Expression of constitutively activated Akt in the mammary gland leads to excess lipid synthesis during pregnancy and lactation

AKT and EZH2 inhibitors kill TNBCs by hijacking mechanisms of involution

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype and has the highest rate of recurrence1. The predominant standard of care for advanced TNBC is systemic chemotherapy with or without immunotherapy; however, responses are typically short lived1,2. Thus, there is an urgent need to develop more effective treatments. Components of the PI3K pathway represent plausible therapeutic targets; more than 70% of TNBCs have alterations in PIK3CA, AKT1 or PTEN3-6. However, in contrast to hormone-receptor-positive tumours, it is still unclear whether or how triple-negative disease will respond to PI3K pathway inhibitors7. Here we describe a promising AKT-inhibitor-based therapeutic combination for TNBC. Specifically, we show that AKT inhibitors synergize with agents that suppress the histone methyltransferase EZH2 and promote robust tumour regression in multiple TNBC models in vivo. AKT and EZH2 inhibitors exert these effects by first cooperatively driving basal-like TNBC cells into a more differentiated, luminal-like state, which cannot be effectively induced by either agent alone. Once TNBCs are differentiated, these agents kill them by hijacking signals that normally drive mammary gland involution. Using a machine learning approach, we developed a classifier that can be used to predict sensitivity. Together, these findings identify a promising therapeutic strategy for this highly aggressive tumour type and illustrate how deregulated epigenetic enzymes can insulate tumours from oncogenic vulnerabilities. These studies also reveal how developmental tissue-specific cell death pathways may be co-opted for therapeutic benefit.

Akt1 is involved in HCV release by promoting endoplasmic reticulum-to-endosome transition of infectious virions

AIMS

Hepatitis C virus (HCV) relies on the viral and host factors to complete its life cycle. It has evolved to profit from Akt activation at some stage in its life cycle through various mechanisms, notably by activating lipogenesis, which is crucial for infectious virions production.

MATERIALS AND METHODS

By employing an Akt-specific inhibitor, the impact of Akt on intracellular and extracellular infectivity was investigated. To ascertain the role of Akt in the HCV life cycle, the two-part cell culture-derived HCV infection protocol utilizing Akt1 small interfering RNAs (siRNAs) was implemented. The impact of Akt1 on intracellular HCV transition was determined using membrane flotation assay and proximity ligation assay coupled with Anti-Rab7 immunoprecipitation and immunofluorescence.

KEY FINDINGS

Akt1 silencing reduced infectious virions release to a degree comparable to that of ApoE, a host component involved in the HCV assembly and release, suggesting Akt1 was critical in the late stage of the HCV life cycle. Extracellular infectivity of HCV was inhibited by brefeldin A, and the inhibitory effect was augmented by Akt1 silencing and partially restored by ectopic Akt1 expression. Immunofluorescence revealed that Akt1 inhibition suppressed the interaction between HCV core protein and lipid droplet. Akt1 silencing impeded the transition of HCV from the endoplasmic reticulum to the endosome and hence inhibited the secretion of HCV infectious virions from the late endosome.

SIGNIFICANCE

Our study demonstrates that Akt1 has an impact on the lipogenesis pathway and plays a critical role in the assembly and secretion of infectious HCV.

Effects of Boron on Fat Synthesis in Porcine Mammary Epithelial Cells

This study aimed to investigate the effect of boron on porcine mammary epithelial cells (PMECs) survival, cell cycle, and milk fat synthesis. PMECs from boron-treated groups were exposed to 0-80 mmol/L boric acid concentrations. Cell counting kit-8 and flow cytometry assays were performed to assess cell survival and the cell cycle, respectively. Triacylglycerol (TAG) levels in PMECs and culture medium were determined by a triacylglycerol kit while PMECs lipid droplet aggregation was investigated via oil red staining. Milk fat synthesis-associated mRNA levels were determined by quantitative real-time polymerase chain reaction (qPCR) while its protein expressions were determined by Western blot. Low (0.2, 0.3, 0.4 mmol/L) and high (> 10 mmol/L) boron concentrations significantly promoted and inhibited cell viabilities, respectively. Boron (0.3 mmol/L) markedly elevated the abundance of G2/M phase cells. Ten mmol/L boron significantly increased the abundances of G0/G1 and S phase cells, but markedly suppressed G2/M phase cell abundance. At 0.3 mmol/L, boron significantly enhanced ERK phosphorylation while at 0.4, 0.8, 1, and 10 mmol/L, it markedly decreased lipid droplet diameters. Boron (10 mmol/L) significantly suppressed ACACA and SREBP1 protein expressions. The FASN protein levels were markedly suppressed by 0.4, 0.8, 1, and 10 mmol/L boron. Both 1 and 10 mmol/L markedly decreased FASN and SREBP1 mRNA expressions. Ten mmol/L boron significantly decreased PPARα mRNA levels. Low concentrations of boron promoted cell viability, while high concentrations inhibited PMECS viabilities and reduced lipid droplet diameters, which shows the implications of boron in pregnancy and lactation.

Parental factors that impact the ecology of human mammary development, milk secretion, and milk composition-a report from "Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN)" Working Group 1

The goal of Working Group 1 in the Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN) Project was to outline factors influencing biological processes governing human milk secretion and to evaluate our current knowledge of these processes. Many factors regulate mammary gland development in utero, during puberty, in pregnancy, through secretory activation, and at weaning. These factors include breast anatomy, breast vasculature, diet, and the lactating parent's hormonal milieu including estrogen, progesterone, placental lactogen, cortisol, prolactin, and growth hormone. We examine the effects of time of day and postpartum interval on milk secretion, along with the role and mechanisms of lactating parent-infant interactions on milk secretion and bonding, with particular attention to the actions of oxytocin on the mammary gland and the pleasure systems in the brain. We then consider the potential effects of clinical conditions including infection, pre-eclampsia, preterm birth, cardiovascular health, inflammatory states, mastitis, and particularly, gestational diabetes and obesity. Although we know a great deal about the transporter systems by which zinc and calcium pass from the blood stream into milk, the interactions and cellular localization of transporters that carry substrates such as glucose, amino acids, copper, and the many other trace metals present in human milk across plasma and intracellular membranes require more research. We pose the question of how cultured mammary alveolar cells and animal models can help answer lingering questions about the mechanisms and regulation of human milk secretion. We raise questions about the role of the lactating parent and the infant microbiome and the immune system during breast development, secretion of immune molecules into milk, and protection of the breast from pathogens. Finally, we consider the effect of medications, recreational and illicit drugs, pesticides, and endocrine-disrupting chemicals on milk secretion and composition, emphasizing that this area needs much more research attention.

New insights into the effect of bisphenol AF exposure on maternal mammary glands at various stages of gestation in mice

Bisphenol AF (BPAF) is the most estrogenic compound among BPA analogs. Mammary glands (MDs) are special organs that undergo repeated cycles of structural development, metabolism, and functional differentiation. Gestation is a sensitive window for MDs. In the present study, plug-positive CD-1 mice were exposed to vehicle (Veh) or 300 μg/kg BPAF through oral gavage every second day during gestation, and maternal MDs were collected from different developmental windows at 9.5, 13.5, and 18.5 d of gestation (gestation day [GD]9.5, GD13.5 and GD18.5). The results showed that gestational BPAF exposure induced a significantly elevated MD density at GD18.5. Non-target metabolomics analysis was used to screen for tyrosine, valine, ornithine, proline, threonine, phenylalanine and asymmetrical dimethylarginine (ADMA) amino acids, which changed significantly at all time points. Furthermore, the mRNA expression levels of genes related to these amino acids also changed significantly. Additionally, amino acid levels in BPAF-treated MGs at GD18.5 were related to the serum ammonia concentration of the corresponding offspring. These results provide a comprehensive view of the adverse effects of BPAF exposure during gestation on the maternal MG structure and function, which may affect milk components during lactation. Moreover, higher amino acids content may lead to amino acid imbalance or hyperammonemia in newborns.

