Moderate High Temperature Condition Induces the Lactation Capacity of Mammary Epithelial Cells Through Control of STAT3 and STAT5 Signaling

Cyclical heat stress during lactation influences the microstructure of the bovine mammary gland

This study aimed to evaluate the impact of heat stress on mammary epithelial cell (MEC) losses into milk, secretory mammary tissue structure, and mammary epithelial cell activity. Sixteen multiparous Holstein cows (632 ± 12 kg BW) approximately 100 d in milk housed in climate-controlled rooms were paired by body weight and randomly allocated to one of 2 treatments, heat stress (HS) or pair feeding thermoneutral (PFTN) using 2 cohorts. Each cohort was subjected to 2 periods of 4 d each. In period 1, both treatments had ad libitum access to a common total mixed ration and were exposed to a controlled daily temperature-humidity index (THI) of 64. In period 2, HS cows were exposed to controlled cyclical heat stress (THI: 74 to 80), while PFTN cows remained at 64 THI and daily dry matter intake was matched to HS. Cows were milked twice daily, and milk yield was recorded at each milking. Individual milk samples on the last day of each period were used to quantify MEC losses by flow cytometry using butyrophilin as a cell surface marker. On the final day of period 2, individual bovine mammary tissue samples were obtained for histomorphology analysis, assessment of protein abundance, and evaluation of gene expression of targets associated with cellular capacity for milk and milk component synthesis, heat response, cellular proliferation, and autophagy. Statistical analysis was performed using the GLIMMIX procedure of SAS. Milk yield was reduced by 4.3 kg by HS (n = 7) compared with PFTN (n = 8). Independent of treatment, MEC in milk averaged 174 cells/mL (2.9% of total cells). There was no difference between HS vs. PFTN cows for MEC shed or concentration in milk. Alveolar area was reduced 25% by HS, and HS had 4.1 more alveoli than PFTN. Total number of nucleated MEC per area were greater in HS (389 ± 1.05) compared with PFTN (321 ± 1.05); however, cell number per alveolus was similar between groups (25 ± 1.5 vs. 26 ± 1.4). There were no differences in relative fold expression for GLUT1, GLUT8, CSN2, CSN3, LALBA, FASN, HSPA5, and HSPA8 in HS compared with PFTN. Immunoblotting analyses showed a decrease abundance for phosphorylated STAT5 and S6K1, and an increase in LC3 II in HS compared with PFTN. These results suggest that even if milk yield differences and histological changes occur in the bovine mammary gland after 4 d of heat exposure, MEC loss into milk, nucleated MEC number per alveolus, and gene expression of nutrient transport, milk component synthesis, and heat stress related targets are unaffected. In contrast, the abundance of proteins related to protein synthesis and cell survival decreased significantly, while an upregulation of proteins associated with autophagy in HS compared with PFTN.

Supplementation of dietary semen vaccariae extracts to lactating sow diets: effects on the production performance, milk components, and gene expression related to mammogenesis

This study aimed to investigate the effects of dietary semen vaccariae extracts (SVE) on the production performance, colostrum components, and relative gene expression related to mammogenesis of lactating sows. 48 pregnant sows were selected and randomly allocated into four groups, with six replicates and two sows per replicate. The first group was the control (CON), while the other groups received the same diet further supplemented with 1.5, 3.0 and 4.5 g SVE per kg (SV1, SV2 and SV3, respectively). Compared with the control group, (1) the average daily gain was increased (p < 0.05) in SV1, SV2, and SV3 during the 11-21 days and 1-21 days of lactation; (2) the serum insulin-like growth factor-1, insulin, prolactin, and estrogen contents in SV1, SV2, and SV3 were increased (p < 0.05) on the 1st and 21st day of lactation; (3) The plasma Lysine, Threonine, and Tryptophan concentrations were also higher (p < 0.05) in SV1, SV2, and SV3 on the 1st and 21st day of lactation; (4) The milk Lysine, Methionine, Threonine, and Tryptophan concentrations were higher (p < 0.05) in SV1, SV2, and SV3 on the 1st and 21st day of lactation; (5) The milk lactose ratio and milk protein content were increased (p < 0.05) in the groups treated with semen vaccariae on the 1st day of lactation, while the milkfat ratio and milk protein content were increased (p < 0.05) in SV2 and SV3 on the 21st day of lactation; (6) the immunoglobulin M, A, and G contents were increased (p < 0.05) in the groups treated with the semen vaccariae on the first day of lactation; and (7) the relative PRLR, STAT5a, FcRn, CSN2, and LALBA expressions were higher (p < 0.05) in the groups treated with the semen vaccariae on the 1st and 21st day of lactation. In this study, the optimum dosage was 3.0 g/kg semen vaccariae, which increased the average daily gain of piglets, total lactation yield, and serum hormone levels, improved the amino acid levels in plasma, and facilitated the milk quality, up-regulated the relative gene expressions in the mammogenesis.

