An epigenome-wide association study of insulin resistance in African Americans

DNA methylation markers of insulin resistance surrogate measures in the Atherosclerosis Risk in Communities (ARIC) study

Insulin resistance (IR) is a risk factor for cardiovascular diseases and type 2 diabetes. Associations between DNA methylation (DNAm) and IR have been less studied in African ancestry (AA) populations than those of European ancestry (EA). We aimed to identify associations between whole blood DNAm and IR in up to 1,811 AA and 964 EA participants from the Atherosclerosis Risk in Communities (ARIC) study. We quantified IR using three surrogate measures: the homeostasis model assessment of insulin resistance (HOMA-IR), the triglyceride-glucose index (TyG), and the triglyceride glucose-body mass index (TyG-BMI). We used ancestry-stratified linear regression models to conduct epigenome-wide association studies of IR, adjusting for batch effects and relevant covariates. Among 484,436 tested CpG sites, 39 were significantly associated with IR, of which 31% (10 in AA and two in EA) were associated with TyG-BMI and not previously reported for IR or related traits. These include a positive association at cg18335991-SEMA7A in AA. SEMA7A inhibits adipogenesis of preadipocytes and lipogenesis of mature adipocytes. DNAm levels at cg18335991 have been reported to be negatively associated with SEMA7A expression in blood. After additionally adjusting for smoking and drinking status, 15 of the 39 significant CpG sites remained significant or suggestive. Our study identified novel IR-associated CpG sites, contributing to a broader understanding of the epigenetic mechanisms underlying IR in diverse populations.

Insulin Sensitivity and Skeletal Muscle Mitochondrial Respiration in Black and White Women With Obesity

OBJECTIVES

Non-Hispanic Black women (BW) have a greater risk of type 2 diabetes (T2D) and insulin resistance (IR) compared to non-Hispanic White women (WW). The mechanisms leading to these differences are not understood, and it is unclear whether synergistic effects of race and obesity impact disease risk. To understand the interaction of race and weight, hepatic and peripheral IR were compared in WW and BW with and without obesity.

METHODS

Hepatic and peripheral IR were measured by a labeled, hyperinsulinemic-euglycemic clamp in BW (n = 32) and WW (n = 32) with and without obesity. Measurements of body composition, cardiorespiratory fitness, and skeletal muscle (SM) respiration were completed. Data were analyzed by mixed model ANOVA.

RESULTS

Subjects with obesity had greater hepatic and peripheral IR and lower SM respiration (P < .001). Despite 14% greater insulin (P = .066), BW tended to have lower peripheral glucose disposal (Rd; P = .062), which was driven by women without obesity (P = .002). BW had significantly lower glucose production (P = .005), hepatic IR (P = .024), and maximal coupled and uncoupled respiration (P < .001) than WW. Maximal coupled and uncoupled SM mitochondrial respiration was strongly correlated with peripheral and hepatic IR (P < .01).

CONCLUSION

While BW without obesity had lower Rd than WW, race and obesity did not synergistically impact peripheral IR. Paradoxically, WW with obesity had greater hepatic IR compared to BW. Relationships between SM respiration and IR persisted across a range of body weights. These data provide support for therapies in BW, like exercise, that improve SM mitochondrial respiration to reduce IR and T2D risk.

Biological Basis of Breast Cancer-Related Disparities in Precision Oncology Era

Precision oncology is based on deep knowledge of the molecular profile of tumors, allowing for more accurate and personalized therapy for specific groups of patients who are different in disease susceptibility as well as treatment response. Thus, onco-breastomics is able to discover novel biomarkers that have been found to have racial and ethnic differences, among other types of disparities such as chronological or biological age-, sex/gender- or environmental-related ones. Usually, evidence suggests that breast cancer (BC) disparities are due to ethnicity, aging rate, socioeconomic position, environmental or chemical exposures, psycho-social stressors, comorbidities, Western lifestyle, poverty and rurality, or organizational and health care system factors or access. The aim of this review was to deepen the understanding of BC-related disparities, mainly from a biomedical perspective, which includes genomic-based differences, disparities in breast tumor biology and developmental biology, differences in breast tumors' immune and metabolic landscapes, ecological factors involved in these disparities as well as microbiomics- and metagenomics-based disparities in BC. We can conclude that onco-breastomics, in principle, based on genomics, proteomics, epigenomics, hormonomics, metabolomics and exposomics data, is able to characterize the multiple biological processes and molecular pathways involved in BC disparities, clarifying the differences in incidence, mortality and treatment response for different groups of BC patients.

