Prediction of an interactive network of genes and validation of protein expression in osteoarthritis subchondral bone. (A) Network analysis was performed on differentially expressed genes in the osteoarthritis (OA) samples by ingenuity pathway analysis (IPA). Relationship labels: A, activated; P, phosphorylation/dephosphorylation. (B), (C), (D), (E) Antibodies against proteins Periostin and Leptin corresponding to genes POSTN and LEP were used to detect protein expression (dark brown staining) by immunohistochemistry of OA subchondral bone. Highly expressed, Periostin could be found in osteoblasts (OB) under the tidemark (TM), in osteocytes (OC) and in lining cells (LC) in the OA medial tibial (MT) regions, but not in the OA lateral tibial (LT) regions. Leptin could barely be detected in the OA MT regions, but was strongly expressed in the OA LT regions. All sections were counterstained light blue with hematoxylin. Scale bar = 0.2 mm.