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Biomedical subjects

A Teti

Publications and source records attributed to A Teti.

At least 91 records · Page 5Linked to original sources
PubMed1989

Immunocytochemical distribution of extracellular matrix receptors in human osteoclasts: a beta 3 integrin is colocalized with vinculin and talin in the podosomes of osteoclastoma giant cells.

Human osteoclasts (OCLs) obtained from cell suspensions of surgically excised giant cell bone tumors (osteoclastomas) were attached to glass coverslips and analyzed by immunofluorescence with antibodies to integrins and cytoskeletal proteins. It was found that in OCLs (i) podosomes, identified by their F-actin core and by interference reflection microscopy, were predominantly found in a peripheral belt as described in avian OCLs; (ii) each F-actin core was surrounded by a ring of vinculin and talin; (iii) beta 1 integrin was diffuse in the ventral membrane; (iv) beta 3 integrin was distributed in intensely fluorescent rings surrounding F-actin cores; (v) beta 2 integrin was absent; (vi) beta 4 integrin was absent. The macrophages detected in the same coverslips displayed podosomes containing beta 2 but not beta 3, fibroblasts showed adhesion plaques positive for beta 1 and beta 3 but not for beta 2, and platelets were intensely positive for beta 3. These results indicate that OCLs produce an integrin complex that is absent in the monocyte-macrophage lineage.

Actins↗
PubMed1989

Cytoplasmic pH regulation and chloride/bicarbonate exchange in avian osteoclasts.

Osteoclasts resorb bone by first attaching to the bone surface and then secreting protons into an isolated extracellular compartment formed at the cell-bone attachment site. This secretion of protons (local acidification) is required to solubilize bone hydroxyapatite crystals and for activity of bone collagen-degrading acid proteases. However, the large quantity of protons required, 2 mol/mol of calcium, would result in an equal accumulation of cytosolic base equivalents. This alkaline load must be corrected to maintain cytosolic pH within physiologic limits. In this study, we have measured cytoplasmic pH with pH-sensitive fluorescent compounds, while varying the extracellular ionic composition of the medium, to determine the nature of the compensatory mechanism used by osteoclasts during bone resorption. Our data show that osteoclasts possess a chloride/bicarbonate exchanger that enables them to maintain normal intracellular pH in the face of a significant proton efflux. This conclusion follows from the demonstration of a dramatic cytoplasmic acidification when osteoclasts that have been incubated in bicarbonate-containing medium are transferred into bicarbonate-free medium. This acidification is absolutely dependent on and proportional to medium [Cl-]. Furthermore, acidification is inhibited by the classic inhibitor of red cell anion exchange, 4,4'-diisothiocyanatostilbene-2,2'-disulfonate, and by diphenylamine-2-carboxylate, an inhibitor of chloride specific channels. However, the acidification process is neither energy nor sodium dependent. The physiologic importance of chloride/bicarbonate exchange is demonstrated by the chloride dependence of recovery from an endogenous or exogenous alkaline load in osteoclasts. We conclude that chloride/bicarbonate exchange is in large part responsible for cytoplasmic pH homeostasis of active osteoclasts, showing that these cells are similar to renal tubular epithelial cells in their regulation of intracellular pH.

Animals↗
PubMed1989

Extracellular protons acidify osteoclasts, reduce cytosolic calcium, and promote expression of cell-matrix attachment structures.

Because metabolic acids stimulate bone resorption in vitro and in vivo, we focused on the cellular events produced by acidosis that might be associated with stimulation of bone remodeling. To this end, we exposed isolated chicken osteoclasts to a metabolic (butyric) acid and observed a fall in both intracellular pH and cytosolic calcium [( Ca2+]i). These phenomena were recapitulated when bone resorptive cells, alkalinized by HCO3 loading, were transferred to a bicarbonate-free environment. The acid-induced decline in osteoclast [Ca2+]i was blocked by either NaCN or Na3VO4, in a Na+-independent fashion, despite the failure of each inhibitor to alter stimulated intracellular acidification. Moreover, K+-induced membrane depolarization also reduced cytosolic calcium in a manner additive to the effect of protons. These findings suggest that osteoclasts adherent to bone lack functional voltage-operated Ca2+ channels, and they reduced [Ca2+]i in response to protons via a membrane residing Ca-ATPase. Most importantly, acidosis enhances formation of podosomes, the contact areas of the osteoclast clear zone, indicating increased adhesion to substrate, an early step in bone resorption. Thus, extracellular acidification of osteoclasts leads to decrements in intracellular pH and calcium, and appears to promote cell-matrix attachment.

Animals↗
PubMed1989

Voltage dependent calcium channel expression in isolated osteoclasts.

