C HUANG1, H YI1, Y SHI1, Q CAO1, X-M CHEN1, C POLLOCK1
1University of Sydney, St Leonards, Australia
Aim: To identify the role of KCa3.1 in mitochondrial quality control in diabetic nephropathy.
Background: Mitochondrial dysfunction is involved in the pathogenesis of diabetic nephropathy. Mitochondrial quality control is characterized by repairing of mitochondrial damage through mitophagy and fission/fusion. It has been shown that blockade of KCa3.1, a potassium channel, ameliorates diabetic renal fibrosis and KCa3.1 activation contributes to dysfunctional tubular autophagy in diabetic nephropathy through PI3K/Akt/mTOR signaling pathways. However, the role of KCa3.1 in mitochondrial quality control is not yet known.
Methods: In vitro human proximal tubular cells (HK2 cells) transfected with scrambled siRNA or KCa3.1 siRNA were exposed to TGF-β1 for 48h. Mitochondrial function and mitochondrial ROS (mtROS) production were assessed. In vivo, diabetes was induced in KCa3.1+/+ and KCa3.1-/- mice by streptozotocin injection. The pro-fission protein dynamin-related protein 1 (Drp1) and pro-fussion protein mitofusin 2 (Mfn2) as well as BCL2 interacting protein 3 (BNIP3) (a mitophagy regulator) were examined by western blotting in HK2 cells and mice kidneys.
Results: The in vitro results showed that TGF-β1 significantly inhibited mitochondrial ATP production rate, compared to the controls, which were significantly reversed by KCa3.1 siRNA in HK2 cells. KCa3.1 gene silencing inhibited TGF-β1-induced significant increase in MitoSOX Red fluorescence in HK2 cells. TGF-β1 significantly increased the expression of Drp1 and BNIP3 in HK2 cells, which were attenuated by KCa3.1 gene silencing. The expression of Mfn2 was not overtly apparent on TGF-β1 stimulation. Consistently, the in vivo results showed significantly increased Drp1 and BNIP3 expression in diabetic KCa3.1 +/+ mice, which were significantly reduced in diabetic KCa3.1-/- mice.
Conclusions: KCa3.1 mediates dysregulation of mitochondrial quality control in diabetic nephropathy.
Dr Chunling Huang is a NHMRC early career research fellow in the renal lab at Kolling Institute, University of Sydney. She has expertise in diabetic kidney disease, animal models of diabetic nephropathy and kidney fibrosis. Her research focuses on the novel therapeutic targets for chronic kidney diseases and the underling mechanisms including inflammation, fibrosis, fibroblast activation and autophagy.