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F C Liu

Publications and source records attributed to F C Liu.

At least 19 recordsLinked to original sources
PubMed1998

Region-dependent dynamics of cAMP response element-binding protein phosphorylation in the basal ganglia.

The cAMP response element-binding protein (CREB) is an activity-dependent transcription factor that is involved in neural plasticity. The kinetics of CREB phosphorylation have been suggested to be important for gene activation, with sustained phosphorylation being associated with downstream gene expression. If so, the duration of CREB phosphorylation might serve as an indicator for time-sensitive plastic changes in neurons. To screen for regions potentially involved in dopamine-mediated plasticity in the basal ganglia, we used organotypic slice cultures to study the patterns of dopamine- and calcium-mediated CREB phosphorylation in the major subdivisions of the striatum. Different durations of CREB phosphorylation were evoked in the dorsal and ventral striatum by activation of dopamine D1-class receptors. The same D1 stimulus elicited (i) transient phosphorylation (</=15 min) in the matrix of the dorsal striatum; (ii) sustained phosphorylation (</=2 hr) in limbic-related structures including striosomes, the nucleus accumbens, the fundus striati, and the bed nucleus of the stria terminalis; and (iii) prolonged phosphorylation (up to 4 hr or more) in cellular islands in the olfactory tubercle. Elevation of Ca2+ influx by stimulation of L-type Ca2+ channels, NMDA, or KCl induced strong CREB phosphorylation in the dorsal striatum but not in the olfactory tubercle. These findings differentiate the response of CREB to dopamine and calcium signals in different striatal regions and suggest that dopamine-mediated CREB phosphorylation is persistent in limbic-related regions of the neonatal basal ganglia. The downstream effects activated by persistent CREB phosphorylation may include time-sensitive neuroplasticity modulated by dopamine.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1997

Hypertonic saline activates protein tyrosine kinases and mitogen-activated protein kinase p38 in T-cells.

OBJECTIVES: In previous in vitro studies, we have found that hypertonic saline (HTS) can augment T-cell proliferation and restore the function of suppressed T-cells. Our animal models have shown that HTS resuscitation reverses immunosuppression after hemorrhage and reduces mortality from sepsis. In the present study, we investigated if and how HTS may influence T-cell signaling and function on a subcellular level. DESIGN: Human peripheral blood mononuclear cells (PBMC) were used to determine the effect of HTS on T-cell interleukin 2 (IL-2) production and proliferation. Human Jurkat T-cells were used to study the effects of HTS on T-cell signal transduction, IL-2 mRNA transcription, and IL-2 expression. MATERIAL AND METHODS: The effect of HTS on T-cell proliferation and IL-2 production was measured with PBMC and Jurkat T-cells. IL-2 mRNA transcription in HTS-treated Jurkat cells was measured by reverse transcriptase polymerase chain reaction. HTS-induced protein tyrosine phosphorylation in Jurkat T-cells was determined by immunoblotting with anti-phosphotyrosine antibodies. Expression in Jurkat cells of the mitogen-activated protein kinase p38 (MAPK p38), a signal transduction protein that is activated by osmotic stress, was determined by immunoblotting with anti-MAPK p38 antibodies. HTS-induced MAPK p38 activation in Jurkat cells was measured with an immune-complex kinase assay using ATF-2 as a substrate. MEASUREMENTS AND MAIN RESULTS: Proliferation of activated human PBMC increased significantly upon addition of HTS to the culture medium. This effect of HTS was paralleled by enhanced IL-2 production of activated PBMC and Jurkat cells and IL-2 mRNA transcription of Jurkat cells. HTS exposure of Jurkat cells caused tyrosine phosphorylation of a number of cellular proteins. We found that Jurkat T-cells expressed MAPK p38 and that it was activated in the presence of HTS. All these effects of HTS on T-cell signaling and function were observed at NaCl concentrations that were within physiologically relevant levels (20-100 mmol/L hypertonicity). CONCLUSIONS: In T-cells, HTS triggers a signaling pathway that includes increased tyrosine phosphorylation of several cellular proteins and activation of MAPK p38. HTS alone does not result in IL-2 mRNA transcription, IL-2 expression, or T-cell proliferation. However, in combination with other stimuli, HTS augments T-cell IL-2 expression and proliferation. We speculate that HTS could "resuscitate" suppressed T-cells in trauma patients by circumvention of, or substituting for, blocked signaling pathways.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1997

Hypertonic saline resuscitation: a tool to modulate immune function in trauma patients?

