FoxO1 deacetylation regulates thyroid hormone-induced transcription of key hepatic gluconeogenic genes

Metabolic Messengers: Thyroid Hormones

Thyroid hormones (THs) are key hormones that regulate development and metabolism in mammals. In man, the major target tissues for TH action are the brain, liver, muscle, heart, and adipose tissue. Defects in TH synthesis, transport, metabolism, and nuclear action have been associated with genetic and endocrine diseases in man. Over the past few years, there has been renewed interest in TH action and the therapeutic potential of THs and thyromimetics to treat several metabolic disorders such as hypercholesterolemia, dyslipidaemia, non-alcoholic fatty liver disease (NAFLD), and TH transporter defects. Recent advances in the development of tissue and TH receptor isoform-targeted thyromimetics have kindled new hope for translating our fundamental understanding of TH action into an effective therapy. This review provides a concise overview of the historical development of our understanding of TH action, its physiological and pathophysiological effects on metabolism, and future therapeutic applications to treat metabolic dysfunction.

Understanding the Relationship between Nonalcoholic Fatty Liver Disease and Thyroid Disease

The prevalence of hypothyroidism in patients with nonalcoholic fatty liver disease (NAFLD) is high (22.4%). Thyroid hormones (THs) regulate many metabolic activities in the liver by promoting the export and oxidation of lipids, as well as de novo lipogenesis. They also control hepatic insulin sensitivity and suppress hepatic gluconeogenesis. Because of its importance in lipid and carbohydrate metabolism, the involvement of thyroid dysfunction in the pathogenesis of NAFLD seems plausible. The mechanisms implicated in this relationship include high thyroid-stimulating hormone (TSH) levels, low TH levels, and chronic inflammation. The activity of the TH receptor (THR)-β in response to THs is essential in the pathogenesis of hypothyroidism-induced NAFLD. Therefore, an orally active selective liver THR-β agonist, Resmetirom (MGL-3196), was developed, and has been shown to reduce liver fat content, and as a secondary end point, to improve nonalcoholic steatohepatitis. The treatment of NAFLD with THR-β agonists seems quite promising, and other agonists are currently under development and investigation. This review aims to shine a light on the pathophysiological and epidemiological evidence regarding this relationship and the effect that treatment with THs and selective liver THR-β agonists have on hepatic lipid metabolism.

Thyroid hormone action and liver disease, a complex interplay

Thyroid hormone action is involved in virtually all physiological processes. It is well known that the liver and thyroid are intimately linked, with thyroid hormone playing important roles in de novo lipogenesis, beta-oxidation (fatty acid oxidation), cholesterol metabolism, and carbohydrate metabolism. Clinical and mechanistic research studies have shown that thyroid hormone can be involved in chronic liver diseases, including alcohol-associated or NAFLD and HCC. Thyroid hormone action and synthetic thyroid hormone analogs can exert beneficial actions in terms of lowering lipids, preventing chronic liver disease and as liver anticancer agents. More recently, preclinical and clinical studies have indicated that some analogs of thyroid hormone could also play a role in the treatment of liver disease. These synthetic molecules, thyromimetics, can modulate lipid metabolism, particularly in NAFLD/NASH. In this review, we first summarize the thyroid hormone signaling axis in the context of liver biology, then we describe the changes in thyroid hormone signaling in liver disease and how liver diseases affect the thyroid hormone homeostasis, and finally we discuss the use of thyroid hormone-analog for the treatment of liver disease.

Triiodothyronine positively regulates endoplasmic reticulum-associated degradation (ERAD) and promotes androgenic signaling in androgen-dependent prostate cancer cells

Thyroid hormones (THs) play crucial roles in numerous physiological processes of nearly all mammalian tissues, including differentiation and metabolism. Deterioration of TH signaling has been associated with several pathologies, including cancer. The effect of highly active triiodothyronine (T3) has been investigated in many in vivo and in vitro cancer models. However, the role of T3 on cancerous prostate tissue is controversial. Recent studies have focused on the characterization of the supportive roles of the endoplasmic reticulum-associated degradation (ERAD) and unfolded protein response (UPR) signaling in prostate cancer (PCa) and investigating new hormonal regulation patterns, including estrogen, progesterone and 1,25(OH)₂D₃. Additionally, androgenic signaling controlled by androgens, which are critical in PCa progression, has been shown to be regulated by other steroid hormones. While the effects of T3 on ERAD and UPR are unknown today, the impact on androgenic signaling is still not understood in PCa. Therefore, we aimed to investigate the molecular action of T3 on the ERAD mechanism and UPR signaling in PCa cells and also extensively examined the effect of T3 on androgenic signaling. Our data strongly indicated that T3 tightly regulates ERAD and UPR signaling in androgen-dependent PCa cells. We also found that T3 stimulates androgenic signaling by upregulating AR mRNA and protein levels and enhancing its nuclear translocation. Additionally, advanced computational studies supported the ligand binding effect of T3 on AR protein. Our data suggest that targeting thyroidal signaling should be considered in therapeutic approaches to be developed for prostate malignancy in addition to other steroidal regulations.

Dietary Succinate Impacts the Nutritional Metabolism, Protein Succinylation and Gut Microbiota of Zebrafish

Succinate is widely used in the food and feed industry as an acidulant, flavoring additive, and antimicrobial agent. This study investigated the effects of dietary succinate on growth, energy budget, nutritional metabolism, protein succinylation, and gut microbiota composition of zebrafish. Zebrafish were fed a control-check (0% succinate) or four succinate-supplemented diets (0.05, 0.10, 0.15, and 0.2%) for 4 weeks. The results showed that dietary succinate at the 0.15% additive amount (S0.15) can optimally promote weight gain and feed intake. Whole body protein, fat, and energy deposition increased in the S0.15 group. Fasting plasma glucose level decreased in fish fed the S0.15 diet, along with improved glucose tolerance. Lipid synthesis in the intestine, liver, and muscle increased with S0.15 feeding. Diet with 0.15% succinate inhibited intestinal gluconeogenesis but promoted hepatic gluconeogenesis. Glycogen synthesis increased in the liver and muscle of S0.15-fed fish. Glycolysis was increased in the muscle of S0.15-fed fish. In addition, 0.15% succinate-supplemented diet inhibited protein degradation in the intestine, liver, and muscle. Interestingly, different protein succinylation patterns in the intestine and liver were observed in fish fed the S0.15 diet. Intestinal proteins with increased succinylation levels were enriched in the tricarboxylic acid cycle while proteins with decreased succinylation levels were enriched in pathways related to fatty acid and amino acid degradation. Hepatic proteins with increased succinylation levels were enriched in oxidative phosphorylation while proteins with decreased succinylation levels were enriched in the processes of protein processing and transport in the endoplasmic reticulum. Finally, fish fed the S0.15 diet had a higher abundance of Proteobacteria but a lower abundance of Fusobacteria and Cetobacterium. In conclusion, dietary succinate could promote growth and feed intake, promote lipid anabolism, improve glucose homeostasis, and spare protein. The effects of succinate on nutritional metabolism are associated with alterations in the levels of metabolic intermediates, transcriptional regulation, and protein succinylation levels. However, hepatic fat accumulation and gut microbiota dysbiosis induced by dietary succinate suggest potential risks of succinate application as a feed additive for fish. This study would be beneficial in understanding the application of succinate as an aquatic feed additive.

