Protein Phosphatase Activity Research Articles

Frontotemporal Lobar Dementia Mutant Tau Impairs Axonal Transport through a Protein Phosphatase 1γ-Dependent Mechanism.

Pathologic tau modifications are characteristic of Alzheimer's disease and related dementias, but mechanisms of tau toxicity continue to be debated. Inherited mutations in tau cause early onset frontotemporal lobar dementias (FTLD-tau) and are commonly used to model mechanisms of tau toxicity in tauopathies. Previous work in the isolated squid axoplasm model demonstrated that several pathogenic forms of tau inhibit axonal transport through a mechanism involving activation of protein phosphatase 1 (PP1). Here, we determined that P301L and R5L FTLD mutant tau proteins elicit a toxic effect on axonal transport as monomeric proteins. We evaluated interactions of wild-type or mutant tau with specific PP1 isoforms (α, β, and γ) to examine how the interaction contributes to this toxic effect using primary rat hippocampal neurons from both sexes. Pull-down and bioluminescence resonance energy transfer experiments revealed selective interactions of wild-type tau with PP1α and PP1γ isoforms, but not PP1β, which were significantly increased by the P301L tau mutation. The results from proximity ligation assays confirmed the interaction in primary hippocampal neurons. Moreover, expression of FTLD-linked mutant tau in these neurons enhanced levels of active PP1, also increasing the pausing frequency of fluorescently labeled vesicles in both anterograde and retrograde directions. Knockdown of PP1γ, but not PP1α, rescued the cargo-pausing effects of P301L and R5L tau, a result replicated by deleting a phosphatase-activating domain in the amino terminus of P301L tau. These findings support a model of tau toxicity involving aberrant activation of a specific PP1γ-dependent pathway that disrupts axonal transport in neurons.SIGNIFICANCE STATEMENT Tau pathology is closely associated with neurodegeneration in Alzheimer's disease and other tauopathies, but the toxic mechanisms remain a debated topic. We previously proposed that pathologic tau forms induce dysfunction and degeneration through aberrant activation of a PP1-dependent pathway that disrupts axonal transport. Here, we show that tau directly interacts with specific PP1 isoforms, increasing levels of active PP1. Pathogenic tau mutations enhance this interaction, further increasing active PP1 levels and impairing axonal transport in isolated squid axoplasm and primary hippocampal neurons. Mutant-tau-mediated impairment of axonal transport was mediated by PP1γ and a phosphatase-activating domain located at the amino terminus of tau. This work has important implications for understanding and potentially mitigating tau-mediated neurotoxicity in tauopathies.

A type-2C protein phosphatase (GhDRP1) participates in cotton (Gossypium hirsutum) response to drought stress.

GhDRP1 acts as a negatively regulator to participate in response to drought stress possibly by modulating ABA signaling pathway and flavonoid biosynthesis pathway which affects stomata movement and thus water loss, ROS scavenging enzymes, and proline accumulation in cotton. Type-2C protein phosphatases (PP2C) may play important roles in plant stress signal transduction. Here, we show the evidence that a cotton PP2C protein GhDRP1 participates in plant response to drought stress. GhDRP1 gene encodes an active type-2C protein phosphatase (PP2C) and its expression is significantly induced in cotton by drought stress. Compared with wild type, the GhDRP1 overexpression (OE) transgenic cotton and Arabidopsis displayed reduced drought tolerance, whereas GhDRP1-silenced (RNAi) cotton showed enhanced drought tolerance. Under drought stress, malondialdehyde content was lower, whereas superoxide dismutase and peroxidase activities, proline content, stomata closure and relative water content were higher in GhDRP1 RNAi plants compared with those in wild type. In contrast, GhDRP1 OE plants showed the opposite phenotype under the same conditions. Expression levels of some stress-related and flavonoid biosynthesis-related genes were altered in GhDRP1 transgenic plants under drought stress. Additionally, GhDRP1 protein could interact with other proteins such as PYLs, SNF1-related protein kinase and GLK1-like protein. Collectively, these data suggest that GhDRP1 participates in plant response to drought stress possibly by modulating ABA signaling pathway and flavonoid biosynthesis pathway which affects stomata movement and thus water loss, ROS scavenging enzymes, and proline accumulation in cotton.

