Biomedical subjects

Yan Chen

Publications and source records attributed to Yan Chen.

At least 37 records · Page 2Linked to original sources

PubMed2006

Activin A functions as a Th2 cytokine in the promotion of the alternative activation of macrophages.

Activin A, a member of the TGF-beta superfamily, is a pluripotent growth and differentiation factor. In this study, we report that murine Th cells produce activin A upon activation. Activin activity in the cultured CD4+ T cells was induced by anti-CD3 cross-linking. Activin betaA mRNA level was increased in response to activation, indicating that activin production in CD4+ T cells is regulated at the mRNA level. Activin production was detected exclusively in CD4+CD25- T cells, but not in CD4+CD25+ regulatory T cells. When CD4+ T cells were differentiated into Th cell subsets, higher activin secretion was detected when cultured under Th2-skewing conditions. The mRNA level of activin betaA was abundant in Th2, but not in Th1 cells. Furthermore, secretion of activin was significantly higher in activated Th2 clones than in Th1 clones. The activin betaA-proximal promoter contains a binding site for c-Maf, a Th2-specific transcriptional factor, at close proximity with an NF-AT binding site. c-Maf was able to synergize with NF-AT to transactivate activin betaA gene, and both factors are implicated in activin betaA transcription in Th2 cells. Activin A induced macrophages to express arginase-1 (M-2 phenotype), whereas it inhibited inducible NO synthase expression (M-1 phenotype) induced by IFN-gamma. Taken together, these observations suggest that activin A is a novel Th2 cytokine that promotes differentiation of macrophages toward the M-2 phenotype.

Activins↗

PubMed2006

Mitochondrial thioredoxin in regulation of oxidant-induced cell death.

Mitochondrial thioredoxin (mtTrx) can be oxidized in response to inducers of oxidative stress; yet the functional consequences of the oxidation have not been determined. This study evaluated the redox status of mtTrx and its association to oxidant-induced apoptosis. Results showed that mtTrx was oxidized after exposure to peroxides and diamide. Overexpression of mtTrx protected against diamide-induced oxidation and cytotoxicity. Oxidation of mtTrx was also achieved by knocking down its reductase; and lead to increased susceptibility to cell death. The data indicate that the redox status of mtTrx is a regulatory mechanism underlying the vulnerability of mitochondria to oxidative injury.

Cell Death↗

PubMed2006

Beta-catenin signaling pathway is crucial for bone morphogenetic protein 2 to induce new bone formation.

Endochondral ossification is recapitulated during bone morphogenetic protein (BMP)-induced ectopic bone formation. Although BMP and beta-catenin have been investigated in bone development and in mesenchymal cells, how they interact in this process is not clear. We implanted recombinant BMP-2 into the muscle of mice to investigate the effect of beta-catenin signaling on BMP-induced in vivo endochondral bone formation. BMP-2 induced expression of several Wnt ligands and their receptors and also activated beta-catenin-mediated T cell factor-dependent transcriptional activity. An adenovirus expressing Dickkopf-1 (Dkk-1, an inhibitor of canonical Wnt pathway) inhibited beta-catenin signaling and endochondral bone formation. Interestingly, Dkk-1 inhibited both chondrogenesis and osteogenesis. Likewise, mice expressing conditional beta-catenin null alleles also displayed an inhibition of BMP-induced chondrogenesis and osteogenesis. This is in contrast to studies of embryonic skeletogenesis, which demonstrate that beta-catenin is required for osteogenesis but is dispensable for chondrogenesis. These findings suggest that embryonic development pathways are not always recapitulated during post-natal regenerative processes, and the biochemical pathways utilized to regulate cell differentiation may be different. During in vivo ectopic bone formation, BMP-2 induces beta-catenin-mediated signaling through Wnt ligands, and beta-catenin is required for both chondrogenesis and osteogenesis.

Alleles↗

PubMed2006

Intragenic deletion of Tgif causes defectsin brain development.

