Carotid chemoreceptor afferent projections to leptin receptor containing neurons in nucleus of the solitary tract

Neurons expressing the leptin receptor (Ob-R) exist within the caudal nucleus of the solitary tract (NTS). Additionally, afferent neurons expressing the Ob-R have been identified within the nodose ganglion and NTS. Furthermore, systemic injections or focal injections of leptin directly into NTS potentiate the response of NTS neurons to carotid chemoreceptor activation. However, the distribution of carotid body afferents in relation to Ob-R containing neurons within NTS is not known. In this study, chemoreceptor afferent fibers were labeled following microinjection of the anterograde tract tracer biotinylated dextran amine (BDA) into the carotid body or petrosal/nodose ganglion of Wistar rats. After a survival period of 10-14 days, the NTS was processed for BDA and Ob-R immunoreactivity. Afferent axons originating in the carotid body were found to project to the lateral (Slt), gelantinosa (Sg), and medial (Sm) subnuclei of the NTS complex. A similar, but more robust distribution of BDA labeled fibers was observed in the NTS complex after injections into the petrosal/nodose ganglion. Carotid body BDA labeled fibers were observed in close apposition to Ob-R immunoreactive neurons in the region of Slt, Sg and Sm. In addition, a small number of carotid body afferents were found to contain both BDA and express Ob-R-like immunoreactivity within the regions of Slt, Sg and Sm. Taken together, these data suggest that leptin may modulate carotid chemoreceptor function not only through direct effects on NTS neurons, but also through a direct effect on carotid body primary afferent fibers that innervate NTS neurons.

Leptin promotes wound healing in the oral mucosa

INTRODUCTION

Leptin, a 16 kDa circulating anti-obesity hormone, exhibits many physiological properties. Recently, leptin was isolated from saliva; however, its function in the oral cavity is still unclear. In this study, we investigated the physiological role of leptin in the oral cavity by focusing on its effect on wound healing in the oral mucosa.

METHODS

Immunohistochemical analysis was used to examine the expression of the leptin receptor (Ob-R) in human/rabbit oral mucosa. To investigate the effect of leptin on wound healing in the oral mucosa, chemical wounds were created in rabbit oral mucosa, and leptin was topically administered to the wound. The process of wound repair was histologically observed and quantitatively analyzed by measuring the area of ulceration and the duration required for complete healing. The effect of leptin on the proliferation, differentiation and migration of human oral mucosal epithelial cells (RT7 cells) was investigated using crystal violet staining, reverse transcription polymerase chain reaction (RT-PCR) and a wound healing assay, respectively.

RESULTS

Ob-R was expressed in spinous/granular cells in the epithelial tissue and vascular endothelial cells in the subepithelial connective tissue of the oral mucosa. Topical administration of leptin significantly promoted wound healing and shortened the duration required for complete healing. Histological analysis of gingival tissue beneath the ulceration showed a denser distribution of blood vessels in the leptin-treated group. Although the proliferation and differentiation of RT7 cells were not affected by leptin, the migration of these cells was accelerated in the presence of leptin.

CONCLUSION

Topically administered leptin was shown to promote wound healing in the oral mucosa by accelerating epithelial cell migration and enhancing angiogenesis around the wounded area. These results strongly suggest that topical administration of leptin may be useful as a treatment to promote wound healing in the oral mucosa.

Characterization of a novel genetically obese mouse model demonstrating early onset hyperphagia and hyperleptinemia

Obesity is a critical risk factor for the development of metabolic syndrome, and many obese animal models are used to investigate the mechanisms responsible for the appearance of symptoms. To establish a new obese mouse model, we screened ∼13,000 ICR mice and discovered a mouse demonstrating spontaneous obesity. We named this mouse "Daruma" after a traditional Japanese ornament. Following the fixation of the genotype, these animals exhibited obese phenotypes according to Mendel's law of inheritance. In the Daruma mouse, the leptin receptor gene sequence carried two base mutations that are good candidates for the variation(s) responsible for the obese phenotype. The Daruma mice developed characteristic visceral fat accumulation at 4 wk of age, and the white adipose and liver tissues exhibited increases in cell size and lipid droplets, respectively. No histological abnormalities were observed in other tissues of the Daruma mice, even after the mice reached 25 wk of age. Moreover, the onset of impaired leptin signaling was early and manifested as hyperleptinemia and hyperinsulinemia. Pair feeding completely inhibited obesity, although these mice rapidly developed hyperphagia and obesity followed by hyperleptinemia when pair feeding ceased and free-access feeding was permitted. Therefore, the Daruma mice exhibited unique characteristics and may be a good model for studying human metabolic syndrome.

