Expression and localisation of leptin and leptin receptor in the mammary gland of the dry and lactating non-pregnant cow

Leptin signaling promotes milk fat synthesis via PI3K/AKT/mTOR/SREBP1 in mammary gland of dairy cow

Milk fat synthesis is tightly regulated by hormones and growth factors. Leptin is a versatile peptide hormone that exerts pleiotropic effects on metabolic pathways. In this study, we evaluated the expression and function of leptin and its long form receptor OB-Rb in dairy cow mammary tissues from different physiological stages and in cultured mammary epithelial cells. The results showed that the expression of leptin and OB-Rb were significantly higher in the mammary tissues of lactating cows as compared with dry cows, suggesting that they are related to milk component synthesis. In cultured dairy cow mammary epithelial cells, leptin treatment significantly increased OB-Rb expression and intracellular triacylglycerol content. Transcriptome analysis identified the difference in gene expression between leptin treated cells and control cells, and 317 differentially expressed genes were identified. Gene ontology and pathway mapping showed that lipid metabolism-related gene expression increased and signal transduction pathway-related genes were the most significantly enriched. Mechanistic studies showed that leptin stimulation enhanced sterol regulatory element-binding protein 1 expression via activating the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) signaling pathway, which in turn up-regulated the expression of genes related to milk fat synthesis. Moreover, we found that fatty acid synthesis precursors, acetate and β-hydroxybutyrate, could positively regulate the expression of leptin and OB-Rb in bovine mammary epithelial cells, thereby potentially increasing milk fat synthesis. Our study provided novel evidence in the regulation of leptin on milk fat production in mammary glands of dairy cows, as well as experimental basis for artificial regulation of milk fat.

Adipocyte-Derived Paracrine Factors Regulate the In Vitro Development of Bovine Mammary Epithelial Cells

The mammary gland is composed of epithelial tissue forming ducts and lobules, and the stroma, composed of adipocytes, connective tissue, and other cell types. The stromal microenvironment regulates mammary gland development by paracrine and cell-cell interactions. In the present study, primary cultures of bovine mammary epithelial cells (bMEC) and bovine adipose-derived stem cells (bASC) subjected to adipogenic differentiation were used to investigate the influence of paracrine factors secreted by preadipocytes and adipocytes on bMEC development. Four types of conditioned media (CM) were collected from undifferentiated preadipocytes (preA) and adipocytes on days: 8, 12, 14 of differentiation. Next, bMEC were cultured for 24 h in CM and cell viability, apoptosis, migratory activity, ability to form spheroids on Matrigel, and secretory activity (alpha S1-casein concentration) were evaluated. CM derived from fully differentiated adipocytes (12 d and 14 d) significantly decreased the number of apoptotic cells in bMEC population and increased the size of spheroids formed by bMEC on Matrigel. CM collected from preadipocytes significantly enhanced bMEC's migration, and stimulated bMEC to produce alpha S1-casein, but only in the presence of prolactin. These results confirm that preadipocytes and adipocytes are important components of the stroma, providing paracrine factors that actively regulate the development of bovine mammary epithelium.

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.

Expression of a recombinant anti-programed cell death 1 antibody in the mammary gland of transgenic mice

Nivolumab, a fully human IgG4 anti-programed cell death 1（PD-1）antibody, is recently one of the most popular and successful therapeutic monoclonal antibodies in clinical use. With the increasing demands for Nivolumab and other therapeutic monoclonal antibodies, the mammary gland bioreactor has been regarded as another choice for the production of recombinant monoclonal antibodies besides mammalian cell culture. Here, we expressed a recombinant human anti-PD-1 antibody in the mammary glands of transgenic mice. Two expression vectors were constructed bearing the heavy and light chains of anti-PD-1 antibody respectively under the control of bovine α_s1-casein promoter. Transgenic mice were then generated by co-microinjection of the two expression cassettes. Three F0 founders with both heavy chain and light chain positive were obtained. Transgenes of both chains were detected to be stably transmitted to the offspring. The recombinant antibody was detected in the milk of transgenic mice with the highest expression level up to 80.52 ± 0.82 mg/L and could specifically binds to the human PD-1 antigen. Therefore, our results suggest the feasibility of anti-PD-1 antibody production in the milk of transgenic animals.

