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Faivre A, Bugarski M, Rinaldi A, Sakhi IB, Verissimo T, Legouis D, Rutkowski JM, Correia S, Kaminska M, Dalga D, Malpetti D, Cippa PE, de Seigneux S, Hall AM. Spatiotemporal Landscape of Kidney Tubular Responses to Glomerular Proteinuria. J Am Soc Nephrol 2024; 35:854-869. [PMID: 38652545 PMCID: PMC11230716 DOI: 10.1681/asn.0000000000000357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Accepted: 04/12/2024] [Indexed: 04/25/2024] Open
Abstract
Key Points
Glomerular proteinuria induces large-scale changes in gene expression along the nephron.Increased protein uptake in the proximal tubule results in axial remodeling and injury.Increased protein delivery to the distal tubule causes dedifferentiation of the epithelium.
Background
Large increases in glomerular protein filtration induce major changes in body homeostasis and are associated with a higher risk of kidney functional decline and cardiovascular disease. We investigated how elevated protein exposure modifies the landscape of tubular function along the entire nephron, to understand the cellular changes that mediate these important clinical phenomena.
Methods
We conducted single-nucleus RNA sequencing, functional intravital imaging, and antibody staining to spatially map transport processes along the mouse kidney tubule. We then delineated how these were altered in a transgenic mouse model of inducible glomerular proteinuria (POD-ATTAC) at 7 and 28 days.
Results
Glomerular proteinuria activated large-scale and pleiotropic changes in gene expression in all major nephron sections. Extension of protein uptake from early (S1) to later (S2) parts of the proximal tubule initially triggered dramatic expansion of a hybrid S1/2 population, followed by injury and failed repair, with the cumulative effect of loss of canonical S2 functions. Proteinuria also induced acute injury in S3. Meanwhile, overflow of luminal proteins to the distal tubule caused transcriptional convergence between specialized regions and generalized dedifferentiation.
Conclusions
Proteinuria modulated cell signaling in tubular epithelia and caused distinct patterns of remodeling and injury in a segment-specific manner.
Podcast
This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/JASN/2024_05_01_ASN0000000000000357.mp3
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Affiliation(s)
- Anna Faivre
- Department of Medicine and Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
| | - Milica Bugarski
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Anna Rinaldi
- Laboratories for Translational Research, Ente Ospedaliero Cantonale, Bellinzona, Switzerland
- Division of Nephrology, Department of Medicine, Ente Ospedaliero Cantonale, Lugano, Switzerland
| | - Imene B Sakhi
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Thomas Verissimo
- Department of Medicine and Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
| | - David Legouis
- Department of Medicine and Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
- Division of Intensive Care, Department of Acute Medicine, University Hospital of Geneva, Geneva, Switzerland
| | | | - Sara Correia
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Monika Kaminska
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Delal Dalga
- Department of Medicine and Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
| | - Daniele Malpetti
- Istituto Dalle Molle di Studi sull'Intelligenza Artificiale (IDSIA), USI/SUPSI, Lugano, Switzerland
| | - Pietro E Cippa
- Laboratories for Translational Research, Ente Ospedaliero Cantonale, Bellinzona, Switzerland
- Division of Nephrology, Department of Medicine, Ente Ospedaliero Cantonale, Lugano, Switzerland
| | - Sophie de Seigneux
- Department of Medicine and Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
- Department of Medicine, Service of Nephrology, Geneva University Hospitals, Geneva, Switzerland
| | - Andrew M Hall
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
- Department of Nephrology, University Hospital Zurich, Zurich, Switzerland
- Zurich Kidney Center, Zurich, Switzerland
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Burmakin M, Gilmour PS, Gram M, Shushakova N, Sandoval RM, Molitoris BA, Larsson TE. Therapeutic α-1-microglobulin ameliorates kidney ischemia-reperfusion injury. Am J Physiol Renal Physiol 2024; 327:F103-F112. [PMID: 38779750 DOI: 10.1152/ajprenal.00067.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2024] [Revised: 04/12/2024] [Accepted: 04/30/2024] [Indexed: 05/25/2024] Open
Abstract
