Control of hepatic gluconeogenesis by the promyelocytic leukemia zinc finger protein

Investigating the association of previously identified genome-wide significant loci (rs10739076 and rs1784692) with PCOS susceptibility and its related traits in Indian women

OBJECTIVE(S)

Polycystic ovary syndrome (PCOS) is a multifactorial endocrinopathy with an enigmatic etiology. Hallmark features include irregular menstrual cycles, insulin resistance and hyperandrogenemia and affected women are prone to development of adverse reproductive and cardiometabolic outcomes like anovulatory infertility, impaired glucose tolerance, type 2 diabetes, dyslipidemia, metabolic syndrome and cardiovascular disease. Genetic underpinnings of PCOS have been investigated extensively using genome-wide association studies, which have led to the identification of several novel susceptibility loci. However, as ethnic diversity contributes to phenotypic and genetic heterogeneity, we undertook the first genetic association study to determine the association of rs10739076 of PLGRKT and rs1784692 of ZBTB16 with PCOS susceptibility and its related traits in Indian women.

STUDY DESIGN

The present case-control study comprised 497 women with PCOS diagnosed according to the Rotterdam criteria and 233 age matched healthy women as controls. All participants were characterized in terms of anthropometric, hormonal and metabolic parameters and the variants were investigated by direct sequencing. Genotypic and genotype-phenotype association of these variants with PCOS susceptibility and its related biochemical and hormonal traits was analyzed with appropriate statistical tests.

RESULTS

The genotypic and allelic frequencies of rs1784692 of ZBTB16 were significantly decreased in lean women with PCOS only, and this variant was associated with lowered insulin levels, HOMA-IR, LH:FSH ratio along with increased ApoA1 levels and QUICKI in them. Although, the PLGRKT variant, rs10739076, showed similar frequency distribution in both lean and obese groups, it was found to be associated with reduced fasting glucose in all women with PCOS.

CONCLUSION(S)

To the best of our knowledge, this is the first study to demonstrate that ZBTB16 variant showed significant association with reduced PCOS susceptibility in lean rather than obese Indian women, highlighting the impact of obesity on determining genetic predisposition to PCOS in Indian women. In contrast, PLGRKT variant did not influence PCOS risk in lean or obese women. Importantly, both variants exerted a protective effect on glucose metabolism, insulin resistance, gonadotropin and lipid levels in women with PCOS. Determination of susceptibility variants for PCOS demand population specific replication studies to ascertain best candidate loci for PCOS.

Hepatic Zbtb18 (Zinc Finger and BTB Domain Containing 18) alleviates hepatic steatohepatitis via FXR (Farnesoid X Receptor)

A lasting imbalance between fatty acid synthesis and consumption leads to non-alcoholic fatty liver disease (NAFLD), coupled with hepatitis and insulin resistance. Yet the details of the underlying mechanisms are not fully understood. Here, we unraveled that the expression of the transcription factor Zbtb18 is markedly decreased in the livers of both patients and murine models of NAFLD. Hepatic Zbtb18 knockout promoted NAFLD features like impaired energy expenditure and fatty acid oxidation (FAO), and induced insulin resistance. Conversely, hepatic Zbtb18 overexpression alleviated hepato-steatosis, insulin resistance, and hyperglycemia in mice fed on a high-fat diet (HFD) or in diabetic mice. Notably, in vitro and in vivo mechanistic studies revealed that Zbtb18 transcriptional activation of Farnesoid X receptor (FXR) mediated FAO and Clathrin Heavy Chain (CLTC) protein hinders NLRP3 inflammasome activity. This key mechanism by which hepatocyte's Zbtb18 expression alleviates NAFLD and consequent liver fibrosis was further verified by FXR's deletion and forced expression in mice and cultured mouse primary hepatocytes (MPHs). Moreover, CLTC deletion significantly abrogated the hepatic Zbtb18 overexpression-driven inhibition of NLRP3 inflammasome activity in macrophages. Altogether, Zbtb18 transcriptionally activates the FXR-mediated FAO and CLTC expression, which inhibits NLRP3 inflammasome's activity alleviating inflammatory stress and insulin resistance, representing an attractive remedy for hepatic steatosis and fibrosis.

Unaltered hepatic wound healing response in male rats with ancestral liver injury

The possibility that ancestral environmental exposure could result in adaptive inherited effects in mammals has been long debated. Numerous rodent models of transgenerational responses to various environmental factors have been published but due to technical, operational and resource burden, most still await independent confirmation. A previous study reported multigenerational epigenetic adaptation of the hepatic wound healing response upon exposure to the hepatotoxicant carbon tetrachloride (CCl4) in male rats. Here, we comprehensively investigate the transgenerational effects by repeating the original CCl4 multigenerational study with increased power, pedigree tracing, F2 dose-response and suitable randomization schemes. Detailed pathology evaluations do not support adaptive phenotypic suppression of the hepatic wound healing response or a greater fitness of F2 animals with ancestral liver injury exposure. However, transcriptomic analyses identified genes whose expression correlates with ancestral liver injury, although the biological relevance of this apparent transgenerational transmission at the molecular level remains to be determined. This work overall highlights the need for independent evaluation of transgenerational epigenetic inheritance paradigms in mammals.

