Plasma membrane calcium pump regulation by metabolic stress

Bioelectric regulation of intestinal stem cells

Proper regulation of ion balance across the intestinal epithelium is essential for physiological functions, while ion imbalance causes intestinal disorders with dire health consequences. Ion channels, pumps, and exchangers are vital for regulating ion movements (i.e., bioelectric currents) that control epithelial absorption and secretion. Recent in vivo studies used the Drosophila gut to identify conserved pathways that link regulators of Ca²⁺, Na⁺ and Cl^- with intestinal stem cell (ISC) proliferation. These studies laid a foundation for using the Drosophila gut to identify conserved proliferative responses triggered by bioelectric regulators. Here, we review these studies, discuss their significance, as well as the advantages of using Drosophila to unravel conserved bioelectrically induced molecular pathways in the intestinal epithelium under physiological, pathophysiological, and regenerative conditions.

Pathophysiological Ionotropic Glutamate Signalling in Neuroinflammatory Disease as a Therapeutic Target

Glutamate signalling is an essential aspect of neuronal communication involving many different glutamate receptors, and underlies the processes of memory, learning and synaptic plasticity. Despite neuroinflammatory diseases covering a range of maladies with very different biological causes and pathophysiologies, a central role for dysfunctional glutamate signalling is becoming apparent. This is not just restricted to the well-described role of glutamate in mediating neurodegeneration, but also includes a myriad of other influences that glutamate can exert on the vasculature, as well as immune cell and glial regulation, reflecting the ability of neurons to communicate with these compartments in order to couple their activity with neuronal requirements. Here, we discuss the role of pathophysiological glutamate signalling in neuroinflammatory disease, using both multiple sclerosis and Alzheimer's disease as examples, and how current steps are being made to harness our growing understanding of these processes in the development of neuroprotective strategies. This review focuses in particular on N-methyl-D-aspartate (NMDA) and 2-amino-3-(3-hydroxy-5-methylisooxazol-4-yl) propionate (AMPA) type ionotropic glutamate receptors, although metabotropic, G-protein-coupled glutamate receptors may also contribute to neuroinflammatory processes. Given the indispensable roles of glutamate-gated ion channels in synaptic communication, means of pharmacologically distinguishing between physiological and pathophysiological actions of glutamate will be discussed that allow deleterious signalling to be inhibited whilst minimising the disturbance of essential neuronal function.

Role of Apoptotic Cell Clearance in Pneumonia and Inflammatory Lung Disease

Pneumonia and inflammatory diseases of the pulmonary system such as chronic obstructive pulmonary disease and asthma continue to cause significant morbidity and mortality globally. While the etiology of these diseases is highly different, they share a number of similarities in the underlying inflammatory processes driving disease pathology. Multiple recent studies have identified failures in efferocytosis-the phagocytic clearance of apoptotic cells-as a common driver of inflammation and tissue destruction in these diseases. Effective efferocytosis has been shown to be important for resolving inflammatory diseases of the lung and the subsequent restoration of normal lung function, while many pneumonia-causing pathogens manipulate the efferocytic system to enhance their growth and avoid immunity. Moreover, some treatments used to manage these patients, such as inhaled corticosteroids for chronic obstructive pulmonary disease and the prevalent use of statins for cardiovascular disease, have been found to beneficially alter efferocytic activity in these patients. In this review, we provide an overview of the efferocytic process and its role in the pathophysiology and resolution of pneumonia and other inflammatory diseases of the lungs, and discuss the utility of existing and emerging therapies for modulating efferocytosis as potential treatments for these diseases.

