Sub-confluent quiescent cultures of vascular adventitial fibroblasts in M199 were stimulated with HG (25mM). (A) Collagen type I alpha 1 mRNA levels were determined by Taqman Real-time PCR analysis at 6 h of HG treatment. 18S rRNA served as the endogenous control. *p<0.05 vs. control, ns- not significant vs. control (One-way ANOVA p< 0.05). (B and C) Protein was isolated and subjected to western blot analysis for detection of collagen type I alpha 1, with β-actin as loading control. *p< 0.05 vs. control, ns- not significant vs. control (One-way ANOVA p<0.05). (D-F) Sub-confluent quiescent cultures of vascular adventitial fibroblasts in M199 were stimulated with HG (25mM). (D) DDR2 mRNA levels were determined by Taqman quantitative real-time PCR analysis at 12 h of HG treatment, with β-actin as loading control. *p< 0.05 vs. control, ns- not significant vs. control (One-way ANOVA p< 0.05). (E and F) Protein was isolated and subjected to western blot analysis for detection of DDR2, with β-actin as loading control. *p< 0.05 vs. control, ns- not significant vs. control (One–way ANOVA p< 0.05). (G and H) Regulatory relationship between DDR2 and collagen type I in HG-treated adventitial fibroblasts. Adventitial fibroblasts were transiently transfected with DDR2 siRNA or scrambled siRNA. Following exposure of the transfected cells to HG for 12 h, collagen type I alpha 1 protein expression was examined by western blot analysis and normalized to β-actin. *p< 0.05 vs. control, ## p< 0.01 vs. HG (One-way ANOVA p< 0.05). Data are representative of three independent experiments, n = 3. Error bars represent SD.