Effects of iron homeostasis on epigenetic age acceleration: a two-sample Mendelian randomization study

Association Between Body Iron Status and Biological Aging

BACKGROUND/OBJECTIVES

Iron is necessary for bodily function, but abnormal levels can increase the risk of chronic diseases. Studies of leukocyte telomere length suggest blood iron levels are positively associated with cellular senescence and accelerated aging. However, associations between blood iron and more robust metrics of biological aging, specifically those based on DNA methylation, have not been examined.

METHODS

In a random sample of women from the Sister Study (n = 1260) with measured serum iron (ferritin, iron, transferrin saturation), we used linear regression models to assess cross-sectional associations between standardized serum iron and three methylation-based biological aging metrics (GrimAgeAccel, PhenoAgeAccel, and DunedinPACE), with and without adjustment for smoking, alcohol, menopause status, education, time since menopause, exercise, and diet.

RESULTS

In adjusted models, a one standard deviation increase in serum ferritin was positively associated with higher standardized levels of DunedinPACE, GrimAgeAccel, and PhenoAgeAccel (DunedinPACE: 0.05, (0.00, 0.10); PhenoAgeAccel: 0.06 (0.00, 0.11); GrimAgeAccel: 0.06 (0.01, 0.11)). In contrast, higher serum iron and transferrin saturation were inversely associated with the biological aging metrics (serum iron, DunedinPACE: -0.02, (-0.07, 0.03); PhenoAgeAccel: -0.04 (-0.10, 0.01); GrimAgeAccel: -0.05 (-0.10, -0.01); transferrin saturation (DunedinPACE: -0.01, (-0.06, 0.05); PhenoAgeAccel: -0.01 (-0.06, 0.05); GrimAgeAccel: -0.05 (-0.10, -0.01))).

CONCLUSIONS

The positive association with ferritin is consistent with the proposed role of oxidative stress in accelerated aging associated with high iron exposure. However, the observed inverse associations with serum iron and transferrin saturation are not consistent with this common explanation, and future studies are needed to examine potential explanations.

Epigenetic modifications of nuclear and mitochondrial DNA are associated with the disturbance of serum iron biomarkers among the metabolically unhealthy obesity school-age children

BACKGROUND

Serum iron biomarkers are disordered on the progression of obesity and its associated metabolic syndrome (MetS). However, limited evidence is explored the interactions between serum iron biomarkers and the incidence of MetS. Thus, the purpose of this study is to discuss whether epigenetic modifications of nuclear and mitochondrial DNA (mtDNA) are associated with the disturbance of serum iron biomarkers among the metabolically unhealthy obesity (MUO) school-age children.

METHODS

A representative cross-sectional study was performed using the data from 104 obesity school-age children, while the subjects without obesity were as controls (n = 65). Then, the 104 obesity subjects were defined as metabolically healthy obesity (MHO, n = 60) and MUO (n = 44) subgroups according to whether they were accompanied with MetS. Their serum metabolic indicators, transferrin receptor 1 (TFR1), transferrin (TF) and genome-wide methylation were determined by the Elisa method. Moreover, the methylation levels of TFR1 and TF were measured by the Bisulfite sequencing PCR (BSP-PCR). Furthermore, the copy number (mtDNA-CN) and methylation of mtDNA were detected by the RT-PCR, while the semi-long RT-PCR was then used to estimate the lesions of mtDNA.

RESULTS

Compared with the control and MHO groups, the levels of MetS related indicators, anthropological characteristics and 8-OHdG were higher, and the concentrations of CAT, GSH-Px, TF, TFR1 and genome-wide methylation were lower in the MUO group in a BMI-independent manner (P < 0.05). Then, the contents of serum iron were lower in both the MHO and MUO groups than those in the control group (P < 0.017). Moreover, they were positively related with the contents of serum CAT and GSH-Px, and negatively with 8-OHdG, TF and TFR1 (P < 0.05). Furthermore, the methylation patterns on the TF, TFR1 and mtDNA were higher in the MUO group than those in the MHO and control groups (P < 0.017), which were negatively correlated with their serum contents (P < 0.05). Meanwhile, the ratio of methylated/unmethylated mtDNA was significantly associated with their mtDNA-CN and lesions (P < 0.05).

