Human skeletal growth factor stimulates collagen synthesis and inhibits proliferation in a clonal osteoblast cell line (MC3T3-E1)

Human skeletal growth factor (hSGF), an 11-kD polypeptide purified from human bone, has been proposed to be a local regulator of bone formation. To investigate the underlying cellular mechanisms in an in vitro model system, we examined the effects of hSGF on proliferation and collagen synthesis in cells of the clonal osteoblast cell line MC3T3-E1. This line was isolated from newborn mouse calvarial cells and retains many characteristics of mature osteoblasts (Sudo, H., et al., (1984) J. Cell Biol. 96:191). A 14-hr treatment with hSGF increased noncollagenous protein synthesis to 215% of unstimulated controls and increased collagen synthesis to 630% of controls as determined by [3H]proline incorporation and high-pressure liquid chromatographic separation of [3H]proline and [3H]hydroxyproline in acid hydrolysates of trichloroacetic acid-insoluble protein. HSGF did not increase cell number over a 48-hr period and caused a reversible inhibition of DNA synthesis. Half-maximal hSGF concentration for stimulation of [3H]proline incorporation and inhibition of [3H]thymidine incorporation was 100 ng/ml. HSGF also inhibited DNA synthesis in cells stimulated by serum. In contrast, hSGF stimulated both collagen synthesis and DNA synthesis in primary cultures of chick embryo bone cells, which may be developmentally less mature than MC3T3-E1 cells. The results suggest that hSGF directly stimulated mature osteoblast matrix synthetic activity and that hSGF has differential effects on proliferation of osteoblast progenitor cells and mature osteoblasts.

Characterization of mitogenic activities extracted from bovine bone matrix

The mitogenic activity in the unfractionated mixture of proteins released from adult bovine bone matrix during demineralization with ethylenediaminetetraacetate (EDTA) has been examined. Bovine bone extract (BBE) from 1 to 25 micrograms protein per ml stimulated proliferation of chick embryo calvaria bone cells, newborn mouse bone cells, and osteoblastlike cell lines MMB-1 and ROS 17/2.8. BBE also stimulated DNA synthesis in cells from chick embryo cartilage, skin and skeletal muscle tissues and fibroblastlike BALB/c 3T3 and NRK cells. BBE contained beta transforming growth factor (TGF) activity (NRK cell colony formation in soft agar in the presence of epidermal growth factor EGF). The cell specificity results suggest that BBE contains more than one growth factor, including a beta TGF and a factor that is not specific for bone cells, and all of the bone derived growth factor activities that have been described previously, including SGF, are apparently present in BBE. Maximal stimulation of chick embryo calvarial cell DNA synthesis by BBE was equal to or exceeded maximal stimulation by nonosseous growth factors that have been reported to stimulate DNA synthesis in bone organ cultures (EGF, fibroblast growth factor, platelet-derived growth factor, insulinlike growth factor I, and multiplication stimulating activity). Combinations of BBE with maximally stimulatory concentrations of each growth factor stimulated DNA synthesis to a greater magnitude than did each growth factor alone. These results suggest that combinations of bone derived and systemic factors can coordinately stimulate bone cell proliferation.

A mouse tumor-derived osteolytic factor stimulates bone resorption by a mechanism involving local prostaglandins production in bone

Culture medium which was conditioned by tissue of a CE mouse breast tumor in vitro contained dose-dependent osteolytic activity. The osteolytic activity was not soluble in dichloromethane and ethylacetate, indicating that it was not attributable to vitamin D metabolites or prostaglandins. However, breast tumor-conditioned medium stimulated production and release of prostaglandin E2 from mouse calvaria in vitro, and the stimulation of bone resorption in vitro by breast tumor-conditioned medium was blocked by a dose of indomethacin that prevented stimulation of mouse calvarial prostaglandin E2 production and release. The resorptive activity of parathyroid hormone (PTH) was not affected by the same dose of indomethacin, suggesting that the osteolytic factor was not PTH. This was further supported by observation that mouse kidney cell cAMP production was stimulated by PTH, but not by the aqueous phase of ethylacetate-extracted breast tumor-conditioned medium. In addition to osteolytic activity, breast tumor-conditioned medium contained a dose-dependent bone cell mitogenic activity, demonstrated by the stimulation of [3H]thymidine incorporation into trichloroacetic acid-insoluble macromolecules and a corresponding increase in bone cell number in monolayer cultures of bone cells. Breast tumor-conditioned medium also contained a dose-dependent transforming growth factor-(TGF-) like activity as defined by its ability to transform anchorage-dependent growth of nontransformed cells to anchorage-independent growth. The TGF in breast tumor-conditioned medium did not compete with epidermal growth factor (EGF) for EGF receptor binding, but its transforming activity was greatly enhanced by EGF, indicating that it was a beta-type TGF. Both the osteolytic and mitogenic activities were nondialyzable, sensitive to reducing agent, and not removable by dichloromethane and ethylacetate extractions. Furthermore, the TGF activity was not removed by ethylacetate extraction. Thus, the possibility that these activities in breast tumor-conditioned medium might be mediated by the same molecule must be considered. In summary, our data suggest that the CE mouse mammary carcinoma cells produce and secrete into the culture medium an osteolytic factor which is neither PTH nor prostaglandin and which stimulates local synthesis in bone of prostaglandin E2 which in turn increases bone resorption in vitro.

