Ghrelin induces cardiac lineage differentiation of human embryonic stem cells through ERK1/2 pathway

Ghrelin delays premature aging in Hutchinson-Gilford progeria syndrome

Hutchinson-Gilford progeria syndrome (HGPS) is a rare and fatal genetic condition that arises from a single nucleotide alteration in the LMNA gene, leading to the production of a defective lamin A protein known as progerin. The accumulation of progerin accelerates the onset of a dramatic premature aging phenotype in children with HGPS, characterized by low body weight, lipodystrophy, metabolic dysfunction, skin, and musculoskeletal age-related dysfunctions. In most cases, these children die of age-related cardiovascular dysfunction by their early teenage years. The absence of effective treatments for HGPS underscores the critical need to explore novel safe therapeutic strategies. In this study, we show that treatment with the hormone ghrelin increases autophagy, decreases progerin levels, and alleviates other cellular hallmarks of premature aging in human HGPS fibroblasts. Additionally, using a HGPS mouse model (LmnaG609G/G609G mice), we demonstrate that ghrelin administration effectively rescues molecular and histopathological progeroid features, prevents progressive weight loss in later stages, reverses the lipodystrophic phenotype, and extends lifespan of these short-lived mice. Therefore, our findings uncover the potential of modulating ghrelin signaling offers new treatment targets and translational approaches that may improve outcomes and enhance the quality of life for patients with HGPS and other age-related pathologies.

Fine particulate matter reduces the pluripotency and proliferation of human embryonic stem cells through ROS induced AKT and ERK signaling pathway

Epidemiological investigations have found that air fine particulate matter (PM) exposure not only causes respiratory and cardiovascular diseases in adults and children, but also affects embryonic development during pregnancy, leading to poor pregnancy outcomes. However, its exact molecular mechanism is still unclear. In this study, human embryonic stem cells (hESCs) were treated with PM at different concentrations then the morphology and proliferation capacity were measured. The mRNA and protein expression of NANOG and OCT4 were detected using quantitative PCR, immunofluorescence, western blotting, and flow cytometry. Reactive oxygen species (ROS) generation and AKT/ERK activation were also measured. Meanwhile, changes in ROS, the expression of NANOG, OCT4, and the AKT/ERK pathways were measured in the hESCs with or without pretreatment of ROS scavenger N-acetylcysteine (NAC) prior to PM exposure. After PM exposure, the proliferation capacity and expression of OCT4 and NANOG at the mRNA and protein levels were downregulated. The ROS level in the hESCs increased after PM exposure, but this increase in ROS was attenuated by pretreatment with NAC. Further analysis showed that the levels of phosphorylated AKT and ERK increased after PM exposure. After pretreatment with NAC, the phosphorylation levels of AKT and ERK, which are crucial for regulating the proliferation, pluripotency, and differentiation of hESC, were significantly attenuated compared with the non-NAC pretreated exposure group. These results suggest that PM exposure may reduce the proliferation and pluripotency of hESC through ROS-mediated AKT/ERK pathways, thereby affecting the long-term development of embryos.

Ghrelin Promotes Proliferation and Inhibits Differentiation of 3T3-L1 and Human Primary Preadipocytes

Objective

Ghrelin is a 28-amino-acid peptide that regulates energy hemostasis, glucose and lipid metabolism. We aimed to explore the effects of ghrelin on the proliferation and differentiation of 3T3-L1 and human primary preadipocytes.

Methods

3-(4,5-Dimethylthiazol-2-yl) 2,5-diphenyl tetrazolium bromide (MTT) spectrophotometry, Oil Red O staining, intracellular glycerol-3-phosphate dehydrogenase (G-3-PDH) assays and semiquantitative reverse transcription polymerase chain reaction were used to investigate the action of ghrelin.

Results

Ghrelin (0.01–1000 ng/ml) significantly increased the numbers of 3T3-L1 cells, and the maximum stimulatory effect was observed with the 10 ng/ml ghrelin treatment for 24 h (p < 0.05). Ghrelin also promoted the proliferation of human primary preadipocytes from 24 h (p < 0.05) to 48 h (p < 0.05) at a concentration of 1000 ng/ml. Further investigation showed that IGF-1 levels were notably increased in ghrelin-treated 3T3-L1 and human preadipocytes, and IGF-1 antibody was capable to attenuate this stimulatory action of ghrelin (all p < 0.05). Additionally, ghrelin significantly suppressed the differentiation of 3T3-L1 and human primary preadipocytes; 10 ng/ml ghrelin notably downregulated G-3-PDH activities in 3T3-L1 cells on day 3 and in human cells from days 4 to 12 following differentiation (all p < 0.05), and the intracellular lipoprotein lipase mRNA levels were lower than that of the controls (p < 0.05). Further investigation showed that the mRNA levels of peroxisome proliferator-activated receptor γ2 (PPARγ2) and CCAAT/enhancer binding protein α (C/EBPs) were also suppressed in ghrelin-treated human differentiating adipocytes.

