title: Oxidative stress-induced alterations in PPAR-γ and associated mitochondrial destabilization contribute to kidney cell apoptosis.
abstract: The mechanism(s) underlying renoprotection by peroxisome proliferator-activated receptor (PPAR)-γ agonists in diabetic and nondiabetic kidney disease are not well understood. Mitochondrial dysfunction and oxidative stress contribute to kidney disease. PPAR-γ upregulates proteins required for mitochondrial biogenesis. Our aim was to determine whether PPAR-γ has a role in protecting the kidney proximal tubular epithelium (PTE) against mitochondrial destabilisation and oxidative stress. HK-2 PTE cells were subjected to oxidative stress (0.2-1.0 mM H₂O₂) for 2 and 18 h and compared with untreated cells for apoptosis, mitosis (morphology/biomarkers), cell viability (MTT), superoxide (dihydroethidium), mitochondrial function (MitoTracker red and JC-1), ATP (luminescence), and mitochondrial ultrastructure. PPAR-γ, phospho-PPAR-γ, PPAR-γ coactivator (PGC)-1α, Parkin (Park2), p62, and light chain (LC)3β were investigated using Western blots. PPAR-γ was modulated using the agonists rosiglitazone, pioglitazone, and troglitazone. Mitochondrial destabilization increased with H₂O₂concentration, ATP decreased (2 and 18 h; P < 0.05), Mitotracker red and JC-1 fluorescence indicated loss of mitochondrial membrane potential, and superoxide increased (18 h, P < 0.05). Electron microscopy indicated sparse mitochondria, with disrupted cristae. Mitophagy was evident at 2 h (Park2 and LC3β increased; p62 decreased). Impaired mitophagy was indicated by p62 accumulation at 18 h (P < 0.05). PPAR-γ expression decreased, phospho-PPAR-γ increased, and PGC-1α decreased (2 h), indicating aberrant PPAR-γ activation and reduced mitochondrial biogenesis. Cell viability decreased (2 and 18 h, P < 0.05). PPAR-γ agonists promoted further apoptosis. In summary, oxidative stress promoted mitochondrial destabilisation in kidney PTE, in association with increased PPAR-γ phosphorylation. PPAR-γ agonists failed to protect PTE. Despite positive effects in other tissues, PPAR-γ activation appears to be detrimental to kidney PTE health when oxidative stress induces damage.
authors.affiliation: Centre for Kidney Disease Research, School of Medicine, The University of Queensland, Translational Research Institute, Brisbane, Queensland, Australia;
authors.forename: David M
authors.initials: DM
authors.lastname: Small
authors.affiliation: Centre for Kidney Disease Research, School of Medicine, The University of Queensland, Translational Research Institute, Brisbane, Queensland, Australia;
authors.forename: Christudas
authors.initials: C
authors.lastname: Morais
authors.affiliation: Centre for Kidney Disease Research, School of Medicine, The University of Queensland, Translational Research Institute, Brisbane, Queensland, Australia; School of Human Movement Studies, The University of Queensland, Brisbane, Queensland, Australia;
authors.forename: Jeff S
authors.initials: JS
authors.lastname: Coombes
authors.affiliation: Centre for Kidney Disease Research, School of Medicine, The University of Queensland, Translational Research Institute, Brisbane, Queensland, Australia; UQ Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia; and.
authors.forename: Nigel C
authors.initials: NC
authors.lastname: Bennett
authors.affiliation: Centre for Kidney Disease Research, School of Medicine, The University of Queensland, Translational Research Institute, Brisbane, Queensland, Australia; Department of Nephrology, Princess Alexandra Hospital, Brisbane, Queensland, Australia.
authors.forename: David W
authors.initials: DW
authors.lastname: Johnson
authors.affiliation: Centre for Kidney Disease Research, School of Medicine, The University of Queensland, Translational Research Institute, Brisbane, Queensland, Australia; g.gobe@uq.edu.au.
authors.forename: Glenda C
authors.initials: GC
authors.lastname: Gobe
mesh_terms: D017209:Apoptosis; D002460:Cell Line; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D063269:Mitochondrial Turnover; D018384:Oxidative Stress; D047495:PPAR gamma / Q000378:metabolism*; D019459:Urothelium / Q000378:metabolism
chemical_list: D047495:PPAR gamma
keywords: mitochondria; oxidative stress; peroxisome proliferator-activated receptor-γ; thiozolidinediones