Polycystin-2 Is Required for Chondrocyte Mechanotransduction and Traffics to the Primary Cilium in Response to Mechanical Stimulation.

Clare L Thompson,Megan Mcfie,Martin M Knight,Philip Beales,Philip Beales,J Paul Chapple,J Paul Chapple

doi:10.3390/ijms22094313

Abstract

Primary cilia and associated intraflagellar transport are essential for skeletal development, joint homeostasis, and the response to mechanical stimuli, although the mechanisms remain unclear. Polycystin-2 (PC2) is a member of the transient receptor potential polycystic (TRPP) family of cation channels, and together with Polycystin-1 (PC1), it has been implicated in cilia-mediated mechanotransduction in epithelial cells. The current study investigates the effect of mechanical stimulation on the localization of ciliary polycystins in chondrocytes and tests the hypothesis that they are required in chondrocyte mechanosignaling. Isolated chondrocytes were subjected to mechanical stimulation in the form of uniaxial cyclic tensile strain (CTS) in order to examine the effects on PC2 ciliary localization and matrix gene expression. In the absence of strain, PC2 localizes to the chondrocyte ciliary membrane and neither PC1 nor PC2 are required for ciliogenesis. Cartilage matrix gene expression (Acan, Col2a) is increased in response to 10% CTS. This response is inhibited by siRNA-mediated loss of PC1 or PC2 expression. PC2 ciliary localization requires PC1 and is increased in response to CTS. Increased PC2 cilia trafficking is dependent on the activation of transient receptor potential cation channel subfamily V member 4 (TRPV4) activation. Together, these findings demonstrate for the first time that polycystins are required for chondrocyte mechanotransduction and highlight the mechanosensitive cilia trafficking of PC2 as an important component of cilia-mediated mechanotransduction.

Highlights

The primary cilium is a microtubule-based signaling organelle essential for numerous cell signaling pathways and biological processes that include differentiation, proliferation, inflammation, and mechanotransduction
Chondrocytes were subjected to mechanical stimulation in the form of 10% cyclic tensile strain (CTS) for 1 h at 0.33 Hz and the effects on matrix gene expression examined
Chondrocytes were subjected to mechanical stimulation in the form of 10% cyclic tensile strain (CTS) for 1 h at3 0.33 of 16 Hz and the effects on matrix gene expression examined

Summary

Introduction

The primary cilium is a microtubule-based signaling organelle essential for numerous cell signaling pathways and biological processes that include differentiation, proliferation, inflammation, and mechanotransduction (for a review, see [1]). Chondrocytes are responsible for maintaining the health of the tissue and regulate cartilage extracellular matrix turnover in response to mechanical stimuli [2,3,4] Disruption of this process results in cartilage degeneration, as seen in cartilage disease such as osteoarthritis (OA, for a review, see [5]). Coveney et al reported that tissue-specific deletion of IFT88 in adolescence results in cartilage thinning associated with an increase in spontaneous arthritis later in adulthood [11]. These mice exhibit a greater level of joint damage following the surgical induction of OA, which is indicative of a chondroprotective role for the cilium through modulation of mechanotransduction [11]

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Results

Conclusion