Thioredoxin-interacting protein mediates dysfunction of tubular autophagy in diabetic kidneys through inhibiting autophagic flux.
Thioredoxin-interacting protein (TXNIP) expression is ubiquitous and is induced by a variety of cellular stresses, including high intracellular glucose. TXNIP is associated with activation of oxidative stress and tubulointerstitial fibrosis in diabetic nephropathy. Autophagy is a major pathway that delivers damaged proteins and organelles to lysosomes to maintain cellular homeostasis. This study aimed to investigate the dysregulation of autophagy and the regulation of TXNIP on autophagy in renal proximal tubular cells (PTCs) under diabetic conditions. The formation of autophagosomes was measured using transmission electron microscopy, and LC3-II, and the effectiveness of autophagic clearance was determined by p62 expression in diabetic kidney and in human PTCs exposed to high glucose (HG). The results collectively demonstrated increased expression of TXNIP, LC3/LC3-II and p62 in renal tubular cells of mice with diabetic nephropathy and in cultured human PTCs exposed to HG (30 mM/l) for 48 h compared with control. The formation of autophagic vacuoles was increased in HG-induced cells. Furthermore, silencing of TXNIP by siRNA transfection reduced autophagic vacuoles and the expression of LC3-II and p62 in human PTCs exposed to HG compared with control and partially reversed the accumulation of LC3-II and p62 induced by bafilomycin A1 (50 nM/l), a pharmacological inhibitor of autophagy which blocks the fusion of autophagosomes with lysosomes and impairs the degradation of LC3-II and p62. Collectively, these results suggest that hyperglycemia leads to dysfunction of autophagy in renal tubular cells and decreases autophagic clearance. HG-induced overexpression of TXNIP may contribute to the dysfunction of tubular autophagy in diabetes.
1] Kolling Institute of Medical Research, Sydney Medical School, University of Sydney, Royal North Shore Hospital, St Leonards, NSW, Australia [2] Xiamen Center of Clinical Laboratory, Xiamen Zhongshan Hospital, Medical College of Xiamen University, Xiamen, China.
Chunling
C
Huang
Kolling Institute of Medical Research, Sydney Medical School, University of Sydney, Royal North Shore Hospital, St Leonards, NSW, Australia.
Mike Z
MZ
Lin
School of Medical Sciences (Discipline of Anatomy and Histology)-The Bosch Institute, University of Sydney, Sydney, NSW, Australia.
Delfine
D
Cheng
1] School of Medical Sciences (Discipline of Anatomy and Histology)-The Bosch Institute, University of Sydney, Sydney, NSW, Australia [2] Australian Centre for Microscopy and Microanalysis, University of Sydney, Sydney, NSW, Australia.
Filip
F
Braet
Kolling Institute of Medical Research, Sydney Medical School, University of Sydney, Royal North Shore Hospital, St Leonards, NSW, Australia.
Carol A
CA
Pollock
Kolling Institute of Medical Research, Sydney Medical School, University of Sydney, Royal North Shore Hospital, St Leonards, NSW, Australia.
Xin-Ming
XM
Chen
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001343:Autophagy / Q000502:physiology*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D003921:Diabetes Mellitus, Experimental / Q000235:genetics / Q000473:pathology / Q000503:physiopathology; D003928:Diabetic Nephropathies / Q000235:genetics / Q000473:pathology* / Q000503:physiopathology*; D055785:Gene Knockdown Techniques; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000473:pathology / Q000503:physiopathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D046529:Microscopy, Electron, Transmission; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D018384:Oxidative Stress; D010588:Phagosomes / Q000378:metabolism / Q000473:pathology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D000071456:Sequestosome-1 Protein; D013879:Thioredoxins / Q000235:genetics / Q000502:physiology*; D051758:Transcription Factor TFIIH; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C490981:Gtf2h1 protein, mouse; C477012:MAP1LC3A protein, human; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D012333:RNA, Messenger; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein; C486715:TXNIP protein, human; D014157:Transcription Factors; C445672:Txnip protein, mouse; D051758:Transcription Factor TFIIH; D013879:Thioredoxins