Acidic preconditioning protects endothelial cells against apoptosis through p38- and Akt-dependent Bcl-xL overexpression

Enhancing endothelial colony-forming cells for treating diabetic vascular complications: challenges and clinical prospects

Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia, leading to various vascular complications. Accumulating evidence indicates that endothelial colony-forming cells (ECFCs) have attractive prospects for repairing and restoring blood vessels. Thus, ECFCs may be a novel therapeutic option for diabetic patients with vascular complications who require revascularization therapy. However, it has been reported that the function of ECFCs is impaired in DM, which poses challenges for the autologous transplantation of ECFCs. In this review, we summarize the molecular mechanisms that may be responsible for ECFC dysfunction and discuss potential strategies for improving the therapeutic efficacy of ECFCs derived from patients with DM. Finally, we discuss barriers to the use of ECFCs in human studies in light of the fact that there are no published reports using these cells in humans.

Role of ATP5G3 in sodium nitroprusside-induced cell death in cervical carcinoma cells

We identified a gene, subunit C3 (ATP5G3) of mitochondrial ATP synthase, that displayed changes in gene expression under oxidative stress. We examined the role of ATP5G3 and its molecular mechanisms in sodium nitroprusside (SNP)-induced cell death using ATP5G3 small interfering RNA (siATP5G3)-transfected HeLa cells. A significant increase in cytotoxicity was observed in the transfected cells treated with SNP, which suggests a protective role of ATP5G3 in SNP-induced cytotoxicity in the cells. The transfected cells treated with photodegraded SNP showed equal cytotoxicity to SNP, and pretreatment with deferoxamine (DFO) completely inhibited this cytotoxicity. Further, cytotoxicity was significantly inhibited by pretreatment with a p38 inhibitor and was accentuated by the p38 activator in cells. Pretreatment with the Bcl-xL inhibitor also significantly accentuated cytotoxicity. The increase in p38 phosphorylation was significantly higher in siATP5G3-transfected cells treated with SNP in immunoblotting, which was inhibited by pretreatment with DFO. The increase in cytotoxicity with siATP5G3 transfection was completely blocked by cotransfection with sip38, and the blocking effect disappeared by cotransfection with additional siBcl-xL, which suggests that the protective role of ATP5G3 is mediated by Bcl-xL via the inhibition of p38 activity. Cytotoxicity was completely blocked by the cotransfection of siATP5G3 with siBax. No change in apoptotic parameters was observed during cytotoxicity. However, pretreatment with lysosomal inhibitors significantly inhibited cytotoxicity and increased p62 protein levels. These findings suggest that ATP5G3 plays a protective role in autophagic cell death/lysosome-associated cell death induced by SNP via the sequential signaling of ROS/p38/Bcl-xL/Bax in HeLa cells.

Synergistic cytotoxicity of perifosine and ABT-737 to colon cancer cells

An acidic environment and hypoxia within the tumour are hallmarks of cancer that contribute to cell resistance to therapy. Deregulation of the PI3K/Akt pathway is common in colon cancer. Numerous Akt-targeted therapies are being developed, the activity of Akt-inhibitors is, however, strongly pH-dependent. Combination therapy thus represents an opportunity to increase their efficacy. In this study, the cytotoxicity of the Akt inhibitor perifosine and the Bcl-2/Bcl-xL inhibitor ABT-737 was tested in colon cancer HT-29 and HCT-116 cells cultured in monolayer or in the form of spheroids. The efficacy of single drugs and their combination was analysed in different tumour-specific environments including acidosis and hypoxia using a series of viability assays. Changes in protein content and distribution were determined by immunoblotting and a "peeling analysis" of immunohistochemical signals. While the cytotoxicity of single agents was influenced by the tumour-specific microenvironment, perifosine and ABT-737 in combination synergistically induced apoptosis in cells cultured in both 2D and 3D independently on pH and oxygen level. Thus, the combined therapy of perifosine and ABT-737 could be considered as a potential treatment strategy for colon cancer.

Inhibition of Aurora Kinase A by Alisertib Reduces Cell Proliferation and Induces Apoptosis and Autophagy in HuH-6 Human Hepatoblastoma Cells

Purpose

Aurora kinase A (AURKA), which belongs to the serine/threonine protein kinase family, has been identified as a key driver of the genesis and progression of diverse tumors. The aim of this study was to determine the clinical significance of AURKA in patients with hepatoblastoma (HB) and the effect of inhibiting AURKA in the HB cell line HuH-6.

