Abstract 599: Smoking-associated AHRR demethylation in cord blood DNA: Impact of CD235a+ nucleated red blood cells

Abstract

Abstract Prenatal tobacco smoke exposure is associated with numerous adverse health outcomes at birth and in later life. Numerous studies have demonstrated that Aryl Hydrocarbon Receptor Repressor gene (AHRR) hypomethylation in umbilical cord blood is significantly associated with prenatal tobacco smoke exposure and is suitable as a fetal exposure biomarker. The mechanism driving this demethylation and whether all cord blood cell types are impacted is unclear. Nucleated red blood cells (nucleated CD235a+ cells, nRBCs) are developmentally immature RBCs that display genome-wide demethylation and are observed at increased frequency in the cord blood of smoking mothers. We assessed if nRBC counts or methylation level affected smoking-associated DNA methylation in the AHRR gene as measured in whole cord blood. We analyzed methylation in DNA from whole cord blood, CD14+ monocytes, and nRBCs across four AHRR CpGs using pyrosequencing and also with Illumina 850K arrays (cg05575921) from smoking (n=34) and nonsmoking (n=19) mothers. nRBCs present in cord blood were determined by conventional CBCs and also estimated with a Houseman deconvolution model. AHRR methylation levels were significantly lower in nRBCs relative to whole blood and CD14+ monocytes. Methylation values at each AHRR CpG averaged 14.6% lower in nRBCs (range 0.4% to 24%, p=3.9E-13) relative to CD14+ monocytes with nonsmokers displaying significantly greater hypomethylation in nRBCs than smokers. Methylation levels at each CpG across the AHRR DMR were strongly associated with either self-reported smoking or cord blood cotinine levels in both CD14+ monocytes (r2=0.45, p=4.6E-08) and nRBCs (r2=0.26, p=1.2E-04). The most significant prenatal smoking effect on methylation occurred in CD14+ monocytes at the CpG located at chr5:373490 (-16.7%, p=6.7E-09), 112nt downstream of cg05575921. For subjects with 850K data, adjusting a regression analysis model with estimated cell-type composition, including nRBC counts or estimates, marginally increased the magnitude and significance of the prenatal smoke exposure effect on AHRR cg05575921 methylation. Prenatal tobacco smoke exposure strongly affects DNA methylation in the AHRR gene and this prenatal smoke exposure biomarker is largely unaffected by cord blood cell type composition. Citation Format: Matthew A. Bergens, Gary S. Pittman, Isabel J. Thompson, Michelle R. Campbell, Xuting Wang, Ma Wan, Cathrine Hoyo, Douglas A. Bell. Smoking-associated AHRR demethylation in cord blood DNA: Impact of CD235a+ nucleated red blood cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 599.