Abstract
Two coding sequence variants (G1 and G2) of Apolipoprotein L1 (APOL1) gene have been implicated as a higher risk factor for chronic kidney diseases (CKD) in African Americans when compared with European Americans. Previous studies have suggested that the APOL1 G1 and G2 variant proteins are more toxic to kidney cells than the wild-type APOL1 G0, but the underlying mechanisms are poorly understood. To determine whether endoplasmic reticulum (ER) stress contributes to podocyte toxicity, we generated human podocytes (HPs) that stably overexpressed APOL1 G0, G1, or G2 (Vec/HPs, G0/HPs, G1/HPs, and G2/HPs). Propidium iodide staining showed that HP overexpressing the APOL1 G1 or G2 variant exhibited a higher rate of necrosis when compared with those overexpressing the wild-type G0 counterpart. Consistently, the expression levels of nephrin and podocin proteins were significantly decreased in the G1- or G2-overexpressing cells despite the maintenance of their mRNA expressions levels. In contrast, the expression of the 78-kDa glucose-regulated protein ((GRP78), also known as the binding Ig protein, BiP) and the phosphorylation of the eukaryotic translation initiation factor 1 (eIF1) were significantly elevated in the G1/HPs and G2/HPs, suggesting a possible occurrence of ER stress in these cells. Furthermore, ER stress inhibitors not only restored nephrin protein expression, but also provided protection against necrosis in G1/HPs and G2/HPs, suggesting that APOL1 risk variants cause podocyte injury partly through enhancing ER stress.
Highlights
Clinical reports have demonstrated that African Americans develop higher rates of progressive nephropathy including focal segmental glomerulosclerosis (FSGS), hypertension-attributed chronic kidney disease (CKD), and HIV-associated nephropathy (HIVAN) when compared with European Americans [1,2]
Results showed that the sequence was exactly the same as of Apolipoprotein L1 (APOL1) G0 described in GenBank at NM 145343, confirming that it was G0 in this podocyte cell line
Results showed that APOL1 mRNA were increased by 41, 26, and 23-folds in APOL1-G0/human podocyte (HP), G1/HPs, and G2/HPs, respectively, when compared with APOL1-Vec/HPs (Figure 1A)
Summary
Clinical reports have demonstrated that African Americans develop higher rates of progressive nephropathy including focal segmental glomerulosclerosis (FSGS), hypertension-attributed chronic kidney disease (CKD), and HIV-associated nephropathy (HIVAN) when compared with European Americans [1,2]. Whether APOL1 risk variants cause increased ER stress in podocytes has not been studied so far. We determined the role of ER stress in the induction of APOL1 variants induced podocyte injury.
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