Acute anoxia stimulates proliferation in adult neural stem cells from the rat brain

Promoting Alzheimer's disease research and therapy with stem cell technology

BACKGROUND

Alzheimer's disease (AD) is a prevalent form of dementia leading to memory loss, reduced cognitive and linguistic abilities, and decreased self-care. Current AD treatments aim to relieve symptoms and slow disease progression, but a cure is elusive due to limited understanding of the underlying disease mechanisms.

MAIN CONTENT

Stem cell technology has the potential to revolutionize AD research. With the ability to self-renew and differentiate into various cell types, stem cells are valuable tools for disease modeling, drug screening, and cell therapy. Recent advances have broadened our understanding beyond the deposition of amyloidβ (Aβ) or tau proteins in AD to encompass risk genes, immune system disorders, and neuron-glia mis-communication, relying heavily on stem cell-derived disease models. These stem cell-based models (e.g., organoids and microfluidic chips) simulate in vivo pathological processes with extraordinary spatial and temporal resolution. Stem cell technologies have the potential to alleviate AD pathology through various pathways, including immunomodulation, replacement of damaged neurons, and neurotrophic support. In recent years, transplantation of glial cells like oligodendrocytes and the infusion of exosomes have become hot research topics.

CONCLUSION

Although stem cell-based models and therapies for AD face several challenges, such as extended culture time and low differentiation efficiency, they still show considerable potential for AD treatment and are likely to become preferred tools for AD research.

Role of hyperpolarization-activated cyclic nucleotide-gated channel HCN2 in embryonic neural stem cell proliferation and differentiation

Hyperpolarization-activated cyclic nucleotide-gated channels (HCN channels) are involved in spontaneous activity in many electrically active cell types such as cardiomyocytes and neurons. In this study, the role of HCN channels in proliferation and migration of Nestin and Sox2 expressing embryonic neural progenitor cells (NPC) originating from the subventricular zone (SVZ) was examined. Immunostaining and PCR data showed that the HCN2 subtype was highly expressed in these cells. Patch clamp recordings revealed a hyperpolarization-activated current, which was sensitive to inhibitors of HCN channels. Using the fluorescence dye bis-(1,3-dibutylbarbituric acid)-trimethineoxonol (DiBAC(4)(3)) we found that a prompt reduction of the extracellular K⁺ concentration, or exposing the cells to acute hypoxia, induced an instant hyperpolarization in the whole cell population. Recovery from low K⁺ induced hyperpolarization after extracellular calcium removal, or by re-oxygenation of hypoxic cells, was sensitive to ZD7288, a HCN channel inhibitor. Treatment of neurosphere cultures from the SVZ with ZD7288 caused a significant and reversible inhibition of neurosphere formation from single cells indicating that proliferation of progenitor cells was reduced. Furthermore, the migration of neuronal cells from neurospheres was considerably retarded in the presence of ZD7288. The results suggest that HCN2 channels are involved in controlling the proliferation of NPC and that HCN2 channel-induced spontaneous electrical activity may trigger the motility response of neurosphere-derived neurons in concert with other ion channels. Furthermore, the response to hypoxia suggests that HCN2 channels may trigger the chemotactic response of NPC to ischemic brain regions seen in many studies.

HIF‑1α in cerebral ischemia (Review)

Cerebral ischemic injury may lead to a series of serious brain diseases, death or different degrees of disability. Hypoxia-inducible factor-1α (HIF-1α) is an oxygen-sensitive transcription factor, which mediates the adaptive metabolic response to hypoxia and serves a key role in cerebral ischemia. HIF-1α is the main molecule that responds to hypoxia. HIF-1α serves an important role in the development of cerebral ischemia by participating in numerous processes, including metabolism, proliferation and angiogenesis. The present review focuses on the endogenous protective mechanism of cerebral ischemia and elaborates on the role of HIF-1α in cerebral ischemia. In addition, it focuses on cerebral ischemia interventions that act on the HIF-1α target, including biological factors, non-coding RNA, hypoxic-ischemic preconditioning and drugs, and expands upon the measures to strengthen the endogenous compensatory response to support HIF-1α as a therapeutic target, thus providing novel suggestions for the treatment of cerebral ischemia.

Bovine Satellite Cells Isolated after 2 and 5 Days of Tissue Storage Maintain the Proliferative and Myogenic Capacity Needed for Cultured Meat Production

Cultured meat is an emerging alternative food technology which aims to deliver a more ethical, sustainable, and healthy muscle-tissue-derived food item compared to conventional meat. As start-up companies are rapidly forming and accelerating this technology, many aspects of this multi-faceted science have still not been investigated in academia. In this study, we investigated if bovine satellite cells with the ability to proliferate and undergo myogenic differentiation could be isolated after extended tissue storage, for the purpose of increasing the practicality for cultured meat production. Proliferation of bovine satellite cells isolated on the day of arrival or after 2 and 5 days of tissue storage were analyzed by metabolic and DNA-based assays, while their myogenic characteristics were investigated using RT-qPCR and immunofluorescence. Extended tissue storage up to 5 days did not negatively affect proliferation nor the ability to undergo fusion and create myosin heavy chain-positive myotubes. The expression patterns of myogenic and muscle-specific genes were also not affected after tissue storage. In fact, the data indicated a positive trend in terms of myogenic potential after tissue storage, although it was non-significant. These results suggest that the timeframe of which viable myogenic satellite cells can be isolated and used for cultured meat production can be greatly extended by proper tissue storage.

