Requirement for B cell linker protein (BLNK) in B cell development

Linker proteins function as molecular scaffolds to localize enzymes with substrates. In B cells, B cell linker protein (BLNK) links the B cell receptor (BCR)-activated Syk kinase to the phosphoinositide and mitogen-activated kinase pathways. To examine the in vivo role of BLNK, mice deficient in BLNK were generated. B cell development in BLNK-/- mice was blocked at the transition from B220+CD43+ progenitor B to B220+CD43- precursor B cells. Only a small percentage of immunoglobulin M++ (IgM++), but not mature IgMloIgDhi, B cells were detected in the periphery. Hence, BLNK is an essential component of BCR signaling pathways and is required to promote B cell development.

Correction of defective protein trafficking of a mutant HERG potassium channel in human long QT syndrome. Pharmacological and temperature effects

The chromosome 7-linked form of congenital long QT syndrome (LQT2) is caused by mutations in the human ether-a-go-go-related gene (HERG) that encodes the rapidly activating delayed rectifier potassium channel. One mechanism for the loss of normal channel function in LQT2 is defective protein trafficking, which results in the failure of the channel protein to reach the plasma membrane. Here we show that the N470D LQT2 mutant protein is trafficking-deficient when expressed at 37 degrees C in HEK293 cells, whereas at 27 degrees C its trafficking to the plasma membrane and channel function are markedly improved. We further show that the antiarrhythmic drug E-4031, which selectively blocks HERG channels, also corrects defective protein trafficking of the N470D mutant and can restore the generation of HERG current. Similar findings were obtained with the drugs astemizole and cisapride, as well as with high concentrations of glycerol. The effect of E-4031 on HERG protein trafficking was concentration-dependent and required low drug concentrations (saturation present at 5 microM), developed rapidly with drug exposure, and occurred post-translationally. These findings suggest that protein misfolding leading to defective trafficking of some HERG LQT mutations may be corrected by specific pharmacological strategies.

[Experimental study on stimulation of guided bone regeneration by acid fibroblast growth factor]

OBJECTIVE

To investigate the effect of acid fibroblast growth factor (aFGF) on guided bone regeneration (GBR), to study whether aFGF can promote the repairing ability of GBR in bone defect.

METHODS

10 mm long segmental defects were created in the diaphyses of both radii in 16 New Zealand rabbits. The defect was bridged with a silicon tube. Human recombinant aFGF was instilled into the tube on the experimental side, while the contralateral tube was instilled with saline as control group. The radiographic, gross and histologic examination of the samples were analyzed at 2, 4, 6 and 8 weeks after operation.

RESULTS

On the experimental side, there was new bone formation in the bone medullary cavity, the endosteum and the section surface of the cortex at 2 weeks. At 4 weeks, at the center of the blood clot in the tube there was new bone formation and bone defect was completely healed at 8 weeks. On the control side, new bone formation was less in every period compared with that of the experimental side. At 8 weeks, there was only partial healing of the bone defect.

CONCLUSION

It can be concluded that aFGF can promote new bone formation and facilitate GBR in bone defect.

Migration and function of glia in the developing Drosophila eye

Although glial cells have been implicated widely in the formation of axon tracts in both insects and vertebrates, their specific function appears to be context-dependent, ranging from providing essential guidance cues to playing a merely facilitory role. Here we examine the role of the retinal basal glia (RBG) in photoreceptor axon guidance in Drosophila. The RBG originate in the optic stalk and have been thought to migrate into the eye disc along photoreceptor axons, thus precluding any role in axon guidance. Here we show the following. (1) The RBG can, in fact, migrate into the eye disc even in the absence of photoreceptor axons in the optic stalk; they also migrate to ectopic patches of differentiating photoreceptors without axons providing a continuous physical substratum. This suggests that glial cells are attracted into the eye disc not through haptotaxis along established axons, but through another mechanism, possibly chemotaxis. (2) If no glial cells are present in the eye disc, photoreceptor axons are able to grow and direct their growth posteriorly as in wild type, but are unable to enter the optic stalk. This indicates that the RBG have a crucial role in axon guidance, but not in axonal outgrowth per se. (3) A few glia close to the entry of the optic stalk suffice to guide the axons into the stalk, suggesting that glia instruct axons by local interaction.

