The epigenetic role of breastfeeding in mammary differentiation.

Maternal milk consumption can cause changes in the mammary epithelium of the offspring that result in the expression of molecules involved in the induction of differentiation, reducing the risk of developing mammary cancer later in life. We previously showed that animals that maintained a higher intake of maternal milk had a lower incidence of mammary cancer. In the present study, we evaluated one of the possible mechanisms by which the consumption of maternal milk could modify the susceptibility to mammary carcinogenesis. We used Sprague Dawley rats reared in litters of 3 (L3), 8 (L8), or 12 (L12) pups per mother in order to generate a differential consumption of milk. Whole mounts of mammary glands were performed to analyze the changes in morphology. Using real-time polymerase chain reaction (PCR), we analyzed the expression of mammary Pinc, Tbx3, Stat6, and Gata3 genes. We use the real-time methylation-specific polymerase chain reaction method to assess the methylation status of Stat6 and Gata3 CpG sites. Our findings show an increase in the size of the epithelial tree and a smaller number of ducts called terminal end buds in L3 vs. L12. We observed an increased expression of mRNA of Stat6, Gata3, Tbx3, and a lower expression of Pinc in L3 with respect to L12. Stat6 and Gata3 are more methylated in the CpG islands of the promoter analyzed in L12 vs. L3. In conclusion, the increased consumption of maternal milk during the postnatal stage generates epigenetic and morphological changes associated with the differentiation of the mammary gland.

Human renal adipose tissue induces the invasion and progression of renal cell carcinoma.

We evaluated the effects of conditioned media (CMs) of human adipose tissue from renal cell carcinoma located near the tumor (hRATnT) or farther away from the tumor (hRATfT), on proliferation, adhesion and migration of tumor (786-O and ACHN) and non-tumor (HK-2) human renal epithelial cell lines. Human adipose tissues were obtained from patients with renal cell carcinoma (RCC) and CMs from hRATnT and hRATfT incubation. Proliferation, adhesion and migration were quantified in 786-O, ACHN and HK-2 cell lines incubated with hRATnT-, hRATfT- or control-CMs. We evaluated versican, adiponectin and leptin expression in CMs from hRATnT and hRATfT. We evaluated AdipoR1/2, ObR, pERK, pAkt y pPI3K expression on cell lines incubated with CMs. No differences in proliferation of cell lines was found after 24 h of treatment with CMs. All cell lines showed a significant decrease in cell adhesion and increase in cell migration after incubation with hRATnT-CMs vs. hRATfT- or control-CMs. hRATnT-CMs showed increased levels of versican and leptin, compared to hRATfT-CMs. AdipoR2 in 786-O and ACHN cells decreased significantly after incubation with hRATfT- and hRATnT-CMs vs. control-CMs. We observed a decrease in the expression of pAkt in HK-2, 786-O and ACHN incubated with hRATnT-CMs. This result could partially explain the observed changes in migration and cell adhesion. We conclude that hRATnT released factors, such as leptin and versican, could enhance the invasive potential of renal epithelial cell lines and could modulate the progression of the disease.

Hypothyroidism advances mammary involution in lactating rats through inhibition of PRL signaling and induction of LIF/STAT3 mRNAs.

Thyroid diseases have deleterious effects on lactation, litter growth and survival, and hinder the suckling-induced hormone release, leading in the case of hyperthyroidism, to premature mammary involution. To determine the effects of hypothyroidism (HypoT) on late lactation, we analyzed the effect of chronic 6-propyl-2-thiouracil (PTU)-induced HypoT on mammary histology and the expression of members of the JAK/STAT/SOCS signaling pathway, milk proteins, prolactin (PRLR), estrogen (ER), progesterone (PR) and thyroid hormone (TR) receptors, markers of involution (such as stat3, lif, bcl2, BAX and PARP) on lactation (L) day 21. HypoT mothers showed increased histological markers of involution compared with control rats, such as adipose/epithelial ratio, inactive alveoli, picnotic nuclei and numerous detached apoptotic cells within the alveolar lumina. We also found decreased PRLR, ß-casein and α-lactoalbumin mRNAs, but increased SOCS1, SOCS3, STAT3 and LIF mRNAs, suggesting a decrease in PRL signaling and induction of involution markers. Furthermore, Caspase-3 and 8 and PARP labeled cells and the expression of structural proteins such as ß-Actin, α-Tubulin and Lamin B were increased, indicating the activation of apoptotic pathways and tissue remodelation. HypoT also increased PRA (mRNA and protein) and erß and decreased erα mRNAs, and increased strongly TRα1, TRß1, PRA and ERα protein levels. These results show that lactating HypoT rats have premature mammary involution, most probably induced by the inhibition of prolactin signaling along with the activation of the LIF-STAT3 pathway.

