Biomedical subjects

Ying Xia

Publications and source records attributed to Ying Xia.

51 records · Page 3Linked to original sources

PubMed2003

MEK kinase 1 regulates c-Jun phosphorylation in the control of corneal morphogenesis.

PURPOSE: To study the in vivo role of MEK kinase 1 (MEKK1) in corneal development. METHODS: Wild type and Mekk1DeltaKD/DeltaKD mice eye tissues were examined by staining with hematoxylin and eosin for morphogenesis and Masson's trichrome for extracellular matrix (ECM) deposition. The cells expressing ECM gene transcripts of Collagen I, Keratocan, and Lumican in corneal stroma were identified by in situ hybridization and the level of Collagen I mRNA in the developing cornea was quantified by real-time RT-PCR. Immunohistochemistry staining was employed to study the expression and N-terminal phosphorylation of c-Jun and the expression of epithelium differentiation markers and intercellular structural proteins of the corneal epithelium. RESULTS: Mekk1DeltaKD/DeltaKD mice exhibited the "eye open at birth" phenotype (EOB), and developed eye defects and severe pathology secondary to impaired eyelid formation. The corneal stroma of Mekk1DeltaKD/DeltaKD fetuses, although exhibiting normal morphology, thickness, and keratocyte proliferation, showed reduced extracellular matrix (ECM) accumulation, corresponding to a decrease in transcription of Lumican, Keratocan, and Collagen I. Immunohistochemistry studies demonstrated that MEKK1 ablation caused a remarkable reduction in the expression of occludin and zonula occluden protein-1 (ZO-1), components of tight junction, but had no effect on the expression of E-cadherin and beta-catenin for adherens junctions, desmoplakin and desmoglein for desmosomes and cytokeratins 12 and 14 for cornea-type epithelial differentiation in the developing cornea. c-Jun was abundantly expressed in the developing corneal epithelium and its phosphorylation was considerably reduced in Mekk1DeltaKD/DeltaKD fetuses. CONCLUSIONS: In addition to its role in eyelid morphogenesis, MEKK1 is crucial for corneal development such that its ablation caused a reduction of ECM deposition in corneal stroma and disturbance of tight junctions in corneal epithelium. c-Jun phosphorylation in corneal epithelium is a downstream event of the MEKK1 pathway, likely contributing to corneal development and function. Altogether, MEKK1 plays a major role in ocular surface morphogenesis and its ablation leads to damage and various eye manifestations at postnatal stages.

Animals↗

PubMed2003

c-Jun N-terminal kinases (JNK) antagonize cardiac growth through cross-talk with calcineurin-NFAT signaling.

The c-Jun N-terminal kinase (JNK) branch of the mitogen-activated protein kinase (MAPK) signaling pathway regulates cellular differentiation, stress responsiveness and apoptosis in multicellular eukaryotic organisms. Here we investigated the functional importance of JNK signaling in regulating differentiated cellular growth in the post-mitotic myocardium. JNK1/2 gene-targeted mice and transgenic mice expressing dominant negative JNK1/2 were determined to have enhanced myocardial growth following stress stimulation or with normal aging. A mechanism underlying this effect was suggested by the observation that JNK directly regulated nuclear factor of activated T-cell (NFAT) activation in culture and in transgenic mice containing an NFAT-dependent luciferase reporter. Moreover, calcineurin Abeta gene targeting abrogated the pro-growth effects associated with JNK inhibition in the heart, while expression of an MKK7-JNK1 fusion protein in the heart partially reduced calcineurin-mediated cardiac hypertrophy. Collectively, these results indicate that JNK signaling antagonizes the differentiated growth response of the myocardium through direct cross-talk with the calcineurin-NFAT pathway. These results also suggest that myocardial JNK activation is primarily dedicated to modulating calcineurin-NFAT signaling in the regulation of differentiated heart growth.

Animals↗

PubMed2003

A role for MEK kinase 1 in TGF-beta/activin-induced epithelium movement and embryonic eyelid closure.

MEKK1-deficient mice show an eye open at birth phenotype caused by impairment in embryonic eyelid closure. MEK kinase 1 (MEKK1) is highly expressed in the growing tip of the eyelid epithelium, which displays loose cell-cell contacts and prominent F-actin fibers in wild-type mice, but compact cell contacts, lack of polymerized actin and a concomitant impairment in c-Jun N-terminal phosphorylation in MEKK1-deficient mice. In cultured keratinocytes, MEKK1 is essential for JNK activation by TGF-beta and activin, but not by TGF-alpha. MEKK1-driven JNK activation is required for actin stress fiber formation, c-Jun phosphorylation and cell migration. However, MEKK1 ablation does not impair other TGF-beta/activin functions, such as nuclear translocation of Smad4. These results establish a specific role for the MEKK1-JNK cascade in transmission of TGF-beta and activin signals that control epithelial cell movement, providing the mechanistic basis for the regulation of eyelid closure by MEKK1. This study also suggests that the signaling mechanisms that control eyelid closure in mammals and dorsal closure in Drosophila are evolutionarily conserved.