The Transplantation Resistance of Type II Diabetes Mellitus Adipose-Derived Stem Cells Is Due to G6PC and IGF1 Genes Related to the FoxO Signaling Pathway

In cases of patients with rapidly progressive diabetes mellitus (DM), autologous stem cell transplantation is considered as one of the regenerative treatments. However, whether the effects of autonomous stem cell transplantation on DM patients are equivalent to transplantation of stem cells derived from healthy persons is unclear. This study revealed that adipose-derived mesenchymal stem cells (ADSC) derived from type II DM patients had lower transplantation efficiency, proliferation potency, and stemness than those derived from healthy persons, leading to a tendency to induce apoptotic cell death. To address this issue, we conducted a cyclopedic mRNA analysis using a next-generation sequencer and identified G6PC3 and IGF1, genes related to the FoxO signaling pathway, as the genes responsible for lower performance. Moreover, it was demonstrated that the lower transplantation efficiency of ADSCs derived from type II DM patients might be improved by knocking down both G6PC3 and IGF1 genes. This study clarified the difference in transplantation efficiency between ADSCs derived from type II DM patients and those derived from healthy persons and the genes responsible for the lower performance of the former. These results can provide a new strategy for stabilizing the quality of stem cells and improving the therapeutic effects of regenerative treatments on autonomous stem cell transplantation in patients with DM.

Regulation of Cancer Metabolism by Deubiquitinating Enzymes: The Warburg Effect

Cancer is a disorder of cell growth and proliferation, characterized by different metabolic pathways within normal cells. The Warburg effect is a major metabolic process in cancer cells that affects the cellular responses, such as proliferation and apoptosis. Various signaling factors down/upregulate factors of the glycolysis pathway in cancer cells, and these signaling factors are ubiquitinated/deubiquitinated via the ubiquitin-proteasome system (UPS). Depending on the target protein, DUBs act as both an oncoprotein and a tumor suppressor. Since the degradation of tumor suppressors and stabilization of oncoproteins by either negative regulation by E3 ligases or positive regulation of DUBs, respectively, promote tumorigenesis, it is necessary to suppress these DUBs by applying appropriate inhibitors or small molecules. Therefore, we propose that the DUBs and their inhibitors related to the Warburg effect are potential anticancer targets.

Thyroid Hormone-Regulated Expression of Period2 Promotes Liver Urate Production

The relationship between thyroid hormones and serum urate is unclear. Our aim is to analyze the correlation between uric acid and thyroid hormones in gout patients and to explore the effect and mechanism of triiodothyronine on liver uric acid production. Eighty men patients with gout were selected to analyze the correlation between blood urate and thyroid function-related hormone levels. Stepwise multiple linear regression was used to analyze factors affecting blood urate in patients with gout. Levels of urate in serum, liver, and cell culture supernatant were measured after triiodothyronine treatment. Purine levels (adenine, guanine, and hypoxanthine) were also measured. Expression levels of Period2 and nucleotide metabolism enzymes were analyzed after triiodothyronine treatment and Period2-shRNA lentivirus transduction. Chromatin immunoprecipitation was used to analyze the effects of triiodothyronine and thyroid hormone receptor-β on Period2 expression. The results showed that in patients FT3 influenced the serum urate level. Furthermore, urate level increased in mouse liver and cell culture supernatant following treatment with triiodothyronine. Purine levels in mouse liver increased, accompanied by upregulation of enzymes involved in nucleotide metabolism. These phenomena were reversed in Period2 knockout mice. Triiodothyronine promoted the binding of thyroid hormone receptor-β to the Period2 promoter and subsequent transcription of Period2. Triiodothyronine also enhanced nuclear expression of Sirt1, which synergistically enhanced Period2 expression. The study demonstrated that triiodothyronine is independently positively correlated with serum urate and liver uric acid production through Period2, providing novel insights into the purine metabolism underlying hyperuricemia/gout pathophysiology.

Exploring the Genetic Conception of Obesity via the Dual Role of FoxO

Obesity or overweight are not superficial problems, constituting a pressing issue. The obesity index has almost tripled since 1975, which is an alarming state. Most of the individuals are currently becoming overweight or have inappropriate body mass index (BMI) conditions. Obesity is characterized by increased fat accumulation and thus poses a higher health risk. There is increased size and volume of fat cells in the body, which usually accounts for obesity. Many investigations have been carried out in this area, such as behavioral improvements, dietary changes, chemical involvements, etc., but presently no such goals are established to manage these health concerns. Based on previous literature reports and our interpretation, the current review indicates the involvement of various transcriptional and transporter functions in modifying the above-mentioned health conditions. Various transcriptional factors such as Forkhead box O1 (FoxO1) impart a significant effect on the physiology and pathology of metabolic dysfunction such as obesity. FoxO1 plays a dual role whether in the progression or suppression of metabolic processes depending on its targets. Thus, in the current study, will be discussed the dual role of FoxO1 in metabolic conditions (such as obesity), also summarizing the role of various other transcriptional factors involved in obesity.

Exploring the Genetic Conception of Obesity via the Dual Role of FoxO

Obesity or overweight are not superficial problems, constituting a pressing issue. The obesity index has almost tripled since 1975, which is an alarming state. Most of the individuals are currently becoming overweight or have inappropriate body mass index (BMI) conditions. Obesity is characterized by increased fat accumulation and thus poses a higher health risk. There is increased size and volume of fat cells in the body, which usually accounts for obesity. Many investigations have been carried out in this area, such as behavioral improvements, dietary changes, chemical involvements, etc., but presently no such goals are established to manage these health concerns. Based on previous literature reports and our interpretation, the current review indicates the involvement of various transcriptional and transporter functions in modifying the above-mentioned health conditions. Various transcriptional factors such as Forkhead box O1 (FoxO1) impart a significant effect on the physiology and pathology of metabolic dysfunction such as obesity. FoxO1 plays a dual role whether in the progression or suppression of metabolic processes depending on its targets. Thus, in the current study, will be discussed the dual role of FoxO1 in metabolic conditions (such as obesity), also summarizing the role of various other transcriptional factors involved in obesity.

