Extensive changes in the transcriptional profile of human adipose tissue including genes involved in oxidative phosphorylation after a 6-month exercise intervention

AIM

Adipose tissue has an important function in total energy homeostasis, and its dysregulation may contribute to lifestyle-related diseases such as type 2 diabetes, cancer and cardiovascular diseases. The aim of this study was to investigate genome-wide mRNA expression in adipose tissue in healthy men before and after an exercise intervention to identify genes or pathways that mediate the beneficial effect of regular exercise. We also investigated the difference in adipose tissue mRNA expression between individuals with or without a family history of type 2 diabetes.

METHODS

The 6-month supervised exercise intervention was conducted in 47 healthy men (age 37.8 ± 4.3 years, BMI 28.5 ± 3.6 kg m(-2) ) with a previous low level of physical activity. RNA was analysed using GeneChip Human Gene 1.0 ST arrays (Affymetrix) before and after the exercise.

RESULTS

We identified 2,560 significant transcripts differentially expressed before vs. after exercise with a false discovery rate (FDR) < 0.1%, including genes encoding the respiratory chain, histone subunits, small nucleolar RNAs and ribosomal proteins. Additionally, pathways enriched in response to exercise include the ribosome, oxidative phosphorylation, proteasome and many metabolic pathways, whereas the WNT and MAPK signalling pathways were down-regulated (FDR < 5%) after exercise. There were no significant differences in mRNA expression between individuals with or without a family history of type 2 diabetes.

CONCLUSION

Exercise increased the expression of genes involved in oxidative phosphorylation, which is the opposite of what has been seen in adipose tissue from elderly or obese individuals with low physical fitness, and our study thereby demonstrates a mechanism for the beneficial effect of exercise.

A novel splicing site mutation of the GPR143 gene in a Chinese X-linked ocular albinism pedigree

Ocular albinism is an X-linked inherited disease characterized by hypopigmentation of the iris and nystagmus. To identify a new disease-causing mutation of ocular albinism, we collected a Han Chinese pedigree with 7 male congenital nystagmus patients over 3 generations. Slit-lamp photography and optical coherence tomography were performed for the proband. Genomic DNA was extracted from a whole blood sample from the proband using the high-salt method. Polymerase chain reaction (PCR) sequencing was carried out for GPR143 and FRMD7 genes. The three-dimensional structures of the wild-type and mutant GPR143 proteins were determined using SWISS-MODEL. The transmission of the disease in the pedigree clearly followed an X-linked pattern. The proband had significant iris and fundus hypopigmentation. Optical coherence tomography showed severe foveal hypoplasias in both eyes of the proband. A novel splicing site (G/C) mutation was found on the boundary of the 6th intron and the 7th exon of the GPR143 gene, resulting in a 9-amino-acid deletion (codons 257-265) in the 6th transmembrane domain of the GPR143 protein. In conclusion, a novel splicing site mutation of the GPR143 gene was found in a Han Chinese congenital ocular albinism pedigree.

Identification of CpG-SNPs associated with type 2 diabetes and differential DNA methylation in human pancreatic islets

AIMS/HYPOTHESIS

To date, the molecular function of most of the reported type 2 diabetes-associated loci remains unknown. The introduction or removal of cytosine-phosphate-guanine (CpG) dinucleotides, which are possible sites of DNA methylation, has been suggested as a potential mechanism through which single-nucleotide polymorphisms (SNPs) can affect gene function via epigenetics. The aim of this study was to examine if any of 40 SNPs previously associated with type 2 diabetes introduce or remove a CpG site and if these CpG-SNPs are associated with differential DNA methylation in pancreatic islets of 84 human donors.

METHODS

DNA methylation was analysed using pyrosequencing.