Block of HERG potassium channels by the antihistamine astemizole and its metabolites desmethylastemizole and norastemizole

INTRODUCTION

The selective H1-receptor antagonist astemizole (Hismanal) causes acquired long QT syndrome. Astemizole blocks the rapidly activating delayed rectifier K+ current I(Kr) and the human ether-a go-go-related gene (HERG) K+ channels that underlie it. Astemizole also is rapidly metabolized. The principal metabolite is desmethylastemizole, which retains H1-receptor antagonist properties, has a long elimination time of 9 to 13 days, and its steady-state serum concentration exceeds that of astemizole by more than 30-fold. A second metabolite is norastemizole, which appears in serum in low concentrations following astemizole ingestion and has undergone development as a new antihistamine drug. Our objective in the present work was to study the effects of desmethylastemizole, norastemizole, and astemizole on HERG K+ channels.

METHODS AND RESULTS

HERG channels were expressed in a mammalian (HEK 293) cell line and studied using the patch clamp technique. Desmethylastemizole and astemizole blocked HERG current with similar concentration dependence (half-maximal block of 1.0 and 0.9 nM, respectively) and block was use dependent. Norastemizole also blocked HERG current; however, block was incomplete and required higher drug concentrations (half-maximal block of 27.7 nM).

CONCLUSIONS

Desmethylastemizole and astemizole cause equipotent block of HERG channels, and these are among the most potent HERG channel antagonists yet studied. Because desmethylastemizole becomes the dominant compound in serum, these findings support the postulate that it becomes the principal cause of long QT syndrome observed in patients following astemizole ingestion. Norastemizole block of HERG channels is weaker; thus, the risk of producing ventricular arrhythmias may be lower. These findings underscore the potential roles of some H1-receptor antagonist metabolites as K+ channel antagonists.

Mechanism of block and identification of the verapamil binding domain to HERG potassium channels

Calcium channel antagonists have diverse effects on cardiac electrophysiology. We studied the effects of verapamil, diltiazem, and nifedipine on HERG K+ channels that encode IKr in native heart cells. In our experiments, verapamil caused high-affinity block of HERG current (IC50=143.0 nmol/L), a value close to those reported for verapamil block of L-type Ca2+ channels, whereas diltiazem weakly blocked HERG current (IC50=17.3 micromol/L), and nifedipine did not block HERG current. Verapamil block of HERG channels was use and frequency dependent, and verapamil unbound from HERG channels at voltages near the normal cardiac cell resting potential or with drug washout. Block of HERG current by verapamil was reduced by lowering pHO, which decreases the proportion of drug in the membrane-permeable neutral form. N-methyl-verapamil, a membrane-impermeable, permanently charged verapamil analogue, blocked HERG channels only when applied intracellularly. Verapamil antagonized dofetilide block of HERG channels, which suggests that they may share a common binding site. The C-type inactivation-deficient mutations, Ser620Thr and Ser631Ala, reduced verapamil block, which is consistent with a role for C-type inactivation in high-affinity drug block, although the Ser620Thr mutation decreased verapamil block 20-fold more than the Ser631Ala mutation. Our findings suggest that verapamil enters the cell membrane in the neutral form to act at a site within the pore accessible from the intracellular side of the cell membrane, possibly involving the serine at position 620. Thus, verapamil shares high-affinity HERG channel blocking properties with other class III antiarrhythmic drugs, and this may contribute to its antiarrhythmic mechanism.

Novel mechanism associated with an inherited cardiac arrhythmia: defective protein trafficking by the mutant HERG (G601S) potassium channel

BACKGROUND

The congenital long-QT syndrome (LQTS) is an inherited disorder characterized by a prolonged cardiac action potential and a QT interval that leads to arrhythmia. Mutations in the human ether-a-go-go-related gene (HERG), which encodes the rapidly activating component of the delayed rectifier current (IKr), cause chromosome 7-linked LQTS (LQT2). Studies of mutant HERG channels in heterologous systems indicate that the mechanisms mediating LQT2 are varied and include mutant subunits that form channels with altered kinetic properties or nonfunctional mutant subunits. We recently reported a novel missense mutation of HERG (G601S) in an LQTS family that we have characterized in the present work.

METHODS AND RESULTS

To elucidate the electrophysiological properties of the G601S mutant channels, we expressed these channels in mammalian cells and Xenopus oocytes. The G601S mutant produced less current than wild-type channels but exhibited no change in kinetic properties or dominant-negative suppression when coexpressed with wild-type subunits. To examine the cellular trafficking of mutant HERG channel subunits, enhanced green fluorescent protein tagging and Western blot analyses were performed. These showed deficient protein trafficking of the G601S mutant to the plasma membrane.