Hypertonic saline (HS) resuscitation has recently gained attention from trauma physicians because it may benefit the immune system of trauma patients. We have found that HS augments in vitro and in vivo immune function of healthy T-cells. In addition, HS restored the function of suppressed T-cells in vitro and in vivo and reduced immunosuppression after hemorrhage, protecting mice from subsequent sepsis. These effects of HS are based on its direct influence on cellular signaling events through specific signaling pathway(s) that include protein tyrosine kinase and mitogen-activated protein kinase p38 activation. HS provides a costimulatory signal that enhances the proliferation of activated T-cells. HS may be able to substitute signals lost through blockage as a result of trauma induced suppressive factors, thereby restoring the function of suppressed T-cells. Although further work is needed to determine the optimal conditions and possible risks of HS resuscitation, the data presented in this short review of our recent work shed a favorable light on HS as a simple but effective tool to modulate cellular immune function after trauma.

Adjuvants, Immunologic↗
PubMed1996

Hypertonic saline resuscitation restores hemorrhage-induced immunosuppression by decreasing prostaglandin E2 and interleukin-4 production.

It was previously shown that hypertonic saline (HTS) enhances in vivo and in vitro cellular immune function of normal mice and reverses in vitro prostaglandin E2 (PGE2)-induced immunosuppression of normal peripheral blood mononuclear cells. Hemorrhage induces immunosuppression despite adequate isotonic fluid resuscitation. The effects of HTS resuscitation on immunosuppression following hemorrhage were studied. A mouse model of hemorrhagic shock was used. Bleeding was performed through a catheter placed in the femoral artery. Phytohemagglutinin-induced splenocyte proliferation and interleukin (IL)-1, IL-2,IL-4, IL-6, IL-10, transforming growth factor beta, and PGE2 plasma levels were measured 2 and 24 hr following hemorrhage and resuscitation with lactated Ringer's and HTS. In vivo cellular immune function was measured using a contact hypersensitivity test. Suppression of splenocyte proliferation (40%) 24 hr following hemorrhage occurred after lactated Ringer's resuscitation. HTS prevented immunosuppression. In vivo cell-mediated immune function 24 hr after hemorrhage was improved by HTS. HTS-resuscitated animals showed significantly lower levels of IL-4 and PGE2, and slightly elevated levels of proinflammatory cytokines (IL-1, IL-2, and IL-6). HTS reverses hemorrhage-induced T-cell suppression by reducing the production and/or release of IL-4 and PGE2.

Animals↗
PubMed1996

Spatiotemporal dynamics of CREB phosphorylation: transient versus sustained phosphorylation in the developing striatum.

The cAMP response element-binding protein (CREB) is a plasticity-associated transcription factor that can potentially integrate cAMP and calcium signals at the gene activation level. We tested for convergent Ser-133 phosphorylation of CREB via dopamine D1/D5 receptors and L-type calcium channels in organotypic cultures of neonatal striatum. We found such convergence only transiently. Sustained CREB phosphorylation by D1/D5 receptor and L-type channel agonists was targeted to opposite (striosome and matrix) cellular phenotypes. Subsequent expression of the CRE-containing gene, c-fos, matched the divergent patterns of sustained CREB phosphorylation, and both divergent patterns could be switched by inhibition of phosphatases, including calcineurin. Control of the duration of CREB phosphorylation may be a critical regulator of CRE-mediated gene expression by dopamine and calcium.

Animals↗
PubMed1996

Immunosuppression after endotoxin shock: the result of multiple anti-inflammatory factors.