Actins↗

PubMed2003

Regulation of insulin gene transcription by ERK1 and ERK2 in pancreatic beta cells.

We show that the mitogen-activated protein kinases ERK1/2 are components of the mechanism by which glucose stimulates insulin gene expression. ERK1/2 activity is required for glucose-dependent transcription from both the full-length rat insulin I promoter and the glucose-sensitive isolated E2A3/4 promoter element in intact islets and beta cell lines. Dominant negative ERK2 and MEK inhibitors suppress glucose stimulation of the rat insulin I promoter and the E2A3/4 element. Overexpression of ERK2 is sufficient to stimulate transcription from the E2A3/4 element. The glucose-induced response is dependent upon ERK1/2 phosphorylation of a subset of transcription factors that include Beta2 (also known as NeuroD1) and PDX-1. Phosphorylation increases their functional activity and results in a cumulative transactivation of the promoter. Thus, ERK1/2 act at multiple points to transduce a glucose signal to insulin gene transcription.

Animals↗

PubMed2003

Host-dependent tumorigenesis of embryonic stem cell transplantation in experimental stroke.

The therapeutical potential of transplantation of undifferentiated and predifferentiated murine embryonic stem cells for the regeneration of the injured brain was investigated in two rodent stroke models. Undifferentiated embryonic stem cells xenotransplanted into the rat brain at the hemisphere opposite to the ischemic injury migrated along the corpus callosum towards the damaged tissue and differentiated into neurons in the border zone of the lesion. In the homologous mouse brain, the same murine embryonic stem cells did not migrate, but produced highly malignant teratocarcinomas at the site of implantation, independent of whether they were predifferentiated in vitro to neural progenitor cells. The authors demonstrated a hitherto unrecognized inverse outcome after xenotransplantation and homologous transplantation of embryonic stem cells, which raises concerns about safety provisions when the therapeutical potential of human embryonic stem cells is tested in preclinical animal models.

Animals↗

PubMed2003

Na+ channel expression and neuronal function in the Na+/H+ exchanger 1 null mutant mouse.

Mice lacking Na(+)/H(+) exchanger 1 (NHE1) suffer from recurrent seizures and die early postnatally. Although the mechanisms for seizures are not well established, our previous electrophysiological work has shown that neuronal excitability and Na(+) current density are increased in hippocampal CA1 neurons of these mutant mice. However, it is unknown whether this increased density is related to altered expression or functional regulation of Na(+) channels. In this work, we asked three questions: is the increased excitability limited to CA1 neurons, is the increased Na(+) current density related to an increased Na(+) channel expression, and, if so, which Na(+) channel subtype(s) is upregulated? Using neurophysiological, autoradiographic, and immunoblotting techniques, we showed that both CA1 and cortical neurons have an increase in membrane excitability and Na(+) current density; Na(+) channel density is selectively upregulated in the hippocampus and cortex (P < 0.05); and Na(+) channel subtype I is significantly increased in the hippocampus and Na(+) channel subtype II is increased in the cortex. Our results demonstrate that mice lacking NHE1 upregulate their Na(+) channel expression in the hippocampal and cortical regions selectively; this leads to an increase in Na(+) current density and membrane excitability. We speculate that neuronal overexcitability due to Na(+) channel upregulation in the hippocampus and cortex forms the basis of epileptic seizures in NHE1 mutant mice.

Action Potentials↗

PubMed2003

[Identification, cloning and sequencing of GST gene of bacterium degrading poly-aromatic hydrocarbons].

A bacterium (designated strain ZX4) able to degrade poly aromatic hydrocarbons was isolated from oil-contaminated soil. Based on analysis of the 16S rDNA sequence, whole cell fatty acid, and Biolog-GN, the strain was identified as Sphingomonas paucimobilis. The detection of GST (Glutathione S-transferase) indicated that the GST from the strain had the activity of conjugating with CDNB and it maybe relate with degradation of PAHs. The PCR product of GST gene from the strain confirmed its presence. Phylogeny analysis based on gst sequence indicated that the strain was relatively close with the strain which can degrade PAH likewise.

Bacterial Proteins↗

PubMed2002

Role of the aryl hydrocarbon receptor in cell cycle regulation.

