Hepatic Energy Metabolism Underlying Differential Lipidomic Responses to High-Carbohydrate and High-Fat Diets in Male Wistar Rats.

BACKGROUND: Low-carbohydrate diets are suggested to exert metabolic benefits by reducing circulating triacylglycerol (TG) concentrations, possibly by enhancing mitochondrial activity. OBJECTIVE: We aimed to elucidate mechanisms by which dietary carbohydrate and fat differentially affect hepatic and circulating TG, and how these mechanisms relate to fatty acid composition. METHODS: Six-week-old, ∼300 g male Wistar rats were fed a high-carbohydrate, low-fat [HC; 61.3% of energy (E%) carbohydrate] or a low-carbohydrate, high-fat (HF; 63.5 E% fat) diet for 4 wk. Parameters of lipid metabolism and mitochondrial function were measured in plasma and liver, with fatty acid composition (GC), high-energy phosphates (HPLC), carnitine metabolites (HPLC-MS/MS), and hepatic gene expression (qPCR) as main outcomes. RESULTS: In HC-fed rats, plasma TG was double and hepatic TG 27% of that in HF-fed rats. The proportion of oleic acid (18:1n-9) was 60% higher after HF vs. HC feeding while the proportion of palmitoleic acid (16:1n-7) and vaccenic acid (18:1n-7), and estimated activities of stearoyl-CoA desaturase, SCD-16 (16:1n-7/16:0), and de novo lipogenesis (16:0/18:2n-6) were 1.5-7.5-fold in HC vs. HF-fed rats. Accordingly, hepatic expression of fatty acid synthase (Fasn) and acetyl-CoA carboxylase (Acaca/Acc) was strongly upregulated after HC feeding, accompanied with 8-fold higher FAS activity and doubled ACC activity. There were no differences in expression of liver-specific biomarkers of mitochondrial biogenesis and activity (Cytc, Tfam, Cpt1, Cpt2, Ucp2, Hmgcs2); concentrations of ATP, AMP, and energy charge; plasma carnitine/acylcarnitine metabolites; or peroxisomal fatty acid oxidation. CONCLUSIONS: In male Wistar rats, dietary carbohydrate was converted into specific fatty acids via hepatic lipogenesis, contributing to higher plasma TG and total fatty acids compared with high-fat feeding. In contrast, the high-fat, low-carbohydrate feeding increased hepatic fatty acid content, without affecting hepatic mitochondrial fatty acid oxidation.

Increased hepatic mitochondrial FA oxidation reduces plasma and liver TG levels and is associated with regulation of UCPs and APOC-III in rats.

Hepatic mitochondrial function, APOC-III, and LPL are potential targets for triglyceride (TG)-lowering drugs. After 3 weeks of dietary treatment with the compound 2-(tridec-12-yn-1-ylthio)acetic acid (1-triple TTA), the hepatic mitochondrial FA oxidation increased more than 5-fold in male Wistar rats. Gene expression analysis in liver showed significant downregulation of APOC-III and upregulation of LPL and the VLDL receptor. This led to lower hepatic (53%) and plasma (73%) TG levels. Concomitantly, liver-specific biomarkers related to mitochondrial biogenesis and function (mitochondrial DNA, citrate synthase activity, and cytochrome c and TFAM gene expression) were elevated. Interestingly, 1-triple TTA lowered plasma acetylcarnitine levels, whereas the concentration of ß-hydroxybutyrate was increased. The hepatic energy state was reduced in 1-triple TTA-treated rats, as reflected by increased AMP/ATP and decreased ATP/ADP ratios, whereas the energy state remained unchanged in muscle and heart. The 1-triple TTA administration induced gene expression of uncoupling protein (UCP)2 and UCP3 in liver. In conclusion, the 1-triple TTA-mediated clearance of blood TG may result from lowered APOC-III production, increased hepatic LPL gene expression, mitochondrial FA oxidation, and (re)uptake of VLDL facilitating drainage of FAs to the liver for ß-oxidation and production of ketone bodies as extrahepatic fuel. The possibility that UCP2 and UCP3 mediate a moderate degree of mitochondrial uncoupling should be considered.

