Role of β-adrenergic receptors in the anti-obesity and anti-diabetic effects of zinc-α2-glycoprotien (ZAG)

CircNOLC1 Promotes Colorectal Cancer Liver Metastasis by Interacting with AZGP1 and Sponging miR-212-5p to Regulate Reprogramming of the Oxidative Pentose Phosphate Pathway

Liver metastasis is a common cause of death in progressive colorectal cancer patients, but the molecular mechanisms remain unclear. Here, it is reported that a conserved and oxidative pentose phosphate pathway-associated circular RNA, circNOLC1, plays a crucial role in colorectal cancer liver metastasis. It is found that circNOLC1 silencing reduces the oxidative pentose phosphate pathway-related intermediate metabolites and elevates NADP+ /NADPH ratio and intracellular ROS levels, thereby attenuating colorectal cancer cell proliferation, migration, and liver metastasis. circNOLC1 interacting with AZGP1 to activate mTOR/SREBP1 signaling, or sponging miR-212-5p to upregulate c-Met expression, both of which can further induce G6PD to activate oxidative pentose phosphate pathway in colorectal cancer liver metastasis. Moreover, circNOLC1 is regulated by the transcription factor YY1 and specifically stabilized HuR induces its parental gene mRNA expression. The associations between circNOLC1 and these signaling molecules are validated in primary CRC and corresponding liver metastasis tissues. These findings reveal that circNOLC1 interacting with AZGP1 and circNOLC1/miR-212-5p/c-Met axis plays a key role in oxidative pentose phosphate pathway-mediated colorectal cancer liver metastasis, which may provide a novel target for precision medicine of colorectal cancer.

Effects of Weight Loss and Aerobic Exercise Training on Adi-Pose Tissue Zinc α2-Glycoprotein and Associated Genes in Obesity

Zinc α2-glycoprotein (ZAG) has been implicated in fatty acid metabolism and utilization and is lower in obese and higher in cachexic adults compared to those of normal weight. Previous studies suggest that ZAG binds to the beta3-adrenergic receptor (β3AR) to influence fatty acid metabolism in adipose tissue by regulating hormone sensitive lipase (HSL). The purpose of this study is to investigate the effects of a six-month weight loss (WL) or aerobic exercise (AEX) intervention on adipose tissue and skeletal muscle ZAG mRNA levels and protein expression, as well as the expression of β3AR, and HSL. Abdominal adipose tissue (AB) and gluteal adipose tissue (Glut) and vastus lateralis muscle biopsies were performed before and after WL (n = 13) or AEX (n = 13). ZAG, HSL, and β3AR expressions were determined by RT-PCR, and ZAG and HSL plasma levels by ELISA. Body weight decreased by 9.69% (p < 0.001) in WL and did not change with AEX. Maximal oxygen consumption (VO2max) increased by 7.1% (p < 0.005) after WL and by 16.69% (p < 0.001) after AEX. WL significantly decreased body weight with a reduction of percentage of fat, fat mass, fat-free mass (FFM). AEX decreased percent fat and increased VO2max, but did not change fat mass and FFM. Abdominal ZAG and HSL mRNA levels did not change significantly after WL or AEX. There were no changes in plasma ZAG, HSL and adipose tissue β3AR mRNA levels after WL and AEX. ZAG, HSL and β3AR mRNA expressions in adipose tissue are positively associated each other. Adipose tissue abdominal and gluteal HSL are negatively associated with HOMA-IR (Homeostatic Model Assessment for Insulin Resistance), and both ZAG and HSL adipose tissue are negatively associated with fasting glucose and the glucose area under the curve. Further work is needed to elucidate the role of ZAG and HSL in the propensity for weight gain and the ability of exercise to mitigate these responses.

Adipose and serum zinc alpha-2-glycoprotein (ZAG) expressions predict longitudinal change of adiposity, wasting and predict survival in dialysis patients

There were limited data on adipose and serum zinc alpha-2-glycoprotein (ZAG) expression and its association with body composition in patients with advanced chronic kidney disease (CKD). This study aimed to quantify adipose and serum ZAG expression and evaluate their association with body composition and its longitudinal change, together with mortality in incident dialysis patients. We performed a single-center prospective cohort study. Patients who were planned for peritoneal dialysis were recruited. ZAG levels were measured from serum sample, subcutaneous and pre-peritoneal fat tissue obtained during peritoneal dialysis catheter insertion. Body composition and functional state were evaluated by bioimpedance spectroscopy and Clinical Frailty Scale respectively at baseline and were repeated 1 year later. Primary outcome was 2-year survival. Secondary outcomes were longitudinal changes of body composition. At baseline, the average adipose and serum ZAG expression was 13.4 ± 130.0-fold and 74.7 ± 20.9 µg/ml respectively. Both adipose and serum ZAG expressions independently predicted adipose tissue mass (ATM) (p = 0.001, p = 0.008, respectively). At 1 year, ATM increased by 3.3 ± 7.4 kg (p < 0.001) while lean tissue mass (LTM) remained similar (p = 0.5). Adipose but not serum ZAG level predicted change in ATM (p = 0.007) and LTM (p = 0.01). Serum ZAG level predicted overall survival (p = 0.005) and risk of infection-related death (p = 0.045) after adjusting for confounders. In conclusion, adipose and serum ZAG levels negatively correlated with adiposity and predicted its longitudinal change of fat and lean tissue mass, whilst serum ZAG predicted survival independent of body mass in advanced CKD patient.

Adipokines, Hepatokines and Myokines: Focus on Their Role and Molecular Mechanisms in Adipose Tissue Inflammation

Chronic low-grade inflammation in adipose tissue (AT) is a hallmark of obesity and contributes to various metabolic disorders, such as type 2 diabetes and cardiovascular diseases. Inflammation in ATs is characterized by macrophage infiltration and the activation of inflammatory pathways mediated by NF-κB, JNK, and NLRP3 inflammasomes. Adipokines, hepatokines and myokines - proteins secreted from AT, the liver and skeletal muscle play regulatory roles in AT inflammation via endocrine, paracrine, and autocrine pathways. For example, obesity is associated with elevated levels of pro-inflammatory adipokines (e.g., leptin, resistin, chemerin, progranulin, RBP4, WISP1, FABP4, PAI-1, Follistatin-like1, MCP-1, SPARC, SPARCL1, and SAA) and reduced levels of anti-inflammatory adipokines such as adiponectin, omentin, ZAG, SFRP5, CTRP3, vaspin, and IL-10. Moreover, some hepatokines (Fetuin A, DPP4, FGF21, GDF15, and MANF) and myokines (irisin, IL-6, and DEL-1) also play pro- or anti-inflammatory roles in AT inflammation. This review aims to provide an updated understanding of these organokines and their role in AT inflammation and related metabolic abnormalities. It serves to highlight the molecular mechanisms underlying the effects of these organokines and their clinical significance. Insights into the roles and mechanisms of these organokines could provide novel and potential therapeutic targets for obesity-induced inflammation.

