Fig 4. Hypoxia induces c-Myc expression via Notch2 signaling.

(A) Proliferation assay of Notch2-KD MSCs. MSCs were cultured under low- or high-oxygen conditions. Notch2 KD was performed using shRNA methods. Control shRNA = scrambled shRNA. (B) Quantitative real-time PCR assay of c-Myc, HIF-1, and HIF-2 gene expression under hypoxic conditions. Normoxia served as a control. (C) Overexpression of c-Myc in Notch2-KD MSCs. Notch2-KD PαS-MSCs with or without c-Myc overexpression was cultured for three passages. (D) Schema of MSC proliferation under low- or high-oxygen conditions. Notch2 expression, together with the downstream expression of c-Myc, is higher under hypoxic conditions than under normoxic conditions. However, c-Myc expression is decreased by a Notch signaling inhibitor (DAPT), leading to the progression of senescence. Overexpression of c-Myc promotes cell proliferation and delays cell aging.