Sirt1-PPARS Cross-Talk in Complex Metabolic Diseases and Inherited Disorders of the One Carbon Metabolism

Sirtuin1 (Sirt1) has a NAD (+) binding domain and modulates the acetylation status of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α) and Fork Head Box O1 transcription factor (Foxo1) according to the nutritional status. Sirt1 is decreased in obese patients and increased in weight loss. Its decreased expression explains part of the pathomechanisms of the metabolic syndrome, diabetes mellitus type 2 (DT2), cardiovascular diseases and nonalcoholic liver disease. Sirt1 plays an important role in the differentiation of adipocytes and in insulin signaling regulated by Foxo1 and phosphatidylinositol 3′-kinase (PI3K) signaling. Its overexpression attenuates inflammation and macrophage infiltration induced by a high fat diet. Its decreased expression plays a prominent role in the heart, liver and brain of rat as manifestations of fetal programming produced by deficit in vitamin B12 and folate during pregnancy and lactation through imbalanced methylation/acetylation of PGC1α and altered expression and methylation of nuclear receptors. The decreased expression of Sirt1 produced by impaired cellular availability of vitamin B12 results from endoplasmic reticulum stress through subcellular mislocalization of ELAVL1/HuR protein that shuttles Sirt1 mRNA between the nucleus and cytoplasm. Preclinical and clinical studies of Sirt1 agonists have produced contrasted results in the treatment of the metabolic syndrome. A preclinical study has produced promising results in the treatment of inherited disorders of vitamin B12 metabolism.

Gestational hypothyroidism elicits more pronounced lipid dysregulation in mice than pre-pregnant hypothyroidism

Thyroid hormone is crucial for regulating lipid and glucose metabolism, which plays essential role in maintaining the health of pregnant women and their offspring. However, the current literature is just focusing on the development of offspring born to the untreated mothers with hypothyroidism, rather than mothers themselves. Additionally, the interaction between hypothyroidism and pregnancy, and its impact on the women's health are still elusive. Therefore, this study was designed to compare the metabolic differences in dams with hypothyroidism starting before pregnancy and after pregnancy. Pre-pregnant hypothyroidism was generated in 5-week-old female C57/BL/6J mice using iodine-deficient diet containing 0.15% propylthiouracil for 4 weeks, and the hypothyroidism was maintained until delivery. Gestational hypothyroidism was induced in dams after mating, using the same diet intervention until delivery. Compared with normal control, gestational hypothyroidism exhibited more prominent increase than pre-pregnant hypothyroidism in plasma total cholesterol and low-density lipoprotein cholesterol, and caused hepatic triglycerides accumulation. Similarly, more significant elevations of protein expressions of SREBP1c and p-ACL, while more dramatic inhibition of CPT1A and LDL-R levels were also observed in murine livers with gestational hypothyroidism than those with pre-pregnant hypothyroidism. Moreover, the murine hepatic levels of total cholesterol and gluconeogenesis were dramatically and equally enhanced in two hypothyroid groups, while plasma triglycerides and protein expressions of p-AKT, p-FoxO1 and APOC3 were reduced substantially in two hypothyroid groups. Taken together, our current study illuminated that gestational hypothyroidism may elicit more pronounced lipid dysregulation in dams than dose the pre-pregnant hypothyroidism.

FoxO1-Dio2 signaling axis governs cardiomyocyte thyroid hormone metabolism and hypertrophic growth

Forkhead box O (FoxO) proteins and thyroid hormone (TH) have well established roles in cardiovascular morphogenesis and remodeling. However, specific role(s) of individual FoxO family members in stress-induced growth and remodeling of cardiomyocytes remains unknown. Here, we report that FoxO1, but not FoxO3, activity is essential for reciprocal regulation of types II and III iodothyronine deiodinases (Dio2 and Dio3, respectively), key enzymes involved in intracellular TH metabolism. We further show that Dio2 is a direct transcriptional target of FoxO1, and the FoxO1-Dio2 axis governs TH-induced hypertrophic growth of neonatal cardiomyocytes in vitro and in vivo. Utilizing transverse aortic constriction as a model of hemodynamic stress in wild-type and cardiomyocyte-restricted FoxO1 knockout mice, we unveil an essential role for the FoxO1-Dio2 axis in afterload-induced pathological cardiac remodeling and activation of TRα1. These findings demonstrate a previously unrecognized FoxO1-Dio2 signaling axis in stress-induced cardiomyocyte growth and remodeling and intracellular TH homeostasis.

N1-Methylnicotinamide Improves Hepatic Insulin Sensitivity via Activation of SIRT1 and Inhibition of FOXO1 Acetylation

OBJECTIVE

To explore the effects of N¹-methylnicotinamide (MNAM) on insulin resistance and glucose metabolism in obese type 2 diabetes mellitus (T2DM) mice and regulatory mechanisms of the NAD-dependent deacetylase sirtuin-1 (SIRT1)/forkhead box protein O1 (FOXO1) pathway.

METHODS

Blood glucose and insulin levels were examined in mice. HE and oil red O staining were used to observe the effects of MNAM on liver lipid deposition in ob/ob mice. Real-time PCR and Western blotting were used to detect expression of gluconeogenesis, insulin signaling-related proteins, and SIRT1/FOXO1 pathway-related proteins. L-O2 cells were cultured as a model of insulin resistance, and MNAM and SIRT1 inhibitors were administered in vivo. Residual glucose and insulin signaling-related proteins were detected and the mechanisms associated with the SIRT1/FOXO1 signaling pathway in insulin resistance explored.

RESULTS

MNAM can effectively reduce levels of fasting blood glucose and insulin, improve liver morphology, and reduce lipid accumulation in obese type 2 diabetes mellitus mice. MNAM also downregulates the key proteins in the gluconeogenesis pathway in the liver, upregulates Sirt1 expression, and reduces acetylation of the FOXO1 protein. In vitro, MNAM could promote the glucose uptake capacity of L-O2 cells induced by palmitic acid (PA), a saturated fatty acid that induces IR in various scenarios, including hepatocytes, improving insulin resistance. As Sirt1 expression was inhibited, the reduction of hepatocyte gluconeogenesis and the regulation of the insulin signaling pathway by MNAM were reversed.

CONCLUSION

MNAM activates SIRT1 and inhibits acetylation of FOXO1, which in turn regulates insulin sensitivity in type 2 diabetic mice, leading to a reduction of hepatic glucose output and improvement of insulin resistance.

Growth Factor-Dependent and -Independent Activation of mTORC2

The target of rapamycin complex 2 (TORC2) was discovered in 2002 in budding yeast. Its mammalian counterpart, mTORC2, was first described in 2004. Soon thereafter it was demonstrated that mTORC2 directly phosphorylates Akt on Ser473, ending a long search for the elusive 'second' insulin-responsive Akt kinase. In this review we discuss key evidence pertaining to the subcellular localization of mTORC2, highlighting a spatial heterogeneity that relates to mTORC2 activation. We summarize current models for how growth factors (GFs), such as insulin, trigger mTORC2 activation, and we provide a comprehensive discussion focusing on a new exciting frontier, the molecular mechanisms underpinning GF-independent activation of mTORC2.

