Biomedical subjects

Lin Gao

Publications and source records attributed to Lin Gao.

At least 19 recordsLinked to original sources

PubMed2006

Aquaporin 4 regulates the effects of ovarian hormones on monoamine neurotransmission.

Aquaporin 4 (AQP4) is the predominant water channels in the brain of mammals. Our previous study has reported that AQP4 knockout induced sex-specific alterations in neurotransmission, indicating that AQP4 might regulate the interaction between sex hormones and neurotransmission. In the present study, we found that AQP4 knockout decreased the concentrations of estrogen and progestogen. Further study showed that exogenous estrogen decreased DA and 5-HT in cortex, reduced DA and 5-HT in striatum, but increased 5-HT in hippocampus in AQP4+/+ male mice. However, in AQP4-/- male mice, exogenous estrogen almost did not alter the levels of neurotransmitters except for decreasing DA in cortex. In female mice, ovariectomy decreased DA in the striatum of AQP4+/+ mice, but did not alter the levels of DA in AQP4-/- mice. These findings reveal for the first time that AQP4 regulates not only water and ion homeostasis but also the functions of ovarian hormone and neurotransmitter.

Animals↗

PubMed2006

Aquaporin-4 deficiency down-regulates glutamate uptake and GLT-1 expression in astrocytes.

The role of aquaporin-4 in water transport has been extensively investigated, while little information exists regarding its contribution to astrocytic functions such as the action to glutamatergic transmission. Since aquaporin-4 has been detected widely co-localized with glutamate transporter 1 (GLT-1) and glutamate transporters also present water transport properties, we investigated the regulative role of aquporin-4 on glutamate transporter using primary cultured astrocytes from aquaporin-4 knockout (AQP4(-/-)) mice. It was demonstrated that lack of aquaporin-4 down-regulated astrocytic expression of GLT-1 but not of glutamate/aspartate transporter (GLAST). The result from [(3)H]D,L-glutamate uptake analysis showed a lower uptake capability in AQP4(-/-) astrocytes. Furthermore, MTT and LDH assays indicated less cellular toxicity induced by excessive glutamate in AQP4(-/-) genotype. These findings provide direct evidences for the first time that aquaporin-4 plays an important role in the function of glutamate transporters. And the present study will improve our understanding of aquaporin-4-glutamanergic biology.

Animals↗

PubMed2006

An inhibitory role for FAK in regulating proliferation: a link between limited adhesion and RhoA-ROCK signaling.

Focal adhesion kinase (FAK) transduces cell adhesion to the extracellular matrix into proliferative signals. We show that FAK overexpression induced proliferation in endothelial cells, which are normally growth arrested by limited adhesion. Interestingly, displacement of FAK from adhesions by using a FAK-/- cell line or by expressing the C-terminal fragment FRNK also caused an escape of adhesion-regulated growth arrest, suggesting dual positive and negative roles for FAK in growth regulation. Expressing kinase-dead FAK-Y397F in FAK-/- cells prevented uncontrolled growth, demonstrating the antiproliferative function of inactive FAK. Unlike FAK overexpression-induced growth, loss of growth control in FAK-/- or FRNK-expressing cells increased RhoA activity, cytoskeletal tension, and focal adhesion formation. ROCK inhibition rescued adhesion-dependent growth control in these cells, and expression of constitutively active RhoA or ROCK dysregulated growth. These findings demonstrate the ability of FAK to suppress and promote growth, and underscore the importance of multiple mechanisms, even from one molecule, to control cell proliferation.

Animals↗

PubMed2006

Aquaporin-4 knockout regulated cocaine-induced behavior and neurochemical changes in mice.

Aquaporin-4 (AQP4) is the predominant water channel of brain, which mediates transmembrane water movement at the blood-brain barrier and at the brain-cerebrospinal fluid interface. It has been reported that AQP4 deletion results in an increase of amino acid and monoamine levels in some brain regions of mice, suggesting that AQP4 may participate in region-specific alterations in brain amino acid and monoamine metabolism. In the present study, we examined whether AQP4 affects neurotransmission in acute and chronic cocaine exposure mice. For this purpose, both wild-type and AQP4 knockout mice were used with locomotor activity evaluation and microdialysis methods. The results reveal that AQP4 deletion attenuated locomotor activity in acute and repeated cocaine exposure mice, and induced a decrease of extracellular dopamine and glutamate levels in the nucleus accumbens (NAc), a brain region known to be critically involved in the addictive properties of cocaine. Therefore, AQP4 may play a role in regulating extracellular cocaine-induced dopamine and glutamate release in the brain reward center, and in turn AQP4 deletion may attenuate cocaine reinforcement and dependence.

