Caffeine induces hyperacetylation of histones at the MEF2 site on the Glut4 promoter and increases MEF2A binding to the site via a CaMK-dependent mechanism

Phytochemical composition of Tibetan tea fermented by Eurotium cristatum and its effects on type 1 diabetes mice and gut microbiota

"Golden-flower" Tibetan tea (GTT) is an innovative dark tea fermented via fungus Eurotium cristatum. To study GTT effects on alleviating the symptoms of type 1 diabetes mellitus (T1DM), GTT's extract (GTTE) was prepared. GTTE chemical compositions were analyzed via HPLC, pyrolysis-gas chromatography-mass (Py-GC-MS) spectrometry analysis, and chemistry analyses. GTTE effects on T1DM were explored on T1DM mice model induced by streptozotocin (STZ). GTTE was composed mainly of tea pigment theabrownin (TB) (49.18%), with high percentages of polysaccharide (16.93%), protein (10.15%), polyphenols (13.90%), amino acids (5.89%), caffeine (1.83%), and flavonoids (0.67%). Py-GC-MS results exhibited that GTTE constituted of phenols, lipids, sugars, and proteins. GTTE attenuated T1DM conditions of mice, relieved their liver and pancreatic injury, restored damaged islet cells, decreased oxidative stress by increasing superoxide dismutase (SOD) and catalase (CAT) levels, modulated cytokine expression leading to the decreasing pro-inflammatory cytokines TNF-α and IL-6, increased anti-inflammatory cytokines IL-4 to improve inflammatory responses, and optimized gut microbiota composition and structure based on high-throughput 16S rDNA sequencing, suggesting multi-channel anti-diabetes mechanisms.

Progress in discovery and development of natural inhibitors of histone deacetylases (HDACs) as anti-cancer agents

The study of epigenetic translational modifications had drawn great interest for the last few decades. These processes play a vital role in many diseases and cancer is one of them. Histone acetyltransferase (HAT) and histone deacetylases (HDACs) are key enzymes involved in the acetylation and deacetylation of histones and ultimately in post-translational modifications. Cancer frequently exhibits epigenetic changes, particularly disruption in the expression and activity of HDACs. It includes the capacity to regulate proliferative signalling, circumvent growth inhibitors, escape cell death, enable replicative immortality, promote angiogenesis, stimulate invasion and metastasis, prevent immunological destruction, and genomic instability. The majority of tumours develop and spread as a result of HDAC dysregulation. As a result, HDAC inhibitors (HDACis) were developed, and they today stand as a very promising therapeutic approach. One of the most well-known and efficient therapies for practically all cancer types is chemotherapy. However, the efficiency and safety of treatment are constrained by higher toxicity. The same has been observed with the synthetic HDACi. Natural products, owing to many advantages over synthetic compounds for cancer treatment have always been a choice for therapy. Hence, naturally available molecules are of particular interest for HDAC inhibition and HDAC has drawn the attention of the research fraternity due to their potential to offer a diverse array of chemical structures and bioactive compounds. This diversity opens up new avenues for exploring less toxic HDAC inhibitors to reduce side effects associated with conventional synthetic inhibitors. The review presents comprehensive details on natural product HDACi, their mechanism of action and their biological effects. Moreover, this review provides a brief discussion on the structure activity relationship of selected natural HDAC inhibitors and their analogues which can guide future research to discover selective, more potent HDACi with minimal toxicity.

The Epigenetic Effects of Coffee

In this review, we discuss the recent knowledge regarding the epigenetic effects of coffee extract and the three essential active ingredients in coffee (caffeine, chlorogenic acid, and caffeic acid). As a popular beverage, coffee has many active ingredients which have a variety of biological functions such as insulin sensitization, improvement of sugar metabolism, antidiabetic properties, and liver protection. However, recent researches have shown that coffee is not only beneficial for human, but also bad, which may be due to its complex components. Studies suggest that coffee extract and its components can potentially impact gene expression via alteration of DNA methylation, histone modifications, and ncRNA expression; thus, exert long lasting impacts on the epigenome. More importantly, coffee consumption during pregnancy has been linked to multiple negative effects on offspring due to epigenetic modifications; on the other hand, it has also been linked to improvements in many diseases, including cancer. Therefore, understanding more about the epigenetic effects associated with coffee components is crucial to finding ways for improving human health.

Caffeine alleviates acute liver injury by inducing the expression of NEDD4L and deceasing GRP78 level via ubiquitination

BACKGROUND

Acute liver injury is liver cell injury that occurs rapidly in a short period of time. Caffeine has been shown to maintain hepatoprotective effect with an unclear mechanism. Endoplasmic reticulum stress (ERS) has significant effects in acute liver injury. Induction of GRP78 is a hallmark of ERS. Whether or not caffeine's function is related to GRP78 remains to be explored.

METHODS

Acute liver injury model was established by LPS-treated L02 cells and in vivo administration of LPS/D-Gal in mice. Caffeine was pre-treated in L02 cells or mice. Gene levels was determined by real-time PCR and western blot. Cell viability was tested by CCK-8 assay and cell apoptosis was tested by flow cytometry. The interaction of GRP78 and NEDD4L was determined by Pull-down and co-immunoprecipitation (Co-IP) assay. The ubiquitination by NEDD4L on GRP78 was validated by in vitro ubiquitination assay.

RESULTS

Caffeine protected liver cells against acute injury induced cell apoptosis and ERS both in vitro and in vivo. Suppression of GRP78 could block the LPS-induced cell apoptosis and ERS. NEDD4L was found to interact with GRP78 and ubiquitinate its lysine of 324 site directly. Caffeine treatment induced the expression of NEDD4L, resulting in the ubiquitination and inhibition of GRP78.

CONCLUSION

Caffeine mitigated the acute liver injury by stimulating NEDD4L expression, which inhibited GRP78 expression via ubiquitination at its K324 site. Low dose of caffeine could be a promising therapeutic treatment for acute liver injury.

The structural basis of histone modifying enzyme specificity and promiscuity: Implications for metabolic regulation and drug design

Histone modifying enzymes regulate chromatin architecture through covalent modifications and ultimately control multiple aspects of cellular function. Disruption of histone modification leads to changes in gene expression profiles and may lead to disease. Both small molecule inhibitors and intermediary metabolites have been shown to modulate histone modifying enzyme activity although our ability to identify successful drug candidates or novel metabolic regulators of these enzymes has been limited. Using a combination of large scale in silico screens and in vivo phenotypic analysis, we identified several small molecules and intermediary metabolites with distinctive HME activity. Our approach using unsupervised learning identifies the chemical fingerprints of both small molecules and metabolites that facilitate recognition by the enzymes active sites which can be used as a blueprint to design novel inhibitors. Furthermore, this work supports the idea that histone modifying enzymes sense intermediary metabolites integrating genes, environment and cellular physiology.

Myocyte Enhancer Factor 2A Plays a Central Role in the Regulatory Networks of Cellular Physiopathology

Cell regulatory networks are the determinants of cellular homeostasis. Any alteration to these networks results in the disturbance of cellular homeostasis and induces cells towards different fates. Myocyte enhancer factor 2A (MEF2A) is one of four members of the MEF2 family of transcription factors (MEF2A-D). MEF2A is highly expressed in all tissues and is involved in many cell regulatory networks including growth, differentiation, survival and death. It is also necessary for heart development, myogenesis, neuronal development and differentiation. In addition, many other important functions of MEF2A have been reported. Recent studies have shown that MEF2A can regulate different, and sometimes even mutually exclusive cellular events. How MEF2A regulates opposing cellular life processes is an interesting topic and worthy of further exploration. Here, we reviewed almost all MEF2A research papers published in English and summarized them into three main sections: 1) the association of genetic variants in MEF2A with cardiovascular disease, 2) the physiopathological functions of MEF2A, and 3) the regulation of MEF2A activity and its regulatory targets. In summary, multiple regulatory patterns for MEF2A activity and a variety of co-factors cause its transcriptional activity to switch to different target genes, thereby regulating opposing cell life processes. The association of MEF2A with numerous signaling molecules establishes a central role for MEF2A in the regulatory network of cellular physiopathology.