De Novo Development of a Quantitative Adverse Outcome Pathway (qAOP) Network for Ultraviolet B (UVB) Radiation Using Targeted Laboratory Tests and Automated Data Mining

Ultraviolet B (UVB) radiation is a natural nonchemical stressor posing potential hazards to organisms such as planktonic crustaceans. The present study was conducted to revisit the lethal effects of UVB on crustaceans, generate new experimental evidence to fill in knowledge gaps, and develop novel quantitative adverse outcome pathways (qAOPs) for UVB. A combination of laboratory and computational approaches was deployed to achieve the goals. For targeted laboratory tests, Daphnia magna was used as a prototype and exposed to a gradient of artificial UVB. Targeted bioassays were used to quantify the effects of UVB at multiple levels of biological organization. A toxicity pathway network was assembled based on the new experimental evidence and previously published data extracted using a novel computational tool, the NIVA Risk Assessment Database (NIVA RAdb). A network of AOPs was developed, and weight of evidence was assessed based on a combination of the current and existing data. In addition, quantitative key event relationships in the AOPs were developed by fitting the D. magna data to predefined models. A complete workflow for assembly and evaluation of qAOPs has been presented, which may serve as a good example for future de novo qAOP development for chemical and nonchemical stressors.

Another Consequence of the Warburg Effect? Metabolic Regulation of Na+/H+ Exchangers May Link Aerobic Glycolysis to Cell Growth

To adjust cell growth and proliferation to changing environmental conditions or developmental requirements, cells have evolved a remarkable network of signaling cascades that integrates cues from cellular metabolism, growth factor availability and a large variety of stresses. In these networks, cellular information flow is mostly mediated by posttranslational modifications, most notably phosphorylation, or signaling molecules such as GTPases. Yet, a large body of evidence also implicates cytosolic pH (pHc) as a highly conserved cellular signal driving cell growth and proliferation, suggesting that pH-dependent protonation of specific proteins also regulates cellular signaling. In mammalian cells, pHc is regulated by growth factor derived signals and responds to metabolic cues in response to glucose stimulation. Importantly, high pHc has also been identified as a hall mark of cancer, but mechanisms of pH regulation in cancer are only poorly understood. Here, we discuss potential mechanisms of pH regulation with emphasis on metabolic signals regulating pHc by Na⁺/H⁺-exchangers. We hypothesize that elevated NHE activity and pHc in cancer are a direct consequence of the metabolic adaptations in tumor cells including enhanced aerobic glycolysis, generally referred to as the Warburg effect. This hypothesis not only provides an explanation for the growth advantage conferred by a switch to aerobic glycolysis beyond providing precursors for accumulation of biomass, but also suggests that treatments targeting pH regulation as a potential anti-cancer therapy may effectively target the result of altered tumor cell metabolism.

Cutting off the fuel supply to calcium pumps in pancreatic cancer cells: role of pyruvate kinase-M2 (PKM2)

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) has poor survival and treatment options. PDAC cells shift their metabolism towards glycolysis, which fuels the plasma membrane calcium pump (PMCA), thereby preventing Ca2+-dependent cell death. The ATP-generating pyruvate kinase-M2 (PKM2) is oncogenic and overexpressed in PDAC. This study investigated the PKM2-derived ATP supply to the PMCA as a potential therapeutic locus.

METHODS

PDAC cell growth, migration and death were assessed by using sulforhodamine-B/tetrazolium-based assays, gap closure assay and poly-ADP ribose polymerase (PARP1) cleavage, respectively. Cellular ATP and metabolism were assessed using luciferase/fluorescent-based assays and the Seahorse XFe96 analyzer, respectively. Cell surface biotinylation identified membrane-associated proteins. Fura-2 imaging was used to assess cytosolic Ca2+ overload and in situ Ca2+ clearance. PKM2 knockdown was achieved using siRNA.

RESULTS

The PKM2 inhibitor (shikonin) reduced PDAC cell proliferation, cell migration and induced cell death. This was due to inhibition of glycolysis, ATP depletion, inhibition of PMCA and cytotoxic Ca2+ overload. PKM2 associates with plasma membrane proteins providing a privileged ATP supply to the PMCA. PKM2 knockdown reduced PMCA activity and reduced the sensitivity of shikonin-induced cell death.

