Correlations between the mRNA expression levels of ACLY, AURKB, CD74, CDKN2D, E2F1, EFEMP1, LIF, and TGM2 were evaluated using hierarchical cluster analyses with the nearest-neighbor algorithm and are presented in a dendrogram that was generated using SPSS version 24.0.
Based on these correlation patterns, AURKB, E2F1, CDKN2D, LIF, and ACLY were allocated to group 1 and CD74, EFEMP1, and TGM2 were allocated to group 2, suggesting the presence of two predominant signaling pathways that determine chondrogenic differentiation potential.
The expression levels of the group 2 genes CD74, EFEMP1, and TGM2 were negatively correlated with donor ages (Table 3 and Figure 6), whereas no significant correlations were found for group 1 genes, suggesting that group 2 genes play predominant roles in age-dependent MSC chondrogenic differentiation potential.
Accordingly, the group 1 genes AURKB , E2F1 [19-21], CDKN2D , LIF [23, 24], and ACLY  participate in cell cycle regulation, whereas the group 2 genes EFEMP1 [26, 27], CD74 [24, 28-30], and TGM2 [31, 32] are involved in the regulation of chondrogenesis.
EFEMP1 (also known as fibulin-3), an ECM protein, is specifically expressed in cartilage and acts as a negative regulator of chondrogenesis .
In this study, the expression levels of the group 2 genes EFEMP1, CD74, and TGM2 were negatively correlated with the donor ages, potentially indicating their characterized roles in chondrogenesis.
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