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Biomedical subjects

Lin Liu

Publications and source records attributed to Lin Liu.

At least 37 records · Page 2Linked to original sources

A novel function of ionotropic gamma-aminobutyric acid receptors involving alveolar fluid homeostasis.

Polarized distribution of chloride channels on the plasma membrane of epithelial cells is required for fluid transport across the epithelium of fluid-transporting organs. Ionotropic gamma-aminobutyric acid receptors are primary ligand-gated chloride channels that mediate inhibitory neurotransmission. Traditionally, these receptors are not considered to be contributors to fluid transport. Here, we report a novel function of gamma-aminobutyric acid receptors involving alveolar fluid homeostasis in adult lungs. We demonstrated the expression of functional ionotropic gamma-aminobutyric acid receptors on the apical plasma membrane of alveolar epithelial type II cells. gamma-Aminobutyric acid significantly increased chloride efflux in the isolated type II cells and inhibited apical to basolateral chloride transport on type II cell monolayers. Reduction of the gamma-aminobutyric acid receptor pi subunit using RNA interference abolished the gamma-aminobutyric acid-mediated chloride transport. In intact rat lungs, gamma-aminobutyric acid inhibited both basal and beta agonist-stimulated alveolar fluid clearance. Thus, we provide molecular and pharmacological evidence that ionotropic gamma-aminobutyric acid receptors contribute to fluid transport in the lung via luminal secretion of chloride. This finding may have the potential to develop clinical approaches for pulmonary diseases involving abnormal fluid dynamics.

Adenoviridae↗

Phage display affords peptides that modulate beta-amyloid aggregation.

As the population ages, the need to develop methods to understand and intercept the processes responsible for protein aggregation diseases is becoming more urgent. The aggregation of the protein beta-amyloid (Abeta) has been implicated in Alzheimer's Disease (AD); however, whether the toxic species is a large, insoluble aggregate or some lower order form is not yet known. Agents that can modulate the aggregation state of Abeta could resolve this controversy by facilitating our understanding of the consequences of aggregation and its underlying mechanism. To date, however, ligands that bind to specific forms of Abeta have not been identified. To address this deficiency, we tested whether phage display could yield such ligands by screening libraries against Abeta in two different states: monomeric or highly aggregated. Intriguingly, the peptides selected had different effects on Abeta aggregation. Peptides selected for binding to monomeric Abeta did not perturb aggregation, but those selected using highly aggregated Abeta increase the rate of aggregation drastically. The latter also alter the morphology of the resulting aggregate. The ability of a peptide to promote aggregation correlated with its affinity for the N-terminal 10 residues of Abeta. This result indicates that the mechanism by which the peptides influence aggregation is related to their affinity for the Abeta N-terminus. Thus, the identification of compounds that bind to this Abeta section can afford agents that affect aggregation. Moreover, the data suggest that endogenous ligands that interact with the N-terminal region can influence the propensity of Abeta to form aggregates and the morphology of those that form. Our data highlight the utility of phage display for identifying ligands that bind to target proteins in different states, and they indicate that such agents can be used to perturb protein aggregation.

Amino Acid Sequence↗

Gene expression profiling identifies regulatory pathways involved in the late stage of rat fetal lung development.

Fetal lung development is a complex biological process that involves temporal and spatial regulations of many genes. To understand the molecular mechanisms of this process, we investigated gene expression profiles of fetal lungs on gestational days 18, 19, 20, and 21, as well as newborn and adult rat lungs. For this analysis, we used an in-house rat DNA microarray containing 6,000 known genes and 4,000 expressed sequence tags (ESTs). Of these, 1,512 genes passed the statistical significance analysis of microarray (SAM) test; an at least twofold change was shown for 583 genes (402 known genes and 181 ESTs) between at least two time points. K-means cluster analysis revealed seven major expression patterns. In one of the clusters, gene expression increased from day 18 to day 20 and then decreased. In this cluster, which contained 10 known genes and 5 ESTs, 8 genes are associated with development. These genes can be integrated into regulatory pathways, including growth factors, plasma membrane receptors, adhesion molecules, intracellular signaling molecules, and transcription factors. Real-time PCR analysis of these 10 genes showed an 88% consistency with the microarray data. The mRNA of LIM homeodomain protein 3a (Lhx3), a transcription factor, was enriched in fetal type II cells. In contrast, pleiotrophin, a growth factor, had a much higher expression in fetal lung tissues than in fetal type II cells. Immunohistochemistry revealed that Lhx3 was localized in fetal lung epithelial cells and pleiotrophin in the mesenchymal cells adjacent to the developing epithelium and blood vessel. Using GenMAPP, we identified four regulatory pathways: transforming growth factor-beta signaling, inflammatory response, cell cycle, and G protein signaling. We also identified two metabolic pathways: glycolysis-gluconeogenesis and proteasome degradation. Our results may provide new insights into the complex regulatory pathways that control fetal lung development.

