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Jamalpoor A, Othman A, Levtchenko EN, Masereeuw R, Janssen MJ. Molecular Mechanisms and Treatment Options of Nephropathic Cystinosis. Trends Mol Med 2021; 27:673-686. [PMID: 33975805 DOI: 10.1016/j.molmed.2021.04.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Revised: 04/12/2021] [Accepted: 04/13/2021] [Indexed: 11/15/2022]
Abstract
Nephropathic cystinosis is a severe, monogenic systemic disorder that presents early in life and leads to progressive organ damage, particularly affecting the kidneys. It is caused by mutations in the CTNS gene, which encodes the lysosomal transporter cystinosin, resulting in intralysosomal accumulation of cystine. Recent studies demonstrated that the loss of cystinosin is associated with disrupted autophagy dynamics, accumulation of distorted mitochondria, and increased oxidative stress, leading to abnormal proliferation and dysfunction of kidney cells. We discuss these molecular mechanisms driving nephropathic cystinosis. Further, we consider how unravelling molecular mechanisms supports the identification and development of new strategies for cystinosis by the use of small molecules, biologicals, and genetic rescue of the disease in vitro and in vivo.
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Affiliation(s)
- Amer Jamalpoor
- Division of Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Faculty of Science, Utrecht University, 3584, CG, Utrecht, The Netherlands
| | - Amr Othman
- Division of Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Faculty of Science, Utrecht University, 3584, CG, Utrecht, The Netherlands
| | - Elena N Levtchenko
- Department of Pediatric Nephrology & Growth and Regeneration, University Hospitals Leuven & KU Leuven, Leuven, Belgium
| | - Rosalinde Masereeuw
- Division of Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Faculty of Science, Utrecht University, 3584, CG, Utrecht, The Netherlands.
| | - Manoe J Janssen
- Division of Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Faculty of Science, Utrecht University, 3584, CG, Utrecht, The Netherlands.
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2
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Bellomo F, Signorile A, Tamma G, Ranieri M, Emma F, De Rasmo D. Impact of atypical mitochondrial cyclic-AMP level in nephropathic cystinosis. Cell Mol Life Sci 2018; 75:3411-3422. [PMID: 29549422 PMCID: PMC11105431 DOI: 10.1007/s00018-018-2800-5] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Revised: 02/20/2018] [Accepted: 03/14/2018] [Indexed: 02/06/2023]
Abstract
Nephropathic cystinosis (NC) is a rare disease caused by mutations in the CTNS gene encoding for cystinosin, a lysosomal transmembrane cystine/H+ symporter, which promotes the efflux of cystine from lysosomes to cytosol. NC is the most frequent cause of Fanconi syndrome (FS) in young children, the molecular basis of which is not well established. Proximal tubular cells have very high metabolic rate due to the active transport of many solutes. Not surprisingly, mitochondrial disorders are often characterized by FS. A similar mechanism may also apply to NC. Because cAMP has regulatory properties on mitochondrial function, we have analyzed cAMP levels and mitochondrial targets in CTNS-/- conditionally immortalized proximal tubular epithelial cells (ciPTEC) carrying the classical homozygous 57-kb deletion (delCTNS-/-) or with compound heterozygous loss-of-function mutations (mutCTNS-/-). Compared to wild-type cells, cystinotic cells had significantly lower mitochondrial cAMP levels (delCTNS-/- ciPTEC by 56% ± 10.5, P < 0.0001; mutCTNS-/- by 26% ± 4.3, P < 0.001), complex I and V activities, mitochondrial membrane potential, and SIRT3 protein levels, which were associated with increased mitochondrial fragmentation. Reduction of complex I and V activities was associated with lower expression of part of their subunits. Treatment with the non-hydrolysable cAMP analog 8-Br-cAMP restored mitochondrial potential and corrected mitochondria morphology. Treatment with cysteamine, which reduces the intra-lysosomal cystine, was able to restore mitochondrial cAMP levels, as well as most other abnormal mitochondrial findings. These observations were validated in CTNS-silenced HK-2 cells, indicating a pivotal role of mitochondrial cAMP in the proximal tubular dysfunction observed in NC.