CONCLUSIONS

Cutting off the PKM2-derived ATP supply to the PMCA represents a novel therapeutic strategy for the treatment of PDAC.

An Adverse Outcome Pathway Linking Organohalogen Exposure to Mitochondrial Disease

Adverse outcome pathways (AOPs) are pragmatic tools in human health hazard characterization and risk assessment. As such, one of the main goals of AOP development is to provide a clear, progressive, and linear mechanistic representation of pertinent toxicological key events (KEs) occurring along the different levels of biological organization. Here, we present an AOP framework that depicts how exposure to organohalogens can lead to mitochondrial disease. Organohalogens are disinfectant by-products (DBPs) found in our drinking water. Chloroform, trichloroacetic acid, and trichlorophenol were selected to represent specific types of organohalogens for the development of this AOP. Although each of these compounds contains chlorine atoms, they differ in aromaticity and solubility, which have a significant impact on their potency. This AOP consists of two main pathways, both of which are triggered by the molecular initiating event (MIE) of excessive reactive oxygen species generation. Pathway 1 details the downstream consequences of oxidative stress, which include mitochondrial DNA damage, protein aggregation, and depolarization of the mitochondrial membrane. Pathway 2 shows the KEs that result from inadequate supply of glutathione, including calcium dysregulation and ATP depletion. Pathways 1 and 2 converge at a common KE: opening of the mitochondrial membrane transition pore (mPTP). This leads to the release of cytochrome c, caspase activation, apoptosis, and mitochondrial disease. This AOP was developed according to the Organisation for Economic Co-operation and Development guidance, including critical consideration of the Bradford Hill criteria for Weight of Evidence assessment and key questions for evaluating confidence. The presented AOP is expected to serve as the basis for designing new toxicological tests as well as the characterization of novel biomarkers for disinfectant by-product exposure and adverse health effects.

The hydroxypyridinone iron chelator CP94 increases methyl-aminolevulinate-based photodynamic cell killing by increasing the generation of reactive oxygen species

Methyl-aminolevulinate-based photodynamic therapy (MAL-PDT) is utilised clinically for the treatment of non-melanoma skin cancers and pre-cancers and the hydroxypyridinone iron chelator, CP94, has successfully been demonstrated to increase MAL-PDT efficacy in an initial clinical pilot study. However, the biochemical and photochemical processes leading to CP94-enhanced photodynamic cell death, beyond the well-documented increases in accumulation of the photosensitiser protoporphyrin IX (PpIX), have not yet been fully elucidated. This investigation demonstrated that MAL-based photodynamic cell killing of cultured human squamous carcinoma cells (A431) occurred in a predominantly necrotic manner following the generation of singlet oxygen and ROS. Augmenting MAL-based photodynamic cell killing with CP94 co-treatment resulted in increased PpIX accumulation, MitoSOX-detectable ROS generation (probably of mitochondrial origin) and necrotic cell death, but did not affect singlet oxygen generation. We also report (to our knowledge, for the first time) the detection of intracellular PpIX-generated singlet oxygen in whole cells via electron paramagnetic resonance spectroscopy in conjunction with a spin trap.

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Augmentation of MAL-based photodynamic cell killing with CP94 increases necrosis.

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CP94 augmentation increases generation of ROS, likely to be mitochondria-localised.

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PpIX-generated ¹O₂ was detected in whole cells by EPR spectroscopy.

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Photodynamic cell killing was dependent primarily on ¹O₂.

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Superoxide/other ROS also contributed to the efficacy of photodynamic cell killing.

Ursodeoxycholic acid induces apoptosis in hepatocellular carcinoma xenografts in mice

AIM: To evaluate the efficacy of ursodeoxycholic acid (UDCA) as a chemotherapeutic agent for the treatment of hepatocellular carcinoma (HCC).

