Antigen recovery and preservation using the microwave irradiation of biological samples for transmission electron microscopy analysis

Most studies using microwave irradiation (MWI) for the preparation of tissue samples have reported an improvement in structural integrity. However, there have been few studies on the effect of microwave (MW) on antigen preservation during sample preparation prior to immunolocalization. This report documents our experience of specimen preparation using an automatic microwave apparatus to obtain antigen preservation and retrieval. We tested the effects of MW processing vs. conventional procedures on the morphology and antigenicity of two different tissues: the brain and mammary gland, whose chemical composition and anatomical organization are quite different. We chose to locate the transcription factor PPARβ/δ using immunocytochemistry on brain tissue sections from hamsters. Antigen retrieval protocols involving MWI were used to restore immunoreactivity. We also studied the efficiency of the ultrastructural immunolocalization of both PPARγ and caveolin-1 following MWI vs. conventional treatment, on mammary gland tissue from mice at 10 days of lactation. Our findings showed that the treatment of tissue samples with MWI, in the context of a process lasting just a few hours from fixation to immunolocalization, enabled similar, or even better, results than conventional protocols. The quantification of immunolabeling for cav-1 indicated an increase in density of up to three-fold in tissues processed in the microwave oven. Furthermore, MW treatment permitted the localization of PPARβ/δ in glutaraldehyde-fixed specimens, which was impossible in the absence of MWI. This study thus showed that techniques involving the use of microwaves could largely improve both ultrastructure and immunodetection.

Intracellular calcium oscillations in articular chondrocytes induced by basic calcium phosphate crystals lead to cartilage degradation

OBJECTIVE

Basic calcium phosphate (BCP) crystals, including octacalcium phosphate (OCP), carbonated-apatite (CA) and hydroxyapatite (HA) crystals are associated with destructive forms of osteoarthritis. Mechanisms of BCP-induced cartilage breakdown remain incompletely understood. We assessed the ability of BCP to induce changes in intracellular calcium (iCa(2+)) content and oscillations and the role of iCa(2+) in BCP-induced cartilage degradation.

METHODS

Bovine articular chondrocytes (BACs) and bovine cartilage explants (BCEs) were stimulated with BCP or monosodium urate (MSU) crystals. iCa(2+) levels were determined by spectrofluorimetry and oscillations by confocal microscopy. mRNA expression of matrix metalloproteinase 3 (MMP-3), a disintegrin and metalloprotease with thrombospondin-like motifs 4 (ADAMTS-4) and ADAMTS-5 was assessed by quantitative real-time PCR. Glycosaminoglycan (GAG) release was measured in the supernatants of BCE cultures.

RESULTS

All three BCP crystals significantly increased iCa(2+) content. OCP also induced iCa(2+) oscillations. Rate of BACs displaying iCa(2+) oscillations increased over time, with a peak after 20 min of stimulation. OCP-induced iCa(2+) oscillations involved both extracellular Ca(2+) (eCa(2+)) influx and iCa(2+) stores. Indeed, OCP-induced iCa(2+) oscillations decreased rapidly in Ca(2+)-free medium. Both voltage- and non-voltage-dependent Ca(2+) channels were involved in eCa(2+) influx. BCP crystal-induced variation in iCa(2+) content was associated with BCP crystal-induced cartilage matrix degradation. However, iCa²(+) was not associated with OCP crystal-induced mRNA expression of MMP-3, ADAMTS-4 or ADAMTS-5.

CONCLUSION

BCP crystals can induce variation in iCa(2+) content and oscillations in articular chondrocytes. Furthermore, BCP crystal-induced changes in iCa(2+) content play a pivotal role in BCP catabolic effects on articular cartilage.

Signaling networks from Gβ1 subunit to transcription factors and actin remodeling via a membrane-located ERβ-related protein in the rapid action of daidzein in osteoblasts

Although estrogen replacement has been the main therapy to prevent and treat osteoporosis, there are concerns about its safety. Phytoestrogens have attracted attention to their potential impacts in osteoporosis prevention and treatment. Among phytoestrogens, the isoflavone daidzein (Dz) acts on transcription via the intracellular estrogen receptors (ER), mainly ERbeta, in osteoblasts, but mimics only part of the estrogen effects. Since estradiol also exerts rapid effects in osteoblasts, we investigated the multistep processes involved in the rapid actions of low (1-100 pM) doses of daidzein. Dz bound to a membrane moiety, related to ERbeta since the calcium response to Dz was blocked by an anti-ERbeta antibody directed against the C-terminus, but not by a double-stranded siRNA specific for ERbeta. This protein was coupled to a pertussis toxin (PTX)-sensitive Gbeta1 subunit whose transducer was PLC-beta2, which triggered a rapid (5 sec) mobilization of calcium from the endoplasmic reticulum. Dz phosphorylated within 15 sec ERK1/2 whose phosphorylation involved two routes: Gbeta1/PLC-beta2/PKC/c-Raf-1/MEK1/2 and Gbeta1/PI3K/cSrc/c-Raf-1/MEK1/2 as shown using several inhibitors. Dz induced rapid (1 min) changes in the actin cytoskeleton via the two routes. The rapid (20 sec) phosphorylation of Elk-1 and CREB by Dz involved Gbeta1 and ERK1/2. All the processes were insensitive to the estradiol antagonist ICI 182,780. In conclusion, the rapid effects of Dz seem to be biologically relevant for the function of osteoblast in bone since the isoflavone activates transcription factors linked to early genes controlling cellular proliferation and differentiation, and modulates actin cytoskeleton which controls cell adhesion, division, or secretion.

