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Int. J. Mol. Sci. 2016, 17(2), 188;

Biological and Chemical Removal of Primary Cilia Affects Mechanical Activation of Chondrogenesis Markers in Chondroprogenitors and Hypertrophic Chondrocytes

1,2,†,* , 1,3
Cell and Molecular Biology Laboratory, Department of Orthopaedics, Alpert Medical School of Brown University/Rhode Island Hospital, 1 Hoppin Street, Suite 402, Providence, RI 02903, USA
Department of Orthopaedics, Affiliated Hospital of Medical College of Qingdao University, Qingdao 266003, China
Bone and Joint Research Center, the First Affiliated Hospital, Frontier Institute of Science and Technology, Xi’an JiaoTong University, Xi’an, 710054, China
These authors contributed equally to this work.
Authors to whom correspondence should be addressed.
Academic Editor: Ali Mobasheri
Received: 10 December 2015 / Revised: 25 January 2016 / Accepted: 26 January 2016 / Published: 4 February 2016
(This article belongs to the Special Issue Apoptotic Chondrocytes and Osteoarthritis)
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Chondroprogenitors and hypertrophic chondrocytes, which are the first and last stages of the chondrocyte differentiation process, respectively, are sensitive to mechanical signals. We hypothesize that the mechanical sensitivity of these cells depends on the cell surface primary cilia. To test this hypothesis, we removed the primary cilia by biological means with transfection with intraflagellar transport protein 88 (IFT88) siRNA or by chemical means with chloral hydrate treatment. Transfection of IFT88 siRNA significantly reduced the percentage of ciliated cells in both chondroprogenitor ATDC5 cells as well as primary hypertrophic chondrocytes. Cyclic loading (1 Hz, 10% matrix deformation) of ATDC5 cells in three-dimensional (3D) culture stimulates the mRNA levels of chondrogenesis marker Type II collagen (Col II), hypertrophic chondrocyte marker Type X collagen (Col X), and a molecular regulator of chondrogenesis and chondrocyte hypertrophy bone morphogenetic protein 2 (BMP-2). The reduction of ciliated chondroprogenitors abolishes mechanical stimulation of Col II, Col X, and BMP-2. In contrast, cyclic loading stimulates Col X mRNA levels in hypertrophic chondrocytes, but not those of Col II and BMP-2. Both biological and chemical reduction of ciliated hypertrophic chondrocytes reduced but failed to abolish mechanical stimulation of Col X mRNA levels. Thus, primary cilia play a major role in mechanical stimulation of chondrogenesis and chondrocyte hypertrophy in chondroprogenitor cells and at least a partial role in hypertrophic chondrocytes. View Full-Text
Keywords: primary cilia; mechanotransduction; chondrocytes primary cilia; mechanotransduction; chondrocytes

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Deren, M.E.; Yang, X.; Guan, Y.; Chen, Q. Biological and Chemical Removal of Primary Cilia Affects Mechanical Activation of Chondrogenesis Markers in Chondroprogenitors and Hypertrophic Chondrocytes. Int. J. Mol. Sci. 2016, 17, 188.

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