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

Intravenous infusion of 5-hydroxytryptophan to mid-lactation Holstein cows transiently affects milk production and circulating amino acid concentrations

In dairy cows, the lactating mammary glands synthesize serotonin, which acts in an autocrine-paracrine manner in the glands and is secreted into the periphery. Serotonin signaling during lactation modulates nutrient metabolism in peripheral tissues such as adipose and liver. We hypothesized that the elevation of circulating serotonin during lactation would increase nutrient partitioning to the mammary glands, thereby promoting milk production. Our objective was to elevate circulating serotonin via intravenous infusion of the serotonin precursor 5-hydroxytryptophan (5-HTP) to determine its effects on mammary supply and extraction efficiency of AA, and milk components production. Twenty-two multiparous mid-lactation Holstein cows were intravenously infused with 5-HTP (1 mg/kg body weight) or saline, in a crossover design with two 21-d periods. Treatments were infused via jugular catheters for 1 h/d, on d 1 to 3, 8 to 10, and 15 to 17 of each period, to maintain consistent elevation of peripheral serotonin throughout the period. Milk and blood samples were collected in the last 96 h of each period. Whole-blood serotonin concentration was elevated above saline control for 96 h after the last 5-HTP infusion. Dry matter intake was decreased for cows receiving 5-HTP, and on average they lost body weight over the 21-d period, in contrast to saline cows who gained body weight. Milk production and milk protein yield were lower in cows receiving 5-HTP during the 3 infusion days, but both recovered to saline cow yields in the days after. Although milk fat yield exhibited a day-by-treatment interaction, no significant difference occurred on any given day. Milk urea nitrogen concentration was lower in 5-HTP cows on the days following the end of infusions, but not different from saline cows on infusion days. Meanwhile, plasma urea nitrogen was not affected by 5-HTP infusion. Circulating concentrations of AA were overall transiently decreased by 5-HTP, with concentrations mostly returning to baseline within 7 h after the end of 5-HTP infusion. Mammary extraction efficiency of AA was unaffected by 5-HTP infusion. Overall, both lactation performance and circulating AA were transiently reduced in cows infused with 5-HTP, despite sustained elevation of circulating serotonin concentration.

Fluoxetine alters rat's milk properties causing impact on offspring's development

Fluoxetine is an antidepressant used to treat several conditions including postpartum depression. This disease causes cognitive, emotional, behavioral and physical changes, negatively affecting the mother, child and family life. However, fluoxetine is excreted in breast milk, causing short and long-term effects on children who were exposed to the drug during lactation, so studies that seek to uncover the consequences of these effects are needed. Thus, the aim of this study was to evaluate the effects of fluoxetine on the nutritional characteristics of milk and on growth and neurobehavioral development of the offspring on a rat model. Lactating rats were divided into 4 groups: control group and three experimental groups, which were treated with different doses of fluoxetine (1, 10 and 20 mg/kg) during the lactation. Dams body weight and milk properties were measured, as well as offspring's growth and physical and neurobehavioral development. Results showed that the use of fluoxetine during lactation decreased dam's body weight and alters milk's properties, leading to a decrease in offspring's growth until adulthood. Therefore, the use of fluoxetine during lactation needs to be cautiously evaluated, with the benefits to the mothers and the associated risk to the offspring carefully balance.

Engineering a Cortisol Sensing Enteric Probiotic

Chronic stress can lead to prolonged adrenal gland secretion of cortisol, resulting in human ailments such as anxiety, post-traumatic stress disorder, metabolic syndrome, diabetes, immunosuppression, and cardiomyopathy. Real time monitoring of chronic increases in cortisol and intervening therapies to minimize the physiological effects of stress would be beneficial to prevent these endocrine related illnesses. Gut microbiota have shown the ability to secrete, respond, and even regulate endocrine hormones. One such microbe, Clostridium scindens, responds transcriptionally to cortisol. We engineered these cortisol responsive genetic elements from C. scindens into an enteric probiotic, E. coli Nissle 1917, to drive the expression of a fluorescent reporter allowing for the designing, testing, and building of a robust and physiologically relevant novel cortisol probiotic sensor. This smart probiotic was further engineered to be more sensitive and to respond to elevated cortisol by expressing tryptophan decarboxylase, thereby bestowing the ability to generate tryptamine and serotonin. Here we show that upon cortisol treatment the smart probiotic produces measurable amounts of tryptamine. Accumulated levels of these neuromodulators should improve mood, anxiety, and depression and drive down cortisol levels. Importantly, this work can serve as a model for the engineering of a sense-and-respond probiotic to modulate the gut-brain axis.

