Biomedical subjects

Wensheng Zhang

Publications and source records attributed to Wensheng Zhang.

At least 19 recordsLinked to original sources

PubMed2006

A model of nitric oxide tubulovascular cross talk in a renal outer medullary cross section.

We developed a two-dimensional model of NO transport in a cross section of the inner stripe (IS) of the rat outer medulla to determine whether tubular and vascular generation of NO result in significant NO concentration (C(NO)) differences between the periphery and the center of vascular bundles and thereby affect medullary blood flow distribution. Following the approach of Layton and Layton (Layton AT, Layton HE. Am J Physiol Renal Physiol 289: F1346-F1366, 2006), the structural heterogeneity of the IS was incorporated in a representative unit consisting of four concentric regions centered on a vascular bundle. Our model suggests that the diffusion distance of NO in the interstitium is limited to a few micrometers. We predict that, under basal conditions, epithelial NO generation raises the average C(NO) in pericytes surrounding peripheral descending vasa recta (DVR) by a few nanomoles relative to that in pericytes surrounding central DVR. The short descending limbs and long ascending limbs are found to exert the greatest effect on C(NO) in pericytes; long descending limbs and short ascending limbs only have a moderate effect, whereas outer medullary collecting ducts, which are situated far from the vascular bundle center, do not affect pericyte C(NO). Our results suggest that selective stimulation of epithelial NO production should significantly raise the periphery-to-center DVR diameter ratio, thereby increasing the outer medulla-to-inner medulla blood flow ratio. However, concomitant increases in epithelial superoxide (O(2)(-)) production would counteract this effect. This model confirms the importance of NO and O(2)(-) interactions in mediating tubulovascular cross talk.

Animals↗

PubMed2006

Mathematical model of nitric oxide convection and diffusion in a renal medullary vas rectum.

In this study, the generation, convection, diffusion, and consumption of nitric oxide (NO) in and around a single renal medullary descending or ascending vas rectum in rat were modeled using CFD. The vascular lumen (with a core RBC-rich layer and a parietal layer), the endothelium, the pericytes and the interstitium were represented as concentric cylinders. We accounted for the generation of NO by vascular endothelial cells, and that by the epithelial cells of medullary thick ascending limbs (mTALs) and inner medullary collecting ducts (IMCDs), the latter via interstitial boundary conditions. Luminal velocity profiles were obtained by modeling blood flow dynamics. Our results suggest that convection (i.e., blood flow per se) does not significantly affect NO concentrations along the cortico-medullary axis, because the latter are mostly determined by the rate of NO production and that of NO consumption by hemoglobin. However, the shear stress-mediated effects of blood flow on NO generation rates, and therefore NO concentrations, were predicted to be important. Finally, we found that unless epithelial NO generation rates (per unit tubular surface area) are at least 10 times lower than endothelium NO generation rates, NO production by mTALs and IMCDs affects vascular NO concentrations, with possible consequences for medullary blood flow distribution.

Animals↗

PubMed2006

Sall4 interacts with Nanog and co-occupies Nanog genomic sites in embryonic stem cells.

Embryonic stem (ES) cells are pluripotent cells with self-renewing property. Nanog is a homeobox transcription factor required to maintain ES cells in a non-differentiated state. Using affinity purification coupled to liquid chromatography-tandem mass spectrometry analysis, we identified Sall4 as a Nanog co-purified protein. Co-immunoprecipitation and glutathione S-transferase pulldown experiments confirmed the interaction between Nanog and Sall4. We showed that Nanog and Sall4 co-occupied Nanog and Sall4 enhancer regions in living ES cells. Knockdown of Nanog or Sall4 by RNA interference led to a reduction in Nanog and Sall4 enhancer activities, providing evidence that these factors are positively regulating these enhancers. Importantly, co-transfection of Sall4 with these ES cell-specific enhancers led to transactivation in heterologous somatic cells. Chromatin immunoprecipitation experiments also showed that Sall4 co-occupied many Nanog binding sites in ES cells. Our data implicate Sall4 as an important component of the transcription regulatory networks in ES cells by cooperating with Nanog. We suggest that Sall4 and Nanog form a regulatory circuit similar to that of Oct4 and Sox2. This study highlights the extensive regulatory loops connecting genes, which encode for key transcription factors in ES cells.

Animals↗

PubMed2005

A method for predicting disease subtypes in presence of misclassification among training samples using gene expression: application to human breast cancer.

