A workflow for 3D-CLEM investigating liver tissue.

Correlative light and electron microscopy (CLEM) is a method used to investigate the exact same region in both light and electron microscopy (EM) in order to add ultrastructural information to a light microscopic (usually fluorescent) signal. Workflows combining optical or fluorescent data with electron microscopic images are complex, hence there is a need to communicate detailed protocols and share tips & tricks for successful application of these methods. With the development of volume-EM techniques such as serial blockface scanning electron microscopy (SBF-SEM) and Focussed Ion Beam-SEM, correlation in three dimensions has become more efficient. Volume electron microscopy allows automated acquisition of serial section imaging data that can be reconstructed in three dimensions (3D) to provide a detailed, geometrically accurate view of cellular ultrastructure. In addition, combining volume-EM with high-resolution light microscopy (LM) techniques decreases the resolution gap between LM and EM, making retracing of a region of interest and eventual overlays more straightforward. Here, we present a workflow for 3D CLEM on mouse liver, combining high-resolution confocal microscopy with SBF-SEM. In this workflow, we have made use of two types of landmarks: (1) near infrared laser branding marks to find back the region imaged in LM in the electron microscope and (2) landmarks present in the tissue but independent of the cell or structure of interest to make overlay images of LM and EM data. Using this approach, we were able to make accurate 3D-CLEM overlays of liver tissue and correlate the fluorescent signal to the ultrastructural detail provided by the electron microscope. This workflow can be adapted for other dense cellular tissues and thus act as a guide for other three-dimensional correlative studies. LAY DESCRIPTION: As cells and tissues exist in three dimensions, microscopy techniques have been developed to image samples, in 3D, at the highest possible detail. In light microscopy, fluorescent probes are used to identify specific proteins or structures either in live samples, (providing dynamic information), or in fixed slices of tissue. A disadvantage of fluorescence microscopy is that only the labeled proteins/structures are visible, while their cellular context remains hidden. Electron microscopy is able to image biological samples at high resolution and has the advantage that all structures in the tissue are visible at nanometer (10-9 m) resolution. Disadvantages of this technique are that it is more difficult to label a single structure and that the samples must be imaged under high vacuum, so biological samples need to be fixed and embedded in a plastic resin to stay as close to their natural state as possible inside the microscope. Correlative Light and Electron Microscopy aims to combine the advantages of both light and electron microscopy on the same sample. This results in datasets where fluorescent labels can be combined with the high-resolution contextual information provided by the electron microscope. In this study we present a workflow to guide a tissue sample from the light microscope to the electron microscope and image the ultra-structure of a specific cell type in the liver. In particular we focus on the incorporation of fiducial markers during the sample preparation to help navigate through the tissue in 3D in both microscopes. One sample is followed throughout the workflow to visualize the important steps in the process, showing the final result; a dataset combining fluorescent labels with ultra-structural detail.

GSK3beta, a centre-staged kinase in neuropsychiatric disorders, modulates long term memory by inhibitory phosphorylation at serine-9.

Accumulating evidence implicates deregulation of GSK3ss as a converging pathological event in Alzheimer's disease and in neuropsychiatric disorders, including bipolar disorder and schizophrenia. Although these neurological disorders share cognitive dysfunction as a hallmark, the role of GSK3ss in learning and memory remains to be explored in depth. We here report increased phosphorylation of GSK3ss at Serine-9 following cognitive training in two different hippocampus dependent cognitive tasks, i.e. inhibitory avoidance and novel object recognition task. Conversely, transgenic mice expressing the phosphorylation defective mutant GSK3ss[S9A] show impaired memory in these tasks. Furthermore, GSK3ss[S9A] mice displayed impaired hippocampal L-LTP and facilitated LTD. Application of actinomycin, but not anisomycin, mimicked GSK3ss[S9A] induced defects in L-LTP, suggesting that transcriptional activation is affected. This was further supported by decreased expression of the immediate early gene c-Fos, a target gene of CREB. The combined data demonstrate a role for GSK3ss in long term memory formation, by inhibitory phosphorylation at Serine-9. The findings are fundamentally important and relevant in the search for therapeutic strategies in neurological disorders associated with cognitive impairment and deregulated GSK3ss signaling, including AD, bipolar disorder and schizophrenia.

