Biaxial strain effects on cells from the inner and outer regions of the meniscus

During knee joint loading, the fibrocartilaginous menisci experience significant spatial variations in mechanical stimuli. Meniscus cells also exhibit significant variations in biosynthesis and gene expression depending on their location within the tissue. These metabolic patterns are consistent with a more chondrocytic phenotype for cells located within the avascular inner two-thirds compared with a more fibroblastic phenotype for cells within the vascularized outer periphery. The spatial distribution of cell biosynthesis and gene expression patterns within the meniscus suggest that cells may exhibit intrinsically different responses to mechanical stimuli. The objective of our study was to test for intrinsic differences in the responsiveness of these meniscus cell populations to an equivalent mechanical stimulus. Cellular biosynthesis and gene expression for extracellular matrix proteins in isolated inner and outer meniscus cells in monolayer were quantified following cyclic biaxial stretch. The results demonstrate that inner and outer meniscus cells exhibit significant differences in matrix biosynthesis and gene expression regardless of stretching condition. Both inner and outer meniscus cells responded to stretch with increased nitric oxide production and total protein synthesis. The results suggest that inner and outer meniscus cells may respond similarly to biaxial stretch in vitro with measures of biosynthesis and gene expression.