Exercise, CaMKII, and type 2 diabetes

Individuals who exercise regularly are protected from type 2 diabetes and other metabolic syndromes, in part by enhanced gene transcription and induction of many signaling pathways crucial in correcting impaired metabolic pathways associated with a sedentary lifestyle. Exercise activates Calmodulin-dependent protein kinase (CaMK)II, resulting in increased mitochondrial oxidative capacity and glucose transport. CaMKII regulates many health beneficial cellular functions in individuals who exercise compared with those who do not exercise. The role of exercise in the regulation of carbohydrate, lipid metabolism, and insulin signaling pathways are explained at the onset. Followed by the role of exercise in the regulation of glucose transporter (GLUT)4 expression and mitochondrial biogenesis are explained. Next, the main functions of Calmodulin-dependent protein kinase and the mechanism to activate it are illustrated, finally, an overview of the role of CaMKII in regulating GLUT4 expression, mitochondrial biogenesis, and histone modification are discussed.

The dichotomous effects of caffeine on homologous recombination in mammalian cells

This study was initiated to examine the effects of caffeine on the DNA damage response (DDR) and homologous recombination (HR) in mammalian cells. A 5 mM caffeine treatment caused the cell cycle to stall at G2/M and cells eventually underwent apoptosis. Caffeine exposure also induced a strong DDR along with subsequent activation of wildtype p53 protein. An unexpected observation was the caffeine-induced depletion of Rad51 (and Brca2) proteins. Consequently, caffeine-treated cells were expected to be inefficient in HR. However, a dichotomy in the HR response of cells to caffeine treatment was revealed. Caffeine treatment rendered cells significantly better at performing the nascent DNA synthesis that accompanies the early strand invasion steps of HR. Additionally, caffeine treatment increased chromatin accessibility and elevated the efficiency of illegitimate recombination. Conversely, the increase in nascent DNA synthesis did not translate into a higher number of gene targeting events. Thus, prolonged caffeine exposure stalls the cell cycle, induces a p53-mediated apoptotic response and a down-regulation of critical HR proteins, and for reasons discussed, stimulates early steps of HR, but not the formation of complete recombination products.

CaMKII and GLUT1 in heart failure and the role of gliflozins

Empagliflozin, a selective sodium-glucose co-transporter 2 (SGLT2) inhibitor, has been shown to reduce mortality and hospitalization for heart failure in diabetic patients in the EMPA-REG-OUTCOME trial (Zinman et al., 2015). Surprisingly, dapagliflozin, another SGLT2 inhibitor, exerted comparable effects on clinical endpoints even in the absence of diabetes mellitus (DAPA-HF trial) (McMurray et al., 2019). There is a myriad of suggested underlying mechanisms ranging from improved glycemic control and hemodynamic effects to altered myocardial metabolism, inflammation, neurohumoral activation and intracellular ion homeostasis. Here, we review the effects of gliflozins on cardiac electro-mechanical coupling with an emphasis on novel CaMKII-mediated pathways and on cardiac glucose and ketone metabolism in the failing heart. We focus on empagliflozin as it is the gliflozin with the most abundant experimental evidence for direct effects on the heart. Where useful, we aim to compare empagliflozin to other gliflozins. To facilitate understanding of empagliflozin-induced alterations, we first give a short summary of the pathophysiological role of CaMKII in heart failure, as well as cardiac changes of glucose and ketone body metabolism in the failing heart.

GluT4: A central player in hippocampal memory and brain insulin resistance

Insulin is now well-established as playing multiple roles within the brain, and specifically as regulating hippocampal cognitive processes and metabolism. Impairments to insulin signaling, such as those seen in type 2 diabetes and Alzheimer's disease, are associated with brain hypometabolism and cognitive impairment, but the mechanisms of insulin's central effects are not determined. Several lines of research converge to suggest that the insulin-responsive glucose transporter GluT4 plays a central role in hippocampal memory processes, and that reduced activation of this transporter may underpin the cognitive impairments seen as a consequence of insulin resistance.

Study on the effect of CaMKKβ-mediated AMPK activation on the glycolysis and the quality of different altitude postmortem bovines longissimus muscle

This study investigated the activity of adenosine monophosphate-activated protein kinase (AMPK), glycolysis, and meat quality index in three altitude bovines during postmortem aging process. Local cattle (altitude:1,500 m), Gannan yak (3,000 m), and Yushu yak (4,500 m) postmortem Longissimus Dorsi (LD) muscle were used. Results indicated that CaCl₂ significantly increased the AMPK activity by increasing the calcium-regulated protein kinase kinase (CaMKKβ) activity. Besides, AMPK activation enhanced the activity of lactate dehydrogenase (LDH) and Ca²⁺ -ATPase and accelerated the rate of muscle maturation during postmortem aging. Moreover, the expression of HIF-1, PRKAA2, and GLUT4 genes in high-altitude Yushu yak was higher than that of low-altitude bovines. CaCl₂ activates AMPK by activating CaMKKβ cascade and accelerates postmortem glycolysis affecting the intramuscular environment, color, and muscle protein degradation to accelerate postmortem muscle maturation, suggesting that AMPK has essential effects on postmortem muscle glycolysis and quality, and can regulate muscle quality by regulating postmortem muscle AMPK activity. PRACTICAL APPLICATIONS: Insufficient postmortem glycolysis usually leads to DFD (dark, firm, and dry) meat. Beef have relatively high incidences of DFD meat, which has an unattractive dark color and causes significant loss to the meat industry. Therefore, AMPK, which can regulate postmortem glycolysis to affect meat quality, is a valid research target.

In vitro and in vivo evidence of hypouricemic and anti-inflammatory activities of Maclura cochinchinensis (Lour.) Corner heartwood extract

Maclura cochinchinensis (Lour.) Corner (MC) heartwood extracts have been used for the treatment of gout, hyperuricemia, and inflammation in Thai traditional medicine. Despite their traditional use, their mechanisms of action remain unknown. The aim of this study was to determine the mechanisms of MC heartwood extract activity using both in vitro and in vivo models . The extraction methods were optimized to yield the highest contents of biochemical compounds and antioxidant activities. The effects of MC heartwood extract on xanthine oxidase and its enzyme kinetics were determined in vitro and the antihyperuricemic effect was evaluated in potassium oxonate (PO)-induced hyperuricemic mice. The anti-inflammatory effect of MC heartwood extract was also tested against lipopolysaccharide-induced proinflammatory mRNA upregulation in RAW 264.7 mouse macrophage cells. Soxhlet extraction of MC heartwood with 70% ethanol produced stronger antioxidant activity, and higher total phenolic and flavonoid contents than conventional methods did (maceration or decoction). By using HPLC, we found that MC contains morin as a major constituent, which may account for its pharmacological activities. Moreover, administration of MC heartwood extract (500 mg/kg) markedly decreased uric acid levels in PO-induced hyperuricemic mice (p < 0.05). MC heartwood extract inhibited the hepatic activity of xanthine oxidase ex vivo by approximately 53%. In addition, MC heartwood extract markedly downregulated mRNA expression of inflammatory mediators (TNF-α, TGF-β, iNOS, and COX-2) and this inhibition was comparable with that of dexamethasone. Therefore, MC heartwood extract is a promising candidate as a natural treatment for inflammation and the hyperuricemia that causes gout.