Direct visualization of intracellular calcium in rat osteoblasts by energy-filtering transmission electron microscopy

Osteoblasts are the highly specialized bone cells responsible for matrix mineralization. Mineralization is a complex, incompletely understood, process involving intracellular calcium homeostasis. Rapid changes in ionized calcium concentration ([Ca(2+)](i)) occur in these cells, but the intracellular distribution of total calcium, which may be involved in matrix mineralization, remains unknown. We have therefore investigated the distribution of total calcium in osteoblasts either ex vivo from rapidly mineralizing neonatal rat bones or in the same cells cultured to confluence before they had entered the mineralization phase, and without stimulation for mineralized matrix formation. All cells were examined bone-untreated (controls) or following the addition of the ionophore ionomycin that induced a large and sustained increase in [Ca(2+)](i). Cryomethods, quick-freezing and freeze-drying, and OsO(4) vapor fixation were employed to preserve the original calcium distribution, and the preservation was verified by secondary ion mass spectrometry (SIMS). Intracellular calcium distribution was identified by energy-filtering transmission electron microscopy (EELS). Scarce calcium signals were recorded from all osteoblasts maintained in buffer (controls). Ionomycin addition resulted in the accumulation of calcium in mitochondria, and more calcium was stored in the mitochondria of osteoblasts involved in mineralization than in those of osteoblasts before mineralization. Moreover, in the former, strong calcium signals were recorded around the junctions between mitochondria and the endoplasmic reticulum. Thus EELS allowed to obtain high-resolution total calcium maps in defined intracellular structures, but only at elevated calcium levels.

Distribution of iron oxide nanoparticles in rat lymph nodes studied using electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI)

Superparamagnetic iron nanoparticles have been developed as contrast agents for magnetic resonance lymphography. The kinetics of uptake of these particles has not yet been accurately determined. We have therefore monitored the distribution of individual iron particles (ferumoxtran, AMI-227, Sinerem) in rat lymph nodes 1.5, 3, 6, 12, and 24 hours after i.v. injection (two rats per time point). The ultrastructural distribution of the iron was determined by energy-filtered transmission electron microscopy (EFTEM). This method allows the identification of elements using element-specific energy-loss electrons. Iron was identified by the Fe-L(2,3) edge (EELS), and iron maps were obtained using iron-specific electrons for imaging (ESI). The background was calculated by simplex optimization (EELS) and by the two-window method (ESI). Ferumoxtran particles were regularly observed at the periphery of the lymph nodes but not in their centers. Isolated iron particles were seen extracellularly within lymph vessels and, 3 hours after injection, as small dots in phagocytic cells. Numerous dense clusters appeared within the cells at later times (6 and 12 hours after injection). These results suggest that the contrast agent moves rapidly across the capillary wall to the lymph and is then taken up by phagocytic cells. J. Magn. Reson. Imaging 2000;12:505-509.

Calcium distribution in high-pressure frozen bone cells by electron energy loss spectroscopy and electron spectroscopic imaging

Subcellular localization of total calcium requires tissue processing that preserves the chemical composition of the samples and a highly sensitive microanalytical technique. In this study rat fetal bone samples were submitted to high-pressure freezing and freeze substitution. Ultrastructural preservation was good in the superficial sections: osteoblasts near the bone mineral had clearly defined plasma and nuclear membranes, dense mitochondria, and numerous ribosomes. Electron energy loss spectroscopy allowed high-resolution calcium-sensitive images to be obtained using ionization edge loss electrons. In biological samples, the Ca-L2,3 signal is superimposed on the carbon edge and artifacts may result from thickness and scattering effects. Therefore the relative thickness was established for each area analyzed (t/lambda <0.5). Background was subtracted using the three-images method, allowing high resolution calcium-sensitive images of intramitochondrial granules and of intracellular compartments, and semiquantitative data from the granules to be obtained. Calcium maps were confirmed by spectra collected on defined areas of the images and the shape of the net Ca-L2,3 edges was compared to the characteristic Ca-L2,3 edge of bone crystals. These procedures will provide new information about total calcium localization in bone cells and the possibility of examining the distribution of other elements.

