Expression and function of leptin and its receptor in dairy goat mammary gland

Morphophysiological Responses of the Goat Mammary Gland to Water Scarcity in Arid and Semi-Arid Environments: Are They Enough to Generate Adaptation to New Climatic Challenges?

Due to climate change, diverse territories of the planet will suffer from water restrictions. Goats are perceived as the most resilient ruminants in this scenario. So, various studies have focused on describing how a lower water intake influences milk production, especially in breeds adapted to desert environments. In water-stress situations, goats lose up to 32% of their body weight (BW), the rate of passage is reduced, and the digestibility of the feed increases. When goats consume water again, the rumen prevents hemolysis and osmotic shock from occurring. Regarding milk production, the response varies depending on the breed and the level of water restriction, maintaining the milk volume or reducing it by up to 41%. Systemically, it decreases the urinary volume and glomerular filtration rate, increasing blood osmolality and the vasopressin (ADH) concentration. Studies are scarce regarding changes in blood flow to the mammary gland, but there would be a reduction in blood flow velocity of up to 40% without changing blood pressure. New studies must be undertaken to determine which breeds or crosses are the best adapted to changing environmental conditions and to improve our understanding of the changes that occur at the morphophysiological level of the caprine mammary gland.

Molecular complexity of mammary glands development: a review of lactogenic differentiation in epithelial cells

The mammary gland is a dynamic organ with various physiological processes like cellular proliferation, differentiation, and apoptosis during the pregnancy-lactation-involution cycle. It is essential to understand the molecular changes during the lactogenic differentiation of mammary epithelial cells (MECs, the milk-synthesizing cells). The MECs are organized as luminal milk-secreting cells and basal myoepithelial cells (responsible for milk ejection by contraction) that form the alveoli. The branching morphogenesis and lactogenic differentiation of the MECs prepare the gland for lactation. This process is governed by many molecular mediators including hormones, growth factors, cytokines, miRNAs, regulatory proteins, etc. Interestingly, various signalling pathways guide lactation and understanding these molecular transitions from pregnancy to lactation will help researchers design further research. Manipulation of genes responsible for milk synthesis and secretion will promote augmentation of milk yield in dairy animals. Identifying protein signatures of lactation will help develop strategies for persistent lactation and shortening the dry period in farm animals. The present review article discusses in details the physiological and molecular changes occurring during lactogenic differentiation of MECs and the associated hormones, regulatory proteins, miRNAs, and signalling pathways. An in-depth knowledge of the molecular events will aid in developing engineered cellular models for studies related to mammary gland diseases of humans and animals.

miR-497 Regulates LATS1 through the PPARG Pathway to Participate in Fatty Acid Synthesis in Bovine Mammary Epithelial Cells

Nutrient metabolism is required to maintain energy balance in animal organisms, and fatty acids play an irreplaceable role in fat metabolism. In this study, microRNA sequencing was performed on mammary gland tissues collected from cows during early, peak, and late lactation to determine miRNA expression profiles. Differentially expressed miRNA (miR-497) was selected for functional studies of fatty acid substitution. Simulants of miR-497 impaired fat metabolism [triacylglycerol (TAG) and cholesterol], whereas knockdown of miR-497 promoted fat metabolism in bovine mammary epithelial cells (BMECs) in vitro. In addition, in vitro experiments on BMECs showed that miR-497 could down-regulate C16:1, C17:1, C18:1, and C20:1 as well as long-chain polyunsaturated fats. Thus, these data expand the discovery of a critical role for miR-497 in mediating adipocyte differentiation. Through bioinformatics analysis and further validation, we identified large tumor suppressor kinase 1 (LATS1) as a target of miR-497. siRNA-LATS1 increased concentrations of fatty acids, TAG, and cholesterol in cells, indicating an active role of LATS1 in milk fat metabolism. In summary, miR-497/LATS1 can regulate the biological processes associated with TAG, cholesterol, and unsaturated fatty acid synthesis in cells, providing an experimental basis for further elucidating the mechanistic regulation of lipid metabolism in BMECs.

