產前全氟碳化物暴露對於PPARγ基因甲基化程度和新生兒的影響

Prenatal Perfluoroalkyl Substances Exposures in Association with Peroxisome Proliferator-Activator Receptor Gamma Gene Methylation Levels and Birth Outcomes

曾紫蕾(FRAN SISCA)

指導教授 ： 劉貞佑

國立臺灣大學/公共衛生學院/環境衛生研究所/碩士(2017年)

https://doi.org/10.6342/NTU201703211

摘要

背景: DNA甲基化是表基因調控的一種，這個過程會導致基因的表現產生改變，但基因序列不變。DNA甲基化也是胚胎發育過程中重要的機制之一。胎兒容易受環境因素的影響，特別是在發育期間，此期間的任何缺陷可能會增加疾病發生的風險。環境改變為基因調控的重要因子，產前暴露全氟碳化物可能連結到新生兒一些不良的健康結果，但機制尚未清楚。過氧化物酶體增殖物活化受體γ(peroxisome proliferator-activator receptor gamma)基因會在胎盤中表現，特別是滋養層，其功能為負責母親和胎兒之間的血液、營養和脂肪酸運送，而新生兒的不良健康結果也與滋養層的失調有相關。
目的: 研究全氟碳化物對於 peroxisome proliferator-activator receptor gamma 的甲基化程度影響。觀察在這個過程中甲基化的程度改變時候是不是會影響新生兒的出生結果。
方法 : 本次研究對象來自於台灣出生世代研究（Taiwan Birth Panel Study），於 2004年4月至2005年1月招募收試者。透過極致液相層析/串聯式質譜儀 （ultra-high-performance liquid chromatography/tandem mass spectrometry）分析臍帶血中的全氟烷基物質，包括全氟辛酸（PFOA）、全氟辛烷磺酸（PFOS）、全氟壬酸（PFNA）、全氟癸酸（PFUA）。經由亞硫酸氫鈉處理之胎盤 DNA 藉由焦磷酸定序（pyrosequencing） 方法分析PPARγ 基因在胎盤的甲基化程度。
結果: 我們有發現一些新生兒健康效應與全氟碳化物暴露存在相關，同時有性別上的差異。LnPFNA 與身長在女孩中有顯著正相關關係。但在男孩中沒有。LnPFOA和LnPFUA與男孩的嬰兒重量指標有顯著負相關。只有 PFUA 產前暴露與PPARγ DNA甲基化有顯著相關 [原始模式: β (95% CI) = -0.95 (-1.9, -0.03), p=0.04; 多重校正 β (95% CI) = -1.1 (-2.1, -0.11), p=0.02] 。進一步將 PFUA 暴露資料分組後，發現和PPARγ DNA甲基化程度呈現劑量效應關係 (ptrend = 0.02) 。與最低PFUA暴露組（<25百分位數）相比，最高PFUA暴（≥75百分位數）露與PPARγ DNA甲基化有顯著相關 [多重校正: β (95% CI) = -3.75 (-7.1, -0.76)] 。在原始或校正模型，PPARγ DNA甲基化程度與新生兒健康效應皆無顯著相關性。
結論: 我們的研究結果指出產前暴露到全氟碳化物可能導致幾個不利的新生兒健康效應。除此之外，產前全氟碳化物暴露與胎盤中PPARγ基因甲基化呈現負相關。我們的研究結果支持全氟碳化物暴露會影響表基因的調控，並在兒童的未來造成一些不良的後果。

關鍵字

基因甲基化 ； 胎盤 ； 全氟碳化物 ； PPARγ ； 產前暴露 ； 新生兒健康效應

並列摘要

Background: DNA methylation is one of the epigenetics modification that allow gene expression changes changes without changing the DNA sequence. DNA methylation is also one of the important mechanisms take part during embryonic development. Fetus are more vulnerable to environmental substances especially during development period, any defects during this period could increase the risk in disease development later. Prenatal exposure to perfluoroalkyl substances can be linked to several adverse health outcomes to newborns, but the mechanisms still remains unclear. Peroxisome proliferator-activator receptor gamma (PPARγ) is expressed in placenta, especially trophoblast, which is responsible for the blood, nutrients and fatty acid transfer between mother and fetus. Several adverse health outcomes of newborns also have been linked to trophoblast dysregulation.

Objective: To investigate the association between exposure effects of perfluoroalkyl substances and PPARγ gene methylation level and study whether the PPARγ methylation changes could be associated with newborn’s birth outcomes.

Methods: The study subjects were from the Taiwan Birth Panel Study. The participants were enrolled from April 2004 to January 2005. The exposure level of perfluoroalkyl substances, including perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorononanoic acid (PFNA), perfluoroundecanoic acid (PFUA) were measured by ultra-high-performance liquid chromatography/tandem mass spectrometry by using cord blood. The DNA methylation of peroxisome proliferator-activator receptor gamma in placenta were quantified using pyrosequencing method. The results were analyzed using statistical method adjusted for potential confounder in multiple regression model.

Result: Some birth outcomes were associated with perfluoroalkyl substances in sex-specific pattern. We observed LnPFNA has significant positive relationship with birth length in girls but not in boys. LnPFOA and LnPFUA were significant negatively associated with ponderal index in boys (p for interaction = 0.36 and 0.8 respectively). Only prenatal exposure to PFUA in natural log transformed were correlated with PPARγ DNA methylation levels in crude and adjusted model [crude: β (95% CI) = -0.95 (-1.9, -0.03), p=0.04; adjusted: β (95% CI) = -1.1 (-2.1, -0.11), p=0.02]. PFUA show a dose-response relationship with PPARγ DNA methylation levels (ptrend = 0.02) in categorized group. Compare to the lowest PFUA exposure group, the highest (≥75th percentile) PFUA expoure was associated with PPARγ DNA methylation levels [adjusted β (95% CI) = -3.75 (-7.1, -0.76)]. PPARγ DNA methylation levels were not significantly associated with birth outcomes, in either crude nor adjusted models.

Conclusion: Our results suggest that prenatal exposure to perfluoroalkyl substances might resulted in several adverse birth outcomes. Other than that, perfluoroalkyl substances were associated with decrease PPARγ methylation level in placenta. Our findings support the hypothesis that perfluoroalkyl substances may generate epigenetics changes and cause some disease outcome later in life.

並列關鍵字

DNA methylation ； placenta ； perfluoroalkyl substances ； PPARγ ； prenatal exposure ； birth outcomes

參考文獻

1. Epigenetics. Environmental Health Perspectives. March 2006;114:8.

2. Bestor TH. The DNA methyltransferasea of mammals. Human Molecular Genetics. 2000;9:8.

3. Suzuki MM, Bird A. DNA methylation landscapes: provocative insights from epigenomics. Nat Rev Genet. Jun 2008;9(6):465-476.

4. Watkins DJ, Wellenius GA, Butler RA, Bartell SM, Fletcher T, Kelsey KT. Associations between serum perfluoroalkyl acids and LINE-1 DNA methylation. Environ Int. Feb 2014;63:71-76.

5. Hsu JY, Hsu JF, Ho HH, Chiang CF, Liao PC. Background levels of persistent organic pollutants in humans from Taiwan: perfluorooctane sulfonate and perfluorooctanoic acid. Chemosphere. Sep 2013;93(3):532-537.