PDGF-BB and bFGF ameliorate radiation-induced intestinal progenitor/stem cell apoptosis via Akt/p53 signaling in mice

Radiation-induced gastrointestinal (GI) syndrome currently has no effective prophylactic or therapeutic treatment. Previous studies and our data have demonstrated the important role of p53 in acute radiation-induced GI syndrome in mice. Many cytokines, such as tumor necrosis factor-α and fibroblast growth factor (bFGF), have been found to protect against radiation-induced intestinal injury, although the underlying mechanisms remain to be identified. Here, we report blockage of p53 through a protein kinase B (Akt) pathway in intestinal progenitor/stem cells or crypt cells as a novel molecular mechanism of growth factor-mediated intestinal radioprotection. Treatment with platelet-derived growth factor (PDGF-BB) or bFGF activated Akt phosphorylation in the intestinal crypt, lessened intestinal crypt p53 expression, decreased radiation-induced apoptosis in mouse intestinal progenitor/stem cell marker leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5)-positive cells by an average of 50%, and increased the survival rate of mice with abdominal radiation by 3 days in average. Conversely, the Akt inhibitor perifosine obstructed growth factor-simulated Akt phosphorylation while promoting radiation-induced p53 expression in intestinal crypts. Importantly, reduced Akt phosphorylation and elevated p53 expression due to the Akt inhibitor perifosine impaired intestinal progenitor/stem cells radioprotection provided by PDGF-BB and bFGF. Consistently, PDGF-BB and bFGF both upregulated Akt activation, suppressed radiation-induced p53 expression, and abrogated radiation-induced apoptosis in IEC-6 cells, although p53 overexpression in IEC-6 cells partially counteracted the radioprotection of PDGF-BB and bFGF. Our data suggest that intestinal crypt radioprotection by PDGF-BB and bFGF is dependent on regulation of Akt/p53 signaling.