Conclusion

Ghrelin promotes the proliferation of 3T3-L1 and human primary preadipocytes by increasing the expression of IGF-1. Ghrelin inhibits murine and human adipocyte differentiation by downregulating PPARγ2 and C/EBPα levels, consequently leading to decreased lipid accumulation and lipogenic enzymes expression.

Ghrelin up-regulates cartilage-specific genes via the ERK/STAT3 pathway in chondrocytes of patients with adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a severe spinal deformity that often occurs during puberty. The occurrence of AIS is suggested to be related to abnormal development of cartilage. Our previous study found increased serum ghrelin levels in AIS patients that may linked to the development of AIS. However, whether ghrelin affects cartilage in AIS patients is unclear. We used quantitative real-time PCR (qRT-PCR) and immunohistochemistry to detect the expression of cartilage-specific genes and the ghrelin receptor, growth hormone secretagogue receptor (GHSR). The mRNA and protein levels of collagen II (COLII), SOX9, AGGRECAN (ACAN) and GHSR were higher in AIS patients than in controls. In addition, the protein levels of GHSR downstream signaling pathway members p-STAT3 (Ser727), and p-ERK1/2 were increased. Furthermore, we treated chondrocytes from AIS patients with 100 nM ghrelin, the cell proliferation assay and Western blotting showed that ghrelin promotes chondrocyte proliferation and enhances COLII, SOX9, ACAN, p-ERK1/2 and p-STAT3 expression, respectively. Interestingly, all these observed alterations were abolished by ghrelin + [D-Lys3]-GHRP-6 (a ghrelin receptor inhibitor) treatment. And after U0126 (an inhibitor of ERK1/2 phosphorylation) treatment, ERK1/2 and STAT3 (Ser727) phosphorylation was simultaneously suppressed indicating that ERK1/2 is an upstream pathway protein of STAT3 (Ser727). In conclusion, ghrelin plays an important role in upregulating cartilage-specific genes on AIS primary chondrocytes by activating ERK/STAT3 signaling pathway.

Protective effect of ghrelin against tilmicosin-induced left ventricular dysfunction in rats

This study was conducted to investigate the possible protective effects of ghrelin against tilmicosin-induced acute ventricular dysfunction in rats. Forty adult male Sprague Dawley rats were randomly divided into 4 equal groups: control, ghrelin, tilmicosin, and ghrelin + tilmicosin. The left ventricular structural and functional parameters together with cardiac biomarker levels were evaluated. The results showed that tilmicosin treatment alone significantly decreased the left ventricular fractional shortening, left ventricular ejection fraction, left ventricular stroke volume, and cardiac output when compared with control group. In addition, tilmicosin led to a significant increase in left ventricular internal dimension in systole and left ventricular fractional end-systolic volume. At the same time, serum lactate dehydrogenase, creatine kinase, and creatine kinase-myocardial B fraction levels were significantly increased in tilmicosin-treated group when compared with control group. However, ghrelin pretreatment significantly prevented the left ventricular internal dimension in systole, left ventricular fractional end-systolic volume, left ventricular stroke volume, left ventricular ejection fraction, left ventricular fractional shortening, and cardiac output changes caused by tilmicosin. Moreover, ghrelin pretreatment could reduce significantly serum lactate dehydrogenase, creatine kinase, and creatine kinase-myocardial B fraction levels. These data indicated that ghrelin treatment may provide a protective effect against tilmicosin-induced left ventricular systolic dysfunction.

Ghrelin Upregulates Hoxb4 Gene Expression in Rat Bone Marrow Stromal Cells

OBJECTIVES

Ghrelin is a peptide which has a proliferative and antiapoptotic effect in many cells including bone marrow stromal cells (BMSCs). Homeobox protein B4 (HOXB4) is a transcription factor involved in stem cell regeneration and survival. The aim of the study was to find out the efect of ghrelin on Hoxb4 expression in BMSCs.