Epigenetic Profiling of Type 2 Diabetes Mellitus: An Epigenome-Wide Association Study of DNA Methylation in the Korean Genome and Epidemiology Study

Diabetes is characterized by persistently high blood glucose levels and severe complications and affects millions of people worldwide. In this study, we explored the epigenetic landscape of diabetes using data from the Korean Genome and Epidemiology Study (KoGES), specifically the Ansung-Ansan (AS-AS) cohort. Using epigenome-wide association studies, we investigated DNA methylation patterns in patients with type 2 diabetes mellitus (T2DM) and those with normal glucose regulation. Differential methylation analysis revealed 106 differentially methylated probes (DMPs), with the 10 top DMPs prominently associated with TXNIP, PDK4, NBPF20, ARRDC4, UFM1, PFKFB2, C7orf50, and ABCG1, indicating significant changes in methylation. Correlation analysis highlighted the association between the leading DMPs (e.g., cg19693031 and cg26974062 for TXNIP and cg26823705 for NBPF20) and key glycemic markers (fasting plasma glucose and hemoglobin A1c), confirming their relevance in T2DM. Moreover, we identified 62 significantly differentially methylated regions (DMRs) spanning 61 genes. A DMR associated with PDE1C showed hypermethylation, whereas DMRs associated with DIP2C, FLJ90757, PRSS50, and TDRD9 showed hypomethylation. PDE1C and TDRD9 showed a strong positive correlation between the CpG sites included in each DMR, which have previously been implicated in T2DM-related processes. This study contributes to the understanding of epigenetic modifications in T2DM. These valuable insights can be utilized in identifying potential biomarkers and therapeutic targets for effective management and prevention of diabetes.

Multi-tissue epigenetic analysis identifies distinct associations underlying insulin resistance and Alzheimer's disease at CPT1A locus

BACKGROUND

Insulin resistance (IR) is a major risk factor for Alzheimer's disease (AD) dementia. The mechanisms by which IR predisposes to AD are not well-understood. Epigenetic studies may help identify molecular signatures of IR associated with AD, thus improving our understanding of the biological and regulatory mechanisms linking IR and AD.

METHODS

We conducted an epigenome-wide association study of IR, quantified using the homeostatic model assessment of IR (HOMA-IR) and adjusted for body mass index, in 3,167 participants from the Framingham Heart Study (FHS) without type 2 diabetes at the time of blood draw used for methylation measurement. We identified DNA methylation markers associated with IR at the genome-wide level accounting for multiple testing (P < 1.1 × 10-7) and evaluated their association with neurological traits in participants from the FHS (N = 3040) and the Religious Orders Study/Memory and Aging Project (ROSMAP, N = 707). DNA methylation profiles were measured in blood (FHS) or dorsolateral prefrontal cortex (ROSMAP) using the Illumina HumanMethylation450 BeadChip. Linear regressions (ROSMAP) or mixed-effects models accounting for familial relatedness (FHS) adjusted for age, sex, cohort, self-reported race, batch, and cell type proportions were used to assess associations between DNA methylation and neurological traits accounting for multiple testing.

RESULTS

We confirmed the strong association of blood DNA methylation with IR at three loci (cg17901584-DHCR24, cg17058475-CPT1A, cg00574958-CPT1A, and cg06500161-ABCG1). In FHS, higher levels of blood DNA methylation at cg00574958 and cg17058475 were both associated with lower IR (P = 2.4 × 10-11 and P = 9.0 × 10-8), larger total brain volumes (P = 0.03 and P = 9.7 × 10-4), and smaller log lateral ventricular volumes (P = 0.07 and P = 0.03). In ROSMAP, higher levels of brain DNA methylation at the same two CPT1A markers were associated with greater risk of cognitive impairment (P = 0.005 and P = 0.02) and higher AD-related indices (CERAD score: P = 5 × 10-4 and 0.001; Braak stage: P = 0.004 and P = 0.01).

CONCLUSIONS

Our results suggest potentially distinct epigenetic regulatory mechanisms between peripheral blood and dorsolateral prefrontal cortex tissues underlying IR and AD at CPT1A locus.

The Transcription Factor HOXA5: Novel Insights into Metabolic Diseases and Adipose Tissue Dysfunction

The transcription factor HOXA5, from the HOX gene family, has long been studied due to its critical role in physiological activities in normal cells, such as organ development and body patterning, and pathological activities in cancer cells. Nonetheless, recent evidence supports the hypothesis of a role for HOXA5 in metabolic diseases, particularly in obesity and type 2 diabetes (T2D). In line with the current opinion that adipocyte and adipose tissue (AT) dysfunction belong to the group of primary defects in obesity, linking this condition to an increased risk of insulin resistance (IR) and T2D, the HOXA5 gene has been shown to regulate adipocyte function and AT remodeling both in humans and mice. Epigenetics adds complexity to HOXA5 gene regulation in metabolic diseases. Indeed, epigenetic mechanisms, specifically DNA methylation, influence the dynamic HOXA5 expression profile. In human AT, the DNA methylation profile at the HOXA5 gene is associated with hypertrophic obesity and an increased risk of developing T2D. Thus, an inappropriate HOXA5 gene expression may be a mechanism causing or maintaining an impaired AT function in obesity and potentially linking obesity to its associated disorders. In this review, we integrate the current evidence about the involvement of HOXA5 in regulating AT function, as well as its association with the pathogenesis of obesity and T2D. We also summarize the current knowledge on the role of DNA methylation in controlling HOXA5 expression. Moreover, considering the susceptibility of epigenetic changes to reversal through targeted interventions, we discuss the potential therapeutic value of targeting HOXA5 DNA methylation changes in the treatment of metabolic diseases.