The Effects of Hypoxia-Reoxygenation in Mouse Digital Flexor Tendon-Derived Cells

Objective

Ischemia-reperfusion injury refers to the exacerbated and irreversible tissue damage caused by blood flow restoration after a period of ischemia. The hypoxia-reoxygenation (H/R) model in vitro is ideal for studying ischemia-reperfusion injury at the cellular level. We employed this model and investigated the effects of cobalt chloride- (CoCl₂-) induced H/R in cells derived from mouse digital flexor tendons.

Materials and Methods

Various H/R conditions were simulated via treatment of tendon-derived cells with different concentrations of CoCl₂ for 24 h, followed by removal of CoCl₂ to restore a normal oxygen state for up to 96 h. Cell viability was measured using the Cell Counting Kit-8 (CCK-8) assay. Cell growth was determined via observation of cell morphology and proliferation. Oxidative stress markers and mitochondrial activity were detected. The expression levels of hypoxia-inducible factor- (HIF-) 1α, vascular endothelial growth factor-A (VEGF-A), collagen I, and collagen III were determined using Western blot (WB), real-time PCR, and immunofluorescence staining. Cellular apoptosis was analyzed via flow cytometry, and the expression of apoptosis-related proteins Bax and bcl-2 was examined using WB.

Results

The cells treated with low concentrations of CoCl₂ showed significantly increased cell viability after reoxygenation. The increase in cell viability was even more pronounced in cells that had been treated with high concentrations of CoCl₂. Under H/R conditions, cell morphology and growth were unchanged, while oxidative stress reaction was induced and mitochondrial activity was increased. H/R exerted opposite effects on the expression of HIF-1α mRNA and protein. Meanwhile, the expression of VEGF-A was upregulated, whereas collagen type I and type III were significantly downregulated. The level of cellular apoptosis did not show significant changes during H/R, despite the significantly increased Bax protein and reduced bcl-2 protein levels that led to an increase in the Bax/bcl-2 ratio during reoxygenation.

Conclusions

Tendon-derived cells were highly tolerant to the hypoxic environments induced by CoCl₂. Reoxygenation after hypoxia preconditioning promoted cell viability, especially in cells treated with high concentrations of CoCl₂. H/R conditions caused oxidative stress responses but did not affect cell growth. The H/R process had a notable impact on collagen production and expression of apoptosis-related proteins by tendon-derived cells, while the level of cellular apoptosis remained unchanged.

Hypoxia stimulates neural stem cell proliferation by increasing HIF‑1α expression and activating Wnt/β-catenin signaling

Evidence indicates that after brain injury, neurogenesis is enhanced in regions such as hippocampus, striatum, and cortex. To study the role of hypoxia-inducible factor-1 (HIF‑1α) and Wnt signaling in cerebral ischemia/hypoxia-induced proliferation of neural stem cells (NSCs), we investigated the proliferation of NSCs, expression of HIF‑1α, and activation of Wnt signaling under conditions of pathologic hypoxia in vitro. NSCs were isolated from 30-day-old Sprague-Dawley rats and subjected to 0.3% oxygen in a microaerophilic incubation system. Cell proliferation was evaluated by measuring the diameter of neurospheres and by bromodeoxyuridine incorporation assays. Real-time quantitative PCR and Western blotting were used to detect mRNA and protein levels of HIF-1α, β-catenin, and cyclin D1 in the NSCs. The results showed that hypoxia increased NSC proliferation and the levels of HIF-1α, β‑catenin, and cyclin D1 (p < 0.05). Blockade of the Wnt signaling pathway decreased hypoxia-induced NSC proliferation, whereas activation of this pathway increased hypoxia-induced NSC proliferation (p < 0.05). Knockdown of HIF-1α with HIF-1α siRNA decreased β‑catenin nuclear translocation and cyclin D1 expression, and inhibited proliferation of NSCs (p < 0.05). These findings indicate that pathologic hypoxia stimulates NSC proliferation by increasing expression of HIF-1α and activating the Wnt/β-catenin signaling pathway. The data suggest that Wnt/β-catenin signaling may play a key role in NSC proliferation under conditions of pathologic hypoxia.

Oxygen Levels Regulate the Development of Human Cortical Radial Glia Cells

The oxygen (O2) concentration is a vital parameter for controlling the survival, proliferation, and differentiation of neural stem cells. A prenatal reduction of O2 levels (hypoxia) often leads to cognitive and behavioral defects, attributable to altered neural development. In this study, we analyzed the effects of O2 levels on human cortical progenitors, the radial glia cells (RGCs), during active neurogenesis, corresponding to the second trimester of gestation. Small changes in O2 levels profoundly affected RGC survival, proliferation, and differentiation. Physiological hypoxia (3% O2) promoted neurogenesis, whereas anoxia (<1% O2) and severe hypoxia (1% O2) arrested the differentiation of human RGCs, mainly by altering the generation of glutamatergic neurons. The in vitro activation of Wnt-β-catenin signaling rescued the proliferation and neuronal differentiation of RGCs subjected to anoxia. Pathologic hypoxia (≤1% O2) also exerted negative effects on gliogenesis, by decreasing the number of O4+ preoligodendrocytes and increasing the number of reactive astrocytes derived from cortical RGCs. O2-dependent alterations in glutamatergic neurogenesis and oligodendrogenesis can lead to significant changes in cortical circuitry formation. A better understanding of the cellular effects caused by changes in O2 levels during human cortical development is essential to elucidating the etiology of numerous neurodevelopmental disorders.

