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Jin Z, Xiao L, Xu X, Miao C, Liu Y. Association between triglyceride-glucose index and acute kidney injury in patients with acute myocardial infarction based on medical information mart for intensive care database: A cross-sectional study. J Med Biochem 2024; 43:153-161. [PMID: 38496026 PMCID: PMC10943466 DOI: 10.5937/jomb0-45219] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2023] [Accepted: 08/18/2023] [Indexed: 03/19/2024] Open
Abstract
Background The relationship between triglyceride glucose (TyG) index and the incidence of acute kidney injury (AKI) in patients with acute myocardial infarction (AMI) is unclear. This study aims to explore the relationship between the two. Methods Participants were enrolled from Medical Information Mart for Intensive Care IV (MIMICIV) and grouping of subjects based on the quartile interval of the TyG index. With the presence of AKI as the main outcome, a logistic regression model was constructed. The correlation of the TyG index with the results obtained was examined by using a restricted cubic spline (RCS) model.
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Affiliation(s)
- Zihan Jin
- Tianjin University of Traditional Chinese Medicine, Tianjin, China
| | - Lu Xiao
- University of Traditional Chinese Medicine, First Teaching Hospital of Tianjin, Tianjin, China
| | - Xinyi Xu
- University of Traditional Chinese Medicine, First Teaching Hospital of Tianjin, Tianjin, China
| | - Changhong Miao
- University of Traditional Chinese Medicine, First Teaching Hospital of Tianjin, Tianjin, China
| | - Yi Liu
- University of Traditional Chinese Medicine, First Teaching Hospital of Tianjin, Tianjin, China
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2
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Abstract
Epigenetics examines heritable changes in DNA and its associated proteins except mutations in gene sequence. Epigenetic regulation plays fundamental roles in kidney cell biology through the action of DNA methylation, chromatin modification via epigenetic regulators and non-coding RNA species. Kidney diseases, including acute kidney injury, chronic kidney disease, diabetic kidney disease and renal fibrosis are multistep processes associated with numerous molecular alterations even in individual kidney cells. Epigenetic alterations, including anomalous DNA methylation, aberrant histone alterations and changes of microRNA expression all contribute to kidney pathogenesis. These changes alter the genome-wide epigenetic signatures and disrupt essential pathways that protect renal cells from uncontrolled growth, apoptosis and development of other renal associated syndromes. Molecular changes impact cellular function within kidney cells and its microenvironment to drive and maintain disease phenotype. In this chapter, we briefly summarize epigenetic mechanisms in four kidney diseases including acute kidney injury, chronic kidney disease, diabetic kidney disease and renal fibrosis. We primarily focus on current knowledge about the genome-wide profiling of DNA methylation and histone modification, and epigenetic regulation on specific gene(s) in the pathophysiology of these diseases and the translational potential of identifying new biomarkers and treatment for prevention and therapy. Incorporating epigenomic testing into clinical research is essential to elucidate novel epigenetic biomarkers and develop precision medicine using emerging therapies.
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3
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Zhang L, Gui T, Console L, Scalise M, Indiveri C, Hausler S, Kullak-Ublick GA, Gai Z, Visentin M. Cholesterol stimulates the cellular uptake of L-carnitine by the carnitine/organic cation transporter novel 2 (OCTN2). J Biol Chem 2020; 296:100204. [PMID: 33334877 PMCID: PMC7948396 DOI: 10.1074/jbc.ra120.015175] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 12/14/2020] [Accepted: 12/17/2020] [Indexed: 12/19/2022] Open
Abstract
The carnitine/organic cation transporter novel 2 (OCTN2) is responsible for the cellular uptake of carnitine in most tissues. Being a transmembrane protein OCTN2 must interact with the surrounding lipid microenvironment to function. Among the main lipid species that constitute eukaryotic cells, cholesterol has highly dynamic levels under a number of physiopathological conditions. This work describes how plasma membrane cholesterol modulates OCTN2 transport of L-carnitine in human embryonic kidney 293 cells overexpressing OCTN2 (OCTN2-HEK293) and in proteoliposomes harboring human OCTN2. We manipulated the cholesterol content of intact cells, assessed by thin layer chromatography, through short exposures to empty and/or cholesterol-saturated methyl-β-cyclodextrin (mβcd), whereas free cholesterol was used to enrich reconstituted proteoliposomes. We measured OCTN2 transport using [3H]L-carnitine, and expression levels and localization by surface biotinylation and Western blotting. A 20-min preincubation with mβcd reduced the cellular cholesterol content and inhibited L-carnitine influx by 50% in comparison with controls. Analogously, the insertion of cholesterol in OCTN2-proteoliposomes stimulated L-carnitine uptake in a dose-dependent manner. Carnitine uptake in cells incubated with empty mβcd and cholesterol-saturated mβcd to preserve the cholesterol content was comparable with controls, suggesting that the mβcd effect on OCTN2 was cholesterol dependent. Cholesterol stimulated L-carnitine influx in cells by markedly increasing the affinity for L-carnitine and in proteoliposomes by significantly enhancing the affinity for Na+ and, in turn, the L-carnitine maximal transport capacity. Because of the antilipogenic and antioxidant features of L-carnitine, the stimulatory effect of cholesterol on L-carnitine uptake might represent a novel protective effect against lipid-induced toxicity and oxidative stress.
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Affiliation(s)
- Lu Zhang
- College of Traditional Chinese Medicine, Innovation Research Institute of Traditional Chinese Medicine, Shandong University of Traditional Chinese Medicine, Jinan, China; Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Ting Gui
- College of Traditional Chinese Medicine, Innovation Research Institute of Traditional Chinese Medicine, Shandong University of Traditional Chinese Medicine, Jinan, China
| | - Lara Console
- Department DiBEST (Biologia, Ecologia, Scienze della Terra) Unit of Biochemistry and Molecular Biotechnology, University of Calabria, Arcavacata di Rende, Italy
| | - Mariafrancesca Scalise
- Department DiBEST (Biologia, Ecologia, Scienze della Terra) Unit of Biochemistry and Molecular Biotechnology, University of Calabria, Arcavacata di Rende, Italy
| | - Cesare Indiveri
- Department DiBEST (Biologia, Ecologia, Scienze della Terra) Unit of Biochemistry and Molecular Biotechnology, University of Calabria, Arcavacata di Rende, Italy
| | - Stephanie Hausler
- Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, University of Zurich, Zurich, Switzerland
| | - Gerd A Kullak-Ublick
- Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, University of Zurich, Zurich, Switzerland; Mechanistic Safety, CMO & Patient Safety, Global Drug Development, Novartis Pharma, Basel, Switzerland
| | - Zhibo Gai
- College of Traditional Chinese Medicine, Innovation Research Institute of Traditional Chinese Medicine, Shandong University of Traditional Chinese Medicine, Jinan, China; Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, University of Zurich, Zurich, Switzerland.
| | - Michele Visentin
- Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, University of Zurich, Zurich, Switzerland.
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4
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De Vusser K, Winckelmans E, Martens D, Lerut E, Kuypers D, Nawrot T, Naesens M. Intrarenal arteriosclerosis and telomere attrition associate with dysregulation of the cholesterol pathway. Aging (Albany NY) 2020; 12:7830-7847. [PMID: 32353828 PMCID: PMC7244056 DOI: 10.18632/aging.103098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Accepted: 03/30/2020] [Indexed: 11/25/2022]
Abstract
BACKGROUND Recently, we demonstrated that arteriosclerosis in the smaller intrarenal arteries is associated with shorter telomere length, independently of history of cardiovascular events and calendar age. This suggests that intrarenal arteriosclerosis reflects replicative senescence, although the underlying molecular alterations remain unclear. RESULTS Shorter intrarenal telomere length associated significantly with the presence of renal arteriosclerosis (T/S ratio 0.91±0.15 vs. 1.20±0.23 with vs. without arteriosclerosis, p=0.007, test cohort; T/S ratio 0.98 ±0.26 vs. 1.03 ±0.18 with vs. without arteriosclerosis, p=0.02, validation cohort). The presence versus absence of intrarenal arteriosclerosis was associated with differential expression of 1472 transcripts. Pathway analysis revealed enrichment of molecules involved in the superpathway of cholesterol biosynthesis as the most significant. The differential expression of these genes was confirmed in the independent validation cohort. Furthermore, the specific mRNA expression of the molecules in the superpathway of cholesterol biosynthesis associated significantly with intrarenal telomere length, and with history of cardiovascular events. INTERPRETATION Our study illustrates that the superpathway of cholesterol biosynthesis interacts with the previously published association between shorter telomere length and arteriosclerosis. METHODS This study included a test cohort of 40 consecutive kidney donors (calendar age 48.0 ± 15), with biopsies obtained prior to transplantation. Intrarenal leucocyte telomere length content was assessed using quantitative RT-PCR. Whole genome microarray mRNA expression analysis was performed using Affymetrix Gene 2.0 ST arrays. We investigated the associations between mRNA gene expression, telomere length as marker of replicative senescence, and intrarenal arteriosclerosis (Banff "cv" score = vascular fibrous intimal thickening = intimal hyperplasia) using adjusted multiple regression models. For biological interpretation and pathway overrepresentation analysis, we used Ingenuity Pathway Analysis. The significant pathways and genes were validated in an independent validation cohort of 173 kidney biopsies obtained prior to transplantation.
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Affiliation(s)
- Katrien De Vusser
- Department of Microbiology and Immunology, KU Leuven - University of Leuven, Leuven, Belgium.,Department of Nephrology and Renal Transplantation, University Hospitals Leuven, Leuven, Belgium
| | - Ellen Winckelmans
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium
| | - Dries Martens
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium
| | - Evelyne Lerut
- Department of Imaging and Pathology, KU Leuven - University of Leuven, Leuven, Belgium.,Department of Pathology, University Hospitals Leuven, Leuven, Belgium
| | - Dirk Kuypers
- Department of Microbiology and Immunology, KU Leuven - University of Leuven, Leuven, Belgium.,Department of Nephrology and Renal Transplantation, University Hospitals Leuven, Leuven, Belgium
| | - Tim Nawrot
- Centre for Environmental Sciences, Hasselt University, Hasselt, Belgium.,Department of Public Health and Primary Care, KU Leuven - University of Leuven, Leuven, Belgium
| | - Maarten Naesens
- Department of Microbiology and Immunology, KU Leuven - University of Leuven, Leuven, Belgium.,Department of Nephrology and Renal Transplantation, University Hospitals Leuven, Leuven, Belgium
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5
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Otopathogenic Staphylococcus aureus Invades Human Middle Ear Epithelial Cells Primarily through Cholesterol Dependent Pathway. Sci Rep 2019; 9:10777. [PMID: 31346200 PMCID: PMC6658548 DOI: 10.1038/s41598-019-47079-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2019] [Accepted: 06/26/2019] [Indexed: 01/20/2023] Open
Abstract
Chronic suppurative otitis media (CSOM) is one of the most common infectious diseases of the middle ear especially affecting children, leading to delay in language development and communication. Although Staphylococcus aureus is the most common pathogen associated with CSOM, its interaction with middle ear epithelial cells is not well known. In the present study, we observed that otopathogenic S. aureus has the ability to invade human middle ear epithelial cells (HMEECs) in a dose and time dependent manner. Scanning electron microscopy demonstrated time dependent increase in the number of S. aureus on the surface of HMEECs. We observed that otopathogenic S. aureus primarily employs a cholesterol dependent pathway to colonize HMEECs. In agreement with these findings, confocal microscopy showed that S. aureus colocalized with lipid rafts in HMEECs. The results of the present study provide new insights into the pathogenesis of S. aureus induced CSOM. The availability of in vitro cell culture model will pave the way to develop novel effective treatment modalities for CSOM beyond antibiotic therapy.
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6
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Kalani MM, Nourmohammadi J, Negahdari B. Osteogenic potential of Rosuvastatin immobilized on silk fibroin nanofibers using argon plasma treatment. Biomed Mater 2018; 14:025002. [DOI: 10.1088/1748-605x/aaec26] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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7
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Erpicum P, Rowart P, Defraigne JO, Krzesinski JM, Jouret F. What we need to know about lipid-associated injury in case of renal ischemia-reperfusion. Am J Physiol Renal Physiol 2018; 315:F1714-F1719. [PMID: 30332314 DOI: 10.1152/ajprenal.00322.2018] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Renal segmental metabolism is reflected by the complex distribution of the main energy pathways along the nephron, with fatty acid oxidation preferentially used in the cortex area. Ischemia/reperfusion injury (IRI) is due to the restriction of renal blood flow, rapidly leading to a metabolic switch toward anaerobic conditions. Subsequent unbalance between energy demand and oxygen/nutrient delivery compromises kidney cell functions, resulting in a complex inflammatory cascade including the production of reactive oxygen species (ROS). Renal IRI especially involves lipid accumulation. Lipid peroxidation is one of the major events of ROS-associated tissue injury. Here, we briefly review the current knowledge of renal cell lipid metabolism in normal and ischemic conditions. Next, we focus on renal lipid-associated injury, with emphasis on its mechanisms and consequences during the course of IRI. Finally, we discuss preclinical observations aiming at preventing and/or attenuating lipid-associated IRI.
