ASGSB 1999 Annual Meeting Abstracts

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THE EFFECTS OF HINDLIMB UNLOADING ON CERTAIN INTEGRINS AND ACTINS IN RAT METATARSALS. M.J. Palm and B. Johnson-Wint. Dept of Biological Sciences, Northern Illinois Univ, De Kalb, IL.

We are interested in the role of integrins and actins in the generation of cellular forces, which move and organize the type-I collagen fibers in dense connective tissue and bone. The integrins that bind type-I collagen are -1/-1, -2/-1, and -3/-1 and the actins used by non-muscle cells to generate force are -actin and -smooth muscle actin. In this study we examine which integrins and actins are being used by bone cells, how much of these integrins and actins the bone cells contain, and if these amounts are sensitive to load on the bone. Unloaded bones were obtained from hindlimb suspended rats and loaded bones from ambulatory rats. Adult and juvenile rats were suspended for five and four weeks respectively with each study having ambulatory controls. Total protein was isolated from metatarsals by the TRI-Reagent® method and -1 integrin, -2 integrin, -3 integrin, -1 integrin, -actin, and -smooth muscle actin were identified and quantified by western blot. No -1 integrin or -2 integrin was detected. Two forms of -3 integrin were detected, a 163 kDa and 100 kDa species, and two forms of -1 integrin were detected, a 107 kDa and 205 kDa species. In adult metatarsals all four protein species showed a statistically significant reduction in the total amount of specific protein, the total amount of specific protein per bone weight, and total amount of specific protein per total extracted protein in the suspended rats compared to the ambulatory controls. Juvenile metatarsals contained the same integrins and showed the same quantity trends but differences between suspended and ambulatory were not statistically significant. Very little -actin was found in any metatarsal extracts. The predominant actin was -smooth muscle actin. These results show that the major collagen binding integrin in bone is -3/-1, that this integrin is sensitive to load and that the major cytoskeletal actin found in this tissue is -smooth muscle actin.

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