Protective effects of ginsenoside Rg1 against oxygen-glucose-deprivation-induced apoptosis in neural stem cells

Oxygen-glucose deprivation (OGD) causes neural damages through stroke-induced ischemia. Neural stem cells (NSCs) have been shown to alleviate ischemia-induced neural damages. However, ischemia reduces NSC survival. Ginsenoside Rg1 exerts anti-inflammatory and anti-oxidative effects, and repairs brain injury-related neural damages. We aimed to investigate whether ginsenoside Rg1 could prevent NSCs from OGD insult. Using multiple techniques, we explored neuroprotective effects of ginsenoside Rg1 on OGD-insulted NSCs. 6h treatment of OGD most significantly decreased NSC viability, and 10-20μM ginsenoside Rg1 efficiently protected NSCs against OGD insult. Annexin V-FITC/propidium iodide (PI) double staining results confirmed that ginsenoside Rg1 significantly reduced the OGD-induced apoptosis in NSCs. OGD-insulted NSCs with ginsenoside Rg1 treatment displayed reduced expressions of pro-apoptotic proteins cleaved Caspase3 and Bax, and elevated expression of anti-apoptotic protein Bcl-2 than the NSCs with OGD insult. Moreover, ginsenoside Rg1 reduced OGD-induced oxidative stress, and inhibited the expression of p-p38 and p-JNK2. Ginsenoside Rg1 protects NSCs against OGD-induced cell apoptosis through regulating the expression of apoptotic signal proteins. In addition, ginsenoside Rg1 attenuates OGD-induced oxidative stress and inhibits p38/JNK2 phosphorylation in NSCs. Our study provides solid evidence for neuroprotective effects of ginsenoside Rg1 and reveals the underlying mechanisms.

Localized hypoxia within the subgranular zone determines the early survival of newborn hippocampal granule cells

The majority of adult hippocampal newborn cells die during early differentiation from intermediate progenitors (IPCs) to immature neurons. Neural stem cells in vivo are located in a relative hypoxic environment, and hypoxia enhances their survival, proliferation and stemness in vitro. Thus, we hypothesized that migration of IPCs away from hypoxic zones within the SGZ might result in oxidative damage, thus triggering cell death. Hypoxic niches were observed along the SGZ, composed of adult NSCs and early IPCs, and oxidative byproducts were present in adjacent late IPCs and neuroblasts. Stabilizing hypoxia inducible factor-1α with dimethyloxallyl glycine increased early survival, but not proliferation or differentiation, in neurospheres in vitro and in newly born SGZ cells in vivo. Rescue experiments in Bax(fl/fl) mutants supported these results. We propose that localized hypoxia within the SGZ contributes to the neurogenic microenvironment and determines the early, activity-independent survival of adult hippocampal newborn cells.

Enhanced differentiation of neural stem cells to neurons and promotion of neurite outgrowth by oxygen-glucose deprivation

Stroke has become the leading cause of mortality worldwide. Hypoxic or ischemic insults are crucial factors mediating the neural damage in the brain tissue of stroke patients. Neural stem cells (NSCs) have been recognized as a promising tool for the treatment of ischemic stroke and other neurodegenerative diseases due to their inducible pluripotency. In this study, we aim to mimick the cerebral hypoxic-ischemic injury in vitro using oxygen-glucose deprivation (OGD) strategy, and evaluate the effects of OGD on the NSC's neural differentiation, as well as the differentiated neurite outgrowth. Our data showed that NSCs under the short-term 2h OGD treatment are able to maintain cell viability and the capability to form neurospheres. Importantly, this moderate OGD treatment promotes NSC differentiation to neurons and enhances the performance of the mature neuronal networks, accompanying increased neurite outgrowth of differentiated neurons. However, long-term 6h and 8h OGD exposures in NSCs lead to decreased cell survival, reduced differentiation and diminished NSC-derived neurite outgrowth. The expressions of neuron-specific microtubule-associated protein 2 (MAP-2) and growth associated protein 43 (GAP-43) are increased by short-term OGD treatments but suppressed by long-term OGD. Overall, our results demonstrate that short-term OGD exposure in vitro induces differentiation of NSCs while maintaining their proliferation and survival, providing valuable insights of adopting NSC-based therapy for ischemic stroke and other neurodegenerative disorders.

Long live the stem cell: the use of stem cells isolated from post mortem tissues for translational strategies

The "stem cell" has become arguably one of the most important biological tools in the arsenal of translational research directed at regeneration and repair. It remains to be seen whether every tissue has its own stem cell niche, although relatively recently a large amount of research has focused on isolating and characterizing tissue-specific stem cell populations, as well as those that are able to be directed to transdifferentiate into a variety of different lineages. Traditionally, stem cells are isolated from the viable tissue of embryonic, fetal, or adult living hosts; from "fresh" donated tissues that have been surgically or otherwise removed (biopsies), or obtained directly from tissues within minutes to several hours post mortem (PM). These human progenitor/stem cell sources remain potentially highly controversial, since they are accompanied by various still-unresolved ethical, social, moral and legal challenges. Due to the limited number of "live" donors, the small amount of material obtained from biopsies and difficulties during purification processes, harvesting from cadaveric material presents itself as an alternative strategy that could provide a hitherto untapped source of stem cells. However, PM stem cells are not without their own unique set of limitations including difficulty of obtaining samples, limited supply of material, variations in delay between death and sample collection, possible lack of medication history and suboptimal retrospective assignment of diagnostic and demographic data. This article is part of a Directed Issue entitled: Regenerative Medicine: The challenge of translation.