TG-interacting factor (TGIF) is a homeodomain-containing protein and functions as a transcriptional repressor within the TGF-beta and retinoic acid signaling pathways. Heterozygous mutations of TGIF have been found in patients with holoprosencephaly (HPE), which is the most common congenital brain malformation in humans. However, targeted null deletions of the entire Tgif gene in mice surprisingly revealed no apparent brain defects. We report here that deletion of the third exon of Tgif gene resulted in a defined spectrum of brain developmental defects including exencephaly, microcephaly, HPE, and abnormalities in embryonic brain ventricle formation and cleavage. These defects could be detected in mice both heterozygous and homozygous for the targeted Tgif deletion. Moreover, expression of dorsal-ventral patterning genes including Shh, Pax6 and Nkx2.2 was altered. The ventricular neuroepithelium exhibited focalized increase of cell proliferation rate and resultant tissue expansion. The incidence of brain abnormalities within the mutant mice was dependent on its genetic background, suggesting that additional genetic modifiers functionally interact with Tgif during embryonic brain development. The intragenic Tgif deletion mouse, therefore, would serve as a useful model that can be used to unravel the genetic complexity implicated in the pathogenesis of HPE.

Animals↗

PubMed2006

Sonic hedgehog promotes CD4+ T lymphocyte proliferation and modulates the expression of a subset of CD28-targeted genes.

Sonic hedgehog (Shh) is a crucial morphogen in the development of numerous tissues and organs, including the nervous system, gastrointestinal tract and lung. Recent findings suggest that Shh plays an important role in thymocyte development and peripheral T cell function. Here we report that the Shh receptors, patched and smoothened, are expressed in resting and activated T cells and their expression is regulated upon T cell activation. Shh protein is also detected on the surface of freshly isolated T cells. Although exogenous Shh alone does not activate resting T cells, it exhibits co-stimulatory activity which is reflected in its ability to potentiate CD3-mediated proliferation and cytokine production by CD4(+) T cells. The co-stimulatory effect is most prominent at sub-optimal TCR stimulation level. Gene expression analysis reveals that Shh signaling in CD4(+) T cells modulates a different set of transcriptional targets from that in neuronal cells. Furthermore, Shh co-stimulation modulates the expression of a subset of CD28-responsive genes, including cyclin A and B cell translocation gene 2.

Animals↗

PubMed2006

Dual-color photon counting histogram analysis of mRFP1 and EGFP in living cells.

We investigate the potential of dual-color photon counting histogram (PCH) analysis to resolve fluorescent protein mixtures directly inside cells. Because of their small spectral overlap, we have chosen to look at the fluorescent proteins EGFP and mRFP1. We experimentally demonstrate that dual-color PCH quantitatively resolves a mixture of EGFP and mRFP1 in cells from a single measurement. To mimic the effect of protein association, we constructed a fusion protein of EGFP and mRFP1 (denoted EGFP-mRFP1). Fluorescence resonant energy transfer within the fusion protein alters the dual-channel brightness of the fluorophores. We describe a model for fluorescence resonant energy transfer effects on the brightness and incorporate it into dual-color PCH analysis. The model is verified using fluorescence lifetime measurements. Dual-color PCH analysis demonstrated that not all of the expressed EGFP-mRFP1 fusion proteins contained a fluorescent mRFP1 molecule. Fluorescence lifetime and emission spectra measurements confirmed this surprising result. Additional experiments show that the missing fluorescent fraction of mRFP1 is consistent with a dark state population of mRFP1. We successfully resolved this mixture of fusion proteins with a single dual-color PCH measurement. These results highlight the potential of dual-color PCH to directly detect and quantify protein mixtures in living cells.

Animals↗

PubMed2006

HPV prevalence, E6 sequence variation and physical state of HPV16 isolates from patients with cervical cancer in Sichuan, China.

