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Mouse-human experimental epigenetic analysis unmasks dietary targets and genetic liability for diabetic phenotypes

ABSTRACT: Using a functional approach to investigate the epigenetics of Type 2 Diabetes (T2D), we combine three lines of evidence – diet-induced epigenetic dysregulation in mouse, epigenetic conservation in humans, and T2D clinical risk evidence – to identify genes implicated in T2D pathogenesis through epigenetic mechanisms related to obesity. Beginning with dietary manipulation of genetically homogeneous mice, we identify differentially DNA-methylated genomic regions. We then replicate these results in adipose samples from lean and obese patients pre- and post-Roux-en-Y gastric bypass, identifying regions where both the location and direction of methylation change is conserved. These regions overlap with 27 genetic T2D risk loci, only one of which was deemed significant by GWAS alone. Functional analysis of genes associated with these regions revealed four genes with roles in insulin resistance, demonstrating the potential general utility of this approach for complementing conventional human genetic studies by integrating cross-species epigenomics and clinical genetic risk.

ORGANISM(S): Mus musculus Homo sapiens

PROVIDER: GSE63981 | GEO | 2015/01/06

SECONDARY ACCESSION(S): PRJNA269687

REPOSITORIES: GEO

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Project description:Type 2 diabetes (T2D) is among the leading causes of death in the U.S. Ethnic differences in T2D prevalence are evident, including especially for Native Hawaiians (NHs) who remain disproportionately affected by it. This difference in T2D susceptibility involves an interplay between genetic and environmental factors, of which epigenetic mechanisms, including DNA methylation (DNAm) provide a novel approach to investigating gene-environment interactions of health and disease. Monocytes, an innate immune cell intrinsic to the inflammatory response, are a fundamental immune cell component that likely underlies T2D pathogenesis, given their involvement in inflammation and inflammation-associated insulin resistance and metabolic dysfunction. From participants enrolled into the Multiethnic Cohort Study (MEC), who self-identified as NH (n=152), Japanese American (JA; n=119), or White (n=121), we investigated monocyte-specific DNAm patterns in participants at a baseline visit, when free of T2D, using the HumanMethylation850K (850K) to determine whether monocytes harbor an ethnic-specific epigenetic signature of T2D risk that precedes T2D diagnosis. Using an epigenome-wide association study (EWAS), we found 904 significantly (q < 0.01) differentially methylated loci (DML) at a 5% difference in DNAm between participants who remained T2D free at a 15-year follow-up (i.e., controls) and those that would be diagnosed with T2D by follow-up (i.e., incident T2D) after adjusted for age, sex, and education level. These methylation differences were enriched at regulatory regions of the genome, including intergenic and intragenic regions. Notably, these DML were able to distinctly stratify NHs by T2D risk groups, however, this signature was inapparent in Whites and JAs. Likewise, NHs in the incident T2D group displayed a higher degree of DNAm variability. Sensitivity analysis with traditional risk factors (fasting glucose and body mass index [BMI]) and neighborhood socioeconomic status (nSES) found these risk factors had minimal effect on T2D risk-associated DML. Next, using a similar approach we found ethnic-specific DML in monocytes that was able to uniquely stratify NHs, JAs, and Whites, however, in NHs this epigenetic landscape displayed a higher degree of DNAm variability. Similarly, these DML were enriched at regulatory regions of the genome. In both cases, we found genes associated with biological functions and pathways relevant to monocyte functionality, including immune activation and cellular metabolism. Due to the higher degree of epigenetic variability in NHs, including especially NHs with T2D risk, we investigated differentially variable CpGs associated with T2D risk and ethnic-differences. We found differentially variable CpGs between T2D risk groups were able to stratify NHs with and without T2D risk, whereas it was unresolvable in JAs and Whites. Ethnic-specific DNAm variability clustered each ethnic population distinctly, and NH controls were further partitioned from NHs with T2D risk. Our findings suggest monocytes harbor a unique DNAm signature associated with T2D risk, which may be related to ethnic differences that underlie DNAm variability in monocytes. The increased epigenetic variability in monocytes from NHs may underlie epigenetic plasticity that could allow these cells to readily respond to adverse environmental conditions throughout the life course that may underlie long-term disease risk, whereas in other less susceptible populations with similar environmental exposure, this epigenetic plasticity may not be apparent in monocytes.

