DNA methylation of the INSR gene as a mediator of the association between prenatal exposure to famine and adulthood waist circumference

Separate and combined effects of famine exposure and menarche age on metabolic syndrome among the elderly: a cross-sectional study in China

BACKGROUND

Epidemiological studies have revealed multiple risk factors for metabolic syndrome. However, there are no consistent findings on the association between famine exposure, age at menarche, and the prevalence of metabolic syndrome. This cross-sectional study aimed to reveal the individual and combined effects of famine exposure and age at menarche on the prevalence of metabolic syndrome among elderly women.

METHODS

Four thousand seven hundred seventy participants between 60 and 93 years of age were selected from the China Health and Retirement Longitudinal Study. Statistical differences between the baseline characteristics of famine exposure, age at menarche, and metabolic syndrome were evaluated using the t-test, F-test, and Chi-square test. Three multivariable-adjusted logistic regression models were used to test the association between famine exposure, age of menarche, and the odds ratio of metabolic syndrome.

RESULTS

Two thousand one hundred ninety-eight (46.08%) participants had metabolic syndrome, while 2572 (53.92%) participants did not. Furthermore, 3068 (64.32%) women reported onset of menarche under 15 years of age, while 1702 (35.68%) women reported onset of menarche above 16 years of age. Regarding the separate association of famine exposure and age of menarche with metabolic syndrome, in model three, the adolescence/adulthood famine exposure group vs. no famine exposure group odds ratio was 2.45 (95% CI 2.02, 2.97), and the older than 16 years vs. younger than 15 years group odds ratio was 1.23 (95% CI 1.09, 1.39), which was the highest odds ratio among the three models. Regarding the combined association of famine exposure and age of menarche with metabolic syndrome, in model three, among the age of menarche ≤ 15 years group, the adolescence/adulthood famine exposure vs. no famine exposure group odds ratio was 2.45 (95% CI: 1.91, 3.14); among the menarche age ≥ 16 years group, the adolescence/adulthood famine exposure stages vs. exposed group odds ratio was 3.27 (95% CI: 2.44, 4.38), which was the highest odds ratio among the three models.

CONCLUSION

These findings suggested that famine exposure and age at menarche, either separately or in combination, were positively associated with the prevalence of metabolic syndrome among older women.

Maternal Periconceptional Folic Acid Supplementation and DNA Methylation Patterns in Adolescent Offspring

BACKGROUND

Folate, including the folic acid form, is a key component of the one-carbon metabolic pathway used for DNA methylation. Changes in DNA methylation patterns during critical development periods are associated with disease outcomes and are associated with changes in nutritional status in pregnancy. The long-term impact of periconceptional folic acid supplementation on DNA methylation patterns is unknown.

OBJECTIVES

To determine the long-term impact of periconceptional folic acid supplementation on DNA methylation patterns, we examined the association of the recommended dosage (400 μg/d) and time period (periconceptional before pregnancy through first trimester) of folic acid supplementation with the DNA methylation patterns in the offspring at age 14-17 y compared with offspring with no supplementation.

METHODS

Two geographic sites in China from the 1993-1995 Community Intervention Program of folic acid supplementation were selected for the follow-up study. DNA methylation at 402,730 CpG sites was assessed using saliva samples from 89 mothers and 179 adolescents (89 male). The mean age at saliva collection was 40 y among mothers (range: 35-54 y) and 15 y among adolescents (range: 14-17 y). Epigenome-wide analyses were conducted to assess the interactions of periconceptional folic acid exposure, the 5,10-methylenetetrahydrofolate reductase (MTHFR)-C677T genotype, and epigenome-wide DNA methylation controlling for offspring sex, geographic region, and background cell composition in the saliva.

RESULTS

In the primary outcome, no significant differences were observed in epigenome-wide methylation patterns between adolescents exposed and those non-exposed to maternal periconceptional folic acid supplementation after adjustment for potential confounders [false discovery rate (FDR) P values < 0.05]. The MTHFR-C677T genotype did not modify this lack of association (FDR P values < 0.05).

CONCLUSIONS

Overall, there were no differences in DNA methylation between adolescents who were exposed during the critical developmental window and those not exposed to the recommended periconceptional/first-trimester dosage of folic acid.

Epigenetics in Precision Nutrition

Precision nutrition is an emerging area of nutrition research, with primary focus on the individual variability in response to dietary and lifestyle factors, which are mainly determined by an individual’s intrinsic variations, such as those in genome, epigenome, and gut microbiome. The current research on precision nutrition is heavily focused on genome and gut microbiome, while epigenome (DNA methylation, non-coding RNAs, and histone modification) is largely neglected. The epigenome acts as the interface between the human genome and environmental stressors, including diets and lifestyle. Increasing evidence has suggested that epigenetic modifications, particularly DNA methylation, may determine the individual variability in metabolic health and response to dietary and lifestyle factors and, therefore, hold great promise in discovering novel markers for precision nutrition and potential targets for precision interventions. This review summarized recent studies on DNA methylation with obesity, diabetes, and cardiovascular disease, with more emphasis put in the relations of DNA methylation with nutrition and diet/lifestyle interventions. We also briefly reviewed other epigenetic events, such as non-coding RNAs, in relation to human health and nutrition, and discussed the potential role of epigenetics in the precision nutrition research.

