Fig. 1

Histopathological progression of spontaneous osteoarthritis with aging in the DH guinea pig model. Row 1 (a) to (e) shows the gross histopathological changes in the knee joint from 1-month to 12-months. Red arrow designated rough surface of knee cartilage, and orange arrows indicated degenerative area. Row 2 (a) to (e) shows the microscopic changes with aging in safranine O-fast green-stained medial tibial plateau cartilages (respectively 1-, 3-, 6-, 9- and 12-month-old). Black arrows designated loss of chondrocytes in lacunas, purple arrows indicated chondrocyte cluster, and green arrows meant multiple cracks of cartilage surface. Row 3 (a) to (e) shows the progressive increase in MGP levels detected by immunohistochemistry, from 1-month to 12-months in medial tibial plateau cartilages. Yellow arrows designate positive MGP-expressed chondrocytes