PTBP1 and Hutchinson-Gilford progeria syndrome: Furthermore, we found that PTBP1 is not only down-regulated in above mentioned four replicative senescence models of human fibroblasts (Fig. 6A) but also down-regulated in other replicative and inducible cellular senescence models (Fig. S5A), aged tissues and Hutchinson-Gilford Progeria Syndrome (HGPS) patients’ skin-derived fibroblasts (Fig. S5B–E).