Biomedical subjects

Zhiheng Yu

Publications and source records attributed to Zhiheng Yu.

9 recordsLinked to original sources

PubMed2006

The polycystin 1-C-terminal fragment stimulates ERK-dependent spreading of renal epithelial cells.

Polycystin 1, the product of the PKD1 gene, is mutated in autosomal dominant polycystic kidney disease, a disease characterized by renal cyst formation and progressive renal failure. We show that expression of the C-terminal domain of human polycystin-1 (PKD1-CT) triggers spreading of isolated inner medullary collecting duct cells, a process mediated by Erk. As inner medullary collecting duct cells spread, PKD1-CT localizes to cell-extracellular matrix contacts, interacts with focal adhesion proteins Fak and paxillin, and stimulates Fak phosphorylation, paxillin phosphorylation, Fak-paxillin association, and formation of small focal complexes. PKD1-CT-mediated spreading requires membrane localization and the integrity of the C-terminal protein binding sites. We additionally show that Pkd1 null proximal tubule cells generated from Pkd1(flox/-):TSLargeT mice by in vitro Cre recombinase transfection demonstrate diminished spreading when compared with Pkd(flox/-) heterozygous parental cells. These findings suggest that membrane-bound PC1 has a central role in regulating morphogenic protein signaling at cell-matrix interfaces in non-confluent cells.

Animals↗

PubMed2006

Polycystin-2 traffics to cilia independently of polycystin-1 by using an N-terminal RVxP motif.

Primary cilia play a key role in the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). The affected proteins, polycystin-1 (PC1) and polycystin-2 (PC2), interact with each other and are expressed in cilia. We found that COOH-terminal truncated PC2 (PC2-L703X), lacking the PC1 interaction region, still traffics to cilia. We examined PC2 expression in several tissues and cells lacking PC1 and found that PC2 is expressed in cilia independently of PC1. We used N-terminal deletion constructs to narrow the domain necessary for cilia trafficking to the first 15 amino acids of PC2 and identified a conserved motif, R6VxP, that is required for cilial localization. The N-terminal 15 amino acids are also sufficient to localize heterologous proteins in cilia. PC2 has endogenous cilia trafficking information and is present in cilia of cells lining cysts that result from mutations in PKD1.

Amino Acid Motifs↗

PubMed2005

Shell distribution on colloidal CdSe/ZnS quantum dots.

Scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) was used to determine the chemical distribution of semiconductor shell material around colloidal core-shell CdSe/ZnS quantum dots (QDs). EELS signals from positions around the QD indicate a well-defined shell of ZnS surrounding the CdSe core, but the distribution of the shell material is highly anisotropic. This nonuniformity may reflect the differences in chemical activity of the crystal faces of the core QD and implies a nonoptimal QD surface passivation.

Journal Article↗

PubMed2004

Polarization surface-charge density of single semiconductor quantum rods.

Electrostatic force microscopy was used to determine that single CdSe quantum rods (QRs) have a permanent polarization surface-charge density, an unexpected observation for supposedly well-shaped particles. The surface charge results from a slight angle between the QR sides and the direction of internal electric polarization. By contrast, despite the large dipole moment expected for CdSe QRs, none was observed. The unavoidable presence of permanently charged surfaces on CdSe QRs has the potential to impede the development of novel devices incorporating these materials.

Journal Article↗

PubMed2004

Calcium dependence of polycystin-2 channel activity is modulated by phosphorylation at Ser812.

Polycystin-2 (PC-2) is a non-selective cation channel that, when mutated, results in autosomal dominant polycystic kidney disease. In an effort to understand the regulation of this channel, we investigated the role of protein phosphorylation in PC-2 function. We demonstrated the direct incorporation of phosphate into PC-2 in cells and tissues and found that this constitutive phosphorylation occurs at Ser(812), a putative casein kinase II (CK2) substrate domain. Ser(812) can be phosphorylated by CK2 in vitro and substitution S812A results in failure to incorporate phosphate in cultured epithelial cells. Non-phosphorylated forms of PC-2 traffic normally in the endoplasmic reticulum and cilial compartments and retain homo- and hetero-multimerization interactions with PC-2 and polycystin-1, respectively. Single-channel studies of PC-2, S812A, and a substitution mutant, T721A, not related to phosphorylation show that PC-2 and S812A function as divalent cation channels with similar current amplitudes across a range of holding potentials; the T721A channel is not functional. Channel open probabilities for PC-2 and S812A show a bell-shaped dependence on cytoplasmic Ca(2+) but there is a shift in this Ca(2+) dependence such that S812A is 10-fold less sensitive to Ca(2+) activation/inactivation than the wild type PC-2 channel. In vivo analysis of PC-2-dependent enhanced intracellular Ca(2+) transients found that S812A resulted in enhanced transient duration and relative amplitude intermediate between control cells and those overexpressing wild type PC-2. Phosphorylation at Ser(812) modulates PC-2 channel activity and factors regulating this phosphorylation are likely to play a role in the pathogenesis of polycystic kidney disease.

Animals↗

PubMed2003

Artifacts in aberration-corrected ADF-STEM imaging.

The introduction of an experimental black level may introduce unintended artifactual details into high-resolution annular dark field scanning transmission electron microscopy (ADF-STEM) lattice images. This article presents the multislice simulation results of such possible situations. Three simulated scanning transmission electron microscopy (STEM) probes of sizes 0.8, 1.2 and 2.0 A are scanned on the surface of a <1;10> oriented Si/Ge crystal. The simulation results suggest that high-frequency artifact peaks will appear in the power spectra when an artificial black level clips the lowest (background) signal. The lowest signal in an ADF-STEM image decreases as the incident probe shrinks in size. Therefore, care must be taken when interpreting the resolution limit of the microscope from images taken with nonzero black level setting, especially in case of sub-A microscope. The simulation result is compared with an experimental image and they agree with each other. The analysis suggests that aberration corrected STEM provide sensitive low level detail.