METHODS: BALB/c nude mice were randomized into four groups 24 h before subcutaneous injection of hepatocarcinoma BEL7402 cells suspended in phosphate buffered saline (PBS) into the right flank. The control group (n = 10) was fed a standard diet while treatment groups (n = 10 each) were fed a standard daily diet supplemented with different concentrations of UDCA (30, 50 and 70 mg/kg per day) for 21 d. Tumor growth was measured once each week, and tumor volume (V) was calculated with the following equation: V = (L × W²) × 0.52, where L is the length and W is the width of the xenograft. After 21 d, mice were killed under ether anesthesia, and tumors were excised and weighed. Apoptosis was evaluated through detection of DNA fragmentation with gel electrophoresis and the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay. Western blot analysis was performed to determine the expression of apoptosis-related proteins BAX, BCL2, APAF1, cleaved caspase-9, and cleaved caspase-3.

RESULTS: UDCA suppressed tumor growth relative to controls. The mean tumor volumes were the following: control, 1090 ± 89 mm³; 30 mg/kg per day, 612 ± 46 mm³; 50 mg/kg per day, 563 ± 38 mm³; and 70 mg/kg per day, 221 ± 26 mm³. Decreased tumor volumes reached statistical significance relative to control xenografts (30 mg/kg per day, P < 0.05; 50 mg/kg per day, P < 0.05; 70 mg/kg per day, P < 0.01). Increasing concentrations of UDCA led to increased DNA fragmentation observed on gel electrophoresis and in the TUNEL assay (control, 1.6% ± 0.3%; 30 mg/kg per day, 2.9% ± 0.5%; 50 mg/kg per day, 3.15% ± 0.7%, and 70 mg/kg per day, 4.86% ± 0.9%). Western blot analysis revealed increased expression of BAX, APAF1, cleaved-caspase-9 and cleaved-caspase-3 proteins, which induce apoptosis, but decreased expression of BCL2 protein, which is an inhibitor of apoptosis, following administration of UDCA.

CONCLUSION: UDCA suppresses growth of BEL7402 hepatocellular carcinoma cells in vivo, in part through apoptosis induction, and is thus a candidate for therapeutic treatment of HCC.

Cardioprotective effect of ammonium glycyrrhizinate against doxorubicin-induced cardiomyopathy in experimental animals

Objective:

The objective of this study was to evaluate the cardioprotective effect of herbal bioactive compound ammonium glycyrrhizinate against doxorubicin-induced cardiomyopathy, in experimental animals.

Materials and Methods:

Ammonium glycyrrhizinate (50, 100, 200 mg/kg, p.o.) was administered for four weeks in albino rats. Cardiomyopathy was induced with a dose of 2.5 mg/kg i.p. of doxorubicin on 1^th, 7^th, 14^th, 21^th, 28^th day in the experimental animals. At the end of the experiment, on 29^th day, serum and heart tissues were collected and hemodynamic, biochemical and histopathological studies were carried out.

Results:

Administration of doxorubicin in normal rats showed significant (P < 0.001) changes in body weight, feed intake, urine output, hemodynamic parameters like (blood pressure, heart rate, cardiac output) and in lipid profile (cholesterol, triglyceride, high density lipoprotein, low density lipoprotein, very low density lipoprotein) indicating cardiomyopathy symptoms. Animals treated with ammonium glycyrrhizinate significantly (P < 0.05) decreased triglyceride, cholesterol, low density lipoprotein (LDL) and very low density lipoprotein (VLDL) levels. Moreover, high density lipoprotein (HDL) levels increased in rats treated with ammonium glycyrrhizinate as compared with the normal group.

Conclusion:

Ammonium glycyrrhizinate is effective in controlling serum lipid profile and cardiac complications in experimentally induced cardiomyopathy in animals.

