The bovine mammary gland expresses multiple functional isoforms of serotonin receptors

Exploring the contribution of mammary-derived serotonin on liver and pancreas metabolism during lactation

During lactation, the murine mammary gland is responsible for a significant increase in circulating serotonin. However, the role of mammary-derived serotonin in energy homeostasis during lactation is unclear. To investigate this, we utilized C57/BL6J mice with a lactation and mammary-specific deletion of the gene coding for the rate-limiting enzyme in serotonin synthesis (TPH1, Wap-Cre x TPH1FL/FL) to understand the metabolic contributions of mammary-derived serotonin during lactation. Circulating serotonin was reduced by approximately 50% throughout lactation in Wap-Cre x TPH1FL/FL mice compared to wild-type mice (TPH1FL/FL), with mammary gland and liver serotonin content reduced on L21. The Wap-Cre x TPH1FL/FL mice had less serotonin and insulin immunostaining in the pancreatic islets on L21, resulting in reduced circulating insulin but no changes in glucose. The mammary glands of Wap-Cre x TPH1FL/FL mice had larger mammary alveolar areas, with fewer and smaller intra-lobular adipocytes, and increased expression of milk protein genes (e.g., WAP, CSN2, LALBA) compared to TPH1FL/FL mice. No changes in feed intake, body composition, or estimated milk yield were observed between groups. Taken together, mammary-derived serotonin appears to contribute to the pancreas-mammary cross-talk during lactation with potential implications in the regulation of insulin homeostasis.

Fecal microbiota transplantation for treatment of irritable bowel syndrome: Current advances and future perspectives

Irritable bowel syndrome (IBS) is a kind of functional gastroin-testinal disorder, characterized by recurrent abdominal pain and altered bowel habits. IBS adversely affects the quality of life of patients for the lack of effective treatment. The etiology of IBS remains poorly known. Previous studies suggested a possible role of gut dysbiosis in IBS pathogenesis. Fecal microbiota transplantation (FMT), which aims to reverse the gut dysbiosis, is a promising strategy in IBS management. In this review, we summarize the role of the gut microbiota in IBS pathogenesis from different aspects. We also review recent studies on efficacy evaluation of FMT in IBS. Besides, we discuss factors affecting the efficacy of FMT, hoping to provide a reference for future IBS treatment strategies targeting the gut microbiota.

Amplifying local serotonin signaling prior to dry-off hastens mammary gland involution and redevelopment in dairy cows

The monoamine serotonin (5-hydroxytryptamine, 5-HT) has been reported to inhibit milk protein gene expression and increase mammary epithelial cell (MEC) tight junction permeability after milk stasis. We hypothesized that increasing serotonin synthesis and signaling within the mammary epithelium before milk stasis would increase systemic and local involution markers, and downregulate the expression of milk protein and tight junction during involution, leading to more efficient tissue growth during the redevelopment phase. Herein, we examined the outcomes of increasing local mammary 5-HT synthesis before milk stasis on involution biomarkers, mammary gland microstructure, and gene and protein expression during the dry period. Multiparous Holstein cows were administered intramammary infusions (via the teat canal) of sterile water (CON, 4 mL/teat, n = 7) or 5-hydroxy-l-tryptophan (5-HTP, serotonin precursor, 20 mg/teat, n = 7) once daily for 5 d before dry-off (d 0). Blood, milk, and mammary secretions were collected and analyzed for components and metabolites. Mammary secretions were collected 12 h after the last milking and on d 1 to 4 during the dry period at 1200 h. Mammary gland biopsies were performed on d 4 (i.e., involution phase) and d 36 (i.e., redevelopment phase) of the dry period for histological and molecular evaluation. Milk protein and tight junction gene expression was quantified via real-time PCR. Hematoxylin and eosin staining, immunohistochemistry (Ki67), and immunofluorescence (serotonin, cleaved caspase 3) were performed to visualize tissue microstructure and to quantify serotonin intensity and cell turnover. Data were analyzed in SAS (SAS Institute Inc.) using 2-way ANOVA. After d 0, mammary secretions of 5-HTP cows had increased concentrations of 5-HT, lactoferrin, and bovine serum albumin. On d 1, 5-HTP cows had greater α-lactalbumin concentrations in plasma relative to CON. Serotonin intensity was increased in the mammary tissue of 5-HTP cows on d 4, relative to CON. On d 4, milk protein and tight junction gene expression was downregulated, MEC number was reduced, and cleaved caspase 3 protein was greater in mammary tissue of 5-HTP cows, relative to CON. On d 36, milk protein genes were upregulated, and the lumen:outer alveolar area and Ki67-positive cells were increased in the mammary tissue of 5-HTP cows, relative to CON. Amplifying serotonin signaling in the mammary epithelium before milk stasis at dry-off achieves greater apoptosis, leading to a reduction in MEC, allowing for greater cell proliferation, which results in more MEC during the redevelopment phase preceding the onset of lactation.

5-Hydroxytryptophan inhibits β-casein biosynthesis and promotes goat mammary epithelial cell apoptosis through the JAK2/STAT5a axis and the HTR7

5-Hydroxytryptamine (5-HT) is an amine produced in both the mammary gland and the central nervous system. Tryptophan hydroxylase 1 (TPH1) catalyzes the conversion of 5-hydroxytryptophan (5-HTP) into l-tryptophan, which is then converted into 5-HT by monoamine-oxidase (MAO-A). In the mammary gland, 5-HT has been shown to have a variety of paracrine-autocrine actions, including suppressing lactation, controlling the destiny of mammary epithelial cells, and maintaining calcium homeostasis throughout the transition from pregnancy to lactation. To examine the effects of 5-HT on the composition of colostrum and milk, a total of 30 transition Guan Zhong dairy goats were intramuscularly injected with 5-HTP (1.0 mg/kg) every morning before feeding from 10 d before the projected parturition date to the day of parturition. The average number of days animals received injections was 8.2 ± 3.2 d. 5-HTP treatment increased serum 5-HT concentration from days 5 to 2 relative to parturition (P < 0.05), and decreased the casein concentration of colostrum (P < 0.05). In the in vitro experiment, mammary epithelial cells isolated from three individual goats' mammary glands were separately treated with 200 μM 5-HTP, 30 μM PCPA (the specific inhibitor of TPH1), or 200 μM 5-HTP + 50 μM SB269970 (the selective antagonist of 5-HTR7). The results showed that 200 μM 5-HTP inhibited the expression of β-casein, downregulated the activity of the JAK2/ STAT5a signaling pathway, and promoted the apoptosis of goat mammary epithelial cells (GMECs) (P < 0.05). When GMECs were treated with 30 μM Four-chloro-dl-phenylalanine (PCPA), a specific inhibitor of 5-HT synthesis, the mRNA expression of STAT5a and the phosphorylated STAT5a protein level were upregulated. The 50 μM SB269970 treatment rescued the effects of 5-HTP on GMECs (P < 0.05). Taken together, the results indicated that 5-HTP exerted an inhibitory effect on β-casein synthesis and a proapoptotic effect in GMECs via HTR7 and the JAK2/STAT5a axis.