Synthesis of 18F-labelled 2-(4'-fluorophenyl)-1,3-benzothiazole and evaluation as amyloid imaging agent in comparison with [11C]PIB.

2-(4'-[(18)F]fluorophenyl)-1,3-benzothiazole was synthesized as a fluorine-18 labelled derivative of the Pittsburg Compound-B (PIB), which has known affinity for amyloid beta and promising characteristics as tracer for in vivo visualisation of amyloid deposits in patients suffering from Alzheimer's disease (AD). Both the nitro-precursor 2-(4'-nitrophenyl)-1,3-benzothiazole and the non-radioactive reference compound were synthesized using a 1-step synthesis pathway. Labelling was achieved by direct aromatic nucleophilic substitution of the nitro-precursor using [(18)F]fluoride by heating for 20 min at 150 degrees C and with a radiochemical yield of 38%. The reference compound showed high affinity for amyloid in an in vitro competition binding study using human AD brain homogenates (K(i)=9.0 nM) and fluorescence imaging of incubated transgenic APP mouse brain slices confirmed binding to amyloid plaques. A biodistribution study in normal mice showed a high brain uptake at 2 min pi (3.20%ID/g) followed by a fast washout (60 min pi: 0.21%ID/g). A dynamic microPET study was performed in a transgenic APP and normal WT mouse, but, similar to [(11)C]PIB, no difference was seen in tracer retention between both kind of mice. The new (18)F-labelled 2-phenylbenzothiazole showed excellent preclinical characteristics comparable with those of the (11)C-labelled PIB.

Deregulation of NMDA-receptor function and down-stream signaling in APP[V717I] transgenic mice.

Evidence is accumulating for a role for amyloid peptides in impaired synaptic plasticity and cognition, while the underlying mechanisms remain unclear. We here analyzed the effects of amyloid peptides on NMDA-receptor function in vitro and in vivo. A synthetic amyloid peptide preparation containing monomeric and oligomeric A beta (1-42) peptides was used and demonstrated to bind to synapses expressing NMDA-receptors in cultured hippocampal and cortical neurons. Pre-incubation of primary neuronal cultures with A beta peptides significantly inhibited NMDA-receptor function, albeit not by a direct pharmacological inhibition of NMDA-receptors, since acute application of A beta peptides did not change NMDA-receptor currents in autaptic hippocampal cultures nor in xenopus oocytes expressing recombinant NMDA-receptors. Pre-incubation of primary neuronal cultures with A beta peptides however decreased NR2B-immunoreactive synaptic spines and surface expression of NR2B containing NMDA-receptors. Furthermore, we extended these findings for the first time in vivo, demonstrating decreased concentrations of NMDA-receptor subunit NR2B and PSD-95 as well as activated alpha-CaMKII in postsynaptic density preparations of APP[V717I] transgenic mice. This was associated with impaired NMDA-dependent LTP and decreased NMDA- and AMPA-receptor currents in hippocampal CA1 region in APP[V717I] transgenic mice. In addition, induction of c-Fos following cued and contextual fear conditioning was significantly impaired in the basolateral amygdala and hippocampus of APP[V717I] transgenic mice. Our data demonstrate defects in NMDA-receptor function and learning dependent signaling cascades in vivo in APP[V717I] transgenic mice and point to decreased surface expression of NMDA-receptors as a mechanism involved in early synaptic defects in APP[V717I] transgenic mice in vivo.

11C-labelled PIB analogues as potential tracer agents for in vivo imaging of amyloid beta in Alzheimer's disease.