RESULTS

We found that 19 of 40 (48%) type 2 diabetes-associated SNPs introduce or remove a CpG site. Successful DNA methylation data were generated for 16 of these 19 CpG-SNP loci, representing the candidate genes TCF7L2, KCNQ1, PPARG, HHEX, CDKN2A, SLC30A8, DUSP9, CDKAL1, ADCY5, SRR, WFS1, IRS1, DUSP8, HMGA2, TSPAN8 and CHCHD9. All analysed CpG-SNPs were associated with differential DNA methylation of the CpG-SNP site in human islets. Moreover, six CpG-SNPs, representing TCF7L2, KCNQ1, CDKN2A, ADCY5, WFS1 and HMGA2, were also associated with DNA methylation of surrounding CpG sites. Some of the type 2 diabetes CpG-SNP sites that exhibit differential DNA methylation were further associated with gene expression, alternative splicing events determined by splice index, and hormone secretion in the human islets. The 19 type 2 diabetes-associated CpG-SNPs are in strong linkage disequilibrium (r² > 0.8) with a total of 295 SNPs, including 91 CpG-SNPs.

CONCLUSIONS/INTERPRETATION

Our results suggest that the introduction or removal of a CpG site may be a molecular mechanism through which some of the type 2 diabetes SNPs affect gene function via differential DNA methylation and consequently contributes to the phenotype of the disease.

Osteocalcin, glucose metabolism, lipid profile and chronic low-grade inflammation in middle-aged and elderly Chinese

AIM

To assess the relationship between serum total osteocalcin and measurements of adiposity, glucose tolerance, lipid profile, adipokine and chronic low-grade inflammation in middle-aged and elderly Chinese subjects.

METHODS

We performed a cross-sectional community-based study in central Shanghai. Serum total osteocalcin was measured by radioimmunoassay in 783 men and 946 post-menopausal women. Their associations with measurements of adiposity, glucose tolerance, lipid profile and chronic low-grade inflammation were examined.

RESULTS

Serum total osteocalcin levels revealed a sexual dimorphism, with post-menopausal women having significantly higher levels than men (P < 0.001). Serum osteocalcin levels of participants with self-reported cardiovascular disease were significantly lower (P = 0.044) than those without. In men, serum osteocalcin levels of participants with the metabolic syndrome were significantly lower than those without the metabolic syndrome (P = 0.036). Serum osteocalcin correlated negatively with fasting serum insulin, homeostasis model assessment of insulin resistance, alanine aminotransferase, triglycerides and total cholesterol, and positively with homeostasis model assessment of β-cell function in both men and post-menopausal women (all P < 0.05). In men, serum osteocalcin correlated negatively with BMI, diastolic blood pressure, fasting plasma glucose and 2-h oral glucose tolerance test glucose after adjustment for age (all P < 0.05). In post-menopausal women, serum osteocalcin correlated negatively with waist-hip ratio, LDL cholesterol and C-reactive protein, and positively with adiponectin (all P < 0.05). Serum osteocalcin was not associated with CXC chemokine ligand 5 level (P > 0.05). Alanine aminotransferase was an independent predictor of serum osteocalcin in both men and post-menopausal women (both P < 0.001). Adiponectin was an independent predictor of serum osteocalcin in post-menopausal women (P = 0.011). Serum osteocalcin was an independent predictor of homeostasis model assessment of β-cell function in both genders (both P < 0.05).

CONCLUSIONS

Serum total osteocalcin was closely associated with glucose and lipid metabolism in both Chinese men and post-menopausal women.

Effects of short-term high-fat overfeeding on genome-wide DNA methylation in the skeletal muscle of healthy young men

AIMS/HYPOTHESIS

Energy-dense diets that are high in fat are associated with a risk of metabolic diseases. The underlying molecular mechanisms could involve epigenetics, as recent data show altered DNA methylation of putative type 2 diabetes candidate genes in response to high-fat diets. We examined the effect of a short-term high-fat overfeeding (HFO) diet on genome-wide DNA methylation patterns in human skeletal muscle.

METHODS

Skeletal muscle biopsies were obtained from 21 healthy young men after ingestion of a short-term HFO diet and a control diet, in a randomised crossover setting. DNA methylation was measured in 27,578 CpG sites/14,475 genes using Illumina's Infinium Bead Array. Candidate gene expression was determined by quantitative real-time PCR.

RESULTS

HFO introduced widespread DNA methylation changes affecting 6,508 genes (45%), with a maximum methylation change of 13.0 percentage points. The HFO-induced methylation changes were only partly and non-significantly reversed after 6-8 weeks. Alterations in DNA methylation levels primarily affected genes involved in inflammation, the reproductive system and cancer. Few gene expression changes were observed and these had poor correlation to DNA methylation.