Long-Term Impact of Neonatal Intake of Oleanolic Acid on the Expression of AMP-Activated Protein Kinase, Adiponectin and Inflammatory Cytokines in Rats Fed with a High Fructose Diet

AMP-activated protein kinase (AMPK) is known to regulate both glucose and lipid metabolism, which play vital roles in the development of metabolic syndrome. One way of regulating AMPK is through hormonal activation using adiponectin. Patients diagnosed with type-2 diabetes (T2D) and obesity exhibit low adiponectin concentration levels in their blood. Moreover, studies have also shown that inflammatory processes play a significant role in the etiology of these metabolic diseases. In this study, the long-term effects of neonatal intake of oleanolic acid (OA) on the AMPK gene, genes associated with glucose transport and lipid metabolism, adiponectin levels, and inflammatory biomarkers in rats fed with a high fructose diet were investigated. Seven day old pups were randomly divided into five groups and treated as follows; 0.5% dimethylsulphoxide v/v in distilled water vehicle control (CON), oleanolic acid (OA, 60 mg/kg), high fructose diet (HF, 20% w/v), high fructose diet combined with oleanolic acid (HF+OA), and high fructose diet combined with metformin (HF+MET, 500 mg/kg). The treatments were administered once daily until day 14. The rats were then weaned at day 21 and fed standard rat chow and had ad libitum access to plain drinking water until day 112. The quantitative polymerase chain reaction (qPCR) was used to analyze the gene expressions of AMPK, Glut-4, Cpt-1, AdipoR1, AdipoR2, TNF-α, and IL-6 in the skeletal muscles. Bio-Plex Pro magnetic bead-based assay was used to measure plasma levels of inflammatory markers (TNF-α, IL-6, VEGF, and MCP-1) while ELISA kits were used to measure adiponectin concentration in blood plasma. The results obtained in this study showed that neonatal supplementation with OA significantly increased AMPK gene expression approximately ~4-fold in OA fed rats compared to those that were fed with HF alone. In addition, glut-4 gene expression was also significantly higher in the OA treatment group compared to all the other experimental groups except the CON group whereas Cpt-1 gene was more expressed when OA was administered alone. Together, these results indicated that OA can play a role in glucose and lipid metabolism gene regulation. Furthermore, the results showed that the OA group had ~1.5-fold increase in adiponectin concentration when comparedto the HF group. Moreover, HF increased levels of inflammatory cytokines, which was attenuated by neonatal administration of OA. Plasma concentration and gene expression in the skeletal muscle for TNF-α and IL-6 were significantly increased in rats that were treated with HF alone when compared to all the other groups. On the contrary, the high levels of TNF-α and IL-6 were reduced when OA was administered. These findings suggest that intake of oleanolic acid during the neonatal stage of development could be a potential strategic intervention for the long-term prevention of metabolic diseases such as T2D and obesity.

High-Throughput Approaches onto Uncover (Epi)Genomic Architecture of Type 2 Diabetes

Type 2 diabetes (T2D) is a complex disorder that is caused by a combination of genetic, epigenetic, and environmental factors. High-throughput approaches have opened a new avenue toward a better understanding of the molecular bases of T2D. A genome-wide association studies (GWASs) identified a group of the most common susceptibility genes for T2D (i.e., TCF7L2, PPARG, KCNJ1, HNF1A, PTPN1, and CDKAL1) and illuminated novel disease-causing pathways. Next-generation sequencing (NGS)-based techniques have shed light on rare-coding genetic variants that account for an appreciable fraction of T2D heritability (KCNQ1 and ADRA2A) and population risk of T2D (SLC16A11, TPCN2, PAM, and CCND2). Moreover, single-cell sequencing of human pancreatic islets identified gene signatures that are exclusive to α-cells (GCG, IRX2, and IGFBP2) and β-cells (INS, ADCYAP1, INS-IGF2, and MAFA). Ongoing epigenome-wide association studies (EWASs) have progressively defined links between epigenetic markers and the transcriptional activity of T2D target genes. Differentially methylated regions were found in TCF7L2, THADA, KCNQ1, TXNIP, SOCS3, SREBF1, and KLF14 loci that are related to T2D. Additionally, chromatin state maps in pancreatic islets were provided and several non-coding RNAs (ncRNA) that are key to T2D pathogenesis were identified (i.e., miR-375). The present review summarizes major progress that has been made in mapping the (epi)genomic landscape of T2D within the last few years.

DNA methylation in the pathogenesis of type 2 diabetes in humans

Background

Type 2 diabetes (T2D) is a multifactorial, polygenic disease caused by impaired insulin secretion and insulin resistance. Genome-wide association studies (GWAS) were expected to resolve a large part of the genetic component of diabetes; yet, the single nucleotide polymorphisms identified by GWAS explain less than 20% of the estimated heritability for T2D. There was subsequently a need to look elsewhere to find disease-causing factors. Mechanisms mediating the interaction between environmental factors and the genome, such as epigenetics, may be of particular importance in the pathogenesis of T2D.

Scope of Review

This review summarizes knowledge of the impact of epigenetics on the pathogenesis of T2D in humans. In particular, the review will focus on alterations in DNA methylation in four human tissues of importance for the disease; pancreatic islets, skeletal muscle, adipose tissue, and the liver. Case–control studies and studies examining the impact of non-genetic and genetic risk factors on DNA methylation in humans will be considered. These studies identified epigenetic changes in tissues from subjects with T2D versus non-diabetic controls. They also demonstrate that non-genetic factors associated with T2D such as age, obesity, energy rich diets, physical activity and the intrauterine environment impact the epigenome in humans. Additionally, interactions between genetics and epigenetics seem to influence the pathogenesis of T2D.

Conclusions

Overall, previous studies by our group and others support a key role for epigenetics in the growing incidence of T2D.

Role of exercise-induced calmodulin protein kinase (CaMK)II activation in the regulation of omega-6 fatty acids and lipid metabolism genes in rat skeletal muscle

Activation of calmodulin dependent protein kinase (CaMK)II by exercise is beneficial in controlling membrane lipids associated with type 2 diabetes and obesity. Regulation of lipid metabolism is crucial in the improvement of type 2 diabetes and obesity associated symptoms. The role of CaMKII in membrane associated lipid metabolism was the focus of this study. Five to six weeks old male Wistar rats were used in this study. GC×GC-TOFMS technique was used to determine the levels of polyunsaturated fatty acids (linoleic acid, arachidonic acid and 11,14-eicosadienoic acid). Carnitine palmitoyltransferase (Cpt-1) and acetyl-CoA carboxylase (Acc-1) genes expression were assessed using quantitative real time PCR (qPCR). From the results, CaMKII activation by exercise increased the levels of arachidonic acid and 11,14-eicosadienoic acid while a decrease in the level of linolenic acid was observed in the skeletal muscle. The results indicated that exercise-induced CaMKII activation increased CPT-1 expression and decreased ACC-1 expression in rat skeletal muscle. All the observed increases with activation of CaMKII by exercise were aborted when KN93, an inhibitor of CaMKII was injected in exercising rats. This study demonstrated that CaMKII activation by exercise regulated lipid metabolism. This study suggests that CaMKII can be a vital target of therapeutic approach in the management of diseases such as type 2 diabetes and obesity that have increased to epidemic proportions recently.

Insulin modulates hippocampally-mediated spatial working memory via glucose transporter-4

The insulin-regulated glucose transporter, GluT4, is a key molecule in peripheral insulin signaling. Although GluT4 is abundantly expressed in neurons of specific brain regions such as the hippocampus, the functional role of neuronal GluT4 is unclear. Here, we used pharmacological inhibition of GluT4-mediated glucose uptake to determine whether GluT4 mediates insulin-mediated glucose uptake in the hippocampus. Consistent with previous reports, we found that glucose utilization increased in the dorsal hippocampus of male rats during spontaneous alternation (SA), a hippocampally-mediated spatial working memory task. We previously showed that insulin signaling within the hippocampus is required for processing this task, and that administration of exogenous insulin enhances performance. At baseline levels of hippocampal insulin, inhibition of GluT4-mediated glucose uptake did not affect SA performance. However, inhibition of an upstream regulator of GluT4, Akt, did impair SA performance. Conversely, when a memory-enhancing dose of insulin was delivered to the hippocampus prior to SA-testing, inhibition of GluT4-mediated glucose transport prevented cognitive enhancement. These data suggest that baseline hippocampal cognitive processing does not require functional hippocampal GluT4, but that cognitive enhancement by supra-baseline insulin does. Consistent with these findings, we found that in neuronal cell culture, insulin increases glucose utilization in a GluT4-dependent manner. Collectively, these data demonstrate a key role for GluT4 in transducing the procognitive effects of elevated hippocampal insulin.

