Urocortin (Ucn1), a member of the corticotrophin-releasing hormone (CRH) family, has been reported to participate in inflammation. The increased expression of intercellular adhesion molecule 1 (ICAM1) plays important roles in inflammation and immune responses. Our previous results demonstrated that Ucn1 significantly enhanced the expression of ICAM1. However, the underlying mechanisms are still unknown. The purpose of this study is to investigate the detailed mechanisms of Ucn1-induced upregulation of ICAM1. Here, we characterized the mechanisms of Ucn1 usage to regulate ICAM1 expression in human umbilical vein endothelial cells (HUVECs). Our data revealed that Ucn1 increased ICAM1 and cyclooxygenase 2 (COX2) expressions in a time-dependent manner via CRH receptor 2 (CRHR2). In addition, COX2 was involved in ICAM1 upregulation. Furthermore, Ucn1 could increase the expression and phosphorylation of cytosolic phospholipases A2 (cPLA2) in a time-dependent manner via CRHR2 and CRHR1. Moreover, ablation of cPLA2 by the inhibitor pyrrophenone or siRNA attenuated the ICAM1 increase induced by Ucn1. In addition, nuclear factor κB (NF-κB) was activated, indicated by the increase in nuclear p65NF-κB expression and phosphorylation of p65NF-κB, depending on cPLA2 and CRHR2 activation. Pyrrolidinedithiocarbamic acid, an inhibitor of NF-κB, abolished the elevation of ICAM1 but not COX2. Also, Ucn1 increased the production of prostaglandin E2 (PGE2) which further activated protein kinase A (PKA)–CREB pathways dependent of cPLA2 via CRHR2. Moreover, the increase in NF-κB phosphorylation was not affected by the selective COX2 inhibitor NS-398 or the PKA inhibitor H89. In conclusion, these data indicate that Ucn1 increase the ICAM1 expression via cPLA2-NF-κB and cPLA2-COX2-PGE2-PKA-CREB pathways by means of CRHR2.
Rong Wan, Yunxin Liu, Li Li, Chao Zhu, Lai Jin and Shengnan Li
Ying Ying, Huazhang Zhu, Zhen Liang, Xiaosong Ma and Shiwei Li
Activation of apoptosis in cardiomyocytes by saturated palmitic acids contributes to cardiac dysfunction in diabetic cardiomyopathy. Beta-catenin (b-catenin) is a transcriptional regulator of several genes involved in survival/anti-apoptosis. However, its role in palmitate-induced cardiomyocyte apoptosis remains unclear. Glucagon-like peptide 1 (GLP1) has been shown to exhibit potential cardioprotective properties. This study was designed to evaluate the role of b-catenin signalling in palmitate-induced cardiomyocyte apoptosis and the molecular mechanism underlying the protective effects of GLP1 on palmitate-stressed cardiomyocytes. Exposure of neonatal rat cardiomyocytes to palmitate increased the fatty acid transporter CD36-mediated intracellular lipid accumulation and cardiomyocyte apoptosis, decreased accumulation and nuclear translocation of active b-catenin, and reduced expression of b-catenin target protein survivin and BCL2. These detrimental effects of palmitate were significantly attenuated by GLP1 co-treatment. However, the anti-apoptotic effects of GLP1 were markedly abolished when b-catenin was silenced with a specific short hairpin RNA. Furthermore, analysis of the upstream molecules and mechanisms responsible for GLP1-associated cardiac protection revealed that GLP1 restored the decreased phosphorylation of protein kinase B (Akt) and glycogen synthase kinase-3b (GSK3b) in palmitate-stimulated cardiomyocytes. In contrast, inhibition of Akt with an Akt-specific inhibitor MK2206 or blockade of GLP1 receptor (GLP1R) with a competitive antagonist exendin-(9–39) significantly abrogated the GLP1-mediated activation of GSK3b/b-catenin signalling, leading to increased apoptosis in palmitate-stressed cardiomyocytes. Collectively, our results demonstrated for the first time that the attenuated b-catenin signalling may contribute to palmitate-induced cardiomyocyte apoptosis, while GLP1 can protect cardiomyocytes from palmitate-induced apoptosis through activation of GLP1R/Akt/GSK3b-mediated b-catenin signalling.