OBJECTIVES: Endotoxin induced suppression of cellular immune function is thought to contribute to septic complications in trauma patients. A rabbit model of endotoxemia was used to determine the relative roles of the anti-inflammatory factors interleukin-4 (IL-4), interleukin-10 (IL-10), transforming growth factor beta1 (TGFbeta1), and prostaglandin E2 (PGE2) in addition to other factors, in inducing immunosuppression. DESIGN: T-cell suppressive factors (TSF) in serum ultrafiltrates were separated and tested for the presence of the known suppressive factors PGE2, IL-4, IL-10, and TGFbeta1. MATERIAL AND METHODS: New Zealand rabbits were injected with 50 microg/kg of purified Escherichia coli lipopolysaccharide. Animals were exsanguinated after 48 hours and serum was separated by ultrafiltration (cutoff 50 kd), TSK HW-40 size exclusion chromatography, and Q-Sepharose anion exchange chromatography. TSF activities of chromatographic fractions and serum samples were measured with a mitogen induced in vitro T-cell proliferation assay. Levels of PGE2, IL-4, IL-10, and TGFbeta1 were measured with enzyme immunoassays. MEASUREMENTS AND MAIN RESULTS: Serum TSF activity, and levels of PGE2, IL-4, IL-10, and TGFbeta1 were increased after endotoxemia. Size exclusion chromatography revealed three major fractions (TSF1-3) with up to 600 times more TSF activity compared with controls. IL-4 and IL-10 were found in TSF1 and TSF3. Further separation of TSF1 by anion exchange chromatography revealed a total of eight different T-cell suppressive factors. TGFbeta1 probably remained in the retentate after ultrafiltration, while PGE2 eluted at a higher retention time. The known anti-inflammatory factors TGFbeta1, IL-10, IL-4, and PGE2 only accounted for 13% of the total serum TSF activity of 614 U/mL. CONCLUSIONS: Lipopolysaccharide shock results in the release of multiple T-cell suppressive factors in addition to known immunosuppressive factors, all of which contribute to the anti-inflammatory response.

Animals↗
PubMed1995

Tumor necrosis factor antibody treatment of septic baboons reduces the production of sustained T-cell suppressive factors.

Post-traumatic septic complications result from impaired cell-mediated immune function, which is caused in part by circulating T-cell suppressive factors (TSFs). We examined whether tumor necrosis factor alpha (TNF-alpha) antibody treatment in a baboon sepsis model influences the production of TSFs, including interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta). Sepsis was induced in anesthetized baboons by Escherichia coli infusion, and caused an increase in plasma levels of TNF, TSF activity, IL-10, and active TGF-beta, as well as a decrease in latent TGF-beta. TNF antibody pretreatment reduced TNF levels by 98%. Transient TSF activity (0-4 h) was only marginally influenced, while sustained TSF activity (8-24 h) was markedly reduced. TSF activity at 24 h correlated with peak TNF levels. IL-10 levels, coinciding with early TSF activity, remained unchanged by anti-TNF treatment. Levels of active TGF-beta and the drop in latent TGF-beta were decreased. We conclude that anti-TNF treatment reduces sustained TSF activity and may partially restore impaired cell-mediated immune function.

Animals↗
PubMed1995

Hypertonic/hyperoncotic fluids reverse prostaglandin E2 (PGE2)-induced T-cell suppression.

In recent years, hypertonic, and hyperoncotic fluids have been examined for their potential to replace conventional isotonic fluids. This study describes the effects of commonly used intravenous fluids on immune function. The action of increased concentrations of hypertonic saline (HTS), hypertonic saline-dextran (HSD), dextran (Dx), albumin (ALB), and hydroxyethylstarch (HET) on in vitro proliferation of phytohemagglutinin-stimulated normal and prostaglandin E2-suppressed human peripheral blood mononuclear cells was tested. At clinically relevant levels, HTS, HSD (20-40 mM hypertonicity), and ALB (2.5 mg/mL) enhanced T-cell proliferation by 65, 75, and 70%, respectively. Dx and HET had little effect. HTS also reversed prostaglandin E2-suppressed (10 ng/mL) T-cell proliferation to normal levels, and HSD enhanced T-cell proliferation by 40%, in contrast to Dx, ALB, and HET which had minimal effects. The results suggest that hypertonic/hyperoncotic solutions might improve prostaglandin-mediated suppression of T-cell function in patients and may be a useful adjunct to reduce the risk of infection.