The association of the adipokine zinc-alpha2-glycoprotein with non-alcoholic fatty liver disease and related risk factors: A comprehensive systematic review

BACKGROUND AND AIM

The adipokine zinc-alpha2-glycoprotein (ZAG), a multidisciplinary protein, is involved in lipid metabolism, glucose homeostasis and energy balance. Accumulating evidence demonstrates that the expression of ZAG is mainly downregulated in obesity and obesity-related conditions. In the present study, we assessed the association of ZAG with non-alcoholic fatty liver disease (NAFLD) and the related risk factors including obesity, metabolic factors and inflammatory parameters, with emphasis on potential mechanisms underlying these associations.

METHODS

PRISMA guidelines were followed in this review. Systematic searches were performed using the PubMed/Medline, ScienceDirect, Scopus, EMBASE, ProQuest and Google Scholar databases, up to August 2020 for all relevant published papers.

RESULTS

Out of 362 records screened, 34 articles were included in the final analysis. According to the studies reviewed here, ZAG appears to exert a protective effect against NAFLD by enhancing mRNA expression levels of peroxisome proliferator-activated receptor α (PPARα) and PPARγ, promoting mRNA expression levels of the lipolysis-related genes, reducing mRNA expression levels of the lipogenesis-related genes, increasing hepatic fatty acid oxidation, ameliorating hepatic steatosis, promoting the activity of brown adipose tissue and the expression of thermogenesis-related genes, modulating energy balance and glucose homeostasis, and elevating plasma levels of healthy adipokines such as adiponectin. ZAG can also be involved in the regulation of inflammatory responses by attenuation of the expression of pro-inflammatory and pro-fibrotic mediators.

CONCLUSION

According to the studies reviewed here, ZAG is suggested to be a promising therapeutic target for NAFLD. However, the favourable effects of ZAG need to be confirmed in prospective cohort studies.

Zinc-α2-glycoprotein promotes skeletal muscle lipid metabolism in cold-stressed mice

Skeletal muscle is the most abundant tissue in the adult body and plays an essential role in maintaining heat production for the entire body. Recently, muscle-derived non-shivering thermogenesis under cold conditions has received much attention. Zinc-α2-glycoprotein (ZAG) is an adipokine that was shown to influence energy metabolism in the adipose tissue. We used ZAG knock-out (ZAG KO) and wild-type (WT) mice to investigate the effect of ZAG on the lipid metabolism of skeletal muscle upon exposure to a low temperature (6°C) for one week. The results show that cold stress significantly increases the level of lipolysis, energy metabolism, and fat browning-related proteins in the gastrocnemius muscle of WT mice. In contrast, ZAG KO mice did not show any corresponding changes. Increased expression of β3-adrenoceptor (β3-AR) and protein kinase A (PKA) might be involved in the ZAG pathway in mice exposed cold stress. Furthermore, expression of lipolysis-related proteins (ATGL and p-HSL) and energy metabolism-related protein (PGC1α, UCP2, UCP3 and COX1) was significantly enhanced in ZAG KO mice after injection of ZAG-recombinant plasmids. These results indicate that ZAG promotes lipid-related metabolism in the skeletal muscle when the animals are exposed to low temperatures. This finding provides a promising target for the development of new therapeutic approaches to improve skeletal muscle energy metabolism.

Does Proteomic Mirror Reflect Clinical Characteristics of Obesity?

Obesity is a frightening chronic disease, which has tripled since 1975. It is not expected to slow down staying one of the leading cases of preventable death and resulting in an increased clinical and economic burden. Poor lifestyle choices and excessive intake of “cheap calories” are major contributors to obesity, triggering type 2 diabetes, cardiovascular diseases, and other comorbidities. Understanding the molecular mechanisms responsible for development of obesity is essential as it might result in the introducing of anti-obesity targets and early-stage obesity biomarkers, allowing the distinction between metabolic syndromes. The complex nature of this disease, coupled with the phenomenon of metabolically healthy obesity, inspired us to perform data-centric, hypothesis-generating pilot research, aimed to find correlations between parameters of classic clinical blood tests and proteomic profiles of 104 lean and obese subjects. As the result, we assembled patterns of proteins, which presence or absence allows predicting the weight of the patient fairly well. We believe that such proteomic patterns with high prediction power should facilitate the translation of potential candidates into biomarkers of clinical use for early-stage stratification of obesity therapy.

Zinc-α2-glycoprotein relieved seizure-Induced neuronal glucose uptake impairment via insulin-like growth factor 1 receptor-regulated glucose transporter 3 expression

Glucose hypometabolism is observed in epilepsy and promotes epileptogenesis. Glucose hypometabolism in epilepsy may be attributed to decreased neuronal glucose uptake, but its molecular mechanism remains unclear. Zinc-α2-glycoprotein (ZAG) is related to glucose metabolism and is reported to suppress seizures. The anti-epileptic effect of ZAG may be attributed to its regulation of neuronal glucose metabolism. This study explored the effect of ZAG on neuronal glucose uptake and its molecular mechanism via insulin-like growth factor 1 receptor (IGF1R)-regulated glucose transporter 3 (GLUT-3) expression. The ZAG level was modulated by lentivirus in primary culture neurons. Neuronal seizure models were induced by Mg²⁺ -free artificial cerebrospinal fluid. We assessed neuronal glucose uptake by the 2-NBDG method and Glucose Uptake Colorimetric Assay Kit. IGF1R was activated by IGF1 and blocked by AXL1717. The expression and distribution of IGF1R and GLUT-3, together with IGF1R phosphorylation, were measured by western blot. The binding between ZAG and IGF1R was determined by coimmunoprecipitation. Neuronal glucose uptake and GLUT-3 expression were significantly decreased by seizure or ZAG knockdown, whereas ZAG over-expression or IGF1 treatment reversed this decrease. The effect of ZAG on neuronal glucose uptake and GLUT-3 expression was blocked by AXL1717. ZAG increased IGF1R distribution and phosphorylation possibly by binding. Additionally, IGF1R increased GLUT-3 activity by increasing GLUT-3 expression. In epilepsy/seizure, neuronal glucose uptake suppression may be attributed to a decrease in ZAG, which suppresses neuronal GLUT-3 expression by regulating the activity of IGF1R. ZAG, IGF1R, and GLUT-3 may be novel potential therapeutic targets of glucose hypometabolism in epilepsy and seizures.

