Single-cell transcriptome profiling reveals multicellular ecosystem of nucleus pulposus during degeneration progression

Abstract

Degeneration of the nucleus pulposus (NP) is a major contributor to intervertebral disc degeneration (IVDD) and low back pain. However, the underlying molecular complexity and cellular heterogeneity remain poorly understood. Here, we first reported a comprehensive single-cell resolution transcriptional landscape of human NP. Six novel human nucleus pulposus cell (NPCs) populations were identified by distinct molecular signatures. The potential functional differences among NPC subpopulations were analyzed at the single-cell level. Predictive genes, transcriptional factors, and signal pathways with respect to degeneration grades were analyzed. We reported that fibroNPCs, one of our identified subpopulations, might be a population for NP regeneration. CD90+NPCs were observed to be progenitor cells in degenerative NP tissues. NP-infiltrating immune cells comprise a previously unrecognized diversity of cell types, including granulocytic myeloid-derived suppressor cells (G-MDSCs). We uncovered CD11b, OLR1, and CD24 as surface markers of NP-derived G-MDSCs. The G-MDSCs were also found to be enriched in mildly degenerated (grade I and II) NP tissues compared to severely degenerated (grade III and IV) NP tissues. Their immunosuppressive function and protective effects for NPCs were revealed. Collectively, this study revealed the NPC type complexity and phenotypic characteristics in NP, providing new insights and clues for IVDD treatment.