Tryptophan Metabolism Acts as a New Anti-Ferroptotic Pathway to Mediate Tumor Growth

Emerging evidence reveals that amino acid metabolism plays an important role in ferroptotic cell death. The conversion of methionine to cysteine is well known to protect tumour cells from ferroptosis upon cysteine starvation through transamination. However, whether amino acids-produced metabolites participate in ferroptosis independent of the cysteine pathway is largely unknown. Here, the authors show that the tryptophan metabolites serotonin (5-HT) and 3-hydroxyanthranilic acid (3-HA) remarkably facilitate tumour cells to escape from ferroptosis distinct from cysteine-mediated ferroptosis inhibition. Mechanistically, both 5-HT and 3-HA act as potent radical trapping antioxidants (RTA) to eliminate lipid peroxidation, thereby inhibiting ferroptotic cell death. Monoamine oxidase A (MAOA) markedly abrogates the protective effect of 5-HT via degrading 5-HT. Deficiency of MAOA renders cancer cells resistant to ferroptosis upon 5-HT treatment. Kynureninase (KYNU), which is essential for 3-HA production, confers cells resistant to ferroptotic cell death, whereas 3-hydroxyanthranilate 3,4-dioxygenase (HAAO) significantly blocks 3-HA mediated ferroptosis inhibition by consuming 3-HA. In addition, the expression level of HAAO is positively correlated with lipid peroxidation and clinical outcome. Together, the findings demonstrate that tryptophan metabolism works as a new anti-ferroptotic pathway to promote tumour growth, and targeting this pathway will be a promising therapeutic approach for cancer treatment.

Systematic Review of the Serotonergic System in the Pathophysiology of Severe Dengue: The Theory of Thrombocytopenia and Vascular Extravasation

BACKGROUND

Severe dengue is characterized by thrombocytopenia, hemorrhaging, and/or capillary extravasation and may be linked to a reduced plasma concentration of serotonin (5-hydroxytriptamine, or 5-HT).

OBJECTIVE

The aim of the current contribution was to conduct a systematic bibliographic review of reports on the role of the peripheral serotonergic system in the pathophysiology of severe dengue.

METHODS

A bibliographic review was carried out of in vivo/in vitro models, clinical trials, and case series studies from 2010-2019. The selective criteria were the use of treatments with serotonin reuptake inhibitors and/or agonists/antagonists of 5-HT receptors and their impact on inflammation, coagulation, and endothelium. Moreover, cross-sectional and cohort studies on the relationship between intraplatelet and plasma 5-HT levels in patients with dengue were also included. The risk of bias in the selected reports was examined with domain-based assessment utilizing Cochrane-type criteria. The main results are summarized in Tables and Figures.

RESULTS

Based on descriptions of the effect of serotonergic drugs on 5-HT levels and the findings of clinical trials of dengue treatment, most receptors of the peripheral serotonergic system, and especially 5-HT2A, seem to participate in regulating serum 5-HT during severe dengue. Therefore, the peripheral serotonergic system probably contributes to thrombocytopenia and capillary extravasation.

CONCLUSION

Regarding dengue, 5-HT may be a key parameter for predicting severity, and an understanding of 5-HT-related mechanisms could possibly facilitate the development of new therapies. These proposals require further research due to the limited number of publications on the role of serotonergic receptors at the peripheral level.

Increasing serotonin concentrations alter calcium metabolism in periparturient dairy goats

Due to the large amounts of calcium transferred to milk from mammary glands, periparturient dairy goats face challenges with calcium metabolism disorder and hypocalcemia. Serotonin (5-hydroxytryptamine, 5-HT), the product of 5-hydroxy-l-tryptophan (5-HTP) catalyzed by tryptophan hydroxylase 1, is a multifunctional monoamine thought to be a homeostatic regulator of the animal. The objective of the current study was to investigate the effects and underlying mechanisms of intramuscular 5-HTP injections on calcium homeostasis in the goat mammary glands. In the in vivo experiment, 30 multiparous Guanzhong dairy goats were randomly assigned to 2 groups, one group was injected with 5-HTP intramuscularly and the other group was injected with normal saline. From the first 10 d of the expected date for delivery, 5-HTP or saline was injected into goats through the shoulder muscle every morning before feeding, with a dose of 1 mg/kg per body weight. In the in vitro experiment, goat mammary epithelial cells (GMEC) were treated with 100 μM 5-HT for the evaluation of 5-HT in calcium transportation. The results demonstrated that 5-HTP treatment had no effect on the basic composition of colostrum (P > 0.05) but increased the serum 5-HT concentrations on days -5, -4, -3, and 5 relative to parturition (P < 0.05). The 5-HTP injection group had greater serum calcium concentration on day 4 and greater serum parathyroid hormone-related protein (PTHrP) on days -5, -4, -1, 3, 4, and 5 compared with the saline injection group (P < 0.05). It was further confirmed that 5-HT could increase intracellular calcium levels by increasing PTHrP and decreasing plasma membrane Ca2+-ATPases1 (PMCA1) in GMEC (P < 0.05). In conclusion, 5-HTP treatment in multiparous goats during the transition period from pregnancy to lactation is a feasible way to protect goats from calcium metabolism disorder.

