α5β1 integrin may be involved in the induction of noncartilaginous collagen expression in dedifferentiating chondrocytes. (a) Chondrocytes obtained from human articular cartilage were cultured in monolayers, and expression of type I procollagen (COL1A1) and type III procollagen (COL3A1) was determined by quantitative PCR at the indicated time points. Change in expression level during culture is shown by relative ratios against that at day 2. Results are mean ± standard error of the mean (SEM) of four independent experiments, each in triplicate. (b), (c) siRNAs for respective integrins were introduced into primary cultured chondrocytes, and cells were cultured in monolayers. Three days later, expression of COL1A1 and COL3A1 was determined by quantitative PCR (b). For some siRNAs, expression of type II procollagen (COL2A1) and aggrecan (ACAN) was also determined (c). Results shown by relative ratios against the cells given control siRNA (Control; open bars). Two or three bars for respective integrin genes indicate the results of respective siRNAs used for the genes. Results are mean ± SEM of four to six independent experiments, each in triplicate. *P <0.05 and **P <0.01 against day 2 or control. (d) Control siRNA or siRNA for α5 or β1 integrin was introduced into chondrocytes, and the cells were cultured in monolayers. Cell morphology was observed 1 day (day 1) or 3 days (day 3) after introduction. Representative images of six independent experiments are shown. Scale bar = 100 μm. GADPH, glyceraldehyde 3-phosphate dehydrogenase.