Blot analyses and immunocytochemistry of neural antigens with digoxigenylated primary and secondary antibodies

Versatile and simple approach to determine astrocyte territories in mouse neocortex and hippocampus

Background

Besides their neuronal support functions, astrocytes are active partners in neuronal information processing. The typical territorial structure of astrocytes (the volume of neuropil occupied by a single astrocyte) is pivotal for many aspects of glia–neuron interactions.

Methods

Individual astrocyte territorial volumes are measured by Golgi impregnation, and astrocyte densities are determined by S100β immunolabeling. These data are compared with results from conventionally applied methods such as dye filling and determination of the density of astrocyte networks by biocytin loading. Finally, we implemented our new approach to investigate age-related changes in astrocyte territories in the cortex and hippocampus of 5- and 21-month-old mice.

Results

The data obtained by our simplified approach based on Golgi impregnation were compared to previously published dye filling experiments, and yielded remarkably comparable results regarding astrocyte territorial volumes. Moreover, we found that almost all coupled astrocytes (as indicated by biocytin loading) were immunopositive for S100β. A first application of this new experimental approach gives insight in age-dependent changes in astrocyte territorial volumes. They increased with age, while cell densities remained stable. In 5-month-old mice, the overlap factor was close to 1, revealing little or no interdigitation of astrocyte territories. However, in 21-month-old mice, the overlap factor was more than 2, suggesting that processes of adjacent astrocytes interdigitate.

Conclusion

Here we verified the usability of a simple, versatile method for assessing astrocyte territories and the overlap factor between adjacent territories. Second, we found that there is an age-related increase in territorial volumes of astrocytes that leads to loss of the strict organization in non-overlapping territories. Future studies should elucidate the physiological relevance of this adaptive reaction of astrocytes in the aging brain and the methods presented in this study might be a powerful tool to do so.

Concomitant detection of beta-amyloid peptides with N-terminal truncation and different C-terminal endings in cortical plaques from cases with Alzheimer's disease, senile monkeys and triple transgenic mice

The disturbed metabolism of beta-amyloid peptides generated from amyloid precursor protein is widely considered as a main factor during the pathogenesis of Alzheimer's disease. A neuropathological hallmark in the brains from cases with Alzheimer's disease are senile plaques mainly composed of hardly soluble beta-amyloid peptides comprising up to 43 amino acids. Age-dependent cortical beta-amyloidosis was also shown in several transgenic mice and old individuals from various mammalian species, e.g., non-human primates. Beta-amyloid(1-42) is believed to be the main component in the core of senile plaques, whereas less hydrophobic beta-amyloid(1-40) predominantly occurs in the outer rim of plaques. Amino-terminally truncated pyroglutamyl-beta-amyloid(pE3-x) was recently found to be a beta-amyloid species of high relevance to the progression of the disease. While a few biochemical studies provided data on the co-occurrence of several beta-amyloid forms, their concomitant histochemical detection is still lacking. Here, we present a novel triple immunofluorescence labelling of amino- and differently carboxy-terminally truncated beta-amyloid peptides in cortical plaques from a case with Alzheimer's disease, senile macaques and baboons, and triple transgenic mice with age-dependent beta-amyloidosis and tau hyperphosphorylation. Additionally, beta-amyloid(pE3-x) and total beta-amyloid were concomitantly detected with beta-amyloid peptides ending with amino acid 40 or 42, respectively. Simultaneous staining of several beta-amyloid species reveals for instance vascular amyloid containing beta-amyloid(pE3-x) in Alzheimer's disease and monkeys, and may contribute to the further elucidation of beta-amyloidosis in neurodegenerative disorders and animal models.

Simultaneous detection of tau phospho-epitopes with haptenylated antibodies

Neurofibrillary tangles as a neuropathological hallmark of Alzheimer's disease are mainly composed of abnormally phosphorylated microtubule-associated protein tau. The present work was primarily focused on the immunohistochemical characterization of recently developed monoclonal antibodies directed against disease-associated epitopes. Anti-phospho-threonine 212/phospho-serine 214 (HPT-1), anti-phospho-threonine 231/phospho-serine 235 (HPT-101) and their biotinylated derivatives were shown to be sensitive markers for the immunohistochemical detection of neuropathological alterations during Alzheimer's disease. Triple carbocyanine immunofluorescence labelling was based on digoxigenylated, fluoresceinated and biotinylated primary antibodies. AT8-immunolabelling of phospho-serine 202 and phospho-threonine 205 combined with HPT-1 and HPT-101-staining revealed similar distribution patterns of the three double-phosphorylated tau epitopes in the neocortex of patients with Alzheimer's disease.