Leptin regulates gonadotropins and steroid receptors in the rats ovary

The leptin hormone is important to satiety and an important link between the nutritional status and reproductive processes. Owing to the contradictory effects of leptin on the ovary and the failure to clarify the precise mechanism by which leptin affects the ovary, our aim was to contribute to evaluation if leptin can directly regulate the gene expression of leptin itself and its receptors, and the expression of several genes related to the ovary function by a model of tissue culture. Ovaries from Wistar dams were used at 90 days of age and were submitted to medium with presence and absence of leptin. The results can demonstrate that leptin regulates gonadotropins and steroid receptors, which could suggest that the ovarian leptin role could be secondary to the changes in these receptors expression in rats.

TNF-α up-regulates protein level and cell surface expression of the leptin receptor by stimulating its export via a PKC-dependent mechanism

Increasing evidence suggests that inflammation/cytokines may modulate hypothalamic responses to leptin, which is a key regulator of energy homeostasis and inflammatory/stress responses. We investigated a possible role of TNF-α, a key early mediator of inflammation, in regulating the expression and trafficking of the long-isoform leptin receptor (LEPRb), the primary mediator of leptin signaling, in cultured cells. We found that TNF-α in a wide range of concentrations up-regulated LEPRb protein level and soluble LEPR (sLEPR) release via ectodomain shedding of LEPRb in multiple cell types, including neuronal cells. TNF-α also acutely increased LEPRb cell surface expression and leptin-induced STAT3 phosphorylation. In contrast, TNF-α had no significant effects on the protein level or cell surface expression of several other transmembrane proteins, including the transferrin receptor and cadherin. The stimulatory effects of TNF-α on LEPRb cell surface expression and sLEPR release were not dependent on de novo protein synthesis or functional lysosomes but were blocked by brefeldin A, suggesting that an intact Golgi or continuous endoplasmic reticulum to Golgi transport of newly synthesized proteins is required for these effects. However, TNF-α did not increase the half-life of cell surface LEPRb. Protein kinase C (PKC) inhibitor GF109203X abrogated the effects of TNF-α, whereas the pan-PKC activator phorbol 12-myristate 13-acetate mimicked the TNF-α effects. Taken together, our results suggest that TNF-α, via activation of PKC, regulates anterograde trafficking and/or degradation of LEPRb in the biosynthetic pathway, leading to concomitant increases in LEPRb protein level, cell surface expression, and sLEPR production. The finding that LEPRb cell surface expression and sLEPR production, key modulators of leptin sensitivity and bioavailability, are direct targets of TNF-α signaling could have a potentially important implication in the regulation of leptin signaling activity in different pathophysiological conditions as diverse as obesity and sepsis.

Estrogen stimulates leptin receptor expression in ATDC5 cells via the estrogen receptor and extracellular signal-regulated kinase pathways

Regulation of the physiological processes of endochondral bone formation during long bone growth is controlled by various factors including the hormones estrogen and leptin. The effects of estrogen are mediated not only through the direct activity of estrogen receptors (ERs) but also through cross talk with other signaling systems implicated in chondrogenesis. The receptors of both estrogen and leptin (OBR (LEPR)) are detectable in growth plate chondrocytes of all zones. In this study, the expression of mRNA and protein of OBR in chondrogenic ATDC5 cells and the effect of 17β-estradiol (E(2)) stimulation were assessed using quantitative PCR and western blotting. We have found that the mRNA of Obr was dynamically expressed during the differentiation of ATDC5 cells over 21 days. Application of E(2) (10(-7) M) at day 14 for 48 h significantly upregulated OBR mRNA and protein levels (P<0.05). The upregulation of Obr mRNA by E(2) was shown to take place in a concentration-dependent manner, with a concentration of 10(-7) M E(2) having the greatest effect. Furthermore, we have confirmed that E(2) affected the phosphorylation of ERK1/2 (MAPK1/MAPK3) in a time-dependent manner where a maximal fourfold change was observed at 10 min following application of E(2). Finally, pretreatment of the cells with either U0126 (ERK1/2 inhibitor) or ICI 182 780 (ER antagonist) blocked the upregulation of OBR by E(2) and prevented the E(2)-induced phosphorylation of ERK. These data demonstrate, for the first time, the existence of cross talk between estrogen and OBR in the regulation of bone growth whereby estrogen regulates the expression of Obr in growth plate chondrocytes via ERs and the activation of ERK1/2 signaling pathways.

