The Involvement of Mutual Inhibition of ERK and mTOR in PLCγ1-Mediated MMP-13 Expression in Human Osteoarthritis Chondrocytes.

Zejun Liu,Bing Zhang,Heguo Cai,Xinpeng Zheng,Chun Xia

doi:10.3390/ijms160817857

Abstract

The issue of whether ERK activation determines matrix synthesis or degradation in osteoarthritis (OA) pathogenesis currently remains controversial. Our previous study shows that PLCγ1 and mTOR are involved in the matrix metabolism of OA cartilage. Investigating the interplays of PLCγ1, mTOR and ERK in matrix degradation of OA will facilitate future attempts to manipulate ERK in OA prevention and therapy. Here, cultured human normal chondrocytes and OA chondrocytes were treated with different inhibitors or transfected with expression vectors, respectively. The levels of ERK, p-ERK, PLCγ1, p-PLCγ1, mTOR, p-mTOR and MMP-13 were then evaluated by Western blotting analysis. The results manifested that the expression level of ERK in human OA chondrocytes was lower than that in human normal articular chondrocytes, and the up-regulation of ERK could promote matrix synthesis, including the decrease in MMP-13 level and the increase in Aggrecan level in human OA chondrocytes. Furthermore, the PLCγ1/ERK axis and a mutual inhibition of mTOR and ERK were observed in human OA chondrocytes. Interestingly, activated ERK had no inhibitory effect on MMP-13 expression in PLCγ1-transformed OA chondrocytes. Combined with our previous study, the non-effective state of ERK activation by PLCγ1 on MMP-13 may be partly attributed to the inhibition of the PLCγ1/mTOR axis on the PLCγ1/ERK axis. Therefore, the study indicates that the mutual inhibition of ERK and mTOR is involved in PLCγ1-mediated MMP-13 expression in human OA chondrocytes, with important implication for the understanding of OA pathogenesis as well as for its prevention and therapy.

Highlights

Osteoarthritis (OA) is a chronic degenerative joint disease, resulting in severe pain and physical disabilities for millions of people worldwide
We investigated the interplays of PLCγ1, mechanistic target of rapamycin (mTOR), and Extracellular signal-regulated kinase (ERK) in human OA chondrocytes
The depletion of ERK by siRNA led to the increase in the level of matrix metalloproteinases (MMPs)-13 and the decrease in the levels of tissue inhibitor of metalloproteinases (TIMPs)-1 and Aggrecan

Summary

Introduction

Osteoarthritis (OA) is a chronic degenerative joint disease, resulting in severe pain and physical disabilities for millions of people worldwide. The degradation of cartilage matrix is one of OA’s pathological features. Chondrocytes, which are responsible for the homeostatic maintenance of cartilage matrix, produce a variety of matrix-anabolic/catabolic enzymes or inhibitors, including matrix metalloproteinases (MMPs), aggrecanases and tissue inhibitor of metalloproteinases (TIMPs) [1]. Multiple signal molecules are involved in the regulation of cartilage matrix synthesis, and elucidating their regulatory mechanisms in chondrocytes is beneficial to preventing cartilage damage and promoting repair. Extracellular signal-regulated kinase (ERK) is one of the MAPK families that is activated by a variety of environmental stress and inflammatory cytokines. Activated ERK mediates cellular responses to intracellular signaling proteins and is involved in a number of physiological and disease processes, including RA (Rheumatoid Arthritis) and OA. The activation of DDR-2 (discoidin domain receptor 2) by intact type II collagen fibrils leads to increased MMP-13 expression via the

Results

Discussion

Conclusion