Animals↗

Determinants of CD4+ T cell recovery during suppressive antiretroviral therapy: association of immune activation, T cell maturation markers, and cellular HIV-1 DNA.

BACKGROUND: Suboptimal CD4+ T cell recovery during antiretroviral therapy (ART) is a common clinical dilemma. METHODS: We analyzed viral and immunologic predictors of CD4+ T cell recovery in 116 human immunodeficiency virus type 1 (HIV-1)-infected subjects who had suppressed viremia (< or = 50 copies/mL) while receiving ART. Successive measurements of T cell immunophenotypes and cellular HIV-1 DNA levels were obtained before and during receipt of ART. On the basis of increases in the CD4+ T cell count, subjects were classified as immunologically concordant (demonstrating an increase of > or = 100 CD4+ T cells/mm3) or discordant (demonstrating an increase of <100 CD4+ T cells/mm3) after 48 weeks of ART. RESULTS: In adjusted analyses, CD4+ and CD8+ T cell activation at baseline was negatively associated with immunologic concordance at week 48 of ART (odds ratio [OR], 0.80 [P = .04] and 0.67 [P = .02], respectively). High memory (CDRA(-)CD62L-) CD8+ T cell counts at baseline (OR, 0.33 [P = .05]) predicted less CD4+ T cell recovery, whereas increased naive CD4+ T cell counts were associated with higher increases in CD4+ T cells (OR, 1.19 [P = .052]). Neither the cell-associated HIV-1 DNA level at baseline (P = .32) nor the cell-associated HIV-1 DNA level at week 48 of ART (P = .42) was associated with immunologic concordance during ART. CONCLUSIONS: These results support the potential clinical usefulness of the baseline determination of immune activation and maturation subsets in the prediction of CD4+ T cell recovery during viral suppression. Furthermore, identification of individuals with reduced potential for CD4+ T cell recovery during ART may provide a rationale for the initiation of early therapy for some patients.

Adult↗

Alveolar type I cells protect rat lung epithelium from oxidative injury.

The lung alveolar surface is covered by two morphologically and functionally distinct cells: alveolar epithelial cell types I and II (AEC I and II). The functions of AEC II, including surfactant release, cell differentiation and ion transport, have been extensively studied. However, relatively little is known regarding the physiological functions of AEC I. Global gene expression profiling of freshly isolated AEC I and II revealed that many genes were differentially expressed in AEC I. These genes have a diversity of functions, including cell defence. Nine out of 10 selected genes were verified by quantitative real-time PCR. Two genes, apolipoprotein E (Apo E) and transferrin, were further characterized and functionally studied. Immunohistochemistry indicated that both proteins were specifically localized in AEC I. Up-regulation of Apo E and transferrin was observed in hyperoxic lungs. Functionally, Apo E and transferrin play a protective role against oxidative stress in an animal model. Our studies suggest that AEC I is not just a simple barrier for gas exchange, but a functional cell that protects alveolar epithelium from injury.

Animals↗

Expression profile of IGF system during lung injury and recovery in rats exposed to hyperoxia: a possible role of IGF-1 in alveolar epithelial cell proliferation and differentiation.