Methods

The expression of AURKA in HB tissue and adjacent normal liver tissue was detected by immunohistochemistry. Then, statistical analysis was performed to evaluate the association between AURKA expression and the clinicopathological characteristics of HB. The effect of AURKA knockdown on cell viability was assessed by CCK-8 assay. EdU and CCK-8 assays, Western blotting, flow cytometry, and transmission electron microscopy (TEM) were used to examine the effect of alisertib (ALS), a selective AURKA small-molecule inhibitor, on the cell cycle, proliferation, apoptosis, and autophagy in HuH-6 human hepatoblastoma cells.

Results

The expression of AURKA was significantly higher in HB tissue than in adjacent normal tissue. Furthermore, high AURKA expression was associated with advanced Children’s Oncology Group (COG) stage and tumor metastasis of HB. In vitro, AURKA knockdown significantly reduced the viability of HuH-6 cells, while ALS treatment significantly suppressed HuH-6 cell proliferation and induced G1-phase cell cycle arrest by reducing cyclin-D1 expression. Moreover, ALS promoted apoptosis and autophagy by decreasing the activity of p38 MAPK in HuH-6 cells.

Conclusion

High expression of AURKA is a potential predictor of poor prognosis in HB patients. AURKA knockdown reduced the viability of HuH-6 cells, and ALS treatment inhibited cell proliferation and induced apoptosis and autophagy via the p38 MAPK signaling pathway. Our results suggest that AURKA may be a novel therapeutic target and ALS a potential therapeutic drug for the treatment of HB.

The Role of the Primary Cilium in Sensing Extracellular pH

Biosensors on the membrane of the vascular endothelium are responsible for sensing mechanical and chemical signals in the blood. Transduction of these stimuli into intracellular signaling cascades regulate cellular processes including ion transport, gene expression, cell proliferation, and/or cell death. The primary cilium is a well-known biosensor of shear stress but its role in sensing extracellular pH change has never been examined. As a cellular extension into the immediate microenvironment, the cilium could be a prospective sensor for changes in pH and regulator of acid response in cells. We aim to test our hypothesis that the primary cilium plays the role of an acid sensor in cells using vascular endothelial and embryonic fibroblast cells as in vitro models. We measure changes in cellular pH using pH-sensitive 2',7'-biscarboxyethy1-5,6-carboxyfluorescein acetoxy-methylester (BCECF) fluorescence and mitogen-activated protein kinase (MAPK) activity to quantify responses to both extracellular pH (pH_o) and intracellular pH (pH_i) changes. Our studies show that changes in pH_o affect pH_i in both wild-type and cilia-less Tg737 cells and that the kinetics of the pH_i response are similar in both cells. Acidic pH_o or pH_i was observed to change the length of primary cilia in wild-type cells while the cilia in Tg737 remained absent. Vascular endothelial cells respond to acidic pH through activation of ERK1/2 and p38-mediated signaling pathways. The cilia-less Tg737 cells exhibit delayed responsiveness to pH_o dependent and independent pH_i acidification as depicted in the phosphorylation profile of ERK1/2 and p38. Otherwise, intracellular pH homeostatic response to acidic pH_o is similar between wild-type and Tg737 cells, indicating that the primary cilia may not be the sole sensor for physiological pH changes. These endothelial cells respond to pH changes with a predominantly K⁺-dependent pH_i recovery mechanism, regardless of ciliary presence or absence.

Metformin triggers the intrinsic apoptotic response in human AGS gastric adenocarcinoma cells by activating AMPK and suppressing mTOR/AKT signaling