MATERIALS AND METHODS

In this experimental study, rat BMSCs were cultivated in Dulbecco's Modified Eagle Medium (DMEM). Passage three BMSCs were treated with ghrelin 100 μM for 48 hours. Real-time polymerase chain reaction (PCR) was carried out from the untreated BMSCs (B), BMSCs treated with 125 μM H₂O₂ (BH), BMSCs treated with 100 μM ghrelin then 125 μM H₂O₂ (BGH) and BMSCs treated with 100 μM ghrelin (BG) groups. For immunofluorescence, cells were incubated with an anti-HOXB4 monoclonal antibody. Primary antibodies were visualized using the Fluorescein isothiocyanate (FITC) method. All data are presented as mean ± SEM and P<0.05 was considered as statistical significant.

RESULTS

Hoxb4 expression significantly increased in the BG compared with BH and BGH groups. Furthermore, 100 μM ghrelin, increased the mean of HOXB4 positive immunoreactive cells compared to the BH group.

CONCLUSIONS

Ghrelin probably enhances proliferation and viability of BMSCs through Hoxb4 upregulation. However, the signaling pathway and other biological outcomes of this effect should be elucidated in different stem cells.

Ghrelin accelerates the cartilagic differentiation of rabbit mesenchymal stem cells through the ERK1/2 pathway

Mesenchymal stem cells (MSCs) can differentiate into chondroblasts, adipocytes, or cartilage under appropriate stimulation. Identifying a mechanism triggering the differentiation of MSCs into cartilage may help develop novel therapeutic approaches for treating heterotopic ossification, the pathological formation of lamellar bone in soft tissue outside the skeleton that can lead to debilitating immobility. Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor, stimulates growth hormone secretion, and has both orexigenic and adipogenic effects. This study sought to understand the potential involvement of the ERK1/2 signaling pathway in the ghrelin-induced growth of rat MSCs (rMSCs). We applied various concentrations of ghrelin to cultured rMSCs by observing the changes in the phosphorylation state of ERK1/2, p38, JNK as well as the type II collagen expression levels by western blot. The highest expression level for both type II collagen was obtained with 600 ng/mL ghrelin at 24 h. We found that the ghrelin-induced differentiation of rMSCs into cartilage was promoted primarily by the ERK1/2 pathway. Our study suggests that ghrelin induced differentiation of rMSCs into cartilage primarily through the ERK1/2 pathway.

Oxidized low-density lipoprotein (ox-LDL) promotes cardiac differentiation of bone marrow mesenchymal stem cells via activating ERK1/2 signaling

BACKGROUND/AIMS

The differentiation efficiency of bone marrow mesenchymal stem cells (BM-MSCs) is low in vivo after transplantation. Therefore, it is necessary to look for effective reagents for enhancing cardiac differentiation of BM-MSCs. It has been reported that cardiac differentiation of stem cells depends on the activation of extracellular signal-regulated protein 1/2 (ERK1/2) signaling. Oxidized low-density lipoprotein (ox-LDL) is a potent reagent for ERK1/2 activation. This indicates that ox-LDL may be a potential reagent to stimulate cardiac differentiation of stem cells. In this study, we investigated the effect of ox-LDL on cardiac differentiation of BM-MSCs and its relationship with ERK1/2 signaling.

METHODS

BM-MSCs were isolated from mouse bone marrow, cultured in DMEM supplemented with 15% FBS, and passaged up to the 3rd passage. Following culture with 5 μg/mL ox-LDL for 3 weeks, the cardiac differentiation of the 3rd passage BM-MSCs was identified by immunostaining, Western blotting, and RT-PCR assays for measuring the expression of cardiac-specific markers. To further explore the role of ERK1/2 signaling in cardiac differentiation of BM-MSCs, we simultaneously exposed BM-MSCs to ERK1/2 inhibitor (U0126) and ox-LDL, and identified the cardiac differentiation again.

RESULTS

The expressions of cardiac-specific markers including α-cardiac actin, α-MHC, β-MHC, ANP, and BNP were markedly increased in BM-MSCs following treatment with ox-LDL (P < .05), which indicates a directional differentiation of BM-MSCs to cardiac cells. Further, ox-LDL could also activate ERK1/2 in BM-MSCs, and application of U0126 markedly inhibited ox-LDL-induced cardiac transformation of BM-MSCs.