Insulin protects pancreatic acinar cells from palmitoleic acid-induced cellular injury

Acute pancreatitis is a serious and sometimes fatal inflammatory disease where the pancreas digests itself. The non-oxidative ethanol metabolites palmitoleic acid (POA) and POA-ethylester (POAEE) are reported to induce pancreatitis caused by impaired mitochondrial metabolism, cytosolic Ca²⁺ ([Ca²⁺]_i) overload and necrosis of pancreatic acinar cells. Metabolism and [Ca²⁺]_i are linked critically by the ATP-driven plasma membrane Ca²⁺-ATPase (PMCA) important for maintaining low resting [Ca²⁺]_i. The aim of the current study was to test the protective effects of insulin on cellular injury induced by the pancreatitis-inducing agents, ethanol, POA, and POAEE. Rat pancreatic acinar cells were isolated by collagenase digestion and [Ca²⁺]_i was measured by fura-2 imaging. An in situ [Ca²⁺]_i clearance assay was used to assess PMCA activity. Magnesium green (MgGreen) and a luciferase-based ATP kit were used to assess cellular ATP depletion. Ethanol (100 mm) and POAEE (100 μm) induced a small but irreversible Ca²⁺ overload response but had no significant effect on PMCA activity. POA (50–100 μm) induced a robust Ca²⁺ overload, ATP depletion, inhibited PMCA activity, and consequently induced necrosis. Insulin pretreatment (100 nm for 30 min) prevented the POA-induced Ca²⁺ overload, ATP depletion, inhibition of the PMCA, and necrosis. Moreover, the insulin-mediated protection of the POA-induced Ca²⁺ overload was partially prevented by the phosphoinositide-3-kinase (PI3K) inhibitor, LY294002. These data provide the first evidence that insulin directly protects pancreatic acinar cell injury induced by bona fide pancreatitis-inducing agents, such as POA. This may have important therapeutic implications for the treatment of pancreatitis.

Glycolytic ATP fuels the plasma membrane calcium pump critical for pancreatic cancer cell survival

Pancreatic cancer is an aggressive cancer with poor prognosis and limited treatment options. Cancer cells rapidly proliferate and are resistant to cell death due, in part, to a shift from mitochondrial metabolism to glycolysis. We hypothesized that this shift is important in regulating cytosolic Ca²⁺ ([Ca²⁺]_i), as the ATP-dependent plasma membrane Ca²⁺ ATPase (PMCA) is critical for maintaining low [Ca²⁺]_i and thus cell survival. The present study aimed to determine the relative contribution of mitochondrial versus glycolytic ATP in fuelling the PMCA in human pancreatic cancer cells. We report that glycolytic inhibition induced profound ATP depletion, PMCA inhibition, [Ca²⁺]_i overload, and cell death in PANC1 and MIA PaCa-2 cells. Conversely, inhibition of mitochondrial metabolism had no effect, suggesting that glycolytic ATP is critical for [Ca²⁺]_i homeostasis and thus survival. Targeting the glycolytic regulation of the PMCA may, therefore, be an effective strategy for selectively killing pancreatic cancer while sparing healthy cells.

Cytosolic calcium regulation in rat afferent vagal neurons during anoxia

Sensory neurons are able to detect tissue ischaemia and both transmit information to the brainstem as well as release local vasoactive mediators. Their ability to sense tissue ischaemia is assumed to be primarily mediated through proton sensing ion channels, lack of oxygen however may also affect sensory neuron function. In this study we investigated the effects of anoxia on isolated capsaicin sensitive neurons from rat nodose ganglion. Acute anoxia triggered a reversible increase in [Ca2+]i that was mainly due to Ca2+-efflux from FCCP sensitive stores and from caffeine and CPA sensitive ER stores. Prolonged anoxia resulted in complete depletion of ER Ca2+-stores. Mitochondria were partially depolarised by acute anoxia but mitochondrial Ca2+-uptake/buffering during voltage-gated Ca2+-influx was unaffected. The process of Ca2+-release from mitochondria and cytosolic Ca2+-clearance following Ca2+ influx was however significantly slowed. Anoxia was also found to inhibit SERCA activity and, to a lesser extent, PMCA activity. Hence, anoxia has multiple influences on [Ca2+]i homeostasis in vagal afferent neurons, including depression of ATP-driven Ca2+-pumps, modulation of the kinetics of mitochondrial Ca2+ buffering/release and Ca2+-release from, and depletion of, internal Ca2+-stores. These effects are likely to influence sensory neuronal function during ischaemia.