In this study the expression of voltage-dependent calcium channels on osteoclast plasma membrane has been investigated. We found that osteoclasts were sensitive to KCl-induced depolarization. In this circumstance a 4 fold transient cytosolic calcium concentration ([Ca2+]i) increase was observed. This increase was dose-dependent. Its half maximal effect was achieved at 30 mM KCl. Voltage sensitive calcium channels in osteoclasts were inhibited by specific antagonists. Nicardipine, a dihydropyridine derivative, was the most effective, inducing complete block of the channels at 10(-6) M. Verapamil (phenylalkylamine) and diltiazem (benzodiazepine) were less effective. These results are consistent with the presence, on the osteoclast membrane, of L-type voltage-sensitive calcium channels.

Animals↗
PubMed1989

Cytoplasmic pH is regulated in isolated avian osteoclasts by a Cl-/HCO3- exchanger.

Osteoclast resorb bone in an acid compartment formed by the bone-attachment site. The low pH of the resorption compartment provides a lysosome-like milieu suitable for acid proteases to degrade collagen. Solubilization of the hydroxyapatite that makes up bone mineral consumes about 2 moles of protons per moles of calcium dissolved, requiring a massive proton flux to maintain a low pH in the resorption compartment. In order to determine how the osteoclast maintains a physiological cytoplasmic pH while secreting massive amounts of acid, we studied the intracellular pH of osteoclasts using esterified fluorescein derivatives while controlling the electrolyte composition of the medium. The principal finding is that osteoclasts have a high capacity for chloride/bicarbonate exchange which enables them to maintain normal intracellular pH in the face of a large loading of base equivalents. Thus, the overall process of proton secretion during bone resorption is similar to the polarized acid elimination by renal epithelia, involving a proton pump on one surface of the cell, and a Cl-/HCO3- exchange to maintain cytoplasmic pH.

Acid-Base Equilibrium↗
PubMed1989

Regulation of podosomes by intracellular pH in avian osteoclasts.

The effects of changes in intracellular pH (pH1) on the organization of the clear zone of isolated avian osteoclasts in culture were studied. The distribution of podosomes, the close contact areas that mediate the adhesion of osteoclasts to the substrate, was investigated by decoration of microfilaments with fluorescent phalloidin. Intracellular acidification by butyric acid induces significant increase of podosome formation at the level of the clear zone compared to controls. Conversely, alkalinization by HCO3- reduces the percentage of osteoclasts with podosomes. A role of pH1 on the adhesion of the osteoclasts to the substrate is hypothesized.

Animals↗
PubMed1989

Immunolocalization of beta 3 subunit of integrins in osteoclast membrane.

Utilizing isolated and cultured osteoclasts it has been possible to establish that they adhere to the substrate through specialized close contact areas, the podosomes, that in fully spread osteoclasts in vitro or in vivo are located within the clear zone. The cytochemical organization of podosomes has further been investigated in order to elucidate their possible involvement in the control of substrate recognition, that precedes bone resorption. An immunofluorescence investigation, performed utilizing human osteoclasts, shows that the beta 2 integrin subunit that in human monocytes is expressed and located in podosomes is absent in human osteoclasts, while the beta 3 subunit of the vitronectin receptor is expressed by osteoclasts, but not by other monocyte-derived cells and colocalizes with vinculin around the actin core of the podosome. The beta 1 subunit of the fibronectin receptors is also found, but with a diffuse pattern, in the osteoclast membrane. These results indicate that podosomes, while present in different cell types, may have in the osteoclast an unique cytochemical organization related to the peculiar function of this cell.

Bone Resorption↗
PubMed1989

Podosome expression in osteoclasts: influence of high extracellular calcium concentration.

In this study the effect of high extracellular calcium concentration has been evaluated, by immunofluorescence, on podosome expression in chicken osteoclasts. Cells were cultured in presence of 0.2 and 4 mM calcium for 90 minutes and microfilaments were detected, after fixation and permeabilization, by decoration with rodhamine conjugated phalloidin. Results showed that increased extracellular calcium concentration induces the inhibition of podosome expression indicating that these close-contact areas are capable of calcium-mediated regulation.

Animals↗
PubMed1989

Intracellular acidification induces decrease of cytosolic calcium in isolated osteoclasts.

In this study the effects of changes in intracellular pH on cytosolic Ca2+ were examined in single isolated osteoclasts. Alkalinization, performed by incubation in HCO3 containing buffer, induced increases in [Ca2+]. Conversely acidification, obtained by incubation in Na-butyrate-containing buffer induced a rapid and sustained decrease of [Ca2+]. The decrease of [Ca2+], during acidification with Na-butyrate was inhibited by VO4, an inhibitor of the Ca2+-ATPase. All these pieces of information indicate that changes in pH1 can modulate osteoclast activity together with modifications of [Ca2+], probably acting as intracellular signals.

Animals↗
PubMed1988

Effect of vitamin A on bone resorption: evidence for direct stimulation of isolated chicken osteoclasts by retinol and retinoic acid.