α-1-Microglobulin (A1M) is a circulating glycoprotein with antioxidant, heme-binding, and mitochondrial protection properties. The investigational drug RMC-035, a modified therapeutic A1M protein, was assessed for biodistribution and pharmacological activity in a broad set of in vitro and in vivo experiments, supporting its clinical development. Efficacy and treatment posology were assessed in various models of kidney ischemia and reperfusion injury (IRI). Real-time glomerular filtration rate (GFR), functional renal biomarkers, tubular injury biomarkers (NGAL and KIM-1), and histopathology were evaluated. Fluorescently labeled RMC-035 was used to assess biodistribution. RMC-035 demonstrated consistent and reproducible kidney protection in rat IRI models as well as in a model of IRI imposed on renal impairment and in a mouse IRI model, where it reduced mortality. Its pharmacological activity was most pronounced with combined dosing pre- and post-ischemia and weaker with either pre- or post-ischemia dosing alone. RMC-035 rapidly distributed to the kidneys via glomerular filtration and selective luminal uptake by proximal tubular cells. IRI-induced expression of kidney heme oxygenase-1 was inhibited by RMC-035, consistent with its antioxidative properties. RMC-035 also dampened IRI-associated inflammation and improved mitochondrial function, as shown by tubular autofluorescence. Taken together, the efficacy of RMC-035 is congruent with its targeted mechanism(s) and biodistribution profile, supporting its further clinical evaluation as a novel kidney-protective therapy.NEW & NOTEWORTHY A therapeutic A1M protein variant (RMC-035) is currently in phase 2 clinical development for renal protection in patients undergoing open-chest cardiac surgery. It targets several key pathways underlying kidney injury in this patient group, including oxidative stress, heme toxicity, and mitochondrial dysfunction. RMC-035 is rapidly eliminated from plasma, distributing to kidney proximal tubules, and demonstrates dose-dependent efficacy in numerous models of ischemia-reperfusion injury, particularly when administered before ischemia. These results support its continued clinical evaluation.
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Affiliation(s)
- Mikhail Burmakin
- Division of Pathology, Department of Laboratory Medicine, Karolinska Institute, Huddinge, Sweden
- Guard Therapeutics International AB, Stockholm, Sweden
| | | | - Magnus Gram
- Pediatrics, Department of Clinical Sciences Lund, Lund University, Lund, Sweden
- Department of Neonatology, Skåne University Hospital, Lund, Sweden
- Biofilms - Research Center for Biointerfaces, Department of Biomedical Science, Faculty of Health and Society, Malmö University, Malmö, Sweden
| | - Nelli Shushakova
- Renal Disease and Transplantation, Phenos GmbH, Hannover, Germany
- Department of Nephrology, Hannover Medical School, Hannover, Germany
| | - Ruben M Sandoval
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | - Bruce A Molitoris
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | - Tobias E Larsson
- Guard Therapeutics International AB, Stockholm, Sweden
- Division of Nephrology, Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Huddinge, Sweden
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Gnaiger E. Complex II ambiguities-FADH 2 in the electron transfer system. J Biol Chem 2024; 300:105470. [PMID: 38118236 PMCID: PMC10772739 DOI: 10.1016/j.jbc.2023.105470] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Revised: 11/01/2023] [Accepted: 11/06/2023] [Indexed: 12/22/2023] Open
Abstract
The prevailing notion that reduced cofactors NADH and FADH2 transfer electrons from the tricarboxylic acid cycle to the mitochondrial electron transfer system creates ambiguities regarding respiratory Complex II (CII). CII is the only membrane-bound enzyme in the tricarboxylic acid cycle and is part of the electron transfer system of the mitochondrial inner membrane feeding electrons into the coenzyme Q-junction. The succinate dehydrogenase subunit SDHA of CII oxidizes succinate and reduces the covalently bound prosthetic group FAD to FADH2 in the canonical forward tricarboxylic acid cycle. However, several graphical representations of the electron transfer system depict FADH2 in the mitochondrial matrix as a substrate to be oxidized by CII. This leads to the false conclusion that FADH2 from the β-oxidation cycle in fatty acid oxidation feeds electrons into CII. In reality, dehydrogenases of fatty acid oxidation channel electrons to the Q-junction but not through CII. The ambiguities surrounding Complex II in the literature and educational resources call for quality control, to secure scientific standards in current communications of bioenergetics, and ultimately support adequate clinical applications. This review aims to raise awareness of the inherent ambiguity crisis, complementing efforts to address the well-acknowledged issues of credibility and reproducibility.