A correction: inhibitory activity in the conditioned medium of embryonic chick bones is due to thymidine

Earlier studies from this laboratory suggested that embryonic chick bones in organ culture released into the culture medium a specific inhibitor of bone cell proliferation as defined by inhibition of [3H]TdR incorporation into DNA. Dialysis and membrane ultrafiltration experiments suggested that the inhibitory substance (IS) had a molecular weight between 6000 and 14,000. However, subsequent studies on the purification of IS have revealed that the inhibitory activity in bone-conditioned medium is of lower molecular weight and has several properties in common with thymidine (TdR): (1) IS coeluted with [3H]TdR upon gel filtration chromatography on Sephadex G-10. (2) IS bound to charcoal but not to cation or anion exchange resins. (3) Bone-conditioned medium decreased incorporation of [3H]TdR into the free [3H]TdR pool of cells in monolayer culture. (4) Conditioned medium inhibited [3H]TdR incorporation into [3H]thymidine monophosphate in a reaction catalyzed by thymidine kinase. The equivalent concentration of TdR in conditioned medium as estimated by thymidine kinase assay was sufficient to account for the reduction in [3H]TdR incorporation into bone cell DNA. No evidence was found for a specific inhibitor of bone cell proliferation other than TdR. Hence we conclude that the inhibitory effect of IS is due to dilution of [3H]TdR by nonradioactive TdR. Furthermore, media conditioned by several tumor cell lines also contained a low-molecular-weight component which inhibited [3H]TdR incorporation. The results suggest that organ- and cell-conditioned media can contain significant concentrations of TdR which can artifactually inhibit [3H]TdR incorporation in cell proliferation assays.

Bone-derived factors active on bone cells

Effects of systemic calcium regulating hormones have been studied extensively, yet mechanisms of bone volume regulation at the local level are poorly understood. Our laboratory has reported evidence for two locally mediated processes of bone volume regulation which function independently of systemic control: (1) coupling of bone formation and resorption and (2) repletion of resorbed bone. These local regulatory mechanisms have been shown to occur in vivo and in vitro. We have reported that embryonic chick tibiae in culture, stimulated to resorb, release a factor in the serum-free culture medium that stimulates bone cell proliferation and bone matrix formation in vitro. We have postulated that this factor could be involved in the coupling mechanism. Subsequently, a similar factor which stimulates bone cell proliferation, collagen synthesis and bone formation in vitro was extracted from embryonic and adult bones. The factor partially purified from human bone, designated as human skeletal growth factor, has molecular weight, heat sensitivity and biological activity similar to the factor found in bone conditioned medium. Many other biologically active factors have also been extracted from bone cells or demineralized bone by different laboratories. Their actions on bone cells range from chemotactic to mitogenic. These recently discovered bone factors emphasize that there is important regulation of bone metabolism at the local level.

Wild mouse retrovirus-induced neurogenic paralysis in laboratory mice. I. Virus replication and expression in central nervous system

Ecotropic wild mouse retrovirus (1504 M)-induced neurogenic paralytic disease has been studied in inbred strains of mice. The major criterion for the successful transmission of the disease in the laboratory strains of mice is inoculation of high titer ecotropic virus in FV-1n strains of mice at newborn stage (less than or equal to 1 day old), Hybridization studies using 1504 M viral cDNA as probe indicate that in nonparalyzed mice, the inoculated virus replicates primarily in spleen tissue, whereas virus replication is evident in both spleen and central nervous system (CNS) tissue of paralyzed mice. Our studies on virus gene expression indicate that both viral gag gene product p30 and env gene product gp70 are expressed in brain, spinal cord and spleen tissues of paralyzed mice. Together, these results indicate that inoculation of neurotropic wild mouse virus into FV-1n strains of newborn laboratory mice is necessary for the establishment of infection in CNS tissue leading to virus replication and expression and resulting in the paralytic disease.

