Chondrocyte-like cells in nucleus pulposus and articular chondrocytes have similar transcriptomic profiles and are paracrine-regulated by hedgehog from notochordal cells and subchondral bone

The nucleus pulposus (NP) is composed of notochordal NP cells (NCs) and chondrocyte-like NP cells (CLCs). CLCs and chondrocytes have been reported to be similar. However, the interactions between CLCs and NCs remain unclear. In this study, to clarify how cells in NP and chondrocytes are regulated, we performed single-cell RNA sequencing (scRNA-seq) analysis of articular cartilage (AC) and NP of cynomolgus monkeys and found that part of CLCs and articular chondrocytes had similar gene expression profiles. These cells were enriched for genes related to GLI1, the nuclear mediator of the hedgehog pathway. In the NP, cell–cell interaction analysis revealed sonic hedgehog (SHH) expression in NCs, resulting in hedgehog signaling to CLCs, whereas no chondrocytes in our AC samples expressed hedgehog ligands. We harvested the nucleus pulposus (NP) from the lumbar IVD (L3/4) and the articular cartilage (AC) from the left femoral condyle of a cynomolgus monkey (3 years old). Additionally, we harvested the AC from the left femoral condyle of another cynomolgus monkey (3 year old). We subjected these samples to scRNA-seq analysis