Potential effects of gingerol topical application on components of the innate immunity in lactating goat mammary glands

In the mammary glands, production of antimicrobial components and formation of less-permeable tight junctions (TJs) are important for safe milk production. Previously, we reported that local heat treatment of udders using disposable heating pad enhances the components of innate immunity in lactating goat mammary glands. Gingerol is a polyphenol present in ginger that can induce heat-like effects. However, oral administration of polyphenols causes a decrease in biological activity through conjugation and metabolic conversion. Here, we investigated the effects of gingerol on antimicrobial components and TJs by topically applying it to lactating goat udders. Gingerol application increased the somatic cell count, cathelicidin-2 concentration, and proportion of polymorphonuclear cells in the milk and interleukin-8 production. Moreover, gingerol treatment enhanced β-defensin-1 production in milk, cultured mammary epithelial cells, and cultured somatic cells. Contrastingly, gingerol treatment did not affect the concentrations of blood-derived components (Na+, albumin, and IgG) in the milk or the TJ barrier function of cultured mammary epithelial cells. These findings suggest that the topical application of gingerol, similar to local heat treatment, to udders enhances the components of innate immunity in mammary glands. These findings may be useful for the prevention of mastitis in milk-producing animals and, hence, safe and stable dairy production.

Culture Models to Investigate Mechanisms of Milk Production and Blood-Milk Barrier in Mammary Epithelial Cells: a Review and a Protocol

Mammary epithelial cells (MECs) are the only cell type that produces milk during lactation. MECs also form less-permeable tight junctions (TJs) to prevent the leakage of milk and blood components through the paracellular pathway (blood-milk barrier). Multiple factors that include hormones, cytokines, nutrition, and temperature regulate milk production and TJ formation in MECs. Multiple intracellular signaling pathways that positively and negatively regulate milk production and TJ formation have been reported. However, their regulatory mechanisms have not been fully elucidated. In addition, unidentified components that regulate milk production in MECs likely exist in foods, for example plants. Culture models of functional MECs that recapitulate milk production and TJs are useful tools for their study. Such models enable the elimination of indirect effects via cells other than MECs and allows for more detailed experimental conditions. However, culture models of MECs with inappropriate functionality may result in unphysiological reactions that never occur in lactating mammary glands in vivo. Here, I briefly review the physiological functions of alveolar MECs during lactation in vivo and culture models of MECs that feature milk production and less-permeable TJs, together with a protocol for establishment of MEC culture with functional TJ barrier and milk production capability using cell culture inserts.

Sweet taste receptor subunit T1R3 regulates casein secretion and phosphorylation of STAT5 in mammary epithelial cells