Ling Wang, Yu-Dong Wang, Wen-Jun Wang, Ying Zhu and Da-Jin Li
Dehydroepiandrosterone (DHEA) may be a promising agent for postmenopausal osteoporosis (PMO), but its mechanism to modulate osteoblasts (OBs) is yet to be explained. To elucidate the effects of DHEA treatment on the ovariectomized (OVX) mice and its mechanisms, we evaluated the morphology of mice bone tissue and expression of proliferating cell nuclear antigen (PCNA) in the vertebrae-derived OB after having treated the OVX animals with DHEA. The results showed that DHEA administration increased the expression of PCNA in OB and changed the bone tissue morphometry of the PMO model. To further investigate this mechanism, the OB was isolated from neonatal mice calvariae by the enzyme-digested assay, exposed to DHEA, and then analyzed for ultrastructure, DNA content, early apoptotic cells, and phosphorylation of extracellular signal-regulated kinase 1/2. It was found that DHEA promoted proliferation and inhibited apoptosis of OB significantly, via mitogen-activated protein kinase signaling pathway independent of either androgen receptor or estrogen receptor, suggesting that it may exert roles via a DHEA-specific receptor directly, not by way of conversion to androgens or estrogens.
Xiaohui Wang, Yidong Li, Xiaoyan Zhu, Yan Wang, Fei Diao and Jian Lu
Glucocorticoid (GC) effectively suppresses immune and inflammatory responses and inhibits the growth of several types of cells, but the role of GC and its receptor on macrophage proliferation is unclear. In our previous work, we found RAW-GR(−) cells (murine macrophage RAW264.7 cells stably transfected with GR-siRNA expression vector by RNA interference) grew faster by about twofold. In this study, we further explored the role and mechanisms of GC/GR on the proliferation of macrophage. We found that the growth of RAW264.7 cells was inhibited by dexamethasone (Dex) in a concentration-dependent manner. The mRNA and protein levels of signal regulatory protein α1 (SIRPA) were induced by GC/GR in RAW264.7 cells and SIRPA expression was decreased remarkably in RAW-GR(−) cells. Overexpression of SIRPA negatively regulated the proliferation of RAW-GR(−) cells, and inhibition of SIRPA expression by a small from RNA interference attenuated Dex-induced proliferation inhibition in RAW264.7 cells. The proliferation inhibition of GC/GR was also found in mouse peritoneal macrophage, which was associated with the increase in SIRPA induced by GC/GR as well. In addition, elevation of the expression of CDK2, cyclinD1, and cyclinB1, but not phosphorylated ERK1/2 and p38, was found in RAW-GR(−) cells. In conclusion, we provided the novel evidences that GC/GR inhibited the growth of RAW264.7 cells and mouse peritoneal macrophage, and the antiproliferative effect of GC/GR on these cells was at least in part a result from GC/GR-induced SIRPA expression. Up-regulation of CDK2, cyclinD1, and cyclinB1 was also related to the increased proliferation of RAW-GR(−) cells.
Ping Li, Yan Hao, Feng-Hui Pan, Min Zhang, Jian-Qiang Ma and Da-Long Zhu
This study investigates the effectiveness and mechanisms of a serum- and glucocorticoid-inducible kinase 1 (SGK1) inhibitor in counteracting hyperglycemia. In an in vivo experiment, we demonstrated that after an 8-week treatment with an SGK1 inhibitor, the fasting blood glucose and HbA1c level significantly decreased in db/db mice. RT-PCR and western blot analyses revealed that intestinal SGK1 and sodium glucose co-transporter 1 (SGLT1) expression were enhanced in db/db mice. Treatment with an SGK1 inhibitor decreased excessive SGLT1 expression in the intestine of db/db mice. In vitro experiments with intestinal IEC-6 cells showed that the co-administration of an SGK1 inhibitor partly reversed the SGLT1 expression and glucose absorption that were induced by dexamethasone. In conclusion, this study revealed that the favorable effect of an SGK1 inhibitor on hyperglycemia is partly due to decreased glucose absorption through SGLT1 in the small intestine. These data collectively suggest that SGK1 may be a potent target for the treatment of diabetes and other metabolic disorders.