CONCLUSIONS

Our results from both the Xenopus oocyte and HEK293 cell expression systems and green fluorescent protein tagging and Western blot analyses support the conclusion that the G601S mutant is a hypomorphic mutation, resulting in a reduced current amplitude. Thus, it represents a novel mechanism underlying LQT2.

The netrin receptor frazzled is required in the target for establishment of retinal projections in the Drosophila visual system

Retinal axons in Drosophila make precise topographic connections with their target cells in the optic lobe. Here we investigate the role of the Netrins and their receptor Frazzled in the establishment of retinal projections. We find that the Netrins, although expressed in the target, are not required for retinal projections. Surprisingly, Frazzled, found on both retinal fibers and target cells, is required in the target for attracting retinal fibers, while playing at best a redundant role in the retinal fibers themselves; this finding demonstrates that target attraction is necessary for topographic map formation. Finally, we show that Frazzled is not required for the differentiation of cells in the target. Our data suggest that Frazzled does not function as a Netrin receptor in attracting retinal fibers to the target; nor does it seem to act as a homotypic cell adhesion molecule. We favor the possibility that Frazzled in the target interacts with a component on the surface of retinal fibers, possibly another Netrin receptor.

[An experimental investigation of inhibition of interferon on lens epithelial cell growth in vitro]

OBJECTIVE

To investigate the inhibition of alpha-interferon (alpha-IFN) and gamma-interferon (gamma-IFN) on rabbit lens epithelial cell (RLEC) proliferation in vitro and their effective concentrations.

METHODS

The second and third passage of RLEC were used for assay. Various concentrations of alpha-IFN or gamma-IFN were added into the culture medium and RLECs were exposed to these drugs. After 24 and 72 hours, the inhibition of RLECs was determined by counting the RLEC numbers on a counting plate and MTT colorimetric assay.

RESULTS

Alpha-IFN and gamma-IFN may reduce the proliferation of RLECs at the concentration of 10(3) - 10(4) IU/ml. The inhibition of gamma-IFN was a little stronger than that of alpha-IFN.

CONCLUSION

The experiment provides a scientific basis for selection of drugs to prevent after cataract.

Three dimensional MRI estimates of brain and spinal cord atrophy in multiple sclerosis

OBJECTIVE

The association between brain atrophy and permanent functional deficits in multiple sclerosis and the temporal relation between atrophy and the clinical disease course have seldom been investigated. This study aims to determine the amount of infratentorial and supratentorial atrophy in patients by comparison with healthy controls, to establish the relation between atrophy and disability, and to derive the rates of volume loss in individual patients from their estimated disease durations.

METHODS

Three dimensional acquired MRI was performed on 20 relapsing-remitting and 20 secondary progressive multiple sclerosis patients and 10 control subjects. Volume data on infratentorial and supratentorial structures were obtained using the Cavalieri method of modern design stereology in combination with point counting. Corpus callosal sectional area and "T2 lesion load" were also determined.

RESULTS

Significantly reduced infratentorial and cerebral white matter volumes and corpus callosal sectional areas occurred in all patients compared with controls (p=0.0001-0.004). Mean estimates of volume loss in the cohort were -21%, -19%, -46%, and -12% for the brain stem, cerebellum, upper cervical cord and white matter, respectively, and -21% for the corpus callosal sectional area. Analysis of the amount of atrophy (volume differences between patients and controls) showed that upper cervical cord and cerebral white matter atrophy correlated with the expanded disability status scale (r=-0.37 and -0.37, p=0.018-0.023) and the Scripps neurologic rating scale scores (r=+0.49 and +0.43, p=0.002-0.007). There was no relation between estimated volume loss in the supratentorial and infratentorial compartments. The "T2 lesion load" was associated with ventricular enlargement and corpus callosal atrophy (r=+0.50 and -0.55, p=0.0003-0.0012). Infratentorial atrophy rates correlated with baseline exacerbation rates (r=-0.50 to -0.48, p=0.0016-0.0021) and were higher in relapsing-remitting than secondary progressive patients (p=0.009-0.02).

