Genetic and pharmacological inhibition of retinoic acid receptor γ function promotes endochondral bone formation.
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.
Translational Research Program in Pediatric Orthopaedics, Division of Orthopaedic Surgery, The Children's Hospital of Philadelphia, 3615 Civic Center Blvd, Abramson Research Center, Suite 902, Philadelphia, Pennsylvania, 19104.|Department of Oral Morphology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan.
Kenta
K
Uchibe
Translational Research Program in Pediatric Orthopaedics, Division of Orthopaedic Surgery, The Children's Hospital of Philadelphia, 3615 Civic Center Blvd, Abramson Research Center, Suite 902, Philadelphia, Pennsylvania, 19104.
Jiyeon
J
Son
Translational Research Program in Pediatric Orthopaedics, Division of Orthopaedic Surgery, The Children's Hospital of Philadelphia, 3615 Civic Center Blvd, Abramson Research Center, Suite 902, Philadelphia, Pennsylvania, 19104.
Colleen
C
Larmour
Translational Research Program in Pediatric Orthopaedics, Division of Orthopaedic Surgery, The Children's Hospital of Philadelphia, 3615 Civic Center Blvd, Abramson Research Center, Suite 902, Philadelphia, Pennsylvania, 19104.
Maurizio
M
Pacifici
Translational Research Program in Pediatric Orthopaedics, Division of Orthopaedic Surgery, The Children's Hospital of Philadelphia, 3615 Civic Center Blvd, Abramson Research Center, Suite 902, Philadelphia, Pennsylvania, 19104.
Motomi
M
Enomoto-Iwamoto
Translational Research Program in Pediatric Orthopaedics, Division of Orthopaedic Surgery, The Children's Hospital of Philadelphia, 3615 Civic Center Blvd, Abramson Research Center, Suite 902, Philadelphia, Pennsylvania, 19104.
Masahiro
M
Iwamoto
D000818:Animals; D001861:Bone Regeneration / Q000187:drug effects*; D001842:Bone and Bones / Q000378:metabolism; D004353:Drug Evaluation, Preclinical; D005260:Female; D051798:Inhibitor of Differentiation Protein 1; D051379:Mice; D010012:Osteogenesis / Q000187:drug effects*; D011897:Random Allocation; D018168:Receptors, Retinoic Acid / Q000037:antagonists & inhibitors* / Q000235:genetics; D012176:Retinoids / Q000494:pharmacology*; D051785:Smad Proteins / Q000378:metabolism; D000097768:Retinoic Acid Receptor gamma
D051798:Inhibitor of Differentiation Protein 1; D018168:Receptors, Retinoic Acid; D012176:Retinoids; D051785:Smad Proteins; D000097768:Retinoic Acid Receptor gamma; C497455:Idb1 protein, mouse
BMP; RARγ; bone defect; cartilage; endochondral bone formation