Novel Roles for the Insulin-Regulated Glucose Transporter-4 in Hippocampally Dependent Memory

The insulin-regulated glucose transporter-4 (GluT4) is critical for insulin- and contractile-mediated glucose uptake in skeletal muscle. GluT4 is also expressed in some hippocampal neurons, but its functional role in the brain is unclear. Several established molecular modulators of memory processing regulate hippocampal GluT4 trafficking and hippocampal memory formation is limited by both glucose metabolism and insulin signaling. Therefore, we hypothesized that hippocampal GluT4 might be involved in memory processes. Here, we show that, in male rats, hippocampal GluT4 translocates to the plasma membrane after memory training and that acute, selective intrahippocampal inhibition of GluT4-mediated glucose transport impaired memory acquisition, but not memory retrieval. Other studies have shown that prolonged systemic GluT4 blockade causes insulin resistance. Unexpectedly, we found that prolonged hippocampal blockade of glucose transport through GluT4-upregulated markers of hippocampal insulin signaling prevented task-associated depletion of hippocampal glucose and enhanced both working and short-term memory while also impairing long-term memory. These effects were accompanied by increased expression of hippocampal AMPA GluR1 subunits and the neuronal GluT3, but decreased expression of hippocampal brain-derived neurotrophic factor, consistent with impaired ability to form long-term memories. Our findings are the first to show the cognitive impact of brain GluT4 modulation. They identify GluT4 as a key regulator of hippocampal memory processing and also suggest differential regulation of GluT4 in the hippocampus from that in peripheral tissues.

SIGNIFICANCE STATEMENT

The role of insulin-regulated glucose transporter-4 (GluT4) in the brain is unclear. In the current study, we demonstrate that GluT4 is a critical component of hippocampal memory processes. Memory training increased hippocampal GluT4 translocation and memory acquisition was impaired by GluT4 blockade. Unexpectedly, whereas long-term inhibition of GluT4 impaired long-term memory, short-term memory was enhanced. These data further our understanding of the molecular mechanisms of memory and have particular significance for type 2 diabetes (in which GluT4 activity in the periphery is impaired) and Alzheimer's disease (which is linked to impaired brain insulin signaling and for which type 2 diabetes is a key risk factor). Both diseases cause marked impairment of hippocampal memory linked to hippocampal hypometabolism, suggesting the possibility that brain GluT4 dysregulation may be one cause of cognitive impairment in these disease states.

Antidiabetic Effects of Tea

Diabetes mellitus (DM) is a chronic endocrine disease resulted from insulin secretory defect or insulin resistance and it is a leading cause of death around the world. The care of DM patients consumes a huge budget due to the high frequency of consultations and long hospitalizations, making DM a serious threat to both human health and global economies. Tea contains abundant polyphenols and caffeine which showed antidiabetic activity, so the development of antidiabetic medications from tea and its extracts is increasingly receiving attention. However, the results claiming an association between tea consumption and reduced DM risk are inconsistent. The advances in the epidemiologic evidence and the underlying antidiabetic mechanisms of tea are reviewed in this paper. The inconsistent results and the possible causes behind them are also discussed.

Exercise increases hyper-acetylation of histones on the Cis-element of NRF-1 binding to the Mef2a promoter: Implications on type 2 diabetes

Exercise brings changes on the chromatin ensuing the upregulation of many genes that confer protection from type 2 diabetes. In type-2 diabetes, critical genes are down-regulated such as those involved in glucose transport (GLUT4, MEF2A) and also oxidative phosphorylation (NRF-1 and its target genes). Recent reports have shown that NRF-1 not only regulate mitochondrial oxidative genes but also controls MEF2A, the main transcription factor for glucose transporter, GLUT4. Such dual control of the two pathways by NRF-1 place it as critical gene in the design of therapeutic modalities much needed to cure or better manage type 2 diabetes. Although it is known that NRF-1 controls these dual pathways (glucose transport and oxidative phosphorylation), the actual molecular mechanisms involved surrounding this regulation remains elusive. NRF-1 itself is regulated through posttranslational modifications (acetylation, methylation and phosphorylation) resulting in enhanced binding to its target genes. This study is therefore aimed at assessing whether CaMKII, a kinase activated by exercise brings about hyper-acetylation of histones in the vicinity of NRF-1 target gene, Mef2a. Five to six weeks old male Wistar rats were used in this study. Chromatin immunoprecipitation (ChIP) assay was used to investigate the extent through which NRF-1 is bound to the Mef2a gene and if this was associated with hyper-acetylation of histones in the region of NRF-1 binding site of the Mef2a gene. Quantitative real time PCR (qPCR) was used to determine the gene expression of MEF2A and NRF-1. Results from this study indicated that exercise-induced CaMKII activation increased hyper-acetylation of histones in the region of NRF-1 binding site on vicinity of Mef2a gene and this was associated with the increased binding of NRF-1 to Mef2a gene. Exercise also increased the expression of NRF-1 and MEF2A genes. Administration of CaMKII inhibitor (KN93) prior to exercise attenuated the observed exercise-induced increase of NRF-1 and MEF2A expressions. In conclusion, this study demonstrated for the first time in our knowledge one mechanism through which NRF-1 regulates MEF2A, pathway critical in glucose transport.

Inhibiting c-Jun N-terminal kinase partially attenuates caffeine-dependent cell death without alleviating the caffeine-induced reduction in mitochondrial respiration in C2C12 skeletal myotubes

Caffeine is a widely consumed stimulant that has previously been shown to promote cytotoxic stress and even cell death in numerous mammalian cell lines. Thus far there is little information available regarding the toxicity of caffeine in skeletal muscle cells. Our preliminary data revealed that treating C2C12 myotubes with 5 mM caffeine for 6 h increased nuclear fragmentation and reduced basal and maximal oxygen consumption rate (OCR) in skeletal myotubes. The purpose of this study was to further elucidate the pathways by which caffeine increased cell death and reduced mitochondrial respiration. We specifically examined the role of c-Jun N-terminal kinase (JNK), which has previously been shown to simultaneously increase caspase-dependent cell death and reduce mitochondrial respiration in other mammalian cell lines. We found that caffeine promoted a dose-dependent increase in cell death in multinucleated myotubes but did not in mononucleated myoblasts. The addition of 10 μM Z-DEVD-FMK, a specific inhibitor of executioner caspases, completely inhibited caffeine-dependent cell death. Further, the addition of 400 μM dantrolene, a specific ryanodine receptor (RYR) inhibitor, prevented the caffeine-dependent increase in cell death and the reduction in basal and maximal OCR. We also discovered that caffeine treatment significantly increased the phosphorylation of JNK and that the addition of 30 μM SP600125 (JNKi), a specific JNK inhibitor, partially attenuated caffeine-induced cell death without preventing the caffeine-dependent reduction in basal and maximal OCR. Our results suggest that JNK partially mediates the increase in caspase-dependent cell death but does not contribute to reduced mitochondrial respiration in caffeine-treated skeletal muscle cells. We conclude that caffeine increased cell death and reduced mitochondrial respiration in a calcium-dependent manner by activating the RYR and promoting reticular calcium release.

Increased Skeletal Muscle GLUT4 Expression in Obese Mice After Voluntary Wheel Running Exercise Is Posttranscriptional

Exercise promotes glucose clearance by increasing skeletal muscle GLUT4-mediated glucose uptake. Importantly, exercise upregulates muscle GLUT4 expression in an insulin-independent manner under conditions of insulin resistance, such as with type 2 diabetes. However, the insulin-independent mechanism responsible for rescued muscle GLUT4 expression is poorly understood. We used voluntary wheel running (VWR) in mice to test the prevailing hypothesis that insulin-independent upregulation of skeletal muscle GLUT4 protein expression with exercise is through increased Glut4 transcription. We demonstrate that 4 weeks of VWR exercise in obese mice rescued high-fat diet-induced decreased muscle GLUT4 protein and improved both fasting plasma insulin and hepatic triacylglyceride levels, but did not rescue muscle Glut4 mRNA. Persistent reduction in Glut4 mRNA suggests that a posttranscriptional mechanism regulated insulin-independent muscle GLUT4 protein expression in response to exercise in lean and obese mice. Reduction of GLUT4 protein in sedentary animals upon treatment with rapamycin revealed mTORC1-dependent GLUT4 regulation. However, no difference in GLUT4 protein expression was observed in VWR-exercised mice treated with either rapamycin or Torin 1, indicating that exercise-dependent regulation on GLUT4 was mTOR independent. The findings provide new insight into the mechanisms responsible for exercise-dependent regulation of GLUT4 in muscle.