During lactation, mammary epithelial cells (MECs) on the apical membrane are in contact with lactose in milk, while MECs on the basolateral membrane are in contact with glucose in blood. Both glucose and lactose are sweeteners that are sensed by a sweet taste receptor. Previously, we have shown that lactose exposure on the basolateral membrane, but not the apical membrane, inhibits casein production and phosphorylation of STAT5 in MECs. However, it remains unclear whether MECs have a sweet taste receptor. In this study, we confirmed that the sweet taste receptor subunit T1R3 existed in both the apical and basolateral membranes of MECs. Subsequently, we investigated the influence of apical and basolateral sucralose as a ligand for the sweet taste receptor using a cell culture model. In this model, upper and lower media were separated by the MEC layer with less-permeable tight junctions. The results showed in the absence of glucose, both apical and basolateral sucralose induced phosphorylation of STAT5, which is a positive transcriptional factor for milk production. In contrast, the T1R3 inhibitor basolateral lactisole reducing phosphorylated STAT5 and secreted caseins in the presence of glucose. Furthermore, exposure of the apical membrane to sucralose in the presence of glucose inhibited the phosphorylation of STAT5. Simultaneously, GLUT1 was partially translocated from the basolateral membrane to the cytoplasm in MECs. These results suggest that T1R3 functions as a sweet receptor and is closely involved in casein production in MECs.

Modulation of Milk and Lipid Synthesis and Secretion in a3-Dimensional Mouse Mammary Epithelial Cell Culture Model: Effects of Palmitate and Orlistat

Human milk synthesis is impacted by maternal diet, serum composition, and substrate uptake and synthesis by mammary epithelial cells (MECs). The milk of obese/high-fat-diet women has an increased fat content, which promote excess infant weight gain and the risk of childhood/adult obesity. Yet, the knowledge of milk synthesis regulation is limited, and there are no established approaches to modulate human milk composition. We established a 3-dimensional mouse MEC primary culture that recreates the milk production pathway and tested the effects of the major saturated fatty acid in human milk (palmitate) and a lipoprotein lipase inhibitor (orlistat) on triglyceride production. Positive immunostaining confirmed the presence of milk protein and intracellular lipid including milk globules in the cytoplasm and extracellular space. The treatment with palmitate activated "milk" production by MECs (β-casein) and the lipid pathway (as evident by increased protein and mRNA expression). Consistent with these cellular changes, there was increased secretion of milk protein and triglyceride in MEC "milk". The treatment with orlistat suppressed milk triglyceride production. Palmitate increased milk and lipid synthesis, partly via lipoprotein lipase activation. These findings demonstrate the ability to examine MEC pathways of milk production via both protein and mRNA and to modulate select pathways regulating milk composition in MEC culture.

How do high ambient temperatures affect infant feeding practices? A prospective cohort study of postpartum women in Bobo-Dioulasso, Burkina Faso

OBJECTIVE

To examine the effects of high ambient temperature on infant feeding practices and childcare.

DESIGN

Secondary analysis of quantitative data from a prospective cohort study.

SETTING

Community-based interviews in the commune of Bobo-Dioulasso, Burkina Faso. Exclusive breastfeeding is not widely practised in Burkina Faso.

PARTICIPANTS

866 women (1:1 urban:rural) were interviewed over 12 months. Participants were interviewed at three time points: cohort entry (when between 20 weeks' gestation and 22 weeks' postpartum), three and nine months thereafter. Retention at nine-month follow-up was 90%. Our secondary analysis focused on postpartum women (n=857).

EXPOSURE

Daily mean temperature (°C) measured at one weather station in Bobo-Dioulasso. Meteorological data were obtained from publicly available archives (TuTiempo.net).

PRIMARY OUTCOME MEASURES

Self-reported time spent breastfeeding (minutes/day), exclusive breastfeeding of infants under 6 months (no fluids other than breast milk provided in past 24 hours), supplementary feeding of infants aged 6-12 months (any fluid other than breast milk provided in past 24 hours), time spent caring for children (minutes/day).

RESULTS

The population experienced year-round high temperatures (daily mean temperature range=22.6°C-33.7°C). Breastfeeding decreased by 2.3 minutes/day (95% CI -4.6 to 0.04, p=0.05), and childcare increased by 0.6 minutes/day (0.06 to 1.2, p=0.03), per 1°C increase in same-day mean temperature. Temperature interacted with infant age to affect breastfeeding duration (p=0.02), with a stronger (negative) association between temperature and breastfeeding as infants aged (0-57 weeks). Odds of exclusive breastfeeding very young infants (0-3 months) tended to decrease as temperature increased (OR=0.88, 0.75 to 1.02, p=0.09). There was no association between temperature and exclusive breastfeeding at 3-6 months or supplementary feeding (6-12 months).

