Expression of human bone-related proteins in the hematopoietic microenvironment.

Abstract

Given the intimate relationship between bone and bone marrow, we hypothesized that the human bone marrow may function as a source (or reservoir) of bone-forming progenitor cells. We observed a population of cells within the bone marrow which produce bone-specific or bone-related proteins. The production of these proteins was developmentally regulated in human long-term bone marrow cell cultures; the bone proteinproducing cells (BPPC) are observed under serum-free, shortterm culture conditions, respond to bone-related and not hematopoietic growth factors, and are derived from a population of low-density, nonadherent, MylO-negative (or low MylO density), marrow cells (MylO is an antigen found on most hematopoietic progenitor cells). Cultivation of marrow-derived BPPC in secondary, serum-containing cultures results in their differentiation into osteoblastlike cells. At this stage of development, BPPC produce an extracellular matrix which incorporates both bone-related proteins and radiolabeled calcium. Human bone marrow BPPC thus represent a newly described cell phenotype important to both bone and hematopoietic cell biology. (J. Clin. Invest. 1990Invest. . 86:1387Invest. -1395

Characterization of circulating osteoblast lineage cells in humans

“…Moreover, molecular analysis demonstrated a common retroviral integration site in clonogenic hematopoietic cells and osteoprogenitors from each of seven animals studied, establishing a shared clonal origin for these cell types. These findings thus lent considerable credence to the previous work of Long et al [3,4] and established that, at least in the experimental paradigm used by Dominici and colleagues [9], non-adherent bone marrow cells have a >10-fold more robust bone-repopulating activity than do adherent bone marrow stromal cells. Moreover, the findings were also consistent with previous work by Olmsted-Davis et al [10] suggesting the presence of a unique progenitor cell with both hematopoietic and osteoblastic differentiation potential in the non-adherent subset of bone marrow cells.…”

“…We found that OCN pos cells isolated using either the antibody we used in our previous work (SC V-19) [14] or the antibody used by Long and colleagues (HT AON-5031) [3,4] identified very similar populations of cells, at least as assessed by flow cytometry and confocal microscopy. While additional studies need to be done further characterizing the cells isolated with the two antibodies, these data do provide some reassurance that the cells identified in our previous work using the SC V-19 antibody are not some type of spurious population staining only with this particular antibody.…”

“…We initially used the anti-OCN antibody utilized in our previous study (SC V-19) [14] and the antibody originally used by Long and colleagues in their work for identifying OCN pos cells in bone marrow (HT AON-5031) [3,4] and verified that both antibodies stained only mineralized matrix and the appropriate cells in normal human bone ( Figure 1A and B). Adjacent muscle or connective tissue of the same section did not stain with the two OCN antibodies ( Figure 1C and D) Human bone incubated just with the secondary antibody served as negative control ( Figure 1E and F).…”

“…Since then, there has been an extensive body of work (summarized in [2]) on the characterization of bone marrow stromal cells with osteoblastic potential in rodent and in human systems. Concurrent with this work, however, Long and colleagues identified, over a decade ago, a non-adherent population of cells in bone marrow with osteogenic potential [3,4]. Rather than selection by adherence to plastic, the primary assay used was cell sorting using antibodies to osteocalcin (OCN), osteonectin, and bone alkaline phosphatase (AP).…”

“…Rather than selection by adherence to plastic, the primary assay used was cell sorting using antibodies to osteocalcin (OCN), osteonectin, and bone alkaline phosphatase (AP). When cultured in the presence of TGF-β and accessory bone marrow cells (the identity of which still remains unclear), OCN positive (OCN pos ) cells proliferated and differentiated into mature osteoblastic cells expressing bone-related genes and capable of mineral deposition [3,4]. Somewhat surprisingly, despite the fact that OCN is a secreted protein, these investigators did not need to permeabilize the cells in order to detect cells producing OCN.…”