Tissue-specific changes in molecular clocks during the transition from pregnancy to lactation in mice

The contribution of circadian clock to the biological processes

All organisms have various circadian, behavioral, and physiological 24-h periodic rhythms, which are controlled by the circadian clock. The circadian clock controls various behavioral and physiological rhythms. In mammals, the primary circadian clock is present in the suprachiasmatic nucleus of the hypothalamus. The rhythm of the circadian clock is controlled by the interaction between negative and positive feedback loops, consisting of crucial clock regulators (including Bmal1 and Clock), three cycles (mPer1, mPer2, and mPer3), and two cryptochromes (Cry1 and Cry2). The development of early mammalian embryos is an ordered and complex biological process that includes stages from fertilized eggs to blastocysts and undergoes important morphological changes, such as blastocyst formation, cell multiplication, and compaction. The circadian clock affects the onset and timing of embryonic development. The circadian clock affects many biological processes, including eating time, immune function, sleep, energy metabolism, and endocrinology, therefore, it is also crucial for overall health, growth and development after birth. This review summarized the effects of the circadian clock in the body's physiological activities. A new strategy is proposed for the prevention of malformations or diseases by regulating the circadian clock or changing circadian rhythms.

Single-Cell Transcription Mapping of Murine and Human Mammary Organoids Responses to Female Hormones

During female adolescence and pregnancy, rising levels of hormones result in a cyclic source of signals that control the development of mammary tissue. While such alterations are well understood from a whole-gland perspective, the alterations that such hormones bring to organoid cultures derived from mammary glands have yet to be fully mapped. This is of special importance given that organoids are considered suitable systems to understand cross species breast development. Here we utilized single-cell transcriptional profiling to delineate responses of murine and human normal breast organoid systems to female hormones across evolutionary distinct species. Collectively, our study represents a molecular atlas of epithelial dynamics in response to estrogen and pregnancy hormones.

Impact of high-fat diet and exposure to constant light on reproductive competence of female ICR mice

Obesity and exposure to light at night are prevalent in modern society and associated with changes in physiology and behavior that can affect a female's ability to support offspring growth during pregnancy and lactation. A 2X3 factor study of ICR mice was conducted to determine the effect of diet [control (CON; 10% fat) or high fat (HF; 60% fat)] and exposure to regular 12 h light:dark cycles (LD) or continuous low (L5) or high (L100) lux of light on gestation length, birth litter size, milk composition and litter growth to lactation day 12. HF diet reduced birth litter size, but increased postnatal d 12 litter weight (P<0.05), whereas constant light tended to increase litter weight (P=0.07). Continuous light increased gestation length, altered dam feed intake, increased serum prolactin and increased final dam and mammary gland weight (P<0.05), while decreasing mammary ATP content and milk lactose (P<0.05). Correlation analysis indicated a positive relationship between final litter weight and mammary size, metabolic stores (e.g. maternal fat pad weight), kcal of feed intake, and gestation length (P<0.05). Although CON mice spent more time eating than HF dams, the calorically dense HF diet was related to greater rates of litter growth to peak lactation. Constant light circadian disrupting effects appear to be confounded by a potential long day photoperiod response exemplified by higher circulating levels of prolactin and increased body and mammary weight of females exposed to these conditions. Other model systems may be better to study the interacting effects of obesity and circadian disruption on reproductive competence.

Single-cell transcription mapping of murine and human mammary organoids responses to female hormones

During female adolescence and pregnancy, rising levels of hormones result in a cyclic source of signals that control the development of mammary tissue. While such alterations are well understood from a whole-gland perspective, the alterations that such hormones bring to organoid cultures derived from mammary glands have yet to be fully mapped. This is of special importance given that organoids are considered suitable systems to understand cross species breast development. Here we utilized single-cell transcriptional profiling to delineate responses of murine and human normal breast organoid systems to female hormones across evolutionary distinct species. Collectively, our study represents a molecular atlas of epithelial dynamics in response to estrogen and pregnancy hormones.