CONCLUSIONS

Our findings suggested that the impairments on the epigenetic modifications of nuclear (genome-wide DNA, TF and TFR1) and mtDNA were associated with the disturbance of serum iron biomarkers to involve in the pathophysiology of MetS among the school-age MUO children.

TRIAL REGISTRATION

This study was approved by the Ethics Committee of Beijing Children's Hospital affiliated to Capital Medical University (No. IEC-C-006-A04-V.06), which was also registered at the website of http://www.chictr.org.cn/showproj.aspx?proj=4673 (No: ChiCTR-OCH-14004900).

Sleep traits causally affect epigenetic age acceleration: a Mendelian randomization study

Sleep disorders (SDs) are a common issue in the elderly. Epigenetic clocks based on DNA methylation (DNAm) are now considered highly accurate predictors of the aging process and are associated with age-related diseases. This study aimed to investigate the causal relationship between sleep traits and the epigenetic clock using Mendelian randomization (MR) analysis. The genome-wide association study (GWAS) statistics for epigenetic clocks (HannumAge, intrinsic epigenetic age acceleration [IEAA], PhenoAge, and GrimAge) and sleep traits were obtained from the UK Biobank (UKB), 23andMe and Finngen. Moreover, crucial instrumental variables (IVs) were evaluated. Inverse variance weighted (IVW), MR-Egger, weighted median (WM), weighted mode, and simple mode methods were employed to assess the causal relationship between them. Multiple analyses were performed for quality control evaluation. Our study showed that self-reported insomnia may speed up the aging process by GrimAge clock, while GrimAge acceleration could faintly reduce self-reported insomnia. Epigenetic clocks mainly influence sleep traits by PhenoAge and GrimAge with weak effects. This may indicate that early interventions of SDs could be a breaking point for aging and age-related diseases. Further studies are required to elucidate the potential mechanisms involved.

Association between epigenetic aging and atrioventricular block: a two-sample Mendelian randomization study

AIMS

Atrioventricular block (AVB) is a prevalent bradyarrhythmia. This study aims to investigate the causal effects of epigenetic aging, as inferred from DNA methylation profiles on the prevalence of AVB by Mendelian randomization (MR) analysis.

METHODS

Genetic instruments for epigenetic aging and AVB were obtained from genome-wide association study data in the Edinburgh DataShare and FinnGen biobanks. Univariable and multivariable MR analyses were conducted to evaluate causal associations. Additionally, we employed sensitivity tests to assess the robustness of the MR findings.

RESULTS

MR analysis showed that genetically predicted GrimAge acceleration was significantly associated with a higher risk of AVB (inverse variance-weighted: p = 0.010, 95% confidence interval (CI) = 1.024-1.196; weighted median: p = 0.031, 95% CI = 1.009-1.215). However, no evidence supported a causal relationship between AVB and epigenetic aging. The association between epigenetic aging and AVB was established using multivariate MR analysis after adjusting for various risk factors. Sensitivity analyses confirmed the reliability and robustness of the results.

CONCLUSION

Our findings suggest that epigenetic aging in GrimAge may increase the risk of AVB, emphasizing the importance of addressing epigenetic aging in strategies for AVB prevention.

Mendelian randomization implicates causal association between epigenetic age acceleration and age-related eye diseases or glaucoma endophenotypes

BACKGROUND

Age-related eye diseases (AREDs) have become increasingly prevalent with the aging population, serving as the leading causes of visual impairment worldwide. Epigenetic clocks are generated based on DNA methylation (DNAm) levels and are considered one of the most promising predictors of biological age. This study aimed to investigate the bidirectional causal association between epigenetic clocks and common AREDs or glaucoma endophenotypes.