OBJECTIVES: Infection with high-risk human papillomavirus (hr-HPV) is an important factor associated with cervical cancer. The genetic mutation of HPV16 E6 and integration of HPV16 DNA in the cervical carcinoma tissues are considered important genetic changes in cervical lesion progression. But the studies of hr-HPV epidemiology are relatively less in the area of Sichuan, China. Therefore, we investigated the prevalence of 9 high-risk subtypes and analyzed the genetic mutation characteristic of HPV16 E6 and physical state of HPV16 DNA. METHODS: The fragments of L1 and E6 genes were amplified by PCR or nested PCR and then directly sequenced. Further, the multiplex PCR for HPV16 E2 and E6 genes was performed for detection of integration. RESULTS: HPV16, 58 and 18 were prominent, accounting for 78.6%, 20.0% and 9.7%, respectively in 145 isolates. E6 variants revealed that the European (EP) prototype and East Asia (EA) strain were 26 (23.0%) and 34 (30.1%), respectively. Furthermore, there were 14 base substitutions in E6 regions of the study group, of which 12 resulted in amino acid changes and the rest was silent mutation. Significantly, the 240G substitution exactly located the P53 degradation site. Overall, 8 of 114 (7.0%) isolates only contained integrated HPV16 DNA, 43 (37.7%) only contained episomal DNA and 63 (55.3%) contained both integrated and episomal DNA. The proportion of disruption of an intact E2 gene in the patients with cervical cancer is much lower than that in the previous studies. CONCLUSIONS: HPV16, 58 and 18 were mainly prevailing subtypes in patients with cervical cancer from Sichuan areas, China and EP/EA strains were predominant in these areas. Some mutations of E6 gene, which lead to the amino acid changes, may be more potentially carcinogenic and the proportion of disruption of an intact E2 gene is much lower.

Adenocarcinoma↗

PubMed2006

Activated c-Fms recruits Vav and Rac during CSF-1-induced cytoskeletal remodeling and spreading in osteoclasts.

Colony-stimulating factor-1 (CSF-1) induces osteoclast spreading that requires activation of c-Src and phosphatidyl inositol 3-kinase (PI3-K), both of which are recruited to activated c-Fms, the CSF-1 receptor. The present report provides evidence that the hemopoietic guanine nucleotide exchange factor (GEF), Vav, and its target GTPase, Rac, lie downstream from this initial signaling complex. CSF-1 treatment of osteoclast-like cells induced translocation of Vav to the plasma membrane, an increase in its phosphotyrosine content, and a concomitant decline in the amount of phosphoinositol 4,5-bisphosphate bound to Vav, changes known to induce Vav's GEF activity. CSF-1 induced the association of Vav and Rac and increased Rac's GTPase activity. CSF-1 also induced rapid translocation of Rac to the periphery of spreading neonatal rat osteoclasts where it co-localized primarily with Vav3 and to a lesser extent with Vav1. Wortmannin, an inhibitor of PI3-K, blocked CSF-1-induced Rac translocation and prevented CSF-1-induced spreading and actin reorganization in osteoclasts. CSF-1-induced osteoclast spreading was not significantly reduced in osteoclasts isolated from Vav1 knock-out mice and Vav1 knock-out mice had normal bone density. Microinjection of constitutively active Rac, but not constitutively active Cdc42 or RhoA, induced lamellipodia formation and osteoclast spreading, mimicking the effects of CSF-1. Dominant-negative Rac blocked CSF-1-induced osteoclast spreading, whereas neither dominant-negative Cdc42 nor C3, an inhibitor of RhoA, affected the response to CSF-1. These data demonstrate that Vav and Rac lie downstream from activated PI3-K in CSF-1-treated osteoclasts and that Rac is required for CSF-1-induced cytoskeletal remodeling in these cells.

Actins↗

PubMed2006

The two helicases of herpes simplex virus type 1 (HSV-1).

Herpes simplex virus type 1 (HSV-1) encodes two helicases both of which are essential for viral DNA synthesis. UL9 binds specifically to the origins of replication and is believed to initiate DNA replication at one of three origins of replication located in the HSV-1 genome. The heterotrimeric helicase-primase complex, encoded by the UL5, UL8 and UL52 genes, is believed to unwind duplex viral DNA at replication forks and to prime lagging strand synthesis. Functional analyses of UL9 and the helicase-primase complex will be discussed with attention to the roles these proteins play during HSV-1 replication.

Antiviral Agents↗

PubMed2006

Auditing as part of the terminology design life cycle.