Thyroid hormone signaling and consequences for cardiac development

The fetal heart undergoes its own growth and maturation stages all while supplying blood and nutrients to the growing fetus and its organs. Immature contractile cardiomyocytes proliferate to rapidly increase and establish cardiomyocyte endowment in the perinatal period. Maturational changes in cellular maturation, size and biochemical capabilities occur, and require, a changing hormonal environment as the fetus prepares itself for the transition to extrauterine life. Thyroid hormone has long been known to be important for neuronal development, but also for fetal size and survival. Fetal circulating 3,5,3'-triiodothyronine (T3) levels surge near term in mammals and are responsible for maturation of several organ systems, including the heart. Growth factors like insulin-like growth factor-1 stimulate proliferation of fetal cardiomyocytes, while thyroid hormone has been shown to inhibit proliferation and drive maturation of the cells. Several cell signaling pathways appear to be involved in this complicated and coordinated process. The aim of this review was to discuss the foundational studies of thyroid hormone physiology and the mechanisms responsible for its actions as we speculate on potential fetal programming effects for cardiovascular health.

Molecular functions and clinical impact of thyroid hormone-triggered autophagy in liver-related diseases

The liver is controlled by several metabolic hormones, including thyroid hormone, and characteristically displays high lysosomal activity as well as metabolic stress-triggered autophagy, which is stringently regulated by the levels of hormones and metabolites. Hepatic autophagy provides energy through catabolism of glucose, amino acids and free fatty acids for starved cells, facilitating the generation of new macromolecules and maintenance of the quantity and quality of cellular organelles, such as mitochondria. Dysregulation of autophagy and defective mitochondrial homeostasis contribute to hepatocyte injury and liver-related diseases, such as non-alcoholic fatty liver disease (NAFLD) and liver cancer.

Thyroid hormones (TH) mediate several critical physiological processes including organ development, cell differentiation, metabolism and cell growth and maintenance. Accumulating evidence has revealed dysregulation of cellular TH activity as the underlying cause of several liver-related diseases, including alcoholic or non-alcoholic fatty liver disease and liver cancer. Data from epidemiologic, animal and clinical studies collectively support preventive functions of THs in liver-related diseases, highlighting the therapeutic potential of TH analogs. Elucidation of the molecular mechanisms and downstream targets of TH should thus facilitate the development of therapeutic strategies for a number of major public health issues.

Here, we have reviewed recent studies focusing on the involvement of THs in hepatic homeostasis through induction of autophagy and their implications in liver-related diseases. Additionally, the potential underlying molecular pathways and therapeutic applications of THs in NAFLD and HCC are discussed.

Activation of SIRT1 by L-serine increases fatty acid oxidation and reverses insulin resistance in C2C12 myotubes

Silent information regulator 1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD⁺)-dependent deacetylase, and the function is linked to cellular metabolism including mitochondrial biogenesis. Hepatic L-serine concentration is decreased significantly in fatty liver disease. We reported that the supplementation of the amino acid ameliorated the alcoholic fatty liver by enhancing L-serine-dependent homocysteine metabolism. In this study, we hypothesized that the metabolic production of NAD⁺ from L-serine and thus activation of SIRT1 contribute to the action of L-serine. To this end, we evaluated the effects of L-serine on SIRT1 activity and mitochondria biogenesis in C2C12 myotubes. L-Serine increased intracellular NAD⁺ content and led to the activation of SIRT1 as determined by p53 luciferase assay and western blot analysis of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) acetylation. L-Serine treatment increased the expression of the genes associated with mitochondrial biogenesis and enhanced mitochondrial mass and function. In addition, L-serine reversed cellular insulin resistance determined by insulin-induced phosphorylation of Akt and GLUT4 expression and membrane translocation. L-Serine-induced mitochondrial gene expression, fatty acid oxidation, and insulin sensitization were mediated by enhanced SIRT1 activity, which was verified by selective SIRT1 inhibitor (Ex-527) and siRNA directed to SIRT1. L-Serine effect on cellular NAD⁺ level is dependent on the L-serine metabolism to pyruvate that is subsequently converted to lactate by lactate dehydrogenase. In summary, these data suggest that L-serine increases cellular NAD⁺ level and thus SIRT1 activity in C2C12 myotubes.

Expression of S100A8 is induced by interleukin‑1α in TR146 epithelial cells through a mechanism involving CCAAT/enhancer binding protein β

Calprotectin in mucosal epidermal keratinocytes has an important role in fighting microbial infections. S100A8 belongs to the S100 protein family and is a subunit of calprotectin (heterodimer complex of S100A8/A9). Interleukin‑1α (IL‑1α) is one of the cytokines produced by oral keratinocytes. The primary aims of the present study were to investigate the effect of IL‑1α on the expression of S100A8 and its underlying molecular mechanism in oral epithelial cells. Determining the molecular mechanism of the induced expression of S100A8 by IL‑1α aims to improve current understanding of the roles of calprotectin during the infection of mucosal epithelial cells. The expression analysis indicated that IL‑1α significantly induced the expression of S100A8 in human TR146 epithelial cells at the mRNA and protein levels, respectively. The reporter assay demonstrated that the upregulatory effect of S100A8 induced by IL‑1α was dependent on the S100A8 promoter specific region (‑165/‑111). The results of electrophoresis mobility shift assay and chromatin immunoprecipitation assay also demonstrated that the CCAAT/enhancer binding protein β (C/EBPβ) binding site (‑113/‑109) in the S100A8 promoter region was involved into the upregulatory effect on the expression of S100A8 induced by IL‑1α. Taken together, these results suggested that the activation of the expression of S100A8 induced by IL‑1α in TR146 epithelial cells involves a mechanism by which the binding activity of C/EBPβ to the specific site (‑113/‑109) of the S100A8 promoter is increased.

Molecular Mechanisms and Signaling Pathways Involved in Sertoli Cell Proliferation

Sertoli cells are somatic cells present in seminiferous tubules which have essential roles in regulating spermatogenesis. Considering that each Sertoli cell is able to support a limited number of germ cells, the final number of Sertoli cells reached during the proliferative period determines sperm production capacity. Only immature Sertoli cells, which have not established the blood-testis barrier, proliferate. A number of hormonal cues regulate Sertoli cell proliferation. Among them, FSH, the insulin family of growth factors, activin, and cytokines action must be highlighted. It has been demonstrated that cAMP/PKA, ERK1/2, PI3K/Akt, and mTORC1/p70SK6 pathways are the main signal transduction pathways involved in Sertoli cell proliferation. Additionally, c-Myc and hypoxia inducible factor are transcription factors which participate in the induction by FSH of various genes of relevance in cell cycle progression. Cessation of proliferation is a pre-requisite to Sertoli cell maturation accompanied by the establishment of the blood-testis barrier. With respect to this barrier, the participation of androgens, estrogens, thyroid hormones, retinoic acid and opioids has been reported. Additionally, two central enzymes that are involved in sensing cell energy status have been associated with the suppression of Sertoli cell proliferation, namely AMPK and Sirtuin 1 (SIRT1). Among the molecular mechanisms involved in the cessation of proliferation and in the maturation of Sertoli cells, it is worth mentioning the up-regulation of the cell cycle inhibitors p21Cip1, p27Kip, and p19INK4, and of the gap junction protein connexin 43. A decrease in Sertoli cell proliferation due to administration of certain therapeutic drugs and exposure to xenobiotic agents before puberty has been experimentally demonstrated. This review focuses on the hormones, locally produced factors, signal transduction pathways, and molecular mechanisms controlling Sertoli cell proliferation and maturation. The comprehension of how the final number of Sertoli cells in adulthood is established constitutes a pre-requisite to understand the underlying causes responsible for the progressive decrease in sperm production that has been observed during the last 50 years in humans.