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Affiliation(s)
- Pauline Erpicum
- Division of Nephrology, University of Liège Academic Hospital , Liège , Belgium.,Groupe Interdisciplinaire de Génoprotéomique Appliquée, Cardiovascular Sciences, University of Liège , Liège , Belgium
| | - Pascal Rowart
- Groupe Interdisciplinaire de Génoprotéomique Appliquée, Cardiovascular Sciences, University of Liège , Liège , Belgium
| | - Jean-Olivier Defraigne
- Groupe Interdisciplinaire de Génoprotéomique Appliquée, Cardiovascular Sciences, University of Liège , Liège , Belgium.,Division of Cardio-Thoracic Surgery, University of Liège Academic Hospital , Liège , Belgium
| | | | - François Jouret
- Division of Nephrology, University of Liège Academic Hospital , Liège , Belgium.,Groupe Interdisciplinaire de Génoprotéomique Appliquée, Cardiovascular Sciences, University of Liège , Liège , Belgium
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8
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Weinberg JM, Bienholz A, Venkatachalam MA. The role of glycine in regulated cell death. Cell Mol Life Sci 2016; 73:2285-308. [PMID: 27066896 PMCID: PMC4955867 DOI: 10.1007/s00018-016-2201-6] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Accepted: 03/18/2016] [Indexed: 01/22/2023]
Abstract
The cytoprotective effects of glycine against cell death have been recognized for over 28 years. They are expressed in multiple cell types and injury settings that lead to necrosis, but are still not widely appreciated or considered in the conceptualization of cell death pathways. In this paper, we review the available data on the expression of this phenomenon, its relationship to major pathophysiologic pathways that lead to cell death and immunomodulatory effects, the hypothesis that it involves suppression by glycine of the development of a hydrophilic death channel of molecular dimensions in the plasma membrane, and evidence for its impact on disease processes in vivo.
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Affiliation(s)
- Joel M Weinberg
- Division of Nephrology, Department of Internal Medicine, Veterans Affairs Ann Arbor Healthcare System and University of Michigan, Room 1560, MSRB II, Ann Arbor, MI, 48109-0676, USA.
| | - Anja Bienholz
- Department of Nephrology, University Duisburg-Essen, 45122, Essen, Germany
| | - M A Venkatachalam
- Department of Pathology, University of Texas Health Science Center, San Antonio, TX, 78234, USA
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9
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Agarwal A, Dong Z, Harris R, Murray P, Parikh SM, Rosner MH, Kellum JA, Ronco C. Cellular and Molecular Mechanisms of AKI. J Am Soc Nephrol 2016; 27:1288-99. [PMID: 26860342 DOI: 10.1681/asn.2015070740] [Citation(s) in RCA: 147] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
In this article, we review the current evidence for the cellular and molecular mechanisms of AKI, focusing on epithelial cell pathobiology and related cell-cell interactions, using ischemic AKI as a model. Highlighted are the clinical relevance of cellular and molecular targets that have been investigated in experimental models of ischemic AKI and how such models might be improved to optimize translation into successful clinical trials. In particular, development of more context-specific animal models with greater relevance to human AKI is urgently needed. Comorbidities that could alter patient susceptibility to AKI, such as underlying diabetes, aging, obesity, cancer, and CKD, should also be considered in developing these models. Finally, harmonization between academia and industry for more clinically relevant preclinical testing of potential therapeutic targets and better translational clinical trial design is also needed to achieve the goal of developing effective interventions for AKI.
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Affiliation(s)
- Anupam Agarwal
- Division of Nephrology, and Nephrology Research and Training Center, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama;
| | - Zheng Dong
- Department of Cellular Biology and Anatomy, Georgia Regents University, Augusta, Georgia
| | - Raymond Harris
- Division of Nephrology, Department of Medicine, Vanderbilt University, Nashville, Tennessee
| | - Patrick Murray
- Department of Medicine, University College of Dublin, Dublin, Ireland
| | - Samir M Parikh
- Division of Nephrology and Center for Vascular Biology Research, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts
| | - Mitchell H Rosner
- Department of Medicine, Nephrology Division, and the Center for Immunity, Inflammation, and Regenerative Medicine, University of Virginia, Charlottesville, Virginia
| | - John A Kellum
- Center for Critical Care Nephrology, Clinical Research, Investigation and Systems Modeling of Acute Illness Center, Department of Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania; and
| | - Claudio Ronco
- Department of Nephrology, Dialysis, and Transplantation, San Bortolo Hospital, and the International Renal Research Institute, 36100 Vicenza, Italy
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10
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Gatticchi L, Bellezza I, Del Sordo R, Peirce MJ, Sidoni A, Roberti R, Minelli A. The Tm7sf2 Gene Deficiency Protects Mice against Endotoxin-Induced Acute Kidney Injury. PLoS One 2015; 10:e0141885. [PMID: 26540160 PMCID: PMC4635018 DOI: 10.1371/journal.pone.0141885] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Accepted: 10/14/2015] [Indexed: 12/18/2022] Open
Abstract
Cholesterol is essential for diverse cellular functions and cellular and whole-body cholesterol homeostasis is highly controlled. Cholesterol can also influence cellular susceptibility to injury. The connection between cholesterol metabolism and inflammation is exemplified by the Tm7sf2 gene, the absence of which reveals an essential role in cholesterol biosynthesis under stress conditions but also results in an inflammatory phenotype, i.e. NF-κB activation and TNFα up-regulation. Here, by using Tm7sf2+/+and Tm7sf2−/− mice, we investigated whether the Tm7sf2 gene, through its role in cholesterol biosynthesis under stress conditions, is involved in the renal failure induced by the administration of LPS. We found that the loss of Tm7sf2 gene results in significantly reduced blood urea nitrogen levels accompanied by decreased renal inflammatory response and neutral lipid accumulation. The increased expression of fatty acids catabolic enzymes reduces the need of the renal autophagy, a known crucial nutrient-sensing pathway in lipid metabolism. Moreover, we observed that the Tm7sf2 insufficiency is responsible for the inhibition of the NF-κB signalling thus dampening the inflammatory response and leading to a reduced renal damage. These results suggest a pivotal role for Tm7sf2 in renal inflammatory and lipotoxic response under endotoxemic conditions.
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Affiliation(s)
- Leonardo Gatticchi
- Department of Experimental Medicine, University of Perugia, Piazzale Gambuli, 06124 Perugia, Italy
| | - Ilaria Bellezza
- Department of Experimental Medicine, University of Perugia, Piazzale Gambuli, 06124 Perugia, Italy
| | - Rachele Del Sordo
- Department of Experimental Medicine, University of Perugia, Piazzale Gambuli, 06124 Perugia, Italy
| | - Matthew J. Peirce
- Department of Experimental Medicine, University of Perugia, Piazzale Gambuli, 06124 Perugia, Italy
| | - Angelo Sidoni
- Department of Experimental Medicine, University of Perugia, Piazzale Gambuli, 06124 Perugia, Italy
| | - Rita Roberti
- Department of Experimental Medicine, University of Perugia, Piazzale Gambuli, 06124 Perugia, Italy
| | - Alba Minelli
- Department of Experimental Medicine, University of Perugia, Piazzale Gambuli, 06124 Perugia, Italy
- * E-mail:
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11
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Zager RA. 'Biologic memory' in response to acute kidney injury: cytoresistance, toll-like receptor hyper-responsiveness and the onset of progressive renal disease. Nephrol Dial Transplant 2013; 28:1985-93. [PMID: 23761460 PMCID: PMC3765022 DOI: 10.1093/ndt/gft101] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Accepted: 03/29/2013] [Indexed: 11/14/2022] Open
Abstract
Following the induction of ischemic or toxin-mediated acute kidney injury (AKI), cellular adaptations occur that 're-program' how the kidney responds to future superimposed insults. This re-programming is not simply a short-lived phenomenon; rather it can persist for many weeks, implying that a state of 'biologic memory' has emerged. These changes can be both adaptive and maladaptive in nature and they can co-exist in time. A beneficial adaptation is the emergence of acquired cytoresistance, whereby a number of physiologic responses develop that serve to protect the kidney against further ischemic or nephrotoxic attack. Conversely, some changes are maladaptive, such as a predisposition to Gram-negative or Gram-positive bacteremia due to a renal tubular up-regulation of toll-like receptor responses. This latter change culminates in exaggerated cytokine production, and with efflux into the systemic circulation, extra-renal tissue injury can result (so-called 'organ cross talk'). Another maladaptive response is a persistent up-regulation of pro-inflammatory, pro-fibrotic and vasoconstrictive genes, culminating in progressive renal injury and ultimately end-stage renal failure. The mechanisms by which this biologic re-programming, or biologic memory, is imparted remain subjects for considerable debate. However, injury-induced, and stable, epigenetic remodeling at pro-inflammatory/pro-fibrotic genes seems likely to be involved. The goal of this editorial is to highlight that the so-called 'maintenance phase' of acute renal failure is not a static one, somewhere between injury induction and the onset of repair. Rather, this period is one in which the induction of 'biologic memory' can ultimately impact renal functional recovery, extra-renal injury and the possible transition of AKI into chronic, progressive renal disease.
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Affiliation(s)
- Richard A. Zager
- The Fred Hutchinson Cancer Research Center, and the University of Washington, Seattle, WA, USA
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12
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Fujikura T, Togawa A, Sun Y, Iwakura T, Yasuda H, Fujigaki Y. Dephosphorylated Ser985 of c-Met is associated with acquired resistance to rechallenge injury in rats that had recovered from uranyl acetate-induced subclinical renal damage. Clin Exp Nephrol 2012; 17:504-14. [PMID: 23250664 DOI: 10.1007/s10157-012-0757-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Accepted: 12/10/2012] [Indexed: 10/27/2022]
Abstract
BACKGROUND We previously reported that rats that had recovered from mild proximal tubule (PT) injury induced by a sub-toxic dose of uranyl acetate (UA) showed partial resistance to a subsequent nephrotoxic dose of UA in association with reduced renal dysfunction and accelerated PT proliferation. We demonstrated that this resistance may involve hepatocyte growth factor (HGF)/c-Met signaling. Here, we examined whether primary cultured tubular cells derived from this model had acquired sensitivity to HGF. METHODS Tubular cells were isolated by collagenase digestion from rat kidneys after recovery from UA-induced mild PT injury and were cultured for 48 h. Their survival and proliferation were examined using the MTS assay/5-bromo-2'-deoxyuridine labeling or MTS assay, respectively, and their migration was assayed using wound-healing and cell scattering assays, with/without HGF. HGF/c-Met signaling was assayed using phospho-specific antibodies. RESULTS HGF-stimulated cultured tubular cells from UA-treated rats showed better survival after UA exposure and higher proliferation and migration than cells from vehicle-treated rats. Furthermore, HGF induced higher phosphorylation of c-Met (Tyr1234/1235) and of its major downstream signals (AKT and extracellular signal-regulated kinase 1/2) with maintained dephosphorylation of Ser985 as a negative regulator of HGF/c-Met signaling in the tubular cells of UA-treated rats compared to those of vehicle-treated rats. Immunohistochemically, dephosphorylated Ser985 was confirmed in PT cells in vivo. CONCLUSIONS These results suggest that elevated sensitivity to HGF, via dephosphorylated Ser985 of c-Met of tubular cells that had recovered from mild tubular injury, may be associated with cytoprotection, accelerated proliferation and migration.
