Immunohistochemical demonstration of the small GTPase RhoA on epoxy-resin embedded sections

Within the Ischemic Penumbra, Sub-Cellular Compartmentalization of Heat Shock Protein 70 Overlaps with Autophagy Proteins and Fails to Merge with Lysosomes

The brain area which surrounds the frankly ischemic region is named the area penumbra. In this area, most cells are spared although their oxidative metabolism is impaired. area penumbra is routinely detected by immunostaining of a molecule named Heat Shock Protein 70 (HSP70). Within the area penumbra, autophagy-related proteins also increase. Therefore, in the present study, the autophagy-related microtubule-associated protein I/II-Light Chain 3 (LC3) was investigated within the area penumbra along with HSP70. In C57 black mice, ischemia was induced by permanent occlusion of the distal part of the middle cerebral artery. Immunofluorescence and electron microscopy show that LC3 and HSP70 are overexpressed and co-localize within the area penumbra in the same cells and within similar subcellular compartments. In the area penumbra, marked loss of co-localization of HSP70 and LC3-positive autophagy vacuoles, with lysosomal-associated membrane protein 1 (LAMP1) or cathepsin-D-positive lysosome vacuoles occurs. This study indicates that, within the area penumbra, a failure of autophagolysosomes depends on defective compartmentalization of LC3, LAMP1 and cathepsin-D and a defect in merging between autophagosomes and lysosomes. Such a deleterious effect is likely to induce a depletion of autophagolysosomes and cell clearing systems, which needs to be rescued in the process of improving neuronal survival.

Spreading of Alpha Synuclein from Glioblastoma Cells towards Astrocytes Correlates with Stem-like Properties

Simple Summary

The present study questions whether cells from glioblastoma multiforme (GBM), which overexpress α-synuclein (α-syn), may alter neighboring non-tumoral astrocyte cell lines. The occurrence of α-syn in GBM correlates with the expression of the stem cell marker nestin. When astrocytes are co-cultured with GBM cells in a trans-well apparatus the occurrence of α-syn and nestin rises remarkably. The increase in α-syn in co-cultured astrocytes is more pronounced at the plasma membrane, which mimics the placement of α-syn in GBM cells. When the mTOR inhibitor rapamycin is administered, GBM-induced expression of α-syn and nestin within co-cultured astrocytes is occluded, and morphological alterations are reverted. In the presence of rapamycin the sub-cellular placement of α-syn is modified being allocated within whorls and vacuoles instead of the plasma membrane. The effects induced by rapamycin occur both in baseline GBM cells and within astrocytes primed by co-cultured GBM cells.

Abstract

Evidence has been recently provided showing that, in baseline conditions, GBM cells feature high levels of α-syn which are way in excess compared with α-syn levels measured within control astrocytes. These findings are consistent along various techniques. In fact, they are replicated by using antibody-based protein detection, such as immuno-fluorescence, immuno-peroxidase, immunoblotting and ultrastructural stoichiometry as well as by measuring α-syn transcript levels at RT-PCR. The present manuscript further questions whether such a high amount of α-syn may be induced within astrocytes, which are co-cultured with GBM cells in a trans-well system. In astrocytes co-cultured with GBM cells, α-syn overexpression is documented. Such an increase is concomitant with increased expression of the stem cell marker nestin, along with GBM-like shifting in cell morphology. This concerns general cell morphology, subcellular compartments and profuse convolutions at the plasma membrane. Transmission electron microscopy (TEM) allows us to assess the authentic amount and sub-cellular compartmentalization of α-syn and nestin within baseline GBM cells and the amount, which is induced within co-cultured astrocytes, as well as the shifting of ultrastructure, which is reminiscent of GBM cells. These phenomena are mitigated by rapamycin administration, which reverts nestin- and α-syn-related overexpression and phenotypic shifting within co-cultured astrocytes towards baseline conditions of naïve astrocytes. The present study indicates that: (i) α-syn increases in astrocyte co-cultured with GBM cells; (ii) α-syn increases in astrocytes along with the stem cell marker nestin; (iii) α-syn increases along with a GBM-like shift of cell morphology; (iv) all these changes are replicated in different GBM cell lines and are reverted by the mTOR inhibitor rapamycin. The present findings indicate that α-syn does occur in high amount within GBM cells and may transmit to neighboring astrocytes as much as a stem cell phenotype. This suggests a mode of tumor progression for GBM cells, which may transform, rather than merely substitute, surrounding tissue; such a phenomenon is sensitive to mTOR inhibition.