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Affiliation(s)
- Francesco Bellomo
- Laboratory of Nephrology, Department of Rare Diseases, Bambino Gesù Children's Hospital, Viale di S. Paolo, 15, 00149, Rome, Italy.
| | - Anna Signorile
- Department of Basic Medical Sciences, Neurosciences and Sense Organs, University of Bari "Aldo Moro", Policlinico, Piazza G. Cesare, 11, 70124, Bari, Italy
| | - Grazia Tamma
- Department of Bioscience, Biotechnologies and Biopharmaceutics, University of Bari "Aldo Moro", Bari, Italy
| | - Marianna Ranieri
- Department of Bioscience, Biotechnologies and Biopharmaceutics, University of Bari "Aldo Moro", Bari, Italy
| | - Francesco Emma
- Laboratory of Nephrology, Department of Rare Diseases, Bambino Gesù Children's Hospital, Viale di S. Paolo, 15, 00149, Rome, Italy
- Division of Nephrology, Department of Pediatric Subspecialties, Bambino Gesù Children's Hospital, Rome, Italy
| | - Domenico De Rasmo
- Department of Basic Medical Sciences, Neurosciences and Sense Organs, University of Bari "Aldo Moro", Policlinico, Piazza G. Cesare, 11, 70124, Bari, Italy.
- Institute of Biomembrane, Bioenergetics and Molecular Biotechnology (IBIOM), National Research Council (CNR), Bari, Italy.
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3
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Zhao X, Han J, Zhu L, Xiao Y, Wang C, Hong F, Jiang P, Guan MX. Overexpression of human mitochondrial alanyl-tRNA synthetase suppresses biochemical defects of the mt-tRNA Ala mutation in cybrids. Int J Biol Sci 2018; 14:1437-1444. [PMID: 30262995 PMCID: PMC6158735 DOI: 10.7150/ijbs.27043] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Accepted: 07/17/2018] [Indexed: 11/13/2022] Open
Abstract
Mutations of mitochondrial transfer RNAs (mt-tRNAs) play a major role in a wide range of mitochondrial diseases because of the vital role of these molecules in mitochondrial translation. It has previously been reported that the overexpression of mitochondrial aminoacyl tRNA synthetases is effective at partially suppressing the defects resulting from mutations in their cognate mt-tRNAs in cells. Here we report a detailed analysis of the suppressive activities of mitochondrial alanyl-tRNA synthetase (AARS2) on mt-tRNAAla 5655 A>G mutant. Mitochondrial defects in respiration, activity of oxidative phosphorylation complexes, ATP production, mitochondrial superoxide, and membrane potential were consistently rescued in m.5655A>G cybrids upon AARS2 expression. However, AARS2 overexpression did not result in a detectable increase in mutated mt-tRNAAla but caused an increase incharged mt-tRNAAla in mutant cybrids, leading to enhanced mitochondrial translation. This indicated that AARS2 improved the aminoacylation activity in the case of m.5655A>G, rather than having a stabilizing effect on the tRNA structure. The data presented in this paper deepen our understanding of the pathogenesis of mt-tRNA diseases.