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Bordoni L, Kristensen AM, Sardella D, Kidmose H, Pohl L, Krag SRP, Schiessl IM. Longitudinal tracking of acute kidney injury reveals injury propagation along the nephron. Nat Commun 2023; 14:4407. [PMID: 37479698 PMCID: PMC10362041 DOI: 10.1038/s41467-023-40037-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Accepted: 07/10/2023] [Indexed: 07/23/2023] Open
Abstract
Acute kidney injury (AKI) is an important risk factor for chronic kidney disease (CKD), but the underlying mechanisms of failed tubule repair and AKI-CKD transition are incompletely understood. In this study, we aimed for dynamic tracking of tubule injury and remodeling to understand if focal injury upon AKI may spread over time. Here, we present a model of AKI, in which we rendered only half of the kidney ischemic. Using serial intravital 2-photon microscopy and genetic identification of cycling cells, we tracked dynamic tissue remodeling in post- and non-ischemic kidney regions simultaneously and over 3 weeks. Spatial and temporal analysis of cycling cells relative to initial necrotic cell death demonstrated pronounced injury propagation and expansion into non-necrotic tissue regions, which predicted tubule atrophy with epithelial VCAM1 expression. In summary, our longitudinal analyses of tubule injury, remodeling, and fate provide important insights into AKI pathology.
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Affiliation(s)
- Luca Bordoni
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
- GliaLab and Letten Centre, Division of Anatomy, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
| | | | - Donato Sardella
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Hanne Kidmose
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Layla Pohl
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
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Choi J, Choi MS, Jeon J, Moon J, Lee J, Kong E, Lucia SE, Hong S, Lee JH, Lee EY, Kim P. In vivo longitudinal 920 nm two-photon intravital kidney imaging of a dynamic 2,8-DHA crystal formation and tubular deterioration in the adenine-induced chronic kidney disease mouse model. BIOMEDICAL OPTICS EXPRESS 2023; 14:1647-1658. [PMID: 37078028 PMCID: PMC10110322 DOI: 10.1364/boe.485187] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Revised: 03/01/2023] [Accepted: 03/20/2023] [Indexed: 05/03/2023]
Abstract
Chronic kidney disease (CKD) is one of the most common renal diseases manifested by gradual loss of kidney function with no symptoms in the early stage. The underlying mechanism in the pathogenesis of CKD with various causes such as high blood pressure, diabetes, high cholesterol, and kidney infection is not well understood. In vivo longitudinal repetitive cellular-level observation of the kidney of the CKD animal model can provide novel insights to diagnose and treat the CKD by visualizing the dynamically changing pathophysiology of CKD with its progression over time. In this study, using two-photon intravital microscopy with a single 920 nm fixed-wavelength fs-pulsed laser, we longitudinally and repetitively observed the kidney of an adenine diet-induced CKD mouse model for 30 days. Interestingly, we could successfully visualize the 2,8-dihydroxyadenine (2,8-DHA) crystal formation with a second-harmonics generation (SHG) signal and the morphological deterioration of renal tubules with autofluorescence using a single 920 nm two-photon excitation. The longitudinal in vivo two-photon imaging results of increasing 2,8-DHA crystals and decreasing tubular area ratio visualized by SHG and autofluorescence signal, respectively, were highly correlated with the CKD progression monitored by a blood test showing increased cystatin C and blood urea nitrogen (BUN) levels over time. This result suggests the potential of label-free second-harmonics generation crystal imaging as a novel optical technique for in vivo CKD progression monitoring.
