Influence of defective bone marrow osteogenesis on fracture repair in an experimental model of senile osteoporosis

Abstract

Bone marrow osteogenesis in senile osteoporotic bone is impaired and, as such, may have significant implications on the successful outcome of fracture repair. Here we utilize a well-established murine model of senile osteoporosis, the P6 strain of senescenceaccelerated mice (SAMP6), to investigate fracture healing in aged osteoporotic bone. A femoral osteotomy was created in SAMP6 and in nonosteoporotic age-matched control R1 senescence-resistant mice (SAMR1). The course of fracture healing was evaluated over a period of 42 days using quantitative mCT and histological analysis. The differentiation capabilities of bone mesenchymal progenitor cells derived from SAMP6 and SAMR1 mice was examined, and their osteogenic potential determined. Although preliminary in vitro analysis confirmed that bone marrow-derived stem cells (BMSC) isolated from SAMP6 mice had a reduced osteogenic capacity, no significant deficit in fracture repair as determined by quantitative mCT could be detected. This was supported by histology assessment, where complete bridging of the fracture gap was evident by day 28 and was fully healed day 42 in both SAMP6 and SAMR1 mice. Further in vitro studies revealed that periostealderived progenitor cells (PDPC) isolated from SAMP6 mice had an osteogenic potential comparable to that observed in SAMR1 mice. In conclusion, fracture healing in SAMP6 mice is not detrimentally affected by impairment of BMSC osteogenesis, suggesting that bone marrow-mediated repair processes are dispensable for normal bone healing in this senile osteoporotic fracture model. Furthermore, the influence of PDPC in the repair process may partly explain the absence of any detectable deficits in fracture repair in SAMP6 mice. ß

Human Serine Protease HTRA1 Positively Regulates Osteogenesis of Human Bone Marrow-derived Mesenchymal Stem Cells and Mineralization of Differentiating Bone-forming Cells Through the Modulation of Extracellular Matrix Protein

“…Based on these properties, HTRA1 may be deemed as a key factor in determining the outcome of diseases such as age-related osteoporosis, where impaired BMSC osteogenesis and upregulated adipogenesis is believed to be a major contributor to the underlying pathology [24,49].…”

“…Well-established differentiation protocols were used to induce and analyze either osteogenesis or adipogenesis in mASCs and E14 129/Ola cells [21] and hBMSCs [24]. For differentiation assays, a starting density of 5,000 and 10,000 cells per square centimeter was used for human and mouse cells, respectively.…”

“…A rigidly stabilized, unilateral mid-diaphyseal osteotomy gap was created in the femurs of SAMR1 mice (n ¼ 5-6 per time point) using a 0.22 mm gigli saw as previously described [24]. The immunohistochemical and immunofluorescence techniques described above were used to detect both HTRA1 and IBSP protein in decalcified paraffin wax sections (8 lm) from mouse femora at various stages of repair (n ¼ 3 per time point).…”

“…6A) [24]. HTRA1 protein was identified in thin paraffin wax bone sections taken from mice at various stages of fracture repair using immunohistochemical staining.…”

Effect of Low-Intensity Pulsed Ultrasound on Bone-Healing Process in Murine Low-Turnover Osteoporosis Model

“…Although, to our knowledge, no studies to date have evaluated bone defect healing in SAMP6, the healing process of femoral fracture with rigid fixation in SAMP6 has been examined by micro-CT and histologically, with no difference with that in SAMR1 reported 32) . This result, however, cannot be compared with those obtained in bone defect models, as there is almost no substantial loss of tissue and periosteum-derived cells contribute dominantly to the healing process in fracture models.…”