Project description:Endoplasmic reticulum (ER) and inflammatory stress responses are two pathophysiologic factors contributing to islet dysfunction and failure in Type 2 Diabetes (T2D). However, how human islet cells respond to these stressors and whether T2D-associated genetic variants modulate these responses is unknown. To fill this knowledge gap, we profiled transcriptional (RNA-seq) and epigenetic (ATAC-seq) remodeling in human islets exposed to ex vivo ER (thapsigargin) or inflammatory (IL-1β+IFN-γ) stress. 5,427 genes (~32%) were associated with stress responses; most were stressor-specific, including upregulation of genes mediating unfolded protein response (e.g. DDIT3, ATF4) and NFKB signaling (e.g. NFKB1, NFKBIA) in ER stress and inflammation respectively. Islet single-cell RNA-seq profiling revealed strong but heterogeneous beta cell ER stress responses, including a distinct beta cell subset that highly expressed apoptotic genes. Epigenetic profiling uncovered 14,968 stress-responsive cis-regulatory elements (CREs; ~14%), the majority of which were stressor-specific, and revealed increased accessibility at binding sites of transcription factors that were induced upon stress (e.g. ATF4 for ER stress, IRF8 for inflammation). Seventy-six stress-responsive CREs overlapped known T2D-associated variants, including 20 residing within CREs that were more accessible upon ER stress. Among these, we linked the rs6917676 T2D risk allele (T) to increased in vivo accessibility of an islet ER stress-responsive CRE and allele-specific beta-cell nuclear factor binding in vitro. We showed that MAP3K5, the only ER stress-responsive gene in this locus, promotes beta cell apoptosis. Consistent with its pro-apoptotic and putative diabetogenic roles, MAP3K5 expression inversely correlated with beta cell abundance in human islets and was upregulated in beta cells from T2D donors. Together, this study provides new genome-wide insights into human islet stress responses and putative mechanisms of T2D genetic variants.

Project description:Endoplasmic reticulum (ER) and inflammatory stress responses are two pathophysiologic factors contributing to islet dysfunction and failure in Type 2 Diabetes (T2D). However, how human islet cells respond to these stressors and whether T2D-associated genetic variants modulate these responses is unknown. To fill this knowledge gap, we profiled transcriptional (RNA-seq) and epigenetic (ATAC-seq) remodeling in human islets exposed to ex vivo ER (thapsigargin) or inflammatory (IL-1β+IFN-γ) stress. 5,427 genes (~32%) were associated with stress responses; most were stressor-specific, including upregulation of genes mediating unfolded protein response (e.g. DDIT3, ATF4) and NFKB signaling (e.g. NFKB1, NFKBIA) in ER stress and cytokine-induced inflammation respectively. Islet single-cell RNA-seq profiling revealed strong but heterogeneous beta cell ER stress responses, including a distinct beta cell subset that highly expressed apoptotic genes. Epigenetic profiling uncovered 14,968 stress-responsive cis-regulatory elements (CREs; ~14%), the majority of which were stressor-specific, and revealed increased accessibility at binding sites of transcription factors that were induced upon stress (e.g. ATF4 for ER stress, IRF8 for cytokine-induced inflammation). Eighty-six stress-responsive CREs overlapped known T2D-associated variants, including 20 residing within CREs that were more accessible upon ER stress. Among these, we linked the rs6917676 T2D risk allele (T) to increased in vivo accessibility of an islet ER stress-responsive CRE and allele-specific beta cell nuclear factor binding in vitro. We showed that MAP3K5, the only ER stress-responsive gene in this locus, promotes beta cell apoptosis. Consistent with its pro-apoptotic and putative diabetogenic roles, MAP3K5 expression inversely correlated with beta cell abundance in human islets and was induced in beta cells from T2D donors. Together, this study provides new genome-wide insights into human islet stress responses and putative mechanisms of T2D genetic variants.

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Mouse-human experimental epigenetic analysis unmasks dietary targets and genetic liability for diabetic phenotypes

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