Effects of a hepatoprotectant and different feed energy sources on milk composition and nutrient partitioning in lactating cows

ABSTRACT The present study aimed at assessing the effects of hepatoprotective agents in diets that contain sources of energy on milk production, milk composition, and nutrient partition in lactating cows. Sixteen Holstein x Gir crossbred mid-lactation cows with an average body weight of 553 ± 85 kg were used in this study. These animals were allocated in a 4x4 Latin square design. A 2x2 factorial arrangement was employed in this feeding experiment. In each treatment, cows received diets with or without a hepatoprotective agent and variable in ground corn grain or citrus pulp as energy sources. Evaluated parameters included nutrient intake and digestibility, milk production, milk composition, energy balance, and nitrogen balance. Performance and nutrient balance variables were assessed and no interaction was observed between the hepatoprotective compounds and the dietary sources of energy. Dry matter intake, milk production and net energy for lactation were higher in corn as an energy source whereas milk fat content was higher in citrus pulp diets. There was a reduction in protein and casein contents in the milk of cows that was supplemented with an hepatoprotective agent. In this study, the hepatoprotective agent improved nitrogen balance in dairy cows. The use of the hepatoprotective compounds in the diet of these lactating cows in confinement reduced the milk protein fraction and favored a higher nitrogen balance in these animals. Retention of nitrogen compounds in the metabolism of lactating cows under confinement is influenced by hepatoprotective agents.

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.

Impact of Fluoxetine Treatment and Folic Acid Supplementation on the Mammary Gland Transcriptome During Peak Lactation

Serotonin is a key regulator of mammary gland homeostasis during lactation. Selective serotonin reuptake inhibitors (SSRIs) are commonly used to treat peripartum depression, but also modulates mammary gland serotonin concentrations and signaling in part through DNA methylation. The objective of this study was to determine mouse mammary transcriptome changes in response to the SSRI fluoxetine and how methyl donor supplementation, achieved by folic acid supplementation, affected the transcriptome. Female C57BL/6J mice were fed either breeder diet (containing 4 mg/kg folic acid) or supplemented diet (containing 24 mg/kg folic acid) beginning 2 weeks prior to mating, then on embryonic day 13 mice were injected daily with either saline or 20 mg/kg fluoxetine. Mammary glands were harvested at peak lactation, lactation day 10, for transcriptomic analysis. Fluoxetine but not folic acid altered circulating serotonin and calcium concentrations, and folic acid reduced mammary serotonin concentrations, however only fluoxetine altered genes in the mammary transcriptome. Fluoxetine treatment altered fifty-six genes. Elovl6 was the most significantly altered gene by fluoxetine treatment along with gene pathways involving fatty acid homeostasis, PPARγ, and adipogenesis, which are critical for milk fat synthesis. Enriched pathways in the mammary gland by fluoxetine revealed pathways including calcium signaling, serotonin receptors, milk proteins, and cellular response to cytokine stimulus which are important for lactation. Although folic acid did not impact specific genes, a less stringent pathway analysis revealed more diffuse effects where folic acid enriched pathways involving negative regulation of gene expression as expected, but additionally enriched pathways involving serotonin, glycolysis, and lactalbumin which are critical for lactation. In conclusion, peripartal SSRI use and folic acid supplementation altered critical genes related to milk synthesis and mammary gland function that are important to a successful lactation. However, folic acid supplementation did not reverse changes in the mammary gland transcriptome altered by peripartal SSRI treatment.

In vitro effects of 5-Hydroxy-L-tryptophan supplementation on primary bovine mammary epithelial cell gene expression under thermoneutral or heat shock conditions

Serotonin (5-HT) is an autocrine-paracrine molecule within the mammary gland regulating homeostasis during lactation and triggering involution after milk stasis. Exposure of dairy cows to hyperthermia during the dry period alters mammary gland involution processes leading to reduced subsequent yields. Herein, primary bovine mammary epithelial cells (pBMEC) under thermoneutral (TN, 37 °C) or heat shock (HS, 41.5 °C) conditions were cultured with either 0, 50, 200, or 500 μM 5-Hydroxy-L-tryptophan (5-HTP; 5-HT precursor) for 8-, 12- or 24-h. Expression of 95 genes involved in 5-HT signaling, involution and tight junction regulation were evaluated using a Multiplex RT-qPCR BioMark Dynamic Array Circuit. Different sets of genes were impacted by 5-HTP or temperature, or by their interaction. All 5-HT signaling genes were downregulated after 8-h of HS and then upregulated after 12-h, relative to TN. After 24-h, apoptosis related gene, FASLG, was upregulated by all doses except TN-200 μM 5-HTP, and cell survival gene, FOXO3, was upregulated by HS-50, 200 and 500 μM 5-HTP, suggesting 5-HTP involvement in cell turnover under HS. Supplementing 5-HTP at various concentrations in vitro to pBMEC modulates the expression of genes that might aid in promoting epithelial cell turn-over during involution in dairy cattle under hyperthermia.

Graduate Student Literature Review: Serotonin and calcium metabolism: A story unfolding

The peripartum period is characterized by dynamic shifts in metabolic, mineral, and immune metabolism as the dairy cow adapts to the demands of lactation. Emphasis over the past decade has been placed on understanding the biology of the large shift in calcium metabolism in particular. Moreover, research has also focused on exploring the role of serotonin during the transition period and lactation and further unraveling its relationship with calcium. This review aimed to demonstrate the integration of calcium physiology during the peripartal period and throughout lactation. More specifically, we sought to discuss the knowledge gained in recent years on calcium metabolism, mammary calcium transport, serotonin metabolism, and the serotonin-calcium axis. Herein we also discuss the challenges and limitations of current research and where that leaves the present understanding of the serotonin-calcium axis as we seek to move forward and continue exploring this interesting relationship.