Functional impairment of endothelial cells by the antimycotic amphotericin B.

We set out to determine the membrane potential (Vm) of the endothelial cell line EA.hy926 and its sensitivity to the antimycotic amphotericin B (AmB), a commonly used antifungal component in cell culture media. We measured the endothelial Vm under various experimental conditions by patch clamp technique and found that Vm of AmB-treated cells is (-12.1 ± 9.3) mV, while in AmB-untreated (control) cells it is (-57.1 ± 4.1) mV. In AmB-free extracellular solutions, Vm recovered toward control levels and this gain in Vm rapidly dissipated upon re-addition of AmB, demonstrating a rapid and reversible effect of AmB on endothelial Vm. The consequences of AmB dependent alterations in endothelial transmembrane potential were tested at the levels of Ca(2+) signaling, of nucleotide concentrations, and energy metabolism. In AmB-treated cells we found substantially reduced Ca(2+) entry (to about 60% of that in control cells) in response to histamine induced endoplasmic reticulum (ER) Ca(2+) depletion, and diminished the ATP-to-ADP ratio (by >30%). Our data demonstrate a marked and experimentally relevant dependence of basic functional parameters of cultured endothelial cells on the presence of the ionophoric antimycotic AmB. The profound and reversible effects of the widely used culture media component AmB need careful consideration when interpreting experimental data obtained under respective culture conditions.

Characterization of rat serum amyloid A4 (SAA4): a novel member of the SAA superfamily.

The serum amyloid A (SAA) family of proteins is encoded by multiple genes, which display allelic variation and a high degree of homology in mammals. The SAA1/2 genes code for non-glycosylated acute-phase SAA1/2 proteins, that may increase up to 1000-fold during inflammation. The SAA4 gene, well characterized in humans (hSAA4) and mice (mSaa4) codes for a SAA4 protein that is glycosylated only in humans. We here report on a previously uncharacterized SAA4 gene (rSAA4) and its product in Rattus norvegicus, the only mammalian species known not to express acute-phase SAA. The exon/intron organization of rSAA4 is similar to that reported for hSAA4 and mSaa4. By performing 5'- and 3'RACE, we identified a 1830-bases containing rSAA4 mRNA (including a GA-dinucleotide tandem repeat). Highest rSAA4 mRNA expression was detected in rat liver. In McA-RH7777 rat hepatoma cells, rSAA4 transcription was significantly upregulated in response to LPS and IL-6 while IL-1α/ß and TNFα were without effect. Luciferase assays with promoter-truncation constructs identified three proximal C/EBP-elements that mediate expression of rSAA4 in McA-RH7777 cells. In line with sequence prediction a 14-kDa non-glycosylated SAA4 protein is abundantly expressed in rat liver. Fluorescence microscopy revealed predominant localization of rSAA4-GFP-tagged fusion protein in the ER.

Metformin Impedes Oxidation of LDL In Vitro.

Metformin is the most commonly prescribed glucose-lowering drug for the treatment of type 2 diabetes. The aim of this study was to investigate whether metformin is capable of impeding the oxidation of LDL, a crucial step in the development of endothelial dysfunction and atherosclerosis. LDL was oxidized by addition of CuCl2 in the presence of increasing concentrations of metformin. The extent of LDL oxidation was assessed by measuring lipid hydroperoxide and malondialdehyde concentrations, relative electrophoretic mobilities, and oxidation-specific immune epitopes. Cytotoxicity of oxLDL in the vascular endothelial cell line EA.hy926 was assessed using the alamarBlue viability test. Quantum chemical calculations were performed to determine free energies of reactions between metformin and radicals typical for lipid oxidation. Metformin concentration-dependently impeded the formation of lipid hydroperoxides, malondialdehyde, and oxidation-specific immune epitopes when oxidation of LDL was initiated by addition of Cu2+. The cytotoxicity of oxLDL was reduced when it was obtained under increasing concentrations of metformin. The quantum chemical calculations revealed that only the reaction of metformin with hydroxyl radicals is exergonic, whereas the reactions with hydroperoxyl radicals or superoxide radical anions are endergonic. Metformin, beside its glucose-lowering effect, might be a suitable agent to impede the development of atherosclerosis and associated CVD. This is due to its capability to impede LDL oxidation, most likely by scavenging hydroxyl radicals.

