Cyclooxygenase-2 regulates PTHrP transcription in human articular chondrocytes and is involved in the pathophysiology of osteoarthritis in rats

Ling-Hua Chang; Chung-Hwan Chen; Shun-Cheng Wu; Je-Ken Chang; Mei-Ling Ho

doi:10.1016/j.jot.2021.06.003

Cyclooxygenase-2 regulates PTHrP transcription in human articular chondrocytes and is involved in the pathophysiology of osteoarthritis in rats

J Orthop Translat. 2021 Aug 12:30:16-30. doi: 10.1016/j.jot.2021.06.003. eCollection 2021 Sep.

Authors

Ling-Hua Chang^{1

2}, Chung-Hwan Chen^{1

2

3

4

5}, Shun-Cheng Wu^{1

2}, Je-Ken Chang^{1

2

3

5}, Mei-Ling Ho^{1

2

6

7

8

9}

Affiliations

¹ Regenerative Medicine and Cell Therapy Research Center, Kaohsiung Medical University, Kaohsiung, Taiwan.
² Orthopedic Research Center, Kaohsiung Medical University, Kaohsiung, Taiwan.
³ Department of Orthopedics, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
⁴ Division of Adult Reconstruction Surgery, Department of Orthopedics, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan.
⁵ Department of Orthopedics, Kaohsiung Municipal Ta-Tung Hospital, Kaohsiung Medical University, Kaohsiung, Taiwan.
⁶ Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
⁷ Department of Physiology, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
⁸ Department of Medical Research, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan.
⁹ Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung, Taiwan.

Abstract

Background: Cyclooxygenase-2 (COX-2) inhibitors are prescribed for the management of osteoarthritis (OA)-associated pain and inflammation. However, the role of COX-2 in normal and osteoarthritic articular chondrocytes has not been well investigated. We hypothesize that COX-2 plays a role in articular chondrocytes under normal conditions and during OA progression.

Methods: In vivo COX-2 levels in articular cartilage of normal and papain-induced osteoarthritic rats were compared. The role of COX-2 in human articular chondrocytes (HACs) was tested in vitro by COX-2 overexpression or activity inhibition. The levels of COX-2 and marker gene for normal function or articular cartilage degeneration were evaluated: mRNA by qRT-PCR; proteins by western blotting or immunohistochemistry; and glycosaminoglycan (GAG) by Safranin O-fast green staining. Parathyroid hormone-related protein (PTHrP) promoter activity was detected with luciferase reporter assays.

Results: In the OA rat study, COX-2 and PTHrP were simultaneously increased in osteoarthritic rat chondrocytes, while increased PTHrP levels were reduced by celecoxib, a COX-2 selective inhibitor. The levels of normal cartilage matrices, GAG and type II collagen decreased, while markers of degeneration, collagen type X and MMP13 were elevated in osteoarthritic articular chondrocytes. Celecoxib rescued the loss of GAG and the increased collagen type X and MMP13 levels. In vitro, COX-2 overexpression in HACs significantly increased Col2a1, Col10a1, PTHrP and MMP13 mRNA expression, which was decreased when COX-2 activity was suppressed. More importantly, COX-2 overexpression upregulated the PTHrP transcription, mRNA expression and protein levels.

Conclusion: COX-2 plays a pathophysiological role by preventing terminal differentiation of articular chondrocytes by upregulating PTHrP expression at the early stage of OA progression.

The translational potential of this article: COX2 up-regulates PTHrP expression in normal and OA articular chondrocytes.

Keywords: Articular chondrocytes; Cyclooxygenase-2 (COX-2); Osteoarthritis (OA); PTHrP; Terminal differentiation.