Advances in circadian clock regulation of reproduction

The mammalian circadian clock is an endogenously regulated oscillator that is synchronized with solar time and cycle within a 24-h period. The circadian clock exists not only in the suprachiasmatic nucleus (SCN) of the hypothalamus, a central pacemaker of the circadian clock system, but also in numerous peripheral tissues known as peripheral circadian oscillators. The SCN and peripheral circadian oscillators mutually orchestrate the diurnal rhythms of various physiological and behavioral processes in a hierarchical manner. In the past two decades, peripheral circadian oscillators have been identified and their function has been determined in the mammalian reproductive system and its related endocrine glands, including the hypothalamus, pituitary gland, ovaries, testes, uterus, mammary glands, and prostate gland. Increasing evidence indicates that both the SCN and peripheral circadian oscillators play discrete roles in coordinating reproductive processes and optimizing fertility in mammals. The present study reviews recent evidence on circadian clock regulation of reproductive function in the hypothalamic-pituitary-gonadal axis and reproductive system. Additionally, we elucidate the effects of chronodisruption (as a result of, for example, shift work, jet lag, disrupted eating patterns, and sleep disorders) on mammalian reproductive performance from multiple aspects. Finally, we propose potential behavioral changes or pharmaceutical strategies for the prevention and treatment of reproductive disorders from the perspective of chronomedicine. Conclusively, this review will outline recent evidence on circadian clock regulation of reproduction, providing novel perspectives on the role of the circadian clock in maintaining normal reproductive functions and in diseases that negatively affect fertility.

Human milk variation is shaped by maternal genetics and impacts the infant gut microbiome

Human milk is a complex mix of nutritional and bioactive components that provide complete nutrition for the infant. However, we lack a systematic knowledge of the factors shaping milk composition and how milk variation influences infant health. Here, we used multi-omic profiling to characterize interactions between maternal genetics, milk gene expression, milk composition, and the infant fecal microbiome in 242 exclusively breastfeeding mother-infant pairs. We identified 487 genetic loci associated with milk gene expression unique to the lactating mammary gland, including loci that impacted breast cancer risk and human milk oligosaccharide concentration. Integrative analyses uncovered connections between milk gene expression and infant gut microbiome, including an association between the expression of inflammation-related genes with IL-6 concentration in milk and the abundance of Bifidobacteria in the infant gut. Our results show how an improved understanding of the genetics and genomics of human milk connects lactation biology with maternal and infant health.

Circadian clocks and their role in lactation competence

Circadian rhythms are 24 h cycles of behavior, physiology and gene expression that function to synchronize processes across the body and coordinate physiology with the external environment. Circadian clocks are central to maintaining homeostasis and regulating coordinated changes in physiology in response to internal and external cues. Orchestrated changes occur in maternal physiology during the periparturient period to support the growth of the fetus and the energetic and nutritional demands of lactation. Discoveries in our lab made over a decade ago led us to hypothesize that the circadian timing system functions to regulate metabolic and mammary specific changes that occur to support a successful lactation. Findings of studies that ensued are summarized, and point to the importance of circadian clocks in the regulation of lactation competence. Disruption of the circadian timing system can negatively affect mammary gland development and differentiation, alter maternal metabolism and impair milk production.

Transcriptome analysis reveals disruption of circadian rhythms in late gestation dairy cows may increase risk for fatty liver and reduced mammary remodeling

Circadian disruption increased insulin resistance and decreased mammary development in late gestation, nonlactating (dry) cows. The objective was to measure the effect of circadian disruption on transcriptomes of the liver and mammary gland. At 35 days before expected calving (BEC), multiparous dry cows were assigned to either control (CON) or phase-shifted treatments (PS). CON was exposed to 16-h light and 8-h dark. PS was exposed to 16-h light to 8-h dark, but phase of the light-dark cycle was shifted 6 h every 3 days. On day 21 BEC, liver and mammary were biopsied. RNA was isolated (n = 6 CON, n = 6 PS per tissue), and libraries were prepared and sequenced using paired-end reads. Reads mapping to bovine genome averaged 27 ± 2 million and aligned to 14,222 protein-coding genes in liver and 15,480 in mammary analysis. In the liver, 834 genes, and in the mammary gland, 862 genes were different (nominal P < 0.05) between PS and CON. In the liver, genes upregulated in PS functioned in cholesterol biosynthesis, endoplasmic reticulum stress, wound healing, and inflammation. Genes downregulated in liver function in cholesterol efflux. In the mammary gland, genes upregulated functioned in mRNA processing and transcription and downregulated genes encoded extracellular matrix proteins and proteases, cathepsins and lysosomal proteases, lipid transporters, and regulated oxidative phosphorylation. Increased cholesterol synthesis and decreased efflux suggest that circadian disruption potentially increases the risk of fatty liver in cows. Decreased remodeling and lipid transport in mammary may decrease milk production capacity during lactation.