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Affiliation(s)
- Xiaoxu Zhao
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, China.,Institute of Genetics Zhejiang University, and Department of Human Genetics, Zhejiang University School of Medicine, Hangzhou, 310058, China
| | - Jiamin Han
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, China.,Institute of Genetics Zhejiang University, and Department of Human Genetics, Zhejiang University School of Medicine, Hangzhou, 310058, China
| | - Ling Zhu
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, China
| | - Yun Xiao
- Institute of Genetics Zhejiang University, and Department of Human Genetics, Zhejiang University School of Medicine, Hangzhou, 310058, China
| | - Chenghui Wang
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, China.,Institute of Genetics Zhejiang University, and Department of Human Genetics, Zhejiang University School of Medicine, Hangzhou, 310058, China
| | - Fang Hong
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, China
| | - Pingping Jiang
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, China.,Institute of Genetics Zhejiang University, and Department of Human Genetics, Zhejiang University School of Medicine, Hangzhou, 310058, China
| | - Min-Xin Guan
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, 310058, China.,Institute of Genetics Zhejiang University, and Department of Human Genetics, Zhejiang University School of Medicine, Hangzhou, 310058, China
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Sumayao R, Newsholme P, McMorrow T. Inducible nitric oxide synthase inhibitor 1400W increases Na + ,K + -ATPase levels and activity and ameliorates mitochondrial dysfunction in Ctns null kidney proximal tubular epithelial cells. Clin Exp Pharmacol Physiol 2018; 45:1149-1160. [PMID: 29924417 DOI: 10.1111/1440-1681.12998] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2017] [Revised: 06/02/2018] [Accepted: 06/11/2018] [Indexed: 02/02/2023]
Abstract
Nitric oxide (NO) has been shown to play an important role in renal physiology and pathophysiology partly through its influence on various transport systems in the kidney proximal tubule. The role of NO in kidney dysfunction associated with lysosomal storage disorder, cystinosis, is largely unknown. In the present study, the effects of inducible nitric oxide synthase (iNOS)-specific inhibitor, 1400W, on Na+ ,K+ -ATPase activity and expression, mitochondrial integrity and function, nutrient metabolism, and apoptosis were investigated in Ctns null proximal tubular epithelial cells (PTECs). Ctns null PTECs exhibited an increase in iNOS expression, augmented NO and nitrite/nitrate production, and reduced Na+ ,K+ -ATPase expression and activity. In addition, these cells displayed depolarized mitochondria, reduced adenosine triphosphate content, altered nutrient metabolism, and elevated apoptosis. Treatment of Ctns null PTECs with 1400W abolished these effects which culminated in the mitigation of apoptosis in these cells. These findings indicate that uncontrolled NO production may constitute the upstream event that leads to the molecular and biochemical alterations observed in Ctns null PTECs and may explain, at least in part, the generalized proximal tubular dysfunction associated with cystinosis. Further studies are needed to realize the potential benefits of anti-nitrosative therapies in improving renal function and/or attenuating renal injury in cystinosis.
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Affiliation(s)
- Rodolfo Sumayao
- Chemistry Department, De La Salle University, Manila, Philippines
| | - Philip Newsholme
- School of Biomedical Sciences, Curtin Health Innovation Research Institute (CHIRI), Curtin University, Perth, Western Australia, Australia
| | - Tara McMorrow
- Conway Institute, School of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland
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Slow progression of renal failure in a child with infantile cystinosis. CEN Case Rep 2018; 7:153-157. [PMID: 29446030 DOI: 10.1007/s13730-018-0316-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Accepted: 02/07/2018] [Indexed: 10/18/2022] Open
Abstract
Cystinosis is a rare autosomal recessive lysosomal transport disorder, characterized by the accumulation of the aminoacid cystine and progressive dysfunction of several organs. Kidneys are severely affected, and the most frequent form, infantile nephropathic cystinosis, presents with growth failure in infancy, renal Fanconi syndrome and end-stage renal disease by the first decade of life. We report of a girl with infantile nephropathic cystinosis that has reached adolescence without the need of renal replacement therapy and without extrarenal manifestations despite her delayed diagnosis and treatment initiation. The girl with this intermediate phenotype was found to have compound heterozygosity of one known (1015G > A) and one novel (587_588insA) mutation in CTNS gene. Our case points to the wide clinical presentation of infantile nephropathic cystinosis and suggest that long-term outcome is not always ominous as generally thought.
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6
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Cherqui S, Courtoy PJ. The renal Fanconi syndrome in cystinosis: pathogenic insights and therapeutic perspectives. Nat Rev Nephrol 2016; 13:115-131. [PMID: 27990015 DOI: 10.1038/nrneph.2016.182] [Citation(s) in RCA: 94] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Cystinosis is an autosomal recessive metabolic disease that belongs to the family of lysosomal storage disorders. It is caused by a defect in the lysosomal cystine transporter, cystinosin, which results in an accumulation of cystine in all organs. Despite the ubiquitous expression of cystinosin, a renal Fanconi syndrome is often the first manifestation of cystinosis, usually presenting within the first year of life and characterized by the early and severe dysfunction of proximal tubule cells, highlighting the unique vulnerability of this cell type. The current therapy for cystinosis, cysteamine, facilitates lysosomal cystine clearance and greatly delays progression to kidney failure but is unable to correct the Fanconi syndrome. This Review summarizes decades of studies that have fostered a better understanding of the pathogenesis of the renal Fanconi syndrome associated with cystinosis. These studies have unraveled some of the early molecular changes that occur before the onset of tubular atrophy and identified a role for cystinosin beyond cystine transport, in endolysosomal trafficking and proteolysis, lysosomal clearance, autophagy and the regulation of energy balance. These studies have also led to the identification of new potential therapeutic targets and here, we outline the potential role of stem cell therapy for cystinosis and provide insights into the mechanism of haematopoietic stem cell-mediated kidney protection.
