Abstract
Mesenchymal stem cells (MSCs) spontaneously assemble into three-dimensional (3D) spheroids under matrix-deficient conditions such as the synovial cavity, although their functional significance has yet to be fully elucidated. In this study, we used concave microwell cultures to promote the spontaneous aggregation of adipose-derived MSCs (ASCs) from OA patients, thereby mimicking the intra-articular microenvironment. We analyzed the paracrine factors of ASC aggregates and compared it with that of conventional 2D monolayer cultures. Notably, 3D aggregation significantly increased the secretion of HGF and VEGF, whereas FGF2 levels remained relatively unchanged. These results indicate that the structural characteristics of ASC aggregates enhance the secretion of key paracrine factors involved in angiogenesis and tissue repair. To functionally evaluate the biological relevance of the secreted factors, conditioned media (CM) from ASC aggregates were applied to human articular chondrocytes. The CM significantly promoted chondrocyte proliferation, an effect that was abolished by the addition of HGF-neutralizing antibodies, thereby highlighting HGF as a central mediator of the regenerative response. Additionally, we further explored whether extracellular factors could modulate growth factor expression such as HGF. In this context, we investigated the impact of low-concentration hyaluronic acid (HA), a key synovial component widely used in OA treatment. Co-treatment with HA not only amplified the expression and secretion of HGF, VEGF, and FGF2, but also promoted ASC proliferation. ASCs forming functional aggregates may exert regenerative effects as active paracrine modulators, and the addition of low-dose hyaluronic acid is expected to further enhance this function, offering a promising strategy for MSC-based osteoarthritis therapy.