Regulation Of Hepatic Glucose Homeostasis Research Articles

SAT034 Exploring The Role Of Zfp664 In Hepatic Glucose Regulation

Abstract Disclosure: A. Tsay: None. J. Wang: None. Genome wide association studies (GWAS) identify the association between variants at genomic loci and common diseases. These variants consist of single nucleotide polymorphisms (SNPs), which can be localized within coding or non-coding regions. The former could affect the functions of proteins encoded by these genes. The latter could modulate the expression of genes contained or localized nearby these SNPs. Several SNPs associated with metabolic disease such as diabetes, obesity, and dyslipidemia are found in and nearby the human ZNF664 gene, which encodes a zinc finger protein that is predicted to be a transcriptional regulator. The mouse homolog of ZNF664 is Zfp664, whose amino acid sequence is identical to ZNF664. To learn whether Zfp664 contains a transcriptional activation or repression function, the expression plasmid harboring the cDNA of full length or deletion mutants of mouse Zfp664 fused to yeast GAL4 DNA binding domain (DBD) was transfected into HEK293T cells along with a luciferase reporter plasmid containing 5 copies of the GAL4 binding sites. We saw decreased luciferase activity in cells overexpressing the GAL4 DBD and full length Zfp664 fusion protein. Thus, Zfp664 acts as a transcriptional repressor. The deletion analysis identified that amino acid 7 to 95 of Zfp664 was required for its transcriptional repressive activity. To test the metabolic function of hepatic Zfp664, 8 weeks old male C57Bl/6J mice were infected with adeno-associated virus (AAV) expressing either scramble small hairpin RNA (shRNA, as a control) or shRNA targeting Zfp664 and then fed a normal chow diet or western diet (42% kcal from fat, 0.2% total cholesterol) for 12 weeks. We found that mice infected with AAV expressing Zfp664 shRNA had a lower expression of Zfp664 in the liver but not in epididymal white adipose tissue and gastrocnemius muscle. Under chow diet feeding, not only did hepatic Zfp664 knockdown not affect glucose tolerance and insulin sensitivity, but it also did not affect fasting glucose, insulin, triglyceride, and total cholesterol levels. In contrast, in mice fed a western diet, hepatic Zfp664 knockdown worsened glucose tolerance and elevated fasting insulin levels. Moreover, the expression of hepatic gluconeogenic genes, such as phosphoenolpyruvate carboxykinase (Pck1) and the catalytic subunit of glucose-6-phosphatase (G6pc), was increased. The fasting plasma triglyceride and total cholesterol levels were not affected by hepatic Zfp664 knockdown in western diet fed mice. Overall, these results discover the novel role of Zfp664 in the regulation of hepatic glucose homeostasis. Presentation: Saturday, June 17, 2023

Glycerol kinase interacts with nuclear receptor NR4A1 and regulates glucose metabolism in the liver

Glycerol kinase (Gyk), consisting of 4 isoforms, plays a critical role in metabolism by converting glycerol to glycerol 3-phosphate in an ATP-dependent reaction. Only Gyk isoform b is present in whole cells, but its function in the nucleus remains elusive. Previous studies have shown that nuclear orphan receptor subfamily 4 group A member (NR4A)-1 is an important regulator of hepatic glucose homeostasis and lipid metabolism in adipose tissue. We aimed to elucidate the functional interaction between nuclear Gyk and NR4A1 during hepatic gluconeogenesis in the unfed state and diabetes. We identified nuclear Gyk as a novel corepressor of NR4A1 in the liver; moreover, this recruitment was dependent on the C-terminal ligand-binding domain instead of the N-terminal activation function 1 domain, which interacts with other NR4A1 coregulators. NR4A1 transcriptional activity was inhibited by Gyk via protein-protein interaction but not enzymatic activity. Moreover, Gyk overexpression suppressed NR4A1 ability to regulate the expression of target genes involved in hepatic gluconeogenesis in vitro and in vivo as well as blood glucose regulation, which was observed in both unfed and diabetic mice. These results highlight the moonlighting function of nuclear Gyk, which was found to act as a coregulator of NR4A1, participating in the regulation of hepatic glucose homeostasis in the unfed state and diabetes.-Miao, L., Yang, Y., Liu, Y., Lai, L., Wang, L., Zhan, Y., Yin, R., Yu, M., Li, C., Yang, X., Ge, C. Glycerol kinase interacts with nuclear receptor NR4A1 and regulates glucose metabolism in the liver.

