Mice Lacking Pten in Osteoblasts Have Improved Intramembranous and Late Endochondral Fracture Healing

Abstract

The failure of an osseous fracture to heal (development of a non-union) is a common and debilitating clinical problem. Mice lacking the tumor suppressor Pten in osteoblasts have dramatic and progressive increases in bone volume and density throughout life. Since fracture healing is a recapitulation of bone development, we investigated the process of fracture healing in mice lacking Pten in osteoblasts (Ocn-cretg/+;Ptenflox/flox). Mid-diaphyseal femoral fractures induced in wild-type and Ocn-cretg/+;Ptenflox/flox mice were studied via micro-computed tomography (µCT) scans, biomechanical testing, histological and histomorphometric analysis, and protein expression analysis. Ocn-cretg/+;Ptenflox/flox mice had significantly stiffer and stronger intact bones relative to controls in all cohorts. They also had significantly stiffer healing bones at day 28 post-fracture (PF) and significantly stronger healing bones at days 14, 21, and 28 PF. At day 7 PF, the proximal and distal ends of the Pten mutant calluses were more ossified. By day 28 PF, Pten mutants had larger and more mineralized calluses. Pten mutants had improved intramembranous bone formation during healing originating from the periosteum. They also had improved endochondral bone formation later in the healing process, after mature osteoblasts are present in the callus. Our results indicate that the inhibition of Pten can improve fracture healing and that the local or short-term use of commercially available Pten-inhibiting agents may have clinical application for enhancing fracture healing.

Loss of Cbl-PI3K interaction modulates the periosteal response to fracture by enhancing osteogenic commitment and differentiation

“…Studies on Phosphatase and tensin homolog (PTEN), a negative regulator of PI3K, revealed that PTEN deletion in osteoprogenitors resulted in their increased proliferation [10] and late stage osteoblast-specific PTEN deletion led to increased bone mineral density [11]. In agreement with these findings, mice lacking PTEN in osteoblasts have improved fracture healing [12]. …”

Fracture healing in mice lacking Pten in osteoblasts: a micro-computed tomography image-based analysis of the mechanical properties of the femur

“…All statistical analyses were conducted with the software R 2.15 (R Foundation for Statistical Computing, Vienna, Austria). Sex was not investigated in the present study as Burgers and co-workers (2013) found sex to be insignificant for K , F max , and healing rate.…”

“…The previous study, approved by the Institutional Animal Use and Care Committee at the Van Andel Research Institute, Grand Rapids, MI, used 96 mice to investigate the influence of Pten on biomechanical properties of the femur during fracture healing (Burgers et al, 2013). Of these mice, the 66 subjected to mechanical testing and micro-computed tomography (μ-CT) imaging were the focus of the present study.…”

“…A mid-diaphyseal fracture was induced in mice 11 to 12 weeks old using the procedure outlined by Burgers and co-workers (2013). Fractures identified as oblique, comminuted, or incomplete were excluded from further mechanical tests.…”

“…Improved fracture healing was found in a study which used four-point bending mechanical testing to assess the healing rate of femoral fractures in Pten-CKO (Burgers et al, 2013). At 28 days post-fracture (PF) Pten-CKO had significantly higher bending stiffness ( K ) and peak force to failure ( F max ) than WT.…”