Ultrastructural double labelling using colloidal gold

Expression patterns of the ectopeptidases aminopeptidase N/CD13 and dipeptidyl peptidase IV/CD26: immunoultrastructural topographic localization on different types of cultured cells

Aminopeptidase N/CD13 and dipeptidyl peptidase IV/CD26 are widespread membrane-bound peptidases involved in fundamental biological processes. Using cryo-ultramicrotomy of cultured cells followed by indirect immunogold labelling, both enzymes appeared to be strongly and regularly labelled on the cell surfaces of human synovial fibroblasts, T-lymphocytes and colon carcinoma cells Caco-2. In the cytoplasm of the synovial fibroblasts gold-labelled vesicle-like structures were found, which we consider to be potential transport vesicles. An abundant and regular expression of CD13 was detected on cultured renal parenchymal cells. On the renal carcinoma cell line Caki-1 cells we found a low, non-homogeneous and clustered CD13-labelling. On cultured renal parenchymal cells and the Caki-1 cells CD26 could not be observed. The expression pattern of CD26 on renal carcinoma cell line Caki-2 cells showed also a slightly clustered distribution. A low density CD26-labelling was present on the squamous cell carcinoma cell line UM-SCC-22B. CD13 was absent in Caki-2 and UM-SCC-22B cells. The presence of both enzymes on the cultured cells enables their ultrastructural investigation under different growth conditions and their involvement in cell-cell interactions. For this purpose, however, further investigations are necessary.

Immunoelectron microscopic single and double labelling of aminopeptidase N (CD 13) and dipeptidyl peptidase IV (CD 26)

Using ultrathin cryosections and immunogold labelling, aminopeptidase N (CD 13) and dipeptidyl peptidase IV (CD 26) were localized on the luminal side of the brush border membrane of proximal tubular cells in human kidney as well as of enterocytes from rat small intestine. Furthermore, both enzymes could be detected on the cell surface of human T lymphocytes and especially aminopeptidase N on human synovial fibroblasts. Gold labelled vesicular structures were also found in the cytoplasm in the apical part of renal proximal tubular cells and synovial fibroblasts. In human kidney the colocalization of the two membrane antigens was possible by using several double labelling methods.

Improved immuno double labelling for cell and structural biology

Colloidal gold is the most widely used electron dense marker in biological electron microscopy. The development of procedures for making gold particles of very defined sizes has made double or even multiple labelling possible using gold of two or more different sizes. Lately a new type of electron dense marker has been developed consisting of ligand-stabilized metal atom clusters rather than colloidal particles. The differences between these two types of markers are highlighted and the advantages of using metal atom clusters for immuno labelling of certain biological specimens are discussed. Possible methods of distinguishing two such cluster labels in double labelling experiments are reviewed.

Non-specific adherence of oxide particles as a means of quantifying protein adsorption on surfaces

This paper reports quantification of a method for measuring amounts of protein adsorbed to a surface; the method is especially useful for revealing macroscopic spatial patterns of adsorption. The experiments tested the effectiveness of iron oxide suspensions adsorbed onto the adsorbed protein to indicate, in separate trials, the amount of either human plasma fibrinogen or human serum albumin (HSA) present on glass slides. Corresponding trials, using radioactively labeled proteins, were performed to calibrate the amount of either albumin or fibrinogen adsorbed onto similar slides out of solutions of varying bulk concentrations. The oxide deposits were quantified using a scanner and an image analysis program. The isotherms produced from the collected data indicate a continuous, monotonic correlation between light absorbed by adherent oxide and surface concentration of protein. The same correlation applies to albumin and fibrinogen when surface concentrations are expressed in weight units. These results confirm that patterns of oxide deposition correspond to patterns of protein deposition and show clearly how qualitative observations, such as those previously reported, can be made quantitative with scanning and digital image analysis.

Involvement of platelets in stimulating osteogenic activity

Osteoblast-like cells have been shown to be sensitive to the proliferative action of a wide variety of growth factors. Many of these growth factors have been isolated from platelets and are thought to be released at local sites in response to injury. In this study, we tested whether human platelet concentrate, as a supplement to basic medium, would support the proliferative and functional activity of human fetal osteoblast-like cells in both short-term and long-term culture. In short-term studies, uptake of [3H]thymidine was increased in platelet-treated cultures by more than 4-fold compared with 10% serum-supplemented controls. When cultured for prolonged periods on coverslips, the cells formed multilayers, with a collagen-based matrix separating the layers. Long-term cultures that were treated with 1.5% (vol/vol) platelets in serum-supplemented medium showed increases in the depth of the multilayers of as much as 36-fold at 30 days after confluence, compared with the 10% serum-supplemented controls; this difference persisted until day 50. Incorporation of growth factor in the matrix was examined with the use of colloidal gold immunoelectron microscopy. Immunogold labeling intensities for transforming growth factor-beta 1 were significantly lower in the platelet-treated cultures at 20 days and then increased to a maximum level of 2.1-fold more than in the controls at 40 days. Labeling intensities for insulin-like growth factor-I and basic fibroblast growth factor were significantly lower in the platelet-treated cultures than in the controls at all stages of culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Thrombospondin co-localises with TGF beta and IGF-I in the extracellular matrix of human osteoblast-like cells and is modulated by 17 beta estradiol