Circadian rhythm in hypothalamic leptin receptor (Ob-Rb) mRNA expressions and cerebrospinal fluid and circulating glucose and leptin levels in lactating rats

In lactating animals, the food consumption increases several-fold for milk supply to the pups. The present study was conducted to clarify the relationship between the hyperphagia during lactation and hypothalamic leptin receptor (Ob-Rb) mRNA expression, cerebrospinal fluid (CSF) and circulating leptin and glucose levels. Food intakes significantly higher in lactation than in non-lactation at all time points (3 points: light phase, 4 points: dark phase) of the day. However, the expression of the hypothalamic Ob-Rb mRNA showed similar circadian rhythms in both the non-lactation and lactation, with only slight differences between the two groups. CSF leptin and glucose levels were constant throughout the day in both non-lactation and lactation, and there was almost no difference between the two groups at each time point. Circulating leptin and glucose levels showed circadian rhythms only in the non-lactating period, and were lower in lactation than in non-lactation, especially in the dark phase. In conclusion, the present study provides evidence that Ob-Rb mRNA expression fluctuates in the lactation period as well as in the non-lactation period, suggesting that the expression profile of whole hypothalamic Ob-Rb may not contribute to the difference in food consumption between lactation and non-lactation, and that chronic decrease in blood glucose levels may be associated with the increase in food consumption during lactation.

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There was no difference in CSF leptin levels between lactating and non-lactating rats.

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Hypothalamic Ob-Rb mRNA expressions showed different circadian rhythms between non-lactation and lactation.

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Chronic decrease in blood glucose levels may be associated with the elevation of food consumption in lactating rats.

Core circadian clock transcription factor BMAL1 regulates mammary epithelial cell growth, differentiation, and milk component synthesis

The role the mammary epithelial circadian clock plays in gland development and lactation is unknown. We hypothesized that mammary epithelial clocks function to regulate mammogenesis and lactogenesis, and propose the core clock transcription factor BMAL1:CLOCK regulates genes that control mammary epithelial development and milk synthesis. Our objective was to identify transcriptional targets of BMAL1 in undifferentiated (UNDIFF) and lactogen differentiated (DIFF) mammary epithelial cells (HC11) using ChIP-seq. Ensembl gene IDs with the nearest transcriptional start site to ChIP-seq peaks were explored as potential targets, and represented 846 protein coding genes common to UNDIFF and DIFF cells and 2773 unique to DIFF samples. Genes with overlapping peaks between samples (1343) enriched cell-cell adhesion, membrane transporters and lipid metabolism categories. To functionally verify targets, an HC11 line with Bmal1 gene knocked out (BMAL1-KO) using CRISPR-CAS was created. BMAL1-KO cultures had lower cell densities over an eight-day growth curve, which was associated with increased (p<0.05) levels of reactive oxygen species and lower expression of superoxide dismutase 3 (Sod3). RT-qPCR analysis also found lower expression of the putative targets, prolactin receptor (Prlr), Ppara, and beta-casein (Csn2). Findings support our hypothesis and highlight potential importance of clock in mammary development and substrate transport.

Single-step genome-wide association studies (GWAS) and post-GWAS analyses to identify genomic regions and candidate genes for milk yield in Brazilian Girolando cattle

Milk production is economically important to the Brazilian agribusiness, and the majority of the country's milk production derives from Girolando (Gir × Holstein) cows. This study aimed to identify quantitative trait loci (QTL) and candidate genes associated with 305-d milk yield (305MY) in Girolando cattle. In addition, we investigated the SNP-specific variances for Holstein and Gir breeds of origin within the sequence of candidate genes. A single-step genomic BLUP procedure was used to identify QTL associated with 305MY, and the most likely candidate genes were identified through follow-up analyses. Genomic breeding values specific for Holstein and Gir were estimated in the Girolando animals using a model that uses breed-specific partial relationship matrices, which were converted to breed of origin SNP effects. Differences between breed of origin were evaluated by comparing estimated SNP variances between breeds. From 10 genome regions explaining most additive genetic variance for 305MY in Girolando cattle, 7 candidate genes were identified on chromosomes 1, 4, 6, and 26. Within the sequence of these 7 candidate genes, Gir breed of origin SNP alleles showed the highest genetic variance. These results indicated QTL regions that could be further explored in genomic selection panels and which may also help in understanding the gene mechanisms involved in milk production in the Girolando breed.

