Acetylation reduces SOX 9 nuclear entry and ACAN gene transactivation in human chondrocytes

Abstract

SummaryChanges in the content of aggrecan, an essential proteoglycan of articular cartilage, have been implicated in the pathophysiology of osteoarthritis (OA), a prevalent age‐related, degenerative joint disease. Here, we examined the effect of SOX9 acetylation on ACAN transactivation in the context of osteoarthritis. Primary chondrocytes freshly isolated from degenerated OA cartilage displayed lower levels of ACAN mRNA and higher levels of acetylated SOX9 compared with cells from intact regions of OA cartilage. Degenerated OA cartilage presented chondrocyte clusters bearing diffused immunostaining for SOX9 compared with intact cartilage regions. Primary human chondrocytes freshly isolated from OA knee joints were cultured in monolayer or in three‐dimensional alginate microbeads (3D). SOX9 was hypo‐acetylated in 3D cultures and displayed enhanced binding to a −10 kb ACAN enhancer, a result consistent with higher ACAN mRNA levels than in monolayer cultures. It also co‐immunoprecipitated with SIRT1, a major deacetylase responsible for SOX9 deacetylation. Finally, immunofluorescence assays revealed increased nuclear localization of SOX9 in primary chondrocytes treated with the NAD SIRT1 cofactor, than in cells treated with a SIRT1 inhibitor. Inhibition of importin β by importazole maintained SOX9 in the cytoplasm, even in the presence of NAD. Based on these data, we conclude that deacetylation promotes SOX9 nuclear translocation and hence its ability to activate ACAN.

Specific miRNA-G Protein-Coupled Receptor Networks Regulate Sox9a/Sox9b Activities to Promote Gonadal Rejuvenation in Zebrafish

“…We identified four putative GPCR molecules and several modifier enzymes responsible for Sox9a and Sox9b posttranscriptional modifications (Table ). Given that Lgr4, GPR157, Grk5l, and Grk4 could, respectively, link to gonadotropins , the Gq‐IP 3 pathway , mTORC1 activity , and small ubiquitin‐related modifier (SUMO) modification , our finding not only supplements the previously described composition and function of GPCR signalsomes , but also clarifies the signal transduction of the gonadotropins/GPCR/MAPK/Sox9a/b switch pathways.…”

LEF1‐mediated MMP13 gene expression is repressed by SIRT1 in human chondrocytes

“…Cells were then lysed [lysis buffer; 10 mM EDTA, 50 mM Tris-HCl (pH 8.0), 1% SDS] and sonicated (Vibra Cell; Sonics and Materials, Newtown, CT, USA) at 50 cycles of 95% amplitude for 30 s, followed by a 45 s incubation on ice, based on Bar Oz et al (34). Samples were then processed using the Low Cell ChIP kit (Diagenode, Liège, Belgium).…”

SOX9 and the many facets of its regulation in the chondrocyte lineage

“…Moreover, a similar change was observed when human articular chondrocytes were treated with a Sirtuin deacetylase cofactor in vitro. This change was thought to be possibly relevant to preliminary observation that SOX9 could be more often cytoplasmic than nuclear in osteoarthritic than in healthy articular chondrocytes (47). Clarifying the trafficking of SOX9 and its regulation in the chondrocyte lineage is thus a warranted topic for future research.…”

“…Relevant to osteoarthritis, pro-inflammatory conditions inactivate SIRT1 through cathepsin-mediated cleavage, a mechanism that may thus contribute to loss of SOX9 activity (60). While the lysine(s) targeted by SIRT1 in SOX9 remain elusive, it was proposed that SIRT1 facilitates SOX9 activity by increasing its nuclear localization (47). Interestingly, SIRT1-mediated deacetylation of SOX2 at lysine K75 occurs during reprogramming of mouse somatic cells into pluripotent stem cells to prevent SOX2 nuclear export and degradation (61,62).…”