Umbilical cord blood cells regulate the differentiation of endogenous neural stem cells in hypoxic ischemic neonatal rats via the hedgehog signaling pathway

Transplantation of umbilical cord blood mononuclear cells (UCBMC) promotes the proliferation of endogenous neural stem cells (NSCs), but it has been unclear whether the proliferating NSCs can differentiate into mature neural cells. Therefore, we explored the effects of UCBMC transplantation on the differentiation of endogenous NSCs and their underlying mechanisms. Seven-day-old Sprague-Dawley rats underwent left carotid ligation followed by hypoxic stress. UCBMC were transplanted 24h after hypoxia ischemia (HI). BrdU/β-tubulin/HNA/DAPI, BrdU/GFAP/HNA/DAPI, Ngn1/DAPI, and BMP4/DAPI were measured by immunofluorescence staining; Shh, Gli1, Ngn1, and BMP4 proteins were measured by western-blot analysis 28 days after transplantation. More newborn neurons and fewer astrocytes were observed in the HI+UCBMC group, its neuronal percentage was higher, and glial percentage was lower compared with the N+UCBMC (P<0.05) and HI+PBS groups (P<0.01), while fewer newborn neurons and more newborn astrocytes were found in the HI+cyclopamine (an antagonist of the hedgehog protein)+UCBMC group compared with the HI+UCBMC group (P<0.01). The expression of Shh, Gli1, and Ngn1 proteins was higher and BMP4 protein was lower in the HI+UCBMC compared with the HI+PBS group (P<0.01) and the HI+cyclopamine+UCBMC group (P<0.01). Linear regression analysis showed that the differentiation of NSCs correlated with expression of Ngn1 and BMP4 proteins (P<0.01). In conclusion, UCBMC promote neuronal differentiation and reduce glial differentiation in hypoxic ischemic neonatal rats via the hedgehog signaling pathway.

Human cadaver multipotent stromal/stem cells isolated from arteries stored in liquid nitrogen for 5 years

Introduction

Regenerative medicine challenges researchers to find noncontroversial, safe and abundant stem cell sources. In this context, harvesting from asystolic donors could represent an innovative and unlimited reservoir of different stem cells. In this study, cadaveric vascular tissues were established as an alternative source of human cadaver mesenchymal stromal/stem cells (hC-MSCs). We reported the successful cell isolation from postmortem arterial segments stored in a tissue-banking facility for at least 5 years.

Methods

After thawing, hC-MSCs were isolated with a high efficiency (12 × 10⁶) and characterized with flow cytometry, immunofluorescence, molecular and ultrastructural approaches.

Results

In early passages, hC-MSCs were clonogenic, highly proliferative and expressed mesenchymal (CD44, CD73, CD90, CD105, HLA-G), stemness (Stro-1, Oct-4, Notch-1), pericyte (CD146, PDGFR-β, NG2) and neuronal (Nestin) markers; hematopoietic and vascular markers were negative. These cells had colony and spheroid-forming abilities, multipotency for their potential to differentiate in multiple mesengenic lineages and immunosuppressive activity to counteract proliferation of phytohemagglutinin-stimulated blood mononuclear cells.

Conclusions

The efficient procurement of stem cells from cadaveric sources, as postmortem vascular tissues, demonstrates that such cells can survive to prolonged ischemic insult, anoxia, freezing and dehydration injuries, thus paving the way for a scientific revolution where cadaver stromal/stem cells could effectively treat patients demanding cell therapies.

Neural stem/progenitor cells display a low requirement for oxidative metabolism independent of hypoxia inducible factor-1alpha expression

Neural stem/progenitor cells (NSPCs) are multipotent cells within the embryonic and adult brain that give rise to both neuronal and glial cell lineages. Maintenance of NSPC multipotency is promoted by low oxygen tension, although the metabolic underpinnings of this trait have not been described. In this study, we investigated the metabolic state of undifferentiated NSPCs in culture, and tested their relative reliance on oxidative versus glycolytic metabolism for survival, as well as their dependence on hypoxia inducible factor-1alpha (HIF-1α) expression for maintenance of metabolic phenotype. Unlike primary neurons, NSPCs from embryonic and adult mice survived prolonged hypoxia in culture. In addition, NSPCs displayed greater susceptibility to glycolytic inhibition compared with primary neurons, even in the presence of alternative mitochondrial TCA substrates. NSPCs were also more resistant than neurons to mitochondrial cyanide toxicity, less capable of utilizing galactose as an alternative substrate to glucose, and more susceptible to pharmacological inhibition of the pentose phosphate pathway by 6-aminonicotinamide. Inducible deletion of exon 1 of the Hif1a gene improved the ability of NSPCs to utilize pyruvate during glycolytic inhibition, but did not alter other parameters of metabolism, including their ability to withstand prolonged hypoxia. Taken together, these data indicate that NSPCs have a relatively low requirement for oxidative metabolism for their survival and that hypoxic resistance is not dependent upon HIF-1α signaling.