The adaptation of maternal energy metabolism to lactation and its underlying mechanisms

Maternal energy metabolism undergoes a singular adaptation during lactation that allows for the caloric enrichment of milk. Changes in the mammary gland, changes in the white adipose tissue, brown adipose tissue, liver, skeletal muscles and endocrine pancreas are pivotal for this adaptation. The present review details the landmark studies describing the enzymatic modulation and the endocrine signals behind these metabolic changes. We will also update this perspective with data from recent studies showing transcriptional and post-transcriptional mechanisms that mediate the adaptation of the maternal metabolism to lactation. The present text will also bring experimental and observational data that describe the long-term consequences that short periods of lactation impose to maternal metabolism.

The role of protein kinases as key drivers of metabolic dysfunction-associated fatty liver disease progression: New insights and future directions

Metabolic dysfunction-associated fatty liver disease (MAFLD), proposed in 2020 is a novel term for non-alcoholic fatty liver disease (NAFLD) which was coined for the first time in 1980. It is a leading cause of the most chronic liver disease and hepatic failure all over the world, and unfortunately, with no licensed drugs for treatment yet. The progress of the disease is driven by the triggered inflammatory process, oxidative stress, and insulin resistance in many pathways, starting with simple hepatic steatosis to non-alcoholic steatohepatitis, fibrosis, cirrhosis, and liver cancer. Protein kinases (PKs), such as MAPK, ErbB, PKC, PI3K/Akt, and mTOR, govern most of the pathological pathways by acting on various downstream key points in MAFLD and regulating both hepatic gluco- lipo-neogenesis and inflammation. Therefore, modulating the function of those potential protein kinases that are effectively involved in MAFLD might be a promising therapeutic approach for tackling this disease. In the current review, we have discussed the key role of protein kinases in the pathogenesis of MAFLD and performed a protein-protein interaction (PPI) network among the main proteins of each kinase pathway with MAFLD-related proteins to predict the most likely targets of the PKs in MAFLD. Moreover, we have reported the experimental, pre-clinical, and clinical data for the most recent investigated molecules that are activating p38-MAPK and AMPK proteins and inhibiting the other PKs to improve MAFLD condition by regulating oxidation and inflammation signalling.

Maternal exposure to polystyrene nanoplastics causes brain abnormalities in progeny

As global plastic production continues to grow, microplastics released from a massive quantity of plastic wastes have become a critical environmental concern. These microplastic particles are found in a wide range of living organisms in a diverse array of ecosystems. In this study, we investigated the biological effects of polystyrene nanoplastic (PSNP) on development of the central nervous system using cultured neural stem cells (NSCs) and mice exposed to PSNP during developmental stages. Our study demonstrates that maternal administration of PSNP during gestation and lactating periods altered the functioning of NSCs, neural cell compositions, and brain histology in progeny. Similarly, PSNP-induced molecular and functional defects were also observed in cultured NSCs in vitro. Finally, we show that the abnormal brain development caused by exposure to high concentrations of PSNP results in neurophysiological and cognitive deficits in a gender-specific manner. Our data demonstrate the possibility that exposure to high amounts of PSNP may increase the risk of neurodevelopmental defects.

Mammary tissue proteomics in a pig model indicates that dietary valine supplementation increases milk fat content via increased de novo synthesis of fatty acid

Milk fat is a major source of energy that determines the growth of neonates. Recently, studies have shown that valine is closely related to lipid metabolism. Therefore, this study was designed to investigate the effects of dietary valine supplementation on milk fat synthesis using a pig model. Thirty gilts were allotted to low (LV, total valine:lysine = 0.63:1), medium (MV, total valine:lysine = 0.73:1), and high (HV, total valine:lysine = 0.93:1) valine feeding levels from Day 75 of gestation till farrowing. The results demonstrated that the concentration of milk fat at Days 1, 3, and 7 of lactation in the HV group was higher than that in the MV and LV groups. The HV group had an increased (p < .05) proportion of total saturated and monounsaturated fatty acids than the other groups. Examination of mammary tissue proteomics in the HV and LV groups revealed 121 differentially expressed proteins (68 upregulated and 53 downregulated in the HV group). The upregulated proteins in the HV group were relevant to some crucial pathways related to milk fat synthesis, including fatty acid biosynthesis and metabolism, the AMPK signaling pathway, and oxidative phosphorylation. Furthermore, the key proteins involved in fatty acid synthesis (ACACA and FASN) were identified, and their expression levels were verified (p < .05) using Western blotting. Our findings revealed that dietary valine supplementation improves milk fat synthesis by modulating the expression of fatty acid synthesis-related proteins in mammary tissues.

Bta-miR-34b controls milk fat biosynthesis via the Akt/mTOR signaling pathway by targeting RAI14 in bovine mammary epithelial cells

BACKGROUND

The biosynthesis of milk fat affects both the technological properties and organoleptic quality of milk and dairy products. MicroRNAs (miRNAs) are endogenous small non-coding RNAs that inhibit the expression of their mRNA targets and are involved in downstream signaling pathways that control several biological processes, including milk fat synthesis. miR-34b is a member of the miR-34 miRNA cluster, which is differentially expressed in the mammary gland tissue of dairy cows during lactation and dry periods. Previous studies have indicated miR-34b is a potential candidate gene that plays a decisive role in regulating milk fat synthesis; therefore, it is important to focus on miR-34b and investigate its regulatory effect on the biosynthesis of milk fat in bovine mammary epithelial cells (BMECs).

RESULTS

In this study, elevated miR-34b levels reduced milk fat synthesis, upregulated 1,999 genes, and downregulated 2,009 genes in BMECs. Moreover, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of differentially expressed genes suggested that miR-34b may play an inhibitory role in milk fat synthesis via the protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway by reducing phosphorylation levels. Notably, the mTOR activator MHY1485 rescued the inhibitory effect of miR-34b. Furthermore, we demonstrated that retinoic acid-induced protein 14 (RAI14) is a target of miR-34b via TargetScan and immunofluorescence assays. RAI14 mRNA and protein levels were significantly decreased by the miR-34b mimic and increased by the miR-34b inhibitor. Moreover, the reduction in RAI14 levels led to the inhibition of the Akt/mTOR signaling pathway.

CONCLUSIONS

Overall, our results identified a miR-34b-RAI14-Akt/mTOR regulatory network, while also providing a theoretical basis for the molecular breeding of dairy cows.

Akt Isoforms: A Family Affair in Breast Cancer

Simple Summary

Breast cancer is the second leading cause of cancer-related death in women in the United States. The Akt signaling pathway is deregulated in approximately 70% of patients with breast cancer. While targeting Akt is an effective therapeutic strategy for the treatment of breast cancer, there are several members in the Akt family that play distinct roles in breast cancer. However, the function of Akt isoforms depends on many factors. This review analyzes current progress on the isoform-specific functions of Akt isoforms in breast cancer.

Abstract

Akt, also known as protein kinase B (PKB), belongs to the AGC family of protein kinases. It acts downstream of the phosphatidylinositol 3-kinase (PI3K) and regulates diverse cellular processes, including cell proliferation, cell survival, metabolism, tumor growth and metastasis. The PI3K/Akt signaling pathway is frequently deregulated in breast cancer and plays an important role in the development and progression of breast cancer. There are three closely related members in the Akt family, namely Akt1(PKBα), Akt2(PKBβ) and Akt3(PKBγ). Although Akt isoforms share similar structures, they exhibit redundant, distinct as well as opposite functions. While the Akt signaling pathway is an important target for cancer therapy, an understanding of the isoform-specific function of Akt is critical to effectively target this pathway. However, our perception regarding how Akt isoforms contribute to the genesis and progression of breast cancer changes as we gain new knowledge. The purpose of this review article is to analyze current literatures on distinct functions of Akt isoforms in breast cancer.

