Inhibiting 4E-BP1 re-activation represses podocyte cell cycle re-entry and apoptosis induced by adriamycin

Podocyte loss is one of the determining factors for the progression toward glomerulosclerosis. Podocyte is terminally differentiated and does not typically proliferate following injury and loss. However, recent evidence suggested that during renal injury, podocyte could re-enter the cell cycle, sensitizing the cells to injury and death, but the molecular mechanisms underlying it, as well as the cell fate determination still remained unclear. Here, using NPHS2 Cre; mT/mG transgenic mice and primary podocytes isolated from the mice, we investigated the effect of mammalian target of rapamycin complex 1 (mTORC1)/4E-binding protein 1 (4E-BP1) signaling pathway on cell cycle re-entry and apoptosis of podocyte induced by adriamycin. It was found that podocyte cell cycle re-entry could be induced by adriamycin as early as the 1st week in vivo and the 2nd hour in vitro, accompanied with 4E-BP1 activation and was followed by podocyte loss or apoptosis from the 4th week in vivo or the 4th hour in vitro. Importantly, targeting 4E-BP1 activation by the RNA interference of 4E-BP1 or pharmacologic rapamycin (inhibitor of mTORC1, blocking mTORC1-dependent phosphorylation of its substrate 4E-BP1) treatment was able to inhibit the increases of PCNA, Ki67, and the S-phase fraction of cell cycle in primary podocyte during 2-6 h of adriamycin treatment, and also attenuated the following apoptotic cell death of podocyte detected from the 4th hour, suggesting that 4E-BP1 could be a regulator to manipulate the amount of cell cycle re-entry provided by differentiated podocyte, and thus regulate the degree of podocyte apoptosis, bringing us a new potential podocyte-protective substance that can be used for therapy.