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

The Gengnianchun recipe attenuates insulin resistance-induced diminished ovarian reserve through inhibiting the senescence of granulosa cells

INTRODUCTION

Insulin resistance (IR) is found in patients with polycystic ovary syndrome (PCOS), but the effects and mechanisms of IR on diminished ovarian reserve (DOR) remain unclear. This study set out to investigate the effects of IR on ovarian reserve; to explore the effects of high concentrations of insulin on the function of ovarian cells in vitro; and to validate the hypothesis that the Gengnianchun recipe (GNC) helps to attenuate DOR caused by IR through reducing the senescence of granulosa cells.

METHODS

Estrus cycle, follicle count, and sex hormone levels were detected to evaluate ovarian function in mice with IR caused by feeding a high-fat diet (HFD). In addition, KGN cells (human granulosa cell line) were treated with high concentrations of insulin. The staining for senescence-associatedβ-galactosidase (SA-β-gal), cell cycle, and expression levels of mRNA and gene proteins related to cell aging were detected in KGN cells treated with high concentrations of insulin. Mice treated with an HFD were fed metformin, GNC, or saline solution for 6 weeks by oral gavage. HOMA-IR, the area under the curve (AUC) of the oral glucose tolerance test (OGTT), levels of fasting blood glucose (FBG), and fasting serum insulin (FINS) were examined to confirm the IR status. Then estrus cycle, follicle count, and sex hormone levels were detected to evaluate ovarian function. Expression levels of mRNA and gene proteins related to cell aging were detected in the ovarian tissue of mice in each group.

RESULTS

The results demonstrated that IR reduced murine ovarian reserves, and high doses of insulin caused granulosa cells to senesce. There was a considerable improvement in HFD-induced IR status in the metformin (Met) and GNC treatment groups. In addition, the expression levels of aging-associated biomarkers were much lower in GNC mice than Met mice; and both the latter groups had considerably lower levels than the HFD group. Moreover, higher follicle counts in different stages and shorter diestrus in the Met or GNC groups compared to the HFD group indicated that ovarian aging could be largely reversed.

DISCUSSION

This work showed that: IR impaired ovarian reserve; high concentrations of insulin induced granulosa cell aging; and GNC attenuated ovarian function through inhibiting IR-induced cell aging.

Muscle-Derived Beige Adipose Precursors Secrete Promyogenic Exosomes That Treat Rotator Cuff Muscle Degeneration in Mice and Are Identified in Humans by Single-Cell RNA Sequencing

BACKGROUND

Muscle atrophy, fibrosis, and fatty infiltration are common to a variety of sports-related and degenerative conditions and are thought to be irreversible. Fibroadipogenic progenitors (FAPs) are multipotent resident muscle stem cells with the capacity to differentiate into fibrogenic as well as white and beige adipose tissue (BAT). FAPs that have assumed a BAT differentiation state (FAP-BAT) have proven efficacious in treating muscle degeneration in numerous injury models.

PURPOSE

To characterize the subpopulation of murine FAPs with FAP-BAT activity, determine whether their promyogenic effect is mediated via exosomes, and analyze human FAPs for an analogous promyogenic exosome-rich subpopulation.

STUDY DESIGN

Controlled laboratory study.

METHODS

FAPs from UCP1 reporter mice were isolated via fluorescence-activated cell sorting and sorted according to the differential intensity of the UCP1 signal observed: negative for UCP1 (UCP1-), intermediate intensity (UCP1+), and high intensity (UCP1++). Bulk RNA sequencing was performed on UCP1-, UCP1+, and UCP1++ FAPs to evaluate distinct characteristics of each population. Exosomes were harvested from UCP1++ FAP-BAT exosomes (Exo-FB) as well as UCP1- non-FAP-BAT exosomes (Exo-nFB) cells using cushioned-density gradient ultracentrifugation and used to treat C2C12 cells and mouse embryonic fibroblasts in vitro, and the myotube fusion index was assessed. Exo-FB and Exo-nFB were then used to treat wild type C57B/L6J mice that had undergone a massive rotator cuff tear. At 6 weeks mice were sacrificed, and supraspinatus muscles were harvested and analyzed for muscle atrophy, fibrosis, fatty infiltration, and UCP1 expression. Single-cell RNA sequencing was then performed on FAPs isolated from human muscle that were treated with the beta-agonist formoterol or standard media to assess for the presence of a parallel promyogenic subpopulation of FAP-BAT cells in humans.

