Isolated osteoblasts from spinal cord-injured rats respond less to mechanical loading as compared with those from hindlimb-immobilized rats.

ABSTRACT

BACKGROUND: The pathogenesis of osteoporosis after spinal cord injury (SCI) may be different from disuse osteoporosis. OBJECTIVE: To investigate whether there is the differential anabolic response to mechanical loading between osteoblasts from SCI rats and those from hindlimb-immobilized rats. METHODS: Femoral bone-marrow was harvested for osteoblast culture from SCI rats, hindlimb-immobilized rats, and control rats 3 weeks after animal model creation. At the stage of differentiation, rat osteoblasts were plated in six-well plates for stretching. Cyclic strains were applied for 48 hours, and then alkaline phosphatase (ALPase) activity, procollagen, and osteocalcin production, and gene expression of osteocalcin, runt-related transcription factor 2 (Runx2), and osterix were measured in osteoblasts from SCI rats, hindlimb-immobilized rats, and control rats. RESULTS: ALPase activity, procollagen, and osteocalcin production, and gene expression of osteocalcin, Runx2, and osterix were significantly lower in osteoblasts after stretching from SCI rats compared with those from hindlimb-immobilized rats. However, there was no significant difference of these parameters between isolated osteoblasts from hindlimb-immobilized rats and those from control rats. CONCLUSION: The activity of isolated osteoblasts from SCI rats was lower than control rats, and this suggested that osteoblasts from SCI rats responded less to mechanical loading as compared with those from control rats.