CONCLUSIONS

Significant cerebral and spinal cord volume reductions occurred in both patient subgroups compared with controls. Functional correlates were found with estimated volume loss in the upper cervical cord and cerebral white matter. Particularly for infratentorial structures, estimated rates of atrophy were higher in relapsing-remitting than secondary progressive patients, suggesting that atrophy, perhaps mainly due to tract degeneration, begins early in multiple sclerosis and may relate predominantly to acute inflammatory events, with or without other gradual non-inflammatory processes later in the disease course.

Regulation of rat pyruvate carboxylase gene expression by alternate promoters during development, in genetically obese rats and in insulin-secreting cells. Multiple transcripts with 5'-end heterogeneity modulate translation

A previous study on the gene structure of rat pyruvate carboxylase revealed that two tissue-specific promoters are responsible for the production of multiple transcripts with 5'-end heterogeneity (Jitrapakdee, S., Booker, G. W., Cassady, A. I., and Wallace, J. C. (1997) J. Biol. Chem. 272, 20522-20530). Here we report transcription and translation regulation of pyruvate carboxylase (PC) expression during development and in genetically obese rats. The abundance of PC mRNAs was low in fetal liver but increased by 2-4-fold within 7 days after birth, concomitant with an 8-fold increase in the amount of immunoreactive PC and its activity and then decreased during the weaning period. Reverse transcriptase polymerase chain reaction analysis indicated that the proximal promoter was activated during the suckling period and reduced in activity at weaning. In genetically obese Zucker rats, adipose PC was 4-5-fold increased, concomitant with a 5-6-fold increase in mRNA level. Reverse transcriptase-polymerase chain reaction analysis also showed that the proximal promoter was activated in the hyperlipogenic condition. Conversely, transcription of the proximal promoter was not detectable in various liver cell lines, suggesting that this promoter was not functional under cell culture conditions. In rat pancreatic islets and insulinoma cells, only transcripts D and E, generated from the distal promoter of the PC gene, were expressed. Glucose increased PC transcripts from the distal promoter when the insulinoma cells were maintained in 10 mM glucose. We conclude that the proximal promoter of the rat PC gene plays a major role in gluconeogenesis and lipogenesis, whereas the distal promoter is necessary for anaplerosis. In vitro translation and in vivo polysome profile analysis indicated that transcripts C and E were translated with similar translational efficiencies that are substantially greater than that of transcript D, suggesting that 5'-untranslated regions play a role in translational control.

Solution structure of N-terminal segment of hepatitis B virus surface antigen Pre-S1

A synthetic peptide, the N-terminus of hepatitis B virus surface antigen Pre-S1, was studied by two-dimensional NMR techniques. A series of(1)H nuclear magnetic resonance experiments were used to complete the identification of spin systems and sequential assignments of this 28-residue peptide. 157 distance constraints and 55 dihedral angle constraints were obtained. 20 structures with the lowest target function were selected by the distance geometry program DIANA. Energy minimization and the following 100 ps time-averaged restrained molecular dynamics (TR-MD) simulation in aqueous solution were performed for each conformer. After TRMD simulation, three locally convergent regions corresponding to residues 22-31, 36-40, 41-46 were found. The averaged pairwise root-mean-square deviation (RMSD) of backbone atoms for them were (1.71+/-0.49)A, (0.76 +/-0.31)A, (1.05 +/- 0.52)A, respectively. Four reverse turns found in these regions, residues 22-25, 37-40, 41-44 and 43-46, correspond to several important antibody binding sites revealed in relevant immunological research.

HERG channel dysfunction in human long QT syndrome. Intracellular transport and functional defects

Mutations in HERG are associated with human chromosome 7-linked congenital long QT (LQT-2) syndrome. We used electrophysiological, biochemical, and immunohistochemical methods to study the molecular mechanisms of HERG channel dysfunction caused by LQT-2 mutations. Wild type HERG and LQT-2 mutations were studied by stable and transient expression in HEK 293 cells. We found that some mutations (Y611H and V822M) caused defects in biosynthetic processing of HERG channels with the protein retained in the endoplasmic reticulum. Other mutations (I593R and G628S) were processed similarly to wild type HERG protein, but these mutations did not produce functional channels. In contrast, the T474I mutation expressed HERG current but with altered gating properties. These findings suggest that the loss of HERG channel function in LQT-2 mutations is caused by multiple mechanisms including abnormal channel processing, the generation of nonfunctional channels, and altered channel gating.

