Abstract
Human meniscus cells have a predominantly fibrogenic pattern of gene expression, but like chondrocytes they proliferate in monolayer culture and lose the expression of type II collagen. We have investigated the potential of human meniscus cells, which were expanded with or without fibroblast growth factor 2 (FGF2), to produce matrix in three-dimensional cell aggregate cultures with a chondrogenic medium at low (5%) and normal (20%) oxygen tension. The presence of FGF2 during the expansion of meniscus cells enhanced the re-expression of type II collagen 200-fold in subsequent three-dimensional cell aggregate cultures. This was increased further (400-fold) by culture in 5% oxygen. Cell aggregates of FGF2-expanded meniscus cells accumulated more proteoglycan (total glycosaminoglycan) over 14 days and deposited a collagen II-rich matrix. The gene expression of matrix-associated proteoglycans (biglycan and fibromodulin) was also increased by FGF2 and hypoxia. Meniscus cells after expansion in monolayer can therefore respond to chondrogenic signals, and this is enhanced by FGF2 during expansion and low oxygen tension during aggregate cultures.
Highlights
The meniscus is a fibrocartilaginous tissue found within the knee joint; it is responsible for shock absorption, load distribution, joint stability and protection of the articular cartilage [1,2,3]
We have investigated the potential of human meniscus cells, which were expanded with or without fibroblast growth factor 2 (FGF2), to produce matrix in three-dimensional cell aggregate cultures with a chondrogenic medium at low (5%) and normal (20%) oxygen tension
In the present study we have investigated the presence of chondrogenic growth factors and hypoxia with human meniscus cells expanded in monolayer culture to determine their chondrogenic potential
Summary
The meniscus is a fibrocartilaginous tissue found within the knee joint; it is responsible for shock absorption, load distribution, joint stability and protection of the articular cartilage [1,2,3]. Isolated primary human meniscus cells show some characteristics similar to those of chondrocytes because during expansion in monolayer culture there is a sharp decrease in the expression of collagen type II and a change to predominantly fibroblast-like morphology [7]. This decline in type II collagen expression is reminiscent of the loss of differentiated phenotype of articular chondrocytes, and the use of these cells for tissue regeneration of meniscus might lead to the production of ECM of inferior biomechanical properties. These include culturing chondrocytes at high cell densities to prevent cell flattening [14], in alginate gels [15] to retain the round chondrocytic morphology, in liquid suspension or in the presence of actindisrupting agents, in the presence of fibroblast growth factor 2 (FGF2) [16], retroviral transduction with Sry-related highmobility group (HMG) box-9 (SOX9) [17], in three-dimen-
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