The role of maternal high fat diet on mouse pup metabolic endpoints following perinatal PFAS and PFAS mixture exposure

Per- and polyfluoroalkyl substances (PFAS) are a family of chemicals that are ubiquitous in the environment. Some of these chemicals, such as perfluorooctanesulfonic acid (PFOS), perfluorohexanesulfonate (PFHxS) and perfluorooctanoic acid (PFOA), are found in human sera and have been shown to cause liver steatosis and reduce postnatal survival and growth in rodents. The purpose of this work is to evaluate the impact of diet and PFAS exposure to mouse dam (mus musculus) on the risk to pup liver and metabolism endpoints later in life, as well as evaluate PFAS partitioning to pups. Timed-pregnant dams were fed a standard chow diet or 60 % kcal high fat diet (HFD). Dams were administered either vehicle, 1 mg/kg PFOA, 1 mg/kg PFOS, 1 mg/kg PFHxS, or a PFAS mixture (1 mg/kg of each PFOA, PFOS, and PFHxS) daily via oral gavage from gestation day 1 until postnatal day (PND) 20. At PND 21, livers of dams and 2 pups of each sex were evaluated for lipid changes while remaining pups were weaned to the same diet as the dam for an additional 10 weeks. Dam and pup serum at PND 21 and PND 90 were also evaluated for PFAS concentration, alanine aminotransferase (ALT), leptin and adiponectin, and glycosylated hemoglobin A1c. Perinatal exposure to a HFD, as expected, increased pup body weight, maternal liver weight, pup liver triglycerides, pup serum ALT, and pup serum leptin. PFOA and the PFAS mixture increased liver weights, and. treatment with all three compounds increased liver triglycerides. The maternal HFD increased dam and pup serum PFAS levels, however, was protective against PFOA-induced increase in serum ALT and observed increases in liver triglycerides. The PFAS mixture had very distinct effects when compared to single compound treatment, suggesting some cumulative effects, particularly when evaluating PFAS transfer from dam to pup. This data highlights the importance of diet and mixtures when evaluating liver effect of PFAS and PFAS partitioning.

Peripheral serotonin regulates glucose and insulin metabolism in Holstein dairy calves

Peripheral serotonin regulates energy metabolism in several mammalian species, however, the potential contribution of serotonergic mechanisms as metabolic and endocrine regulators in growing dairy calves remain unexplored. Objectives were to characterize the role of serotonin in glucose and insulin metabolism in dairy calves with increased serotonin bioavailability. Milk replacer was supplemented with saline, 5-hydroxytryptophan (90 mg/d), or fluoxetine (40 mg/d) for 10-d (n = 8/treatment). Blood was collected daily during supplementation and on days 2, 7, and 14 during withdrawal. Calves were euthanized after 10-d supplementation or 14-d withdrawal periods to harvest liver and pancreas tissue. 5-hydroxytryptophan increased circulating insulin concentrations during the supplementation period, whereas both treatments increased circulating glucose concentration during the withdrawal period. The liver and pancreas of preweaned calves express serotonin factors (ie, TPH1, SERT, and cell surface receptors), indicating their ability to synthesize, uptake, and respond to serotonin. Supplementation of 5-hydroxytryptophan increased hepatic and pancreatic serotonin concentrations. After the withdrawal period, fluoxetine cleared from the pancreas but not liver tissue. Supplementation of 5-hydroxytryptophan upregulated hepatic mRNA expression of serotonin receptors (ie, 5-HTR1B, -1D, -2A, and -2B), and downregulated pancreatic 5-HTR1F mRNA and insulin-related proteins (ie, Akt and pAkt). Fluoxetine-supplemented calves had fewer pancreatic islets per microscopic field with reduced insulin intensity, whereas 5-hydroxytryptophan supplemented calves had increased islet number and area with greater insulin and serotonin and less glucagon intensities. After the 14-d withdrawal of 5-hydroxytryptophan, hepatic mRNA expression of glycolytic and gluconeogenic enzymes were simultaneously downregulated. Improving serotonin bioavailability could serve as a potent regulator of endocrine and metabolic processes in dairy calves.

Serotonin activates glycolysis and mitochondria biogenesis in human breast cancer cells through activation of the Jak1/STAT3/ERK1/2 and adenylate cyclase/PKA, respectively

BACKGROUND

Although produced by several types of tumours, the role of serotonin on cancer biology is yet to be understood.

METHODS

The effects of serotonin (5-HT) on human breast cancer cells proliferation, signalling pathways and metabolic profile were evaluated by cytometry, western blotting, qPCR, enzymology and confocal microscopy.

RESULTS

Our results revealed that incubation of MCF-7 cells with 10 µM 5-HT increased cell growth rate by 28%, an effect that was prevented by the 5-HTR2A/C antagonist, ketanserin. Conversely, increasing concentrations of 5-HT promoted glucose consumption and lactate production by MCF-7 cells. We also showed that increased glucose metabolism is provoked by the upregulation of pyruvate kinase M2 (PKM2) isoform through 5-HTR2A/C-triggered activation of Jak1/STAT3 and ERK1/2 subcellular pathways. However, we noticed a decrease in the rate of produced lactate per consumed glucose as a function of the hormone concentration, suggesting a disruption of the Warburg effect. The latter effect is due to 5-HTR2A/C-dependent mitochondrial biogenesis and metabolism, which is triggered by adenylyl cyclase/PKA, enhancing the oxidation of lactate within these cells.