CONCLUSIONS

Ox-LDL induces cardiac differentiation of BM-MSCs via activation of ERK1/2 signaling.

Ghrelin protected neonatal rat cardiomyocyte against hypoxia/reoxygenation injury by inhibiting apoptosis through Akt-mTOR signal

Reducing reperfusion period myocardial cell damage is efficient to reduce myocardial ischemia-reperfusion injury. Ghrelin can increase myocardial contractility, improve heart failure caused by myocardial infarction. This study aimed to investigate the protective effect of Ghrelin on myocardial hypoxia/reoxygenation (H/R) injury of neonatal rat cardiomyocytes (NRCMs) and to explore the mechanisms. We isolated the NRCMs, established myocardial H/R model, blocked growth hormone secretagogue receptor (GHSR) by siRNA technique, examined cell activity by MTT and LDH assay, detected apoptosis by Hoechst 33258 staining and flow cytometry and determined the expression levels of apoptosis related proteins and signaling pathway proteins by western blot. We found that Ghrelin can significantly improve cell activity and decrease apoptosis after H/R, however this effect was abolished by GHSR-siRNA. In addition, we found that Ghrelin can significantly increase the expression of Bcl-2 but inhibit the level of Bax and caspase-3. Further mechanism study found that the phosphorylation level of signaling pathway protein Akt and mTOR in Ghrelin treated group were significantly higher than that in other groups. In conclusion, Ghrelin can reduce the H/R damage on NRCMs and inhibit the apoptosis by activating Akt-mTOR signaling pathway.

Infarcted cardiac microenvironment may hinder cardiac lineage differentiation of human embryonic stem cells

Microenvironment regulates cell fate and function. In this study, we investigated the effects of the infarcted cardiac microenvironment on cardiac differentiation of human embryonic stem cells (hESCs). hESCs were intramyocardially transplanted into infarcted or uninjured rat hearts. After 4 weeks, mesodermal and cardiac lineage markers were detected by immunofluorescence. Cardiac function was assessed by echocardiography. hESCs were differentiated in vitro under hypoxic (5% O₂ ), low-nutrient (5% FBS), or control condition. The numbers of beating clusters, proportions of cardiac troponin T (cTnT)-positive cells, and relative levels of cardiac-specific markers were determined. Results showed that in both uninjured and infarcted hearts, hESCs survived, underwent development, and formed intracardiac grafts, with a higher proportion in the uninjured hearts. However, cells that were double positive for human fetal liver kinase 1 (Flk1), a marker of cardiac progenitors, and human β-tubulin, a marker for labeling human cells, were found in the uninjured hearts but not in the infarcted hearts. hESC transplantation did not restore the cardiac function of acutely infarcted rats. In vitro, low FBS treatment was associated with fewer beating clusters, a lower proportion of cTnT-positive cells and lower levels of cardiac troponin I (cTnI) and α-myosin heavy chain (α-MHC) expression than those in the control. Conversely, hypoxia treatment was associated with a higher proportion of cTnT-positive cells and higher levels of cTnI expression. In conclusion, transplanted hESCs differentiate toward Flk1-positive cardiac progenitors in the uninjured but not infarcted hearts. The infarcted cardiac microenvironment recapitulated is unsuitable for cardiac differentiation of hESCs, likely due to nutrient deprivation.

GHSR deficiency suppresses neointimal formation in injured mouse arteries

Growth hormone secretagogue receptor (GHSR) is involved in appetite regulation and energy homeostasis. In the present study, we examined the role of GHSR in neointimal formation following vascular injury. In the mouse model of femoral artery wire injury, we found that vessel intima-to-media ratio was significantly reduced in GHSR deficiency (GHSR^-/-) mice compared with that in wild-type mice. Immunohistochemical staining showed that the smooth muscle cell (SMCs) in the neointima were significantly decreased in the injured arteries of GHSR^-/- mice which was associated with decreased SMC proliferation and migration. Furthermore, immunoblotting demonstrated that, in cultured rat aortic SMCs, small interfering RNA-mediated GHSR knockdown suppressed the activation of Akt and ERK1/2 signaling pathway. These findings suggested a novel role of GHSR in neointimal formation likely via promoting the proliferation and migration of SMCs involving Akt and ERK1/2 signaling. Therefore, GHSR may be a potential therapeutic target in restenosis and vascular remodeling.