The transcription factor Yin Yang 1 is an activator of BACE1 expression

The beta-site amyloid precursor protein-cleaving enzyme 1 (BACE1) is a prerequisite for the generation of beta-amyloid peptides, the principle constituents of senile plaques in the brains of patients with Alzheimer's disease (AD). BACE1 expression and enzymatic activity are increased in the AD brain, but the regulatory mechanisms of BACE1 expression are largely unknown. Here we show that Yin Yang 1 (YY1), a highly conserved and multifunctional transcription factor, binds to its putative recognition sequence within the BACE1 promoter and stimulates BACE1 promoter activity in rat pheochromocytoma 12 (PC12) cells, rat primary neurones and astrocytes. In rat brain YY1 and BACE1 are widely expressed by neurons, but there was only a minor proportion of neurones that co-expressed YY1 and BACE1, suggesting that YY1 is not required for constitutive neuronal BACE1 expression. Resting astrocytes in the untreated rat brain did not display either YY1 or BACE1 immunoreactivity. When chronically activated, however, astrocytes expressed both YY1 and BACE1 proteins, indicating that YY1 is important for the stimulated BACE1 expression by reactive astrocytes. This is further emphasized by the expression of YY1 and BACE1 by reactive astrocytes in proximity to beta-amyloid plaques in the AD brain. Our observations suggest that interfering with expression, translocation or binding of YY1 to its BACE1 promoter-specific sequence may have therapeutic potential for treating patients with AD.

Astrocytic expression of the Alzheimer's disease beta-secretase (BACE1) is stimulus-dependent

The beta-site APP-cleaving enzyme (BACE1) is a prerequisite for the generation of beta-amyloid peptides, which give rise to cerebrovascular and parenchymal beta-amyloid deposits in the brain of Alzheimer's disease patients. BACE1 is neuronally expressed in the brains of humans and experimental animals such as mice and rats. In addition, we have recently shown that BACE1 protein is expressed by reactive astrocytes in close proximity to beta-amyloid plaques in the brains of aged transgenic Tg2576 mice that overexpress human amyloid precursor protein carrying the double mutation K670N-M671L. To address the question whether astrocytic BACE1 expression is an event specifically triggered by beta-amyloid plaques or whether glial cell activation by other mechanisms also induces BACE1 expression, we used six different experimental strategies to activate brain glial cells acutely or chronically. Brain sections were processed for the expression of BACE1 and glial markers by double immunofluorescence labeling and evaluated by confocal laser scanning microscopy. There was no detectable expression of BACE1 protein by activated microglial cells of the ameboid or ramified phenotype in any of the lesion paradigms studied. In contrast, BACE1 expression by reactive astrocytes was evident in chronic but not in acute models of gliosis. Additionally, we observed BACE1-immunoreactive astrocytes in proximity to beta-amyloid plaques in the brains of aged Tg2576 mice and Alzheimer's disease patients.

Ontogenetic changes in protein level of amyloid precursor protein (APP) in growth cones and synaptosomes from rat brain and prenatal expression pattern of APP mRNA isoforms in developing rat embryo

To elucidate the functional role of the amyloid precursor protein (APP) during brain ontogeny, developmental changes of APP levels in growth cones and synaptosomes were studied from embryonic day 14 up to postnatal day (PD) 400 using Western analysis. APP level in growth cones was low during prenatal stages of development, but demonstrating a continuous increase from PD 3 up to PD 10. Highest concentration of APP in synaptosomes was found between PD 7 and 10, followed by a considerable decrease up to PD 30 and persisting at this level up to PD 400. In situ hybridization to differentiate between APP695 mRNA, APP751 mRNA and APP770 mRNA revealed distinct age-related expression pattern of various APP isoforms. During prenatal brain development APP695 mRNA is maximally expressed in brain structures, containing differentiating nerve cells. APP751 and APP770 mRNA isoforms are diffusely distributed in the embryo throughout the prenatal period examined and their expression is higher in peripheral organs such as skin, lung, liver and bones as compared to the brain. The increase of APP level during synaptogenesis suggests a functional role of APP in the processes of neurite outgrowth and cell targeting as well as in the maintenance of the functional integrity of synapses in the mature brain. The APP695 isoform seems to be the major form involved in embryonic brain maturation.