The effects of retinol (vitamin A) and retinoic acid on primary cultures of isolated chicken osteoclasts have been studied. The experiments were performed to establish the direct actions of these two agents on the organization of cytoskeletal structures, on the acid phosphatase contents, and on the bone resorption activities of these cells. The results showed that by treating the cultures with retinol or retinoic acid, from 10(-8) to 10(-5) M, there were dose-related responses of the osteoclasts. Adhesion to the substratum was stimulated by increasing the number of cells exhibiting the specialized dot-like adhesion structures, or podosomes, which represent the active part of the sealing zone. The treatments also induced rearrangement of the microtubular patterns with reversible depolymerization of microtubules. Acid phosphatase activity was significantly higher both in vitamin A-treated osteoclasts and in their media. When [3H]proline-labeled bone particles were added to the retinoid-treated osteoclasts, the release of [3H]proline was increased significantly compared to controls. These results suggest that the two vitamin A metabolites cause several modifications of the metabolic status of isolated osteoclasts that result in augmented rates of bone resorption.

Acid Phosphatase↗
PubMed1988

The distribution of podosomes in osteoclasts cultured on bone laminae: effect of retinol.

Osteoclasts, isolated and purified from the medullary bone of calcium-deficient egg-laying hens, adhere to glass coverslips in vitro by means of specialized protrusions of the ventral membrane, denoted podosomes. These structures represent dotlike close-contact adhesion sites in which most cytoskeletal proteins involved in linking the plasma membrane to microfilaments are organized according to a specific and previously described pattern also shared by many oncogene-transformed cells. We show now that podosomes are not only a feature of osteoclasts adhering to artificial glass surfaces but are also present in the ventral membrane of osteoclasts adhering to bone laminae. Moreover, the quantity and the topography of podosomes may be modulated by retinol, which increases bone-resorbing activity of osteoclasts both in vivo and in vitro. A comparative transmission electron microscopy study of osteoclasts adhering on bone laminae in vitro or in vivo indicates that podosomes with identical features are present in the clear zone of the osteoclasts in either condition. Since podosomes are the sealing structures of the clear zone, podosome formation may represent one of the modifications involved in the reorganization process of the osteoclast that precedes bone resorption.

Acid Phosphatase↗
PubMed1988

The effects of parathyroid hormone or 1,25-dihydroxyvitamin D3 on monocyte-osteoclast fusion.

3H-thymidine-labeled blood monocytes were cultured with osteoclasts in the presence or absence of parathyroid hormone or 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in order to evaluate (1) the percentage of monocytes capable of fusing with osteoclasts, (2) if parathyroid hormone or 1,25(OH)2D3 influences the contribution of blood monocytes to osteoclast nuclear turnover. We found that within 24 hours of culture, about 8% of blood monocytes fuse with osteoclasts regardless of the presence of parathyroid hormone (PTH) or 1,25(OH)2D3. On the other hand, formation of non-osteoclastic giant cells by fusion of monocytes is enhanced by 5 x 10(-9) M 1,25(OH)2D3 but only in the presence of the bone resorptive cells.

Acid Phosphatase↗
PubMed1987

Rous sarcoma virus-transformed fibroblasts and cells of monocytic origin display a peculiar dot-like organization of cytoskeletal proteins involved in microfilament-membrane interactions.

By immunofluorescence and interference reflection microscopy (IRM) we found that F-actin and a group of cytoskeletal proteins involved in microfilament-membrane interaction, including vinculin, alpha-actinin, fimbrin and talin, are specifically organized in discrete dot-like structures corresponding to cell-substratum contact sites in both monocytes and monocyte-derived cells such as macrophages and osteoclasts. These proteins have a precise topological distribution; vinculin and talin form a doughnut-like ring, while actin, fimbrin and alpha-actinin are organized in dots matching the rings. An identical dot-like organization of F-actin and associated cytoskeletal proteins was also detected in malignant fibroblasts transformed by Rous Sarcoma virus (RSV) but not in the corresponding untransformed cells in culture. It is concluded that RSV transformation induces fibroblasts to express a cytoskeletal organization and a pattern of adhesion that are normally found in cells of monocytic origin. We propose that the occurrence of this cytoskeletal organization in RSV-transformed fibroblasts and in monocyte-derived cells may reflect a common ability to migrate across anatomical boundaries.

Actin Cytoskeleton↗
PubMed1987

Ultrastructural evaluation of the microslicing method for the study of temporal bone pathology.

Microslices 3 mm thick from undecalcified human temporal bones were prepared with a special cutting machine and then processed for SEM and TEM in order to evaluate advantages and disadvantages of the microslicing technique for the study of the temporal bone pathology. In the examined microslices there was some mechanical distortion of the membranous labyrinth, detachment of soft tissues from bone and a considerable amount of contamination by bone dust and debris which are circulated during sectioning. For SEM the method therefore has limited value. For TEM a relatively contamination free area can be found some distance from the cutting surface of each microslice.

Cochlea↗