PATZ1 down-regulates FADS1 by binding to rs174557 and is opposed by SP1/SREBP1c.

The FADS1 and FADS2 genes in the FADS cluster encode the rate-limiting enzymes in the synthesis of long-chain polyunsaturated fatty acids (LC-PUFAs). Genetic variation in this region has been associated with a large number of diseases and traits many of them correlated to differences in metabolism of PUFAs. However, the causative variants leading to these associations have not been identified. Here we find that the multiallelic rs174557 located in an AluYe5 element in intron 1 of FADS1 is functional and lies within a PATZ1 binding site. The derived allele of rs174557, which is the common variant in most populations, diminishes binding of PATZ1, a transcription factor conferring allele-specific downregulation of FADS1. The PATZ1 binding site overlaps with a SP1 site. The competitive binding between the suppressive PATZ1 and the activating complex of SP1 and SREBP1c determines the enhancer activity of this region, which regulates expression of FADS1.

HDAC7 is overexpressed in human diabetic islets and impairs insulin secretion in rat islets and clonal beta cells.

AIMS/HYPOTHESIS: Pancreatic beta cell dysfunction is a prerequisite for the development of type 2 diabetes. Histone deacetylases (HDACs) may affect pancreatic endocrine function and glucose homeostasis through alterations in gene regulation. Our aim was to investigate the role of HDAC7 in human and rat pancreatic islets and clonal INS-1 beta cells (INS-1 832/13). METHODS: To explore the role of HDAC7 in pancreatic islets and clonal beta cells, we used RNA sequencing, mitochondrial functional analyses, microarray techniques, and HDAC inhibitors MC1568 and trichostatin A. RESULTS: Using RNA sequencing, we found increased HDAC7 expression in human pancreatic islets from type 2 diabetic compared with non-diabetic donors. HDAC7 expression correlated negatively with insulin secretion in human islets. To mimic the situation in type 2 diabetic islets, we overexpressed Hdac7 in rat islets and clonal beta cells. In both, Hdac7 overexpression resulted in impaired glucose-stimulated insulin secretion. Furthermore, it reduced insulin content, mitochondrial respiration and cellular ATP levels in clonal beta cells. Overexpression of Hdac7 also led to changes in the genome-wide gene expression pattern, including increased expression of Tcf7l2 and decreased expression of gene sets regulating DNA replication and repair as well as nucleotide metabolism. In accordance, Hdac7 overexpression reduced the number of beta cells owing to enhanced apoptosis. Finally, we found that inhibiting HDAC7 activity with pharmacological inhibitors or small interfering RNA-mediated knockdown restored glucose-stimulated insulin secretion in beta cells that were overexpressing Hdac7. CONCLUSIONS/INTERPRETATION: Taken together, these results indicate that increased HDAC7 levels caused beta cell dysfunction and may thereby contribute to defects seen in type 2 diabetic islets. Our study supports HDAC7 inhibitors as a therapeutic option for the treatment of type 2 diabetes.

Nucleosome regulatory dynamics in response to TGFß.

Nucleosomes play important roles in a cell beyond their basal functionality in chromatin compaction. Their placement affects all steps in transcriptional regulation, from transcription factor (TF) binding to messenger ribonucleic acid (mRNA) synthesis. Careful profiling of their locations and dynamics in response to stimuli is important to further our understanding of transcriptional regulation by the state of chromatin. We measured nucleosome occupancy in human hepatic cells before and after treatment with transforming growth factor beta 1 (TGFß1), using massively parallel sequencing. With a newly developed method, SuMMIt, for precise positioning of nucleosomes we inferred dynamics of the nucleosomal landscape. Distinct nucleosome positioning has previously been described at transcription start site and flanking TF binding sites. We found that the average pattern is present at very few sites and, in case of TF binding, the double peak surrounding the sites is just an artifact of averaging over many loci. We systematically searched for depleted nucleosomes in stimulated cells compared to unstimulated cells and identified 24 318 loci. Depending on genomic annotation, 44-78% of them were over-represented in binding motifs for TFs. Changes in binding affinity were verified for HNF4α by qPCR. Strikingly many of these loci were associated with expression changes, as measured by RNA sequencing.