Zinc-alpha2-glycoprotein, dysglycaemia and insulin resistance: a systematic review and meta-analysis

To systematically review the current literature investigating associations between zinc-alpha2-glycoprotein (ZAG) and dysglycaemia (including type 2 diabetes (T2DM), poly-cystic-ovary syndrome (PCOS), pre-diabetes or insulin resistance). This included relationships between ZAG and continuous measures of insulin and glucose. Additionally, we performed a meta-analysis to estimate the extent that ZAG differs between individuals with or without dysglycaemia; whilst examining the potential influence of adiposity. A systematic search was performed on four databases for studies on circulating ZAG concentrations in adult human populations, comparing healthy controls to individuals with dysglycaemia. Key characteristics, including the mean ZAG concentrations (mg∙L^-1), and any correlational statistics between ZAG and continuous measures of glucose, glycated haemoglobin (HbA1c) or insulin were extracted. Meta-analyses were performed to compare metabolically healthy controls to cases, and on studies that compared controls and cases considered overweight or obese (body mass index (BMI) ≥25 kg^.m²). 1575 papers were identified and 14 studies (16 cohorts) were considered eligible for inclusion. Circulating ZAG was lower in individuals with dysglycaemia compared to metabolically healthy controls (-4.14 [-8.17, -0.11] mg^.L^-1; I² = 98.5%; p < 0.001). When using data from only studies with overweight or obese groups with or without dysglycaemia (three studies (four cohorts); pooled n = 332), the difference in circulating ZAG was no longer significant (-0.30 [-3.67, 3.07] mg^. L^-1; I² = 28.0%; p = 0.225). These data suggest that ZAG may be implicated in dysglycaemia, although there was significant heterogeneity across different studies and the mediating effect of adiposity cannot be excluded. Therefore, more research is needed before robust conclusions can be drawn.

Zinc-α2-Glycoprotein Knockout Influenced Genes Expression Profile in Adipose Tissue and Decreased the Lipid Mobilizing After Dexamethasone Treatment in Mice

Zinc-α2-glycoprotein (ZAG), as an adipokine, plays an important role in lipid metabolism. However, its influence on whole gene expression profile in adipose tissue is not known. Under stress condition, how ZAG affects the lipid metabolism is also unclear. Therefore, in this study ZAG systemic knockout (KO) mice were used as a model to reveal the genes expression profile in visceral fat tissues of ZAG KO mice and wild-type mice by genome-wide microarray screening. Then dexamethasone (DEX) was used to explore the effect of ZAG deletion on body fat metabolism under stress. Our results showed that 179 genes were differentially expressed more than 1.5 times between ZAG KO mice and wild type mice, of which 26 genes were upregulated dramatically and 153 genes were significantly downregulated. Under DEX simulated stress, ZAG systemic knockout in vivo resulted in a markedly decrease of triglycerides (TG) and nonesterified fatty acid (NEFA) content in in plasma. Similarly, for lipid catabolism, ZAG KO led to a significant increase of phosphorylated HSL (p-HSL) protein and a rising tendency of adipose triglyceride lipase (ATGL) protein relative to those of the DEX group. For lipid anabolism, fatty acid synthase (FAS) and adiponectin protein expression in visceral fat rose notably in ZAG KO mice after DEX treatment. In conclusion, ZAG knockout can affect the gene expression profile of adipose tissue, reduce elevated TG and NEFA levels in plasma, and alter lipid metabolism under DEX treatment. These findings provide new insights into the mechanism of lipid metabolic disorders in response to stress.

Zinc-α2-glycoprotein as an inhibitor of amine oxidase copper-containing 3

Zinc-α2-glycoprotein (ZAG) is a major plasma protein whose levels increase in chronic energy-demanding diseases and thus serves as an important clinical biomarker in the diagnosis and prognosis of the development of cachexia. Current knowledge suggests that ZAG mediates progressive weight loss through β-adrenergic signalling in adipocytes, resulting in the activation of lipolysis and fat mobilization. Here, through cross-linking experiments, amine oxidase copper-containing 3 (AOC3) is identified as a novel ZAG binding partner. AOC3-also known as vascular adhesion protein 1 (VAP-1) and semicarbazide sensitive amine oxidase (SSAO)-deaminates primary amines, thereby generating the corresponding aldehyde, H2O2 and NH3. It is an ectoenzyme largely expressed by adipocytes and induced in endothelial cells during inflammation. Extravasation of immune cells depends on amine oxidase activity and AOC3-derived H2O2 has an insulinogenic effect. The observations described here suggest that ZAG acts as an allosteric inhibitor of AOC3 and interferes with the associated pro-inflammatory and anti-lipolytic functions. Thus, inhibition of the deamination of lipolytic hormone octopamine by AOC3 represents a novel mechanism by which ZAG might stimulate lipolysis. Furthermore, experiments involving overexpression of recombinant ZAG reveal that its glycosylation is co-regulated by oxygen availability and that the pattern of glycosylation affects its inhibitory potential. The newly identified protein interaction between AOC3 and ZAG highlights a previously unknown functional relationship, which may be relevant to inflammation, energy metabolism and the development of cachexia.

Zinc-α2-glycoprotein promotes browning of white adipose tissue in cold-exposed male mice

The promotion of white adipose tissue (WAT) browning has emerged as a promising therapeutic target to increase energy expenditure and decrease weight gain. Zinc-α2-glycoprotein (ZAG) is a newly identified adipokine that regulates lipid metabolism. It shows high expression in brown adipose tissue (BAT), but whether ZAG plays a key role in the browning of white adipose tissue is still largely unclear. In the present study, we explored the relationship between ZAG and the browning of WAT in cold-exposed ZAG knockout (KO) mice and 3T3-L1 adipocytes with overexpressed ZAG. The results showed that cold stress induced marked accumulation of ZAG in wild type (WT) mice. Additionally, ZAG deficiency inhibited the loss of body weight and adipose tissue weight in cold stressed mice. ZAG KO mice were resistant to cold-induced expression of browning markers and energy metabolism in WAT. Furthermore, replenishment ZAG plasmid improved the reduction in cold-induced browning of WAT in ZAG KO mice. In vitro, ZAG overexpression promoted browning and mitochondrial biogenesis and increased the expression of β3-AR and P-P38 in 3T3-L1 adipocytes. These findings demonstrate that ZAG can promote the browning of white adipose tissue and can serve as a potential therapeutic target for treating metabolic diseases such as obesity.