MOTIVATION: An accurate diagnostic and prediction will not be achieved unless the disease subtype status for every training sample used in the supervised learning step is accurately known. Such an assumption requires the existence of a perfect tool for disease diagnostic and classification, which is seldom available in the majority of the cases. Thus, the supervised learning step has to be conducted with a statistical model that contemplates and handles potential mislabeling in the input data. RESULTS: A procedure for handling potential mislabeling among training samples in the prediction of disease subtypes using gene expression data was proposed. A real data-based simulation study about the estrogen receptor status (ER+/ER-) of breast cancer patients was conducted. The results demonstrated that when 1-4 training samples (N = 30) were artificially mislabeled, the proposed method was able not only in correcting the ER status of mislabeled training samples but also more importantly in predicting the ER status of validation samples as well as using 'true' training data.

Algorithms↗

PubMed2005

A model of glucose transport and conversion to lactate in the renal medullary microcirculation.

In this study, we modeled mathematically the transport of glucose across renal medullary vasa recta and its conversion to lactate by anaerobic glycolysis. Uncertain parameter values were determined by seeking good agreement between predictions and experimental measurements of lactate generation rates, as well as glucose and lactate concentration ratios between the papilla and the corticomedullary junction; plausible kinetic rate constant and permeability values are summarized in tabular form. Our simulations indicate that countercurrent exchange of glucose from descending (DVR) to ascending vasa recta (AVR) in the outer medulla (OM) and upper inner medulla (IM) severely limits delivery to the deep inner medulla, thereby limiting medullary lactate generation. If the permeability to glucose of OMDVR and IMDVR is taken to be the same and equal to 4 x 10(-4) cm/s, the fraction of glucose that bypasses the IM is calculated as 54%; it is predicted as 37% if the presence of pericytes in OMDVR reduces the glucose permeability of these vessels by a factor of 2 relative to that of IMDVR. Our results also suggest that red blood cells (RBCs) act as a reservoir that reduces the bypass of glucose from DVR to AVR. The rate of lactate generation by anaerobic glycolysis of glucose supplied by blood from glomerular efferent arterioles is predicted to range from 2 to 8 nmol/s, in good agreement with lower estimates obtained from the literature (Bernanke D and Epstein FH. Am J Physiol 208: 541-545, 1965; Bartlett S, Espinal J, Janssens P, and Ross BD. Biochem J 219: 73-78, 1984).

Anaerobiosis↗

PubMed2005

Hedgehog-regulated Costal2-kinase complexes control phosphorylation and proteolytic processing of Cubitus interruptus.

Hedgehog (Hh) proteins control animal development by regulating the Gli/Ci family of transcription factors. In Drosophila, Hh counteracts phosphorylation by PKA, GSK3, and CKI to prevent Cubitus interruptus (Ci) processing through unknown mechanisms. Here, we show that these kinases physically interact with the kinesin-like protein Costal2 (Cos2) to control Ci processing and that Hh inhibits such interaction. Cos2 is required for Ci phosphorylation in vivo, and Cos2-immunocomplexes (Cos2IPs) phosphorylate Ci and contain PKA, GSK3, and CKI. By using a Kinesin-Cos2 chimeric protein that carries Cos2-interacting proteins to the microtubule plus end, we demonstrated that these kinases bind Cos2 in intact cells. PKA, GSK3, and CKI directly bind the N- and C-terminal regions of Cos2, both of which are essential for Ci processing. Finally, we showed that Hh signaling inhibits Cos2-kinase complex formation. We propose that Cos2 recruits multiple kinases to efficiently phosphorylate Ci and that Hh inhibits Ci phosphorylation by specifically interfering with kinase recruitment.

Animals↗

PubMed2005

Reciprocal transcriptional regulation of Pou5f1 and Sox2 via the Oct4/Sox2 complex in embryonic stem cells.

Embryonic stem cells (ESCs) are pluripotent cells that can either self-renew or differentiate into many cell types. Oct4 and Sox2 are transcription factors essential to the pluripotent and self-renewing phenotypes of ESCs. Both factors are upstream in the hierarchy of the transcription regulatory network and are partners in regulating several ESC-specific genes. In ESCs, Sox2 is transcriptionally regulated by an enhancer containing a composite sox-oct element that Oct4 and Sox2 bind in a combinatorial interaction. It has previously been shown that Pou5f1, the Oct4 gene, contains a distal enhancer imparting specific expression in both ESCs and preimplantation embryos. Here, we identify a composite sox-oct element within this enhancer and show that it is involved in Pou5f1 transcriptional activity in ESCs. In vitro experiments with ESC nuclear extracts demonstrate that Oct4 and Sox2 interact specifically with this regulatory element. More importantly, by chromatin immunoprecipitation assay, we establish that both Oct4 and Sox2 bind directly to the composite sox-oct elements in both Pou5f1 and Sox2 in living mouse and human ESCs. Specific knockdown of either Oct4 or Sox2 by RNA interference leads to the reduction of both genes' enhancer activities and endogenous expression levels in addition to ESC differentiation. Our data uncover a positive and potentially self-reinforcing regulatory loop that maintains Pou5f1 and Sox2 expression via the Oct4/Sox2 complex in pluripotent cells.

