreasing β-catenin. NF-α1 induced differentiation of NSCs to astrocytes by enhancing Glial Fibrillary Acidic Protein (GFAP) expression through activating the ERK1/2-Sox9 signaling pathway. Cultured E13.5 cortical stem cells from NF-α1-knockout mice showed decreased astrocyte numbers compared to wild-type mice, which was rescued by treatment with NF-α1. In vivo, immunocytochemistry of brain sections and Western blot analysis of neocortex of mice showed a gradual increase of NF-α1 expression from E14.5 to P1 and a surge of GFAP expression at P1, the time of increase in astrogenesis. Importantly, NF-α1-Knockout mice showed ∼49% fewer GFAP positive astrocytes in the neocortex compared to WT mice at P1. Thus, NF-α1 is critical for regulating antiproliferation and cell fate determination, through differentiating embryonic stem cells to GFAP-positive astrocytes for normal neurodevelopment. Stem Cells 2017;35:557-571.

Identification of β-Dystrobrevin as a Direct Target of miR-143: Involvement in Early Stages of Neural Differentiation

Duchenne Muscular Dystrophy, a genetic disorder that results in a gradual breakdown of muscle, is associated to mild to severe cognitive impairment in about one-third of dystrophic patients. The brain dysfunction is independent of the muscular pathology, occurs early, and is most likely due to defects in the assembly of the Dystrophin-associated Protein Complex (DPC) during embryogenesis. We have recently described the interaction of the DPC component β-dystrobrevin with members of complexes that regulate chromatin dynamics, and suggested that β-dystrobrevin may play a role in the initiation of neuronal differentiation. Since oxygen concentrations and miRNAs appear as well to be involved in the cellular processes related to neuronal development, we have studied how these factors act on β-dystrobrevin and investigated the possibility of their functional interplay using the NTera-2 cell line, a well-established model for studying neurogenesis. We followed the pattern of expression and regulation of β-dystrobrevin during the early stages of neuronal differentiation induced by exposure to retinoic acid (RA) under hypoxia as compared with normoxia, and found that β-dystrobrevin expression is regulated during RA-induced differentiation of NTera-2 cells. We also found that β-dystrobrevin pattern is delayed under hypoxic conditions, together with a delay in the differentiation and an increase in the proliferation rate of cells. We identified miRNA-143 as a direct regulator of β-dystrobrevin expression, demonstrated that β-dystrobrevin is expressed in the nucleus and showed that, in line with our previous in vitro results, β-dystrobrevin is a repressor of synapsin I in live cells. Altogether the newly identified regulatory pathway miR-143/β-dystrobrevin/synapsin I provides novel insights into the functions of β-dystrobrevin and opens up new perspectives for elucidating the molecular mechanisms underlying the neuronal involvement in muscular dystrophy.

Notch signaling represses hypoxia-inducible factor-1α-induced activation of Wnt/β-catenin signaling in osteoblasts under cobalt-mimicked hypoxia

The modification of Wnt and Notch signaling pathways by hypoxia, and its association with osteoblast proliferation and apoptosis remain to be fully elucidated. To investigate Wnt-Notch crosstalk, and its role in hypoxia-induced osteoblast proliferation and apoptosis regulation, the present study investigated the effects of cobalt-mimicked hypoxia on the mouse pre-osteoblast-like cell line, MC3T3-E1, when the Notch signals were repressed using a γ-secretase inhibitor DAPT. The data showed that the cobalt-mimicked hypoxia suppressed cell proliferation under normal conditions, but increased cell proliferation under conditions of Notch repression, in a concentration-dependent manner. The results of western blot and reverse transcription-quantitative polymerase chain reaction analyses showed that the cobalt treatment increased the levels of activated β-catenin protein and the expression levels of the target genes, axis inhibition protein 2 and myelocytomatosis oncogene, under DAPT-induced Notch repression. However, no significant changes were found in the expression levels of the Notch intracellular domain protein or the Notch target gene, hes1. In a β-catenin gene-knockdown experiment, the proliferation of the MC3T3-E1 cells under hypoxia were decreased by DAPT treatment, and knockdown of the expression of hypoxia-inducible factor-1α (HIF-1α) suppressed the cobalt-induced increase in Wnt target gene levels. No significant difference in cell proliferation rate was found following DAPT treatment when the expression of HIF-1α was knocked down. The results of the present study showed the opposing effects of Wnt and Notch signaling under cobalt-mimicked hypoxia, which were partially regulated by HIF-1α, The results also showed that osteoblast proliferation was dependent on Wnt-Notch signal crosstalk.