Novel vascular graft grown within recipient's own peritoneal cavity

A method by which to overcome the clinical symptoms of atherosclerosis is the insertion of a graft to bypass an artery blocked or impeded by plaque. However, there may be insufficient autologous mammary artery for multiple or repeat bypass, saphenous vein may have varicose degenerative alterations that can lead to aneurysm in high-pressure sites, and small-caliber synthetic grafts are prone to thrombus induction and occlusion. Therefore, the aim of the present study was to develop an artificial blood conduit of any required length and diameter from the cells of the host for autologous transplantation. Silastic tubing, of variable length and diameter, was inserted into the peritoneal cavity of rats or rabbits. By 2 weeks, it had become covered by several layers of myofibroblasts, collagen matrix, and a single layer of mesothelium. The Silastic tubing was removed from the harvested implants, and the tube of living tissue was everted such that it now resembled a blood vessel with an inner lining of nonthrombotic mesothelial cells (the "intima"), with a "media" of smooth muscle-like cells (myofibroblasts), collagen, and elastin, and with an outer collagenous "adventitia." The tube of tissue (10 to 20 mm long) was successfully grafted by end-to-end anastomoses into the severed carotid artery or abdominal aorta of the same animal in which they were grown. The transplant remained patent for at least 4 months and developed structures resembling elastic lamellae. The myofibroblasts gained a higher volume fraction of myofilaments and became responsive to contractile agonists, similar to the vessel into which they had been grafted. It is suggested that these nonthrombogenic tubes of living tissue, grown in the peritoneal cavity of the host, may be developed as autologous coronary artery bypass grafts or as arteriovenous access fistulae for hemodialysis patients.

Selective in vivo fluorescence labelling of cholinergic neurons containing p75(NTR) in the rat basal forebrain

The cholinergic system of the rat basal forebrain is used as a model for the homologous region in humans which is highly susceptible to neuropathological alterations as in Alzheimer's disease. Cholinergic cells in the basal forebrain express the low-affinity neurotrophin receptor p75NTR. This has been utilized for selective immunolesioning of cholinergic neurons after internalization of an immunotoxin composed of anti-p75NTR and the ribosome-inactivating toxin saporin. However, the goal of many studies may be not the lesion, but the identification of cholinergic cells after other experimentally induced alterations in the basal forebrain. Therefore, a novel cholinergic marker was prepared by conjugating the monoclonal antibody 192IgG directed against p75NTR with the bright red fluorochrome carbocyanine 3 (Cy3). Three days after intraventricular injection of Cy3-192IgG the fluorescence microscopic analysis revealed a pattern of Cy3-labelled cells matching the distribution of cholinergic neurons. Apparently the marker was internalized within complexes of p75NTR and Cy3-192IgG which were then retrogradely transported to the cholinergic perikarya of the basal forebrain. In addition to the even labelling of somata, a strong punctate-like Cy3-immunofluorescence was seen in structures resembling lysosomes. The specificity of the in vivo staining was proven by subsequent immunolabelling of choline acetyltransferase (ChAT) with green fluorescent Cy2-tagged secondary antibodies. In the medial septum, the diagonal band and the nucleus basalis only cholinergic neurons were marked by Cy3-192IgG. In parallel experiments, digoxigenylated 192IgG was not detectable within cholinergic basal forebrain neurons after intraventricular injection. Presumably, this modified antibody could not be internalized. On the other hand, digoxigenylated 192IgG was found to be an excellent immunocytochemical marker for p75NTR as shown by double labelling including highly sensitive mouse antibodies directed against ChAT. Based on the present findings, future applications of the apparently non-toxic Cy3-192IgG and other antibodies for fluorescent in vivo and in vitro labelling are discussed.