Uncovering the Gut-Liver Axis Biomarkers for Predicting Metabolic Burden in Mice

Western diet (WD) intake, aging, and inactivation of farnesoid X receptor (FXR) are risk factors for metabolic and chronic inflammation-related health issues ranging from metabolic dysfunction-associated steatotic liver disease (MASLD) to dementia. The progression of MASLD can be escalated when those risks are combined. Inactivation of FXR, the receptor for bile acid (BA), is cancer prone in both humans and mice. The current study used multi-omics including hepatic transcripts, liver, serum, and urine metabolites, hepatic BAs, as well as gut microbiota from mouse models to classify those risks using machine learning. A linear support vector machine with K-fold cross-validation was used for classification and feature selection. We have identified that increased urine sucrose alone achieved 91% accuracy in predicting WD intake. Hepatic lithocholic acid and serum pyruvate had 100% and 95% accuracy, respectively, to classify age. Urine metabolites (decreased creatinine and taurine as well as increased succinate) or increased gut bacteria (Dorea, Dehalobacterium, and Oscillospira) could predict FXR deactivation with greater than 90% accuracy. Human disease relevance is partly revealed using the metabolite-disease interaction network. Transcriptomics data were also compared with the human liver disease datasets. WD-reduced hepatic Cyp39a1 (cytochrome P450 family 39 subfamily a member 1) and increased Gramd1b (GRAM domain containing 1B) were also changed in human liver cancer and metabolic liver disease, respectively. Together, our data contribute to the identification of noninvasive biomarkers within the gut-liver axis to predict metabolic status.

Hepatic ZBTB22 promotes hyperglycemia and insulin resistance via PEPCK1-driven gluconeogenesis

Excessive gluconeogenesis can lead to hyperglycemia and diabetes through as yet incompletely understood mechanisms. Herein, we show that hepatic ZBTB22 expression is increased in both diabetic clinical samples and mice, being affected by nutritional status and hormones. Hepatic ZBTB22 overexpression increases the expression of gluconeogenic and lipogenic genes, heightening glucose output and lipids accumulation in mouse primary hepatocytes (MPHs), while ZBTB22 knockdown elicits opposite effects. Hepatic ZBTB22 overexpression induces glucose intolerance and insulin resistance, accompanied by moderate hepatosteatosis, while ZBTB22-deficient mice display improved energy expenditure, glucose tolerance, and insulin sensitivity, and reduced hepatic steatosis. Moreover, hepatic ZBTB22 knockout beneficially regulates gluconeogenic and lipogenic genes, thereby alleviating glucose intolerance, insulin resistance, and liver steatosis in db/db mice. ZBTB22 directly binds to the promoter region of PCK1 to enhance its expression and increase gluconeogenesis. PCK1 silencing markedly abolishes the effects of ZBTB22 overexpression on glucose and lipid metabolism in both MPHs and mice, along with the corresponding changes in gene expression. In conclusion, targeting hepatic ZBTB22/PEPCK1 provides a potential therapeutic approach for diabetes.

4-Methylumbelliferone Targets Revealed by Public Data Analysis and Liver Transcriptome Sequencing

4-methylumbelliferone (4MU) is a well-known hyaluronic acid synthesis inhibitor and an approved drug for the treatment of cholestasis. In animal models, 4MU decreases inflammation, reduces fibrosis, and lowers body weight, serum cholesterol, and insulin resistance. It also inhibits tumor progression and metastasis. The broad spectrum of effects suggests multiple and yet unknown targets of 4MU. Aiming at 4MU target deconvolution, we have analyzed publicly available data bases, including: 1. Small molecule library Bio Assay screening (PubChemBioAssay); 2. GO pathway databases screening; 3. Protein Atlas Database. We also performed comparative liver transcriptome analysis of mice on normal diet and mice fed with 4MU for two weeks. Potential targets of 4MU public data base analysis fall into two big groups, enzymes and transcription factors (TFs), including 13 members of the nuclear receptor superfamily regulating lipid and carbohydrate metabolism. Transcriptome analysis revealed changes in the expression of genes involved in bile acid metabolism, gluconeogenesis, and immune response. It was found that 4MU feeding decreased the accumulation of the glycogen granules in the liver. Thus, 4MU has multiple targets and can regulate cell metabolism by modulating signaling via nuclear receptors.

Mouse promyelocytic leukemia zinc finger protein (PLZF) regulates hepatic lipid and glucose homeostasis dependent on SIRT1

Previous studies have demonstrated that promyelocytic leukemia zinc finger protein (PLZF) promotes the expression of gluconeogenic genes and hepatic glucose output, which leads to hyperglycemia. However, the role played by PLZF in regulating lipid metabolism is not known. In this study, we aimed to examine the function of PLZF in regulating hepatic lipid and glucose homeostasis and the underlying mechanisms. The expression of PLZF was determined in different mouse models with regard to non-alcoholic fatty liver disease (NAFLD). In the next step, adenoviruses that express PLZF (Ad-PLZF) or PLZF-specific shRNA (Ad-shPLZF) were utilized to alter PLZF expression in mouse livers and in primary hepatocytes. For the phenotype of the fatty liver, histologic and biochemical analyses of hepatic triglyceride (TG), serum TG and cholesterol levels were carried out. The underlying molecular mechanism for the regulation of lipid metabolism by PLZF was further explored using luciferase reporter gene assay and ChIP analysis. The results demonstrated that PLZF expression was upregulated in livers derived from ob/ob, db/db and diet-induced obesity (DIO) mice. Liver PLZF-overexpressing C57BL/6J mice showed fatty liver phenotype, liver inflammation, impaired glucose tolerance and insulin sensitivity. On the other hand, hepatic PLZF knockdown in db/db and DIO mice alleviated hepatic steatosis. Of note, we found that PLZF activates SREBP-1c gene transcription through binding directly to the promoter fragment of this gene, which would induce a repressor-to-activator conversion depending on its interaction with SIRT1 in the role played by PLZF in the transcription process through deacetylation. Thus, PLZF is identified as an essential regulator of hepatic lipid and glucose metabolism, where the modulation of its liver expression could open up a therapeutic path for treating NAFLD.