Mex3c mutation affects lactation through impairing milk ejection in female mice

Mouse Mex3c encodes RNA-binding proteins of variant length through alternative splicing. Its mutation results in multiple defects including growth retardation, perturbed energy balance, and defective antiviral innate immunity. Here we report that Mex3c mutation affects mammary gland development and lactation in female mice. Pups of Mex3c mutant dams die of starvation soon after birth. Milk contents are present in the alveoli but deficient in the ducts of the mammary glands in mutant mice. Mutant mice do not show prolactin or oxytocin deficiency. They also develop myoepithelial cells in the mammary glands. Mex3c is expressed in the mammary gland epithelium. Our data suggest that functional defects in mammary gland epithelium or myoepithelial cells could cause lactation defects.

Got Milk? Identifying and Characterizing Lactation Defects in Genetically-Engineered Mouse Models

The ability to produce and expel milk is important for the health and survival of all mammals. Nevertheless, our understanding of the molecular events underlying the execution of this process remains incomplete. Whilst impaired mammary gland development and lactational competence remains the subject of focused investigations, defects in these events may also be an unintended consequence of genetic manipulation in rodent models. In this technical report, we outline established and emerging methods to characterize lactation phenotypes in genetically-engineered mouse models. We discuss important considerations of common models, optimized conditions for mating and the importance of litter size and standardization. Methods for quantifying milk production and quality, as well as protocols for wholemount preparation, immunohistochemistry and the preparation of RNA and protein lysates are provided. This review is intended to help guide researchers new to the field of mammary gland biology in the systematic analysis of lactation defects and in the preparation of samples for more focused mechanistic investigations.

Valine increases milk fat synthesis in mammary gland of gilts through stimulating AKT/MTOR/SREBP1 pathway†

Lactating mammary glands are among the most active lipogenic organs and provide a large percentage of bioactive lipids and calories for infant growth. The branched-chain amino acid (BCAA) valine is known to modulate fatty acids synthesis in adipose tissue; however, its effects on fat metabolism and the underlying mechanisms in mammary glands remain to be determined. Valine supplementation during late pregnancy significantly increased the contents of total milk fat, triglyceride, sphingomyelin, and polyunsaturated fatty acids in the colostrum of gilts. Further study in porcine mammary epithelial cells (PMECs) confirmed that valine upregulated the phosphorylation levels of AKT-activated MTOR and subsequently induced the nuclear accumulation of sterol regulatory element binding protein 1 (SREBP1), thus increasing the expression of proteins related to fatty acids synthesis and intracellular triacylglycerol content. Inhibition of AKT/MTOR signaling or silencing of SREBP1 in PMECs downregulates the expression of proteins related to fatty acids synthesis and intracellular triacylglycerol content. Our findings indicated that valine enhanced milk fat synthesis of colostrum in porcine mammary glands via the AKT/MTOR/SREBP1 signaling pathway.

PGC-1α induced browning promotes involution and inhibits lactation in mammary glands

The PPARγ coactivator 1α (PGC-1α) is a transcriptional regulator of mitochondrial biogenesis and oxidative metabolism. Recent studies have highlighted a fundamental role of PGC-1α in promoting breast cancer progression and metastasis, but the physiological role of this coactivator in the development of mammary glands is still unknown. First, we show that PGC-1α is highly expressed during puberty and involution, but nearly disappeared in pregnancy and lactation. Then, taking advantage of a newly generated transgenic mouse model with a stable and specific overexpression of PGC-1α in mammary glands, we demonstrate that the re-expression of this coactivator during the lactation stage leads to a precocious regression of the mammary glands. Thus, we propose that PGC-1α action is non-essential during pregnancy and lactation, whereas it is indispensable during involution. The rapid preadipocyte-adipocyte transition, together with an increased rate of apoptosis promotes a premature mammary glands involution that cause lactation defects and pup growth retardation. Overall, we provide new insights in the comprehension of female reproductive cycles and lactation deficiency, thus opening new roads for mothers that cannot breastfeed.

Profiling solute-carrier transporters in key metabolic tissues during the postpartum evolution of mammary epithelial cells from nonsecretory to secretory

Modifications in the abundance of solute-carrier (SLC) transcripts in tandem with adjustments in genes-associated with energy homeostasis during the postpartum transition of the mammary epithelial cells (MEC) from nonsecretory to secretory is pivotal for supporting milk synthesis. The goal of this study was to identify differentially expressed SLC genes across key metabolic tissues between late pregnancy and onset of lactation. Total RNA was isolated from the mammary, liver, and adipose tissues collected from rat dams on day 20 of pregnancy (P20) and day 1 of lactation (L1) and gene expression was measured with Rat 230 2.0 Affymetrix GeneChips. LIMMA was utilized to identify the differential gene expression patterns between P20 and L1 tissues. Transcripts engaged in conveying anions, cations, carboxylates, sugars, amino acids, metals, nucleosides, vitamins, and fatty acids were significantly increased (P < 0.05) in MEC during the P20 to L1 shift. Downregulated (P < 0.05) genes in the mammary during the physiological transition included GLUT8 and SLC45a3. In the liver, SLC genes encoding for anion, carbonyl, and nucleotide sugar transporters were upregulated (P < 0.05) at L1. while genes facilitating transportation of anions and hexose were increased (P < 0.05), from P20 to L1 in the adipose tissue. GLUT1 and GLUT4 in the liver, along with GLUT4 and SGLT2 in the adipose tissue, were repressed (P < 0.05) at L1. Our results illustrate that MEC exhibit dynamic molecular plasticity during the nonsecretory to secretory transition and increase biosynthetic capacity through a coordinated tissue specific SLC transcriptome modification to facilitate substrate transfer.

Seipin deficiency leads to increased endoplasmic reticulum stress and apoptosis in mammary gland alveolar epithelial cells during lactation

Seipin is an integral endoplasmic reticulum (ER) membrane protein encoded by Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2/Bscl2) gene. Most litters (59%) from Bscl2-/- dams mated with wild type (WT) (Bscl2+/+) males did not survive postnatal day 5 (PND5) and pups (Bscl2+/-) lacked milk in their stomachs. The survived litters had reduced pup survival rate at PND21. It was hypothesized that seipin was critical for lactation. Bscl2 was upregulated and highly detected in the lactation day 1 (LD1) WT mammary gland alveolar epithelial cells. LD1 Bscl2-/- mammary glands lacked adipocytes and alveolar clusters and had varied alveolar morphology: from interconnected mammary gland alveoli with dilated lumen and sloughed epithelial cells to undifferentiated mammary gland alveoli with unexpanded lumen. Comparable levels of whey acidic protein (WAP, a major component in rodent milk) staining and Nile Red lipid droplet staining between WT and Bscl2-/- LD1 alveolar epithelial cells indicated normal milk protein synthesis and lipid syntheses in LD1 Bscl2-/- mammary glands. Significantly reduced percentage of larger lipid droplets was detected in LD1 Bscl2-/- alveoli with unexpanded lumen. There was no obviously impaired proliferation detected by PCNA staining but increased apoptosis detected by cleaved caspase-3 staining in LD1 Bscl2-/- alveolar epithelial cells. Increased expression of protein disulfide isomerase and binding immunoglobulin protein in the LD1 Bscl2-/- mammary gland alveolar epithelial cells indicated increased ER stress. This study demonstrates increased ER stress and apoptosis in LD1 Bscl2-/- mammary gland alveolar epithelial cells and reveals a novel in vivo function of seipin in lactation.