Effect of leptin on the growth and expression of STAT3 in yak mammary epithelial cells

Background and Aim: Leptin (LEP) is an autocrine and paracrine factor produced by the fat pad and acinar epithelial cells of the breast. This study aimed to investigate the effects of LEP on yak mammary epithelial cells (YMECs) and the expression of STAT3. In addition, we evaluated the possible effects of prolactin (PRL) on the function of LEP. Materials and Methods: The YMECs were treated with 0, 50, 100, 200, 400, and 800 ng/mL LEP for 48 h in the absence of PRL and the presence of 500 ng/mL PRL. The growth activity of YMECs was measured using the cell counting kit-8 assay. The changes in the lactation signaling pathway-related factor STAT3 were detected at the mRNA, protein, and protein phosphorylation levels using the reverse transcriptase-quantitative polymerase chain reaction and Western blotting. To explore whether LEP affects the activation of STAT3 through JAK2/JAK3 in YMECs, the JAK2/3 signaling pathway inhibitor AG490 was used at a fixed concentration of LEP. Results: Each concentration of LEP significantly promoted the expression of STAT3 mRNA (p < 0.05) in YMECs in the presence of PRL. In the absence of PRL, all concentrations of LEP were found to inhibit the expression of the STAT3 protein (p < 0.05). The expression of the STAT3 protein in YMECs was found to first increase followed by a decrease with an increase in the concentration of LEP. In addition, the phosphorylation level of STAT3 increased in all groups, except the 100 ng/mL concentration group. The STAT3 phosphorylation trend and protein expression were different, such that the level of protein phosphorylation was higher than that of the STAT3 protein (p < 0.05). The addition of AG490 reduced the expression of the STAT3 mRNA, STAT3 protein, and STAT3 phosphorylation in the LEP and LEP + PRL groups. Conclusion: Altogether, the results indicated that different concentrations of LEP exerted varying effects on the growth of YMECs and the expression of STAT3, and the activity of STAT3 was primarily activated by JAK2. The addition of LEP can effectively inhibit the downregulation of the JAK2/STAT3 signal pathway by AG490, mitigate its inhibitory effect on the proliferation of YMECs, and reduce apoptosis. We believe that these findings will provide a theoretical and experimental basis for future research in this field.

Circ11103 Interacts with miR-128/PPARGC1A to Regulate Milk Fat Metabolism in Dairy Cows

The quality of milk is inseparable from its milk components, and fatty acid content is a key factor affecting the quality of milk. In this study, the miRNA and mRNA profiles of the bovine mammary gland tissue during the dry period and the peak lactation period were determined through high-throughput sequencing. In total, 72 miRNA-mRNA regulatory pathways were screened, including miR-128/PPARGC1A regulatory pathways. miR-128 can directly target PPARGC1A and inhibit its expression. In addition, the study also observed that there was a miR-128 binding site in the sequence of the circular RNA circ11103, and circ11103 significantly reduced the expression of miR-128. circ11103 upregulated the triglyceride levels in bovine mammary epithelial cells (BMECs) and increased the contents of unsaturated fatty acids. However, miR-128 decreased triglyceride and cholesterol levels in BMECs. This study aims to analyze the mechanism governing the regulatory effect of circ11103 on milk fat metabolism, which provides new insights into improving milk quality.

miR-497 regulates fatty acid synthesis via LATS2 in bovine mammary epithelial cells

Both mRNA and miRNA play an important role in the regulation of mammary fatty acid metabolism and milk fat synthesis.

MiR-16a Regulates Milk Fat Metabolism by Targeting Large Tumor Suppressor Kinase 1 (LATS1) in Bovine Mammary Epithelial Cells