Efficient generation of human embryonic stem cell-derived cardiac progenitors based on tissue-specific enhanced green fluorescence protein expression

Cardiac progenitor cells (CPCs) are committed to the cardiac lineage but retain their proliferative capacity before becoming quiescent mature cardiomyocytes (CMs). In medical therapy and research, the use of human pluripotent stem cell-derived CPCs would have several advantages compared with mature CMs, as the progenitors show better engraftment into existing heart tissues, and provide unique potential for cardiovascular developmental as well as for pharmacological studies. Here, we demonstrate that the CAG promoter-driven enhanced green fluorescence protein (EGFP) reporter system enables the identification and isolation of embryonic stem cell-derived CPCs. Tracing of CPCs during differentiation confirmed up-regulation of surface markers, previously described to identify cardiac precursors and early CMs. Isolated CPCs express cardiac lineage-specific transcripts, still have proliferating capacity, and can be re-aggregated into embryoid body-like structures (CAG-EGFP(high) rEBs). Expression of troponin T and NKX2.5 mRNA is up-regulated in long-term cultured CAG-EGFP(high) rEBs, in which more than 90% of the cells become Troponin I positive mature CMs. Moreover, about one third of the CAG-EGFP(high) rEBs show spontaneous contractions. The method described here provides a powerful tool to generate expandable cultures of pure human CPCs that can be used for exploring early markers of the cardiac lineage, as well as for drug screening or tissue engineering applications.

Ghrelin accelerates the growth and osteogenic differentiation of rabbit mesenchymal stem cells through the ERK1/2 pathway

Background

Mesenchymal stem cells (MSCs) can differentiate into chondroblasts, adipocytes, or osteoblasts under appropriate stimulation. Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor (GHSR), stimulates growth hormone (GH) secretion, and has both orexigenic and adipogenic effects. This study sought to understand the potential involvement of members of MAPK serine/threonine kinases in the ghrelin-induced growth of rabbit MSCs ( rBMSC).

Methods

We applied various concentrations of ghrelin to cultured rBMSC and observed the growth rate of the cells by MTT, changes in the phosphorylation state of ERK1/2, JNK and p38, and the expression levels of ALP, Runx2, and Osterix by wetern blot.

Results

We found that the growth and osteogenic differentiation of ghrelin-treated rBMSC are promoted primarily by phosphorylated ERK1/2, and that this phosphorylation, as well p38 phosphorylation, is mediated by GHSR.

Conclusions

Our study suggests that ghrelin promotes the growth and osteogenic differentiation of rBMSC primarily through the ERK1/2 pathway.

Limb ischemic preconditioning protects against contrast-induced acute kidney injury in rats via phosphorylation of GSK-3β

Contrast-induced acute kidney injury (CI-AKI) resulting from the use of intravascular iodinated contrast media for diagnostic and interventional cardiovascular procedures is associated with substantial morbidity and mortality. Despite preventative measures intended to mitigate the risk of CI-AKI, there remains a need for a novel and effective therapeutic approach. Limb ischemic preconditioning (LIPC), where short-term ischemia/reperfusion is applied to an arm prior to administration of the contrast agent, has been shown in several trials to preserve renal function in patients at high risk for CI-AKI. However, the underlying mechanism by which this procedure provides renoprotection against contrast media insults is not known. Here, we explored the molecular mechanism(s) of LIPC-induced protection of the kidneys from CI-AKI, particularly the role of phosphorylated glycogen synthase kinase-3β (GSK-3β). We used a novel CI-AKI model consisting of 5/6 nephrectomized (NE) rats at 6 weeks after the ablative surgery. LIPC- or sham-treated rats were administered iohexol (10 ml/kg, 3.5 gI) via the tail vein. The results showed that LIPC protected the kidneys against iohexol-induced injury. This protective effect was accompanied by the attenuation of renal dysfunction, tubular damage, apoptosis, mitochondrial swelling, oxidative stress, and inflammation. Furthermore, LIPC-induced renoprotection was blocked via treatment with inhibitors of PI3K (wortmannin or LY294002), but not ERK (U0126 or PD98059). LIPC also increased the protein expression levels of phospho-Akt, phospho-GSK-3β, and nuclear Nrf2, and decreased the levels of nuclear NF-κB. A specific GSK-3β inhibitor (SB216763) mimicked this effect of LIPC, by inhibiting the opening of the mitochondrial permeability transition pore and reducing the levels of oxidative stress and inflammation via activation of Nrf2 and suppression of NF-κB. The above results demonstrate that LIPC induces protection against CI-AKI, making this procedure a promising strategy for preventing CI-AKI. In particular, this renoprotective effect involves the phosphorylation of GSK-3β.