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Affiliation(s)
- Stephanie Cherqui
- Department of Pediatrics, Division of Genetics, University of California San Diego, 9500 Gilman Drive, MC 0734, La Jolla, California 92093-0734, USA
| | - Pierre J Courtoy
- Cell biology, de Duve Institute and Université catholique de Louvain, UCL-Brussels, 75 Avenue Hippocrate, B-1200 Brussels, Belgium
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7
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Simpkins JA, Rickel KE, Madeo M, Ahlers BA, Carlisle GB, Nelson HJ, Cardillo AL, Weber EA, Vitiello PF, Pearce DA, Vitiello SP. Disruption of a cystine transporter downregulates expression of genes involved in sulfur regulation and cellular respiration. Biol Open 2016; 5:689-97. [PMID: 27142334 PMCID: PMC4920189 DOI: 10.1242/bio.017517] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Cystine and cysteine are important molecules for pathways such as redox signaling and regulation, and thus identifying cellular deficits upon deletion of the Saccharomyces cerevisiae cystine transporter Ers1p allows for a further understanding of cystine homeostasis. Previous complementation studies using the human ortholog suggest yeast Ers1p is a cystine transporter. Human CTNS encodes the protein Cystinosin, a cystine transporter that is embedded in the lysosomal membrane and facilitates the export of cystine from the lysosome. When CTNS is mutated, cystine transport is disrupted, leading to cystine accumulation, the diagnostic hallmark of the lysosomal storage disorder cystinosis. Here, we provide biochemical evidence for Ers1p-dependent cystine transport. However, the accumulation of intracellular cystine is not observed when the ERS1 gene is deleted from ers1-Δ yeast, supporting the existence of modifier genes that provide a mechanism in ers1-Δ yeast that prevents or corrects cystine accumulation. Upon comparison of the transcriptomes of isogenic ERS1+ and ers1-Δ strains of S. cerevisiae by DNA microarray followed by targeted qPCR, sixteen genes were identified as being differentially expressed between the two genotypes. Genes that encode proteins functioning in sulfur regulation, cellular respiration, and general transport were enriched in our screen, demonstrating pleiotropic effects of ers1-Δ. These results give insight into yeast cystine regulation and the multiple, seemingly distal, pathways that involve proper cystine recycling. Summary: We identify genes that are differentially expressed in yeast lacking vacuolar cystine transporter Ers1p in order to find pathways, such as respiration and sulfur regulation, that are associated with cystine homeostasis.
