Multiple cellular responses to serotonin contribute to epithelial homeostasis

Effects of rumen-protected 5-hydroxytryptophan on circulating serotonin concentration, behaviour, and mammary gland involution in goats

The risk of acquiring new intramammary infections is high at the end of lactation, especially for the high milk-producing dairy animals. Resistance to bacterial infection increases following the completion of mammary gland involution after milking cessation. The serotonin precursor 5-hydroxytryptophan (5-HTP) could accelerate involution by increasing circulating serotonin levels, but ruminal microbes may degrade 5-HTP if orally administered to adult ruminants. It is unclear whether rumen-protected 5-HTP could effectively mediate circulating serotonin (5-hydroxytryptamine, 5-HT) and therefore accelerate mammary gland involution in ruminants. Goats were used as a model in the current study to investigate the effects of rumen-protected 5-HTP on behaviour, 5-HT metabolism, and mammary involution in ruminants. In the first experiment, 16 female Dazu black goats were assigned to one of four groups in a randomised block design. The treatments included a basal diet plus 0, 4, 20, or 100 mg/kg BW of rumen-protected 5-HTP. Serum was collected at 0, 3, 6, 12, and 24 h after offering the rumen-protected 5-HTP in the morning feed, and the behaviours were monitored. In the second experiment, 12 female Dazu black goats (Somatic cell count < 250 000) were randomly assigned to the control (basal diet) or rumen-protected 5-HTP group (basal diet plus 20 mg/kg BW). Milk or mammary secretions were manually collected aseptically on d -1, 1, 2, 3, 4, and 5 around weaning. The results depicted that rumen-protected 5-HTP supplementation elevated circulating 5-HTP and 5-hydroxyindole acetic acid concentrations, while 20 mg/kg BW of rumen-protected 5-HTP supplementation lowered the goats' locomotive activity. A high concentration of rumen-protected 5-HTP (100 mg/kg BW) increased serum alkaline phosphatase and gamma-glutamyl transpeptidase concentrations. Moreover, oral supplementation with 20 mg/kg BW of rumen-protected 5-HTP accelerated mammary gland involution and reduced feed intake in goats after weaning. These results demonstrate that oral supplementation with rumen-protected 5-HTP influences 5-HT metabolism and accelerates mammary gland involution after milking cessation in ruminants.

Effects of Serotonin on Cell Viability, Permeability of Bovine Mammary Gland Epithelial Cells and Their Transcriptome Analysis

Serotonin (5-HT) has been reported to play an important role in mammary gland involution that is defined as the process through which the gland returns to a nonlactating state. However, the overall picture of the regulatory mechanisms of 5-HT and the effects of serotonylation on mammary gland involution still need to be further investigated. The current study aimed to investigate the effects of 5-HT on global gene expression profiles of bovine mammary epithelial cells (MAC-T) and to preliminarily examine whether the serotonylation involved in the mammary gland involution by using Monodansylcadaverine (MDC), a competitive inhibitor of transglutaminase 2. Results showed that a high concentration of 5-HT decreased viability and transepithelial electrical resistance (TEER) in MAC-T cells. Transcriptome analysis indicated that 2477 genes were differentially expressed in MAC-T cells treated with 200 μg/mL of 5-HT compared with the control group, and the Notch, p53, and PI3K-Akt signaling pathways were enriched. MDC influenced 5-HT-induced MAC-T cell death, fatty acid synthesis, and the formation and disruption of tight junctions. Overall, a high concentration of 5-HT is able to accelerate mammary gland involution, which may be regulated through the Notch, p53, and PI3K-Akt signaling pathways. Serotonylation is involved in bovine mammary gland involution.