Mitochondria in traumatic brain injury and mitochondrial-targeted multipotential therapeutic strategies

Traumatic brain injury (TBI) is a major health and socioeconomic problem throughout the world. It is a complicated pathological process that consists of primary insults and a secondary insult characterized by a set of biochemical cascades. The imbalance between a higher energy demand for repair of cell damage and decreased energy production led by mitochondrial dysfunction aggravates cell damage. At the cellular level, the main cause of the secondary deleterious cascades is cell damage that is centred in the mitochondria. Excitotoxicity, Ca(2+) overload, reactive oxygen species (ROS), Bcl-2 family, caspases and apoptosis inducing factor (AIF) are the main participants in mitochondria-centred cell damage following TBI. Some preclinical and clinical results of mitochondria-targeted therapy show promise. Mitochondria- targeted multipotential therapeutic strategies offer new hope for the successful treatment of TBI and other acute brain injuries.

P2X7 receptor-mediated calcium dynamics in HEK293 cells: experimental characterization and modelling approach

The P2X7 receptor (P2X7R) induces ionotropic Ca²⁺ signalling in different cell types. It plays an important role in the immune response and in the nervous system. Here, the mechanisms underlying intracellular Ca²⁺ variations evoked by 3'-O-(4-benzoyl)benzoyl-ATP (BzATP), a potent agonist of the P2X7R, in transfected HEK293 cells, are investigated both experimentally and theoretically. We propose a minimal model of P2X7R that is capable of reproducing, qualitatively and quantitatively, the experimental data. This approach was also adopted for the P2X7R variant, which lacks the entire C-terminus tail (trP2X7R). Then we introduce a biophysical model describing the Ca²⁺ dynamics in HEK293. Our model gives an account of the ionotropic Ca²⁺ influx evoked by BzATP on the basis of the kinetics model of P2X7R. To explain the complex Ca²⁺ responses evoked by BzATP, the model predicted that an impairment in Ca²⁺ extrusion flux through the plasma membrane is a key factor for Ca²⁺ homeostasis in HEK293 cells.

Insulin protects pancreatic acinar cells from cytosolic calcium overload and inhibition of plasma membrane calcium pump

Acute pancreatitis is a serious and sometimes fatal inflammatory disease of the pancreas without any reliable treatment or imminent cure. In recent years, impaired metabolism and cytosolic Ca(2+) ([Ca(2+)](i)) overload in pancreatic acinar cells have been implicated as the cardinal pathological events common to most forms of pancreatitis, regardless of the precise causative factor. Therefore, restoration of metabolism and protection against cytosolic Ca(2+) overload likely represent key therapeutic untapped strategies for the treatment of this disease. The plasma membrane Ca(2+)-ATPase (PMCA) provides a final common path for cells to "defend" [Ca(2+)](i) during cellular injury. In this paper, we use fluorescence imaging to show for the first time that insulin treatment, which is protective in animal models and clinical studies of human pancreatitis, directly protects pancreatic acinar cells from oxidant-induced cytosolic Ca(2+) overload and inhibition of the PMCA. This protection was independent of oxidative stress or mitochondrial membrane potential but appeared to involve the activation of Akt and an acute metabolic switch from mitochondrial to predominantly glycolytic metabolism. This switch to glycolysis appeared to be sufficient to maintain cellular ATP and thus PMCA activity, thereby preventing Ca(2+) overload, even in the face of impaired mitochondrial function.