Melatonin facilitates adipose‐derived mesenchymal stem cells to repair the murine infarcted heart via the SIRT1 signaling pathway

Mesenchymal stem cells (MSCs)‐based therapy provides a promising therapy for the ischemic heart disease (IHD). However, engrafted MSCs are subjected to acute cell death in the ischemic microenvironment, characterized by excessive inflammation and oxidative stress in the host's infarcted myocardium. Melatonin, an indole, which is produced by many organs including pineal gland, has been shown to protect bone marrow MSCs against apoptosis although the mechanism of action remains elusive. Using a murine model of myocardial infarction (MI), this study was designed to evaluate the impact of melatonin on adipose‐derived mesenchymal stem cells (AD‐MSCs)‐based therapy for MI and the underlying mechanism involved with a focus on silent information regulator 1(SIRT1) signaling. Our results demonstrated that melatonin promoted functional survival of AD‐MSCs in infarcted heart and provoked a synergetic effect with AD‐MSCs to restore heart function. This in vivo effect of melatonin was associated with alleviated inflammation, apoptosis, and oxidative stress in infarcted heart. In vitro studies revealed that melatonin exert cytoprotective effects on AD‐MSCs against hypoxia/serum deprivation (H/SD) injury via attenuating inflammation, apoptosis, and oxidative stress. Mechanistically, melatonin enhanced SIRT1 signaling, which was accompanied with the increased expression of anti‐apoptotic protein Bcl2, and decreased the expression of Ac‐FoxO1, Ac‐p53, Ac‐NF‐ΚB, and Bax. Taken together, our findings indicated that melatonin facilitated AD‐MSCs‐based therapy in MI, possibly through promoting survival of AD‐MSCs via SIRT1 signaling. Our data support the promise of melatonin as a novel strategy to improve MSC‐based therapy for IHD, possibly through SIRT1 signaling evocation.     

Melatonin enhances alkaline phosphatase activity in differentiating human adult mesenchymal stem cells grown in osteogenic medium via MT2 melatonin receptors and the MEK/ERK (1/2) signaling cascade

The goals of this study were to determine (a) if melatonin enhances human adult mesenchymal stem cell (hAMSC) differentiation into osteoblasts as assessed by measuring alkaline phosphatase (ALP) enzyme activity, and (b) identify potential signal transduction pathways that mediate this process. ALP activity significantly increased in hAMSCs following a 10-day incubation in osteogenic medium, relative to hAMSCs incubated in basal growth medium alone. Melatonin (50 nm), added in combination with the osteogenic medium, significantly increased ALP activity relative to osteogenic medium alone. Co-exposure of hAMSCs to osteogenic medium supplemented with melatonin and either pertussis toxin or the melatonin receptor antagonists, luzindole or 4P-PDOT (MT2 receptor selective), inhibited the melatonin-induced increase in ALP activity, indicating the involvement of melatonin receptors, in particular, MT2 receptors. Assessment of melatonin receptor function following exposure to osteogenic medium containing either vehicle or melatonin produced dichotomous results. That is, if the differentiation of hAMSCs into an osteoblast was induced by osteogenic medium alone, then 2-[125I]-iodomelatonin binding and melatonin receptor function increased. However, examination of melatonin receptor function following chronic melatonin exposure, an exposure that resulted in a 50% enhancement in ALP activity, revealed that these receptors were desensitized. This was reflected by a complete loss in specific 2-[125I]-iodomelatonin binding as well as melatonin efficacy to inhibit forskolin-induced cAMP accumulation. Further characterization of the mechanisms underlying melatonin's effects on these differentiation processes revealed that MEK (1/2) and ERK (1/2), epidermal growth factor receptors, metalloproteinase and clathrin-mediated endocytosis were essential while PKA was not. Our results are consistent with a role for melatonin in osteoblast differentiation. If so, then, the decrease in plasma melatonin levels observed in humans during late adulthood may further enhance susceptibility to osteoporosis.     