Adult↗
PubMed1995

Dopaminergic regulation of transcription factor expression in organotypic cultures of developing striatum.

Dopamine is a major neurotransmitter in neural systems innervating the striatum, and dopamine receptors are expressed during early pattern formation in the developing striatum. To test for the functional responsiveness of developing striatal neurons to dopaminergic stimulation, we established an organotypic slice culture of newborn rat striatum. We analyzed the effects of dopamine receptor agonists and of adenylate cyclase and protein kinase activation on striatal neurons by measuring the induction of Fos-like and Fra-like proteins in the cultured striatum. Fos-like and Fra-like proteins were induced in striatal neurons by activation of D1-like dopamine receptors but not by activation of D2-like receptors. The induction of Fos-like protein was mainly in striosomes and a medial compartment next to the ventricular zone, whereas Fra-like protein was induced in the striatal matrix as well. cAMP analogs and forskolin induced widespread expression of both Fos-like and Fra-like proteins. Our findings thus suggest that neurons of developing striosome and matrix compartments not only have different functional coupling of D1-like receptors to adenylate cyclase, but also have distinct maturational programs for dopaminergic regulation of individual transcription factors. Finally, despite evidence that protein kinase was involved in the induction of Fos-like protein, experiments with kinase inhibitors suggested that the induction of Fos-like protein had unusual pharmacological characteristics and raised the possibility that a novel protein kinase A-like molecule may have been involved in the induction. The cultured striatal slice preparation should provide a valuable tool for analyzing the molecular determinants of striatal development and function.

Amino Acid Sequence↗
PubMed1994

Effects of trauma on immune cell function: impairment of intracellular calcium signaling.

Immunosuppression following injury influences infectious morbidity and mortality. Impaired T-cell activation conceding to inadequate antigen recognition contributes to this immunosuppression. Successful activation and proliferation of T-cells requires precisely specified levels of intracellular calcium thresholds and peak signals. The purpose of this study was to evaluate intracellular calcium signaling following injury. Hospitalized blunt and penetrating trauma patients in a Level 1 Trauma Center following injury and sepsis were tested for immune cell calcium signaling. Peripheral blood mononuclear cells (PBMC) were isolated and calcium signaling tested with Fura-2 AM. PBMC from trauma patients had significantly depressed values of baseline, peak and sustained levels of intracellular calcium prior to and following phytohemagglutinin stimulation when compared to normal controls. This deficit in intracellular calcium signaling is more severe in septic trauma patients (60% reduction). Suppression of calcium signaling appears to be mediated by at least, in part, circulating serum factors. Prostaglandin E2 seems to have a limited contribution to this effect as it is suppressive only when in direct contact with PBMC. Immune cell activation failure can in part be explained by the inadequacy of calcium signaling; restoration of immunocompetence following trauma will have to be addressed by strategies to restore calcium signaling, a vital step necessary for T-cell proliferation following antigen recognition.

Calcium↗
PubMed1994

Hypertonic saline enhances cellular immune function.