Comparative Analysis of Zearalenone Effects on Thyroid Receptor Alpha (TRα) and Beta (TRβ) Expression in Rat Primary Cerebellar Cell Cultures

Thyroid receptors play an important role in postnatal brain development. Zearalenone (ZEN), a major mycotoxin of Fusarium fungi, is well known to cause serious health problems in animals and humans through various mechanisms, including the physiological pathways of thyroid hormone (TH). In the present study, we aimed to investigate the expression of thyroid receptors α (TRα) and β (TRβ) in primary cerebellar neurons in the presence or absence of glia and following ZEN treatment, using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blot. Primary cerebellar granule cells were treated with low doses of ZEN (0.1 nM) in combination with physiologically relevant concentrations of l-thyroxine (T4), 3,3′,5-triiodo-l-thyronine (T3) and 17β-estradiol (E2). Expression levels of TRα and TRβ at mRNA and protein levels were slightly modified by ZEN administered alone; however, along with thyroid and steroid hormones, modelling the physiological conditions, expression levels of TRs varied highly depending on the given treatment. Gene expression levels were also highly modulated by the presence or absence of glial cells, with mostly contrasting effects. Our results demonstrate divergent transcriptional and translational mechanisms involved in the expression of TRs implied by ZEN and hormonal milieu, as well as culturing conditions.

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.

Comparison of Individual and Combined Effects of Four Endocrine Disruptors on Estrogen Receptor Beta Transcription in Cerebellar Cell Culture: The Modulatory Role of Estradiol and Triiodo-Thyronine

Background: Humans and animals are continuously exposed to a number of environmental substances that act as endocrine disruptors (EDs). While a growing body of evidence is available to prove their adverse health effects, very little is known about the consequences of simultaneous exposure to a combination of such chemicals; Methods: Here, we used an in vitro model to demonstrate how exposure to bisphenol A, zearalenone, arsenic, and 4-methylbenzylidene camphor, alone or in combination, affect estrogen receptor β (ERβ) mRNA expression in primary cerebellar cell cultures. Additionally, we also show the modulatory role of intrinsic biological factors, such as estradiol (E2), triiodo-thyronine (T3), and glial cells, as potential effect modulators; Results: Results show a wide diversity in ED effects on ERβ mRNA expression, and that the magnitude of these ED effects highly depends on the presence or absence of E2, T3, and glial cells; Conclusion: The observed potency of the EDs to influence ERβ mRNA expression, and the modulatory role of E2, T3, and the glia suggests that environmental ED effects may be masked as long as the hormonal milieu is physiological, but may tend to turn additive or superadditive in case of hormone deficiency.

Leptin gene in rabbit: cloning and expression in mammary epithelial cells during pregnancy and lactation

Leptin is known as a cytokine mostly produced by fat cells and implicated in regulation of energy metabolism and food intake but has also been shown to be involved in many physiological mechanisms such as tissue metabolism and cell differentiation and proliferation. In particular, leptin influences the development of mammary gland. Although leptin expression in mammary gland has been studied in several species, no data are available in the rabbit. Leptin transcripts in this species have been described as being encoded by only two exons rather than three as in other species. Our focus was to clone and sequence the rabbit leptin cDNA and to prepare the recombinant biologically active protein for validation of the proper sequence and then to describe leptin expression in rabbit mammary gland during different stages of pregnancy and lactation. The leptin sequence obtained was compared with those of other species, and genome alignment demonstrated that the rabbit leptin gene is also encoded by three exons. Additionally, we analyzed the expression of leptin during pregnancy and lactation. Leptin mRNA was weakly expressed throughout pregnancy, whereas mRNA levels were higher during lactation, with a significant increase between days 3 and 16. Leptin transcripts and protein were localized in luminal epithelial cells, thus indicating that leptin synthesis occurs in this compartment. Therefore, mammary synthesized leptin may constitute a major regulator of mammary gland development by acting locally as an autocrine and/or paracrine factor. Furthermore, our results support the possible physiological role of leptin in newborns through consumption of milk.

Ligand-induced changes in Oestrogen and thyroid hormone receptor expression in the developing rat cerebellum: A comparative quantitative PCR and Western blot study

Oestrogen (E2) and thyroid hormones (THs) are key regulators of cerebellar development. Recent reports implicate a complex mechanism through which E2 and THs influence the expression levels of each other's receptors (ERs and TRs) to precisely mediate developmental signals and modulate signal strength. We examined the modulating effects of E2 and THs on the expression levels of their receptor mRNAs and proteins in cultured cerebellar cells obtained from 7-day-old rat pups. Cerebellar granule cell cultures were treated with either E2, THs or a combination of these hormones, and resulting receptor expression levels were determined by quantitative PCR and Western blot techniques. The results were compared to non-treated controls and to samples obtained from 14-day-old in situ cerebella. Additionally, we determined the glial effects on the regulation of ER-TR expression levels. The results show that (i) ER and TR expression depends on the combined presence of E2 and THs; (ii) glial cells mediate the hormonal regulation of neuronal ER-TR expression and (iii) loss of tissue integrity results in characteristic changes in ER-TR expression levels. These observations suggest that both E2 and THs, in adequate amounts, are required for the precise orchestration of cerebellar development and that alterations in the ratio of E2/THs may influence signalling mechanisms involved in neurodevelopment. Comparison of data from in vitro and in situ samples revealed a shift in receptor expression levels after loss of tissue integrity, suggesting that such adjusting/regenerative mechanisms may function after cerebellar tissue injury as well.

