Aaron M. Marshall

Mammary gland homeostasis employs serotonergic regulation of epithelial tight junctions

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-HT7) 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.

Altered serotonin physiology in human breast cancers favors paradoxical growth and cell survival

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.

Serotonin Transport and Metabolism in the Mammary Gland Modulates Secretory Activation and Involution

CONTEXT Serotonin [5-hydroxytryptamine (5-HT)] is an important local regulator of lactation homeostasis; however, the roles for the serotonin reuptake transporter and monoamine oxidase have not been known. OBJECTIVE The aim of the study was to determine whether drugs that impact 5-HT affect human lactation physiology. DESIGN AND SETTING We conducted laboratory studies of human and animal models and an observational study of the onset of copious milk secretion in postpartum women at a university medical center. PARTICIPANTS We studied women expecting their first live-born infant; exclusion criteria were: referred to the medical center for another medical condition, known contraindication to breastfeed, and less than 19 yr of age and unable to obtain parental consent. INTERVENTION(S) The mothers were interviewed. The cell and animal studies consisted of a variety of biochemical, pharmacological, and genetic interventions. MAIN OUTCOME MEASURE(S) The human subjects outcome was prevalence of delayed onset of copious milk secretion. The cell and animal outcomes were physiological and morphological. RESULTS Inhibiting serotonin reuptake in mammary epithelial cells altered barrier function, and the effects were amplified by coadministering a monoamine oxidase inhibitor. Direct delivery of fluoxetine by slow-release pellets caused localized involution. TPH1 knockout mice displayed precocious secretory activation. Among a cohort of 431 women, those taking SSRI were more likely (P = 0.02) to experience delayed secretory activation. CONCLUSIONS 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.

In vitro multipotent differentiation and barrier function of a human mammary epithelium

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.

Serotonin and Serotonin Transport in the Regulation of Lactation

Serotonin (5-HT), classically known as a neurotransmitter involved in regulating sleep, appetite, memory, sexual behavior, neuroendocrine function and mood is also synthesized in epithelial cells located in many organs throughout the body, including the mammary gland. The function of epithelial 5-HT is dependent on the expression of the 5-HT receptors in a particular system. The conventional components of a classic 5-HT system are found within the mammary gland; synthetic enzymes (tryptophan hydroxylase I, aromatic amino acid decarboxylase), several 5-HT receptors and the 5-HT reuptake transporter (SERT). In the mammary gland, two actions of 5-HT through two different 5-HT receptor subtypes have been described: negative feedback on milk synthesis and secretion, and stimulation of parathyroid hormone related-protein, a calcium-mobilizing hormone. As with neuronal systems, the regulation of 5-HT activity is multifactorial, but one seminal component is reuptake of 5-HT from the extracellular space following its release. Importantly, the wide availability of selective 5-HT reuptake inhibitors (SSRI) allows the manipulation of 5-HT activity in a biological system. Here, we review the role of 5-HT in mammary gland function, review the biochemistry, genetics and physiology of SERT, and discuss how SERT is vital to the function of the mammary gland.

Intraluminal volume homeostasis: A common sertonergic mechanism among diverse epithelia.

Volume homeostasis is a common physiological phenomenon for fluid secreting organs, such as exocrine and endocrine glands. It is a manifestation of a finite intraluminal space and an ever changing demand for secretory fluids. Volume homeostasis addresses issues of fluid secretion, storage and clearance for efficient functioning. Here we discuss the evidence gathered over the past 2-3 decades on serotonins role as a feedback inhibitor of secretion in the mammary gland, salivary gland, liver, pancreas, lung, thyroid gland and prostate gland. We propose that serotonin action is a common mechanism of regulating intraductal volume homeostasis.

Intraluminal volume homeostasis

Volume homeostasis is a common physiological phenomenon for fluid secreting organs, such as exocrine and endocrine glands. It is a manifestation of a finite intraluminal space and an ever changing demand for secretory fluids. Volume homeostasis addresses issues of fluid secretion, storage and clearance for efficient functioning. Here we discuss the evidence gathered over the past 2-3 decades on serotonin’s role as a feedback inhibitor of secretion in the mammary gland, salivary gland, liver, pancreas, lung, thyroid gland and prostate gland. We propose that serotonin action is a common mechanism of regulating intraductal volume homeostasis.

Estrogen receptor alpha deletion enhances the metastatic phenotype of Ron overexpressing mammary tumors in mice

BackgroundThe receptor tyrosine kinase family includes many transmembrane proteins with diverse physiological and pathophysiological functions. The involvement of tyrosine kinase signaling in promoting a more aggressive tumor phenotype within the context of chemotherapeutic evasion is gaining recognition. The Ron receptor is a tyrosine kinase receptor that has been implicated in the progression of breast cancer and evasion of tamoxifen therapy.ResultsHere, we report that Ron expression is correlated with in situ, estrogen receptor alpha (ERα)-positive tumors, and is higher in breast tumors following neoadjuvant tamoxifen therapy. We also demonstrate that the majority of mammary tumors isolated from transgenic mice with mammary specific-Ron overexpression (MMTV-Ron mice), exhibit appreciable ER expression. Moreover, genetic-ablation of ERα, in the context of Ron overexpression, leads to delayed mammary tumor initiation and growth, but also results in an increased metastasis.ConclusionsRon receptor overexpression is associated with ERα-positive human and murine breast tumors. In addition, loss of ERα on a Ron overexpressing background in mice leads to the development of breast tumors which grow slower but which exhibit more metastasis and suggests that targeting of ERα, as in the case of tamoxifen therapy, may reduce the growth of Ron overexpressing breast cancers but may cause these tumors to be more metastatic.

Transgender Medicine Curriculum: Integration Into an Organ System–Based Preclinical Program

Introduction There is a recognized and articulated need for health professionals to understand the definitions, health disparities, and medical management of transgender patients. This recognition comes organically from students requesting more information, and top-down from governing bodies such as the AAMC or the Liaison Committee on Medical Education. Surveys of North American medical schools indicate that training in transgender medicine (specifically, the process of transition) is infrequent and inadequate. One problem underlying this trend may be the lack of resources to help conceptualize and roll out a transgender medicine curriculum. Methods Here, we report the integration of training in transgender medicine into the organ system–based course Endocrine-Reproduction. This transgender curriculum includes coverage of basic science, clinical management, ethics, and clinical skills. The curriculum leverages an already existing, health care disparity–focused curriculum but adds (1) a didactic component for dissemination and discussion of basic science principles applied to transgender patients and (2) a mock initial encounter between a physician and patient with gender dysphoria. Results Following the first-time implementation of the transgender curriculum, students were surveyed, with a large majority reporting feeling more prepared to care for transgender patients. Discussion We conclude that including a multidisciplinary transgender medicine curriculum in medical school advances the goal of creating safe, effective physicians by providing fundamental knowledge about an underserved population of patients, as well as exampled application of that knowledge.