Role of IFT88 in icariin‑regulated maintenance of the chondrocyte phenotype.

Maintenance of the chondrocyte phenotype is crucial for cartilage repair during tissue engineering. Intraflagellar transport protein 88 (IFT88) is an essential component of primary cilia, shuttling signals along the axoneme. The hypothesis of the present study was that IFT88 could exert an important role in icariin‑regulated maintenance of the chondrocyte phenotype. To this end, the effects of icariin on proliferation and differentiation of the chondrogenic cell line, ATDC5, were explored. Icariin‑treated ATDC5 cells and primary chondrocytes expressed IFT88. Icariin has been demonstrated to aid in the maintenance of the articular cartilage phenotype in a rat model of post‑traumatic osteoarthritis (PTOA). Icariin promoted chondrocyte proliferation and expression of the chondrogenesis marker genes, COL II and SOX9, increased ciliary assembly, and upregulated IFT88 expression in a concentration‑ and time‑dependent manner. Icariin‑treated PTOA rats secreted more cartilage matrix compared with the controls. Knockdown of IFT88 expression with siRNA reduced extracellular signal‑regulated kinase (ERK) phosphorylation, and icariin upregulated IFT88 expression by promoting ERK phosphorylation. Thus, IFT88 serves a major role in icariin‑mediated maintenance of the chondrocyte phenotype, promoting ciliogenesis and IFT88 expression by increasing ERK phosphorylation. Icariin may therefore be useful for maintenance of the cartilage phenotype during tissue engineering.