Liver X receptor-α activation enhances cholesterol secretion in lactating mammary epithelium

Liver X receptors (LXRs) are ligand-dependent transcription factors activated by cholesterol metabolites. These receptors induce a suite of target genes required for de novo synthesis of triglycerides and cholesterol transport in many tissues. Two different isoforms, LXRα and LXRβ, have been well characterized in liver, adipocytes, macrophages, and intestinal epithelium among others, but their contribution to cholesterol and fatty acid efflux in the lactating mammary epithelium is poorly understood. We hypothesize that LXR regulates lipogenesis during milk fat production in lactation. Global mRNA analysis of mouse mammary epithelial cells (MECs) revealed multiple LXR/RXR targets upregulated sharply early in lactation compared with midpregnancy. LXRα is the primary isoform, and its protein levels increase throughout lactation in MECs. The LXR agonist GW3965 markedly induced several genes involved in cholesterol transport and lipogenesis and enhanced cytoplasmic lipid droplet accumulation in the HC11 MEC cell line. Importantly, in vivo pharmacological activation of LXR increased the milk cholesterol percentage and induced sterol regulatory element-binding protein 1c (Srebp1c) and ATP-binding cassette transporter a7 (Abca7) expression in MECs. Cumulatively, our findings identify LXRα as an important regulator of cholesterol incorporation into the milk through key nodes of de novo lipogenesis, suggesting a potential therapeutic target in women with difficulty initiating lactation.

Milk lipid regulation at the maternal-offspring interface

Milk lipids provide a large proportion of energy, nutrients, essential fatty acids, and signaling molecules for the newborns, the synthesis of which is a tightly controlled process. Dysregulated milk lipid production and composition may be detrimental to the growth, development, health and survival of the newborns. Many genetically modified animal models have contributed to our understanding of milk lipid regulation in the lactating mammary gland. In this review, we discuss recent advances in our knowledge of the mechanisms that control milk lipid biosynthesis and secretion during lactation, and how maternal genetic and dietary defects impact milk lipid composition and consequently offspring traits.

Attenuation of Mammary Gland Dysplasia and Feeding Difficulties in Tabby Mice by Fetal Therapy

Hypohidrotic ectodermal dysplasias (HED) are hereditary differentiation disorders of multiple ectodermal structures including the mammary gland. The X-linked form of HED (XLHED) is caused by a lack of the secreted signaling molecule ectodysplasin A1 (EDA1) which is encoded by the gene EDA and belongs to the tumor necrosis factor (TNF) superfamily. Although male patients (hemizygous) are usually more severely affected by XLHED, heterozygous female carriers of an EDA mutation may also suffer from a variety of symptoms, in particular from abnormal development of their breasts. In Tabby mice, a well-studied animal model of XLHED, EDA1 is absent. We investigated the effects of prenatal administration of Fc-EDA, a recombinant EDA1 replacement protein, on mammary gland development in female Tabby mice. Intra-amniotic delivery of Fc-EDA to fetal animals resulted later in improved breastfeeding and thus promoted the growth of their offspring. In detail, such treatment led to a normalization of the nipple shape (protrusion, tapering) that facilitated sucking. Mammary glands of treated female Tabby mice also showed internal changes, including enhanced branching morphogenesis and ductal elongation. Our findings indicate that EDA receptor stimulation during development has a stable impact on later stages of mammary gland differentiation, including lactation, but also show that intra-amniotic administration of an EDA1 replacement protein to fetal Tabby mice partially corrects the mammary gland phenotype in female adult animals.

Quercetin improves postpartum hypogalactia in milk-deficient mice via stimulating prolactin production in pituitary gland

Postpartum dysgalactia is a common clinical problem for lactating women. Seeking out the safe and efficient phytoestrogens will be a promising strategy for postpartum dysgalactia therapy. In this study, the postpartum mice within four groups, including control group, the model group, and the treatment groups intragastrically administrated with normal saline, bromocriptine, bromocriptine plus 17α-ethinyl estradiol, and bromocriptine plus quercetin, respectively, were used. The results showed that quercetin, a kind of natural phytoestrogen, could efficiently promote lactation yield and mammary gland development in the agalactosis mice produced by bromocriptine administration. Mechanically, quercetin, such as 17α-ethinyl estradiol, significantly stimulated prolactin (PRL) production and deposition in the mammary gland in the agalactosis mice determined by western blotting, quantitative polymerase chain reaction, and enzyme-linked immunosorbent assay, respectively. Furthermore, quercetin could increase the expression of β-casein, stearoyl-CoA desaturase, fatty acid synthase, and α-lactalbumin in the breast tissues that are responsible for the production of fatty acid, lactose, and galactose in the milk at the transcriptional level determined by quantitative polymerase chain reaction. Specifically, quercetin promoted primary mammary epithelial cell proliferation and stimulated prolactin receptor (PRLR) expression probably via AKT activation in vitro. In conclusion, this study indicates that estrogen-like quercetin promotes mammary gland development and lactation yield in milk-deficient mice, probably via stimulating PRL expression and release from the pituitary gland, as well as induces PRLR expression in primary mammary epithelial cells.

Th-POK regulates mammary gland lactation through mTOR-SREBP pathway

The Th-inducing POK (Th-POK, also known as ZBTB7B or cKrox) transcription factor is a key regulator of lineage commitment of immature T cell precursors. It is yet unclear the physiological functions of Th-POK besides helper T cell differentiation. Here we show that Th-POK is restrictedly expressed in the luminal epithelial cells in the mammary glands that is upregulated at late pregnancy and lactation. Lineage restrictedly expressed Th-POK exerts distinct biological functions in the mammary epithelial cells and T cells in a tissue-specific manner. Th-POK is not required for mammary epithelial cell fate determination. Mammary gland morphogenesis in puberty and alveologenesis in pregnancy are phenotypically normal in the Th-POK-deficient mice. However, Th-POK-deficient mice are defective in triggering the onset of lactation upon parturition with large cellular lipid droplets retained within alveolar epithelial cells. As a result, Th-POK knockout mice are unable to efficiently secret milk lipid and to nurse the offspring. Such defect is mainly attributed to the malfunctioned mammary epithelial cells, but not the tissue microenvironment in the Th-POK deficient mice. Th-POK directly regulates expression of insulin receptor substrate-1 (IRS-1) and insulin-induced Akt-mTOR-SREBP signaling. Th-POK deficiency compromises IRS-1 expression and Akt-mTOR-SREBP signaling in the lactating mammary glands. Conversely, insulin induces Th-POK expression. Thus, Th-POK functions as an important feed-forward regulator of insulin signaling in mammary gland lactation.

Akt Serine/Threonine Kinase 1 Regulates de Novo Fatty Acid Synthesis through the Mammalian Target of Rapamycin/Sterol Regulatory Element Binding Protein 1 Axis in Dairy Goat Mammary Epithelial Cells

Akt serine/threonine kinase acts as a central mediator in the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway, regulating a series of biological processes. In lipid metabolism, Akt activation regulates a series of gene expressions, including genes related to intracellular fatty acid synthesis. However, the regulatory mechanisms of Akt in dairy goat mammary lipid metabolism have not been elaborated. In this study, the coding sequences of goat Akt1 gene were cloned and analyzed. Gene expression of Akt1 in different lactation stages was also investigated. For in vitro studies, a eukaryotic expression vector of Akt1 was constructed and transfected to goat mammary epithelial cells (GMECs), and specific inhibitors of Akt/mammalian target of rapamycin (mTOR) signaling were applied to GMECs. Results showed that Akt1 protein was highly conserved, and its mRNA was highly expressed in midlactation. In vitro studies indicated that Akt1 phosphorylation activated mTOR and subsequently enhanced sterol regulatory element binding protein 1 (SREBP1), thus increasing intracellular triacylglycerol content. Inhibition of Akt/mTOR signaling down-regulated the gene expression of lipogenic genes. Overall, Akt1 plays an important role in regulating de novo fatty acid synthesis in goat mammary epithelial cells, and this process probably is through the mTOR/SREBP1 axis.