CONCLUSIONS

Women spent considerably less time breastfeeding (~25 minutes/day) during the hottest, compared with coolest, times of the year. Climate change adaptation plans for health should include advice to breastfeeding mothers during periods of high temperature.

Lactose on the basolateral side of mammary epithelial cells inhibits milk production concomitantly with signal transducer and activator of transcription 5 inactivation

Mammary epithelial cells (MECs) are the only cells capable of synthesizing lactose. During lactation, alveolar MECs secrete lactose through the apical membrane into the alveolar lumen, whereas alveolar tight junctions (TJs) block the leakage of lactose into the basolateral sides of the MECs. However, lactose leaks from the alveolar lumen into the blood plasma in the mastitis and after weaning. This exposes the basolateral membrane of MECs to lactose. The relationship between lactose in blood plasma and milk production has been suggested. The present study determined whether lactose exposure on the basolateral membrane of mouse MECs adversely affects milk production in vitro. Restricted exposure to lactose on the basolateral side of the MECs was performed using a culture model, in which MECs on the cell culture insert exhibit milk production and less-permeable TJs. The results indicated that lactose exposure on the basolateral side inhibited casein and lipid production in the MECs. Interestingly, lactose exposure on the apical side did not show detectable effects on milk production in the MECs. Basolateral lactose exposure also caused the inactivation of STAT5, a primary transcriptional factor for milk production. Furthermore, p38 and JNK were activated by basolateral lactose exposure. The activation of p38 and JNK following anisomycin treatment reduced phosphorylated STAT5, and inhibitors of p38 blocked the reduction of phosphorylated STAT5 by basolateral lactose exposure. These findings suggest that lactose functions as a partial inhibitor for milk production but only when it directly makes contact with the basolateral membrane of MECs.

How Climate Change May Threaten Progress in Neonatal Health in the African Region

Climate change is likely to have wide-ranging impacts on maternal and neonatal health in Africa. Populations in low-resource settings already experience adverse impacts from weather extremes, a high burden of disease from environmental exposures, and limited access to high-quality clinical care. Climate change is already increasing local temperatures. Neonates are at high risk of heat stress and dehydration due to their unique metabolism, physiology, growth, and developmental characteristics. Infants in low-income settings may have little protection against extreme heat due to housing design and limited access to affordable space cooling. Climate change may increase risks to neonatal health from weather disasters, decreasing food security, and facilitating infectious disease transmission. Effective interventions to reduce risks from the heat include health education on heat risks for mothers, caregivers, and clinicians; nature-based solutions to reduce urban heat islands; space cooling in health facilities; and equitable improvements in housing quality and food systems. Reductions in greenhouse gas emissions are essential to reduce the long-term impacts of climate change that will further undermine global health strategies to reduce neonatal mortality.

Local Heat Treatment of Goat Udders Influences Innate Immune Functions in Mammary Glands

Heat stress and mastitis adversely affect milk production in dairy ruminants. Although the udder temperature is elevated in both conditions, the influence of this local temperature rise on milk production and immune function of ruminant mammary glands remains unclear. To address this question, we heated the mammary glands of goats by covering one half of the udder with a disposable heating pad for 24 h, the other uncovered half served as a control. Sixteen Tokara goats (1-5 parity) and three Shiba goats (1-2 parity) at the mid-lactation stage were individually housed, fed 0.6 kg of hay cubes and 0.2 kg of barley per day, and had free access to water and trace-mineralized salt blocks. Milk samples were collected every 6 h for 24 h after covering (n = 16), and deep mammary gland tissue areas were collected after 24 h (n = 5). The concentrations of antimicrobial components [lactoferrin, β-defensin-1, cathelicidin-2, cathelicidin-7, and immunoglobulin A (IgA)] in milk were measured by the enzyme-linked immunosorbent assay (ELISA). The localization of IgA was examined by immunohistochemistry. The mRNA expression and protein concentrations of C-C motif chemokine ligand-28 (CCL-28) and interleukin (IL)-8 in the mammary gland tissue were measured using quantitative polymerase chain reaction and ELISA, respectively. The somatic cell count in milk was significantly higher in the local heat-treatment group than in the control group after 12 h of treatment. The treatment group had significantly higher concentrations of cathelicidin-2 and IgA than the control group after 24 h of treatment. In addition, the number of IgA-positive cells in the mammary stromal region and the concentration of CCL-28 in the mammary glands were increased by local heat treatment. In conclusion, a local rise in udder temperature enhanced the innate immune function in mammary glands by increasing antimicrobial components.

