Homeostatic control of volume within the alveolar spaces of the mammary gland has been proposed to involve a feedback system mediated by serotonin signaling. In this article, we describe some of the mechanisms underlying this feedback based on studies of a human normal mammary epithelial cell line (MCF10A) and mouse mammary epithelium. Mammary serotonin was elevated during lactation and after injection of 5-hydroxytryptophan (5-HTP). The genes encoding the serotonin reuptake transporter (SERT) and the type 7 serotonin receptor (5-HT 7) were expressed in human and mouse mammary epithelial cells, and serotonin caused a concentration-dependent increase of cAMP in MCF10A cells. Mouse and human mammary epithelial cells formed polarized membranes, in which tight junction activity was monitored. Treatment of mammary epithelial membranes with serotonin receptor antagonists increased their transepithelial electrical resistance (TEER). Antagonist and agonist effects on TEER were mediated by receptors on the basolateral face of the membranes. Our results suggest a process in which serotonin accumulates in the interstitial fluid surrounding the mammary secretory epithelium and is detected by 5-HT7 receptors, whereupon milk secretion is inhibited. One mechanism responsible for this process is serotonin-mediated opening of tight junctions, which dissipates the transepithelial gradients necessary for milk secretion.lactation ͉ MCF10A ͉ milk protein ͉ serotonin receptor ͉ serotonin transporter

IntroductionThe breast microenvironment can either retard or accelerate the events associated with progression of latent cancers. However, the actions of local physiological mediators in the context of breast cancers are poorly understood. Serotonin (5-HT) is a critical local regulator of epithelial homeostasis in the breast and other organs. Herein, we report complex alterations in the intrinsic mammary gland serotonin system of human breast cancers.MethodsSerotonin biosynthetic capacity was analyzed in human breast tumor tissue microarrays using immunohistochemistry for tryptophan hydroxylase 1 (TPH1). Serotonin receptors (5-HT1-7) were analyzed in human breast tumors using the Oncomine database. Serotonin receptor expression, signal transduction, and 5-HT effects on breast cancer cell phenotype were compared in non-transformed and transformed human breast cells.ResultsIn the context of the normal mammary gland, 5-HT acts as a physiological regulator of lactation and involution, in part by favoring growth arrest and cell death. This tightly regulated 5-HT system is subverted in multiple ways in human breast cancers. Specifically, TPH1 expression undergoes a non-linear change during progression, with increased expression during malignant progression. Correspondingly, the tightly regulated pattern of 5-HT receptors becomes dysregulated in human breast cancer cells, resulting in both ectopic expression of some isoforms and suppression of others. The receptor expression change is accompanied by altered downstream signaling of 5-HT receptors in human breast cancer cells, resulting in resistance to 5-HT-induced apoptosis, and stimulated proliferation.ConclusionsOur data constitutes the first report of direct involvement of 5-HT in human breast cancer. Increased 5-HT biosynthetic capacity accompanied by multiple changes in 5-HT receptor expression and signaling favor malignant progression of human breast cancer cells (for example, stimulated proliferation, inappropriate cell survival). This occurs through uncoupling of serotonin from the homeostatic regulatory mechanisms of the normal mammary epithelium. The findings open a new avenue for identification of diagnostic and prognostic markers, and valuable new therapeutic targets for managing breast cancer.

Medications that perturb serotonin balance dysregulate lactation, and the effects are consistent with those predicted by the physiological effects of intramammary 5-HT bioactivity. Mothers taking serotonergic drugs may need additional support to achieve their breastfeeding goals.

As demonstrated by a variety of animal studies, barrier function in the mammary epithelium is essential for a fully functioning and differentiated gland. However, there is a paucity of information on barrier function in human mammary epithelium. Here, we have established characteristics of a polarizing differentiating model of human mammary epithelial cells capable of forming a high-resistance/low-conductance barrier in a predictable manner, viz., by using MCF10A cells on permeable membranes. Inulin flux decreased and transepithelial electrical resistance (TEER) increased over the course of several days after seeding MCF10A cells on permeable membranes. MCF10A cells exhibited multipotent phenotypic differentiation into layers expressing basal and lumenal markers when placed on permeable membranes, with at least two distinct cell phenotypes. A clonal subline of MCF10A, generated by culturing stem-like cells under non-adherent conditions, also generated a barrier-forming epithelial membrane with cells expressing markers of both basal and lumenal differentiation (CD10 and MUC1, respectively). Progressive changes associated with differentiation, including wholesale inhibition of cell-cycle genes and stimulation of cell and tissue morphogenic genes, were observed by gene expression profiling. Clustering and gene ontology categorization of significantly altered genes revealed a pattern of lumenal epithelial-cell-specific differentiation.

The role of human dissection in modern medical curricula has been a topic of intense debate. In part, this is because dissection can be time‐consuming and curricular hours are being monitored more carefully. This has led some to question the efficacy and importance of dissection as a teaching method. While this topic has received considerable attention in the literature, the question of how dissection impacts learning has been difficult to evaluate in a real‐world, high‐stakes setting since participation in dissection is often one of many variables. In this study, this challenge was overcome due to a change in the curriculum of a Special Master Program (SMP) that permitted a comparison between two years of students that learned anatomy using prosection only and two years of students that participated in dissection laboratories. Since each class of SMP students took courses in the medical school, and the medical school anatomy curriculum was constant, medical student performance served as a control throughout the study period. Results demonstrate that SMP students who learned through prosection had lower performance on anatomy practical and written examinations compared to medical students. When the SMP program changed and students started participating in dissection, there were measurable improvements in both practical and written examinations. These findings provide evidence of dissection’s role in learning and applying anatomy knowledge both within and outside the gross anatomy laboratory.