Glucocorticoid receptors in epithelial cells isolated from the mammary glands of pregnant and lactating rats

We have isolated epithelial cell clusters from mammary glands of pregnant and lactating rats by collagenase—hyaluronidase—deoxyribonuclease digestion, followed by Ficoll density-gradient centrifugation. dusters of >90% viable cells were identified by light microscopy as essentially devoid of other cell types; the integrity of their subcellular organelles verfied by electron microscopy. Binding characteristics of the synthetic glucocorticoid [³H]dexamethasone were studied in cytosols prepared from isolated cell clusters. Cytosols from both pregnant and lactating rats bound [³H]dexamethasone with high affinity to a single class of low capacity binding sites. In both types of cytosol the dissociation constant (K_d 4°C ～/nM) of the binding was similar; the number of sites per cell in lactating rats was ～ double that in pregnant rats. The specificity of binding was typical of a classical glucocorticoid receptor, with a hierarchy of affinity by competition studies dexamethasone > progesterone > aldosterone ? testosterone = estradiol. In particular, no difference in progesterone affinity for these glucocorticoid receptors was seen between pregnancy and lactation. This suggests that reported differences in inhibitory action of progesterone, pregnancy versus post-partum, are not glucocorticoid-receptor mediated.     

Real-time detection of insulin-like growth factor-1 stimulation of the MAC-T bovine mammary epithelial cell line

Binding of growth factors by cell-surface receptors is an essential means by which cell regulate normaltissue growth and differentiation. Exposure to growth factors is often transient, and our goal was to determine whether short-term exposure to insulin-like growth factor-1 (IGF-1) would lead to activation, assayed as cell proliferation, of mammary epithelial cells. The MAC-T cell line is an immortalized bovine mammary epithelial cell line, chosen as our model mammary cell line because of its known sensitivity to IGF-1. Using the Cytosensor Microphysiometer System, a biosensor capable of measuring extracellular acidification, we were able to measure activation of the cellsowing to IGF-1 addition in real time and found that peak acidification occurred in only 14 min. We show that this rapid response to IGF-1 is dose dependent and specific for IGF-1. A significant increase in [³H]thymidine incorporation by cells after a similar short-term exposure to IGF-1 suggests that the measured increase in extracellular acidification following IGF-1 addition is physiologically relevant. This technology offers a new, novel, and rapid means for the study of IGF-1 activity, as well as the screening of IGF-1 inhibitors, in mammary epithelial cells.     

Melatonin synthesis and melatonin-membrane receptor (MT1) expression during rat thymus development: role of the pineal gland

To gain insight into the relationship between thymus and pineal gland during rat development, the melatonin content as well as the activity and expression of the two key enzymes for melatonin biosynthesis, i.e. N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT), were studied in the thymus at fetal and postnatal stages. Moreover, melatonin-membrane receptor (MT1) expression was also analyzed. We found both the expression and activity of thymic NAT and HIOMT at 18 days of fetal life. Additionally, there is production of melatonin in the thymus as well as MT1 expression at this fetal age. These results show values higher in day-time than at night-time. The pineal gland begins to produce significant levels of melatonin around postnatal day 16, and this synthesis shows a circadian rhythm with high values during the dark period; therefore the nocturnal serum melatonin may inhibit thymic melatonin production. To document this, we report an increased melatonin content of the thymus in pinealectomized rats compared with sham-pinealectomized. In conclusion, these results show, for the first time, the presence of the biosynthetic machinery of melatonin and melatonin production in developing rat thymus and that the pineal gland may regulate this process.     

