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Biomedical subjects

Chen Chen

Publications and source records attributed to Chen Chen.

At least 73 records · Page 4Linked to original sources
PubMed2005

Acetate and propionate short chain fatty acids stimulate adipogenesis via GPCR43.

It has recently been discovered that G protein-coupled receptors (GPCR) 41 and 43 are characterized by having the short chain fatty acids acetate and propionate as their ligands. The objective of this study was to investigate the involvement of GPCR41, GPCR43, and their ligands in the process of adipogenesis. We measured the levels of GPCR41 and GPCR43 mRNA in both adipose and other tissues of the mouse. GRP43 mRNA expression was higher in four types of adipose tissue than in other tissues, whereas GPCR41 mRNA was not detected in any adipose tissues. A high level of GPCR43 expression was found in isolated adipocytes, but expression level was very low in stromal-vascular cells. Expression of GPCR43 was up-regulated in adipose tissues of mice fed a high-fat diet compared with those fed a normal-fat diet. GPCR43 mRNA could not be detected in confluent and undifferentiated 3T3-L1 adipocytes; however, the levels rose with time after the initiation of differentiation. GPCR41 expression was not detected in confluent and differentiated adipocytes. Acetate and propionate treatments increased lipids present as multiple droplets in 3T3-L1 adipocytes. Propionate significantly elevated the level of GPCR43 expression during adipose differentiation, with up-regulation of PPAR-gamma2. Small interfering RNA mediated a reduction of GPCR43 mRNA in 3T3-L1 cells and blocked the process of adipocyte differentiation. In addition, both acetate and propionate inhibited isoproterenol-induced lipolysis in a dose-dependent manner. We conclude that acetate and propionate short chain fatty acids may have important physiological roles in adipogenesis through GPCR43, but not through GPCR41.

3T3-L1 Cells↗
PubMed2005

ERM is required for transcriptional control of the spermatogonial stem cell niche.

Division of spermatogonial stem cells produces daughter cells that either maintain their stem cell identity or undergo differentiation to form mature sperm. The Sertoli cell, the only somatic cell within seminiferous tubules, provides the stem cell niche through physical support and expression of surface proteins and soluble factors. Here we show that the Ets related molecule (ERM) is expressed exclusively within Sertoli cells in the testis and is required for spermatogonial stem cell self-renewal. Mice with targeted disruption of ERM have a loss of maintenance of spermatogonial stem cell self-renewal without a block in normal spermatogenic differentiation and thus have progressive germ-cell depletion and a Sertoli-cell-only syndrome. Microarray analysis of primary Sertoli cells from ERM-deficient mice showed alterations in secreted factors known to regulate the haematopoietic stem cell niche. These results identify a new function for the Ets family transcription factors in spermatogenesis and provide an example of transcriptional control of a vertebrate stem cell niche.

Animals↗
PubMed2005

Somatostatin increases voltage-gated K+ currents in GH3 cells through activation of multiple somatostatin receptors.

The secretion of GH by somatotropes is inhibited by somatostatin (SRIF) through five specific membrane receptors (SSTRs). SRIF increases both transient outward (IA) and delayed rectifying (IK) K+ currents. We aim to clarify the subtype(s) of SSTRs involved in K+ current enhancement in GH3 somatotrope cells using specific SSTR subtype agonists. Expression of all five SSTRs was confirmed in GH3 cells by RT-PCR. Nystatin-perforated patch clamp was used to record voltage-gated K+ currents. We first established the presence of IA and IK type K+ currents in GH3 cells using different holding potentials (-40 or -70 mV) and specific blockers (4-aminopirimidine and tetraethylammonium chloride). SRIF (200 nM) increased the amplitude of both IA and IK in a fully reversible manner. Various concentrations of each specific SRTR agonist were tested on K+ currents to find the maximal effective concentration. Activation of SSTR2 and SSTR4 by their respective agonists, L-779,976 and L-803,087 (10 nM), increased K+ current amplitude without preference to IA or IK, and abolished any further increase by SRIF. Activation of SSTR1 and SSTR5 by their respective agonists, L-797,591 or L-817,818 (10 nM), increased K+ current amplitude, but SRIF evoked a further increase. The SSTR3 agonist L-797,778 (10 nM) did not affect the K+ currents or the response to SRIF. These results indicate that SSTR1, -2, -4, and -5 may all be involved in the enhancement of K+ currents by SRIF but that only the activation of SSTR2 or -4 results in the full activation of K+ current caused by SRIF.