Phospho-Tudor-SN coordinates with STAT5 to regulate prolactin-stimulated milk protein synthesis and proliferation of bovine mammary epithelial cells

Tudor staphylococcal nuclease (Tudor-SN) participates in milk synthesis and cell proliferation in response to prolactin (PRL) and plays a regulatory role on mTOR phosphorylation. However, the complicated molecular mechanism of Tudor-SN regulating milk protein synthesis and cell proliferation still remains to be illustrated. In present study, we observed that the proteins level of phosphorylated Tudor-SN and phosphorylated STAT5 were simultaneously enhanced upon PRL treatment in bovine mammary epithelial cells (BMECs). Tudor-SN overexpression and knockdown experiment showed that Tudor-SN positively regulated the synthesis of milk protein, cell proliferation and the phosphorylation of STAT5, which was dependent on Tudor-SN phosphorylation. STAT5 knockdown experiment showed that Tudor-SN stimulated mTOR pathway through regulating STAT5 activation, which was required for PRL to activate the mTOR pathway. Thus, these results demonstrate the primary mechanism of Tudor-SN coordinating with STAT5 to regulate milk protein synthesis and cell proliferation under stimulation of PRL in BMECs, which may provide some new perspectives for increasing milk production.

Suppressive effects of curcumin on milk production without inflammatory responses in lactating mammary epithelial cells

BACKGROUND

Curcumin is a naturally occurring polyphenol found in Curcuma longa with multiple therapeutic properties, such as anti-inflammatory, wound healing and anti-cancer effects. Curcuma longa is also used as a galactagogue to improve milk production during lactation.

PURPOSE

To assess curcumin could have therapeutic potential for breastfeeding mothers, we investigated whether and how curcumin influences milk production in lactating mammary epithelial cells (MECs) at the cellular and molecular levels.

METHODS

We prepared a lactating MEC culture model that produced milk components and formed less-permeable tight junctions (TJs) to investigate the molecular mechanism of curcumin on milk production, TJs, and inflammation in vitro.

RESULTS

Curcumin downregulated milk production in lactation MECs concurrently with inactivation of lactogenesis-relating signaling (STAT5 and glucocorticoid receptor). The maintenance of a less-permeable TJ barrier was also confirmed, although the TJ protein claudin-4 increased. Curcumin inactivated NFκB and STAT3 signaling, which are closely involved in inflammatory responses in weaning and mastitis mammary glands. The expression levels of IL-1β and TNF-α were also decreased by curcumin treatment. Furthermore, curcumin blocked activation of inflammatory signaling by lipopolysaccharide treatment in MECs, similar to those in MECs that were treated with diclofenac sodium. The drastic phosphorylation of ERK was induced by curcumin treatment in the absence of EGF. U0126, an inhibitor of ERK phosphorylation, attenuated the adverse effects of curcumin on lactating MECs.

CONCLUSION

The results of the present study suggests that curcumin downregulates milk production via inactivation of STAT5 and GR signaling with concurrent suppression of inflammatory responses via STAT3 and NFκB signaling in MECs. These findings provide new insights into the role of curcumin as a mild suppressor of milk production without inflammatory damages in breastfeeding mothers.