ErbB3 drives mammary epithelial survival and differentiation during pregnancy and lactation

Background

During pregnancy, as the mammary gland prepares for synthesis and delivery of milk to newborns, a luminal mammary epithelial cell (MEC) subpopulation proliferates rapidly in response to systemic hormonal cues that activate STAT5A. While the receptor tyrosine kinase ErbB4 is required for STAT5A activation in MECs during pregnancy, it is unclear how ErbB3, a heterodimeric partner of ErbB4 and activator of phosphatidyl inositol-3 kinase (PI3K) signaling, contributes to lactogenic expansion of the mammary gland.

Methods

We assessed mRNA expression levels by expression microarray of mouse mammary glands harvested throughout pregnancy and lactation. To study the role of ErbB3 in mammary gland lactogenesis, we used transgenic mice expressing WAP-driven Cre recombinase to generate a mouse model in which conditional ErbB3 ablation occurred specifically in alveolar mammary epithelial cells (aMECs).

Results

Profiling of RNA from mouse MECs isolated throughout pregnancy revealed robust Erbb3 induction during mid-to-late pregnancy, a time point when aMECs proliferate rapidly and undergo differentiation to support milk production. Litters nursed by ErbB3^KO dams weighed significantly less when compared to litters nursed by ErbB3^WT dams. Further analysis revealed substantially reduced epithelial content, decreased aMEC proliferation, and increased aMEC cell death during late pregnancy. Consistent with the potent ability of ErbB3 to activate cell survival through the PI3K/Akt pathway, we found impaired Akt phosphorylation in ErbB3^KO samples, as well as impaired expression of STAT5A, a master regulator of lactogenesis. Constitutively active Akt rescued cell survival in ErbB3-depleted aMECs, but failed to restore STAT5A expression or activity. Interestingly, defects in growth and survival of ErbB3^KO aMECs as well as Akt phosphorylation, STAT5A activity, and expression of milk-encoding genes observed in ErbB3^KO MECs progressively improved between late pregnancy and lactation day 5. We found a compensatory upregulation of ErbB4 activity in ErbB3^KO mammary glands. Enforced ErbB4 expression alleviated the consequences of ErbB3 ablation in aMECs, while combined ablation of both ErbB3 and ErbB4 exaggerated the phenotype.

Conclusions

These studies demonstrate that ErbB3, like ErbB4, enhances lactogenic expansion and differentiation of the mammary gland during pregnancy, through activation of Akt and STAT5A, two targets crucial for lactation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-017-0893-7) contains supplementary material, which is available to authorized users.

Biosynthesis of milk fat, protein, and lactose: roles of transcriptional and posttranscriptional regulation

The demand for high-quality milk is increasing worldwide. The efficiency of milk synthesis can be improved by taking advantage of the accumulated knowledge of the transcriptional and posttranscriptional regulation of genes coding for proteins involved in the synthesis of fat, protein, and lactose in the mammary gland. Research in this area is relatively new, but data accumulated in the last 10 years provide a relatively clear picture. Milk fat synthesis appears to be regulated, at least in bovines, by an interactive network between SREBP1, PPARγ, and LXRα, with a potential role for other transcription factors, such as Spot14, ChREBP, and Sp1. Milk protein synthesis is highly regulated by insulin, amino acids, and amino acid transporters via transcriptional and posttranscriptional routes, with the insulin-mTOR pathway playing a central role. The transcriptional regulation of lactose synthesis is still poorly understood, but it is clear that glucose transporters play an important role. They can also cooperatively interact with amino acid transporters and the mTOR pathway. Recent data indicate the possibility of nutrigenomic interventions to increase milk fat synthesis by feeding long-chain fatty acids and milk protein synthesis by feeding amino acids. We propose a transcriptional network model to account for all available findings. This model encompasses a complex network of proteins that control milk synthesis with a cross talk between milk fat, protein, and lactose regulation, with mTOR functioning as a central hub.

Lactogenic hormones regulate mammary protein synthesis in bovine mammary epithelial cells via the mTOR and JAK–STAT signal pathways

The expression of CSN3, hormone receptor, the expression of genes regulating the mTOR, JAK–STAT signal pathways, and the relative content of к-casein as well as total casein were determined in the present study to explore the mechanism of the effect of lactogenic hormones on milk-protein synthesis in bovine mammary epithelial cells. The results showed that apoptosis of the cells was increased by inhibitor LY294002, while the expressions of genes encoding PKB, Rheb, PRAS40 and S6K1 in the mTOR signal pathway, JAK2, STAT5A in the JAK–STAT signal pathway, and genes encoding INSR, PRLR, NR3C1 and CSN3 were all downregulated, and the relative contents of κ-casein and total casein were decreased in the mammary epithelial cells compared with those in the control group. Comparatively, the inhibitory effects of AG-490 were more profound than those of LY294002, and the double block using both inhibitors had a greater effect than the single block. The CSN3 gene expression was downregulated and the content of milk casein was decreased by the inhibitors. In addition, the expression of the hormone receptor genes was downregulated. Our results suggest that lactogenic hormones, via their receptors in the membrane, regulated the JAK–STAT and m-TOR signal pathways, and affected cell proliferation and apoptosis, leading to changes in milk-protein synthesis.

ZnT4 (SLC30A4)-null ("lethal milk") mice have defects in mammary gland secretion and hallmarks of precocious involution during lactation

During lactation, highly specialized secretory mammary epithelial cells (MECs) produce and secrete huge quantities of nutrients and nonnutritive factors into breast milk. The zinc (Zn) transporter ZnT4 (SLC30A4) transports Zn into the trans-Golgi apparatus for lactose synthesis, and across the apical cell membrane for efflux from MECs into milk. This is consistent with observations in "lethal milk" (lm/lm) mice, which have a truncation mutation in SLC30A4, and present with not only low milk Zn concentration, but also smaller mammary glands, decreased milk volume, and lactation failure by lactation day 2. However, the molecular underpinnings of these defects are not understood. Here, we used lactating C57BL/6J(lm/lm) (ZnT4-null) mice to explore the consequences of a ZnT4-null phenotype on mammary gland function during early lactation. Lactating C57BL/6J(lm/lm) mice had significantly fewer, smaller, and collapsed alveoli comprising swollen, lipid-filled MECs during early lactation. These defects were associated with decreased Akt expression and STAT5 activation, indicative of defects in MEC secretion. In addition, increased expression of ZnT2, TNF-α, and cleaved e-cadherin concomitant with increased activation of STAT3 implicated the loss of ZnT4 in precocious activation of involution. Collectively, our study indicates that the loss of ZnT4 has profound consequences on MEC secretion and may promote tissue remodeling in the mammary gland during early lactation.

Fatty acid transport and transporters in muscle are critically regulated by Akt2

Muscle contains various fatty acid transporters (CD36, FABPpm, FATP1, FATP4). Physiological stimuli (insulin, contraction) induce the translocation of all four transporters to the sarcolemma to enhance fatty acid uptake similarly to glucose uptake stimulation via glucose transporter-4 (GLUT4) translocation. Akt2 mediates insulin-induced, but not contraction-induced, GLUT4 translocation, but its role in muscle fatty acid transporter translocation is unknown. In muscle from Akt2-knockout mice, we observed that Akt2 is critically involved in both insulin-induced and contraction-induced fatty acid transport and translocation of fatty acid translocase/CD36 (CD36) and FATP1, but not of translocation of fatty acid-binding protein (FABPpm) and FATP4. Instead, Akt2 mediates intracellular retention of both latter transporters. Collectively, our observations reveal novel complexities in signaling mechanisms regulating the translocation of fatty acid transporters in muscle.

