Figure 1.

The roles of disc cell senescence in the pathogenesis of intervertebral disc degeneration. The senescent disc cells are unable to replicate, thus, the loss of functional cells occurs in discs. Furthermore, the senescence-associated secreted phenotype (SASP) of disc cells is characterized by a catabolic and pro-inflammatory phenotype. Senescent disc cells secrete matrix proteases to enhance extracellular matrix (ECM) catabolism in intervertebral disc. Meanwhile, pro-inflammatory cytokines secreted by senescent disc cells promote the senescence of surrounding disc cells and the infiltration of immune cells in discs, reinforcing the inflammation in the microenvironment of degenerative discs. As a result, disc degeneration is accelerated. NP, nucleus pulposus. AF, annulus fibrosus.