Effect of incubation temperature on lactogenic function of goat milk-derived mammary epithelial cells

In general, goat mammary epithelial cells (MECs) are cultured in vitro under 37 °C. We demonstrated previously that goat MECs differentiate under 37 °C although their body temperature is approximately 39 °C. This study aimed to investigate the influence of 39 °C on lactogenic differentiation of goat milk-derived MECs. The results revealed that HSP70 gene was significantly elevated at 1 h after an exposure to 39 °C but declined at 48 h thereafter. Oxidative stress status was not significantly affected by 39 °C. Expressions of CSN2, β-GALT1, α-LA, and Akt genes tended to increase after the differentiation under 39 °C. Secretion of lactose under 39 °C was not significantly lower than 37 °C. In conclusion, incubation temperature at 39 °C does not dramatically affect lactogenic function of goat milk-derived MECs.

Menthol from Mentha piperita Suppresses the Milk Production of Lactating Mammary Epithelial Cells In Vivo and In Vitro

SCOPE

Peppermint is traditionally used as an antigalactagogue in breastfeeding women. However, the suppressive mechanism remains unclear. The authors investigate whether and how peppermint influences milk production at the cellular and molecular levels.

METHODS AND RESULTS

A lactating mammary epithelial cell (MEC) culture model that produces major milk components is prepared. Peppermint oil (PMO) suppresses β-casein production in conjunction with the induced enlargement of cytoplasmic lipid droplets (CLDs). PMO also significantly inactivates STAT5 and mTOR in the lactogenic signaling pathway. Menthol treatment, which is a primary PMO component, leads to decreases in β-casein production, enlarged CLDs, the inactivated STAT5 and mTOR. Eucalyptol and menthyl acetate, other components of peppermint, does not show suppressive effects on lactating MECs. The inactivation of STAT5 and mTOR upon menthol administration is also evident in alveolar MECs of lactating mice. Furthermore, lactating MECs expresses TRPM8 and TRPA1, which are menthol receptors known as cold receptors. Agonists of TRPM8 and TRPA1 suppresses β-casein production and inactivation of STAT5 and mTOR in the lactating MECs.

CONCLUSION

These findings indicate that peppermint has potential as an antigalactagogue. Menthol is suggested to be an active compound in peppermint. TRPM8 and TRPA1 may function as receptors for menthol.

Distinct Expression Patterns of Fibrillar Collagen Types I, III, and V in Association with Mammary Gland Remodeling during Pregnancy, Lactation and Weaning

The mammary gland structurally and functionally remodels during pregnancy, during lactation and after weaning. There are three types of fibrillar collagens, types I, III, and V, in mammary stromal tissue. While the importance of the fibrillar structure of collagens for mammary morphogenesis has been suggested, the expression patterns of each type of fibrillar collagen in conjunction with mammary remodeling remain unclear. In this study, we investigated their expression patterns during pregnancy, parturition, lactation and involution. Type I collagen showed a well-developed fibril structure during pregnancy, but the fibrillar structure of type I collagen then became sparse at parturition and during lactation, which was concurrent with the downregulation of its mRNA and protein levels. The well-developed fibrillar structure of type I collagen reappeared after weaning. On the other hand, type V collagen showed a well-developed fibrillar structure and upregulation in the lactation period but not in the periods of pregnancy and involution. Type III collagen transiently developed a dense fibrillar network at the time of parturition and exhibited drastic increases in mRNA expression. These results indicate that each type of fibrillar collagen is distinctly involved in structural and functional remodeling in mammary glands during pregnancy, parturition, lactation, and involution after weaning. Furthermore, in vitro studies of mammary epithelial cells showed regulatory effects of type I collagen on cell adhesion, cell proliferation, ductal branching, and β-casein secretion. Each type of fibrillar collagen may have different roles in defining the cellular microenvironment in conjunction with structural and functional mammary gland remodeling.