Melatonin attenuates choroidal neovascularization by regulating macrophage/microglia polarization via inhibition of RhoA/ROCK signaling pathway

Choroidal neovascularization (CNV) is an important characteristic of advanced wet age-related macular degeneration (AMD) and leads to severe visual impairment among elderly patients. Previous studies have demonstrated that melatonin induces several biological effects related to antioxidation, anti-inflammation, and anti-angiogenesis. However, the role of melatonin in CNV, and its underlying mechanisms, has not been investigated thus far. In this study, we found that melatonin administration significantly reduced the scale and volume of CNV lesions, suppressed vascular leakage, and inhibited the capacity of vascular proliferation in the laser-induced mouse CNV model. Additionally, the results also show that the melatonin-treated retinal microglia in the laser-induced mice exhibited enhanced expression of M1-type markers, such as iNOS, CCL-3, CCL-5, and TNF-α, as well as decreased production of M2-type markers, such as Arg-1, Fizz-1, IL-10, YM-1, and CD206, indicating that melatonin switched the macrophage/microglia polarization from pro-angiogenic M2 phenotype to anti-angiogenic M1 phenotype. Furthermore, the RhoA/ROCK signaling pathway was activated during CNV formation, yet was suppressed after an intraperitoneal injection of melatonin. In conclusion, melatonin attenuated CNV, reduced vascular leakage, and inhibited vascular proliferation by switching the macrophage/microglia polarization from M2 phenotype to M1 phenotype via inhibition of RhoA/ROCK signaling pathway in CNV. This suggests that melatonin could be a novel agent for the treatment of AMD.     

鞭毛蛋白致肺微血管内皮细胞炎症诱发共培养肺泡上皮细胞炎症的级联放大效应与信号传导通路

目的探讨鞭毛蛋白感染后炎症级联放大效应与信号传导通路。方法建立Transwell共培养体系,将人肺微血管内皮细胞株（ human pulmonary microvascular endothelial cells, HPMECs ）接种于Transwell小室的下层,培养2h后,将人Ⅱ型肺泡上皮细胞A549细胞株接种于小室的上层与HPMECs共培养15d。实验分为3组：HPMECs与A549细胞共培养空白对照组、鞭毛蛋白（2μg／mL）感染HPMECs再与A549细胞共培养组（实验组I）、HPMECs加DAPT（Notch信号阻断剂,终浓度10μmol／L）预处理再行鞭毛蛋白感染与A549细胞共培养组（实验组Ⅱ）。用ELISA法检测各组HPMECs和A549细胞培养上清液TNF-α蛋白表达,检测HPMECs上清液Notchl蛋白表达水平。结果与共培养空白对照组比较,鞭毛蛋白感染HPMECs后,共培养HPMECs和A549细胞上清液TNF-α蛋白[（11．45±1．59）pg／mLvs（6．13土0．86）pg／mL,（P〈0．01）、（9．93±1．46）pg／mLvs（5．895：0．83）pg／mL,（P〈0．01）]和HPMECs上清液中Notchl蛋白[（7．03±1．06）pg／mL坩（5．39±0．76）pg／mL,（P〈0．05）]表达水平皆明显升高,提示鞭毛蛋白引起HPMECs炎症,且向A549细胞传导级联放大,而HPMECs使用Notch信号阻断剂处理后,HPMECs上清液Notchl蛋白表达水平明显降低[（3．78±0．53）pg／mLvs（7．03±1．06）pg／mL,（P〈0．01）],共培养A549细胞上清液TNF-α蛋白表达水平也显著下降[（7．47±1．05）pg／mL坩（9．93±1．46）pg／mL,（P〈0．05）],表明HPMECs炎症反应经过Notch信号通路传导向A549细胞级联放大。结论鞭毛蛋白感染肺微血管内皮细胞能引起炎症反应,并可能经过Notch信号通路传导向肺泡上皮细胞级联放大。     

Activation of insulin and IGF-1 signaling pathways by melatonin through MT1 receptor in isolated rat pancreatic islets

Melatonin diminishes insulin release through the activation of MT1 receptors and a reduction in cAMP production in isolated pancreatic islets of neonate and adult rats and in INS-1 cells (an insulin-secreting cell line). The pancreas of pinealectomized rats exhibits degenerative pathological changes with low islet density, indicating that melatonin plays a role to ensure the functioning of pancreatic beta cells. By using immunoprecipitation and immunoblotting analysis we demonstrated, in isolated rat pancreatic islets, that melatonin induces insulin growth factor receptor (IGF-R) and insulin receptor (IR) tyrosine phosphorylation and mediates the activities of the PI3K/AKT and MEK/ERKs pathways, which are involved in cell survival and growth, respectively. Thus, the effects of melatonin on pancreatic islets do not involve a reduction in cAMP levels only. This indoleamine may regulate growth and differentiation of pancreatic islets by activating IGF-I and insulin receptor signaling pathways.     