Effect of serotonin on the cell viability of the bovine mammary alveolar cell-T (MAC-T) cell line

5-Hydroxytryptamine (5-HT), a monoamine, as a local regulator in the mammary gland is a chemical signal produced by the mammary epithelium cell. In cows, studies have shown that 5-HT is associated with epithelial cell apoptosis during the degenerative phase of the mammary gland. However, studies in other tissues have shown that 5-HT can effectively promote cell viability. Whether 5-HT could have an effect on mammary cell viability in dairy cows is still unknown. The purpose of this study was to determine: (1) effect of 5-HT on the viability of bovine mammary epithelial cells and its related signaling pathways, (2) interaction between prolactin (PRL) and 5-HT on the cell viability. The bovine mammary alveolar cell-T (MAC-T) were cultured with different concentrations of 5-HT for 12, 24, 48 or 72 hours, and then were assayed using cell counting kit-8, polymerase chain reaction (PCR) and immunobloting. The results suggested that 20 μM 5-HT treatment for 12 or 24 h promote cell viability, which was mainly induced by the activation of 5-HT receptor (5-HTR) 1B and 4, because the increase caused by 5-HT vanished when 5-HTR 1B and 4 was blocked by SB224289 and SB204070. And protein expression of mammalian target of rapamycin (mTOR), eukaryotic translation elongation factor 2 (eEF2), janus kinase 2 (JAK2) and signal transducer and activator of transcription 5 (STAT5) were decreased after blocking 5-HT 1B and 4 receptors. When MAC-T cells were treated with 5-HT and PRL simultaneously for 24 h, both the cell viability and the level of mTOR protein were significantly higher than that cultured with 5-HT or PRL alone. In conclusion, our study suggested that 5-HT promotes the viability of MAC-T cells by 5-HTR 1B and/or 4. Furthermore, there is a reciprocal relationship between PRL and 5-HT.

Mammary homeostasis in the mother-offspring dyad

Homeostasis during lactation is a special case in which the unit for regulation is a dyad comprising the mother and her currently nursing offspring (the mother-offspring dyad). This arrangement is not a trivial. A litter of mice can have a mass greater than the mother and nutrient demands that far exceed her. Homeostasis for milk secretion, appetite, and calcium metabolism must come under integrated control, responding seamlessly to the needs of the mother and the offspring. Serotonin (5-HT) is a primary local regulator of mammary homeostasis. 5-HT synthesis in the mammary epithelium is high during lactation and increases during milk stasis. Two important functions are attributed to the 5-HT system. Firstly, when alveolar spaces are filled with milk 5-HT inhibits milk secretion and opens tight junctions. This feedback induces early phases of involution. Secondly, 5-HT induces synthesis and secretion of parathyroid hormone-related peptide (PTHrP).

Effect of circadian system disruption on the concentration and daily oscillations of cortisol, progesterone, melatonin, serotonin, growth hormone, and core body temperature in periparturient dairy cattle

Metabolic, circadian, sleep, and reproductive systems are integrated and reciprocally regulated, but the understanding of the mechanism is limited. To study this integrated regulation, the circadian timing system was disrupted by exposing late pregnant nonlactating (dry) cows to chronic shifts in the light-dark phase, and rhythms of body temperature and circulating cortisol (CORT), progesterone (P4), serotonin (5HT), melatonin (MEL), and growth hormone (GH) concentrations were measured. Specifically, across 2 identical studies (1 and 2), at 35 d before expected calving (BEC) multiparous cows were assigned to control (CON; n = 24) and exposed to 16 h light and 8 h dark or phase shift (PS; n = 24) treatments and exposed to 6-h light-dark phase shifts every 3 d until parturition. All cows were exposed to control lighting after calving. Blood samples were collected in the first study at 0600 h on d 35 BEC, d 21 BEC, and 2 d before calving, and d 0, 2, 9, 15, and 22 postpartum (PP). A subset of cows (n = 6/group) in study 1 was blood sampled every 4 h over 48 h beginning on d 23 BEC, 9 BEC, and 5 PP. Body temperature was measured every 30 min (n = 8-16/treatment) for 48 h at 23 BEC and 9 BEC in both studies; and at 14 PP and 60 PP only in study 2. Treatment did not affect levels of CORT, GH, or P4 at 0600 h, but overall level of 5HT was lower and MEL higher in PS cows across days sampled. A 2-component versus single-component cosinor model better described [>coefficient of determination (R²); <Akaike information criterion and <Bayesian information criterion] daily oscillations of all hormones and temperature for both treatments. Circadian rhythm fit (R²) of body temperature and MEL increased from 23 BEC to 9 BEC in CON and was marked by loss of feeding time influence on oscillations in both treatments. Both treatments exhibited circadian rhythms of CORT at 9 BEC, CON cows also exhibited circadian rhythms in P4 at 23 BEC, and 5HT at 9 BEC. Daily oscillations in temperature and hormones, except CORT, were affected by PS treatment in the prepartum and were associated with longer gestation. In the PP, circadian rhythmicity was lost or diminished for all hormones and body temperature in both treatments. Stronger rhythms of body temperature and multiple hormones at 1 wk prepartum may indicate a synchronizing cue to time parturition. Therefore, dairy systems may need to consider management factors that affect circadian clocks in late-gestation cows.