In vivo expression of an alternatively spliced human tumor message that encodes a truncated form of cathepsin B. Subcellular distribution of the truncated enzyme in COS cells

Cathepsin B is a lysosomal cysteine protease whose increased expression is believed to be linked to the malignant progression of tumors. Alternative splicing and the use of alternative transcription initiation sites in humans produce cathepsin B mRNAs that differ in their 5'- and 3'-untranslated ends. Some human tumors also contain cathepsin B-related transcripts that lack exon 3 which encodes the N-terminal signal peptide and 34 of the 62-amino acid inhibitory propeptide. In this study we show that one such transcript, CB(-2,3), which is missing exons 2 and 3, is likely to be a functional message in tumors. Thus, CB(-2,3) was found to be otherwise complete, containing the remainder of the cathepsin B coding sequence and the part of the 3'-untranslated region that is common to all previously characterized cathepsin B mRNAs in humans. Its in vitro translation product can be folded to produce enzymatic activity against the cathepsin B-specific substrate, Nalpha-benzyloxycarbonyl-L-Arg-L-Arg-4-methylcoumaryl-7-amide. Endogenous CB(-2,3) from the metastatic human melanoma cell line, A375M, co-sediments with polysomes, indicating that it engages the eukaryotic translation machinery in these cells. Epitope-tagged forms of the truncated cathepsin B from CB(-2,3) are produced in amounts comparable to the normal protein after transient transfection into COS cells. Immunofluorescence microscopy and subcellular fractionation show this novel tumor form of cathepsin B to be associated with nuclei and other membranous organelles, where it is likely to be bound to the cytoplasmic face of the membranes. This subcellular distribution was different from the lysosomal pattern shown by the epitope-tagged, full-length cathepsin B in COS cells. These results indicate that the message missing exons 2 and 3 is likely to be translated into a catalytically active enzyme, and that alternative splicing (exon skipping) could contribute to the aberrant intracellular trafficking of cathepsin B that is observed in some human cancers.

[The processing of Gekko gecko and the pharmacological action of its different parts]

Both pharmacologic and toxic experiments are made on different parts of Gekko gecko Linnaeus. The results show that Gekko gecko Linnaeus' heads and its feet have obvious pharmacological action without any toxic or side effects, which provides a sound basis for the increase in its clinical utilization and the expansion of its medicinal parts as well as guarantee of safety and effectiveness after taking the medicine.

[Mechanism and treatment of malignant glaucoma]

OBJECTIVE

To investigate the possible mechanism and the treatment of malignant glaucoma.

METHODS

The onsets of 34 eyes in 23 cases of malignant glaucoma were analyzed and the patients were treated with medicine, lens extraction, vitrectomy, anterior chamber plastic operation or combined procedures.

RESULTS

The effective rate in medical treatment was 35.3%. Combined procedures (lens extraction associated with vitrectomy and anterior chamber plastic operation) were all successful.

CONCLUSIONS

The possible mechanism of malignant glaucoma may be concerned with the formation of membranoid substance among vitreous face, ciliary body and posterior iris. Those who failured to medical therapy and were treated with combined operations may have good effect.

Properties of HERG channels stably expressed in HEK 293 cells studied at physiological temperature

We have established stably transfected HEK 293 cell lines expressing high levels of functional human ether-a go-go-related gene (HERG) channels. We used these cells to study biochemical characteristics of HERG protein, and to study electrophysiological and pharmacological properties of HERG channel current at 35 degrees C. HERG-transfected cells expressed an mRNA band at 4.0 kb. Western blot analysis showed two protein bands (155 and 135 kDa) slightly larger than the predicted molecular mass (127 kDa). Treatment with N-glycosidase F converted both bands to smaller molecular mass, suggesting that both are glycosylated, but at different levels. HERG current activated at voltages positive to -50 mV, maximum current was reached with depolarizing steps to -10 mV, and the current amplitude declined at more positive voltages, similar to HERG channel current expressed in other heterologous systems. Current density at 35 degrees C, compared with 23 degrees C, was increased by more than twofold to a maximum of 53.4 +/- 6.5 pA/pF. Activation, inactivation, recovery from inactivation, and deactivation kinetics were rapid at 35 degrees C, and more closely resemble values reported for the rapidly activating delayed rectifier K+ current (I(Kr)) at physiological temperatures. HERG channels were highly selective for K+. When we used an action potential clamp technique, HERG current activation began shortly after the upstroke of the action potential waveform. HERG current increased during repolarization to reach a maximum amplitude during phases 2 and 3 of the cardiac action potential. HERG contributed current throughout the return of the membrane to the resting potential, and deactivation of HERG current could participate in phase 4 depolarization. HERG current was blocked by low concentrations of E-4031 (IC50 7.7 nM), a value close to that reported for I(Kr) in native cardiac myocytes. Our data support the postulate that HERG encodes a major constituent of I(Kr) and suggest that at physiological temperatures HERG contributes current throughout most of the action potential and into the postrepolarization period.