Early weaning modulates eating behavior and promotes hypofunction of the serotonergic (5HT) system in juvenile male rats

Early life stress (ELS) has been associated with developmental impairments. Early weaning (EW) is a postnatal stress model consisting of interruption of lactation and maternal care. The 5HT-system has been associated with neurobehavioral modulations promoted by ELS. Thus, the present work aims to investigate the effects of early weaning on feeding behavior and serotonergic system of juvenile male rats. For this, rats were submitted to early (PND15) or natural (PND30) weaning and had the body weight, food intake in circadian phases, and food intake in response to fenfluramine assessed. mRNA expression of serotoninergic receptors (5HT1A and 5HT2C) and transporter (SERT) was assessed in the hypothalamus and brainstem, as well as NPY and POMC mRNA expression in hypothalamus. The results show that early weaning promoted changes in the percentage of weight gain during lactation period and increase in body weight at PND40. It was also observed that EW promoted increase and decrease in food intake in light and dark phase, respectively, and leads to a decreased action of fenfluramine on inhibition of food intake. In addition, early weaning promoted increased NPY and SERT mRNA expression in the hypothalamus and 5HT2C in the brainstem. Together, the data indicate that the stress caused by early weaning impairs the eating behavior of juvenile male rats through hypofunction of the 5HT-system.

Pregnancy rest-activity patterns are related to salivary cortisol rhythms and maternal-fetal health indicators in women from a disadvantaged population

Irregular rest-activity patterns can disrupt metabolic and hormonal physiology and potentially lead to disease. Little is known regarding rest-activity patterns during gestation and their association with hormonal rhythms and health in pregnant women. We conducted a pilot study to determine if 24 h rest-activity was related to saliva cortisol rhythms and maternal-fetal health in an economically disadvantaged population. Primiparous women wore a wrist actigraphy device for a week to record activity during gestational weeks 22 (G22; n = 50) and 32 (G32; n = 46) and postpartum week one (PPW1; n = 39). Participants collected saliva samples every 4 hr over a 24 hr period during G22 (n = 22), G32 (n = 20) and 24–48 hr postnatal (n = 20), and cortisol concentrations were measured with ELISA. Circadian rhythmicity was assessed using autocorrelation coefficient (r24) and cosinor analysis. Blood glucose levels, body mass index (BMI), gestational disease data, and gestational age of infant at birth were abstracted from medical charts. Time of cortisol peak (acrophase) during G22 was related with acrophase of activity (r = 0.66; p = 0.001) and blood glucose levels (r = 0.58; p = 0.006). During G22, minutes of wake after sleep onset was positively related to cortisol mesor and AUC (p <0.05). Rest-activity r24, R², and mesor during G32 were positively (p<0.05) associated with gestational age of infant at birth. Across all three time points r24 of activity was related with cortisol amplitude (r = 0.33; p = 0.01). Findings support a relationship between rest-activity patterns and saliva cortisol rhythms during pregnancy. The association of less robust activity rhythms with earlier gestational age of infant at birth indicates a potential link between circadian system disruption and maternal-fetal health outcomes.

Supply of methionine and arginine alters phosphorylation of mechanistic target of rapamycin (mTOR), circadian clock proteins, and α-s1-casein abundance in bovine mammary epithelial cells

Methionine (Met) and arginine (Arg) regulate casein protein abundance through alterations in activity of the mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway.

Integrative analysis of transcriptomic data related to the liver of laying hens: from physiological basics to newly identified functions

BACKGROUND

At sexual maturity, the liver of laying hens undergoes many metabolic changes to support vitellogenesis. In published transcriptomic approaches, hundreds of genes were reported to be overexpressed in laying hens and functional gene annotation using gene ontology tools have essentially revealed an enrichment in lipid and protein metabolisms. We reanalyzed some data from a previously published article comparing 38-week old versus 10-week old hens to give a more integrative view of the functions stimulated in the liver at sexual maturity and to move beyond current physiological knowledge. Functions were defined based on information available in Uniprot database and published literature.

RESULTS

Of the 516 genes previously shown to be overexpressed in the liver of laying hens, 475 were intracellular (1.23-50.72 fold changes), while only 36 were predicted to be secreted (1.35-66.93 fold changes) and 5 had no related information on their cellular location. Besides lipogenesis and protein metabolism, we demonstrated that the liver of laying hens overexpresses several clock genes (which supports the circadian control of liver metabolic functions) and was likely to be involved in a liver/brain/liver circuit (neurotransmitter transport), in thyroid and steroid hormones metabolisms. Many genes were associated with anatomical structure development, organ homeostasis but also regulation of blood pressure. As expected, several secreted proteins are incorporated in yolky follicles but we also evidenced that some proteins are likely participating in fertilization (ZP1, MFGE8, LINC00954, OVOCH1) and in thyroid hormone maturation (CPQ). We also proposed that secreted proteins (PHOSPHO1, FGF23, BMP7 but also vitamin-binding proteins) may contribute to the development of peripheral organs including the formation of medullar bones to provide labile calcium for eggshell formation. Thirteen genes are uniquely found in chicken/bird but not in human species, which strengthens that some of these genes may be specifically related to avian reproduction.

