Calcium-Sensing Receptors in Chondrocytes and Osteoblasts Are Required for Callus Maturation and Fracture Healing in Mice

Abstract

Calcium and its putative receptor (CaSR) control skeletal development by pacing chondrocyte differentiation and mediating osteoblast (OB) function during endochondral bone formation—an essential process recapitulated during fracture repair. Here, we delineated the role of the CaSR in mediating transition of callus chondrocytes into the OB lineage and subsequent bone formation at fracture sites and explored targeting CaSRs pharmacologically to enhance fracture repair. In chondrocytes cultured from soft calluses at a closed, unfixed fracture site, extracellular [Ca2+] and the allosteric CaSR agonist (NPS‐R568) promoted terminal differentiation of resident cells and the attainment of an osteoblastic phenotype. Knockout (KO) of the Casr gene in chondrocytes lengthened the chondrogenic phase of fracture repair by increasing cell proliferation in soft calluses but retarded subsequent osteogenic activity in hard calluses. Tracing growth plate (GP) and callus chondrocytes that express Rosa26‐tdTomato showed reduced chondrocyte transition into OBs (by >80%) in the spongiosa of the metaphysis and in hard calluses. In addition, KO of the Casr gene specifically in mature OBs suppressed osteogenic activity and mineralizing function in bony calluses. Importantly, in experiments using PTH (1‐34) to enhance fracture healing, co‐injection of NPS‐R568 not only normalized the hypercalcemic side effects of intermittent PTH (1‐34) treatment in mice but also produced synergistic osteoanabolic effects in calluses. These data indicate a functional role of CaSR in mediating chondrogenesis and osteogenesis in the fracture callus and the potential of CaSR agonism to facilitate fracture repair. © 2019 American Society for Bone and Mineral Research.

Local injections of β-NGF accelerates endochondral fracture repair by promoting cartilage to bone conversion

“…micro-computed tomography (μCT). μCT analysis was performed as previously described 15,85 . Fracture tibias were dissected free of attached muscle 14 days post-fracture, fixed in 4% PFA and stored in 70% ethanol.…”

Aberrant upregulation of CaSR promotes pathological new bone formation in ankylosing spondylitis

“…ª 2020 The Authors EMBO Molecular Medicine 12: e12109 | 2020 (Goltzman & Hendy, 2015;Cheng et al, 2020). Knockdown of CaSR inhibited chondrogenesis of MSCs and hypertrophy and bone-forming matrix secretion of chondrocytes (Cheng et al, 2020). However, hyperstimulation of CaSR did not enhance chondrogenic differentiation of MSCs.…”

“…CaSR plays a critical role in modulating chondrogenic differentiation, chondrocyte maturation and subsequent endochondral ossification (Goltzman & Hendy, 2015; Cheng et al , 2020). Knockdown of CaSR inhibited chondrogenesis of MSCs and hypertrophy and bone‐forming matrix secretion of chondrocytes (Cheng et al , 2020). However, hyperstimulation of CaSR did not enhance chondrogenic differentiation of MSCs.…”

“…Previous studies and the current study suggest that both endochondral ossification and intramembrane ossification are important in pathological new bone formation in AS. CaSR plays a critical role in modulating chondrogenic differentiation, chondrocyte maturation and subsequent endochondral ossification (Goltzman & Hendy, 2015; Cheng et al , 2020). Knockdown of CaSR inhibited chondrogenesis of MSCs and hypertrophy and bone‐forming matrix secretion of chondrocytes (Cheng et al , 2020).…”

“…Several studies have confirmed that CaSR plays a pivotal role in modulating differentiation and mineralization of osteogenic precursor cells (Chang et al , 2008; Hendy & Canaff, 2016; Hannan et al , 2018b). Activation of CaSR downstream pathways in osteoblasts promotes osteogenic differentiation in vitro , while ablating CaSR expression specifically in osteoblasts suppresses osteogenic activity and the mineralizing function in bony calluses and leads to decreased bone mass in animal models (Chang et al , 2008; Dvorak‐Ewell et al , 2011; Gonzalez‐Vazquez et al , 2014; Cheng et al , 2020).…”