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Affiliation(s)
- Tomoyuki Fujikura
- Internal Medicine 1, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashiku, Hamamatsu, Shizuoka, 431-3192, Japan
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13
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Wang XT, Li J, Liu L, Hu N, Jin S, Liu C, Mei D, Liu XD. Tissue cholesterol content alterations in streptozotocin-induced diabetic rats. Acta Pharmacol Sin 2012; 33:909-17. [PMID: 22705727 DOI: 10.1038/aps.2012.50] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
AIM Diabetes is associated with elevated serum total cholesterol level and disrupted lipoprotein subfractions. The aim of this study was to examine alterations in the tissue cholesterol contents closely related to diabetic complications. METHODS Intraperitoneal injection of streptozotocin was used to induce type 1 diabetes in adult male Sprague-Dawley rats. On d 35 after the injection, liver, heart, intestine, kidney, pancreas, cerebral cortex and hippocampus were isolated from the rats. The content of total and free cholesterol in the tissues was determined using HPLC. The ATP-binding cassette protein A1 (ABCA1) protein and ApoE mRNA were measured using Western blot and QT-PCR analyses, respectively. RESULTS In diabetic rats, the level of free cholesterol was significantly decreased in the peripheral tissues, but significantly elevated in hippocampus, as compared with those in the control rats. Diabetic rats showed a trend of decreasing the total cholesterol level in the peripheral tissues, but significant change was only found in kidney and liver. In diabetic rats, the level of the ABCA1 protein was significantly increased in the peripheral tissues and cerebral cortex; the expression of ApoE mRNA was slightly decreased in hippocampus and cerebral cortex, but the change had no statistical significance. CONCLUSION Type 1 diabetes decreases the free cholesterol content in the peripheral tissues and increases the free cholesterol content in hippocampus. The decreased free cholesterol level in the peripheral tissues may be partly due to the increased expression of the ABCA1 protein.
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14
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Lhoták S, Sood S, Brimble E, Carlisle RE, Colgan SM, Mazzetti A, Dickhout JG, Ingram AJ, Austin RC. ER stress contributes to renal proximal tubule injury by increasing SREBP-2-mediated lipid accumulation and apoptotic cell death. Am J Physiol Renal Physiol 2012; 303:F266-78. [PMID: 22573382 DOI: 10.1152/ajprenal.00482.2011] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Renal proximal tubule injury is induced by agents/conditions known to cause endoplasmic reticulum (ER) stress, including cyclosporine A (CsA), an immunosuppressant drug with nephrotoxic effects. However, the underlying mechanism by which ER stress contributes to proximal tubule cell injury is not well understood. In this study, we report lipid accumulation, sterol regulatory element-binding protein-2 (SREBP-2) expression, and ER stress in proximal tubules of kidneys from mice treated with the classic ER stressor tunicamycin (Tm) or in human renal biopsy specimens showing CsA-induced nephrotoxicity. Colocalization of ER stress markers [78-kDa glucose regulated protein (GRP78), CHOP] with SREBP-2 expression and lipid accumulation was prominent within the proximal tubule cells exposed to Tm or CsA. Prolonged ER stress resulted in increased apoptotic cell death of lipid-enriched proximal tubule cells with colocalization of GRP78, SREBP-2, and Ca(2+)-independent phospholipase A(2) (iPLA(2)β), an SREBP-2 inducible gene with proapoptotic characteristics. In cultured HK-2 human proximal tubule cells, CsA- and Tm-induced ER stress caused lipid accumulation and SREBP-2 activation. Furthermore, overexpression of SREBP-2 or activation of endogenous SREBP-2 in HK-2 cells stimulated apoptosis. Inhibition of SREBP-2 activation with the site-1-serine protease inhibitor AEBSF prevented ER stress-induced lipid accumulation and apoptosis. Overexpression of the ER-resident chaperone GRP78 attenuated ER stress and inhibited CsA-induced SREBP-2 expression and lipid accumulation. In summary, our findings suggest that ER stress-induced SREBP-2 activation contributes to renal proximal tubule cell injury by dysregulating lipid homeostasis.
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Affiliation(s)
- Sárka Lhoták
- Hamilton Centre for Kidney Research, St. Joseph's Healthcare Hamilton, 50 Charlton Ave. East, Hamilton, Ontario, Canada
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15
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Narayanavari SA, Sritharan M, Haake DA, Matsunaga J. Multiple leptospiral sphingomyelinases (or are there?). MICROBIOLOGY-SGM 2012; 158:1137-1146. [PMID: 22422753 DOI: 10.1099/mic.0.057737-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Culture supernatants of leptospiral pathogens have long been known to haemolyse erythrocytes. This property is due, at least in part, to sphingomyelinase activity. Indeed, genome sequencing reveals that pathogenic Leptospira species are richly endowed with sphingomyelinase homologues: five genes have been annotated to encode sphingomyelinases in Leptospira interrogans. Such redundancy suggests that this class of genes is likely to benefit leptospiral pathogens in their interactions with the mammalian host. Surprisingly, sequence comparison with bacterial sphingomyelinases for which the crystal structures are known reveals that only one of the leptospiral homologues has the active site amino acid residues required for enzymic activity. Based on studies of other bacterial toxins, we propose that leptospiral sphingomyelinase homologues, irrespective of their catalytic activity, may possess additional molecular functions that benefit the spirochaete. Potential secretion pathways and roles in pathogenesis are discussed, including nutrient acquisition, dissemination, haemorrhage and immune evasion. Although leptospiral sphingomyelinase-like proteins are best known for their cytolytic properties, we believe that a better understanding of their biological role requires the examination of their sublytic properties as well.
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Affiliation(s)
| | - Manjula Sritharan
- Department of Animal Sciences, University of Hyderabad, Hyderabad, India
| | - David A Haake
- Department of Medicine, University of California at Los Angeles, Los Angeles, CA, USA.,Department of Urology, University of California at Los Angeles, Los Angeles, CA, USA.,Division of Infectious Diseases, VA Greater Los Angeles Healthcare System, Los Angeles, CA, USA.,Department of Microbiology, Immunology, and Molecular Genetics, University of California at Los Angeles, Los Angeles, CA, USA
| | - James Matsunaga
- Research Service, VA Greater Los Angeles Healthcare System, Los Angeles, CA, USA.,Department of Medicine, University of California at Los Angeles, Los Angeles, CA, USA
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16
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Zager RA, Johnson ACM, Becker K. Acute unilateral ischemic renal injury induces progressive renal inflammation, lipid accumulation, histone modification, and "end-stage" kidney disease. Am J Physiol Renal Physiol 2011; 301:F1334-45. [PMID: 21921025 PMCID: PMC3233867 DOI: 10.1152/ajprenal.00431.2011] [Citation(s) in RCA: 124] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Accepted: 09/08/2011] [Indexed: 01/04/2023] Open
Abstract
There is an emerging concept in clinical nephrology that acute kidney injury (AKI) can initiate chronic kidney disease (CKD). However, potential mechanisms by which this may occur remain elusive. Hence, this study tested the hypotheses that 1) AKI triggers progressive activation of selected proinflammatory genes, 2) there is a relative failure of compensatory anti-inflammatory gene expression, 3) proinflammatory lipid accumulation occurs, 4) these changes correspond with "gene-activating" histone acetylation, and 5) in concert, progressive renal disease results. CD-1 mice were subjected to 30 min of unilateral renal ischemia. Assessments were made 1 day, 1 wk, or 3 wk later. Results were contrasted to those observed in uninjured contralateral kidneys or in kidneys from normal mice. Progressive renal injury occurred throughout the 3-wk postischemic period, as denoted by stepwise increases in neutrophil gelatinase-associated lipocalin gene induction and ongoing histologic damage. By 3 wk postischemia, progressive renal disease was observed (massive tubular dropout; 2/3rds reduction in renal weight). These changes corresponded with progressive increases in proinflammatory cytokine/chemokine gene expression (MCP-1, TNF-α, TGF-β1), a relative failure of anti-inflammatory enzyme/cytokine (heme oxygenase-1; IL-10) upregulation, and progressive renal lipid (cholesterol/triglyceride) loading. Stepwise increases in collagen III mRNA and collagen deposition (Sirius red staining) indicated a progressive profibrotic response. Postischemic dexamethasone treatment significantly preserved renal mass, indicating functional significance of the observed proinflammatory state. Progressive gene-activating H3 acetylation was observed by ELISA, rising from 5% at baseline to 75% at 3 wk. This was confirmed by chromatin immunoprecipitation assay of target genes. In sum, these results provide experimental support for the clinical concept that AKI can trigger CKD, this is partially mediated by progressive postischemic inflammation, ongoing lipid accumulation results (potentially evoking "lipotoxicity"), and increasing histone acetylation at proinflammatory/profibrotic genes may contribute to this self-sustaining injury-promoting state.
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Affiliation(s)
- Richard A Zager
- Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N., Seattle, WA 98109, USA.
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17
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Acquired resistance to rechallenge injury in rats that recovered from mild renal damage induced by uranyl acetate: accelerated proliferation and hepatocyte growth factor/c-Met axis. Clin Exp Nephrol 2011; 15:666-675. [DOI: 10.1007/s10157-011-0453-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2011] [Accepted: 04/07/2011] [Indexed: 11/27/2022]
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18
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Johnson AC, Ware LB, Himmelfarb J, Zager RA. HMG-CoA reductase activation and urinary pellet cholesterol elevations in acute kidney injury. Clin J Am Soc Nephrol 2011; 6:2108-13. [PMID: 21799150 DOI: 10.2215/cjn.02440311] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
BACKGROUND AND OBJECTIVES Experimental acute kidney injury (AKI) activates the HMG-CoA reductase (HMGCR) gene, producing proximal tubule cholesterol loading. AKI also causes sloughing of proximal tubular cell debris into tubular lumina. This study tested whether these two processes culminate in increased urinary pellet cholesterol content, and whether the latter has potential AKI biomarker utility. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS Urine samples were collected from 29 critically ill patients with (n = 14) or without (n= 15) AKI, 15 patients with chronic kidney disease, and 15 healthy volunteers. Centrifuged urinary pellets underwent lipid extraction, and the extracts were assayed for cholesterol content (factored by membrane phospholipid phosphate content). In vivo HMGCR activation was sought by measuring levels of RNA polymerase II (Pol II), and of a gene activating histone mark (H3K4m3) at exon 1 of the HMGCR gene (chromatin immunoprecipitation assay of urine chromatin samples). RESULTS AKI+ patients had an approximate doubling of urinary pellet cholesterol content compared with control urine samples (versus normal; P < 0.001). The values significantly correlated (r, 0.5; P < 0.01) with serum, but not urine, creatinine concentrations. Conversely, neither critical illness without AKI nor chronic kidney disease raised pellet cholesterol levels. Increased HMGCR activity in the AKI+ patients was supported by three- to fourfold increased levels of Pol II, and of H3K4m3, at the HMGCR gene (versus controls or AKI- patients). CONCLUSIONS (1) Clinical AKI, like experimental AKI, induces HMGCR gene activation; (2) increased urinary pellet cholesterol levels result; and (3) urine pellet cholesterol levels may have potential AKI biomarker utility. The latter will require future testing in a large prospective trial.
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Affiliation(s)
- Ali Cm Johnson
- Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
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19
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Abstract
Cellular cholesterol homeostasis is a fundamental and highly regulated process. Transcription factors known as sterol regulatory element binding proteins (SREBPs) coordinate the expression of many genes involved in the biosynthesis and uptake of cholesterol. Dysregulation of SREBP activation and cellular lipid accumulation has been associated with endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR). This review will provide an overview of ER stress and the UPR as well as cholesterol homeostasis and SREBP regulation, with an emphasis on their interaction and biological relevance.
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20
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Rodriguez ME, Kim J, Delos Santos GB, Azizuddin K, Berlin J, Anderson VE, Kenney ME, Oleinick NL. Binding to and photo-oxidation of cardiolipin by the phthalocyanine photosensitizer Pc 4. JOURNAL OF BIOMEDICAL OPTICS 2010; 15:051604. [PMID: 21054078 PMCID: PMC2945736 DOI: 10.1117/1.3484256] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Revised: 05/20/2010] [Accepted: 05/26/2010] [Indexed: 05/30/2023]
Abstract
Cardiolipin is a unique phospholipid of the mitochondrial inner membrane. Its peroxidation correlates with release of cytochrome c and induction of apoptosis. The phthalocyanine photosensitizer Pc 4 binds preferentially to the mitochondria and endoplasmic reticulum. Earlier Förster resonance energy transfer studies showed colocalization of Pc 4 and cardiolipin, which suggests cardiolipin as a target of photodynamic therapy (PDT) with Pc 4. Using liposomes as membrane models, we find that Pc 4 binds to cardiolipin-containing liposomes similarly to those that do not contain cardiolipin. Pc 4 binding is also studied in MCF-7c3 cells and those whose cardiolipin content was reduced by treatment with palmitate. Decreased levels of cardiolipin are quantified by thin-layer chromatography. The similar level of binding of Pc 4 to cells, irrespective of palmitate treatment, supports the lack of specificity of Pc 4 binding. Thus, factors other than cardiolipin are likely responsible for the preferential localization of Pc 4 in mitochondria. Nonetheless, cardiolipin within liposomes is readily oxidized by Pc 4 and light, yielding apparently mono- and dihydroperoxidized cardiolipin. If similar products result from exposure of cells to Pc 4-PDT, they could be part of the early events leading to apoptosis following Pc 4-PDT.