Elevated serotonin coordinates mammary metabolism in dairy cows

Serotonin plays a diverse role in maternal and mammary metabolism. Recent research in the dairy cow has shown a relationship between serotonin and calcium, with increased serotonin concentrations improving calcium homeostasis in the peri‐partum dairy cow. Therefore, the objective was to elucidate how administration of 5‐hydroxy‐l‐tryptophan (5‐HTP), the immediate precursor to serotonin, altered serotonin and calcium metabolism in lactating dairy cows. Twelve mid‐late lactation multiparous cows were blocked by parity, production and days in milk and allocated to a daily intravenous infusion of (i) 1.5 mg/kg of 5‐HTP (n = 6) or (ii) saline (n = 6) for 3 consecutive days. Milk samples were collected daily. Blood samples were collected before and after each infusion with mammary biopsies and blood samples collected at 48, 56, and 72 h relative to termination of first infusion. Infusion of 5‐HTP increased (p = 0.001) circulating serotonin concentrations and decreased blood calcium via a transient hypocalcemia immediately after each infusion (p = 0.02). Treatment with 5‐HTP increased milk calcium concentrations (p = 0.02) and calcium release‐activated channel protein 1 (ORAI1) mRNA at 56 h and protein at 48 h relative to termination of first infusion (p = 0.008 and p = 0.09, respectively). Fifty‐six hours from termination of the first infusion mRNA of parathyroid hormone‐related protein and mammary serotonin content were increased relative to control (p = 0.03 and p = 0.05, respectively). These findings demonstrate the ability of 5‐HTP infusion to increase circulating serotonin concentrations and alter endocrine and mammary autocrine/paracrine calcium and serotonin metabolism in the lactating dairy cow.

Serotonin regulates maternal calcium homeostasis during the perinatal period of sheep

The goal of this experiment was to demonstrate the ability of an infusion of serotonin (5-HT; 5-hydroxytryptamine) precursors to increase 5-HT production during the transition from pregnancy to lactation and its effects on gene expression related to calcium (Ca) transporters in the mammary gland and bone resorption markers in the femur. Thirty pregnant Bamei mutton sheep were randomly assigned to 3 experimental groups. All groups received a daily intravenous infusion of saline (control group; n = 10), saline containing 0.178 mg of L-tryptophan/kg body weight (BW) (TRP group, n = 10) or 0.178 mg of 5-hydroxytryptophan/kg BW (5-HTP group, n = 10), beginning on day 7 of prepartum and continuing until delivery. Serum (pre- and postpartum), milk (postpartum), and femur and mammary gland tissue (day 9) were collected. Sheep infused with 5-HTP had a larger total serum Ca concentration on days 3, 6, 15, and 30 of lactation and total milk Ca concentration on days 3, 6, 12, and 15 of lactation compared with that of the control group. Sheep infused with 5-HTP and TRP increased blood and milk concentrations of 5-HT on days 3, 6, 9, and 30 of lactation and parathyroid hormone-related protein (PTHrP) on day 3 of prepartum and on days 3, 6, and 15 of lactation (P < 0.05). In addition, compared to that of the control group, the TRP or 5-HTP infusion upregulated PTHrP, a sodium/calcium exchanger, plasma membrane Ca2+ ATPase 2, secretory pathway Ca2+ ATPase 1, and calcium sensing receptor mRNA expression in mammary gland and receptor-activated nuclear factor kappa-B ligand mRNA expression in the femur, but had no effect on receptor-activated nuclear factor kappa-B and osteoprotegerin mRNA expression in the femur (P < 0.05). This suggests that 5-HT and PTHrP may be involved in regulating maternal Ca homeostasis during the transition from pregnancy to lactation in the sheep.

Species-specific models in toxicology: in vitro epithelial barriers

Species-specific in vitro epithelial barriers represent interesting predictive tools for risk assessment evaluation in toxicological studies. Moreover, these models could be applied either as stand-alone methods for the study of absorption, bioavailability, excretion, transport, effects of xenobiotics, or through an Integrated Testing Strategy. The aim of this review is to give a comprehensive overview of in vitro species-specific epithelial barrier models from bovine, dog and swine. Bovine mammary epithelial barrier as a fundamental instrument for the evaluation of the toxicant excretion, the blood brain barrier as a useful first approach in toxicological and pharmacological studies, the porcine intestinal barrier, the canine skin barrier, and finally the pulmonary barrier from bovine and swine species are described in this review.

Review: Endocrine pathways to regulate calcium homeostasis around parturition and the prevention of hypocalcemia in periparturient dairy cows

Calcium homeostasis is crucial for the normal function of the organism. Parathyroid hormone, calcitriol and calcitonin play critical roles in the homeostatic regulation of calcium. Serotonin and prolactin have also been shown to be involved in the regulation of calcium homeostasis. In modern dairy cows, the endocrine pathways controlling calcium homeostasis during non-lactating and non-pregnant physiological states are unable to fully support the increased demand of calcium required for milk synthesis at the onset of lactation. This review describes different endocrine systems associated with the regulation of calcium homeostasis in mammalian species around parturition with special focus on dairy cows. Additionally, classic and novel strategies to reduce the incidence of hypocalcemia in parturient dairy cows are discussed.

Tryptophan Supplementation Increases Reproduction Performance, Milk Yield, and Milk Composition in Lactating Sows and Growth Performance of Their Piglets

Tryptophan (Trp) can produce bioactive compounds for appetite regulation, calcium mobilization, and mammary gland homeostasis via a serotonin pathway. This study evaluated the effects of Trp supplementation on the reproduction performance, milk yield, and composition of lactating sows, growth performance of their piglets, and the secretion function of porcine mammary epithelial cells (PMECs). The infrared emulsion analyzer and ELISA analyses revealed that feeding sows with a 0.12% Trp addition increased ( P < 0.05) sow average daily feed intake, milk yield, milk calcium concentration, average daily gain of piglets, fatty acid synthase (FAS) and lactose synthase (LS), β-casein secretion, intracellular Ca²⁺ level, the expression of calcium binding protein CaM, and the activity of CaMKII. In a cellular experiment of PMECs treated with Trp, ELISA and flow cytometry analyses revealed that the pretreatment of a Trp hydroxylase inhibitor reduced ( P < 0.05) FAS and LS synthesis, the intracellular Ca²⁺ level, and the activity of CaMKII. In conclusion, Trp supplementation at 0.12% increased sows' reproductive performance, milk yield, and calcium concentration and piglets' growth performance. Milk yield increased by Trp was linked to 5-hydroxytryptamine-mediated synthesis of FAS, LS, and β-casein in PMECs, while the increase in calcium concentration was attributed to increasing CaM expression and CAMKII activity.

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.