The role of diet and exercise in the transgenerational epigenetic landscape of T2DM

Epigenetic changes are caused by biochemical regulators of gene expression that can be transferred across generations or through cell division. Epigenetic modifications can arise from a variety of environmental exposures including undernutrition, obesity, physical activity, stress and toxins. Transient epigenetic changes across the entire genome can influence metabolic outcomes and might or might not be heritable. These modifications direct and maintain the cell-type specific gene expression state. Transient epigenetic changes can be driven by DNA methylation and histone modification in response to environmental stressors. A detailed understanding of the epigenetic signatures of insulin resistance and the adaptive response to exercise might identify new therapeutic targets that can be further developed to improve insulin sensitivity and prevent obesity. This Review focuses on the current understanding of mechanisms by which lifestyle factors affect the epigenetic landscape in type 2 diabetes mellitus and obesity. Evidence from the past few years about the potential mechanisms by which diet and exercise affect the epigenome over several generations is discussed.

Disclosing caffeine action on insulin sensitivity: effects on rat skeletal muscle

Caffeine, a non-selective adenosine antagonist, has distinct effects on insulin sensitivity when applied acutely or chronically. Herein, we investigated the involvement of adenosine receptors on insulin resistance induced by single-dose caffeine administration. Additionally, the mechanism behind adenosine receptor-mediated caffeine effects in skeletal muscle was assessed. The effect of the administration of caffeine, 8-cycle-1,3-dipropylxanthine (DPCPX, A1 antagonist), 2-(2-Furanyl)-7-(2-phenylethyl)-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine (SCH58261, A2A antagonist) and 8-(4-{[(4-cyanophenyl)carbamoylmethyl]-oxy}phenyl)-1,3-di(n-propyl)xanthine (MRS1754, A2B antagonist) on whole-body insulin sensitivity was tested. Skeletal muscle Glut4,5'-AMP activated protein kinase (AMPK) and adenosine receptor protein expression were also assessed. The effect of A1 and A2B adenosine agonists on skeletal muscle glucose uptake was evaluated in vitro. Sodium nitroprussiate (SNP, 10nM), a nitric oxide (NO) donor, was used to evaluate the effect of NO on insulin resistance induced by adenosine antagonists. Acute caffeine decreased insulin sensitivity in a concentration dependent manner (Emax=55.54±5.37%, IC50=11.61nM), an effect that was mediated by A1 and A2B adenosine receptors. Additionally, acute caffeine administration significantly decreased Glut4, but not AMPK expression, in skeletal muscle. We found that A1, but not A2B agonists increased glucose uptake in skeletal muscle. SNP partially reversed DPCPX and MRS1754 induced-insulin resistance. Our results suggest that insulin resistance induced by acute caffeine administration is mediated by A1 and A2B adenosine receptors. Both Glut4 and NO seem to be downstream effectors involved in insulin resistance induced by acute caffeine.

Enhancement of glucose uptake in mouse skeletal muscle cells and adipocytes by P2Y6 receptor agonists

Glucose uptake by peripheral tissues such as skeletal muscles and adipocytes is important in the maintenance of glucose homeostasis. We previously demonstrated that P2Y₆ receptor (P2Y₆R) agonists protect pancreatic islet cells from apoptosis and stimulate glucose-dependent insulin release. Here, we investigated the effects of P2Y₆R activation on glucose uptake in insulin target tissues. An agonist of the P2Y₆R, P¹-(5′-uridine)-P³-(5′-N⁴-methoxycytidine)-triphosphate (MRS2957), significantly increased the uptake of [³H]2-deoxyglucose in mouse C2C12 myotubes and 3T3-L1 adipocytes, and this stimulation was significantly decreased by a selective P2Y₆R antagonist N,N″-1,4-butanediyl-bis[N′-(3-isothiocyanatophenyl)thiourea] (MRS2578). Pre-incubation with Compound C (an inhibitor of 5′-AMP-activated protein kinase, AMPK), or AMPK siRNA abolished the stimulatory effect of MRS2957 on glucose uptake. Also, MRS2957 (60 min incubation) increased recruitment of the facilitated glucose transporter-4 (GLUT4) to the cell membrane, which was blocked by MRS2578. Treatment of C2C12 myotubes with MRS2957 induced significant phosphorylation of AMPK, which increase GLUT4 expression through histone deacetylase (HDAC)5 signaling. Glucose uptake in primary mouse adipocytes from wild-type mice was stimulated upon P2Y₆R activation by either MRS2957 or native agonist UDP, and the P2Y₆R effect was antagonized by MRS2578. However, in adipocytes from P2Y₆R-knockout mice P2Y₆R agonists had no effect on glucose uptake, and there was no change in the glucose uptake by insulin. Our results indicate that the P2Y₆R promotes glucose metabolism in peripheral tissues, which may be mediated through AMPK signaling.

Epigenetic mechanisms of memory formation and reconsolidation

Memory consolidation involves transcriptional control of genes in neurons to stabilize a newly formed memory. Following retrieval, a once consolidated memory destabilizes and again requires gene transcription changes in order to restabilize, a process referred to as reconsolidation. Understanding the molecular mechanisms of gene transcription during the consolidation and reconsolidation processes could provide crucial insights into normal memory formation and memory dysfunction associated with psychiatric disorders. In the past decade, modifications of epigenetic markers such as DNA methylation and posttranslational modifications of histone proteins have emerged as critical transcriptional regulators of gene expression during initial memory formation and after retrieval. In light of the rapidly growing literature in this exciting area of research, we here examine the most recent and latest evidence demonstrating how memory acquisition and retrieval trigger epigenetic changes during the consolidation and reconsolidation phases to impact behavior. In particular we focus on the reconsolidation process, where we discuss the already identified epigenetic regulators of gene transcription during memory reconsolidation, while exploring other potential epigenetic modifications that may also be involved, and expand on how these epigenetic modifications may be precisely and temporally controlled by important signaling cascades critical to the reconsolidation process. Finally, we explore the possibility that epigenetic mechanisms may serve to regulate a system or circuit level reconsolidation process and may be involved in retrieval-dependent memory updating. Hence, we propose that epigenetic mechanisms coordinate changes in neuronal gene transcription, not only during the initial memory consolidation phase, but are triggered by retrieval to regulate molecular and cellular processes during memory reconsolidation.

Exercise: putting action into our epigenome

Most human phenotypes are influenced by a combination of genomic and environmental factors. Engaging in regular physical exercise prevents many chronic diseases, decreases mortality risk and increases longevity. However, the mechanisms involved are poorly understood. The modulating effect of physical (aerobic and resistance) exercise on gene expression has been known for some time now and has provided us with an understanding of the biological responses to physical exercise. Emerging research data suggest that epigenetic modifications are extremely important for both development and disease in humans. In the current review, we summarise findings on the effect of exercise on epigenetic modifications and their effects on gene expression. Current research data suggest epigenetic modifications (DNA methylation and histone acetylation) and microRNAs (miRNAs) are responsive to acute aerobic and resistance exercise in brain, blood, skeletal and cardiac muscle, adipose tissue and even buccal cells. Six months of aerobic exercise alters whole-genome DNA methylation in skeletal muscle and adipose tissue and directly influences lipogenesis. Some miRNAs are related to maximal oxygen consumption (VO(2max)) and VO(2max) trainability, and are differentially expressed amongst individuals with high and low VO(2max). Remarkably, miRNA expression profiles discriminate between low and high responders to resistance exercise (miR-378, -26a, -29a and -451) and correlate to gains in lean body mass (miR-378). The emerging field of exercise epigenomics is expected to prosper and additional studies may elucidate the clinical relevance of miRNAs and epigenetic modifications, and delineate mechanisms by which exercise confers a healthier phenotype and improves performance.

Dietary stimulators of GLUT4 expression and translocation in skeletal muscle: a mini-review

Chronic insulin resistance can lead to type II diabetes mellitus, which is also directly influenced by an individual's genetics as well as their lifestyle. Under normal circumstances, insulin facilitates glucose uptake in skeletal muscle and adipose tissue by stimulating glucose transporter 4 (GLUT4) translocation and activity. GLUT4 activity is directly correlated with the ability to clear elevated blood glucose and insulin sensitivity. In diabetes, energy excess and prolonged hyperinsulinemia suppress muscle and adipose response to insulin, in part through reduced GLUT4 membrane levels. This work uniquely describes much of the experimental data demonstrating the effects of various dietary components on GLUT4 expression and translocation in skeletal muscle. These observations implicate several individual dietary chemicals as potential adjuvant therapies in the maintenance of diabetes and insulin resistance.