Melatonin ameliorates high fat diet-induced diabetes and stimulates glycogen synthesis via a PKCζ-Akt-GSK3β pathway in hepatic cells

Abstract:  Low levels of melatonin in circulation had been reported to be related to the development of diabetes. Melatonin administration in animals increases hepatic glycogen content to lower blood glucose. However, the signaling pathway for these effects is still unclear. The present study shows that intraperitoneal injection of 10 mg/kg melatonin ameliorated glucose utilization and insulin sensitivity in high fat diet-induced diabetic mice with an increase in hepatic glycogen and improvement in liver steatosis. We used HepG2 cells to investigate the signaling pathways for the melatonin-stimulated hepatic glycogen increment. Treatment of HepG2 cells with 1 n m melatonin markedly increased glycogen synthesis which was blocked by the melatonin receptor antagonist luzindole. In addition, melatonin increased the phosphorylation of subcellular signals at the level of protein kinase C ζ (PKCζ), Akt, and glycogen synthase kinase 3β (GSK3β) while the increase in glycogen synthesis induced by melatonin was inhibited by PKCζ pseudo-peptide. However, 3',5'-cyclic adenosine monophosphate-activated protein kinase (AMPK) was not influenced by melatonin treatment. Taken together, melatonin improves glucose intolerance and insulin resistance in high fat diet-induced diabetic mice and stimulates glycogen synthesis via a PKCζ-Akt-GSK3β pathway in HepG2 cells.     

Combination of melatonin and Wnt‐4 promotes neural cell differentiation in bovine amniotic epithelial cells and recovery from spinal cord injury

Although melatonin has been shown to exhibit a wide variety of biological functions, its effects on promoting differentiation of neural cells remain unknown. Wnt signaling mediates major developmental processes during embryogenesis and regulates maintenance, self‐renewal, and differentiation of adult mammalian stem cells. However, the role of the noncanonical Wnt pathway during neurogenesis remains poorly understood. In this study, the amniotic epithelial cells ( AECs) were isolated from bovine amnion and incubated with various melatonin concentrations (0.01, 0.1, 1, 10, or 100 μm ) and 5 × 10^?5 m all‐trans retinoic acid (RA) for screening optimum culture medium of neural differentiation, compared with each groups, 1 μm melatonin and 5 × 10^?5 m RA were selected to induce neural differentiation of AECs, and then siMT1, siMT2, oWnt‐4, and siWnt‐4 were expressed in AECs to research role of these genes in neural differentiation. Efficiency of neural differentiation was evaluated after expressed above genes using flow cytometry. Cell function of neural cells was demonstrated in vivo using spinal cord injury model after cell transplantation, and damage repair of spinal cord was assessed using cell tracking and Basso, Beattie, Bresnahan Locomotor Rating Scale scores. Results demonstrated that melatonin stimulated melatonin receptor 1, which subsequently increased bovine amniotic epithelial cell vitality and promoted differentiation into neural cells. This took place through cooperation with Wnt‐4. Additionally, following cotreatment with melatonin and Wnt‐4, neurogenesis gene expression was significantly altered. Furthermore, single inhibition of melatonin receptor 1 or Wnt‐4 expression decreased expression of neurogenesis‐related genes, and bovine amniotic epithelial cell‐derived neural cells were successfully colonized into injured spinal cord, which suggested participation in tissue repair.     