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Affiliation(s)
- Jieun Choi
- Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- KI for Health Science and Technology (KIHST), Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Min-Sun Choi
- Department of Internal Medicine, Soonchunhyang University Cheonan Hospital, Cheonan, 31151, Republic of Korea
- BK21 Four Project, College of Medicine, Soonchunhyang University, Cheonan, 31151, Republic of Korea
| | - Jehwi Jeon
- Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- KI for Health Science and Technology (KIHST), Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Jieun Moon
- KI for Health Science and Technology (KIHST), Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Jingu Lee
- KI for Health Science and Technology (KIHST), Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Eunji Kong
- Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- KI for Health Science and Technology (KIHST), Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Stephani Edwina Lucia
- Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- KI for Health Science and Technology (KIHST), Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Sujung Hong
- KI for Health Science and Technology (KIHST), Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
| | - Ji-Hye Lee
- Department of Pathology, Soonchunhyang University Cheonan Hospital, Cheonan, 31151, Republic of Korea
| | - Eun Young Lee
- Department of Internal Medicine, Soonchunhyang University Cheonan Hospital, Cheonan, 31151, Republic of Korea
- BK21 Four Project, College of Medicine, Soonchunhyang University, Cheonan, 31151, Republic of Korea
- Institute of Tissue Regeneration, College of Medicine, Soonchunhyang University, Cheonan, 31151, Republic of Korea
| | - Pilhan Kim
- Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- KI for Health Science and Technology (KIHST), Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
- Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea
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Hall AM, de Seigneux S. Metabolic mechanisms of acute proximal tubular injury. Pflugers Arch 2022; 474:813-827. [PMID: 35567641 PMCID: PMC9338906 DOI: 10.1007/s00424-022-02701-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 04/12/2022] [Accepted: 05/02/2022] [Indexed: 12/11/2022]
Abstract
Damage to the proximal tubule (PT) is the most frequent cause of acute kidney injury (AKI) in humans. Diagnostic and treatment options for AKI are currently limited, and a deeper understanding of pathogenic mechanisms at a cellular level is required to rectify this situation. Metabolism in the PT is complex and closely coupled to solute transport function. Recent studies have shown that major changes in PT metabolism occur during AKI and have highlighted some potential targets for intervention. However, translating these insights into effective new therapies still represents a substantial challenge. In this article, in addition to providing a brief overview of the current state of the field, we will highlight three emerging areas that we feel are worthy of greater attention. First, we will discuss the role of axial heterogeneity in cellular function along the PT in determining baseline susceptibility to different metabolic hits. Second, we will emphasize that elucidating insult specific pathogenic mechanisms will likely be critical in devising more personalized treatments for AKI. Finally, we will argue that uncovering links between tubular metabolism and whole-body homeostasis will identify new strategies to try to reduce the considerable morbidity and mortality associated with AKI. These concepts will be illustrated by examples of recent studies emanating from the authors' laboratories and performed under the auspices of the Swiss National Competence Center for Kidney Research (NCCR Kidney.ch).
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Affiliation(s)
- Andrew M Hall
- Institute of Anatomy, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
- Department of Nephrology, University Hospital Zurich, Zurich, Switzerland.
| | - Sophie de Seigneux
- Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
- Department of Medicine, Service of Nephrology, Geneva University Hospitals, Geneva, Switzerland
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Abstract
Fluorescence microscopy has represented a crucial technique to explore the cellular and molecular mechanisms in the field of biomedicine. However, the conventional one-photon microscopy exhibits many limitations when living samples are imaged. The new technologies, including two-photon microscopy (2PM), have considerably improved the in vivo study of pathophysiological processes, allowing the investigators to overcome the limits displayed by previous techniques. 2PM enables the real-time intravital imaging of the biological functions in different organs at cellular and subcellular resolution thanks to its improved laser penetration and less phototoxicity. The development of more sensitive detectors and long-wavelength fluorescent dyes as well as the implementation of semi-automatic software for data analysis allowed to gain insights in essential physiological functions, expanding the frontiers of cellular and molecular imaging. The future applications of 2PM are promising to push the intravital microscopy beyond the existing limits. In this review, we provide an overview of the current state-of-the-art methods of intravital microscopy, focusing on the most recent applications of 2PM in kidney physiology.