Role of adipokine zinc-α2-glycoprotein in coronary heart disease

Zinc-α₂-glycoprotein (AZGP1) is a newly identified adipokine that is associated with lipid metabolism and vascular fibrosis. Although adipokines contribute to lipid dysfunction and its related diseases, including stroke and coronary heart disease (CHD), the role of AZGP1 remains unclear. In this study, the role of AZGP1 in atherosclerosis and CHD was investigated. Serum AZGP1 levels from control (n = 84) and CHD (n = 91) patients were examined by ELISA and its relationship with various clinical parameters was analyzed. Immunohistochemistry and immunofluorescence were used to detect the expression of AZGP1 and its receptor in coronary atherosclerotic arteries. THP-1 and human embryonic kidney 293 cells were used to verify its anti-inflammatory role in atherosclerosis. Serum AZGP1 levels in CHD patients were lower than controls (P < 0.01) and independently associated with CHD prevalence (P = 0.021). AZGP1 levels also inversely correlated with the Gensini score. Immunohistochemistry and immunofluorescence showed that AZGP1 and its receptor β₃-adrenoceptor (β₃-AR) colocalized in lipid-rich areas of atherosclerotic plaques, particularly around macrophages. In vitro, AZGP1 had no effect on foam cell formation but showed anti-inflammatory effects through its regulation of JNK/AP-1 signaling. In summary, AZGP1 is an anti-inflammatory agent that can be targeted for CHD treatment.

Adipokine zinc-α2-glycoprotein alleviates lipopolysaccharide-induced inflammatory responses through the β3-AR/PKA/CREB pathway

Humans and animals frequently experience dysmetabolism induced by inflammation. Zinc-α2-glycoprotein (ZAG), a newly identified adipokine, is potentially involved in lipid metabolism. Our previous study revealed that the ZAG content increased after lipopolysaccharide (LPS) treatment. To clarify ZAG's possible effects on inflammatory responses and lipid metabolism, we used gene overexpression and knockout mice as models to investigate the function of ZAG during inflammation. The results showed that LPS increased plasma triglyceride, non-esterified fatty acid and hepatic triglyceride, while ZAG overexpression decreased these effects. Furthermore, ZAG overexpression weakened inflammatory responses, suppressed lipogenesis, and improved mitochondrial function during inflammation. ZAG overexpression also increased β3-adrenoreceptor, protein kinase A, and phosphorylated cyclic adenosine monophosphate-response element binding protein (CREB), promoted the combination of CREB and CREB-binding protein (CBP), and competitively inhibited the combination of nuclear factor-κB and CBP. After ZAG knockout, LPS-induced the hyperlipidemia worsened. ZAG knockout aggravated inflammatory responses, promoted lipogenesis, and weakened mitochondrial function during inflammation. ZAG knockout also decreased β3-adrenoreceptor and protein kinase A. The present study demonstrated that ZAG alleviated lipid metabolism disorders by weakening inflammatory responses. The β3-adrenoreceptor/protein kinase A/CREB pathway mediated the effects of ZAG on inflammation. These results will provide new insight for research on anti-inflammation.

Expression and Function of Zinc-α2-Glycoprotein

Zinc-α2-glycoprotein (ZAG), encoded by the AZGP1 gene, is a major histocompatibility complex I molecule and a lipid-mobilizing factor. ZAG has been demonstrated to promote lipid metabolism and glucose utilization, and to regulate insulin sensitivity. Apart from adipose tissue, skeletal muscle, liver, and kidney, ZAG also occurs in brain tissue, but its distribution in brain is debatable. Only a few studies have investigated ZAG in the brain. It has been found in the brains of patients with Krabbe disease and epilepsy, and in the cerebrospinal fluid of patients with Alzheimer disease, frontotemporal lobe dementia, and amyotrophic lateral sclerosis. Both ZAG protein and AZGP1 mRNA are decreased in epilepsy patients and animal models, while overexpression of ZAG suppresses seizure and epileptic discharges in animal models of epilepsy, but knowledge of the specific mechanism of ZAG in epilepsy is limited. In this review, we summarize the known roles and molecular mechanisms of ZAG in lipid metabolism and glucose metabolism, and in the regulation of insulin sensitivity, and discuss the possible mechanisms by which it suppresses epilepsy.

ZAG alleviates HFD-induced insulin resistance accompanied with decreased lipid depot in skeletal muscle in mice

Over the past two decades, intramuscular lipids have been viewed as a cause of insulin resistance due to their ability to suppress insulin-stimulated glucose uptake in skeletal muscle. Zinc-α2-glycoprotein (ZAG) is an adipokine involved in lipolysis of white adipose tissue (WAT). To investigate the action of ZAG on insulin resistance induced by a high-fat diet (HFD), which affects the intramuscular fat, mice were divided into three groups, normal diet, HFD, and ZAG treatment under HFD (HFZ). The results showed that the insulin sensitivity of ZAG-treated mice was significantly improved. The body weight, WAT weight, and intramuscular fat were significantly decreased in the HFZ group compared with the HFD group. The lipolytic enzymes, including phosphorylation of hormone-sensitive lipase and adipose triglyceride lipase, were significantly upregulated in the skeletal muscle of mice that received the ZAG treatment compared with the HFD group. Insulin signaling proteins, such as phosphorylation of insulin receptor substrate 1 and cell membrane glucose transporter type 4, were also significantly increased in the skeletal muscle of the ZAG-treated group. Furthermore, a metabolic rate study showed that ZAG overexpression increases the respiratory exchange ratio and heat production. In vitro, ZAG treatment promotes glucose uptake and decreases intracellular lipids in C2C12 myotubes. Taken together, these data showed that overexpression of ZAG alleviates HFD-induced insulin resistance in mice, along with decreasing the lipid content of skeletal muscle.