Although several studies have shown that an induction of insulin-like growth factor (IGF) components occurs during hyperoxia-mediated lung injury, the role of these components in tissue repair is not well known. The present study aimed to elucidate the role of IGF system components in normal tissue remodeling. We used a rat model of lung injury and remodeling by exposing rats to > 95% oxygen for 48 h and allowing them to recover in room air for up to 7 days. The mRNA expression of IGF-I, IGF-II, and IGF-1 receptor (IGF-1R) increased during injury. However, the protein levels of these components remained elevated until day 3 of the recovery and were highly abundant in alveolar type II cells. Among IGF binding proteins (IGFBPs), IGFBP-5 mRNA expression increased during injury and at all the recovery time points. IGFBP-2 and -3 mRNA were also elevated during injury phase. In an in vitro model of cell differentiation, the expression of IGF-I and IGF-II increased during trans-differentiation of alveolar epithelial type II cells into type-I like cells. The addition of anti-IGF-1R and anti-IGF-I antibodies inhibited the cell proliferation and trans-differentiation to some extent, as evident by cell morphology and the expression of type I and type II cell markers. These findings demonstrate that the IGF signaling pathway plays a critical role in proliferation and differentiation of alveolar epithelium during tissue remodeling.

Animals↗

Identification of contrastive and comparable school neighborhoods for childhood obesity and physical activity research.

UNLABELLED: The neighborhood social and physical environments are considered significant factors contributing to children's inactive lifestyles, poor eating habits, and high levels of childhood obesity. Understanding of neighborhood environmental profiles is needed to facilitate community-based research and the development and implementation of community prevention and intervention programs. We sought to identify contrastive and comparable districts for childhood obesity and physical activity research studies. We have applied GIS technology to manipulate multiple data sources to generate objective and quantitative measures of school neighborhood-level characteristics for school-based studies. GIS technology integrated data from multiple sources (land use, traffic, crime, and census tract) and available social and built environment indicators theorized to be associated with childhood obesity and physical activity. We used network analysis and geoprocessing tools within a GIS environment to integrate these data and to generate objective social and physical environment measures for school districts. We applied hierarchical cluster analysis to categorize school district groups according to their neighborhood characteristics. We tested the utility of the area characterizations by using them to select comparable and contrastive schools for two specific studies. RESULTS: We generated school neighborhood-level social and built environment indicators for all 412 Chicago public elementary school districts. The combination of GIS and cluster analysis allowed us to identify eight school neighborhoods that were contrastive and comparable on parameters of interest (land use and safety) for a childhood obesity and physical activity study. CONCLUSION: The combination of GIS and cluster analysis makes it possible to objectively characterize urban neighborhoods and to select comparable and/or contrasting neighborhoods for community-based health studies.

Adolescent↗

Identification of rat lung--prominent genes by a parallel DNA microarray hybridization.

BACKGROUND: The comparison of organ transcriptomes is an important strategy for understanding gene functions. In the present study, we attempted to identify lung-prominent genes by comparing the normal transcriptomes of rat lung, heart, kidney, liver, spleen, and brain. To increase the efficiency and reproducibility, we first developed a novel parallel hybridization system, in which 6 samples could be hybridized onto a single slide at the same time. RESULTS: We identified the genes prominently expressed in the lung (147) or co-expressed in lung-heart (23), lung-liver (37), lung-spleen (203), and lung-kidney (98). The known functions of the lung-prominent genes mainly fell into 5 categories: ligand binding, signal transducer, cell communication, development, and metabolism. Real-time PCR confirmed 13 lung-prominent genes, including 5 genes that have not been investigated in the lung, vitamin D-dependent calcium binding protein (Calb3), mitogen activated protein kinase 13 (Mapk13), solute carrier family 29 transporters, member 1 (Slc29a1), corticotropin releasing hormone receptor (Crhr1), and lipocalin 2 (Lcn2). CONCLUSION: The lung-prominent genes identified in this study may provide an important clue for further investigation of pulmonary functions.

Animals↗

qPCR-DAMS: a database tool to analyze, manage, and store both relative and absolute quantitative real-time PCR data.

Quantitative real-time PCR is an important high-throughput method in the biomedical sciences. However, existing software has limitations in handling both relative and absolute quantification. We designed quantitative PCR data analysis and management system (qPCR-DAMS), a database tool based on Access 2003, to deal with such shortcomings by the addition of integrated mathematical procedures. qPCR-DAMS allows a user to choose among four methods for data processing within a single software package: 1) ratio relative quantification, 2) absolute level, 3) normalized absolute expression, and 4) ratio absolute quantification. qPCR-DAMS also provides a tool for multiple reference gene normalization. qPCR-DAMS has three quality control steps and a data display system to monitor data variation. In summary, qPCR-DAMS is a handy tool for real-time PCR users.