The molecular basis of mammary gland development and epithelial differentiation

Our understanding of the molecular events underpinning the development of mammalian organ systems has been increasing rapidly in recent years. With the advent of new and improved next-generation sequencing methods, we are now able to dig deeper than ever before into the genomic and epigenomic events that play critical roles in determining the fates of stem and progenitor cells during the development of an embryo into an adult. In this review, we detail and discuss the genes and pathways that are involved in mammary gland development, from embryogenesis, through maturation into an adult gland, to the role of pregnancy signals in directing the terminal maturation of the mammary gland into a milk producing organ that can nurture the offspring. We also provide an overview of the latest research in the single-cell genomics of mammary gland development, which may help us to understand the lineage commitment of mammary stem cells (MaSCs) into luminal or basal epithelial cells that constitute the mammary gland. Finally, we summarize the use of 3D organoid cultures as a model system to study the molecular events during mammary gland development. Our increased investigation of the molecular requirements for normal mammary gland development will advance the discovery of targets to predict breast cancer risk and the development of new breast cancer therapies.

The Role of Serotonin in Breast Cancer Stem Cells

Breast tumors were the first tumors of epithelial origin shown to follow the cancer stem cell model. The model proposes that cancer stem cells are uniquely endowed with tumorigenic capacity and that their aberrant differentiation yields non-tumorigenic progeny, which constitute the bulk of the tumor cell population. Breast cancer stem cells resist therapies and seed metastases; thus, they account for breast cancer recurrence. Hence, targeting these cells is essential to achieve durable breast cancer remissions. We identified compounds including selective antagonists of multiple serotonergic system pathway components required for serotonin biosynthesis, transport, activity via multiple 5-HT receptors (5-HTRs), and catabolism that reduce the viability of breast cancer stem cells of both mouse and human origin using multiple orthologous assays. The molecular targets of the selective antagonists are expressed in breast tumors and breast cancer cell lines, which also produce serotonin, implying that it plays a required functional role in these cells. The selective antagonists act synergistically with chemotherapy to shrink mouse mammary tumors and human breast tumor xenografts primarily by inducing programmed tumor cell death. We hypothesize those serotonergic proteins of diverse activity function by common signaling pathways to maintain cancer stem cell viability. Here, we summarize our recent findings and the relevant literature regarding the role of serotonin in breast cancer.

Transcriptomic analysis investigating the interaction between peripheral serotonin and high-fat diet feeding on mammary gene expression in midlactation mice