Serotonin induces parathyroid hormone-related protein in goat mammary gland

During lactation, large amounts of calcium are exported from the mammary gland into milk to ensure skeletal growth of the offspring. Recent studies revealed that serotonin (5-HT) is essential to stimulate skeletal calcium resorption for milk synthesis. Our objective was to explore the correlation between circulating 5-HT and serum calcium and parathyroid hormone-related protein (PTHrP) concentrations around parturition in dairy goats. We also investigated the effect of 5-HT on PTHrP expression in cultured primary goat mammary epithelial cells (GMEC). Blood samples of multiparous Guanzhong dairy goats were collected on day -5 to 3 postpartum for analysis of serum concentrations of calcium, 5-HT, and PTHrP. Results revealed that from day -3 to 0 postpartum serum calcium and 5-HT concentrations decreased progressively, but serum PTHrP concentration only had a sharp drop in the postpartum period sampled. Correlation analysis of circulating 5-HT and serum calcium and PTHrP concentrations on day 1 and 2 postpartum revealed that low serum 5-HT concentration was positively correlated with serum total calcium or PTHrP concentration. By knocking down tryptophan hydroxylase-1 (TPH1) or adding 5-hydroxytryptophan (5-HTP) to decrease or increase the levels of 5-HT in GMEC, we observed that 5-HTP increased PTHrP expression in a dose-dependent manner and siTPH1 decreased PTHrP protein expression. Furthermore, 5-HT increased mRNA abundance of calcium-sensing receptor (CaSR) in a dose-dependent manner and decreased the expression of plasma membrane Ca2+ ATPase-1 (PMCA1). Taken together, 5-HT seems to induce PTHrP expression in goat mammary cells during and after parturition. These findings suggest that increasing 5-HT biosynthesis could be a potential therapeutic target for prevention of hypocalcemia in dairy goats.

Could use of Selective Serotonin Reuptake Inhibitors During Lactation Cause Persistent Effects on Maternal Bone?

The lactating mammary gland elegantly coordinates maternal homeostasis to provide calcium for milk. During lactation, the monoamine serotonin regulates the synthesis and release of various mammary gland-derived factors, such as parathyroid hormone-related protein (PTHrP), to stimulate bone resorption. Recent evidence suggests that bone mineral lost during prolonged lactation is not fully recovered following weaning, possibly putting women at increased risk of fracture or osteoporosis. Selective Serotonin Reuptake Inhibitor (SSRI) antidepressants have also been associated with reduced bone mineral density and increased fracture risk. Therefore, SSRI exposure while breastfeeding may exacerbate lactational bone loss, compromising long-term bone health. Through an examination of serotonin and calcium homeostasis during lactation, lactational bone turnover and post-weaning recovery of bone mineral, and the effect of peripartum depression and SSRI on the mammary gland and bone, this review will discuss the hypothesis that peripartum SSRI exposure causes persistent reductions in bone mineral density through mammary-derived PTHrP signaling with bone.

TRIENNIAL LACTATION SYMPOSIUM/BOLFA: Serotonin and the regulation of calcium transport in dairy cows

The mammary gland regulates maternal metabolism during lactation. Numerous factors within the tissue send signals to shift nutrients to the mammary gland for milk synthesis. Serotonin is a monoamine that has been well documented to regulate several aspects of lactation among species. Maintenance of maternal calcium homeostasis during lactation is a highly evolved process that is elegantly regulated by the interaction of the mammary gland with the bone, gut, and kidney tissues. It is well documented that dietary calcium is insufficient to maintain maternal calcium concentrations during lactation, and mammals must rely on bone resorption to maintain normocalcemia. Our recent work focused on the ability of the mammary gland to function as an accessory parathyroid gland during lactation. It was demonstrated that serotonin acts to stimulate parathyroid hormone-related protein (PTHrP) in the mammary gland during lactation. The main role of mammary-derived PTHrP during mammalian lactation is to stimulate bone resorption to maintain maternal calcium homeostasis during lactation. In addition to regulating PTHrP, it was shown that serotonin appears to directly affect calcium transporters and pumps in the mammary gland. Our current working hypothesis regarding the control of calcium during lactation is as follows: serotonin directly stimulates PTHrP production in the mammary gland through interaction with the sonic hedgehog signaling pathway. Simultaneously, serotonin directly increases calcium movement into the mammary gland and, subsequently, milk. These 2 direct actions of serotonin combine to induce a transient maternal hypocalcemia required to further stimulate PTHrP production and calcium mobilization from bone. Through these 2 routes, serotonin is able to improve maternal calcium concentrations. Furthermore, we have shown that Holstein and Jersey cows appear to regulate calcium in different manners and also respond differently to serotonergic stimulation of the calcium pathway. Our data in rodents and cows indicate that serotonin and calcium are working through a unique feedback loop with PTHrP during lactation to regulate milk calcium and maternal calcium homeostasis.

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.

Characterization of mammary-specific disruptions for Tph1 and Lrp5 during murine lactation

Serotonin is a homeostatic regulator of the mammary gland during lactation. The contribution of mammary-derived serotonin to circulating serum serotonin concentrations was previously unknown. We have developed mice with mammary-specific disruptions of tryptophan hydroxylase 1 (Tph1) or low-density lipoprotein receptor-related protein 5 (Lrp5) that are induced during late pregnancy and lactation via use of the whey acidic protein (WAP)-Cre cre-lox system. Our objective was to characterize dams with a lactation- and mammary-specific disruption of Lrp5 (WAP-Cre × Lrp5^FL/FL) or Tph1 (WAP-Cre × Tph1^FL/FL). Milk yield and pup weights were recorded throughout lactation. Dams were euthanized on d10 postpartum and mammary glands and duodenal tissue were harvested. WAP-Cre × Lrp5^FL/FL dams had elevated serotonin concentrations in both the mammary gland and circulation compared to controls. In contrast, WAP-Cre × Tph1^FL/FL dams had decreased mammary gland and serum serotonin concentrations compared to controls. Alveolar morphology, milk yield, and pup weights were similar. Mammary-derived serotonin makes a significant contribution to circulating serotonin concentrations during lactation, with no effect on milk yield or alveolar morphology. These transgenic models can and should be confidently used in future lactation studies to further elucidate the contribution of serotonin to the maintenance of lactation.

Serum metabolomic profile in genetically modified cows carrying human α‑lactalbumin gene

The present study aimed to investigate the serum metabolomic profiles in genetically modified cows carrying and expressing human lactalbumin α (LALBA) and non‑LALBA cows, and identify altered metabolic characteristics following the genetic modification. Serum biochemistry indexes were measured according to protocols recommended by International Federation of Clinical Chemistry. The metabolomic profiles were determined using the serum samples collected from LALBA (n=6) and non‑LALBA cows (n=6). Welch's two‑sample t‑test was used to identify the metabolites that significantly differed between the LALBA and non‑LALBA groups (fold‑change ≠ 1 and P<0.05), followed by random forest and pathway analysis. The serum biochemistry indexes of LALBA and non‑LALBA cows were within the normal ranges of healthy cows. A total of 273 metabolites were detected, among which 79 metabolites, including 46 increased and 33 decreased metabolites, differed significantly between the LALBA and non‑LALBA groups. Random forest analysis identified 30 potential key metabolites, including 14 elevated and 16 reduced metabolites. These metabolites were primarily involved in pathways concerning the metabolism of leucine, isoleucine, valine, tryptophan and lipids, such as myristate and eicosapentaenoate. However, the serum in LALBA cow had unique metabolomic signature compared with non‑LALBA cows. The accumulation of polyunsaturated fatty acids and amino acids, and the reduced levels of long chain saturated fatty acids in serum may benefit LALBA cows. However, further investigations are required to validate these benefits and the corresponding mechanisms.

