Genetic Deletion of Calcium-independent Phospholipase A 2 γ Protects Mice from Diabetic Nephropathy
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Calcium-independent phospholipase A 2 γ (iPLA 2 γ) is localized in glomerular epithelial cells (GECs)/podocytes at the mitochondria and endoplasmic reticulum, and can mediate release of arachidonic acid and prostanoids. Global knockout (KO) of iPLA 2 γ in mice did not cause albuminuria, but resulted in mitochondrial structural abnormalities and enhanced autophagy in podocytes. In acute glomerulonephritis, deletion of iPLA 2 γ exacerbated albuminuria and podocyte injury. This study addresses the role of iPLA 2 γ in diabetic nephropathy. Hyperglycemia was induced in male mice with streptozotocin (STZ). STZ induced progressive albuminuria in control mice (over 21 weeks), while albuminuria did not increase in iPLA 2 γ KO mice, remaining comparable to untreated groups. Despite similar exposure to STZ, the STZ-treated iPLA 2 γ KO mice developed a lower level of hyperglycemia compared to STZ-treated control. However, there was no significant correlation between the degree of hyperglycemia and albuminuria, and even iPLA 2 γ KO mice with greatest hyperglycemia did not develop significant albuminuria. Mortality at 21 weeks was greatest in diabetic control mice. Sclerotic glomeruli and enlarged glomerular capillary loops were increased significantly in diabetic control compared to diabetic iPLA 2 γ KO mice. Glomerular matrix was expanded in diabetic mice, with control exceeding iPLA 2 γ KO. Glomerular autophagy (increased LC3-II and decreased p62) was enhanced in diabetic iPLA 2 γ KO mice compared to control. Treatment of cultured GECs with H 2 O 2 resulted in increased cell death in control GECs compared to iPLA 2 γ KO, and the increase was slightly greater in medium with high glucose compared to low glucose. H 2 O 2 -induced cell death was not affected by inhibition of prostanoid production with indomethacin. In conclusion, mice with global deletion of iPLA 2 γ are protected from developing chronic glomerular injury in diabetic nephropathy. This is associated with increased glomerular autophagy.