Perturbation of cytosolic calcium by 2-aminoethoxydiphenyl borate and caffeine affects zebrafish myofibril alignment

The objective of the current study was to investigate the effects of Ca(2+) levels on myofibril alignment during zebrafish embryogenesis. To investigate how altered cytoplasmic Ca(2+) levels affect myofibril alignment, we exposed zebrafish embryos to 2-aminothoxyldiphenyl borate (2-APB; an inositol 1,4,5-trisphosphate receptor inhibitor that reduces cytosolic Ca(2+) levels) and caffeine (a ryanodine receptor activator that enhances cytosolic Ca(2+) levels). The results demonstrated that the most evident changes in zebrafish embryos treated with 2-APB were shorter body length, curved trunk and malformed somite boundary. In contrast, such malformed phenotypes were evident neither in untreated controls nor in caffeine-treated embryos. Subtle morphological changes, including changes in muscle fibers, F-actin and ultrastructures were easily observed by staining with specific monoclonal antibodies (F59 and α-laminin), fluorescent probes (phalloidin) and by transmission electron microscopy. Our data suggested that: (1) the exposure to 2-APB and/or caffeine led to myofibril misalignment; (2) 2-APB-treated embryos displayed split and short myofibril phenotypes, whereas muscle fibers from caffeine-treated embryos were twisted and wavy; and (3) zebrafish embryos co-exposed to 2-APB and caffeine resulted in normal myofibril alignment. In conclusion, we proposed that cytosolic Ca(2+) is important for myogenesis, particularly for myofibril alignment.

Suppression of the GLUT4 adaptive response to exercise in fructose-fed rats

Exercise-induced increase in skeletal muscle GLUT4 expression is associated with hyperacetylation of histone H3 within a 350-bp DNA region surrounding the myocyte enhancer factor 2 (MEF2) element on the Glut4 promoter and increased binding of MEF2A. Previous studies have hypothesized that the increase in MEF2A binding is a result of improved accessibility of this DNA segment. Here, we investigated the impact of fructose consumption on exercise-induced GLUT4 adaptive response and directly measured the accessibility of the above segment to nucleases. Male Wistar rats (n = 30) were fed standard chow or chow + 10% fructose or maltodextrin drinks ad libitum for 13 days. In the last 6 days five animals per group performed 3 × 17-min bouts of intermittent swimming daily and five remained untrained. Triceps muscles were harvested and used to measure 1) GLUT4, pAMPK, and HDAC5 contents by Western blot, 2) accessibility of the DNA segment from intact nuclei using nuclease accessibility assays, 3) acetylation level of histone H3 and bound MEF2A by ChIP assays, and 4) glycogen content. Swim training increased GLUT4 content by ∼66% (P < 0.05) but fructose and maltodextrin feeding suppressed the adaptation. Accessibility of the DNA region to MNase and DNase I was significantly increased by swimming (∼2.75- and 5.75-fold, respectively) but was also suppressed in trained rats that consumed fructose or maltodextrin. Histone H3 acetylation and MEF2A binding paralleled the accessibility pattern. These findings indicate that both fructose and maltodextrin modulate the GLUT4 adaptive response to exercise by mechanisms involving chromatin remodeling at the Glut4 promoter.

Associations of green tea and rock tea consumption with risk of impaired fasting glucose and impaired glucose tolerance in Chinese men and women

OBJECTIVE

To explore the associations of green tea and rock tea consumption with risk of impaired fasting glucose (IFG) and impaired glucose tolerance (IGT).

METHODS

A multistage, stratified, cluster, random-sampling method was used to select a representative sample from Fujian Province in China. In total, 4808 subjects without cardiovascular disease, hypertension, cancer, or pancreatic, liver, kidney, or gastrointestinal diseases were enrolled in the study. A standard questionnaire was used to gather data on tea (green, rock, and black) consumption and other relevant factors. The assessment of impaired glucose regulation (IGR) was using 75-g oral glucose tolerance test (OGTT), the diagnostic criteria of normal glucose tolerance was according to American Diabetes Association.

RESULTS

Green tea consumption was associated with a lower risk of IFG, while rock tea consumption was associated with a lower risk of IGT. The adjusted odds ratios for IFG for green tea consumption of <1, 1-15, 16-30, and >30 cups per week were 1.0 (reference), 0.42 (95% confidence intervals (CI) 0.27-0.65), 0.23 (95% CI, 0.12-0.46), and 0.41 (95% CI, 0.17-0.93), respectively. The adjusted odds ratios for IGT for rock tea consumption of <1, 1-15, 16-30, and >30 cups per week were 1.0 (reference), 0.69 (95% CI, 0.48-0.98), 0.59 (95% CI, 0.39-0.90), and 0.64 (95% CI, 0.43-0.97), respectively. A U-shaped association was observed, subjects who consumed 16-30 cups of green or rock tea per week having the lowest odds ratios for IFG or IGT.

CONCLUSIONS

Consumption of green or rock tea may protect against the development of type 2 diabetes mellitus in Chinese men and women, particularly in those who drink 16-30 cups per week.

Regulation of mitochondrial biogenesis and GLUT4 expression by exercise

Endurance exercise training can induce large increases mitochondria and the GLUT4 isoform of the glucose transporter in skeletal muscle. For a long time after the discovery in the 1960s that exercise results in an increase in muscle mitochondria, there was no progress in elucidation of the mechanisms involved. The reason for this lack of progress was that nothing was known regarding how expression of the genes-encoding mitochondrial proteins is coordinately regulated. This situation changed rapidly after discovery of transcription factors that control transcription of genes-encoding mitochondrial proteins and, most importantly, the discovery of peroxisome proliferator-gamma coactivator-1α (PGC-1α). This transcription coactivator binds to and activates transcription factors that regulate transcription of genes-encoding mitochondrial proteins. Thus, PGC-1α activates and coordinates mitochondrial biogenesis. It is now known that exercise rapidly activates and induces increased expression of PGC-1α. The exercise-generated signals that lead to PGC-1α activation and increased expression are the increases in cytosolic Ca(2+) and decreases in ATP and creatine phosphate (∼P). Ca(2+) mediates its effect by activating CAMKII, while the decrease in ∼P mediates its effect via activation of AMPK. Expression of the GLUT4 isoform of the glucose transporter is regulated in parallel with mitochondrial biogenesis via the same signaling pathways. This review describes what is known regarding the regulation of mitochondrial biogenesis and GLUT4 expression by exercise. A major component of this review deals with the physiological and metabolic consequences of the exercise-induced increase in mitochondria and GLUT4.

Exercise, GLUT4, and skeletal muscle glucose uptake

Glucose is an important fuel for contracting muscle, and normal glucose metabolism is vital for health. Glucose enters the muscle cell via facilitated diffusion through the GLUT4 glucose transporter which translocates from intracellular storage depots to the plasma membrane and T-tubules upon muscle contraction. Here we discuss the current understanding of how exercise-induced muscle glucose uptake is regulated. We briefly discuss the role of glucose supply and metabolism and concentrate on GLUT4 translocation and the molecular signaling that sets this in motion during muscle contractions. Contraction-induced molecular signaling is complex and involves a variety of signaling molecules including AMPK, Ca(2+), and NOS in the proximal part of the signaling cascade as well as GTPases, Rab, and SNARE proteins and cytoskeletal components in the distal part. While acute regulation of muscle glucose uptake relies on GLUT4 translocation, glucose uptake also depends on muscle GLUT4 expression which is increased following exercise. AMPK and CaMKII are key signaling kinases that appear to regulate GLUT4 expression via the HDAC4/5-MEF2 axis and MEF2-GEF interactions resulting in nuclear export of HDAC4/5 in turn leading to histone hyperacetylation on the GLUT4 promoter and increased GLUT4 transcription. Exercise training is the most potent stimulus to increase skeletal muscle GLUT4 expression, an effect that may partly contribute to improved insulin action and glucose disposal and enhanced muscle glycogen storage following exercise training in health and disease.