RESULTS

Flow cytometry analysis of sorted UCP1 reporter mouse FAPs revealed a trimodal distribution of UCP1 signal intensity, which correlated with 3 distinct transcriptomic profiles characterized with bulk RNA sequencing. UCP1++ cells were marked by high mitochondrial gene expression, BAT markers, and exosome surface makers; UCP1- cells were marked by fibrogenic markers; and UCP1+ cells were characterized differential enrichment of white adipose tissue markers. Exo-FB treatment of C2C12 cells resulted in robust myotube fusion, while treatment of mouse embryonic fibroblasts resulted in differentiation into myotubes. Treatment of cells with Exo-nFB resulted in poor myotube formation. Mice that were treated with Exo-FB at the time of rotator cuff injury demonstrated markedly reduced muscle atrophy and fatty infiltration as compared with treatment with Exo-nFB or phosphate-buffered saline. Single-cell RNA sequencing of human FAPs from the rotator cuff revealed 6 distinct subpopulations of human FAPs, with one subpopulation demonstrating the presence of UCP1+ beige adipocytes with a distinct profile of BAT, mitochondrial, and extracellular vesicle-associated markers.

CONCLUSION

FAP-BAT cells form a subpopulation of FAPs with upregulated beige gene expression and exosome production that mediate promyogenic effects in vitro and in vivo, and they are present as a transcriptomically similar subpopulation of FAPs in humans.

CLINICAL RELEVANCE

FAP-BAT cells and their exosomes represent a potential therapeutic avenue for treating rotator cuff muscle degeneration.

Adipokine ZAG Alters Depression-Like Behavior by Regulating Oxidative Stress in Hippocampus

Zinc-α2-glycoprotein (ZAG) is an adipokine involved in body metabolism, and now it has been shown to be present in the brain and play a role in some neurological diseases such as epilepsy and Alzheimer's disease. In the present study, we employed ZAG knockout (KO) mice to investigate the effects of ZAG on behaviors after fasting and in vitro used overexpression (OV) ZAG in HT-22 cells to further clarify the possibly underlying mechanism. The results showed that ZAG exists widely in the brain tissues of mice and significantly increased during fasting. In ZAG KO group the depression-like behaviors were significantly increased after fasting for 24 hours, meanwhile the hippocampal reactive oxygen species (ROS) content was significantly increased. In vitro, serum deprivation led to the increasing of neuronal death and ROS, the reduced mitochondrial membrane potential and ATP levels, while ZAG overexpression alleviated these negative effects. The β3 adrenoreceptor (β3AR)/protein kinase A (PKA)/cAMP response element-binding (CREB) pathway possibly mediated the effects of ZAG on antioxidation. These results proposed a possible target for novel therapeutic approaches to the treatment of depression and provide potential link between adipose tissue and psychiatric disease.

Effect of a single bout of resistance exercise on zinc-α2-glycoprotein

CONTEXT

Resistance exercise training has recently been considered as an effective type of training to increase energy metabolism and insulin sensitivity. However, mechanisms of the resistance training-induced improvements in energy metabolism and insulin sensitivity have not been fully understood. Zinc-α2-glycoprotein (ZAG), which is a novel adipokine, has beneficial effects on energy metabolism and insulin sensitivity.

OBJECTIVE

We investigated the effect of a single bout of resistance exercise on the ZAG concentration.

