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Jiannan Zhang, Xin Li, Yawei Zhou, Lin Cui, Jing Li, Chenlei Wu, Yiping Wan, Juan Li and Yajun Wang

The interaction of melanocortin-4 (MC4R) and melanocortin-3 (MC3R) receptors with proopiomelanocortin (POMC)-derived peptides (e.g. α-MSH), agouti-related protein (AgRP) and melanocortin-2 receptor accessory protein 2 (MRAP2) is suggested to play critical roles in energy balance of vertebrates. However, evidence on their interaction in birds remains scarce. Our study aims to reveal their interaction in chickens and the results showed that (1) chicken (c-)MC3R and cMC4R expressed in Chinese hamster ovary (CHO) cells can be activated by α-MSH and ACTH1–39 equipotently, monitored by a pGL3-CRE-luciferase reporter system; (2) cMC3R and cMC4R, when co-expressed with cMRAP2 (or cMRAP, a cMRAP2 homolog), show increased sensitivity to ACTH treatment and thus likely act as ACTH-preferring receptors, and the interaction between cMC3R/cMC4R and cMRAP2 was demonstrated by co-immunoprecipitation assay; (3) both cMC3R and cMC4R display constitutive activity when expressed in CHO cells, as monitored by dual-luciferase reporter assay, and cMRAP2 (and cMRAP) can modulate their constitutive activity; (4) AgRP inhibits the constitutive activity of cMC3R/cMC4R, and it also antagonizes ACTH/α-MSH action on cMC4R/cMC3R, indicating that AgRP functions as the inverse agonist and antagonist for both receptors. These findings, together with the co-expression of cMC4R, cMC3R, cMRAP2, cAgRP and cPOMC in chicken hypothalamus detected by quantitative real-time PCR, suggest that within the hypothalamus, α-MSH/ACTH, AgRP and MRAP2 may interact at the MC4R(/MC3R) interface to control energy balance. Furthermore, our data provide novel proof for the involvement of MRAP2 (and MRAP) in fine-tuning the constitutive activity and ligand sensitivity and selectivity of both MC3R and MC4R in vertebrates.

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Chan-Juan Ma, Ai-Fang Nie, Zhi-Jian Zhang, Zhi-Guo Zhang, Li Du, Xiao-Ying Li and Guang Ning

Genipin, a compound derived from Gardenia jasminoides Ellis fruits, has been used over the years in traditional Chinese medicine to treat symptoms of type 2 diabetes. However, the molecular basis for its antidiabetic effect has not been fully revealed. In this study, we investigated the effects of genipin on glucose uptake and signaling pathways in C2C12 myotubes. Our study demonstrates that genipin stimulated glucose uptake in a time- and dose-dependent manner. The maximal effect was achieved at 2 h with a concentration of 10 μM. In myotubes, genipin promoted glucose transporter 4 (GLUT4) translocation to the cell surface, which was observed by analyzing their distribution in subcellular membrane fraction, and increased the phosphorylation of insulin receptor substrate-1 (IRS-1), AKT, and GSK3β. Meanwhile, genipin increased ATP levels, closed KATP channels, and then increased the concentration of calcium in the cytoplasm in C2C12 myotubes. Genipin-stimulated glucose uptake could be blocked by both the PI3-K inhibitor wortmannin and calcium chelator EGTA. Moreover, genipin increases the level of reactive oxygen species and ATP in C2C12 myotubes. These results suggest that genipin activates IRS-1, PI3-K, and downstream signaling pathway and increases concentrations of calcium, resulting in GLUT4 translocation and glucose uptake increase in C2C12 myotubes.

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Li Juan He, Min Liang, Fan Fan Hou, Zhi Jian Guo, Di Xie and Xun Zhang

There is evidence that inflammatory processes are involved in the development and/or progression of diabetic nephropathy. However, effective treatment for inflammation in the kidneys of diabetic is practically unknown. The rhizomes of Picrorhiza scrophulariiflora (PS) are a traditional medication long used to treat inflammatory diseases. The aim of the present study was to test the hypothesis that the ethanol extract of PS (EPS) may reduce inflammation in patients with diabetic kidneys. Streptozotocin-induced diabetic rats were randomly assigned to two groups treated with a gavage of either EPS or vehicle. A group of non-diabetic control rats was treated concurrently. Compared with vehicle-treated diabetic rats, EPS-treated animals displayed a significant decrease in renal macrophage infiltration and overexpression of chemokine (C-C motif) ligand 2 (CCL2) and TGFB1. This was associated with attenuation of the structural and functional abnormalities of early diabetic nephropathy, such as glomerular hypertrophy, mesangial expansion, and albuminuria. Administration of EPS significantly reduced NADPH oxidase-dependent superoxide generation and decreased expression of malondialdehyde and advanced oxidation protein products in diabetic kidney. These data suggest that EPS might improve diabetic nephropathy, probably through inhibition of redox-sensitive inflammation.

