Pluripotent hemopoietic stem cells give rise to osteoclasts in vitro: effects of rGM-CSF

Advanced glycation endproducts stimulate interleukin-6 production by human bone-derived cells

Advanced glycation endproducts (AGEs), which result from nonenzymatic reactions of glucose with tissue proteins, have been shown to accumulate on long-lived proteins in advanced aging and diabetes mellitus. Thus, AGEs have been implicated in some of the chronic complications associated with these disorders. In this study, we investigated the effects of the glucose-modified protein on the production of the potent bone resorption factors by cells derived from explants of human bone. AGEs stimulated the release of interleukin-6 (IL-6) in the culture supernatants from the bone-derived cells and increased the levels of IL-6 mRNA in the cells. By contrast, the levels of IL-11 in the culture supernatants were not altered by AGEs, and the other bone resorption factors IL-1 alpha and IL-1 beta were undetectable (< 1.0 pg/ml) either without or with the treatment of AGEs. Electrophoretic mobility-shift assays revealed that the transcription nuclear factor-kappa B, which is critical for the inducible expression of IL-6, was activated in the nuclear extracts from mouse osteoblastic MC3T3-E1 cells treated with AGEs. These results suggest that AGEs are involved in bone remodeling modulation by stimulating IL-6 production in human bone-derived cells.

Estrogen, cytokines, and pathogenesis of postmenopausal osteoporosis

In summary, available data demonstrate that IL-1 and TNF are the causative agents underlying the bone loss induced by estrogen deficiency. Indeed, these factors are produced in bone and the bone marrow, released in larger amounts from cells of estrogen-deficient subjects, and indispensable for reproducing the effects of estrogen deficiency in bone. These observations support the hypothesis that the bone sparing effect of estrogen is due to the ability of the hormone to block osteoclastogenesis, the activation of mature osteoclasts and, as recently demonstrated, the rate of apoptotic osteoclast death. Although IL-1 and TNF play a prominent causal role in these events, the bone-sparing effect of estrogen is mediated by numerous cytokines which, by simultaneously stimulating multiple target cells, induce effects that are not accounted for by any one single factor (Fig. 2). The ability of estrogen to regulate some, but not all, the cytokines involved in this process is not inconsistent with this hypothesis because cytokines have potent synergistic effects. Thus, a considerable increase in bone resorption may result from a relatively small increase in the concentration of only a few of the bone-resorbing factors present in the bone microenvironment. This concept is best illustrated by the study of Miyaura et al. demonstrating that the concentrations of either IL-1, IL-6, IL-6 receptor, or prostaglandins detected in the bone marrow of OVX mice are insufficient to account for the increased bone resorption caused by estrogen withdrawal. In contrast, the increase in bone resorption induced by OVX can be explained by the cumulative effects of these cytokines. Thus, a better understanding of the cooperative effects of cytokines and a recognition that the contribution of individual cytokines to postmenopausal bone loss varies with the passage of time after menopause are necessary to fully understand the mechanism of action of estrogen in bone. Although the relevance of individual bone-targeting cytokines in species specific, the development of transgenic mice with activatable or deactivatable promoters is likely to result in a further clarification of the integrated action of estrogen-regulated cytokines in human bone cells and lay the foundations for the use of cytokine inhibitors in the treatment of postmenopausal osteoporosis.

Establishment and characterization of stromal cell lines that support differentiation of murine hematopoietic blast cells into osteoclast-like cells