Hypochlorite-modified high-density lipoprotein promotes induction of HO-1 in endothelial cells via activation of p42/44 MAPK and zinc finger transcription factor Egr-1.

Modification/chlorination of high-density lipoprotein (HDL) by hypochlorous acid (HOCl), formed by the myeloperoxidase-H2O2-chloride system of activated phagocytes, converts an anti-atherogenic lipoprotein into a pro-inflammatory lipoprotein particle. Chlorinated HDL is present in human lesion material, binds to and is internalized by endothelial cells and impairs expression and activity of endothelial nitric oxide synthase. The present study aimed at clarifying whether exposure of endothelial cells to pro-inflammatory HOCl-HDL impacts on expression of heme oxygenase-1, a potential rescue pathway against endothelial dysfunction. Our findings revealed that HDL modified by HOCl, added as reagent or generated enzymatically, induced phosphorylation of p42/44 mitogen-activated protein kinase, expression of transcription factor early growth response-1 (Egr-1) and enhanced expression of heme oxygenase-1 in human endothelial cells. Upregulation of heme oxygenase-1 could be blocked by an inhibitor upstream of p42/44 mitogen-activated protein kinase and/or knockdown of Egr-1 by RNA-interference. Electrophoretic mobility shift assays demonstrated HOCl-HDL-mediated induction of the Egr-1 DNA binding activity. Immunocytochemical and immunoblotting experiments demonstrated HOCl-HDL-induced translocation of Egr-1 to the nucleus. The present study demonstrates a novel compensatory pathway against adverse effects of HOCl-HDL, providing cytoprotection in a number of pathological conditions including cardiovascular disease.

A fatty acid analogue targeting mitochondria exerts a plasma triacylglycerol lowering effect in rats with impaired carnitine biosynthesis.

L-carnitine is important for the catabolism of long-chain fatty acids in the mitochondria. We investigated how the triacylglycerol (TAG)-lowering drug 2-(tridec-12-yn-1-ylthio)acetic acid (1-triple TTA) influenced lipid metabolism in carnitine-depleted, 3-(2,2,2-trimethylhydrazinium)propionate dehydrate (Mildronate; meldonium)-treated male Wistar rats. As indicated, carnitine biosynthesis was impaired by Mildronate. However, TAG levels of both plasma and liver were decreased by 1-triple TTA in Mildronate-treated animals. This was accompanied by increased gene expression of proteins involved in mitochondrial activity and proliferation and reduced mRNA levels of Dgat2, ApoB and ApoCIII in liver. The hepatic energy state was reduced in the group of Mildronate and 1-triple TTA as reflected by increased AMP/ATP ratio, reduced energy charge and induced gene expression of uncoupling proteins 2 and 3. The increase in mitochondrial fatty acid oxidation was observed despite low plasma carnitine levels, and was linked to strongly induced gene expression of carnitine acetyltransferase, translocase and carnitine transporter, suggesting an efficient carnitine turnover. The present data suggest that the plasma TAG-lowering effect of 1-triple TTA in Mildronate-treated rats is not only due to increased mitochondrial fatty acid oxidation reflected by increased mitochondrial biogenesis, but also to changes in plasma clearance and reduced TAG biosynthesis.

Ethyl pyruvate inhibits oxidation of LDL in vitro and attenuates oxLDL toxicity in EA.hy926 cells.