Antifibrotic activity of acylated and unacylated ghrelin

Fibrosis can affect almost all tissues and organs, it often represents the terminal stage of chronic diseases, and it is regarded as a major health issue for which efficient therapies are needed. Tissue injury, by inducing necrosis/apoptosis, triggers inflammatory response that, in turn, promotes fibroblast activation and pathological deposition of extracellular matrix. Acylated and unacylated ghrelin are the main products of the ghrelin gene. The acylated form, through its receptor GHSR-1a, stimulates appetite and growth hormone (GH) release. Although unacylated ghrelin does not bind or activate GHSR-1a, it shares with the acylated form several biological activities. Ghrelin peptides exhibit anti-inflammatory, antioxidative, and antiapoptotic activities, suggesting that they might represent an efficient approach to prevent or reduce fibrosis. The aim of this review is to summarize the available evidence regarding the effects of acylated and unacylated ghrelin on different pathologies and experimental models in which fibrosis is a predominant characteristic.

Agonists of growth hormone-releasing hormone stimulate self-renewal of cardiac stem cells and promote their survival

The beneficial effects of agonists of growth hormone-releasing hormone receptor (GHRH-R) in heart failure models are associated with an increase in the number of ckit(+) cardiac stem cells (CSCs). The goal of the present study was to determine the presence of GHRH-R in CSCs, the effect of GHRH-R agonists on their proliferation and survival, and the mechanisms involved. We investigated the expression of GHRH-R in CSCs of different species and the effect of GHRH-R agonists on their cell proliferation and survival. GHRH-R is expressed in ckit(+) CSCs isolated from mouse, rat, and pig. Treatment of porcine CSCs with the GHRH-R agonist JI-38 significantly increased the rate of cell division. Similar results were observed with other GHRH-R agonists, MR-356 and MR-409. JI-38 exerted a protective effect on survival of porcine CSCs under conditions of oxidative stress induced by exposure to hydrogen peroxide. Treatment with JI-38 before exposure to peroxide significantly reduced cell death. A similar effect was observed with MR-356. Addition of GHRH-R agonists to porcine CSCs induced activation of ERK and AKT pathways as determined by increased expression of phospho-ERK and phospho-AKT. Inhibitors of ERK and AKT pathways completely reversed the effect of GHRH-R agonists on CSC proliferation. Our findings extend the observations of the expression of GHRH-R by CSCs and demonstrate that GHRH-R agonists have a direct effect on proliferation and survival of CSCs. These results support the therapeutic use of GHRH-R agonists for stimulating endogenous mechanisms for myocardial repair or for preconditioning of stem cells before transplantation.

Activation of glucagon-like peptide-1 receptor inhibits tumourigenicity and metastasis of human pancreatic cancer cells via PI3K/Akt pathway

AIMS

It has been reported that glucagon-like peptide-1 (GLP-1) agents are associated with an increased risk of pancreatic cancer in patients with type 2 diabetes. Reports have indicated that GLP-1 promotes pancreatic metaplasia and premalignant lesions. The aims of this study were to determine the effects of GLP-1-based therapy on pancreatic cancer cells.

METHODS

Immunohistochemistry was used to investigate GLP-1 receptor (GLP-1R) expression in 30 human pancreatic cancer tissues. We also analysed associated clinicopathological data and each patient's prognosis. Two human pancreatic cancer cell lines were used to evaluate the in vitro effects of the GLP-1R agonist liraglutide on cell growth, migration and invasion. Mouse xenograft models of human pancreatic cancer were established to evaluate the effects of liraglutide in vivo.

RESULTS

Human pancreatic cancer tissues showed lower levels or a lack of GLP-1R expression when compared with levels in the tumour-adjacent pancreatic tissues. Negative GLP-1R expression occurred more frequently in advanced tumours with larger diameters and lymphatic metastasis, and was associated with a poor prognosis. GLP-1R activation with liraglutide inhibited tumourigenicity and metastasis of human pancreatic cancer cells in vitro and in vivo. Akt activation was dose-dependently inhibited by liraglutide, and the PI3K inhibitors, LY294002 and wortmannin, displayed similar suppressive effects to liraglutide in human pancreatic cancer cells.