Traditionally, the aryl hydrocarbon receptor (AHR) is considered to be a ligand-activated receptor and transcription factor responsible for the induction of drug-metabolizing enzymes. Its role in the combinatorial matrix of cell functions was neatly established long before the first report of an AHR cDNA sequence was published. Only recently, other functions of this protein have begun to be recognized. This review addresses novel findings relating to AHR functions that have resulted from experimental approaches markedly outside traditional receptor analyses. Here we examine the aspects of AHR biology relevant to its role in cell cycle regulation, from the activation of mitogen-activated protein kinases to the cross-talk between AHR and the RAS pathway and the functional significance of the interaction between AHR and the retinoblastoma protein. We have attempted to provide the reader with a balanced interpretation of the evidence, highlighting areas of consensus as well as areas still being contested.

Animals↗

PubMed2002

MEKK1 plays a critical role in activating the transcription factor C/EBP-beta-dependent gene expression in response to IFN-gamma.

IFN-gamma induces a number of genes to up-regulate cellular responses by using specific transcription factors and the cognate elements. We recently discovered that CCAAT/enhancer-binding protein-beta (C/EBP-beta) induces gene transcription through an IFN-response element called gamma-IFN-activated transcriptional element (GATE). Using mutant cells, chemical inhibitors, and specific dominant negative inhibitors, we show that induction of GATE-driven gene expression depends on MEK1 (mitogen-activated protein kinase kinase/extracellular signal-regulated protein kinase kinase) and ERKs (extracellular signal-regulated protein kinases) but is independent of Raf-1. Interestingly in cells lacking the MEKK1 gene or expressing the dominant negative MEKK1, ERK activation, and GATE dependent gene expression is inhibited. A dominant negative MEKK1 blocks C/EBP-beta-driven gene expression stimulated by IFN-gamma. These studies describe an IFN-gamma-stimulated pathway that involves MEKK1-MEK1-ERK1/2 kinases to regulate C/EBP-beta-dependent gene expression.

Animals↗

PubMed2002

Cellular cardiomyoplasty improves survival after myocardial injury.

BACKGROUND: Cellular cardiomyoplasty is discussed as an alternative therapeutic approach to heart failure. To date, however, the functional characteristics of the transplanted cells, their contribution to heart function, and most importantly, the potential therapeutic benefit of this treatment remain unclear. METHODS AND RESULTS: Murine ventricular cardiomyocytes (E12.5-E15.5) labeled with enhanced green fluorescent protein (EGFP) were transplanted into the cryoinjured left ventricular walls of 2-month-old male mice. Ultrastructural analysis of the cryoinfarction showed a complete loss of cardiomyocytes within 2 days and fibrotic healing within 7 days after injury. Two weeks after operation, EGFP-positive cardiomyocytes were engrafted throughout the wall of the lesioned myocardium. Morphological studies showed differentiation and formation of intercellular contacts. Furthermore, electrophysiological experiments on isolated EGFP-positive cardiomyocytes showed time-dependent differentiation with postnatal ventricular action potentials and intact beta-adrenergic modulation. These findings were corroborated by Western blotting, in which accelerated differentiation of the transplanted cells was detected on the basis of a switch in troponin I isoforms. When contractility was tested in muscle strips and heart function was assessed by use of echocardiography, a significant improvement of force generation and heart function was seen. These findings were supported by a clear improvement of survival of mice in the cardiomyoplasty group when a large group of animals was analyzed (n=153). CONCLUSIONS: Transplanted embryonic cardiomyocytes engraft and display accelerated differentiation and intact cellular excitability. The present study demonstrates, as a proof of principle, that cellular cardiomyoplasty improves heart function and increases survival on myocardial injury.

Animals↗

PubMed2002

Residential radon and lung cancer risk in a high-exposure area of Gansu Province, China.

In the general population, evaluation of lung cancer risk from radon in houses is hampered by low levels of exposure and by dosimetric uncertainties due to residential mobility. To address these limitations, the authors conducted a case-control study in a predominantly rural area of China with low mobility and high radon levels. Included were all lung cancer cases diagnosed between January 1994 and April 1998, aged 30-75 years, and residing in two prefectures. Randomly selected, population-based controls were matched on age, sex, and prefecture. Radon detectors were placed in all houses occupied for 2 or more years during the 5-30 years prior to enrollment. Measurements covered 77% of the possible exposure time. Mean radon concentrations were 230.4 Bq/m(3) for cases (n = 768) and 222.2 Bq/m(3) for controls (n = 1,659). Lung cancer risk increased with increasing radon level (p < 0.001). When a linear model was used, the excess odds ratios at 100 Bq/m(3) were 0.19 (95% confidence interval: 0.05, 0.47) for all subjects and 0.31 (95% confidence interval: 0.10, 0.81) for subjects for whom coverage of the exposure interval was 100%. Adjusting for exposure uncertainties increased estimates by 50%. Results support increased lung cancer risks with indoor radon exposures that may equal or exceed extrapolations based on miner data.

Adult↗

PubMed2002

Cellular cardiomyoplasty in a transgenic mouse model.