Zinc alpha2 glycoprotein protects against obesity-induced hepatic steatosis

BACKGROUND/AIM

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis, impaired insulin sensitivity, and chronic low-grade inflammation. Our previous studies indicated that zinc alpha2 glycoprotein (ZAG) alleviates palmitate (PA)-induced intracellular lipid accumulation in hepatocytes. This study is to further characterize the roles of ZAG on the development of hepatic steatosis, insulin resistance (IR), and inflammation.

METHODS

ZAG protein levels in the livers of NAFLD patients, high-fat diet (HFD)-induced or genetically (ob/ob) induced obese mice, and in PA-treated hepatocytes were determined by western blotting. C57BL/6J mice injected with an adenovirus expressing ZAG were fed HFD for indicated time to induce hepatic steatosis, IR, and inflammation, and then biomedical, histological, and metabolic analyses were conducted to identify pathologic alterations in these mice. The molecular mechanisms underlying ZAG-regulated hepatic steatosis were further explored and verified in mice and hepatocytes.

RESULTS

ZAG expression was decreased in NAFLD patient liver biopsy samples, obese mice livers, and PA-treated hepatocytes. Simultaneously, ZAG overexpression alleviated intracellular lipid accumulation via upregulating adiponectin and lipolytic genes (FXR, PPARα, etc.) while downregulating lipogenic genes (SREBP-1c, LXR, etc.) in obese mice as well as in cultured hepatocytes. ZAG improved insulin sensitivity and glucose tolerance via activation of IRS/AKT signaling. Moreover, ZAG significantly inhibited NF-ĸB/JNK signaling and thus resulting in suppression of obesity-associated inflammatory response in hepatocytes.

CONCLUSIONS

Our results revealed that ZAG could protect against NAFLD by ameliorating hepatic steatosis, IR, and inflammation.

Effects of adipokine zinc-α2-glycoprotein on adipose tissue metabolism after dexamethasone treatment

Zinc-α2-glycoprotein (ZAG) has been demonstrated to play a role in stimulating lipid mobilization under normal conditions. However, further studies are required to determine whether ZAG overexpression can alleviate the reduction in plasma lipid levels under stress conditions. In the present study, we investigated the effects of ZAG on lipometabolism in white adipose tissue (WAT) after dexamethasone (DEX) stimulation using C57BL/6 male mice as the experimental models. Transcript and protein levels of genes associated with the β-adrenoreceptor (β-AR)/cyclic adenosine monophosphate/protein kinase a (PKA) pathway, lipid mobilization, and energy metabolism were determined by quantitative real-time polymerase chain reaction and Western blotting. Plasma levels of nonesterified fatty acid (NEFA) were measured using an automatic biochemical analyzer. Results indicated that plasma NEFA levels were decreased in the DEX group, but NEFA levels were rescued by ZAG overexpression. ZAG overexpression resulted in the upregulation of β3-AR and phosphorylated PKA protein relative to those of the DEX group. Analysis of lipometabolism showed that protein levels of phosphorylated hormone-sensitive lipase was reduced upon DEX treatment but were restored by ZAG overexpression. For energy metabolism, ZAG significantly upregulated the protein expression of carnitine palmitoyltransferase1a and cytochrome c oxidase subunit 1 relative to those of the DEX group. In conclusion, ZAG could alleviate DEX-induced decrease in plasma NEFA levels and this could be associated with the promoting lipid mobilization in WAT.

Zinc-α2-Glycoprotein Is Associated with Obesity in Chinese People and HFD-Induced Obese Mice

Zinc-α2-glycoprotein (ZAG) plays an important role in the regulation of body weight, body fat, and glucose metabolism. In this study, we first measured ZAG levels in serum and ZAG mRNA levels in subcutaneous white adipose tissue (sWAT) among overweight/obese patients and lean control subjects. Second, we investigated the effects of ZAG administration on the body weight, body fat and glucose metabolism of high-fat diet (HFD)-induced obese ICR mice and the possible mechanisms involved. The results showed that serum ZAG and mRNA levels in sWAT were significantly decreased in overweight/obese patients and that both showed a negative association with body mass index (BMI) and body weight after adjustment for age and sex. Further partial correlation analysis found that ZAG mRNA expression was positively related with several WAT browning-related genes, including uncoupling protein 1 (UCP1) (r = 0.67) and peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1a) (r = 0.60), in the sWAT of all subjects. Additionally, intraperitoneal injection of a ZAG expression plasmid (5 μg/injection, four times a week) in HFD-induced obese mice for 8 weeks demonstrated that ZAG overexpression significantly decreased body weight and WAT mass, and greatly increased the glucose tolerance of obese mice, as shown by the intraperitoneal glucose tolerance test (IPGTT) and intraperitoneal insulin tolerance test (IPITT). The staining of UCP1-positive adipocytes was significantly stronger in the sWAT of ZAG-treated obese mice than in that of obese control mice. The mRNA and protein levels of PGC1α in sWAT were significantly increased to 2.2- and 5.3-fold, respectively, compared with HFD obese mice, and there was a strong positive correlation between the expression levels of Zag and Pgc1α in mouse sWAT (r = 0.74). A similar phenomenon was also observed in visceral white adipose tissue (vWAT): the mRNA and protein levels of PGC1α were increased to 1.9- and 3.6-fold, respectively, when obese mice were treated with ZAG. In conclusion, ZAG levels in both sWAT and serum are inversely related with BMI and body weight in Chinese subjects. The action of ZAG on body weight, fat mass and glucose metabolism may be realized through activating PGC1α expression in sWAT and vWAT, then promoting WAT browning in obese mice.

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.

Improved adipose tissue metabolism after 5-year growth hormone replacement therapy in growth hormone deficient adults: The role of zinc-α2-glycoprotein