Database Management Systems↗

Human umbilical cord blood-derived stromal cell, a new resource of feeder layer to expand human umbilical cord blood CD34+ cells in vitro.

Allogeneic transplantation with human umbilical cord blood (hUCB) in adult recipients is mainly limited by a low CD34+ cell dose. To break the limit, hUCB as a novel source of hUCB-derived stromal cells was incorporated in an attempt to expand CD34+ cells from hUCB in vitro. Cord blood CD34 cells were separated by MACS system. HUCB-derived stromal cells were cultured by the Dexter system and characterized by morphologic, immunophenotypical, and functional analysis. We studied the effects of hUCB-derived stromal cells, cytokines, and hUCB-derived stromal cells combined with cytokines on expansion of hUCB CD34 cells. The CD34+ cells were assessed for the degree of expansion and the number of colony-forming units in semisolid culture. Our research found that hUCB-derived stromal cells were mainly composed of three kinds of cell components, with CD106, CD29, CD44, CD45, CD50, CD68, CD31, Fn, Lm, and collagen IV positive, but CD34 negative immunophenotype. Functionally, it was discovered by cell cycle and growth curve analyses that the capability of colony and parietal layer formation of hUCB-derived stromal cells was poorer than that of BM stromal cells, and the doubling time of hUCB-derived stromal cells was longer than that of BM stromal cells. It was indicated by ELISA and RT-PCR that hUCB-derived stromal cells express higher level of TPO and less GM-CSF and SCF than BM stromal cell. Adherent layer of hUCB-derived stromal cells alone or combining with cytokines, increased CD34+ cell expansion. In vitro formation of CFUs by expanded CCD34 cells was significantly higher than that of unexpanded CD34+ cells (P < 0.05). When cocultured with hUCB-derived stromal cells in the presence of cytokines, cell growth was significantly enhanced: CD34 cells by 8.02 +/- 0.96-fold, CFU-GM by 217.60 +/- 6.72-fold, CFU-E by 1940.80 +/- 52.78-fold, and CFU-Mg by 142.60 +/- 4.39-fold. HUCB-derived stromal cells have significant superiority on the expansion of CFU-Mg (P < 0.05). The results indicate that human umbilical cord blood-derived stromal cells may be a suitable feeder layer for expansion of hematopoietic progenitors from hUCB in vitro.

Antigens, CD34↗

Involvement of caspase-3 pathway in anti-apoptotic action of methionine enkephalin on CEM x 174 cells in prolonged infection with simian immunodeficiency virus in vitro.

The roles of methionine enkephalin, as an immunomodulator, on immunodeficiency virus-induced apoptosis of lymphocytes during prolonged infection are still unclear. In the present study, we evaluated the effects of methionine enkephalin on the viability, the profile of cell cycle and apoptosis, as well as the expression of apoptosis-related genes in CEM x 174 cells infected with simian immunodeficiency virus for 72 h. Our data demonstrated that methionine enkephalin maintains the viability of cells during the period of prolonged infection. Following co-incubation with the virus, CEM x 174 cells were arrested at S phase, with increased mortality as a result of apoptosis. Methionine enkephalin could abolish virus-induced over-expression of caspase-3. Taken together all findings, we conclude that methionine enkephalin may maintain the viability of SIV-infected cells via suppressing the expression of caspase-3, which may have clinical implications in opioid peptide therapy for AIDS.

Apoptosis↗

Effect of cholesterol depletion on exocytosis of alveolar type II cells.