Novel Transcriptional Mechanisms for Regulating Metabolism by Thyroid Hormone

The thyroid hormone plays a key role in energy and nutrient metabolisms in many tissues and regulates the transcription of key genes in metabolic pathways. It has long been believed that thyroid hormones (THs) exerted their effects primarily by binding to nuclear TH receptors (THRs) that are associated with conserved thyroid hormone response elements (TREs) located on the promoters of target genes. However, recent transcriptome and ChIP-Seq studies have challenged this conventional view as discordance was observed between TH-responsive genes and THR binding to DNA. While THR association with other transcription factors bound to DNA, TH activation of THRs to mediate effects that do not involve DNA-binding, or TH binding to proteins other than THRs have been invoked as potential mechanisms to explain this discrepancy, it appears that additional novel mechanisms may enable TH to regulate the mRNA expression. These include activation of transcription factors by SIRT1 via metabolic actions by TH, the post-translational modification of THR, the THR co-regulation of transcription with other nuclear receptors and transcription factors, and the microRNA (miR) control of RNA transcript expression to encode proteins involved in the cellular metabolism. Together, these novel mechanisms enlarge and diversify the panoply of metabolic genes that can be regulated by TH.

Thyroid hormone receptor and ERRα coordinately regulate mitochondrial fission, mitophagy, biogenesis, and function

Thyroid hormone receptor β1 (THRB1) and estrogen-related receptor α (ESRRA; also known as ERRα) both play important roles in mitochondrial activity. To understand their potential interactions, we performed transcriptome and ChIP-seq analyses and found that many genes that were co-regulated by both THRB1 and ESRRA were involved in mitochondrial metabolic pathways. These included oxidative phosphorylation (OXPHOS), the tricarboxylic acid (TCA) cycle, and β-oxidation of fatty acids. TH increased ESRRA expression and activity in a THRB1-dependent manner through the induction of the transcriptional coactivator PPARGC1A (also known as PGC1α). Moreover, TH induced mitochondrial biogenesis, fission, and mitophagy in an ESRRA-dependent manner. TH also induced the expression of the autophagy-regulating kinase ULK1 through ESRRA, which then promoted DRP1-mediated mitochondrial fission. In addition, ULK1 activated the docking receptor protein FUNDC1 and its interaction with the autophagosomal protein MAP1LC3B-II to induce mitophagy. siRNA knockdown of ESRRA, ULK1, DRP1, or FUNDC1 inhibited TH-induced autophagic clearance of mitochondria through mitophagy and decreased OXPHOS. These findings show that many of the mitochondrial actions of TH are mediated through stimulation of ESRRA expression and activity, and co-regulation of mitochondrial turnover through the PPARGC1A-ESRRA-ULK1 pathway is mediated by their regulation of mitochondrial fission and mitophagy. Hormonal or pharmacologic induction of ESRRA expression or activity could improve mitochondrial quality in metabolic disorders.

Direct effects of thyroid hormones on hepatic lipid metabolism

It has been known for a long time that thyroid hormones have prominent effects on hepatic fatty acid and cholesterol synthesis and metabolism. Indeed, hypothyroidism has been associated with increased serum levels of triglycerides and cholesterol as well as non-alcoholic fatty liver disease (NAFLD). Advances in areas such as cell imaging, autophagy and metabolomics have generated a more detailed and comprehensive picture of thyroid-hormone-mediated regulation of hepatic lipid metabolism at the molecular level. In this Review, we describe and summarize the key features of direct thyroid hormone regulation of lipogenesis, fatty acid β-oxidation, cholesterol synthesis and the reverse cholesterol transport pathway in normal and altered thyroid hormone states. Thyroid hormone mediates these effects at the transcriptional and post-translational levels and via autophagy. Given these potentially beneficial effects on lipid metabolism, it is possible that thyroid hormone analogues and/or mimetics might be useful for the treatment of metabolic diseases involving the liver, such as hypercholesterolaemia and NAFLD.

Metabolic Effects of the Intracellular Regulation of Thyroid Hormone: Old Players, New Concepts

Thyroid hormones (THs) are key determinants of cellular metabolism and regulate a variety of pathways that are involved in the metabolism of carbohydrates, lipids and proteins in several target tissues. Notably, hyperthyroidism induces a hyper-metabolic state characterized by increased resting energy expenditure, reduced cholesterol levels, increased lipolysis and gluconeogenesis followed by weight loss, whereas hypothyroidism induces a hypo-metabolic state characterized by reduced energy expenditure, increased cholesterol levels, reduced lipolysis and gluconeogenesis followed by weight gain. Thyroid hormone is also a key regulator of mitochondria respiration and biogenesis. Besides mirroring systemic TH concentrations, the intracellular availability of TH is potently regulated in target cells by a mechanism of activation/inactivation catalyzed by three seleno-proteins: type 1 and type 2 iodothyronine deiodinase (D1 and D2) that convert the biologically inactive precursor thyroxine T4 into T3, and type 3 iodothyronine deiodinase (D3) that inactivates TH action. Thus, the pleiotropic effects of TH can fluctuate among tissues and strictly depend on the cell-autonomous action of the deiodinases. Here we review the mechanisms of TH action that mediate metabolic regulation. This review traces the critical impact of peripheral regulation of TH by the deiodinases on the pathways that regulate energy metabolism and the balance among energy intake, expenditure and storage in specific target tissues.

Role of thyroid hormone in hepatic gene regulation, chromatin remodeling, and autophagy

Thyroid hormone (TH) actions on development and metabolism have been studied ever since the discovery of thyroxine almost a century ago. Initial studies focused on the physiological and biochemical actions of TH. Later, the cloning of the thyroid hormone receptor (THR) isoforms and the development of techniques enabled the study of TH regulation of complex cellular processes (such as gene transcription). Recently we found that TH activates secondary transcription factors such as FOXO1, to amplify gene transcription; and also is a potent inducer of autophagy that was critical for fatty acid β-oxidation in the liver. This review summarizes the recent advancements in our understanding of TH regulation of gene expression of metabolic genes (via co-regulators/transcription factors and epigenetic control) and autophagy in the liver. Our deeper understanding of TH action recently has led to the development of tissue- and THR isoform-specific TH mimetics that may be useful for the treatment of metabolic disorders.

