| The objective of this study was to characterize changes in gene expression following contraction-induced injury using microarray analysis. Six C57B/6 mice (3–4 mo of age, 27.78 ± 3.31 g) performed 75 lengthening contractions of the extensor digitorum longus (EDL) while anesthetized. The EDL was excised from ambulatory controls (n = 3) and experimental animals 6 and 72 h after the contraction protocol. Pooled samples of 33P-dATP radiolabeled cDNA derived from the EDLs were hybridized to a membrane array consisting of 1185 named genes from the mouse genome. Post-hybridization analysis revealed 127 genes that were up-regulated 2 fold, and 7 genes that were down-regulated 50% or more relative to control at 6 or 72 h. Using k-means cluster analysis, 4 up-regulated and 3 down-regulated clusters were generated based on similarities in patterns of changes in gene expression. Cluster #1 and #2 contained primarily immediate early genes (IEG), heat shock proteins (HSP), and genes associated with inflammation that were elevated at 6 h and remained elevated at 72 h. Interestingly, IEGs elevated at 6 h consisted of genes related to both growth (c-fos, jun, EGR-1) and differentiation (BTG-2, Tob) indicating these contrasting physiological processes are initiated early in recovery from muscle injury. Clusters #3 and #4 contained genes that were not elevated at 6 h, but expressed at least 2 fold at 72 h. These clusters included genes relating to growth (c-myc), differentiation (myogenin), inflammation (clusterin, osteopontin), DNA repair (RAD23) and structural components (vimentin, integrinα7). Elevated expression of genes for DNA repair may be indicative of impairment of proliferating cells, such as activated muscle precursor cells, as the cell-cycle may not progress until DNA repair is complete. Genes down-regulated at 6 h, but returned to baseline at 72 h (cluster # 6; yin yang 1, nuclear factor-1B) were indicative of elevated retinoblastoma product (pRb) activity associated with differentiation. Cluster #7 contained genes (SOX4, WSB-2) related to immune function that were reduced greater than 50% at 6 h, but decreased less than 50% at 72 h. In conclusion, microarray technology, in conjunction with cluster analysis, revealed seven patterns of gene expression that begin to elucidate complex molecular events following contraction-induced injury. |