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Affiliation(s)
- Myriam E Rodriguez
- Case Western Reserve University, Department of Radiation Oncology, Cleveland, Ohio 44106-4942, USA
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21
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Abstract
Cytoresistance is the term used to describe the response of the proximal tubule cells to various stress inducers via cholesterol accumulation. However, the role of extensive exercise as a renal insult has not been examined. In this study, the effect of heavy muscle activity on proximal tubule cytoresistance was investigated. Results obtained from rats subjected to running a treadmill for five days were compared to those of controls. Extensive muscle activity-induced soleus citrate synthase and blood lactate elevation were associated with normal MAP, RBF, and GFR. Blood electrolytes and cholesterol levels remained unchanged, whereas the total and free cholesterol accumulations in the proximal tubule cells of the exercised group were higher than controls. Cholesterol-loaded tubules were more resistant (as proved by LDH release) to an ATP-depleted/calcium overloaded second stress. These data clearly demonstrate that heavy muscle activity induces cholesterol accumulation in the proximal tubules of kidney, without influencing ATP generation.
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Affiliation(s)
- Selma Cirrik
- Akdeniz University, Department of Physiology, 07070 Campus, Antalya, Turkey.
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22
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Acquired resistance to rechallenge injury in rats recovered from subclinical renal damage with uranyl acetate--Importance of proliferative activity of tubular cells. Toxicol Appl Pharmacol 2009; 243:104-10. [PMID: 19931553 DOI: 10.1016/j.taap.2009.11.018] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Revised: 10/25/2009] [Accepted: 11/10/2009] [Indexed: 02/07/2023]
Abstract
Animals recovered from acute renal failure are resistant to subsequent insult. We investigated whether rats recovered from mild proximal tubule (PT) injury without renal dysfunction (subclinical renal damage) acquire the same resistance. Rats 14 days after recovering from subclinical renal damage, which was induced by 0.2 mg/kg of uranyl acetate (UA) (sub-toxic dose), were rechallenged with 4 mg/kg of UA (nephrotoxic dose). Fate of PT cells and renal function were examined in response to nephrotoxic dose of UA. All divided cells after sub-toxic dose of UA insult were labeled with bromodeoxyuridine (BrdU) for 14 days then the number of PT cells with or without BrdU-labeling was counted following nephrotoxic dose of UA insult. Rats recovered from subclinical renal damage gained resistance to nephrotoxic dose of UA with reduced renal dysfunction, less severity of peak damage (necrotic and TUNEL+ apoptotic cells) and accelerated PT cell proliferation, but with earlier peak of PT damage. The decrease in number of PT cells in the early phase of rechallenge injury with nephrotoxic UA was more in rats pretreated with sub-toxic dose of UA than vehicle pretreated rats. The exaggerated loss of PT cells was mainly caused by the exaggerated loss of BrdU+ divided cells. In contrast, accelerated cell proliferation in rats recovered from sub-toxic dose of UA was observed mainly in BrdU- non-divided cells. The findings suggest that rats recovered from subclinical renal damage showed partial acquired resistance to nephrotoxic insult. Accelerated recovery with increased proliferative activity of non-divided PT cells after subclinical renal damage may mainly contribute to acquired resistance.
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23
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Galea AM, Brown AJ. Special relationship between sterols and oxygen: were sterols an adaptation to aerobic life? Free Radic Biol Med 2009; 47:880-9. [PMID: 19559787 DOI: 10.1016/j.freeradbiomed.2009.06.027] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2009] [Revised: 06/19/2009] [Accepted: 06/19/2009] [Indexed: 11/18/2022]
Abstract
A fascinating link between sterols and molecular oxygen (O(2)) has been a common thread running through the fundamental work of Konrad Bloch, who elucidated the biosynthetic pathway for cholesterol, to recent work supporting a role of sterols in the sensing of O(2). Synthesis of sterols by eukaryotes is an O(2)-intensive process. In this review, we argue that increased levels of O(2) in the atmosphere not only made the evolution of sterols possible, but that these sterols may in turn have provided the eukaryote with an early defence mechanism against O(2). The idea that nature crafted sterols as a feedback loop to adapt to, or help protect against, the hazards of O(2) is novel and enticing. We marshal several lines of evidence to support this thesis: (1) coincidence of atmospheric O(2) and sterol evolution; (2) sterols regulate O(2) entry into eukaryotic cells and organelles; (3) sterols act as O(2) sensors across eukaryotic life; (4) sterols serve as a primitive cellular defence against O(2) (including reactive oxygen species). Therefore, sterols may have evolved in eukaryotes partially as an adaptive response to the rise of terrestrial O(2), rather than merely as a consequence of it.
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Affiliation(s)
- Anne M Galea
- School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney NSW, 2052, Australia
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24
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Naito M, Bomsztyk K, Zager RA. Renal ischemia-induced cholesterol loading: transcription factor recruitment and chromatin remodeling along the HMG CoA reductase gene. THE AMERICAN JOURNAL OF PATHOLOGY 2008; 174:54-62. [PMID: 19095962 DOI: 10.2353/ajpath.2009.080602] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Acute kidney injury evokes renal tubular cholesterol synthesis. However, the factors during acute kidney injury that regulate HMG CoA reductase (HMGCR) activity, the rate-limiting step in cholesterol synthesis, have not been defined. To investigate these factors, mice were subjected to 30 minutes of either unilateral renal ischemia or sham surgery. After 3 days, bilateral nephrectomy was performed and cortical tissue extracts were prepared. The recruitment of RNA polymerase II (Pol II), transcription factors (SREBP-1, SREBP-2, NF-kappaB, c-Fos, and c-Jun), and heat shock proteins (HSP-70 and heme oxygenase-1) to the HMGCR promoter and transcription region (start/end exons) were assessed by Matrix ChIP assay. HMGCR mRNA, protein, and cholesterol levels were determined. Finally, histone modifications at HMGCR were assessed. Ischemia/reperfusion (I/R) induced marked cholesterol loading, which corresponded with elevated Pol II recruitment to HMGCR and increased expression levels of both HMGCR protein and mRNA. I/R also induced the binding of multiple transcription factors (SREBP-1, SREBP-2, c-Fos, c-Jun, NF-kappaB) and heat shock proteins to the HMGCR promoter and transcription regions. Significant histone modifications (increased H3K4m3, H3K19Ac, and H2A.Z variant) at these loci were also observed but were not identified at either the 5' and 3' HMGCR flanking regions (+/-5000 bps) or at negative control genes (beta-actin and beta-globin). In conclusion, I/R activates the HMGCR gene via multiple stress-activated transcriptional and epigenetic pathways, contributing to renal cholesterol loading.
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Affiliation(s)
- Masayo Naito
- Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
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25
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Zager RA. Uremia induces proximal tubular cytoresistance and heme oxygenase-1 expression in the absence of acute kidney injury. Am J Physiol Renal Physiol 2008; 296:F362-8. [PMID: 19036845 DOI: 10.1152/ajprenal.90645.2008] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Acute kidney injury (AKI) induces adaptive responses within proximal tubular (PT) cells that serve to protect them from further ischemic or toxic damage. However, it is not known whether uremia, a potential consequence of AKI, independently alters susceptibility to tubular injury. To address this issue, we subjected CD-1 mice to bilateral ureteral transection (BUTx), which produces uremia (blood urea nitrogen approximately 150 mg/dl) in the absence of direct renal damage. PT segments were then isolated from BUTx and control mice and subjected to in vitro hypoxic injury. Additionally, "in vitro uremia" was modeled in isolated tubules or in cultured PT (HK-2) cells by addition of 1) peritoneal dialysate (obtained from mice with bilateral ureteral obstruction), 2) peritoneal fluid (from BUTx mice), or 3) normal human urine (pH 7.4, with and without boiling). Effects on injury severity (lactate dehydrogenase release) were assessed. Finally, because uremia is a prooxidant state, it was hypothesized that BUTx would increase renal lipid peroxidation (malondialdehyde) and induce heme oxygenase-1 (HO-1), a redox-sensitive cytoprotective protein. BUTx conferred striking protection against hypoxic damage. This could be partially modeled in tubules and HK-2 cells by induction of in vitro uremia. Urine's protective action was heat labile (largely destroyed by boiling). BUTx caused a tripling of renal malondialdehyde and HO-1 protein levels. Increased HO-1 transcription was likely involved, as indicated by a tripling of HO-1 mRNA and RNA polymerase II binding along the HO-1 gene (chromatin immunoprecipitation assay). "Gene-activating" histone modifications [H3K4 trimethylation (H3K4m3) and histone 2 variant (H2A.Z)] at HO-1 gene loci were also observed. Uremia, per se, can contribute to the AKI-induced cytoresistance. Low-molecular-weight, heat-labile, cytoprotective factor(s) and uremia-induced renal stress responses (e.g., HO-1 gene activation) are likely involved. Finally, renal HO-1 induction following AKI may reflect direct cell injury effects and adaptations to uremia.
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Affiliation(s)
- Richard A Zager
- Fred Hutchinson Cancer Research Center, 1100 Fairview Ave. N, Rm. D2-190, Seattle, WA 98109, USA.
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26
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Abstract
Many of the studies of acute renal injury have been conducted in young mice usually during their rapid growth phase; yet, the impact of age or growth stage on the degree of injury is unknown. To address this issue, we studied three forms of injury (endotoxemic-, glycerol-, and maleate-induced) in mice ranging in age from adolescence (3 weeks) to maturity (16 weeks). The severity of injury within each model significantly correlated with weight and age. We also noticed a progressive age-dependent reduction in renal cholesterol content, a potential injury modifier. As the animals grew and aged they also exhibited stepwise decrements in the mRNAs of HMG CoA reductase and the low density lipoprotein receptor, two key cholesterol homeostatic genes. This was paralleled by decreased amounts of RNA polymerase II and the transcription factor SREBP1/2 at the reductase and lipoprotein receptor gene loci as measured by chromatin immunoprecipitation. Our study shows that the early phase of mouse growth can profoundly alter renal susceptibility to diverse forms of experimental acute renal injury.
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Kasturi S, Ismail-Beigi F. Effect of thyroid hormone on the distribution and activity of Na, K-ATPase in ventricular myocardium. Arch Biochem Biophys 2008; 475:121-7. [PMID: 18457653 DOI: 10.1016/j.abb.2008.04.019] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2008] [Revised: 04/16/2008] [Accepted: 04/17/2008] [Indexed: 01/29/2023]
Abstract
Employing detergent-free sucrose-density gradient fractionation method we isolated cholesterol-rich lighter membrane fractions containing approximately 10% of protein, approximately 30% of cholesterol in membranes of ventricular myocardium. Cholesterol-rich lighter membrane fractions contain >70% of Na, K-ATPase and caveolins 1 and 3 and <10% of beta-actin. Treatment of hypothyroid rats with T(3) increased the relative abundance of both alpha1 and beta1 Na, K-ATPase subunits in total membranes by 4- to 5-fold (with no change in caveolin-3), and resulted in 1.9-fold increase in enzyme activity. T(3)-induced Na, K-ATPase subunits were preferentially distributed to the lighter fractions (#s 4, 5 and 6); and increased abundance of alpha1 and beta1 were 34-70% and 43-68%, respectively. We conclude that the activity of Na, K-ATPase is not uniform in cardiac membranes, and while a significant amount of Na, K-ATPase is present in cardiac cholesterol-rich membrane fractions, the intrinsic activity is significantly less than the enzyme present in relatively cholesterol-poor membranes.
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Affiliation(s)
- Sriram Kasturi
- Division of Clinical and Molecular Endocrinology, Department of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4951, USA
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28
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Zager RA, Johnson ACM, Lund S. ‘Endotoxin tolerance’: TNF-α hyper-reactivity and tubular cytoresistance in a renal cholesterol loading state. Kidney Int 2007; 71:496-503. [PMID: 17228359 DOI: 10.1038/sj.ki.5002092] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The term 'endotoxin tolerance' defines a state in which prior endotoxin (lipopolysaccharide (LPS)) exposure induces resistance to subsequent LPS attack. However, its characteristics within kidney have not been well defined. Hence, this study tested the impact of LPS 'preconditioning' (LPS-PC; 18 or 72 h earlier) on: (i) selected renal inflammatory mediators (tumor necrosis factor (TNF)-alpha, interleukin-10 (IL-10), monocyte chemotactic protein-1 (MCP-1), inducible nitric oxide synthase (iNOS), Toll-like receptor 4 (TLR4); protein or mRNA); (ii) cholesterol homeostasis (a stress reactant); and (iii) isolated proximal tubule (PT) vulnerability to hypoxia or membrane cholesterol (cholesterol oxidase/esterase) attack. Two hours post LPS injection, LPS-PC mice manifested reduced plasma TNF-alpha levels, consistent with systemic LPS tolerance. However, in kidney, paradoxical TNF-alpha hyper-reactivity (protein/mRNA) to LPS existed, despite normal TLR4 protein levels. PT TNF-alpha levels paralleled renal cortical results, implying that PTs were involved. LPS-PC also induced: (i) renal cortical iNOS, IL-10 (but not MCP-1) mRNA hyper-reactivity; (ii), PT cholesterol loading, and (iii) cytoresistance to hypoxia and plasma membrane cholesterol attack. A link between cholesterol homeostasis and cell LPS responsiveness was suggested by observations that cholesterol reductions in HK-2 cells (methylcyclodextrin), or reductions in HK-2 membrane fluidity (A2C), blunted LPS-mediated TNF-alpha/MCP-1 mRNA increases. In sum: (i) systemic LPS tolerance can be associated with renal hyper-responsiveness of selected components within the LPS signaling cascade (e.g., TNF-alpha, iNOS, IL-10); (ii) PT cytoresistance against hypoxic/membrane injury coexists; and (iii) LPS-induced renal/PT cholesterol accumulation may mechanistically contribute to each of these results.