TRPV4 Increases the Expression of Tight Junction Protein-Encoding Genes via XBP1 in Mammary Epithelial Cells

Simple Summary

Mammary glands are exocrine tissue, capable of secreting adequate amounts of milk protein during lactation. Each mammary gland is occupied by numerous alveoli. Each alveolus is composed of a single layer of mammary epithelial cells, adipose tissue, and ducts. Recent studies indicate that mild heat treatment of mammary epithelial cells at 39 °C has activated milk production. These results suggest that temperature may influence the physiological functions of mammary epithelial cells. In this study, we found that the temperature-sensitive transient receptor potential vanilloid 4 (TRPV4) was involved in the increase of β-casein and TJ protein-encoding gene expression in response to mild heat treatment. On the other hand, severe heat treatment (41 °C) reduced the cell viability. Moreover, the Trpv4 mRNA level was significantly increased at Day 15 of gestation when the mammary alveoli are formed. TRPV4 is activated not only by temperature but also by mechanical forces that guide mammary epithelial development in the normal mammary gland. Our data suggest that TRPV4 has a possible function in mammary gland development.

Abstract

Mild heat stress (39 °C–40 °C) can positively regulate cell proliferation and differentiation. Indeed, mild heat treatment at 39 °C enhances the less-permeable tight junctions (TJs) formation and milk production in mammary epithelial cells. However, the molecular mechanisms of this response have not yet been delineated. In this study, the involvement of temperature-sensitive transient receptor potential vanilloid 4 (TRPV4) in the increase of β-casein and TJ protein-encoding gene expression in response to mild heat treatment (39 °C) has been explored using HCll mouse mammary epithelial cells. Severe heat treatment (41 °C) induced the transcriptional level of Chop (C/EBP homologous protein; proapoptotic marker) and reduced the cell viability. It is speculated that the difference in unfolded protein response (UPR) gene expression upon stimulation at 39 °C vs. 41 °C controls cell survival vs. cell death. The accumulation of Trpv4 mRNA was significantly higher in 39 °C heat treatment cells. The β-casein, Zo-1 (zona occludens-1), Ocln (occludin), and Cldn3 (claudin 3) transcript levels were significantly increased in response to the addition of a selective TRPV4 channel agonist (GSK1016790A) at 37 °C. TRPV4 stimulation with GSK1016790A also increased the X-box-binding protein 1 splicing form (Xbp1s) at the transcript level. The increase in the mRNA levels of β-casein, Zo-1, Ocln, and Cldn3 in response to 39 °C heat treatment was suppressed by XBP1 knockdown. Moreover, the transcript level of Trpv4 was significantly increased at Day 15 of gestation, and its expression declined after 1 day of lactation. TRPV4 is activated not only by temperature but also by mechanical forces, such as cell stretching and shear stress, which guide mammary epithelial development in a normal mammary gland. These findings provide new insights of the possible function of TRPV4 in mammary gland development.

Adverse Effects of Coumestrol and Genistein on Mammary Morphogenesis and Future Milk Production Ability of Mammary Epithelial Cells

Isoflavones are a class of flavonoids present in legumes and are called phytoestrogens because of their estrogen-like activity. Endogenous estrogen is well known to regulate mammary gland morphogenesis during pregnancy. Each isoflavone also has different physiological activities. However, it is difficult to investigate the direct effect of each isoflavone in mammary morphogenesis in vivo because isoflavones are metabolized into different isoflavones by enteric bacteria. In this study, investigated are the direct influences of coumestrol, daidzein, and genistein on mammary structure development and future milk production ability of mammary epithelial cells (MECs) using in vitro culture models. Mouse MECs are cultured in Matrigel with basic fibroblast growth factor and epidermal growth factor to induce ductal branching and alveolar formation, respectively. Coumestrol and genistein inhibit ductal branching and alveolar formation by affecting the proliferation and migration of MECs with the induction of apoptosis. Daidzein hardly influences mammary structure development. Furthermore, pretreatment with coumestrol adversely affects the induction of milk production ability of MECs. These results suggest that each isoflavone differentially influences mammary morphogenesis and future milk production by affecting MEC behaviors. These results also suggest that the culture models are effective to study mammary epithelial morphogenesis in vitro.