Growth hormone (GH) supplementation therapy to adults with GH deficiency has beneficial effects on adipose tissue lipid metabolism, improving thus adipocyte functional morphology and insulin sensitivity. However, molecular nature of these effects remains unclear. We therefore tested the hypothesis that lipid-mobilizing adipokine zinc-α2-glycoprotein is causally linked to GH effects on adipose tissue lipid metabolism. Seventeen patients with severe GH deficiency examined before and after the 5-year GH replacement therapy were compared with age-, gender- and BMI-matched healthy controls. Euglycemic hyperinsulinemic clamp was used to assess whole-body and adipose tissue-specific insulin sensitivity. Glucose tolerance was determined by oGTT, visceral and subcutaneous abdominal adiposity by MRI, adipocyte size morphometrically after collagenase digestion, lipid accumulation and release was studied in differentiated human primary adipocytes in association with GH treatment and zinc-α2-glycoprotein gene silencing. Five-year GH replacement therapy improved glucose tolerance, adipose tissue insulin sensitivity and reduced adipocyte size without affecting adiposity and whole-body insulin sensitivity. Adipose tissue zinc-α2-glycoprotein expression was positively associated with whole-body and adipose tissue insulin sensitivity and negatively with adipocyte size. GH treatment to adipocytes in vitro increased zinc-α2-glycoprotein expression (>50%) and was paralleled by enhanced lipolysis and decreased triglyceride accumulation (>35%). Moreover, GH treatment improved antilipolytic action of insulin in cultured adipocytes. Most importantly, silencing zinc-α2-glycoprotein eliminated all of the GH effects on adipocyte lipid metabolism. Effects of 5-year GH supplementation therapy on adipose tissue lipid metabolism and insulin sensitivity are associated with zinc-α2-glycoprotein. Presence of this adipokine is required for the GH action on adipocyte lipid metabolism in vitro.

Zinc-α2-Glycoprotein Exerts Antifibrotic Effects in Kidney and Heart

Zinc-α2-glycoprotein (AZGP1) is a secreted protein synthesized by epithelial cells and adipocytes that has roles in lipid metabolism, cell cycling, and cancer progression. Our previous findings in AKI indicated a new role for AZGP1 in the regulation of fibrosis, which is a unifying feature of CKD. Using two models of chronic kidney injury, we now show that mice with genetic AZGP1 deletion develop significantly more kidney fibrosis. This destructive phenotype was rescued by injection of recombinant AZGP1. Exposure of AZGP1-deficient mice to cardiac stress by thoracic aortic constriction revealed that antifibrotic effects were not restricted to the kidney but were cardioprotective. In vitro, recombinant AZGP1 inhibited kidney epithelial dedifferentiation and antagonized fibroblast activation by negatively regulating TGF-β signaling. Patient sera with high levels of AZGP1 similarly attenuated TGF-β signaling in fibroblasts. Taken together, these findings indicate a novel role for AZGP1 as a negative regulator of fibrosis progression, suggesting that recombinant AZGP1 may have translational effect for treating fibrotic disease.

Adipokine zinc-α2-glycoprotein regulated by growth hormone and linked to insulin sensitivity

OBJECTIVE

Hypertrophic obesity is associated with impaired insulin sensitivity and lipid-mobilizing activity of zinc-α2-glycoprotein. Adipose tissue (AT) of growth hormone (GH) -deficient patients is characterized by extreme adipocyte hypertrophy due to defects in AT lipid metabolism. It was hypothesized that zinc-α2-glycoprotein is regulated by GH and mediates some of its beneficial effects in AT.

METHODS

AT from patients with GH deficiency and individuals with obesity-related GH deficit was obtained before and after 5-year and 24-month GH supplementation therapy. GH action was tested in primary human adipocytes. Relationships of GH and zinc-α2-glycoprotein with adipocyte size and insulin sensitivity were evaluated in nondiabetic patients with noncancerous cachexia and hypertrophic obesity.

RESULTS

AT in GH-deficient adults displayed a substantial reduction of zinc-α2-glycoprotein. GH therapy normalized AT zinc-α2-glycoprotein. Obesity-related relative GH deficit was associated with almost 80% reduction of zinc-α2-glycoprotein mRNA in AT. GH increased zinc-α2-glycoprotein mRNA in both AT of obese men and primary human adipocytes. Interdependence of GH and zinc-α2-glycoprotein in regulating AT morphology and metabolic phenotype was evident from their relationship with adipocyte size and AT-specific and whole-body insulin sensitivity.

CONCLUSIONS

The results demonstrate that GH is involved in regulation of AT zinc-α2-glycoprotein; however, the molecular mechanism linking GH and zinc-α2-glycoprotein in AT is yet unknown.

Subcutaneous adipose tissue zinc-α2-glycoprotein is associated with adipose tissue and whole-body insulin sensitivity

OBJECTIVE

To examine the regulatory aspects of zinc-α2-glycoprotein (ZAG) association with obesity-related insulin resistance.

METHODS

ZAG mRNA and protein were analyzed in subcutaneous adipose tissue (AT) and circulation of lean, obese, prediabetic, and type 2 diabetic men; both subcutaneous and visceral AT were explored in lean and extremely obese. Clinical and ex vivo findings were corroborated by results of in vitro ZAG silencing experiment.

RESULTS

Subcutaneous AT ZAG was reduced in obesity, with a trend to further decrease with prediabetes and type 2 diabetes. ZAG was 3.3-fold higher in subcutaneous than in visceral AT of lean individuals. All differences were lost in extreme obesity. Obesity-associated changes in AT were not paralleled by alterations of circulating ZAG. Subcutaneous AT ZAG correlated with adiposity, adipocyte hypertrophy, whole-body and AT insulin sensitivity, mitochondrial content, expression of GLUT4, PGC1α, and adiponectin. Subcutaneous AT ZAG and adipocyte size were the only predictors of insulin sensitivity, independent on age and BMI. Silencing ZAG resulted in reduced adiponectin, IRS1, GLUT4, and PGC1α gene expression in primary human adipocytes.

CONCLUSIONS

ZAG in subcutaneous, but not in visceral AT, was markedly reduced in obesity. Clinical, cellular, and molecular evidence indicate that ZAG plays an important role in modulating whole-body and AT insulin sensitivity.

The relationship between renal function and plasma concentration of the cachectic factor zinc-alpha2-glycoprotein (ZAG) in adult patients with chronic kidney disease

Zinc-α2-glycoprotein (ZAG), a potent cachectic factor, is increased in patients undergoing maintenance dialysis. However, there is no data for patients before initiation of renal replacement therapy. The purpose of the present study was to assess the relationship between plasma ZAG concentration and renal function in patients with a large range of glomerular filtration rate (GFR). Plasma ZAG concentration and its relationship to GFR were investigated in 71 patients with a chronic kidney disease (CKD) stage 1 to 5, 17 chronic hemodialysis (HD), 8 peritoneal dialysis (PD) and 18 non-CKD patients. Plasma ZAG concentration was 2.3-fold higher in CKD stage 5 patients and 3-fold higher in HD and PD patients compared to non-CKD controls (P<0.01). The hemodialysis session further increased plasma ZAG concentration (+39%, P<0.01). An inverse relationship was found between ZAG levels and plasma protein (r_s = −0.284; P<0.01), albumin (r_s = −0.282, P<0.05), hemoglobin (r_s = −0.267, P<0.05) and HDL-cholesterol (r_s = −0.264, P<0.05) and a positive correlation were seen with plasma urea (r_s = 0.283; P<0.01). In multiple regression analyses, plasma urea and HDL-cholesterol were the only variables associated with plasma ZAG (r² = 0.406, P<0.001). In CKD-5 patients, plasma accumulation of ZAG was not correlated with protein energy wasting. Further prospective studies are however needed to better elucidate the potential role of ZAG in end-stage renal disease.

