Posttranslational modifications of platelet adhesion receptors

Platelets play a key role in normal hemostasis, whereas pathological platelet adhesion is involved in various cardiovascular events. The underlying cause in cardiovascular events involves plaque rupture leading to subsequent platelet adhesion, activation, release, and eventual thrombosis. Traditional antithrombotic drugs often target the signal transduction process of platelet adhesion receptors by influencing the synthesis of some key molecules, and their effects are limited. Posttranslational modifications (PTMs) of platelet adhesion receptors increase the functional diversity of the receptors and affect platelet physiological and pathological processes. Antithrombotic drugs targeting PTMs of platelet adhesion receptors may represent a new therapeutic idea. In this review, various PTMs, including phosphorylation, glycosylation, ubiquitination, nitrosylation, methylation, lipidation, and proteolysis, of three platelet adhesion receptors, glycoprotein Ib-IX-V (GPIb-IX-V), glycoprotein VI (GPVI), and integrin α_IIbβ_3, are reviewed. It is important to comprehensively understand the PTMs process of platelet adhesion receptors.

The potential of the novel NAD+ supplementing agent, SNH6, as a therapeutic strategy for the treatment of Friedreich's ataxia

Friedreich's ataxia (FA) is due to deficiency of the mitochondrial protein, frataxin, which results in multiple pathologies including a deadly, hypertrophic cardiomyopathy. Frataxin loss leads to deleterious accumulations of redox-active, mitochondrial iron, and suppressed mitochondrial bioenergetics. Hence, there is an urgent need to develop innovative pharmaceuticals. Herein, the activity of the novel compound, 6-methoxy-2-salicylaldehyde nicotinoyl hydrazone (SNH6), was assessed in vivo using the well-characterized muscle creatine kinase (MCK) conditional frataxin knockout (KO) mouse model of FA. The design of SNH6 incorporated a dual-mechanism mediating: (1) NAD+-supplementation to restore cardiac bioenergetics; and (2) iron chelation to remove toxic mitochondrial iron. In these studies, MCK wild-type (WT) and KO mice were treated for 4-weeks from the asymptomatic age of 4.5-weeks to 8.5-weeks of age, where the mouse displays an overt cardiomyopathy. SNH6-treatment significantly elevated NAD+ and markedly increased NAD+ consumption in WT and KO hearts. In SNH6-treated KO mice, nuclear Sirt1 activity was also significantly increased together with the NAD+-metabolic product, nicotinamide (NAM). Therefore, NAD+-supplementation by SNH6 aided mitochondrial function and cardiac bioenergetics. SNH6 also chelated iron in cultured cardiac cells and also removed iron-loading in vivo from the MCK KO heart. Despite its dual beneficial properties of supplementing NAD+ and chelating iron, SNH6 did not mitigate cardiomyopathy development in the MCK KO mouse. Collectively, SNH6 is an innovative therapeutic with marked pharmacological efficacy, which successfully enhanced cardiac NAD+ and nuclear Sirt1 activity and reduced cardiac iron-loading in MCK KO mice. No other pharmaceutical yet designed exhibits both these effective pharmacological properties.

The effects of edible chitosan-based coatings on flavor quality of raw grass carp (Ctenopharyngodon idellus) fillets during refrigerated storage

This study investigated the effects of chitosan-based coatings on flavor retention of refrigerated grass carp fillets by using various indicators: free amino acids (FAA), nucleotides, trimethylamine (TMA), volatile profile, sensory quality, and electronic nose analysis. The results indicated that chitosan-based coatings contributed to the significant reduction of off-flavor compounds, such as TMA, hypoxanthine (Hx) and histidine, and accumulation of inosine monophosphate (IMP) and umami-associated FAA. GC-MS analysis showed 23 volatile organic compounds, including many C₅-C₉ aldehydes and alcohols in the fresh fillets. The coating treatments, especially chitosan-clove bud essential oil composite coatings, sharply reduced the relative content of off-odor volatiles, such as hexanal, octanal and 1-octen-3-ol. According to the results of the sensory evaluation and electronic nose analyses, chitosan coating combined with glycerol monolaurate and clove bud essential oil was a promising method to improve the edibility of grass carp fillets by maintaining flavor quality during refrigerated storage.