OBJECTIVE: To develop and test an auditing methodology for detecting errors in medical terminologies satisfying systematic inheritance. This methodology is based on various abstraction taxonomies that provide high-level views of a terminology and highlight potentially erroneous concepts. DESIGN: Our auditing methodology is based on dividing concepts of a terminology into smaller, more manageable units. First, we divide the terminology's concepts into areas according to their relationships/roles. Then each multi-rooted area is further divided into partial-areas (p-areas) that are singly-rooted. Each p-area contains a set of structurally and semantically uniform concepts. Two kinds of abstraction networks, called the area taxonomy and p-area taxonomy, are derived. These taxonomies form the basis for the auditing approach. Taxonomies tend to highlight potentially erroneous concepts in areas and p-areas. Human reviewers can focus their auditing efforts on the limited number of problematic concepts following two hypotheses on the probable concentration of errors. RESULTS: A sample of the area taxonomy and p-area taxonomy for the Biological Process (BP) hierarchy of the National Cancer Institute Thesaurus (NCIT) was derived from the application of our methodology to its concepts. These views led to the detection of a number of different kinds of errors that are reported, and to confirmation of the hypotheses on error concentration in this hierarchy. CONCLUSION: Our auditing methodology based on area and p-area taxonomies is an efficient tool for detecting errors in terminologies satisfying systematic inheritance of roles, and thus facilitates their maintenance. This methodology concentrates a domain expert's manual review on portions of the concepts with a high likelihood of errors.

Biology↗

PubMed2006

Augmenter of liver regeneration promotes hepatocyte proliferation induced by Kupffer cells.

AIM: To observe the effects of augmenter of liver regeneration (ALR) on Kupffer cells and to determine whether ALR promotes hepatocyte proliferation induced by Kupffer cells. METHODS: Kupffer cells and hepatocytes were cultured in vitro and various concentrations of recombinant rat ALR (rrALR) were added. 3H-thymidine, BrdU and 3H-leucine incorporation was determined in cultured Kupffer cells and hepatocytes, in hepatocytes conditioned by Kupffer cells, and in associated medium. rrALR was labeled by iodination and used to determine its binding activity by Scatchard analysis in Kupffer cells and primarily cultured rat hepatocytes. RESULTS: rrALR stimulated DNA replication in Kupffer cells and protein synthesis both in cells and in medium in a non-concentration-dependent manner. The effect was significant at the concentration of 1 microg/L ALR. However, rrALR had no effect on primarily cultured hepatocytes, when hepatocytes were cultured with the Kupffer cell medium conditioned by ALR, DNA replication and protein synthesis in hepatocytes increased significantly at the concentration of 1 microg/L ALR. When the ALR concentration was increased, its effect on hepatocyte proliferation decreased to the basal level. Scatchard analysis indicated the presence of a single class of high affinity receptors with a dissociation constant (Kd) of 0.883 nmol/L and a maximum binding capacity (Bmax) of 126.1 pmol/g protein in the rat Kupffer cells. CONCLUSION: ALR can promote hepatocyte proliferation induced by Kupffer cells, which is associated with the concentration of ALR, suggesting that Kupffer cells play a dual role in liver regeneration.

Animals↗

PubMed2006

Genetic variations of the NR3C1 gene in children with sporadic nephrotic syndrome.

Previous studies have demonstrated that the genetic variations of glucocorticoid receptor gene (NR3C1) are associated with both familial steroid resistance and acquired steroid resistance in some diseases, such as Cushing's disease, leukemia, lupus nephritis, and female pseudohermaphroditism. In this study, we examined the genetic variations of NR3C1 in 35 children with sporadic steroid-resistant nephrotic syndrome (SRNS), and in 83 cases with sporadic steroid-sensitive NS (SSNS) using polymerase chain reaction, denaturing high-performance liquid chromatography and DNA sequencing, and analyzed possible associations between NR3C1 variants and steroid resistance in sporadic NS. No causative mutations were found; however, six previously identified and six novel polymorphisms, 1206C > T, 1374A > G, 2382C > T, 2193T > G, IVS7-68_-63delAAAAAA, and IVS8-9C > G, were detected. Two novel haplotypes, [1374A > G; IVS7-68_-63delAAAAAA; IVS8-9C > G; 2382C > T] and [1896C > T; 2166C > T; 2430T > C], of NR3C1 were also identified in sporadic NS and controls. The odds ratios (95% Confidence Interval) for the two novel NR3C1 haplotypes in the sporadic nephrotic children at risk of steroid resistance were 4.970 (0.889-27.788) and 2.194 (0.764-6.306), respectively, but the association between NR3C1 haplotypes and steroid resistance was not significant. Further studies on the possible association between the two novel NR3C1 haplotypes and steroid resistance in sporadic NS in larger cohorts are required.