Hypertonic saline (HTS) resuscitation improves outcome after trauma. We studied the effect of HTS on immune function. In vitro T-cell proliferation of human and rabbit peripheral blood mononuclear cells (PBMC) was doubled at 25 mM increased extracellular Na+ concentrations. Further increased hypertonicity (more than 40 mM with human cells, and 80 mM with rabbit cells) caused progressive suppression of proliferation. Human and rabbit monocyte functions (tumor necrosis factor production) were augmented by 300% at 30 mM hypertonicity, indicating that HTS-enhanced accessory cell function of monocytes may cause increased T-cell proliferation. Substitution of HTS with KCl also enhanced T-cell proliferation, suggesting an involvement of osmotic effects. HTS (up to 30 mM) increased Ca2+i of nonstimulated human PBMC. HTS injection in rabbits increased cell-mediated immune function (delayed-type hypersensitivity reaction). Our findings suggest that increased plasma osmolality may up-regulate cellular immune function. HTS resuscitation of trauma patients may thus reverse posttraumatic immunosuppression and reduce the risk of sepsis.

Animals↗
PubMed1993

Improved rapid photometric assay for quantitative measurement of PMN migration.

We developed an improved quantitative method to measure in vitro polymorphonuclear leukocyte (PMN) migration using an assembly consisting of a 96-well chamber, polycarbonate filter membrane, and a 96-well microtiter plate. The convenience in setup and counting of migrated cells using this method allows processing of 80 samples and 16 controls in a short assay time of only 2 h. The peroxidase contained in PMNs was used as a marker enzyme to determine the number of migrated cells. Peroxidase released from lysed migrated cells was detected with an enzymatic method utilizing o-dianisidine as substrate. Photometric measurement was performed with a conventional microtiter plate reader at a wavelength of 405 nm. Optical density readings obtained using the enzymatic assay correlated with the number of migrated cells in a linear fashion up to 1 x 10(5) cells/well. The sensitivity of the enzymatic assay was sufficient to determine cell counts as low as 500 PMNs. PMNs lost no measurable amounts of peroxidase during the migration assay when ZAS was used as the chemoattractant. A calibration method was developed to make corrections for variations in the peroxidase content of different cell preparations and changes in the peroxidase content of cells exposed to the chemoattractant. High speed, convenient handling, and the use of standard laboratory equipment result in low cost per assay and make this migration assay ideally suited to research and clinical applications.

Cell Migration Inhibition↗
PubMed1993

Intrastriatal grafts derived from fetal striatal primordia--IV. Host and donor neurons are not intermixed.

Embryonic striatal grafts transplanted into excitotoxin-damaged host striatum develop a heterogeneous structure in which some regions resemble striatum but others do not. In the experiments reported here, we tested for the possibility that the regions resembling striatum were actually derived from host neurons that migrated into the grafts, rather than being derived from donor cells. We placed embryonic striatal grafts into host brains in which striatal cells had been multiply pulse-labeled with [3H]thymidine. Four groups of host rats were exposed to [3H]thymidine at embryonic days 12 and 13-15, 15-18, 16-19, or 20 to postnatal day 1, and were allowed to reach maturity. One week prior to grafting, lesions of the caudoputamen were made unilaterally in each host rat by injecting ibotenic acid. At grafting, dissociated cells from embryonic days 14-16 rat striatal primordia were injected bilaterally into the host caudoputamen. The locations of [3H]thymidine-labeled neurons were analysed by autoradiography eight to 16.5 months post-grafting. Despite the presence of many intensely labeled neurons in the host striatum of rats in all four groups, intensely labeled neurons were rarely found in the cores of grafts. A few weakly labeled small cells appeared in the graft cores, and occasional strongly or weakly labeled medium-sized cells appeared at the margins of the graft zones. Some perivascular cells associated with blood vessels in the grafts were also weakly labeled, but the gliotic tissue surrounding the graft zones was not labeled. These results suggest that very few host striatal neurons migrate into the cores of intrastriatal grafts, or that, if they do, such neurons return to the host striatum or do not survive. At most, surviving host striatal neurons have limited spatial interactions with donor cells at the margins of the grafts, both in the damaged and in the intact host striatal environment. These observations, combined with our previous finding that [3H]thymidine-labeled cells derived from embryonic day 15 striatal primordia do not appear in the host striatum, indicate that no extensive mutual migrations of striatal donor neurons and host neurons occur in the zones of grafting.

Animals↗
PubMed1992

Heterogeneous development of calbindin-D28K expression in the striatal matrix.