BACKGROUND: Recent progress in the cardiotypic differentiation of embryonic and somatic stem cells opens novel prospects for the treatment of cardiovascular disorders. The aim of the present study was to develop a novel surgical approach that allows standardized cellular cardiomyoplasty in mouse with low-perioperative mortality. METHODS: Reproducible transmural lesions were generated by cryoinjury followed by intramural injection of embryonic cardiomyocytes using a newly designed holding device and vital dye staining. This approach was validated with a transgenic mouse model, in which the live reporter gene-enhanced green fluorescent protein (EGFP) is under control of a cardiac-specific promoter. RESULTS: The perioperative mortality was 10%. The engrafted EGFP-positive cardiomyocytes could be identified in a high percentage (72.2%, n=36) of operated animals. CONCLUSIONS: This novel approach enables reliable cellular replacement therapy in mouse and greatly facilitates the analysis of its molecular, cellular, and functional efficacy.

Animals↗

PubMed2002

Activation of mitogen-activated protein kinases (MAPKs) by aromatic hydrocarbons: role in the regulation of aryl hydrocarbon receptor (AHR) function.

The aromatic hydrocarbon (Ah) receptor (AHR) is the only known cellular receptor of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and of many other widespread environmental contaminants that cause diverse toxic effects in animals and humans. Most, if not all, the biological effects of TCDD are mediated by the activation of AHR, which is a ligand-activated transcription factor required for ligand-induced expression of several detoxification genes, including those encoding for cytochrome P450 enzymes CYP1A1, CYP1A2, and CYP1B1. Environmental agents also activate several mitogen-activated protein kinase (MAPK) pathways, believed to modulate transcription factor function and to regulate gene expression. However, the contribution to TCDD toxicity resulting from cross-talk between AHR and MAPK pathways has yet to be determined. In this study, we show that TCDD and other AHR ligands induced the immediate activation of the extracellular signal-regulated kinases and the Jun N-terminal kinases, but not the p38 MAPKs. MAPK activation by TCDD did not require the AHR, since it occurred equally well in AHR-negative CV-1 cells and in Ahr (-/-) mouse embryonic fibroblasts as in AHR-positive cells. Distinct from serum factors and the tumor promoter TPA-induced MAPKs, which resulted in transcriptional activation of ELK or c-JUN, TCDD-stimulated MAPKs were critical for the induction of AHR-dependent gene transcription and CYP1A1 expression. These data indicate that AHR ligands elicit AHR-independent non-genomic events that are essential for AHR activation and function.

Animals↗

PubMed2002

Lung cancer and indoor exposure to coal and biomass in rural China.

Incomplete combustion of coal in homes has been linked with lung cancer in China. We report on a lung cancer case-control study in a rural area of China, where many residents live in underground dwellings and burn coal and unprocessed biomass (crop residues, wood, sticks, and twigs) for heating and cooking. We interviewed 846 patients with lung cancer (626 men, 220 women; aged 30 to 75 years) diagnosed between 1994 and 1998, and 1740 population-based controls. The odds ratio for lung cancer associated with coal use compared with that for biomass in the house of longest residence was 1.29 (95% confidence interval, 1.03 to 1.61), adjusted for smoking and socioeconomic status. The risk for lung cancer increased relative to the percentage of time that coal was used over the past 30 years (P = 0.02). Our findings suggest that coal may contribute to the risk of lung cancer in this rural area of China.

Adult↗

PubMed2002

Neuroprotective role of delta-opioid receptors in cortical neurons.

We recently demonstrated that delta-opioid receptor (DOR) activation protects cortical neurons against glutamate-induced injury. Because glutamate is a mediator of hypoxic injury in neurons, we hypothesized that DOR is involved in neuroprotection during O2 deprivation and that its activation/inhibition may alter neuronal susceptibility to hypoxic stress. In this work, we tested the effect of opioid receptor activation and inhibition on cultured cortical neurons in hypoxia (1% O2). Cell injury was assessed by lactate dehydrogenase release, morphology-based quantification, and live/dead staining. Our results show that 1) immature neurons (days 4 and 6) were not significantly injured by hypoxia until 72 h of exposure, whereas day 8 neurons were injured after only 24-h hypoxia; 2) DOR inhibition (naltrindole) caused neuronal injury in both day 4 and day 8 normoxic cultures and further augmented hypoxic injury in these neurons; 3) DOR activation ([D-Ala2,D-Leu5]enkephalin) reduced neuronal injury in day 8 cultures after 24 h of normoxic or hypoxic exposure and attenuated naltrindole-induced injury with prolonged exposure; and 4) mu- or kappa-opioid receptor inhibition (beta-funaltrexamine or nor-binaltorphimine) had little effect on neurons in either normoxic or hypoxic conditions. Collectively, these data suggest that DOR plays a crucial role in neuroprotection in normoxic and hypoxic environments.

Animals↗