Journal Article↗

PubMed2002

STAT1 and STAT3 mediate thrombin-induced expression of TIMP-1 in human glomerular mesangial cells.

BACKGROUND: Thrombin exhibits numerous biological effects on glomerular resident cells, such as cell proliferation, release and synthesis of cytokines and collagen, expressions of metalloproteinases and their inhibitors, especially tissue inhibitor of metalloproteinase-1 (TIMP-1). However, the signaling mechanisms underlying these cellular events have not been fully elucidated. The present study was designed to examine the role of signal transducers and activators of transcription (STAT) in thrombin-induced TIMP-1 expression in human mesangial cells. METHODS: Cultured human glomerular mesangial cells were incubated with thrombin up to 12 hours. The effects of the antisense of STAT1 and antisense of STAT3 on stimulated TIMP-1 mRNA levels and DNA-binding activities of both STAT1 and STAT3 were determined using Northern blot, electrophoretic mobility shift assay (EMSA), and supershift assay. RESULTS: Cultured human mesangial cells constitutively expressed TIMP-1, and thrombin induced TIMP-1 gene transcription in a time- and dose-dependent manner. Hirudin, a specific inhibitor of thrombin, could block thrombin-induced TIMP-1 expression. Thrombin also induced STAT-DNA binding activity in a similar time- and dose-dependent manner. In order to examine the role of STAT in thrombin-induced TIMP-1 expression, STAT1 and STAT3 antisense oligonucleotides were used. EMSA showed that STAT1 and STAT3 antisense oligonucleotides could inhibit both thrombin-induced STAT-DNA binding activities and TIMP-1 mRNA expression; the supershift assay showed that the SIF band consisted of STAT1 and STAT3 proteins. CONCLUSIONS: Both STAT1 and STAT3 may be involved, at least in part, in thrombin-induced expression of the TIMP-1 gene in cultured human mesangial cells.

Cells, Cultured↗

PubMed2002

Inhibition of apoptosis in rat mesangial cells by tissue inhibitor of metalloproteinase-1.

BACKGROUND: Tissue inhibitor of metalloproteinase-1 (TIMP-1) is an important inhibitor of extracellular matrix degradation. Recently, it was reported that TIMP-1 also could inhibit apoptosis in B type lymphocyte. This study was designed to examine the effects of TIMP-1 on mesangial cell apoptosis. METHODS: The full-length cDNA of TIMP-1 was cloned and used to construct two recombinant vectors, TIMP-1S and TIMP-1AS, encoding sense TIMP-1 and antisense TIMP-1, respectively. The vectors were transfected into rat mesangial cells (RMC) and their expressions detected by Northern and Western blotting. Apoptosis was induced by serum deprivation, and was monitored for DNA fragmentation by TUNEL assay and DNA laddering. In addition, the expression of endogenous TIMP-1, matrix metalloprotein-2 (MMP-2), and MMP-9, as well as apoptosis-related genes Bcl-2 and Bax were investigated. RESULTS: TIMP-1AS transfection induced a suppression of TIMP-1 expression accompanied by an earlier onset of apoptosis, and TIMP-1S transfection induced TIMP-1 over-expression accompanied by a much later onset of apoptosis. A neutralizing antibody of TIMP-1 restored the sensitivity of TIMP-1S-transfected RMC to serum deprivation, but a synthetic matrix metalloproteinase inhibitor BB-94 did not influence the sensitivity of TIMP-1S-transfected RMC to serum deprivation. Finally, TIMP-1 over-expression inhibited the expression of Bax but with no effect on the expression of Bcl-2. CONCLUSION: TIMP-1 inhibits the serum deprivation-induced apoptosis in RMC, in which Bax might be involved.

Animals↗

PubMedDate not supplied

Sodium dicarboxylate cotransporter-1 expression in renal tissues and its role in rat experimental nephrolithiasis.

BACKGROUND: Nephrolithiasis is a common disease with a high recurrence rate; however, calcium stone pathogenesis remains unknown because of complex multiple factors. Hypocitraturia induced by citrate transport disturbance is known to be involved in nephrolithiasis development. Sodium dicarboxylate cotransporter (NaDC) mediates citrate uptake from the renal proximal tubule. However, the role of NaDC in nephrolithiasis is unclear. This study aimed to investigate NaDC-1 expression in rat renal proximal tubule epithelial cells and its relationship with experimental nephrolithiasis. METHODS: Male Wastar rats were divided into control, ethylene glycol (EG)-treated and potassium citrate-treated groups. Calcium oxalate (CaOx) crystal deposition and histological changes in the kidneys were examined with anatomical and light microscopes. The plasma and urinary biochemical parameters, such as citrate, oxalate etc, were analyzed by routine biochemical methods. NaDC-1 mRNA expression in kidneys was determined by northern blot analysis, the change in NaDC-1 protein abundance was detected by immunohistochemistry. RESULTS: It was found that NaDC-1 expression and its mRNA significantly increased in the EG group when compared with controls. Increased NaDC-1 expression was associated with a decline in urinary citrate excretion. Potassium citrate administration could significantly down-regulate NaDC-1 expression and its mRNA, and elevate urinary citrate content alleviate renal pathological changes and reduce nephrolithiasis occurrence. CONCLUSION: Increased NaDC-1 expression on the renal proximal tubule epithelial cells could play an important role in nephrolithiasis development, suggesting it could be a therapeutic target for the treatment of nephrolithiasis.

Animals↗