Blockage of the HERG human cardiac K+ channel by the gastrointestinal prokinetic agent cisapride

Cisapride, a gastrointestinal prokinetic agent, is known to cause long Q-T syndrome and ventricular arrhythmias. The cellular mechanism is not known. The human ether-á-go-go-related gene (HERG), which encodes the rapidly activating delayed rectifier K+ current and is important in cardiac repolarization, may serve as a target for the action of cisapride. We tested the hypothesis that cisapride blocks HERG. The whole cell patch-clamp recording technique was used to study HERG channels stably expressed heterologously in HEK293 cells. Under voltage-clamp conditions, cisapride block of HERG is dose dependent with a half-maximal inhibitory concentration of 6.5 nM at 22 degrees C (n = 25 cells). Currents rapidly recovered with drug washout. The onset of block by cisapride required channel activation indicative of open or inactivated state blockage. Block of HERG with cisapride after channel activation was voltage dependent. At -20 mV, 10 nM cisapride reduced HERG tail-current amplitude by 5%, whereas, at + 20 mV, the tail-current amplitude was reduced by 45% (n = 4 cells). At -20 and + 20 mV, 100 nM cisapride reduced tail-current amplitude by 66 and 90%, respectively. We conclude that cisapride is a potent blocker of HERG channels expressed in HEK293 cells. This effect may account for the clinical occurrence of Q-T prolongation and ventricular arrhythmias observed with cisapride.

Restoration of thymocyte development and function in zap-70-/- mice by the Syk protein tyrosine kinase

The Syk family of protein tyrosine kinases, consisting of ZAP-70 and Syk, associate with the pre- and alphabeta T cell antigen receptors (TCRs) and undergo tyrosine phosphorylation and activation following receptor engagement. Thymocyte development in zap-70-/- mice is blocked at the CD4+CD8+ TCR(lo) stage. The presence of Syk in the thymus has raised the possibility that Syk may be able to mediate TCR function. To determine if Syk can play a role in thymocyte development, we generated zap-70-/- mice expressing a human syk cDNA. Syk expression restored both thymocyte development and function. In addition, Syk function required the CD45 transmembrane protein tyrosine phosphatase. Hence, ZAP-70 and Syk can play overlapping functions and exhibit similar regulatory mechanisms in mediating alphabeta T cell development.

Effect of thiols on cadmium-induced expression of metallothionein and other oxidant stress genes in rat lung epithelial cells

This study examined cadmium-induced alterations in metallothionein-1 (MT), glutathione-S-transferase Ya (GST), and heme oxygenase-1 (HO) gene expression in an adult rat lung epithelial cell line. Elevations in MT mRNA and HO mRNA occurred as early as 1 h after exposure to a sub-toxic concentration of CdCl(2) (10 microM) whereas GST expression did not increase significantly until 4 h after Cd addition. At t = 8 h, levels of GST, MT, and HO mRNA were elevated 9-fold, 27-fold, and 44-fold, respectively, over basal expression. By 24 h, MT expression was almost back to baseline levels. GST mRNA and HO mRNA were also reduced, compared to 8 h, but to a lesser extent than MT expression. The MT gene was more responsive to low Cd concentrations (5 microM) than the genes for HO or GST whereas HO was induced more than the others at higher Cd doses (10-20 microM). Pro-oxidant conditions play a role in Cd-induced gene expression, as suggested by the rapid decline (15-30 min) in glutathione (GSH), amounting to 25-30% of baseline, that occurred after exposure to 10 microM CdCl(2). This was followed by resynthesis of GSH to a concentration higher than the initial. Depleting GSH by treatment of cells with buthionine sulfoximine (BSO) enhanced Cd-induced expression of MT, GST, and HO whereas thiol supplementation, by treatment with N-acetyl cysteine (NAC), had an attenuating effect. BSO and NAC pretreatment had no effect on basal gene expression or Cd uptake. In summary, this study has shown that: (1) Cd increases MT, GST, and HO gene expression in a time- and dose-dependent fashion: (2) MT gene expression appears to be most sensitive to Cd whereas the HO gene is most inducible at higher Cd concentrations; (3) Cd-induced expression is enhanced by GSH depletion and suppressed by thiol supplementation.

