Inhibiting and stimulating effects of TGF-β1 on osteoclastic bone resorption in fetal mouse bone organ cultures

Abstract

The effects of TGF-beta 1 on osteoclastic resorption of fetal mouse calvaria and long bones at various stages of development was studied in organ culture. In resorbing calvariae and long bones with an established marrow cavity TGF-beta 1 (4-10 ng/ml) had a stimulating effect on 45Ca release that was partially inhibited by indomethacin. In primitive long bones, however, which were explanted before osteoclast invasion and excavation of a marrow cavity had started, TGF-beta 1 (1-4 ng/ml) inhibited 45Ca release by an indomethacin-insensitive mechanism. Histomorphometry of long bones after staining for tartrate-resistant acid phosphatase (TRAP) revealed that TGF-beta 1 treatment inhibited the migration of TRAP-positive cells from periosteum to developing marrow cavity and inhibited cell fusion. However, the formation of (mononuclear) TRAP-positive cells in the periosteum-perichondrium was strongly enhanced. These data suggest that TGF-beta 1 modulates various steps in the cascade of osteoclast development, recruitment, and activation in different ways, involving both prostaglandin-mediated and prostaglandin-independent pathways. Therefore the net effect of exogenous TGF-beta 1 on osteoclastic resorption in bone organ cultures depends on the relative prevalence of osteoclast progenitors, precursors, and mature osteoclasts in the tissue under study.

TGF-β Family Signaling in Connective Tissue and Skeletal Diseases

“…It is now understood that TGF-b acts as a chemoattractant and recruits both preosteoblast mesenchymal stromal cells and preosteoclasts to areas of bone remodeling (Pfeilschifter et al 1990;Pilkington et al 2001;Tang et al 2009). TGF-b can promote bone resorption by directly regulating proliferation, differentiation, and survival of osteoclasts (Tashjian et al 1985;Dieudonne et al 1991;Kaneda et al 2000) or indirectly by regulating the expression and secretion of pro-osteoclastic proteins in osteoblasts (Quinn et al 2001;Mohammad et al 2009;Tang and Alliston 2013). The TGF-b effects on osteoblasts are dose-dependent, with low doses increasing secretion of RANKL and suppressing expression of OPG to promote osteoclastogenesis, and high doses suppressing RANKL and increasing OPG to inhibit osteoclastogenesis (Karst et al 2004).…”

Biochemical markers in preclinical models of osteoporosis

“…The models range from very simple in vitro testing systems for resorption and formation (Baron et al 1985, Nefussi et al 1985, Bellows et al 1986, Nordstrom et al 1995, Li et al 1999, Massey & Flanagan 1999, Shalhoub et al 2000, Rawadi et al 2003, Ogasawara et al 2004, to the more complex ex vivo systems (Dieudonne et al 1991, Blavier & Delaisse 1995, Mundy et al 1999, Engsig et al 2000a, Chiusaroli et al 2003, Garrett 2003, and finally to the in vivo models, such as the rat ovariectomised (OVX) model, which mimics human osteoporosis to some extent (Vanderschueren et al 1992, Dempster et al 1995, Cenci et al 2000, Wu et al 2003.…”

“…To study osteoclast development and function three ex vivo models are generally used. These are the murine metatarsal model, which is a development model, and the tibia and calvaria models, which are resorption models (Dieudonne et al 1991, Corboz et al 1992, Hofstetter et al 1992, Leloup et al 1994, Blavier & Delaisse 1995, Engsig et al 2000a, Engsig et al 2000b. Originally, all three models were based on radiolabelling, where pregnant mice were labelled with 45 Ca 2' and bones from the embryos were isolated.…”

“…A characteristic of this model is that the release of 45 Ca 2' is dependent on differentiation and recruitment of osteoclasts into the developing site in the marrow (Dieudonne et al 1991, Blavier & Delaisse 1995. Furthermore, the bone resorption and recruitment of the osteoclasts can in the metatarsals model be investigated histologically (Leloup et al 1994, Blavier & Delaisse 1995, Engsig et al 2000a.…”

“…The tibia and the calvaria models directly detect bone resorption (Dieudonne et al 1991, Engsig et al 2000a, as they are based on the presence of mature resorbing osteoclasts. The difference between the two models lies in the bone type evaluated.…”