PKCε is a regulator of hypertrophic differentiation of chondrocytes in osteoarthritis

Objective: Osteoarthritis (OA) is a common and highly debilitating degenerative disease whose complex pathogenesis and the multiplicity of the molecular processes involved, hinder its complete understanding. Protein Kinase C (PKC) novel isozyme PKC epsilon recently proved to be an interesting molecule for further investigations as it can represent an intriguing, newactor in the acquisition of a OA phenotype by the chondrocyte. Design: PKC epsilon was modulated in primary chondrocytes from human OA patient knee cartilage samples by means of short hairpin RNA (ShRNA) and the expression of cartilage specific markers observed at mRNA and protein level. The involvement of Histone deacetylases (HDACs) signaling pathway was also investigated through the use of specific inhibitors MS-275 and Inhibitor VIII. Results: PKC epsilon loss induces up-regulation of Runt-domain transcription factor (RUNX2), Metalloproteinase 13 (MMP13) and Collagen X (COL10) as well as an enhanced calcium deposition in OA chondrocyte cultures. In parallel, PKC epsilon knock-down also leads to SOX9 and Collagen II (COL2) down-modulation and to a lower deposition of glycosaminoglycans (GAGs) in the extracellular matrix (ECM). This novel regulatory role of PKCe over cartilage hypertrophic phenotype is exerted via an HDAC-mediated pathway, as HDAC2 and HDAC4 expression is modulated by PKC epsilon. HDAC2 and HDAC4, in turn, are at least in part responsible for the modulation of the master transcription factors RUNX2 and SOX9, key regulators of chondrocyte phenotype. Conclusions: PKC epsilon prevents the phenotypic progression of the OA chondrocyte, acting on cartilage specific markers through the modulation of the transcription factors SOX9 and RUNX2. The loss of PKC epsilon enhances, in fact, the OA hypertrophic phenotype, with clear implications in the pathophysiology of the disease. (C) 2016 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.