Chronic caffeine intake reverses age-induced insulin resistance in the rat: effect on skeletal muscle Glut4 transporters and AMPK activity

The role of caffeine consumption on insulin action is still under debate. The hypothesis that chronic caffeine intake reverses aging-induced insulin resistance in the rat was tested in this work. The mechanism by which caffeine restores insulin sensitivity was also investigated. Six groups of rats were used: 3 months old (3 M), 3 months old caffeine-treated (3MCaf), 12 months old (12 M), 12 months old caffeine-treated (12MCaf), 24 months old (24 M), and 24 months old caffeine-treated (24MCaf). Caffeine was administered in drinking water (1 g/l) during 15 days. Insulin sensitivity was assessed by means of the insulin tolerance test. Blood pressure, body weight, visceral and total fat, fasting glycemia and insulinemia, plasma nonesterified fatty acids (NEFA), total antioxidant capacity (TAC), cortisol, nitric oxide, and catecholamines were monitored. Skeletal muscle Glut4 and 5'-AMP activated protein kinase (AMPK) protein expression and activity were also assessed. Aged rats exhibited diminished insulin sensitivity accompanied by hyperinsulinemia and normoglycemia, increased visceral and total fat, decreased TAC and plasma catecholamines, and also decreased skeletal muscle Glut4 and AMPK protein expression. Chronic caffeine intake restored insulin sensitivity and regularized circulating insulin and NEFA in both aging models. Caffeine neither modified skeletal muscle AMPK expression nor activity in aged rats; however, it decreased visceral and total fat in 12 M rats and it restored skeletal muscle Glut4 expression to control values in 24 M rats. We concluded that chronic caffeine intake reverses aging-induced insulin resistance in rats by decreasing NEFA production and also by increasing Glut4 expression in skeletal muscle.

Effects of chronic caffeine administration on blood glucose levels and on glucose tolerance in healthy and diabetic rats

OBJECTIVE

To analyse the effect of chronic caffeine use on risk reduction and prognosis of diabetes mellitus.

METHODS

In this 60-day study, five groups of 11 healthy male Wistar rats were selected to receive one of four doses (37.5, 56.2, 75.0 or 93.0 mg/kg per day) of caffeine orally or no caffeine (control). The effect of caffeine on glycaemia and glucose tolerance was evaluated. After 15 days, each group was treated with 60 mg/kg of streptozotocine to induce diabetes mellitus, and glycaemia and glucose tolerance were assessed for a further 45 days.

RESULTS

In nondiabetic rats, caffeine had no effect on blood glucose. Compared with controls, the fasting blood glucose levels declined significantly in two caffeine-treated groups (93.0 mg/kg per day and 56.2 mg/kg per day) during the first 15 days following diabetes induction. Glucose tolerance was significantly improved 120 min after glucose loading in all caffeine-treated groups. The mean ± SE half-maximal effective concentration of caffeine was 35.79 ± 2.44 mg/dl.

CONCLUSIONS

Blood glucose levels decreased, and glucose tolerance improved, in diabetic rats administered increasing doses of caffeine.

Synergistic effect of caffeine and glucocorticoids on expression of surfactant protein B (SP-B) mRNA

Administration of glucocorticoids and caffeine is a common therapeutic intervention in the neonatal period, but possible interactions between these substances are still unclear. The present study investigated the effect of caffeine and different glucocorticoids on expression of surfactant protein (SP)-B, crucial for the physiological function of pulmonary surfactant. We measured expression levels of SP-B, various SP-B transcription factors including erythroblastic leukemia viral oncogene homolog 4 (ErbB4) and thyroid transcription factor-1 (TTF-1), as well as the glucocorticoid receptor (GR) after administering different doses of glucocorticoids, caffeine, cAMP, or the phosphodiesterase-4 inhibitor rolipram in the human airway epithelial cell line NCI-H441. Administration of dexamethasone (1 µM) or caffeine (5 mM) stimulated SP-B mRNA expression with a maximal of 38.8±11.1-fold and 5.2±1.4-fold increase, respectively. Synergistic induction was achieved after co-administration of dexamethasone (1 mM) in combination with caffeine (10 mM) (206±59.7-fold increase, p<0.0001) or cAMP (1 mM) (213±111-fold increase, p = 0.0108). SP-B mRNA was synergistically induced also by administration of caffeine with hydrocortisone (87.9±39.0), prednisolone (154±66.8), and betamethasone (123±6.4). Rolipram also induced SP-B mRNA (64.9±21.0-fold increase). We detected a higher expression of ErbB4 and GR mRNA (7.0- and 1.7-fold increase, respectively), whereas TTF-1, Jun B, c-Jun, SP1, SP3, and HNF-3α mRNA expression was predominantly unchanged. In accordance with mRNA data, mature SP-B was induced significantly by dexamethasone with caffeine (13.8±9.0-fold increase, p = 0.0134). We found a synergistic upregulation of SP-B mRNA expression induced by co-administration of various glucocorticoids and caffeine, achieved by accumulation of intracellular cAMP. This effect was mediated by a caffeine-dependent phosphodiesterase inhibition and by upregulation of both ErbB4 and the GR. These results suggested that caffeine is able to induce the expression of SP-transcription factors and affects the signaling pathways of glucocorticoids, amplifying their effects. Co-administration of caffeine and corticosteroids may therefore be of benefit in surfactant homeostasis.

The role of CaMKII in regulating GLUT4 expression in skeletal muscle

Contractile activity during physical exercise induces an increase in GLUT4 expression in skeletal muscle, helping to improve glucose transport capacity and insulin sensitivity. An important mechanism by which exercise upregulates GLUT4 is through the activation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in response to elevated levels of cytosolic Ca(2+) during muscle contraction. This review discusses the mechanism by which Ca(2+) activates CaMKII, explains research techniques currently used to alter CaMK activity in cells, and highlights various exercise models and pharmacological agents that have been used to provide evidence that CaMKII plays an important role in regulating GLUT4 expression. With regard to transcriptional mechanisms, the key research studies that identified myocyte enhancer factor 2 (MEF2) and GLUT4 enhancer factor as the major transcription factors regulating glut4 gene expression, together with their binding domains, are underlined. Experimental evidence showing that CaMK activation induces hyperacetylation of histones in the vicinity of the MEF2 domain and increases MEF2 binding to its cis element to influence MEF2-dependent Glut4 gene expression are also given along with data suggesting that p300 might be involved in acetylating histones on the Glut4 gene. Finally, an appraisal of the roles of other calcium- and non-calcium-dependent mechanisms, including the major HDAC kinases in GLUT4 expression, is also given.

Histone deacetylase modulators provided by Mother Nature

Protein acetylation status results from a balance between histone acetyltransferase and histone deacetylase (HDAC) activities. Alteration of this balance leads to a disruption of cellular integrity and participates in the development of numerous diseases, including cancer. Therefore, modulation of these activities appears to be a promising approach for anticancer therapy. Histone deacetylase inhibitors (HDACi) are epigenetically active drugs that induce the hyperacetylation of lysine residues within histone and non-histone proteins, thus affecting gene expression and cellular processes such as protein-protein interactions, protein stability, DNA binding and protein sub-cellular localization. Therefore, HDACi are promising anti-tumor agents as they may affect the cell cycle, inhibit proliferation, stimulate differentiation and induce apoptotic cell death. Over the last 30 years, numerous synthetic and natural products, including a broad range of dietary compounds, have been identified as HDACi. This review focuses on molecules from natural origins modulating HDAC activities and presenting promising anticancer activities.

MEF2A binding to the Glut4 promoter occurs via an AMPKα2-dependent mechanism

PURPOSE

The role of AMP-activated protein kinase α2 (AMPKα2) in regulating MEF2A nucleus translocation, nuclear histone deacetylase 5 (HDAC5) association with MEF2, HDAC5 nuclear export, MEF2A binding to the Glut4 promoter, and GLUT4 expression was investigated.