Identification of genetic variation in NOD-like receptor 2 gene and influence of polymorphism on gene structure and function in buffalo (Bubalus bubalis)

Nucleotide-binding oligomerization domain (NOD)-like receptor 2 is one of the important mediators of innate as well as adaptive immune response to microbial infections. In this study, NOD-like receptor-2 was characterized by determining the full gene sequence and analyzing genetic diversity in Indian buffaloes. Sequence analysis of buffalo NOD2 revealed 3042 nucleotides long ORF, encoding 1013 amino acids from 12 exons. Domain structure analysis indicated existence of 8 leucine-rich repeat (LRR) domains in buffalo, cattle, sheep and mouse, along with central NACHT/NOD domain and two N-terminal CARD domains. Comparative sequence analysis among different buffalo breeds identified 46 polymorphic sites in NOD2 gene. Among coding region SNPs, 10 were non-synonymous, 7 synonymous and 3 were present in 5'UTR. Genotyping of two nsSNPs, revealed significant differences in the allele frequencies, distinguishing swamp and riverine buffaloes, having different utilities. Association analysis with mastitis in dairy buffaloes indicated significant variation in allelic frequencies at G1135A locus, between mastitis affected and non-affected animals. Further, NOD2 gene expression was quantified in different riverine buffalo tissues, using real-time PCR and lymph node displayed highest expression, compared to others organs included in the study. Overall, the study revealed buffalo NOD2 gene attributes, important to understand species specific immune response in ruminants.

Increased serum serotonin improves parturient calcium homeostasis in dairy cows

Hypocalcemia in dairy cows is caused by the sudden increase in calcium demand by the mammary gland for milk production at the onset of lactation. Serotonin (5-HT) is a key factor for calcium homeostasis, modulating calcium concentration in blood. Therefore, it is hypothesized that administration of 5-hydroxy-l-tryptophan (5-HTP), a 5-HT precursor, can increase 5-HT concentrations in blood and, in turn, induce an increase in blood calcium concentration. In this study, 20 Holstein dairy cows were randomly assigned to 2 experimental groups. Both groups received a daily i.v. infusion of 1 L of either 0.9% NaCl (C group; n = 10) or 0.9% NaCl containing 1 mg of 5-HTP/kg of BW (5-HTP group, n = 10). Infusions started d 10 before the estimated parturition and ceased the day of parturition, resulting in at least 4 d of infusion (8.37 ± 0.74 d of infusion). Until parturition, blood samples were collected every morning before the infusions, after parturition samples were taken daily until d 7, and a final sample was collected on d 30. Milk yield was recorded during this period. No differences between groups were observed for blood glucose, magnesium, and β-hydroxybutyrate. Cows receiving the 5-HTP infusion showed an increase in fatty acid concentrations from d -3 to -1 before parturition. Serum 5-HT concentrations were increased at d -4 related to parturition until d 5 postpartum in the 5-HTP group compared with the C group. In addition, cows from the 5-HTP group had increased 5-HT concentrations in colostrum, but not in mature milk, on d 7 postpartum. Serum calcium concentrations decreased in both groups around parturition; however, calcium remained higher in the 5-HTP group than in controls, with a significant difference between groups on d 1 (1.62 ± 0.08 vs. 1.93 ± 0.09 mmol/L in control and 5-HTP groups, respectively) and d 2 (1.83 ± 0.06 vs. 2.07 ± 0.07 mmol/L in control and 5-HTP groups, respectively). Additionally, colostrum yield (first milking) was lower in the 5-HTP group compared with the C group, but without consequences on colostrum IgG concentrations. Milk yield did not differ between groups during the rest of the experiment. The study data were consistent with the concept that infusion of 5-HTP to dairy cows increases blood 5-HT concentrations, which in turn is a significant regulatory component in the chain of effectors that affect calcium status around parturition, hence the occurrence of clinical or subclinical hypocalcemia.

Technical note: Isolation and characterization of porcine mammary epithelial cells

Within the mammary gland, functional synthesis of milk is performed by its epithelial (alveolar) cells. The availability of a stable mammary epithelial cell line is essential for biochemical studies to elucidate cellular and molecular mechanisms responsible for nutritional regulation of lactation. Therefore, porcine mammary epithelial cells (PMEC) were isolated from mammary glands of a 9-mo-old nonpregnant and nonlactating gilt and cultured to establish a nonimmortalized cell line. These cells were characterized by expression of cytokeratin-18 (an intermediate filament specific for epithelial cells), β-casein (a specific marker for mammary epithelial cells), and α-lactalbumin. In culture, the PMEC doubled in number every 24 h and maintained a cobblestone morphology, typical for cultured epithelial cells, for at least 15 passages. Addition of 0.2 to 2 μg/mL prolactin to culture medium for 3 d induced the production of β-casein and α-lactalbumin by PMEC in a dose-dependent manner. Thus, we have successfully developed a useful PMEC line for future studies of cellular and molecular regulation of milk synthesis by mammary epithelial cells of the sow.

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 and calcium homeostasis during the transition period

The transition from pregnancy to lactation puts significant, sudden demands on maternal energy and calcium reserves. Although most mammals are able to effectively manage these metabolic adaptations, the lactating dairy cow is acutely susceptible to transition-related disorders because of the high amounts of milk being produced. Hypocalcemia is a common metabolic disorder that occurs at the onset of lactation. Hypocalcemia is also known to result in poor animal welfare conditions. In addition, cows that develop hypocalcemia are more susceptible to a host of other negative health outcomes. Different feeding tactics, including manipulating the dietary cation-anion difference and administering low-calcium diets, are commonly used preventative strategies. Despite these interventions, the incidence of hypocalcemia in the subclinical form is still as high as 25% to 30% in the United States dairy cow population, with a 5% to 10% incidence of clinical hypocalcemia. In addition, although there are various effective treatments in place, they are administered only after the cow has become noticeably ill, at which point there is already significant metabolic damage. This emphasizes the need for developing alternative prevention strategies, with the monoamine serotonin implicated as a potential therapeutic target. Our research in rodents has shown that serotonin is critical for the induction of mammary parathyroid hormone-related protein, which is necessary for the mobilization of bone tissue and subsequent restoration of maternal calcium stores during lactation. We have shown that circulating serotonin concentrations are positively correlated with serum total calcium on the first day of lactation in dairy cattle. Administration of serotonin's immediate precursor through feeding, injection, or infusion to various mammalian species has been shown to increase circulating serotonin concentrations, with positive effects on other components of maternal metabolism. Most recently, preliminary data suggest that manipulation of the serotonergic axis precalving may positively affect postcalving calcium dynamics. Combined, our research suggests a potential mechanism by which serotonin acts on the mammary gland to maintain circulating maternal calcium concentrations. Further research into serotonin's potential as a therapeutic target could contribute significantly as a preventive strategy against hypocalcemia in early lactation dairy cows.