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Affiliation(s)
| | - Kirby E Rickel
- Biology Department, Augustana University, Sioux Falls, SD, USA 57197
| | - Marianna Madeo
- Sanford Research Children's Health Research Center, Sioux Falls, SD, USA 57104
| | - Bethany A Ahlers
- Biology Department, Augustana University, Sioux Falls, SD, USA 57197
| | | | - Heidi J Nelson
- Biology Department, Augustana University, Sioux Falls, SD, USA 57197
| | - Andrew L Cardillo
- Sanford Research Children's Health Research Center, Sioux Falls, SD, USA 57104
| | - Emily A Weber
- Biology Department, Augustana University, Sioux Falls, SD, USA 57197
| | - Peter F Vitiello
- Sanford Research Children's Health Research Center, Sioux Falls, SD, USA 57104
| | - David A Pearce
- Sanford Research Children's Health Research Center, Sioux Falls, SD, USA 57104
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8
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Sansanwal P, Li L, Sarwal MM. Inhibition of intracellular clusterin attenuates cell death in nephropathic cystinosis. J Am Soc Nephrol 2014; 26:612-25. [PMID: 25071085 DOI: 10.1681/asn.2013060577] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Nephropathic cystinosis, characterized by accumulation of cystine in the lysosomes, is caused by mutations in CTNS. The molecular and cellular mechanisms underlying proximal tubular dysfunction and progressive renal failure in nephropathic cystinosis are largely unclear, and increasing evidence supports the notion that cystine accumulation alone is not responsible for the end organ injury in cystinosis. We previously identified clusterin as potentially involved in nephropathic cystinosis. Here, we studied the expression of clusterin in renal proximal tubular epithelial cells obtained from patients with nephropathic cystinosis. The cytoprotective secretory form of clusterin, as evaluated by Western blot analysis, was low or absent in cystinosis cells compared with normal primary cells. Confocal microscopy revealed elevated levels of intracellular clusterin in cystinosis cells. Clusterin in cystinosis cells localized to the nucleus and cytoplasm and showed a filamentous and punctate aggresome-like pattern compared with diffuse cytoplasmic staining in normal cells. In kidney biopsy samples from patients with nephropathic cystinosis, clusterin protein expression was mainly limited to the proximal tubular cells. Furthermore, expression of clusterin overlapped with the expression of apoptotic proteins (apoptosis-inducing factor and cleaved caspase-3) and autophagy proteins (LC3 II and p62). Silencing of the clusterin gene resulted in a significant increase in cell viability and attenuation of apoptosis in cystinosis cells. Results of this study identify clusterin as a pivotal factor in the cell injury mechanism of nephropathic cystinosis and provide evidence linking cellular stress and injury to Fanconi syndrome and progressive renal injury in nephropathic cystinosis.
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Affiliation(s)
- Poonam Sansanwal
- California Pacific Medical Center Research Institute, San Francisco, California;
| | - Li Li
- Department of Genetics and Genomic Sciences, Mount Sinai School of Medicine, New York, New York; and
| | - Minnie M Sarwal
- California Pacific Medical Center Research Institute, San Francisco, California; Department of Surgery, Univeristy of California, San Francisco, School of Medicine, San Francisco, California
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Sansanwal P, Sarwal MM. p62/SQSTM1 prominently accumulates in renal proximal tubules in nephropathic cystinosis. Pediatr Nephrol 2012; 27:2137-2144. [PMID: 22714671 DOI: 10.1007/s00467-012-2227-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/10/2011] [Revised: 05/18/2012] [Accepted: 05/22/2012] [Indexed: 01/07/2023]
Abstract
BACKGROUND Nephropathic cystinosis, a lysosomal storage disorder, is associated with generalized proximal tubular dysfunction and progressive renal failure. The underlying molecular and cellular mechanisms leading to renal tubular injury remain largely unknown. Abnormal induction of autophagy has been shown in cystinosis. We have studied the autophagic flux in cystinosis by evaluating autophagy-specific substrates. METHODS LC3 and p62 expression was evaluated by (1) immunohistochemistry performed on kidney biopsies obtained from four nephropathic cystinosis patients, four patients with renal injury due to causes other than cystinosis, and four normal kidney tissues and (2) fluorescence imaging in cultured renal proximal tubular epithelial (RPTE) cells obtained from four nephropathic cystinosis patients and two lots of normal primary RPTE cells, both in basal and starvation conditions. p62 expression was also corroborated by western blot analysis in RPTE cells. RESULTS There was a significant buildup of p62 protein in patients with nephropathic cystinosis, specifically in the proximal tubules in kidney biopsies and RPTE cells (p = 0.0004), and the accumulation was further enhanced upon starvation. Cystinotic RPTE cells exhibited a significant co-localization of p62 with LC3. CONCLUSIONS Our findings indicate a potential block in the autophagic flux in cystinosis, thus providing key insights into the underlying mechanisms of tubular injury in cystinosis.
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Affiliation(s)
- Poonam Sansanwal
- California Pacific Medical Center Research Institute, 475 Brannan Street, Ste 220, San Francisco, CA, 94107, USA.
| | - Minnie M Sarwal
- California Pacific Medical Center Research Institute, 475 Brannan Street, Ste 220, San Francisco, CA, 94107, USA.