Pittsburgh Compound-B (PIB) is currently being evaluated clinically for in vivo visualization of amyloid plaques in patients with Alzheimer's disease (AD). We have synthesized three structural isomers of 6-hydroxy-2-(4'-aminophenyl)-1,3-benzothiazole, performed radiolabelling with carbon-11 and investigated their in vivo and in vitro properties. Specific binding to amyloid plaques was demonstrated in vitro using post-mortem brain homogenates of AD patients, transgenic AD mice brain sections and post-mortem human AD brain sections. In normal mice, initial brain uptake (at 2 min p.i.) was high and was followed by a fast wash-out. The three structural analogues have a high potential as tracer agents for in vivo visualization of amyloid plaques in AD patients.

Glycogen synthase kinase-3beta, or a link between amyloid and tau pathology?

Phosphorylation is the most common post-translational modification of cellular proteins, essential for most physiological functions. Deregulation of phosphorylation has been invoked in disease mechanisms, and the case of Alzheimer's disease (AD) is no exception: both in the amyloid pathology and in the tauopathy are kinases deeply implicated. The glycogen synthase kinase-3 (GSK-3) isozymes participate in diverse cellular processes and important signalling pathways and have been implicitly linked to diverse medical problems, i.e. from diabetes and cancer to mood disorders and schizophrenia, and in the neurodegeneration of AD. Here, we review specific aspects of GSK-3 isozymes in the framework of recent data that we obtained in novel transgenic mouse models that robustly recapitulate the pathology and mechanistical problems of AD.

Modulation of synaptic plasticity and Tau phosphorylation by wild-type and mutant presenilin1.

The function of presenilin1 (PS1) in intra-membrane proteolysis is undisputed, as is its role in neurodegeneration in FAD, in contrast to its exact function in normal conditions. In this study, we analyzed synaptic plasticity and its underlying mechanisms biochemically in brain of mice with a neuron-specific deficiency in PS1 (PS1(n-/-)) and compared them to mice that expressed human mutant PS1[A246E] or wild-type PS1. PS1(n-/-) mice displayed a subtle impairment in Schaffer collateral hippocampal long-term potentiation (LTP) as opposed to normal LTP in wild-type PS1 mice, and a facilitated LTP in mutant PS1[A246E] mice. This finding correlated with, respectively, increased and reduced NMDA receptor responses in PS1[A246E] mice and PS1(n-/-) mice in hippocampal slices. Postsynaptically, levels of NR1/NR2B NMDA-receptor subunits and activated alpha-CaMKII were reduced in PS1(n-/-) mice, while increased in PS1[A246E] mice. In addition, PS1(n-/-) mice, displayed reduced paired pulse facilitation, increased synaptic fatigue and lower number of total and docked synaptic vesicles, implying a presynaptic function for wild-type presenilin1, unaffected by the mutation in PS1[A246E] mice. In contrast to the deficiency in PS1, mutant PS1 activated GSK-3beta by decreasing phosphorylation on Ser-9, which correlated with increased phosphorylation of protein tau at Ser-396-Ser-404 (PHF1/AD2 epitope). The synaptic functions of PS1, exerted on presynaptic vesicles and on postsynaptic NMDA-receptor activity, were concluded to be independent of alterations in GSK-3beta activity and phosphorylation of protein tau.

Transgenic mouse models for Alzheimer's disease: the role of GSK-3B in combined amyloid and tau-pathology.