The role of microorganisms in the degradation of adenosine triphosphate (ATP) in chill-stored common carp (Cyprinus carpio) fillets

Biochemical and microbial changes after harvest strongly affect the final quality and shelf life of fish and fish products. In this study, the role of microbes in the degradation of adenosine triphosphate (ATP), and the origin of adenosine monophosphate deaminase (AMPD) and acid phosphatase (ACP) in common carp fillets during different stages of chilled storage (at 4°C) were investigated. The content of ATP, ADP, AMP, IMP, HxR, and Hx, the activity of AMPD and ACP, and the total count of viable, Aeromonas, Pseudomonas, H₂S-producing bacteria, and lactic acid bacteria were examined. Results indicated that the population of microbial communities in control samples increased with storage time, and Pseudomonas peaked on the 10th day of storage. Changes in AMPD activity were less related to the abundance of microbes during the entire storage period. However, ACP was derived from both fish muscle and microbial secretion during the middle and late stages of storage. Degradation of ATP to IMP was not affected by spoilage bacteria, but the hydrolysis of IMP, and the transformation of HxR to Hx was affected considerably by the spoilage bacteria.

The impact of stunning methods on stress conditions and quality of silver carp (Hypophthalmichthys molitrix) fillets stored at 4°C during 72h postmortem

This study aimed to evaluate different stunning methods [percussion (T1), immersion in ice/water slurry (T2), and gill cut (T3)] on quality and stress conditions of silver carp (Hypophthalmichthys molitrix) fillets stored at 4°C in 72h postmortem. Rigor index (RI%), behavioral analysis, levels of lactic acid and muscle glycogen were measured for stress level evaluation. Meanwhile, sensory assessment, texture properties, cooking loss, adenosine triphosphate (ATP) related compounds, adenosine monophosphate deaminase (ADA) activity, and acid phosphatase (ACP) activity were analyzed. The least stress condition, significantly (P<0.05) higher initial glycogen content was observed in T1. Ice/water stunning reduced the rate of ATP degradation, reflected in the lowest K value during 72h. Aversive behaviors, significantly (P<0.05) higher cooking loss, hypoxanthine riboside (HxR) content, and lower sensory score were observed in T3. The results indicated that gill cut in aquatic processing industry should be avoided for inferior quality and aversive reactions during stunning.

Effects of different concentrations of metal ions on degradation of adenosine triphosphate in common carp (Cyprinus carpio) fillets stored at 4°C: An in vivo study

The impact of different concentrations of Na(+), K(+), Ca(2+), Mg(2+), Fe(2+), and Zn(2+) on the degradation of adenosine triphosphate (ATP) and the influence of these ions on the activity of adenosine monophosphate deaminase (AMP-deaminase) and acid phosphatase (ACP) in common carp fillets (in vivo) during 4°C storage was examined. The content of ATP, inosine monophosphate (IMP), and hypoxanthine (Hx), and the activity of AMP-deaminase and ACP were determined. Results indicated that the effects of different concentrations of six kinds of metal ions on AMP-deaminase and ACP were not the same. Na(+), K(+), Fe(2+), and Zn(2+) enhanced AMP-deaminase activity, which led to the rapid degradation of ATP and to the generation of a large quantity of IMP within a short time. Ca(2+) and Mg(2+) delayed the change in AMP-deaminase and ACP activity in carp and caused a further delay in the degradation of ATP. Fe(2+) and Zn(2+) inhibited ACP activity, which reduced the decomposition of IMP and the formation of Hx.

ATP is not involved in α1-adrenoceptor-mediated vasoconstriction in resistance arteries

Recent publications suggest that α1-adrenoceptor stimulation by exogenous agonists such as phenylephrine in resistance arteries cause contraction through the release of ATP from within the vascular smooth muscle cells. This ATP exits the cell through pannexin-1 channels to act back "autocrine-like" on P2 receptors on the smooth muscle that cause the contraction. In this work we directly test this hypothesis by using a selective P2X1 purinoceptor antagonist NF449 (1-10µM) against phenylephrine and ATP concentration-response curves in small mesenteric arteries of the rat and thoracodorsal arteries of the mouse. We show that NF449 is a simple competitive antagonist of ATP with a pKB of 6.43 and 6.41 in rat and mouse arteries, respectively, but did not antagonise phenylephrine concentration-response curves. This work cautions against the growing overstated role of the reputed pannexin-1/ATP release axis following α1-adrenoceptor activation in small resistance arteries.