Adolescent↗

PubMed2006

Dual-color time-integrated fluorescence cumulant analysis.

We introduce dual-color time-integrated fluorescence cumulant analysis (TIFCA) to analyze fluorescence fluctuation spectroscopy data. Dual-color TIFCA utilizes the bivariate cumulants of the integrated fluorescent intensity from two detection channels to extract the brightness in each channel, the occupation number, and the diffusion time of fluorophores simultaneously. Detecting the fluorescence in two detector channels introduces the possibility of differentiating fluorophores based on their fluorescence spectrum. We derive an analytical expression for the bivariate factorial cumulants of photon counts for arbitrary sampling times. The statistical accuracy of each cumulant is described by its variance, which we calculate by the moments-of-moments technique. A method that takes nonideal detector effects such as dead-time and afterpulsing into account is developed and experimentally verified. We perform dual-color TIFCA analysis on simple dye solutions and a mixture of dyes to characterize the performance and accuracy of our theory. We demonstrate the robustness of dual-color TIFCA by measuring fluorescent proteins over a wide concentration range inside cells. Finally we demonstrate the sensitivity of dual-color TIFCA by resolving EGFP/EYFP binary mixtures in living cells with a single measurement.

Animals↗

PubMed2006

Significance of serum IgA in patients with acute hepatitis E virus infection.

AIM: To study the significance of serum anti-hepatitis E virus (HEV) IgA in patients with hepatitis E. METHODS: A new method was established to assay anti-HEV IgA, which could be detected in the middle phase of the infection. We compared anti-HEV IgA assay with anti-HEV IgM and anti-HEV IgG assay in sera from 60 patients with positive HEV-RNA. RESULTS: The 60 patients with positive HEV-RNA had both anti-HEV IgA and anti-HEV IgM and 410 patients with negative HEV-RNA were used as control. Periodic serum samples obtained from 60 patients with hepatitis E were tested for HEV RNA, anti-HEV IgM, anti-HEV IgA and anti-HEV IgG. Their HEV-RNA was detectable in the serum until 20 +/- 11 d. We used anti-HEV IgM and anti-HEV IgA assay to detect HEV infection and positive results were found in 90 +/- 15 d and 120 +/- 23 d respectively, the positive rate of anti-HEV IgA was higher than that of anti-HEV IgM and HEV-RNA (P < 0.05). CONCLUSION: The duration of anti-HEV IgA in serum is longer than that of anti-HEV IgM, and anti-HEV IgA assay is a good method to detect HEV infection.

Acute Disease↗

PubMed2006

Stimulation of HIV-1 minus strand strong stop DNA transfer by genomic sequences 3' of the primer binding site.

The mechanism of human immunodeficiency virus 1 (HIV-1) minus strand transfer was examined using a genomic RNA sequence-based donor-acceptor template system. The donor RNA, D199, was a 199-nucleotide sequence from the 5'-end of the genome to the primer binding site (PBS) and shared 97 nucleotides of homology with the acceptor RNA. To investigate the influence of RNA structure on transfer, a second donor RNA, D520, was generated by extending the 3'-end of D199 to include an additional 321 nucleotides of the genome. The position of priming, length of homology with the acceptor, and length of cDNA synthesized were identical with the two donors. Interestingly, at 200% NC coating, donor D520 yielded a transfer efficiency of about 75% compared with about 35% with D199. A large proportion of the D520 promoted transfers occurred after the donor RNA was copied to the end. Analysis of donor RNA cleavage, the acceptor invasion site and R homology requirements indicated that transfers with D520 involved a similar but more efficient acceptor invasion mechanism compared with D199. RNA structure probing by RNase T1 and the RT pause profile during synthesis indicated conformational differences between D199 and D520 in the starting structure, and in dynamic structures formed during synthesis within the R region. Overall observations suggest that regions 3' of the primer binding site influence the conformation of the R region of D520 to facilitate steps that promote strand transfer.