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.

Transcriptomic Analysis of the Mouse Mammary Gland Reveals New Insights for the Role of Serotonin in Lactation

Serotonin regulates numerous processes in the mammary gland. Our objective was to discover novel genes, pathways and functions which serotonin modulates during lactation. The rate limiting enzyme in the synthesis of non-neuronal serotonin is tryptophan-hydroxylase (TPH1). Therefore, we used TPH1 deficient dams (KO; serotonin deficient, n = 4) and compared them to wild-type (WT; n = 4) and rescue (RC; KO + 100 mg/kg 5-hydroxytryptophan injected daily, n = 4) dams. Mammary tissues were collected on day 10 of lactation. Total RNA extraction, amplification, library preparation and sequencing were performed following the Illumina mRNA-Seq. Overall, 97 and 204 genes (false discovery rate, FDR ≤ 0.01) exhibited a minimum of a 2-fold expression difference between WT vs. KO and WT vs. RC dams, respectively. Most differentially expressed genes were related to calcium homeostasis, apoptosis regulation, cell cycle, cell differentiation and proliferation, and the immune response. Additionally, gene set enrichment analysis using Gene Ontology and Medical Subject Headings databases revealed the alteration of several biological processes (FDR ≤ 0.01) including fat cell differentiation and lipid metabolism, regulation of extracellular signal-related kinase and mitogen-activated kinase cascades, insulin resistance, nuclear transport, membrane potential regulation, and calcium release from the endoplasmic reticulum into the cytosol. The majority of the biological processes and pathways altered in the KO dams are central for mammary gland homeostasis. Increasing peripheral serotonin in the RC dams affects specific pathways that favor lactation. Our data confirms the importance of serotonin during lactation in the mammary gland.

Increasing serotonin concentrations alter calcium and energy metabolism in dairy cows

A 4×4 Latin square design in which varied doses (0, 0.5, 1.0, and 1.5 mg/kg) of 5-hydroxy-l-tryptophan (5-HTP, a serotonin precursor) were intravenously infused into late-lactation, non-pregnant Holstein dairy cows was used to determine the effects of serotonin on calcium and energy metabolism. Infusion periods lasted 4 days, with a 5-day washout between periods. Cows were infused at a constant rate for 1 h each day. Blood was collected pre- and 5, 10, 30, 60, 90, and 120 min post-infusion, urine was collected pre- and post-infusion, and milk was collected daily. All of the 5-HTP doses increased systemic serotonin as compared to the 0 mg/kg dose, and the 1.0 and 1.5 mg/kg doses increased circulating glucose and non-esterified fatty acids (NEFA) and decreased beta-hydroxybutyrate (βHBA) concentrations. Treatment of cows with either 1.0 or 1.5 mg/kg 5-HTP doses decreased urine calcium elimination, and the 1.5 mg/kg dose increased milk calcium concentrations. No differences were detected in the heart rates, respiration rates, or body temperatures of the cows; however, manure scores and defecation frequency were affected. Indeed, cows that received 5-HTP defecated more, and the consistency of their manure was softer. Treatment of late-lactation dairy cows with 5-HTP improved energy metabolism, decreased loss of calcium into urine, and increased calcium secretion into milk. Further research should target the effects of increasing serotonin during the transition period to determine any benefits for post-parturient calcium and glucose metabolism.

Serotonin receptor expression is dynamic in the liver during the transition period in Holstein dairy cows

Nonneuronal serotonin (5-HT) participates in glucose metabolism, but little is known regarding the actions of 5-HT in the liver during the transition period in dairy cattle. Here, we explore circulating patterns of 5-HT and characterize the hepatic 5-HT receptor and glucose transporter profiles around calving in multiparous Holstein dairy cows (n = 6, average lactation = 4 ± 1.9). Concentrations of serum 5-HT decreased on day -3 compared with -5 and -7 precalving (167.7 ± 80 vs 1511.1 ± 602 ng/mL). 5-HT nadir was on day -1 precalving and remained low postcalving (481.4 ± 49 ng/mL). Plasma glucose concentrations decreased precalving (P = 0.008) and were positively correlated with 5-HT during the precalving period (r = 0.55, P = 0.043). On day 1, postcalving hepatic messenger RNA expression of 5-HT1D, 2B, 3C, 6, and 7 receptors were decreased compared with day -7 (P < 0.048). The 5-HT3A and 5-HT3B decreased on day 7. The 5-HT2A increased on days 1 and 7 compared with -7 (P < 0.05). The 5-HT1F and 5-HT1A receptors were increased 2.5- and 3.8-fold on day 7, respectively, compared with days -7 and 1 (P < 0.046). The 5-HT5A was not detected, and 5-HT4 was detected on days -7 and 1 only. Expression of Glut-2,-5 and SGLT1 were decreased on days 1 and 7 compared with -7 (P < 0.05), whereas Glut-1 was increased on day 7 compared with -7 (P < 0.05). These results indicate that 5-HT could be important for liver glucose homeostasis possibly through receptor mediated signaling at specific times. Additional research is needed to further explore the functional role of these receptors in the liver during the transition from pregnancy to lactation.