Occurrence of Total and Proteinase K-Resistant Alpha-Synuclein in Glioblastoma Cells Depends on mTOR Activity

Simple Summary

The accumulation of alpha-synuclein (α-syn) is considered a pathological hallmark of the neurodegenerative disorders known as synucleinopathies. The clearance of α-syn depends on autophagy activity, which is inhibited by the mechanistic target of rapamycin (mTOR). Thus, it is likely that α-syn accumulation may occur whenever mTOR is overactive and autophagy is suppressed. In fact, the lack of effective autophagy increases the amount of α-syn and may produce protein aggregation. Therefore, in the present study, we questioned whether cells from glioblastoma multiforme (GBM), a lethal brain neoplasm, wherein mTOR is upregulated and autophagy is suppressed, may overexpress α-syn. In fact, a large quantity of α-syn is measured in GBM cells compared with astrocytes, which includes proteinase K-resistant α-syn. Rapamycin, while inhibiting mTOR activity, significantly reduces the amount of α-syn and allocates α-syn within autophagy-like vacuoles.

Abstract

Alpha-synuclein (α-syn) is a protein considered to be detrimental in a number of degenerative disorders (synucleinopathies) of which α-syn aggregates are considered a pathological hallmark. The clearance of α-syn strongly depends on autophagy, which can be stimulated by inhibiting the mechanistic target of rapamycin (mTOR). Thus, the overexpression of mTOR and severe autophagy suppression may produce α-syn accumulation, including the proteinase K-resistant protein isoform. Glioblastoma multiforme (GBM) is a lethal brain tumor that features mTOR overexpression and severe autophagy inhibition. Cell pathology in GBM is reminiscent of a fast, progressive degenerative disorder. Therefore, the present work questions whether, as is analogous to neurons during degenerative disorders, an overexpression of α-syn occurs within GBM cells. A high amount of α-syn was documented in GBM cells via real-time PCR (RT-PCR), Western blotting, immunohistochemistry, immuno-fluorescence, and ultrastructural stoichiometry, compared with the amount of β- and γ-synucleins and compared with the amount of α-syn counted within astrocytes. The present study indicates that (i) α-syn is overexpressed in GBM cells, (ii) α-syn expression includes a proteinase-K resistant isoform, (iii) α-syn is dispersed from autophagy-like vacuoles to the cytosol, (iv) α-syn overexpression and cytosol dispersion are mitigated by rapamycin, and (v) the α-syn-related GBM-like phenotype is mitigated by silencing the SNCA gene.

Subcellular Localization of Connexin 26 in Cardiomyocytes and in Cardiomyocyte-Derived Extracellular Vesicles

Connexins (Cxs) are a family of membrane-spanning proteins, expressed in vertebrates and named according to their molecular weight. They are involved in tissue homeostasis, and they function by acting at several communication levels. Cardiac Cxs are responsible for regular heart function and, among them, Cx26 and Cx43 are widely expressed throughout the heart. Cx26 is present in vessels, as well as in cardiomyocytes, and its localization is scattered all over the cell aside from at the intercalated discs as is the case for the other cardiac Cxs. However, having been found in cardiomyocytes only recently, both its subcellular localization and its functional characterization in cardiomyocytes remain poorly understood. Therefore, in this study we aimed to obtain further data on the localization of Cx26 at the subcellular level. Our TEM immunogold analyses were performed on rat heart ventricles and differentiated H9c2 cardiac cell sections as well as on differentiated H9c2 derived extracellular vesicles. The results confirmed the absence of Cx26 at intercalated discs and showed the presence of Cx26 at the level of different subcellular compartments. The peculiar localization at the level of extracellular vesicles suggested a specific role for cardiac Cx26 in inter-cellular communication in an independent gap junction manner.