Effects of energy restriction on thyroid hormone metabolism in chickens

Energy restriction induces changes in thyroid hormone economy in the form of a complex adaptation mechanism, in order to conserve energy storage and protein reserves. In the present work, thyroid hormone serum concentrations, hepatic deiodinase enzyme activities and hepatic deiodinase mRNA expression were examined after feed restriction and fasting. We demonstrate that during energy restriction, T 3 concentration is lowered due to a decreased T 4 activation and increased T 3 inactivation. We show that hepatic type-I deiodinase (D1) is not affected by energy restriction, however, hepatic D2 is decreased on both transcriptional and enzyme activity levels. Furthermore, hepatic D3 is increased after feed restriction in the liver. We also show that the hypothalamic feedback is not involved in the changes in serum T 3 and T 4 concentrations. Our data indicate that D2 enzyme contributes to the special hormone-exporting role of the chicken liver and this enzyme can be modulated by feed restriction.

Glycogenic induction of thyroid hormone conversion and leptin system activation in the liver of postpartum dairy cows

In the regulation of energy metabolism, the liver plays an important role in the reinforcement of energy production. In periparturient cows the energy homeostasis turns into a negative energy balance that may shift the physiological regulation of energy balance towards pathological processes. Propylene glycol (PG), as a complementary source of energy used in the nutrition of dairy cows, alters systemic thyroid hormone economy; however, the exact mechanism through which highly glycogenic feed supplements impact liver metabolism is little known. Previous studies showed that only leptin receptors are expressed in the liver of cows, and now we report that leptin mRNA is expressed in the liver of cows as well. The present results show that the mRNA of leptin and its receptors are differentially modulated by the increased energy content of the feed consumed. Simultaneous changes in hepatic type I deiodinase activity suggest that hepatic modulation of the leptin system by PG supplementation may be mediated by an increased local thyroxine-triiodothyronine conversion. Since PG supplementation with simultaneous T4-T3 turnover and increased hepatic leptin- and short-form leptin receptor mRNA were not associated with a significant change in hepatic total lipid levels, it is suggested that the leptin system, directly or indirectly modulated by thyroid hormones, may represent a local defence mechanism to prevent fatty liver formation.

Malignant transformation of mammary epithelial cells increases expression of leptin and leptin receptor

Both normal and malignant mammary tissues have been shown to produce leptin and express leptin receptors. This study compared the expression of leptin and leptin receptor mRNA in a variety of normal and malignant mammary epithelial cell lines and observed that in general the malignant lines expressed higher levels of leptin and leptin receptor mRNA than nonmalignant lines. Furthermore, oncogenic transformation of nonmalignant cell lines increased expression of leptin and leptin receptor, with expression of ErbB2 giving particularly high levels of expression of long-form leptin receptor. In addition, nonmalignant cells exhibited little or no increase in DNA synthesis following leptin treatment, whereas oncogene-transformed cells had increased DNA synthesis in response to leptin. These effects varied among oncogenes, with ErbB2-transformed cells showing particularly high expression of leptin receptor mRNA and high response to leptin.

Pregnancy stage and number of fetuses may influence maternal plasma leptin in ewes

Maternal plasma leptin is elevated in ewes during pregnancy. The authors studied whether there was any relation between maternal plasma leptin and insulin concentrations, the number of fetuses and the circulating and faecal levels of gestagens. At the end of the breeding season in January the ovarian activity of Prolific Merino ewes was induced/synchronised with gestagen + eCG treatment. Ewes were inseminated artificially (AI) by laparoscopy. Blood and faecal samples were collected before AI (day 0) and again 41, 81 and 101 days later. The plasma levels of leptin (pL), insulin and progesterone (pP4), and the faecal P4 metabolite (P4-met) content were determined. The day 0 level of pL was significantly higher in pregnant (n = 24) than in non-pregnant ewes (n = 32). By day 41 the pL of pregnant animals had doubled, it showed a further moderate increase on day 81, and decreased slightly thereafter. During pregnancy pP4 and faecal P4-met rose continuously and were positively correlated at all stages. The mean levels of pL and pP4 and the faecal content of P4-met were lower in ewes bearing single (n = 12) than in those with 2 (n = 6) or 3-5 fetuses (n = 6). Analysis of variance demonstrated significant differences according to the number of fetuses in the pL and pP4, but not in P4-met (p = 0.042, 0.044, and 0.051, respectively). Leptin showed positive correlation with insulin before the AI but not during pregnancy. On days 41 and 81 pL showed a slight positive correlation with P4 and P4-met, which decreased slightly by day 101. This study shows that although leptinaemia is affected by the number of fetuses and the level of P4, pregnancy stage is a more important regulator than these additional factors.