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Da-Long Ren, Ai-Ai Sun, Ya-Juan Li, Min Chen, Shu-Chao Ge and Bing Hu

Neutrophil migration to inflammatory sites is the fundamental process of innate immunity among organisms against pathogen invasion. As a major sleep adjusting hormone, melatonin has also been proved to be involved in various inflammatory events. This study aimed to evaluate the impact of exogenous melatonin on neutrophil migration to the injury site in live zebrafish and further investigate whether ERK signaling is involved in this process. Using the tail fin transection model, the fluorescently labeled neutrophil was in vivo visualized in transgenic Tg(lyz:EGFP), Tg(lyz:DsRed) zebrafish. We found that exogenous melatonin administration dramatically inhibited the injury-induced neutrophil migration in a dose-dependent and time-dependent manner. The inhibited effect of melatonin on neutrophil migration could be attenuated by melatonin receptor 1, 2, and 3 antagonists. The ERK phosphorylation level was significantly decreased post injury when treated with melatonin. The blocking of ERK activation with inhibitor PD0325901 suppressed the number of migrated neutrophils in response to injury. However, the activation of ERK with the epidermal growth factor could impair the inhibited effect of melatonin on neutrophil migration. We also detected that PD0325901 significantly suppressed the in vivo neutrophils transmigrating over the vessel endothelial cell using the transgenic Tg(flk:EGFP);(lyz:DsRed) line labeled as both vessel and neutrophil. Taking all of these data together, the results indicated that exogenous melatonin had an anti-migratory effect on neutrophils by blocking the ERK phosphorylation signal, and it led to the subsequent adhesion molecule expression. Thus, the crossing of the vessel endothelial cells of neutrophils became difficult.

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Juan Kong, Yunzi Chen, Guojun Zhu, Qun Zhao and Yan Chun Li

Leptin is an adipose tissue-derived hormone that plays a critical role in energy homeostasis. Vitamin D has been shown to regulate energy metabolism, but the relationship between vitamin D and leptin is unclear. Leptin expression and secretion was reduced in vitamin D receptor (VDR)-null mice and increased in transgenic (Tg) mice overexpressing the VDR in adipocytes; however, as leptin is mainly determined by fat mass, it is unclear whether the vitamin D hormone directly regulates leptin expression. To address this question, we determined the effect of vitamin D on leptin expression in vivo and ex vivo. One-week treatment of WT mice with the vitamin D analog RO-27-5646 led to a significant increase in adipose leptin mRNA transcript and serum leptin levels. Moreover, in adipose tissue cultures, 1,25-dihydroxyvitamin D markedly stimulated mRNA expression and secretion of leptin, but not resistin, in adipose tissues obtained from WT mice, but not from VDR-null mice, and leptin upregulation induced by 1,25-dihydroxyvitamin D was more robust in adipose tissues obtained from VDR Tg mice compared with WT mice. These data demonstrate that 1,25-dihydroxyvitamin D stimulates adipose leptin production in a VDR-dependent manner, suggesting that vitamin D may affect energy homeostasis through direct regulation of leptin expression.

Free access

Qiong Lv, Rufei Gao, Chuan Peng, Juan Yi, Lulu Liu, Shumin Yang, Danting Li, Jinbo Hu, Ting Luo, Mei Mei, Ying Song, Chaodong Wu, Xiaoqiu Xiao and Qifu Li

Bisphenol A (BPA), one of the most common environmental endocrine disruptors, is considered to promote hepatic lipid deposition. However, the mechanism has not been fully elucidated. The polarization of Kupffer cells (KCs) plays an important role in hepatic inflammation by promoting pro-inflammatory M1 phenotype (M1KCs), which contributes to dysregulated lipid metabolism. The purpose of this study is to investigate the role of KC polarization in BPA-induced hepatosteatosis in male mice. In this study, we examined hepatic lipid contents and quantified M1KC in BPA-treated CD1 mice, and further explored the interaction between KCs and hepatocytes using conditional HepG2 cell culture. BPA treatment significantly increased hepatic fat contents in CD1 mice, accompanied by increased number of pro-inflammatory M1KCs and enhanced secretion of inflammatory cytokines. Increased lipid contents were also observed in HepG2 cells treated with BPA. Interestingly, higher TG contents were observed in HepaG2 cells treated with conditional media from BPA-treated KCs, compared with those treated with BPA directly. Incubation of KCs with BPA promoted the polarization of KCs to pro-inflammatory M1 dominant subtypes, which was blocked by estrogen antagonist ICI182780. Taken together, our results revealed that M1KCs polarization is involved in BPA-induced hepatic fat deposition, which is possibly associated with the estrogen receptor signaling pathway.

