Differentiation of heterogeneous phenotypes in human osteoblast cultures in response to 1,25-dihydroxyvitamin D3

The Characteristics Of Human Bone-Derived Cells (HBDCS) during osteogenesis in vitro

BACKGROUND

The primary human bone-derived cell culture technique is used as a model to study human osteogenesis. Compared to cell line cultures, primary osteoprogenitor and osteoblast cultures provide more complex information about osteogenesis, bone remodeling and regeneration than cell line cultures.

METHODS

In this study, we isolated human bone-derived cells (HBDCs) and promoted their differentiation into osteoblasts. The following parameters were evaluated: cell number and viability, total protein expression, alkaline phosphatase activity, collagenous matrix production and osteogenic genes expression, i.e., gene coding for type I collagen and alkaline phosphatase.

RESULTS

It was proved the results show that HBDCs intensively proliferate during the first 7 days of culture followed by differentiation accompanied by an increase in alkaline phosphatase activity. Moreover, it was observed that during the differentiation of HBDCs, the expression of integrin β1 increased.

CONCLUSIONS

The process was also accompanied by changes in cell shape and rearrangement of the actin cytoskeleton and focal contacts containing FAK and the integrin β1 subunit. We suggest that the β1 integrin subunit may be a suitable new target in studies of the differentiation of primary human osteoblasts in culture.

N-acetylcysteine protects dental pulp stromal cells from HEMA-induced apoptosis by inducing differentiation of the cells

Resin-based materials are now widely used in dental restorations. Although the use of these materials is aesthetically appealing to patients, it carries the risk of local and systemic adverse effects. The potential risks are direct damage to the cells and induction of immune-based hypersensitivity reactions. Dental pulp stromal cells (DPSCs) and oral keratinocytes are the major cell types which may come in contact with dental resins such as 2-hydroxyethyl methacrylate (HEMA) after dental restorations. Here we show that N-acetylcysteine (NAC) inhibits HEMA-induced apoptotic cell death and restores the function of DPSCs and oral epithelial cells. NAC inhibits HEMA-mediated toxicity through induction of differentiation in DPSCs, because the genes for dentin sialoprotein, osteopontin (OPN), osteocalcin, and alkaline phosphatase, which are induced during differentiation, are also induced by NAC. Unlike NAC, vitamins E and C, which are known antioxidant compounds, failed to prevent either HEMA-mediated cell death or the decrease in VEGF secretion by human DPSCs. More importantly, when added either alone or in combination with HEMA, vitamin E and vitamin C did not increase the gene expression for OPN, and in addition vitamin E inhibited the protective effect of NAC on DPSCs. NAC inhibited the HEMA-mediated decrease in NF-kappaB activity, thus providing a survival mechanism for the cells. Overall, the studies reported in this paper indicate that undifferentiated DPSCs have exquisite sensitivity to HEMA-induced cell death, and their differentiation in response to NAC resulted in an increased NF-kappaB activity, which might have provided the basis for their increased protection from HEMA-mediated functional loss and cell death.

Human osteopenic bone-derived osteoblasts: essential amino acids treatment effects

The development of in vitro cell culture methods has made it possible to study bone cell metabolism and growth and obtain a deeper insight into the pathophysiology of common orthopedic diseases such as osteoporosis. After analyzing the effect of two essential amino acids, L-arginine (Arg) and L-lysine (Lys), in previous in vitro and in vivo studies, the present authors investigated the administration of Arg and Lys in osteoblasts derived from human osteopenic bone. After isolation, osteoblasts were cultured in DMEM supplemented with either Arg (0.625 mg/ml/day, Arg Group) or Lys (0.587 mg/ml/day, Lys Group), or both of them (Arg-Lys Group), whereas the Control Group was sham-treated. After 7 days the following parameters were tested in all groups: MTT proliferation test, Alkaline Phosphatase (ALP), Nitric Oxide (NO), Calcium (Ca), Phosphorus (P), Osteocalcin (OC), C-Terminal Procollagen type I (PICP), Interleukin-6 (IL-6), Transforming Growth Factor-beta 1 (TGF-beta 1), Platelet Derived Growth Factor (PDGF) and Insulin-Like Growth Factor-I (IGF-I). Results were compared with those obtained from human healthy bone to verify the effect of the amino acids on osteoblasts derived from pathological tissue. In addition, a comparison was also made with the results obtained from rat osteopenic bone to assess reliability of the in vitro model. The current results support previous findings and indicate that Arg and Lys stimulation has a positive effect on osteoblast proliferation, activation and differentiation. Therefore, administration of these amino acids may be useful in clinical treatment and prevention of osteoporosis.