CONCLUSIONS/INTERPRETATION

The genome-wide DNA methylation changes induced by the short-term HFO diet could have implications for our understanding of transient epigenetic regulation in humans and its contribution to the development of metabolic diseases. The slow reversibility suggests a methylation build-up with HFO, which over time may influence gene expression levels.

First-degree relatives of type 2 diabetic patients have reduced expression of genes involved in fatty acid metabolism in skeletal muscle

CONTEXT

First-degree relatives of patients with type 2 diabetes (FH+) have been shown to have decreased energy expenditure and decreased expression of mitochondrial genes in skeletal muscle. In previous studies, it has been difficult to distinguish whether mitochondrial dysfunction and differential regulation of genes are primary (genetic) or due to reduced physical activity, obesity, or other correlated factors.

OBJECTIVE

The aim of this study was to investigate whether mitochondrial dysfunction is a primary defect or results from an altered metabolic state.

DESIGN

We compared gene expression in skeletal muscle from 24 male subjects with FH and 26 without FH matched for age, glucose tolerance, VO(2peak) (peak oxygen uptake), and body mass index using microarrays. Additionally, type fiber composition, mitochondrial DNA content, and citrate synthase activity were measured. The results were followed up in an additional cohort with measurements of in vivo metabolism.

RESULTS

FH+ vs. FH- subjects showed reduced expression of mitochondrial genes (P = 2.75 × 10(-6)), particularly genes involved in fatty acid metabolism (P = 4.08 × 10(-7)), despite similar mitochondrial DNA content. Strikingly, a 70% reduced expression of the monoamine oxidase A (MAOA) gene was found in FH+ vs. FH- individuals (P = 0.0009). Down-regulation of the genes involved in fat metabolism was associated with decreased in vivo fat oxidation and increased glucose oxidation examined in an additional cohort of elderly men.

CONCLUSIONS

These results suggest that genetically altered fatty acid metabolism predisposes to type 2 diabetes and propose a role for catecholamine-metabolizing enzymes like MAOA in the regulation of energy metabolism.

Effect of progesterone on colonic motility and fecal output in mice with diarrhea

BACKGROUND

  Patients with diarrhea and slow transit constipation (STC) have high 5-HT levels. In STC, the high 5-HT levels have been difficult to explain, as 5-HT stimulates peristalsis. Over expression of progesterone (P4) receptors in epithelial and muscle cells of the colon may reconcile this contradiction because P4 decreases SERT and increases 5-HT levels, but their effects are rendered ineffective because of the impaired muscle contraction.

AIMS

  We examined whether P4 treatment could reduce the stool output in two mouse diarrheal models because of higher 5-HT levels, the SERT knock-out (KO), and the fluoxetine-treated mice.

METHODS

  Contractility of colon circular muscle strips from wild mice was studied. Fecal water and dry fecal output were measured daily over a 4-day period in wild and SERT-KO mice and in fluoxetine-treated mice treated with IM saline or P4. 5-HT levels were measured using ELISA.

KEY RESULTS

  Progesterone blocked the spontaneous and stimulated phasic contractions. Fecal water output measured in two consecutive 4-day periods was not different in wild and SERT-KO mice. The fecal output in the SERT-KO mice was higher than in wild mice. P4 treatment reduced the 4-day fecal output in both groups compared with saline treatment. Oral fluoxetine treatment increased 5-HT levels in wild mice and increased the 4-day fecal output compared with oral saline. P4 treatment caused a decrease in the fecal output in both groups.

CONCLUSIONS & INFERENCES

  Progesterone decreased the contractility of circular muscle strips, and reduced the fecal output in two diarrheal models, the SERT-KO and fluoxetine-treated mice.