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Affiliation(s)
- R A Zager
- Department of Medicine, University of Washington, Seattle, Washington 98109-1024, USA.
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29
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Zager RA, Johnson ACM, Hanson SY, Lund S. Acute nephrotoxic and obstructive injury primes the kidney to endotoxin-driven cytokine/chemokine production. Kidney Int 2006; 69:1181-8. [PMID: 16395275 DOI: 10.1038/sj.ki.5000022] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Gram-negative sepsis is a frequent complication in patients with acute renal failure. This study tested whether acute tubular injury, for example, induced by cisplatin (CP) or urinary tract obstruction, enhances renal cytokine responses to endotoxin (lipopolysaccharide (LPS)), potentially contributing to tissue damage. CD-1 mice were subjected to CP or vehicle injection. After 24 or 72 h, LPS or its vehicle was given. At 2 h post LPS or vehicle administration, plasma/renal cortical tumor necrosis factor (TNF)-alpha, monocyte chemoattractant protein-1 (MCP-1), and interleukin-10, and their corresponding renal cortical mRNAs were assessed (representing pro-anti-inflammatory cytokines, and a chemokine, respectively). Comparable studies were conducted in mice 24 h post unilateral ureteral obstruction (UUO). Cultured human proximal tubular (HK-2) cell TNF-alpha responses to CP+/-LPS were also assessed. CP alone caused either minimal or no increases in cytokine levels. However, CP dramatically augmented cytokine responses to LPS (up to 5-10 x vs LPS alone). The cytokine increases were paralleled by changes in their mRNAs. UUO also sensitized to LPS. CP alone did not alter HK-2 cell TNF-alpha/mRNA. However, CP 'primed' the cells to LPS (approximately 50-100% greater TNF-alpha/mRNA increases vs LPS alone). CP+LPS also caused synergistic cell death (lactate dehydrogenase release). We conclude that (1) diverse forms of tubular injury can sensitize the kidney to LPS, increasing cytokine production; (2) proximal tubules are involved; (3) LPS 'priming' has broad-based consequences, impacting diverse pro- and anti-inflammatory pathways; and (4) increased transcriptional events may be at least partially involved.
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Affiliation(s)
- R A Zager
- Department of Medicine, University of Washington, Seattle, Washington, USA.
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30
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Wang Y, Moser AH, Shigenaga JK, Grunfeld C, Feingold KR. Downregulation of liver X receptor-alpha in mouse kidney and HK-2 proximal tubular cells by LPS and cytokines. J Lipid Res 2005; 46:2377-87. [PMID: 16106051 DOI: 10.1194/jlr.m500134-jlr200] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The acute-phase response (APR) suppresses type II nuclear hormone receptors and alters the expression of their target genes involved in lipid metabolism in the liver and heart. Therefore, we examined the expression of liver X receptor/retinoid X receptor (LXR/RXR) and their target genes in kidney from mice treated with lipopolysaccharide (LPS) and in human proximal tubular HK-2 cells treated with interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha). We found that LXRalpha and RXRalpha expression was suppressed by LPS in kidney and by IL-1beta or TNF-alpha in HK-2 cells. The decrease in LXRalpha/RXRalpha expression was associated with a decrease in the expression of several LXRalpha target genes [apolipoprotein E (apoE), ABCA1, ABCG1, and sterol-regulatory element binding protein-1c (SREBP-1c)] and a decrease in ligand-induced apoE expression. Moreover, IL-1beta and TNF-alpha significantly reduced liver X receptor response element (LXRE)-driven transcription as measured by LXRE-linked luciferase activity. However, overexpression of LXRalpha/RXRalpha only partially restored the cytokine-mediated reduction in LXRE-linked luciferase activity. Additionally, expression of the LXR coactivators peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC1alpha) and steroid receptor coactivator-2 (SRC-2) was decreased by IL-1beta or TNF-alpha. We conclude that the APR suppresses the expression of both nuclear receptors LXRalpha/RXRalpha and several LXRalpha coactivators in kidney, which could be a mechanism for coordinately regulating the expression of multiple LXR target genes that play important roles in lipid metabolism in kidney during the APR.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily G, Member 1
- ATP-Binding Cassette Transporters/metabolism
- Animals
- Apolipoproteins E/metabolism
- Blotting, Northern
- Cell Line
- Cells, Cultured
- Cytokines/metabolism
- DNA Primers/chemistry
- DNA-Binding Proteins/biosynthesis
- DNA-Binding Proteins/metabolism
- Dose-Response Relationship, Drug
- Down-Regulation
- Fatty Acids/metabolism
- Female
- Heat-Shock Proteins/metabolism
- Histone Acetyltransferases
- Humans
- Inflammation
- Interleukin-1/metabolism
- Kidney/metabolism
- Kidney Tubules/cytology
- Lipopolysaccharides/metabolism
- Liver X Receptors
- Luciferases/metabolism
- Mice
- Mice, Inbred C57BL
- Models, Statistical
- Nuclear Receptor Coactivator 1
- Orphan Nuclear Receptors
- Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha
- RNA/metabolism
- RNA, Messenger/metabolism
- Receptors, Cytoplasmic and Nuclear/biosynthesis
- Receptors, Cytoplasmic and Nuclear/metabolism
- Retinoid X Receptor alpha/metabolism
- Reverse Transcriptase Polymerase Chain Reaction
- Sterol Regulatory Element Binding Protein 1/metabolism
- Time Factors
- Transcription Factors/metabolism
- Transcription, Genetic
- Transfection
- Tumor Necrosis Factor-alpha/metabolism
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Affiliation(s)
- Yuwei Wang
- Department of Medicine, University of California San Francisco, CA 94121, USA
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31
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Zager RA, Johnson ACM, Hanson SY. Renal tubular triglyercide accumulation following endotoxic, toxic, and ischemic injury. Kidney Int 2005; 67:111-21. [PMID: 15610234 DOI: 10.1111/j.1523-1755.2005.00061.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
BACKGROUND Cholesterol accumulates in renal cortical proximal tubules in response to diverse forms of injury or physiologic stress. However, the fate of triglycerides after acute renal insults is poorly defined. This study sought new insights into this issue. METHODS CD-1 mice were subjected to three diverse models of renal stress: (1) endotoxemia [Escherichia coli lipopolysaccharide (LPS), injection]; (2) ischemia/reperfusion (I/R); or (3) glycerol-induced rhabdomyolysis. Renal cortical, or isolated proximal tubule, triglyceride levels were measured approximately 18 hours later. To gain mechanistic insights, triglyceride levels were determined in (1) proximal tubules following exogenous phospholipase A(2) (PLA(2)) treatment; (2) cultured HK-2 cells after mitochondrial blockade (antimycin A) +/- serum; or (3) HK-2 cells following "septic" (post-LPS) serum, or exogenous fatty acid (oleate) addition. RESULTS Each form of in vivo injury evoked three-to fourfold triglyceride increases in renal cortex and/or proximal tubules. PLA(2) treatment of proximal tubules evoked acute, dose-dependent, triglyceride formation. HK-2 cell triglyceride levels rose with antimycin A. With serum present, antimycin A induced an exaggerated triglyceride loading state (vs. serum alone or antimycin A alone). "Septic" serum stimulated HK-2 triglyceride formation (compared to control serum). Oleate addition caused striking HK-2 cell triglyceride accumulation. Following oleate washout, HK-2 cells were sensitized to adenosine triphosphate (ATP) depletion or oxidant attack. CONCLUSION Diverse forms of renal injury induce dramatic triglyceride loading in proximal tubules/renal cortex, suggesting that this is a component of a cell stress response. PLA(2) activity, increased triglyceride/triglyceride substrate (e.g., fatty acid) uptake, and possible systemic cytokine (e.g., from LPS) stimulation, may each contribute to this result. Finally, in addition to being a marker of prior cell injury, accumulation of triglyceride (or of its constituent fatty acids) may predispose tubules to superimposed ATP depletion or oxidant attack.
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Affiliation(s)
- Richard A Zager
- Department of Medicine, University of Washington, and Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
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32
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Smith RD, Babiychuk EB, Noble K, Draeger A, Wray S. Increased cholesterol decreases uterine activity: functional effects of cholesterol alteration in pregnant rat myometrium. Am J Physiol Cell Physiol 2005; 288:C982-8. [PMID: 15613497 DOI: 10.1152/ajpcell.00120.2004] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Uterine quiescence is essential for successful pregnancy. Cholesterol and triglycerides are markedly increased in pregnancy. Cholesterol is enriched in microdomains of the plasma membrane known as rafts and caveolae. Both lipid rafts and caveolae have been implicated in cellular signaling cascades. The purpose of this work was to investigate whether manipulation of cholesterol content alters uterine contractility. Late pregnancy (19–21 days) rats were humanely euthanized and strips of longitudinal myometrium were then dissected. Force and Ca2+ measurements were simultaneously recorded and cholesterol increased by the addition of 5 mg/ml cholesterol or 0.25 mg/ml low-density lipoproteins (LDLs) or reduced by 2% methyl-β-cyclodextrin (MCD) or 2 U/ml cholesterol oxidase addition to the perfusate. Both LDLs and cholesterol profoundly inhibited spontaneous uterine force production and associated Ca2+ transients; frequency, amplitude, and duration of contraction were all significantly reduced compared with preceding control contractions. Force and Ca2+ were also reduced by cholesterol when 1 nM oxytocin was used to stimulate the myometrium. Uterine activity was significantly increased by cholesterol extraction with MCD or cholesterol oxidase treatment. Electron microscopy confirmed the lipid raft disrupting effect of MCD, as formerly electron microscopy-visible caveolae in the myometrial cell membrane all but disappeared after MCD treatment. These data show that uterine smooth muscle cell cholesterol content is critically important for functional activity. A novel finding of our study is that cholesterol is inhibitory for force generation. It may be one of the mechanisms operating to maintain uterine quiescence throughout gestation and may also contribute to difficulties in labor suffered by obese women.
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Affiliation(s)
- R D Smith
- Dept. of Physiology, The University of Liverpool, Crown St., Liverpool, L69 3BX, UK.
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33
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Bellott AC, Patel KC, Burkholder TJ. Reduction of caveolin-3 expression does not inhibit stretch-induced phosphorylation of ERK2 in skeletal muscle myotubes. J Appl Physiol (1985) 2005; 98:1554-61. [PMID: 15516368 DOI: 10.1152/japplphysiol.01070.2004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mechanotransduction is critical to the maintenance and growth of skeletal muscle, but the mechanism by which cellular deformations are converted to biochemical signals remains unclear. Among the earliest and most ubiquitous responses to mechanical stimulation is the phosphorylation and activation of mitogen-activated protein kinases, in particular ERK2. Caveolin-3 (CAV-3) binds ERK2 and its upstream activators in inactive states on the caveolae of resting muscle. Caveolae are deformed by stretch, and it was hypothesized that this deformation might disrupt the CAV-3-dependent inhibition of ERK2 to affect stretch-induced activation. Stretch-induced phosphorylation of ERK2 in myotubes was both amplitude and velocity dependent, consistent with a viscoelastic mechanism, such as deformation of caveolae. Chemical disruption of caveolae by cholesterol depletion increased ERK2 activation by up to 176%. Small interfering RNA oligomers were then used to knock down expression of CAV-3 in cultured myotubes before mechanical stimulation, with the expectation that reducing CAV-3 expression would eliminate the stretch-induced activation of ERK2. Knockdown reduced CAV-3 protein content by 55% but did not significantly alter the stretch-induced increase in ERK2 phosphorylation, suggesting that CAV-3 is not an essential element of the mechanotransduction pathway, although the limited extent of knockdown limits the strength of this conclusion.