Metformin is commonly used to treat patients with type 2 diabetes and is associated with a decreased risk of cancer. Previous studies have demonstrated that metformin can act alone or in synergy with certain anticancer agents to achieve anti-neoplastic effects on various types of tumors via adenosine monophosphate-activated protein kinase (AMPK) signaling. However, the role of metformin in AMPK-mediated apoptosis of human gastric cancer cells is poorly understood. In the current study, metformin exhibited a potent anti-proliferative effect and induced apoptotic characteristics in human AGS gastric adenocarcinoma cells, as demonstrated by MTT assay, morphological observation method, terminal deoxynucleotidyl transferase dUTP nick end labeling and caspase-3/7 assay kits. Western blot analysis demonstrated that treatment with metformin increased the phosphorylation of AMPK, and decreased the phosphorylation of AKT, mTOR and p70S6k. Compound C (an AMPK inhibitor) suppressed AMPK phosphorylation and significantly abrogated the effects of metformin on AGS cell viability. Metformin also reduced the phosphorylation of mitogen-activated protein kinases (ERK, JNK and p38). Additionally, metformin significantly increased the cellular ROS level and included loss of mitochondrial membrane potential (ΔΨm). Metformin altered apoptosis-associated signaling to downregulate the BAD phosphorylation and Bcl-2, pro-caspase-9, pro-caspase-3 and pro-caspase-7 expression, and to upregulate BAD, cytochrome c, and Apaf-1 proteins levels in AGS cells. Furthermore, z-VAD-fmk (a pan-caspase inhibitor) was used to assess mitochondria-mediated caspase-dependent apoptosis in metformin-treated AGS cells. The findings demonstrated that metformin induced AMPK-mediated apoptosis, making it appealing for development as a novel anticancer drug for the treating gastric cancer.

Complete inhibition of phosphatase and tensin homolog promotes the normal and oxygen-glucose deprivation/reperfusion-injured PC12 cells to cell death

Introduction: Lipid phosphatase and tensin homolog deleted from chromosome 10 (PTEN) antagonizes phosphoinositide 3-kinase (PI3K)/AKT cell survival pathway. The effect of PTEN inhibitors has been rarely examined on cell survival following reperfusion injury. In this study, we investigated the neuroprotective effect of SF1670, as a new PTEN inhibitor, on an in vitro stroke-like model.

Methods: PC12 cells were exposed to oxygen-glucose deprivation/reperfusion (OGD/R). The cells were treated in five conditions as follows: normoxic normoglycemic (NO/NG); 60 minutes OGD; 60 minutes OGD and 6 h reperfusion (OGD/R); OGD/R treated with 10 µM SF1670 (OGD/R-SF), and NO/NG treated with 10 µM SF1670 (NO/NG-SF). Then, phosphorylation levels of AKT, P38 in PC12 cells were measured by immunoblotting. The cell viability was also determined by colorimetric assay.

Results: The results of immunoblotting revealed that following OGD/R the levels of phospho-AKT (p-AKT) significantly decreased, compared to NO/NG cells (P < 0.05). However, the ratio of p-AKT/total AKT significantly increased in the presence of SF1670 in the OGD/R-SF group, compared to the OGD/R condition. On the other hand, SF1670 significantly reduced the p-P38 MAPK and p-JNK levels, compared to OGD/R cells. Moreover, cell viability significantly decreased in the OGD and OGD/R condition compared to NO/NG cells. Surprisingly, SF-treated cells (OGD/R-SF and NO/NG-SF group) showed low cell viability compared to NO/NG condition.

Conclusion: Overall, our results demonstrated that complete inhibition of phosphatase activity of PTEN not only did not exhibit neuroprotective effect but also promoted PC12-deprived cells to death.

Acidic stress induces apoptosis and inhibits angiogenesis in human bone marrow-derived endothelial progenitor cells

Bone marrow-derived endothelial progenitor cells (BM-EPCs) are exposed to acidotic environments in a variety of physiological and pathological conditions, including in tumors. However, the effect of acidosis on the function of BM-EPCs is still not fully understood. In the present study, BM-EPCs were isolated and cultured at an extracellular pH (pHe) of 6.5 or pHe 7.4 in vitro prior to various experiments being performed. Cellular proliferation, migration and tube formation ability were detected by DNA content quantification, Transwell assay and Matrigel-based angiogenesis assay. ELISA and western blot analysis measured protein secretion and expression, respectively. The results demonstrated that BM-EPCs cultured at pHe 6.5 compared with at pHe 7.4 demonstrated: Induced apoptosis; inhibited cellular proliferation, migration and adhesion; markedly reduced vascular endothelial growth factor (VEGF) expression; and the capacity to incorporate into vascular networks. Acidic pHe 6.5 induced ratio expression of B-cell lymphoma 2 (Bcl2)/Bcl2 associated X-protein (Bax), which in turn induced apoptosis, and inhibited cellular proliferation and other functional activities, with involvement of activation of VEGF receptor 2, protein kinase B and p38 mitogen activated protein kinase. These observations raise the possibility that the acidic extracellular environment may perform an important role in the vasculogenesis of BM-EPCs in tumor microenvironments. Therefore, culturing cancer cells at a lower pH that simulates endogenous tumor conditions may improve retention of the cellular heterogeneity identified in tumors.

