Kindling-induced overexpression of Homer 1A and its functional implications for epileptogenesis

Despite an extensive research on the molecular basis of epilepsy, the essential players in the epileptogenic process leading to epilepsy are not known. Gene expression analysis is one strategy to enhance our understanding of the genes contributing to the functional neuronal changes underlying epileptogenesis. In the present study, we used the novel MPSS (massively parallel signature sequencing) method for analysis of gene expression in the rat kindling model of temporal lobe epilepsy. Kindling by repeated electrical stimulation of the amygdala resulted in the differential expression of 264 genes in the hippocampus compared to sham controls. The most strongly induced gene was Homer 1A, an immediate early gene involved in the modulation of glutamate receptor function. The overexpression of Homer 1A in the hippocampus of kindled rats was confirmed by RT-PCR. In order to evaluate the functional implications of Homer 1A overexpression for kindling, we used transgenic mice that permanently overexpress Homer 1A. Immunohistochemical characterization of these mice showed a marked Homer 1A overexpression in glutamatergic neurons of the hippocampus. Kindling of Homer 1A overexpressing mice resulted in a retardation of seizure generalization compared to wild-type controls. The data demonstrate that kindling-induced epileptogenesis leads to a striking overexpression of Homer 1A in the hippocampus, which may represent an intrinsic antiepileptogenic and anticonvulsant mechanism in the course of epileptogenesis that counteracts progression of the disease.

Characterization of the role of the "MT-loop": an eight-amino acid insertion specific to progelatinase A (MMP2) activating membrane-type matrix metalloproteinases

Progelatinase A (proGLA) activation is thought to be initiated almost exclusively by the type I transmembrane members of the membrane type matrix metalloproteinase family (MT-MMP): MT1, -2, -3, and -5-MMP (MMP14, -15, -16, and -24). One difference between these enzymes and the other MMP family members is the insertion of eight amino acids between strands betaII and III in the catalytic domain. In MT1-MMP, the best characterized of these enzymes to date, these residues consist of (163)PYAYIREG(170). To investigate the role of this region of MT1-MMP on its catalytic activities, we have made a variety of mutations and deletions in both soluble and membrane-bound forms of the enzyme. Characterization of the activity of the soluble forms toward peptides and fibrinogen revealed that neither mutation nor deletion of residues 163-170 significantly impaired catalytic function, suggesting these residues have little influence on conformation of the active site cleft. Equally none of the mutants showed significant differences in K(I)(app) for the N-terminal inhibitory domain of TIMP2, again indicating that mutation or deletion of resides 163-170 has no major effect on the overall topology of the active site of MT1-MMP. However, characterization of the kinetics of activation of proGLA with and without its gelatin binding region by the mutants generated have shown that efficient activation of proGLA is, at least in part, through an interaction with residues 163-170 of MT1-MMP. The expression, localization, and processing from the 63- to the 60/45-kDa forms of wild-type and key mutant forms of MT1-MMP were also examined by transient transfection in Chinese hamster ovary cells, but no differences were observed. Processing and activation of proGLA was also examined in transiently transfected cells. All the mutants examined were able process proGLA but, as found with the soluble forms, were kinetically impaired when compared with wild-type MT1-MMP.

Tyrosine 36 plays a critical role in the interaction of the AB loop of tissue inhibitor of metalloproteinases-2 with matrix metalloproteinase-14

The tissue inhibitor of metalloproteinases-2 (TIMP-2) is potentially an important inhibitor of all known matrix metalloproteinases (MMPs). However, it has been shown to undergo specific interactions with both MMP-2 (gelatinase A) and MMP-14 (MT1-MMP), and it has been proposed that these three proteins function as a cell surface-based activation cascade for matrix metalloproteinases and as a focus of proteolytic activity. In this study, we have carried out mutagenesis and kinetic analyses to examine the unique interactions between the AB loop of TIMP-2 and MMP-14. The results demonstrate that the major binding contribution of the AB loop is due solely to residue Tyr-36 at the tip of the hairpin. From this work, we propose that TIMP-2 may be engineered to abrogate MMP-14 binding, whereas its binding properties for other MMPs, including MMP-2, are maintained. Mutants of TIMP-2 with more directed specificity may be of use in gene therapeutic approaches to human disease.