Abstract MP236: PI3Kgamma-PP2A Axis In Regulation Of SERCA Function

Genetic deletion of Phosphoinositide 3-kinase (PI3Kγ) in mice (PI3Kγ -/- ) results in increased cAMP levels and enhanced ventricular rate/contractility. We investigated whether PI3Kγ plays a role in cardiac contractility by altering intracellular calcium recycling. Caffeine treatment of adult cardiomyocytes from PI3Kγ -/- mice showed significantly reduced calcium reuptake by sarcoendoplasmic reticulum (SR) indicating that PI3Kγ locally regulates SR function. This resulted in elevated levels of intracellular calcium for prolonged period following caffeine. Our findings show that delayed re-uptake of calcium was caused by changes in phosphorylation of phospholamban (PLN), a major regulator of SR calcium reuptake. PI3Kγ -/- cardiomyocytes showed significantly reduced PLN phosphorylation due to increase in PLN-associated protein phosphatase (PP) activity as reflected by decreased demethylated-PP2A. Abrogation of PLN phosphorylation in the PI3Kγ -/- cardiomyocytes shows that the loss in the steady-state phosphorylation of PLN leads to increased inhibition of SERCA. This inhibition is reflected by the slow reuptake of calcium by the SR in the PI3Kγ -/- cardiomyocytes. Concomitantly, significant interaction was observed between SERCA and PLN in the PI3Kγ -/- hearts compared to the controls. Consistently, the altered calcium regulation in the cardiomyocytes of PI3Kγ -/- can be restored by inhibition of PP by okadaic acid. Unexpectedly, cardiomyocyte-specific overexpression of kinase-dead PI3Kγ (PI3Kγ inact ) in the global PI3Kγ -/- cardiomyocytes normalized caffeine induced calcium reuptake, restored PLN phosphorylation, and decreased PLN-associated PP activity reflected by increased demethylated-PP2A. These studies bring-to-fore an unrecognized kinase-independent regulation of PLN by PI3Kγ through PP2A with implications in deleterious cardiac remodeling as PI3Kγ is significantly upregulated following cardiac stress.

ULK1 phosphorylation of striatin activates protein phosphatase 2A and autophagy

The evolutionarily conserved ULK1 kinase complex acts as gatekeeper of canonical autophagy and regulates induction of autophagosome biogenesis. To better understand control of ULK1 and analyze whether ULK1 has broader functions that are also linked to the later steps of autophagy, we perform comprehensive phosphoproteomic analyses. Combining invivo with invitro data, we identify numerous direct ULK1 target sites within autophagy-relevant proteins that are critical for autophagosome maturation and turnover. In addition, we highlight an intimate crosstalk between ULK1 and several phosphatase complexes. ULK1 is not only a PP2A target but also directly phosphorylates the regulatory PP2A subunit striatin, activating PP2A and serving as positive feedback to promote autophagy-dependent protein turnover. Thus, ULK1 and phosphatase activities are tightly coordinated to robustly regulate protein degradation by autophagy.

Low-level cadmium doses do not jeopardize the insulin secretion pathway of β-cell models until the onset of cell death

BackgroundCadmium is an inescapable environmental pollutant that permeates the food chain and has been debatably associated with diabetes in humans. Purpose and proceduresTo probe the specific impact of low-level cadmium exposure on insulin production, largely sub-cytotoxic (50–500 nM) concentrations of cadmium chloride challenged the INS-1 and MIN6 rodent models of pancreatic β-cells for the longest possible time, up to 4 days, before sub-culturing. Main findingsThe concentration of detectable oxidants, the pattern of the actin cytoskeleton, the translocation of β-catenin, the activity of protein phosphatases, calcium traffic, and the phosphorylation status of several key signaling nodes, such as AMP kinase and mitogen activated kinases including nuclear translocation of Extracellular signal-Regulated Kinase, were all insensitive to the applied very low cadmium doses. Accordingly, low-level cadmium exposure did not alter the insulin secretion ability, the functional hallmark of β-cells, before the onset of cell death. ConclusionsThese data define an operational toxicological threshold for these cellular models of β-cells that should be useful to address insulin secretion and the diabetogenic effects of chronic low-level cadmium exposure in animal models and in humans.

