Cell-substratum interaction of cultured avian osteoclasts is mediated by specific adhesion structures.

Abstract

The cell-substratum interaction was studied in cultures of osteoclasts isolated from the medullary bone of laying hens kept on low calcium diet. In fully spread osteoclasts, cellsubstratum adhesion mostly occurred within a continuous paramarginal area that corresponded also to the location of a thick network of intermediate filaments of the vimentin type. In this area, regular rows of short protrusions contacting the substratum and often forming a cup-shaped adhesion area were observed in the electron microscope. These short protrusions showed a core of F-actin-containing material presumably organized as a network of microfilaments and surrounded by a rosette-like structure in which vinculin and o~-actinin were found by immunofluorescence microscopy. Rosettes were superposable to dark circles in interference-reflection microscopy and thus represented circular forms of close cell-substratum contact. The core of ventral protrusions also contained, beside F-actin, fimbrin and a-actinin. Villin was absent. This form of cell-substratum contact occurring at the tip of a short ventral protrusion differed from other forms of cell-substratum contact and represented an osteoclastspecific adhesion device that might also be present in in vivo osteoclasts as well as in other normal and transformed cell types.Osteoclasts are specialized cells involved in bone resorption. Even if many aspects of their function in bone physiology are not yet known, their morphology and ultrastructure are known in some detail (1,15,18). In particular, a ruffled border has been identified and described by both electron microscopy and microcinematography as a highly motile peripheral area probably involved primarily in bone resorption (17). An organelle-free area called "clear zone" or "sealing zone" (18) immediately adjacent to the ruffled border has been described. Schenk et al. (28) have suggested that the clear zone provides the osteoclast with a tight bone attachment area; King and Holtrop (21) have shown, in this same area, organized bundles of actin filaments ending within short processes contacting the bone surface. Further evidence that the clear zone is a specialized site of attachment has been provided also in different experimental conditions (27,30).Recently, a technique for isolating and culturing functional osteoclasts free of other cell types has been developed (36, 39); using this isolation procedure, the cytoskeleton of osteoclasts has been studied in vitro by means of immunofluorescence microscopy (37). A major finding was that in most osteoclasts, and especially in those highly flattened, multiple actin-containing dots were located in the area that topographically and ultrastructuraUy corresponds to the clear zone observed in vivo. In this same area, dot-like points of close adhesion and a belt of intermediate filaments of the vimentin type were also located, while fibronectin was excluded from the whole attachment area (37). Having in mind the idea that the whole idea corresponding to the clear zone could represent a...

Rho GTPases in osteoclasts: Orchestrators of podosome arrangement

“…They are formed by a F-actin core surrounded by a ring of scaffolding proteins such as vinculin, paxillin or talin. Interference-reflection microscopy indicated that the ring is in close proximity to the substratum suggesting that it mediates cell adhesive property (Marchisio et al, 1984). In agreement with that observation, integrins are localized at the ring and excluded from the core.…”

“…Podosomes were then described as major adhesion structures found in monocytes and osteoclasts (Marchisio et al, 1984). They are formed by a F-actin core surrounded by a ring of scaffolding proteins such as vinculin, paxillin or talin.…”

Regulators of G protein signaling 12 promotes osteoclastogenesis in bone remodeling and pathological bone loss

“…F-actin ring podosome belt formation is a prerequisite for OC bone resorption. 28,29 We used rhodamine-phalloidin staining to assess F-actin ring formation in primary OCs induced by M-CSF/RANKL from the bone marrow cells of the control and CD11b;Rgs12 fl/fl mice. About 60% of OCs from the control mice had complete and organized F-actin rings; whereas, only about 40% of OCs from CD11b;Rgs12 fl/fl mice had wellformed F-actin rings (Figures 5a and b, Po0.01).…”

Podosomes at a glance

“…Podosomes are typically formed in cells of the monocytic lineage, such as macrophages (Lehto et al, 1982;Linder et al, 1999), osteoclasts (Marchisio et al, 1984) or (immature) dendritic cells (Burns et al, 2001). However, they can also be found or induced in a variety of other cell types, including smooth muscle cells (Gimona et al, 2003) and endothelial cells (Moreau et al, 2003;Osiak et al, 2005).…”