Coexpression of CD4 and CD8alpha on rat T-cells in whole blood: a sensitive marker for monitoring T-cell immunosuppressive drugs

The aim of this study was to develop a new quantitative method for measuring in vitro the effects of T-cell immunosuppressive drugs by flow cytometry. Rat whole blood samples were stimulated with the T-cell mitogen succinylated concanavalin A in the presence or absence of different drugs. After 3 days, the expression of CD25 and CD8alpha in mitogen-stimulated CD4(+) cells increased 10- to 20-fold as measured by flow cytometry. Drug efficacy and potency was calculated based on dose-response curves of the drug-mediated decrease in CD4(+)/CD8alpha(+)/CD25(+) cells. The expression of CD8alpha in mitogen-stimulated CD4(+) cells was blocked completely by calcineurin inhibitors (cyclosporine A and FK-506), and partially by rapamycin and SDZ-RAD. The IC(50) (50% inhibitory concentration) values obtained were (mean+/-S.E.): 99.5+/-16.6 nM for cyclosporine A, 10.4+/-1.3 nM for FK-506, 1.8+/-0.7 nM for rapamycin, and 6.4+/-1.1 nM for SDZ-RAD. Our results show, for the first time, that CD8alpha, used as an activation antigen, is a sensitive marker for monitoring T-cell immunosuppression.

Activation of pro-astacin. Immunological and model peptide studies on the processing of immature astacin, a zinc-endopeptidase from the crayfish Astacus astacus

To contribute knowledge of the processing and activation of invertebrate proteolytic enzymes, we studied the metalloprotease astacin, a digestive enzyme from the freshwater crayfish Astacus astacus (decapod crustacean). It is the prototype of the protein family of astacins, members of which occur in organisms from bacteria to man and are involved in a variety of physiological reactions. According to its genomic structure, astacin is produced as a zymogen [Geier, G., Jacob, E., Stöcker, W. & Zwilling, R. (1997) Arch. Biochem. Biophys. 337, 300-307]. To localize and follow the processing of pro-astacin in different parts of the digestive tract, we synthesized two peptides covering the pro part of pro-astacin and raised antibodies against them. In addition, antiserum against the whole active astacin was produced. Using immunohistochemical investigation, we detected pro-astacin in the F cells of the hepatopancreas and all the way into the tubular lumen and the collecting ducts of this gland. Immunoblot assays revealed only active astacin, and never pro-astacin, present in the cardiac stomach. We conclude from these studies that astacin is secreted into the lumen of the hepatopancreatic tubules in its pro form and is activated on its way to the stomach. To investigate which of the two endopeptidases found in the digestive tract of crayfish, astacin or trypsin, is responsible for cleaving the propeptide from pro-astacin, we synthesized different peptides that mimick the activation site. MS analysis of the cleavage products of astacin and trypsin showed that astacin is capable of catalyzing its own activation. Any contribution of trypsin would require the successive action of an aminopeptidase. Substituting glycine for arginine at position -1 of the activation site does not prevent astacin activity. As most members of the astacin protein family have basic amino-acid residues in this position, in these cases also astacin-specific cleavage would be possible.

Microcephaly with normal intelligence, and chorioretinopathy

An 18-year-old girl had microcephaly without mental or neurological disabilities. She had hypoplastic mandible, long cup-shaped ears, bilateral incurved little fingers, bilateral retinal pigmentation, and scattered areas of depigmentation as well as a history of osteochondroma. However, genetic test for mutation analysis of exon 15 of the APC gene showed negative results. To the best of our knowledge, this is the third case to be reported with microcephaly, normal intelligence, and bilateral congenital hypertrophy of the retinal pigment epithelium (CHRPE).

Rotary cell culture system (RCCS): a new method for cultivating hepatocytes on microcarriers

