Exercise-induced FNDC5/irisin protects nucleus pulposus cells against senescence and apoptosis by activating autophagy

Intervertebral disc degeneration (IVDD) is a major cause of low back pain (LBP), and excessive senescence and apoptosis of nucleus pulposus (NP) cells are major pathological changes in IVDD. Physical exercise could effectively delay the process of intervertebral disc degeneration; however, its mechanism is still largely unknown. Irisin is an exercise-induced myokine released upon cleavage of the membrane-bound precursor protein fibronectin type III domain-containing protein 5 (FNDC5), and its levels increase after physical exercise. Here, we show that after physical exercise, FNDC5/irisin levels increase in the circulation and NP, senescence and apoptosis are reduced, autophagy is activated in NP tissue, and the progression of IVDD is delayed. Conversely, after knocking out FNDC5, the benefits of physical exercise are compromised. Moreover, the overexpression of FNDC5 in NP tissue effectively alleviated the degeneration of the intervertebral disc (IVD) in rats. By showing that FNDC5/irisin is an important mediator of the beneficial effects of physical exercise in the IVDD model, the study proposes FNDC5/irisin as a novel agent capable of activating autophagy and protecting NP from senescence and apoptosis.