Melatonin recovers sleep phase delayed by MK-801 through the melatonin MT2 receptor- Ca2+-CaMKII-CREB pathway in the ventrolateral preoptic nucleus

Melatonin (MLT) is widely used to treat sleep disorders although the underlying mechanism is still elusive. In mice, using wheel-running detection, we found that exogenous MLT could completely recover the period length prolonged by N-methyl-D-aspartate receptor (NMDAR) impairment due to the injection of the NMDAR antagonist MK-801, a preclinical model of psychosis. The analysis of the possible underlying mechanisms indicated that MLT could regulate the homeostatic state in the ventrolateral preoptic nucleus (VLPO) instead of the circadian process in the suprachiasmatic nucleus (SCN). In addition, our data showed that MK-801 decreased Ca²⁺-related CaMKII expression and CREB phosphorylation levels in the VLPO, and MLT could rescue these intracellular impairments but not NMDAR expression levels. Accordingly, Gcamp6 AAV virus was injected in-vivo to further monitor intracellular Ca²⁺ levels in the VLPO, and MLT demonstrated a unique ability to increase Ca²⁺ fluorescence compared with MK-801-injected mice. Additionally, using the selective melatonin MT₂ receptor antagonist 4-phenyl-2-propionamidotetralin (4P-PDOT), we discovered that the pharmacological effects of MLT upon NMDAR impairments were mediated by melatonin MT₂ receptors. Using electroencephalography/electromyography (EEG/EMG) recordings, we observed that the latency to the first nonrapid eye movement (NREM) sleep episode was delayed by MK-801, and MLT was able to recover this delay. In conclusion, exogenous MLT by acting upon melatonin MT₂ receptors rescues sleep phase delayed by NMDAR impairment via increasing intracellular Ca²⁺ signaling in the VLPO, suggesting a regulatory role of the neurohormone on the homeostatic system.     

Lesion-targeted thrombopoietin potentiates vasculogenesis by enhancing motility and enlivenment of transplanted endothelial progenitor cells via activation of Akt/mTOR/p70S6kinase signaling pathway

Thrombopoietin (TPO), a physiological regulator of megakaryocyte and platelet development, is a multifunctional positive regulator in early hematopoiesis by hematopoietic stem cells. In this study, we investigated the effect of TPO on endothelial progenitor cells (EPCs) for therapeutic vasculogenesis in vitro and in vivo, and the intracellular signaling mechanism exerting the activity of EPCs. 7-day culture-expanded EPCs derived from human peripheral blood mononuclear cells were applied to each assay. Flow cytometry demonstrated the expression of c-Mpl, the receptor of TPO, in cultured EPCs. In vitro experiments revealed enhanced migration and survival of cultured EPCs by TPO. In vivo, TPO was intramuscularly administered into the foci of ischemic hindlimbs in athymic nude mice, immediately followed by intravenous injection of cultured EPCs, to assess the booster effect of TPO on vascular regeneration. At day 4 post-transplantation, transplanted EPCs were 1.7-fold higher in TPO-treated animals compared to control. At day 28, blood perfusion was recovered in the TPO-treated group, accompanied by an increase in microvascular density. The signaling transduction pathway underlying TPO-mediated activities of cultured EPCs was assessed by Western blotting. TPO induced sequential phosphorylations of Akt to p70S6kinase through mTOR. Inhibition of the PI3-kinase/Akt/mTOR/p70S6kinase signaling pathway negated the biological functions of cultured EPCs, either migration (by LY294002 for PI3-kinase and Rapamycin for mTOR) or survival and tubulogenesis (by Rapamycin). These findings provide evidence that TPO possesses booster potential for therapeutic vasculogenesis, by activating the PI3-kinase/Akt/mTOR/p70S6kinase pathway crucial to the biological activities of EPCs.     