The Rotary Cell Culture System (RCCS) is a new technology for growing anchorage dependent or suspension cells in the laboratory. The RCCS is a horizontally rotated, bubble free disposable culture vessel with diffusion gas exchange. The system provides a reproducible, complex 3D in vitro culture system with large cell masses. During cell growing the rotation speed can be adjusted to compensate for increased sedimentation rates. The unique environment of low shear forces, high mass transfer, and microgravity, provides very good cultivating conditions for many cell types, cell aggregates or tissue particles in a standard tissue culture laboratory. The system enables to culture HepG2 cells on Cytodex 3 microcarriers (mcs) to high densities. We inoculated 2 x 10(5)/ml HepG2 cells and 200 mg Cytodex 3 mcs in 50 ml Williams E medium (incl. 10% FCS) allowing them to attach to the mcs in the rotating vessel (rotation rate 14-20 rpm). HepG2 cells readily attached to the mcs while the vessel was rotating. Attachment of HepG2 to the mcs was about 50% after 24 hrs and 100 % within 48 hrs. After 72 hrs of rotary culturing small aggregates of Hep G2 on mcs were built. HepG2 cells and the aggregates rotated with the vessel and did not settle within the vessel or collide with the wall of the vessel. We conclude that this new RCCS is an excellent technology for culturing HepG2 cells on Cytodex 3 mcs. The system is easy to handle and enables to culture anchorage dependent cells to high densities in a short period.

Microspheres based detoxification system: in vitro study and mathematical estimation of filter performance

Because of the closed plasma (secondary) circuit in the Microspheres based Detoxification System (MDS), a convective blood purification system, the same amount of filtrated plasma is backfiltrated into the blood circuit. Therefore, there is no direct way to determine the ultrafiltrate production rate, which is an important factor of efficiency. The only possible way to estimate the filtration properties of the filter is to consider pressure values. In this study the pressure distribution in the filter was investigated in vitro. To explain the results and to calculate inaccessible parameters, a mathematical model was established which also considered the asymmetric behaviour of the filter membrane. The result was a linear pressure gradient, agreement with the measurements was reasonably good (calculated primary pressure loss differs <13% from measured value when using mean measured filter resistance as model parameter). Linear pressure distribution offers the possibility of easily calculating the filtration length, a parameter which can be used to estimate the filter condition. The comparison between calculated filtration and backfiltration rates offers an instrument of control for these values.

Intermediates and products formed during fatty acid alpha-oxidation in cucumber (Cucumis sativus)

Fatty acid alpha-oxidation is an essential metabolic pathway both in plants and in mammals which is still not completely understood. We previously described and purified an alpha-oxidation enzyme in cucumber which has been used in the present investigation of the alpha-oxidation reaction mechanism. Free fatty acids, and not the CoA thioesters, were found to undergo alpha-oxidation in cucumber. 2-Hydroxy- and 2-oxopalmitic acids were identified as palmitic acid alpha-oxidation intermediates by high-performance liquid chromatography and gas chromatography-mass spectrometry analysis in cucumber subcellular 150,000 x g(max) pellets obtained by differential centrifugation. Incubation of purified alpha-oxidation enzyme with [1-14C]palmitic acid resulted in the formation of both the above-described intermediates and the Cn-1 product, pentadecanal, and 14CO2. Besides 14CO2, 14C-formate was identified as an alpha-oxidation product from [1-14C]palmitic acid in cucumber subcellular fractions. Fe2+ stimulated the 14CO2 and 14C-formate production, and the addition of ascorbate and 2-oxoglutarate together with Fe2+ resulted in optimal alpha-oxidation activities, suggesting a dioxygenase reaction mechanism, as previously shown in mammals. NADPH and, to a lesser extent, NADH stimulated the total 14C-formate plus 14CO2 production but had only slight or no effects on 14CO2 production. H2O2 showed concentration-dependent inhibitory effects, while FAD had neither effect on 14CO2 nor 14CO2 plus 14C-formate production. The results in the present study demonstrate that an alpha-oxidation enzyme in cucumber is capable of oxidizing palmitic acid via 2-hydroxy- and 2-oxo-palmitic acid to produce pentadecanal and CO2. In contrast to the subcellular 150,000 x g(max) fraction, the purified alpha-oxidation enzyme could neither produce formate nor convert 14C-formate into 14C02, indicating two possible alpha-oxidation routes in cucumber.

