However, these procedures are major risk factors for the early development of osteoarthritis (OA). Current treatment options include partial and total meniscectomies, depending on the extent of meniscal injury. In human meniscus, the capillary plexus supplies only the outer one third whereas the inner two thirds are avascular if left untreated, defects in this portion do not heal and may lead to further joint degeneration. Unfortunately, the reparative capacity of the meniscus is hindered by limited vascularization. The ECM consists predominantly of type I collagen throughout, type II collagen in the inner meniscus, and proteoglycans, of which aggrecan is predominant. The capacity to perform these functions is by virtue of its extracellular matrix (ECM) composition and assembly, which is accomplished entirely by meniscus fibrochondrocytes.
The meniscus of the knee joint serves a variety of critical functions that include shock absorption, cartilage protection, and joint stability. Additionally, other hypertrophic genes, MMP-13 and Indian Hedgehog ( IHh), were highly expressed by 4-fold and 18-fold, respectively, in co-cultures of MCI:MSCs relative to co-cultures of MCO:MSCs. The expression of collagen × ( COL10A1) mRNA was 2-fold higher in co-cultures of MCI:MSCs relative to co-cultures of MCO:MSCs. The mRNA expression level of Sox9 was similar in all pellet cultures. Increased collagen II protein expression was visible by collagen II immuno-histochemistry. Collagen II ( COL2A1) mRNA expression increased significantly in co-cultures of both MCO and MCI with MSCs compared to their own controls (mono-cultures of MCO and MCI respectively) but only the co-cultures of MCO:MSCs were significantly increased compared to MSC control mono-cultures. The expression of collagen I ( COL1A2) mRNA increased in co-cultured cells relative to mono-cultures of MCO and MCI but not compared to MSC mono-cultures.
The DNA content of the tissues from co-cultured cells was not statistically different from tissues formed from mono-cultures of MSCs, MCI and MCO. However, the expression level of aggrecan was highest in mono-cultures of MSCs but similar in the other four groups. Co-cultures of MCI or MCO with MSCs produced the same amount of matrix in the tissue formed.
Co-culture of inner (MCI) or outer (MCO) meniscus cells with MSCs resulted in neo-tissue with increased (up to 2.2-fold) proteoglycan (GAG) matrix content relative to tissues formed from mono-cultures of MSCs, MCI and MCO.
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