This study aimed to establish and characterize a new stromal cell line that supports the proliferation of hematopoietic blast cells and their differentiation into osteoclast-like cells. Cells isolated from the calvaria of neonatal Balb/c mice were subcultured every 2 to 4 days at 1.2 x 10(4) cells/cm2. After 18 passages the cells had become immortalized and were designated as MCHT-1. MCHT-1 cells were found to support the proliferation of hematopoietic blast cells and their differentiation into osteoclast-like cells when these two cells were co-cultured in the presence of 1 alpha,25(OH)2D3 and dexamethasone. However, because the MCHT-1 cells showed heterogeneity, cloning was performed and each clone was characterized. All the clones obtained supported the proliferation of hematopoietic blast cells and their differentiation into osteoclast-like cells irrespective of their obvious differences in growth capacities and cytochemical characteristics. However, the time-course of the appearance of osteoclast-like cells differed among clones. The supportive effect of these clonal stromal cells on differentiation of hematopoietic blast cells into osteoclast-like cells was completely dependent on the presence of 1 alpha,25(OH)2D3 and dexamethasone. These clonal MCHT-1 cells are expected to be useful for precise analysis of the proliferation and differentiation of osteoclasts.

Osteoclast development in the coculture system of periostless metatarsal bones and hemopoietic cells studied by in situ hybridization with a probe for Y chromosomes

In the coculture system of periostless metatarsal bones of 17-day-old fetal mice and osteoclast progenitors, osteoclasts will develop. Our goal in the present report was to provide further evidence that in the coculture system of fetal metatarsal bone rudiments with hemopoietic cells, the osteoclasts developing inside the bone rudiments are exclusively derived from the cells suspended in the plasma clot and not from endogenous precursor cells of the bone explants themselves, by using the technique of in situ hybridization with a probe for the mouse Y chromosome. Osteoclast formation in unstripped male metatarsal rudiments, occurring after 3-4 days of culture, was compared with osteoclast formation in cocultures of female metatarsal rudiments and male bone marrow cells, occurring after 5-6 days of culture. Osteoclasts were recognized by their tartrate-resistant acid phosphatase activity. In paraffin sections of cultured male metatarsals, the mean percentage of microscopically identifiable osteoclast nuclei, in which the Y chromosome could be detected, was 43.1 +/- 4.2% (n = 12). For cocultures of female metatarsal bones and male bone marrow cells this mean percentage was 40.9 +/- 5.7% (n = 17). Statistical comparison by means of the two sample t-test indicated no significant difference in the percentages of osteoclast nuclei containing the Y chromosome for both groups. We concluded that the osteoclasts do derive from cocultured cells and not from precursor cells in the bone explant itself.(ABSTRACT TRUNCATED AT 250 WORDS)

The cell biology of bone

Bone remodelling and repair are accomplished by the co-ordinated activity of cells of the osteoclast and osteoblast lineages. Small changes in the balance between formation and resorption will, when magnified by repeated cycles, lead to significant reduction in bone mass and strength, ultimately resulting in fracture. This review focuses on the cellular features of bone remodelling and the known regulators of bone cell function. These include systemic and local factors, both soluble and contained within the complex extracellular matrix of bone.

Defective osteoclast differentiation and function in the osteopetrotic (os) rabbit

We tested the ability of normal osteoclast progenitors found in neonatal liver and bone marrow to develop into functional osteoclasts when co-cultured with metatarsals from newborn osteopetrotic rabbits; the latter inherit an osteoclast incompetence resistant to cure by bone marrow transplantation. This system, developed by Burger and colleagues, has been shown to produce normal, functional osteoclasts when used with normal metatarsals. Our study tested the competence of the mutant skeletal microenvironment for differentiation of normal osteoclasts. Mutant and normal metatarsals were cultured alone or with normal liver, spleen, or bone marrow for up to 14 days. All normal cultures possessed a marrow cavity and contained numerous osteoclasts with cytochemical characteristics (tartrate-resistant acid phosphatase) of active cells. Mutant metatarsals co-cultured with normal spleen, liver, or bone marrow failed to develop a marrow cavity (evidence in itself of reduced bone resorption) and had osteoclasts reduced in both numbers and cytochemically detectable activity. Similar metatarsal cultures of an osteopetrotic rat mutation (incisors--absent) curable by bone-marrow transplantation exhibited marrow cavity development in mutant metatarsals co-cultured with normal spleen. These data suggest that the skeletal environment of osteopetrotic rabbits contains an inhibitor or lacks a promoter of osteoclast differentiation and function.