Zinc-α2-Glycoprotein Modulates AKT-Dependent Insulin Signaling in Human Adipocytes by Activation of the PP2A Phosphatase

Objective

Evidence from mouse models suggests that zinc-α2-glycoprotein (ZAG) is a novel anti-obesity adipokine. In humans, however, data are controversial and its physiological role in adipose tissue (AT) remains unknown. Here we explored the molecular mechanisms by which ZAG regulates carbohydrate metabolism in human adipocytes.

Methods

ZAG action on glucose uptake and insulin action was analyzed. β1 and β2-adrenoreceptor (AR) antagonists and siRNA targeting PP2A phosphatase were used to examine the mechanisms by which ZAG modulates insulin sensitivity. Plasma levels of ZAG were measured in a lean patient cohort stratified for HOMA-IR.

Results

ZAG treatment increased basal glucose uptake, correlating with an increase in GLUT expression, but induced insulin resistance in adipocytes. Pretreatment of adipocytes with propranolol and a specific β1-AR antagonist demonstrated that ZAG effects on basal glucose uptake and GLUT4 expression are mediated via β1-AR, whereas inhibition of insulin action is dependent on β2-AR activation. ZAG treatment correlated with an increase in PP2A activity. Silencing of the PP2A catalytic subunit abrogated the negative effect of ZAG on insulin-stimulated AKT phosphorylation and glucose uptake but not on GLUT4 expression and basal glucose uptake. ZAG circulating levels were unchanged in a lean patient cohort stratified for HOMA-IR. Neither glucose nor insulin was associated with plasma ZAG.

Conclusions

ZAG inhibits insulin-induced glucose uptake in human adipocytes by impairing insulin signaling at the level of AKT in a β2-AR- and PP2A-dependent manner.     

Zinc-α2-Glycoprotein Is Unrelated to Gestational Diabetes: Anthropometric and Metabolic Determinants in Pregnant Women and Their Offspring

Context

Zinc-α2-Glycoprotein (ZAG) is an adipokine with lipolytic action and is positively associated with adiponectin in adipose tissue. We hypothesize that ZAG may be related with hydrocarbonate metabolism disturbances observed in gestational diabetes mellitus (GDM).

Objective

The aim of this study was to analyze serum ZAG concentration and its relationship with carbohydrate metabolism in pregnant women and its influence on fetal growth.

Design

207 pregnant women (130 with normal glucose tolerance (NGT) and 77 with GDM) recruited in the early third trimester and their offspring were studied. Cord blood was obtained at delivery and neonatal anthropometry was assessed in the first 48 hours. ZAG was determined in maternal serum and cord blood.

Results

ZAG concentration was lower in cord blood than in maternal serum, but similar concentration was observed in NGT and GDM pregnant women. Also similar levels were found between offspring of NGT and GDM women. In the bivariate analysis, maternal ZAG (mZAG) was positively correlated with adiponectin and HDL cholesterol, and negatively correlated with insulin and triglyceride concentrations, and HOMA index. On the other hand, cord blood ZAG (cbZAG) was positively correlated with fat-free mass, birth weight and gestational age at delivery. After adjusting for confounding variables, gestational age at delivery and HDL cholesterol emerged as the sole determinants of cord blood ZAG and maternal ZAG concentrations, respectively.

Conclusion

mZAG was not associated with glucose metabolism during pregnancy. ZAG concentration was lower in cord blood compared with maternal serum. cbZAG was independently correlated with gestational age at delivery, suggesting a role during the accelerated fetal growth during latter pregnancy.     

The Role of Zinc in Thrombosis and Pulmonary Embolism in the Course of Antiphospholipid Syndrome (APS)—Short Review

Antiphospholipid antibodies may occur in the course of various diseases, but its presence is not necessarily associated with clinical symptoms. Zinc has multiple biological roles. For example, it stabilizes the cell’s membrane and regulates its functions by influencing the synthesis of phospholipids and its distribution. The present review focuses on the possible associations between zinc and antiphospholipid antibodies and with the symptoms of antiphospholipid syndrome.     

Metabolism of 17α-methyl-5α-dihydrotestosterone in the rabbit

17α-Methyl-5α-dihydrotestosterone and the reduced metabolites, 17α-methyl-5α-androstane-3α, 17β-diol and -3β, 17β-diol together with two hydroxylated metabolites, 17α-methyl-5α-androstane-3β, 15α, 17β-triol and 17α-methyl-5α-androstane-3α, 6α, 17β-triol were isolated and identified in the urine of rabbits orally dosed with 17α-methyl-5α-dihydrotestosterone. Formation of the C-6 hydroxylated derivative demonstrates that the 4,6-enolization of a 4-en-3-one is not a necessary requirement for hydroxylation at C-6 of the androstane nucleus in the rabbit. No evidence was obtained for the presence of 17α-methyl/17β-hydroxyl epimerization.     