Animals↗
PubMed2005

Chk2 regulates transcription-independent p53-mediated apoptosis in response to DNA damage.

The tumor suppressor protein p53 plays a central role in the induction of apoptosis in response to genotoxic stress. The protein kinase Chk2 is an important regulator of p53 function in mammalian cells exposed to ionizing radiation (IR). Cells derived from Chk2-deficient mice are resistant to the induction of apoptosis by IR, and this resistance has been thought to be a result of the defective transcriptional activation of p53 target genes. It was recently shown, however, that p53 itself and histone H1.2 translocate to mitochondria and thereby induces apoptosis in a transcription-independent manner in response to IR. We have now examined whether Chk2 also regulates the transcription-independent induction of apoptosis by p53 and histone H1.2. The reduced ability of IR to induce p53 stabilization in Chk2-deficient thymocytes was associated with a marked impairment of p53 and histone H1 translocation to mitochondria. These results suggest that Chk2 regulates the transcription-independent mechanism of p53-mediated apoptosis by inducing stabilization of p53 in response to IR.

Animals↗
PubMed2005

Oestrogen replacement in vivo rescues the dysfunction of pituitary somatotropes in ovariectomised aromatase knockout mice.

The mechanism of regulation of growth hormone (GH) secretion by oestrogens and androgens is still controversial. Available data on the action of oestrogens on GH expression and secretion in somatotropes is poorly understood. We previously reported that the aromatase knockout (ArKO) mouse with oestrogen deficiency and excessive androgen levels had dysfunctional somatotropes. In order to clarify the influence of androgen and oestrogen, we investigated the in vivo treatment of ovariectomised (OVX) ArKO mice with exogenous oestradiol (E2) on the mRNA expression of GH, GH-secretagogue receptor (GHS-R), GH-releasing hormone receptor (GHRH-R), pituitary-specific transcription factor (Pit-1), and somatostatin receptors (sst1-5) in pituitary glands. Circulating plasma GH levels were also evaluated. The results showed that ArKO/OVX mice have a low expression of pituitary GH, GHRH-R, GHS-R and Pit-1, and significantly reduced GH levels. Treatment of female ArKO/OVX (E2-deficient without excessive androgen) mice with E2 for 21 days enhanced expression of pituitary GHRH-R and Pit-1 to 151 and 168%, respectively, of that in mice without treatment. E2 treatment increased GH expression and plasma levels in ArKO/OVX mice to levels comparable with those in wild-type female mice. We conclude therefore that long-term E2 replacement rescues the dysfunction of somatotropes in ArKO/OVX mice through increases in expression of GH, GHRH-R, and Pit-1 in the pituitary somatotropes, whereas the level of androgen in this oestrogen-deficient female mouse does not significantly influence the function of somatotropes.

Androgens↗
PubMed2005

GH-releasing peptides improve cardiac dysfunction and cachexia and suppress stress-related hormones and cardiomyocyte apoptosis in rats with heart failure.

Growth hormone (GH)-releasing peptides (GHRP), a class of synthetic peptidyl GH secretagogues, have been reported to exert a cardioprotective effect on cardiac ischemia. However, whether GHRP have a beneficial effect on chronic heart failure (CHF) is unclear, and the present work aims to clarify this issue. At 9 wk after pressure-overload CHF was created by abdominal aortic banding in rats, one of four variants of GHRP (GHRP-1, -2, and -6 and hexarelin, 100 mug/kg) or saline was injected subcutaneously twice a day for 3 wk. Echocardiography and cardiac catheterization were performed to monitor cardiac function and obtain blood samples for hormone assay. GHRP treatment significantly improved left ventricular (LV) function and remodeling in CHF rats, as indicated by increased LV ejection fraction, LV end-systolic pressure, and diastolic posterior wall thickness and decreased LV end-diastolic pressure and LV end-diastolic dimension. GHRP also significantly alleviated development of cardiac cachexia, as shown by increases in body weight and tibial length in CHF rats. Plasma CA, renin, ANG II, aldosterone, endothelin-1, and atrial natriuretic peptide were significantly elevated in CHF rats but were significantly decreased in GHRP-treated CHF rats. GHRP suppressed cardiomyocyte apoptosis and increased cardiac GH secretagogue receptor mRNA expression in CHF rats. GHRP also decreased myocardial creatine kinase release in hypophysectomized rats subjected to acute myocardial ischemia. We conclude that chronic administration of GHRP alleviates LV dysfunction, pathological remodeling, and cardiac cachexia in CHF rats, at least in part by suppressing stress-induced neurohormonal activations and cardiomyocyte apoptosis.