Yan-ping Xu, Jia-jun Zhu, Fen Cheng, Ke-wen Jiang, Wei-zhong Gu, Zheng Shen, Yi-dong Wu, Li Liang and Li-zhong Du
Effective treatment and/or prevention strategies for neonatal persistent pulmonary hypertension of the newborn (PPHN) have been an important topic in neonatal medicine. However, mechanisms of impaired pulmonary vascular structure in hypoxia-induced PPHN are poorly understood and consequently limit the development of effective treatment. In this study, we aimed to explore the molecular signaling cascades in the lungs of a PPHN animal model and used primary cultured rat pulmonary microvascular endothelial cells to analyze the physiological benefits of ghrelin during the pathogenesis of PPHN. Randomly selected newborn rats were exposed to hypoxia (10–12%) or room air and received daily s.c. injections of ghrelin (150 μg/kg) or saline. After 2 weeks, pulmonary hemodynamics and morphometry were assessed in the rats. Compared with the control, hypoxia increased pulmonary arterial pressure, right ventricle (RV) hypertrophy, and arteriolar wall thickness. Ghrelin treatment reduced both the magnitude of PH and the RV/(left ventricle+septum (Sep)) weight ratio. Ghrelin protected neonatal rats from hypoxia-induced PH via the upregulation of phosphorylation of glycogen synthase kinase 3β (p-GSK3β)/β-catenin signaling and associated with β-catenin translocation to the nucleus in the presence of growth hormone secretagogue receptor-1a. Our findings suggest that s.c. administration of ghrelin improved PH and attenuated pulmonary vascular remodeling after PPHN. These beneficial effects may be mediated by the regulation of p-GSK3β/β-catenin expression. We propose ghrelin as a novel potential therapeutic agent for PPHN.
Xueting Wang, Zhiran Zou, Zhihui Yang, Shan Jiang, Yapeng Lu, Dan Wang, Zhangji Dong, Sha Xu and Li Zhu
Hypoxia-inducible factor-1 (HIF1) is a critical transcription factor involved in cell response to hypoxia. Under physiological conditions, its ‘a’ subunit is rapidly degraded in most tissues except testes. HIF1 is stably expressed in Leydig cells, which are the main source of testosterone for male, and might bind to the promoter region of steroidogenic acute regulatory protein (STAR), which is necessary for the testosterone synthesis, according to software analysis. This study aims to identify the binding sites of HIF1 on Star promoter and its transcriptional regulation of STAR to affect testosterone synthesis. Testosterone level and steroid synthesis-related proteins were determined in male Balb/C mice exposed to hypoxia (8% O2). While HIF1 was upregulated, the testosterone level was significantly decreased. This was further confirmed by in vitro experiments with rat primary Leydig cells or TM3 cells exposed to hypoxia (1% O2), CoCl2 or DFX to raise HIF1. The decline of testosterone was reversed by pregnenolone but not cAMP, indicating the cholesterol transport disorder as the main cause. In agreement, STAR expression level was decreased in response to HIF1, while 3b-hydroxysteroid dehydrogenase, 17b-hydroxysteroid dehydrogenase and p450scc did not exhibit significant changes. By ChIP, EMSA supershift and dual-luciferase reporter assays, HIF1 was found to bind to the Star promoter region and repress the expression of STAR. Mutation assays identified three HIF1-binding sites on mouse Star promoter. These findings indicate that HIF1 represses STAR transcription through directly binding to the Staar promoter at −2082/−2078, −2064/−2060 and −1910/−1906, leading to the negative regulation of testosterone synthesis.
Hui Juan Zhu, Hui Pan, Xu Zhe Zhang, Nai Shi Li, Lin Jie Wang, Hong Bo Yang and Feng Ying Gong
Myostatin is a critical negative regulator of skeletal muscle development, and has been reported to be involved in the progression of obesity and diabetes. In the present study, we explored the effects of myostatin on the proliferation and differentiation of 3T3-L1 preadipocytes by using 3-[4,5-dimethylthiazol-2-yl] 2,5-diphenyl tetrazolium bromide spectrophotometry, intracellular triglyceride (TG) assays, and real-time quantitative RT-PCR methods. The results indicated that recombinant myostatin significantly promoted the proliferation of 3T3-L1 preadipocytes and the expression of proliferation-related genes, including Cyclin B2, Cyclin D 1, Cyclin E1, Pcna, and c-Myc, and IGF1 levels in the medium of 3T3-L1 were notably upregulated by 35.2, 30.5, 20.5, 33.4, 51.2, and 179% respectively (all P<0.01) in myostatin-treated 3T3-L1 cells. Meanwhile, the intracellular lipid content of myostatin-treated cells was notably reduced as compared with the non-treated cells. Additionally, the mRNA levels of Ppar γ, Cebp α, Gpdh, Dgat, Acs1, Atgl, and Hsl were significantly downregulated by 22–76% in fully differentiated myostatin-treated adipocytes. Finally, myostatin regulated the mRNA levels and secretion of adipokines, including Adiponectin, Resistin, Visfatin, and plasminogen activator inhibitor-1 (PAI-1) in 3T3-L1 adipocytes (all P<0.001). Above all, myostatin promoted 3T3-L1 proliferation by increasing the expression of cell-proliferation-related genes and by stimulating IGF1 secretion. Myostatin inhibited 3T3-L1 adipocyte differentiation by suppressing Ppar γ and Cebp α expression, which consequently deceased lipid accumulation in 3T3-L1 cells by inhibiting the expression of critical lipogenic enzymes and by promoting the expression of lipolytic enzymes. Finally, myostatin modulated the expression and secretion of adipokines in fully differentiated 3T3-L1 adipocytes.