Milk contains a number of beneficial fatty acids including short and medium chain and unsaturated conjugated and nonconjugated fatty acids. In this study, microRNA sequencing of mammary tissue collected in early-, peak-, mid-, and late-lactation periods was performed to determine the miRNA expression profiles. miR-16a was one of the differentially expressed miRNA and was selected for in-depth functional studies pertaining to fatty acid metabolism. The mimic of miR-16a impaired fat metabolism [triacylglycerol (TAG) and cholesterol] while knock-down of miR-16a promoted fat metabolism in vitro in bovine mammary epithelial cells (BMECs). In addition, the in vitro work with BMECs also revealed that miR-16a had a negative effect on the cellular concentration of cis 9-C18:1, total C18:1, C20:1, and C22:1 and long-chain polyunsaturated fatty acids. Therefore, these data suggesting a negative effect on fatty acid metabolism extend the discovery of the key role of miR-16a in mediating adipocyte differentiation. Through a combination of bioinformatics analysis, target gene 3' UTR luciferase reporter assays, and western blotting, we identified large tumor suppressor kinase 1 (LATS1) as a target of miR-16a. Transfection of siRNA-LATS1 into BMECs led to increases in TAG, cholesterol, and cellular fatty acid concentrations, suggesting a positive role of LATS1 in mammary cell fatty acid metabolism. In summary, data suggest that miR-16a regulates biological processes associated with intracellular TAG, cholesterol, and unsaturated fatty acid synthesis through LATS1. These data provide a theoretical and experimental framework for further clarifying the regulation of lipid metabolism in mammary cells of dairy cows.

TRIENNIAL LACTATION SYMPOSIUM/BOLFA: Adipokines affect mammary growth and function in farm animals

The essential role of mammary fat pads in mammary growth and morphogenesis was the first indication that biologically active molecules, secreted from adipocytes or other stromal cells, could regulate endocrine cues for growth and function of the mammary gland. The presence of leptin and adiponectin receptors in mammary tissues suggested that locally produced or circulating adipokines could affect mammary growth and function. Herein, we present the current knowledge on the role of adipokines in mammary cell proliferation and differentiation and in lactogenesis and galactopoiesis in farm animals. We also address the role of milk adipokines in the neonate. Accumulating evidence suggests that adipokines could act as metabolic sensors, regulating mammary growth and function in periods of metabolic adaptations such as late pregnancy and early lactation. Indeed, different experiments reported that adiponectin and leptin expression varies according to physiological stages and nutritional status of the animal. The current review also demonstrates that adipokines, such as leptin and adiponectin, are important regulators of the action of lactogenic hormones in the mammary gland. Findings also suggest important roles for adipokines in growth and intestinal maturation of the neonate.

Obesity impairs lactation performance in mice by inducing prolactin resistance

Obesity reduces breastfeeding success and lactation performance in women. However, the mechanisms involved are not entirely understood. In the present study, female C57BL/6 mice were chronically exposed to a high-fat diet to induce obesity and subsequently exhibited impaired offspring viability (only 15% survival rate), milk production (33% reduction), mammopoiesis (one-third of the glandular area compared to control animals) and postpartum maternal behaviors (higher latency to retrieving and grouping the pups). Reproductive experience attenuated these defects. Diet-induced obese mice exhibited high basal pSTAT5 levels in the mammary tissue and hypothalamus, and an acute prolactin stimulus was unable to further increase pSTAT5 levels above basal levels. In contrast, genetically obese leptin-deficient females showed normal prolactin responsiveness. Additionally, we identified the expression of leptin receptors specifically in basal/myoepithelial cells of the mouse mammary gland. Finally, high-fat diet females exhibited altered mRNA levels of ERBB4 and NRG1, suggesting that obesity may involve disturbances to mammary gland paracrine circuits that are critical in the control of luminal progenitor function and lactation. In summary, our findings indicate that high leptin levels are a possible cause of the peripheral and central prolactin resistance observed in obese mice which leads to impaired lactation performance.

Transcriptome analysis of the mammary gland from GH transgenic goats during involution