CONCLUSIONS

We showed that serotonin, through 5-HTR2A/C, interferes with breast cancer cells proliferation and metabolism by triggering two distinct signalling pathways: Jak1/STAT3 that boosts glycolysis through upregulation of PKM2, and adenylyl cyclase/PKA that enhances mitochondrial biogenesis.

Morphological, hormonal, and molecular changes in different maternal tissues during lactation and post-lactation

Milk supply and quality during lactation are critical for progeny survival. Maternal tissues and metabolism, influenced by hormonal changes, undergo modification during lactation to sustain breastfeeding. Two organs that suffer essential adjustment are the mammary glands and the bone; however, renal calcium conservation and calcium absorption from the intestine are also modified. Lactation leads to a transient loss of bone minerals to provide adequate amounts of minerals, including calcium for milk production. Physiological, metabolic, and molecular changes in different tissues participate in providing nutrients for milk production. After weaning, the histological, metabolic, and hormonal modifications that take place in lactation are reverted, and bone remineralization is a central function at this time. This study focuses on the hormonal, metabolic, molecular, and tissue modifications that occur in mammary glands, bone, intestine, and kidneys in the mother during lactation and post-weaning periods.

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.

Litter Size Reduction Induces Metabolic and Histological Adjustments in Dams throughout Lactation with Early Effects on Offspring

In the present study we analyzed morphological and metabolic alterations in dams nursing small litters and their consequences to offspring throughout lactation. Offspring sizes were adjusted to Small Litter (SL, 3 pups/ dam) and Normal Litter (NL, 9 pups/ dam). Body weight, food intake, white adipose tissue (WAT) content, histological analysis of the pancreas, mammary gland (MG) and brown adipose tissue (BAT) as well as, plasma parameters and milk composition were measured in dams and pups on the 7th, 14th and 21st days of lactation. In general, SL-dams presented higher body weight and retroperitoneal fat content, elevated fat infiltration in BAT, reduced islets size and hyperglycemia throughout lactation in relation to NL-dams (p<0.05). Moreover, MG from SL-dams had reduced alveoli development and high adipocytes content, resulting in milk with elevated energetic value and fat content in relation to NL-dams (p<0.05). Maternal states influenced offspring anthropometric conditions during lactation, offspring-SL displayed higher body weight and growth, hyperglycemia, augmented lipid deposition in BAT and elevated islet. Thus, maternal histological and metabolic changes are due to modifications to nursing small litters and reinforce the importance of preserving maternal health during lactation avoiding early programming effects on offspring preventing metabolic consequences later in life.

Cellular stress and AMPK links metformin and diverse compounds with accelerated emergence from anesthesia and potential recovery from disorders of consciousness

The neural correlates of consciousness and the mechanisms by which general anesthesia (GA) modulate such correlates to induce loss of consciousness (LOC) has been described as one of the biggest mysteries of modern medicine. Several cellular targets and neural circuits have been identified that play a critical role in LOC induced by GA, including the GABAA receptor and ascending arousal nuclei located in the basal forebrain, hypothalamus, and brain stem. General anesthetics (GAs) including propofol and inhalational agents induce LOC in part by potentiating chloride influx through the GABAA receptor, leading to neural inhibition and LOC. Interestingly, nearly all GAs used clinically may also induce paradoxical excitation, a phenomenon in which GAs promote neuronal excitation at low doses before inducing unconsciousness. Additionally, emergence from GA, a passive process that occurs after anesthetic removal, is associated with lower anesthetic concentrations in the brain compared to doses associated with induction of GA. AMPK, an evolutionarily conserved kinase activated by cellular stress (e.g. increases in calcium [Ca2+] and/or reactive oxygen species [ROS], etc.) increases lifespan and healthspan in several model organisms. AMPK is located throughout the mammalian brain, including in neurons of the thalamus, hypothalamus, and striatum as well as in pyramidal neurons in the hippocampus and cortex. Increases in ROS and Ca2+ play critical roles in neuronal excitation and glutamate, the primary excitatory neurotransmitter in the human brain, activates AMPK in cortical neurons. Nearly every neurotransmitter released from ascending arousal circuits that promote wakefulness, arousal, and consciousness activates AMPK, including acetylcholine, histamine, orexin-A, dopamine, and norepinephrine. Several GAs that are commonly used to induce LOC in human patients also activate AMPK (e.g. propofol, sevoflurane, isoflurane, dexmedetomidine, ketamine, midazolam). Various compounds that accelerate emergence from anesthesia, thus mitigating problematic effects associated with delayed emergence such as delirium, also activate AMPK (e.g. nicotine, caffeine, forskolin, carbachol). GAs and neurotransmitters also act as preconditioning agents and the GABAA receptor inhibitor bicuculline, which reverses propofol anesthesia, also activates AMPK in cortical neurons. We propose the novel hypothesis that cellular stress-induced AMPK activation links wakefulness, arousal, and consciousness with paradoxical excitation and accelerated emergence from anesthesia. Because AMPK activators including metformin and nicotine promote proliferation and differentiation of neural stem cells located in the subventricular zone and the dentate gyrus, AMPK activation may also enhance brain repair and promote potential recovery from disorders of consciousness (i.e. minimally conscious state, vegetative state, coma).