High glucose induces apoptosis and suppresses proliferation of adult rat neural stem cells following in vitro ischemia

Background

Post-stroke hyperglycemia appears to be associated with poor outcome from stroke, greater mortality, and reduced functional recovery. Focal cerebral ischemia data support that neural stem cells (NSCs) play an important role in post-ischemic repair. Here we sought to evaluate the negative effects of hyperglycemia on the cellular biology of NSCs following anoxia, and to test whether high glucose affects NSC recovery from ischemic injury.

Results

In this study, we used immortalized adult neural stem cells lines and we induced in vitro ischemia by 6 h oxygen and glucose deprivation (OGD) in an anaerobic incubator. Reperfusion was performed by returning cells to normoxic conditions and the cells were then incubated in experimental medium with various concentrations of glucose (17.5, 27.75, 41.75, and 83.75 mM) for 24 h. We found that high glucose (≥27.75 mM) exposure induced apoptosis of NSCs in a dose-dependent manner after exposure to OGD, using an Annexin V/PI apoptosis detection kit. The cell viability and proliferative activity of NSCs following OGD in vitro, evaluated with both a Cell Counting kit-8 (CCK-8) assay and a 5-ethynyl-2’-deoxyuridine (EdU) incorporation assay, were inhibited by high glucose exposure. Cell cycle analysis showed that high glucose exposure increased the percentage of cells in G0/G1-phase, and reduced the percentage of cells in S-phase. Furthermore, high glucose exposure was found to significantly induce the activation of c-Jun N-terminal protein kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) and suppress extracellular signal-regulated kinase 1/2 (ERK1/2) activity.

Conclusions

Our results demonstrate that high glucose induces apoptosis and inhibits proliferation of NSCs following OGD in vitro, which may be associated with the activation of JNK/p38 MAPK pathways and the delay of G1-S transition in the cells.

Proliferation and differentiation of neural stem cells co-cultured with cerebral microvascular endothelial cells after oxygen-glucose deprivation

Various stem cells, including neural stem cells (NSCs), have been extensively studied in stroke models, but how to increase neuronal differentiation rate of NSCs remains unresolved, particularly in a damaged environment. The purpose of this study was to investigate the effects of cerebral microvascular endothelial cells (CMECs) on the neurogenesis of NSCs with or without oxygen-glucose deprivation (OGD). The NSCs acquired from primary culture were immunostained to prove cell purity. Survival and proliferation of NSCs were determined after the co-culture with CMECs for 7 days. After removing the CMECs, NSCs were randomly divided into two groups as follows: OGD and non-OGD groups. Both groups were maintained in differentiation culture for 4 days to evaluate the differentiation rate. Mouse embryo fibroblast (MEF) cells co-cultured with NSCs served as control group. NSCs co-cultured with CMECs had an increase in size (on the 7th day: 89.80±26.12 μm vs. 73.08±15.01 μm, P<0.001) (n=12) and number [on the 7th day: 6.33±5.61/high power objective (HP) vs. 2.23±1.61/HP, P<0.001] (n=12) as compared with those co-cultured with MEF cells. After further differentiation culture for 4 days, NSCs co-cultured with CMECs had an increase in neuronal differentiation rate in OGD and non-OGD groups, but not in the control group (15.16% and 16.07% vs. 8.81%; both P<0.001) (n=6). This study provided evidence that OGD could not alter the effects of CMECs in promoting the neuronal differentiation potential of NSCs. These findings may have important implications for the development of new cell therapies for cerebral vascular diseases.

Effects of acute hypoxia/acidosis on intracellular pH in differentiating neural progenitor cells

The response of differentiating mouse neural progenitor cells, migrating out from neurospheres, to conditions simulating ischemia (hypoxia and extracellular or intracellular acidosis) was studied. We show here, by using BCECF and single cell imaging to monitor intracellular pH (pH(i)), that two main populations can be distinguished by exposing migrating neural progenitor cells to low extracellular pH or by performing an acidifying ammonium prepulse. The cells dominating at the periphery of the neurosphere culture, which were positive for neuron specific markers MAP-2, calbindin and NeuN had lower initial resting pH(i) and could also easily be further acidified by lowering the extracellular pH. Moreover, in this population, a more profound acidification was seen when the cells were acidified using the ammonium prepulse technique. However, when the cell population was exposed to depolarizing potassium concentrations no alterations in pH(i) took place in this population. In contrast, depolarization caused an increase in pH(i) (by 0.5 pH units) in the cell population closer to the neurosphere body, which region was positive for the radial cell marker (GLAST). This cell population, having higher resting pH(i) (pH 6.9-7.1) also responded to acute hypoxia. During hypoxic treatment the resting pH(i) decreased by 0.1 pH units and recovered rapidly after reoxygenation. Our results show that migrating neural progenitor cells are highly sensitive to extracellular acidosis and that irreversible damage becomes evident at pH 6.2. Moreover, our results show that a response to acidosis clearly distinguishes two individual cell populations probably representing neuronal and radial cells.

