Regulation of Type II Collagen Expression by Histone Deacetylase in Articular Chondrocytes

Abstract

Histone deacetylase (HDAC) regulates various cellular processes by modulating gene expression. Here, we investigated the role of HDAC in the expression of type II collagen, a marker of differentiated chondrocytes. We found that HDAC activity in primary articular chondrocytes decreases during dedifferentiation induced by serial monolayer culture and that the activity recovered during redifferentiation induced by three-dimensional culture in a cell pellet. Inhibition of HDAC with trichostatin A or PXD101 was sufficient to block type II collagen expression in primary culture chondrocytes. HDAC inhibition also blocked the redifferentiation of dedifferentiated chondrocytes by suppressing the synthesis and accumulation of type II collagen. HDAC inhibition promoted the expression of Wnt-5a, which is known to inhibit type II collagen expression, and knockdown of Wnt-5a blocked the ability of HDAC inhibitors to suppress type II collagen expression. In addition, the induction of Wnt-5a expression by HDAC inhibitors was associated with acetylation of the Wnt-5a promoter. Taken together, our results suggest that HDAC promotes type II collagen expression by suppressing the transcription of Wnt-5a.Differentiation of uncommitted mesenchymal cells into chondrocytes is initiated by the proliferation and recruitment of chondrogenic mesenchymal cells into condensations. These precartilage condensations develop into cartilage nodules containing differentiated chondrocytes. Chondrogenesis can be mimicked by micromass culture of mesenchymal cells in vitro. Differentiated chondrocytes are characterized by the ability to synthesize cartilage-specific extracellular matrix molecules including type II collagen and sulfated proteoglycans, which are necessary for normal cartilage development (1, 2). The activity of cartilage-specific matrix molecule synthesis by the differentiated chondrocytes is unstable and rapidly lost in response to certain environmental changes. For instance, proinflammatory cytokines such as interleukin (IL) 2 -1␤ cause the loss of differentiated chondrocyte phenotypes (dedifferentiation) by halting the synthesis of cartilage-specific matrix molecules (3, 4). Chondrocyte dedifferentiation is also induced by serial monolayer culture and is accompanied by a gradual shift in the expression of type II collagen and aggrecan to type I and III collagen and versican, respectively (5, 6). Dedifferentiated chondrocytes redifferentiate in three-dimensional culture in an alginate gel or cell pellet (6, 7). Although maintenance of a differentiated chondrocyte phenotype is important for cartilage homeostasis, the detailed mechanisms of the differentiation and dedifferentiation of chondrocytes remain largely unknown. Because chondrocyte differentiation/dedifferentiation is regulated by various soluble factors including growth factors and cytokines, we hypothesized that histone deacetylase (HDAC) may regulate the differentiation status of chondrocytes. HDAC modulates the growth and differentiation of various cell types by governing...

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