Animals↗

PubMed2006

Neuroprotection by transgenic expression of glucose-6-phosphate dehydrogenase in dopaminergic nigrostriatal neurons of mice.

Oxidative damage to dopaminergic nigrostriatal (DNS) neurons plays a central role in the pathogenesis of Parkinson's disease (PD). Glucose-6-phosphate dehydrogenase (G6PD) is a key cytoprotective enzyme that provides NADPH, the major source of the reducing equivalents of a cell. Mutations of this enzyme are the most common enzymopathies worldwide. We have studied in vivo the role of G6PD overexpressed specifically in the DNS pathway and show that the increase of G6PD activity in the soma and axon terminals of DNS neurons, separately from other neurons or glial cells, protects them from parkinsonism. Analysis of DNS neurons by histological, neurochemical, and functional methods showed that even a moderate increase of G6PD activity rendered transgenic mice more resistant than control littermates to the toxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The neuroprotective action of G6PD was also observed in aged animals despite that they had a greater susceptibility to MPTP. Therefore, overexpression of G6PD in dopaminergic neurons or pharmacological activation of the native enzyme should be considered as potential therapeutic strategies to PD.

Animals↗

PubMed2006

Comprehensive protein profiling by multiplexed capillary zone electrophoresis using cross-linked polyacrylamide coated capillaries.

We have recently developed a new process to create cross-linked polyacrylamide (CPA) coatings on capillary walls to suppress protein-wall interactions. Here, we demonstrate CPA-coated capillaries for high-efficiency (>2 x 10(6) plates per meter) protein separations by capillary zone electrophoresis (CZE). Because CPA virtually eliminates electroosmotic flow, positive and negative proteins cannot be analyzed in a single run. A "one-sample-two-separation" approach is developed to achieve a comprehensive protein analysis. High throughput is achieved through a multiplexed CZE system.

Acrylic Resins↗

PubMed2005

Sex- and region-specific alterations of basal amino acid and monoamine metabolism in the brain of aquaporin-4 knockout mice.

Aquaporin-4 (AQP4), a predominant water channel of the brain, mediates transmembrane water movement at the blood-brain barrier and brain-cerebrospinal fluid interface. A broad pattern of evidence indicates that AQP4 and regulators of its expression are potential targets for treatment of brain swelling, but whether it participates in the regulation of neurotransmission has not been reported. We examined neurochemical differences between AQP4-knockout and wild-type mice with particular focus on neurotransmission. Basal tissue neurotransmitter and metabolite levels were measured by high-performance liquid chromatography. Significant sex- and region-specific differences of amino acids and monoamines were found in the brain of wild-type and AQP4-knockout mice. In cortex, striatum, and hippocampus of male AQP4-knockout mice, an increase of glutamine and decrease of aspartate were observed. Glutamate was increased only in female AQP4-knockout mice. The lack of AQP4 failed to affect the levels of gamma-aminobutyric acid and taurine. In the medial prefrontal cortex of AQP4-knockout mice, the levels of serotonin and norepinephrine were increased, but no significant change in dopamine level was found. In the striatum of male AQP4-knockout mice, the levels of dopamine and serotonin were remarkably increased, which was not found in female mice. In the hypothalamus of AQP4-knockout mice, only the serotonin level was altered. These results provide the first evidence that the lack of AQP4 expression is accompanied by sex- and region-specific alterations in brain amino acid and monoamine metabolism.

Amino Acids, Basic↗

PubMed2005

From nanochannel-induced proton conduction enhancement to a nanochannel-based fuel cell.

The apparent proton conductivity inside a nanochannel can be enhanced by orders of magnitude due to the electric double layer overlap. A nanochannel filled with an acidic solution is thus a micro super proton conductor, and an array of such nanochannels forms an excellent proton conductive membrane. Taking advantage of this effect, a new class of proton exchange membrane is developed for micro fuel cell applications.

Electric Conductivity↗

PubMed2005

[Determination of oxidation-reduction level in patients with rheumatoid arthritis].