Regulation PP2Ac methylation ameliorating autophagy dysfunction caused by Mn is associated with mTORC1/ULK1 pathway

Manganese (Mn) exposure leads to autophagy dysfunction and causes neurodegenerative diseases such as Parkinson's syndrome and Alzheimer's disease. However, the mechanism of neurotoxicity of Mn has been less clear. The methylation of the protein phosphatase 2A catalytic subunit determines the dephosphorylation activity of protein phosphatase and plays an important role in autophagy regulation. In this investigation, we established a model of Mn (0–2000 μmol/L) exposure to N2a cells for 12 h, used the PPME-1 inhibitor ABL-127, and constructed an LCMT1-overexpressing N2a cell line. We also regulated the PP2Ac methylation level and explored the effect of PP2Ac methylation on Mn-induced (0–1000 μmol/L) N2a cellular autophagy. Our results showed that Mn > 500 μmol/L induced N2a cell damage and increased oxidative stress. Moreover, Mn modulated autophagy in N2a cells by downregulating PP2Ac methylation, which regulated mTORC1 signaling pathway activation. Both ABL-127 and LCMT1 overexpression can upregulate PP2Ac methylation in parallel with ameliorating N2a cell abnormal autophagy induced by Mn, Briefly, the upregulation of PP2Ac methylation can ameliorate the autophagy disorder of N2a by Mn and effectively alleviate Mn-induced cytotoxicity and oxidative stress, indicating that regulation of autophagy is a protective strategy against Mn-induced neurotoxicity.

Alternative Splicing of MoPTEN Is Important for Growth and Pathogenesis in Magnaporthe oryzae.

Human PTEN, a dual-phosphatase tumor suppressor, is frequently dysregulated by alternative splicing. Fungi harbor PTEN homologs, but alternative splicing of fungal PTENs has not been reported as far as we know. Here, we described an alternative splicing case in the PTEN homolog of Magnaporthe oryzae (MoPTEN). Two splice variants of MoPTEN were detected and identified, which are resulted from an intron retention and exclusion (MoPTEN-1/2). Both proteins were different in lipid and protein phosphatase activity and in expression patterns. The MoPTEN deletion mutant (ΔMoPTEN) showed the defects in conidiation, appressorium formation, and pathogenesis. ΔMoPTEN could be completely restored by MoPTEN, but rescued partially by MoPTEN-1 in the defect of conidium and appressorium formation, and by MoPTEN-2 in the defect of invasive development. Assays to assess sensitivity to oxidative stress reveal the involvement of MoPTEN-2 in scavenging exogenous and host-derived H2O2. Taken together, MoPTEN undergoes alternative splicing, and both variants cooperatively contribute to conidium and appressorium development, and invasive hyphae growth in plant cells, revealing a novel disease development pathway in M. oryzae.

Formation of Giant Lipid Vesicle Containing Dual Functions Facilitates Outer Membrane Phospholipase.

Giant lipid vesicles are used to study artificial cell models, as well as the encapsulation of biomolecules, and the reconstitution of membrane proteins on these vesicles. Recently, complex reactions in giant vesicles have been controlled by reconstituting numerous kinds of biomolecules. However, it is challenging to generate giant lipid vesicles containing a diverse set of proteins at concentrations sufficient to ensure proper functioning. Here, we describe an artificial cell model showing dual functions of small molecule transportation and small vesicle budding, using a dual functional membrane protein (transportation and phosphatase activity) called the outer membrane phospholipase (OmpLA). To the best of our knowledge, we have revealed for the first time the transportation of ions or small molecules through OmpLA on the charged lipid bilayer. The lipid composition controlled the orientation of OmpLA through proteinase K digestion. Finally, OmpLA enzyme activity of phospholipid hydrolysis caused the budding of small vesicles.

Short- and Long-Term Adaptation to Altered Levels of Glucose: Fifty Years of Scientific Adventure.

