Understanding the Action of RARγ Agonists on Human Osteochondroma Explants.

Sonia A Garcia,Aidan Fisher,Vincent Ng,Casey Codd,Masahiro Iwamoto,Hongying Tian,John E Herzenberg,Joshua M Abzug,Ashley Cellini,Yuka Imamura-Kawasawa,Motomi Enomoto-Iwamoto

doi:10.3390/ijms21082686

Abstract

Osteochondromas are cartilage-capped growths located proximate to the physis that can cause skeletal deformities, pain, limited motion, and neurovascular impingement. Previous studies have demonstrated retinoic acid receptor gamma (RARγ) agonists to inhibit ectopic endochondral ossification, therefore we hypothesize that RARγ agonists can target on established osteochondromas. The purpose of this study was to examine the action of RARγ agonist in human osteochondromas. Osteochondroma specimens were obtained during surgery, subjected to explant culture and were treated with RARγ agonists or vehicles. Gene expression analysis confirmed the up-regulation of RARγ target genes in the explants treated with NRX 204647 and Palovarotene and revealed strong inhibition of cartilage matrix and increased extracellular matrix proteases gene expression. In addition, immunohistochemical staining for the neoepitope of protease-cleaved aggrecan indicated that RARγ agonist treatment stimulated cartilage matrix degradation. Interestingly, cell survival studies demonstrated that RARγ agonist treatment stimulated cell death. Moreover, RNA sequencing analysis indicates changes in multiple molecular pathways due to RARγ agonists treatment, showing similarly to human growth plate chondrocytes. Together, these findings suggest that RARγ agonist may exert anti-tumor function on osteochondromas by inhibiting matrix synthesis, promoting cartilage matrix degradation and stimulating cell death.

Highlights

Osteochondroma is the most common benign bone tumor in children
Cartilage caps were excised from osteochondroma specimens (Table S1), dissected to create 3–5 mm3 pieces (Figure 1A) and subjected to explant culture
Osteochondroma explants were treated with RARγ agonists (NRX204647 or Palovarotene) for 4 or 7 days

Summary

Introduction

Osteochondroma is the most common benign bone tumor in children. Osteochondromas are cartilage-capped tumors that are located proximate to the growth plate and can be either solitary or multiple osteochondromas (MO) [1,2]. Developing osteochondromas can cause skeletal deformities and disturbance on neurovascular structures or nearby tendons causing discomfort and limited motion [3,4,5]. The anatomical location of osteochondroma prolongs surgery since it requires the mobilization of neurovascular and other critical structures away from the existing osteochondroma [5,7,8]. There are many risks associated with surgery and the development of a pharmacological therapy is a promising non-surgical alternative to potentially prevent the development and/or treat existing osteochondromas [5]

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Results