The Role of Placental Hormones in Mediating Maternal Adaptations to Support Pregnancy and Lactation

During pregnancy, the mother must adapt her body systems to support nutrient and oxygen supply for growth of the baby in utero and during the subsequent lactation. These include changes in the cardiovascular, pulmonary, immune and metabolic systems of the mother. Failure to appropriately adjust maternal physiology to the pregnant state may result in pregnancy complications, including gestational diabetes and abnormal birth weight, which can further lead to a range of medically significant complications for the mother and baby. The placenta, which forms the functional interface separating the maternal and fetal circulations, is important for mediating adaptations in maternal physiology. It secretes a plethora of hormones into the maternal circulation which modulate her physiology and transfers the oxygen and nutrients available to the fetus for growth. Among these placental hormones, the prolactin-growth hormone family, steroids and neuropeptides play critical roles in driving maternal physiological adaptations during pregnancy. This review examines the changes that occur in maternal physiology in response to pregnancy and the significance of placental hormone production in mediating such changes.

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.

Transposable elements, placental development, and oocyte activation: Cellular stress and AMPK links jumping genes with the creation of human life

Transposable elements (TEs), also known as "jumping genes", are DNA sequences first described by Nobel laureate Barbara McClintock that comprise nearly half of the human genome and are able to transpose or move from one genomic location to another. As McClintock also noted that a genome "shock" or stress may induce TE activation and transposition, accumulating evidence suggests that cellular stress (e.g. mediated by increases in intracellular reactive oxygen species [ROS] and calcium [Ca2+], etc.) induces TE mobilization in several model organisms and L1s (a member of the retrotransposon class of TEs) are active and capable of retrotransposition in human oocytes, human sperm, and in human neural progenitor cells. Cellular stress also plays a critical role in human placental development, with cytotrophoblast (CTB) differentiation leading to the formation of the syncytiotrophoblast (STB), a cellular layer that facilitates nutrient and gas exchange between the mother and the fetus. Syncytin-1, a protein that promotes fusion of CTB cells and is necessary for STB formation, and its receptor is found in human sperm and human oocytes, respectively, and increases in ROS and Ca2+ promote trophoblast differentiation and syncytin-1 expression. Cellular stress is also essential in promoting human oocyte maturation and activation which, similar to TE mobilization, can be induced by compounds that increase intracellular Ca2+ and ROS levels. AMPK is a master metabolic regulator activated by increases in ROS, Ca2+, and/or an AMP(ADP)/ATP ratio increase, etc. as well as compounds that induce L1 mobilization in human cells. AMPK knockdown inhibits trophoblast differentiation and AMPK-activating compounds that promote L1 mobility also enhance trophoblast differentiation. Cellular stressors that induce TE mobilization (e.g. heat shock) also promote oocyte maturation in an AMPK-dependent manner and the antibiotic ionomycin activates AMPK, promotes TE activation, and induces human oocyte activation, producing normal, healthy children. Metformin promotes AMPK-dependent telomerase activation (critical for telomere maintenance) and induces activation of the endonuclease RAG1 (promotes DNA cleavage and transposition) via AMPK. Both RAG1 and telomerase are derived from TEs. It is our hypothesis that cellular stress and AMPK links TE activation and transposition with placental development and oocyte activation, facilitating both human genome evolution and the creation of all human life. We also propose the novel observation that various cellular stress-inducing compounds (e.g. metformin, resveratrol, etc.) may facilitate beneficial TE activation and transposition and enhance fertilization and embryological development through a common mechanism of AMPK activation.

Potential Impact of Metabolic and Gut Microbial Response to Pregnancy and Lactation in Lean and Diet-Induced Obese Rats on Offspring Obesity Risk

SCOPE

Maternal obesity programs metabolic dysfunction in offspring, increasing their susceptibility to obesity and metabolic diseases in later life. Moreover, pregnancy and lactation are associated with many metabolic adaptations, yet it is unclear how diet-induced maternal obesity may interrupt these processes.

METHODS AND RESULTS

¹ H NMR serum metabolomics analysis was performed on samples collected pre-pregnancy and in pregnant and lactating lean and high fat/sucrose (HFS) diet-induced obese Sprague-Dawley rats to identify maternal metabolic pathways associated with developmental programming of offspring obesity. Gut microbial composition was assessed using qPCR. Offspring of HFS dams had nearly 40% higher adiposity at weaning compared to offspring of lean dams. While pregnancy and lactation were associated with distinct maternal metabolic changes common to both lean and obese dams, we identified several metabolic differences, potentially implicating dysregulated one-carbon and mammary gland metabolism in the metabolic programming of obesity. Gut microbial composition was significantly altered with obesity, and both gestation and lactation were accompanied by changes in gut microbiota.

