Mesenchymal stem cells (MSCs) hold tremendous promise in regenerative medicine; however their mode of action remains to be precisely established. Direct cell-cell transfer of stem cell material to resident cells has been shown to promote tissue repair processes, while soluble trophic factors secreted by the stem cells can also stimulate repair. In order to examine these possibilities further in the meniscus, bone marrow MSCs and meniscal cells were co-cultured in micro-mass pellet cultures. The influence of fibroblast growth factor-2 (FGF-2) and fibroblast growth factor-18 (FGF-18) on meniscal pellet cultures were also assessed to mimic the action of soluble trophic factors. Immunolocalisation of the extracellular matrix (ECM) components, type I and II collagen and aggrecan (ACAN), were used to determine the response of the meniscal cells. Meniscal cell proliferation was significantly elevated by MSC co-culture; elevated deposition of type I collagen and type II collagen and ACAN was also observed. FGF-2 and FGF-18 also increased these ECM components in pellet culture. Cross-talk between meniscal cells and MSCs (and FGF-2 and FGF-18 to a lesser extent) thus positively influenced cell proliferation and matrix production conducive to tissue replenishment and repair which would be expected to be re-capitulated in vivo upon administration of stem cells to meniscal defects.
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