Describing and understanding the pathological processes which devastate the brain of Alzheimer's disease (AD) patients remains a major target for experimental biology. We approached this problem by generating different types of single and double transgenic mice that develop pathological hallmarks of AD. In APP-V717 mice, the progression from intracellular amyloid to diffuse and senile plaques with vascular deposits, is preceded by early defects in cognition and LTP. In Tau-P301L mice, the morbid tauopathy with intracellular filaments, cause mortality before age 1 year. Ageing APP-V717IxTau-P301L double tg mice (14-17 months) have combined AD-like pathology in hippocampus and cortex consisting of amyloid plaques and neurofibrillary tangles. Remarkably, while Tau-P301L mice die before age 1 year, the APP-V717IxTau-P301L double tg mice survive much longer, which correlates with alleviation of tauopathy in hindbrain, despite aggravation in forebrain. This hypothesis is corroborated in Tau-P301LxGSK-3B double transgenic mice, which have also an extended lifespan relative to Tau-P301L mice, that correlates with reduction of brainstem tauopathy. At the same time, Tau-P301LxGSK-3B mice have dramatic forebrain tauopathy, with "tangles in almost all neurons", although without hyper-phosphorylation of Tau. The data corroborate the hypothesis that GSK-3B is the missing link between the amyloid and tau-pathology, and position GSK-3B as prominent player in the pathogenesis in AD.

Evaluation of a new immunoassay to measure sirolimus blood concentrations compared to a tandem mass-spectrometric chromatographic analysis.

A new immunoassay of sirolimus based on the microparticle enzyme immunoassay (MEIA) principle has been developed with collaboration of Abbott Diagnostics. Laboratories and Axis-Shield. Our laboratory evaluated this new assay on 153 whole blood samples (EDTA) drawn from a population of renal (n = 141) and hepatic (n = 12) transplant patients. Each blood sample was analyzed simultaneously by MEIA (Y) and by a reference method (X) used routinely in our laboratory, namely, liquid chromatography tandem mass spectrometry (LC-MS/MS). The statistical analysis of Passing-Bablok produced the following results: Spearman r value = 0.95, slope = 1.15 and intercept with the Y axis = +0.2 ng/mL. The observed global overestimation of 15% compared to the reference method could be explained by the cross-reactivity of sirolimus metabolites with the antibody. A complementary analysis taking into account the transplanted organ (kidney versus hepatic) did not show any significant difference between the populations, most likely owing to the low number of hepatic transplantation samples. The analytical performance of the MEIA method showed CV < or =10% and a limit of quantification of 1.5 ng/mL, which were acceptable for routine clinical monitoring. In conclusion, the MEIA method has shown robust, stable, reproducible, features with an excellent correlation with the reference LC-MS/MS method.

Noninvasive in vivo MRI detection of neuritic plaques associated with iron in APP[V717I] transgenic mice, a model for Alzheimer's disease.

Transgenic mice overexpressing the London mutant of human amyloid precursor protein (APP[V717I]) in neurons develop amyloid plaques in the brain, thus demonstrating the most prominent neuropathological hallmark of Alzheimer's disease. In vivo 3D T2*-weighted MRI on these mice (24 months of age) revealed hypointense brain inclusions that affected the thalamus almost exclusively. Upon correlating these MRI observations with a panel of different histologic staining techniques, it appeared that only plaques that were positive for both thioflavin-S and iron were visible on the MR images. Numerous thioflavin-S-positive plaques in the cortex that did not display iron staining remained invisible to MRI. The in vivo detection of amyloid plaques in this mouse model, using the intrinsic MRI contrast arising from the iron associated with the plaques, creates an unexpected opportunity for the noninvasive investigation of the longitudinal development of the plaques in the same animal. Thus, this work provides further research opportunities for analyzing younger APP[V717I] mouse models with the knowledge of the final outcome at 24 months of age.

R115866 inhibits all-trans-retinoic acid metabolism and exerts retinoidal effects in rodents.

