Decrease in the expression of the type 1 PTH/PTHrP receptor (PTH1R) on chondrocytes in animals with osteoarthritis

Background: To evaluate the expression of the type 1 PTH/PTHrP receptor (PTH1R) on chondrocytes from hyaline cartilage over the course of osteoarthritis (OA). Methods: In 12 NZW rabbits, the anterior cruciate ligament (ACL) was resected to create anterior instability of the knee. In 12 control rabbits, only a sham operation, without resection of the ACL, was performed. Four animals from each group were killed at 3, 6, and 12 weeks. After opening the knee joint, OA was macroscopically graded and hyaline cartilage of the load-bearing area was evaluated histologically according to the Mankin scale and by immunostaining for PTH1R. Results: There was a positive linear correlation between the time after surgery and the macroscopic and histologic OA scores. The scores in the control group were constant over the time course. Immunostaining showed significantly less expression of PTH1R in the experimental compared to the control group after 6 (P < 0.05) and 12 weeks (P < 0.01). In the experimental group, a negative linear correlation between PTH1R expression and macroscopic and histologic grades was found. Conclusions: The results show an in vivo decrease in the expression of PTH1R on chondrocytes over the time course of OA. Further studies are needed to evaluate whether new treatment approaches could evolve from this knowledge.