Metabolism of 17β-hydroxy-2α,3α-cyclopropano-5α-androstane in the rabbit

The neutral urinary excretion products of 17β-hydroxy-2α,3α-cyclopropano-5α-androstane from the rabbit, dosed orally, were investigated. Column chromatography yielded five crystalline metabolites which were identified by GLC and spectroscopic measurements. Three of these substances were hydroxylated in the 4α-position and one in the 6a-position with the cyclopropane ring intact. The fifth substance, 17β-hydroxy-3β-methyl-5α-androstan-2-one, can be derived from initial hydroxylation of the cyclopropane ring at C-2 followed by ring opening. The dosed substance and triol material was shown to be present by GLC and m.s. measurements. GLC determinations show that hydroxylation has occurred at C-4?C-6>C-2.     

Inborn Errors in Purine Metabolism: Role of 5′-Nucleotidases and Their Involvement in the Etiology of Neurological Impairments

A number of scientists have been involved for decades in the study of nucleotide metabolism in different species of living beings. We are, therefore, aware of the relevant roles of purine compounds and of the many different ways in which these compounds influence cell life, acting both inside and outside the cells. Nevertheless, the consequences of an alteration (lack of expression, or hypo- or hyperexpression) in the activity of enzymes involved in the metabolism of these compounds are sometimes surprising, and far from being mechanistically explained. Alterations in enzyme activities involved in nucleotide metabolism are frequently associated with syndromes characterized by two different types of problems – one, metabolic, which is expected and can be easily explained, and the second, neurological and behavioral. Neurological and behavioral impairments are more difficult to explain and show a very high degree of individual variability. The molecular bases of the neurological impairment linked to purine metabolism disorders have been extensively studied. These studies have generated a lot of hypotheses but very few certainties. In this short review, neurological and behavioral symptoms linked to the dysfunction of some enzymes involved in purine synthesis, catabolism, and salvage will be briefly described, with particular attention to their metabolic and regulatory consequences. Finally, attention will be focused on the 5′-nucleotidase family members and on their involvement in the regulation of purine and pyrimidine metabolism.     

Role of FcαR EC2 region in extracellular membrane localization

The FcαR receptor (CD89) binds to the constant region of Immunoglobulin (Ig) A to mediate mucosal immunity [1–2]. FcαR consist of five exons: two that code for the signal peptide regions S1 & S2, two for the extracellular regions EC1 and EC2, and the final exon for the transmembrane/cytoplasmic tail region [3]. Previously, we reported that the EC1 region plays an essential role for extracellular membrane localization of the receptor [4], where the absence of EC1 would prevent the variants from localizing to the cell surface, even with a full signal peptide. In the case of FcαR Variant 4 (lacking the S2 region only), there was some “leakiness” to membrane surface localization.     

Metabolism of a glutathione conjugate of 2-hydroxyoestradiol-17β in the adult male rat

Adult male rats with cannulated or ligated bile ducts were given S-(2-hydroxyoestradiol-1-yl)[(35)S]glutathione, S-(2-hydroxy[6,7-(3)H(2)]oestradiol-1-yl)glutathione or S-(2-hydroxyoestradiol-1-yl)[glycine-(3)H]glutathione by intraperitoneal injection. The recovery of radioactivity in the bile of bile duct-cannulated rats was 33-86% and in the urine of bile duct-ligated rats was 54-105%. Oestrogen thioether derivatives of glutathione, cysteinylglycine, cysteine and N-acetylcysteine were isolated from bile; only the N-acetylcysteine derivatives could be identified in the urine. The steroid moiety was characterized by microchemical tests before and after treatment with Raney nickel: 2-hydroxyoestradiol-17beta was released from the glutathione conjugate, and 2-hydroxyoestrone and 2-hydroxyoestrone 3-methyl ether from the other conjugates. From intact rats the recovery of administered radioactivity was about 15% in the urine and 5% in the faeces over a period of several days and the radioactivity appeared to be largely protein-bound. The results demonstrate that injected oestrogen-glutathione conjugate undergoes conversion into N-acetylcysteine derivatives in vivo. Oestrogen-glutathione conjugates formed in the intact rat may be excreted in an apparently non-steroidal, possibly protein-bound form, which would not be detected by current analytical techniques.     