FOXO1 and FOXO3 Cooperatively Regulate Innate Lymphoid Cell Development

Natural killer (NK) cells play roles in viral clearance and early surveillance against malignant transformation, yet our knowledge of the underlying mechanisms controlling their development and functions remain incomplete. To reveal cell fate-determining pathways in NK cell progenitors (NKP), we utilized an unbiased approach and generated comprehensive gene expression profiles of NK cell progenitors. We found that the NK cell program was gradually established in the CLP to preNKP and preNKP to rNKP transitions. In line with FOXO1 and FOXO3 being co-expressed through the NK developmental trajectory, the loss of both perturbed the establishment of the NK cell program and caused stalling in both NK cell development and maturation. In addition, we found that the combined loss of FOXO1 and FOXO3 caused specific changes to the composition of the non-cytotoxic innate lymphoid cell (ILC) subsets in bone marrow, spleen, and thymus. By combining transcriptome and chromatin profiling, we revealed that FOXO TFs ensure proper NK cell development at various lineage-commitment stages through orchestrating distinct molecular mechanisms. Combined FOXO1 and FOXO3 deficiency in common and innate lymphoid cell progenitors resulted in reduced expression of genes associated with NK cell development including ETS-1 and their downstream target genes. Lastly, we found that FOXO1 and FOXO3 controlled the survival of committed NK cells via gene regulation of IL-15Rβ (CD122) on rNKPs and bone marrow NK cells. Overall, we revealed that FOXO1 and FOXO3 function in a coordinated manner to regulate essential developmental genes at multiple stages during murine NK cell and ILC lineage commitment.

Identification of Candidate Genes Regulating Carcass Depth and Hind Leg Circumference in Simmental Beef Cattle Using Illumina Bovine Beadchip and Next-Generation Sequencing Analyses

Genome-wide association studies are a robust means of identifying candidate genes that regulate economically important traits in farm animals. The aim of this study is to identify single-nucleotide polymorphisms (SNPs) and candidate genes potentially related to carcass depth and hind leg circumference in Simmental beef cattle. We performed Illumina Bovine HD Beadchip (~670 k SNPs) and next-generation sequencing (~12 million imputed SNPs) analyses of data from 1252 beef cattle, to which we applied a linear mixed model. Using a statistical threshold (p = 0.05/number of SNPs identified) and adopting a false discovery rate (FDR), we identified many putative SNPs on different bovine chromosomes. We identified 12 candidate genes potentially annotated with the markers identified, including CDKAL1 and E2F3, related to myogenesis and skeletal muscle development. The identification of such genes in Simmental beef cattle will help breeders to understand and improve related traits, such as meat yield.

Lactational High Fat Diet in Mice Causes Insulin Resistance and NAFLD in Male Offspring Which Is Partially Rescued by Maternal Metformin Treatment

Maternal metabolic disease and diet during pregnancy and lactation have important implications for the programming of offspring metabolic disease. In addition, high-fat diets during pregnancy and lactation can predispose the offspring to non-alcoholic fatty liver disease (NAFLD), a rising health threat in the U.S. We developed a model of maternal high-fat feeding exclusively during the lactation period. We previously showed that offspring from dams, given lactational high-fat diet (HFD), are predisposed to obesity, glucose intolerance, and inflammation. In separate experiments, we also showed that lactational metformin treatment can decrease offspring metabolic risk. The purpose of these studies was to understand the programming implications of lactational HFD on offspring metabolic liver disease risk. Dams were fed a 60% lard-based HFD from the day of delivery through the 21-day lactation period. A subset of dams was also given metformin as a co-treatment. Starting at weaning, the offspring were fed normal fat diet until 3 months of age; at which point, a subset was challenged with an additional HFD stressor. Lactational HFD led male offspring to develop hepatic insulin resistance. The post-weaning HFD challenge led male offspring to progress to NAFLD with more severe outcomes in the lactational HFD-challenged offspring. Co-administration of metformin to lactating dams on HFD partially rescued the offspring liver metabolic defects in males. Lactational HFD or post-weaning HFD had no impact on female offspring who maintained a normal insulin sensitivity and liver phenotype. These findings indicate that HFD, during the lactation period, programs the adult offspring to NAFLD risk in a sexually dimorphic manner. In addition, early life intervention with metformin via maternal exposure may prevent some of the liver programming caused by maternal HFD.