BACKGROUND: Ethyl pyruvate (EP) exerts anti-inflammatory and anti-oxidative properties. The aim of our study was to investigate whether EP is capable of inhibiting the oxidation of LDL, a crucial step in atherogenesis. Additionally, we examined whether EP attenuates the cytotoxic effects of highly oxidized LDL in the human vascular endothelial cell line EA.hy926. METHODS: Native LDL (nLDL) was oxidized using Cu2+ ions in the presence of increasing amounts of EP. The degree of LDL oxidation was quantified by measuring lipid hydroperoxide (LPO) and malondialdehyde (MDA) concentrations, relative electrophoretic mobilities (REMs), and oxidation-specific immune epitopes. The cytotoxicity of these oxLDLs on EA.hy926 cells was assessed by measuring cell viability and superoxide levels. Furthermore, the cytotoxicity of highly oxidized LDL on EA.hy926 cells under increasing concentrations of EP in the media was assessed including measurements of high energy phosphates (ATP). RESULTS: Oxidation of nLDL using Cu2+ ions was remarkably inhibited by EP in a concentration-dependent manner, reflected by decreased levels of LPO, MDA, REM, oxidation-specific epitopes, and diminished cytotoxicity of the obtained oxLDLs in EA.hy926 cells. Furthermore, the cytotoxicity of highly oxidized LDL on EA.hy926 cells was remarkably attenuated by EP added to the media in a concentration-dependent manner reflected by a decrease in superoxide and an increase in viability and ATP levels. CONCLUSIONS: EP has the potential for an anti-atherosclerotic drug by attenuating both, the oxidation of LDL and the cytotoxic effect of (already formed) oxLDL in EA.hy926 cells. Chronic administration of EP might be beneficial to impede the development of atherosclerotic lesions.

Anticoagulant action of low, physiologic, and high albumin levels in whole blood.

Albumin is the most abundant plasma protein. Critical illness is often associated with altered, predominately decreased, serum albumin levels. This hypoalbuminaemia is usually corrected by administration of exogenous albumin. This study aimed to track the concentration-dependent influence of albumin on blood coagulation in vitro. Whole blood (WB) samples from 25 volunteers were prepared to contain low (19.3 ± 7.7 g/L), physiological (45.2 ± 7.8 g/L), and high (67.5 ± 18.1 g/L) levels of albumin. Haemostatic profiling was performed using a platelet function analyzer (PFA) 200, impedance aggregometry, a Cone and Platelet analyzer (CPA), calibrated automated thrombogram, and thrombelastometry (TEM). Platelet aggregation-associated ATP release was assessed via HPLC analysis. In the low albumin group, when compared to the physiological albumin group, we found: i) shortened PFA 200-derived closure times indicating increased primary haemostasis; ii) increased impedance aggregometry-derived amplitudes, slopes, ATP release, as well as CPA-derived average size indicating improved platelet aggregation; iii) increased TEM-derived maximum clot firmness and alpha angles indicating enhanced clot formation. TEM measurements indicated impaired clot formation in the high albumin group compared with the physiological albumin group. Thus, albumin exerted significant anticoagulant action. Therefore, low albumin levels, often present in cancer or critically ill patients, might contribute to the frequently occurring venous thromboembolism.

Orthostatic Challenge Shifts the Hemostatic System of Patients Recovered from Stroke toward Hypercoagulability.

Aims: The objective of our study was to assess the effects of orthostatic challenge on the coagulation system in patients with a history of thromboembolic events and to assess how they compared with age-matched healthy controls. Methods: Twenty-two patients with histories of ischemic stroke and 22 healthy age-matched controls performed a sit-to-stand test. Blood was collected prior to- and at the end of- standing in the upright position for 6 min. Hemostatic profiling was performed by determining thrombelastometry and calibrated automated thrombogram values, indices of thrombin generation, standard coagulation times, markers of endothelial activation, plasma levels of coagulation factors and copeptin, and hematocrit. Results: Orthostatic challenge caused a significant endothelial and coagulation activation in patients (Group 1) and healthy controls (Group 2): Plasma levels of prothrombin fragment F1+2 were increased by approximately 35% and thrombin/antithrombin-complex (TAT) increased 5-fold. Several coagulation variables were significantly altered in Group 1 but not in Group 2: Coagulation times (CTs) were significantly shortened and alpha angles, peak rate of thrombin generation (VELINDEX), tissue factor (TF) and copeptin plasma levels were significantly increased (comparison between standing and baseline). Moreover, the shortening of CTs and the rise of copeptin plasma levels were significantly higher in Group 1 vs. Group 2 (comparison between groups). Conclusion: The coagulation system of patients with a history of ischemic stroke can be more easily shifted toward a hypercoagulable state than that of healthy controls. Attentive and long-term anticoagulant treatment is essential to keep patients from recurrence of vascular events.