Association of Prenatal Famine Exposure With Inflammatory Markers and Its Impact on Adulthood Liver Function Across Consecutive Generations

Although there has been increasing recognition that famine exposure in the fetal stage damages liver function in adulthood, this deteriorated effect could be extended to the next generation remains vague. This study aimed to explore whether famine exposure was associated with liver function in the two consecutive generations, and its association with the mediation role of inflammatory markers. We analyzed the data of 2,681 participants from Suihua rural area, Heilongjiang Province, China. According to the date of birth, the participants were classified as fetal exposed and nonexposed. The F2 subjects were classified as having no parents exposed to famine, maternal famine exposure, paternal famine exposure, or parental famine exposure. In the mixed-effect models, prenatal exposure to famine was associated with the elevation of Δ aspartate aminotransferase (ΔAST) (β: 0.22, 95% CI: 0.01, 0.43) and Δ alanine aminotransferase (ΔALT) (β: 0.42, 95% CI: 0.19, 0.66) levels in F1 adults. The mediation analysis showed that the inflammatory markers including serum C-reactive protein (CRP) and tumor necrosis factor-alpha (TNF-α) might mediate the famine-liver function association. This longitudinal data were consistent with the hypothesis that the inflammatory markers explained part of the influence of prenatal famine exposure on liver function injury, and the natal mechanism was needed to be elucidated in the future study.

Prenatal famine exposure and adult health outcomes: an epigenetic link

Numerous human chronic pathological conditions depend on epigenetic modifications induced by environmental triggers throughout sensitive stages early in development. Developmental malnutrition is regarded as one of the most important risk factors in these processes. We present an overview of studies that the initiation and progression of many diseases are largely dependent on persisting epigenetic dysregulation caused by environmental insults early in life. For particular disorders, candidate genes were identified that underlie these associations. The current study assessed the most convincing evidence for the epigenetic link between developmental malnutrition and adult-life disease in the human population. These findings were obtained from quasi-experimental studies (so-called 'natural experiments'), i.e. naturally occurring environmental conditions in which certain subsets of the population have differing levels of exposure to a supposed causal factor. Most of this evidence was derived on the DNA methylation level. We discussed DNA methylation as a key player in epigenetic modifications that can be inherited through multiple cell divisions. In this Perspective article, an overview of the quasi-experimental epidemiological evidence for the role of epigenetic mechanisms in the developmental programming by early-life undernutrition is provided.

The Effect and Potential Mechanism of Maternal Micronutrient Intake on Offspring Glucose Metabolism: An Emerging Field

Diabetes has become the most common metabolic disease around the world. In addition to genetic and environmental factors in adulthood, the early life environment is critical to the progression of diabetes in adults, especially the environment during the fetal period; this concept is called “fetal programming.” Substantial evidence has illustrated the key role of early life macronutrient in programming metabolic diseases. Recently, the effect of maternal micronutrient intake on offspring glucose metabolism during later life has become an emerging field. This review focuses on updated human and animal evidence about the effect of maternal micronutrient status on offspring glucose metabolism and the underlying mechanism.

Environmental Exposures around Conception: Developmental Pathways Leading to Lifetime Disease Risk

Environment around conception can influence the developmental programme with lasting effects on gestational and postnatal phenotype and with consequences for adult health and disease risk. Peri-conception exposure comprises a crucial part of the 'Developmental Origins of Health and Disease' (DOHaD) concept. In this review, we consider the effects of maternal undernutrition experienced during the peri-conception period in select human models and in a mouse experimental model of protein restriction. Human datasets indicate that macronutrient deprivation around conception affect the epigenome, with enduring effects on cardiometabolic and neurological health. The mouse model, comprising maternal low protein diet exclusively during the peri-conception period, has revealed a stepwise progression in altered developmental programming following induction through maternal metabolite deficiency. This progression includes differential effects in extra-embryonic and embryonic cell lineages and tissues, leading to maladaptation in the growth trajectory and increased chronic disease comorbidities. The timeline embraces an array of mechanisms across nutrient sensing and signalling, cellular, metabolic, epigenetic and physiological processes with a coordinating role for mTORC1 signalling proposed. Early embryos appear active participants in environmental sensing to optimise the developmental programme for survival but with the trade-off of later disease. Similar adverse health outcomes may derive from other peri-conception environmental experiences, including maternal overnutrition, micronutrient availability, pollutant exposure and assisted reproductive treatments (ART) and support the need for preconception health before pregnancy.

DNA methylation as a mediator of associations between the environment and chronic diseases: A scoping review on application of mediation analysis

DNA methylation (DNAm) is one of the most studied epigenetic modifications. DNAm has emerged as a key biological mechanism and biomarkers to test associations between environmental exposure and outcomes in epidemiological studies. Although previous studies have focused on associations between DNAm and either exposure/outcomes, it is useful to test for mediation of the association between exposure and outcome by DNAm. The purpose of this scoping review is to introduce the methodological essence of statistical mediation analysis and to examine emerging epidemiological research applying mediation analyses. We conducted this scoping review for published peer-reviewed journals on this topic using online databases (PubMed, Scopus, Cochrane, and CINAHL) ending in December 2020. We extracted a total of 219 articles by initial screening. After reviewing titles, abstracts, and full texts, a total of 69 articles were eligible for this review. The breakdown of studies assigned to each category was 13 for smoking (18.8%), 8 for dietary intake and famine (11.6%), 6 for other lifestyle factors (8.7%), 8 for clinical endpoints (11.6%), 22 for environmental chemical exposures (31.9%), 2 for socioeconomic status (SES) (2.9%), and 10 for genetic factors and race (14.5%). In this review, we provide an exposure-wide summary for the mediation analysis using DNAm levels. However, we found heterogenous methods and interpretations in mediation analysis with typical issues such as different cell compositions and tissue-specificity. Further accumulation of evidence with diverse exposures, populations and with rigorous methodology will be expected to provide further insight in the role of DNAm in disease susceptibility.