Hypoxia and Its Acid-Base Consequences: From Mountains to Malignancy

Hypoxia, depending upon its magnitude and circumstances, evokes a spectrum of mild to severe acid-base changes ranging from alkalosis to acidosis, which can alter many responses to hypoxia at both non-genomic and genomic levels, in part via altered hypoxia-inducible factor (HIF) metabolism. Healthy people at high altitude and persons hyperventilating to non-hypoxic stimuli can become alkalotic and alkalemic with arterial pH acutely rising as high as 7.7. Hypoxia-mediated respiratory alkalosis reduces sympathetic tone, blunts hypoxic pulmonary vasoconstriction and hypoxic cerebral vasodilation, and increases hemoglobin oxygen affinity. These effects and others can be salutary or counterproductive to tissue oxygen delivery and utilization, based upon magnitude of each effect and summation. With severe hypoxia either in the setting of profound arterial hemoglobin desaturation and reduced O2 content or poor perfusion (ischemia) at the global or local level, metabolic and hypercapnic acidosis develop along with considerable lactate formation and pH falling to below 6.8. Although conventionally considered to be injurious and deleterious to cell function and survival, both acidoses may be cytoprotective by various anti-inflammatory, antioxidant, and anti-apoptotic mechanisms which limit total hypoxic or ischemic-reperfusion injury. Attempts to correct acidosis by giving bicarbonate or other alkaline agents under these circumstances ahead of or concurrent with reoxygenation efforts may be ill advised. Better understanding of this so-called "pH paradox" or permissive acidosis may offer therapeutic possibilities. Rapidly growing cancers often outstrip their vascular supply compromising both oxygen and nutrient delivery and metabolic waste disposal, thus limiting their growth and metastatic potential. However, their excessive glycolysis and lactate formation may not necessarily represent oxygen insufficiency, but rather the Warburg effect-an attempt to provide a large amount of small carbon intermediates to supply the many synthetic pathways of proliferative cell growth. In either case, there is expression and upregulation of many genes involved in acid-base homeostasis, in part by HIF-1 signaling. These include a unique isoform of carbonic anhydrase (CA-IX) and numerous membrane acid-base transporters engaged to maintain an optimal intracellular and extracellular pH for maximal growth. Inhibition of these proteins or gene suppression may have important therapeutic application in cancer chemotherapy.

Hypoxia-induced force increase (HIFI) is a novel mechanism underlying the strengthening of labor contractions, produced by hypoxic stresses

For successful birth, contractions need to become progressively stronger. The underlying mechanisms are unknown, however. We have found that a novel mechanism, hypoxia-induced force increase (HIFI), is switched on selectively, at term, and is essential to strengthening contractions. HIFI is initiated as contractions cyclically reduce blood flow and produce repeated hypoxic stresses, with associated metabolic and transcriptomic changes. The increases in contractility are a long-lasting, oxytocin-independent, intrinsic mechanism present only in the full-term pregnant uterus. HIFI is inhibited by adenosine receptor antagonism and blockade of cyclooxygenase-2 signaling, and partially reproduced by brief episodes of acidic (but not alkalotic) pH. HIFI explains how labor can progress despite paradoxical metabolic challenge, and provides a new mechanistic target for the 1 in 10 women suffering dysfunctional labor because of poor contractions.

The mitochondrial Na(+)/Ca(2+) exchanger may reduce high glucose-induced oxidative stress and nucleotide-binding oligomerization domain receptor 3 inflammasome activation in endothelial cells

Background

The mitochondrial Na⁺/Ca²⁺ exchanger, NCLX, plays an important role in the balance between Ca²⁺ influx and efflux across the mitochondrial inner membrane in endothelial cells. Mitochondrial metabolism is likely to be affected by the activity of NCLX because Ca²⁺ activates several enzymes of the Krebs cycle. It is currently believed that mitochondria are not only centers of energy production but are also important sites of reactive oxygen species (ROS) generation and nucleotide-binding oligomerization domain receptor 3 (NLRP3) inflammasome activation.

Methods & Results

This study focused on NCLX function, in rat aortic endothelial cells (RAECs), induced by glucose. First, we detected an increase in NCLX expression in the endothelia of rats with diabetes mellitus, which was induced by an injection of streptozotocin. Next, colocalization of NCLX expression and mitochondria was detected using confocal analysis. Suppression of NCLX expression, using an siRNA construct (siNCLX), enhanced mitochondrial Ca²⁺ influx and blocked efflux induced by glucose. Unexpectedly, silencing of NCLX expression induced increased ROS generation and NLRP3 inflammasome activation.