Development of optimized AAV3 serotype vectors: mechanism of high-efficiency transduction of human liver cancer cells

Our recent studies have revealed that among the 10 different commonly used adeno-associated virus (AAV) serotypes, AAV3 vectors transduce human liver cancer cells extremely efficiently because these cells express high levels of human hepatocyte growth factor receptor (hHGFR), and AAV3 utilizes hHGFR as a cellular co-receptor for viral entry. In this report, we provide further evidence that both extracellular as well as intracellular kinase domains of hHGFR are involved in AAV3 vector entry and AAV3-mediated transgene expression. We also document that AAV3 vectors are targeted for degradation by the host cell proteasome machinery, and that site-directed mutagenesis of surface-exposed tyrosine (Y) to phenylalanine (F) residues on AAV3 capsids significantly improves the transduction efficiency of Y701F, Y705F and Y731F mutant AAV3 vectors. The transduction efficiency of the Y705+731F double-mutant vector is significantly higher than each of the single mutants in liver cancer cells in vitro. In immunodeficient mouse xenograft models, direct intratumoral injection of AAV3 vectors also led to high-efficiency transduction of human liver tumor cells in vivo. We also document here that the optimized tyrosine-mutant AAV3 vectors lead to increased transduction efficiency following both intratumoral and tail-vein injections in vivo. The optimized tyrosine-mutant AAV3 serotype vectors containing proapoptotic genes should prove useful for the potential gene therapy of human liver cancers.

Insulin promoter DNA methylation correlates negatively with insulin gene expression and positively with HbA(1c) levels in human pancreatic islets

AIMS/HYPOTHESIS

Although recent studies propose that epigenetic factors influence insulin expression, the regulation of the insulin gene in type 2 diabetic islets is still not fully understood. Here, we examined DNA methylation of the insulin gene promoter in pancreatic islets from patients with type 2 diabetes and non-diabetic human donors and related it to insulin expression, HbA(1c) levels, BMI and age.

METHODS

DNA methylation was analysed in 25 CpG sites of the insulin promoter and insulin mRNA expression was analysed using quantitative RT-PCR in pancreatic islets from nine donors with type 2 diabetes and 48 non-diabetic donors.

RESULTS

Insulin mRNA expression (p = 0.002), insulin content (p = 0.004) and glucose-stimulated insulin secretion (p = 0.04) were reduced in pancreatic islets from patients with type 2 diabetes compared with non-diabetic donors. Moreover, four CpG sites located 234 bp, 180 and 102 bp upstream and 63 bp downstream of the transcription start site (CpG -234, -180, -102 and +63, respectively), showed increased DNA methylation in type 2 diabetic compared with non-diabetic islets (7.8%, p = 0.03; 7.1%, p = 0.02; 4.4%, p = 0.03 and 9.3%, p = 0.03, respectively). While insulin mRNA expression correlated negatively (p < 1 × 10(-6)), the level of HbA(1c) correlated positively (p ≤ 0.01) with the degree of DNA methylation for CpG -234, -180 and +63. Furthermore, DNA methylation for nine additional CpG sites correlated negatively with insulin mRNA expression (p ≤ 0.01). Also, exposure to hyperglycaemia for 72 h increased insulin promoter DNA methylation in clonal rat beta cells (p = 0.005).

CONCLUSIONS/INTERPRETATIONS

This study demonstrates that DNA methylation of the insulin promoter is increased in patients with type 2 diabetes and correlates negatively with insulin gene expression in human pancreatic islets.

Prolactin suppresses malonyl-CoA concentration in human adipose tissue

Prolactin is best known for its involvement in lactation, where it regulates mechanisms that supply nutrients for milk production. In individuals with pathological hyperprolactinemia, glucose and fat homeostasis have been reported to be negatively influenced. It is not previously known, however, whether prolactin regulates lipogenesis in human adipose tissue. The aim of this study was to investigate the effect of prolactin on lipogenesis in human adipose tissue in vitro. Prolactin decreased the concentration of malonyl-CoA, the product of the first committed step in lipogenesis, to 77+/-6% compared to control 100+/-5% (p=0.022) in cultured human adipose tissue. In addition, prolactin was found to decrease glucose transporter 4 ( GLUT4) mRNA expression, which may cause decreased glucose uptake. In conclusion, we propose that prolactin decreases lipogenesis in human adipose tissue as a consequence of suppressed malonyl-CoA concentration in parallel with decreased GLUT-4 expression. In the lactating woman, this regulation in adipose tissue may enhance the provision of nutrients for the infant instead of nutrients being stored in adipose tissue. In hyperprolactinemic individuals, a suppressed lipogenesis could contribute to an insulin resistant state with consequences for the health.