Unique transcriptomic changes underlie hormonal interactions during mammary histomorphogenesis in female pigs

Authors: TROTT, JOSEPHINE - University Of California, Davis; SCHENNINK, ANKE - University Of California, Davis; HORIGAN, KATHERINE - University Of Vermont; Lemay, Danielle; COHEN, JULIA - University Of California, Davis; FAMULA, THOMAS - University Of California, Davis; DRAGON, JULIE - University Of Vermont; HOVEY, RUSSELL - University Of California, Davis

Submitted to: Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2021
Publication Date: 12/16/2021
Citation: Trott, J.F., Schennink, A., Horigan, K.C., Lemay, D.G., Cohen, J.R., Famula, T.R., Dragon, J.A., Hovey, R.C. 2021. Unique transcriptomic changes underlie hormonal interactions during mammary histomorphogenesis in female pigs. Endocrinology. 163(3). Article bqab256. https://doi.org/10.1210/endocr/bqab256.
DOI: https://doi.org/10.1210/endocr/bqab256

Interpretive Summary: The growth and development of the mammary gland, which produces milk as the sole nutrition for human neonates, is dependent on the interplay of three hormones: estradiol, progesterone, and prolactin. How these hormones regulate breast development is not completely known. Using a pig model of mammary development, the response to each hormone was analyzed in isolation and in combination. The growth and cellular composition of the mammary gland resulting from each hormone combination was associated with unique patterns of gene expression. During normal breast development, the mature gland contains cells that form specialized structures that function during milk production and are unable to change further into the uncontrolled cell proliferation of breast cancer. This study reveals that the synergy of two of the hormones, estradiol and prolactin, leads to the expression of genes that result in normal mammary gland development and lower cancer risk

Technical Abstract: A successful lactation as well as the risk for developing breast cancer both depend on the growth and differentiation of the mammary epithelium, which is tightly controlled by ovarian steroids (17beta-estradiol [E] and progesterone [P]) and pituitary-derived prolactin (PRL). How these individual hormones, and their combinations, regulate breast development has only been partly resolved due to the challenges that come with studying or manipulating the breast. Here we document transcriptomic changes within the mammary gland (MG) of pigs in response to all combinations of these hormones as an authentic model for hormonal regulation of human breast development. Peripubertal female pigs (n=32) were ovariectomized and treated with 2-bromo-aergocryptine to eliminate endogenous E, P and PRL, then treated (n=4) with all possible combinations of exogenous E, medroxyprogesterone 17-acetate (as a source of P), and either haloperidol (to induce PRL secretion) or 2-bromo-a-ergocryptine. The frequency of mitosis receptors for E and P (ESR1 and PGR, respectively) and phosphorylated STAT5 within the MG epithelium was quantified by immunohistochemistry alongside the relative frequency of terminal ductal lobular units (TDLU). Total RNA from the MG parenchyma was analyzed on Affymetrix GeneChip Porcine Genome Arrays. Estrogen, either alone or in combination with PRL, altered the expression of ~20% of all detectable genes. Whereas E induced a transcriptomic response reflecting cell cycle progression and mitosis, PRL stimulated responses associated with fatty acid metabolism, lymphocyte proliferation, and an inflammatory response. Abundance of PGR and the phosphorylation of STAT5 in response to PRL were markedly enhanced by E. To link the various hormone-induced changes to the genome, transcriptomic data were regressed against several quantitative measures of the MG phenotype. The expression of 16 genes was correlated with E-induced proliferation in the MG across all treatments, while expression of 1045 genes 4 was changed in association with E-induced terminal bud formation. There were 322 E-regulated genes having expression that correlated with the formation of TDLU type-2, and 185 E-regulated genes correlated with TDLU-3 incidence. There were 731 genes correlated with ESR1 abundance, and 346 genes correlated with PGR frequency, of which 254 were E-regulated. These data provide an important link between the hormone-regulated genome and phenome of the mammary gland in a species having a complex histoarchitecture that is also present in the human breast. In particular, our findings highlight an underexplored synergy between the actions of E and PRL during the course of this development.