bulk RNA-seq of human nucleusus pulposus from disc-degenerated patients

Failure of the nucleus pulposus (NP) causes intervertebral disc (IVD) disease and associated low-back pain, which are highly prevalent among the aged populations. Molecular and cellular changes underpinning the structural failures in age-associated IVD diseases (IDDs) remain poorly elucidated. Here, we first identified that TAGLN, which encodes the cytoskeleton regulator transgelin, was transcribed in healthy NPs of both human and mouse, but diminished with ageing. Immunostaining showed that TAGLN were expressed on the peripheral of mouse NP (periNP). Lineage analyses in Tagln-CreERT2 mice showed that NP cells were derived from Tagln+ cells in the periNP. The PeriNP cells were proliferative and can differentiate into the inner NP (innerNP). These Tagln+ cells and their descendants diminish with ageing or puncture-induced degeneration. Single-cell transcriptomics from neonatal and adult Tagln-CreERT2 IVDs confirmed that Tagln descendants uniquely populate the NP, wherein four sub-populations were identified: chondrocyte-like, Cd228+, Tagln+ and Car3+. Immunostaining confirmed Car3 expressed in innerNP. Computational analysis indicated the lineage trajectory from Tagln+ to Car3+ sub-population, along with the involvement of Fos/Jun/TGFβ cascades and partial epithelial-to-mesenchymal transition process. Removal of TGFβ mediator Smad4 by notochord specific Foxa2mNE-Cre resulted in decreased Tagln+ cells and abnormal disc morphology, resembling disc degeneration. Our study generates a single-cell transcriptomic atlas for healthy IVD, identifies Tagln+ PeriNP cells as a progenitor pool crucial for the IVD homeostasis, and provides potential targets for regenerative cell therapy against IVD degeneration.