shRNA construct against matrix metalloproteinase 2 (MMP-2) (shMMP2) impairs annulus fibrosus (AF) cell-mediated remodeling of collagen gels. Histology images of collagen gels containing (a) no cells, (b) nontransduced AF cells, (c) a pure population of cells transduced with shMMP2, (d) a pure population of cells transduced with shNon, and (e) a mixed population of shMMP2-transduced and nontransduced cells. All gels were cultured for 7 days. Images for (a) through (d) were taken at 400×; scale bars represent 50 μm. Image for (e) was taken at 100×; scale bar represents 200 μm. Noninfected AF cells (b) and shNon-transduced cells (d) were shown to restructure collagen gels. These cells appeared elongated and anchored to the fibers. Cells transduced with shMMP2 (c) appeared similar to gels without cells (a), with little to no restructuring of the collagen network and rounded cells. In gels containing mixed populations of cells (e), collagen fibers were reorganized but rounded cells were clearly visible without reorganization of fibers in their immediate surroundings.