Phosphoproteomics of the goat milk fat globule membrane: New insights into lipid droplet secretion from the mammary epithelial cell

Mechanisms of milk lipid secretion are highly controversial. Analyzing the fine protein composition of the "milk fat globule membrane" (MFGM), the triple-layered membrane surrounding milk lipid droplets (LDs) can provide mechanistic clues to better understand LD biosynthesis and secretion pathways in mammary epithelial cells (MECs). We therefore combined a high-sensitive Q-Exactive LC-MS/MS analysis of MFGM-derived peptides to the use of an in-house database intended to improve protein identification in the goat species. Using this approach, we performed the identification of 442 functional groups of proteins in the MFGM from goat milk. To get a more dynamic view of intracellular mechanisms driving LD dynamics in the MECs, we decided to investigate for the first time whether MFGM proteins were phosphorylated. MFGM proteins were sequentially digested by lysine-C and trypsin proteases and the resulting peptides were fractionated by a strong cation exchange chromatography. Titanium beads were used to enrich phosphopeptides from strong cation exchange chromatography eluted fractions. This approach lets us pinpoint 271 sites of phosphorylation on 124 unique goat MFGM proteins. Enriched GO terms associated with phosphorylated MFGM proteins were protein transport and actin cytoskeleton organization. Gained data are discussed with regard to lipid secretory mechanisms in the MECs. All MS data have been deposited in the ProteomeXchange with identifier PXD001039 (http://proteomecentral.proteomexchange.org/dataset/PXD001039).

MicroRNA-152 regulates DNA methyltransferase 1 and is involved in the development and lactation of mammary glands in dairy cows

MicroRNAs (miRNAs) are a class of small non-coding, endogenous regulatory RNAs that function by controlling gene expression at the post-transcriptional level. Using small RNA sequencing and qRT-PCR techniques, we found that the expression of miR-152 was significantly increased during lactation in the mammary glands of dairy cows producing high quality milk compared with that in cows producing low quality milk. Furthermore, DNA methyltransferase 1 (DNMT1), which is a target of miR-152, was inversely correlated with the expression levels of miR-152 in the mammary glands of dairy cows. Dairy cow mammary epithelial cells (DCMECs) were used as in vitro cell models to study the function of miR-152. The forced expression of miR-152 in DCMECs resulted in a marked reduction of DNMT1 at both mRNA and protein levels. This in turn led to a decrease in global DNA methylation and increased the expression of two lactation-related genes, serine/threonine protein kinase Akt (Akt) and peroxisome proliferator-activated receptor gamma (Pparγ). In contrast, inhibition of miR-152 showed the opposite results. By using an electronic Coulter counter (CASY-TT) and flow cytometer, we discovered that miR-152 enhanced the viability and multiplication capacity of DCMECs. In conclusion, miR-152 plays an important role in the development and lactation processes in the mammary glands of dairy cows. Our data provide insights into dairy cow mammary gland development and lactation.

Maternal obesity reduces milk lipid production in lactating mice by inhibiting acetyl-CoA carboxylase and impairing fatty acid synthesis

Maternal metabolic and nutrient trafficking adaptations to lactation differ among lean and obese mice fed a high fat (HF) diet. Obesity is thought to impair milk lipid production, in part, by decreasing trafficking of dietary and de novo synthesized lipids to the mammary gland. Here, we report that de novo lipogenesis regulatory mechanisms are disrupted in mammary glands of lactating HF-fed obese (HF-Ob) mice. HF feeding decreased the total levels of acetyl-CoA carboxylase-1 (ACC), and this effect was exacerbated in obese mice. The relative levels of phosphorylated (inactive) ACC, were elevated in the epithelium, and decreased in the adipose stroma, of mammary tissue from HF-Ob mice compared to those of HF-fed lean (HF-Ln) mice. Mammary gland levels of AMP-activated protein kinase (AMPK), which catalyzes formation of inactive ACC, were also selectively elevated in mammary glands of HF-Ob relative to HF-Ln dams or to low fat fed dams. These responses correlated with evidence of increased lipid retention in mammary adipose, and decreased lipid levels in mammary epithelial cells, of HF-Ob dams. Collectively, our data suggests that maternal obesity impairs milk lipid production, in part, by disrupting the balance of de novo lipid synthesis in the epithelial and adipose stromal compartments of mammary tissue through processes that appear to be related to increased mammary gland AMPK activity, ACC inhibition, and decreased fatty acid synthesis.

Rosiglitazone, a PPAR-γ agonist, fails to attenuate CLA-induced milk fat depression and hepatic lipid accumulation in lactating mice

Our objective was to investigate the combination of rosiglitazone (ROSI) and conjugated linoleic acid (CLA) on mammary and hepatic lipogenesis in lactating C57Bl/6 J mice. Twenty-four lactating mice were randomly assigned to one of four treatments applied from postpartum day 6 to day 10. Treatments included: (1) control diet, (2) control plus 1.5 % dietary CLA (CLA) substituted for soybean oil, (3) control plus daily intra-peritoneal (IP) rosiglitazone injections (10 mg/kg body weight) (ROSI), and (4) CLA plus ROSI (CLA-ROSI). Dam food intake and milk fat concentration were depressed with CLA. However, no effects were observed with ROSI. The CLA-induced milk fat depression was due to reduced expression for mammary lipogenic genes involved in de-novo fatty acid (FA) synthesis, FA uptake and desaturation, and triacyglycerol synthesis. Liver weight (g/100 g body weight) was increased by CLA due to an increase in lipid accumulation triggering a compensatory reduction in mRNA abundance of hepatic lipogenic enzymes, including acetyl-CoA carboxylase I and stearoyl-CoA desaturase I. On the contrary, no effects were observed with ROSI on hepatic and mammary lipogenic gene and enzyme expression. Overall, feeding CLA to lactating mice induced milk fat depression and increased hepatic lipid accumulation, probably due to the presence of trans-10, cis-12 CLA isomer, while ROSI failed to significantly attenuate both hepatic steatosis and reduction in milk fat content.

Thyroid hormone responsive protein Spot14 enhances catalysis of fatty acid synthase in lactating mammary epithelium

Thyroid hormone responsive protein Spot 14 has been consistently associated with de novo fatty acid synthesis activity in multiple tissues, including the lactating mammary gland, which synthesizes large quantities of medium chain fatty acids (MCFAs) exclusively via FASN. However, the molecular function of Spot14 remains undefined during lactation. Spot14-null mice produce milk deficient in total triglyceride and de novo MCFA that does not sustain optimal neonatal growth. The lactation defect was rescued by provision of a high fat diet to the lactating dam. Transgenic mice overexpressing Spot14 in mammary epithelium produced total milk fat equivalent to controls, but with significantly greater MCFA. Spot14-null dams have no diminution of metabolic gene expression, enzyme protein levels, or intermediate metabolites that accounts for impaired de novo MCFA. When [(13)C] fatty acid products were quantified in vitro using crude cytosolic lysates, native FASN activity was 1.6-fold greater in control relative to Spot14-null lysates, and add back of Spot14 partially restored activity. Recombinant FASN catalysis increased 1.4-fold and C = 14:0 yield was enhanced 4-fold in vitro following addition of Spot14. These findings implicate Spot14 as a direct protein enhancer of FASN catalysis in the mammary gland during lactation when maximal MCFA production is needed.

Lipid transport in the lactating mammary gland

Mammalian cells depend on phospholipid (PL) and fatty acid (FA) transport to maintain membrane structure and organization, and to fuel and regulate cellular functions. In mammary glands of lactating animals, copious milk secretion, including large quantities of lipid in some species, requires adaptation and integration of PL and FA synthesis and transport processes to meet secretion demands. At present few details exist about how these processes are regulated within the mammary gland. However, recent advances in our understanding of the structural and molecular biology of membrane systems and cellular lipid trafficking provide insights into the mechanisms underlying the regulation and integration of PL and FA transport processes the lactating mammary gland. This review discusses the PL and FA transport processes required to maintain the structural integrity and organization of the mammary gland and support its secretory functions within the context of current molecular and cellular models of their regulation.

