Discovery and application of postnatal nucleus pulposus progenitors essential for intervertebral disc homeostasis and degeneration.

Intervertebral disc degeneration (IDD) results from dysfunction of nucleus pulposus cells (NPs) and exhaustion of NP progenitors (ProNPs). Cellular applications of NPs during IDD are currently limited by lack of in vivo studies showing whether NPs are heterogenous and contain ProNPs throughout postnatal stages. Here, using single-cell RNA sequencing of purified NPs, we mapped four molecularly defined populations and identified Urotensin II receptor (UTS2R)-expressing postnatal ProNPs, which markedly exhausted during IDD, in mouse and human specimens. Lineage tracing showed that UTS2R+ ProNPs preferentially reside in the NP periphery with its niche factor-Tenascin-C and give rise to functional NPs. We also demonstrate that transplanting UTS2R+ ProNPs with Tenascin-C to injured intervertebral discs attenuates the progression of IDD. Our findings provide a novel NP cell atlas, identify resident ProNPs with regenerative potential and reveal promising diagnostic and therapeutic targets for IDD. To produce a cell atlas of purified NPs along with their representative cellular functions, Shh-Cre;Ai9+ single NP cells were harvested from 1-month-old Shh-Cre;Ai9 mice and analyzed with a BD Rhapsody Single-Cell RNA Sequencing platform.