Genetic and pharmacological inhibition of retinoic acid receptor γ function promotes endochondral bone formation

Abstract

The nuclear retinoic acid receptors (RARs) play key roles in skeletal development and endochondral ossification. Previously, we showed that RARγ regulates chondrogenesis and that pharmacological activation of RARγ blocked heterotopic ossification (HO), pathology in which endochondral bone forms in soft tissues. Thus, we reasoned that pharmacological inhibition of RARγ should enhance endochondral ossification, leading to a potential therapeutic strategy for bone deficiencies. We created surgical bone defects in wild type and RARγ-null mice and monitored bone healing. Fibrous, cartilaginous, and osseous tissues formed in both groups by day 7, but more cartilaginous tissue formed in mutants within and around the defects compared to controls. Next, we implanted a mixture of Matrigel and rhBMP2 subdermally to induce ectopic endochondral ossification. Administration of RARγ antagonists significantly stimulated ectopic bone formation in wild type but not in RARγ-null mice. The antagonist-induced increases in bone formation were preceded by increases in cartilage formation and were accompanied by higher levels of phosphorylated Smad1/5/8 (pSmad1/5/8) compared to vehicle-treated control. Higher pSmad1/5/8 levels were also observed in cartilaginous tissues forming in healing bone defects in RARγ-null mice, and increases in pSmad1/5/8 levels and Id1-luc activity were observed in RARγ antagonist-treated chondrogenic cells in culture. Our data show that genetic or pharmacological interference with RARγ stimulates endochondral bone formation and does so at least in part by stimulating canonical BMP signaling. This pharmacologic strategy could represent a new tool to enhance endochondral bone formation in the setting of various orthopedic surgical interventions and other skeletal deficiencies. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1096-1105, 2017.

PRC2 Is Dispensablein Vivofor β-Catenin-Mediated Repression of Chondrogenesis in the Mouse Embryonic Cranial Mesenchyme

“…For example, Twist1 is positively regulated by Wnt/β-catenin signaling, and conditional deletion of Twist1 partially phenocopies the ectopic chondrogenesis found in the En1Cre/+ ; R26R/+ ;β -catenin fl/ Δ mutants ( Komori et al 1997 ; Goodnough et al 2012 ). The retinoic acid (RA) signaling pathway can interact with Wnt/β-catenin signaling, and it can promote chondrocyte development and function in vitro ( Yasuhara et al 2010 ; Uchibe et al 2017 ). RA signaling pathway components are robustly expressed in the control CM.…”

The traumatic bone: trauma-induced heterotopic ossification

“…The ligands of the BMP signaling pathway, BMPs-2 and 4 have been known to induce bone formation for several decades. 75,76 The majority of studies have traditionally utilized this fact to recreate HO in vivo 77–79 or dissect mechanistic basis of HO in vitro. 18,80 Bone morphogenetic protein 2 is the most commonly used ligand to induce ectopic bone formation and is typically mixed with a ‘scaffold’, which can be either a resorbable synthetic polysaccharide-based hydrogels, 81 or a biological matrix, like collagen or the commercially available extracellular matrix complex matrigel.…”

MicroRNA‑410 participates in the pathological process of postmenopausal osteoporosis by downregulating bone morphogenetic protein‑2

“…BMP-2 has been reported to be a member of transforming growth factor-β supergene family (12), and serves important roles in osteogenesis (13), fracture healing (14) and bone formation (15). BMP-2 further serves important roles in the process of ossification, by stimulating the differentiation of pluripotent stromal stem cells into osteoblasts and enhancing the functions of osteoblasts (16)(17)(18). There are various approaches to regulate BMP-2 expression, including the use of microRNAs (miRs), which has been widely studied.…”