Patterns of circulating serotonin and related metabolites in multiparous dairy cows in the peripartum period

Dairy cows are challenged to maintain Ca and glucose homeostasis during the transition period. Serotonin (5-HT) is a monoamine that modulates Ca and glucose homeostasis in rodents. Serotonin is positively correlated with Ca and glucose status in dairy cows on d 1 of lactation. However, the pattern of circulating concentrations of 5-HT over the course of a 305-d lactation is unknown. In this observational, longitudinal study, we examined the metabolite patterns of 5-HT, Ca, glucose, parathyroid hormone-related protein, and β-hydroxybutyrate on 2 commercial dairy farms in south-central Wisconsin. Cows sampled on farm 1 were multiparous Jersey cows (n=30) that calved within a 23-d period; cows on farm 2 were multiparous Holstein cows (n=35) that calved within a 20-d period. Blood samples were collected daily between d -5 and d 10 relative to parturition and on d 30, 60, 90, 150, and 300 of lactation. Farms 1 and 2 were analyzed individually because of the presence of a farm effect in the initial analysis; a time effect was present on both farms. Concentrations of 5-HT decreased near parturition compared with prepartum by 57.9 and 29.5% on farm 1 and 2, respectively. Transition period 5-HT nadirs were observed on d 1 on farm 1, and on d 1 and 9 on farm 2. Serotonin recovered to prepartum concentrations by d 5 on farm 1. On farm 2, 5-HT recovered to prepartum concentrations by d 4, with a subsequent decrease of 34.6% on d 9 to a level similar to that observed on d 1. Furthermore, 5-HT increased markedly in cows on both farms near peak lactation (d 60, 90, and 150) and decreased on d 300. Compared with prepartum concentrations, Ca decreased by 34.2 and 11.2% on farms 1 and 2, respectively. Circulating total Ca nadir was observed on d 1 on both farms. Circulating 5-HT and circulating Ca were positively correlated during the early lactation period (d 1 to 5 and d 6 to 10) on farm 1 (r=0.31 and r=0.22, respectively) and d 6 to 10 on farm 2 (r=0.16). Circulating 5-HT and glucose were negatively correlated during the early lactation period (d 1 to 5) on farm 1 (r=-0.21) and during mid-lactation (d 30 to 150) on farm 2 (r=-0.26). Milk 5-HT and milk total Ca were positively correlated on farm 2 (r=0.34). These results demonstrate that 5-HT concentrations change dynamically throughout the transition period, with a pattern similar to that of total Ca concentrations. Further research using controlled experiments should be aimed at discerning the association between 5-HT and Ca and between 5-HT and glucose in dairy cows.

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.

Peripheral serotonin regulates maternal calcium trafficking in mammary epithelial cells during lactation in mice

Lactation is characterized by massive transcellular flux of calcium, from the basolateral side of the mammary alveolar epithelium (blood) into the ductal lumen (milk). Regulation of calcium transport during lactation is critical for maternal and neonatal health. The monoamine serotonin (5-HT) is synthesized by the mammary gland and functions as a homeostatic regulation of lactation. Genetic ablation of tryptophan hydroxylase 1 (Tph1), which encodes the rate-limiting enzyme in non-neuronal serotonin synthesis, causes a deficiency in circulating serotonin. As a consequence maternal calcium concentrations decrease, mammary epithelial cell morphology is altered, and cell proliferation is decreased during lactation. Here we demonstrate that serotonin deficiency decreases the expression and disrupts the normal localization of calcium transporters located in the apical (PMCA2) and basolateral (CaSR, ORAI-1) membranes of the lactating mammary gland. In addition, serotonin deficiency decreases the mRNA expression of calcium transporters located in intracellular compartments (SERCA2, SPCA1 and 2). Mammary expression of serotonin receptor isoform 2b and its downstream pathways (PLCβ3, PKC and MAP-ERK_1/2) are also decreased by serotonin deficiency, which might explain the numerous phenotypic alterations described above. In most cases, addition of exogenous 5-hydroxy-L-tryptophan to the Tph1 deficient mice rescued the phenotype. Our data supports the hypothesis that serotonin is necessary for proper mammary gland structure and function, to regulate blood and mammary epithelial cell transport of calcium during lactation. These findings can be applicable to the treatment of lactation-induced hypocalcemia in dairy cows and can have profound implications in humans, given the wide-spread use of selective serotonin reuptake inhibitors as antidepressants during pregnancy and lactation.

Short communication: Timing of first milking affects serotonin (5-HT) concentrations

Hormonal signals differentially regulate the timing of parturition, as well lactogenesis and, potentially, colostrum formation in the mammary gland. Non-neuronal serotonin (5-HT) is a homeostatic regulator of the mammary gland. In the current study, we manipulated the timing of first milking to investigate its effects on serum 5-HT and calcium concentrations in the maternal and calf circulation, as well as in colostrum. Twenty-three cows were randomly assigned to a control (CON; n=10) group, milked for the first time at 4h postcalving, or a treatment (TRT; n=13) group, milked for the first time approximately 1 d before calving in addition to 4h postcalving. Maternal blood samples were collected for 4 d precalving, 3 times daily, and 1 blood sample was taken 4h postcalving. Calf blood samples were collected 4 (before first colostrum feeding) and 12h after birth, and at 3 wk of age. Calves from both treatments were fed colostrum from their respective mothers. Serum 5-HT concentrations were greater in CON cows and decreased significantly in TRT cows after milking was initiated precalving (951 vs. 524 ± 111 ng/mL, respectively). Cow serum calcium concentrations were affected by time, beginning to decrease 1 d precalving until 4h postcalving, but this drop in serum calcium was more pronounced in TRT cows. Serum 5-HT and calcium concentrations were negatively correlated (r=-0.57) for the CON cows and positively correlated (r=0.6) for the TRT cows. Maternal calcium and 5-HT decreased similarly due to precalving milking. Calcium and 5-HT concentrations were greater in colostrum collected from TRT cows milked precalving. Overall, calves had higher circulating 5-HT concentrations than cows, and calves born to TRT cows had increased 5-HT concentrations compared with the CON. Precalving milking could affect 5-HT synthesis within the mammary gland and therefore affect maternal 5-HT and calcium concentrations. Further research is needed in ruminants to assess the extent of 5-HT placental transfer, its role on pre- and postnatal development of the calf, the importance of its presence in colostrum, and potential long-term effects on calf health.

New concepts of breast cell communication to bone

Lactation is the most extreme case of normal physiological bone loss during a lifetime, and breast cancers have a strong tendency to metastasize to bone. In both the physiological and pathological circumstances, parathyroid hormone-related peptide (PTHrP) plays a central role. Until recently there were no regulatory mechanisms to explain the induction of endocrine PTHrP secretion from breast cells during lactation. The mammary epithelium possesses a local serotonin signaling system which drives PTHrP expression during lactation and in breast cancer cells. The mammary gland serotonin system is highly induced in response to alveolar dilation due to milk secretion. Discovery of serotonergic control of PTHrP suggests that it may be possible to manipulate the breast-to-bone axis by targeting serotonin signaling.

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.