OBJECTIVE: To examine the oxidation or reduction products in patients with rheumatism arthritis (RA), and investigate the relationship between oxidation or reduction products and occurrence and development of RA. METHODS: The serum levels of total ascorbic acid (TAA), dehydroascorbic acid (DHAA)/TAA, vitamin E, advanced oxidation protein products (AOPP) and malondialdehyde (MDA) were detected by high-performance liquid chromatography with electrochemical detection in 83 RA patients and 30 healthy adults. Correlation analysis of AOPP, MDA and hs-CRP was performed. RESULTS: Compared with normal control group, significantly higher serum MDA, DHAA/TAA, and AOPP levels were detected in RA patients (P<0.05), but vitamin E showed no significant difference (P<0.05). Linear regression analysis showed that MDA (P<0.01) was positively but AOPP (P>0.05) negatively correlated to hs-CRP. CONCLUSIONS: Oxidation or reduction products in serum of RA patients increases significantly, which may be an important mechanism for the occurrence and development of RA. Serum AOPP and MDA levels can reflect the oxidation status in RA patients.

Adult↗

PubMed2004

Cross-linked polyacrylamide coating for capillary isoelectric focusing.

Polyacrylamide has been used for capillary wall coating for decades. The coating chemistry includes two main steps: (i) attachment of a bifunctional reagent containing a vinyl group to the silica surface and (ii) extension of the anchored vinyl groups through acrylamide polymerization. Since the introduction of this method, many modifications and improvements have been made. However, few of them are successful for routine capillary isoelectric focusing. One of the major problems is the presence of some microspots in which the silica surfaces are poorly coated. Cross-linking the polyacrylamide molecules anchored around these poorly coated spots seems to be a straightforward solution to this problem. Attempts have been made toward this direction, but cross-linked polyacrylamide coatings have not been demonstrated to be much superior over linear polyacrylamide ones. In this report, we have reexamined this approach and demonstrated that cross-linked polyacrylamide could be excellent for capillary isoelectric focusing. A simple device and a new coating protocol have been developed to produce this coating reliably and reproducibly. Compared to the commercial linear polyacrylamide and hydroxypropyl cellulose coatings for CIEF, the cross-linked polyacrylamide coating is much more stable and robust although their initial performances are comparable.

Acrylic Resins↗

PubMed2004

Isoforms of the polarity protein par6 have distinct functions.

PAR-6 is essential for asymmetric division of the Caenorhabditis elegans zygote. It is also critical for cell polarization in many other contexts throughout the Metazoa. The Par6 protein contains a PDZ domain and a partial CRIB (Cdc42/Rac interactive binding) domain, which mediate interactions with other polarity proteins such as Par3, Cdc42, Pals1, and Lgl. A family of mammalian Par6 isoforms (Par6A-D) has been described, but the significance of this diversification has been unclear. Here we demonstrate that Par6 family members localize differently when expressed in Madin-Darby canine kidney epithelial cells and have distinct effects on tight junction (TJ) assembly. Par6B localizes to the cytosol and inhibits TJ formation, but Par6A co-localizes predominantly with the TJ marker ZO-1 at cell-cell contacts and does not affect junctions. These functional differences correlate with differences in Pals1 binding; Par6B interacts strongly with Pals1, whereas Par6A binds weakly to Pals1 even in the presence of active Cdc42. Pals1 has a low affinity for the isolated CRIB-PDZ domain of Par6A, but analysis of chimeras showed that in addition Pals1 binding is blocked by an inhibitory property of the N terminus of Par6A. Unexpectedly, the localization of Par6A to cell-cell contacts is Cdc42-independent.

Amino Acid Sequence↗

PubMed2004

Induction of the glucose-6-phosphate dehydrogenase gene expression by chronic hypoxia in PC12 cells.

We studied the regulation of glucose-6-phosphate dehydrogenase (G6PD) gene expression by chronic hypoxia. G6PD mRNA level and activity were increased in PC12 cells by hypoxia in a dose- and time-dependent manner. Cobalt chloride and dimethyloxalylglycine, which can mimic hypoxia, also activated G6PD gene expression. Interestingly, hypoxia-induced G6PD expression followed a time course much slower than that of phosphoglycerate kinase 1 (PGK1), a hypoxia-inducible factor (HIF)-dependent glycolytic enzyme. Hypoxic-G6PD induction was almost negligible in non-excitable Buffalo rat liver cells, although in these cells PGK1 was strongly upregulated by low PO(2). Furthermore, G6PD but not PGK1 induction was blocked by the antioxidants glutathione and N-acetylcysteine. These results suggest the dependence of G6PD gene expression on HIF and intracellular redox status and the differential hypoxic regulation of glucose-metabolizing enzymes.