METHODS

Nine healthy men were enrolled. They performed a single bout of resistance exercise (bench press and leg press) consisting of 10 repetitions of five sets at 70% of maximum strength with 90-s rests in between sets. Blood samples were obtained before and after acute resistance exercise to measure the ZAG concentration.

RESULTS

The serum ZAG concentration significantly increased following acute resistance exercise.

CONCLUSION

This result suggests that a single bout of resistance exercise may enhance the ZAG concentration.

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 and the Innovative Zinc-α2-Glycoprotein Adipokine Play an Important Role in Lipid Metabolism: A Critical Review

Numerous studies indicate that zinc and the new zinc-related adipokine, zinc-α2-glycoprotein (ZAG), are involved in lipid metabolism. Excess body fat lowers blood concentrations of Zn and ZAG, leading not only to the development of obesity but also to other components of the metabolic syndrome. Zinc homeostasis disorders in the body negatively affect the lipid profile and cytokine secretion. Zinc appears to be a very important ZAG homeostasis regulator. The physiological effects of ZAG are related to lipid metabolism, but studies show that ZAG also affects glucose metabolism and is linked to insulin resistance. ZAG has a zinc binding site in its structure, which may indicate that ZAG mediates the effect of zinc on lipid metabolism. The review aimed to verify the available studies on the effects of zinc and ZAG on lipid metabolism. A literature review within the scope of this research area was conducted using articles available in PubMed (including MEDLINE), Web of Science and Cochrane Library databases. An analysis of available studies has shown that zinc improves hepatic lipid metabolism and has an impact on the lipid profile. Numerous studies have found that zinc supplementation in overweight individuals significantly reduced blood levels of total cholesterol, LDL (Low-density lipoprotein)cholesterol and triglycerides, potentially reducing cardiovascular morbidity and mortality. Some results also indicate that it increases HDL-C (High-density lipoprotein) cholesterol levels. ZAG has been shown to play a significant role in reducing obesity and improving insulin sensitivity, both in experimental animal model studies and in human studies. Furthermore, ZAG at physiologically relevant concentrations increases the release of adiponectin from human adipocytes. In addition, ZAG has been shown to inhibit in vitro leptin production. Further studies are needed to provide more data on the role of zinc and zinc-α2-glycoprotein.

Development of a prediction model for mortality and cardiovascular outcomes in older adults taking into account AZGP1

Zinc-alpha 2-glycoprotein (AZGP1) is a serum protein with postulated functions in metabolism, cancer and cardiovascular disease. We developed new prediction models for mortality or cardiovascular events investigating the predictive potential of serum AZGP1 in a community-based cohort of older adults. We measured AZGP1 (μg/ml) in stored serum samples of 930 individuals of the Berlin Initiative Study, a prospective, population-based cohort of adults aged ≥ 70. We determined the prognostic potential of 20 knowledge-based predictors including AZGP1 for the outcomes of mortality or the composite endpoint of death and cardiovascular events (stroke, myocardial infarction (MI)) using Cox models; their model fit was evaluated with calibration plots, goodness-of-fit tests and c-indices. During median follow-up of 48.3 months, 70 incident strokes, 38 incident MI and 234 deaths occurred. We found no associations or correlations between AZGP1 and other candidate variables. After multivariable Cox regression with backward-selection AZGP1 remained in both models for mortality (HR = 0.44, 95%CI: 0.24–0.80) and for the composite endpoint (HR = 0.43, 95%CI: 0.23–0.82). Within newly built prediction models, we found that increased AZGP1 levels were predictive for lower risk of mortality and the composite endpoint in older adults. AZGP1 as a predictor warrants further validation in older adults.

