Proinflammatory
cytokines play an important role in the systemic and focal bone loss associated with chronic inflammatory diseases. Targeting these
cytokines with biologics and small molecules has led to a major improvement of the bone health of patients with inflammatory
arthritis.
Cytokines from the
IL-17 family have been shown to be involved in the pathogenesis of several diseases such as spondyloarthritis,
psoriatic arthritis, or
psoriasis.
IL-17A has been the first described and the most studied. The recent development of targeted
therapies against
IL-17A or its receptor and their efficacy has confirmed the importance of this
cytokine in the development of inflammatory diseases. The aim of this review was to describe the effects of the
IL-17 family and more particularly of
IL-17A on bone and cartilage tissues. At the cellular level,
IL-17A is proosteoclastogenic whereas its effects on osteoblasts depend on the stage of differentiation of these cells. In vivo,
IL-17A is not required for normal bone homeostasis but plays an important role in bone loss notably in an ovariectomized mouse model of
osteoporosis. Preliminary data from clinical trials showed a stabilisation of bone density in patients treated with anti-IL-17A
antibodies.
IL-17A plays a central role in the cartilage damage through the induction of
collagenases and by decreasing the expression of their inhibitors in synergy with the other proinflammatory
cytokines. The prevention of structural damage by anti-IL-17A
therapies has been demonstrated in several pivotal clinical trials. Overall, blocking the
IL-17A pathway seems to have a positive effect on the bone and cartilage damage observed in inflammatory
arthritis. Differences and specificity of these effects compared to those already described with other biologics such as anti-TNF
therapies remain to be explored.