Fractionated plasma separation and adsorption system: a novel system for blood purification to remove albumin bound substances

The removal of albumin bound substances has gained increasing interest in different diseases, especially in acute and chronic liver disease. Therefore, a new system, the fractionated plasma separation and adsorption (FPSA) system, was developed based on combined membrane and adsorbent blood purification techniques. The most important contribution to the FPSA system was the development of a new polysulfone hollow-fiber filter, which is characterized by a sieving coefficient of 0.89 for human serum albumin (HSA) but only of 0.17 for fibrinogen, and 0 (zero) for IgM immunoglobulins. Using a closed filtrate circuit connected to the new polysulfone filter which integrates 1 or 2 adsorption columns and also a high flux dialyzer adapted to a dialysis machine, the FPSA system opens excellent possibilities for the relatively specific removal of albumin bound substances from the blood such as albumin bound bilirubin or even tryptophan. In comparison to other systems (for example, the Molecular Adsorbent Recirculating System [MARS] and albumin dialysis systems), the FPSA system enables much higher elimination of strongly bound albumin substances. The first clinical investigations have recently started based on a modified dialysis machine designed with all necessary safety measures.

Spontaneous formation of intercellular bile canaliculi and hybrid biliary-pancreatic canaliculi in co-culture of hepatocytes and exocrine pancreas cells from carp

When cultured together in a primary serum-free hormone-free system, hepatocytes and exocrine pancreas cells from the carp, Cyprinus carpio, spontaneously establish unique morphological structures that do not occur in vivo. These structures include intercellular bile canaliculi between neighbouring hepatocytes and hybrid canaliculi between hepatocytes and pancreas cells. In vivo, carp hepatocytes form only unicellular bile canaliculi; hybrid canaliculi between hepatocytes and exocrine pancreas cells do not exist at all in nature. This study shows that, in an artificial environment, cells are able spontaneously to establish novel morphological structures that are absent in the animal from which the cells have been obtained.

Protein thermal stability, hydrogen bonds, and ion pairs

Researchers in both academia and industry have expressed strong interest in comprehending the mechanisms responsible for enhancing the thermostability of proteins. Many and different structural principles have been postulated for the increased stability. Here, 16 families of proteins with different thermal stability were theoretically examined by comparing their respective fractional polar atom surface areas and the number and type of hydrogen bonds and salt links between explicit protein atoms. In over 80% of the families, correlations were found between the thermostability of the familial members and an increase in the number of hydrogen bonds as well as an increase in the fractional polar surface which results in added hydrogen bonding density to water. Thus increased hydrogen bonding may provide the most general explanation for thermal stability in proteins. The number of ion pairs was also found to increase with thermal stability in two-thirds of the families tested; however, their rate of addition was only about one-sixth that for internal hydrogen bonds amongst the protein atoms. The preferred residue exchanges and surface atom types useful in engineering enhanced stability were also examined.

A novel field generator for magnetic stimulation in cell culture experiments

A novel field generator specially designed to examine the influence of low frequency magnetic fields on specific cell material was constructed and characterized. The exposure unit described in this paper consists of a controller unit and three sets of coils. The field generator permits a precious definition of the revelant signal parameters and allows the superposition of alternating current (AC) and direct current (DC) magnetic fields. Critical system parameters were monitored continuously. The three sets of coils, each arranged in the Helmholtz Configuration were characterized. After data processing and visualization the results showed a constant and homogeneous field within the experimental area. The special coil design also allows their use in an incubator.

Protein thermal stability: hydrogen bonds or internal packing?

Thermally stable proteins are of interest for several reasons. They can be used to improve the efficiency of many industrial processes and provide insight into the general mechanisms of protein folding and stabilization. Comparison of tertiary structural properties of several protein families with members of different thermostability should help to delineate the role of individual factors in achieving stability at high temperature. In this work, 16 protein families with at least one known thermophilic and one known mesophilic tertiary structure were examined for the number and type of hydrogen bonds and salt links, polar surface composition, internal cavities and packing densities, and secondary structural composition. The results show a consistent increase in the number of hydrogen bonds and in polar surface area fraction with increased thermostability.

Morphology and physiology of digestive epithelia in Decapod crustaceans

The anatomy and cellular composition of the digestive tract of decapod crustaceans is in many aspects considerably different from the vertebrate system. These differences include primarily the gastric mill and a sophisticated filter apparatus in the stomach and the hepatopancreatic tubule system with its bi-directional movement of fluids. Further differences are the lack of a strongly acidic pH and pepsin in the stomach. Consequently, many of the physiological processes are fundamentally different as well, particularly the physical and chemical processing of the feed and the synthesis, storage and mode of action of the digestive enzymes. The hepatopancreas is a central organ of metabolism and includes functions which, in vertebrates, are confined to intestine, liver and pancreas.