Thyroid Hormone Upregulates Zinc-α2-glycoprotein Production in the Liver but Not in Adipose Tissue

Overproduction of zinc-α₂-glycoprotein by adipose tissue is crucial in accounting for the lipolysis occurring in cancer cachexia of certain malignant tumors. The main aim of this study was to explore whether thyroid hormone could enhance zinc-α₂-glycoprotein production in adipose tissue. In addition, the regulation of zinc-α₂-glycoprotein by thyroid hormone in the liver was investigated. We performed in vitro (HepG2 cells and primary human adipocytes) and in vivo (C57BL6/mice) experiments addressed to examine the effect of thyroid hormone on zinc-α₂-glycoprotein production (mRNA and protein levels) in liver and visceral adipose tissue. We also measured the zinc-α₂-glycoprotein serum levels in a cohort of patients before and after controlling their hyperthyroidism. Our results showed that thyroid hormone up-regulates zinc-α₂-glycoprotein production in HepG2 cells in a dose-dependent manner. In addition, the zinc-α₂-glycoprotein proximal promoter contains functional thyroid hormone receptor binding sites that respond to thyroid hormone treatment in luciferase reporter gene assays in HepG2 cells. Furthermore, zinc-α₂-glycoprotein induced lipolysis in HepG2 in a dose-dependent manner. Our in vivo experiments in mice confirmed the up-regulation of zinc-α₂-glycoprotein induced by thyroid hormone in the liver, thus leading to a significant increase in zinc-α₂-glycoprotein circulating levels. However, thyroid hormone did not regulate zinc-α₂-glycoprotein production in either human or mouse adipocytes. Finally, in patients with hyperthyroidism a significant reduction of zinc-α₂-glycoprotein serum levels was detected after treatment but was unrelated to body weight changes. We conclude that thyroid hormone up-regulates the production of zinc-α₂-glycoprotein in the liver but not in the adipose tissue. The neutral effect of thyroid hormones on zinc-α₂-glycoprotein expression in adipose tissue could be the reason why zinc-α₂-glycoprotein is not related to weight loss in hyperthyroidism.     

Epidemiology of Dengue Disease in Malaysia (2000–2012): A Systematic Literature Review

A literature survey and analysis was conducted to describe the epidemiology of dengue disease in Malaysia between 2000 and 2012. Published literature was searched for epidemiological studies of dengue disease, using specific search strategies for each electronic database; 237 relevant data sources were identified, 28 of which fulfilled the inclusion criteria. The epidemiology of dengue disease in Malaysia was characterized by a non-linear increase in the number of reported cases from 7,103 in 2000 to 46,171 in 2010, and a shift in the age range predominance from children toward adults. The overall increase in dengue disease was accompanied by a rise in the number, but not the proportion, of severe cases. The dominant circulating dengue virus serotypes changed continually over the decade and differed between states. Several gaps in epidemiological knowledge were identified; in particular, studies of regional differences, age-stratified seroprevalence, and hospital admissions.

Protocol registration

PROSPERO #CRD42012002293

Author summary

Dengue disease is a tropical and subtropical mosquito-borne viral illness, and is a major health concern in Malaysia. We conducted this literature analysis and review to describe the epidemiology of dengue disease in Malaysia between 2000 and 2012, to determine the impact of dengue disease on the Malaysian population, and to identify future research priorities. We used well-defined methods to search and identify relevant research, and data were selected according to predetermined inclusion criteria. This long-term review highlights the changing epidemiology of dengue fever in Malaysia. Although the overall incidence has stabilized in recent years, dengue disease remains a public health burden. Our review demonstrates an increased incidence of all forms of dengue disease and a predominantly adult age distribution. Changes in circulating dengue virus serotypes may have implications for the incidence and severity of dengue disease. Increasing levels of rainfall, humidity, temperature, and urbanization have been identified as risk factors for dengue disease outbreak. We believe that the recent improvements to the surveillance system in Malaysia should, if pursued over the next few years, greatly improve our understanding of the burden of dengue fever and enable us to monitor the impact of disease control measures in the future.     

Role of Cholesterol in APP Metabolism and Its Significance in Alzheimer’s Disease Pathogenesis

Alzheimer’s disease (AD) is a complex multifactorial neurodegenerative disorder believed to be initiated by accumulation of amyloid β (Aβ)-related peptides derived from proteolytic processing of amyloid precursor protein (APP). Research over the past two decades provided a mechanistic link between cholesterol and AD pathogenesis. Genetic polymorphisms in genes regulating the pivotal points in cholesterol metabolism have been suggested to enhance the risk of developing AD. Altered neuronal membrane cholesterol level and/or subcellular distribution have been implicated in aberrant formation, aggregation, toxicity, and degradation of Aβ-related peptides. However, the results are somewhat contradictory and we still do not have a complete understanding on how cholesterol can influence AD pathogenesis. In this review, we summarize our current understanding on the role of cholesterol in regulating the production/function of Aβ-related peptides and also examine the therapeutic potential of regulating cholesterol homeostasis in the treatment of AD pathology.     

