EVC protein regulates sonic hedgehog signalling during human intervertebral disc development and degeneration
Notochord-derived cells (NCs) in the developing nucleus pulposus (NP) maintain its hydrated extracellular matrix, essential for the shock-absorbing function of the intervertebral disc (IVD). The aging-associated loss of NCs initiates IVD degeneration, contributing to back pain. Despite their critical role in IVD homeostasis, little is known about human NCs. To identify key regulators and inform regenerative therapies, we characterised the proteomic profile of human fetal NCs, identifying Ellis-van Creveld (EVC) syndrome protein as the top enriched protein in the NC population.  EVC was expressed in fetal, paediatric, and adult human NP, localising to the primary cilium of NP cells. Its expression positively correlated with Hedgehog (Hh) signalling activity. Using Evc knockout mouse models and CRISPR-engineered human EVC knockout NP cells, we demonstrate that EVC enhanced Sonic hedgehog (Shh) signalling in NP cells, played a vital role in maintaining NP cell phenotype, and regulated extracellular matrix composition. Evc knockout mice exhibited delayed embryonic vertebral body ossification. Both Shh activation and EVC expression helped mitigate NP fibrosis. In contrast, TGF-ß signalling downregulated EVC expression and altered Gli3 processing.  This study identifies EVC as a regulator of IVD formation and maintenance, uncovering molecular mechanisms by which downregulation of Shh signalling leads to disc degeneration. EVC emerges as a mediator of Shh and TGF-ß crosstalk in NP cells. As such, EVC may be a promising target for strategies aimed at preventing or reversing disc degeneration and promoting tissue regeneration.