Identification Of Pip4k2 Beta As A Mechanical Stimulus Responsive Gene And Its Expression During Musculoskeletal Tissue Healing

To investigate the mechano-transduction system of cells, we identified genes responsive to a cyclic mechanical stimulus. MC3T3.E1 cells were cultured on a computer-controlled vacuum-pump-operated device designed to provide a cyclic mechanical stimulus. A maximum elongation of 15% of membrane at 10 cycles/min (3 s extension followed by 3 s relax per cycle) was repeated for 48 h. By means of a differential display, the gene expression pattern of cells exposed to the stimulus was compared with that of unexposed cells. As a result, a gene fragment that was exclusively expressed in mechanically stressed cells was identified. By using expressed sequence tag walking together with the oligo-capping method, this gene was identified as phosphatidylinositol 4-phosphate 5-kinase type II beta (initially known as Pip5k2 beta but now reclassified as Pip4k2 beta). The specific up-regulation of Pip4k2 beta upon mechanical stimulus was also confirmed by using another apparatus, viz. a computer-controlled linearized-stepping motor system. To examine the involvement of the cyclic mechanical stimulus in the regulation of Pip4k2 beta expression in musculoskeletal tissue, we created an Achilles tendon transection model in rabbits. The temporal expression of Pip4k2 beta was assessed by means of a quantitative reverse-transcribed polymerase chain reaction. In the gastrocnemius muscle, expression of Pip4k2 beta rapidly decreased 1 week after transection but was restored to normal levels at 4 weeks. In the Achilles tendon, however, expression remained decreased until 4 weeks after transection. We suggest that the expression of Pip4k2 beta can be used as a marker for cells receiving a suitable mechanical stimulus.