CONCLUSIONS

This study gives additional hypotheses on some molecular actors and mechanisms that are involved in basic physiological function of the liver at sexual maturity of hen. It also revealed some additional functions that accompany reproductive capacities of laying hens, and that are usually underestimated when using classical gene ontology approaches.

Early weaning disrupts feeding patterns in female juvenile rats through 5HT-system modulations

Convergent evidence in literature shows that rapid disruption of maternal care and breastfeeding due to an early weaning protocol changes the development of several neurobehavioral patterns in rodents, including the circadian pattern of feeding. The serotoninergic system has been associated with the control of feeding patterns. Therefore, we aim to evaluate the patterns of feeding, the mRNA expression of 5 H T-1b, 5 H T-2c, and SERT on the hypothalamus, brainstem, and the body weight of female juvenile Wistar rats, submitted to early (PND15) or regular (PND30) weaning. The results demonstrate that early weaning promotes an increase in food intake in a 24 -h period, in the dark phase of the circadian cycle and in the four-hour time intervals at the beginning of the dark and light phases. Also, early weaning decreases the mRNA expression of 5 H T-1b, 5 H T-2c, and SERT on the hypothalamus, but increases it on the brainstem. Additionally, early weaning promotes an increase in body weight. Therefore, the present data demonstrate that early weaning changes the patterns of feeding in juvenile female rats and suggests that this behavioral modification is due to the modulations promoted in the 5 H T-system.

Disrupted circadian clocks and altered tissue mechanics in primary human breast tumours

BACKGROUND

Circadian rhythms maintain tissue homeostasis during the 24-h day-night cycle. Cell-autonomous circadian clocks play fundamental roles in cell division, DNA damage responses and metabolism. Circadian disruptions have been proposed as a contributing factor for cancer initiation and progression, although definitive evidence for altered molecular circadian clocks in cancer is still lacking. In this study, we looked at circadian clocks in breast cancer.

METHODS

We isolated primary tumours and normal tissues from the same individuals who had developed breast cancer with no metastases. We assessed circadian clocks within primary cells of the patients by lentiviral expression of circadian reporters, and the levels of clock genes in tissues by qPCR. We histologically examined collagen organisation within the normal and tumour tissue areas, and probed the stiffness of the stroma adjacent to normal and tumour epithelium using atomic force microscopy.

RESULTS

Epithelial ducts were disorganised within the tumour areas. Circadian clocks were altered in cultured tumour cells. Tumour regions were surrounded by stroma with an altered collagen organisation and increased stiffness. Levels of Bmal1 messenger RNA (mRNA) were significantly altered in the tumours in comparison to normal epithelia.

CONCLUSION

Circadian rhythms are suppressed in breast tumour epithelia in comparison to the normal epithelia in paired patient samples. This correlates with increased tissue stiffness around the tumour region. We suggest possible involvement of altered circadian clocks in the development and progression of breast cancer.

Rapid Communication: Period2 gene silencing increases the synthesis of αs-casein protein in bovine mammary epithelial cells

(), a core clock gene, encodes a circadian rhythm protein which has been shown to control mammary metabolism in rodents. Whether regulates milk component synthesis such as α-casein protein in bovine mammary cells is unknown. Thus, we used gene silencing technology to determine if silencing could affect α-casein synthesis and cell growth in cultured primary bovine mammary epithelial cells (BMEC). The BMEC were established by enzymatic digestion of mammary tissue from mid-lactation cows. A transient-transfection technique was used to insert a small interfering RNA (siRNA) oligonucleotide specific for to inhibit transcription. Control and siRNA-transfected cells were cultured for 48 h. qRT-PCR and ELISA analysis showed that silencing enhanced the synthesis of 2 kinds of α-casein ( < 0.05) through upregulating the mRNA level of and ( < 0.01). Furthermore, the 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT) results demonstrated that cell proliferation was not affected ( > 0.05). These data led us to hypothesize that PER2 protein may potentially play an important role in the control of milk protein synthesis and, hence, represents a target that can be used to regulate protein synthesis rate during lactation.