Developmental programming mediated by complementary roles of imprinted Grb10 in mother and pup

Developmental programming links growth in early life with health status in adulthood. Although environmental factors such as maternal diet can influence the growth and adult health status of offspring, the genetic influences on this process are poorly understood. Using the mouse as a model, we identify the imprinted gene Grb10 as a mediator of nutrient supply and demand in the postnatal period. The combined actions of Grb10 expressed in the mother, controlling supply, and Grb10 expressed in the offspring, controlling demand, jointly regulate offspring growth. Furthermore, Grb10 determines the proportions of lean and fat tissue during development, thereby influencing energy homeostasis in the adult. Most strikingly, we show that the development of normal lean/fat proportions depends on the combined effects of Grb10 expressed in the mother, which has the greater effect on offspring adiposity, and Grb10 expressed in the offspring, which influences lean mass. These distinct functions of Grb10 in mother and pup act complementarily, which is consistent with a coadaptation model of imprinting evolution, a model predicted but for which there is limited experimental evidence. In addition, our findings identify Grb10 as a key genetic component of developmental programming, and highlight the need for a better understanding of mother-offspring interactions at the genetic level in predicting adult disease risk.

Underlying mechanisms involved in the decrease of milk secretion during Escherichia coli endotoxin induced mastitis in lactating mice

Mastitis, the inflammation of mammary glands resulting from bacterial infection, disrupts milk production in lactating mammary glands. In this study, we injected lipopolysaccharide (LPS), one of the endotoxins from Escherichia coli into mouse mammary glands to disrupt milk production, and we investigated the influence of LPS on nutrient uptake, synthesis, and secretion processes for milk component production in alveolar epithelial cells (AEC). The expression of genes relevant to the three-staged milk component production process (nutrient uptake, synthesis, and secretion of milk components) were down-regulated within 12 h after LPS injection in AEC. The internalization of glucose transporter 1 (GLUT-1) from the basolateral membrane to the cytoplasm occurred in accordance with the down-regulation of gene expression 3 h after LPS injection. The abnormal localization of adipophilin and beta-casein was also observed in the LPS-injected mammary glands. SLC7A1, an amino acid transporter, was up-regulated 3 and 6 h after LPS injection. Furthermore, the inactivation of signal transducer and activator of transcription 5 (STAT5) and the activation of STAT3 and nuclear factor-kappa B (NFkappaB) occurred 3 h after LPS injection. These results indicate that the nutrient uptake, synthesis, and secretion of milk components in AEC are rapidly shut down in the lactating mammary glands after LPS injection.

The insulin receptor plays an important role in secretory differentiation in the mammary gland

Insulin is known to be an important regulator of milk secretion in the lactating mammary gland. Here we examine the role of insulin signaling in mammary development in pregnancy using a mouse with a floxed insulin receptor (IR) crossed with a mouse expressing Cre specifically in the mammary gland. In the mammary glands of these IR(fl/fl) Cre(+) mice, expression of IR is significantly diminished throughout development. Glands from these mice had 50% fewer alveoli at midpregnancy; casein and lipid droplets were diminished by 60 and 75%, respectively, indicating a role for IR both in alveolar development and differentiation. In an acinar preparation from mammary epithelial cells (MEC) isolated from pregnant mice, insulin stimulated lumen formation, mammary cell size, acinar size, acinar casein content, and the formation of lipid droplets with a Km of ∼1.7 nM. IGF-I and IGF-II had no effect at concentrations below 50 nM, and a function blocking antibody to the IGF type 1 receptor did not alter the response to insulin. We conclude that insulin interacting with IR is essential for mammary differentiation during murine pregnancy. Using array analysis, we then examined the expression of genes up- or downregulated >1.5-fold in the IR(fl/fl) Cre(+) MECs, finding significant downregulation of differentiation specific genes and upregulation of cell cycle and extracellular matrix genes. We conclude that insulin fosters differentiation and may inhibit cell proliferation in the mammary gland of the midpregnant mouse.

Pregnancy in postpartum estrus induces inflammatory milk production and catagen specific pup skin inflammation in interleukin-10 deficient mice

BACKGROUND

The interleukin 10 deficient mice (IL-10(-/-)) showed high incidence of pup alopecia compared to other strains, and pup alopecia was caused by skin inflammation and was recoverable. Pup alopecia of B6.IL-10(-/-) might be related with maternal factor and interleukin-10 deficient phenotype.

OBJECTIVE

The objectives of this study were elucidating of maternal factors for inflammatory milk production and characterization of pup alopecia in IL-10(-/-) mice.

METHODS

Incidences of pup alopecia were analyzed with 13 breeding cases. Comparison between control and alopecia pups and its dams, were conducted with histological examination (H&E, TUNEL assay, immunohistochemistry for F4/80, iNOS, CD206, Gr-1, CD4, CD8, CD11c and CD326), fostering test, forced weaning test, qPCR for tyrosine hydroxylase, flow cytometry, IL-10 inhibition test, BMDM stimulation test and LC/MS analysis.

RESULTS

Presence of pregnancy in postpartum estrus showed significant correlation with inflammatory milk production and mammary gland involution in B6.IL-10(-/-) mice. There were no different mass in inflammatory milk, but different ionization intensity was detected. Inflammatory milk directly induced hepatocyte steatosis, catagen stage specific hair breaking and alopeicia in pups. Histologically, hypertropy of outer root sheath and macrophage/neutrophil infiltration were typical.

CONCLUSION

B6.IL-10(-/-) dam with stress such as PPE could produce untimely mammary gland involution and inflammatory milk production. Interleukin 10 is important for maternal stress regulation and protecting inflammatory milk production, also influence severity of pup skin inflammation and alopecia. Remarkably, inflammatory milk induced hepatocyte steatosis, and it could indicate there is abnormal lipid metabolism. This was first report for catagen specific alopecia in mouse.

Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets

Very-low-carbohydrate diets or ketogenic diets have been in use since the 1920s as a therapy for epilepsy and can, in some cases, completely remove the need for medication. From the 1960s onwards they have become widely known as one of the most common methods for obesity treatment. Recent work over the last decade or so has provided evidence of the therapeutic potential of ketogenic diets in many pathological conditions, such as diabetes, polycystic ovary syndrome, acne, neurological diseases, cancer and the amelioration of respiratory and cardiovascular disease risk factors. The possibility that modifying food intake can be useful for reducing or eliminating pharmaceutical methods of treatment, which are often lifelong with significant side effects, calls for serious investigation. This review revisits the meaning of physiological ketosis in the light of this evidence and considers possible mechanisms for the therapeutic actions of the ketogenic diet on different diseases. The present review also questions whether there are still some preconceived ideas about ketogenic diets, which may be presenting unnecessary barriers to their use as therapeutic tools in the physician's hand.

The role of adipocyte XBP1 in metabolic regulation during lactation

The adipocyte is central to organismal metabolism and exhibits significant functional and morphological plasticity during its formation and lifespan. Remarkable transformations of this cell occur during obesity and lactation, and thus it is essential to gain a better understanding of adipocyte function in these two metabolic processes. Considering the critical importance of the cellular organelle endoplasmic reticulum (ER) in adapting to fluctuations in synthetic processes, we explored the role of XBP1, a central regulator of ER adaptive responses, in adipocyte formation and function. Unexpectedly, deletion of adipocyte-XBP1 in vivo in mice (XBP1ΔAd) had no effect on adipocyte formation or on systemic homeostatic metabolism in mice fed a a regular or high-fat diet. However, during lactation, XBP1ΔAd dams displayed increased adiposity, decreased milk production, and decreased litter growth as compared with control dams. Moreover, we demonstrate that XBP1 is regulated during lactation and responds to prolactin to alter lipogenic gene expression. These results demonstrate a role for adipocyte-XBP1 in the regulation of lactational metabolism.

