RANKL and osteoprotegerin expression of dermal fibroblasts after incubation with AGE-BSA. (a and c) Contrary to fibroblast-like synovial cells (FLS), advanced glycation end products-modified (AGE)-BSA significantly upregulated the receptor activator of nuclear factor kappa B ligand (RANKL) mRNA and protein expression of dermal fibroblasts. (*P < 0.05, n = 3). (b and c) The respective mRNA osteoprotegerin expression was significantly reduced after one day of AGE-BSA (*P < 0.05, n = 3). However, the osteoprotegerin protein level was reduced only marginally by AGE-BSA in dermal fibroblasts. GAPDH = glyceraldehyde 3-phosphate dehydrogenase.