A modified rhTGF-beta1 and rhBMP-2 are effective in initiating a chondro-osseous differentiation pathway in bone marrow cells cultured in vitro.

Rat bone marrow cells were cultured in vitro in a collagen-gel medium at 0.5% fetal bovine serum concentration for 10 days in the presence of recombinant human transforming growth factor-beta-1, genetically engineered to contain a collagen binding domain (rhTGF-beta1-F2), or a commercial rhTGF-beta1. To compare the effects of TGF-betas with other growth factors in which the osteogenic capacity has been widely documented, a recombinant human bone morphogenetic protein (rhBMP-2) was evaluated. Once serum conditions compatible with growth were re-established, the selected cells were cultured for 6 more days in the presence of the growth factor. In the last 2 days, dexamethasone (dex) and beta-glycerophosphate (beta-GP) were added to promote osteogenesis. After this 16-day period, cells were placed into diffusion chambers or demineralized bone matrix (DBM) implants, and implanted subdermally on the backs of rats for 28 days. Biochemical, histological, and immunohistochemistry analysis provided evidence of cartilage (commercial rhTGF-beta1-treated cells), osteoid (rhTGF-beta1-F2-treated cells), and bone tissues (rhBMP-2 treated cells), inside the diffusion chambers, whereas bone, cartilage, and osteoid were observed inside the DBM implants under any of the three growth factors effect. Our study advances the technology capable of selecting a cell population from bone marrow that, in the presence of rhTGF-beta1 or rhBMP-2 in vitro, achieves chondro-osteogenic potential in vitro and in vivo.

The number and generative capacity of human B lymphocyte progenitors, measured in vitro and in vivo, is higher in umbilical cord blood than in adult or pediatric bone marrow.

The lack of human B lymphocyte development in beige/nude/XID (bnx) mice is in sharp contrast to the robust development observed in another immune deficient strain, the NOD/SCID mouse. The ability to generate human B lymphocytes in the NOD/SCID, but not bnx mouse has been hypothesized to be caused by differences in the microenvironments or systemic cytokine concentrations. In the current studies we report that the differences in development can be primarily attributed to the source of the progenitors transplanted into the mice. The prior studies in bnx mice used cultured pediatric or adult bone marrow (BM) as the source of the CD34+ cells, whereas the NOD/SCID studies have predominantly used fresh or cultured umbilical cord blood (UCB). We have analyzed BM and UCB for the number of human CD34+/CD38- cells capable of in vitro B lymphocyte development, and have found a lower frequency of B lymphocyte generation in BM. The individual B lymphocyte clones that developed from bone marrow produced 100-fold fewer cells than the UCB-derived clones. In agreement with the in vitro studies, human B lymphocytes developed in bnx mice from both CD34+ and CD34+/CD38- cells isolated from human umbilical cord blood, but not from equivalent numbers of CD34+ and CD34+/CD38- progenitors from bone marrow. Therefore, the lower generative capacity, and frequency of B lymphocyte precursors in human marrow may be responsible for the previous results that showed a lack of B lymphocyte development in bnx mice.

Demineralized bone matrix mediates differentiation of bone marrow stromal cells in vitro: effect of age of cell donor.

Bone maintenance requires a continuous source of osteoblasts throughout life. Its remodeling and regeneration during fracture repair is ensured by osteoprogenitor stem cells which are part of the stroma of the bone marrow (BM). Many investigators have reported that in cultured BM stromal cells there is a cell population that will differentiate along an osteogenic lineage if stimulated by the addition of osteogenic inducers, such as dexamethasone (dex), beta-glycerophosphate (beta-GP), transforming growth factor beta-1 (TGF-beta 1) and bone morphogenetic protein-2 (BMP-2). Here we report the effects of demineralized bone matrix (DBM) on the osteogenic differentiation of BM stromal cells in vitro, using morphological criteria, alkaline phosphatase (AP) activity, and calcium accumulation. DBM and DBM-conditioned medium (DBMcm) enhanced bone formation in the presence of dex and beta-GP, whereas DBM particles caused changes in the cell phenotype. Temporal expression of total and skeletal AP by BM stromal cells from 4-week-old rats showed a biphasic pattern enhanced by DBM and suggesting the presence of two cell populations. In one population, AP synthesis reaches a maximum during the first week in culture, following which cells either die or loose their ability to synthesize AP. A second, less abundant population begins to proliferate and synthesize AP during the second and third weeks. The synthesis of AP, which often decreases by the third week, can be maintained at high levels only if DBM is added to the cultures. BM stromal cells isolated from 24- and 48-week-old rats showed a decrease or loss of this biphasic AP expression pattern compared with cells isolated from 4-week-old rats. The addition of DBM to cultures derived from 24- and 48-week-old rats stimulated mostly the second cell population to synthesize AP, suggesting that DBM contains a factor(s) that acts on a specific bone marrow cell population by increasing the proliferation of active cells or inducing the differentiation of dormant cells.

