Proteolipid-lipid relationships in normal and vitamin D-deficient chick cartilage

Abstract

Previous studies have shown that in vitro calcification of chick epiphyseal cartilage matrix vesicles is proteolipid-dependent. The purpose of this research is to examine the role of proteolipid in cartilage calcification in vivo by comparing the proteolipid concentration of normal and vitamin D-deficient chick epiphyseal cartilage, the relationship of proteolipid to other tissue lipids, and its ability to support in vitro apatite formation. Proteolipid was isolated from the upper growth centers (reserve cell zone, upper proliferative zone) and lower growth centers (lower proliferative, hypertrophic, and calcified cartilage zones) of long-bone epiphyses from 3-week-old normal and rachitic male white leghorn chicks by Sephadex LH-20 chromatography of the crude phospholipid component of the total lipid extract. In both normal and rachitic tissue the proteolipid/dry weight and proteolipid/total lipid ratios were greater in the lower growth center than in the upper zones. No statistically significant change in the proteolipid/total lipid ratio in rachitic tissues relative to comparable cell zones in normal cartilages was observed. However, there was an increase in the nonproteolipid phospholipid content of rachitic tissues, altering the relative proteolipid/phospholipid composition. Whereas proteolipids from normal tissue supported in vitro calcification, proteolipids from rachitic tissues did not, indicating a direct effect of vitamin D on proteolipid structure. These data support the hypothesis that failure of rachitic cartilage to calcify in vivo may be due in part to alterations in phospholipid and proteolipid metabolism.

Biological Calcification

“…They are particularly plentiful in areas of early calcification, as shown by 32 P-orthophosphate incorporation into phospholipids: these accumulate at the calcification front and show a turnover pattern different from that of the phospholipids which can be extracted before decalcification (Eisenberg et al 1970). The proteolipid/dry weight and proteolipid/total lipid ratios were greater in the lower than in the upper (resting) part of the epiphyseal cartilage (Boyan and Ritter 1984). The presence of phospholipids in epiphyseal cartilage was confirmed by combining malachite green fixation with phospholipase A 2 -gold complex, a method which localizes phospholipids: the labeling intensity was higher at the periphery of the calcification nodules than in the central, fully calcified matrix Zini et al 1996).…”

Differential Regulation of Growth Plate Chondrocytes by 1α,25-(OH)2D3and 24R,25-(OH)2D3 Involves Cell-maturation-specific Membrane-receptor-activated Phospholipid Metabolism

“…These observations also suggest that 1 ␣ ,25 -(OH) 2 D 3 may exert some of its effects via changes in phosphate. Rickets can be treated by increasing the serum Ca ++ concentration (Holtrop et al ., 1986), in part because the matrix vesicles produced by rachitic chondrocytes contain competent nucleational sites for calcium phosphate deposition to occur if Ca ++ is present (Howell et al ., 1978;Boyan and Ritter, 1984). Treatment of rickets with 1 ␣ ,25-(OH) 2 D 3 is particularly effective, since this vitamin D metabolite not only facilitates Ca ++ transport (Norman et al ., 1992), but also modulates other aspects of the physiology of the growth plate chondrocytes, including increases in local phosphate, resulting in optimal restoration of function.…”

Action of 1,25-dihydroxyvitamin D3 on phospholipid metabolism of human bone cells in culture

“…The list ofcell types responding in such a way continues to grow, and to date includes enterocytes and intestinal brush border membranes (Max, Goodman & Rasmussen, 1978;O'Docherty, 1979;Fontaine, Matsumoto, Goodman & Rasmussen, 1981;Karsenty, Lacour, Ulmann et al 1985), renal brush border membranes (Kurnik, Huskey & Hruska, 1987;Tsutsumi, Alvarez, Avioli & Hruska, 1985), cartilage (Boyan & Ritter, 1984), bone (Boskey & Timchak, 1983), an osteoblast-like cell line, (Matsumoto, Kawanobe, Morita & Ogata, 1985), and skeletal muscle and myoblasts (Boland, Norman, Ritz & Hasselbach, 1985).…”