Inflammation Improves Glucose Homeostasis through IKKβ-XBP1s Interaction

It is widely believed that inflammation associated with obesity has an important role in the development of type 2 diabetes. IκB kinase beta (IKKβ) is a crucial kinase that responds to inflammatory stimuli such as tumor necrosis factor α (TNF-α) by initiating a variety of intracellular signaling cascades and is considered to be a key element in the inflammation-mediated development of insulin resistance. We show here, contrary to expectation, that IKKβ-mediated inflammation is a positive regulator of hepatic glucose homeostasis. IKKβ phosphorylates the spliced form of X-Box Binding Protein 1 (XBP1s) and increases the activity of XBP1s. We have used three experimental approaches to enhance the IKKβ activity in the liver of obese mice and observed increased XBP1s activity, reduced ER stress, and a significant improvement in insulin sensitivity and consequently in glucose homeostasis. Our results reveal a beneficial role of IKKβ-mediated hepatic inflammation in glucose homeostasis.

Inositol 1,4,5-trisphosphate receptor type II (InsP3R-II) is reduced in obese mice, but metabolic homeostasis is preserved in mice lacking InsP3R-II.

Inositol 1,4,5-trisphosphate receptor type II (InsP3R-II) is the most prevalent isoform of the InsP3R in hepatocytes and is concentrated under the canalicular membrane, where it plays an important role in bile secretion. We hypothesized that altered calcium (Ca(2+)) signaling may be involved in metabolic dysfunction, as InsP3R-mediated Ca(2+) signals have been implicated in the regulation of hepatic glucose homeostasis. Here, we find that InsP3R-II, but not InsP3R-I, is reduced in the livers of obese mice. In our investigation of the functional consequences of InsP3R-II deficiency, we found that organic anion secretion at the canalicular membrane and Ca(2+) signals were impaired. However, mice lacking InsP3R-II showed no deficits in energy balance, glucose production, glucose tolerance, or susceptibility to hepatic steatosis. Thus, our results suggest that reduced InsP3R-II expression is not sufficient to account for any disruptions in metabolic homeostasis that are observed in mouse models of obesity. We conclude that metabolic homeostasis is maintained independently of InsP3R-II. Loss of InsP3R-II does impair secretion of bile components; therefore, we suggest that conditions of obesity would lead to a decrease in this Ca(2+)-sensitive process.

B-Cell Translocation Gene 2 Regulates Hepatic Glucose Homeostasis via Induction of Orphan Nuclear Receptor Nur77 in Diabetic Mouse Model

B-cell translocation gene 2 (BTG2) is a member of an emerging gene family that is involved in cellular functions. In this study, we demonstrate that BTG2 regulates glucose homeostasis via upregulation of Nur77 in diabetic mice. Hepatic BTG2 gene expression was elevated by fasting and forskolin. Overexpression of Btg2 increased the expression of hepatic gluconeogenic genes and blood glucose output and subsequently impaired glucose and insulin tolerance. Upregulation of the transcriptional activity of Nur77, gluconeogenic genes, and glucose production by forskolin was observed by Btg2 transduction, but not in Btg2 knockdown. BTG2-stimulated glucose production and glucose-6-phosphatase promoter activity were attenuated by dominant-negative Nur77. Coimmunoprecipitation and chromatin immunoprecipitation assays showed that BTG2 induced Nur77 occupancy on the glucose-6-phosphatase promoter via a physical interaction. Btg2 gene expression was increased in streptozotocin-treated and db/db mice. Finally, impairment of glucose homeostasis, such as the increase of blood glucose, glucose intolerance, and insulin intolerance, was elevated in diabetic mice, whereas this phenomenon was abolished in knockdown of Btg2. Together, these data suggest that BTG2 participates in the regulation of hepatic glucose homeostasis, which means that BTG2 might serve as a potential therapeutic target for combating metabolic dysfunction.

