FOXO3a accumulation and activation accelerate oxidative stress-induced podocyte injury

Podocyte injury is the primary cause of glomerular injury in diabetic nephropathy (DN). Advanced oxidation protein products (AOPPs), the triggers and markers of oxidative stress in DN, have been linked to podocyte damage. However, the underlying mechanism is not yet clear. Here, we investigated the potential role of FOXO3a, a key transcription factor in the response to stress, in mediating AOPPs-induced podocyte injury. We found that FOXO3a expression was increased in the glomeruli of kidney biopsies from patients with DN and it was positively correlated with proteinuria. The serum from patients with DN significantly increased FOXO3a and its downstream genes FasL and Bim, thereby inducing the high level of cleaved caspase3 and the loss of nephrin and podocin expressions in podocytes. Blockade of AOPPs signaling by a neutralizing antibody against the receptor of advanced glycation end products (alpha RAGE) abolished the effect of DN serum on podocytes, confirming the pathogenic role of AOPPs in DN serum. Downregulation of FOXO3a decreased AOPPs-induced podocyte apoptosis and restored the levels of podocyte markers nephrin and podocin, and upregulation of FOXO3a exacerbated these changes in podocytes after AOPPs treatment. Furthermore, FOXO3a specifically activated proapoptotic genes in podocytes only in the presence of AOPPs. Mechanistically, AOPPs increased the FOXO3a protein levels by inhibiting their autophagic degradation in a ROS/mTOR-dependent manner. Moreover AOPPs activated the accumulated FOXO3a by maintaining FOXO3a in the nucleus, and this process was dependent on ROS-mediated AKT signaling deactivation. These studies suggest that FOXO3a plays a critical role in mediating AOPPs-induced podocyte injury and reveal a new mechanistic linkage of oxidative stress, FOXO3a activation and podocyte injury in DN.