DNA microarray analysis identifies CKS2 and LEPR as potential markers of meningioma recurrence

Meningiomas are the most frequent intracranial tumors. Surgery can be curative, but recurrences are possible. We performed gene expression analyses and loss of heterozygosity (LOH) studies looking for new markers predicting the recurrence risk. We analyzed expression profiles of 23 meningiomas (10 grade I, 10 grade II, and 3 grade III) and validated the data using quantitative polymerase chain reaction (qPCR). We performed LOH analysis on 40 meningiomas, investigating chromosomal regions on 1p, 9p, 10q, 14q, and 22q. We found 233 and 268 probe sets to be significantly down- and upregulated, respectively, in grade II or III meningiomas. Genes downregulated in high-grade meningiomas were overrepresented on chromosomes 1, 6, 9, 10, and 14. Based on functional enrichment analysis, we selected LIM domain and actin binding 1 (LIMA1), tissue inhibitor of metalloproteinases 3 (TIMP3), cyclin-dependent kinases regulatory subunit 2 (CKS2), leptin receptor (LEPR), and baculoviral inhibitor of apoptosis repeat-containing 5 (BIRC5) for validation using qPCR and confirmed their differential expression in the two groups of tumors. We calculated ΔCt values of CKS2 and LEPR and found that their differential expression (C-L index) was significantly higher in grade I than in grade II or III meningiomas (p < .0001). Interestingly, the C-L index of nine grade I meningiomas from patients who relapsed in <5 years was significantly lower than in grade I meningiomas from patients who did not relapse. These findings indicate that the C-L index may be relevant to define the progression risk in meningioma patients, helping guide their clinical management. A prospective analysis on a larger number of cases is warranted.

The detection of 3 leptin receptor isoforms in crucian carp gill and the influence of fasting and hypoxia on their expression

To understand leptin signaling pathway in the crucian carp (Carassius carassius), we cloned 3 leptin receptor isoform complementary DNAs (ie, the long form [cclpr-L], the short form [cclpr-s1], and the secreted form [cclpr-s2]). Variant cclpr-L had a 3,255-bp open reading frame and a complete intracellular domain with box 1 and box 2 consensus sequences. By contrast, cclpr-s1 contained only 4 amino acids in its intracellular domain, without the "box 1" motif, which is conserved among membrane-bound leptin receptor short isoforms in mammals. Variant cclpr-s2 had no transmembrane domain, suggesting that it is a soluble form of the receptor, and alternative splicing of cclpr-s2 mRNA employs a different mechanism for the generation of soluble leptin receptor by intron retention. The fasting-treated fish showed significantly lower cclpr-L mRNA levels in gill tissue than the control group, whereas cclpr-s2 mRNA levels did not vary significantly among the groups. Treatment with hypoxia significantly increased mRNA levels of both cclpr-L and cclpr-s2 in gill tissue. To our knowledge, this is the first study of leptin receptor isoforms expression in teleosts.

Nociceptin/orphanin FQ suppresses the excitability of neurons in the ventromedial nucleus of the hypothalamus

Nociceptin or orphanin FQ (N/OFQ) stimulates food intake when injected into the ventromedial nucleus of the hypothalamus (VMN). The VMN negatively regulates energy balance in part by tonically activating proopiomelanocortin arcuate neurons, thereby suppressing food intake. However, it is not clear how orexigenic neurotransmission within the VMN can stimulate food intake. We tested the hypothesis that the orexigenic action of N/OFQ results from its inhibition of anorexigenic VMN neurons. We studied the effects of N/OFQ on the electrical properties of anorexigenic VMN neurons in acute brain slices. Ionic mechanisms underlying the actions of N/OFQ were studied using whole cell patch-clamp recordings from VMN neurons expressing the anorexigenic leptin receptor (LepRb). Bath application of N/OFQ to LepRb-expressing VMN neurons elicited a robust, reversible membrane hyperpolarization that suppressed neuronal excitability by raising the action potential firing threshold and cell rheobase. N/OFQ activated a postsynaptic, G-protein coupled, inwardly rectifying potassium (GIRK) current that was sensitive to G-protein inactivation, blocked by the GIRK blocker SCH23390, and occluded by the GABAB agonist and potent GIRK activator, baclofen. Application of the selective N/OFQ receptor antagonist SB-612111 blocked the inhibitory effects of N/OFQ. We concluded that N/OFQ directly inhibited VMN neurons by activating a GIRK. These results implicate the site-specific contributions of orexigenic neuropeptides at VMN neurons to suppress anorexigenic output. This study thus advances our understanding regarding the contributions of the VMN to hypothalamic regulation of energy balance.