CONCLUSION

Diet-induced maternal obesity and consumption of an obesogenic maternal diet results in differential metabolic and gut microbial adaptations to pregnancy and lactation; these maladaptations may be directly involved in maternal programming of offspring susceptibility to obesity.

The Diverse Metabolic Roles of Peripheral Serotonin

Serotonin (5-hydroxytryptamine or 5-HT) is a multifunctional bioamine with important signaling roles in a range of physiological pathways. Almost all of the 5-HT in our bodies is synthesized in specialized enteroendocrine cells within the gastrointestinal (GI) mucosa called enterochromaffin (EC) cells. These cells provide all of our circulating 5-HT. We have long appreciated the important contributions of 5-HT within the gut, including its role in modulating GI motility. However, evidence of the physiological and clinical significance of gut-derived 5-HT outside of the gut has recently emerged, implicating 5-HT in regulation of glucose homeostasis, lipid metabolism, bone density, and diseases associated with metabolic syndrome, such as obesity and type 2 diabetes. Although a new picture has developed in the last decade regarding the various metabolic roles of peripheral serotonin, so too has our understanding of the physiology of EC cells. Given that they are scattered throughout the lining of the GI tract within the epithelial cell layer, these cells are typically difficult to study. Advances in isolation procedures now allow the study of pure EC-cell cultures and single cells, enabling studies of EC-cell physiology to occur. EC cells are sensory cells that are capable of integrating cues from ingested nutrients, the enteric nervous system, and the gut microbiome. Thus, levels of peripheral 5-HT can be modulated by a multitude of factors, resulting in both local and systemic effects for the regulation of a raft of physiological pathways related to metabolism and obesity.

Lactational challenges in transition dairy cows

Lactation evolved to be the core functional system of providing maternal care in mammalian species. The mammary gland provides an ideally composed nutrient source for the newborn. In addition, colostrum provides passive immunisation after birth, and each suckling process supports the establishment and maintenance of a close mother–offspring bonding. The importance of lactation for the survival of the offspring is represented by a high metabolic priority of the mammary gland within the organism of the lactating animal. Therefore, animal breeding for high milk production has been quite successful, and modern breeding methods have allowed an enormous increase in the performance within only few generations of cows. Mainly in early lactation, most of the available nutrients are directed to the mammary gland, both those from feed, and those mobilised from body tissue. Therefore, milk production can be maintained at a high level despite a negative energy balance. However, the high metabolic load and mobilisation of body tissue requires adequate endocrine and metabolic regulation, which can be successful or less successful in individual animals, i.e. the dairy cow population consists of both metabolically robust and metabolically vulnerable dairy cows. While robust animals adapt adequately, vulnerable cows show often high plasma concentrations of non-esterified fatty acids and β-hydroxybutyrate, and are prone to various production-related diseases. In pasture- or forage-based feeding systems, an additional challenge is a limited availability of nutrients for milk production. Forage feeding without complementary concentrate leads to enormous metabolic disorders in high-yielding cows, but is tolerated in dairy cows with a moderate genetic-performance level.

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.

Maternal dietary vitamin D carry-over alters offspring growth, skeletal mineralisation and tissue mRNA expressions of genes related to vitamin D, calcium and phosphorus homoeostasis in swine

Maternal dietary vitamin D carry-over effects were assessed in young pigs to characterise skeletal abnormalities in a diet-induced model of kyphosis. Bone abnormalities were previously induced and bone mineral density (BMD) reduced in offspring from sows fed diets with inadequate vitamin D3. In a nested design, pigs from sows (n 23) fed diets with 0 (-D), 8·125 (+D) or 43·750 (++D) µg D3/kg from breeding through lactation were weaned and, within litter, fed nursery diets arranged as a 2×2 factorial design with 0 (-D) or 7·0 (+D) µg D3/kg, each with 95 % (95P) or 120 % (120P) of P requirements. Selected pigs were euthanised before colostrum consumption at birth (0 weeks, n 23), weaning (3 weeks, n 22) and after a growth period (8 weeks, n 185) for BMD, bone mechanical tests and tissue mRNA analysis. Pigs produced by +D or ++D sows had increased gain at 3 weeks (P<0·05), and at 8 weeks had increased BMD and improved femur mechanical properties. However, responses to nursery diets depended on maternal diets (P<0·05). Relative mRNA expressions of genes revealed a maternal dietary influence at birth in bone osteocalcin and at weaning in kidney 24-hydroxylase (P<0·05). Nursery treatments affected mRNA expressions at 8 weeks. Detection of a maternal and nursery diet interaction (P<0·05) provided insights into the long-term effects of maternal nutritional inputs. Characterising early stages of bone abnormalities provided inferences for humans and animals about maternal dietary influence on offspring skeletal health.

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.

Glucose-induced abnormal egg-laying rate in Caenorhabditis elegans

High glucose reduced the egg-laying rate of the nematode Caenorhabditis elegans and was dependent on serotonergic signaling. Antidiabetic drugs of the biguanide and thiazolidine classes ameliorated the detrimental effect of glucose on egg-laying rate, suggesting the possibility that this quick and easy assay system may be applicable to whole-animal screening for novel antidiabetic drugs, at least, of these classes.