Binding characteristics of wild mouse type C virus to mouse spinal cord and spleen cells

Binding characteristics of mouse spinal cord and spleen cells to naturally occurring, ecotropic (paralytogenic and lymphomagenic 1504M virus) and amphotropic (lymphomagenic 1504A virus) retroviruses of wild mice were investigated. 125I-labeled ecotropic (N-tropic) virus bound efficiently to both spinal cord and spleen cells from SWR/J mice (Fv-1n), but labeled amphotropic (N-tropic) virus bound efficiently only to spleen cells. The extent of binding of 1504M virus to the spinal cord cells was related to the time of incubation and to the amount of labeled input virus. 1504M virus bound to both glial and neuronal subpopulations of the spinal cord with almost equal efficiency. Binding of 125I-labeled 1504M virus to SWR/J mouse spinal cord cells was competitively inhibited by unlabeled homologous virus, whereas an excess of unlabeled 1504A virus inhibited only 10% of the ecotropic virus binding. Unlabeled 1504M virus almost completely inhibited the low-level binding of 125I-labeled 1504A virus to spinal cord cells. The different extent of binding of 1504M virus to spinal cord cells from different strains of mice (SWR/J, NIH Swiss, BALB/c-Jax, Lake Casitas wild, and CD-1) correlated with the susceptibility to paralysis in these strains of mice after inoculation with 1504M virus. Although the spinal cord cells of BALB/c mice contained a moderate amount of 1504M virus receptor sites, these mice were resistant to virus-induced paralysis because of their Fv-1b genotype. Our results indicate that the receptor sites for wild mouse ecotropic retrovirus are strain and organ specific and suggest that the presence of such receptors in central nervous system tissue may be a prerequisite for a successful virus infection and paralysis induction in Fv-1n mice.

Binding studies of a sialic acid-specific lectin from the horseshoe crab Carcinoscorpius rotunda cauda with various sialoglycoproteins

Interaction of the sialic acid-specific lectin carcinoscorpin with various sialoglycoproteins was studied by using radioiodinated lectin. The binding of carcinoscorpin was dependent not only on sialic acid content but also on the type of glycosidic linkage and form (branched or linear) of the carbohydrate chains. Carcinoscorpin has different classes of binding sites, and binding follows a phenomenon of positive co-operativity. The effect of Ca2+ concentration on the binding was studied, and the optimal concentration was found to be 0.02 M. Effect of pH, temperature and other bivalent metal ions are also reported. From haemagglutination- and precipitation-inhibition studies, it was concluded that carcinoscorpin has multispecificity towards acidic sugars, and its relation to the biological role of the lectin in the horseshoe crab is discussed.

Age-related changes in rat muscle collagen

Age-related studies of collagen in slow, fast and cardiac muscle of the rat indicate that different fractions of collagen as well as total collagen content vary with age and type of muscle. The total collagen level increases by 30% in slow, 40% in fast and 50% in cardiac muscle as age advances from 5 to 25 months. Collagen of the muscles of old animals is less susceptible to the collagen-degrading enzyme when compared to the young, and the activity of the enzyme decreases significantly with age. The decrease in (1) the solubility of collagen; (2) the amount of hydroxyproline released at 65 degrees C, and (3) the increase in the resistance of collagen to the degrading enzyme seen with aging, indicates that the stability of collagen increases in these muscles with aging.

The occurrence and treatment of false positive reactions in enzyme-linked immunosorbent assays (ELISA) for the presence of fungal antigens in clinical samples

Non-specific positive reactions have been revealed in enzyme-linked immunosorbent assays (ELISA) of sera for the presence of fungal antigen. These false positives were recognized by their occurrence in tests for both Candida albicans and Aspergillus fumigatus antigens and by their response to dithiothreitol, combined with their reaction with non-immune rabbit globulin. A scheme is proposed which differentiates between true and false positive reactions. Use of fractionated anti-fungal globulin in conjugates reduced the incidence of false positive results in sera from hospitalized patients and eliminated them from sera of healthy subjects. The test scheme was applied to two panels of sera containing samples from patients with (a) invasive candidosis and (b) invasive aspergillosis. The relevance of ELISA tests for the detection of fungal antigen in human serum is discussed.

Age related changes in muscle protein degradation

In vitro autolytic degradation of sarcoplasmic proteins in red, white and cardiac muscles increases with advance in age and with increase in temperature, the rate varying with age. Higher activity is seen in the alkaline range in all age groups. Ca2+ activated proteolytic activity also increases with advance in age.

Collagen in aging muscles

The salt, acid and insoluble collagen fractions were estimated in red, white and cardiac muscles of 10-, 15- and 20-month-old albino rats. The total collagen level with reference to total proteins is more in red than in white and cardiac muscle. Accumulation of more of insoluble collagen and decrease in salt extractable collagen is seen in all three muscles with aging.