Zinc

Since the discovery of manifest Zn deficiency in 1961, the increasing number of studies demonstrated the association between altered Zn status and multiple diseases. In this chapter, we provide a review of the most recent advances on the role of Zn in health and disease (2010-20), with a special focus on the role of Zn in neurodegenerative and neurodevelopmental disorders, diabetes and obesity, male and female reproduction, as well as COVID-19. In parallel with the revealed tight association between ASD risk and severity and Zn status, the particular mechanisms linking Zn2+ and ASD pathogenesis like modulation of synaptic plasticity through ProSAP/Shank scaffold, neurotransmitter metabolism, and gut microbiota, have been elucidated. The increasing body of data indicate the potential involvement of Zn2+ metabolism in neurodegeneration. Systemic Zn levels in Alzheimer's and Parkinson's disease were found to be reduced, whereas its sequestration in brain may result in modulation of amyloid β and α-synuclein processing with subsequent toxic effects. Zn2+ was shown to possess adipotropic effects through the role of zinc transporters, zinc finger proteins, and Zn-α2-glycoprotein in adipose tissue physiology, underlying its particular role in pathogenesis of obesity and diabetes mellitus type 2. Recent findings also contribute to further understanding of the role of Zn2+ in spermatogenesis and sperm functioning, as well as oocyte development and fertilization. Finally, Zn2+ was shown to be the potential adjuvant therapy in management of novel coronavirus infection (COVID-19), underlining the perspectives of zinc in management of old and new threats.

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.

Association between circulating zinc-α2-glycoprotein levels and the different phenotypes of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) diagnosis combines various clinical phenotypes. The definition of PCOS is still controversial because insulin resistance (IR) and dysmetabolism do not constitute PCOS diagnostic criteria. We analyzed whether a circulating biomarker zinc-α2-glycoprotein (ZAG) related to IR and metabolic dysfunction can predict PCOS phenotypes. We then recruited 100 PCOS patients and 99 healthy women as the control group to assess the relationship between ZAG and metabolic characteristics. The euglycemic-hyperinsulinemic clamp helped assess insulin sensitivity, and the enzyme immunometric assay was deployed for ZAG levels. Our PCOS cohort presented sixty-nine patients with hyperandrogenism, eighty-six patients with chronic oligoanovulation, and eighty-one patients with polycystic ovaries by ultrasonographic evaluation. Additionally, the circulating ZAG levels were considerably reduced in all PCOS patients compared with healthy women (p < 0.05 or p < 0.01). Additionally, sixty-nine PCOS patients had IR, and circulating ZAG levels were also different among the phenotypes. Furthermore, the normoandrogenic type specifically exhibited the highest circulating ZAG levels among all PCOS phenotypes (p < 0.05 or p < 0.01). Additionally, normoandrogenic phenotype patients had reduced HOMA-IR scores and greater M-values than those in the classic phenotypes (p < 0.05). The circulating ZAG levels, however, were not associated with oligoanovulation but were correlated with hyperandrogenism and PCO morphology. In summary, circulating ZAG levels serve as suitable PCOS phenotype biomarkers, aiding physicians to identify women who merit screening.

Role of Zinc in Zinc-α2-Glycoprotein Metabolism in Obesity: a Review of Literature

Excessive adipose tissue promotes the manifestation of endocrine disorders such as reduction of the secretion of zinc-α2-glycoprotein (ZAG), an adipokine with anti-inflammatory and lipid-mobilizing activity. The molecular structure of this adipokine includes binding sites for zinc, a trace element with important antioxidant and immunological proprieties that also participates in energy metabolism and stimulates the function of ZAG. The objective of this review is to highlight current data on the metabolism of ZAG in obesity and the role of zinc in this process. The identified studies show that subjects with obesity have low serum concentrations of zinc and ZAG, as well as low expression of the genes encoding this protein. Thus, zinc appears to be an important regulator of the homeostasis of ZAG in the body; however, alterations in the metabolism of zinc in obesity appear to compromise the functions of ZAG. Therefore, further studies are needed to clarify the relationship between zinc and ZAG metabolism and its repercussions in obesity.