Periprosthetic strain magnitude-dependent upregulation of type I collagen synthesis in human osteoblasts through an ERK1/2 pathway

Human osteoblasts sense mechanical stimulation and synthesise type I collagen in periprosthetic osseointegration following total hip arthroplasty. However, the regulation of type I collagen synthesis by periprosthetic strain is unclear because the cellular-level strain magnitude remains unknown to date. Fortunately, the tissue-level strain in implanted femurs is measurable. According to the mechanism of strain amplification, the tissue-level strain was amplified 20 times to stretch human osteoblasts in this study. Elongation of 0.8-3.2% enhanced the mRNA level of type I collagen, whereas the release of procollagen type I C propeptide only increased at 2.4% and 3.2% elongation. Type I collagen expression increased with the activation of ERK1/2 phosphorylation in a strain-magnitude-dependent manner, whereas JNK and P38 were unaffected. The responses were completely inhibited by blocking the ERK1/2 pathway with U0126. The results indicate that type I collagen synthesis in human osteoblasts depends on the level of periprosthetic strain and ERK1/2 activation.