Biomedical subjects

M Shakibaei

Publications and source records attributed to M Shakibaei.

59 records · Page 4Linked to original sources

PubMed1993

Matrix changes during long-term cultivation of cartilage (organoid or high-density cultures).

In high density (organoid or micromass) cultures of prechondrogenic mesenchymal cells from limb buds of 12-day-old mouse embryos typical cartilaginous tissue develops after 3 days. Immunomorphological investigations have shown that it contains the typical components of the cartilaginous matrix, such as collagen type II and cartilage-specific proteoglycans. After a 2-week cultivation period hypertrophic cartilage cells develop to an increasing extent. Many of these cells as well as normal chondroblasts detach from the matrix from the 2nd week in vitro onwards to assume a fibroblast-like appearance. At the same time thick (25-65 nm) collagenous fibrils occur at the surface of these cells. These thick fibrils contain collagen type I, as shown by immunomorphology. Hence, in these older cartilage cultures chondroblasts change their synthesis programme or direction of differentiation. Consequently, a model for the study of "dedifferentiation" of cartilage and possibly also transformation of cartilage cells to osteoblasts has become available.

Animals↗

PubMedDate not supplied

Endocytosis of integrin alpha 5 beta 1 (fibronectin receptor) of mouse peritoneal macrophages in vitro: an immunoelectron microscopic study.

Localization and dynamic aspects of fibronectin receptor (alpha 5 beta 1 integrin) were investigated by immunoelectron microscopy on freshly isolated mouse peritoneal macrophages and after cultivation in vitro. This receptor has only been characterized biochemically. Identity of macrophages was proved by binding of the antibody against the F4/80 specific macrophage marker. Demonstration of fibronectin receptor and mouse macrophage marker on the plasma membrane revealed that these glycoproteins were rapidly endocytosed within the first minutes after isolation. Endocytotic uptake of these glycoproteins was demonstrated by double immunolabeling and secondary labeling with gold particles of different size. Label was found in endocytotic and lysosome-like vesicles, but not in coated vesicles. During further cultivation the macrophage marker reappeared again on the plasma membrane after 3 hr, but the fibronectin receptor was not demonstrable. Treatment with cytochalasin B in culture and incubation at 4 degrees C resulted in strongly labeled plasma membrane and inhibition of internalization. In contrast to macrophages, alpha 5 beta 1 integrin was demonstrable on marmoset skin fibroblasts even after 3 days in culture. In this cell type, endocytotic uptake was solely detectable in coated vesicles. These results suggest a high endocytotic activity of macrophages after isolation leading to a rapid disappearance of both glycoproteins, whereby, in contrast to the fibronectin receptor, only the macrophage marker is recycled again. These data indicate a change in plasma membrane (receptor content) after isolation and cultivation of macrophages and cell-specific differences in vitro.

Amino Acid Sequence↗

PubMedDate not supplied

Immunoelectron microscopic studies on the specific adhesion of Trypanosoma congolense to cultured vascular endothelial cells.

Bloodstream forms of Trypanosoma congolense were cocultivated in vitro with vascular endothelial cells. The trypanosomes adhere specifically to the endothelial surfaces of the anterior part of their flagella, as shown by scanning and transmission electron microscopy. The interaction between parasite and host cell is very tight, and frequently the accumulation of endocytotic vesicles near the contact site is observed. Immunoelectron microscopy revealed a compound distributed over the total surface of the trypanosomes and reacting with antibodies against the beta 1 integrin chain, but no reaction was found with anti-alpha 1 or anti-alpha 2 antibodies. Integrins are typical adhesion molecules and are now shown to be present at the surface of T. congolense by electron microscopy and by immunofluorescence. A direct participation of this substance in the specific adhesion to endothelium, however, could not be proven.

Animals↗

PubMedDate not supplied

Cell surface interactions between Trypanosoma congolense and macrophages during phagocytosis in vitro.

Trypanosoma congolense bloodstream forms preincubated with a high titer of anti-variant surface antigen (VSG)-specific antibody, a low amount of anti-VSG plus complement-active mouse serum (MS), MS alone, and trypsin were cocultivated with mouse peritoneal macrophages in vitro. Immunofluorescence as well as transmission and scanning electron microscopy revealed that upon attachment to the macrophages' surface, trypanosomes opsonized with anti-VSG/MS formed opsonized filopodia, which were rapidly internalized by the phagocytes. Although these cells attached as frequently as anti-VSG or trypsin-pretreated parasites, the rate of phagocytosis of anti-VSG/MS pretreated trypanosomes was reduced significantly. Trypanosomes pretreated with high antibody titers alone were lysed on the surface of the macrophages before phagocytosis was completed. Parasites opsonized with complement alone adhered only occasionally and were rarely phagocytosed. Trypsin-treated trypanosomes, which served as positive control cells, rapidly attached and remained intact until ingulfment by the macrophages was completed. Untreated control parasites did not attach to the macrophages and were not phagocytosed. Cocultivation of macrophages with anti-VSG/MS-opsonized trypanosomes caused internalization of the flagellum by membrane fusion. Filopodia formation by T. congolense is thus correlated with a marked reduction in phagocytosis even in the presence of only a sublytic antibody titer.

Animals↗

PubMedDate not supplied

Comparative evaluation of ultrastructural changes in articular cartilage of ofloxacin-treated and magnesium-deficient immature rats.

Ultrastructural changes in immature articular cartilage were studied after treatment of 5-wk-old rats with ofloxacin-a fluoroquinolone-and in magnesium deficiency. Magnesium deficiency was induced by feeding a magnesium-deficient diet for 9 days; the condition was confirmed by measuring the concentrations of the mineral in plasma, bone, and cartilage samples of the animals by atomic absorption spectrophotometry. Oral administration of single doses of 600 or 1,200 mg ofloxacin/kg body weight and magnesium deficiency were sufficient to induce gross structural cartilage defects. Alterations observed on the ultrastructural level showed striking similarities in magnesium-deficient rats and in rats treated with single doses of 600 mg ofloxacin/kg body weight. Typical observations were (a) bundle-shaped, electron-dense aggregates on the surface and in the cytoplasm of chondrocytes, (b) detachment of the cell membrane from the matrix and necrotic chondrocytes, (c) reduction of the extracellular matrix, and (d) swelling of cell organelles such as mitochondria. These findings further substantiate the histological finding that quinolone treatment and a dietarily induced magnesium-deficiency induce indistinguishable pathological conditions in immature joint cartilage, and they suggest that quinolone-induced arthropathy is probably caused by a reduction of functionally available magnesium (ionized Mg2+) in cartilage (42). Furthermore, they provide a basis for aimed studies with human cartilage samples from quinolone-treated patients that might be available postmortally or after hip replacement surgery.

Aging↗