Distinct expression patterns of aquaporin 3 and 5 in ductal and alveolar epithelial cells in mouse mammary glands before and after parturition

Milk osmolarity maintains an isotonic status for suckling infants during lactation. However, it remains unclear how the water content in milk is regulated in lactating mammary glands. In lactating mammary alveoli and ducts, mammary epithelial cells (MECs) are in direct contact with milk. In this study, we focus on two types of water channels, aquaporin 3 (AQP3) and AQP5, in alveolar and ductal MECs before and after parturition. AQP3 showed diffuse localization in the cytoplasm of ductal MECs but concentrated localization in the basolateral membrane of alveolar MECs during the late pregnancy and lactation periods. Translocation of AQP5 from the cytoplasm toward the apical membrane occurred in ductal MECs immediately before parturition. Subsequently, we examined the hormonal influences on the expression of AQP3 and AQP5 in cultured MECs in vitro. Progesterone and estrogen distinctly increased AQP3 and AQP5 in cultured MECs, respectively. Cotreatment with prolactin and dexamethasone significantly decreased both AQP3 and AQP5. Prolactin also facilitated the translocation of AQP5 into the apical membrane of MECs. In cultured MECs, AQP3 was homogeneously expressed in MECs, whereas AQP5 showed different expression levels between MECs regardless of the hormonal treatment. Different activation states of the prolactin/STAT5 pathway were also observed between ductal and alveolar MECs. These findings suggest that the expression pattern of AQP3 and AQP5 is distinctly regulated by lactogenic hormones in alveolar and ductal MECs before and after parturition. AQP5 expressed in ductal MECs may function as a water channel to regulate milk osmolarity in mice.

Nicotine directly affects milk production in lactating mammary epithelial cells concurrently with inactivation of STAT5 and glucocorticoid receptor in vitro

Nicotine from tobacco smoke is absorbed into the bloodstream and transferred into breast milk in breastfeeding mothers. Smoking causes a decrease in breast milk volume, adverse changes to the milk composition, and a shortened lactation period. Breast milk is produced by mammary epithelial cells (MECs) in mammary glands during lactation. However, it remains unclear whether nicotine directly affects milk production in lactating MECs. To address this issue, we prepared a culture model with high milk production ability and less-permeable tight junctions (TJs) by seeding mouse MECs on a cell culture insert. Lactating MECs showed expression of α2, α3, β2, and β4 of nicotinic acetylcholine receptors. The high concentration of nicotine at 10-100 μM inhibited β-casein secretion and caused abnormal localization of TJ proteins. We subsequently investigated whether nicotine at a physiological concentration could affect lactating MECs. Nicotine at 1.0 μM directly inhibited α- and β-casein secretion in lactating MECs concurrently with inactivation of STAT5 and glucocorticoid receptor without affecting the TJ barrier. Nicotine treatment also induced MEC apoptosis concurrently with inactivation of Akt. These results support the adverse effects of nicotine on breastfeeding in smoking mothers.

Mild heat stress induces transcription of the β-casein gene via unfolded protein response-activated XBP1 signaling in undifferentiated mammary epithelial cells

It has been reported that the expression of β-casein, a representative milk protein, increases when mammary epithelial cells are exposed to mild heat stress at 39°C. However, the direct effects and detailed molecular mechanisms have not yet been elucidated. In this study, we investigated the relationship between an increase in β-casein expression and the unfolded protein response (UPR) under mild heat stress. After reaching confluence, HC11 cells were incubated at 37°C (control) or 39°C (mild heat stress) without differentiation medium, and the expression levels of β-casein and UPR-related genes were assessed. It was revealed that, even with this mild heat treatment (39°C), β-casein expression in HC11 cells increased at the transcriptional level without differentiation induction. The expression levels of X-box binding protein 1 (XBP1) and activating transcription factor 6 alpha (ATF6α) were significantly higher in cells cultured at 39°C compared to those cultured at 37°C. Moreover, the increase in β-casein mRNA expression levels by mild heat treatment was suppressed in XBP1 or ATF6α knockdown cells generated by siRNA for XBP1 or ATF6α respectively. Thus, these results demonstrate that ATF6α and XBP1 is involved in the increase of β-casein expression following mild heat treatment.