The Autophagy-Related Organelle Autophagoproteasome Is Suppressed within Ischemic Penumbra

The peri-infarct region, which surrounds the irreversible ischemic stroke area is named ischemic penumbra. This term emphasizes the borderline conditions for neurons placed within such a critical region. Area penumbra separates the ischemic core, where frank cell loss occurs, from the surrounding healthy brain tissue. Within such a brain region, nervous matter, and mostly neurons are impaired concerning metabolic conditions. The classic biochemical marker, which reliably marks area penumbra is the over-expression of the heat shock protein 70 (HSP70). However, other proteins related to cell clearing pathways are modified within area penumbra. Among these, autophagy proteins like LC3 increase in a way, which recapitulates Hsp70. In contrast, components, such as P20S, markedly decrease. Despite apparent discrepancies, the present study indicates remarkable overlapping between LC3 and P20S redistribution within area penumbra. In fact, the amount of both proteins is markedly reduced within vacuoles. Specifically, a massive loss of LC3 + P20S immuno-positive vacuoles (autophagoproteasomes) is reported here. This represents the most relevant sub-cellular alteration here described in cell clearing pathways within area penumbra. The functional significance of these findings remains to be determined and it will take a novel experimental stream to decipher the fine-tuning of such a phenomenon.

Stoichiometric Analysis of Shifting in Subcellular Compartmentalization of HSP70 within Ischemic Penumbra

The heat shock protein (HSP) 70 is considered the main hallmark in preclinical studies to stain the peri-infarct region defined area penumbra in preclinical models of brain ischemia. This protein is also considered as a potential disease modifier, which may improve the outcome of ischemic damage. In fact, the molecule HSP70 acts as a chaperonine being able to impact at several level the homeostasis of neurons. Despite being used routinely to stain area penumbra in light microscopy, the subcellular placement of this protein within area penumbra neurons, to our knowledge, remains undefined. This is key mostly when considering studies aimed at deciphering the functional role of this protein as a determinant of neuronal survival. The general subcellular placement of HSP70 was grossly reported in studies using confocal microscopy, although no direct visualization of this molecule at electron microscopy was carried out. The present study aims to provide a direct evidence of HSP70 within various subcellular compartments. In detail, by using ultrastructural morphometry to quantify HSP70 stoichiometrically detected by immuno-gold within specific organelles we could compare the compartmentalization of the molecule within area penumbra compared with control brain areas. The study indicates that two cell compartments in control conditions own a high density of HSP70, cytosolic vacuoles and mitochondria. In these organelles, HSP70 is present in amount exceeding several-fold the presence in the cytosol. Remarkably, within area penumbra a loss of such a specific polarization is documented. This leads to the depletion of HSP70 from mitochondria and mostly cell vacuoles. Such an effect is expected to lead to significant variations in the ability of HSP70 to exert its physiological roles. The present findings, beyond defining the neuronal compartmentalization of HSP70 within area penumbra may lead to a better comprehension of its beneficial/detrimental role in promoting neuronal survival.

Morphology, clearing efficacy, and mTOR dependency of the organelle autophagoproteasome

The interplay between autophagy (ATG) and ubiquitin proteasome (UP) cell-clearing systems was recently evidenced at biochemical and morphological levels, where subunits belonging to both pathways co-localize within a novel organelle named autophagoproteasome (APP). We previously documented that APP occurs at baseline conditions, while it is hindered by neurotoxicant administration. This is bound to the activity of the mechanistic target of rapamycin (mTOR), since APP is stimulated by mTOR inhibition, which in turn, is correlated with cell protection. In this brief report, we provide novel morphological and biochemical evidence on APP, suggesting the presence of active UP subunits within ATG vacuoles. Although a stream of interpretation considers such a merging as a catabolic pathway to clear inactive UP subunits, our data further indicate that UP-ATG merging may rather provide an empowered catalytic organelle.