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Affiliation(s)
- Anne Claire Bellott
- School of Applied Physiology, Georgia Institute of Technology, 281 Ferst Dr., Atlanta, GA 30332-0356, USA
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34
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Zager RA, Johnson ACM, Hanson SY. Proximal tubular cytochrome c efflux: determinant, and potential marker, of mitochondrial injury. Kidney Int 2004; 65:2123-34. [PMID: 15149325 DOI: 10.1111/j.1523-1755.2004.00638.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND Cytochrome c (cyt c) is released from mitochondria after tissue injury, but little is known of its subsequent fate. This study was undertaken to ascertain: (1) does cyt c readily gain access to the extracellular space; (2) if so, what are some determinants of this process; and (3) might cyt c release be a potentially useful marker of in vivo tissue damage. METHODS Isolated mouse proximal tubules (PT) were subjected to site 1 (rotenone; Rot), site 2 (antimycin A, AA), or site 3 (hypoxic) respiratory chain blockade (+/- 2 mmol/L glycine, to prevent plasma membrane disruption/cell death). Alternatively, oxidant injury was imposed (Fe(2+) or cholesterol oxidase). Extra- and intracellular cyt c levels were quantified by Western blot. Plasma or urine cyt c levels were also determined after rhabdomyolysis or ischemic acute renal failure (ARF) (in mice), or clinical ARF. RESULTS AA, Rot, and hypoxia caused variable degrees of PT cyt c release (AA >> rot approximately hypoxia), but at most, <20% of total cell content was involved. In contrast, Fe(2+) evoked approximately 65% cyt c efflux, and cholesterol oxidation caused approximately 100% cyt c release. Glycine did not block cyt c efflux, dissociating this process from plasma membrane disruption/necrotic cell death. After rhabdomyolysis, plasma cyt c levels rose and correlated with the severity of ARF (r, 0.93 vs. BUNs). Cyt c was detected in urine after both experimental and clinical ARF. CONCLUSION Cell cyt c release is dependent on the site and the type of mitochondrial injury sustained. Oxidative injury, in general, and cholesterol oxidation, in particular, seem particularly relevant in this regard. After mitochondrial release, cyt c traverses plasma membranes, eventuating in the extracellular space. The data suggest that plasma and/or urine cyt c appearance might function as a clinically useful in vivo marker of mitochondrial stress and the tissue injury sustained.
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Affiliation(s)
- Richard A Zager
- Department of Medicine, University of Washington, and Fred Hutchinson Cancer Research Center, Seattle, 98109, USA.
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35
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Zager RA, Johnson ACM, Hanson SY. Proximal tubular cholesterol loading after mitochondrial, but not glycolytic, blockade. Am J Physiol Renal Physiol 2003; 285:F1092-9. [PMID: 12952856 DOI: 10.1152/ajprenal.00187.2003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Diverse forms of injury cause proximal tubular cholesterol accumulation. However, underlying mechanisms in general, and those involved with ATP depletion injury in particular, remain poorly defined. To help elucidate this issue, cholesterol homeostasis and its determinants were assessed after partial ATP depletion states. Serum-exposed HK-2 cells were subjected to mild ATP depletion, induced by mitochondrial inhibition (antimycin A; AA) or glycolytic blockade (2-deoxyglucose; DG). Four or 18 h later, cell cholesterol levels, hydroxymethylglutaryl (HMG)-CoA reductase (HMGCR), the LDL receptor (LDL-R), and ABCA1/SR-B1 cholesterol transporters were assessed. AA and DG each induced mild, largely sublethal ATP depletion injury. Each also caused significant HMGCR increments and SR-B1 decrements and left ABCA1 intact. In contrast, only AA increased the LDL-R, and only AA evoked a cholesterol-loading state (approximately 25% up). One-half of this increase was statin inhibitable, and one-half could be blocked by serum deletion, implying that both synthetic and nonsynthetic (e.g., LDL-R transport) pathways were involved. The AA-induced HMGCR and LDL-R protein changes were paralleled by their mRNAs, suggesting the presence of altered transcriptional events. We conclude that 1) sublethal ATP depletion, whether induced by mitochondrial or glycolytic blockade, can upregulate HMGCR and decrease SR-B1, and these changes represent a previously unrecognized ATP depletion "phenotype"; 2) mitochondrial blockade can also upregulate the LDL-R and evoke a cholesterol-loading state; 3) the latter likely occurs via synthetic and transport pathways; and 4) the mitochondrion may be a critical, and previously unrecognized, determinant of postinjury cell cholesterol homeostasis, potentially by impacting the LDL-R.
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Affiliation(s)
- Richard A Zager
- Fred Hutchinson Cancer Research Center, University of Washington, Rm. D2-190, 1100 Fairview Avenue N, Seattle, WA 98109, USA.
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36
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Zager RA, Johnson ACM, Hanson SY, Shah VO. Acute tubular injury causes dysregulation of cellular cholesterol transport proteins. THE AMERICAN JOURNAL OF PATHOLOGY 2003; 163:313-20. [PMID: 12819036 PMCID: PMC1868170 DOI: 10.1016/s0002-9440(10)63655-3] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 03/18/2003] [Indexed: 11/23/2022]
Abstract
Acute renal injury causes accumulation of free and esterified cholesterol (FC, CE) in proximal tubules, mediated, at least in part, by increased cholesterol synthesis. Normally, this would trigger compensatory mechanisms such as increased efflux and decreased influx to limit or reverse the cholesterol overload state. This study sought to determine the integrity of these compensatory pathways following acute renal damage. Rhabdomyolysis-induced acute renal failure was induced in mice by glycerol injection. Normal mice served as controls. After 18 hours, BUN levels and renal cortical FC/CE content were determined. Expression of ABCA-1 and SR-B1 (cholesterol efflux proteins) were assessed by Western blot. Renal cortical LDL receptor (LDL-R; a cholesterol importer) regulation was gauged by quantifying its mRNA. To obtain proximal tubule cell-specific data, the impact of oxidant (Fe) stress on cultured HK-2 cell LDL-R, SR-B1, and ABCA-1 proteins and their mRNAs (versus controls) was assessed. Glycerol evoked marked azotemia and striking FC/CE increments (44%, 384%, respectively). Paradoxically, renal cortical SR-B1 and ABCA-1 protein reductions and LDL-R mRNA increments resulted. Fe-induced injury suppressed HK-2 cell SR-B1, ABCA-1, and their mRNAs. LDL-R protein rose with the in vitro Fe challenge. Renal tubular cell injury causes dysregulation of SR-B1, ABCA-1, and LDL-R protein expression, changes which should contribute to a cholesterol overload state. Reductions in HK-2 cell SR-B1 and ABCA-1 mRNAs and increases in renal cortical LDL-R mRNA imply that this dysregulation reflects, at least in part, altered genomic/transcriptional events.
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Affiliation(s)
- Richard A Zager
- Fred Hutchinson Cancer Research Center, the University of Washington, Seattle, Washington, USA.
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37
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Mahmoudi M, Willgoss D, Cuttle L, Yang T, Pat B, Winterford C, Endre Z, Johnson DW, Gobé GC. In vivo and in vitro models demonstrate a role for caveolin-1 in the pathogenesis of ischaemic acute renal failure. J Pathol 2003; 200:396-405. [PMID: 12845636 DOI: 10.1002/path.1368] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Caveolae and their proteins, the caveolins, transport macromolecules; compartmentalize signalling molecules; and are involved in various repair processes. There is little information regarding their role in the pathogenesis of significant renal syndromes such as acute renal failure (ARF). In this study, an in vivo rat model of 30 min bilateral renal ischaemia followed by reperfusion times from 4 h to 1 week was used to map the temporal and spatial association between caveolin-1 and tubular epithelial damage (desquamation, apoptosis, necrosis). An in vitro model of ischaemic ARF was also studied, where cultured renal tubular epithelial cells or arterial endothelial cells were subjected to injury initiators modelled on ischaemia-reperfusion (hypoxia, serum deprivation, free radical damage or hypoxia-hyperoxia). Expression of caveolin proteins was investigated using immunohistochemistry, immunoelectron microscopy, and immunoblots of whole cell, membrane or cytosol protein extracts. In vivo, healthy kidney had abundant caveolin-1 in vascular endothelial cells and also some expression in membrane surfaces of distal tubular epithelium. In the kidneys of ARF animals, punctate cytoplasmic localization of caveolin-1 was identified, with high intensity expression in injured proximal tubules that were losing basement membrane adhesion or were apoptotic, 24 h to 4 days after ischaemia-reperfusion. Western immunoblots indicated a marked increase in caveolin-1 expression in the cortex where some proximal tubular injury was located. In vitro, the main treatment-induced change in both cell types was translocation of caveolin-1 from the original plasma membrane site into membrane-associated sites in the cytoplasm. Overall, expression levels did not alter for whole cell extracts and the protein remained membrane-bound, as indicated by cell fractionation analyses. Caveolin-1 was also found to localize intensely within apoptotic cells. The results are indicative of a role for caveolin-1 in ARF-induced renal injury. Whether it functions for cell repair or death remains to be elucidated.
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Affiliation(s)
- Mitra Mahmoudi
- Department of Molecular and Cellular Pathology, School of Medicine, University of Queensland, Herston, Brisbane, Australia 4006
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38
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Abstract
Evidence has accumulated over the past few years to suggest that specialized plasma membrane regions enriched in cholesterol and glycolipids, called 'lipid rafts', are primarily involved in the initiation and propagation of the signal transduction cascade associated with lymphocyte activation. Considering the multitude of recent and often contradictory data, however, it appears that a critical reconsideration of the role of lipid rafts in lymphocyte activation is necessary and timely, particularly in light of a series of new experimental results that challenge the traditional view of the role of lipid rafts in lymphocyte activation.
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Affiliation(s)
- Paola Pizzo
- Department of Biomedical Sciences, University of Padova, via G Colombo 3, 35121 Padova, Italy
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39
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Li HY, Appelbaum FR, Willman CL, Zager RA, Banker DE. Cholesterol-modulating agents kill acute myeloid leukemia cells and sensitize them to therapeutics by blocking adaptive cholesterol responses. Blood 2003; 101:3628-34. [PMID: 12506040 DOI: 10.1182/blood-2002-07-2283] [Citation(s) in RCA: 153] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mevalonate pathway produces many critical substances in cells, including sterols essential for membrane structure and isoprenoids vital to the function of many membrane proteins. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase is a rate-limiting enzyme in the mevalonate pathway. Because cholesterol is a product of this pathway, HMG-CoA reductase inhibitors (statins) are used to treat hypercholesterolemia. Statins are also toxic to several malignancies, including acute myeloid leukemia (AML). Although this toxicity has been attributed to the inhibition of Ras/Rho isoprenylation, we have previously shown that statin toxicity in primary AML cells (AMLs) does not correlate with Ras isoprenylation or with activating Ras mutations. In other studies, we have shown that hypoxic and oxidant injuries induce cholesterol increments in renal tubule cells and that statins sensitize these cells to injury by blocking protective cholesterol responses. We now demonstrate that exposing particular AMLs to radiochemotherapy induces much greater cellular cholesterol increments than those seen in similarly treated normal bone marrow. Treatment of these AMLs with mevastatin or zaragozic acid (which inhibits cholesterol synthesis but not isoprenoid synthesis) attenuates the cholesterol increments and sensitizes cells to radiochemotherapy. The extent of toxicity is affected by the availability of extracellular lipoproteins, further suggesting that cellular cholesterol is critical to cell survival in particular AMLs. Because zaragozic acid does not inhibit isoprenoid synthesis, these data suggest that cholesterol modulation is an important mechanism whereby statins exert toxic effects on some AMLs and that cholesterol modulators may improve therapeutic ratios in AML by impacting cholesterol-dependent cytoresistance.
