Figure 4. Effects of circulatory factors on expression of cellular senescence markers in IVDs in mouse heterochronic parabiotants. qRT-PCR quantitation of disc p16INK4a (A) and p21Cip1 (B) mRNAs. Western blot of p21Cip1 (C) and p53 (D) protein. Graphs on the right of the Western blot showed quantitation of these proteins normalized to actin. Data shown are mean ± SD of 5 independent experiments for RT-PCR and 4 experiments for Western blot, *p < 0.05. **p < 0.01.