Induction of muscle-related gene expression in loose connective tissue fibroblasts in response to static tissue stretch

Current knowledge of mechanically-induced regulation of gene expression in fibroblast is mostly based on experiments using prolonged cyclical stretching of either cultured cells or load-bearing connective tissues such as tendons and ligaments. In this study, we have examined the effect of static tissue stretch on fibroblasts within loose connective tissue using in vivo and ex vivo models. In an in vivo trunk side bending model, one side of the trunk of the mouse was stretched while the other side was shortened under anesthesia for 90 minutes. In the ex vivo method, whole subcutaneous tissue explants (including skin, subcutaneous muscle and subcutaneous tissue) from both sides of the trunk were incubated ex vivo either stretched or not stretched (shortened) for 24 hours. Tissue stretch or shortening was followed by immediate dissection of the loose connective tissue layer on both sides of the trunk, RNA extraction and gene expression analysis using Affymetrix mouse gene arrays. In both in vivo and ex vivo experiments, a large cluster of genes related to skeletal muscle function and carbohydrate metabolism was up-regulated in the stretched, compared with the shortened, connective tissue samples. However, there were few differentially expressed matrix-related genes, and in particular no change in collagen genes. Immunohistochemical staining for myosin after tissue stretch for 24 hours ex vivo showed increased myosin immunoreactivity in fibroblasts within the stretched compared with the shortened tissue samples. These results suggest that dynamic modulation of muscle-related gene expression is a normal physiological response of loose connective tissue fibroblasts to changes in tissue length..

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