My graduate and postdoctoral training in metabolism and enzymology eventually led me to study the short- and long-term regulation of glucose and lipid metabolism. In the early phase of my career, my trainees and I identified, purified, and characterized a variety of phosphofructokinase enzymes from mammalian tissues. These studies led us to discover fructose 2,6-P2, the most potent activator of phosphofructokinase and glycolysis. The discovery of fructose 2,6-P2 led to the identification and characterization of the tissue-specific bifunctional enzyme 6-phosphofructo-2-kinase:fructose 2,6-bisphosphatase. We discovered a glucose signaling mechanism by which the liver maintains glucose homeostasis by regulating the activities of this bifunctional enzyme. With a rise in glucose, a signaling metabolite, xylulose 5-phosphate, triggers rapid activation of a specific protein phosphatase (PP2ABδC), which dephosphorylates the bifunctional enzyme, thereby increasing fructose 2,6-P2 levels and upregulating glycolysis. These endeavors paved the way for us to initiate the later phase of my career in which we discovered a new transcription factor termed the carbohydrate response element binding protein (ChREBP). Now ChREBP is recognized as the masterregulator controlling conversion of excess carbohydrates to storage of fat in the liver. ChREBP functions as a central metabolic coordinator that responds to nutrients independently of insulin. The ChREBP transcription factor facilitates metabolic adaptation to excess glucose, leading to obesity and its associated diseases.

MiR-21 and mRNA PTEN Expression Levels and Biomarker Potential in Breast Cancer

MiR-21 has been linked to tumorigenesis, development, and metastasis in tumor pathogenesis. All human cancers, including breast cancer, have increased expression of MiR-21, which is the only miRNA that has increased expression. PTEN expression was found to be reduced in the majority of solid tumors, including breast cancer. Since lymph node metastatic factors, estrogen receptor status, tumor grade, and tumor node metastasis (TNM) all decreased PTEN expression, the PTEN expression profile may be a very useful prognostic marker in breast cancer. PTEN inhibits PIP3 (phosphatidylinositol 3,4,5-triphosphate) activity by having protein phosphatase and lipid phosphatase activity that is the polar opposite of PI3K (Phosphatidyl Inositol 3-Kinase). The aim of this research was to see how often miR-21 and mRNA PTEN were expressed at different stages of breast cancer and whether they could be used as prognostic markers. This type of research is an observational study with a cross-sectional design. The sample size of 43 people came from breast cancer patients. Analysis of miR-21 expression and mRNA PTEN using Real-Time qPCR. The results showed that miR-21 expression increased 1.32 times at an advanced stage compared to an early stage, while mRNA PTEN expression decreased 1.33 fold at an advanced stage compared to an early stage. According to the findings, miR-21 expression in the blood plasma of breast cancer patients was upregulated at an advanced stage compared to an early stage and downregulated mRNA PTEN expression. MiR-21 which is increased at an advanced stage has the potential to be a poor prognostic marker at the stage of breast cancer. The change in miR-21 expression can be a good candidate as a molecular prognostic marker and for future research the role of miR-21 in breast cancer progression will further enrich the scientific repertoire, especially in the health and clinical fields.

Phosphatase and Tensin Homolog in Non-neoplastic Digestive Disease: More Than Just Tumor Suppressor.

The Phosphatase and tensin homolog (PTEN) gene is one of the most important tumor suppressor genes, which acts through its unique protein phosphatase and lipid phosphatase activity. PTEN protein is widely distributed and exhibits complex biological functions and regulatory modes. It is involved in the regulation of cell morphology, proliferation, differentiation, adhesion, and migration through a variety of signaling pathways. The role of PTEN in malignant tumors of the digestive system is well documented. Recent studies have indicated that PTEN may be closely related to many other benign processes in digestive organs. Emerging evidence suggests that PTEN is a potential therapeutic target in the context of several non-neoplastic diseases of the digestive tract. The recent discovery of PTEN isoforms is expected to help unravel more biological effects of PTEN in non-neoplastic digestive diseases.