Progesterone-induced blocking factor (PIBF) and trophoblast invasiveness

Controlled trophoblast invasion is a key process during human placentation and a prerequisite for successful pregnancy. Progesterone is one of the factors to regulate trophoblast invasiveness. Progesterone-induced blocking factor (PIBF) is a progesterone-induced molecule expressed by the trophoblast, and also by tumors. The distribution of PIBF within the first-trimester decidua coincides with sites of trophoblast invasion. Another molecule that has been implicated in the control of trophoblast invasiveness is placental leptin. Leptin inhibits the secretion of progesterone by cytotrophoblast. The aim of this work was to investigate the possible interaction of PIBF and leptins in regulating trophoblast invasion. Paraffin-embedded sections from normal first-trimester placentae, partial moles, complete moles, and choriocarcinomas were reacted with PIBF, leptin, and leptin receptor specific antibodies. PIBF-deficient trophoblast cells were generated using siRNA and leptin receptor was detected on Western blot analysis. The lysates of PIBF-treated cells were used for detecting leptin expression in a protein array. PIBF was expressed in both normal first-trimester villous trophoblast and in partial mole. Compared with this, PIBF expression was markedly decreased in complete mole and absent in choriocarcinoma. Neither leptinR nor leptin were detected in partial mole, whereas both of these molecules were present in complete mole and choriocarcinoma. Leptin receptor expression was upregulated in PIBF-deficient cells, while leptin expression was decreased in PIBF-treated cells. These data suggest that PIBF affects the expression of leptin and its receptor, and that PIBF expression is inversely related to trophoblast invasiveness.

Leptin resistance and desensitization of hypophagia during prolonged inflammatory challenge

Acute exposure to bacterial lipopolysaccharide (LPS) is a potent inducer of immune response as well as hypophagia. Nevertheless, desensitization of responses to LPS occurs during long-term exposure to endotoxin. We induced endotoxin tolerance, injecting repeated (6LPS) LPS doses compared with single (1LPS) treatment. 1LPS, but not 6LPS group, showed decreased food intake and body weight, which was associated with an increased plasma leptin and higher mRNA expression of OB-Rb, MC4R, and SOCS3 in the hypothalamus. Hypophagia induced by 1LPS was associated with lower levels of 2-arachidonoylglycerol (2-AG), increased number of p-STAT3 neurons, and decreased AMP-activated protein kinase (AMPK) activity. Desensitization of hypophagia in the 6LPS group was related to high 2-AG, with no changes in p-STAT3 or increased p-AMPK. Leptin decreased food intake, body weight, 2-AG levels, and AMPK activity and enhanced p-STAT3 in control rats. However, leptin had no effects on 2-AG, p-STAT3, or p-AMPK in the 1LPS and 6LPS groups. Rats treated with HFD to induce leptin resistance showed neither hypophagia nor changes in p-STAT3 after 1LPS, suggesting that leptin and LPS recruit a common signaling pathway in the hypothalamus to modulate food intake reduction. Desensitization of hypophagia in response to repeated exposure to endotoxin is related to an inability of leptin to inhibit AMPK phosphorylation and 2-AG production and activate STAT3. SOCS3 is unlikely to underlie this resistance to leptin signaling in the endotoxin tolerance. The present model of prolonged inflammatory challenge may contribute to further investigations on mechanisms of leptin resistance.

H-FABP and LEPR gene expression profile in skeletal muscles and liver during ontogenesis in various breeds of pigs

The genes coding for H-FABP (heart acid-binding protein) and LEPR (leptin receptor) are considered to be candidates for lipid metabolism and thus affect fat deposition in pigs. The aim of our study was to assess the amount of H-FABP and LEPR transcript in the skeletal muscles (m. longissimus dorsi, m. semimembranosus) and liver of pigs of various ages. The experiments were carried out on 5 popular breeds of swine raised in Poland which exhibit different levels of fat tissue. Furthermore, we examined the effect of H-FABP and LEPR genotypes (HinfI, HpaII, and HaeIII for H-FABP and HpaII for LEPR) on the expression abundance of these genes. We confirmed a statistically significant relationship between the breed (P<.001), type of tissue (LEPR P<.001; H-FABP P<.01), and age of the animal (P<.05) on the abundance of mRNA transcript of both genes. In all breeds, the expression of the leptin receptor gene increased significantly (P<.01) with age in muscle tissue, whereas this relationship was not observed in liver tissue. However, the expression of the H-FABP gene in muscles did not change with age or breed, although in the liver expression levels were high in young (60 and 90 d) pigs. In conclusion, H-FABP and LEPR genes are strongly related to the development and function of fat tissue in pigs.