Suppressive role of E3 ubiquitin ligase FBW7 in type I diabetes in non-obese diabetic mice through mediation of ubiquitination of EZH2

The current study tried to uncover the molecular mechanism of E3 ubiquitin ligase F-box and WD repeat domain-containing 7 (FBW7) in a heritable autoimmune disease, type I diabetes (T1D). After streptozotocin-induced T1D model establishment in non-obese diabetic (NOD) mouse, the protein expression of FBW7, enhancer of zeste homolog 2 (EZH2), and Zinc finger and BTB domain containing 16 (ZBTB16) was quantified. Next, splenocytes and pancreatic beta cells were isolated to measure the production of pro-inflammatory cytokines in splenocytes, as well as islet beta-cell apoptosis. Additionally, the stability of EZH2 induced by FBW7 was analyzed by cycloheximide chase assay. The binding affinity of FBW7 and EZH2 and the consequence of ubiquitination were monitored by co-immunoprecipitation assay. Last, a chromatin immunoprecipitation assay was employed to analyze the accumulation of EZH2 and H3K27me3 at the ZBTB16 promoter region. Our study demonstrated downregulated FBW7 and ZBTB16 and upregulated EZH2 in diabetic NOD mice. Overexpression of FBW7 in the NOD mice inhibited pro-inflammatory cytokine release in the splenocytes and the apoptosis of islets beta cells. FBW7 destabilized EZH2 and accelerated ubiquitin-dependent degradation. EZH2 and H3K27me3 downregulated the ZBTB16 expression by accumulating in the ZBTB16 promoter and methylation. FBW7 upregulates the expression of ZBTB16 by targeting histone methyltransferase EZH2 thus reducing the occurrence of T1D.

Suppressor of cytokine signalling-2 controls hepatic gluconeogenesis and hyperglycemia by modulating JAK2/STAT5 signalling pathway

Hepatic gluconeogenesis plays a crucial role in maintaining blood glucose homeostasis in mammals. Globe knockout of suppressor of cytokine signalling-2 (SOCS2), a feedback inhibitor of cytokine signalling, has been shown resistant to high-fat-diet (HFD)-induced hepatic steatosis with impaired glucose tolerance in mice. However, the underlying mechanism of SOCS2 regulates hepatic glucose homeostasis still undefined. In the present study, we demonstrated that the hepatic SOCS2 expression is markedly reduced in fasted C57BL/6 J mice or db/db mice. Moreover, hepatic SOCS2 expression levels are induced by metformin treatment. Ablation of SOCS2 attenuates suppressing effects of metformin on gluconeogenesis in hepatocytes. Gain- and loss-of-function studies indicated that SOCS2 regulates hepatic gluconeogenic genes expression and glucose output by mediating JAK2/STAT5 signalling pathway in db/db mice. Mechanistically, we observed that SOCS2 inactivates STAT5 by attenuating the interaction between JAK2 and STAT5, which in turn reduces hepatic gluconeogenesis. The present study reveals a critical role of SOCS2 in regulating hepatic gluconeogenesis. The inhibitory effect of metformin on gluconeogenesis is mediated, at least in part, by upregulating SOCS2 and therefore reducing hepatic gluconeogenic genes expression. SOCS2 may represent a new therapeutic target for the treatment of diabetes.

Hypogalactia in mammary quarters adjacent to lipopolysaccharide-infused quarters is associated with transcriptional changes in immune genes

Infusion of lipopolysaccharides (LPS) into a mammary gland can provoke inflammatory responses and impair lactation in both the infused gland and neighboring glands. To gain insight into the mechanisms controlling the spatiotemporal response to localized mastitis in lactating dairy cows, we performed RNA sequencing on mammary tissue from quarters infused with LPS, neighboring quarters in the same animals, and control quarters from untreated animals at 3 and 12 h postinfusion. Differences in gene expression were annotated to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Comparing mammary transcriptomes from all 3 treatments revealed 3,088 and 1,644 differentially expressed (DE) genes at 3 and 12 h, respectively. Of these genes, >95% were DE only in LPS-infused quarters and represented classical responses to LPS: inflammation, apoptosis, tissue remodeling, and altered cell signaling and metabolism. Although relatively few genes were DE in neighboring quarters (56 at 3 h; 74 at 12 h), these represented several common pathways. At 3 h, tumor necrosis factor (TNF), nuclear factor-κB, and nucleotide-binding and oligomerization domain (NOD)-like receptor signaling pathways were identified by the upregulation of anti-inflammatory (NFKBIA, TNFAIP3) and cell adhesion molecule (VCAM1, ICAM1) genes in neighboring glands. Additionally, at 12 h, several genes linked to 1-carbon and serine metabolism were upregulated. Some responses were also regulated over time. The proinflammatory response in LPS-infused glands diminished between 3 and 12 h, indicating tight control over transcription to re-establish homeostasis. In contrast, 2 glucocorticoid-responsive genes, FKBP5 and ZBTB16, were among the top DE genes upregulated in neighboring quarters at both time points, indicating potential regulation by glucocorticoids. We conclude that a transient, systemic immune response was sufficient to disrupt lactation in neighboring glands. This response may be mediated directly by proinflammatory factors from the LPS-infused gland or indirectly by secondary factors released in response to systemic inflammatory signals.

