[NADPH oxidase Nox4, a putative therapeutic target in osteoarthritis]

The NADPH oxidases, Nox, are transmembrane hemoproteins, whose exclusive function is to reduce molecular oxygen to produce superoxide anion O2°- and consequently highly reactive oxidant and toxic oxygen species, ROS. Among the 7 NADPH oxidases expressed in humans, Nox4 is the sole Nox isoform present in human primary chondrocytes. Nox4 was suggested as one of the main actors involved in cartilage degradation in osteoarthritis. The stimulation of chondrocytes, the only cell present in cartilage, by IL-1β results in the activation of Nox4. This leads to an increase of ROS production which in turn could regulate signaling pathways sensitive to oxidative stress such as gene-encoding matrix metalloproteases MMP1, MMP13 and Adamalysin ADAMTS4. A deep understanding of Nox4 structure/function and mechanisms of regulation could lead both to the identification of new therapeutic targets and to the development of innovative strategies for appropriate osteoarthritis treatment.