Animals↗
PubMed2005

Arylation of diarylamines catalyzed by Ni(II)-PPh3 system.

[reaction: see text]. The cross-coupling of bromomagnesium diarylamides, generated in situ from diarylamines, with aryl bromides or iodides can be effected with a simple NiCl2(PPh3)2-PPh3 catalyst system under relatively mild conditions. This coupling reaction is an inexpensive, convenient, and practical method, functioning as an alternative to the corresponding Pd-catalyzed or Cu-mediated process for the synthesis of triarylamines.

Journal Article↗
PubMed2005

A potent and selective nonpeptide antagonist of the melanocortin-4 receptor induces food intake in satiated mice.

Optimization on a series of piperazinebenzylamines resulted in analogues with low nanomolar binding at the human MC4 receptor but weak affinity (Ki > 500 nM) at the MC3 receptor. Compound 14c was identified to be a potent MC4R antagonist (Ki = 3.2 nM) with a selectivity of 240-fold over MC3R. It proved to be an insurmountable antagonist in a cAMP assay. Compound 14c potently stimulated food intake in satiated mice when given by intracerebroventricular administration.

Animals↗
PubMed2005

PDGF-D contributes to neointimal hyperplasia in rat model of vessel injury.

In this study, we determined the role of PDGF-D, a new member of the PDGF family, in a rat model of balloon injured artery made with a 2F catheter in Sprague-Dawley male rats. PDGF-D expression was studied in the injured and control segments of abdominal aorta. The function of PDGF-D was evaluated in rat vascular smooth muscle cells stably transfected with PDGF-D gene. We found that in normal abdominal aorta, PDGF-D was highly expressed in adventia, moderate in endothelia, and unidentified in media. Stable transfection of PDGF-D gene into vascular smooth muscle cells increased the cell migration by 2.2-fold, and the proliferation by 2.3-fold, respectively, and MMP-2 production and activity as well. These results support the fact that PDGF-D is involved in the formation of neointimal hyperplasia induced by balloon catheter injury and may serve as a target in preventing vascular restenosis after coronary angioplasty.

Animals↗
PubMed2005

The regulation of feeding and metabolic rate and the prevention of murine cancer cachexia with a small-molecule melanocortin-4 receptor antagonist.

Cachexia is metabolic disorder characterized by anorexia, an increased metabolic rate, and loss of lean body mass. It is a relatively common disorder, and is a pathological feature of diseases such as cancer, HIV infection, and renal failure. Recent studies have demonstrated that cachexia brought about by a variety of illnesses can be attenuated or reversed by blocking activation of the melanocortin 4 subtype receptor (MC4-R) within the central nervous system. Although the potential use of central MC4-R antagonists for the treatment of cachexia was supported by these studies, utility was limited by the need to deliver these agents intracerebroventricularly. In the current study, we present a series of experiments demonstrating that peripheral administration of a small molecule MC4-R antagonist can effectively stimulate daytime (satiated) food intake as well as decrease basal metabolic rate in normal animals. Furthermore, this compound attenuated cachexia and preserved lean body mass in a murine cancer model. These data clearly demonstrate the potential of small molecule MC4-R antagonists in the treatment of cachexia and underscore the importance of melanocortin signaling in the development of this metabolic disorder.

Animals↗
PubMed2005

Rational design, synthesis, and structure-activity relationships of aryltriazoles as novel corticotropin-releasing factor-1 receptor antagonists.

Following the discovery of the very high binding affinity of 4-anilinopyrimidines against corticotropin-releasing factor receptor-1 (CRF(1)) (e.g., 1, K(i) = 2 nM), a new series of triazoles bearing different groups has been synthesized and evaluated. The compounds were prepared by cyclizations of N-acyl-S-methylisothioureas with alkylhydrazines or by cyclizations with hydrazine followed by alkylation. While members of this series showed potent binding affinity against CRF(1) receptor, there were important differences between the different regio- (7 and 12) and stereoisomeric aryltriazoles where the R(1) or R(2) side chain in 7 has an asymmetric center. In terms of overall potency, aryltriazole analogues such as 7r bearing an N-(alpha-branched benzyl)-N-propylamino side chain were the most potent, followed by analogues such as 7a, with an N-bis(cyclopropyl)methyl-N-propylamino side chain, and analogues such as 7m, with an N-(alpha-branched aliphatic)-N-propylamino side chain. While the N-propyl group was crucial for high potency, we hypothesized that the terminal methyl mimicked the 5-methyl of pyrazolo[1,5-a]pyrimidines 3 and 4. Correlation of the low-energy conformers of compounds of type 3 and 7 generated by computational analyses was very good. The size and shape of the N-alkyl group dramatically changed the potency of the triazoles, which is in contrast to the SAR seen for bicyclic CRF(1) antagonists. In general, the S-enantiomer was much more potent than the corresponding R-isomer. Furthermore, to a limited extent in the aryltriazole series the substituent on the 5-phenyl ring changed the potency up to 9-fold. (S)-1-Methyl-3-[N-(4-fluorophenylpentyl)-N-propyl]amino-5-(2-methoxy-4-dichlorophenyl)-1H-[1,2,4]triazole [(S)-7r] showed very potent binding affinity (K(i) = 2.7 nM) to CRF(1) receptors with an IC(50) of 49 nM in a cAMP inhibition assay.