In the present study, we attempted to trace the development of the striatal matrix by analyzing the ontogenetic expression of calbindin-D28K (calbindin), a calcium binding protein selectivity expressed in medium-sized neurons of the matrix compartment of the mature rat's caudoputamen. The localization of calbindin was documented in a series of developing rat brains, as was the compartmental location of these cells relative to tyrosine hydroxylase (TH)-immunostained dopamine islands, sites of future striosomes. Medium-sized striatal neurons appeared in the striatum at embryonic day (E) 20, and from their first appearance, the calbindin-positive neurons had highly heterogeneous distributions. They first formed a latticework of patches and bands in a ventral region of the caudoputamen. By postnatal day (P) 7, this early calbindin-positive lattice had evolved into a mosaic in which circumscript pockets of low calbindin-like immunoreactivity appeared in more extensive calbindin-rich surrounds. With further development, the mosaic gradually encroached on all but the dorsolateral caudoputamen, a district that is calbindin-poor at adulthood. A special lateral branch of the striatal calbindin system was also identified, distinct from the rest of the calbindin-positive mosaic in several developmental characteristics. In the parts of the caudoputamen where the developing calbindin system and dopamine island system were both present, the dopamine islands invariably lay in calbindin-poor zones. Most dopamine islands, however, only filled parts of the corresponding calbindin-poor zones. Moreover, there were some calbindin-poor zones for which TH-positive dopamine islands could not be detected. Thus during development, calbindin was expressed in the extrastriosomal matrix of the striatum, but the matrix could be divided into calbindin-rich and calbindin-poor zones. In the calbindin-rich regions, there were patches of especially intense calbindin expression and zones of weaker expression. These results suggest that there is neurochemical heterogeneity in the striatal matrix during the prolonged developmental period in which the early calbindin-positive lattice expands to form the calbindin-positive matrix of the mature striatum. Surprisingly, calbindin expression in the matrix, although eventually distributed in strictly complementary fashion to striosomes, does not originate as a system complementary to dopamine islands. The prolonged disparity between the borders of dopamine islands and calbindin-poor zones, and the different spatiotemporal schedules of development of the islands and the calbindin gaps suggest instead that the final match between the borders of striosomes and surrounding matrix results from dynamic processes occurring early in postnatal development. Candidate mechanisms for the gradual adjustment of these borders are proposed.

Aging↗
PubMed1992

The enzymatic and release characteristics of sheep neutrophil elastase: a comparison with human neutrophil elastase.

Sheep are often used to study tissue damage following shock after traumatic injury and in the course of other diseases. The processes involved are thought to be caused at least in part by elastase released from polymorphonuclear leukocytes (PMNs). Since little is known about elastase and its role as a mediator of tissue damage in sheep, we studied the biochemical properties and release characteristics to sheep leukocyte elastase (SLE) in comparison of those of human leukocyte elastase (HLE). Both enzymes showed similar molecular masses, amino-acid compositions, N-terminal amino-acid sequences, and abilities to digest elastin substrates. Differences, however, were found in kinetic parameters measured with the elastase-specific substrate N-methoxysuccinyl-(L-alanyl)2-L-prolyl-L- valine-4-nitroanilide (MeoSuc-AAPV-pNa). The Michaelis constant (Km) of ovine elastase was nearly 10 times higher (1.82 mM) than the Km of HLE (0.21 mM). Values of SLE calculated for kcat were 70% and for kcat/Km 8% of corresponding values determined for HLE. In addition, significant differences between sheep and human PMNs were found in in vitro stimulation experiments. In contrast to human PMNs, sheep neutrophils released no active elastase, and only 50 to 70% of the H2O2 produced by human PMNs. This failure to release active elastase could not be explained by a lower elastase content of sheep PMNs, as there were no significant differences found between the elastase contents of sheep and human PMNs. We conclude that elastase liberated by stimulated sheep PMNs is inactivated by a concomitantly released proteinase inhibitor also located within the sheep PMNs.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