Zinc Finger Transcription Factor Zbtb16 Coordinates the Response to Energy Deficit in the Mouse Hypothalamus

The central nervous system controls feeding behavior and energy expenditure in response to various internal and external stimuli to maintain energy balance. Here we report that the newly identified transcription factor zinc finger and BTB domain containing 16 (Zbtb16) is induced by energy deficit in the paraventricular (PVH) and arcuate (ARC) nuclei of the hypothalamus via glucocorticoid (GC) signaling. In the PVH, Zbtb16 is expressed in the anterior half of the PVH and co-expressed with many neuronal markers such as corticotropin-releasing hormone (Crh), thyrotropin-releasing hormone (Trh), oxytocin (Oxt), arginine vasopressin (Avp), and nitric oxide synthase 1 (Nos1). Knockdown (KD) of Zbtb16 in the PVH results in attenuated cold-induced thermogenesis and improved glucose tolerance without affecting food intake. In the meantime, Zbtb16 is predominantly expressed in agouti-related neuropeptide/neuropeptide Y (Agrp/Npy) neurons in the ARC and its KD in the ARC leads to reduced food intake. We further reveal that chemogenetic stimulation of PVH Zbtb16 neurons increases energy expenditure while that of ARC Zbtb16 neurons increases food intake. Taken together, we conclude that Zbtb16 is an important mediator that coordinates responses to energy deficit downstream of GCs by contributing to glycemic control through the PVH and feeding behavior regulation through the ARC, and additionally reveal its function in controlling energy expenditure during cold-evoked thermogenesis via the PVH. As a result, we hypothesize that Zbtb16 may be involved in promoting weight regain after weight loss.

Maternal High-Sucrose Diet Affects Phenotype Outcome in Adult Male Offspring: Role of Zbtb16

Overnutrition in pregnancy and lactation affects fetal and early postnatal development, which can result in metabolic disorders in adulthood. We tested a hypothesis that variation of the Zbtb16 gene, a significant energy metabolism regulator, modulates the effect of maternal high-sucrose diet (HSD) on metabolic and transcriptomic profiles of the offspring. We used the spontaneously hypertensive rat (SHR) strain and a minimal congenic rat strain SHR-Zbtb16, carrying the Zbtb16 gene allele originating from the PD/Cub rat, a metabolic syndrome model. Sixteen-week-old SHR and SHR-Zbtb16 rat dams were fed either standard diet (control groups) or a high-sucrose diet (HSD, 70% calories as sucrose) during pregnancy and 4 weeks of lactation. In dams of both strains, we observed an HSD-induced increase of cholesterol and triacylglycerol concentrations in VLDL particles and a decrease of cholesterol and triacylglycerols content in medium to very small LDL particles. In male offspring, exposure to maternal HSD substantially increased brown fat weight in both strains, decreased triglycerides in LDL particles, and impaired glucose tolerance exclusively in SHR. The transcriptome assessment revealed networks of transcripts reflecting the shifts induced by maternal HSD with major nodes including mir-126, Hsd11b1 in the brown adipose tissue, Pcsk9, Nr0b2 in the liver and Hsd11b1, Slc2a4 in white adipose tissue. In summary, maternal HSD feeding during pregnancy and lactation affected brown fat deposition and lipid metabolism in adult male offspring and induced major transcriptome shifts in liver, white, and brown adipose tissues. The Zbtb16 variation present in the SHR-Zbtb16 led to several strain-specific effects of the maternal HSD, particularly the transcriptomic profile shifts of the adult male offspring.

SHR-Zbtb16 minimal congenic strain reveals nutrigenetic interaction between Zbtb16 and high-sucrose diet

Both prenatal and postnatal excessive consumption of dietary sucrose or fructose was shown to be detrimental to health and contributing to pathogenesis of metabolic syndrome. Our knowledge of genetic determinants of individual sensitivity to sucrose-driven metabolic effects is limited. In this study, we have tested the hypothesis that a variation of metabolic syndrome-related gene, Zbtb16 (Zinc Finger and BTB Domain Containing 16 will affect the reaction to high-sucrose diet (HSD) content in "matched" nutritional exposition settings, i.e. maternal HSD with re-exposition to HSD in adulthood vs. standard diet. We compared metabolic profiles of adult males of spontaneously hypertensive rats (SHR) and a single-gene, minimal congenic strain SHR-Zbtb16 fed either standard diet or exposed to HSD prenatally throughout gestation and nursing and again at the age of 6 months for the period of 14 days. HSD exposition led to increased adiposity in both strains and decrease of glucose tolerance and cholesterol (Ch) concentrations in majority of low-density lipoprotein (LDL) particle classes and in very large and large high-density lipoprotein (HDL) in SHR-Zbtb16 male offspring. There was a similar pattern of HSD-induced increase of triacylglycerols in chylomicrons and very low-density lipoprotein (VLDL) of both strains, though the increase of (triacylglycerol) TAG content was clearly more pronounced in SHR. We observed significant STRAIN*DIET interactions for the smallest LDL particles as their TAG content decreased in SHR-Zbtb16 and did not change in SHR in response to HSD. In summary, we provide evidence of nutrigenetic interaction between Zbtb16 and HSD in context of pathogenesis of metabolic syndrome.