Leptin Does Not Act Directly on Mammary Epithelial Cells in Prepubertal Dairy Heifers

The mammary gland of prepubertal dairy heifers consists of parenchyma expanding into the stroma, a matrix of connective and adipose tissue. High planes of nutrition increase stromal mass, but inhibit growth of parenchyma. The parenchyma consists of epithelial cells proliferating in response to growth factors such as insulin like growth factor-I (IGF-I). These observations have led to the hypothesis that elevated planes of nutrition increase leptin production, which in turn inhibits IGF-I-mediated epithelial cell proliferation. To assess this possibility, heifers were offered planes of nutrition sustaining average daily gains of 715 g/d (normal; NP) or 1,202 g/d (high; HP) from 42 d of age until slaughter at 240 kg. At slaughter, HP heifers had 2-fold greater plasma leptin concentration and 3-fold greater leptin mRNA abundance in mammary stroma and parenchyma. To assess the causal nature between leptin and parenchymal development, the induction of signaling events and functional responses in the MAC-T cell line and in primary mammary epithelial cells by leptin was examined. Leptin did not induce phosphorylation of signal transducers and activators of transcription (STAT)3, STAT5, extracellular signal-regulated kinase (ERK1/2), or AKT/Protein kinase B. Consistent with its inability to signal, leptin did not alter basal- or IGF-I-stimulated thymidine incorporation or increase suppressors of cytokine signaling 3 (SOCS3) expression in these cells. Transcripts corresponding to the short leptin receptor form were present in mammary tissue, but those corresponding to the long signaling form were not detected in either mammary tissue or cells. In conclusion, elevated planes of nutrition increase leptin synthesis in mammary stroma, but leptin does not act directly on bovine mammary epithelial cells.

Partial cloning and localisation of leptin and its receptor in the one-humped camel (Camelus dromedarius)

Based on the studies and results presented here, leptin and its receptor were expressed by adipose tissue, mammary alveolar epithelial cells, liver hepatocytes, and the lining epithelium of the bile duct of the one-humped camel (Camelus dromedarius). Our observations support the biological importance of leptin in the mammary gland as well as the likely local effect of leptin on the peripheral tissues. We suggest that there may be an association between hepatic leptin and the lipogenic activity of the liver in the dromedary camel.

Thyroid hormone metabolism in the brain of domestic animals

The action of thyroid hormones in the brain is strictly regulated, since these hormones play a crucial role in the development and in the physiological functioning of the central nervous system. It has been shown by many authors that brain tissue represents a special site of thyroid hormone handling. A relative independence of this tissue of the actual thyroid status was shown by our research group in birds and mammals. Hypothyroid animals can maintain a close to normal level of triiodothyronine in the brain tissue for extended periods. This phenomenon is due to at least three regulating mechanisms. (1) Uptake of thyroid hormones is enhanced. It was shown that the uptake by the telencephalon of labelled triiodothyronine (T3) was much higher in thyroidectomized (TX) animals than in controls or in thyroidectomized and T3 supplemented ones. (2) Conversion of thyroxine into triiodothyronine is increased. One of the most important elements of this process is the adjustment of the expression and activity of the type II deiodinase of the brain to a higher level. Enzyme kinetic studies, expression of TRalpha and beta nuclear thyroid hormone receptors and--after cloning the chicken type II deiodinase--in situ hybridization studies clearly supported the central role of the conversion process. (3) The rate of loss of triiodothyronine from the brain tissue is slowed down under hypothyroid conditions as evidenced by our hormone kinetic studies.

Expression and localisation of leptin and leptin receptor in the mammary gland of the dry and lactating non-pregnant cow

Leptin and leptin receptor were studied in the mammary gland of non-pregnant dry and lactating cows. Using RT-PCR it was demonstrated that leptin and its short (Ob-Ra) and long (Ob-Rb) receptor isoforms are expressed both in the dry and the lactating mammary gland tissue. Tissue distribution of leptin and its receptor mRNA transcripts were examined by in situ hybridisation, while the leptin protein was localised by immunohistochemistry. Although in situ hybridisation is semiquantitative, our morphological data suggest that the epithelial leptin mRNA expression of the lactating gland is higher than that of the dry gland. To compare the leptin mRNA levels between dry and lactating udders competitive PCR was used, which showed no difference in leptin expression for the whole mammary tissues. The lack of difference in total leptin mRNA levels is explained by the high adipose tissue content of the dry mammary gland. Leptin and its receptor transcripts are expressed mainly in the epithelial cells of lactating cows, while in dry mammary tissue the signal is found in the stromal tissues as well. The results provide additional evidence that locally produced leptin takes part in the regulation and maintenance of mammary epithelial cell activity.