5-HT 2 receptor mediates high-fat diet-induced hepatic steatosis and very low density lipoprotein overproduction in rats

BACKGROUND

5-HT has been shown to mediate abnormality of hepatic lipid metabolism through activation of mammalian target of rapamycin (mTOR). However, it is unclear whether 5-HT is directly involved in high-fat diet (HFD)-induced hepatic steatosis.

MATERIALS AND METHODS

Male rats were allocated into seven groups with control, either HFD feeding, 5-HT treatment, or HFD feeding and 5-HT treatment with or without sarpogrelate treatment, all of which were executed for 4 weeks. HepG2 cells were exposed to 5-HT or palmitic acid (PA) with or without rapamycin or Sar treatment.

RESULTS

Rats fed with HFD or exposed to 5-HT led to abnormalities with activated hepatic mTOR-S6K pathway, overproduction of hepatic triglycerides and VLDL with steatosis, and hyperlipidemia, which were exacerbated by a combination of HFD and 5-HT. Sarpogrelate significantly inhibited above abnormalities induced by HFD and 5-HT, alone or in a combination. Additionally, HFD caused up-regulation of 5-HT2 receptors (5-HT₂R), including 5-HT_2AR and 5-HT_2BR, and 5-HT synthesis in the liver, without obvious influence on other 5-HT receptors gene expression. In HepG2 cells, both PA and 5-HT induced overproduction of triglycerides and VLDL with lipid droplets, and PA up-regulated 5-HT_2AR and 5-HT_2BR expression and 5-HT synthesis as well. Rapamycin fully abolished PA or 5-HT-induced mTOR activation, which was more effective than sarpogrelate. However, the inhibitory effects of rapamycin on PA or 5-HT-induced overproduction of triglycerides and VLDL were less than sarpogrelate.

CONCLUSIONS

Up-regulation of hepatic 5-HT₂R and 5-HT synthesis by HFD is crucial for HFD-induced overproduction of hepatic triglycerides and VLDL with hyperlipidemia.

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.

Serum serotonin reduced the expression of hepatic transporter Mrp2 and P-gp via regulating nuclear receptor CAR in PI-IBS rats

Hepatic transporters and drug metabolizing enzymes (DMEs) play important roles in the pharmacological effects and (or) side-effects of many drugs, and are regulated by several mediators, including neurotransmitters. This work aimed to investigate whether serum levels of 5-hydroxytryptamine (5-HT) affected the expression of hepatic transporters or DMEs. The expression of hepatic transporters was assessed using the Western-blot technique in a 2,4,6-trinitrobenzenesulfonic-acid-induced rat model of post-infectious irritable bowel syndrome (PI-IBS), in which serum levels of 5-HT were significantly elevated. To further clarify the underlying mechanism, the 5-HT precursor 5-hydroxytryptophan (5-HTP) and the 5-HT depleting agent parachlorophenylalanine (pCPA) were applied to adjust serum levels of 5-HT. Serum levels of 5-HT were measured using LC-MS/MS; the expression of hepatic transporters, DMEs, and nuclear receptors were examined by Western-blot technique. Our results showed that in PI-IBS rats the expression of multidrug resistance protein 2 (Mrp2) was significantly decreased, while colonic enterochromaffin cell density and serum levels of 5-HT were all significantly increased. Moreover, 5-HTP treatment significantly increased serum levels of 5-HT and decreased the expression of Mrp2 and glycoprotein P (P-gp), whereas treatment with pCPA markedly decreased serum levels of 5-HT and increased the expression of Mrp2 and P-gp. Our results indicated that serum 5-HT regulates the expression of Mrp2 and P-gp, and the underlying mechanism may be related to the altered expression of the nuclear receptor constitutive androstane receptor (CAR).

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.

The developmental disruptions of serotonin signaling may involved in autism during early brain development

Autism is a developmental disorder defined by the presence of a triad of communication, social and stereo typical behavioral characteristics with onset before 3years of age. In spite of the fact that there are potential environmental factors for autistic behavior, the dysfunction of serotonin during early development of the brain could be playing a role in this prevalence rise. Serotonin can modulate a number of developmental events, including cell division, neuronal migration, cell differentiation and synaptogenesis. Hyperserotonemia during fetal development results in the loss of serotonin terminals through negative feedback. The increased serotonin causes a decrease of oxytocin in the paraventricular nucleus of the hypothalamus and an increase in calcitonin gene-related peptide (CGRP) in the central nucleus of the amygdale, which are associated with social interactions and vital in autism. However, hyposerotonemia may be also relevant to the development of sensory as well as motor and cognitive faculties. And the paucity of placenta-derived serotonin should have potential importance when the pathogenesis of autism is considered. This review briefly summarized the developmental disruptions of serotonin signaling involved in the pathogenesis of autism during early development of the brain.

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.