Hepatic expression and cellular distribution of the glucose transporter family

Glucose and other carbohydrates are transported into cells using members of a family of integral membrane glucose transporter (GLUT) molecules. To date 14 members of this family, also called the solute carrier 2A proteins have been identified which are divided on the basis of transport characteristics and sequence similarities into several families (Classes 1 to 3). The expression of these different receptor subtypes varies between different species, tissues and cellular subtypes and each has differential sensitivities to stimuli such as insulin. The liver is a contributor to metabolic carbohydrate homeostasis and is a major site for synthesis, storage and redistribution of carbohydrates. Situations in which the balance of glucose homeostasis is upset such as diabetes or the metabolic syndrome can lead metabolic disturbances that drive chronic organ damage and failure, confirming the importance of understanding the molecular regulation of hepatic glucose homeostasis. There is a considerable literature describing the expression and function of receptors that regulate glucose uptake and release by hepatocytes, the most import cells in glucose regulation and glycogen storage. However there is less appreciation of the roles of GLUTs expressed by non parenchymal cell types within the liver, all of which require carbohydrate to function. A better understanding of the detailed cellular distribution of GLUTs in human liver tissue may shed light on mechanisms underlying disease pathogenesis. This review summarises the available literature on hepatocellular expression of GLUTs in health and disease and highlights areas where further investigation is required.

Control of Adipose Tissue Inflammation Through TRB1

OBJECTIVEBased on its role as an energy storage compartment and endocrine organ, white adipose tissue (WAT) fulfills a critical function in the maintenance of whole-body energy homeostasis. Indeed, WAT dysfunction is connected to obesity-related type 2 diabetes triggered at least partly by an inflammatory response in adipocytes. The pseudokinase tribbles (TRB) 3 has been identified by us and others as a critical regulator of hepatic glucose homeostasis in type 2 diabetes and WAT lipid homeostasis. Therefore, this study aimed to test the hypothesis that the TRB gene family fulfills broader functions in the integration of metabolic and inflammatory pathways in various tissues.RESEARCH DESIGN AND METHODSTo determine the role of TRB family members for WAT function, we profiled the expression patterns of TRB13 under healthy and metabolic stress conditions. The differentially expressed TRB1 was functionally characterized in loss-of-function animal and primary adipocyte models.RESULTSHere, we show that the expression of TRB1 was specifically upregulated during acute and chronic inflammation in WAT of mice. Deficiency of TRB1 was found to impair cytokine gene expression in white adipocytes and to protect against high-fat diet–induced obesity. In adipocytes, TRB1 served as a nuclear transcriptional coactivator for the nuclear factor κB subunit RelA, thereby promoting the induction of proinflammatory cytokines in these cells.CONCLUSIONSAs inflammation is typically seen in sepsis, insulin resistance, and obesity-related type 2 diabetes, the dual role of TRB1 as both a target and a (co) activator of inflammatory signaling might provide a molecular rationale for the amplification of proinflammatory responses in WAT in these subjects.

Sodium arsenite induces orphan nuclear receptor SHP gene expression via AMP-activated protein kinase to inhibit gluconeogenic enzyme gene expression

Sodium arsenite has been demonstrated to alter the expression of genes associated with glucose homeostasis in tissues involved in the pathogenesis of type 2 diabetes; however, the underlying molecular mechanism has not been fully elucidated yet. In this study, we report that the sodium arsenite-induced gene expression of the small heterodimer partner (SHP; NR0B2), an atypical orphan nuclear receptor, regulates the expression of hepatic gluconeogenic genes. Sodium arsenite augments hepatic SHP mRNA levels in an AMP-activated protein kinase (AMPK)-dependent manner. Sodium arsenite activated AMPK and was shown to perturb cellular ATP levels. The arsenite-induced SHP mRNA level was blocked by adenoviral overexpression of dominant negative AMPK (Ad-dnAMPKalpha) or by the AMPK inhibitor compound C in hepatic cell lines. We demonstrated the dose-dependent induction of SHP mRNA levels by sodium arsenite and repressed the forskolin/dexamethasone-induced gene expression of the key hepatic gluconeogenic genes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase). Ad-dnAMPKalpha blocked the repressive effects of arsenite-induced SHP on PEPCK and G6Pase. Sodium arsenite inhibited the promoter activity of PEPCK and G6Pase, and this repression was abolished by small interfering (si)RNA SHP treatments. The knockdown of SHP expression by oligonucleotide siRNA SHP or adenoviral siRNA SHP released the sodium arsenite-mediated repression of forskolin/dexamethasone-stimulated PEPCK and G6Pase gene expression in a variety of hepatic cell lines. Results from our study suggest that sodium arsenite induces SHP via AMPK to inhibit the expression of hepatic gluconeogenic genes and also provide us with a novel molecular mechanism of arsenite-mediated regulation of hepatic glucose homeostasis.