Mechanical load stimulates expression of novel genes in vivo and in vitro in avian flexor tendon cells

Objective: Our experiments were designed to test the hypothesis that tendon cells might respond differently to applied strain in vitro than in vivo. Design: We tested cells in whole tendons from exercised chickens and from i solated surface (TSC) and internal tendon (TIF) in vitro that were subjecte d to mechanical strain. We hypothesized that tendon cells differentially ex press genes in response to mechanical loading in vivo and in vitro. Methods: We utilized an in-vivo exercise model in which chickens were run o n a treadmill in an acute loading regime for 1 h 45 min with the balance of time at rest to 6 h total time. Gene expression was analyzed by a differen tial display technique. In addition, isolated avian flexor digitorum profun dus TSC and TIF cells were subjected to cyclic stretching at 1 Hz, 5% avera ge elongation for 6 h, +/- PDGF-BB, IGF-I, TGF-beta 1, PTH, estrogen, PGE(2 ), or no drug and/or no load. mRNA was then collected and samples were subj ected to differential display analysis. Conclusions: Load with or without growth factor and hormone treatments indu ced expression of novel genes as well as some known genes that were novel t o tendon cells. We conclude that the study of gene expression in mechanical ly loaded cells in vivo and in vitro will lead to the discovery of novel an d important marker proteins that may yield clues to positive and negative c ell strain responses that are protective under one set of conditions and de structive under another.