Impairment of Bone Healing by Insulin Receptor Substrate-1 Deficiency

Abstract

Insulin receptor substrate-1 (IRS-1) is an essential molecule for intracellular signaling of insulin-like growth factor (IGF)-I and insulin, both of which are potent anabolic regulators of bone and cartilage metabolism. To investigate the role of IRS-1 in bone regeneration, fracture was introduced in the tibia, and its healing was compared between wild-type (WT) mice and mice lacking the IRS-1 gene (IRS-1 ؊/؊ mice). Among 15 IRS-1 ؊/؊ mice, 12 remained in a non-union state even at 10 weeks after the operation, whereas all 15 WT mice showed a rigid bone union at 3 weeks. This impairment was because of the suppression of callus formation with a decrease in chondrocyte proliferation and increases in hypertrophic differentiation and apoptosis. Reintroduction of IRS-1 to the IRS-1 ؊/؊ fractured site using an adenovirus vector significantly restored the callus formation. In the culture of chondrocytes isolated from the mouse growth plate, IRS-1 ؊/؊ chondrocytes showed less mitogenic ability and Akt phosphorylation than WT chondrocytes. An Akt inhibitor decreased the IGF-Istimulated DNA synthesis of chondrocytes more potently in the WT culture than in the IRS-1 ؊/؊ culture. We therefore conclude that IRS-1 deficiency impairs bone healing at least partly by inhibiting chondrocyte proliferation through the phosphatidylinositol 3-kinase/Akt pathway, and we propose that IRS-1 can be a target molecule for bone regenerative medicine.

Oxidative Stress Inhibits Insulin-like Growth Factor-I Induction of Chondrocyte Proteoglycan Synthesis through Differential Regulation of Phosphatidylinositol 3-Kinase-Akt and MEK-ERK MAPK Signaling Pathways

“…Studies in chondrocytes from transgenic mice with an IRS-1 deletion have demonstrated that IRS-1 activity is required for IGF-I stimulation of Akt but not ERK1/2 (39). We noted an increase in phosphorylation of IRS-1 at Ser-312 and Ser-616 in OA cells and in normal cells treated with tBHP.…”

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

“…Nonetheless, both IGF-I and IGF-II signal through IGF-I receptors that are widely distributed on the different cell types in the fracture and throughout the fracture repair process (Wang et al 1995). The importance of the IGF signaling pathway in fracture healing has recently been supported by the absence of callus formation in mice deficient in a major intracellular mediator of IGF-I receptor signal transduction, insulin receptor substrate-1 (IRS-1; Shimoaka et al 2004). The greater severity of fracture impairment in IRS-1 KO mice than in PAPP-A KO mice may reflect the differing roles of these proteins, i.e.…”

“…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).…”

Krüppel-like Factor 5 Causes Cartilage Degradation through Transactivation of Matrix Metalloproteinase 9

“…Bone Fracture Experiment-A transverse osteotomy was created at the midshaft of the right tibia using a bone saw and was internally stabilized with an intramedullary nail using the inner pin of a spinal needle of 22-or 23-gauge diameter depending on the size of the cavity, as we reported previously (22,23). For histological analyses, specimens of the harvested tibias were fixed with 4% paraformaldehyde, decalcified with EDTA, dehydrated with ethanol, embedded in paraffin, and cut into 5-m sections.…”