Animals↗

PubMed2004

Model of transient drug diffusion across cornea.

A mathematical model of solute transient diffusion across the cornea to the anterior chamber of the eye was developed for topical drug delivery. Solute bioavailability was predicted given solute molecular radius and octanol-to-water distribution coefficient (Phi), ocular membrane ultrastructural parameters, tear fluid hydrodynamics, as well as solute distribution volume (Vd) and clearance rate (Cla) in the anterior chamber. The results suggest that drug bioavailability is primarily determined by solute lipophilicity. In human eyes, bioavailability is predicted to range between 1% and 5% for lipophilic molecules (Phi>1), and to be less than 0.5% for hydrophilic molecules (Phi<0.01). The simulations indicate that the distribution coefficient that maximizes bioavailability is on the order of 10. It was also found that the maximum solute concentration in the anterior chamber (Cmax) and the time needed to reach Cmax significantly depend on Phi, Vd, and Cla. Consistent with experimental findings, model predictions suggest that drug bioavailability can be increased by lowering the conjunctival-to-corneal permeability ratio and reducing precorneal solute drainage. Because of its mechanistic basis, this model will be useful to predict drug transport kinetics and bioavailability for new compounds and in diseased eyes.

Algorithms↗

PubMed2004

Determinants of basal nitric oxide concentration in the renal medullary microcirculation.

In this study, we modeled the production, transport, and consumption of nitric oxide (NO) in the renal medullary microcirculation under basal conditions. To yield agreement with reported NO concentrations of approximately 60-140 nM in medullary tissues (Zou AP and Cowley AW Jr. Hypertension 29: 194-198, 1997; Am J Physiol Regul Integr Comp Physiol 279: R769-R777, 2000) and 3 nM in plasma (Stamler JS, Jaraki O, Osborne J, Simon DI, Keaney J, Vita J, Singel D, Valeri CR, and Loscalzo J. Proc Natl Acad Sci USA 89: 7674-7677, 1992), the permeabilities of red blood cells (RBCs), vascular walls, and pericytes to NO are all predicted to lie between 0.01 and 0.1 cm/s, and the NO production rate by vasa recta endothelium is estimated to be on the order of 10(-14) mumol.mum(-2).s(-1). Our results suggest that the concentration of NO in RBCs, which is essentially controlled by the kinetics of NO scavenging by hemoglobin, is approximately 0.01 nM, that is, 10(3) times lower than that in plasma, pericytes, and interstitium. Because the basal concentration of NO in pericytes is on the order of 10 nM, it may be too low to active guanylate cyclase, i.e., to induce vasorelaxation. Our simulations also indicate that basal superoxide concentrations may be too low to affect medullary NO levels but that, under pathological conditions, superoxide may be a very significant scavenger of NO. We also found that although oxygen is a negligible NO scavenger, medullary hypoxia may significantly enhance NO concentration gradients along the corticomedullary axis.

Animals↗

PubMed2004

[DNA microarray reveals changes in gene expression of endothelial cells under shear stress].

cDNA microarray technology is used as a powerful tool for rapid, comprehensive, and quantitative analysis of gene profiles of cultured human umbilical vein endothelial cells(HUVECs) in the normal static group and the shear stressed (4.20 dyne/cm2, 2 h) group. The total RNA from normal static cultured HUVECs was labeled by Cy3-dCTP, and total RNA of HUVECs from the paired shear stressed experiment was labeled by Cy5-dCTP. The expression ratios reported are the average from the two separate experiments. After bioinformatics analysis, we identified a total of 108 genes (approximately 0.026%) revealing differential expression. Of these 53 genes expressions were up-regulated, the most enhanced ones being human homolog of yeast IPP isomerase, human low density lipoprotein receptor gene, Squalene epoxidase gene, 7-dehydrocholesterol reductase, and 55 were down-regulated, the most decreased ones being heat shock 70 kD protein 1, TCB gene encoding cytosolic thyroid hormone-binding protein in HUVECs exposed to low shear stress. These results indicate that the cDNA microarray technique is effective in screening the differentially expressed genes in endothelial cells induced by various experimental conditions and the data may serve as stimuli to further researches.

