Fig 2: The expressions of Hub genes in the mouse meniscus cells. A SA-β-gal staining of mouse senescent meniscus cells induced by IL-1β (10 ng/ml) for 48 h. Scale bar: 500 μm. B, D Apoptotic analysis detected by Annexin V/7AAD after IL-1β disposition. C Detection of the expressions of hub genes in senescent meniscus cells via qRT-PCR. We normalized the gene expression levels to GAPDH. E Immunofluorescence analysis of hub genes after treating meniscus cells with10ng/ml IL-1β for 48 h. Scale bars, 50 μm. RRM2 ribonucleotide reductase regulatory subunit M2; AURKB aurora kinase B; CDK1 cyclin dependent kinase 1; TIMP1 tissue inhibitor of metalloproteinases 1; GAPDH Glyceraldehyde 3-phosphate dehydrogenase. n = 6 per group, mean ± S.E.M., *P < 0.05, **P < 0.01 in comparison with the control group

Fig 3: Network construction of lncRNA-miRNA-mRNA. A The mRNA-miRNA network was constructed by using the miRWalk website (The five miRNAs most associated with the common hub gene are highlighted in light blue). B Meaningful signal pathways about the 5 miRNAs by utilizing the DIANA-miRPath. C The lncRNA–miRNA–mRNA regulatory network (The orange nodes represent the lncRNAs, the yellow nodes represent key miRNAs, and the red nodes represent the hub genes). RRM2 ribonucleotide reductase regulatory subunit M2; AURKB aurora kinase B; CDK1 cyclin dependent kinase 1; TIMP1 tissue inhibitor of metalloproteinases 1

Fig 4: The PPI network and Hub genes analysis. A PPI network of all DEGs (The red codes represent upregulated genes in the elderly, the blue codes represent downregulated genes in the elderly, and the size of the nodes represents the correlation between them). Hub gene networks obtained from the PPI network relying on B the Maximal Clique Centrality (MCC) algorithm, C the Maximum Neighborhood Component (MNC) algorithm, D the Degree algorithm, and E the Edge Percolated Component (EPC) algorithm of the Cytoscape plugin cytoHubba. F The Venn diagram showed the identified hub genes (RRM2, AURKB, CDK1, and TIMP1). G The heatmap of common hub genes identified by Metascape was colored by –log10 (P-value). PPI protein–protein interaction; DEGs differentially expressed genes; RRM2 ribonucleotide reductase regulatory subunit M2; AURKB aurora kinase B; CDK1 cyclin dependent kinase 1; TIMP1 tissue inhibitor of metalloproteinases 1

Fig 5: RRM2 expression was decreased in vitro and in vivo after DOX treatment. (A) Compared with the CTR group, the mRNA expression of RRM2 in primary cardiomyocytes was decreased after DOX treatment (n = 6). (B) Compared with the CTR group, the mRNA expression of RRM2 in hearts was lower after DOX treatment (n = 6). (C,D) RRM2 protein levels in primary cardiomyocytes treated with DOX (n = 4). (E,F) RRM2 protein levels in hearts 5 days after DOX treatment (n = 4). ** indicates p < 0.01. *** indicates p < 0.001.