Effect of hypothyroidism on the expression of nuclear receptors and their co-regulators in mammary gland during lactation in the rat.

Thyroid hormones (TH) regulate mammary function. Hypothyroidism (HypoT) has deleterious effects on lactation, litter growth and survival. We analyzed the effect of chronic 6-propyl-2-thiouracil (PTU)-induced HypoT in the expression of nuclear receptors, co-regulators and oxytocin receptor (OTR) on lactation (L) days 2, 7 and 14. TH receptors (TRs) were increased on L7 at mRNA and protein levels, except TRα protein, that fell on L14. HypoT decreased TRα2 mRNA on L7 and TRα1 protein on L2, while TRß1 protein increased on L14. HypoT increased estrogen receptor ß (ERß) mRNA on L7 but decreased its protein levels on L14. Progesterone receptor A (PRA) mRNA decreased from L2 to L14 while PRB increased, and at protein levels PRA levels showed a nadir on L7, while PRB peaked. HypoT decreased PRA mRNA and protein and increased PRB mRNA at L14. Nuclear receptor co-activator (NCOA) 1 and RXRα mRNA showed an opposite pattern to the TRs, while NCOA2 increased at L14; HypoT blocked the variations in NCOA1 and NCOA2. HypoT increased NCOR1 on L2 and decreased OTR at L2 and circulating estradiol and NCOR2 at L14. In controls the most notable changes occurred on L7, suggesting it is a key inflection point in mammary metabolism. The low levels of TRα1, NCOA1 and OTR, and increased NCOR1 produced by HypoT on L2 may hinder the mammary ability to achieve normal milk synthesis and ejection, leading to defective lactation. Later on, altered ER and PR expression may impair further mammary function.

Inhibitory role of ERß on anterior pituitary cell proliferation by controlling the expression of proteins related to cell cycle progression.

Considering that the role of ERß in the growth of pituitary cells is not well known, the aim of this work was to determine the expression of ERß in normal and tumoral cells and to investigate its implications in the proliferative control of this endocrine gland, by analyzing the participation of cyclin D1, Cdk4 and p21. Our results showed that the expression of ERß decreased during pituitary tumoral development induced by chronic E2 stimulation. The 20 ± 1.6% of normal adenohypophyseal cells expressed ERß, with this protein being reduced in the hyperplastic/adenomatous pituitary: at 20 days the ERß+ population was 10.7 ± 2.2%, while after 40 and 60 days of treatment an almost complete loss in the ERß expression was observed (40 d: 1 ± 0.6%; 60 d: 2 ± 0.6%). The ERα/ß ratio increased starting from tumors at 40 days, mainly due to the loss of ERß expression. The cell proliferation was analyzed in normal and hyperplastic pituitary and also in GH3ß- and GH3ß+ which contained different levels of ERß expression, and therefore different ERα/ß ratios. The over-expression of ERß inhibited the GH3 cell proliferation and expression of cyclin D1 and ERα. Also, the ERß activation by its agonist DPN changed the subcellular localization of p21, inducing an increase in the p21 nuclear expression, where it acts as a tumoral suppressor. These results show that ERß exerts an inhibitory role on pituitary cell proliferation, and that this effect may be partially due to the modulation of some key regulators of the cell cycle, such as cyclin D1 and p21. These data contribute significantly to the understanding of the ER effects in the proliferative control of pituitary gland, specifically related to the ERß function in the E2 actions on this endocrine gland.

Effects of parity and serum prolactin levels on the incidence and regression of DMBA-induced tumors in OFA hr/hr rats.

Prolactin (PRL) is a key player in the development of mammary cancer. We studied the effects of parity or hyperprolactinemia on mammary carcinogenesis in OFA hr/hr treated with 7,12-dimethylbenzanthracene. They were divided into three groups: nulliparous (Null), primiparous (PL, after pregnancy and lactation), and hyperprolactinemic rats (I, implanted in the arcuate nucleus with 17ß-estradiol). The tumor incidence was similar in the three groups. However, a higher percentage of regressing tumors was evident in the PL group. Serum PRL, mammary development, and mammary ß-casein content were higher in I rats compared to Null. The expression of hormone receptors was similar in the different groups. However, mammary tissue from PL rats bearing tumors had increased expression of PRL and estrogen alpha receptors compared to rats free of tumors. Our results suggest that serum PRL levels do not have relevance on the incidence of tumors, probably because the low levels of PRL in OFA rats are not further decreased by PL like in other strains. However, supraphysiological levels of PRL affect carcinogenesis. PL induces regression of the tumors due to the differentiation produced on the mammary cells. Alterations in the expression of hormonal receptors may be involved in progression and regression of tumors.