Abstract
MicroRNAs (miRNAs) play an essential role in articular cartilage development and growth. However, the exact mechanisms involved in this process remain unknown. In the present study, we investigated the biological functions of miR-27b during hypertrophic differentiation of rat articular chondrocytes. Based on in situ hybridization and immunohistochemistry, we report that miR-27b expression is reduced in the hypertrophic zone of articular cartilage, but expression of peroxisome proliferator-activated receptor γ (Pparγ) is increased. Dual-luciferase reporter gene assay and Western blot analysis demonstrated that Pparγ2 is a target of miR-27b. Overexpression of miR-27b inhibited expression of Pparγ2, as well as type X collagen (Col10a1) and matrix metalloproteinase 13 (Mmp13), while significantly promoting the expression of Sex-determining Region-box 9 (Sox9) and type II collagen (Col2a1) at both the mRNA and protein levels. Rosiglitazone, a Pparγ agonist, suppressed Col2a1 expression, while promoting expression of runt-related transcription factor 2 (Runx2) and Col10a1 in a concentration-dependent manner. siRNA-mediated knockdown of Pparγ2 caused an increase in protein levels of Col2a1. The present study demonstrates that miR-27b regulates chondrocyte hypertrophy in part by targetting Pparγ2, and that miR-27b may have important therapeutic implications in cartilage diseases.
Highlights
In developing long bones, chondrocytes of the articular cartilage and growth plate show a columnar arrangement, consisting of three characteristic layers with different cellular morphologies and proliferation properties: resting, proliferative, and hypertrophic
We report for the first time that miR-27b is significantly down-regulated during hypertrophic cartilage differentiation, and that overexpression of miR-27b promotes the expression of Type II collagen (Col2a1) and Sex-determining Region-box 9 (Sox9)
We confirm that Pparγ2 is a target gene of miR-27b, which controls chondrocyte differentiation by regulating Pparγ2 protein expression
Summary
Chondrocytes of the articular cartilage and growth plate show a columnar arrangement, consisting of three characteristic layers with different cellular morphologies and proliferation properties: resting, proliferative, and hypertrophic. Chondrocyte hypertrophy is a key step during bone development, whereby chondrocytes sharply alter their program and start synthesizing type X collagen (Col10a1), as well as other mineralizing cartilage matrix components. This switch is important for the genesis of osteoclasts and for recruiting blood vessels to the ossification center. Along with invading vascular tissue, c 2018 The Author(s).
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