Clock-dependent and system-driven oscillators interact in the suprachiasmatic nuclei to pace mammalian circadian rhythms

Circadian clocks drive biological rhythms with a period of approximately 24 hours and keep in time with the outside world through daily resetting by environmental cues. While this external entrainment has been extensively investigated in the suprachiasmatic nuclei (SCN), the role of internal systemic rhythms, including daily fluctuations in core temperature or circulating hormones remains debated. Here, we show that lactating mice, which exhibit dampened systemic rhythms, possess normal molecular clockwork but impaired rhythms in both heat shock response gene expression and electrophysiological output in their SCN. This suggests that body rhythms regulate SCN activity downstream of the clock. Mathematical modeling predicts that systemic feedback upon the SCN functions as an internal oscillator that accounts for in vivo and ex vivo observations. Thus we are able to propose a new bottom-up hierarchical organization of circadian timekeeping in mammals, based on the interaction in the SCN between clock-dependent and system-driven oscillators.

Adrenal gland plasticity in lactating rats and mice is sufficient to maintain basal hypersecretion of corticosterone

Increased basal glucocorticoid secretion and a reduced glucocorticoid response during acute stress, despite only minor changes in the secretion of the major secretagogue adrenocorticotropic hormone (ACTH), have been documented in the peripartum period in several species. We recently showed that the adrenal gland, the site of glucocorticoid synthesis, undergoes substantial postpartum-associated plasticity in the rat at mid-lactation. Here, we asked the question whether adrenal changes already take place around parturition in the rat and in another species, namely the mouse. After demonstrating that several components of the adrenal machinery mediating cholesterol supply for steroidogenesis, including protein levels of hormone-sensitive lipase, low-density lipoprotein receptor (LDLR) and scavenger receptor class-B type-1 (SRB1), are upregulated, while hydroxymethylglutaryl coenzyme A reductase (HMGCR) is downregulated in the lactating rat one day after delivery, as previously observed at mid-lactation, we demonstrated profound changes in the mouse. In detail, protein expression of LDLR, SRB1, HMGCR and adrenal lipid store density were increased in the mouse adrenal one day after parturition as tested via western blot analysis and oil-red lipid staining, respectively. Moreover, using in vitro culture techniques, we observed that isolated adrenal explants from lactating mice secreted higher levels of corticosterone under basal conditions, but showed impaired responsiveness to ACTH, mimicking the in vivo scenario. These results suggest that mechanisms of adaptation in the maternal adrenal after delivery, namely increased cholesterol availability and decreased ACTH sensitivity, are crucial for the basal increase in circulating glucocorticoids and maternal stress hyporesponsiveness that are typical of this period.

Gestational disruptions in metabolic rhythmicity of the liver, muscle, and placenta affect fetal size

Maternal metabolic adaptations are essential for successful pregnancy outcomes. We investigated how metabolic gestational processes are coordinated, whether there is a functional link with internal clocks, and whether disruptions are related to metabolic abnormalities in pregnancy, by studying day/night metabolic pathways in murine models and samples from pregnant women with normally grown and large-for-gestational age infants. In early mouse pregnancy, expression of hepatic lipogenic genes was up-regulated and uncoupled from the hepatic clock. In late mouse pregnancy, rhythmicity of energy metabolism-related genes in the muscle followed the patterns of internal clock genes in this tissue, and coincided with enhanced lipid transporter expression in the fetoplacental unit. Diurnal triglyceride patterns were disrupted in human placentas from pregnancies with large-for-gestational age infants and this overlapped with an increase in BMAL1 expression. Metabolic adaptations in early pregnancy are uncoupled from the circadian clock, whereas in late pregnancy, energy availability is mediated by coordinated muscle-placenta metabolic adjustments linked to internal clocks. Placental triglyceride oscillations in the third trimester of human pregnancy are lost in large-for-gestational age infants and may be regulated by BMAL1. In summary, disruptions in metabolic and circadian rhythmicity are associated with increased fetal size, with implications for the pathogenesis of macrosomia.-Papacleovoulou, G., Nikolova, V., Oduwole, O., Chambers, J., Vazquez-Lopez, M., Jansen, E., Nicolaides, K., Parker, M., Williamson, C. Gestational disruptions in metabolic rhythmicity of the liver, muscle, and placenta affect fetal size.