Transcription factor 19 interacts with histone 3 lysine 4 trimethylation and controls gluconeogenesis via the nucleosome-remodeling-deacetylase complex

Transcription factor 19 (TCF19) has been reported as a type 1 diabetes-associated locus involved in maintenance of pancreatic β cells through a fine-tuned regulation of cell proliferation and apoptosis. TCF19 also exhibits genomic association with type 2 diabetes, although the precise molecular mechanism remains unknown. It harbors both a plant homeodomain and a forkhead-associated domain implicated in epigenetic recognition and gene regulation, a phenomenon that has remained unexplored. Here, we show that TCF19 selectively interacts with histone 3 lysine 4 trimethylation through its plant homeodomain finger. Knocking down TCF19 under high-glucose conditions affected many metabolic processes, including gluconeogenesis. We found that TCF19 overexpression represses de novo glucose production in HepG2 cells. The transcriptional repression of key genes, induced by TCF19, coincided with NuRD (nucleosome-remodeling-deacetylase) complex recruitment to the promoters of these genes. TCF19 interacted with CHD4 (chromodomain helicase DNA-binding protein 4), which is a part of the NuRD complex, in a glucose concentration-independent manner. In summary, our results show that TCF19 interacts with an active transcription mark and recruits a co-repressor complex to regulate gluconeogenic gene expression in HepG2 cells. Our study offers critical insights into the molecular mechanisms of transcriptional regulation of gluconeogenesis and into the roles of chromatin readers in metabolic homeostasis.

BRD4 promotes p63 and GRHL3 expression downstream of FOXO in mammary epithelial cells

Bromodomain-containing protein 4 (BRD4) is a member of the bromo- and extraterminal (BET) domain-containing family of epigenetic readers which is under intensive investigation as a target for anti-tumor therapy. BRD4 plays a central role in promoting the expression of select subsets of genes including many driven by oncogenic transcription factors and signaling pathways. However, the role of BRD4 and the effects of BET inhibitors in non-transformed cells remain mostly unclear. We demonstrate that BRD4 is required for the maintenance of a basal epithelial phenotype by regulating the expression of epithelial-specific genes including TP63 and Grainy Head-like transcription factor-3 (GRHL3) in non-transformed basal-like mammary epithelial cells. Moreover, BRD4 occupancy correlates with enhancer activity and enhancer RNA (eRNA) transcription. Motif analyses of cell context-specific BRD4-enriched regions predicted the involvement of FOXO transcription factors. Consistently, activation of FOXO1 function via inhibition of EGFR-AKT signaling promoted the expression of TP63 and GRHL3. Moreover, activation of Src kinase signaling and FOXO1 inhibition decreased the expression of FOXO/BRD4 target genes. Together, our findings support a function for BRD4 in promoting basal mammary cell epithelial differentiation, at least in part, by regulating FOXO factor function on enhancers to activate TP63 and GRHL3 expression.

Ubiquitin Ligases and Posttranslational Regulation of Energy in the Heart: The Hand that Feeds

Heart failure (HF) is a costly and deadly syndrome characterized by the reduced capacity of the heart to adequately provide systemic blood flow. Mounting evidence implicates pathological changes in cardiac energy metabolism as a contributing factor in the development of HF. While the main source of fuel in the healthy heart is the oxidation of fatty acids, in the failing heart the less energy efficient glucose and glycogen metabolism are upregulated. The ubiquitin proteasome system plays a key role in regulating metabolism via protein-degradation/regulation of autophagy and regulating metabolism-related transcription and cell signaling processes. In this review, we discuss recent research that describes the role of the ubiquitin-proteasome system (UPS) in regulating metabolism in the context of HF. We focus on ubiquitin ligases (E3s), the component of the UPS that confers substrate specificity, and detail the current understanding of how these E3s contribute to cardiac pathology and metabolism. © 2017 American Physiological Society. Compr Physiol 7:841-862, 2017.

Inactivation of Sirt1 in mouse livers protects against endotoxemic liver injury by acetylating and activating NF-κB

Sirtuin 1 (Sirt1) is a deacetylase that regulates many cellular processes in the liver, and so far its role in endotoxemic liver injury is elusive. So we conditionally inactivate Sirt1 in murine hepatocytes to determine its role in d-galactosamine (GalN)/lipopolysaccharide (LPS)-induced liver damage, which is a well-established experimental model mimicking septic liver injury and fulminant hepatitis. Ablation of Sirt1 shows remarkable protection against GalN/LPS-induced liver injury, which is a result of enhanced NF-κB response because knockdown of RelA/p65 negates the protective effect of Sirt1 knockout. Mechanistically, NF-κB p65 is maintained in a hyperacetylated, DNA-binding competent state in tumor necrosis factor-α (TNF-α)-challenged albumin-Cre⁺ (AlbCre⁺) hepatocytes. Transfection of hepatocytes with a recombinant acetylated p65 expression construct replicates the protection afforded by Sirt1 knockout. Transfection of AlbCre⁺ hepatocytes with a recombinant wild-type Sirt1 construct, rather than a deacetylase-defective one, compromises NF-κB activation and resensitizes hepatocytes to TNF-α-induced apoptosis. Taken together, our results demonstrate that Sirt1 deacetylates p65 and compromises NF-κB activity in hepatocytes when confronted with LPS/TNF-α stimulation, leading to increased susceptibility to endotoxemic injury. These findings identify a possible protein effector to maneuver the hepatic NF-κB signaling pathway under inflammatory circumstances and a feasible way to increase hepatocellular resistance to endotoxin/TNF-α toxicity.

MicroRNA-877-5p is involved in the trovafloxacin-induced liver injury

Trovafloxacin develops severe hepatotoxicity; however, the underlying mechanism of the trovafloxacin-induced liver injury has not been cleared. It has been shown that microRNAs (miRNAs) can be involved in the development of drug-induced liver injuries. We performed a miRNA microarray analysis to identify hepatic miRNAs that were induced or reduced by trovafloxacin in mice. It was demonstrated that miR-877-5p was the most increased miRNA in the mouse liver 24h after the trovafloxacin administration. To investigate the role of miR-877-5p in the liver, we established miR-877-5p-overexpressed HepG2 cells. Microarray analysis detected altered expressions in 2077 (>2-fold) and 1547 (<0.5-fold) genes in the miR-877-5p overexpressing cells compared to the mock cells. Especially, SLCO4C1, PEPCK, MT1M, HIST1H2BM, LGI1, and PLA2G2A were markedly increased or decreased in the miR-877-5p overexpressing cells. We conducted a correlation analysis between the expression levels of miR-877-5p and the six genes in eight miR-877-5p stably-expressed clones. It was shown that the PEPCK expression levels were correlated with miR-877-5p expression levels. PEPCK is associated with development of apoptotic cell death; therefore, the increased miR- 877-5p-induced PEPCK can be a trigger that is involved in the development of trovafloxacin-induced liver injury.