Neuroprotective Effects of Curcumin in Methamphetamine-Induced Toxicity

Curcumin (CUR), a natural polyphenol extracted from rhizome of the Curcuma longa L, has received great attention for its multiple potential health benefits as well as disease prevention. For instance, CUR protects against toxic agents acting on the human body, including the nervous system. In detail, CUR possesses, among others, strong effects as an autophagy activator. The present study indicates that CUR counteracts methamphetamine (METH) toxicity. Such a drug of abuse is toxic by disturbing the autophagy machinery. We profited from an unbiased, low variable cell context by using rat pheochromocytoma PC12 cell line. In such a system, a strong protection was exerted by CUR against METH toxicity. This was associated with increased autophagy flux, merging of autophagosomes with lysosomes and replenishment of autophagy vacuoles with LC3, which instead is moved out from the vacuoles by METH. This is expected to enable the autophagy machinery. In fact, while in METH-treated cells the autophagy substrates α-synuclein accumulates in the cytosol, CUR speeds up α-synuclein clearance. Under the effects of CUR LC3 penetrate in autophagy vacuoles to commit them to cell clearance and promotes the autophagy flux. The present data provide evidence that CUR counteracts the neurotoxic effects induced by METH by promoting autophagy.

Ultrastructural Localization of Histidine-rich Glycoprotein in Skeletal Muscle Fibers: Colocalization With AMP Deaminase

Histidine-rich glycoprotein (HRG) is a plasma protein synthesized by the liver. We have given the first evidence of a tissue localization of HRG demonstrating its presence in skeletal muscle, associated with the zinc enzyme AMP deaminase (AMPD1). Moreover, we have shown that muscle cells do not synthesize HRG, but they can internalize it from plasma. We have recently demonstrated by confocal laser scanning microscopy that in human skeletal muscle, HRG is mainly localized in the myofibrils, preferentially at the I-band of the sarcomere, in the sarcoplasm, and in the nuclei. Using transmission electron microscopy and immunogold analysis, we carried out this study on human and rat normal skeletal muscles with the purpose to deepen the ultrastructural localization of HRG in skeletal muscle fibers. The immunogold analysis evidenced the presence of HRG in the sarcomeres, mainly in the I-band and to a less extent in the A-band, in the heterochromatin of nuclei, and in the sarcoplasmic reticulum. The colocalization of HRG and skeletal muscle AMPD1 was also analyzed. A colabeling of HRG and AMPD1 was evident at sarcomeric, sarcoplasmic reticulum, and nuclear levels. The significance of these interesting and new results is discussed in this article.

mTOR Modulates Methamphetamine-Induced Toxicity through Cell Clearing Systems

Methamphetamine (METH) is abused worldwide, and it represents a threat for public health. METH exposure induces a variety of detrimental effects. In fact, METH produces a number of oxidative species, which lead to lipid peroxidation, protein misfolding, and nuclear damage. Cell clearing pathways such as ubiquitin-proteasome (UP) and autophagy (ATG) are involved in METH-induced oxidative damage. Although these pathways were traditionally considered to operate as separate metabolic systems, recent studies demonstrate their interconnection at the functional and biochemical level. Very recently, the convergence between UP and ATG was evidenced within a single organelle named autophagoproteasome (APP), which is suppressed by mTOR activation. In the present research study, the occurrence of APP during METH toxicity was analyzed. In fact, coimmunoprecipitation indicates a binding between LC3 and P20S particles, which also recruit p62 and alpha-synuclein. The amount of METH-induced toxicity correlates with APP levels. Specific markers for ATG and UP, such as LC3 and P20S in the cytosol, and within METH-induced vacuoles, were measured at different doses and time intervals following METH administration either alone or combined with mTOR modulators. Western blotting, coimmunoprecipitation, light microscopy, confocal microscopy, plain transmission electron microscopy, and immunogold staining were used to document the effects of mTOR modulation on METH toxicity and the merging of UP with ATG markers within APPs. METH-induced cell death is prevented by mTOR inhibition, while it is worsened by mTOR activation, which correlates with the amount of autophagoproteasomes. The present data, which apply to METH toxicity, are also relevant to provide a novel insight into cell clearing pathways to counteract several kinds of oxidative damage.