Cell Division↗

PubMed2003

The Drosophila Ste20 family kinase dMST functions as a tumor suppressor by restricting cell proliferation and promoting apoptosis.

In a genetic screen for mutations that restrict cell growth and organ size, we identified a new tumor suppressor gene, dMST, which encodes the Drosophila homolog of the mammalian Ste20 kinase family members MST1 and MST2. Loss-of-function mutations in dMST result in overgrown tissues containing more cells of normal size. dMST mutant cells exhibit elevated levels of Cyclin E and DIAP1, increased cell growth and proliferation, and impaired apoptosis. dMST forms a complex with Sav and Wts, two tumor suppressors also implicated in regulating both cell proliferation and apoptosis, suggesting that they act in common pathways.

Amino Acid Sequence↗

PubMed2003

Cloning and characterization of rice HMGB1 gene.

We isolated a 918 bp long full-length rice HMGB1 cDNA, which has an open reading frame of 471 bp encoding 157 amino acids, with a central domain of high sequence similarity to the HMG-box domain of other plant HMGB1 proteins. RNA gel blot analysis indicated that rice HMGB1 gene is constitutively expressed in various tissues and organs. Southern hybridization and sequence analyses suggested that a single copy of the HMGB1 gene composed of seven exons and six introns exists in rice. We have also cloned a 1755 bp long 5' flanking region of the rice HMGB1 gene, which can be regarded as its promoter. 5' deletion analysis of this promoter indicated that positive cis-elements residing between -1400 and -1115 are important to enhance quantitative expression, whereas negative cis-elements between -1755 and -1400 and between -1115 and -351 inhibit expression.

5' Flanking Region↗

PubMed2003

Theoretical effects of UTB urea transporters in the renal medullary microcirculation.

A mathematical model of transport in the renal medullary microcirculation was used to investigate the role of the UTB urea transporter expressed in descending vasa recta (DVR) endothelia and red blood cell (RBC) membranes. Our simulations suggest that UTB raises RBC and plasma and interstitial urea concentrations by facilitating radial diffusion of the solute and therefore serves to increase the contribution of urea to the corticomedullary osmolality gradient, assuming no secondary effects on tubular transport. However, by lowering transmural urea concentration gradients, UTB reduces water efflux from DVR through aquaporin-1 (AQP1) water channels, thereby decreasing plasma sodium concentration. The net result of these competing effects on the osmolality gradient depends on the fraction of filtered urea that is reabsorbed by vasa recta. We also found that the contribution of UTB to water transport across DVR and RBCs is negligible, even in the absence of AQP1. Our model predicts that UTB plays a significant role, however, in reducing the shrinking and swelling of RBCs as blood flows along the medulla.

Animals↗

PubMed2003

Characterization of the interaction of wheat HMGa with linear and four-way junction DNAs.

Wheat HMGa protein is a typical member of the plant HMGA family. It has four AT hooks and a histone H1-like region. A panel of deletion mutants of HMGa was generated to study the role of different regions of HMGa in its binding to 4H (a synthetic DNA that mimics the in vivo structure of intermediates of homologous recombination and DNA repair) and linear DNAs. Although the histone H1-like region of HMGa does not bind to 4H or linear DNAs, it does enhance the binding. Mutants with any two adjacent AT hooks show specific binding to both 4H and linear P268 (and P31) with different binding affinities, which is partly due to the flanking regions between AT hooks. Conformational studies indicate that the alpha-helical content of HMGa increases significantly when it binds to 4H compared to that after binding to P31, linear DNA. In contrast, linear DNA, but not 4H, undergoes substantial conformational change when it binds to HMGa, indicating that linear DNA is relatively more flexible than 4H. A more significant difference in the affinities of binding of the mutants of HMGa to 4H was observed compared to their affinities of binding to linear DNA, P31. These differences could be due to the rigidity of the DNA and the characters of the AT hook regions in the mutants.

Amino Acid Sequence↗

PubMed2003

Rice HMGB1 protein recognizes DNA structures and bends DNA efficiently.

We analyzed the DNA-binding and DNA-bending properties of recombinant HMGB1 proteins based on a rice HMGB1 cDNA. Electrophoretic mobility shift assay demonstrated that rice HMGB1 can bind synthetic four-way junction (4H) DNA and DNA minicircles efficiently but the binding to 4H can be completed out by HMGA and histone H1. Conformational changes were detected by circular dichroism analysis with 4H DNA bound to various concentrations of HMGB1 or its truncated forms. T4 ligase-mediated circularization assays with short DNA fragments of 123 bp showed that the protein is capable of increasing DNA flexibility. The 123-bp DNA formed closed circular monomers efficiently in its presence, similar to that in an earlier study on maize HMG. Additionally, our results show for the first time that the basic N-terminal domain enhances the affinity of the plant HMGB1 protein for 4H DNA, while the acidic C-terminal domain has the converse effects.

