Genetic Ablation of Calcium-independent Phospholipase A2\u03b3 Exacerbates Glomerular Injury in Adriamycin Nephrosis in Mice

Hanan Elimam,José R. Navarro-Betancourt,Andrey V. Cybulsky,Julie Guillemette,Joan Papillon

doi:10.1038/s41598-019-52834-x

Hanan Elimam, José R. Navarro-Betancourt + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-52834-x

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Abstract

Genetic ablation of calcium-independent phospholipase A2γ (iPLA2γ) in mice results in marked damage of mitochondria and enhanced autophagy in glomerular visceral epithelial cells (GECs) or podocytes. The present study addresses the role of iPLA2γ in glomerular injury. In adriamycin nephrosis, deletion of iPLA2γ exacerbated albuminuria and reduced podocyte number. Glomerular LC3-II increased and p62 decreased in adriamycin-treated iPLA2γ knockout (KO) mice, compared with treated control, in keeping with increased autophagy in KO. iPLA2γ KO GECs in culture also demonstrated increased autophagy, compared with control GECs. iPLA2γ KO GECs showed a reduced oxygen consumption rate and increased phosphorylation of AMP kinase (pAMPK), consistent with mitochondrial dysfunction. Adriamycin further stimulated pAMPK and autophagy. After co-transfection of GECs with mito-YFP (to label mitochondria) and RFP-LC3 (to label autophagosomes), or RFP-LAMP1 (to label lysosomes), there was greater colocalization of mito-YFP with RFP-LC3-II and with RFP-LAMP1 in iPLA2γ KO GECs, compared with WT, indicating enhanced mitophagy in KO. Adriamycin increased mitophagy in WT cells. Thus, iPLA2γ has a cytoprotective function in the normal glomerulus and in glomerulopathy, as deletion of iPLA2γ leads to mitochondrial damage and impaired energy homeostasis, as well as autophagy and mitophagy.

Highlights

Glomerular visceral epithelial cells (GECs) or podocytes play a critical role in the maintenance of glomerular permselectivity[1,2]
We and others have demonstrated that independent phospholipase A2γ (iPLA2γ) is localized subcellularly at the endoplasmic reticulum and mitochondria, and localization is dependent on the N-terminal region of iPLA2γ5–7. iPLA2γ may be active under basal and stimulated conditions; the latter was dependent on phosphorylation at Ser-511 and/or Ser-515 via mitogen-activated protein kinase-interacting kinase 1 (MNK1)[6]
We demonstrated that podocytes in aging iPLA2γ KO mice (10–11 months of age) show injury to plasma membranes and mitochondria, as well as an increased number of autophagosomes, these mice did not develop albuminuria[4]

Summary

Introduction

Glomerular visceral epithelial cells (GECs) or podocytes play a critical role in the maintenance of glomerular permselectivity[1,2]. The role of iPLA2γ in mitochondrial bioenergetic function and its importance in cellular energy metabolism and homeostasis was previously identified in several tissues, including heart, skeletal muscle, liver, and brain. IPLA2γ deletion induced marked disruption in mitochondrial phospholipid homeostasis in the brains of aging mice, resulting in enlarged and degenerating mitochondria, leading to enhanced autophagy and cognitive dysfunction[11]. Given the importance of mitochondrial function and autophagy in the maintenance of homeostasis in podocytes[16,22], our focus has been on the interaction of iPLA2γ with these two processes. We demonstrate that deletion of iPLA2γ in young mice exacerbates podocyte injury and enhances autophagy in adriamycin nephrosis, an experimental model of human focal segmental glomerulosclerosis (FSGS). In GECs derived from iPLA2γ KO mice, we show mitochondrial dysfunction, as well as enhanced autophagy and mitophagy

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