METHODS

Instrumental variables for epigenetic clocks, AREDs, and glaucoma endophenotypes were obtained from corresponding genome-wide association study data of European descent. Bidirectional two-sample Mendelian randomization (MR) was employed to explore the causal relationship between epigenetic clocks and AREDs or glaucoma endophenotypes. Multivariable MR (MVMR) was used to determine whether glaucoma endophenotypes mediated the association of epigenetic clocks with glaucoma. Multiple sensitivity analyses were conducted to confirm the robustness of MR estimates.

RESULTS

The results showed that an increased intrinsic epigenetic age acceleration (HorvathAge) was significantly associated with an increased risk of primary open-angle glaucoma (OR = 1.04, 95% CI 1.02 to 1.06, P = 6.1E-04). The epigenetic age acceleration (EEA) of HannumAge was related to a decreased risk of primary angle-closure glaucoma (OR = 0.92, 95% CI 0.86 to 0.99, P = 0.035). Reverse MR analysis showed that age-related cataract was linked to decreased HannumAge (β = -0.190 year, 95% CI -0.374 to -0.008, P = 0.041). The EEA of HannumAge (β = -0.85 μm, 95% CI -1.57 to -0.14, P = 0.019) and HorvathAge (β = -0.63 μm, 95% CI -1.18 to -0.08, P = 0.024) were associated with decreased central corneal thickness (CCT). PhenoAge was related to an increased retinal nerve fiber layer thickness (β = 0.06 μm, 95% CI 0.01 to 0.11, P = 0.027). MVMR analysis found no mediation effect of CCT in the association of HannumAge and HorvathAge with glaucoma. DNAm-based granulocyte proportions were significantly associated with presbyopia, rhegmatogenous retinal detachment, and intraocular pressure (P < 0.05). DNAm-based plasminogen activator inhibitor-1 levels were significantly related to age-related macular degeneration and intraocular pressure (P < 0.05).

CONCLUSION

The present study revealed a causal association between epigenetic clocks and AREDs. More research is warranted to clarify the potential mechanisms of the biological aging process in AREDs.

Causal effects of denture wearing on epigenetic age acceleration and the mediating pathways: a mendelian randomization study

BACKGROUND

The epigenetic-age acceleration (EAA) represents the difference between chronological age and epigenetic age, reflecting accelerated biological aging. Observational studies suggested that oral disorders may impact DNA methylation patterns and aging, but their causal relationship remains largely unexplored. This study aimed to investigate potential causal associations between dental traits and EAA, as well as to identify possible mediators.

METHODS

Using summary statistics of genome-wide association studies of predominantly European ancestry, we conducted univariable and multivariable Mendelian randomization (MR) to estimate the overall and independent effects of ten dental traits (dentures, bleeding gums, painful gums, loose teeth, toothache, ulcers, periodontitis, number of teeth, and two measures of caries) on four EAA subtypes (GrimAge acceleration [GrimAA], PhenoAge acceleration [PhenoAA], HannumAge acceleration [HannumAA] and intrinsic EAA [IEAA]), and used two-step Mendelian randomization to evaluate twelve potential mediators of the associations. Comprehensive sensitivity analyses were used to verity the robustness, heterogeneity, and pleiotropy.

RESULTS

Univariable inverse variance weighted MR analyses revealed a causal effect of dentures on greater GrimAA (β: 2.47, 95% CI: 0.93-4.01, p = 0.002), PhenoAA (β: 3.00, 95% CI: 1.15-4.85, p = 0.001), and HannumAA (β: 1.96, 95% CI: 0.58-3.33, p = 0.005). In multivariable MR, the associations remained significant after adjusting for periodontitis, caries, number of teeth and bleeding gums. Three out of 12 aging risk factors were identified as mediators of the association between dentures and EAA, including body mass index, body fat percentage, and waist circumference. No evidence for reverse causality and pleiotropy were detected (p > 0.05).