To understand the role of peripheral serotonin and its interaction with diet in midlactation mammary gene expression, our study uses tryptophan hydroxylase 1 knockout (Tph1-KO) mice fed a high-fat diet (HFD). It has previously been demonstrated that HFD feeding increases inflammatory and immune pathways in peak lactation mammary glands of mice and increases pup mortality in wild-type (WT) mice compared with dams fed a low-fat diet (LFD). Peripheral serotonin inhibition has been associated with resistance to obesity in male mice fed an HFD. Little is known about the function of Tph1 and how peripheral serotonin affects mammary gland function during pregnancy and lactation. In this study, WT and Tph1-KO models were used to investigate global transcriptomic changes in peak lactation mammary glands when dams were fed either an HFD or LFD. WT and Tph1-KO female mice were assigned to either an LFD or HFD beginning at 3 wk of age (n = 4/group). Dams were euthanized on lactation day 11. Differentially expressed genes (DEGs) were first filtered by adjusted P value (cutoff ≤ 0.05) and fold-change (FC, cutoff ≥2). Genes were further filtered by mean normalized read count with a cutoff ³10. We did not observe many differentially expressed genes in WT and Tph1-KO dams fed LFD. However, 3,529 DEGs were observed between WT-HFD and Tph1-KO-HFD mice, including cell cycle regulation and MAPK pathways being significantly enriched. Further research is required to completely understand the physiological significance of our results on peak lactation mammary physiology and the contribution of serotonin.

Short communication: Ketosis, feed restriction, and an endotoxin challenge do not affect circulating serotonin in lactating dairy cows

Circulating serotonin (5-hydroxytryptamine; 5-HT) appears to be associated with various energetic disorders and hypocalcemia during the transition period. The objective of this study was to evaluate the effects of ketosis, feed restriction (FR), and endotoxin challenge (models in which energetic and calcium metabolism are markedly altered) on circulating 5-HT in lactating Holstein cows. Blood samples were obtained from 3 separate experiments; circulating β-hydroxybutyrate (BHB), nonesterified fatty acids (NEFA), and glucose were measured in all 3 experiments, whereas ionized calcium (iCa²⁺) was measured only in the endotoxin challenge. In the ketosis study, blood samples from cows clinically diagnosed with ketosis (n = 9) or classified as healthy (n = 9) were obtained from a commercial dairy farm at d -7, 3, and 7 relative to calving. Ketosis was diagnosed using a urine-based test starting at 5 d in milk. There was no effect of health status on circulating 5-HT and no association between 5-HT and BHB, NEFA, or glucose; however, 5-HT concentrations progressively decreased following calving. In the FR experiment, mid-lactation cows were either fed ad libitum (n = 3) or restricted to 20% of their ad libitum intake (n = 5) for 5 d. There were no FR effects on circulating 5-HT, nor was FR correlated with energetic metabolites. In the immune activation model, mid-lactation cows were intravenously challenged with either lipopolysaccharide (LPS; 1.5 µg/kg of BW; n = 6) or sterile saline (control; n = 6). Administering LPS decreased (56%) blood iCa²⁺ but had no effect on circulating 5-HT, nor was there a correlation between circulating 5-HT and NEFA, BHB, or iCa²⁺. Circulating 5-HT tended to be positively correlated (r = 0.54) with glucose in Holstein cows administered LPS. In summary, in contrast to expectations, circulating 5-HT was unaffected in models of severely disturbed energetic and Ca²⁺ homeostasis.

High polymorphism rates in well-known T cell epitopes restricted by protective HLA alleles during HIV infection are associated with rapid disease progression in early-infected MSM in China

T cell epitopes restricted by several protective HLA alleles, such as B*57, B*5801, B*27, B*51 and B*13, have been very well defined over the past two decades. We investigated 32 well-known T cell epitopes restricted by protective HLA molecules among 54 Chinese men who have sex with men (MSM) at the early stage of HIV-1 infection. Subjects in our cohort carrying protective HLA types did not exhibit slow CD4 T cell count decline (P = 0.489) or low viral load set points (P = 0.500). Variations occurred in 96.88% (31/32) of the known wild-type epitopes (rate 1.85-100%), and the variation rates of the strains of two CRF01_AE lineages were significantly higher than those of non-CRF01_AE strains (76.82% vs. 48.96%, P = 0.004; 71.27% vs. 8.96%, P = 0.025). Subjects infected with CRF01_AE exhibited relatively rapid disease progression (P = 0.035). Therefore, the lack of wild-type protective T cell epitopes restricted by classic protective HLA alleles in CRF01_AE HIV-1 strains may be one of the reasons why rapid disease progression is observed in Chinese MSM with HIV-1 infection.