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Molitoris BA, Sandoval RM, Yadav SPS, Wagner MC. Albumin Uptake and Processing by the Proximal Tubule: Physiologic, Pathologic and Therapeutic Implications. Physiol Rev 2022; 102:1625-1667. [PMID: 35378997 PMCID: PMC9255719 DOI: 10.1152/physrev.00014.2021] [Citation(s) in RCA: 46] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
For nearly 50 years the proximal tubule (PT) has been known to reabsorb, process, and either catabolize or transcytose albumin from the glomerular filtrate. Innovative techniques and approaches have provided insights into these processes. Several genetic diseases, nonselective PT cell defects, chronic kidney disease (CKD), and acute PT injury lead to significant albuminuria, reaching nephrotic range. Albumin is also known to stimulate PT injury cascades. Thus, the mechanisms of albumin reabsorption, catabolism, and transcytosis are being reexamined with the use of techniques that allow for novel molecular and cellular discoveries. Megalin, a scavenger receptor, cubilin, amnionless, and Dab2 form a nonselective multireceptor complex that mediates albumin binding and uptake and directs proteins for lysosomal degradation after endocytosis. Albumin transcytosis is mediated by a pH-dependent binding affinity to the neonatal Fc receptor (FcRn) in the endosomal compartments. This reclamation pathway rescues albumin from urinary losses and cellular catabolism, extending its serum half-life. Albumin that has been altered by oxidation, glycation, or carbamylation or because of other bound ligands that do not bind to FcRn traffics to the lysosome. This molecular sorting mechanism reclaims physiological albumin and eliminates potentially toxic albumin. The clinical importance of PT albumin metabolism has also increased as albumin is now being used to bind therapeutic agents to extend their half-life and minimize filtration and kidney injury. The purpose of this review is to update and integrate evolving information regarding the reabsorption and processing of albumin by proximal tubule cells including discussion of genetic disorders and therapeutic considerations.
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Affiliation(s)
- Bruce A. Molitoris
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, United States
- Dept.of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | - Ruben M. Sandoval
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | - Shiv Pratap S. Yadav
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | - Mark C. Wagner
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, United States
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Martins JR, Haenni D, Bugarski M, Polesel M, Schuh C, Hall AM. Intravital kidney microscopy: entering a new era. Kidney Int 2021; 100:527-535. [PMID: 34015315 DOI: 10.1016/j.kint.2021.02.042] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Revised: 02/01/2021] [Accepted: 02/16/2021] [Indexed: 02/07/2023]
Abstract
The development of intravital imaging with multiphoton microscopy has had a major impact on kidney research. It provides the unique opportunity to visualize dynamic behavior of cells and organelles in their native environment and to relate this to the complex 3-dimensional structure of the organ. Moreover, changes in cell/organelle function can be followed in real time in response to physiological interventions or disease-causing insults. However, realizing the enormous potential of this exciting approach has necessitated overcoming several substantial practical hurdles. In this article, we outline the nature of these challenges and how a variety of technical advances have provided effective solutions. In particular, improvements in laser/microscope technology, fluorescent probes, transgenic animals, and abdominal windows are collectively making previously opaque processes visible. Meanwhile, the rise of machine learning-based image analysis is facilitating the rapid generation of large amounts of quantitative data, amenable to deeper statistical interrogation. Taken together, the increased capabilities of multiphoton imaging are opening up huge new possibilities to study structure-function relationships in the kidney in unprecedented detail. In addition, they are yielding important new insights into cellular mechanisms of tissue damage, repair, and adaptive remodeling during disease states. Thus, intravital microscopy is truly entering an exciting new era in translational kidney research.
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Affiliation(s)
- Joana R Martins
- Center for Microscopy and Image Analysis, University of Zurich, Zurich, Switzerland
| | - Dominik Haenni
- Center for Microscopy and Image Analysis, University of Zurich, Zurich, Switzerland; Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Milica Bugarski
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | | | - Claus Schuh
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Andrew M Hall
- Institute of Anatomy, University of Zurich, Zurich, Switzerland; Department of Nephrology, University Hospital Zurich, Zurich, Switzerland.
