Bone Abstracts

Introduction: Recent data suggest that imbalances in lipid metabolism affect the function of both osteoblasts and osteoclasts and thus bone quality. Here we investigated the role of apolipoprotein A-I (ApoA-I), a key-element of HDL biogenesis, in the regulation of cardinal genes/proteins that regulate lipoblasts and osteoblasts in mice.

Materials and methods: We used apoA-I deficient (ApoA-I^−/−) and wild-type (C57BL/6) mice (10 animals/group). Following sacrifice, lumbar vertebrae and femora were removed for histological analyses and in vitro experiments. Bone marrow mesenchymal stem cells (BMMSC) were isolated from mice femora, and then cultured and differentiated towards osteoblasts. BMMSC were assessed for the expression of the lipoblastic and osteoblastic master regulators PPARγ and Runx2, respectively, with the use of western blotting, flow cytometry (FC) and RT-PCR analyses. At day 21, osteoblasts were stained with von Kossa and alkaline phosphatase and examined for the expression of the ostoblast-specific markers osterix, osteopontin and osteocalcin expression using FC.

Results: BMMSCs obtained from the ApoA-I^−/− mice displayed significant increase in PPARγ and significant decrease in Runx2 expression at both protein and mRNA levels. Osterix, osteopontin and osteocalcin expression levels were significantly reduced in osteoblasts derived from the ApoA-1^−/− compared to the C57BL/6 group. Von Kossa and alkaline phosphatase stains were reduced in the ApoA-1^−/− compared to the control group.

Conclusions: ApoA-I deficiency reduces the expression of molecules associated with bone formation, while it favors the expression of lipoblastic markers in mice. Our findings highlight the interesting possibility that perturbation in ApoA-I and thus in HDL matabolism may predispose to the development of osteoporosis in mice.

Acknowledgments: This study is supported by ‘The European Community’s Seventh Framework Programme (FP7-IR-Grant-PIRG06-GA-256402)’ and The University of Patras ‘Karatheodori’ Research Grant (#D155) (All awarded to DJ Papachristou) and is part of the research network ‘OsteoNet’ of the University of Patras activities.