Free access

Min Hu, Yuehui Zhang, Jiaxing Feng, Xue Xu, Jiao Zhang, Wei Zhao, Xiaozhu Guo, Juan Li, Edvin Vestin, Peng Cui, Xin Li, Xiao-ke Wu, Mats Brännström, Linus R Shao and Håkan Billig

Impaired progesterone (P4) signaling is linked to endometrial dysfunction and infertility in women with polycystic ovary syndrome (PCOS). Here, we report for the first time that elevated expression of progesterone receptor (PGR) isoforms A and B parallels increased estrogen receptor (ER) expression in PCOS-like rat uteri. The aberrant PGR-targeted gene expression in PCOS-like rats before and after implantation overlaps with dysregulated expression of Fkbp52 and Ncoa2, two genes that contribute to the development of uterine P4 resistance. In vivo and in vitro studies of the effects of metformin on the regulation of the uterine P4 signaling pathway under PCOS conditions showed that metformin directly inhibits the expression of PGR and ER along with the regulation of several genes that are targeted dependently or independently of PGR-mediated uterine implantation. Functionally, metformin treatment corrected the abnormal expression of cell-specific PGR and ER and some PGR-target genes in PCOS-like rats with implantation. Additionally, we documented how metformin contributes to the regulation of the PGR-associated MAPK/ERK/p38 signaling pathway in the PCOS-like rat uterus. Our data provide novel insights into how metformin therapy regulates uterine P4 signaling molecules under PCOS conditions.

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Yuehui Zhang, Min Hu, Wenyan Jia, Guoqi Liu, Jiao Zhang, Bing Wang, Juan Li, Peng Cui, Xin Li, Susanne Lager, Amanda Nancy Sferruzzi-Perri, Yanhua Han, Songjiang Liu, Xiaoke Wu, Mats Brännström, Linus R Shao and Håkan Billig

Women with polycystic ovary syndrome (PCOS) have hyperandrogenism and insulin resistance and a high risk of miscarriage during pregnancy. Similarly, in rats, maternal exposure to 5α-dihydrotestosterone (DHT) and insulin from gestational day 7.5 to 13.5 leads to hyperandrogenism and insulin resistance and subsequently increased fetal loss. A variety of hormonal and metabolic stimuli are able to trigger different types of regulated cell death under physiological and pathological conditions. These include ferroptosis, apoptosis and necroptosis. We hypothesized that, in rats, maternal hyperandrogenism and insulin-resistance-induced fetal loss is mediated, at least in part, by changes in the ferroptosis, apoptosis and necroptosis pathways in the gravid uterus and placenta. Compared with controls, we found that co-exposure to DHT and insulin led to decreased levels of glutathione peroxidase 4 (GPX4) and glutathione, increased glutathione + glutathione disulfide and malondialdehyde, aberrant expression of ferroptosis-associated genes (Acsl4, Tfrc, Slc7a11, and Gclc), increased iron deposition and activated ERK/p38/JNK phosphorylation in the gravid uterus. In addition, we observed shrunken mitochondria with electron-dense cristae, which are key features of ferroptosis-related mitochondrial morphology, as well as increased expression of Dpp4, a mitochondria-encoded gene responsible for ferroptosis induction in the uteri of rats co-exposed to DHT and insulin. However, in the placenta, DHT and insulin exposure only partially altered the expression of ferroptosis-related markers (e.g. region-dependent GPX4, glutathione + glutathione disulfide, malondialdehyde, Gls2 and Slc7a11 mRNAs, and phosphorylated p38 levels). Moreover, we found decreased expression of Dpp4 mRNA and increased expression of Cisd1 mRNA in placentas of rats co-exposed to DHT and insulin. Further, DHT + insulin-exposed pregnant rats exhibited decreased apoptosis in the uterus and increased necroptosis in the placenta. Our findings suggest that maternal hyperandrogenism and insulin resistance causes the activation of ferroptosis in the gravid uterus and placenta, although this is mediated via different mechanisms operating at the molecular and cellular levels. Our data also suggest that apoptosis and necroptosis may play a role in coordinating or compensating for hyperandrogenism and insulin-resistance-induced ferroptosis when the gravid uterus and placenta are dysfunctional.