Short communication: Differences in distribution of serotonin receptor subtypes in the mammary gland of sheep, goats, and cows during lactation and involution

Serotonin receptors (5-HTR) are present in the mammary tissue of mouse, humans, cows, and rats. In these species, serotonin is important for the mammary gland function and lactation performance. The mammary gland expression of 5-HTR in small dairy ruminants has yet to be described. In the present study, primer sequences were developed to amplify 5-HTR (1A, 1D, 1E,1B, 1F, 2A, 2B, 2C, 3a, 4, 5a, 6, and 7) using real-time quantitative PCR for the detection of mRNA expression in mammary tissue of dairy sheep, goats, and cows. The distribution of commonly expressed 5-HTR between the 3 species (1B, 1E, 2A, 2B, 4, and 7) was analyzed in the mammary tissue of late-lactation and dried-off sheep, goats, and cows using immunohistochemical staining. Real-time quantitative PCR analysis showed that the 3 studied species expressed receptors 5-HTR1B, 1E, 2A, 2B, 4, and 7. Goats and sheep expressed 5-HTR1D and 5a; 5-HTR1A and 1F were expressed only in sheep. The mammary epithelial cells were positively stained for all the studied receptors by immunohistochemistry (5-HTR1B, 1E, 2A, 2B, 4, and 7). The endothelial cells of blood vessels were positively stained for 5-HTR1B, 2A, 2B, and 7 in all the species. Additionally, 5-HTR1E was present in cow endothelium. The myoepithelial cells stained positively for 5-HTR1E in all the species, and 5-HTR4 myoepithelial staining was present only in cows and sheep. Between the lactating and dried-off mammary glands, the location of 5-HTR in the epithelial cells changed from a cytoplasmic reaction in lactating udders to a reaction in the apical region in dry udders. These results showed that the distribution of 5-HTR subtypes in the mammary gland of dairy ruminants vary among species, tissue type, and stage of gland development. These findings warrant future studies aimed at understanding whether the differences in 5-HTR subtype expression and location accounts for the differences in milk secretion and lactocyte activity among cows, goats, and sheep.

Interaction of 5-hydroxy-l-tryptophan and negative dietary cation-anion difference on calcium homeostasis in multiparous peripartum dairy cows

Hypocalcemia affects almost 50% of all dairy cows. Our laboratory has previously demonstrated that infusions of the serotonin precursor 5-hydroxy-l-tryptophan (5-HTP) increase circulating calcium concentrations in the Holstein transition cow. It is unknown whether feeding a negative dietary cation-anion difference (DCAD) diet alters the relationship between 5-HTP and hypocalcemia. The main objective of this study was to determine whether feeding a negative DCAD (-DCAD) diet before calving in conjunction with 5-HTP treatment could further diminish the magnitude of hypocalcemia at the time of calving. We used a randomized complete block design with a 2 × 2 factorial arrangement. Thirty-one multiparous Holstein cows were fed either a positive (+13 mEq/100 g) or negative (-13 mEq/100 g) DCAD diet 21 d before parturition and were intravenously infused daily with saline or 5-HTP (1 mg/kg) starting 7 d before the estimated date of parturition. Cows were blocked by parity and were randomly assigned to 1 of 4 treatment groups: positive DCAD plus saline, positive DCAD plus 5-HTP, negative DCAD plus saline, and negative DCAD plus 5-HTP, resulting in n = 8 per group. Total calcium (tCa), ionized calcium (iCa), and feed intake were recorded. The iCa was elevated prepartum in the -DCAD/5-HTP group compared with the other treatment groups as well as on d 0 and 1 postpartum. Although differences in tCa were not significant across the pre- or postpartum periods, tCa was numerically higher on d 0 and significantly higher on d 1 in -DCAD/5-HTP cows compared with all other groups. Prepartum the -DCAD/5-HTP treatment group ate less than the other treatment groups; however, postpartum dry matter intake differences were not significant. These findings demonstrate that feeding a -DCAD diet in conjunction with 5-HTP prepartum can increase postpartum circulating iCa concentrations and therefore diminish the magnitude of hypocalcemia at the time of parturition.