Connexin 26 Expression in Mammalian Cardiomyocytes

Connexins are a family of membrane-spanning proteins named according to their molecular weight. They are known to form membrane channels mediating cell-cell communication, which play an essential role in the propagation of electrical activity in the heart. Cx26 has been described in a number of tissues but not in the heart, and its mutations are frequently associated with deafness and skin diseases. The aim of this study was to assess the possible Cx26 expression in heart tissues of different mammalian species and to demonstrate its localization at level of cardiomyocytes. Samples of pig, human and rat heart and H9c2 cells were used for our research. Immunohistochemical and molecular biology techniques were employed to test the expression of Cx26. Interestingly, this connexin was found in cardiomyocytes, at level of clusters scattered over the cell cytoplasm but not at level of the intercalated discs where the other cardiac connexins are usually located. Furthermore, the expression of Cx26 in H9c2 myoblast cells increased when they were differentiated into cardiac-like phenotype. To our knowledge, the expression of Cx26 in pig, human and rat has been demonstrated for the first time in the present paper.

Rapamycin promotes differentiation increasing βIII-tubulin, NeuN, and NeuroD while suppressing nestin expression in glioblastoma cells

Glioblastoma cells feature mammalian target of rapamycin (mTOR) up-regulation which relates to a variety of effects such as: lower survival, higher infiltration, high stemness and radio- and chemo-resistance. Recently, it was demonstrated that mTOR may produce a gene shift leading to altered protein expression. Therefore, in the present study we administered different doses of the mTOR inhibitor rapamycin to explore whether the transcription of specific genes are modified. By using a variety of methods we demonstrate that rapamycin stimulates gene transcription related to neuronal differentiation while inhibiting stemness related genes such as nestin. In these experimental conditions, cell phenotype shifts towards a pyramidal neuron-like shape owing long branches. Rapamycin suppressed cell migration when exposed to fetal bovine serum (FBS) while increasing the cell adhesion protein phospho-FAK (pFAK). The present study improves our awareness of basic mechanisms which relate mTOR activity to the biology of glioblastoma cells. These findings apply to a variety of effects which can be induced by mTOR regulation in the brain. In fact, the ability to promote neuronal differentiation might be viewed as a novel therapeutic pathway to approach neuronal regeneration.

The Autophagoproteasome a Novel Cell Clearing Organelle in Baseline and Stimulated Conditions

Protein clearing pathways named autophagy (ATG) and ubiquitin proteasome (UP) control homeostasis within eukaryotic cells, while their dysfunction produces neurodegeneration. These pathways are viewed as distinct biochemical cascades occurring within specific cytosolic compartments owing pathway-specific enzymatic activity. Recent data strongly challenged the concept of two morphologically distinct and functionally segregated compartments. In fact, preliminary evidence suggests the convergence of these pathways to form a novel organelle named autophagoproteasome. This is characterized in the present study by using a cell line where, mTOR activity is upregulated and autophagy is suppressed. This was reversed dose-dependently by administering the mTOR inhibitor rapamycin. Thus, we could study autophagoproteasomes when autophagy was either suppressed or stimulated. The occurrence of autophagoproteasome was shown also in non-human cell lines. Ultrastructural morphometry, based on the stochiometric binding of immunogold particles allowed the quantitative evaluation of ATG and UP component within autophagoproteasomes. The number of autophagoproteasomes increases following mTOR inhibition. Similarly, mTOR inhibition produces overexpression of both LC3 and P20S particles. This is confirmed by the fact that the ratio of free vs. autophagosome-bound LC3 is similar to that measured for P20S, both in baseline conditions and following mTOR inhibition. Remarkably, within autophagoproteasomes there is a slight prevalence of ATG compared with UP components for low rapamycin doses, whereas for higher rapamycin doses UP increases more than ATG. While LC3 is widely present within cytosol, UP is strongly polarized within autophagoproteasomes. These fine details were evident at electron microscopy but could not be deciphered by using confocal microscopy. Despite its morphological novelty autophagoproteasomes appear in the natural site where clearing pathways (once believed to be anatomically segregated) co-exist and they are likely to interact at molecular level. In fact, LC3 and P20S co-immunoprecipitate, suggesting a specific binding and functional interplay, which may be altered by inhibiting mTOR. In summary, ATG and UP often represent two facets of a single organelle, in which unexpected amount of enzymatic activity should be available. Thus, autophagoproteasome may represent a sophisticated ultimate clearing apparatus.