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Affiliation(s)
- Henry Y Li
- Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109-1024, USA
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40
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Tuttle KR, Worrall NK, Dahlstrom LR, Nandagopal R, Kausz AT, Davis CL. Predictors of ARF after cardiac surgical procedures. Am J Kidney Dis 2003; 41:76-83. [PMID: 12500223 DOI: 10.1053/ajkd.2003.50025] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
BACKGROUND In a pilot study, a low preoperative serum ferritin level predicted increased risk for acute renal failure (ARF) after cardiopulmonary bypass. It was hypothesized that this may reflect a decreased ability to bind free iron and defend against oxidative stress. However, the pilot study was performed in a small number of patients (n = 30) operated on by a single surgeon. The purpose of this study was to validate whether the serum ferritin level predicts ARF in a larger sample. METHODS The present study evaluated 120 patients who underwent procedures performed by eight surgeons at another tertiary referral center. Data were collected prospectively and included patient characteristics, laboratory studies, procedure types, and postoperative course. ARF was defined as a 25% or greater increase in creatinine level 48 hours after surgery. RESULTS The frequency of ARF was 42%, but no patient required dialysis therapy. Preoperative serum ferritin levels did not differ in the groups with and without ARF (158 +/- 119 and 163 +/- 125 ng/mL, respectively), and rates of ARF did not differ when examined by ferritin quartiles. ARF was more frequent in those who underwent valve surgery (54% versus 35% in patients who did not undergo valve procedures; P = 0.044). The odds ratio for ARF after valve surgery was 2.58 (95% confidence interval, 1.06 to 6.29; P = 0.037), adjusted for longer times of surgery and aortic cross-clamp. Most excess ARF occurred in those who underwent aortic valve replacement (AVR; 62%; P = 0.014 versus nonvalve procedures). CONCLUSION Low preoperative serum ferritin level was not confirmed to predict ARF after cardiac surgery. Valve procedures, particularly AVR, increased the risk for ARF.
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Affiliation(s)
- Katherine R Tuttle
- Research Department, Heart Institute of Spokane, Seattle, WA 99204-2340, USA.
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41
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Johnson ACM, Yabu JM, Hanson S, Shah VO, Zager RA. Experimental glomerulopathy alters renal cortical cholesterol, SR-B1, ABCA1, and HMG CoA reductase expression. THE AMERICAN JOURNAL OF PATHOLOGY 2003; 162:283-91. [PMID: 12507911 PMCID: PMC1851117 DOI: 10.1016/s0002-9440(10)63819-9] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 09/30/2002] [Indexed: 11/16/2022]
Abstract
Previous studies indicate that acute tubular injury causes free cholesterol (FC) and cholesteryl ester (CE) accumulation within renal cortex/proximal tubules. This study assessed whether similar changes occur with glomerulopathy/nephrotic syndrome, in which high-circulating/filtered lipoprotein levels increase renal cholesterol supply. Potential adaptive changes in cholesterol synthetic/transport proteins were also assessed. Nephrotoxic serum (NTS) or passive Heymann nephritis (PHN) was induced in Sprague-Dawley rats. Renal injury (blood urea nitrogen, proteinuria) was assessed 2 and 7 days (NTS), or 10 and 30 days (PHN) later. FC and CE levels in renal cortex, isolated glomeruli, and proximal tubule segments were determined. SR-B1 (a CE influx protein), ABCA1 (a FC exporter), and HMG CoA reductase protein/mRNA levels were also assessed. FC was minimally elevated in renal cortex (0 to 15%), the majority apparently localizing to proximal tubules. More dramatic CE elevations were found ( approximately 5 to 15x), correlating with the severity of proteinuria at any single time point (r >/= 0.85). Cholesterol increments were associated with decreased SR-B1, increased ABCA1, and increased HMG CoA reductase (HMGCR) protein and its mRNA. Tubule (HK-2) cell culture data indicated that SR-B1 and ABCA1 levels are responsive to cholesterol supply. Experimental nephropathy can increase renal FC, and particularly CE, levels, most notably in proximal tubules. These changes are associated with adaptations in SR-B1 and ABCA1 expression, which are physiologically appropriate changes for a cholesterol overload state. However, HMGCR protein/mRNA increments can also result. These seem to reflect a maladaptive response, potentially contributing to a cell cholesterol overload state.
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MESH Headings
- ATP Binding Cassette Transporter 1
- ATP-Binding Cassette Transporters/metabolism
- Animals
- Blotting, Western
- CD36 Antigens/metabolism
- Cell Line
- Cholesterol/metabolism
- Cholesterol Esters/metabolism
- Disease Models, Animal
- Disease Progression
- Glomerulonephritis/metabolism
- Glomerulonephritis/pathology
- Humans
- Hydroxymethylglutaryl CoA Reductases/genetics
- Hydroxymethylglutaryl CoA Reductases/metabolism
- Kidney Cortex/metabolism
- Kidney Cortex/pathology
- Kidney Function Tests
- Kidney Tubules, Proximal/cytology
- Kidney Tubules, Proximal/metabolism
- Male
- Membrane Proteins
- RNA, Messenger/metabolism
- Rats
- Rats, Sprague-Dawley
- Receptors, Immunologic
- Receptors, Lipoprotein
- Receptors, Scavenger
- Scavenger Receptors, Class B
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Affiliation(s)
- Ali C M Johnson
- Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA
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42
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Zager RA, Johnson ACM, Hanson SY. Sepsis syndrome stimulates proximal tubule cholesterol synthesis and suppresses the SR-B1 cholesterol transporter. Kidney Int 2003; 63:123-33. [PMID: 12472775 DOI: 10.1046/j.1523-1755.2003.00735.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Previous studies demonstrate that renal cortical/proximal tubule cholesterol accumulation is part of the renal "stress response." The present study was performed to help define underlying mechanisms, using experimental sepsis as a test model. METHODS Male CD-1 mice and female low-density lipoprotein receptor (LDLR) knockout mice were injected with a heat-killed Escherichia coli suspension. Renal cortex and serum were obtained from these and control mice either 4, 6, or 18 hours later. Tissues samples were assayed for free cholesterol (FC), cholesteryl esters (CE), HMG CoA reductase (HMGCR) mRNA, and SR-B1 [the high-density lipoprotein (HDL) receptor/cholesterol transporter]. Statin effects on renal cortical HMGCR mRNA and FC/CE levels also were assessed. Finally, the impact of serum from septic versus normal mice on cultured proximal tubule (HK-2) cell cholesterol levels was assessed. RESULTS Sepsis induced approximately 30% and 300 to 500% increases in renal FC and CE content, respectively. Cholesterol accumulation was not blunted in LDLR-/- mice versus their controls. Statin therapy also did not alter sepsis-induced renal FC/CE accumulation. However, statin treatment exerted no discernible intra-renal activity (for example, no rise in renal HMGCR mRNA), despite significant extra-renal activity (25% reduction in serum cholesterol; 400% increase in hepatic HMGCR mRNA). HK-2 cells exposed to septic serum sustained a 40% cholesterol increase, compared to cells exposed to control serum. This response was completely statin inhibited, proving that de novo synthesis was involved. Sepsis markedly suppressed renal levels of SR-B1 (an FC efflux protein). Renal HMGCR mRNA did not fall despite sepsis triggered cholesterol loading, indicating a failure of negative feedback activity. CONCLUSIONS Sepsis-induced renal cholesterol accumulation is not simply an intrinsic renal response, since it can be enhanced by circulating "stress factors" that drive HMGCR activity. Sepsis also down-regulates SR-B1. Thus, decreased cell FC efflux, coupled with increased synthesis, may synergistically induce the post-sepsis cholesterol overload state.
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MESH Headings
- Animals
- Atorvastatin
- Blood Proteins/pharmacology
- CD36 Antigens/genetics
- CD36 Antigens/metabolism
- Cholesterol/biosynthesis
- Cholesterol/blood
- Escherichia coli
- Female
- Gene Expression/drug effects
- Heptanoic Acids/pharmacology
- Hydroxymethylglutaryl CoA Reductases/genetics
- Hydroxymethylglutaryl-CoA Reductase Inhibitors/pharmacology
- Kidney Cortex/metabolism
- Kidney Cortex/physiopathology
- Kidney Tubules, Proximal/cytology
- Kidney Tubules, Proximal/metabolism
- Kidney Tubules, Proximal/physiopathology
- Male
- Membrane Proteins
- Mice
- Mice, Inbred Strains
- Mice, Knockout
- Pyrroles/pharmacology
- RNA, Messenger/analysis
- Receptors, Immunologic
- Receptors, LDL/genetics
- Receptors, Lipoprotein
- Receptors, Scavenger
- Scavenger Receptors, Class B
- Systemic Inflammatory Response Syndrome/metabolism
- Systemic Inflammatory Response Syndrome/physiopathology
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Affiliation(s)
- Richard A Zager
- Department of Medicine, University of Washington, and the Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
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43
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Zager RA, Shah VO, Shah HV, Zager PG, Johnson ACM, Hanson S. The mevalonate pathway during acute tubular injury: selected determinants and consequences. THE AMERICAN JOURNAL OF PATHOLOGY 2002; 161:681-92. [PMID: 12163393 PMCID: PMC1850732 DOI: 10.1016/s0002-9440(10)64224-1] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 05/13/2002] [Indexed: 02/04/2023]
Abstract
Renal injury evokes tubular cholesterol accumulation, mediated in part by increased HMG CoA reductase (HMGCR) levels. The present study was undertaken to define potential molecular determinants of these changes and to ascertain the relative importance of increased cholesterol production versus mevalonate pathway-driven protein prenylation, on the emergence of the so-called postrenal injury "cytoresistant state." Cultured proximal tubule (HK-2) cells were subjected to Fe or ATP depletion injury, followed 1 to 24 hours later by assessments of: 1) sterol transcription factor expression (SREBP)-1 and -2); 2) HMGCR mRNA levels; and 3) Ras/Rho prenylation. HMGCR mRNA and Ras/Rho prenylation were also assessed after in vivo ischemic and Fe-mediated renal damage. Using specific inhibitors, the relative importance of protein prenylation versus terminal cholesterol synthesis on HK-2 cell susceptibility to injury was also assessed. Acute injury induced HK-2 cell SREBP disruption and reductions in HMGCR mRNA. Renal cortical HMGCR mRNA also fell in response to either in vivo ischemic or Fe-mediated oxidant damage. At 24 hours after in vitro/in vivo injury, a time of cholesterol buildup, no increase in Ras/Rho prenylation was observed. Prenylation inhibitors did not sensitize HK-2 cells to injury. Conversely, squalene synthase (terminal cholesterol synthesis) blockade sensitized HK-2 cells to both Fe and ATP depletion attack. We concluded that: 1) acute tubular cell injury can destroy SREBPs and lower HMGCR mRNA. This suggests that posttranscriptional/translational events are responsible for HMGCR enzyme and cholesterol accumulation after renal damage. 2) Injury-induced cholesterol accumulation appears dissociated from increased protein prenylation. 3) Cholesterol accumulation, per se, seems to be the dominant mechanism by which the mevalonate pathway contributes to the postrenal injury cytoresistant state.
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Affiliation(s)
- Richard A Zager
- Department of Medicine, the University of Washington, and the Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA.
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Zager RA, Johnson A, Hanson S, dela Rosa V. Altered cholesterol localization and caveolin expression during the evolution of acute renal failure. Kidney Int 2002; 61:1674-83. [PMID: 11967017 DOI: 10.1046/j.1523-1755.2002.00316.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Renal cortical/proximal tubule cholesterol accumulation, with preferential localization within plasma membrane "detergent resistant microdomains" (DRMs: rafts/caveolae), is a hallmark of the maintenance phase of acute renal failure (ARF). This study addressed two related issues: (1) Are maintenance-phase cholesterol increases accompanied by an up-regulation of caveolin, a DRM/caveolar-associated cholesterol binding protein? (2) Is DRM cholesterol/caveolin homeostasis acutely altered during the induction phase of ARF? METHODS Mouse kidneys were subjected to ischemia +/- reperfusion (I/R) followed by assessment of cholesterol DRM partitioning. Acute cell injury effects on potential caveolin release from isolated proximal tubules or into urine also were assessed. Finally, renal cortical/isolated proximal tubule caveolin levels were determined 18 hours after I/R or myoglobinuric ARF. RESULTS Acute ischemia causes a rapid shift of cholesterol into cortical DRMs (>22%). Cholesterol migration into DRMs also was observed in ATP-depleted cultured proximal tubule (HK-2) cells. Acute hypoxic or toxic tubule injury induced plasma membrane caveolin release (Western blot). By the maintenance phase of ARF, marked renal cortical/proximal tubule caveolin increases resulted. CONCLUSIONS Acute proximal tubular injury damages caveolar/DRM structures, as determined by cholesterol maldistribution and caveolin release. Post-injury, there is a dramatic up-regulation of renal cortical/proximal tubule caveolin, suggesting an increased caveolar mass. These findings indicate, to our knowledge for the first time, that dysregulation of caveolae/raft microdomain expression is a correlate of, and potential participant in, the induction and maintenance phases of ischemic and toxic forms of experimental ARF.
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Affiliation(s)
- Richard A Zager
- Department of Medicine, University of Washington, and Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA.