Complex functionality of protein phosphatase 1 isoforms in the heart

Protein phosphatase 1(PP1) is a key regulator of cardiac function through dephosphorylating serine/threonine residues within target proteins to oppose the function of protein kinases. Studies from failing hearts of animal models and human patients have demonstrated significant increase of PP1 activity in myocardium, while elevated PP1 activity in transgenic mice leads to cardiac dysfunction, suggesting that PP1 might be a therapeutic target to ameliorate cardiac dysfunction in failing hearts. In fact, cardiac overexpression of inhibitor 1, the endogenous inhibitor of PP1, increases cardiac contractility and suppresses heart failure progression. However, this notion of PP1 inhibition for heart failure treatment has been challenged by recent studies on the isoform-specific roles of PP1 in the heart. PP1 is a holoenzyme composed of catalytic subunits (PP1α, PP1β, or PP1γ) and regulatory proteins that target them to distinct subcellular locations for functional specificity. This review will summarize how PP1 regulates phosphorylation of some of the key cardiac proteins involved in Ca2+ handling and cardiac contraction, and the potential role of PP1 isoforms in controlling cardiac physiology and pathophysiology.

Role of Receptor Protein Tyrosine Phosphatases (RPTPs) in Insulin Signaling and Secretion.

Changes in lifestyle in developed countries have triggered the prevalence of obesity and type 2 diabetes mellitus (T2DM) in the latest years. Consequently, these metabolic diseases associated to insulin resistance, and the morbidity associated with them, accounts for enormous costs for the health systems. The best way to face this problem is to identify potential therapeutic targets and/or early biomarkers to help in the treatment and in the early detection. In the insulin receptor signaling cascade, the activities of protein tyrosine kinases and phosphatases are coordinated, thus, protein tyrosine kinases amplify the insulin signaling response, whereas phosphatases are required for the regulation of the rate and duration of that response. The focus of this review is to summarize the impact of transmembrane receptor protein tyrosine phosphatase (RPTPs) in the insulin signaling cascade and secretion, and their implication in metabolic diseases such as obesity and T2DM.

Protein tyrosine phosphatase receptor type C (PTPRC or CD45)

The leucocyte common antigen, protein tyrosine phosphatase receptor type C (PTPRC), also known as CD45, is a transmembrane glycoprotein, expressed on almost all haematopoietic cells except for mature erythrocytes, and...

The role of PP5 and PP2C in cardiac health and disease

Protein phosphatases are important, for example, as functional antagonists of β-adrenergic stimulation of the mammalian heart. While β-adrenergic stimulations increase the phosphorylation state of regulatory proteins and therefore force of contraction in the heart, these phosphorylations are reversed and thus force is reduced by the activity of protein phosphatases. In this context the role of PP5 and PP2C is starting to unravel. They do not belong to the same family of phosphatases with regard to sequence homology, many similarities with regard to location, activation by lipids and putative substrates have been worked out over the years. We also suggest which pathways for regulation of PP5 and/or PP2C described in other tissues and not yet in the heart might be useful to look for in cardiac tissue. Both phosphatases might play a role in signal transduction of sarcolemmal receptors in the heart. Expression of PP5 and PP2C can be increased by extracellular stimuli in the heart. Because PP5 is overexpressed in failing animal and human hearts, and because overexpression of PP5 or PP2C leads to cardiac hypertrophy and KO of PP5 leads to cardiac hypotrophy, one might argue for a role of PP5 and PP2C in heart failure. Because PP5 and PP2C can reduce, at least in vitro, the phosphorylation state of proteins thought to be relevant for cardiac arrhythmias, a role of these phosphatases for cardiac arrhythmias is also probable. Thus, PP5 and PP2C might be druggable targets to treat important cardiac diseases like heart failure, cardiac hypertrophy and cardiac arrhythmias.

Trypanosoma brucei Tim50 Plays Critical role in Parasite survival in mammalian hosts