Thyroid hormone-mediated autophagy and mitochondrial turnover in NAFLD

Non-alcoholic fatty liver disease (NAFLD) is a fast-growing silent epidemic that is present in both developed and developing countries. Initially thought as a benign deposition of lipids in the liver, it now has been shown to be a major risk factor for type II diabetes and one of the leading causes of cirrhosis. Recent findings suggest that dysregulation of mitochondrial homeostasis and autophagy play critical roles in the hepatocyte injury and insulin resistance of NAFLD. Thyroid hormone (TH) is a major stimulator of hepatic autophagy and mitochondrial function. Decreased TH action has been associated with NAFLD in man. In this review, we highlight some of the new discoveries that demonstrate the roles of TH in hepatic mitochondrial homeostasis via mitophagy and their implications for NAFLD.

Nongenomic actions of thyroid hormone

The nongenomic actions of thyroid hormone begin at receptors in the plasma membrane, mitochondria or cytoplasm. These receptors can share structural homologies with nuclear thyroid hormone receptors (TRs) that mediate transcriptional actions of T3, or have no homologies with TR, such as the plasma membrane receptor on integrin αvβ3. Nongenomic actions initiated at the plasma membrane by T4 via integrin αvβ3 can induce gene expression that affects angiogenesis and cell proliferation, therefore, both nongenomic and genomic effects can overlap in the nucleus. In the cytoplasm, a truncated TRα isoform mediates T4-dependent regulation of intracellular microfilament organization, contributing to cell and tissue structure. p30 TRα1 is another shortened TR isoform found at the plasma membrane that binds T3 and mediates nongenomic hormonal effects in bone cells. T3 and 3,5-diiodo-L-thyronine are important to the complex nongenomic regulation of cellular respiration in mitochondria. Thus, nongenomic actions expand the repertoire of cellular events controlled by thyroid hormone and can modulate TR-dependent nuclear events. Here, we review the experimental approaches required to define nongenomic actions of the hormone, enumerate the known nongenomic effects of the hormone and their molecular basis, and discuss the possible physiological or pathophysiological consequences of these actions.

Chronic HMGCR/HMG-CoA reductase inhibitor treatment contributes to dysglycemia by upregulating hepatic gluconeogenesis through autophagy induction

Statins (HMGCR/HMG-CoA reductase [3-hydroxy-3-methylglutaryl-CoA reductase] inhibitors) are widely used to lower blood cholesterol levels but have been shown to increase the risk of type 2 diabetes mellitus. However, the molecular mechanism underlying diabetogenic effects remains to be elucidated. Here we show that statins significantly increase the expression of key gluconeogenic enzymes (such as G6PC [glucose-6-phosphatase] and PCK1 (phosphoenolpyruvate carboxykinase 1 [soluble]) in vitro and in vivo and promote hepatic glucose output. Statin treatment activates autophagic flux in HepG2 cells. Acute suppression of autophagy with lysosome inhibitors in statin treated HepG2 cells reduced gluconeogenic enzymes expression and glucose output. Importantly, the ability of statins to increase gluconeogenesis was impaired when ATG7 was deficient and BECN1 was absent, suggesting that autophagy plays a critical role in the diabetogenic effects of statins. Moreover autophagic vacuoles and gluconeogenic genes expression in the liver of diet-induced obese mice were increased by statins, ultimately leading to elevated hepatic glucose production, hyperglycemia, and insulin resistance. Together, these data demonstrate that chronic statin therapy results in insulin resistance through the activation of hepatic gluconeogenesis, which is tightly coupled to hepatic autophagy. These data further contribute to a better understanding of the diabetogenic effects of stains in the context of insulin resistance.

Hepatic FOXO1 Target Genes Are Co-regulated by Thyroid Hormone via RICTOR Protein Deacetylation and MTORC2-AKT Protein Inhibition

MTORC2-AKT is a key regulator of carbohydrate metabolism and insulin signaling due to its effects on FOXO1 phosphorylation. Interestingly, both FOXO1 and thyroid hormone (TH) have similar effects on carbohydrate and energy metabolism as well as overlapping transcriptional regulation of many target genes. Currently, little is known about the regulation of MTORC2-AKT or FOXO1 by TH. Accordingly, we performed hepatic transcriptome profiling in mice after FOXO1 knockdown in the absence or presence of TH, and we compared these results with hepatic FOXO1 and THRB1 (TRβ1) ChIP-Seq data. We identified a subset of TH-stimulated FOXO1 target genes that required co-regulation by FOXO1 and TH. TH activation of FOXO1 was directly linked to an increase in SIRT1-MTORC2 interaction and RICTOR deacetylation. This, in turn, led to decreased AKT and FOXO1 phosphorylation. Moreover, TH increased FOXO1 nuclear localization, DNA binding, and target gene transcription by reducing AKT-dependent FOXO1 phosphorylation in a THRB1-dependent manner. These events were associated with TH-mediated oxidative phosphorylation and NAD(+) production and suggested that downstream metabolic effects by TH can post-translationally activate other transcription factors. Our results showed that RICTOR/MTORC2-AKT can integrate convergent hormonal and metabolic signals to provide coordinated and sensitive regulation of hepatic FOXO1-target gene expression.

Thyroid hormone receptor regulates most genes independently of fibroblast growth factor 21 in liver

Thyroid hormone (TH) acts through specific receptors (TRs), which are conditional transcription factors, to induce fibroblast growth factor 21 (FGF21), a peptide hormone that is usually induced by fasting and that influences lipid and carbohydrate metabolism via local hepatic and systemic endocrine effects. While TH and FGF21 display overlapping actions when administered, including reductions in serum lipids, according to the current models these hormones act independently in vivo. In this study, we examined mechanisms of regulation of FGF21 expression by TH and tested the possibility that FGF21 is required for induction of hepatic TH-responsive genes. We confirm that active TH (triiodothyronine (T3)) and the TRβ-selective thyromimetic GC1 increase FGF21 transcript and peptide levels in mouse liver and that this effect requires TRβ. T3 also induces FGF21 in cultured hepatocytes and this effect involves direct actions of TRβ1, which binds a TRE within intron 2 of FGF21. Gene expression profiles of WT and Fgf21-knockout mice are very similar, indicating that FGF21 is dispensable for the majority of hepatic T3 gene responses. A small subset of genes displays diminished T3 response in the absence of FGF21. However, most of these are not obviously directly involved in T3-dependent hepatic metabolic processes. Consistent with these results, T3-dependent effects on serum cholesterol are maintained in the Fgf21(-/-) background and we observe no effect of the Fgf21-knockout background on serum triglycerides and glucose. Our findings indicate that T3 regulates the genes involved in classical hepatic metabolic responses independently of FGF21.