Myocardial energy metabolism and ultrastructure with polarizing and depolarizing cardioplegia in a porcine model.

OBJECTIVES: This study investigated whether the novel St. Thomas' Hospital polarizing cardioplegic solution (STH-POL) with esmolol/adenosine/magnesium offers improved myocardial protection by reducing demands for high-energy phosphates during cardiac arrest compared to the depolarizing St. Thomas' Hospital cardioplegic solution No 2 (STH-2). METHODS: Twenty anaesthetised pigs on tepid cardiopulmonary bypass were randomized to cardiac arrest for 60 min with antegrade freshly mixed, repeated, cold, oxygenated STH-POL or STH-2 blood cardioplegia every 20 min. Haemodynamic variables were continuously recorded. Left ventricular biopsies, snap-frozen in liquid nitrogen or fixed in glutaraldehyde, were obtained at Baseline, 58 min after cross-clamp and 20 and 180 min after weaning from bypass. Adenine nucleotides were evaluated by high-performance liquid chromatography, myocardial ultrastructure with morphometry. RESULTS: With STH-POL myocardial creatine phosphate was increased compared to STH-2 at 58 min of cross-clamp [59.9 ± 6.4 (SEM) vs 44.5 ± 7.4 nmol/mg protein; P < 0.025], and at 20 min after reperfusion (61.0 ± 6.7 vs 49.0 ± 5.5 nmol/mg protein; P < 0.05), ATP levels were increased at 20 min of reperfusion with STH-POL (35.4 ± 1.1 vs 32.4 ± 1.2 nmol/mg protein; P < 0.05). Mitochondrial surface-to-volume ratio was decreased with polarizing compared to depolarizing cardioplegia 20 min after reperfusion (6.74 ± 0.14 vs 7.46 ± 0.13 µm 2 /µm 3 ; P = 0.047). None of these differences were present at 180 min of reperfusion. From 150 min of reperfusion and onwards, cardiac index was increased with STH-POL; 4.8 ± 0.2 compared to 4.0 ± 0.2 l/min/m 2 ( P = 0.011) for STH-2 at 180 min. CONCLUSIONS: Polarizing STH-POL cardioplegia improved energy status compared to standard STH-2 depolarizing blood cardioplegia during cardioplegic arrest and early after reperfusion.

Activation of the MAPK/Akt/Nrf2-Egr1/HO-1-GCLc axis protects MG-63 osteosarcoma cells against 15d-PGJ2-mediated cell death.

Despite considerable efforts to improve treatment modalities for osteosarcoma (OS), patient survival remains poor mainly due to pro-survival pathways in OS cells. Among others, prostaglandins (PGs) are the potent regulators of bone homoeostasis and OS pathophysiology. Therefore, the present study aimed to elucidate the impact of 15-deoxy-Δ(12,14)-PGJ2 (15d-PGJ2, a stable PGD2 degradation product) on cell death/cell survival pathways in p53-deficient MG-63 OS cells. Our findings show that 15d-PGJ2 induces generation of reactive oxygen species that promote p38 MAPK activation and subsequent Akt phosphorylation. This pathway induced nuclear expression of Nrf2 and Egr1, and increased transcription of haem oxygenase-1 (HO-1) and the catalytic subunit of glutamate cysteine ligase (GCLc), catalysing the first step in GSH synthesis. Silencing of Nrf2, Egr1 and HO-1 significantly elevated 15d-PGJ2-mediated reduction of cellular metabolic activity. Activation of cell survival genes including HO-1 and GCLc inhibited 15d-PGJ2-induced cleavage of pro-caspase-3 and PARP. Annexin V/propidium iodide staining showed an increase in early/late apoptotic cells in response to 15d-PGJ2. The observed 15d-PGJ2-mediated signalling events are independent of PGD2 receptors (DP1 and DP2) and PPARγ. In addition, the electrophilic carbon atom C9 is a prerequisite for the observed activity of 15d-PGJ2. The present data show that the intracellular redox imbalance acted as a node and triggered both death and survival pathways in response to 15d-PGJ2. Pharmacological or genetic interference of the pro-survival pathway, the p38 MAPK/Akt/Nrf2-Egr1/HO-1-GCLc axis, sensitizes MG-63 cells towards 15d-PGJ2-mediated apoptosis.

