Abstract
BackgroundMechanical overload applied on the articular cartilage may play an important role in the pathogenesis of osteoarthritis. However, the mechanism of chondrocyte mechanotransduction is not fully understood. The purpose of this study was to assess the effects of compressive mechanical stress on interleukin-1 receptor (IL-1R) and matrix-degrading enzyme expression by three-dimensional (3D) cultured ATDC5 cells. In addition, the implications of transient receptor potential vanilloid 4 (TRPV4) channel regulation in promoting effects of compressive mechanical loading were elucidated.MethodsATDC5 cells were cultured in alginate beads with the growth medium containing insulin-transferrin-selenium and BMP-2 for 6 days. The cultured cell pellet was seeded in collagen scaffolds to produce 3D-cultured constructs. Cyclic compressive loading was applied on the 3D-cultured constructs at 0.5 Hz for 3 h. The mRNA expressions of a disintegrin and metalloproteinases with thrombospondin motifs 4 (ADAMTS4) and IL-1R were determined with or without compressive loading, and effects of TRPV4 agonist/antagonist on mRNA expressions were examined. Immunoreactivities of reactive oxygen species (ROS), TRPV4 and IL-1R were assessed in 3D-cultured ATDC5 cells.ResultsIn 3D-cultured ATDC5 cells, ROS was induced by cyclic compressive loading stress. The mRNA expression levels of ADAMTS4 and IL-1R were increased by cyclic compressive loading, which was mostly prevented by pyrollidine dithiocarbamate. Small amounts of IL-1β upregulated ADAMTS4 and IL-1R mRNA expressions only when combined with compressive loading. TRPV4 agonist suppressed ADAMTS4 and IL-1R mRNA levels induced by the compressive loading, whereas TRPV4 antagonist enhanced these levels. Immunoreactivities to TRPV4 and IL-1R significantly increased in constructs with cyclic compressive loading.ConclusionCyclic compressive loading induced mRNA expressions of ADAMTS4 and IL-1R through reactive oxygen species. TRPV4 regulated these mRNA expressions, but excessive compressive loading may impair TRPV4 regulation. These findings suggested that TRPV4 regulates the expression level of IL-1R and subsequent IL-1 signaling induced by cyclic compressive loading and participates in cartilage homeostasis.
Highlights
Mechanical overload applied on the articular cartilage may play an important role in the pathogenesis of osteoarthritis
transient receptor potential vanilloid 4 (TRPV4) regulated these mRNA expressions, but excessive compressive loading may impair TRPV4 regulation. These findings suggested that TRPV4 regulates the expression level of interleukin-1 receptor (IL-1R) and subsequent IL-1 signaling induced by cyclic compressive loading and participates in cartilage homeostasis
Chondrogenic ATDC5 cells seeded in the type-I collagen scaffold ATDC5 cells were cultured in alginate beads with the growth medium containing insulin-transferrin-selenium and bone morphogenetic protein (BMP)-2 for 6 days
Summary
Mechanical overload applied on the articular cartilage may play an important role in the pathogenesis of osteoarthritis. Compressive stress on the cartilage results in various environmental changes, such as osmotic pressure, fluid flows and tensile stress, which lead to different biological responses [12,13,14,15], most important mechanisms underlying mechanical stressinduced cartilage degradation is overproduction of matrix-degrading enzymes, such as matrix metalloproteinase (MMPs) and a disintegrin and metalloproteinases with thrombospondin motifs 4 (ADAMTS) [16]. In this context, reactive oxygen species (ROS) reportedly acts as integral factors in intracellular signaling mechanisms to produce matrix-degrading enzymes [17]
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