Author Correction: ATAC-seq reveals alterations in open chromatin in pancreatic islets from subjects with type 2 diabetes.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

ATAC-seq reveals alterations in open chromatin in pancreatic islets from subjects with type 2 diabetes.

Impaired insulin secretion from pancreatic islets is a hallmark of type 2 diabetes (T2D). Altered chromatin structure may contribute to the disease. We therefore studied the impact of T2D on open chromatin in human pancreatic islets. We used assay for transposase-accessible chromatin using sequencing (ATAC-seq) to profile open chromatin in islets from T2D and non-diabetic donors. We identified 57,105 and 53,284 ATAC-seq peaks representing open chromatin regions in islets of non-diabetic and diabetic donors, respectively. The majority of ATAC-seq peaks mapped near transcription start sites. Additionally, peaks were enriched in enhancer regions and in regions where islet-specific transcription factors (TFs), e.g. FOXA2, MAFB, NKX2.2, NKX6.1 and PDX1, bind. Islet ATAC-seq peaks overlap with 13 SNPs associated with T2D (e.g. rs7903146, rs2237897, rs757209, rs11708067 and rs878521 near TCF7L2, KCNQ1, HNF1B, ADCY5 and GCK, respectively) and with additional 67 SNPs in LD with known T2D SNPs (e.g. SNPs annotated to GIPR, KCNJ11, GLIS3, IGF2BP2, FTO and PPARG). There was enrichment of open chromatin regions near highly expressed genes in human islets. Moreover, 1,078 open chromatin peaks, annotated to 898 genes, differed in prevalence between diabetic and non-diabetic islet donors. Some of these peaks are annotated to candidate genes for T2D and islet dysfunction (e.g. HHEX, HMGA2, GLIS3, MTNR1B and PARK2) and some overlap with SNPs associated with T2D (e.g. rs3821943 near WFS1 and rs508419 near ANK1). Enhancer regions and motifs specific to key TFs including BACH2, FOXO1, FOXA2, NEUROD1, MAFA and PDX1 were enriched in differential islet ATAC-seq peaks of T2D versus non-diabetic donors. Our study provides new understanding into how T2D alters the chromatin landscape, and thereby accessibility for TFs and gene expression, in human pancreatic islets.

The Lysine Demethylase KDM5B Regulates Islet Function and Glucose Homeostasis.

AIMS: Posttranslational modifications of histones and transcription factors regulate gene expression and are implicated in beta-cell failure and diabetes. We have recently shown that preserving H3K27 and H3K4 methylation using the lysine demethylase inhibitor GSK-J4 reduces cytokine-induced destruction of beta-cells and improves beta-cell function. Here, we investigate the therapeutic potential of GSK-J4 to prevent diabetes development and examine the importance of H3K4 methylation for islet function. MATERIALS AND METHODS: We used two mouse models of diabetes to investigate the therapeutic potential of GSK-J4. To clarify the importance of H3K4 methylation, we characterized a mouse strain with knockout (KO) of the H3K4 demethylase KDM5B. RESULTS: GSK-J4 administration failed to prevent the development of experimental diabetes induced by multiple low-dose streptozotocin or adoptive transfer of splenocytes from acutely diabetic NOD to NODscid mice. KDM5B-KO mice were growth retarded with altered body composition, had low IGF-1 levels, and exhibited reduced insulin secretion. Interestingly, despite secreting less insulin, KDM5B-KO mice were able to maintain normoglycemia following oral glucose tolerance test, likely via improved insulin sensitivity, as suggested by insulin tolerance testing and phosphorylation of proteins belonging to the insulin signaling pathway. When challenged with high-fat diet, KDM5B-deficient mice displayed similar weight gain and insulin sensitivity as wild-type mice. CONCLUSION: Our results show a novel role of KDM5B in metabolism, as KDM5B-KO mice display growth retardation and improved insulin sensitivity.

Lysine demethylase inhibition protects pancreatic ß cells from apoptosis and improves ß-cell function.