Animals↗
PubMed2005

Efficient synthesis of bicyclic oxazolino- and thiazolino[3,2-c]pyrimidine-5,7-diones and its application to the synthesis of GnRH antagonists.

Treatment of various 2-methyl oxazolines or thiazolines with chlorocarbonyl isocyanate gives the corresponding bicyclic oxazolino- or thiazolino[3,2-c]pyrimidin-5,7-dione derivatives in very good yield. This reaction has been applied to the rapid syntheses of human gonadotropin-releasing hormone (hGnRH) receptor antagonists for SAR study, resulting in 13e with binding affinity in the low nanomolar range (4.5 nM).

Binding, Competitive↗
PubMed2005

3-[(2R)-Amino-2-phenylethyl]-1-(2,6-difluorobenzyl)-5-(2-fluoro-3-methoxyphenyl)- 6-methylpyrimidin-2,4-dione (NBI 42902) as a potent and orally active antagonist of the human gonadotropin-releasing hormone receptor. Design, synthesis, and in vitro and in vivo characterization.

Further structure-activity relationship studies of a series of substituted uracils at the 1, 3, and 5 positions resulted in the discovery of several potent antagonists of the human gonadotropin-releasing hormone receptor. Uracils bearing a side chain derived from phenylglycinol at the 3-position were shown to be orally bioavailable in monkeys. 3-[(2R)-Amino-2-phenylethyl]-1-(2,6-difluorobenzyl)-5-(2-fluoro-3-methoxyphenyl)-6-methylpyrimidin-2,4-dione (R-13b, NBI 42902) displayed subnanomolar binding affinity (K(i) = 0.56 nM) and was a potent functional antagonist (IC(50) = 3.0 nM in Ca(2+) flux assay) at the human GnRH receptor. It also bound to the monkey GnRH receptor with high affinity (K(i) = 3.9 nM). In addition, R-13bhad good plasma exposure in cynomolgus monkeys after oral administration, with a C(max) of 737 ng/mL and an AUC of 2392 ng/mL.h at a 10 mg/kg dose. Moreover, oral administration of R-13b to castrated male cynomolgus monkeys resulted in a significant decrease in serum levels of luteinizing hormone. These results demonstrate that compounds from this series of uracils are potent GnRH antagonists with good oral bioavailability and efficacy in nonhuman primates.

Administration, Oral↗
PubMed2005

Identification of agonists and antagonists of the human melanocortin-4 receptor from piperazinebenzylamines.

SAR studies of a series of piperazinebenzylamines resulted in identification of potent agonists and antagonists of the human melanocortin-4 receptor. Thus, the 1,2,3,4-tetrahydroisoquinolin-1-ylacetyl compound 12e and the quinolin-3-ylcarbonyl analogue 12l possessed K(i) values of 6.3 and 4.5 nM, respectively. Interestingly, 12e was a full agonist with an EC(50) value of 31 nM, and 12l was a weak partial agonist (IA=17%) and functioned as an antagonist (IC(50)=300 nM).

Benzylamines↗
PubMed2005

A convenient one-pot synthesis of asymmetric 1,3,5-triazine-2,4,6-triones and its application towards a novel class of gonadotropin-releasing hormone receptor antagonists.

A convenient one-pot synthetic route was developed for the preparation of asymmetric 1,3-dialkyl-1,3,5-triazine-2,4,6-triones from readily available alkyl- or aryl-isocyanates, primary amines and N-chlorocarbonyl isocyanate in excellent yields. Subsequent alkylation with N-protected amino alcohols afforded the desired 1,3,5-triazine-2,4,6-triones in good yields. This methodology was applied to the synthesis of a chemical library acting as antagonists of the hGnRH receptor.

Alkylation↗