Animals↗

PubMed2004

Selective growth inhibition of tumor cells by a novel histone deacetylase inhibitor, NVP-LAQ824.

We have synthesized a histone deacetylase inhibitor, NVP-LAQ824, a cinnamic hydroxamic acid, that inhibited in vitro enzymatic activities and transcriptionally activated the p21 promoter in reporter gene assays. NVP-LAQ824 selectively inhibited growth of cancer cell lines at submicromolar levels after 48-72 h of exposure, whereas higher concentrations and longer exposure times were required to retard the growth of normal dermal human fibroblasts. Flow cytometry studies revealed that both tumor and normal cells arrested in the G(2)-M phase of the cell cycle after compound treatment. However, an increased sub-G(1) population at 48 h (reminiscent of apoptotic cells) was observed only in the cancer cell line. Annexin V staining data supported our hypothesis that NVP-LAQ824 induced apoptosis in tumor and transformed cells but not in normal cells. Western blotting experiments showed an increased histone H3 and H4 acetylation level in NVP-LAQ824-treated cancer cells, suggesting that the likely in vivo target of NVP-LAQ824 was histone deacetylase(s). Finally, NVP-LAQ824 exhibited antitumor effects in a xenograft animal model. Together, our data indicated that the activity of NVP-LAQ824 was consistent with its intended mechanism of action. This novel histone deacetylase inhibitor is currently in clinical trials as an anticancer agent.

Animals↗

PubMed2004

Leaky termination at premature stop codons antagonizes nonsense-mediated mRNA decay in S. cerevisiae.

The Nonsense-Mediated mRNA Decay (NMD) pathway mediates the rapid degradation of mRNAs that contain premature stop mutations in eukaryotic organisms. It was recently shown that mutations in three yeast genes that encode proteins involved in the NMD process, UPF1, UPF2, and UPF3, also reduce the efficiency of translation termination. In the current study, we compared the efficiency of translation termination in a upf1Delta strain and a [PSI(+)] strain using a collection of translation termination reporter constructs. The [PSI(+)] state is caused by a prion form of the polypeptide chain release factor eRF3 that limits its availability to participate in translation termination. In contrast, the mechanism by which Upf1p influences translation termination is poorly understood. The efficiency of translation termination is primarily determined by a tetranucleotide termination signal consisting of the stop codon and the first nucleotide immediately 3' of the stop codon. We found that the upf1Delta mutation, like the [PSI(+)] state, decreases the efficiency of translation termination over a broad range of tetranucleotide termination signals in a unique, context-dependent manner. These results suggest that Upf1p may associate with the termination complex prior to polypeptide chain release. We also found that the increase in readthrough observed in a [PSI(+)]/upf1Delta strain was larger than the readthrough observed in strains carrying either defect alone, indicating that the upf1Delta mutation and the [PSI(+)] state influence the termination process in distinct ways. Finally, our analysis revealed that the mRNA destabilization associated with NMD could be separated into two distinct forms that correlated with the extent the premature stop codon was suppressed. The minor component of NMD was a 25% decrease in mRNA levels observed when readthrough was >/=0.5%, while the major component was represented by a larger decrease in mRNA abundance that was observed only when readthrough was </=0.5%. This low threshold for the onset of the major component of NMD indicates that mRNA surveillance is an ongoing process that occurs throughout the lifetime of an mRNA.

Codon, Nonsense↗

PubMed2003

Structure of Cdc42 in a complex with the GTPase-binding domain of the cell polarity protein, Par6.

Cdc42 is a small GTPase that is required for cell polarity establishment in eukaryotes as diverse as budding yeast and mammals. Par6 is also implicated in metazoan cell polarity establishment and asymmetric cell divisions. Cdc42.GTP interacts with proteins that contain a conserved sequence called a CRIB motif. Uniquely, Par6 possesses a semi-CRIB motif that is not sufficient for binding to Cdc42. An adjacent PDZ domain is also necessary and is required for biological effects of Par6. Here we report the crystal structure of a complex between Cdc42 and the Par6 GTPase-binding domain. The semi-CRIB motif forms a beta-strand that inserts between the four strands of Cdc42 and the three strands of the PDZ domain to form a continuous eight-stranded sheet. Cdc42 induces a conformational change in Par6, detectable by fluorescence resonance energy transfer spectroscopy. Nuclear magnetic resonance studies indicate that the semi-CRIB motif of Par6 is at least partially structured by the PDZ domain. The structure highlights a novel role for a PDZ domain as a structural scaffold.