Conclusions

These findings suggest that NCLX affects glucose-dependent mitochondrial Ca²⁺ signaling, thereby regulating ROS generation and NLRP3 inflammasome activation in high glucose conditions. In the early stages of high glucose stimulation, NCLX expression increases to compensate in order to self-protect mitochondrial maintenance, stability, and function in endothelial cells.

Regulation of inflammation by extracellular acidification and proton-sensing GPCRs

Under ischemic and inflammatory circumstances, such as allergic airway asthma, rheumatoid arthritis, atherosclerosis, and tumors, extracellular acidification occurs due to the stimulation of anaerobic glycolysis. An acidic microenvironment has been shown to modulate pro-inflammatory or anti-inflammatory responses, including cyclooxygenase-2 (COX-2) expression, prostaglandin synthesis, and cytokine expression, in a variety of cell types, and thereby to exacerbate or ameliorate inflammation. However, molecular mechanisms underlying extracellular acidic pH-induced actions have not been fully understood. Recent studies have shown that ovarian cancer G protein-coupled receptor 1 (OGR1)-family G protein-coupled receptors (GPCRs) can sense extracellular pH or protons, which in turn stimulates intracellular signaling pathways and subsequent diverse cellular responses. In the present review, I discuss extracellular acidic pH-induced inflammatory responses and related responses in inflammatory cells, such as macrophages and neutrophils, and non-inflammatory cells, such as smooth muscle cells and endothelial cells, focusing especially on proton-sensing GPCRs.

Preconditioning with hypercapnic acidosis: hope for the ischemic brain

Acidosis is an important stress factor triggering cell death under ischemic stress. Accordingly, short acidic pretreatment, i.e. acidic preconditioning, has been used to protect heart and liver. Now the beneficial effect of pretreatment with hypercapnic acidosis against ischemia/reperfusion-induced cell death has also been shown for the brain. The possible underlying cellular mechanisms of the protection as well as role of acidic and hypercapnic sensing are briefly discussed.

Acidosis promotes Bcl-2 family-mediated evasion of apoptosis: involvement of acid-sensing G protein-coupled receptor Gpr65 signaling to Mek/Erk

Acidosis arises in solid and lymphoid malignancies secondary to altered nutrient supply and utilization. Tumor acidosis correlates with therapeutic resistance, although the mechanism behind this effect is not fully understood. Here we show that incubation of lymphoma cell lines in acidic conditions (pH 6.5) blocks apoptosis induced by multiple cytotoxic metabolic stresses, including deprivation of glucose or glutamine and treatment with dexamethasone. We sought to examine the role of the Bcl-2 family of apoptosis regulators in this process. Interestingly, we found that acidic culture causes elevation of both Bcl-2 and Bcl-xL, while also attenuating glutamine starvation-induced elevation of p53-up-regulated modulator of apoptosis (PUMA) and Bim. We confirmed with knockdown studies that these shifts direct survival decisions during starvation and acidosis. Importantly, the promotion of a high anti- to pro-apoptotic Bcl-2 family member ratio by acidosis renders cells exquisitely sensitive to the Bcl-2/Bcl-xL antagonist ABT-737, suggesting that acidosis causes Bcl-2 family dependence. This dependence appears to be mediated, in part, by the acid-sensing G protein-coupled receptor, GPR65, via a MEK/ERK pathway.

Acidic preconditioning protects against ischemia-induced brain injury

Ischemic preconditioning protects against cerebral ischemia. Recent investigations indicated that acidic preconditioning (APC) protects against ischemia-induced cardiomyocytes injury. However, it is not clear whether APC can protect against cerebral ischemia. To address this issue, C57BL/6 mice were exposed 3 times at 10-min intervals to a normoxic atmosphere containing 20% CO(2) for 5 min before being further subjected to bilateral common carotid artery occlusion. APC reversed the ischemia-induced brain injury as revealed by improved performance in passive avoidance experiments and decreased neuron loss in the hippocampal CA1 region. Consistently, both APC-treated brain slices and primary cultured neurons were more resistant to oxygen-glucose-deprivation (OGD)-induced injury, in a pH- and time-dependent manner, as revealed by reversed cell/tissue viability. In addition, the APC treatment prevented OGD-induced mitochondrial transmembrane potential loss and apoptosis, which was inhibited by the mitochondrial permeability transport pore opener atractyloside. Taken together, these findings indicated that APC protects against ischemia-induced neuronal injury. The beneficial effects may be attributed, at least in part, to decreased mitochondria-dependent neuronal apoptosis.