CONCLUSIONS

GLP-1R activation has an antitumour effect on human pancreatic cancers via inhibition of the PI3K/Akt pathway. This finding suggests that GLP-1-based therapies may be beneficial, rather than harmful, in treating type 2 diabetic patients with pancreatic cancer.

Graphene enhances the cardiomyogenic differentiation of human embryonic stem cells

Graphene has drawn attention as a substrate for stem cell culture and has been reported to stimulate the differentiation of multipotent adult stem cells. Here, we report that graphene enhances the cardiomyogenic differentiation of human embryonic stem cells (hESCs) at least in part, due to nanoroughness of graphene. Large-area graphene on glass coverslips was prepared via the chemical vapor deposition method. The coating of the graphene with vitronectin (VN) was required to ensure high viability of the hESCs cultured on the graphene. hESCs were cultured on either VN-coated glass (glass group) or VN-coated graphene (graphene group) for 21 days. The cells were also cultured on glass coated with Matrigel (Matrigel group), which is a substrate used in conventional, directed cardiomyogenic differentiation systems. The culture of hESCs on graphene promoted the expression of genes involved in the stepwise differentiation into mesodermal and endodermal lineage cells and subsequently cardiomyogenic differentiation compared with the culture on glass or Matrigel. In addition, the culture on graphene enhanced the gene expression of cardiac-specific extracellular matrices. Culture on graphene may provide a new platform for the development of stem cell therapies for ischemic heart diseases by enhancing the cardiomyogenic differentiation of hESCs.

Ghrelin gene products in acute and chronic inflammation

Ghrelin gene products--the peptides ghrelin, unacylated ghrelin, and obestatin--have several actions on the immune system, opening new perspectives within neuroendocrinology, metabolism and inflammation. The aim of this review is to summarize the available evidence regarding the less known role of these peptides in the machinery of inflammation and autoimmunity, outlining some of their most promising therapeutic applications.

Characterization of a far-red analog of ghrelin for imaging GHS-R in P19-derived cardiomyocytes

Ghrelin and its receptor, the growth hormone secretagogue receptor (GHS-R), are expressed in the heart, and may function to promote cardiomyocyte survival, differentiation and contractility. Previously, we had generated a truncated analog of ghrelin conjugated to fluorescein isothiocyanate for the purposes of determining GHS-R expression in situ. We now report the generation and characterization of a far-red ghrelin analog, [Dpr(3)(octanoyl), Lys(19)(Cy5)]ghrelin (1-19), and show that it can be used to image changes in GHS-R in developing cardiomyocytes. We also generated the des-acyl analog, des-acyl [Lys(19)(Cy5)]ghrelin (1-19) and characterized its binding to mouse heart sections. Receptor binding affinity of Cy5-ghrelin as measured in HEK293 cells overexpressing GHS-R1a was within an order of magnitude of that of fluorescein-ghrelin and native human ghrelin, while the des-acyl Cy5-ghrelin did not bind GHS-R1a. Live cell imaging in HEK293/GHS-R1a cells showed cell surface labeling that was displaced by excess ghrelin. Interestingly, Cy5-ghrelin, but not the des-acyl analog, showed concentration-dependent binding in mouse heart tissue sections. We then used Cy5-ghrelin to track GHS-R expression in P19-derived cardiomyocytes. Live cell imaging at different time points after DMSO-induced differentiation showed that GHS-R expression preceded that of the differentiation marker aMHC and tracked with the contractility marker SERCA 2a. Our far-red analog of ghrelin adds to the tools we are developing to map GHS-R in developing and diseased cardiac tissues.

The growth hormone secretagogue receptor: its intracellular signaling and regulation

The growth hormone secretagogue receptor (GHSR), also known as the ghrelin receptor, is involved in mediating a wide variety of biological effects of ghrelin, including: stimulation of growth hormone release, increase of food intake and body weight, modulation of glucose and lipid metabolism, regulation of gastrointestinal motility and secretion, protection of neuronal and cardiovascular cells, and regulation of immune function. Dependent on the tissues and cells, activation of GHSR may trigger a diversity of signaling mechanisms and subsequent distinct physiological responses. Distinct regulation of GHSR occurs at levels of transcription, receptor interaction and internalization. Here we review the current understanding on the intracellular signaling pathways of GHSR and its modulation. An overview of the molecular structure of GHSR is presented first, followed by the discussion on its signaling mechanisms. Finally, potential mechanisms regulating GHSR are reviewed.