Mammary glands are organs for milk production in female mammals. Growth hormone (GH) is known to affect the growth and development of the mammary gland, as well as to increase milk production in dairy goats. This study performed a comprehensive expression profiling of genes expressed in the mammary gland of early involution GH transgenic (n=4) and non-transgenic goats (n=4) by RNA sequencing. RNA was extracted from mammary gland tissues collected at day 3 of involution. Gene expression analysis was conducted by Illumina RNA sequencing and sequence reads were assembled and analyzed using TopHat. FPKM (fragments per kilobase of exon per million) values were analyzed for differentially expressed genes using the Cufflinks package. Gene ontology analysis of differentially expressed genes was categorized using agriGO, while KEGG pathway analysis was performed with the online KEGG automatic annotation server. Our results revealed that 75% of NCBI goat annotated genes were expressed during early involution. A total of 18,323 genes were expressed during early involution in GH transgenic goats, compared with 18,196 expressed genes during early involution of non-transgenic goats. In these expressed genes, the majority (17,589) were ubiquitously expressed in GH transgenic and non-transgenic goats. However, there were 745 differentially expressed genes, 421 of which were upregulated and 324 were downregulated in GH transgenic goats. GO and KEGG pathway analysis showed that these genes were involved in mammary gland physiology, including cell adhesion molecules, ECM-receptor interaction, Jak-STAT signaling pathway, and fat metabolism. Our results demonstrated that the GH receptor was strongly affected in GH transgenic goats, which may activate the IGF-1/Stat3 signaling pathway. Overall, our study provided a global view of the transcriptome during involution of GH transgenic and non-transgenic goats, which increases our understanding of the biology of involution in the goat.

Go with the flow-biology and genetics of the lactation cycle

Lactation is a dynamic process, which evolved to meet dietary demands of growing offspring. At the same time, the mother's metabolism changes to meet the high requirements of nutrient supply to the offspring. Through strong artificial selection, the strain of milk production on dairy cows is often associated with impaired health and fertility. This led to the incorporation of functional traits into breeding aims to counteract this negative association. Potentially, distributing the total quantity of milk per lactation cycle more equally over time could reduce the peak of physiological strain and improve health and fertility. During lactation many factors affect the production of milk: food intake; digestion, absorption, and transportation of nutrients; blood glucose levels; activity of cells in the mammary gland, liver, and adipose tissue; synthesis of proteins and fat in the secretory cells; and the metabolic and regulatory pathways that provide fatty acids, amino acids, and carbohydrates. Whilst the endocrine regulation and physiology of the dynamic process of milk production seems to be understood, the genetics that underlie these dynamics are still to be uncovered. Modeling of longitudinal traits and estimating the change in additive genetic variation over time has shown that the genetic contribution to the expression of a trait depends on the considered time-point. Such time-dependent studies could contribute to the discovery of missing heritability. Only very few studies have estimated exact gene and marker effects at different time-points during lactation. The most prominent gene affecting milk yield and milk fat, DGAT1, exhibits its main effects after peak production, whilst the casein genes have larger effects in early lactation. Understanding the physiological dynamics and elucidating the time-dependent genetic effects behind dynamically expressed traits will contribute to selection decisions to further improve productive and healthy breeding populations.

Exogenous leptin administered intramuscularly induces sex hormone disorder and Ca loss via downregulation of Gnrh and PI3K expression

Obesity is a public health problem that increases the risk of metabolic disease, infertility, and other chronic health problems. The present study aimed to develop a new rat model for sex hormone disorder with overweight and Ca loss by intramuscular injection of exogenous leptin (LEP). Thirty female Sprague-Dawley (SD) rats (40 days old) were injected thrice intramuscularly with LEP or keyhole limpet hemocyanin immunogen. The following analyses were performed to determine the development of appetite, overweight, reproductive related-hormones, and calcium (Ca)/phosphorus (Pi) in SD rats: measurement of Lee’s index, body weight, food intake; serum Ca, Pi, and hormone tests by enzyme-linked immunosorbent analysis; histological analysis of abdominal fat; real-time polymerase chain reaction analysis of neuropeptide Y, pro-opiomelanocortin, gonadotropin-releasing hormone (Gnrh) mRNA, and gonadotropin-releasing hormone receptor (Gnrhr) mRNA expression; and western blotting analysis of enzyme phosphatidylinositol-3-kinase (PI3K). Rats injected with LEP immunogen displayed significantly increased body weight, food intake, Lee’s index, serum LEP, serum cortisol, fat deposition in the abdomen, and decreased hormones including follicle stimulating hormone, luteinizing hormone, estradiol, cholecystokinin, and Ca. Exogenous LEP administered intramuscularly also downregulate Gnrh and PI3K. In conclusion, exogenous LEP administered intramuscularly is a novel animal model for sex hormones disorder with overweight and Ca loss in SD rats. The downregulation of PI3K and Gnrh may be involved in the development of this animal model.