Obesity, inflammation, and lung injury (OILI): the good

Obesity becomes pandemic, predisposing these individuals to great risk for lung injury. In this review, we focused on the anti-inflammatories and addressed the following aspects: adipocytokines and obesity, inflammation and other mechanisms, adipocytokines and lung injury in obesity bridged by inflammation, and potential therapeutic targets. To sum up, the majority of evidence supported that adiponectin, omentin, and secreted frizzled-related protein 5 (SFRP5) were reduced significantly in obesity, which is associated with increased inflammation, indicated by increase of TNFα and IL-6, through activation of toll-like receptor (TLR4) and nuclear factor light chain κB (NF-κB) signaling pathways. Administration of these adipocytokines promotes weight loss and reduces inflammation. Zinc-α2-glycoprotein (ZAG), vaspin, IL-10, interleukin-1 receptor antagonist (IL-1RA), transforming growth factor β (TGF-β1), and growth differentiation factor 15 (GDF15) are also regarded as anti-inflammatories. There were controversial reports. Furthermore, there is a huge lack of studies for obesity related lung injury. The effects of adiponectin on lung transplantation, asthma, chronic obstructive pulmonary diseases (COPD), and pneumonia were anti-inflammatory and protective in lung injury. Administration of IL-10 agonist reduces mortality of acute lung injury in rabbits with acute necrotizing pancreatitis, possibly through inhibiting proinflammation and strengthening host immunity. Very limited information is available for other adipocytokines.

Zinc-alpha2-glycoprotein in patients with acute and chronic kidney disease

BACKGROUND

Zinc-alpha2-glycoprotein (AZGP1) is a secreted protein which is synthesized in a variety of cell types. AZGP1 has functionally been implicated in lipid metabolism, the regulation of cell cycling and cancer progression. Previous studies have shown increased circulating AZGP1 levels in patients with chronic kidney disease but AZGP1 has not been investigated in acute kidney injury (AKI). In this study, serum AZGP1 levels were measured in acute and chronic kidney disease to test for a correlation to renal function and other clinical parameters.

METHODS

We performed ELISA based measurements of AZGP1 serum levels in 21 patients suffering from grade 3 AKI and in 20 chronic hemodialysis patients. In AKI patients, AZGP1 was first measured before initiation of acute renal replacement therapy and a second measurement was done during renal functional recovery. Sera of healthy blood donors served as controls. The association of AZGP1 with acute and chronic renal dysfunction was analysed, as well as the correlation with clinical parameters, body composition and biochemical variables.

RESULTS

Levels of circulating AZGP1 were significantly elevated in AKI patients. High initial levels of AZGP1 correlated with extra-renal complications but not with parameters of renal function. At follow-up, AZGP1 levels were still increased but now correlated significantly with creatinine, eGFR and urea. Circulating AZGP1 in chronic hemodialysis patients was higher than in AKI patients. An association to parameters of lipid metabolism was not found.

CONCLUSIONS

This study illustrates that circulating AZGP1 is not only elevated in chronic hemodialysis patients but also sharply increases during the early phase of AKI. The unexpected association with extra-renal complications during AKI needs further exploration as it might point to unknown biological effects of AZGP1.

Zinc-α2-glycoprotein as a marker of fat catabolism in humans

PURPOSE OF REVIEW

Cachexia development is a feature of cancer as well as other chronic diseases. Fat mass loss appears of greatest importance in cachexia, as it is related to poorer survival. Zinc-α2-glycoprotein (ZAG), firstly isolated in human plasma 50 years ago, has emerged as a novel adipokine, which plays an important role in mobilization and utilization of lipids. This review will focus on recent evidences of ZAG as a fat catabolic marker in cancer and other diseases complicated by cachexia.

RECENT FINDINGS

ZAG is a lipolytic factor produced by certain cachexia-inducing tumuors and by adipose tissue. It increases lipolysis in white adipose tissue through cyclic-AMP pathway and stimulates uncoupling protein-1 in brown adipose tissue leading to heat generation. In cancer cachexia, ZAG release from white adipocytes is elevated and closely related to body weight loss. In cardiac cachexia, ZAG and circulating free fatty acids are closely related, suggesting a causative role in fat catabolism.

SUMMARY

ZAG may play an important role, probably as an autocrine/paracrine modulator of adipose mass in cachexia. A better comprehension of ZAG involvement in fat wasting mechanisms will be useful in the development of new therapeutic agents.

Detection of thermogenesis in rodents in response to anti-obesity drugs and genetic modification

Many compounds and genetic manipulations are claimed to confer resistance to obesity in rodents by raising energy expenditure. Examples taken from recent and older literature, demonstrate that such claims are often based on measurements of energy expenditure after body composition has changed, and depend on comparisons of energy expenditure divided by body weight. This is misleading because white adipose tissue has less influence than lean tissue on energy expenditure. Application of this approach to human data would suggest that human obesity is usually due to a low metabolic rate, which is not an accepted view. Increased energy expenditure per animal is a surer way of demonstrating thermogenesis, but even then it is important to know whether this is due to altered body composition (repartitioning), or increased locomotor activity rather than thermogenesis per se. Regression analysis offers other approaches. The thermogenic response to some compounds has a rapid onset and so cannot be due to altered body composition. These compounds usually mimic or activate the sympathetic nervous system. Thermogenesis occurs in, but may not be confined to, brown adipose tissue. It should not be assumed that weight loss in response to these treatments is due to thermogenesis unless there is a sustained increase in 24-h energy expenditure. Thyroid hormones and fibroblast growth factor 21 also raise energy expenditure before they affect body composition. Some treatments and genetic modifications alter the diurnal rhythm of energy expenditure. It is important to establish whether this is due to altered locomotor activity or efficiency of locomotion. There are no good examples of compounds that do not affect short-term energy expenditure but have a delayed effect. How and under what conditions a genetic modification or compound increases energy expenditure influences the decision on whether to seek drugs for the target or take a candidate drug into clinical studies.

