PTHrP promotes subchondral bone formation in TMJ-OA

International Journal of Oral Science ARTICLE www.nature.com/ijos OPEN PTHrP promotes subchondral bone formation in TMJ-OA 1234567890();,: Jun Zhang1,2,3, Caixia Pi1, Chen Cui1, Yang Zhou1, Bo Liu2, Juan Liu2, Xin Xu1, Xuedong Zhou1 and Liwei Zheng 1✉ PTH-related peptide (PTHrP) improves the bone marrow micro-environment to activate the bone-remodelling, but the coordinated regulation of PTHrP and transforming growth factor-β (TGFβ) signalling in TMJ-OA remains incompletely understood. We used disordered occlusion to establish model animals that recapitulate the ordinary clinical aetiology of TMJ-OA. Immunohistochemical and histological analyses revealed condylar fibrocartilage degeneration in model animals following disordered occlusion. TMJ-OA model animals administered intermittent PTHrP (iPTH) exhibited significantly decreased condylar cartilage degeneration. Micro-CT, histomorphometry, and Western Blot analyses disclosed that iPTH promoted subchondral bone formation in the TMJ-OA model animals. In addition, iPTH increased the number of osterix (OSX)-positive cells and osteocalcin (OCN)-positive cells in the subchondral bone marrow cavity. However, the number of osteoclasts was also increased by iPTH, indicating that subchondral bone volume increase was mainly due to the iPTH-mediated increase in the bone-formation ability of condylar subchondral bone. In vitro, PTHrP treatment increased condylar subchondral bone marrow-derived mesenchymal stem cell (SMSC) osteoblastic differentiation potential and upregulated the gene and protein expression of key regulators of osteogenesis. Furthermore, we found that PTHrP-PTH1R signalling inhibits TGFβ signalling during osteoblastic differentiation. Collectively, these data suggested that iPTH improves OA lesions by enhancing osteoblastic differentiation in subchondral bone and suppressing aberrant active TGFβ signalling. These findings indicated that PTHrP, which targets the TGFβ signalling pathway, may be an effective biological reagent to prevent and treat TMJ-OA in the clinic. International Journal of Oral Science (2022)14:37 INTRODUCTION The temporomandibular joint (TMJ) is a complex, active synovial joint. TMJ osteoarthritis (TMJ-OA) is a severe temporomandibular disorder that can affect patient quality of life.1 Its pathology mainly manifests as cartilage degeneration, unbalanced reconstruction of cartilage bone, and chronic inflammation of the synovial tissue.2 TMJ-OA treatments, which include physical therapy, laser therapy and joint perfusion, mainly eliminate pain.3 Although these treatments can remit the symptoms and signs of TMJ-OA, they are not ideal for eliminating or improving the destruction of tissue structure in the cartilage and subchondral bone.4 Therefore, a regenerative treatment that can also prevent changes in TMJ cartilage and subchondral bone may be a longterm effective solution to TMJ-OA lesions. Under physiological conditions, the maintenance of TMJ stability depends on the biomechanical interaction between condylar cartilage and subchondral bone.5 Subchondral bone in the early OA has a lower bone mass and exhibits high bone remodelling compared with the healthy joint.6 This suggests that abnormalities in the coupling of osteoblast and osteoclast are critical to the pathogenesis of OA.7 The reconstruction of bone mainly manifests as a decrease in subchondral bone mass in OA.8,9 With TMJ-OA lesion development, a large number of osteogenesis factors promote subchondral bone sclerosis to further aggravate the degradation and destruction of the cartilage matrix.10 In human OA patients and OA mouse models, transforming growth factor-β (TGFβ) signalling was found to be enhanced in the ; https://doi.org/10.1038/s41368-022-00189-x subchondral bone.11 Moreover, our previous study showed that occlusion disorder and ageing models with the OA phenotype had abnormal high levels of TGFβ signalling expression, which suggests that TGFβ signalling may be an etiological factor involved in the onset of TMJ-OA.12 Parathyroid hormone (PTH) is a calcium-modulated hormone secreted by the parathyroid gland.13 PTH-related peptide (PTHrP), which includes two fragments, PTH (1–84) and PTH (1–34), binds parathyroid hormone 1 receptor (PTH1R) on osteoblast cell membranes and activates downstream signals to regulate bone metabolism.14 PTH induces the differentiation and formation of osteoblasts as the basis for the treatment of osteoporosis.15 On the other hand, PTH increases the number and vitality of osteoclasts and promotes bone resorption. PTH could improve OA progression in knee OA animal model.16 Our group research results showed that PTH administration could inhibit p16ink4a and ameliorate the age-related bone marrow microenvironment.17 PTH was also found to promote osteoblast proliferation, survival and differentiation. In contrast, TGFβ signalling limits bone formation by restricting osteoblast maturation.18 Although PTH and TGFβ are well known to exert complementary effects, the coordinated regulation of these opposing effects in TMJ-OA is not fully comprehended. Thus, we analysed the effect and coordinated regulation of PTHrP administration and TGFβ signalling in TMJ-OA models. In this study, intermittent PTHrP (iPTH) was found to ameliorate condylar cartilage degradation and promote subchondral bone 1 State Key Laboratory of Oral Diseases & National Clinical Research Center for Oral Diseases & West China Hospital of Stomatology, Sichuan University, Chengdu, China; 2Yunnan Key Laboratory of Stomatology, Kunming, China and 3Department of, Affiliated Stomatological Hospital, Kunming Medical University, Kunming, China Correspondence: Liwei Zheng () Received: 15 December 2021 Revised: 13 June 2022 Accepted: 15 June 2022 PTHrP promotes subchondral bone formation in TMJ-OA Zhang et al. 2 a d SB Mankin score CC ** 8 2.0 FC/CC FC e * 2.5 F P M H 1.5 1.0 0.5 6 4 2 0 0.0 Sham Sham TMJ-OA TMJ-OA b Sham TMJ-OA FC CC Sham 0.2 0.10 0.05 0.00 Sham TMJ-OA TMJ-OA Sham SB h TMJ-OA * 0.15 Tb.Sp/mm 300 μm μCT 0.4 0.0 CC * 0.15 0.6 Tb.Th/mm FC SB c g ** 0.8 (BV/TV)/% Safranin-O HE f 0.10 0.05 0.00 Sham TMJ-OA Fig. 1 The aetiology of TMJ-OA cartilage and subchondral bone c. a H&E staining of the condylar process. FC, fibrous cartilage; F, fibrous zone; P, proliferative zone; M, mature chondroblast zone; CC, calcification zone; H, hypertrophic layer. b TMJ-OA model rat sagittal sections were stained with H&E (top) and glycosaminoglycan (red) safranin O/Fast Green (bottom). Scale bars: 20 μm. c Representative μCT images showing subchondral bone of sham and TMJ-OA model rats. Scale bars: 300 μm. d FC/CC and e Mankin score in sham and TMJ-OA model rats. *P < 0.05, **P < 0.01. f–h Quantitative μCT data of sham and TMJ-OA rats. *P < 0.05, **P < 0.01. n = 8–10 formation in TMJ condyles. Moreover, PTHrP-induced condylar subchondral bone marrow-derived mesenchymal stem cell (SMSCs) diffe (...truncated)