Fig. 2: Identification of late-stage NPCs with upregulated SRGN expression.

a–c Monocle pseudotime trajectory showing the progression of Met-, SR-, Adh- IR-, Pro- and Fibro-NPCs. d Tree plot of the monocle pseudotime trajectory showing the progression of 6 subclusters of NPCs. e Tree plot of the monocle pseudotime trajectory showing the progression of MDD and SDD NPCs. f–h A single-cell atlas revealed the cell distributions of NPCs in the MDD and SDD groups (g), the subcluster composition of NPCs (f), and the proportions of each subcluster in MDD and SDD NPCs (h). i SRGN expression in MDD and SDD tissues by scRNA-seq analysis. j The screening RT‒qPCR results showed the expression of candidate marker genes of degenerative NPCs. k UMAP plot of SRGN expression. l Pseudotime kinetics of SRGN, FBLN1, COL1A1 and COL2A1 in each subcluster of NPCs. m, n MRI images and Pfirrmann grades of human discs and H&E and IHC staining of SRNG expression in different degenerative human NP specimens (red arrows: SRGN+ NPCs; original magnification ×100, ×400, scale bar = 200 µm, 50 µm). o, p IF staining of SRGN (green) in normal NP samples compared to degenerated NP samples (original magnification ×400, scale bar = 50 µm). q–s IF staining of the late-stage NPC markers FBLN1 (red) and SRGN (green) and the degenerative indicators COL1A (red) and COL2A1 (green) in tissue samples from mouse IVDs (original magnification ×100, ×400, scale bar = 400 μm, 100 µm). MDD mild degenerative discs, SDD severe degenerative discs, CTR control group, AFP annulus fibrosus puncture group, AF annulus fibrosus, CEP cartilaginous end plate, NP nucleus pulposus. n = 5 each group. Data in 2i are presented as the median±interquartile range as appropriate, and the p value was determined by the unpaired Wilcox rank sum test. Data in (j) and (m–s) are presented as the mean ± standard deviation, and p values were determined by a two-tailed unpaired t test. Source data are provided as a Source Data file.