Notch signaling pathway regulates proliferation and differentiation of immortalized Müller cells under hypoxic conditions in vitro

Previous studies have indicated that Müller glia in chick and fish retinas can re-enter the cell cycle, express progenitor genes, and regenerate neurons via the Notch signaling pathway in response to retinal damage or growth factors. Here, we investigated the role of Notch signaling and the effect of hypoxia, as a means to induce retinal damage, on the proliferation of an immortalized Müller cell line (rMC-1 cells). Our data showed that rMC-1 cells expressed Müller glia and neural and retinal progenitor markers but did not express neuronal or retinal markers. Hypoxia increased rMC-1 cell proliferation by activating the positive cell-cycle regulators, cyclins A and D1, as well as the neural and retinal progenitor markers, Notch1, Hes1, nestin, Sox2, Msi1, Pax6, and NeuroD1. However, hypoxia did not significantly influence the expression of Müller glial markers GS, CRALBP, and cyclin D3 or the death of the rMC-1 cells. The increase in cell proliferation induced by hypoxia was greatly attenuated by blocking Notch signaling with the inhibitor DAPT, resulting in the reduced expression of positive cell-cycle regulators (cyclins A and D1) and neural and retinal progenitor markers (Notch1, Hes1, Sox2, Pax6, and NeuroD1). Blockade of the Notch signaling pathway by DAPT after hypoxia promoted the differentiation of rMC-1 cells to neurons, as demonstrated by the induction of neural marker (Tuj1), retinal amacrine (Syntaxin1), and retinal ganglion cell (Brn3b) markers, although the expression of the latter marker was low. Taken together, our data indicate that Notch signaling is required for proliferation under hypoxic conditions either by activating the positive cell-cycle regulators or by skewing their de-differentiation towards a neural progenitor lineage. These findings indicate that the Notch signaling pathway regulates hypoxia-induced proliferation and differentiation of Müller glia.

mGluR5 is involved in proliferation of rat neural progenitor cells exposed to hypoxia with activation of mitogen-activated protein kinase signaling pathway

Hypoxia/ischemia induces proliferation of neural progenitor cells (NPCs) in rodent and human brain; however, the mechanisms remain unknown. We investigated the effects of metabotropic glutamate receptor 5 (mGluR5) on NPC proliferation under hypoxia, the expression of cyclin D1, and the activation of the mitogen-activated protein kinases (MAPKs) signaling pathway in cell culture. The results showed that hypoxia induced mGluR5 expression on NPCs in vitro. Under hypoxia, the mGluR5 agonists DHPG and CHPG significantly increased NPC proliferation in cell activity, diameter of neurospheres, bromodeoxyuridine (BrdU) incorporation and cell division, and expression of cyclin D1, with decreasing cell death. The mGluR5 siRNA and antagonist MPEP decreased the NPC proliferation and expression of cyclin D1, with increasing cell death. Phosphorylated JNK and ERK increased with the proliferation of NPCs after DHPG and CHPG treatment under hypoxia, while p-p38 level decreased. These results demonstrate that the expression of mGluR5 was upregulated during the proliferation of rat NPCs stimulated by hypoxia in vitro. The activation of the ERK and JNK signaling pathway and the expression of cyclin D1 were increased in this process. These finding suggest the involvement of mGluR5 in rat NPC proliferation and provide a target molecule in neural repair after ischemia/hypoxia injury of CNS.

Physiological oxygen level is critical for modeling neuronal metabolism in vitro

In vitro models are important tools for studying the mechanisms that govern neuronal responses to injury. Most neuronal culture methods employ nonphysiological conditions with regard to metabolic parameters. Standard neuronal cell culture is performed at ambient (21%) oxygen levels, whereas actual tissue oxygen levels in the mammalian brain range from 1% to 5%. In this study, we examined the consequences of oxygen level on the viability and metabolism of primary cultures of cortical neurons. Our results indicate that physiological oxygen level (5% O(2)) has a beneficial effect on cortical neuronal survival and mitochondrial function in vitro. Moreover, oxygen level affects metabolic fluxes: glucose uptake and glycolysis was enhanced at physiological oxygen level, whereas glucose oxidation and fatty acid oxidation were reduced. Adenosine monophosphate-activated protein kinase (AMPK) was more activated in 5% O(2) and appears to play a role in these metabolic effects. Inhibiting AMPK activity with compound C decreased glucose uptake, intracellular ATP level, and viability in neurons cultured in 5% O(2). These data indicate that oxygen level is an important parameter to consider when modeling neuronal responses to stress in vitro.

Combinated transplantation of neural stem cells and collagen type I promote functional recovery after cerebral ischemia in rats

Using tissue engineering, a complex of neural stem cells (NSCs) and collagen type I was transplanted for the therapy of cerebral ischemic injury. NSCs from E14 d rats were dissociated and cultured by neurosphere formation in serum-free medium in the presence of basic fibroblast growth factor (bFGF), then seeded onto collagen to measure cell adhesive ability. BrdU was added to the culture medium to label the NSCs. Wistar rats (n=100) were subjected to 2-hour middle cerebral artery occlusion. After 24 hours of reperfusion, rats were assigned randomly to five groups: NSCs-collagen repair group, NSCs repair group, unseeded collagen repair group, MCAO medium group, and sham group. Neurological, immunohistological and electronic microscope assessments were performed to examine the effects of these treatments. Scanning electronic microscopy showed that NSCs assemble in the pores of collagen. At 3, 7, 15, and 30 d after transplantation of the NSC-collagen complex, some of the engrafted NSCs survive, differentiate and form synapses in the brains of rats subjected to cerebral ischemia. Six d after transplantation of the NSC-collagen complex into the brains of ischemic rats, the collagen began to degrade; 30 d after transplantation, the collagen had degraded completely. The implantation of NSCs and type I collagen facilitated the structural and functional recovery of neural tissue following ischemic injury.