Amino Acid Sequence↗

PubMed2003

[The synthesis of MT in rat myocardial fibroblasts].

OBJECTIVE: To study the influence on the synthesis of metallothionein (MT) induced by lipopolysaccharide (LPS), basic fibroblast growth factor (bFGF), oxidized low-density lipoproteins (oxLDL) and ZnCl2 in rat myocardial fibroblasts. METHODS: The content of MT was measured by 109Cd-Hb saturation method and RT-PCR was used to determine the expression of MT mRNA. RESULTS: All of the stimulus in this experiment increased the synthesis of MT in myocardial fibroblasts. Compared with control, 1 and 5 mg.L-1 LPS increased the content of MT by 94% and 130% (P < 0.01), 0.2 and 1.0 mg.L-1 bFGF by 41% and 59% (P < 0.01), 2 and 10 mg.L-1 oxLDL by 23% (P < 0.05) and 41% (P < 0.01) respectively. 1,2 and 5 mg.L-1 ZnCl2 increased the content of MT by 66%, 99% and 149% (P < 0.01) in a concentration-dependent manner. 2-8 mg.L-1 ZnCl2 increased the content of MT1 mRNA by 69%-129%, MT2 mRNA by 31%-60% (P < 0.01). But 10 mg.L-1 ZnCl2 didn't stimulate the synthesis of MT more significantly, probably because ZnCl2 of high concentration damaged myocardial fibroblasts and decreased the survival rate of the cells. CONCLUSION: Many stimulus such as LPS, bFGF, oxLDL and ZnCl2 can induce the synthesis of MT, and ZnCl2 can increase the expression of MT mRNA in rat myocardial fibroblasts.

Animals↗

PubMed2003

Inhibition of taurine transport by high concentration of glucose in cultured rat cardiomyocytes.

Cultured rat cardiomyocytes were treated with 10, 20, and 30 mmol/L glucose and 30 mmol/L glucose plus protein kinase C (PKC) inhibitor, Chelerythrine. In the 20 and 30 mmol/L glucose-treated cells, taurine contents reduced by 15% and 27% (P<.05), respectively, taurine transporter (TAUT) mRNA levels reduced by 47% and 64% (P<.05), respectively, and cysteine sulfinate decarboxylase (CSD) mRNA reduced slightly, but not significantly. Time-dependent taurine uptakes reduced in the 10, 20, and 30 mmol/L glucose-treated cells, and time-dependent taurine release reduced in the 30 mmol/L glucose-treated cells. The Vmax of taurine transport decreased by 18%, 30%, and 35% (P<.05) in the 10, 20, and 30 mmol/L glucose-treated cells, respectively, while Km of taurine transport remained unchanged. When PKC inhibitor, Chelerythrine, combined with 30 mmol/L glucose was treated with the cells, the lowered taurine content, taurine uptake, taurine release, and Vmax of taurine transport caused by 30 mmol/L glucose were eliminated. These results demonstrate that high glucose considerably and specifically decreases intracellular taurine content, taurine transport activity, and TAUT mRNA, possibly through PKC-mediated transcriptional and posttranslational pathways.

Alkaloids↗

PubMed2003

Direct interaction of two polarity complexes implicated in epithelial tight junction assembly.

Tight junctions help establish polarity in mammalian epithelia by forming a physical barrier that separates apical and basolateral membranes. Two evolutionarily conserved multi-protein complexes, Crumbs (Crb)-PALS1 (Stardust)-PATJ (DiscsLost) and Cdc42-Par6-Par3-atypical protein kinase C (aPKC), have been implicated in the assembly of tight junctions and in polarization of Drosophila melanogaster epithelia. Here we identify a biochemical and functional link between these two complexes that is mediated by Par6 and PALS1 (proteins associated with Lin7). The interaction between Par6 and PALS1 is direct, requires the amino terminus of PALS1 and the PDZ domain of Par6, and is regulated by Cdc42-GTP. The transmembrane protein Crb can recruit wild-type Par6, but not Par6 with a mutated PDZ domain, to the cell surface. Expression of dominant-negative PALS1-associated tight junction protein (PATJ) in MDCK cells results in mis-localization of PALS1, members of the Par3-Par6-aPKC complex and the tight junction marker, ZO-1. Similarly, overexpression of Par6 in MDCK cells inhibits localization of PALS1 to the tight junction. Our data highlight a previously unrecognized link between protein complexes that are essential for epithelial polarity and formation of tight junctions.

Animals↗