Alveolar epithelial type II cells secrete lung surfactant via exocytosis. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNARE) are implicated in this process. Lipid rafts, the cholesterol- and sphingolipid-rich microdomains, may offer a platform for protein organization on the cell membrane. We tested the hypothesis that lipid rafts organize exocytotic proteins in type II cells and are essential for the fusion of lamellar bodies, the secretory granules of type II cells, with the plasma membrane. The lipid rafts, isolated from type II cells using 1% Triton X-100 and a sucrose gradient centrifugation, contained the lipid raft markers, flotillin-1 and -2, whereas they excluded the nonraft marker, Na+-K+ ATPase. SNAP-23, syntaxin 2, and VAMP-2 were enriched in lipid rafts. When type II cells were depleted of cholesterol, the association of SNAREs with the lipid rafts was disrupted and the formation of fusion pore was inhibited. Furthermore, the cholesterol-depleted plasma membrane had less ability to fuse with lamellar bodies, a process mediated by annexin A2. The secretagogue-stimulated secretion of lung surfactant from type II cells was also reduced by methyl-beta-cyclodextrin. When the raft-associated cell surface protein, CD44, was cross-linked using anti-CD44 antibodies, the CD44 clusters were observed. Syntaxin 2, SNAP-23, and annexin A2 co-localized with the CD44 clusters, which were cholesterol dependent. Our results suggested that lipid rafts may form a functional platform for surfactant secretion in alveolar type II cells, and raft integrity was essential for the fusion between lamellar bodies with the plasma membrane.

Animals↗

Effects of oocyte activation and sperm preparation on the development of porcine embryos derived from in vitro-matured oocytes and intracytoplasmic sperm injection.

The objective was to determine the effects of various methods of oocyte activation and sperm pretreatment on development of porcine embryos derived from in vitro-matured oocytes and intracytoplasmic sperm injection (ICSI). The second polar body was extruded in the majority (>78.4%) of in vitro-matured (IVM) oocytes 4h after electrical pulse activation. In embryos generated by ICSI and sham-ICSI, a combination of an electrical pulse, with various chemical activators 4 h later, improved (P < 0.05) blastocyst formation rate compared to activation only with a pulse. Treatment with 6-dimethylaminopurine (DMAP) after electrical activation significantly increased the oocyte activation rate. The effects of exposure of sperm to repeated freeze-thaw cycles (without cryoprotectant) on oocyte activation and the effects of sperm pre-incubated with dithiothreitol (DTT) or Triton X-100 on early embryo development were also examined. Blastocyst formation rates after ICSI did not differ between motile sperm and those rendered immotile by one-time freezing and thawing without cryoprotectant. However, sperm rendered immotile by three cycles of freezing/thawing without cryoprotectant had a significantly lower blastocyst formation rate. Although oocytes injected with sperm pre-incubated with Triton X-100 had a higher normal fertilization rate than those pre-incubated with DTT or one-time frozen/thawed sperm, rates of blastocyst formation and cell numbers were similar among the three groups. In conclusion, various methods of oocyte activation and sperm preparation significantly affected the developmental capacity of early porcine embryos derived from IVM and ICSI.

Animals↗

Arsenite induces aberrations in meiosis that can be prevented by coadministration of N-acetylcysteine in mice.

OBJECTIVE: To evaluate in vitro effects of arsenite and of arsenite plus N-acetylcysteine on mouse oocyte meiosis. DESIGN: Morphological study using mouse oocytes submitted to in vitro maturation (IVM). SETTING: Laboratory of reproductive biology. ANIMAL(S): Six-week-old CD-1 mice superovulated with pregnant mare serum gonadotropin. INTERVENTION(S): During IVM, mouse oocytes were exposed to arsenite alone or to arsenite plus N-acetylcysteine. MAIN OUTCOME MEASURE(S): Meiotic anomalies were assessed using immunofluorescence microscopy and PolScope (Cambridge Research and Instrumentation, Boston, MA) imaging. RESULT(S): In vitro arsenite administration produced dose-dependent and time-dependent meiotic anomalies, characterized by spindle disruption or chromosome misalignment. After 12-14 hours of IVM, exposure to 2 microg/mL of arsenite for 12-14 hours or to 8 microg/mL of arsenite for 2 hours arrested oocyte maturation at the germinal vesicle or germinal-vesicle breakdown stage. Exposure to 4 microg/mL of arsenite for 2 hours arrested oocyte maturation at metaphase I stage in 95% of exposed oocytes (80% exhibiting abnormalities) after 12-14 hours in IVM. After 12-14 hours in IVM, of the oocytes exposed to 2 microg/mL of arsenite for 2 hours, only 15% reached the meiosis II stage (5% exhibiting abnormalities). After 15-17 hours in IVM, however, of the oocytes exposed to 2 microg/mL of arsenite for 2 hours, 65.2% reached the meiosis II stage (43.5% exhibiting abnormalities). Co-administration of N-acetylcysteine prevented the arsenite-induced meiotic abnormalities and the delayed IVM. CONCLUSION(S): In vitro arsenite exposure caused meiotic abnormalities that were prevented by co-administration of N-acetylcysteine, suggesting that arsenite-induced meiotic aberrations are mediated by reactive oxygen species.

