Metal Impacts on miRNAs in Human Milk and Contributions to Early Childhood Growth - PROJECT SUMMARY Accelerated growth in early childhood increases risk for obesity, a leading cause of morbidity and mortality. Identifying factors that influence early programming of growth and adiposity is critical for addressing the current obesity epidemic. This is especially important for rural populations, which have a higher burden of obesity in the U.S. Metal exposures disproportionately impact rural populations and increasingly have been associated with adiposity in childhood. However, underlying mechanisms are largely unknown. Breastfeeding protects against childhood obesity and supplies bioactive compounds to the infant that contribute to metabolic programming, which may be altered by environmental toxicant exposures. Human milk is a particularly rich source of microRNAs (miRNAs), which regulate gene expression and play key roles in developmental programming and energy homeostasis. These miRNAs primarily originate in the mammary epithelium and are highly stable when carried by extracellular vesicles and particles (EVPs). Experimental studies have demonstrated that milk-derived miRNAs survive digestion and reach peripheral tissues involved in weight regulation. Preliminary findings from our group indicate that prenatal exposure to metals contribute to accelerated growth in infancy and that human milk miRNAs with known roles in adipogenesis and energy homeostasis are highly sensitive to these same exposures during sensitive windows of mammary gland remodeling (periconception and pregnancy). The proposed research will test the hypothesis that metal exposures during these windows of susceptibility alter the miRNA composition of human milk due to perturbed mammary gland remodeling, contributing to accelerated growth and adiposity in early childhood. We will test these hypotheses in the New Hampshire Birth Cohort Study (NHBCS), a rural pregnancy cohort of private well users in northern New England that is particularly vulnerable to metals exposure. To assess the generalizability of results, we will conduct validation analyses in the Mother’s Milk Study, an urban cohort of Latino mother-child dyads in Southern California. In exploratory analyses, we will use a systems biology approach to integrate other components of the human milk matrix (microbiome, metabolomics, macronutrients, cell composition) to gain a more holistic understanding of human milk miRNA contributions to early growth. Small RNA-sequencing will be used to comprehensively profile miRNAs in EVPs isolated from 400 NHBCS human milk samples collected approximately six weeks postpartum. Genome-wide DNA methylation will be profiled for the cellular fraction of the same milk samples to measure cell composition. Findings from the proposed research will improve understanding of the contributions of an understudied class of epigenetic regulators in human milk to metal impacts on early growth. These results may inform preventive interventions and clinical guidelines that promote human milk quality and reduce early life disparities in obesity.