Olfactory epithelial organotypic slice cultures: a useful tool for investigating olfactory neural development

An in vitro slice culture was established for investigating olfactory neural development. The olfactory epithelium was dissected from embryonic day 13 rats; 400 microns slices were cultured for 5 days in serum-free medium on Millicell-CM membranes coated with different substrates. The slices were grown in the absence of their appropriate target, the olfactory bulb, or CNS derived glia. The cultures mimic many features of in vivo development. Cells in the olfactory epithelium slices differentiate into neurons that express olfactory marker protein (OMP). OMP-positive cells have the characteristic morphology of olfactory receptor neurons: a short dendrite and a single thin axon. The slices support robust axon outgrowth. In single-label experiments, many axons expressed neural specific tubulin, growth-associated protein 43 and OMP. Axons appeared to grow equally well on membranes coated with type I rat tail collagen, laminin or fibronectin. The cultures exhibit organotypic polarity with an apical side rich in olfactory neurons and a basal side supporting axon outgrowth. Numerous cells migrate out of the slices, of which a small minority was identified as neurons based on the expression of neural specific tubulin and HuD, a nuclear antigen, expressed exclusively in differentiated neurons. Most of the migrating cells, however, were positive for glial fibrillary acidic protein and S-100, indicating that they are differentiated glia. A subpopulation of these glial cells also expressed low-affinity nerve growth factor receptors, indicating that they are olfactory Schwann cells. Both migrating neurons and glia were frequently associated with axons growing out of the slice. In some cases, axons extended in advance of migrating cells. This suggests that olfactory receptor neurons in organotypic cultures require neither a pre-established glial/neuronal cellular terrain nor any target tissue for successful axon outgrowth. Organotypic olfactory epithelial slice cultures may be useful for investigating cellular and molecular mechanisms that regulate early olfactory development and function.

Pulmonary metallothionein expression in rats following single and repeated exposure to cadmium aerosols

This study examined the expression of metallothionein (MT) isoforms in the lungs of Lewis rats exposed to Cadmium (Cd) aerosols. With the use of isoform-specific oligonucleotide probes and Northern hybridization analysis, we demonstrated that a dramatic, rapid, and coordinate increase occurred in pulmonary MT-1 mRNA and MT-2 mRNA following Cd inhalation exposure. MT mRNAs levels reached a maximum at 2 h post-exposure and remained above control levels at 96 h after exposure. A considerable lag between the time of maximal elevations in MT mRNAs and MT protein accumulation was observed and suggested that regulatory mechanisms in addition to transcriptional control could be involved. MT expression (protein and mRNA) and Cd lung burden were directly related to aerosol Cd concentration. In situ hybridization and immunohistochemistry studies showed good correlation between the localization of MT protein and MT mRNAs. However, staining for MT protein and MT mRNA was not uniformly distributed in the lung. MT was particularly prominent within the alveolar compartment. Even within this area, however, heterogeneity of MT expression was evident. Experiments were subsequently conducted to determine whether prior exposure to Cd modulates the transcriptional activity of MT genes such that there is a greater elevation in gene expression upon reexposure to Cd. Surprisingly, animals pretreated with Cd exhibited a smaller incremental increase in MT mRNA levels in response to subsequent Cd exposure than controls with no prior treatment. Moreover, MT mRNA levels were elevated to a similar extent regardless of whether animals were exposed to Cd aerosols for 1, 2, or 3 weeks (3 h/day; 5 days/week). MT protein and lung Cd burden, on the other hand, exhibited an increasing linear trend as a function of exposure number. In summary, this study has demonstrated that: (1) the lung responds to Cd inhalation exposure by increasing MT mRNA and MT protein levels; (2) MT expression is prominent within alveolar cells but not all cells are MT positive; and (3) Cd-pretreatment does not increase the transcriptional potential of MT genes when the animal is subsequently reexposed to Cd.