Human obesity reduces the number of hepatic leptin receptor (ob-R) expressing NK cells

OBJECTIVE

In the industrialized world, obesity is an increasing socioeconomic health problem. Obese subjects have a higher risk of developing several types of cancer. NK cells are an integral component of the innate immune system, able to destruct tumor cells. The adipokine leptin plays a crucial role in the development of obesity and its related diseases. Peripheral leptin signaling is modulated by the liver.

METHODS

The aim of this study was to evaluate the number of hepatic NK cells (CD56+) and the number of leptin-receptor positive (Ob-R+) cells in the livers of five normal-weight and five obese humans. Livers were removed during autopsy and accurately defined sections were stained immunohistochemically and CD56+, Ob-R+, and double-positive cells were quantified.

RESULTS

Results revealed a dramatic reduction of NK cells and Ob-R-expressing NK cells in the livers of obese individuals.

CONCLUSIONS

The present study demonstrates, for the first time, body-weight-dependent numbers of hepatic NK cells. This supports the hypothesis of obesity-associated alterations of immune cell numbers in different human organs.

Curcumin eliminates leptin's effects on hepatic stellate cell activation via interrupting leptin signaling

Nonalcoholic steatohepatitis (NASH) is commonly found in patients with obesity and is often accompanied with abnormally elevated levels of plasma leptin, i.e. hyperleptinemia. A relatively high population of NASH patients develops hepatic fibrosis, even cirrhosis. Hepatic stellate cells (HSCs) are the major effector cells during liver fibrogenesis and could be activated by leptin. The antioxidant curcumin, a phytochemical from turmeric, has been shown to suppress HSC activation in vitro and in vivo. This project is to evaluate the effect of curcumin on leptin-induced HSC activation and to elucidate the underlying mechanisms. We hypothesize that curcumin abrogates the stimulatory effect of leptin on HSC activation by interrupting leptin signaling and attenuating leptin-induced oxidative stress. Curcumin eliminates the stimulatory effects of leptin on regulating expression of genes closely relevant to HSC activation. Curcumin interrupts leptin signaling by reducing phosphorylation levels of leptin receptor (Ob-R) and its downstream intermediators. In addition, curcumin suppresses gene expression of Ob-R in HSCs, which requires the activation of endogenous peroxisome proliferator-activated receptor-gamma and de novo synthesis of glutathione. In conclusion, our results demonstrate that curcumin abrogates the stimulatory effect of leptin on HSC activation in vitro by reducing the phosphorylation level of Ob-R, stimulating peroxisome proliferator-activated receptor-gamma activity, and attenuating oxidative stress, leading to the suppression of Ob-R gene expression and interruption of leptin signaling. These results provide novel insights into therapeutic mechanisms of curcumin in inhibiting HSC activation and intervening liver fibrogenesis associated with hyperleptinemia in NASH patients.

A test of the lipostat theory in a seasonal (ovine) model under natural conditions reveals a close relationship between adiposity and melanin concentrating hormone expression

A study was undertaken in Corriedale ewes to test the lipostat theory using data obtained from a model of seasonal change in food intake and body composition. The theory predicts adipose-derived factors signal to the brain and vice versa, to maintain homeostasis. It is held that leptin acts on cells in the brain to regulate food intake and energy expenditure, through "first order" neurons in the arcuate nucleus (ARC). These cells are thought to receive information that is relayed to "second order" neurons, to regulate food intake and other functions. In this study, groups (n=4-5) of ovariectomized ewes were maintained under natural conditions and sampled at various points across the year. Food intake, body composition and indices of metabolic function were measured prior to collection of brains for in situ hybridization analysis. Expression of genes encoding for neuropeptide Y (NPY), pro-opiomelanocortin (POMC), orexin (ORX), melanin concentrating hormone (MCH) and leptin receptor (ObRb) was quantified. NPY gene expression was high when food intake was also high but, across the year, changes in NPY and POMC gene expression did not correspond predictably to plasma leptin levels or leptin receptor gene expression. Negative correlation was found between adiposity (omental and whole body fat) and gene expression of MCH and ORX, suggesting that changes in expression of genes for "second order" orexigenic peptides are closely linked to changes of metabolic state, even when similar relationships cannot be shown for expression of genes in "first order" neurons. These data provide support for the lipostat theory.