Coated Glass Slides TACAS Are Applicable to Heat-Assisted Immunostaining and In Situ Hybridization at the Electron Microscopy Level

We performed pre-embedding electron microscopic study for visualizing the antigen and genome of severe fever with thrombocytopenia syndrome (SFTS) virus in the cytoplasm of macrophages of the human splenic red pulp, both requesting preheating treatment of sections. To pursue this, coated glass slides with unique characteristics are needed. Namely, during staining they must prevent detaching off sections, but after staining the sections must be transferred to epoxy resin. Aminopropyltriexoxysilane-coated glass slides, widely used for immunostaining, were resistant to transfer to epoxy resin. In contrast, coated glass slides designated as Thinlayer Advanced Cytology Assay System (TACAS) were suitable for this purpose. The technique is also applicable to the coated glass slide-requiring cytology practice, in which immunocytochemical evaluation is needed after cell transfer to another glass slide.

Heat-induced Antigen Retrieval in Conventionally Processed Epon-embedded Specimens: Procedures and Mechanisms

We studied the effectiveness of heat-induced antigen retrieval (HIAR) in conventionally processed, epon-embedded specimens and the mechanisms of HIAR in the specimens. Frozen sections were first immunostained to examine the possibility of using HIAR for 18 antigens to avoid the effects of epoxy resin embedment. The antigenicity of 7 out of 18 antigens was retrieved with glutaraldehyde fixation followed by osmium tetroxide treatment whereas none were retrieved with glutaraldehyde fixation without post-osmication. Six antigens also exhibited positive immunostaining in semi-thin epon sections when the sections were deplasticized with sodium ethoxide followed by autoclaving. In the immunoelectron microscopy with the post-embedding method, positive reactions with fine ultrastructures were obtained using HIAR without deplasticization. These results suggested that osmium tetroxide binds to ethylene double bonds (which are introduced into protein crosslinks by glutaraldehyde) and forms an extremely stable resonance interaction with the Schiff bases, thus destabilizing the protein crosslinks. Heating also further degrades these crosslinks. The present study demonstrated that archival epon blocks can be useful resources for immunohistochemical studies for both light and electron microscopy.

Immunoelectron microscopic observation of chicken glucagon-like peptide (GLP)-1-containing cells in tissues derived from thin section, paraffin block and conventional method

The purpose of the present study was to investigate the possibility of immunoelectron microscopic observation of endocrine cells in paraffin-embedded tissues. The procedure, which involves reprocessing from sliced tissues and immunohistochemical staining by colloidal-gold immunolabeling of paraffin sections from paraffin blocks, was able to reveal the fine characteristics of secretory granules containing glucagon-like peptide-1. Morphometric analyses of the secretory granules showed no significant differences between the reprocessing procedure and a conventional post-embedding procedure, which was performed as a control. The reprocessing procedure has some advantages besides providing information on secretory granules containing the amino acid peptide. For example, the same cell can be observed under both a light microscope and the electron microscope. In addition, the high-electron densities of silver-enhanced gold particles are easily recognized, and the boundary between the profile of the granules and the immunogold labeling is clearly shown at the electron microscopic level. Furthermore, the procedure, which is inexpensive and does not require special devices, can effectively use precious samples that are already paraffin-embedded and unable to be obtained twice, such as the case for endangered animals and rare pathological tissues. To the best of our knowledge, the present study is the first to report the advantages of the reprocessing method for sliced paraffin sections of gut endocrine cells.