Phosphofructokinase-1 Negatively Regulates Neurogenesis from Neural Stem Cells

Phosphofructokinase-1 (PFK-1), a major regulatory glycolytic enzyme, has been implicated in the functions of astrocytes and neurons. Here, we report that PFK-1 negatively regulates neurogenesis from neural stem cells (NSCs) by targeting pro-neural transcriptional factors. Using in vitro assays, we found that PFK-1 knockdown enhanced, and PFK-1 overexpression inhibited the neuronal differentiation of NSCs, which was consistent with the findings from NSCs subjected to 5 h of hypoxia. Meanwhile, the neurogenesis induced by PFK-1 knockdown was attributed to the increased proliferation of neural progenitors and the commitment of NSCs to the neuronal lineage. Similarly, in vivo knockdown of PFK-1 also increased neurogenesis in the dentate gyrus of the hippocampus. Finally, we demonstrated that the neurogenesis mediated by PFK-1 was likely achieved by targeting mammalian achaete-scute homologue-1 (Mash 1), neuronal differentiation factor (NeuroD), and sex-determining region Y (SRY)-related HMG box 2 (Sox2). All together, our results reveal PFK-1 as an important regulator of neurogenesis.

Involvement of Cold Inducible RNA-Binding Protein in Severe Hypoxia-Induced Growth Arrest of Neural Stem Cells In Vitro

Neonatal hypoxia is the leading cause of brain damage with birth complications. Many studies have reported proliferation-promoting effect of mild hypoxia on neural stem cells (NSCs). However, how severe hypoxia influences the behavior of NSCs has been poorly explored. In the present study, we investigated the effects of 5, 3, and 1 % oxygen exposure on NSCs in vitro. MTT, neurosphere assay, and 5-ethynyl-2′-deoxyuridine (EdU) incorporation revealed a quick growth arrest of C17.2 cells and primary NSCs induced by 1 % oxygen exposure. Cell cycle analysis showed that this hypoxia exposure caused a significant increase of cells in G0/G1 phase and decrease of cells in S phase that is associated with decrease of Cyclin D1. Interestingly, the expression of cold inducible RNA-binding protein (CIRBP), a cold responsive gene reacting to multiple cellular stresses, was decreased in parallel with the 1 % oxygen-induced proliferation inhibition. Forced expression of CIRBP under hypoxia could restore the proliferation of NSCs, as showed by EdU incorporation and cell cycle analysis. Furthermore, the expression of Cyclin D1 under hypoxia was also restored by CIRBP overexpression. Taken together, these data suggested a growth-suppressing effect of severe hypoxia on NSCs and, for the first time, revealed a novel role of CIRBP in hypoxia-induced cell cycle arrest, suggesting that modulating CIRBP may be utilized for preventing hypoxia-induced neonatal brain injury.

Oxygen Tension Within the Neurogenic Niche Regulates Dopaminergic Neurogenesis in the Developing Midbrain

Oxygen tension is an important factor controlling stem cell proliferation and maintenance in various stem cell populations with a particular relevance in midbrain dopaminergic progenitors. Further studies have shown that the oxygen-dependent transcription factor hypoxia-inducible factor 1α (HIF-1α) is involved in these processes. However, all available studies on oxygen effects in dopaminergic neuroprogenitors were performed in vitro and thus it remains unclear whether tissue oxygen tension in the embryonic midbrain is also relevant for the regulation of dopaminergic neurogenesis in vivo. We thus dissect here the effects of oxygen tension in combination with HIF-1α conditional knockout on dopaminergic neurogenesis by using a novel experimental design allowing for the control of oxygen tension within the microenvironment of the neurogenic niche of the murine fetal midbrain in vivo. The microenvironment of the midbrain dopaminergic neurogenic niche was detected as hypoxic with oxygen tensions below 1.1%. Maternal oxygen treatment of 10%, 21%, and 75% atmospheric oxygen tension for 48 h translates into robust changes in fetal midbrain oxygenation. Fetal midbrain hypoxia hampered the generation of dopaminergic neurons and is accompanied with restricted fetal midbrain development. In contrast, induced hyperoxia stimulated proliferation and differentiation of dopaminergic progenitors during early and late embryogenesis. Oxygen effects were not directly mediated through HIF-1α signaling. These data--in agreement with in vitro data-indicate that oxygen is a crucial regulator of developmental dopaminergic neurogenesis. Our study provides the initial framework for future studies on molecular mechanisms mediating oxygen regulation of dopaminergic neurogenesis within the fetal midbrain as its natural environment.

Regulation of cell proliferation by hypoxia-inducible factors

Hypoxia is a physiological cue that impacts diverse physiological processes, including energy metabolism, autophagy, cell motility, angiogenesis, and erythropoiesis. One of the key cell-autonomous effects of hypoxia is as a modulator of cell proliferation. For most cell types, hypoxia induces decreased cell proliferation, since an increased number of cells, with a consequent increase in O2 demand, would only exacerbate hypoxic stress. However, certain cell populations maintain cell proliferation in the face of hypoxia. This is a common pathological hallmark of cancers, but can also serve a physiological function, as in the maintenance of stem cell populations that reside in a hypoxic niche. This review will discuss major molecular mechanisms by which hypoxia regulates cell proliferation in different cell populations, with a particular focus on the role of hypoxia-inducible factors.