Reduced intestinal absorption of dipeptides via PepT1 in mice with diet-induced obesity is associated with leptin receptor down-regulation

Leptin is a major determinant of energy homeostasis, acting both centrally and in the gastrointestinal tract. We previously reported that acute leptin treatment enhances the absorption of di- and tripeptides via the proton-dependent PepT1 transporter. In this study, we investigated the long term effect of leptin on PepT1 levels and activity in Caco2 cell monolayers in vitro. We then assessed the significance of the regulation of PepT1 in vivo in a model of diet-induced obesity. We demonstrated that 1) leptin regulated PepT1 at the transcriptional level, via the MAPK pathway, and at the translational level, via ribosomal protein S6 activation, in Caco2 cells and 2) this activation was systematically followed by a time- and concentration-dependent loss of leptin action reflecting desensitization. Deciphering this desensitization, we demonstrated that leptin induced a down-regulation of its own receptor protein and mRNA expression. More importantly, we showed, in mice with diet-induced obesity, that a 4-week hypercaloric diet resulted in a 46% decrease in PepT1-specific transport, because of a 30% decrease in PepT1 protein and a 50% decrease in PepT1 mRNA levels. As shown in Caco2 cells, these changes in PepT1 were supported by a parallel 2-fold decrease in leptin receptor expression in mice. Taken together, these results indicate that during induction of obesity, leptin resistance may also occur peripherally in the gastrointestinal tract, disrupting the absorption of oligopeptides and peptidomimetic drugs.

Leptin-leptin receptor are involved in angiogenesis in human hepatocellular carcinoma

Recent evidence in vitro and in vivo indicates that leptin, an adipose tissue-secreted hormone which is involved in the regulation of satiety, metabolic rate and thermogenesis, is implicated in angiogenesis. However, the role of leptin-mediated angiogenesis in hepatic carcinogenesis has not yet been completely elucidated. In this study, we have correlated microvascular density and leptin/leptin receptor (Ob-R) expression in endothelial and tumor cells with the histopathological type in human hepatocellular carcinoma (HCC). For this purpose, specimens of 40 primary HCC were submitted to immunohistochemical investigation using anti-CD31, anti-leptin and anti-Ob-R antibodies. Poorly-differentiated HCC had a higher degree of vascularization than other stages and leptin/Ob-R expression in both tumor and endothelial cells increased in parallel with the grade of malignancy and was highly correlated with the degree of angiogenesis. In the chick embryo chorioallantoic membrane in vivo assay, HCC biopsy specimens induced a strong angiogenic response, which was counteracted by an anti-leptin antibody. Taken together, these findings indicate that leptin/Ob-R correlate with angiogenesis and tumor progression in patients with HCC and that an anti-leptin antibody exerts an angiostatic activity in HCC.

Photoperiod affects gene expression of leptin and leptin receptors in adipose tissue from lactating dairy cows

Leptin is mainly secreted by adipocytes and is implicated in the regulation of metabolic status, feed intake, and body condition. Day length (DL) can affect leptin gene expression and secretion. The aim of the study was to evaluate the effect of DL on gene expression of leptin and leptin receptors in adipose tissue (AT). Four lactating and pregnant Holstein cows were housed in a climate-controlled chamber for 51 d. The first 30 d were used to adapt animals to the new housing conditions. During that period the DL adopted was 12 h light:12 h dark (12:12). The experimental period included 3 different and consecutive phases: 7 d of neutral DL (12:12); 7 d of long DL (18 h light:6 h dark); and 7 d of short DL (6 h light:18 h dark). Subcutaneous AT biopsies were performed at the end of each phase. Prolactin, growth hormone, cortisol, leptin, glucose, nonesterified fatty acids, beta-OH-butyrate, and cholesterol were determined in plasma samples. Abundance of leptin mRNA, and Ob-Ra and Ob-Rb leptin receptor mRNA were determined in AT samples by ribonuclease protection assay. Day length did not affect feed intake or body condition score. Exposure to short DL significantly reduced milk yield (13.1 +/- 2.2 vs. 15.8 +/- 1.7 and 16.0 +/- 2.0 kg/d for short vs. neutral and long DL, respectively). Plasma leptin, growth hormone, cortisol, nonesterified fatty acids, beta-OH-butyrate, and glucose were not affected by DL; cholesterol was lowest under short DL (3.93 +/- 0.38 vs. 4.36 +/- 0.39 and 4.07 +/- 0.38 mmol/L for short vs. neutral and long DL, respectively). Prolactin increased under long DL (134.82 +/- 16.94 vs. 81.98 +/- 20.25 and 96.16 +/- 0.38 ng/mL for long vs. neutral and short DL, respectively). Gene expression of leptin and its receptors was affected by DL. Leptin mRNA increased under long DL (11.91 +/- 0.84 vs. 7.82 +/- 0.84 and 7.56 +/- 0.84 pg of mRNA/microg of total RNA for long vs. neutral and short DL, respectively). Leptin receptors Ob-Ra and Ob-Rb mRNA were higher under long DL, whereas Ob-Ra and Ob-Rb mRNA were lower under short DL (Ob-Ra: 1.91 +/- 0.41, 2.49 +/- 0.41, and 0.65 +/- 0.41 pg of mRNA/microg of total RNA for neutral, long, and short DL, respectively; Ob-Rb: 5.29 +/- 0.79, 5.98 +/- 0.68, and 2.02 +/- 0.70 pg of mRNA/microg of total RNA for neutral, long, and short DL, respectively). Results of the present study appear to exclude an effect of feed intake and metabolic status on leptin gene expression. A prolactin-mediated effect of photoperiod on AT leptin modulation may be proposed in lactating dairy cows.