Acetylcysteine↗

The telomere theory of reproductive senescence in women.

PURPOSE OF REVIEW: A unifying theory of reproductive aging, based on telomere shortening, is proposed. RECENT FINDINGS: Telomere shortening may mediate both 'hits' involved in reproductive aging, that is late exit from the fetal production line and long interval to ovulation in the adult. SUMMARY: As women age egg dysfunction increases, with meiotic nondisjunction, embryonic arrest, apoptosis, and miscarriage. Egg dysfunction results from two 'hits' - reduced formation of chiasmata during fetal oogenesis, and accumulation of reactive oxygen damage during the prolonged interval until ovulation. Late exit from a production line during oogenesis presumably contributes to the first hit. The later insult also involves meiotic spindle abnormalities. Telomeres, repetitive sequences of DNA, cap chromosome ends and dissipate during divisions. Oocytes do not divide, but oogonia do, and telomerase, the enzyme responsible for maintaining telomere length, is inefficient, and remains inactive in oocytes and embryos until blastocyst stage. Reactive oxygen also shortens telomeres, so the prolonged interval between birth and ovulation would further shorten telomeres from chronic exposure to reactive oxygen. In support of this theory, experimental shortening of telomeres in mice produced a phenotype similar to reproductive aging in women, with abnormal chiasmata, spindles, cell cycles, apoptosis, and genomic instability, and telomere length in human eggs correlated with in-vitro fertilization outcome.

Cellular Senescence↗

Expression of basic fibroblast growth factor results in the decrease of myostatin mRNA in murine C2C12 myoblasts.

During the development and regeneration of skeletal muscle, many growth factors, such as basic fibroblast growth factor (bFGF, FGF-2) and myostatin, have been shown to play regulating roles. bFGF contributes to promote proliferation and to inhibit differentiation of skeletal muscle, whereas myostatin plays a series of contrasting roles. In order to elucidate whether the expression of bFGF has any relationship with the expression of myostatin in skeletal muscle cells, we constructed a eukaryotic expression vector for the expression of exogenous bFGF in murine C2C12 myoblasts. Quantitative RT-PCR assays indicated that with the increase of the expression of exogenous bFGF gene, the expression of endogenous myostatin gene was suppressed at mRNA level and protein level.

Animals↗

Overexpressed heat shock protein 70 protects cells against DNA damage caused by ultraviolet C in a dose-dependent manner.

Heat shock protein 70 (Hsp70) comprises proteins that have been reported to protect cells, tissues, and organisms against damage from a wide variety of stressful stimuli; however, little is known about whether Hsp70 protects against DNA damage. In this study, we investigated the relationship between Hsp70 expression and the levels of ultraviolet C (UVC)-induced DNA damage in A549 cells with normal, inhibited, and overexpressed Hsp70 levels. Hsp70 expression was inhibited by treatment with quercetin or overexpressed by transfection of plasmids harboring the hsp70 gene. The level of DNA damage was assessed by the comet assay. The results showed that the levels of DNA damage (shown as the percentage of comet cells) in A549 cells increased in all cells after exposure to an incident dose of 0, 10, 20, 40, and 80 J/m2 whether Hsp70 was inhibited or overexpressed. This response was dose dependent: a protection against UVC-induced DNA damage in cells with overexpressed Hsp70 was observed at UVC dose 20 J/m2 with a maximum at 40 J/m2 when compared with cells with normal Hsp70 levels and in quercetin-treated cells. This differential protection disappeared at 80 J/m2. These results suggest that overexpressed Hsp70 might play a role in protecting A549 cells from DNA damage caused by UVC irradiation, with a threshold of protection from at UVC irradiation-induced DNA damage by Hsp70. The detailed mechanism how Hsp70 is involved in DNA damage and possible DNA repair warrants further investigation.

Cell Line, Tumor↗