Biology of glucose transport in the mammary gland

Glucose is the major precursor of lactose, which is synthesized in Golgi vesicles of mammary secretory alveolar epithelial cells during lactation. Glucose is taken up by mammary epithelial cells through a passive, facilitative process, which is driven by the downward glucose concentration gradient across the plasma membrane. This process is mediated by facilitative glucose transporters (GLUTs), of which there are 14 known isoforms. Mammary glands mainly express GLUT1 and GLUT8, and GLUT1 is the predominant isoform with a Km of ~10 mM and transport activity for mannose and galactose in addition to glucose. Mammary glucose transport activity increases dramatically from the virgin state to the lactation state, with a concomitant increase in GLUT expression. The increased GLUT expression during lactogenesis is not stimulated by the accepted lactogenic hormones. New evidence indicates that a possible low oxygen tension resulting from increased metabolic rate and oxygen consumption may play a major role in stimulating glucose uptake and GLUT1 expression in mammary epithelial cells during lactogenesis. In addition to its primary presence on the plasma membrane, GLUT1 is also expressed on the Golgi membrane of mammary epithelial cells and is likely involved in facilitating the uptake of glucose and galactose to the site of lactose synthesis. Because lactose synthesis dictates milk volume, regulation of GLUT expression and trafficking represents potentially fruitful areas for further research in dairy production. In addition, this research will have pathological implications for the treatment of breast cancer because glucose uptake and GLUT expression are up-regulated in breast cancer cells to accommodate the increased glucose need.

Differential expression of serotonin, tryptophan hydroxylase and monoamine oxidase A in the mammary gland of the Myotis velifer bat

The mammary gland has long drawn the attention of the scientific community due to the limited knowledge of some fundamental aspects involved in the control of its function. Myotis velifer, a microchiropteran species, provides an interesting model to study some of the regulatory factors involved in the control of the mammary gland cycle. Having an asynchronous, monoestrous reproductive pattern, female M. velifer bats undergo drastic morphological changes of the breast during the reproductive cycle. Current research on non-chiropteran mammals indicates that serotonin (5-HT) plays a major role in the intraluminal volume homeostasis of the mammary gland during lactation; however, an analysis of both the expression and localization of the main components of the serotonergic system in the bat mammary gland is lacking. Thus, the objectives of the present study were: to describe the gross and histological anatomy of the mammary gland of M. velifer to establish the lactation period for this species; to analyze the distribution and expression of the main serotonergic components in the mammary tissues of these bats under the physiological conditions of lactation, involution and the resting phase; and to provide information on the involvement of 5-HT in the regulation of the physiological function of this organ. To assess the expression and localization of serotonergic components, multiple immunofluorescence, Western blot and HPLC methods were used. 5-HT and the enzyme that catalyzes its synthesis (TPH) were located in both myoepithelial and luminal epithelial cells, while the enzyme responsible for the catabolism of this neurohormone (MAO A) was found in luminal epithelial cells as well as in secreted products. We also found an increased expression of serotonergic components during lactation, indicating that elements of the serotonergic system may play an important role in lactation in this species of bat in a way similar to that of other mammal species.

Short communication: Circulating serotonin (5-HT) concentrations on day 1 of lactation as a potential predictor of transition-related disorders

The monoamine serotonin (5-hydroxytryptamine; 5-HT) has been described as a homeostatic regulator of lactation. Recently, our laboratory determined that 5-HT is involved in the regulation of calcium and glucose homeostasis during the transition period in rodents. More specifically, we demonstrate that 5-HT is responsible for calcium mobilization from bone and upregulation of hepatic gluconeogenic enzymes and mammary gland glucose transporters. Our objective was to investigate the correlation between circulating 5-HT concentrations and circulating ionized calcium, parathyroid hormone-related protein (PTHrP), and glucose concentrations on d 1 postpartum. We also investigated the correlation between circulating 5-HT and milk fever and ketosis incidence and severity in multiparous Holstein cows at the onset of lactation. Blood samples were collected from 42 multiparous cows on d 1 of lactation and analyzed for 5-HT, calcium, glucose, and PTHrP. Milk fever (determined subjectively for each cow on d 1 postpartum) and ketosis incidence and severity (scale 1 to 4, determined objectively for each cow during the first 10 d postpartum) were recorded for all animals. Serum 5-HT was positively correlated with serum calcium and with plasma PTHrP (r>0.37). Serum 5-HT was negatively correlated with milk fever incidence and with ketosis severity (most severe ketosis incidence recorded during the first 10 d postpartum; r<-0.33). Serum calcium and plasma glucose concentrations were negatively correlated with milk fever and ketosis severity, respectively (r<-0.39). These data indicate that 5-HT potentially plays a role in the regulation of calcium and glucose homeostasis during the transition period in cattle, which we previously demonstrated in rodents. Increased circulating concentrations of 5-HT might decrease milk fever at the onset of lactation and ketosis severity during the first 10 d postpartum in dairy cows. Understanding this physiological axis could help describe the underlying mechanisms associated with these periparturient metabolic disorders in dairy cows.