Individual osteoblasts in the developing calvaria express different gene repertoires

Several studies in vitro and a few in vivo have suggested that mature osteoblasts heterogeneously express osteoblast markers. In one recent study of the osteoblasts associated with bone nodules formed in vitro in rat calvaria cell populations, extensive diversity was documented in the overall gene repertoires expressed. To address whether comparable heterogeneity is evident in vivo, we investigated the expression of nine osteoblast lineage markers by both in situ hybridization and immunohistochemistry. At 21 days of fetal rat development, the calvaria is a rapidly growing bone with distinct maturational zones that are readily observed in coronal sections; that is, an osteogenic front emerging at sagittal and coronal sutures is adjacent to areas of growing trabeculae of bone, followed by more mature areas of remodeling bone. Based on expression patterns, markers can be divided into two categories. One category comprises markers that are globally expressed by all osteoblasts irrespective of their position in the calvaria. Of those tested, only two, alkaline phosphatase and the pth/pthrp receptor, fit into this category. All other markers analyzed, including transcription factors (c-fos and msx-2), matrix molecules (bone sialoprotein, osteopontin, and osteocalcin), and a hormone (pthrp), were differentially expressed only in subpopulations of osteoblasts, based on cell maturational status, environment (ectocranial vs. endocranial surfaces), and microenvironment (adjacent osteoblasts). Preosteoblasts and osteocytes in different regions of the calvaria also expressed different subsets of the lineage markers. Mechanisms responsible for generating differential gene expression profiles appear to be both transcriptional and posttranscriptional. These results indicate that postproliferative, morphologically indistinguishable osteoblasts are not a homogeneous class of cells, but instead are molecularly diverse. The present results also raise the possibility that lineage progression and/or maintenance of the differentiated state may be adaptable in the calvaria.

Mild heat shock induces proliferation, alkaline phosphatase activity, and mineralization in human bone marrow stromal cells and Mg-63 cells in vitro

Bone formation has been shown to be stimulated by local diathermy in vivo; however, the mechanisms involved in this heat-induced osteogenesis are unclear. In this study, we investigated the direct effect of temperature on human bone marrow-derived stromal cells (BMSCs) and the human osteoblast-like, osteosarcoma-derived MG-63 cells in culture conditions. Both cell types were shown to tolerate the transient exposure to mild heat shock conditions (1 h at 39-41 degrees C), and long-term (96 h) exposure at 39 degrees C stimulated DNA synthesis in BMSC but caused growth arrest in MG-63 cells. Furthermore, 1-h exposure to higher temperatures (42.5-45 degrees C) or continuous 96-h exposure to 40 degrees C or 41 degrees C inhibited the proliferation of both BMSCs and MG63 cells. The level of alkaline phosphatase (ALP) in these cells linearly correlated with the increase in temperature, and the ALP expression, either at the basal level or in response to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], was enhanced after a single 1-h exposure to 42.5 degrees C. In addition, continuous incubation at 39 degrees C or repeated transient exposure to 39/41 degrees C greatly enhanced the ability of BMSCs to form mineralizing nodules. The heat shock protein HSP70, which was expressed constitutively by BMSCs, was found to be up-regulated by hyperthermia (39 degrees C) and down-regulated at 33 degrees C. The expression of HSP70 could be induced in MG-63 cells by both low- and high-temperature conditions. These data suggest that treatment with a mild heat shock induces the proliferation and differentiation of osteoprogenitor cells, and the direct effects of temperature on bone-forming cells might be one of the mechanisms involved in heat-induced bone formation in vivo.

Recombinant human insulin-like growth factor-binding protein-5 stimulates bone formation parameters in vitro and in vivo

Insulin-like growth factor-binding protein-5 (rhIGFBP-5) is stored in bone and stimulates osteoblast cell proliferation in vitro. Bone formation is dependent on the number and activity of osteoblasts. We therefore evaluated the ability of recombinant human (rh) IGFBP-5 to increase osteoblast activity in vitro; both alkaline phosphatase (ALP) activity and osteocalcin levels showed a dose-dependent increase. In in vivo time-course studies, daily s.c. administration of 50 microg rhIGFBP-5/day/mouse significantly increased serum osteocalcin levels by day 7, and these levels were sustained through day 21. We further evaluated whether rhIGFBP-5 was as effective as IGF-I. Daily s.c. administration of rhIGFBP-5 (50 microg/day), IGF-I (13 microg/day), or IGF-I plus rhIGFBP-5 complex for 9 days increased serum osteocalcin levels by 58%, 65%, and 81% (P < 0.001 in all) and femoral bone extract ALP activity by 85% (P < 0.001), 29% (P < 0.05), and 13% (P = NS), respectively, and decreased carboxyl-terminal cross-linked telopeptide of type I collagen by 29% (P < 0.05), 20% (P = NS), and 12.5% (P = NS), respectively. One s.c. injection of rhIGFBP-5 (50 microg/mouse) increased serum osteocalcin and bone ALP activity by 21% (P < 0.05) and 27% (P < 0.02), respectively, after 5 days, but did not significantly increase serum IGF-I (1, 6, or 24 h/postinjection), suggesting that the effects of rhIGFBP-5 on bone are not mediated by increasing circulating IGF-I. Our data demonstrate that systemic administration of rhIGFBP-5, either alone or in combination with IGF-I, increases bone formation parameters in vivo.