Potential transfer of neurotoxic amino acid β-N-methylamino-alanine (BMAA) from mother to infant during breast-feeding: Predictions from human cell lines

β-N-methylamino-alanine (BMAA) is a non-protein amino acid produced by cyanobacteria, diatoms and dinoflagellates. BMAA has potential to biomagnify in a terrestrial food chain, and to bioaccumulate in fish and shellfish. We have reported that administration of [¹⁴C]l-BMAA to lactating mice and rats results in a mother to off-spring transfer via the milk. A preferential enantiomer-specific uptake of [¹⁴C]l-BMAA has also been demonstrated in differentiated murine mammary epithelium HC11 cells. These findings, together with neurotoxic effects of BMAA demonstrated both in vitro and in vivo, highlight the need to determine whether such transfer could also occur in humans. Here, we used four cell lines of human origin to examine and compare the transport of the two BMAA enantiomers in vitro. The uptake patterns of [¹⁴C]l- and [¹⁴C]d-BMAA in the human mammary MCF7 cell line were in agreement with the results in murine HC11 cells, suggesting a potential secretion of BMAA into human breast milk. The permeability coefficients for both [¹⁴C]l- and [¹⁴C]d-BMAA over monolayers of human intestinal Caco2 cells supported an efficient absorption from the human intestine. As a final step, transport experiments confirmed that [¹⁴C]l-and [¹⁴C]d-BMAA can be taken up by human SHSY5Y neuroblastoma cells and even more efficiently by human U343 glioblastoma cells. In competition experiments with various amino acids, the ASCT2 specific inhibitor benzylserine was the most effective inhibitor of [¹⁴C]l-BMAA uptake tested here. Altogether, our results suggest that BMAA can be transferred from an exposed mother, via the milk, to the brain of the nursed infant.

CLOCK regulates mammary epithelial cell growth and differentiation

Circadian clocks influence virtually all physiological processes, including lactation. Here, we investigate the role of the CLOCK gene in regulation of mammary epithelial cell growth and differentiation. Comparison of mammary morphology in late-pregnant wild-type and ClockΔ19 mice, showed that gland development was negatively impacted by genetic loss of a functional timing system. To understand whether these effects were due, in part, to loss of CLOCK function in the gland, the mouse mammary epithelial cell line, HC11, was transfected with short hairpin RNA that targeted Clock (shClock). Cells transfected with shClock expressed 70% less Clock mRNA than wild-type (WT) HC11 cultures, which resulted in significantly depressed levels of CLOCK protein (P < 0.05). HC11 lines carrying shClock had four-fold higher growth rates (P < 0.05), and the percentage of cells in G1 phase was significantly higher (90.1 ± 1.1% of shClock vs. 71.3 ± 3.6% of WT-HC11) following serum starvation. Quantitative-PCR (qPCR) analysis showed shClock had significant effects (P < 0.0001) on relative expression levels of Ccnd1, Wee1, and Tp63 qPCR analysis of the effect of shClock on Fasn and Cdh1 expression in undifferentiated cultures and cultures treated 96 h with dexamethasone, insulin, and prolactin (differentiated) found levels were reduced by twofold and threefold, respectively (P < 0.05), in shClock line relative to WT cultures. Abundance of CDH1 and TP63 proteins were significantly reduced in cultures transfected with shClock These data support how CLOCK plays a role in regulation of epithelial cell growth and differentiation in the mammary gland.

Circadian clocks and breast cancer

Circadian clocks respond to environmental time cues to coordinate 24-hour oscillations in almost every tissue of the body. In the breast, circadian clocks regulate the rhythmic expression of numerous genes. Disrupted expression of circadian genes can alter breast biology and may promote cancer. Here we overview circadian mechanisms, and the connection between the molecular clock and breast biology. We describe how disruption of circadian genes contributes to cancer via multiple mechanisms, and link this to increased tumour risk in women who work irregular shift patterns. Understanding the influence of circadian rhythms on breast cancer could lead to more efficacious therapies, reformed public health policy and improved patient outcome.

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.

Zinc Finger Homeodomain Factor Zfhx3 Is Essential for Mammary Lactogenic Differentiation by Maintaining Prolactin Signaling Activity