Atypical signaling of metabotropic glutamate receptor 1 in human melanoma cells

The metabotropic glutamate 1 (mGlu1) receptor has emerged as a novel target for the treatment of metastatic melanoma and various other cancers. Our laboratory has demonstrated that a selective, non-competitive mGlu1 receptor antagonist slows human melanoma growth in vitro and in vivo. In this study, we sought to determine if the activation of a canonical G protein-dependent signal transduction cascade, which is often used as an output of mGlu1 receptor activity in neuronal cells, correlated with mGlu1 receptor-mediated melanoma cell viability. Glutamate, the endogenous ligand of mGlu1 receptors, significantly increased melanoma cell viability, but did not stimulate phosphoinositide (PI) hydrolysis in several human melanoma cell lines. In contrast, melanoma cell viability was not increased by quisqualate, a highly potent mGlu1 receptor agonist, or DHPG, a selective group I mGlu receptor agonist. Similarly to glutamate, quisqualate also failed to stimulate PI hydrolysis in mGlu1 receptor-expressing melanoma cells. These results suggest that the canonical G protein-dependent signal transduction cascade is not coupled to mGlu1 receptors in all human melanoma cells. On the other hand, dynamin inhibition selectively decreased viability of mGlu1 receptor-expressing melanoma cells, suggesting that a mechanism requiring internalization may control melanoma cell viability. Taken together, these data demonstrate that the approaches commonly used to study mGlu1 receptor function and signaling in other systems may be inappropriate for studying mGlu1 receptor-mediated melanoma cell viability.

SC-III3, a novel scopoletin derivative, induces autophagy of human hepatoma HepG2 cells through AMPK/mTOR signaling pathway by acting on mitochondria

(E)-3-(4-chlorophenyl)-N-(7-hydroxy-6-methoxy-2-oxo-2H-chromen-3-yl) acrylamide (SC-III3), a newly synthesized derivative of scopoletin, was previously shown to reduce the viability of HepG2 cells and tumor growth of HepG2 xenograft mouse model. It induces the death of HepG2 cells by a way irrelevant to apoptosis and necrosis. To shed light on the cytotoxic mechanisms of SC-III3, the present study addresses whether and how it can induce autophagic cell death. When HepG2 cells were incubated with various concentrations of SC-III3, autophagic vacuoles could be observed by transmission electron microscopy and monodansylcadaverine staining. Increased expressions of LC3-II to LC3-I and Beclin-1, required for autophagosome formation, were accompanied. These characteristics integrally indicated that SC-III3 could initiate autophagy in HepG2 cells. N-acetyl-l-cysteine (NAC), a ROS scavenger, could reverse SC-III3-caused ROS accumulation, but it did not affect SC-III3-induced autophagy, suggesting that ROS was not involved in SC-III3-mediated autophagy in HepG2 cells. SC-III3 significantly depressed mitochondrial function, as evidenced by disruption of mitochondrial transmembrane potential and loss of the mitochondrial cristae structure, as well as decrease of Cox-I, Cox-III, Cox-IV, and ATP levels. The autophagy and activation of AMPK-TSC2-mTOR-p70s6k pathways induced by SC-III3 in HepG2 cells could be efficiently blocked by pre-treatments of compound C (an inhibitor of AMPK). Moreover, addition of extracellular ATP to the cell culture media could reverse SC-III3-caused activation of AMPK-TSC2-mTOR-p70s6k pathway, autophagy and cell viability decrease in HepG2 cells. Collectively, SC-III3 leads to autophagy through inducing mitochondrial dysfunction, depleting ATP, and activating AMPK-mTOR pathway, which thus reflects the cytotoxic effect of SC-III3 in HepG2 cells.

The mechanism of improved pullulan production by nitrogen limitation in batch culture of Aureobasidium pullulans

Batch culture of Aureobasidium pullulans CCTCC M 2012259 for pullulan production at different concentrations of ammonium sulfate and yeast extract was investigated. Increased pullulan production was obtained under nitrogen-limiting conditions, as compared to that without nitrogen limitation. The mechanism of nitrogen limitation favoring to pullulan overproduction was revealed by determining the activity as well as gene expression of key enzymes, and energy supply for pullulan biosynthesis. Results indicated that nitrogen limitation increased the activities of α-phosphoglucose mutase and glucosyltransferase, up-regulated the transcriptional levels of pgm1 and fks genes, and supplied more ATP intracellularly, which were propitious to further pullulan biosynthesis. The economic analysis of batch pullulan production indicated that nitrogen limitation could reduce more than one third of the cost of raw materials when glucose was supplemented to a total concentration of 70 g/L. This study also helps to understand the mechanism of other polysaccharide overproduction by nitrogen limitation.