Iron distribution in thalassemic bone by energy-loss spectroscopy and electron spectroscopic imaging

Iron overload occurs frequently in thalassemia as a consequence of regular blood transfusions, and iron has been found to accumulate in bone, but skeletal toxicity of iron is not clearly established. In this study, bone biopsies of thalassemic patients were investigated by light (n = 6) and electron microscopy (n = 8) in order to analyze iron distribution and possible iron-associated cellular lesions. Sections (5 microns thick) were used for histomorphometry and iron histochemistry. Ultrathin sections were examined with an energy filtering transmission electron microscope. Iron was identified by electron energy loss spectroscopy (EELS), and iron distribution was visualized by electron spectroscopic imaging (ESI) associated with computer-assisted treatment (two-window method). This study shows that EELS allows the detection of 4500-9000 iron atoms, and that computer-assisted image processing is essential to eliminate background and to obtain the net distribution of an element by ESI. This study shows also that stainable iron was present along trabecular surfaces, mineralizing surfaces, and on cement lines in the biopsies of all patients. Moreover, iron was detected by EELS in small granules (diffusely distributed or condensed in large clusters), in osteoid tissue, and in the cytoplasm of bone cells, but not in the mineralized matrix. The shape and size (9-13 nm) of these granules were similar to those reported for ferritin. As for iron toxicity, all patients had osteoid volume and thickness and osteoblast surface in the normal range. Stainable iron surfaces did not correlate with osteoblast surfaces, plasma ferritin concentrations, or the duration of transfusion therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Les cartilages calcifiés de la petite roussette (Scyliorhinus canicula L., Chondrichthyens): histologie et ultrastructure

The ultrastructure of the mandibular tesserae and of the calcifications of the double cone in the vertebrae were studied in the lesser spotted dogfish, Scyliorhinus canicula. New evidence is provided that shows with certainty that chondrocytes degenerate in the tesserae. Ultrastructural study of the collagen substrate in the tesserae also suggested new concepts on collagen organization in the tesserae: very thick collagen fibers have a radial arrangement in the superficial portion of each tessera and evidence also points to the probable noncollagenic nature of the substrate of the Liesegang rings. Observation of early tesseral stages strongly suggests that these formations have a dual origin, which might explain the different configurations of the tesserae: globular on the inner surface and parallel to the collagen fibers on the external surface. The presence or absence of bone in the tesserae will have to be examined anew since this study seems to indicate that the tesserae are entirely cartilaginous in this dogfish. Examination of serial sections of the axial skeleton has shown that the complex structures of the skeleton have very different aspects at different sectional levels in the vertebra. However, at all sectional levels, the double calcified cone seems to be composed of a calcified fibrous cartilage in which chondrocytes degenerate. Our observations on the tesserae and on the double cone clearly demonstrate the degenerative process of the chondrocytes in these structures. Our results also show that, in contrast to other species, this dogfish has no vascularization in any of its cartilages, calcified or not.[Journal translation]

Pathologic features of the femoral heads in a patient aged 14 1/2 years with spondyloepiphyseal dysplasia with osteoarthritis

We describe a patient with spondyloepiphyseal dysplasia and precocious hip osteoarthritis. Bilateral hip arthroplasty was performed at the age of 14 1/2 years. Pathologic examination revealed severe osteoarthritic deformities: flattened and deformed femoral heads, were almost completely covered by abnormal cartilaginous, fibrocartilaginous and fibrous tissues showing intense degenerative and regenerative processes. The electron microscopic examination of chondrocytes showed large intracytoplasmic accumulations of glycogen and of microfilaments and many small vesicles suggesting intense micropinocytosis and/or microexocytosis.

Étude ultrastructurale de l'os des vertèbres du Sélacien Scyliorhinus canicula L

The neural arches of the vertebrae of Scyliorhinus canicula were studied in detail. The extremities of each half arch consist of two pyramids of fibrous cartilage. These contain rows of convergent collagen fibers in the shape of a fan. The cells are arranged in series without forming real columns and without becoming enlarged. The central area of each arch contains a band of calcified cartilage with degenerating cells and numerous gaps that are invaded by urchin-shaped calcifications. This blade of cartilage is squeezed between an internal band of lamellar bone and an external nonlamellar zone of bone. The internal bony zone is bordered by osteoblasts and contains elongated osteocytes, many showing signs of degeneration. The external zone contains osteocytes joined by small canaliculi. Areas of resorption by mononucleated cells can be observed at the border of the external bone zone. These cells project digitations that the calcified border where fragmented collagen fibers are present; they react positively to acid phosphatases and show numerous signs of pynocytosis.[Journal translation]

[Dysplasia spondylo-epiphysealis congenita: its heterogeneity (author's transl)]

A study of epiphyseal cartilage in two children presenting with all the clinical and radiologic features of the dysplasia spondylo-epiphysealis congenita showed abnormalities different from those usually described. In addition to dilatations of the endoplasmic reticulum, there were two types of inclusions observed in the chondrocytes, granules and spirilla, which were limited by a smooth membrane. The intercellular matrix consisted of a dense tangle of fine fibers and numerous dense granules. These findings suggest a heterogeneity for this disease.