The zinc finger homeobox 3 (ZFHX3, also named ATBF1 for AT motif binding factor 1) is a transcription factor that suppresses prostatic carcinogenesis and induces neuronal differentiation. It also interacts with estrogen receptor α to inhibit cell proliferation and regulate pubertal mammary gland development in mice. In the present study, we examined whether and how Zfhx3 regulates lactogenic differentiation in mouse mammary glands. At different stages of mammary gland development, Zfhx3 protein was expressed at varying levels, with the highest level at lactation. In the HC11 mouse mammary epithelial cell line, an in vitro model of lactogenesis, knockdown of Zfhx3 attenuated prolactin-induced β-casein expression and morphological changes, indicators of lactogenic differentiation. In mouse mammary tissue, knock-out of Zfhx3 interrupted lactogenesis, resulting in underdeveloped glands with much smaller and fewer alveoli, reduced β-casein expression, accumulation of large cytoplasmic lipid droplets in luminal cells after parturition, and failure in lactation. Mechanistically, Zfhx3 maintained the expression of Prlr (prolactin receptor) and Prlr-Jak2-Stat5 signaling activity, whereas knockdown and knock-out of Zfhx3 in HC11 cells and mammary tissues, respectively, decreased Prlr expression, Stat5 phosphorylation, and the expression of Prlr-Jak2-Stat5 target genes. These findings indicate that Zfhx3 plays an essential role in proper lactogenic development in mammary glands, at least in part by maintaining Prlr expression and Prlr-Jak2-Stat5 signaling activity.

Recent advances on the circadian gene PER2 and metabolic rhythm of lactation of mammary gland

Due to regulation by circadian rhythm, the lactation of the mammary gland has rhythmicity. As one of prominent members of period protein family which regulates biological rhythms, PER2 plays an important role in developing the milk duct and maintaining the polarity and the morphology of the mammary epithelium; at the same time, it is also closely related with the metabolism of milk protein and milk fat. This paper summarized recent researches on PER2 gene and related researches on mammary gland development and metabolism to provide some information for the studies of the theory and technology on physiological functions of the mammary gland and milk quality control.

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.

Does Circadian Disruption Play a Role in the Metabolic-Hormonal Link to Delayed Lactogenesis II?

Breastfeeding improves maternal and child health. The American Academy of Pediatrics recommends exclusive breastfeeding for 6 months, with continued breastfeeding for at least 1 year. However, in the US, only 18.8% of infants are exclusively breastfed until 6 months of age. For mothers who initiate breastfeeding, the early post-partum period sets the stage for sustained breastfeeding. Mothers who experience breastfeeding problems in the early post-partum period are more likely to discontinue breastfeeding within 2 weeks. A major risk factor for shorter breastfeeding duration is delayed lactogenesis II (DLII; i.e., onset of milk "coming in" more than 72 h post-partum). Recent studies report a metabolic-hormonal link to DLII. This is not surprising because around the time of birth the mother's entire metabolism changes to direct nutrients to mammary glands. Circadian and metabolic systems are closely linked, and our rodent studies suggest circadian clocks coordinate hormonal and metabolic changes to support lactation. Molecular and environmental disruption of the circadian system decreases a dam's ability to initiate lactation and negatively impacts milk production. Circadian and metabolic systems evolved to be functional and adaptive when lifestyles and environmental exposures were quite different from modern times. We now have artificial lights, longer work days, and increases in shift work. Disruption in the circadian system due to shift work, jet-lag, sleep disorders, and other modern life style choices are associated with metabolic disorders, obesity, and impaired reproduction. We hypothesize that DLII is related to disruption of the mother's circadian system. Here, we review literature that supports this hypothesis, and describe interventions that may help to increase breastfeeding success.

Transcriptomes reveal alterations in gravity impact circadian clocks and activate mechanotransduction pathways with adaptation through epigenetic change

Few studies have investigated the impact of alterations in gravity on mammalian transcriptomes. Here, we describe the impact of spaceflight on mammary transcriptome of late pregnant rats and the effect of hypergravity exposure on mammary, liver, and adipose transcriptomes in late pregnancy and at the onset of lactation. RNA was isolated from mammary collected on pregnancy day 20 from rats exposed to spaceflight from days 11 to 20 of gestation. To measure the impact of hypergravity on mammary, liver, and adipose transcriptomes we isolated RNA from tissues collected on P20 and lactation day 1 from rats exposed to hypergravity beginning on pregnancy day 9. Gene expression was measured with Affymetrix GeneChips. Microarray analysis of variance revealed alterations in gravity affected the expression of genes that regulate circadian clocks and activate mechanotransduction pathways. Changes in these systems may explain global gene expression changes in immune response, metabolism, and cell proliferation. Expression of genes that modify chromatin structure and methylation was affected, suggesting adaptation to gravity alterations may proceed through epigenetic change. Altered gravity experiments offer insights into the role of forces omnipresent on Earth that shape genomes in heritable ways. Our study is the first to analyze the impact of alterations in gravity on transcriptomes of pregnant and lactating mammals. Findings provide insight into systems that sense gravity and the way in which they affect phenotype, as well as the possibility of sustaining life beyond Earth's orbit.