Grandmother's Diet Matters: Early Life Programming with Sucrose Influences Metabolic and Lipid Parameters in Second Generation of Rats

Early life exposure to certain environmental stimuli is related to the development of alternative phenotypes in mammals. A number of these phenotypes are related to an increased risk of disease later in life, creating a massive healthcare burden. With recent focus on the determination of underlying causes of common metabolic disorders, parental nutrition is of great interest, mainly due to a global shift towards a Western-type diet. Recent studies focusing on the increase of food or macronutrient intake don't always consider the source of these nutrients as an important factor. In our study, we concentrate on the effects of high-sucrose diet, which provides carbohydrates in form of sucrose as opposed to starch in standard diet, fed in pregnancy and lactation in two subsequent generations of spontaneously hypertensive rats (SHR) and congenic SHR-Zbtb16 rats. Maternal sucrose intake increased fasting glycaemia in SHR female offspring in adulthood and increased their chow consumption in gravidity. High-sucrose diet fed to the maternal grandmother increased brown fat weight and HDL cholesterol levels in adult male offspring of both strains, i.e., the grandsons. Fasting glycaemia was however decreased only in SHR offspring. In conclusion, we show the second-generation effects of maternal exposition to a high-sucrose diet, some modulated to a certain extent by variation in the Zbtb16 gene.

SWI/SNF complex subunit BAF60a represses hepatic ureagenesis through a crosstalk between YB-1 and PGC-1α

Objective

Ureagenesis predominantly occurs in the liver and functions to remove ammonia, and the dysregulation of ureagenesis leads to the development of hyperammonemia. Recent studies have shown that ureagenesis is under the control of nutrient signals, but the mechanism remains elusive. Therefore, intensive investigation of the molecular mechanism underlying ureagenesis will shed some light on the pathology of metabolic diseases related to ammonia imbalance.

Methods

Mice were fasted for 24 h or fed a high-fat diet (HFD) for 16 weeks. For human evaluation, we obtained a public data set including 41 obese patients with and without hepatic steatosis. We analyzed the expression levels of hepatic BAF60a under different nutrient status. The impact of BAF60a on ureagenesis and hyperammonemia was assessed by using gain- and loss-of-function strategies. The molecular chaperons mediating the effects of BAF60a on ureagenesis were validated by molecular biological strategies.

Results

BAF60a was induced in the liver of both fasted and HFD-fed mice and was positively correlated with body mass index in obese patients. Liver-specific overexpression of BAF60a inhibited hepatic ureagenesis, leading to the increase of serum ammonia levels. Mechanistically, BAF60a repressed the transcription of Cps1, a rate-limiting enzyme, through interaction with Y-box protein 1 (YB-1) and by switching the chromatin structure of Cps1 promoter into an inhibitory state. More importantly, in response to different nutrient status, PGC-1α (as a transcriptional coactivator) and YB-1 competitively bound to BAF60a, thus selectively regulating hepatic fatty acid β-oxidation and ureagenesis.

Conclusion

The BAF60a-YB-1 axis represses hepatic ureagenesis, thereby contributing to hyperammonemia under overnutrient status. Therefore, hepatic BAF60a may be a novel therapeutic target for the treatment of overnutrient-induced urea cycle disorders and their associated diseases.

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HFD-feeding increases hepatic BAF60a expression, while inhibits ureagenesis genes.

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BAF60a represses Cps1 transcription and ureagenesis, causing ammonia accumulation.

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YB-1 binds to BAF60a and mediates the inhibitory effects of BAF60a on ureagenesis.

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BAF60a mediates crosstalk between hepatic ureagenesis and fatty acid oxidation.

Zbtb7c is a critical gluconeogenic transcription factor that induces glucose-6-phosphatase and phosphoenylpyruvate carboxykinase 1 genes expression during mice fasting

Gluconeogenesis is essential for blood glucose homeostasis during fasting and is regulated by various enzymes, which are encoded by gluconeogenic genes. Those genes are controlled by various transcription factors. Zinc finger and BTB domain-containing 7c (Zbtb7c, also called Kr-pok) is a BTB-POZ family transcription factor with proto-oncogenic activity. Previous findings have indicated that Zbtb7c is involved in the regulation of fatty acid biosynthesis, suggesting an involvement also in primary metabolism. We found here that fasting induced Zbtb7c expression in the mouse liver and in primary liver hepatocytes. We also observed that Zbtb7c-knockout mice have decreased blood glucose levels, so we investigated whether Zbtb7c plays a role in gluconeogenesis. Indeed, differential gene expression analysis of Zbtb7c-knockout versus wild type mouse livers showed downregulated transcription of gluconeogenic genes encoding the glucose 6-phosphatase catalytic subunit (G6pc) and phosphoenolpyruvate carboxykinase 1 (Pck1), while Zbtb7c expression upregulated these two genes, under fasting conditions. Mechanistically, we found that when complexed with histone deacetylase 3 (Hdac3), Zbtb7c binds insulin response elements (IREs) within the G6pc and Pck1 promoters. Moreover, complexed Zbtb7c deacetylated forkhead box O1 (Foxo1), thereby increasing Foxo1 binding to the G6pc and Pck1 IREs, resulting in their transcriptional activation. These results demonstrate Zbtb7c to be a crucial metabolic regulator of blood glucose homeostasis, during mammalian fasting.

ZBTB16 and metabolic syndrome: a network perspective

Metabolic syndrome is a prevalent, complex condition. The search for genetic determinants of the syndrome is currently undergoing a paradigm enhancement by adding systems genetics approaches to association studies. We summarize the current evidence on relations between an emergent new candidate, zinc finger and BTB domain containing 16 (ZBTB16) transcription factor and the major components constituting the metabolic syndrome. Information stemming from studies on experimental models with altered Zbtb16 expression clearly shows its effect on adipogenesis, cardiac hypertrophy and fibrosis, lipid levels and insulin sensitivity. Based on current evidence, we provide a network view of relations between ZBTB16 and hallmarks of metabolic syndrome in order to elucidate the potential functional links involving the ZBTB16 node. Many of the identified genes interconnecting ZBTB16 with all or most metabolic syndrome components are linked to immune function, inflammation or oxidative stress. In summary, ZBTB16 represents a promising pleiotropic candidate node for metabolic syndrome.