15-deoxy-Δ¹²,¹4-PGJ2 promotes inflammation and apoptosis in cardiomyocytes via the DP2/MAPK/TNFα axis.

BACKGROUND: Prostaglandins (PGs), lipid autacoids derived from arachidonic acid, play a pivotal role during inflammation. PGD2 synthase is abundantly expressed in heart tissue and PGD2 has recently been found to induce cardiomyocyte apoptosis. PGD2 is an unstable prostanoid metabolite; therefore the objective of the present study was to elucidate whether its final dehydration product, 15-deoxy-Δ¹²,¹4-PGJ2 (15d-PGJ2, present at high levels in ischemic myocardium) might cause cardiomyocyte damage. METHODS AND RESULTS: Using specific (ant)agonists we show that 15d-PGJ2 induced formation of intracellular reactive oxygen species (ROS) and phosphorylation of p38 and p42/44 MAPKs via the PGD2 receptor DP2 (but not DP1 or PPARγ) in the murine atrial cardiomyocyte HL-1 cell line. Activation of the DP2-ROS-MAPK axis by 15d-PGJ2 enhanced transcription and translation of TNFα and induced apoptosis in HL-1 cardiomyocytes. Silencing of TNFα significantly attenuated the extrinsic (caspase-8) and intrinsic apoptotic pathways (bax and caspase-9), caspase-3 activation and downstream PARP cleavage and γH2AX activation. The apoptotic machinery was unaffected by intracellular calcium, transcription factor NF-κB and its downstream target p53. Of note, 9,10-dihydro-15d-PGJ2 (lacking the electrophilic carbon atom in the cyclopentenone ring) did not activate cellular responses. Selected experiments performed in primary murine cardiomyocytes confirmed data obtained in HL-1 cells namely that the intrinsic and extrinsic apoptotic cascades are activated via DP2/MAPK/TNFα signaling. CONCLUSIONS: We conclude that the reactive α,ß-unsaturated carbonyl group of 15d-PGJ2 is responsible for the pronounced upregulation of TNFα promoting cardiomyocyte apoptosis. We propose that inhibition of DP2 receptors could provide a possibility to modulate 15d-PGJ2-induced myocardial injury.

Association of myeloperoxidase with total and cardiovascular mortality in individuals undergoing coronary angiography--the LURIC study.

BACKGROUND: The phagocytic enzyme myeloperoxidase (MPO) acts as a front-line defender against microorganisms. However, increased MPO levels have been found to be associated with complex and calcified atherosclerotic lesions and incident cardiovascular disease. Therefore, this study aimed to investigate a predictive role of MPO, a biomarker of inflammation and oxidative stress, for total and cardiovascular mortality in patients referred to coronary angiography. METHODS AND RESULTS: MPO plasma concentrations along with eight MPO polymorphisms were determined in 3036 participants of the Ludwigshafen Risk and Cardiovascular Health study (median follow-up 7.75 years). MPO concentrations were positively associated with age, diabetes, smoking, markers of systemic inflammation (interleukin-6, fibrinogen, C-reactive protein, serum amyloid A) and vascular damage (vascular cellular adhesion molecule-1 and intercellular adhesion molecule-1) but negatively associated with HDL-cholesterol and apolipoprotein A-I. After adjustment for cardiovascular risk factors MPO concentrations in the highest versus the lowest quartile were associated with a 1.34-fold risk (95% CI: 1.09-1.67) for total mortality. In the adjusted model the hazard ratio for cardiovascular mortality in the highest MPO quartile was 1.42 (95% CI: 1.07-1.88). Five MPO polymorphisms were positively associated with MPO concentrations but not with mortality. Using Mendelian randomization, we did not obtain evidence for a causal association of MPO with either total or cardiovascular mortality. CONCLUSIONS: MPO concentrations but not genetic variants at the MPO locus are independently associated with risk for total and cardiovascular mortality in coronary artery disease patients.