Serotoninergic and Circadian Systems: Driving Mammary Gland Development and Function

Since lactation is one of the most metabolically demanding states in adult female mammals, beautifully complex regulatory mechanisms are in place to time lactation to begin after birth and cease when the neonate is weaned. Lactation is regulated by numerous different homeorhetic factors, all of them tightly coordinated with the demands of milk production. Emerging evidence support that among these factors are the serotonergic and circadian clock systems. Here we review the serotoninergic and circadian clock systems and their roles in the regulation of mammary gland development and lactation physiology. We conclude by presenting our hypothesis that these two systems interact to accommodate the metabolic demands of lactation and thus adaptive changes in these systems occur to maintain mammary and systemic homeostasis through the reproductive cycles of female mammals.

Serotonin regulates β-casein expression via 5-HT7 receptors in human mammary epithelial MCF-12A cells

We previously reported that serotonin (5-hydroxytryptamine; 5-HT) suppresses β-casein expression, a differentiation marker in mammary epithelial cells, via inhibition of the signal transducer and activator of transcription 5 (STAT5) phosphorylation in the human mammary epithelial cell line, MCF-12A. In this study, we investigated the expression pattern of the different 5-HT receptor subtypes in MCF-12A cells, and identified the receptors involved in 5-HT-mediated suppression of β-casein protein expression. β-Casein mRNA expression was inhibited by 30 µM 5-HT in a time-dependent manner. Treatment with 30 µM 5-HT for 72 h decreased β-casein protein levels and STAT5 phosphorylation (pSTAT5). The cells expressed four 5-HT receptors subtypes (5-HTR1D, 2B, 3A, and 7) at the mRNA and protein level, and their expression was elevated by prolactin (PRL) treatment. Additionally, the mRNA levels of 5-HTR1D and 5-HTR7 were significantly higher than the other 5-HT receptors in the cells. Tryptophan hydroxylase 1 mRNA was detectable in the cells in the absence of PRL, and PRL treatment significantly increased its expression. β-Casein and pSTAT5/STAT5 levels in the cells co-treated with 5-HT and a selective 5-HTR1D inhibitor, BRL15572, were equal to those observed in cells treated with 5-HT alone. However, in the cells co-treated with 5-HT and a selective 5-HTR7 inhibitor, SB269970, β-casein and pSTAT5/STAT5 levels increased in a SB269970 concentration-dependent manner. In conclusion, we showed that 5-HT regulates β-casein expression via 5-HTR7 in MCF-12A human mammary epithelial cells.

Effect of nanostructured thin film on minimally invasive surgery devices applications: characterization, cell cytotoxicity evaluation and an animal study in rat

BACKGROUND

Minimally invasive surgery is performed using an endoscope and other instruments including the electrosurgical units. However, concerns including surgical smoke, tissue sticking and thermal injury are remaining in electrosurgery.

AIMS

Accordingly, a newly developed electrosurgical electrode coating with hydrogenated Cu-incorporated diamond-like carbon (DLC-Cu) film is purposed to improve the instrument performance.

METHODS

The morphologies of DLC-Cu surfaces were characterized using transmission electron microscopy, scanning electron microscopy and atomic force microscopy. In this study, lesions were made on the liver lobes of adult rats, using a monopolar electrosurgical unit equipped with untreated stainless steel electrodes or treated-electrodes. Animals were killed for evaluations at 0, 3, 7 and 28 days postoperatively.