Expression and function of leptin and its receptor in mouse mammary gland

Leptin is an autocrine and paracrine factor which affects the development of duct, formation of gland alveolus, expression of milk protein gene and onset involution of mammary gland. In order to know the function and mechanism of leptin in mammary gland, the protein expression and localization of leptin and its long form receptor (OB-Rb) were detected by a confocal laser scanning microscope. To study the impacts of leptin on mammary gland and leptin signal transduction pathway in pregnancy-, lactation-and involution-stage mammary gland, explants were cultured and Western blotting was used. The results showed that in the whole development cycle of mammary gland, the expression of leptin and OB-Rb was in positive correlation. In virgin the leptin expression was the highest and then decreased in pregnancy. In lactation the expression of leptin was low and upgraded in involution, and recovered to the original level about virgin on involution 13 d. The localization of leptin and OB-Rb revealed that leptin induced the expression of OB-Rb specifically and controlled the development and physiological function of the mammary gland by binding to OB-Rb. In pregnancy stage, leptin stimulated proliferation and differentiation of ductal epithelial cells by JAK-MAPK signal pathway. In lactation, leptin induced gene expression of beta-casein by JAK-STAT5 signal pathway, and in involution leptin induced mammary epithelial cell apoptosis and mammary gland restitution by JAK-STAT3 signal pathway.

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.

Expression of leptin and long form of leptin receptor genes and proteins in pituitary of cyclic and pregnant pigs

Leptin is a multifunctional regulator in numerous tissues, including the pituitary. It is not known, whether the porcine pituitary is a source of leptin synthesis and possesses the leptin receptor protein. It is also unknown, if a relationship exists between expression levels of these proteins in the pituitary and physiological status of sows. Therefore, the aim of the study was 1] to examine, by Western-blotting analysis, the expression levels of leptin and the long form of leptin receptor (OB-Rb) in the porcine anterior (AP) and posterior (NP) pituitary gland during mid- and late-luteal phases of the oestrous cycle (days 10 - 12 and 14 - 16) as well as during two stages of early pregnancy (days 14 - 16 and 30 - 32); and 2] to localise, using in situ hybridisation method (ISH), the expression of leptin and OB-Rb genes in the pituitary gland in the above mentioned stages of the cycle and pregnancy. Western-blotting analysis showed that leptin protein expression in AP was higher in the late-luteal phase than in the mid-luteal phase, while OB-Rb protein expression in both lobes was higher in the mid-luteal phase. In turn, during pregnancy leptin protein content in AP and OB-Rb protein content in NP were more pronounced on days 14 - 16 than on days 30 - 32. Comparison of leptin and OB-Rb protein expression levels in AP between the mid-luteal phase and two periods of pregnancy showed, respectively, stimulation of leptin protein and inhibition of OB-Rb protein expressions during both examined stages of pregnancy. Taking AP from late-luteal phase as the point of reference, it was revealed stimulation of leptin expression during earlier period of pregnancy, whereas on days 30 - 32 of pregnancy both the hormone and its receptor expressions were diminished. In turn, comparison of leptin and OB-Rb protein expression levels in NP between the late-luteal phase and days 14 - 16 or 30 - 32 of pregnancy showed inhibition of leptin protein expression and stimulation of OB-Rb protein expression during pregnancy. Moreover, ISH studies localised leptin and OB-Rb mRNAs expression in the cells of AP as well as NP tissue during the two stages of the cycle and pregnancy. In conclusion, our findings suggest that leptin is produced within the pituitary in the pig and may participate in auto/paracrine manner in the regulation of this gland function during the luteal phase of the oestrous cycle and early pregnancy.