Milk lipid secretion: recent biomolecular aspects

Neonates of most species depend on milk lipids for calories, fat-soluble vitamins, and bioactive lipid components for growth and development during the postnatal period. To meet neonatal nutrition and development needs, the mammary gland has evolved efficient mechanisms for synthesizing and secreting large quantities of lipid during lactation. Although the biochemical steps involved in milk lipid synthesis are understood, the identities of the genes mediating these steps and the molecular physiology of milk lipid production and secretion have only recently begun to be understood in detail through advances in mouse genetics, gene expression analysis, protein structural properties, and the cell biology of lipid metabolism. This review discusses emerging data about the molecular, cellular, and structural determinants of milk lipid synthesis and secretion within the context of physiological functions.

Overexpression of miR-30b in the developing mouse mammary gland causes a lactation defect and delays involution

Background

MicroRNA (miRNA) are negative regulators of gene expression, capable of exerting pronounced influences upon the translation and stability of mRNA. They are potential regulators of normal mammary gland development and of the maintenance of mammary epithelial progenitor cells. This study was undertaken to determine the role of miR-30b on the establishment of a functional mouse mammary gland. miR-30b is a member of the miR-30 family, composed of 6 miRNA that are highly conserved in vertebrates. It has been suggested to play a role in the differentiation of several cell types.

Methodology/Principal Findings

The expression of miR-30b was found to be regulated during mammary gland development. Transgenic mice overexpressing miR-30b in mammary epithelial cells were used to investigate its role. During lactation, mammary histological analysis of the transgenic mice showed a reduction in the size of alveolar lumen, a defect of the lipid droplets and a growth defect of pups fed by transgenic females. Moreover some mammary epithelial differentiated structures persisted during involution, suggesting a delay in the process. The genes whose expression was affected by the overexpression of miR-30b were characterized by microarray analysis.

Conclusion/Significance

Our data suggests that miR-30b is important for the biology of the mammary gland and demonstrates that the deregulation of only one miRNA could affect lactation and involution.

Maternal western diet causes inflammatory milk and TLR2/4-dependent neonatal toxicity

For all newborn mammals, mother's milk is the perfect nourishment, crucial for their postnatal development. Here we report that, unexpectedly, maternal western diet consumption in mice causes the production of toxic milk that contains excessive long chain and saturated fatty acids, which triggers ceramide accumulation and inflammation in the nursing neonates, manifested as alopecia. This neonatal toxicity requires Toll-like-receptors (TLR), but not gut microbiota, because TLR2/4 deletion or TLR4 inhibition confers resistance, whereas germ-free mice remain sensitive. These findings unravel maternal western diet-induced inflammatory milk secretion as a novel aspect of the metabolic syndrome at the maternal offspring interface.

SnoN regulates mammary gland alveologenesis and onset of lactation by promoting prolactin/Stat5 signaling

Mammary epithelial cells undergo structural and functional differentiation at late pregnancy and parturition to produce and secrete milk. Both TGF-β and prolactin pathways are crucial regulators of this process. However, how the activities of these two antagonistic pathways are orchestrated to initiate lactation has not been well defined. Here, we show that SnoN, a negative regulator of TGF-β signaling, coordinates TGF-β and prolactin signaling to control alveologenesis and lactogenesis. SnoN expression is induced at late pregnancy by the coordinated actions of TGF-β and prolactin. The elevated SnoN promotes Stat5 signaling by enhancing its stability, thereby sharply increasing the activity of prolactin signaling at the onset of lactation. SnoN-/- mice display severe defects in alveologenesis and lactogenesis, and mammary epithelial cells from these mice fail to undergo proper morphogenesis. These defects can be rescued by an active Stat5. Thus, our study has identified a new player in the regulation of milk production and revealed a novel function of SnoN in mammary alveologenesis and lactogenesis in vivo through promotion of Stat5 signaling.

Lactation and neonatal nutrition: defining and refining the critical questions

This paper resulted from a conference entitled "Lactation and Milk: Defining and refining the critical questions" held at the University of Colorado School of Medicine from January 18-20, 2012. The mission of the conference was to identify unresolved questions and set future goals for research into human milk composition, mammary development and lactation. We first outline the unanswered questions regarding the composition of human milk (Section I) and the mechanisms by which milk components affect neonatal development, growth and health and recommend models for future research. Emerging questions about how milk components affect cognitive development and behavioral phenotype of the offspring are presented in Section II. In Section III we outline the important unanswered questions about regulation of mammary gland development, the heritability of defects, the effects of maternal nutrition, disease, metabolic status, and therapeutic drugs upon the subsequent lactation. Questions surrounding breastfeeding practice are also highlighted. In Section IV we describe the specific nutritional challenges faced by three different populations, namely preterm infants, infants born to obese mothers who may or may not have gestational diabetes, and infants born to undernourished mothers. The recognition that multidisciplinary training is critical to advancing the field led us to formulate specific training recommendations in Section V. Our recommendations for research emphasis are summarized in Section VI. In sum, we present a roadmap for multidisciplinary research into all aspects of human lactation, milk and its role in infant nutrition for the next decade and beyond.

[mRNA expression of lipogenic genes in mouse mammary gland in different lactation stages]

To investigate the expression pattern of lipogenic genes in mammary gland of mouse in different lactation stages, the relative mRNA abundance and expression of 20 genes involved in milk fat synthesis and secretion of lactating mammary tissues were assessed using real-time PCR. Results revealed the significant upregulation of mRNA expression for both high abundant genes (abundance > 5%), such as LPL, ACACA, SCD, XDH, BTN, and ADFP and moderate abundant genes (5% > abundance > 1%), such as CD36, FASN, AGPAT6, and DGAT in lactation stages compared to pregnancy (P < 0.05). The mRNA expression of lipogenic enzyme genes for ACACA, SCD, FASN, AGPAT6, and DGAT exhibited lower expression lever in early (6 d) and late (18 d) lactation stages but higher expression level at middle stage (12 d), demonstrating a low-high-low pattern. Besides, the mRNA levels of some gene regulators were also measured. The mRNA expression of SREBF gene increased gradually along with the lactation, which showed a 10-fold elevation at middle stage (12 d). The expression pattern of SREBF gene was the same as lipogenic enzyme genes, suggesting that SREBF may play an important role in the regulation of lipogenic enzyme genes in the lactating mammary gland.

Is there a role for carbohydrate restriction in the treatment and prevention of cancer?

Over the last years, evidence has accumulated suggesting that by systematically reducing the amount of dietary carbohydrates (CHOs) one could suppress, or at least delay, the emergence of cancer, and that proliferation of already existing tumor cells could be slowed down. This hypothesis is supported by the association between modern chronic diseases like the metabolic syndrome and the risk of developing or dying from cancer. CHOs or glucose, to which more complex carbohydrates are ultimately digested, can have direct and indirect effects on tumor cell proliferation: first, contrary to normal cells, most malignant cells depend on steady glucose availability in the blood for their energy and biomass generating demands and are not able to metabolize significant amounts of fatty acids or ketone bodies due to mitochondrial dysfunction. Second, high insulin and insulin-like growth factor (IGF)-1 levels resulting from chronic ingestion of CHO-rich Western diet meals, can directly promote tumor cell proliferation via the insulin/IGF1 signaling pathway. Third, ketone bodies that are elevated when insulin and blood glucose levels are low, have been found to negatively affect proliferation of different malignant cells in vitro or not to be usable by tumor cells for metabolic demands, and a multitude of mouse models have shown anti-tumorigenic properties of very low CHO ketogenic diets. In addition, many cancer patients exhibit an altered glucose metabolism characterized by insulin resistance and may profit from an increased protein and fat intake.

In this review, we address the possible beneficial effects of low CHO diets on cancer prevention and treatment. Emphasis will be placed on the role of insulin and IGF1 signaling in tumorigenesis as well as altered dietary needs of cancer patients.