Bovine mammary epithelial cell cultures for the study of mammary gland functions

In the present study, the analysis of epithelial cells derived from various sources was undertaken, beginning from the mammary gland tissue through the primary cultures and their subsequent passages. The objective of the study was the comparative analysis of the stage in which the epithelial cells obtained from individuals in different lactation cycles and disparate phases of cell culture growth are the most suitable for morphological research and analysis of gene expression activity. The cultures of primary bovine mammary epithelial cells and passages were identified morphologically using immunocytochemical methods. After positive identification, real-time PCRs were performed for the analysis of the expression level of casein genes, whey protein genes, and butyrophilin gene. The most stable reference genes in real-time PCRs for the mammary gland tissue and cell cultures were also determined. Of the reference genes, the UXT and GAPDH genes appeared to be the most stable ones for the mammary gland tissue samples and epithelial cell cultures. The results obtained allowed concluding that the mammary gland samples collected from heifers constituted the most effective material for the initiation of primary cultures. The primary cultures formed characteristic for the mammary gland tissue dome structures, which images were obtained using confocal microscopy. The highest levels of expression of the CSN1S1, CSN1S2, CSN2, and CSN3 genes were detected in primary cultures. The levels of expression of whey protein genes (LALBA and BGL) were highest in the second passage. The most abundant expression of the BTN1A1 gene was observed in primary cultures and the third passage. On the basis of the whole experiment, it can be concluded that primary cultures and cells of the second passage derived from heifer individuals appeared to be the best materials for the analysis of mammary gland function and gene expression activity.

Serotonin (5-HT) affects expression of liver metabolic enzymes and mammary gland glucose transporters during the transition from pregnancy to lactation

The aim of this experiment was to demonstrate the ability of feeding serotonin (5-HT; 5-hydroxytryptamine) precursors to increase 5-HT production during the transition from pregnancy to lactation and the effects this has on maternal energy metabolism in the liver and mammary gland. Pregnant rats (n = 45) were fed one of three diets: I) control (CON), II) CON supplemented with 0.2% 5-hydroxytryptophan (5-HTP) or III) CON supplemented with 1.35% L-tryptophan (L-TRP), beginning on d13 of pregnancy through d9 of lactation (d9). Serum (pre and post-partum), milk (daily), liver and mammary gland tissue (d9) were collected. Serum 5-HT was increased in the 5-HTP fed dams beginning on d20 of gestation and remained elevated through d9, while it was only increased on d9 in the L-TRP fed dams. 5-HT levels were increased in mammary gland and liver of both groups. Additionally, 5-HTP fed dams had serum and milk glucose levels similar to the CON, while L-TRP had decreased serum (d9) and milk glucose (all dates evaluated). Feeding 5-HTP resulted in increased mRNA expression of key gluconeogenic and glycolytic enzymes in liver and glucose transporters 1 and 8 (GLUT-1, -8) in the mammary gland. We demonstrated the location of GLUT-8 in the mammary gland both in the epithelial and vascular endothelial cells. Finally, phosphorylated 5′ AMP-activated protein kinase (pAMPK), a known regulator of intracellular energy status, was elevated in mammary glands of 5-HTP fed dams. Our results suggest that increasing 5-HT production during the transition from pregnancy to lactation increases mRNA expression of enzymes involved in energy metabolism in the liver, and mRNA abundance and distribution of glucose transporters within the mammary gland. This suggests the possibility that 5-HT may be involved in regulating energy metabolism during the transition from pregnancy to lactation.

Identification of Appropriate Reference Genes for qRT-PCR Analysis of Heat-Stressed Mammary Epithelial Cells in Riverine Buffaloes (Bubalus bubalis)

Gene expression studies require appropriate normalization methods for proper evaluation of reference genes. To date, not many studies have been reported on the identification of suitable reference genes in buffaloes. The present study was undertaken to determine the panel of suitable reference genes in heat-stressed buffalo mammary epithelial cells (MECs). Briefly, MEC culture from buffalo mammary gland was exposed to 42 °C for one hour and subsequently allowed to recover at 37 °C for different time intervals (from 30 m to 48 h). Three different algorithms, geNorm, NormFinder, and BestKeeper softwares, were used to evaluate the stability of 16 potential reference genes from different functional classes. Our data identified RPL4, EEF1A1, and RPS23 genes to be the most appropriate reference genes that could be utilized for normalization of qPCR data in heat-stressed buffalo MECs.

Serotonin as a homeostatic regulator of lactation

Serotonin (5-HT), a neurotransmitter produced in mammary epithelial cells (MECs), acts via autocrine-paracrine mechanisms on MECs to regulate milk secretion in a variety of species. Recent studies in dairy cows reported that 5-HT ligands affect milk yield and composition. We determined the mRNA expression of bovine 5-HT receptor (5-HTR) subtypes in bovine mammary tissue (BMT) and cultured bovine MECs. We then used pharmacologic agents to evaluate functional activities of 5-HTR subtypes. The mRNAs for five receptor isoforms (5-HTR1B, 5-HTR2A, 5-HTR2B, 5-HTR4, and 5-HTR7) were identified by conventional reverse transcription PCR, real-time PCR, and in situ hybridization in BMT. In addition to luminal MEC expression, 5-HTR4 was expressed in myoepithelium, and 5-HTR1B, HTR2A, and HTR2B were expressed in small mammary blood vessels. Studies to date report that there are multiple 5-HTR isoforms in mammary tissue of rodents, humans, and cattle. Inhibition of the 5-HT reuptake transporter with selective 5-HT reuptake inhibitors (SSRIs) disrupted tight junctions and decreased milk protein mRNA expression in mouse, human, and bovine mammary cells. Selective 5-HT reuptake inhibitors act to increase the cellular exposure to 5-HT by preventing reuptake of 5-HT by the cell and eventual degradation. Increasing 5-HT concentration in milk via inhibiting its reuptake (SSRI), or by increasing the precursor for 5-HT synthesis 5-hydroxytryptophan, accelerated decline in milk synthesis at dry-off. We conclude that the 5-HT system in mammary tissue acts as a homeostatic regulator of lactation.

Mammary gland serotonin regulates parathyroid hormone-related protein and other bone-related signals

Breast cells drive bone demineralization during lactation and metastatic cancers. A shared mechanism among these physiological and pathological states is endocrine secretion of parathyroid hormone-related protein (PTHrP), which acts through osteoblasts to stimulate osteoclastic bone demineralization. The regulation of PTHrP has not been accounted for fully by any conventional mammotropic stimuli or tumor growth factors. Serotonin (5-HT) synthesis within breast epithelial cells is induced during lactation and in advancing breast cancer. Here we report that serotonin deficiency (knockout of tryptophan hydroxylase-1) results in a reduction of mammary PTHrP expression during lactation, which is rescued by restoring 5-HT synthesis. 5-HT induced PTHrP expression in lactogen-primed mammary epithelial cells from either mouse or cow. In human breast cancer cells 5-HT induced both PTHrP and the metastasis-associated transcription factor Runx2/Cbfa1. Based on receptor expression and pharmacological evidence, the 5-HT2 receptor type was implicated as being critical for induction of PTHrP and Runx2. These results connect 5-HT synthesis to the induction of bone-regulating factors in the normal mammary gland and in breast cancer cells.