Figure 1.

CDK8 expression level is increased in MSCs and their progeny with aging

(A) The t-SNE plot of color-coded clustering of 1-, 1.5-, 3-, and 16-month cells (top, n = 8,753 cells) and the violin plots of cell-specific marker gene expression (bottom).

(B) CDK8 expression levels of each cluster by age (^∗∗∗p < 0.001).

(C) Expression levels of transcription-related CDKs at the indicated time points of MSCs (^∗∗∗p < 0.001).

(D) Expression levels of transcription-related CDKs expressed in 1-, 1.5-, 3-, and 16-month MSCs (^∗∗∗p < 0.001).

(E) CDK8 expression levels of 1-, 1.5-, 3-, and 16-month datasets among each cluster (^∗∗∗p < 0.001).

(F) Protein levels of CDK8, p-STAT1^Ser727, STAT1, p-STAT3^Ser727 and STAT3 in MSCs, OBs, and CHs. β-Actin served as a loading control (n = 3 independent replicates, ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001).

(G and H) The enrichment plots for aging-related gene sets in MSCs, OBPs, and OBs.

(I) CDK8 expression levels in PαS MSCs compared with juvenile (2-week-old) and aged (2-year-old) mice (n = 4, ^∗p < 0.05).

(J) Protein levels of CDK8 in aged MSCs. β-Actin served as a loading control (n = 4 independent replicates, ^∗∗p < 0.01).

(K) Flow cytometric analysis of cell size in aged MSCs (n = 4 independent replicates, ^∗∗∗p < 0.001) and protein levels of CDK8 normalized by cell size (n = 4 independent replicates, ^∗∗p < 0.01). Statistical significance was detected using the Steel test in (D).

t-SNE, t-distributed stochastic neighbor embedding; MSC, mesenchymal stem cell; OBP, osteoblast progenitor; OB, osteoblast; OCYs, osteocytes; CHs, chondrocytes; PαS, PDGFRα⁺ Sca-1⁺; FSC, forward scatter.