CaSR modulates proliferation of the superficial zone cells in temporomandibular joint cartilage via the PTHrP nuclear localization sequence

Abstract

Abstract Objective The superficial zone cells in temporomandibular joint (TMJ) cartilage are proliferative. The purpose of the present work was to delineate the relation of calcium-sensing receptor (CaSR) and parathyroid hormone-related peptide (PTHrP) nuclear localization sequence, and their role in the proliferation behaviors of the superficial zone cells. Methods A gain- and loss-of-function strategy were used in an in vitro fluid flow shear stress (FFSS) model and an in vivo bilateral elevation bite (BAE) model, which showed TMJ cartilage thickening. CaSR and PTHrP nuclear localization sequence (PTHrP87 − 139), were modulated through treating the isolated superficial zone cells with activator/SiRNA and via deleting CaSR or PTHrP gene in mice with the promoter gene of proteoglycan 4 (Prg4-CreERT2) in the tamoxifen-inducible pattern with or without additional injection of cinacalcet, the CaSR agonist, or PTHrP87 − 139 peptide. Results FFSS stimulated CaSR and PTHrP expression, and accelerated proliferation of the Prg4-expressing superficial zone cells, in which process CaSR acted as an up-streamer of PTHrP. Prg4-specific knockout of CaSR or PTHrP reduced the cartilage thickness, suppressed the proliferation and early differentiation of the superficial zone cells, and inhibited cartilage thickening and matrix production promoted by BAE. Injections of CaSR agonist Cinacalcet could not improve the phenotype caused by PTHrP mutation. Injections of PTHrP87 − 139 peptide rescued the TMJ cartilage from knockout of CaSR gene. Conclusions CaSR modulates proliferation of the superficial zone cells in TMJ cartilage through activation of PTHrP nuclear localization sequence. Our data support the therapeutic target of CaSR in promoting PTHrP production in superficial zone cartilage.