Inhibition of preadipocyte differentiation and adipogenesis by zinc-α2-glycoprotein treatment in 3T3-L1 cells

Aims/Introduction

Zinc‐α2‐glycoprotein (ZAG) is associated with the loss of adipose tissue in cancer cachexia, and has recently been proposed to be a candidate factor in the regulation of bodyweight. The aim of the study was to investigate the effects of ZAG on the proliferation and differentiation of 3T3‐L1 preadipocytes.

Materials and Methods

3‐(4,5‐Dimethylthiazol‐2‐yl) 2,5‐diphenyl tetrazolium bromide (MTT) spectrophotometry, Oil Red O staining, intracellular triglyceride assays, real‐time quantitative reverse transcription polymerase chain reaction and transient transfection methods were used to explore the action of ZAG.

Results

Ectopic ZAG expression significantly stimulates 3T3‐L1 cells proliferation in a dose‐ and time‐dependent manner. The maximum influence of ZAG on proliferation was 1.43‐fold higher than what was observed in control cells. This effect was observed 144 h after transfection with 0.16 μg of murine ZAG (mZAG) plasmid (P < 0.001). The intracellular lipids content in mZAG over‐expressing cells were decreased as much as 37% when compared with the control cells after differentiation (P < 0.05, P < 0.01). The messenger ribonucleic acid levels of peroxisome proliferators‐activated receptor‐γ (PPARγ), CCAAT enhancer‐binding protein‐α (C/EBPα) and the critical lipogenic gene, fatty acid synthase (FAS), are also downregulated by up to 50% in fully differentiated ZAG‐treated adipocytes. ZAG suppresses FAS messenger ribonucleic acid expression by reducing FAS promoter activity.

Conclusions

Zinc‐α2‐glycoprotein stimulates the proliferation and inhibits the differentiation of 3T3‐L1 murine preadipocytes. The inhibitory action of ZAG on cell differentiation might be a result of the attenuation of the expression of PPARγ, C/EBPα and the lipogenic‐specific enzyme FAS by reducing FAS promoter activity.

White adipose tissue overproduces the lipid-mobilizing factor zinc α2-glycoprotein in chronic kidney disease

Chronic kidney disease (CKD) is frequently associated with protein-energy wasting, a recognized strong predictive factor of mortality. Zinc α2-glycoprotein (ZAG) is a new adipokine involved in body weight control through its lipid-mobilizing activity. Here we tested whether the uremic environment in CKD could alter ZAG production by white adipose tissue and contribute to CKD-associated metabolic disturbances. Compared with normal plasma, uremic plasma induced a significant increase in ZAG synthesis (124%), was associated with a significant increase in basal lipolysis (31%), and significantly blunted lipogenesis (-53%) in 3T3-L1 adipocytes in vitro. In 5/6 nephrectomized rats and mice in vivo, there was a significant decrease in white adipose tissue accretion (-44% and -43%, respectively) and a significantly higher white adipose tissue content of ZAG protein than in sham-operated, pair-fed control animals (498% and 106%, respectively). Subcutaneous white adipose tissue biopsies from patients with end-stage renal disease exhibited a higher content of ZAG (573%) than age-matched controls. Thus, the ZAG content is increased in white adipose tissue from patients or animal models with CKD. Overproduction of ZAG in CKD could be a major contributor to metabolic disturbances associated with CKD.

Contrasts between the effects of zinc-α2-glycoprotein, a putative β3/2-adrenoceptor agonist and the β3/2-adrenoceptor agonist BRL35135 in C57Bl/6 (ob/ob) mice

Previous studies by Tisdale et al. have reported that zinc-α(2)-glycoprotein (ZAG (AZGP1)) reduces body fat content and improves glucose homeostasis and the plasma lipid profile in Aston (ob/ob) mice. It has been suggested that this might be mediated via agonism of β(3)- and possibly β(2)-adrenoceptors. We compared the effects of dosing recombinant human ZAG (100 μg, i.v.) and BRL35135 (0.5 mg/kg, i.p.), which is in rodents a 20-fold selective β(3)- relative to β(2)-adrenoceptor agonist, given once daily for 10 days to male C57Bl/6 Lep(ob)/Lep(ob) mice. ZAG, but not BRL35135, reduced food intake. BRL35135, but not ZAG, increased energy expenditure acutely and after sub-chronic administration. Only BRL35135 increased plasma concentrations of glycerol and non-esterified fatty acid. Sub-chronic treatment with both ZAG and BRL35135 reduced fasting blood glucose and improved glucose tolerance, but the plasma insulin concentration 30 min after administration of glucose was lowered only by BRL35135. Both ZAG and BRL35135 reduced β(1)-adrenoceptor mRNA levels in white adipose tissue, but only BRL35135 reduced β(2)-adrenoceptor mRNA. Both ZAG and BRL35135 reduced β(1)-adrenoceptor mRNA levels in brown adipose tissue, but neither influenced β(2)-adrenoceptor mRNA, and only BRL35135 increased β(3)-adrenoceptor and uncoupling protein-1 (UCP1) mRNA levels in brown adipose tissue. Thus, ZAG and BRL35135 had similar effects on glycaemic control and shared some effects on β-adrenoceptor gene expression in adipose tissue, but ZAG did not display the thermogenic effects of the β-adrenoceptor agonist, nor did it increase β(3)-adrenoceptor or UCP1 gene expression in brown adipose tissue. ZAG does not behave as a typical β(3/2)-adrenoceptor agonist.

The adaptable major histocompatibility complex (MHC) fold: structure and function of nonclassical and MHC class I-like molecules

The MHC fold is found in proteins that have a range of functions in the maintenance of an organism's health, from immune regulation to fat metabolism. Well adapted for antigen presentation, as seen for peptides in the classical MHC molecules and for lipids in CD1 molecules, the MHC fold has also been modified to perform Fc-receptor activity (e.g., FcRn) and for roles in host homeostasis (e.g., with HFE and ZAG). The more divergent MHC-like molecules, such as some of those that interact with the NKG2D receptor, represent the minimal MHC fold, doing away with the α3 domain and β2m while maintaining the α1/α2 platform domain for receptor engagement. Viruses have also co-opted the MHC fold for immune-evasive functions. The variations on the theme of a β-sheet topped by two semiparallel α-helices are discussed in this review, highlighting the fantastic adaptability of this fold for good and for bad.