Intracellular albumin overload elicits endoplasmic reticulum stress and PKC-delta/p38 MAPK pathway activation to induce podocyte apoptosis

Podocyte injury is closely related to proteinuria and the progression of chronic kidney disease (CKD). Currently, there is no conclusive understanding about the mechanisms involved in albumin overload and podocyte apoptosis response. In this study, we sought to explore the ways by which intracellular albumin can mediate podocyte apoptosis. Here, immortalized mouse podocytes were treated with bovine serum albumin (BSA) at different times and concentrations, in the presence or absence of SB203580 (0.1 µM, inhibitor of mitogen-activated-protein kinase – p38MAPK). Using immunofluorescence images, flow cytometry and immunoblotting, we observed a time-dependent intracellular accumulation of fluorescent albumin-FITC-BSA, followed by concentration-and time-dependent effect of intracellular albumin overload on podocyte apoptosis, which was mediated by increased expression of the chaperone glucose-regulated-protein 78 (GRP 78) and phosphorylated inositol-requiring enzyme 1 alpha (pIRE1-α), as well as protein kinase C delta (PKC-δ), p38MAPK and cleaved caspase 12 expression. SB203580 prevented the cleavage of caspase 12 and the albumin-mediated podocyte apoptosis. These results suggest that intracellular albumin overload is associated with endoplasmic reticulum (ER) stress and upregulation of PKC-δ/p38MAPK/caspase 12 pathway, which may be a target for future therapeutic of albumin-induced podocyte apoptosis.