Base Sequence↗

PubMed2003

Interaction of wheat high-mobility-group proteins with four-way-junction DNA and characterization of the structure and expression of HMGA gene.

Plant high-mobility-group (HMG) chromosomal proteins are the most abundant and ubiquitous nonhistone proteins found in the nuclei of higher eukaryotes. There are only two families of HMG proteins, namely, HMGA and HMGB in plants. The cDNA encoding wheat HMGa protein was isolated and characterized. Wheat HMGA cDNA encodes a protein of 189 amino acid residues. At its N terminus, there is a histone H1-like structure, which is a common feature of plant HMGA proteins, followed by four AT-hook motifs. Polymerase chain reaction results show that the gene contains a single intron of 134 bp. All four AT-hook motifs are encoded by the second exon. Northern blot results show that the expression of HMGA gene is much higher in organs undergoing active cell proliferation. Gel retardation analysis show that wheat HMGa, b, c and histone H1 bind to four-way-junction DNA with high binding affinity, but affinity is dramatically reduced with increasing Mg(2+) and Na(+) ion concentration. Competition binding studies show that proteins share overlapping binding sites on four-way-junction DNA. HMGd does not bind to four-way-junction DNA.

AT-Hook Motifs↗

PubMed2002

Oxygen transport across vasa recta in the renal medulla.

In this model of oxygen transport in the renal medullary microcirculation, we predicted that the net amount of oxygen reabsorbed from vasa recta into the interstitium is on the order of 10(-6) mmol/s, i.e., significantly lower than estimated medullary oxygen requirements based on active sodium reabsorption. Our simulations confirmed a number of experimental findings. Low medullary PO(2) results from the countercurrent arrangement of vessels and an elevated vasa recta permeability to oxygen, as well as high metabolic needs. Diffusional shunting of oxygen between descending vasa recta (DVR) and ascending vasa recta also explains why a 20-mmHg decrease in initial PO(2) at the corticomedullary junction only leads to a small drop in papillary tip PO(2) (<2 mmHg with baseline parameter values). Conversely, small changes in the consumption rate of DVR-supplied oxygen, in blood flow rate, in hematocrit, or in capillary permeability to oxygen, beyond certain values sharply reduce interstitial PO(2). Without erythrocytes, papillary tip PO(2) cannot be maintained above 10 mmHg, even when oxygen consumption is zero.

Animals↗

PubMed2002

[Time-dependent effects of interleukin-8 gene expression in endothelial cells exposed on fluid shear stress].

Fluid shear stress plays an important role in vascular biology. In vivo, endothelial cells are continuously exposed to mechanical shear stress generated by the flowing blood. Previous studies have identified the exposure of vascular endothelial cells to fluid mechanical forces can modulate the expression of many genes involved in vascular physiology and pathophysiology. To investigate the role of fluid shear stress on IL-8 expression in human umbilical vein endothelial cells (HUVECs), we employed quantitative reversal transcription-polymerase chain reaction (qRT-PCR) to assay the expression of IL-8 mRNA. Here we show that IL-8 mRNA did not express in HUVECs untreated with fluid shear stress. IL-8 mRNA expression increased when HUVECs exposed to fluid shear stress for 1 h, and it reached the summit when HUVECs exposed to fluid shear stress for 2 h. Then IL-8 expression gradually decreased at 3 h of stimulation by shear stress and remained at a constant level throughout the time course of the study. The increase of IL-8 expression by shear stress was time-dependent. The biphasic response of IL-8 gene expression was found in experiments in which the applied shear stress was 2.23 dyne/cm2, 4.20 dyne/cm2, or 6.08 dyne/cm2. IL-8 gene expression in response to shear stress was very similar to NF-kappa B in response to shear stress. The induction of IL-8 gene expression by fluid shear stress is probably due to the activation of NF-kappa B. This in vitro study demonstrates the expression of IL-8 gene can be regulated by shear stress. Fluid shear stress induces a biphasic response of human IL-8 gene expression in HUVECs. These considerations suggest that IL-8 expression induced by fluid shear stress in HUVECs may play an important role in the genesis and development of both inflammation and arterioatherosclerosis.

Cells, Cultured↗