Primary cilia integrity governs TRPV4-mediated NF-κB/COL2 signaling in osteoarthritis pathogenesis

Abstract

Chondrocyte mechanotransduction dysfunction is a key feature of osteoarthritis (OA). Previous studies have demonstrated that primary cilia play a crucial role in chondrocyte mechanosensation and signal transduction. Transient Receptor Potential Vanilloid 4 (TRPV4), which is highly expressed on primary cilia, is a critical mechanotransduction protein and one of the most important Ca²⁺ channels. However, the interplay between the mechanism of primary cilia-mediated signaling and that of TRPV4 channel regulation remains poorly understood. Here, we demonstrate that OA chondrocytes and Intraflagellar Transport Protein 88 (Ift88) conditional knockout (cKO) mice exhibit reduced ciliary incidence resulting in cartilage degeneration. TRPV4 expression inversely correlated with ciliary integrity, increasing as cilia were lost. In cilia-intact healthy chondrocytes, TRPV4 antagonism inhibited Ca²⁺-dependent NF-κB activation while promoting type II collagen (COL2) synthesis. These effects were abolished by Interleukin-1 beta (IL-1β)-induced ciliary defect or IFT88 deficiency. Chromatin immunoprecipitation (ChIP) analysis revealed disrupted p65 binding to the COL2 promoter upon the loss of ciliary integrity. Crucially, Ift88 cKO chondrocytes showed unresponsiveness of the TRPV4 channel, as confirmed by Ca²⁺ flux and changes in the expression levels of NF-κB and COL2. Our findings position primary cilia as indispensable regulators of TRPV4-mediated NF-κB - COL2 signaling, offering mechanistic insights into OA pathogenesis and identifying IFT88 as a therapeutic checkpoint.