CONCLUSIONS

Our findings supported the causal effects of genetic liability for denture wearing on epigenetic aging, with partial mediation by obesity. More attention should be paid to the obesity-monitoring and management for slowing EAA among denture wearers.

Epigenetic age acceleration and risk of aortic valve stenosis: a bidirectional Mendelian randomization study

BACKGROUND

Aortic valve stenosis (AVS) is the most prevalent cardiac valve lesion in developed countries, and pathogenesis is closely related to aging. DNA methylation-based epigenetic clock is now recognized as highly accurate predictor of the aging process and associated health outcomes. This study aimed to explore the causal relationship between epigenetic clock and AVS by conducting a bidirectional Mendelian randomization (MR) analysis.

METHODS

Summary genome-wide association study statistics of epigenetic clocks (HannumAge, HorvathAge, PhenoAge, and GrimAge) and AVS were obtained and assessed for significant instrumental variables from Edinburgh DataShare (n = 34,710) and FinnGen biobank (cases = 9870 and controls = 402,311). The causal association between epigenetic clock and AVS was evaluated using inverse variance weighted (IVW), weighted median (WM), and MR-Egger methods. Multiple analyses (heterogeneity analysis, pleiotropy analysis, and sensitivity analysis) were performed for quality control assessment.

RESULTS

The MR analysis showed that the epigenetic age acceleration of HorvathAge and PhenoAge was associated with an increased risk of AVS (HorvathAge: OR = 1.043, P = 0.016 by IVW, OR = 1.058, P = 0.018 by WM; PhenoAge: OR = 1.058, P = 0.005 by IVW, OR = 1.053, P = 0.039 by WM). Quality control assessment proved our findings were reliable and robust. However, there was a lack of evidence supporting a causal link from AVS to epigenetic aging.

CONCLUSION

The present MR analysis unveiled a causal association between epigenetic clocks, especially HorvathAge and PhenoAge, with AVS. Further research is required to elucidate the underlying mechanisms and develop strategies for potential interventions.

Associations of maternal serum concentration of iron-related indicators with birth outcomes in Chinese: a pilot prospective cohort study

BACKGROUND

Previous studies of maternal iron and birth outcomes have been limited to single indicators that do not reflect the comprehensive relationship with birth outcomes. We aimed to investigate the relationship between maternal iron metabolism and neonatal anthropometric indicators using comprehensive iron-related indicators.

METHODS

A total of 914 Chinese mother-child dyads were enrolled in this prospective study. Subjects' blood samples were collected at ≤ 14 weeks of gestation. Serum concentrations of iron-related indicators were measured by enzyme-linked immunosorbent assay (ELISA). Femur length was measured by B-ultrasound nearest delivery. Neonatal anthropometric indicators were collected from medical records.

RESULTS

After adjustment for potential covariates, higher iron (per one standard deviation, SD increase) was detrimentally associated with - 0.22 mm lower femur length, whereas higher transferrin (per one SD increase) was associated with 0.20 mm higher femur length. Compared with normal subjects (10th-90th percentiles), subjects with extremely high (> 90th percentile) iron concentration were detrimentally associated with lower femur length, birth weight, and chest circumference, and a higher risk of low birth weight, LBW (HR: 3.92, 95%CI: 1.28, 12.0). Subjects with high concentration of soluble transferrin receptor, sTFR and transferrin (> 90th percentile) were associated with higher femur length. Subjects with low concentration of iron and ferritin concentrations (< 10th percentile) were associated with a higher risk of LBW (HR: 4.10, 95%CI: 1.17, 14.3) and macrosomia (HR: 2.79, 95%CI: 1.06, 7.35), respectively.

CONCLUSIONS

Maternal iron overload in early pregnancy may be detrimentally associated with neonatal anthropometric indicators and adverse birth outcomes.