Thrombospondin (TSP) is a multifunctional glycoprotein which is synthesised by several cell types including osteoblasts, and incorporated into the extracellular matrix (ECM) of these cells. The function and regulation of TSP in bone is not clear. In this study, using a long term culture model of human osteoblast-like cells, we examined the distribution of TSP in the ECM and its modulation by added estradiol. In this model the osteoblast-like cells form a regular multilayer which continues to increase in depth up to 50 days post confluence. In the ECM of these cultures and in 19-week fetal bone, the bone markers osteocalcin and alkaline phosphatase were diffusely distributed in the matrix. In contrast, labelling for TSP was concentrated, confined to the banded collagen and its immediately adjacent ECM. This pattern of labelling resembled that of the growth factors transforming growth factor beta-I (TGF beta), and insulin-like growth factor-I (IGF-I), with which TSP label co-localised. Labelling intensities were comparable between fetal bone and the in vitro material for TSP, TGF beta and IGF-I. TSP label was present by 10 days post confluence, reached a maximum by 20 days, and declined slowly thereafter, a time course which was similar to that of IGF-I. Incubation of osteoblast-like cell cultures with 17 beta estradiol resulted in an increase in multilayer depth and a maximal 3-fold increase in TSP labeling at 30 days as well as approximately 2-fold increases for TGF beta and IGF-I. The dose-response relationship for these responses to estradiol treatment was biphasic with maximal increases at 10(-10) M-10(-11) M of added estradiol. Treatment with 17 alpha estradiol produced labelling intensities that were not significantly different from controls. Studies with other cell types have suggested that TSP may be involved in modulation of growth factor activity. The similarities between TSP, TGF beta and IGF-I, in terms of their distribution and regulation by 17 beta estradiol treatment, may indicate a role for TSP in modulating bone cell proliferation and function through interaction with local growth factors.

Modulation of growth factor incorporation into ECM of human osteoblast-like cells in vitro by 17 beta-estradiol

Human fetal osteoblast-like cells formed a regular multilayered structure in vitro with an extensive collagen-based extracellular matrix. With colloidal gold immunocytochemistry, labels for alkaline phosphatase and osteocalcin were distributed in a relatively diffuse pattern, in contrast to the bone growth factors, insulin-like growth factors I and II (IGF-I and IGF-II), transforming growth factor-beta 1 (TGF-beta 1), and basic fibroblast growth factor, which were colocalized in the collagenous matrix of the multilayer. The inclusion of 17 beta-estradiol (10(-11) to 10(-9) M) in the culture medium increased multilayer depths, increased labeling for IGF-I, IGF-II, and TGF-beta 1, and resulted in earlier detection of TGF-beta 1 label. In contrast, the increase in multilayer depth resulting from treatment with human platelets, an exogenous source of growth factors, was not accompanied by an increase in matrix IGF-I, IGF-II, or TGF-beta 1 label, suggesting a particular effect of estradiol to facilitate this process. Because growth factors in bone matrix may act as coupling agents when released during resorption, reduced growth factor incorporation in the presence of reduced sex steroid concentrations may lead to uncoupling of resorption and subsequent formation.

Immunogold localization of TGF beta 1 protein and mRNA in human skin using a colloidal gold/digoxygenin system

Tissue preservation, and immunogold cytochemical and in-situ hybridization labelling intensities vary according to the preparatory protocols used. We wished to determine which preparative protocols produce optimal preservation, protein and mRNA labelling. Nine combinations of fixative and embedding resin were therefore studied using postembedding immunoelectron microscopy and a novel immunogold digoxygenin in situ hybridization (ISH) system, to quantitate the presence of transforming growth factor beta 1 (TGF beta 1) protein and message in human skin. The best preservation was observed in tissue fixed in 1% glutaraldehyde and embedded in LR White resin or low acid glycolmethacrylate resin (LA-GMA). Preservation was poor in tissue fixed with 1% glutaraldehyde and fair in 4% paraformaldeyde, when embedded in Unicryl. Ethanediol dehydration coupled with LA-GMA embedding resulted in reasonable preservation. Based on quantitative measures of the labelling density for TGF beta 1 protein and mRNA, immunogold labelling was adequate with 1% glutaraldehyde fixation coupled with LR White or LA-GMA resins, and also with 4% paraformaldehyde and LR White resin, but was best with ethanediol dehydration and LA-GMA embedding. ISH labelling under basal conditions was best in LA-GMA with 1% glutaraldehyde or 4% paraformaldehyde. The ISH label in tissue fixed with 1% glutaraldehyde and embedded in LA-GMA was significantly increased by treatment with proteinase K. Overall, ethanediol dehydration was associated with a good immunoelectron microscopic (IEM) label while LA-GMA with 1% glutaraldehyde or 4% paraformaldehyde resulted in a consistently detectable ISH label. LA-GMA embedding with 1% glutaraldehyde fixation gave a good result with both IEM and ISH labelling.

Double immunogold labelling demonstrating expression of recombinant genes for production of an anti-fertility vaccine

The multiple antibody technique for double immunogold labelling for the simultaneous localization of two antigens with negative staining was utilized to demonstrate the expression of recombinant genes in bacteria, with the primary antibodies being raised in different host species. For the production of a vaccine for immunological control of fertility, a multi-functional plasmid vector was introduced into the bacterium Pseudomonas aeruginosa containing the Dichelobacter nodosus fimbrial subunit gene with a grafted amino acid sequence of luteinizing hormone releasing hormone (LHRH) peptide. Fimbriae of this recombinant, when run on a SDS-polyacrylamide electrophoresis gel, gave a single broad band for LHRH peptide/D. nodosus subunit and were harvested to produce the anti-fertility vaccine which, when injected into mice, produced atrophy of the testes with absence of sperm, resulting in reversible castration. Double immunogold labelling of the recombinant P. aeruginosa bacteria demonstrated fimbriae with strong expression of the LHRH-peptide, expression of the D. nodosus subunit and absence of host fimbriae.