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10
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Bugarski M, Ghazi S, Polesel M, Martins JR, Hall AM. Changes in NAD and Lipid Metabolism Drive Acidosis-Induced Acute Kidney Injury. J Am Soc Nephrol 2021; 32:342-356. [PMID: 33478973 PMCID: PMC8054907 DOI: 10.1681/asn.2020071003] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Accepted: 10/30/2020] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND The kidney plays an important role in maintaining normal blood pH. Metabolic acidosis (MA) upregulates the pathway that mitochondria in the proximal tubule (PT) use to produce ammonia and bicarbonate from glutamine, and is associated with AKI. However, the extent to which MA causes AKI, and thus whether treating MA would be beneficial, is unclear. METHODS Gavage with ammonium chloride induced acute MA. Multiphoton imaging of mitochondria (NADH/membrane potential) and transport function (dextran/albumin uptake), oxygen consumption rate (OCR) measurements in isolated tubules, histologic analysis, and electron microscopy in fixed tissue, and urinary biomarkers (KIM-1/clara cell 16) assessed tubular cell structure and function in mouse kidney cortex. RESULTS MA induces an acute change in NAD redox state (toward oxidation) in PT mitochondria, without changing the mitochondrial energization state. This change is associated with a switch toward complex I activity and decreased maximal OCR, and a major alteration in normal lipid metabolism, resulting in marked lipid accumulation in PTs and the formation of large multilamellar bodies. These changes, in turn, lead to acute tubular damage and a severe defect in solute uptake. Increasing blood pH with intravenous bicarbonate substantially improves tubular function, whereas preinjection with the NAD precursor nicotinamide (NAM) is highly protective. CONCLUSIONS MA induces AKI via changes in PT NAD and lipid metabolism, which can be reversed or prevented by treatment strategies that are viable in humans. These findings might also help to explain why MA accelerates decline in function in CKD.
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Affiliation(s)
- Milica Bugarski
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Susan Ghazi
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | | | - Joana R. Martins
- Institute of Anatomy, University of Zurich, Zurich, Switzerland,Center for Microscopy and Image Analysis, University of Zurich, Zurich, Switzerland
| | - Andrew M. Hall
- Institute of Anatomy, University of Zurich, Zurich, Switzerland,Department of Nephrology, University Hospital Zurich, Zurich, Switzerland
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11
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Abstract
Kidneys are highly aerobic organs and their function is tightly coupled to mitochondrial energy production. Renal tubular cells, particularly the proximal tubule (PT), require an abundance of mitochondria to provide sufficient energy for regulating fluid and electrolyte balance. Meanwhile, mitochondrial defects are implicated in a range of different kidney diseases. Multiphoton microscopy (MP) is a powerful tool that allows detailed study of mitochondrial morphology, dynamics, and function in kidney tissue. Here, we describe how MP can be used to image mitochondria in kidney tubular cells, either ex vivo in tissue slices or in vivo in living rodents, using both endogenous and exogenous fluorescent molecules. Moreover, changes in mitochondrial signals can be followed in real time in response to different insults or stimuli, in parallel with other important readouts of kidney tubular function, such as solute uptake and trafficking.
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Affiliation(s)
- Milica Bugarski
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Susan Ghazi
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Andrew M Hall
- Institute of Anatomy, University of Zurich, Zurich, Switzerland.
- Department of Nephrology, University Hospital Zurich, Zurich, Switzerland.
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12
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Gong L, Pan Q, Yang N. Autophagy and Inflammation Regulation in Acute Kidney Injury. Front Physiol 2020; 11:576463. [PMID: 33101057 PMCID: PMC7546328 DOI: 10.3389/fphys.2020.576463] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Accepted: 08/25/2020] [Indexed: 12/19/2022] Open
Abstract
Autophagy at an appropriate juncture in the cell cycle exerts protective effects in acute kidney injury (AKI), whereas abnormal autophagy may lead to cell death. Inflammatory response plays a pivotal role in the pathophysiological process of kidney injury and repair during AKI. Several studies have reported an interaction between autophagy and inflammation in the pathogenesis of AKI. This review outlines recent advances in the investigation of the role of autophagy in inflammatory response regulation based on the following aspects. (1) Autophagy inhibits inflammatory responses induced in AKI through the regulation of mTOR and AMPK pathways and the inhibition of inflammasomes activation. (2) Autophagy can also help in the regulation of inflammatory responses through the nuclear factor kappa B pathway, which is beneficial to the recovery of kidney tissues. These studies reviewed here provide better insight into the mechanisms underlying the protective effects of the autophagy-inflammatory pathway. Through this review, we suggest that the autophagy-inflammatory pathway may serve as an alternative target for the treatment of AKI.