Neuropathologic and biochemical changes during disease progression in liver X receptor beta-/- mice, a model of adult neuron disease

In amyotrophic lateral sclerosis (ALS), there is selective degeneration of motor neurons that leads to paralysis and death. Although the etiology of ALS is unclear, its heterogeneity suggests that a combination of factors (endogenous and/or environmental) may induce progressive motor neuron stress that results in the activation of different cell death pathways. Alterations of brain cholesterol homeostasis have recently been considered as possible cofactors in many neurodegenerative disorders, including ALS. The liver X receptor beta (LXRbeta) receptor is involved in lipogenesis and cholesterol metabolism, and we previously found that adult-onset motor neuron pathology occurs in LXRbeta mice. Here, we investigated neuromuscular alterations of LXRbeta mice from ages 3 to 24 months. Increased cholesterol levels, gliosis, and inflammation preceded motor neuron loss and clinical disease onset; the mice showed progressivemotor neuron deficits starting from age 7 months. The numbers ofmotor neurons and neuromuscular junctions were decreased in 24-month-old mice, but neither paralysis nor reduced life span was observed. Moreover, other spinal neurons were also lost in these mice. These results suggest that LXRbeta may inhibit neuroinflammation and maintain cholesterol homeostasis, and that LXRbeta mice represent a potential model for investigating the role of cholesterol in ALS and other neurodegenerative disorders.

Oxygen tension modulates neurite outgrowth in PC12 cells through a mechanism involving HIF and VEGF

Cell-based approaches are a promising therapeutic strategy for treating injuries to the nervous system, but the optimal means to promote neurite extension and direct cellular behavior are unclear. Previous studies have examined the behavior of neural-like cells in ambient air (21% oxygen tension), yet these conditions are not representative of the physiological oxygen microenvironment of neural tissues. We hypothesized that neuronal differentiation of a model neural cell line (PC12) could be controlled by modulating local oxygen tension. Compared to ambient conditions, PC12 cells cultured in reduced oxygen exhibited significant increases in neurite extension and total neurite length, with 4% oxygen yielding the highest levels of both indicators. We confirmed neurite extension was mediated through oxygen-responsive mechanisms using small molecules that promote or inhibit HIF-1α stabilization. The hypoxic target gene Vegf was implicated as a neurotrophic factor, as neurite formation at 21% oxygen was mimicked with exogenous VEGF, and a VEGF-neutralizing antibody attenuated neurite formation under reduced oxygen conditions. These findings demonstrate that behavior of neural-like cells is driven by the oxygen microenvironment via VEGF function, and suggest promising approaches for future applications in neural repair.

Mild hypoxia enhances proliferation and multipotency of human neural stem cells

Background

Neural stem cells (NSCs) represent an optimal tool for studies and therapy of neurodegenerative diseases. We recently established a v-myc immortalized human NSC (IhNSC) line, which retains stem properties comparable to parental cells. Oxygen concentration is one of the most crucial environmental conditions for cell proliferation and differentiation both in vitro and in vivo. In the central nervous system, physiological concentrations of oxygen range from 0.55 to 8% oxygen. In particular, in the in the subventricular zone niche area, it's estimated to be 2.5 to 3%.

Methodology/Principal Findings

We investigated in vitro the effects of 1, 2.5, 5, and 20% oxygen concentrations on IhNSCs both during proliferation and differentiation. The highest proliferation rate, evaluated through neurosphere formation assay, was obtained at 2.5 and 5% oxygen, while 1% oxygen was most noxious for cell survival. The differentiation assays showed that the percentages of β-tubIII+ or MAP2+ neuronal cells and of GalC+ oligodendrocytes were significantly higher at 2.5% compared with 1, 5, or 20% oxygen at 17 days in vitro. Mild hypoxia (2.5 to 5% oxygen) promoted differentiation into neuro-oligodendroglial progenitors as revealed by the higher percentage of MAP2+/Ki67+ and GalC+/Ki67+ residual proliferating progenitors, and enhanced the yield of GABAergic and slightly of glutamatergic neurons compared to 1% and 20% oxygen where a significant percentage of GFAP+/nestin+ cells were still present at 17 days of differentiation.

Conclusions/Significance

These findings raise the possibility that reduced oxygen levels occurring in neuronal disorders like cerebral ischemia transiently lead to NSC remaining in a state of quiescence. Conversely, mild hypoxia favors NSC proliferation and neuronal and oligodendroglial differentiation, thus providing an important advance and a useful tool for NSC-mediated therapy of ischemic stroke and neurodegenerative diseases like Parkinson's disease, multiple sclerosis, and Alzheimer's disease.