The SDF-1/CXCR4 axis in stem cell preconditioning

We review the pivotal role of the stromal derived factor (SDF)-1 chemokine in tissue ischaemia and how it orchestrates the rapid revascularization of injured, ischaemic, and regenerating tissues via the CXC chemokine receptors CXCR4 and CXCR7. Furthermore, we discuss the effects of preconditioning (PC), which is a well-known protective phenomenon for tissue ischaemia. The positive effect of both hypoxic and acidic PC on progenitor cell therapeutic potential is reviewed, while stressing the role of the SDF-1/CXCR4 axis in this process.

Kaempferol induces apoptosis in ovarian cancer cells through activating p53 in the intrinsic pathway

Ovarian cancer is a significant malignancy for women in the western world, and its death rate has remained unchanged over the past 50 years, leaving room for proper chemoprevention. Kaempferol is a natural flavonoid widely distributed in fruits and vegetables, and epidemiological studies have found a negative correlation between kaempferol consumption and ovarian cancer risk. To understand the mechanism behind this negative correlation, we investigated kaempferol's ability to induce apoptosis in A2780/CP70, A2780/wt, and OVCAR-3 ovarian cancer cell lines. Kaempferol inhibited cell proliferation but did not cause necrosis in all 3 cell lines. For the apoptosis, caspase 3/7 levels were induced in a concentration-dependent manner by kaempferol treatment, with A2780/wt cells being the most responsive. This induction can be diminished by pre-treatment with a caspase-9 inhibitor, indicating an intrinsic apoptosis pathway. Western blot analysis revealed that protein levels of Bcl-x(L) were decreased in ovarian cancer cells, while p53, Bad, and Bax proteins were up-regulated by kaempferol treatment. Our data indicate that kaempferol induces apoptosis in ovarian cancer cells through regulating pro-apoptotic and anti-apoptotic protein expressions in the intrinsic apoptosis pathways, and is a good candidate for the chemoprevention of ovarian cancers in humans. Further studies in animal models and clinical trials are therefore warranted.

Ex vivo acidic preconditioning enhances bone marrow ckit+ cell therapeutic potential via increased CXCR4 expression

Aims

The chemokine receptor CXCR4 modulates endothelial progenitor cell migration, homing, and differentiation, and plays a key role in cardiovascular regeneration. Here we examined the effect of ex vivo acidic preconditioning (AP) on CXCR4 expression and on the regenerative potential of mouse bone marrow (BM) ckit⁺ cells.

Methods and results

Acidic preconditioning was achieved by exposing BM ckit⁺ cells to hypercarbic acidosis (pH 7.0) for 24 h; control cells were kept at pH 7.4. Acidic preconditioning enhanced CXCR4 and stromal cell-derived factor 1 (SDF-1) mRNA levels, as well as CXCR4 phosphorylation. Acidic preconditioning ability to modulate CXCR4 expression depended on cytosolic calcium [Ca²⁺]_i mobilization and on nitric oxide (NO), as determined by [Ca²⁺]_i buffering with BAPTA, and by treatment with the NO donor (DETA/NO) and the NO synthase inhibitor (L-NAME). Further, AP increased SDF-1-driven chemotaxis, transendothelial migration, and differentiation toward the endothelial lineage in vitro. In a mouse model of hindlimb ischaemia, control and AP ckit⁺ cells were transplanted into the ischaemic muscle; AP cells accelerated blood flow recovery, increased capillary, and arteriole number as well as the number of regenerating muscle fibres vs. control. These effects were abolished by treating AP cells with L-NAME.

Conclusion

Acidic preconditioning represents a novel strategy to enhance BM ckit⁺ cell therapeutic potential via NO-dependent increase in CXCR4 expression.