Single-Gene Congenic Strain Reveals the Effect of Zbtb16 on Dexamethasone-Induced Insulin Resistance

BACKGROUND

Glucocorticoids (GCs) are potent therapeutic agents frequently used for treatment of number of conditions, including hematologic, inflammatory, and allergic diseases. Both their therapeutic and adverse effects display significant interindividual variation, partially attributable to genetic factors. We have previously isolated a seven-gene region of rat chromosome 8 sensitizing to dexamethasone (DEX)-induced dyslipidemia and insulin resistance (IR) of skeletal muscle. Using two newly derived congenic strains, we aimed to investigate the effect of one of the prime candidates for this pharmacogenetic interaction, the Zbtb16 gene.

METHODS

Adult male rats of SHR-Lx.PD5^PD-Zbtb16 (n = 9) and SHR-Lx.PD5^SHR-Zbtb16 (n = 8) were fed standard diet (STD) and subsequently treated with DEX in drinking water (2.6 µg/ml) for 3 days. The morphometric and metabolic profiles of both strains including oral glucose tolerance test, triacylglycerols (TGs), free fatty acids, insulin, and C-reactive protein levels were assessed before and after the DEX treatment. Insulin sensitivity of skeletal muscle and visceral adipose tissue was determined by incorporation of radioactively labeled glucose.

RESULTS

The differential segment of SHR-Lx.PD5^SHR-Zbtb16 rat strain spans 563 kb and contains six genes: Htr3a, Htr3b, Usp28, Zw10, Tmprss5, and part of Drd2. The SHR-Lx.PD5^PD-Zbtb16 minimal congenic strain contains only Zbtb16 gene on SHR genomic background and its differential segment spans 254 kb. Total body weight was significantly increased in SHR-Lx.PD5^PD-Zbtb16 strain compared with SHR-Lx.PD5^SHR-Zbtb16 , however, no differences in the weights of adipose tissue depots were observed. While STD-fed rats of both strains did not show major differences in their metabolic profiles, after DEX treatment the SHR-Lx.PD5^PD-Zbtb16 congenic strain showed increased levels of TGs, glucose, and blunted inhibition of lipolysis by insulin. Both basal and insulin-stimulated incorporation of radioactively labeled glucose into skeletal muscle glycogen were significantly reduced in SHR-Lx.PD5^PD-Zbtb16 strain, but the insulin sensitivity of adipose tissue was comparable between the two strains.

CONCLUSION

The metabolic disturbances including impaired glucose tolerance, dyslipidemia, and IR of skeletal muscle observed after DEX treatment in the congenic SHR-Lx.PD5^PD-Zbtb16 reveal the Zbtb16 locus as a possible sensitizing factor for side effects of GC therapy.

Reactive Oxygen Species Regulate the Inflammatory Function of NKT Cells through Promyelocytic Leukemia Zinc Finger

Reactive oxygen species (ROS) are byproducts of aerobic metabolism and contribute to both physiological and pathological conditions as second messengers. ROS are essential for activation of T cells, but how ROS influence NKT cells is unknown. In the present study, we investigated the role of ROS in NKT cell function. We found that NKT cells, but not CD4 or CD8 T cells, have dramatically high ROS in the spleen and liver of mice but not in the thymus or adipose tissues. Accordingly, ROS-high NKT cells exhibited increased susceptibility and apoptotic cell death with oxidative stress. High ROS in the peripheral NKT cells were primarily produced by NADPH oxidases and not mitochondria. We observed that sorted ROS-high NKT cells were enriched in NKT1 and NKT17 cells, whereas NKT2 cells were dominant in ROS-low cells. Furthermore, treatment of NKT cells with antioxidants led to reduced frequencies of IFN-γ- and IL-17-expressing cells, indicating that ROS play a role in regulating the inflammatory function of NKT cells. The transcription factor promyelocytic leukemia zinc finger (PLZF) seemed to control the ROS levels. NKT cells from adipose tissues that do not express PLZF and those from PLZF haplodeficient mice have low ROS. Conversely, ROS were highly elevated in CD4 T cells from mice ectopically expressing PLZF. Thus, our findings demonstrate that PLZF controls ROS levels, which in turn governs the inflammatory function of NKT cells.