Dystrophic calcification and mineralization during bone induction: biochemical differences.

The calcification of implants of glutaraldehyde-cross linked collagenous tissues and collagen was studied in young and old rats and compared to bone induction by non-crosslinked osteogenically active demineralized bone matrix (DBM). Glutaraldehyde-crosslinked implants of DBM, tendon, and cartilage calcified in young but not in old animals and accumulated only trace amounts of BGP (Bone Gla protein, osteocalcin). Alkaline phosphatase activity and BGP was high in implants of DBM and undetectable in crosslinked implants. To try and understand why bone formation is so significantly reduced in older Fischer 344 rats, we developed a system which consists of cylinders of DBM sealed at the ends with a Millipore filter. Cells originating from 20 day old embryo donors were introduced into the chambers prior to subcutaneousmplantation. After 4 weeks of implantation in 26 month old rats, the cylinders containing embryonic calvaria or muscle cells were found to be full of bone and/or cartilage.

Biochemical differences between dystrophic calcification of cross-linked collagen implants and mineralization during bone induction.

Ectopic calcification of diseased tissues or around prosthetic implants can lead to serious disability. Therefore, calcification of implants of glutaraldehyde-cross-linked collagenous tissues and reconstituted collagen was compared with mineralization induced by demineralized bone matrix (DBM). Whereas implants of DBM accumulated large amounts of calcium and a bone-specific gamma-carboxyglutamic acid protein (BGP or osteocalcin) following implantation in both young and older rats, implants of cross-linked pericardium calcified with only traces of BGP. Glutaraldehyde-cross-linked DBM failed to calcify after implantation in 8-month-old rats for 2-16 weeks. Implants of cross-linked type I collagen exhibited small calcific deposits 2 weeks postimplantation but calcium content eventually dropped to levels equal to those of soft tissues as the implants were resorbed. The calcium content of DBM implanted in 1- and 8-month-old rats reached comparable levels after 4 weeks, but the BGP content was approximately twice as high in the younger animals than in the older ones. Glutaraldehyde-cross-linked implants of DBM, tendon, and cartilage calcified significantly in young but not in old animals. This form of dystrophic calcification was associated with only trace amounts of BGP. Alkaline phosphatase activity was high in implants of DBM and undetectable in implants of cross-linked collagenous tissues. These results show that implants of glutaraldehyde-cross-linked collagenous tissues and reconstituted collagen calcify to different extents depending upon their origin and the age of the host, and that the mechanism of dystrophic calcification differs significantly from the process of mineralization associated with bone induction as reflected by alkaline phosphatase activity and BGP accumulation.

Increased epidermal transglutaminase activity following 2,3,7,8-tetrachlorodibenzo-p-dioxin: in vivo and in vitro studies with mouse skin.

In previous studies it has been shown that topical treatment of hairless mice with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) induces hyperproliferation and hyperkeratinization in the epidermis of hairless mice. The present investigation demonstrated that such TCDD-induced morphological changes in skin in vivo are accompanied by increased levels in activity of epidermal transglutaminase (ETG), the enzyme associated with terminal epidermal differentiation. Exposure of mouse epidermal cells in tissue culture to 10(-9) M TCDD also resulted in a significant increase in ETG activity, despite the fact that morphologically these cultures (grown at 0.07 mM ionic calcium concentrations) exhibited no signs of terminal differentiation. Thus one mechanism of action of TCDD in inducing cutaneous changes appears to relate to the stimulation of increased ETG levels.

Decreased induction of aryl hydrocarbon hydroxylase activity in hyperproliferative hairless mouse epidermis.

Hairless mice were treated topically with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to induce experimental chloracne. The aryl hydrocarbon hydroxylase (AHH) activity in the epidermis was monitored. TCDD is a potent inducer of AHH activity in normal skin. However, as continued TCDD application induced hyperproliferative and hyperkeratotic changes in the epidermis, the AHH activity decreased. Similar suppression in AHH activity was demonstrated in epidermis made hyperplastic by (a) tape stripping of stratum corneum and (b) repeated application of 50% oleic acid. This suggests that the epidermal AHH response varies with the state of epidermal differentiation. In the hairless mouse, AHH activity in hyperplastic epidermis is lower than that in normal epidermis.