Expression of parathyroid hormone‐related peptide and insulin‐like growth factor I during rat fracture healing

Abstract

Parathyroid hormone-related peptide (PTHrP) and insulin-like growth factor I (IGF-I) are both involved in the regulation of bone and cartilage metabolisms and their interaction has been reported in osteoblasts. To investigate the interaction of PTHrP and IGF-I during fracture healing, the expression of mRNA for PTHrP and IGF-I, and receptors for PTHlPTHrP and IGF were examined during rat femoral fracture healing using an in situ hybridization method and an immunohistochemistry method, respectively. During intramembranous ossification, PTHrP mRNA, IGF-I mRNA and IGF receptors were detected in preosteoblasts, differentiated osteoblasts and osteocytes in the newly formed trabecular bone. PTHlPTHrP receptors were markedly detected in osteoblasts and osteocytes, but only barely so in preosteoblasts. During cartilaginous callus formation, PTHrP mRNA was expressed by mesenchymal cells and proliferating chondrocytes. PTHlPTHrP receptors were detected in proliferating chondrocytes and early hypertrophic chondrocytes. IGF-I mRNA and IGF receptor were co-expressed by mesenchymal cells, proliferating chondrocytes, and early hypertrophic chondrocytes. At the endochondral ossification front, osteoblasts were positive for PTHrP and IGF-I mRNA as well as their receptors. These results suggest that IGF-I is involved in cell proliferation or differentiation in mesenchymal cells, periosteal cells, osteoblasts and chondrocytes in an autocrine andlor paracrine fashion. Furthermore, PTHrP may be involved in primary callus formation presumably co-operating with IGF-I in osteoblasts and osteocytes, and by regulating chondrocyte differentiation in endochondral ossification. IntroductionDuring fracture healing, several cellular events occur simultaneously and/or sequentially: inflammatory reaction, chondrogenesis, intramembranous ossification and endochondral ossification, resulting in the formation of a fracture callus followed by bony union. These dynamic events of bone metabolism are biologically regulated and can be investigated representatively in animal fracture models [15]. It has been reported that various local regulators such as cytokines and growth factors are expressed during fracture healing suggesting they regulate proliferation and/or differentiation of cells involved in fracture healing [11,39]. Since many growth factors regulate biological reaction of cells in co-operation with other factors or modulate the function of other factors [9,10,36], these interaction between different local regulators may be important for the well-organized repair process of fracture healing.Parathyroid hormone-related peptide (PTHrP) was originally isolated from tumors associated with humoral hypercalcemia of malignancy [34]. It has been reported that PTHrP is expressed in a wide variety of fetal and neonatal tissues [8,37], and acts in an autocrine/paracrine fashion binding with the same receptor as parathyroid hormone (PTH) does [16]. During embryonal cartilage development, PTHrP is expressed in the perichondrium induced by Indian ...

Pregnancy associated plasma protein-A is necessary for expeditious fracture healing in mice

“…In explants from the post-fracture day 5 calluses, there is also a degree of IGFBP-4 proteolysis, independent of exogenous IGF-II in the assay. This suggests that the levels of IGF being produced by the callus at this time point are increased, as previously reported (Okazaki et al 2003, Wildemann et al 2004) and consistent with the findings of IGF-independent IGFBP-4 proteolysis in bone cells . Interestingly, the amount of proteolysis appears to be reduced in the day 12 calluses compared with the day 5 calluses in WT mice.…”

“…At this point, we do not know whether PAPP-A is regulating IGF-I or IGF-II (or both) during fracture repair. We propose that it is IGF-I based on the fact that IGF-I is known to be expressed in the rodent fracture model (Wang et al 1995, Okazaki et al 2003, Shimoaka et al 2004, Wildemann et al 2004 and IGF-I is the predominant IGF expressed by rodent bone cells (Conover & Rosen 2002). However, IGF-II message can be found in the rodent growth plate, perhaps recapitulating skeletal growth in the fetal and neonatal periods (Shinar et al 1993).…”

“…Indeed, fracture repair recapitulates the process of new bone formation at the epiphyseal growth plate (Ferguson et al 1999, Gerstenfeld et al 2003, and the IGFs were discovered based on their essential role in this new bone formation required for linear growth (Le Roith et al 2001). IGF-I and IGF-I receptor expression have been shown to have widespread distribution within the callus in most cell types and differentiation stages of the osteoblast lineage, in the newly proliferating and early hypertrophic chondrocytes, and in mesenchymal cells (Andrew et al 1993, Trippel 1998, Okazaki et al 2003, Wildemann et al 2004. Moreover, IGFs are mitogenic in vitro for cells important in fracture healing, including chondrocytes and osteoblasts, and IGF-I has been shown to stimulate proteoglycan synthesis in growth plate chondrocytes and collagen synthesis in bone (Vetter et al 1986, McCarthy et al 1989, Wergedal et al 1990, Conover & Rosen 2002.…”

A Perspective: Engineering Periosteum for Structural Bone Graft Healing

“…Specifically administration of the amino terminal fragment PTH 1-34 demonstrated stimulatory effects on healing in various animal models including fracture-healing models [3,45,66,96] and bone-grafting models [1,35]. The mechanism by which PTH stimulates bone healing is not well understood.…”

“…Several recent studies suggest PTH exerts its anabolic actions at both the early stage and the late stage of bone healing [3,64]. Intermittent treatment of PTH altered the expression of IGFs and Wnt signaling in fracture-healing models [43,66].…”