ZBTB16 Gene Variability Influences Obesity-Related Parameters and Serum Lipid Levels in Czech Adults

The data derived from rat models and the preliminary results of human studies provide strong indices of involvement of common ZBTB16 variants in a range of cardiovascular and metabolic traits. This cross-sectional study in the Caucasian cohort of 1517 Czech adults aimed to verify the hypothesis that ZBTB16 gene variation directly affects obesity and serum lipid levels. Genotyping of nine polymorphisms of the ZBTB16 gene (rs11214863, rs593731, rs763857, rs2846027, rs681200, rs686989, rs661223, rs675044, rs567057) was performed. A multivariate bidirectional regression with the reduction of dimensionality (O2PLS model) revealed relationships between basal lipid levels and anthropometric parameters and some minor ZBTB16 alleles. In men, the predictors – age and presence of minor ZBTB16 alleles of rs686989, rs661223, rs675044, rs567057 – were associated with significantly higher body mass index, waist to hip ratio, body adiposity index, waist and abdominal circumferences, higher total cholesterol and LDL cholesterol and explained 20 % of variability of these variables. In women, the predictors – age and presence of the rs686989 minor T allele – were also associated with increased anthropometric parameters and total cholesterol and LDL cholesterol but the obtained O2PLS model explained only 7.8 % of the variability of the explained variables. Our study confirmed that the selected gene variants of the transcription factor ZBTB16 influence the obesity-related parameters and lipid levels. This effect was more pronounced in men.

Downregulation of Plzf Gene Ameliorates Metabolic and Cardiac Traits in the Spontaneously Hypertensive Rat

The spontaneously hypertensive rat (SHR), one of the most widely used model of essential hypertension, is predisposed to left ventricular hypertrophy, myocardial fibrosis, and metabolic disturbances. Recently, quantitative trait loci influencing blood pressure, left ventricular mass, and heart interstitial fibrosis were genetically isolated within a minimal congenic subline that contains only 7 genes, including mutant Plzf (promyelocytic leukemia zinc finger) candidate gene. To identify Plzf as a quantitative trait gene, we targeted Plzf in the SHR using the transcription activator-like effector nuclease technique and obtained SHR line harboring targeted Plzf gene with a premature stop codon. Because the Plzf targeted allele is semilethal, morphologically normal heterozygous rats were used for metabolic and hemodynamic analyses. SHR- Plzf +/− heterozygotes versus SHR wild-type controls exhibited reduced body weight and relative weight of epididymal fat, lower serum and liver triglycerides and cholesterol, and better glucose tolerance. In addition, SHR- Plzf +/− rats exhibited significantly increased sensitivity of adipose and muscle tissue to insulin action when compared with wild-type controls. Blood pressure was comparable in SHR versus SHR- Plzf +/− ; however, there was significant amelioration of cardiomyocyte hypertrophy and cardiac fibrosis in SHR- Plzf +/− rats. Gene expression profiles in the liver and expression of selected genes in the heart revealed differentially expressed genes that play a role in metabolic pathways, PPAR (peroxisome proliferator-activated receptor) signaling, and cell cycle regulation. These results provide evidence for an important role of Plzf in regulation of metabolic and cardiac traits in the rat and suggest a cross talk between cell cycle regulators, metabolism, cardiac hypertrophy, and fibrosis.

Transcriptional and Chromatin Regulation during Fasting - The Genomic Era

An elaborate metabolic response to fasting is orchestrated by the liver and is heavily reliant on transcriptional regulation. In response to hormones (glucagon, glucocorticoids) many transcription factors (TFs) are activated and regulate various genes involved in metabolic pathways aimed at restoring homeostasis: gluconeogenesis, fatty acid oxidation, ketogenesis, and amino acid shuttling. We summarize recent discoveries regarding fasting-related TFs with an emphasis on genome-wide binding patterns. Collectively, the findings we discuss reveal a large degree of cooperation between TFs during fasting that occurs at motif-rich DNA sites bound by a combination of TFs. These new findings implicate transcriptional and chromatin regulation as major determinants of the response to fasting and unravels the complex, multi-TF nature of this response.

Pharmacogenomic analysis of retinoic-acid induced dyslipidemia in congenic rat model

Background

All-trans retinoic acid (ATRA, tretinoin) is a vitamin A derivative commonly used in the treatment of diverse conditions ranging from cancer to acne. In a fraction of predisposed individuals, the administration of ATRA is accompanied by variety of adverse metabolic effects, particularly by the induction of hyperlipidemia. We have previously derived a minimal congenic SHR.PD-(D8Rat42-D8Arb23)/Cub (SHR-Lx) strain sensitive to ATRA-induced increase of triacylglycerols and cholesterol under condition of high-sucrose diet. SHR-Lx differs only by 7 genes of polydactylous rat (PD/Cub) origin from its spontaneously hypertensive rat (SHR) progenitor strain.

Methods

Adult male rats of SHR and SHR-Lx strains were fed standard diet (STD) and experimental groups were subsequently treated with ATRA (15 mg/kg) via oral gavage for 16 days, while still on STD. We contrasted the metabolic profiles (including free fatty acids, triacylglycerols (TG) and cholesterol (C) in 20 lipoprotein fractions) between SHR and SHR-Lx under conditions of standard diet and standard diet + ATRA. We performed transcriptomic analysis of muscle tissue (m. soleus) in all groups using Affymetrix GeneChip Rat Gene 2.0 ST Arrays followed by Ingenuity Pathway Analysis and real-time PCR validation.

Results

In response to ATRA, SHR-Lx reacted with substantially greater rise in TG and C concentrations throughout the lipoprotein spectrum (two-way ANOVA strain * RA interaction significant for C content in chylomicrons (CM), VLDL and LDL as well as total, CM and HDL-TG).

Conclusions

According to our modeling of metabolic and signalization pathways using differentially expressed genes we have identified a network with major nodes (including Sirt3, Il1b, Cpt1b and Pparg) likely to underlie the observed strain specific response to ATRA.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-511X-13-172) contains supplementary material, which is available to authorized users.