Melatonin modulation of intracellular signaling pathways in hepatocarcinoma HepG2 cell line: role of the MT1 receptor

Melatonin reduces proliferation in many different cancer cell lines. However, studies on the oncostatic effects of melatonin in hepatocarcinoma are limited. We have previously demonstrated that melatonin administration induces cycle arrest, apoptosis, and changes in the expression of its specific receptors in HepG2 human hepatocarcinoma cells. In this study, we used the receptor antagonist luzindole to assess the contribution of MT1 melatonin membrane receptor to melatonin effects on cell viability, mitogen-activated protein kinase (MAPKs) activation, and cAMP levels. Additionally, effects of MT1 inhibition on mRNA levels of cytosolic quinone reductase type-2 (NQO2) receptor and nuclear retinoic acid-related orphan receptor alpha (RORα) were tested. Melatonin, at 1000 and 2500 μm, significantly reduced cell viability. Pre-incubation with luzindole partially inhibited the effects of melatonin on cell viability. Melatonin at 2500 μm significantly reduced cAMP levels, and this effect was partially blocked by luzindole. Both melatonin concentrations increased the expression of phosphorylated p38, ERK, and JNK. ERK activation was completely abolished in the presence of luzindole. NQO2 but not RORα mRNA level significantly increased in luzindole-treated cells. Results obtained provide evidence that the melatonin effects on cell viability and proliferation in HepG2 cells are partially mediated through the MT1 membrane receptor, which seems to be related also with melatonin modulation of cAMP and ERK activation. This study also highlights a possible interplay between MT1 and NQO2 melatonin receptors in liver cancer cells.     

Melatonin regulates the activities of ovary and delays the fertility decline in female animals via MT1/AMPK pathway

Female fertility irreversibly declines with aging, and this is primarily associated with the decreased quality and quantity of oocytes. To evaluate whether a long‐term of melatonin treatment would improve the fertility of aged mice, different concentrations of melatonin (10^?3, 10^?5, 10^?7 mol/L) were supplemented into drinking water. Melatonin treatments improved the litter sizes of mice at the age of 24 weeks. Mice treated with 10^?5 mol/L melatonin had the largest litter size among other concentrations. At this optimal concentration, melatonin not only significantly increased the total number of oocytes but also their quality, having more oocytes with normal morphology that could generate more blastocyst after in vitro fertilization in melatonin (10^?5 mol/L)‐treated group than that in the controls. When these blastocysts were transferred to recipients, the litter size was also significantly larger in melatonin treated mice than that in controls. The increases in TAOC and SOD level and decreases in MDA were detected in ovaries and uterus from melatonin‐treated mice compared to the controls. Melatonin reduced ROS level and maintained mitochondrial membrane potential in the oocytes cultured in vitro. Mechanistically studies revealed that the beneficial effects of melatonin on oocytes were mediated by MT1 receptor and AMPK pathway. Thereafter, MT1 knocking out (MT1‐KO) were generated and shown significantly reduced number of oocytes and litter size. The expression of SIRT1, C‐myc, and CHOP were downregulated in the ovary of MT1‐KO mice, but SIRT1 and p‐NF‐kB protein level were elevated in response to disturbed redox balance. The results have convincingly proven that melatonin administration delays ovary aging and improves fertility in mice via MT1/AMPK pathway.     

Melatonin attenuates myocardial ischemia‐reperfusion injury via improving mitochondrial fusion/mitophagy and activating the AMPK‐OPA1 signaling pathways

Optic atrophy 1 (OPA1)‐related mitochondrial fusion and mitophagy are vital to sustain mitochondrial homeostasis under stress conditions. However, no study has confirmed whether OPA1‐related mitochondrial fusion/mitophagy is activated by melatonin and, consequently, attenuates cardiomyocyte death and mitochondrial stress in the setting of cardiac ischemia‐reperfusion (I/R) injury. Our results indicated that OPA1, mitochondrial fusion, and mitophagy were significantly repressed by I/R injury, accompanied by infarction area expansion, heart dysfunction, myocardial inflammation, and cardiomyocyte oxidative stress. However, melatonin treatment maintained myocardial function and cardiomyocyte viability, and these effects were highly dependent on OPA1‐related mitochondrial fusion/mitophagy. At the molecular level, OPA1‐related mitochondrial fusion/mitophagy, which was normalized by melatonin, substantially rectified the excessive mitochondrial fission, promoted mitochondria energy metabolism, sustained mitochondrial function, and blocked cardiomyocyte caspase‐9‐involved mitochondrial apoptosis. However, genetic approaches with a cardiac‐specific knockout of OPA1 abolished the beneficial effects of melatonin on cardiomyocyte survival and mitochondrial homeostasis in vivo and in vitro. Furthermore, we demonstrated that melatonin affected OPA1 stabilization via the AMPK signaling pathway and that blockade of AMPK repressed OPA1 expression and compromised the cardioprotective action of melatonin. Overall, our results confirm that OPA1‐related mitochondrial fusion/mitophagy is actually modulated by melatonin in the setting of cardiac I/R injury. Moreover, manipulation of the AMPK‐OPA1‐mitochondrial fusion/mitophagy axis via melatonin may be a novel therapeutic approach to reduce cardiac I/R injury.     

