Inhibition of autophagy increases apoptosis during re-warming after cold storage in renal tubular epithelial cells

Prolonged cold storage and re-warming (CS/REW) of kidneys are risk factors for delayed graft function (DGF). Studies in renal tubular epithelial cells (RTECs) have determined apoptosis and autophagy in models of either cold storage (CS) or re-warming alone. The effect of both cold storage and re-warming on apoptosis and autophagy, in RTECS is not known and is relevant to DGF as the kidney is subjected to both CS and re-warming. We hypothesized that CS/REW of RTECs would induce autophagy that protects against apoptosis. In CS/REW, there was increased autophagic flux of RTECs. Autophagy inhibition using an Atg5 siRNA resulted in increased cleaved caspase-3 and increased apoptotic cells (on both morphology and annexin V staining) during CS/REW. The effect of autophagy inhibition on necrosis in RTECs is unknown. There were increased necrosis and caspase-1, a mediator of necrosis, during CS/REW, and the Atg5 siRNA had no effect on necrosis and caspase-1. In a kidney transplant model, there was an increase in LC3 II, a marker of autophagy, in kidneys transplanted after cold storage. In summary, autophagic flux is increased during CS/REW. Autophagy inhibition resulted in increased cleaved caspase-3 and increased apoptosis during CS/REW without an effect on necrosis or caspase-1. In conclusion, autophagy inhibition in RTECs after CS/REW induces apoptotic cell death and may be deleterious as a therapy to decrease DGF.