3' Flanking Region↗

PubMed2006

Effect of fluid resuscitation on ryanodine receptor in macaques with endotoxic shock.

OBJECTIVE: Our recent study demonstrated that sodium bicarbonate improved cardiac function in macaque models with early-phase endotoxic shock. In the present study, we investigated further the ryanodine receptor/calcium release-channel (RyR) and calcium pump after fluid resuscitation of macaques with early-phase endotoxic shock. METHODS: Twenty-four anaesthetised macaques were assigned to four groups. Nineteen animals were given an intravenous dose of 2.8 mgkg(-1) lipopolysaccharide (LPS). Sixty minutes after the LPS challenge, the animals were given (i) 5 mLkg(-1) normal saline (Ns group, n = 6), (ii) 5 mLkg(-1) of 5% sodium bicarbonate (Sb group, n = 6) or (iii) 5 mLkg(-1) of 3.5% hypertonic sodium chloride (Hs group, n = 7). The control group (Co group, n = 5) received 1 mLkg(-1) normal saline and then with 5 mLkg(-1) normal saline 60 min later. RESULTS: Endotoxin produced a reduction of the density of RyR but did not alter the affinity of RyR. Compared with normal saline, sodium bicarbonate or hypertonic saline induced a restoration of density of RyR but did not influence the affinity of RyR and the calcium pump. CONCLUSION: Up-regulation of RyR performance in myocardium following administration of sodium bicarbonate contributes to the improvement of cardiac function in macaques in the early phase of endotoxic shock.

Animals↗

PubMed2006

Regulation of proliferation and gene expression in cultured human aortic smooth muscle cells by resveratrol and standardized grape extracts.

Epidemiologic studies suggest that low to moderate consumption of red wine is inversely associated with the risk of coronary heart disease; the protection is in part attributed to grape-derived polyphenols, notably trans-resveratrol, present in red wine. It is not clear whether the cardioprotective effects of resveratrol can be reproduced by standardized grape extracts (SGE). In the present studies, we determined, using cultured human aortic smooth muscle cells (HASMC), growth and specific gene responses to resveratrol and SGE provided by the California Table Grape Commission. Suppression of HASMC proliferation by resveratrol was accompanied by a dose-dependent increase in the expression of tumor suppressor gene p53 and heat shock protein HSP27. Using resveratrol affinity chromatography and biochemical fractionation procedures, we showed by immunoblot analysis that treatment of HASMC with resveratrol increased the expression of quinone reductase I and II, and also altered their subcellular distribution. Growth of HASMC was significantly inhibited by 70% ethanolic SGE; however, gene expression patterns in various cellular compartments elicited in response to SGE were substantially different from those observed in resveratrol-treated cells. Further, SGE also differed from resveratrol in not being able to induce relaxation of rat carotid arterial rings. These results indicate that distinct mechanisms are involved in the regulation of HASMC growth and gene expression by SGE and resveratrol.

Aorta↗

PubMed2006

Protection against oxidant-induced apoptosis by mitochondrial thioredoxin in SH-SY5Y neuroblastoma cells.

Mitochondrial oxidative stress plays important roles in aging and age-related degenerative disorders. The newly identified mitochondrial thioredoxin (mtTrx; Trx2) is a key component of the mitochondrial antioxidant system which is responsible for the clearance of reactive intermediates and repairs proteins with oxidative damage. Here, we show that in cultured SH-SY5Y human neuroblastoma 1cells, overexpression of mtTrx inhibited apoptosis and loss of mitochondrial membrane potential induced by a chemical oxidant, tert-butylhydroperoxide (tBH). The effects of calcium ionophore (Br-A23187) were not affected by mtTrx, suggesting the protection was specific against oxidative injury. The mitochondrial glutathione pool was oxidized by tBH, and this oxidation was not inhibited by increased mtTrx. Consequently, the antioxidant function of mtTrx is not redundant, but rather in addition, to that of GSH. Mutations of Cys90 and Cys93 to serines rendered mtTrx ineffective in protection against tBH-induced cytoxicity. These data indicate that mtTrx controls the mitochondrial redox status independently of GSH and is a key component of the defensive mechanism against oxidative stress in cultured neuronal cells.

Anti-Bacterial Agents↗