Lithium chloride-induced primary cilia recovery enhances biosynthetic response of chondrocytes to mechanical stimulation

Mechanical stimulation is commonly used in cartilage tissue engineering for enhancing tissue formation and improving the mechanical properties of resulting engineered tissues. However, expanded chondrocytes tend to dedifferentiate and lose expression of their primary cilia, which is necessary for chondrocyte mechanotransduction. As treatment with lithium chloride (LiCl) can restore passaged chondrocytes in monolayer, in this study, we investigated whether this approach would be effective in 3D culture and restore chondrocyte mechanosensitivity. Chondrocytes at different passages (P0 to P2) were treated with 0-50 mM LiCl for 24 h, with different pre-culture durations (0 to 4 days). The primary cilia incidence and length were measured in α-tubulin-stained images. Treated chondrocytes were cultured with or without dynamic compression to evaluate the effect of LiCl-induced primary cilia expression on matrix synthesis by mechanically stimulated chondrocytes. LiCl treatment of chondrocytes in 3D agarose culture increased primary cilia incidence and length, with significant increases in incidence and length using 50 mM LiCl compared to other concentrations (P < 0.05). This effect was further optimized by including a 4-day pre-culture prior to the 24-h 50 mM LiCl treatment. Importantly, LiCl-induced primary cilia expression increased chondrocyte mechanosensitivity. When stimulated with dynamic compression, LiCl-treated P1 chondrocytes increased collagen (1.4-fold, P < 0.1) and proteoglycan (1.5-fold, P < 0.05) synthesis compared to untreated, unstimulated cells. The LiCl treatment method described here can be used to restore primary cilia in passaged chondrocytes, transforming them into a mechanosensitive cell source for cartilage tissue engineering.