Trypanosoma brucei, the infectious agent for African trypanosomiasis, undergoes various developmental processes during its digenetic life cyclethat includes a major alteration in mitochondrial activities. It is known that changes in mitochondrial functions is critical for the parasite to adapt in different environmental conditions, however, the communication mechanism between this single organelle with the rest of the cell is not clear in T. brucei. Mitochondrial inner membrane protein translocase, TbTim50, have a pair of characteristic DXDX(T/V) phosphatase signature motifs. Here we showed that the recombinant TbTim50, specifically binds with Phosphatidic acid (PA). We have also demonstrated that, TbTim50 possesses a protein phosphatase activity and also able to hydrolyze phosphatidic acid (PA). This is suggesting that TbTim50 likely possesses both protein and lipid phosphatase activities. TbTim50 knockdown (KD) decreased the levels of cardiolipin in comparison to control. Cardiolipin is known to play important roles in various mitochondrial functions. RT-PCR analysis also showed that TbTim50 KD increased expression of multiple genes specific for the stumpy form, a non-dividing differentiated bloodstream form of T. brucei. Importantly, we observed that TbTim50 depleted parasites were unable to establish infection in mice and rats. These results indicates that TbTim50 is essential for overall mitochondrial functions and play a critical role in parasite infectivity in animals.

TRPC1‐mediated Ca2+signaling enhances intestinal epithelial restitution by increasing α4 association with PP2Ac after wounding

Gut epithelial restitution after superficial wounding is an important repair modality regulated by numerous factors including Ca2+ signaling and cellular polyamines. Transient receptor potential canonical‐1 (TRPC1) functions as a store‐operated Ca2+ channel in intestinal epithelial cells (IECs) and its activation increases epithelial restitution by inducing Ca2+ influx after acute injury. α4 is a multiple functional protein and implicated in many aspects of cell functions by modulating protein phosphatase 2A (PP2A) stability and activity. Here we show that the clonal populations of IECs stably expressing TRPC1 (IEC‐TRPC1) exhibited increased levels of α4 and PP2A catalytic subunit (PP2Ac) and that TRPC1 promoted intestinal epithelial restitution by increasing α4/PP2Ac association. The levels of α4 and PP2Ac proteins increased significantly in stable IEC‐TRPC1 cells and this induction in α4/PP2Ac complexes was accompanied by an increase in IEC migration after wounding. α4 silencing by transfection with siRNA targeting α4 (siα4) or PP2Ac silencing destabilized α4/PP2Ac complexes in stable IEC‐TRPC1 cells and repressed cell migration over the wounded area. Increasing the levels of cellular polyamines by stable transfection with the Odc gene stimulated α4 and PP2Ac expression and enhanced their association, thus also promoting epithelial restitution after wounding. In contrast, depletion of cellular polyamines by treatment with α‐difluoromethylornithine reduced α4/PP2Ac complexes and repressed cell migration. Ectopic overexpression of α4 partially rescued rapid epithelial repair in polyamine‐deficient cells. These results indicate that activation of TRPC1‐mediated Ca2+ signaling enhances cell migration primarily by increasing α4/PP2Ac associations after wounding and this pathway is tightly regulated by cellular polyamines.

Optimization of dietary pyridoxine improved growth performance, hematological indices, antioxidant capacity, intestinal enzyme activity, non-specific immune response, and liver pyridoxine concentration of fingerling major carp Catla catla (Hamilton)

The current research work was undertaken to evaluate the requirement of fingerling Catla catla (3.7 ± 0.5 g) for dietary pyridoxine. Triplicate groups of fingerling were fed casein-gelatin based iso-nitrogenous and isocaloric diets (350 g/kg Crude Protein; 16.72 Kj/g Gross Energy) containing eight different levels of pyridoxine (0, 0.5, 1, 2, 4, 6, 8 and 10 mg/kg diet) to satiation for 16 weeks. All the growth parameters were positively affected by increasing concentrations of dietary pyridoxine up to 4 mg/kg diet. Erythrocyte (RBC), hematocrit (Ht), hemoglobin (Hb), alanine (ALT) and aspartate aminotransferase (AST) activities were significantly (P < 0.05) affected and increased up to 4 mg pyridoxine per kg diet. Thiobarbituric acid reactive substances (TBARS) values were found to be highest in fish fed basal diet which decreased with the increase of dietary pyridoxine up to 4 mg/kg whereas, liver superoxide dismutase (SOD) and catalase (CAT) activities increased with incremental levels of dietary pyridoxine up to 4 mg/kg diet. Intestinal protease, amylase and lipase activities significantly (P < 0.05) increased as the amounts of dietary pyridoxine increased up to 4 mg/kg and then leveled off. Fish fed 4 mg/kg pyridoxine reflected significantly higher (P < 0.05) lysozyme, tissue serum protein and alkaline phosphatase activities than fish fed the pyridoxine-deficient diets. However, liver saturation was achieved in fish fed 8 mg pyridoxine per kg diet. Broken-line regression analysis of growth parameters, RNA/DNA ratio, SOD, protease, lysozyme and the liver pyridoxine concentration data against varying levels of dietary pyridoxine indicated the requirement in the range of 3.20–6.87 mg/kg.