The cell death protease Kex1p is essential for hypochlorite-induced apoptosis in yeast.

Following microbial pathogen invasion, the human immune system of activated phagocytes generates and releases the potent oxidant hypochlorous acid (HOCl), which contributes to the killing of menacing microorganisms. Though tightly controlled, HOCl generation by the myeloperoxidase-hydrogen peroxide-chloride system of neutrophils/monocytes may occur in excess and lead to tissue damage. It is thus of marked importance to delineate the molecular pathways underlying HOCl cytotoxicity in both microbial and human cells. Here, we show that HOCl induces the generation of reactive oxygen species (ROS), apoptotic cell death and the formation of specific HOCl-modified epitopes in the budding yeast Saccharomyces cerevisiae. Interestingly, HOCl cytotoxicity can be prevented by treatment with ROS scavengers, suggesting oxidative stress to mediate the lethal effect. The executing pathway involves the pro-apoptotic protease Kex1p, since its absence diminishes HOCl-induced production of ROS, apoptosis and protein modification. By characterizing HOCl-induced cell death in yeast and identifying a corresponding central executor, these results pave the way for the use of Saccharomyces cerevisiae in HOCl research, not least given that it combines both being a microorganism as well as a model for programmed cell death in higher eukaryotes.

LPA-induced suppression of periostin in human osteosarcoma cells is mediated by the LPA(1)/Egr-1 axis.

Lysophosphatidic acid (LPA), a naturally occurring bioactive phospholipid, mediates a multitude of (patho)physiological events including activation of mitogen-activated protein kinases (MAPKs). As LPA may induce cellular reponses in human osteosarcoma, the present study aimed at investigating expression of various LPA receptors, LPA-mediated activation of MAPK via G-protein coupling, and expression of early response genes in a cellular model for human osteosarcoma. We show that MG-63 cells express three members of the endothelial differentiation gene (Edg) family of G-protein coupled receptor transcripts (LPA(1-3)) but only two (LPA(4/5)) out of three members of the non-Edg family LPA receptor transcripts. Stimulation of MG-63 cells with LPA or synthetic LPA receptor agonists resulted in p42/44 MAPK phosphorylation via LPA(1)-LPA(3) receptors. Using pharmacological inhibitors, we show that LPA-mediated phosphorylation of p42/44 MAPK by LPA receptor engagement is transmitted by G(αi)-dependent pathways through the Src family of tyrosine kinases. As a consequence, a rapid and transient upregulation of the zinc finger transcription factor early growth response-1 (Egr-1) was observed. Egr-1 expression was strictly mediated via G(αi)/Src/p42/44 MAPK pathway; no involvement of the G(αq/11)/PLC/PKC or the PLD/PI3 kinase/Akt pathways was found. LPA-induced expression of functional Egr-1 in MG-63 cells could be confirmed by electrophoretic mobility shift assay. LPA-induced Egr-1 upregulation was accompanied by a time-dependent decrease of periostin (previously called osteoblast-specific factor 2), a cell adhesion protein for pre-osteoblasts. Silencing of LPA(1) and/or Egr-1 in MG-63 cells reversed LPA-mediated suppression of periostin. We here demonstrate a crosslink between Egr-1 and periostin in cancer cells, in particular in human osteosarcoma.