Annexin A6 regulates catabolic events in articular chondrocytes via the modulation of NF-κB and Wnt/ß-catenin signaling.

Takeshi Minashima,Thorsten Kirsch,Masaru Katoh

doi:10.1371/journal.pone.0197690

Abstract

Annexin A6 (AnxA6) is expressed in articular chondrocytes at levels higher than in other mesenchymal cell types. However, the role of AnxA6 in articular chondrocytes is not known. Here we show that complete lack of AnxA6 functions resulted in increased ß-catenin activation in Wnt3a-treated murine articular chondrocytes, whereas AnxA6 expressing articular chondrocytes showed decreased ß-catenin activation. High expression of AnxA6 in human articular chondrocytes showed the highest inhibition of Wnt/ß-catenin signaling. Inhibition of Wnt/ß-catenin signaling activity by AnxA6 together with cytosolic Ca2+ was achieved by interfering with the plasma membrane association of the Wnt signaling complex. AnxA6 also affected the cross-talk between Wnt/ß-catenin signaling and NF-κB signaling by decreasing ß-catenin activity and increasing NF-κB activity in Wnt3a-, interleukin-1beta (IL-1ß)-, and combined Wnt3a/IL-1ß-treated cells. Wnt3a treatment increased the mRNA levels of catabolic markers (cyclooxygenase-2, interleukin-6, inducible nitric oxide synthase) to a much lesser degree than IL-1ß treatment in human articular chondrocytes, and decreased the mRNA levels of matrix metalloproteinase-13 (MMP-13) and articular cartilage markers (aggrecan, type II collagen). Furthermore, Wnt3a decreased the mRNA levels of catabolic markers and MMP-13 in IL-1ß-treated human articular chondrocytes. High expression of AnxA6 resulted in decreased mRNA levels of catabolic markers, and increased MMP-13 and articular cartilage marker mRNA levels in Wnt3a-treated human articular chondrocytes, whereas leading to increased mRNA levels of catabolic markers and MMP-13 in human articular chondrocytes treated with IL-1ß, or combined Wnt3a and IL-1ß. Our findings define a novel role for AnxA6 in articular chondrocytes via its modulation of Wnt/ß-catenin and NF-κB signaling activities and the cross-talk between these two signaling pathways.

Highlights

Very little is known about the role of annexins in articular cartilage despite the rapid progress in the understanding of the role of annexins in various other tissues and diseases, including Alzheimer’s disease, autoimmunity, cancer, diabetes, and cardiovascular diseases [1,2,3,4]
Complete absence of Annexin A6 (AnxA6) resulted in increased Wnt/ß-catenin signaling as indicated by the increased luciferase activity from the TOPFlash reporter in vehicle-treated and Wnt3a-treated articular chondrocytes isolated from AnxA6-/- mice compared to vehicle-treated and Wnt3a-treated chondrocytes isolated from WT littermates
In this study we present evidence that AnxA6 is a novel regulator of the canonical Wnt signaling pathway in articular chondrocytes

Summary

Introduction

Very little is known about the role of annexins in articular cartilage despite the rapid progress in the understanding of the role of annexins in various other tissues and diseases, including Alzheimer’s disease, autoimmunity, cancer, diabetes, and cardiovascular diseases [1,2,3,4]. Previous studies have shown that low levels of Wnt/ß-catenin signaling are required for maintenance of normal articular cartilage function and that deregulation of this pathway contributes to the development and progression of cartilage degeneration and OA pathology [6, 8, 9, 14, 15, 16]. Signaling pathways, such as NF-κB and Wnt/ß-catenin signaling pathways, have to be tightly regulated, and de-regulation of these pathways can have severe consequences

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