Growth signaling promotes chronological aging in budding yeast by inducing superoxide anions that inhibit quiescence

Inhibition of growth signaling pathways protects against aging and age-related diseases in parallel with reduced oxidative stress. The relationships between growth signaling, oxidative stress and aging remain unclear. Here we report that in Saccharomyces cerevisiae, alterations in growth signaling pathways impact levels of superoxide anions that promote chronological aging and inhibit growth arrest of stationary phase cells in G0/G1. Factors that decrease intracellular superoxide anions in parallel with enhanced longevity and more efficient G0/G1 arrest include genetic inactivation of growth signaling pathways that inhibit Rim15p, which activates oxidative stress responses, and downregulation of these pathways by caloric restriction. Caloric restriction also reduces superoxide anions independently of Rim15p by elevating levels of H₂O₂, which activates superoxide dismutases. In contrast, high glucose or mutations that activate growth signaling accelerate chronological aging in parallel with increased superoxide anions and reduced efficiency of stationary phase G0/G1 arrest. High glucose also activates DNA damage responses and preferentially kills stationary phase cells that fail to arrest growth in G0/G1. These findings suggest that growth signaling promotes chronological aging in budding yeast by elevating superoxide anions that inhibit quiescence and induce DNA replication stress. A similar mechanism likely contributes to aging and age-related diseases in complex eukaryotes.

Upregulation of PTEN by peroxynitrite contributes to cytokine-induced apoptosis in pancreatic beta-cells

Phosphatase and tensin homolog (PTEN), a tumor suppressor gene, by negatively regulating the PI3K-Akt signaling pathway, participates in multiple biological processes such as cell proliferation, apoptosis, differentiation, and migration. Recent studies show that selective deletion of PTEN in pancreatic beta-cells leads to resistance to streptozotocin (STZ)-induced diabetes, but the mechanism is unclear. One major mechanism underlying STZ toxicity is cytokine-mediated beta-cell destruction in which oxidative stress plays a key role. The present study investigated the role of PTEN in cytokine-induced beta-cell apoptosis, and further explored whether oxidative stress, particularly peroxynitrite formation, could regulate PTEN-Akt pathway. Incubation of betaTC-6 cells with cytokine mixture (IL-1beta, TNF-alpha, and IFN-gamma) or exogenous peroxynitrite significantly increased apoptotic cell percentage, elevated PTEN and p-PTEN levels, and inhibited Akt activation. Transfection with PTEN-specific siRNA protected betaTC-6 cells from cytokine or peroxynitrite-mediated cell apoptosis and partially reversed Akt inhibition. Furthermore, nitrotyrosine formation, an indicator of peroxynitrite production, was significantly elevated after cytokine treatment. Preventing peroxynitrite formation by administrating NAC/L: -NMMA, or scavenging peroxynitrite directly by UA, attenuated cytokine-induced PTEN upregulation, Akt inhibition, and beta-cell apoptosis. These findings suggest that peroxynitrite-mediated PTEN upregulation plays an important role in cytokine-induced pancreatic beta-cell apoptosis.

SLC4A7 sodium bicarbonate co-transporter controls mitochondrial apoptosis in ischaemic coronary endothelial cells

AIMS

Bicarbonate transport has been shown to participate in apoptosis under ischaemic stress. However, the precise transporting mechanisms involved in ischaemic apoptosis are unknown and were thus the aim of the present study.

METHODS AND RESULTS

Rat coronary endothelial cells (EC) were exposed to simulated in vitro ischaemia for 2 h, and apoptosis was subsequently determined by chromatin staining and caspase-3 activity analysis. By examining the expression of bicarbonate transporters (BT) in EC by reverse transcriptase polymerase chain reaction and western blotting, a marked expression of the electroneutral sodium bicarbonate co-transporter (SLC4A7) was defined. To analyse the potential role of this transporter during apoptosis, a selective inhibitor (S0859, Sanofi-Aventis) was applied. Treatment with S0859 significantly increased caspase-3 activity and elevated the number of apoptotic EC. These results were comparable with an unselective inhibition of all BT due to withdrawal of bicarbonate in the anoxic medium. Knockdown of SLC4A7 in EC by transfecting appropriate siRNA similarly increased apoptosis of EC under simulated ischaemia. The initial characterization of the participating mechanisms of SLC4A7-dependent apoptosis revealed an activation of the mitochondrial pathway of apoptosis, i.e. cleavage of caspase-9 and binding of Bax to mitochondria. In contrast, no activation of the endoplasmic reticulum-dependent pathway (caspase-12 cleavage) or the extrinsic apoptotic pathway (caspase-8 cleavage) was found. Finally, a mitochondrial localization of SLC4A7 was demonstrated.

CONCLUSION

The electroneutral sodium bicarbonate co-transporter SLC4A7 localizes in mitochondria and suppresses the ischaemia-induced activation of the mitochondrial pathway of apoptosis in coronary EC.