Hypoxia stimulates proliferation of rat neural stem cells with influence on the expression of cyclin D1 and c-Jun N-terminal protein kinase signaling pathway in vitro

Ischemia/hypoxia is known to induce the neural stem cells proliferation and neural differentiation in rodent and human brain; however its mechanisms remain largely unknown. In this study we investigated the effect of hypoxia on neural stem cells (NSCs) proliferation with the expression of cyclin D1 and the phosphorylation of mitogen-activated protein kinases (MAPK) signaling molecules. NSCs were cultured from cortex of fetal Sprague-Dawley rats on embryonic day 5.5. The hypoxia was made using a microaerophilic incubation system. The NSCs proliferation was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, diameter measurement of neurospheres, bromodeoxyuridine (BrdU) incorporation assay and cell cycle analysis. The cell death of NSCs was evaluated by terminal dUTP nick-end labeling (TUNEL) assay. The expression of cyclin D1, phosphorylated extracellular signal regulated kinase (ERK), c-Jun N-terminal protein kinase (JNK) and p38 were analyzed by immunoblotting assay. The results showed that hypoxia increased NSCs proliferation in cell amount, diameter of neurospheres, BrdU incorporation and cell division, and the highest proliferation of the NSCs was observed with 12 h hypoxic treatment; hypoxia did not decrease cell death of NSCs; after hypoxic treatment, the expression of cyclin D1 increased, meanwhile P-JNK2 level increased, P-p38 decreased, and no significant change in P-ERK2 level compared to normoxic cultures. JNK inhibitor SP600125 attenuated the increase of cyclin D1 induced by hypoxia. These findings propose that hypoxia increases cyclin D1 expression through activation of JNK in NSCs of rat in vitro, suggesting a novel possible mechanism for hypoxia-induced proliferation of NSCs.

Impaired autolysosome formation correlates with Lamp-2 depletion: role of apoptosis, autophagy, and necrosis in pancreatitis

BACKGROUND & AIMS

Acute pancreatitis constitutes a life-threatening condition in which pancreatic acinar cells undergo massive cell death. We investigated the incidence of apoptosis, autophagy, and necrosis affecting acinar cells in the early onset of acute pancreatitis induced by chronic alcohol feeding and acute endotoxemia.

METHODS

Rats were fed either an ethanol-containing or a control diet over 14 weeks and killed 3 or 24 hours after a single lipopolysaccharide injection. Apoptosis, necrosis, and autophagy of pancreatic acinar cells were assessed by histology, electron microscopy, immunofluorescence, and biochemical methods.

RESULTS

The combination of alcohol exposure and endotoxemia resulted in the depletion of several lysosomal proteins including lysosomal-associated membrane protein-2 (Lamp-2), a protein that is required for the proper fusion of autophagosomes with lysosomes. Accordingly, Lamp-2 depletion correlated with the accumulation of autophagosomes and a relative paucity of autolysosomes, reduced adenosine-5'-triphosphate levels, and a switch from apoptotic to necrotic cell death. This switch to necrosis was accompanied by reduced caspase activation and the nuclear release of the proinflammatory factor high mobility group box 1. Importantly, human patients with alcoholic pancreatitis also exhibited local Lamp-2 depletion, which points to a crucial role for Lamp-2 and autophagy in pancreatic acinar cell death.

CONCLUSIONS

Our data suggest that acinar cell vacuolization in pancreatitis is mediated by an endotoxemia-induced inhibition of the late stage of autophagy. The combination of alcohol and endotoxemia attenuated apoptosis response yet enhanced acinar cell necrosis. The depletion of lysosomal proteins plays a critical role in the early onset of acute pancreatitis.

Oxygen: a master regulator of pancreatic development?

Beyond its role as an electron acceptor in aerobic respiration, oxygen is also a key effector of many developmental events. The oxygen-sensing machinery and the very fabric of cell identity and function have been shown to be deeply intertwined. Here we take a first look at how oxygen might lie at the crossroads of at least two of the major molecular pathways that shape pancreatic development. Based on recent evidence and a thorough review of the literature, we present a theoretical model whereby evolving oxygen tensions might choreograph to a large extent the sequence of molecular events resulting in the development of the organ. In particular, we propose that lower oxygenation prior to the expansion of the vasculature may favour HIF (hypoxia inducible factor)-mediated activation of Notch and repression of Wnt/beta-catenin signalling, limiting endocrine cell differentiation. With the development of vasculature and improved oxygen delivery to the developing organ, HIF-mediated support for Notch signalling may decline while the beta-catenin-directed Wnt signalling is favoured, which would support endocrine cell differentiation and perhaps exocrine cell proliferation/differentiation.

AMP-activated protein kinase phosphorylates retinoblastoma protein to control mammalian brain development

AMP-activated protein kinase (AMPK) is an evolutionarily conserved metabolic sensor that responds to alterations in cellular energy levels to maintain energy balance. While its role in metabolic homeostasis is well documented, its role in mammalian development is less clear. Here we demonstrate that mutant mice lacking the regulatory AMPK beta1 subunit have profound brain abnormalities. The beta1(-/-) mice show atrophy of the dentate gyrus and cerebellum, and severe loss of neurons, oligodendrocytes, and myelination throughout the central nervous system. These abnormalities stem from reduced AMPK activity, with ensuing cell cycle defects in neural stem and progenitor cells (NPCs). The beta1(-/-) NPC deficits result from hypophosphorylation of the retinoblastoma protein (Rb), which is directly phosphorylated by AMPK at Ser(804). The AMPK-Rb axis is utilized by both growth factors and energy restriction to increase NPC growth. Our results reveal that AMPK integrates growth factor signaling with cell cycle control to regulate brain development.