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Affiliation(s)
- Li Gong
- Experimental Animal Center, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Qingjun Pan
- Key Laboratory of Prevention and Management of Chronic Kidney Disease of Zhanjiang City, Institute of Nephrology, Affiliated Hospital of Guangdong Medical University, Zhanjiang, China
| | - Nianlan Yang
- School of Health Professions, University of Alabama at Birmingham, Birmingham, AL, United States
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Polesel M, Hall AM. Axial differences in endocytosis along the kidney proximal tubule. Am J Physiol Renal Physiol 2019; 317:F1526-F1530. [DOI: 10.1152/ajprenal.00459.2019] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The proximal tubule (PT) reabsorbs filtered proteins via receptor-mediated endocytosis to prevent energetically inefficient wasting in the urine. Recent intravital imaging studies have suggested that protein reabsorption occurs in early (S1) segments, which have a very high capacity. In contrast, uptake of fluid phase substrates also occurs in distal (S2) segments. In this article, we will review these findings and their implications for understanding integrated proximal tubular function, patterns of damage caused by endocytosed toxins, and the origins of proteinuria. We will also discuss whether compensatory downstream increases in protein uptake might occur in disease states, and the environmental factors that could drive these changes.
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Affiliation(s)
| | - Andrew M. Hall
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
- Department of Nephrology, University Hospital Zurich, Zurich, Switzerland
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Ghazi S, Polesel M, Hall AM. Targeting glycolysis in proliferative kidney diseases. Am J Physiol Renal Physiol 2019; 317:F1531-F1535. [DOI: 10.1152/ajprenal.00460.2019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Glycolytic activity is increased in proliferating cells, leading to the concept that glycolysis could be a therapeutic target in cystic diseases and kidney cancer. Preclinical studies using the glucose analog 2-deoxy-d-glucose have shown promise; however, inhibiting glycolysis in humans is unlikely to be without risks. While proximal tubules are predominantly aerobic, later segments are more glycolytic. Understanding exactly where and why glycolysis is important in the physiology of the distal nephron is thus crucial in predicting potential adverse effects of glycolysis inhibitors. Live imaging techniques could play an important role in the process of characterizing cellular metabolism in the functioning kidney. The goal of this review is to briefly summarize recent findings on targeting glycolysis in proliferative kidney diseases and to highlight the necessity for future research focusing on glycolysis in the healthy kidney.
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Affiliation(s)
- Susan Ghazi
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | | | - Andrew M. Hall
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
- Department of Nephrology, University Hospital Zurich, Zurich, Switzerland
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Abstract
The mammalian kidney relies on abundant mitochondria in the renal tubule to generate sufficient ATP to provide the energy required for constant reclamation of solutes from crude blood filtrate. The highly metabolically active cells of the renal tubule also pair their energetic needs to the regulation of diverse cellular processes, including energy generation, antioxidant responses, autophagy and mitochondrial quality control. Nicotinamide adenine dinucleotide (NAD+) is essential not only for the harvesting of energy from substrates but also for an array of regulatory reactions that determine cellular health. In acute kidney injury (AKI), substantial decreases in the levels of NAD+ impair energy generation and, ultimately, the core kidney function of selective solute transport. Conversely, augmentation of NAD+ may protect the kidney tubule against diverse acute stressors. For example, NAD+ augmentation can ameliorate experimental AKI triggered by ischaemia–reperfusion, toxic injury and systemic inflammation. NAD+-dependent maintenance of renal tubular metabolic health may also attenuate long-term profibrotic responses that could lead to chronic kidney disease. Further understanding of the genetic, environmental and nutritional factors that influence NAD+ biosynthesis and renal resilience may lead to novel approaches for the prevention and treatment of kidney disease. Here, the authors discuss evidence for a role of NAD+ imbalance in the pathogenesis of acute kidney injury (AKI) and chronic kidney disease (CKD). They suggest that disruption of NAD+ metabolism may contribute to mechanistic links among AKI, CKD and ageing. NAD+ has critical roles in the generation of ATP from fuel substrates and as a substrate for important enzymes that regulate cellular health and stress responses. The renal tubule is highly metabolically active and requires a constant supply of ATP to provide the energy required to pump solutes across unfavourable gradients. Experimental acute kidney injury (AKI) induced by various insults rapidly leads to a decrease in NAD+ levels that probably results from a combination of reduced NAD+ biosynthesis and increased NAD+ consumption. Renal NAD+ levels can be augmented using vitamin B3 analogues and related nutritional precursors. NAD+ augmentation can prevent and/or treat various aetiologies of experimental AKI and might also attenuate long-term profibrotic responses following AKI, suggesting a potential role in the treatment of chronic kidney disease.
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