Long-term hipothyroidism produces mammary genetic and epigenetic changes

PERSIA, FA; SANTIANO, FLAVIA E.; LÓPEZ-FONTANA, CONSTANZA M; JAHN, GRACIELA A.; BERNAL, GN; BRUNA, FLAVIA; GÓMEZ, SILVINA E; HAPON, MARÍA B.; CAMPO VERDE ARBOCCO F; BERNAL, GN; BRUNA, FLAVIA; GÓMEZ, SILVINA E; HAPON, MARÍA B.; CAMPO VERDE ARBOCCO F; ZYLA, LEILA E; SASSO, CORINA V.; PISTONE CREYDT, V; CARÓN, RUBÉN W.; ZYLA, LEILA E; SASSO, CORINA V.; PISTONE CREYDT, V; CARÓN, RUBÉN W.; PERSIA, FA; SANTIANO, FLAVIA E.; LÓPEZ-FONTANA, CONSTANZA M; JAHN, GRACIELA A.

Congreso; XXXVI Reunión Anual de la Sociedad de Biología de Cuyo; 2018

The mammary tissue is one of the few ones whose terminal differentiation is completed in adult life through lactation. In this process, the mammary genome is subject to epigenetic modifications that result in the selective expression of differentiation-associated genes and the establishment of the mammary transcriptome. After weaning, massive involution occurs and the tissue returns to a pregestation-like stage. This proliferation, differentiation and apoptosis cycle is regulated by lactogenic, ovarian and thyroid hormones. Thyroid pathologies such as hypothyroidism (hypoT) have an impact on the lactoma (lactation transcriptome), impairing the mammary epithelial cell ability to express differentiation genes. Despite this, the long-term impact of hipoT on mammary gland, and if hypoT alters the mammary epithelial cell epigenome are both unknown. To determine the long-term hypoT impact on mammary transcriptome, we used female virgin Sprague Dawley rats of 55 and 130 days old without treatment, female 130 day old rats that underwent a cycle of pregnancy, lactation and involution without treatment and a PTU treated 130 day old female rats that underwent a cycle of pregnancy, lactation and involution. Using real-time PCR, we evaluated the mRNA expression levels of differentiation-associated genes, such as gata-3, pinc, ncoa-1, ncoa-2, and stat6; and by methyl-specific PCR (MSPCR) we analyzed the methylation of two promoter regions of stat6 gene. The analysis of gene expression showed that the long-term hypoT altered the mammary transcriptome differentially and that it had a special impact on ncoa-2, a gene associated with histones modification. Also, hypoT changed the mRNA expression of two mammary epithelial differentiation-associated genes, stat6 and gata3, both related to alveolar development. In addition, the methylation analysis of the stat6 gene showed that hypoT increases the CpG island methylation level upstream of the transcription initiation site. Our results show that the hypoT deleterious effect on the mammary gland is not limited to lactation but in long-term alters the mammary epithelial cell ability to express differentiation-associated genes and genes associated to transcriptional modification of histones. Also, changes in the methylation level of stat6 gene show that the hypoT effect is beyond the function of the transcription factor associated to the receptor and that the pathology itself leads changes in the mammary cell epigenome.