Quantum dot immunocytochemical localization of somatostatin in somatostatinoma by Widefield Epifluorescence, super-resolution light, and immunoelectron microscopy

Quantum dot nanocrystal probes (QDs) have been used for detection of somatostatin hormone in secretory granules of somatostatinoma tumor cells by immunofluorescence light microscopy, super-resolution light microscopy, and immunoelectron microscopy. Immunostaining for all modalities was done using sections taken from an epoxy resin-embedded tissue specimen and a similar labeling protocol. This approach allowed assessment of labeling at light microscopy level before examination at super-resolution and electron microscopy level and was a significant aid in interpretation. Etching of ultrathin sections with saturated sodium metaperiodate was a critical step presumably able to retrieve some tissue antigenicity masked by processing in epoxy resin. Immunofluorescence microscopy of QD-immunolabeled sections showed somatostatin hormone localization in cytoplasmic granules. Some variable staining of tumor gland-like structures appeared related to granule maturity and dispersal of granule contents within the tumor cell cytoplasm. Super-resolution light microscopy demonstrated localization of somatostatin within individual secretory granules to be heterogeneous, and this staining pattern was confirmed by immunoelectron microscopy.

Detecting microcalcifications in atherosclerotic plaques by a simple trichromic staining method for epoxy embedded carotid endarterectomies

Atherosclerotic plaques have a high probability of undergoing rapid progression to stenosis, becoming responsible of acute coronary syndrome or stroke. Microcalcifications may act as enhancers of atherosclerotic plaque vulnerability. Considering that calcifications with a diameter smalller than 10 µm in paraffin embedded tissue are rather difficult to detect, our aim was to analyze microcalcifications on semithin sections from epoxy resin embedded samples of carotid endarterectomies using an original trichromic stain (methylene blue-azur B - basic fuchsine - alizarin red). We have compared samples stained either with our method, methylene blue-azur B alone or with Von Kossa staining, and methylene blue-azur B -basic fuchsine alone or with Von Kossa staining.

Our method resulted to be simple and fast (ca. 2 min), it gives a sharp general contrast for all structures and allows to easy identify collagen and elastin. In addition, gray-green colour associated to intracellular lipid droplets evidences foam cells, which are particularly abundant in endarterectomies samples. Mast cells and their metachromatic granules are also well recognized. Calcifications over 0,5 µm are clearly recognizable. In conclusion, microcalcifications are clearly distinguished from the extracellular matrix in spite of their reduced dimensions. Methylene blue-azur B-basic fuchsine-alizarin red method is easy to use, reproducible, and is particularly suitable for the identification of microcalcifications in the morphological analysis of atherosclerotic plaques.

State of the art in antigen retrieval for immunohistochemistry

The masking effects of antigens by chemical fixation, processing, embedding media interactions, represent a serious problem for immunohistochemical purposes. Fortunately, different approaches in antigen retrieval exist. These techniques are relatively recent and continuously expanding. This review focuses on the present state of the art in antigen retrieval methods for immunohistochemistry in light and electron microscopy. Moreover, a brief discussion on the chemical aspects of fixation, mechanism of retrieval, as well as its efficacy, is given.

The intensity of immunogold labeling of deplasticized acrylic sections compared to deplasticized epoxy sections—Theoretical deductions and experimental data

The purpose of this study was to compare the level of immunogold labeling of deplasticized acrylic sections and deplasticized epoxy sections. Pure protein gels of IgG, albumin and thyroglobulin were produced by glutaraldehyde fixation and embedded in non-crosslinked acrylic resin (Technovit 9100) and epoxy resin (Epon 812), respectively. Ultrathin sections of acrylic and epoxy resin were separately deplasticized in 2-methoxyethyl acetate (MEA) and sodium ethoxide. Quantitative immunogold labeling was performed with anti-IgG, anti-albumin and anti-thyroglobulin antibodies on sections of the corresponding protein gels. For all antibodies tested, the intensity of labeling for deplasticized acrylic sections was significantly higher (two to four times) than for the corresponding deplasticized epoxy sections. The results fit with a theoretically deduced relation: the quotient of the labeling of two deplasticized sections of different resins is equivalent to the square root of the quotient of the labeling of the similar sections not exposed to any kind of pre-treatment. The practical significance of the results is that immunolabeling of deplasticized non-crosslinked acrylic resin results in more intense immunogold labeling than deplasticized epoxy sections. Deplasticizing is most useful when the requirements for ultrastructural preservation according to conventional criteria are moderate. Our theoretically deduced results also indicate that deplasticized Technovit (or other non-crosslinked acrylic resins) sections will be significantly better suited for immunolabeling at the light microscopic level than deplasticized epoxy sections.