Transcriptional changes control ß-cell survival in response to inflammatory stress. Posttranslational modifications of histone and non-histone transcriptional regulators activate or repress gene transcription, but the link to cell-fate signaling is unclear. Inhibition of lysine deacetylases (KDACs) protects ß cells from cytokine-induced apoptosis and reduces type 1 diabetes incidence in animals. We hypothesized that also lysine demethylases (KDMs) regulate ß-cell fate in response to inflammatory stress. Expression of the demethylase Kdm6B was upregulated by proinflammatory cytokines suggesting a possible role in inflammation-induced ß-cell destruction. Inhibition of KDM6 demethylases using the selective inhibitor GSK-J4 protected insulin-producing cells and human and mouse islets from cytokine-induced apoptosis by blunting nuclear factor (NF)-κB signaling and endoplasmic reticulum (ER) stress response gene expression. GSK-J4 furthermore increased expression of insulin gene and glucose-stimulated insulin secretion. Expression of genes regulating purinergic and cytokine ligand-receptor interactions was downregulated following GSK-J4 exposure, while expression of genes involved in cell maintenance and survival was upregulated. These data suggest that KDMs are important regulators of inflammation-induced ß-cell dysfunction and death.

Epigenetic alterations in blood mirror age-associated DNA methylation and gene expression changes in human liver.

AIM: To study the impact of aging on DNA methylation and mRNA expression in human liver. EXPERIMENTAL PROCEDURES: We analysed genome-wide DNA methylation and gene expression in human liver samples using Illumina 450K and HumanHT12 expression BeadChip arrays. RESULTS: DNA methylation analysis of ∼455,000 CpG sites in human liver revealed that age was significantly associated with altered DNA methylation of 20,396 CpG sites. Comparison of liver methylation data with published methylation data in other tissues showed that vast majority of the age-associated significant CpG sites overlapped between liver and blood, whereas a smaller overlap was found between liver and pancreatic islets or adipose tissue, respectively. We identified 151 genes whose liver expression also correlated with age. CONCLUSIONS: We identified age-associated DNA methylation and expression changes in human liver that are partly reflected by epigenetic alterations in blood.

lobChIP: from cells to sequencing ready ChIP libraries in a single day.

BACKGROUND: ChIP-seq is the method of choice for genome-wide studies of protein-DNA interactions. We describe a new method for ChIP-seq sample preparation, termed lobChIP, where the library reactions are performed on cross-linked ChIP fragments captured on beads. RESULTS: The lobChIP method was found both to reduce time and cost and to simplify the processing of many samples in parallel. lobChIP has an early incorporation of barcoded sequencing adaptors that minimizes the risk of sample cross-contamination and can lead to reduced amount of adaptor dimers in the sequencing libraries, while allowing for direct decross-linking and amplification of the sample. CONCLUSIONS: With results for histone modifications and transcription factors, we show that lobChIP performs equal to or better than standard protocols and that it makes it possible to go from cells to sequencing ready libraries within a single day.

ChIP-seq in steatohepatitis and normal liver tissue identifies candidate disease mechanisms related to progression to cancer.

BACKGROUND: Steatohepatitis occurs in alcoholic liver disease and may progress to liver cirrhosis and hepatocellular carcinoma. Its molecular pathogenesis is to a large degree unknown. Histone modifications play a key role in transcriptional regulations as marks for silencing and activation of gene expression and as marks for functional elements. Many transcription factors (TFs) are crucial for the control of the genes involved in metabolism, and abnormality in their function may lead to disease. METHODS: We performed ChIP-seq of the histone modifications H3K4me1, H3K4me3 and H3K27ac and a candidate transcription factor (USF1) in liver tissue from patients with steatohepatitis and normal livers and correlated results to mRNA-expression and genotypes. RESULTS: We found several regions that are differentially enriched for histone modifications between disease and normal tissue, and qRT-PCR results indicated that the expression of the tested genes strongly correlated with differential enrichment of histone modifications but is independent of USF1 enrichment. By gene ontology analysis of differentially modified genes we found many disease associated genes, some of which had previously been implicated in the etiology of steatohepatitis. Importantly, the genes associated to the strongest histone peaks in the patient were over-represented in cancer specific pathways suggesting that the tissue was on a path to develop to cancer, a common complication to the disease. We also found several novel SNPs and GWAS catalogue SNPs that are candidates to be functional and therefore needs further study. CONCLUSION: In summary we find that analysis of chromatin features in tissue samples provides insight into disease mechanisms.