Melatonin and its receptor MT1 are involved in the downstream reaction to luteinizing hormone and participate in the regulation of luteinization in different species

The functions of melatonin in preovulatory fluid remain elusive. In the current study, we observed that the extremely high level of expression of MT1 in mice granulosa cells was rapidly induced by hCG (equivalent LH) within 2 hours and this was referred as MT1 surge. In cumulus cells, serotonin N‐acetyltransferase (SNAT) was also upregulated by hCG and led to elevated melatonin levels in ovarian follicle fluid. Melatonin application before MT1 surge significantly promoted embryo implantation, and this was probably attributed to a rise in progesterone levels in the serum. The mechanistic studies indicated that melatonin/MT1 (MLT/MT1) signaling remarkably improved the expression of corpus luteum marker genes, that is, Akr1c18 and Cyp11a1. High‐throughput sequencing results suggested that extracellular matrix (ECM) receptor interaction, focal adhesion, and activation of PI3K/Akt pathway which are involved in granulosa cell luteinization might mediate the actions of MLT/MT1 signal. In addition, this effect on luteinization was compared in different species. It was verified that high melatonin levels exist in serum at estrum of cows and help to improve the first estrus fecundation rate. These results suggested that both melatonin and MT1 are involved in the downstream reaction of hCG (LH) and they play important roles in luteinization. These findings provide the novel information on the physiology of melatonin in animal reproduction.     

Melatonin induces pro‐apoptotic signaling pathway in human pancreatic carcinoma cells (PANC‐1)

Abstract: Pancreatic cancer is a highly lethal disease with a poor prognosis for long‐term survival rate at all stages of invasiveness. It responds poorly to radio‐ and chemotherapy because the tumor cells are resistant to apoptosis. Melatonin has been reported to inhibit pancreatic cancer growth in experimental studies in animals but the effect of melatonin on cultured human pancreatic carcinoma cells has not been tested. Moreover, we have recently shown that melatonin stimulates production of two major anti‐apoptotic heat shock proteins, HSP27 and HSP 90, in pancreatic carcinoma cells. This study investigated the changes in intrinsic pathway of apoptosis at the mitochondrial level and cascade of caspases in human pancreatic carcinoma cells (PANC‐1) cells subjected to melatonin and/or luzindole. Melatonin (10^?8–10^?12 m ), the nonselective melatonin receptor antagonist, luzindole (10^?8–10^?12 m ) or a combination of both agents were added to PANC‐1 cell cultures. Cells were harvested, and the cytoplasmic proteins were isolated after 24 and 48 hr of incubation and analyzed employing co‐immunoprecipitation and western blot. Administration of melatonin to the PANC‐1 cells resulted in the stimulation of Bcl‐2/Bax and caspase‐9 proteins levels. The strongest signal of these pro‐apoptotic factors was observed at the low concentration (10^?12 m ) of melatonin. Pretreatment with luzindole alone and prior to the addition of melatonin reversed the stimulatory effect of this indoloamine on Bcl‐2/Bax and caspase‐9 proteins expression in PANC‐1 cells. This is the first study to demonstrate a pro‐apoptotic effect of low (physiological) concentration of melatonin on the pancreatic carcinoma cells. In conclusion, melatonin induced pro‐apoptotic pathways in human pancreatic carcinoma, probably by interaction with the Mel‐1 A/B receptors.