Investigation of the adolescent female breast transcriptome and the impact of obesity

Abstract

Background: Early life environmental exposures affect breast development and breast cancer risk in adulthood. The breast is particularly vulnerable during puberty when mammary epithelial cells proliferate exponentially. In overweight/obese (OB) women, inflammation increases breast aromatase expression and estrogen synthesis and promotes estrogen-receptor (ER)-positive breast cancer. In contrast, recent epidemiological studies suggest that obesity during childhood decreases future breast cancer risk. Studies on environmental exposures and breast cancer risk have thus far been limited to animal models. Here, we present the first interrogation of the human adolescent breast at the molecular level and investigate how obesity affects the immature breast. Methods: We performed RNA-seq in 62 breast tissue samples from adolescent girls/young women (ADOL; mean age 17.8 years) who underwent reduction mammoplasty. Thirty-one subjects were non-overweight/obese (NOB; mean BMI 23.4 kg/m 2) and 31 were overweight/obese (OB; BMI 32.1 kg/m 2). We also compared our data to published mammary transcriptome datasets from women (mean age 39 years) and young adult mice, rats, and macaques. Results: The ADOL breast transcriptome showed limited (30%) overlap with other species, but 88% overlap with adult women for the 500 most highly expressed genes in each dataset; only 43 genes were shared by all groups. In ADOL, there were 120 differentially expressed genes (DEG) in OB compared with NOB samples (p adj < 0.05). Based on these DEG, Ingenuity Pathway Analysis (IPA) identified the cytokines CSF1 and IL-10 and the chemokine receptor CCR2 as among the most highly activated upstream regulators, suggesting increased inflammation in the OB breast. Classical ER targets (e.g., PR, AREG) were not differentially expressed, yet IPA identified the ER and PR and growth factors/receptors (VEGF, HGF, HER3) and kinases (AKT1) involved in hormone-independent ER activation as activated upstream regulators in OB breast tissue.

Inflammatory Biomarkers and Breast Cancer Risk: A Systematic Review of the Evidence and Future Potential for Intervention Research

“…Similar to the studies of inflammatory blood biomarkers and breast cancer risk, there is currently a complete absence of information on the effect of inflammation during key windows of susceptibility on breast cancer risk, even though we know that the pregnancy/lactation cycle induces an inflammatory state akin to wound healing and that breasts also change in form and function around the menopausal transition, a time in life when subgroups of women also experience weight gain and increases in other chronic disease risk factors [10]. Further, in a recent study evaluating transcriptomic pathways differentially expressed in breast tissue samples from overweight/obese (OB) vs. normal weight adolescents, analyses identified inflammatory genes (cytokines CSF1 and IL-10, chemokine receptor CCR2) as among the most highly activated upstream regulators in the OB breast [52]. This suggests that there are innate inflammatory responses within the OB breast even in early life, again supporting a need to study windows of susceptibility.…”

Risk Factors Associated with Severe Macromastia among Adolescents and Young Women

“…17 Some have postulated that adipose tissue itself may contribute significantly to breast size, but our institution’s analysis of reduction mammaplasty specimens, specifically glandular tissue, does not support this theory. 18 RNA sequencing data from these specimens has demonstrated inflammatory transcriptional changes among obese adolescents that may potentiate estrogen action in the immature breast microenvironment. 18 Moreover, our macromastia severity value calculation normalizes breast resection mass to body surface area, and therefore minimizes the likelihood of large body habitus confounding our assessment of hypertrophy severity.…”

“…18 RNA sequencing data from these specimens has demonstrated inflammatory transcriptional changes among obese adolescents that may potentiate estrogen action in the immature breast microenvironment. 18 Moreover, our macromastia severity value calculation normalizes breast resection mass to body surface area, and therefore minimizes the likelihood of large body habitus confounding our assessment of hypertrophy severity. 11 The role of adipose tissue as an important endocrine organ cannot be discounted.…”

A Transcriptomic and Proteomic Atlas of Obesity and Type 2 Diabetes in Cynomolgus Monkeys

“…Regardless, we observed 65 shared DEGs showing the same-direction change in the abdominal WAT of obese monkeys with the results from the Lee et al study 5 . For the Burkholder et al study using breast tissue 12 , we identified 15 overlapping same-direction DEGs in the abdominal WAT. No overlapping DEGs with same-direction changes were detected in the results from other studies.…”

“…However, the molecular mechanisms of how these loci regulate gene expression and impact protein function remain poorly understood. Previous studies have investigated the transcriptomes or proteomes of obese patients in tissues including blood 3,4 , adipose tissues [5][6][7][8] , liver 9 , muscle 8,10,11 , breast 12 , granulosa cells 13 , and sperm 14 . However, these studies have yielded inconclusive and sometimes conflicting results about obesity-related molecular changes 15 .…”