Activated Protein Phosphatase 2A Disrupts Nutrient Sensing Balance Between Mechanistic Target of Rapamycin Complex 1 and Adenosine Monophosphate-Activated Protein Kinase, Causing Sarcopenia in Alcohol-Associated Liver Disease.

Despite the high clinical significance of sarcopenia in alcohol-associated cirrhosis, there are currently no effective therapies because the underlying mechanisms are poorly understood. We determined the mechanisms of ethanol-induced impaired phosphorylation of mechanistic target of rapamycin complex 1 (mTORC1) and adenosine monophosphate-activated protein kinase (AMPK) with consequent dysregulated skeletal muscle protein homeostasis (balance between protein synthesis and breakdown). Differentiated murine myotubes, gastrocnemius muscle from mice with loss and gain of function of regulatory genes following ethanol treatment, and skeletal muscle from patients with alcohol-associated cirrhosis were used. Ethanol increases skeletal muscle autophagy by dephosphorylating mTORC1, circumventing the classical kinase regulation by protein kinase B (Akt). Concurrently and paradoxically, ethanol exposure results in dephosphorylation and inhibition of AMPK, an activator of autophagy and inhibitor of mTORC1 signaling. However, AMPK remains inactive with ethanol exposure despite lower cellular and tissue adenosine triphosphate, indicating a "pseudofed" state. We identified protein phosphatase (PP) 2A as a key mediator of ethanol-induced signaling and functional perturbations using loss and gain of function studies. Ethanol impairs binding of endogenous inhibitor of PP2A to PP2A, resulting in methylation and targeting of PP2A to cause dephosphorylation of mTORC1 and AMPK. Activity of phosphoinositide 3-kinase-γ (PI3Kγ), a negative regulator of PP2A, was decreased in response to ethanol. Ethanol-induced molecular and phenotypic perturbations in wild-type mice were observed in PI3Kγ-/- mice even at baseline. Importantly, overexpressing kinase-active PI3Kγ but not the kinase-dead mutant reversed ethanol-induced molecular perturbations. Our study describes the mechanistic underpinnings for ethanol-mediated dysregulation of protein homeostasis by PP2A that leads to sarcopenia with a potential for therapeutic approaches by targeting the PI3Kγ-PP2A axis.

Effect of occupational exposure to heavy metals on the liver functions in persons working in cable manufacturing factory in Nnewi

Occupational exposure to hazardous metals or heavy metals has remained an issue of public health importance owing to the grave implications it has on human health. This study evaluated the effect of occupational exposure to heavy metals on the liver functions in persons working in a cable manufacturing factory in Nnewi. A total of 79 apparently healthy individuals comprising of 39 persons working in cable producing factory (test group) and 40 control participants aged between 18 and 56 years were recruited for the study. Five millilitres (5mls) of venous blood sample was collected from each individual into plain container for the evaluation of biochemical parameters. Serum total protein (TP), albumin (ALB), direct bilirubin (DB), total bilirubin (TB), aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities were assayed for using standard laboratory methods. Results showed significant increases in the AST (27.552.08 Vs 9.150.13) and ALP (238.3724.40 Vs 20.700.48) activities and in levels of TP (7.820.27 Vs7.100.04) and DB (4.140.30 Vs 2.670.07) in cable factory workers when compared with the control subjects (p0.05). Furthermore, gender differences were observed in the values of DB, AST, and ALP compared with control. Results also showed no significant effects of age and length of service (LOS) on the liver function status of factory workers studied. Thus, this study revealed no liver impairment among the cable factory workers studied as a result of occupational exposure. This could be attributable to the short term duration of exposure of the factory workers. Keywords: Occupational exposure, Heavy metals, Liver, Liver functions, Cable factory, Age, LOS, Gender.