Chunheng Mo, Long Huang, Lin Cui, Can Lv, Dongliang Lin, Liang Song, Guoqiang Zhu, Juan Li and Yajun Wang
The two structurally and functionally related peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB) play critical roles in many physiological/pathological processes in mammals. However, the information regarding the expression and functionality of avian NMB, GRP and their receptors is limited. Here, we characterized cNMB, cGRP and their receptors (cNMBR, cGRPR and cBRS3) in chickens. Our results showed that: (1) cNMBR and cGRPR expressed in CHO cells could be potently activated by cNMB and cGRP, respectively, as monitored by cell-based luciferase reporter assays, indicating that cNMBR and cGRPR are cNMB- and cGRP-specific receptors; strikingly, BRS3 of chickens (/spotted gars), which is orthologous to mouse bombesin receptor subtype-3 (BRS3), could be potently activated by GRP and NMB, demonstrating that both peptides are the endogenous ligands for chicken (/spotted gar) BRS3; (2) quantitative real-time PCR (qPCR) revealed that cGRPR is widely expressed in chicken tissues with abundant expression in the ovary, pancreas, proventriculus, spinal cord and brain, whereas cNMB, cNMBR and cBRS3 are mainly expressed in the brain and testes; (3) interestingly, qPCR, Western blot and immunostaining revealed that cGRP is predominantly expressed in the anterior pituitary and mainly localized to LH-cells, suggesting that cGRP is likely a novel pituitary hormone in chickens. In summary, our data help to uncover the roles of GRP, NMB and their receptors in birds, and provide the first persuasive evidence from an evolutionary prospective that in vertebrates, GRP and NMB are the endogenous ligands for BRS3, an orphan receptor that has puzzled endocrinologists for more than two decades.
Siyi Zhu, Hongchen He, Chengfei Gao, Guojing Luo, Ying Xie, Haiming Wang, Li Tian, Xiang Chen, Xijie Yu and Chengqi He
We examined the effects of tumor necrosis factor-α (TNFα) and interleukin-6 (IL6) gene knockout in preserving the bone loss induced by ovariectomy (OVX) and the mechanisms involved in bone metabolism. Twenty female wild-type (WT), TNFα-knockout (TNFα−/−) or IL6-knockout (IL6−/−) mice aged 12 weeks were sham-operated (SHAM) or subjected to OVX and killed after 4 weeks. Bone mass and skeletal microarchitecture were determined using micro-CT. Bone marrow stromal cells (BMSCs) from all three groups (WT, TNFα−/− and IL6−/−) were induced to differentiate into osteoblasts or osteoclasts and treated with 17-β-estradiol. Bone metabolism was assessed by histological analysis, serum analyses and qRT-PCR. OVX successfully induced a high turnover in all mice, but a repair effect was observed in TNFα−/− and IL6−/− mice. The ratio of femoral trabecular bone volume to tissue volume, trabecular number and trabecular thickness were significantly decreased in WT mice subjected to OVX, but increased in TNFα−/− mice (1.62, 1.34, 0.27-fold respectively; P < 0.01) and IL6−/− mice (1.34, 0.80, 0.22-fold respectively; P < 0.01). Furthermore, we observed a 29.6% increase in the trabecular number in TNFα−/− mice when compared to the IL6−/− mice. Both, TNFα−/− and IL6−/− BMSCs exhibited decreased numbers of TRAP-positive cells and an increase in ALP-positive cells, with or without E2 treatment (P < 0.05). While the knockout of TNFα or IL6 significantly upregulated mRNA expressions of osteoblast-related genes (Runx2 and Col1a1) and downregulated osteoclast-related mRNA for TRAP, MMP9 and CTSK in vivo and in vitro, TNFα knockout appeared to have roles beyond IL6 knockout in upregulating Col1a1 mRNA expression and downregulating mRNA expressions of WNT-related genes (DKK1 and Sost) and TNF-related activation-induced genes (TRAF6). TNFα seemed to be more potentially invasive in inhibiting bone formation and enhancing TRAF6-mediated osteoclastogenesis than IL6, implying that the regulatory mechanisms of TNFα and IL6 in bone metabolism may be different.