Acidosis, hypoxia and bone

Bone homeostasis is profoundly affected by local pH and oxygen tension. It has long been recognised that the skeleton contains a large reserve of alkaline mineral (hydroxyapatite), which is ultimately available to neutralise metabolic H(+) if acid-base balance is not maintained within narrow limits. Bone cells are extremely sensitive to the direct effects of pH: acidosis inhibits mineral deposition by osteoblasts but it activates osteoclasts to resorb bone and other mineralised tissues. These reciprocal responses act to maximise the availability of OH(-) ions from hydroxyapatite in solution, where they can buffer excess H(+). The mechanisms by which bone cells sense small pH changes are likely to be complex, involving ion channels and receptors in the cell membrane, as well as direct intracellular effects. The importance of oxygen tension in the skeleton has also long been known. Recent work shows that hypoxia blocks the growth and differentiation of osteoblasts (and thus bone formation), whilst strongly stimulating osteoclast formation (and thus bone resorption). Surprisingly, the resorptive function of osteoclasts is unimpaired in hypoxia. In vivo, tissue hypoxia is usually accompanied by acidosis due to reduced vascular perfusion and increased glycolytic metabolism. Thus, disruption of the blood supply can engender a multiple negative impact on bone via the direct actions of reduced pO(2) and pH on bone cells. These observations may contribute to our understanding of the bone disturbances that occur in numerous settings, including ageing, inflammation, fractures, tumours, anaemias, kidney disease, diabetes, respiratory disease and smoking.

p38 mitogen-activated protein kinase promotes cell survival in response to DNA damage but is not required for the G(2) DNA damage checkpoint in human cancer cells

p38 mitogen-activated protein kinase (MAPK) is rapidly activated by stresses and is believed to play an important role in the stress response. While Chk1 is known to mediate G(2) DNA damage checkpoint control, p38 was also reported to have an essential function in this checkpoint control. Here, we have investigated further the roles of p38 and Chk1 in the G(2) DNA damage checkpoint in cancer cells. We find that although p38 activation is strongly induced by DNA damage, its activity is not required for the G(2) DNA damage checkpoint. In contrast, Chk1 kinase is responsible for the execution of G(2) DNA damage checkpoint control in p53-deficient cells. The inhibition of p38 activity has no effect on Chk1 activation and gamma-H2AX expression. Global gene expression profiling of cancer cells in response to tumor necrosis factor alpha (TNF-alpha) revealed that p38 plays a strong prosurvival role through the coordinated downregulation of proapoptotic genes and upregulation of prosurvival genes. We show that the inhibition of p38 activity during G(2) DNA damage checkpoint arrest triggers apoptosis in a p53-independent manner with a concurrent decrease in the level of Bcl2 family proteins. Our results suggest that although p38 MAPK is not required for the G(2) DNA damage checkpoint function, it plays an important prosurvival role during the G(2) DNA damage checkpoint response through the upregulation of the Bcl2 family proteins.

Functional erythropoietin receptor is undetectable in endothelial, cardiac, neuronal, and renal cells

Erythropoiesis stimulating agents (ESAs) have been reported to activate erythropoietin receptors (EpoR) on cell types, including endothelial, neuronal, renal tubule, and cardiac cells. ESAs have also been reported to promote angiogenesis. However, those findings are controversial and confounded by methodologic issues. We show that EpoR mRNA was detected in essentially all cell types examined, including primary human endothelial, renal, cardiac, and neuronal cells but 10- to 100-fold lower than Epo-responsive cells using quantitative reverse-transcribed polymerase chain reaction. Total endothelial EpoR protein examined using a new monoclonal antibody was low to undetectable. Surface EpoR on endothelial cells was not detected using [(125)I]-rHuEpo surface-binding studies. There was no evidence of ESA-induced intracellular signaling in endothelial cells. There was a similar lack of EpoR expression and signaling in other cell types examined. Experiments were performed examining ESA function on these cells. An in vivo rat corneal angiogenesis assay demonstrated neo-vessel formation in response to recombinant human vascular endothelial growth factor (rHuVEGF). However, recombinant mouse Epo did not induce vessel formation. Similarly, ESAs did not reproducibly provide cytoprotection to neuronal, renal, or cardiac cells. Taken together, our data challenge the notion of presence or function of EpoR on nonhematopoietic cells, and call into question the preclinical basis for clinical studies exploring direct, "pleiotropic" actions of ESAs.