Expression of leptin and its receptor in female breast cancer in relation with selected apoptotic markers

Leptin and its receptor may be engaged in pathogenesis of breast cancer among various human tumors. In vitro investigations showed leptin-mediated escalation of estrogen synthesis and boosted activity of estrogen receptor ERalpha. Furthermore, leptin induced growth of malignant cells, counteracted apoptosis and stimulated cell migration as well as overexpression of angiogenic factors and degrading enzymes that split network of intercellular matrix. On the other side, leptin has been reported to favor apoptosis, lately. Proapoptotic effect of leptin action was revealed in interstitial cells of bone marrow and adipocytes. Our past reports provide evidences for overexpression of leptin and its receptor in breast cancer in comparison with benign mammary lesions. In current study we aimed at assessment of eventual relationships between leptin, leptin receptor and selected protein regulators of apoptosis in breast cancer. We applied immunohistochemistry for leptin, leptin receptor, anti-apoptotic Bcl-2 and Bcl-xL as well as pro-apoptotic Bak and Bax expression assessment in 106 cases of human breast cancers. The immunoreaction was graded and statistically evaluated. Expression of leptin was positively correlated with Bcl-xL, Bak and Bax (p<0.001, r=0.614; p<0.001, r=0.518; p<0.001, r=0.511, respectively). Statistical significances were noted between expression of leptin receptor and Bcl-xL or Bax (p=0.011, r=0.210; p<0.001, r=0.313, respectively). No correlation was encountered between leptin and Bcl-2, either leptin receptor and Bcl-2 or leptin receptor and Bak. On the basis of obtained results, leptin system could interfere in balance among expressions of pro- and anti-apoptotic proteins and regulate cell turnover and--by means of it--facilitate breast cancer progression.

The transcript expression profile of the leptin receptor-coding gene assayed with the oligonucleotide microarray technique--could this be an anorexia nervosa marker?

Anorexia nervosa is a serious eating disorder with the highest mortality rate of any psychiatric disorder. The DSM-IV classification differentiates two AN types: the restricting type (AN-R) and the binge-eating/purging type (AN-BP). Leptin (LEP) levels can be thought of as a signal to the body of its energy reserves. The leptin receptor (including all its mRNA isoforms) is expressed in many tissues. Our aim was to discover the transcript expression profile of the LEP receptor-coding gene in the peripheral blood mononuclears in AN-R and AN-BP patients. Three young women suffering from Anorexia nervosa (one with AN-BP and two with AN-R) took part in the study, along with three non-anorexic subjects as our reference group. LEP receptor gene expression was examined using the oligonucleotide microarray method (HG-U133A, Affymetrix). The results were normalized using RMAExpress. Next, the accumulation analysis method was used (clustering). Hierarchical clustering resulted in three groups of separate clusters. The first group (cluster I) consisted of AN-R patients. The next group (cluster II) consisted of reference group patients suffering from different psychic disorders not related to eating disorders. Cluster III consisted of two patients--the first with AN-BP and the second with an adaptive disorder.

Leptin expression in human primary skeletal muscle cells is reduced during differentiation

We found leptin to be strongly expressed in undifferentiated human myoblasts derived from biopsies of the thigh (Musculus vastus lateralis). Both mRNA expression and secretion of leptin were reduced during in vitro differentiation into primary myotubes. However, the expression of the leptin receptor (OB-Rb) mRNA, was unchanged during differentiation of the muscle cells. Administration of recombinant leptin had no effect on leptin, myogenin, myoD, or GLUT4 mRNA expressions during the period of cellular differentiation. A functional leptin receptor was demonstrated by an acute leptin-induced 1.5-fold increase in ERK activity (P = 0.029). Although mRNA expression of regulation of suppressor of cytokine signaling-3 (SOCS-3) mRNA expression was unaltered, leptin significantly stimulated fatty acid oxidation after 6 h measured as acid soluble metabolites (ASM). Palmitic acid (PA), oleic acid (OA), and eicosapentaenoic acid (EPA), known to modulate leptin expression in other tissues, had no effect on mRNA expression or secretion of leptin from human myotubes. In conclusion, we demonstrate that leptin is highly expressed in undifferentiated human myoblasts and the expression is reduced during differentiation to mature myotubes. The role of leptin in these cells needs to be further characterized.