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Wellington CL, Walker EKY, Suarez A, Kwok A, Bissada N, Singaraja R, Yang YZ, Zhang LH, James E, Wilson JE, Francone O, McManus BM, Hayden MR. ABCA1 mRNA and protein distribution patterns predict multiple different roles and levels of regulation. J Transl Med 2002; 82:273-83. [PMID: 11896206 DOI: 10.1038/labinvest.3780421] [Citation(s) in RCA: 227] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Mutations in ABCA1 cause the allelic disorders familial hypolipoproteinemia and Tangier Disease. To identify where ABCA1 was likely to have a functional role, we determined the cellular and tissue-specific patterns of murine ABCA1 expression. RT-PCR and Western blot analysis on dissected murine tissues demonstrated broad expression of ABCA1 mRNA and protein in many tissues with prominent protein expression in liver, testis, and adrenal tissue. In situ hybridization and immunohistochemistry experiments demonstrated specific patterns of ABCA1 expression at the cellular level, with hepatocytes, the epithelial lining of the digestive system and bladder, the proximal convoluted tubule of the kidney, and Purkinje and cortical pyramidal neurons containing abundant ABCA1 protein. Significant discordance between relative mRNA and protein expression patterns suggests the possibility of post-transcriptional regulation of ABCA1 expression in selected cells or tissues. We also show that ABCA1 protein levels are up-regulated specifically in the liver after exposure to an atherogenic diet for 7 days, supporting a major role for the liver in dietary modulation of HDL-C levels. Our observations show that ABCA1 is expressed in a pattern consistent with its role in HDL-C metabolism. Additionally, ABCA1 may have important functional roles in other cell types independent of HDL-C regulation.
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Affiliation(s)
- Cheryl L Wellington
- Centre for Molecular Medicine and Therapeutics, St. Paul's Hospital/Providence Health Care-University of British Columbia, Canada
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Zager RA, Johnson A. Renal cortical cholesterol accumulation is an integral component of the systemic stress response. Kidney Int 2001; 60:2299-310. [PMID: 11737603 DOI: 10.1046/j.1523-1755.2001.00071.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Direct tubular injury (such as ischemia or myohemoglobinuria) increases renal cortical cholesterol content. This study explored whether systemic forms of stress (such as heat shock or sepsis) can trigger renal cholesterol accumulation, and if so, whether increased 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (HMGCR) expression might be involved. METHODS Male CD-1 mice were subjected to glycerol-induced myohemoglobinuria (MH), systemic heat shock (HS), or E. coli sepsis. Free cholesterol (FC), cholesteryl esters (CE), and HMGCR (Western blot) levels were assessed 18 hours later. Statin effects on renal cholesterol levels and on the severity of MH-acute renal failure (ARF) were also determined. RESULTS Sepsis and HS each induced dramatic FC and CE increments, comparable to those observed with myohemoglobinuria, and without inducing acute tubular necrosis (ATN). Part of the cholesterol increments was localized within plasma membrane (detergent resistant) microdomains (for example, rafts/caveolae). HS and MH each increased renal HMGCR, as well as HS protein (HSP-72) expression. Oxidant stress (Fe) imposed on cultured proximal tubule (HK-2) cells also enhanced HMGCR content. Conversely, sepsis did not raise renal HMGCR or HSP-72 levels. Statin therapy decreased the severity of MH-ARF and renal cholesterol content. However, this appeared to arise from a statin-mediated decrease in glycerol-induced extrarenal tissue damage (myolysis/LDH release). CONCLUSIONS Cholesterol appears to be a renal 'acute phase reactant' with tissue levels increasing with either systemic stress (such as, heat shock, sepsis), or direct tissue damage (such as ATN). Increased HMGCR expression can contribute to this result. Mechanisms other than HMGCR induction also can mediate stress-induced cholesterol increments (for example, in the case of sepsis), and statins can mitigate MH-ARF. However, systemic anti-inflammatory effects, rather than a primary renal action, appear more likely to be involved.
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Affiliation(s)
- R A Zager
- Department of Medicine, University of Washington, and Fred Hutchinson Cancer Research Center, Seattle,Washington 98109-1024, USA.
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Abstract
BACKGROUND MDR P glycoproteins may help transport plasma membrane free cholesterol (FC) to the endoplasmic reticulum (ER), where it undergoes acylation, forming cholesterol esters (CE). This study assessed whether P glycoprotein inhibitors alter renal tubular FC/CE expression, thereby altering cell integrity. METHODS Mouse proximal tubule segments (PTS) were exposed to chemically dissimilar P glycoprotein inhibitors [progesterone (prog), trifluoperazine (TFP), or cyclosporine A (CsA)]. Their effects on FC/CE and adenosine 5'-triphosphate (ATP) levels, phospholipid expression, lipid peroxidation, and cell viability (lactate dehydrogenase release; LDH) were assessed. P glycoprotein inhibitor effects on cultured proximal tubular (HK-2) cell viability and susceptibility to Fe-induced oxidant stress were also addressed. RESULTS When applied to PTS, prog, TFP, and, to lesser extent, CsA induced dose-dependent ATP reductions (< or =90%), CE decrements (approximately 40%), and LDH release (< or =60%). No concomitant changes in lipid peroxidation or phospholipid profiles were observed. Ouabain did not preserve tubular ATP, suggesting that decreased ATP production, rather than increased consumption, was operative. Mechanisms leading to cell lysis were not identical, as glycine and arachidonic acid blocked prog- but not TFP-mediated cell death. When prog-driven CE reductions were attenuated in PTS with a procycling agent (cholesterol oxidase), decreased cell death resulted. P glycoprotein inhibitors also caused dose-dependent HK-2 cell death. Blocking Fe-mediated CE formation ( approximately x10) with sublethal CsA doses led to a marked increase in Fe-mediated cell death. CONCLUSIONS P glycoproteins may be critical to tubule cholesterol transport. If blocked with pharmacologic agents, decreased ATP production, overt cell lysis, and/or a marked propensity to superimposed tubular cell injury can result.
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Affiliation(s)
- R A Zager
- Department of Medicine, University of Washington, Seattle, Washington, USA.
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Samuel BU, Mohandas N, Harrison T, McManus H, Rosse W, Reid M, Haldar K. The Role of Cholesterol and Glycosylphosphatidylinositol-anchored Proteins of Erythrocyte Rafts in Regulating Raft Protein Content and Malarial Infection. J Biol Chem 2001; 276:29319-29. [PMID: 11352913 DOI: 10.1074/jbc.m101268200] [Citation(s) in RCA: 152] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human erythrocytes are terminally differentiated, nonendocytic cells that lack all intracellular organelles. Here we show that their plasma membranes contain detergent-resistant membrane rafts that constitute a small fraction (4%) of the total membrane protein, with a complex mixture of proteins that differentially associate with rafts. Depletion of raft-cholesterol abrogates association of all proteins with no significant effect on cholesterol:protein ratios in the rest of the membrane, lipid asymmetry, deformability, or transport properties of the bilayer, indicating that cholesterol is critical for protein assembly into rafts and suggesting that rafts have little influence on several erythrocyte functions. Erythrocytes from patients with paroxysmal nocturnal hemoglobinuria, which lack glycosylphosphatidylinositol-anchored proteins, show significant elevation in raft-cholesterol but no increase in raft protein association, suggesting that raft assembly does not require glycosylphosphatidylinositol-anchored proteins, raft proteins do not bind directly to cholesterol, and only threshold levels of raft-cholesterol are critical for protein recruitment. Loss of glycosylphosphatidylinositol-anchored proteins had no effect on erythrocytic infection by malarial parasite or movement of raft markers into the parasite's vacuole. However, infection is blocked following raft-cholesterol disruption, suggesting that erythrocyte rafts can be functionally exploited and providing the first evidence for the involvement of host rafts in an apicomplexan infection.
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Affiliation(s)
- B U Samuel
- Department of Pathology, Northwestern University, Chicago, Illinois 60611, USA
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Zager RA, Andoh T, Bennett WM. Renal cholesterol accumulation: a durable response after acute and subacute renal insults. THE AMERICAN JOURNAL OF PATHOLOGY 2001; 159:743-52. [PMID: 11485932 PMCID: PMC1850565 DOI: 10.1016/s0002-9440(10)61745-2] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 05/03/2001] [Indexed: 01/31/2023]
Abstract
UNLABELLED Proximal tubular cholesterol levels rise within 18 hours of diverse forms of acute renal tubular injury (eg, myoglobinuria, ischemia/reperfusion, urinary tract obstruction). These increments serve to protect against further bouts of tubular attack (so-called "acquired cytoresistance"). Whether these cholesterol increments are merely transitory, or persist into the maintenance phase of acute renal failure (ARF), has not been previously defined. Furthermore, whether subacute/insidious tubular injury [eg, cyclosporine A (CSA), tacrolimus toxicity], nontubular injury (eg, acute glomerulonephritis), or physiological stress (eg, mild dehydration) impact renal cholesterol homeostasis have not been addressed. This study sought to resolve these issues. Male CD-1 mice were subjected to glycerol-induced ARF. Renal cortical-free cholesterol (FC) and cholesterol ester (CE) levels were determined 3, 5, 7, or 14 days later, and the values contrasted to prevailing blood-urea nitrogen concentrations. The impact of 40 minutes of unilateral renal ischemia plus reflow (3 to 6 days) on mouse cortical FC/CE content was also assessed. Additionally, FC/CE levels were measured in rat renal cortex either 10 days after CSA or tacrolimus therapy, or 48 hours after induction of nephrotoxic serum nephritis. Finally, the impact of overnight dehydration on mouse renal cortical/medullary FC/CE profiles was determined. Compared to sham-treated animals, glycerol, CSA, tacrolimus, ischemia-reperfusion, and nephrotoxic serum each induced dramatic CE +/- FC elevations, rising as much as 10x control values. In the glycerol model, striking correlations (r = 0.99) between FC/CE and blood-urea nitrogen levels were observed. The FC/CE increases were specific to damaged kidney (glycerol did not raise hepatic FC/CE; unilateral renal ischemia did not alter contralateral renal FC/CE levels). Overnight dehydration raised renal CE levels, most notably in the medulla. CONCLUSIONS FC/CE accumulation is a hallmark of the maintenance phase of ischemic and nephrotoxic ARF, and can reflect its severity. That cholesterol accumulation can result from glomerular injury and dehydration suggests that it is a generic renal stress response, with potential relevance extending beyond just the phenomenon of acquired cytoresistance.
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Affiliation(s)
- R A Zager
- Department of Medicine, Fred Hutchinson Cancer Center, University of Washington, 1100 Fairview Ave. N, Rm. D2-190, Seattle, WA 98109, USA.
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Zager RA, Johnson A, Anderson K, Wright S. Cholesterol ester accumulation: an immediate consequence of acute in vivo ischemic renal injury. Kidney Int 2001; 59:1750-61. [PMID: 11318945 DOI: 10.1046/j.1523-1755.2001.0590051750.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Cholesterol is a major constituent of plasma membranes, and recent evidence indicates that it is up-regulated during the maintenance phase of acute renal failure (ARF). However, cholesterol's fate and that of the cholesterol ester (CE) cycle [shuttling between free cholesterol (FC) and CEs] during the induction phase of ARF have not been well defined. The present studies sought to provide initial insights into these issues. METHODS FC and CE were measured in mouse renal cortex after in vivo ischemia (15 and 45 minutes)/reperfusion (0 to 120 minutes) and glycerol-induced myoglobinuria (1 to 2 hours). FC/CE were also measured in (1) cultured human proximal tubule (HK-2) cells three hours after ATP depletion and in (2) isolated mouse proximal tubule segments (PTSs) subjected to plasma membrane damage (with cholesterol oxidase, sphingomyelinase, phospholipase A2, or cytoskeletal disruption with cytochalasin B). The impact of cholesterol synthesis inhibition (with mevastatin) and FC traffic blockade (with progesterone) on injury-evoked FC/CE changes was also assessed. RESULTS In vivo ischemia caused approximately threefold to fourfold CE elevations, but not FC elevations, that persisted for at least two hours of reperfusion. Conversely, myoglobinuria had no effect. Isolated CE increments were observed in ATP-depleted HK-2 cells. Neither mevastatin nor progesterone blocked this CE accumulation. Plasma membrane injury induced with sphingomyelinase or cholesterol oxidase, but not with phospholipase A(2) or cytochalasin B, increased tubule CE content. High CE levels, induced with cholesterol oxidase, partially blocked hypoxic PTS attack. CONCLUSIONS In vivo ischemia/reperfusion acutely increases renal cortical CE, but not FC, content, indicating perturbed CE/FC cycling. The available data suggest that this could stem from specific types of plasma membrane damage, which then increase FC flux via aberrant pathways to the endoplasmic reticulum, where CE formation occurs. That CE levels are known to inversely correlate with both renal and nonrenal cell injury suggests the potential relevance of these observations to the induction phase of ischemic ARF.
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Affiliation(s)
- R A Zager
- University of Washington and Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA.
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