All-trans-retinoic acid (RA) regulates epithelial differentiation and growth through activation of specific nuclear RA receptors (RARs). Because high-rate metabolism largely impairs the biological efficacy of RA, we have sought for compounds capable of inhibiting the metabolic breakdown of the retinoid. This study identifies R115866 as a novel inhibitor of the cytochrome P450 (CYP)-mediated metabolism of RA. In vitro, nanomolar concentrations of R115866 inhibited the conversion of RA by CYP26, a RA-inducible RA metabolizing enzyme. In vivo, oral administration of R115866 (2.5 mg/kg) to rats induced marked and transient increases of endogenous RA levels in plasma, skin, fat, kidney, and testis. Consistent with its ability to enhance endogenous RA content in tissues, R115866 was found to exert retinoidal activities. Like RA, the title compound: 1) inhibited vaginal keratinization in estrogen-stimulated rats; 2) induced epidermal hyperplasia in mouse ear skin; 3) transformed mouse tail epidermis from a para- to an orthokeratotic skin type; and 4) up-regulated the CYP26 mRNA expression in rat liver. Furthermore, we found that the keratinization-suppressive and CYP26-inducing activities of R115866 could be reversed by concomitant administration of the RAR antagonist, AGN193109. Our data characterize R115866 as a potent, orally active inhibitor of RA metabolism, capable of enhancing RA levels and displaying retinoidal actions. These activities are reversed by RAR antagonism, supporting the idea that the actions of R115866 result from increased availability of endogenous RA and improved RAR triggering.

The epidermal architecture of an in vitro reconstructed human skin equivalent (Advanced Tissue Sciences Skin2 Models ZK 1300/2000).

We investigated the epidermal ultrastructure of an organotypic skin culture model over a culture period of one week. At delivery, the stratified keratinizing epidermis consists of a basal layer with hemidesmosomes, a spinous layer with desmosomes, a granular layer with keratohyalin and membrane coating granules, a horny layer enclosing many lipid droplets. At the epidermal-dermal junction laminae lucida and densa are evident. After 7 days of culture the multilayered cornifying aspect persists; the number of viable cell layers remains constant. Spinous cells display abundant glycogen deposits. In the granular layer keratohyalin granules are more abundant. Both the size and number of hemidesmosomes increase. Anchoring fibrils are observed. From a structural point of view the model remains stable and well differentiated in culture and, therefore, may be well suited for pharmacological purposes.

Liarozole, an inhibitor of retinoic acid metabolism, exerts retinoid-mimetic effects in vivo.

Liarozole is an imidazole-containing compound that inhibits the cytochrome P-450-dependent metabolism of all-trans-retinoic acid (RA). In vitro, liarozole (IC50, 2.2 microM) suppressed the P-450-mediated conversion of RA to more polar metabolites by hamster liver microsomes. In vivo, it enhanced the plasma level of RA from mostly undetectable values (less than 0.5 ng/ml) in control rats to 1.4 +/- 0.1 and 2.9 +/- 0.1 ng/ml in animals treated p.o. with 5 and 20 mg/kg of liarozole, respectively. Moreover, liarozole possessed antikeratinizing activity: when dosed subchronically (5-20 mg/kg, once daily for 3 days) to ovariectomized rats, the compound reversed the vaginal keratinization induced in these animals by estrogenic stimulation. Dose response experiments indicated that the antikeratinizating effect of liarozole was as potent as that of RA. One-dimensional electrophoresis and immunoblotting of extracted vaginal epithelia showed that liarozole shared with RA the ability to inhibit the synthesis of high molecular weight (57-60 kDa) keratin proteins, and to enhance the expression of the 45 to 47 kDa keratin polypeptides. Furthermore, we found that antikeratinizing doses of liarozole doubled the RA concentration in the vagina of ovariectomized rats: the mean amount of RA extracted from 200 mg of vaginal tissue was increased from 1.1 +/- 0.1 ng in vehicle-treated animals to 2.2 +/- 0.2 and 2.6 +/- 0.2 ng after treatment with 5 and 20 mg/kg of liarozole, respectively. These findings indicate that liarozole, an inhibitor of RA metabolism and RA produce similar morphologic and biochemical effects on the differentiation process of rat vaginal epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)