Diverse roles of SIRT1 in cancer biology and lipid metabolism

SIRT1, an NAD⁺-dependent deacetylase, has been described in the literature as a major player in the regulation of cellular stress responses. Its expression has been shown to be altered in cancer cells, and it targets both histone and non-histone proteins for deacetylation and thereby alters metabolic programs in response to diverse physiological stress. Interestingly, many of the metabolic pathways that are influenced by SIRT1 are also altered in tumor development. Not only does SIRT1 have the potential to regulate oncogenic factors, it also orchestrates many aspects of metabolism and lipid regulation and recent reports are beginning to connect these areas. SIRT1 influences pathways that provide an alternative means of deriving energy (such as fatty acid oxidation and gluconeogenesis) when a cell encounters nutritive stress, and can therefore lead to altered lipid metabolism in various pathophysiological contexts. This review helps to show the various connections between SIRT1 and major pathways in cellular metabolism and the consequence of SIRT1 deregulation on carcinogenesis and lipid metabolism.

New avenues for regulation of lipid metabolism by thyroid hormones and analogs

Weight loss due to negative energy balance is a goal in counteracting obesity and type 2 diabetes mellitus. The thyroid is known to be an important regulator of energy metabolism through the action of thyroid hormones (THs). The classic, active TH, 3,5,3'-triiodo-L-thyronine (T3) acts predominantly by binding to nuclear receptors termed TH receptors (TRs), that recognize TH response elements (TREs) on the DNA, and so regulate transcription. T3 also acts through "non-genomic" pathways that do not necessarily involve TRs. Lipid-lowering therapies have been suggested to have potential benefits, however, the establishment of comprehensive therapeutic strategies is still awaited. One drawback of using T3 in counteracting obesity has been the occurrence of heart rhythm disturbances. These are mediated through one TR, termed TRα. The end of the previous century saw the exploration of TH mimetics that specifically bind to TR beta in order to prevent cardiac disturbances, and TH derivatives such as 3,5-diiodo-L-thyronine (T2), that possess interesting biological activities. Several TH derivatives and functional analogs have low affinity for the TRs, and are suggested to act predominantly through non-genomic pathways. All this has opened new perspectives in thyroid physiology and TH derivative usage as anti-obesity therapies. This review addresses the pros and cons of these compounds, in light of their effects on energy balance regulation and on lipid/cholesterol metabolism.

Cross-talk between SIRT1 and endocrine factors: effects on energy homeostasis

The mammalian sirtuins (SIRT1-7) are a family of highly conserved nicotine adenine dinucleotide (NAD(+))-dependent deacetylases that act as cellular sensors to detect energy availability. SIRT1 is a multifaceted protein that is involved in a wide variety of cellular processes. SIRT1 is activated in response to caloric restriction, acting on multiple targets in a wide range of tissues. SIRT1 regulates the role of multiple hormones implicated in energy balance, including glucose and lipid metabolism. Here, we review the relevant role of SIRT1 as a mediator of endocrine function of several hormones to modulate energy balance. In addition, we analyze the potential of targeting SIRT1 for the treatment of obesity and type 2 diabetes mellitus.

Thyroid hormone regulation of hepatic lipid and carbohydrate metabolism

Thyroid hormone (TH) has important roles in regulating hepatic lipid, cholesterol, and glucose metabolism. Recent findings suggest that clinical conditions such as non-alcoholic fatty liver disease and type 2 diabetes mellitus, which are associated with dysregulated hepatic metabolism, may involve altered intracellular TH action. In addition, TH has key roles in lipophagy in lipid metabolism, mitochondrial quality control, and the regulation of metabolic genes. In this review, we discuss recent findings regarding the functions of TH in hepatic metabolism, the relationship between TH and metabolic disorders, and the potential therapeutic use of thyromimetics to treat metabolic dysfunction in the liver.

Genomic profiling of type-1 adult diabetic and aged normoglycemic mouse liver

BACKGROUND

Hyperglycemia induces chromatin remodeling with consequences on differential gene expression in mouse hepatocytes, similar to what occurs during aging. The liver is the central organ for the regulation of glucose homeostasis and xenobiotic and lipid metabolism and is affected by insulin signaling. The precise transcriptional profiling of the type-1 diabetic liver and its comparison to aging have not been elucidated yet.

METHODS

Here, we studied the differential genomic expression of mouse liver cells under adult hyperglycemic and aged normoglycemic conditions using expression arrays.

RESULTS

Differential gene expression involved in an increase in glucose and impaired lipid metabolism were detected in the type-1 diabetic liver. In this regard, Ppargc1a presents an increased expression and is a key gene that might be regulating both processes. The differential gene expression observed may also be associated with hepatic steatosis in diabetic mouse liver, as a secondary disease. Similarly, middle-aged mice presented differential expression of genes involved in glucose, lipid and xenobiotic metabolism. These genes could be associated with an increase in polyploidy, but the consequences of differential expression were not as drastic as those observed in diabetic animals.

CONCLUSIONS

Taken together, these findings provide new insights into gene expression profile changes in type-1 diabetic liver. Ppargc1a was found to be the key-gene that increases glucose metabolism and impairs lipid metabolism impairment. The novel results reported here open new areas of investigation in diabetic research and facilitate the development of new strategies for gene therapy.

Sodium meta-arsenite ameliorates hyperglycemia in obese diabetic db/db mice by inhibition of hepatic gluconeogenesis

Sodium meta-arsenite (SA) is implicated in the regulation of hepatic gluconeogenesis-related genes in vitro; however, the effects in vivo have not been studied. We investigated whether SA has antidiabetic effects in a type 2 diabetic mouse model. Diabetic db/db mice were orally intubated with SA (10 mg kg(-1) body weight/day) for 8 weeks. We examined hemoglobin A1c (HbA1c), blood glucose levels, food intake, and body weight. We performed glucose, insulin, and pyruvate tolerance tests and analyzed glucose production and the expression of gluconeogenesis-related genes in hepatocytes. We analyzed energy metabolism using a comprehensive animal metabolic monitoring system. SA-treated diabetic db/db mice had reduced concentrations of HbA1c and blood glucose levels. Exogenous glucose was quickly cleared in glucose tolerance tests. The mRNA expressions of genes for gluconeogenesis-related enzymes, glucose 6-phosphatase (G6Pase), and phosphoenolpyruvate carboxykinase (PEPCK) were significantly reduced in the liver of SA-treated diabetic db/db mice. In primary hepatocytes, SA treatment decreased glucose production and the expression of G6Pase, PEPCK, and hepatocyte nuclear factor 4 alpha (HNF-4α) mRNA. Small heterodimer partner (SHP) mRNA expression was increased in hepatocytes dependent upon the SA concentration. The expression of Sirt1 mRNA and protein was reduced, and acetylated forkhead box protein O1 (FoxO1) was induced by SA treatment in hepatocytes. In addition, SA-treated diabetic db/db mice showed reduced energy expenditure. Oral intubation of SA ameliorates hyperglycemia in db/db mice by reducing hepatic gluconeogenesis through the decrease of Sirt1 expression and increase in acetylated FoxO1.