Ccn2a-FGFR1-SHH signaling is necessary for intervertebral disc homeostasis and regeneration in adult zebrafish

Intervertebral disc (IVD) degeneration is the primary cause of back pain in humans. However, the cellular and molecular pathogenesis of IVD degeneration is poorly understood. This study shows that zebrafish IVDs possess distinct and non-overlapping zones of cell proliferation and cell death. We find that, in zebrafish, cellular communication network factor 2a (ccn2a) is expressed in notochord and IVDs. Although IVD development appears normal in ccn2a mutants, the adult mutant IVDs exhibit decreased cell proliferation and increased cell death leading to IVD degeneration. Moreover, Ccn2a overexpression promotes regeneration through accelerating cell proliferation and suppressing cell death in wild-type aged IVDs. Mechanistically, Ccn2a maintains IVD homeostasis and promotes IVD regeneration by enhancing outer annulus fibrosus cell proliferation and suppressing nucleus pulposus cell death through augmenting FGFR1-SHH signaling. These findings reveal that Ccn2a plays a central role in IVD homeostasis and regeneration, which could be exploited for therapeutic intervention in degenerated human discs.

Automated summary

This study shows that zebrafish intervertebral discs (IVDs) have distinct zones of cell proliferation and cell death. The cellular communication network factor 2a (ccn2a) is expressed in notochord and IVDs in zebrafish. Mutants of ccn2a exhibit decreased cell proliferation and increased cell death in adult IVDs, leading to degeneration. Overexpression of Ccn2a promotes regeneration in aged IVDs by enhancing cell proliferation and suppressing cell death. Mechanistically, Ccn2a maintains IVD homeostasis and regeneration by enhancing outer annulus fibrosus cell proliferation and suppressing nucleus pulposus cell death through augmenting FGFR1-SHH signaling. These findings suggest that Ccn2a could be a potential therapeutic target for degenerated human discs.