RESULTS

Treated-electrodes generate less sticking tissues and adhesive blood cells. Thermography revealed that the surgical temperature in liver tissue from the treated-electrode was significantly lower than the untreated-electrode. Total injury area of livers treated with treated-electrodes was significantly smaller than the untreated-electrodes treatment. Moreover, treated-electrodes caused a relatively smaller area of lateral thermal injury, a smaller area of fibrotic tissue and a faster process of remodeling than the untreated-electrodes. Western blot analysis showed that rats treated with treated-electrode expressed lower levels of NF-κB, caspase-3 and MMP-9 than untreated-electrode. Immunofluorescence staining for caspase-3 revealed that the untreated-electrode caused more serious injury.

CONCLUSIONS

This study reveals that the plating of electrodes with hydrogenated Cu-incorporated diamond-like carbon film is an efficient method for improving the performance of electrosurgical units, and should benefit wound remodeling. However, more tests must be carried out to confirm these promising findings in human patients.

Serotonin suppresses β-casein expression via inhibition of the signal transducer and activator of transcription 5 (STAT5) protein phosphorylation in human mammary epithelial cells MCF-12A

Serotonin (5-hydroxytryptamine; 5-HT) has an important physiological role in controlling lactation, namely, milk volume homeostasis, within mammary glands. The objectives of this study were to evaluate whether exogenous 5-HT can suppress β-casein expression, a differentiation marker, produced in human mammary epithelial cells, and to determine whether 5-HT can attenuate β-casein signaling via the prolactin (PRL) receptor (PRLr) and Janus kinase 2/signal transducer and activator of transcription 5 (STAT5) pathway. PRL treatment increased the mRNA level of β-casein in the MCF-12A human mammary epithelial cell line, and the highest level occurred at days 7 and 14 of culture. In contrast, PRLr expression was not affected significantly by PRL treatment. PRL treatment in MCF-12A cells increased levels of β-casein and phosphorylated STAT5 (pSTAT5) proteins in a concentration-dependent manner, with a slight increase of STAT5 protein. β-Casein expression was inhibited by 0.1 mM 5-HT in a time-dependent manner. Additionally, treatment with 0.1 mM 5-HT for 72 h decreased protein levels of β-casein and pSTAT5, with a slight decrease in STAT5 levels. These results suggest that exogenous 5-HT can inhibit STAT5 phosphorylation, resulting in a decrease in β-Casein expression. In conclusion, we showed that exogenous 5-HT decreased β-casein expression in MCF-12A human mammary epithelial cells, and that 5-HT was responsible for inhibiting phosphorylation of STAT5, resulting in a decline in lactational function.

The type 7 serotonin receptor, 5-HT 7 , is essential in the mammary gland for regulation of mammary epithelial structure and function

Autocrine-paracrine activity of serotonin (5-hydroxytryptamine, 5-HT) is a crucial homeostatic parameter in mammary gland development during lactation and involution. Published studies suggested that the 5-HT₇ receptor type was important for mediating several effects of 5-HT in the mammary epithelium. Here, using 5-HT₇ receptor-null (HT7KO) mice we attempt to understand the role of this receptor in mediating 5-HT actions within the mammary gland. We demonstrate for the first time that HT7KO dams are inefficient at sustaining their pups. Histologically, the HT7KO mammary epithelium shows a significant deviation from the normal secretory epithelium in morphological architecture, reduced secretory vesicles, and numerous multinucleated epithelial cells with atypically displaced nuclei, during lactation. Mammary epithelial cells in HT7KO dams also display an inability to transition from lactation to involution as normally seen by transition from a columnar to a squamous cell configuration, along with alveolar cell apoptosis and cell shedding. Our results show that 5-HT₇ is required for multiple actions of 5-HT in the mammary glands including core functions that contribute to changes in cell shape and cell turnover, as well as specialized secretory functions. Understanding these actions may provide new interventions to improve lactation performance and treat diseases such as mastitis and breast cancer.

Serotonergic reinforcement of intestinal barrier function is impaired in irritable bowel syndrome

BACKGROUND

Alterations in serotonergic (5-HT) metabolism and/or intestinal integrity have been associated with irritable bowel syndrome (IBS).