Metabolism of 17β-hydroxy-2-hydroxymethylene-5α-androstan-3-one in the rabbit

An acidic metabolite, 2α-carboxy-5α-androstane-3α, 16α, 17αtriol and two neutral metabolites, 2α-hydroxymethyl-5α-androstane-3α, 17α-diol, and 2α-hydroxymethyl-5α-androstane-3α, 16α, 17α-triol have been identified in the urine of rabbits orally dosed with 17β-hydroxy-2-hydroxymethylene-5α-androstan-3-one. 2α-Hydroxymethyl-5α-androstane-3α, 16α, 17α-triol was previously obtained from the urine of rabbits dosed with 17β-hydroxy-2α-methyl-5α-androstan-3-one. The acidic metabolite was the major urinary excretion product.     

Metabolism of 17α-methyl-5β-dihydrotestosterone in the rabbit

17α-Methy1-5β-androstane-3α, 17β-diol together with the hydroxylated metabolites 17α-methyl-5β-androstane-1β, 3α, 17β-triol, 17α-methyl-5β-androstane-3α, 12β, 17β-triol, 17α-methyl-5β-androstane-3α, 16α, 17β-triol and 17α-methyl-5β-androstane-3α, 16β, 17β-triol were isolated and identified in the urine of rabbits orally dosed with 17α-methyl-5β-dihydrotestosterone. Biotransformations differ from the 5α-series where hydroxylation occurred at C-6 and C-15. In both series, the C-3 equatorial epimer was the major urinary excretion product among the non-hydroxylated metabolites. The 5β-compound was more resistant to metabolic hydroxylation than the 5α-compound. No evidence for epimerization at the C-17 position was observed.     

The Voltage-Gated Calcium Channel γ Subunits: A Review of the Literature

Members of the voltage-gated calcium channel y subunit gene family (Cacng), have been rapidly discovered since the discovery of the identification of the mouse gamma2 gene (Cacng2) and its association with the stargazer mutant mouse line. The fact that this mutant mouse line exists has allowed researchers to gain insights into the function of the gamma2 subunit. For example, stargazer mice have elevated levels of neuropeptide Y production, very low cerebellar brain derived neurotrophic factor production, and diminished cerebellar GABAA alpha6 and beta3 production. Study of this mutant mouse line has also revealed that the gamma2 subunit is involved in AMPA receptor trafficking and targeting to the synaptic membrane. For the most part, the effect of gamma2 subunits on the electrophysiology of voltage-gated calcium channels is to downregulate calcium channel activity by causing a hyperpolarizing shift in the inactivation curve. This finding and the association of these subunits with AMPA receptor trafficking has led some researchers to question the actual role of the gamma subunits. This article reviews the discovery, cellular localization, tissue distribution, and function of the eight members of the Cacng family.     

Role of phosphatidylinositol 4,5-bisphosphate in the activation of cytosolic phospholipase A2-α

Cytosolic phospholipase A₂-α (cPLA₂) plays an important role in the release of arachidonic acid and in cell injury. Activation of cPLA₂ is dependent on a rise in cytosolic Ca²⁺ concentration, membrane association via the Ca²⁺-dependent lipid binding (CaLB) domain, and phosphorylation. This study addresses the activation of cPLA₂ via potential association with membrane phosphatidylinositol 4,5-bisphosphate (PIP₂), including the role of a “pleckstrin homology (PH)-like” region of cPLA₂ (amino acids 263-354). In cells incubated with complement, phorbol myristate acetate + the Ca²⁺ ionophore, A23187, or epidermal growth factor + A23187, expression of the PH domain of phospholipase C-δ1 (which sequesters membrane PIP₂) attenuated cPLA₂ activity. Stimulated cPLA₂ activity was also attenuated by the expression of cPLA₂ 135-366, or cPLA₂ 2-366, and expression of a PIP₂-specific 5′-phosphatase. However, in a yeast-based assay that tests the ability of proteins to bind to membrane lipids, including PIP₂, with high affinity, only cPLA₂ 1-200 (CaLB domain) was able to interact with membrane lipids, whereas cPLA₂s 135-366, 2-366, 201-648, and 1-648 were unable to do so. Therefore, cPLA₂ activity can be modulated by sequestration or depletion of cellular PIP₂, although the interaction of cPLA₂ with membrane PIP₂ appears to be indirect, or of weak affinity.