METHODS

This was investigated in muscles from AMPKα2 overexpression (OE) mice, AMPKα2 knockout (KO) mice, and corresponding wild-type (WT) mice that had undertaken a 28-d program of treadmill training by: 1) AMPKα-Thr172 phosphorylation by Western blot, 2) total and nuclear MEF2A by Western blot, 3) nuclear HDAC5 association with MEF2 by coimmunoprecipitation, 4) total and nuclear HDAC5 by Western blot, 5) bound MEF2A at the Glut4 MEF2 cis-element by chromatin immunoprecipitation, and 6) GLUT4 expression by real-time polymerase chain reaction and Western blot.

RESULTS

OE or KO of AMPKα2 isoform heightened or attenuated the training-induced increase in nuclear MEF2A content, Glut4 promoter-bound MEF2A. However, OE or KO of the AMPKα2 isoform did not have any effect on the content of nuclear HDAC5 association with MEF2 after 28 d of exercise training, although 35% lower nuclear HDAC5 protein content was found in α2-OE training muscles. Lastly, OE of the α2-isoform was associated with 120% and 155% higher GLUT4 protein and mRNA in training muscles. However, the training-induced increases of GLUT4 protein and mRNA contents were normal in α2-KO muscles despite the reduced AMPK signaling.

CONCLUSIONS

Exercise training increases the nuclear MEF2A content and binding of MEF2A to their binding sites on the Glut4 gene by an AMPKα2-dependent mechanism, but intracellular signaling molecules other than AMPKα2 are important in regulating training-induced HDAC5 nuclear export. Furthermore, although AMPKα2 mediates the training-induced increase in Glut4 promoter-bound MEF2A, the present data do not support an essential role of AMPKα2 in regulating training-induced GLUT4 expression in skeletal muscle.

Epigenetic regulation of glucose transporters in non-small cell lung cancer

Due to their inherently hypoxic environment, cancer cells often resort to glycolysis, or the anaerobic breakdown of glucose to form ATP to provide for their energy needs, known as the Warburg effect. At the same time, overexpression of the insulin receptor in non-small cell lung cancer (NSCLC) is associated with an increased risk of metastasis and decreased survival. The uptake of glucose into cells is carried out via glucose transporters or GLUTs. Of these, GLUT-4 is essential for insulin-stimulated glucose uptake. Following treatment with the epigenetic targeting agents histone deacetylase inhibitors (HDACi), GLUT-3 and GLUT-4 expression were found to be induced in NSCLC cell lines, with minimal responses in transformed normal human bronchial epithelial cells (HBECs). Similar results for GLUT-4 were observed in cells derived from liver, muscle, kidney and pre-adipocytes. Bioinformatic analysis of the promoter for GLUT-4 indicates that it may also be regulated by several chromatin binding factors or complexes including CTCF, SP1 and SMYD3. Chromatin immunoprecipitation studies demonstrate that the promoter for GLUT-4 is dynamically remodeled in response to HDACi. Overall, these results may have value within the clinical setting as (a) it may be possible to use this to enhance fluorodeoxyglucose (18F) positron emission tomography (FDG-PET) imaging sensitivity; (b) it may be possible to target NSCLC through the use of HDACi and insulin mediated uptake of the metabolic targeting drugs such as 2-deoxyglucose (2-DG); or (c) enhance or sensitize NSCLC to chemotherapy.

Caffeine activates preferentially α1-isoform of 5'AMP-activated protein kinase in rat skeletal muscle

AIM

Caffeine activates 5'AMP-activated protein kinase (AMPK), a signalling intermediary implicated in the regulation of glucose, lipid and energy metabolism in skeletal muscle. Skeletal muscle expresses two catalytic α subunits of AMPK, α1 and α2, but the isoform specificity of caffeine-induced AMPK activation is unclear. The aim of this study was to determine which α isoform is preferentially activated by caffeine in vitro and in vivo using rat skeletal muscle.

METHODS

Rat epitrochlearis muscle was isolated and incubated in vitro in the absence or presence of caffeine. In another experiment, the muscle was dissected after intravenous injection of caffeine. Isoform-specific AMPK activity, the phosphorylation status of AMPKα Thr(172) and acetyl-CoA carboxylase (ACC) Ser(79) , the concentrations of ATP, phosphocreatine (PCr) and glycogen, and 3-O-methyl-d-glucose (3MG) transport activity were estimated.

RESULTS

Incubation of isolated epitrochlearis muscle with 1 mm of caffeine for 15 min increased AMPKα1 activity, but not AMPKα2 activity; concentrations of ATP, PCr and glycogen were not affected. Incubation with 3 mm of caffeine activated AMPKα2 and reduced PCr and glycogen concentrations. Incubation with 1 mm of caffeine increased the phosphorylation of AMPK and ACC and enhanced 3MG transport. Intravenous injection of caffeine (5 mg kg(-1) ) predominantly activated AMPKα1 and increased 3MG transport without affecting energy status.

CONCLUSION

Our results suggest that of the two α isoforms of AMPK, AMPKα1 is predominantly activated by caffeine via an energy-independent mechanism and that the activation of AMPKα1 increases glucose transport and ACC phosphorylation in skeletal muscle.

Regulation of exercise-induced fiber type transformation, mitochondrial biogenesis, and angiogenesis in skeletal muscle

Skeletal muscle exhibits superb plasticity in response to changes in functional demands. Chronic increases of skeletal muscle contractile activity, such as endurance exercise, lead to a variety of physiological and biochemical adaptations in skeletal muscle, including mitochondrial biogenesis, angiogenesis, and fiber type transformation. These adaptive changes are the basis for the improvement of physical performance and other health benefits. This review focuses on recent findings in genetically engineered animal models designed to elucidate the mechanisms and functions of various signal transduction pathways and gene expression programs in exercise-induced skeletal muscle adaptations.

Histone modifications and exercise adaptations

The spatial association between genomic DNA and histone proteins within chromatin plays a key role in the regulation of gene expression and is largely governed by post-translational modifications to histone proteins, particularly H3 and H4. These modifications include phosphorylation, acetylation, and mono-, di-, and tri-methylation, and while some are associated with transcriptional repression, acetylation of lysine residues within H3 generally correlates with transcriptional activation. Histone acetylation is regulated by the balance between the activities of histone acetyl transferase (HAT) and histone deacetylase (HDAC). In skeletal muscle, the class II HDACs 4, 5, 7, and 9 play a key role in muscle development and adaptation and have been implicated in exercise adaptations. As just one example, exercise results in the nuclear export of HDACs 4 and 5, secondary to their phosphorylation by CaMKII and AMPK, two kinases that are activated during exercise in response to changes in sarcoplasmic Ca(2+) levels and energy status, in association with increased GLUT4 expression in human skeletal muscle. Unraveling the complexities of the so-called "histone code" before and after exercise is likely to lead to a greater understanding of the regulation of exercise/activity-induced alterations in skeletal muscle gene expression and reinforce the importance of skeletal muscle plasticity in health and disease.

Exercise-induced histone modifications in human skeletal muscle

Skeletal muscle adaptations to exercise confer many of the health benefits of physical activity and occur partly through alterations in skeletal muscle gene expression. The exact mechanisms mediating altered skeletal muscle gene expression in response to exercise are unknown. However, in recent years, chromatin remodelling through epigenetic histone modifications has emerged as a key regulatory mechanism controlling gene expression in general. The purpose of this study was to examine the effect of exercise on global histone modifications that mediate chromatin remodelling and transcriptional activation in human skeletal muscle in response to exercise. In addition, we sought to examine the signalling mechanisms regulating these processes. Following 60 min of cycling, global histone 3 acetylation at lysine 9 and 14, a modification associated with transcriptional initiation, was unchanged from basal levels, but was increased at lysine 36, a site associated with transcriptional elongation. We examined the regulation of the class IIa histone deacetylases (HDACs), which are enzymes that suppress histone acetylation and have been implicated in the adaptations to exercise. While we found no evidence of proteasomal degradation of the class IIa HDACs, we found that HDAC4 and 5 were exported from the nucleus during exercise, thereby removing their transcriptional repressive function. We also observed activation of the AMP-activated protein kinase (AMPK) and the calcium-calmodulin-dependent protein kinase II (CaMKII) in response to exercise, which are two kinases that induce phosphorylation-dependent class IIa HDAC nuclear export. These data delineate a signalling pathway that might mediate skeletal muscle adaptations in response to exercise.