AIMS

To assess the effects of the precursor of 5-HT, 5-hydroxytryptophan (5-HTP), on mucosal 5-HT availability and intestinal integrity, and to assess potential differences between healthy controls and IBS patients.

METHODS

Fifteen IBS patients and 15 healthy volunteers participated in this randomised double-blind placebo-controlled study. Intestinal integrity was assessed by dual-sugar test and by determining the mucosal expression of tight junction proteins after ingestion of an oral bolus of 100 mg 5-HTP or placebo. Mucosal serotonergic metabolism was assessed in duodenal biopsy samples.

RESULTS

5-HTP administration significantly increased mucosal levels of 5-HIAA, the main metabolite of 5-HT, in both healthy controls (7.1 ± 1.7 vs. 2.5 ± 0.7 pmol/mg, 5-HTP vs. placebo, P = 0.02) and IBS patients (20.0 ± 4.8 vs. 8.1 ± 1.3 pmol/mg, 5-HTP vs. placebo, P = 0.02), with the latter group showing a significantly larger increase. Lactulose/L-rhamnose ratios were significantly lower after administration of 5-HTP (P < 0.05) in healthy controls and were accompanied by redistribution of zonula occludens-1 (ZO-1), pointing to reinforcement of the barrier. In IBS, expression of the tight junction proteins was significantly lower compared to healthy controls, and 5-HTP resulted in a further decrease in occludin expression.

CONCLUSIONS

Oral 5-HTP induced alterations in mucosal 5-HT metabolism. In healthy controls, a reinforcement of the intestinal barrier was seen whereas such reaction was absent in IBS patients. This could indicate the presence of a serotonin-mediated mechanism aimed to reinforce intestinal barrier function, which seems to dysfunction in IBS patients.

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.

Serotonin: a local regulator in the mammary gland epithelium

Serotonin (5-hydroxytryptamine, 5-HT) is a very simple molecule that plays key roles in complex communication mechanisms within the animal body. In the mammary glands, serotonin biosynthesis and secretion are induced in response to dilation of the alveolar spaces. Since its discovery several years ago, mammary 5-HT has been demonstrated to perform two homeostatic functions. First, serotonin regulates lactation and initiates the transition into the earliest phases of involution. Second, serotonin is a local signal that induces parathyroid hormone-related peptide (PTHrP), which allows the mammary gland to drive the mobilization of calcium from the skeleton. These processes use different receptor types, 5-HT7 and 5-HT2, respectively. In this review, we provide synthetic perspectives on the fundamental processes of lactation homeostasis and the adaptation of calcium homeostasis for lactation. We analyze the role of the intrinsic serotonin system in the physiological regulation of the mammary glands. We also consider the importance of the mammary serotonin system in pathologies and therapies associated with lactation and breast cancer.

Life without peripheral serotonin: insights from tryptophan hydroxylase 1 knockout mice reveal the existence of paracrine/autocrine serotonergic networks

Since its identification, 75 years ago, the monoamine serotonin (5-HT) has attracted considerable attention toward its role as a neurotransmitter in the central nervous system. Yet, increasing evidence, from a growing number of research groups, substantiates the fact that 5-HT regulates important nonneuronal functions. Peripheral 5-HT, synthesized by the enzyme tryptophan hydroxyase (Tph) in intestinal cells, was assumed to be distributed throughout the entire body by blood platelets and to behave as a pleiotropic hormone. A decade ago, generation of a mouse model devoid of peripheral 5-HT lead to the discovery of a second isoform of the enzyme Tph and also suggested that 5-HT might act as a local regulator in various organs. The objective of this review is to highlight the newly discovered functions played by the monoamine using the Tph1 KO murine model and to outline current findings that led to the discovery of complete serotonergic systems in unexpected organs. Within an organ, both the presence of local Tph enzymatic activity and serotonergic components are of particular importance as they support the view that 5-HT meets the criteria to be qualified as a monoamine with a paracrine/autocrine function.

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 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.