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Sansanwal P, Li L, Hsieh SC, Sarwal MM. Insights into novel cellular injury mechanisms by gene expression profiling in nephropathic cystinosis. J Inherit Metab Dis 2010; 33:775-86. [PMID: 20865335 DOI: 10.1007/s10545-010-9203-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2010] [Revised: 08/18/2010] [Accepted: 08/24/2010] [Indexed: 01/27/2023]
Abstract
Nephropathic cystinosis is a rare, inherited metabolic disease caused by functional defects of cystinosin associated with mutations in the CTNS gene. The mechanisms underlying the phenotypic alterations associated with this disease are not well known. In this study, gene expression profiles in peripheral blood of nephropathic cystinosis patients (N = 7) were compared with controls (N = 7) using microarray technology. In unsupervised hierarchical clustering analysis, cystinosis samples co-clustered, and 1,604 genes were significantly differentially expressed between both groups. Gene ontology analysis revealed that differentially expressed genes in cystinosis were enriched in cell organelles such as mitochondria, lysosomes, and endoplasmic reticulum (p ≤ 0.030). The majority of the differentially regulated genes were involved in oxidative phosphorylation, apoptosis, mitochondrial dysfunction, endoplasmic reticulum stress, antigen processing and presentation, B-cell-receptor signaling, and oxidative stress (p ≤ 0.003). Validation of selected genes involved in apoptosis and oxidative phosphorylation was performed by quantitative real-time polymerase chain reaction (PCR). Electron microscopy and confocal imaging of cystinotic renal proximal tubular epithelial cells further confirmed anomalies in the cellular organelles and pathways identified by microarray analysis. Further analysis of these genes and pathways may offer critical insights into the clinical spectrum of cystinosis patients and ultimately lead to novel links for targeted therapy.
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Affiliation(s)
- Poonam Sansanwal
- Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA.
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11
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Wilmer MJ, Emma F, Levtchenko EN. The pathogenesis of cystinosis: mechanisms beyond cystine accumulation. Am J Physiol Renal Physiol 2010; 299:F905-16. [PMID: 20826575 DOI: 10.1152/ajprenal.00318.2010] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Renal proximal tubules are highly sensitive to ischemic and toxic insults and are affected in diverse genetic disorders, of which nephropathic cystinosis is the most common. The disease is caused by mutations in the CTNS gene, encoding the lysosomal cystine transporter cystinosin, and is characterized by accumulation of cystine in the lysosomes throughout the body. In the majority of the patients, this leads to generalized proximal tubular dysfunction (also called DeToni-Debré-Fanconi syndrome) in the first year and progressive renal failure during the first decade. Extrarenal organs are affected by cystinosis as well, with clinical symptoms manifesting mostly after 10 yr of age. The cystine-depleting agent cysteamine significantly improves life expectancy of patients with cystinosis, but offers no cure, pointing to the complexity of the disease mechanism. In this review, current knowledge on the pathogenesis of cystinosis is described and placed in perspective of future research.
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Affiliation(s)
- Martijn J Wilmer
- Dept. of Pediatric Nephrology, Univ. Hospitals Leuven, Herestraat 49, 3000 Leuven, Belgium
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12
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Kumar A, Bachhawat AK. A futile cycle, formed between two ATP-dependant gamma-glutamyl cycle enzymes, gamma-glutamyl cysteine synthetase and 5-oxoprolinase: the cause of cellular ATP depletion in nephrotic cystinosis? J Biosci 2010; 35:21-5. [PMID: 20413906 DOI: 10.1007/s12038-010-0004-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Cystinosis, an inherited disease caused by a defect in the lysosomal cystine transporter (CTNS), is characterized by renal proximal tubular dysfunction. Adenosine triphosphate (ATP) depletion appears to be a key event in the pathophysiology of the disease, even though the manner in which ATP depletion occurs is still a puzzle. We present a model that explains how a futile cycle that is generated between two ATP-utilizing enzymes of the gamma-glutamyl cycle leads to ATP depletion. The enzyme gamma-glutamyl cysteine synthetase (gamma-GCS), in the absence of cysteine, forms 5-oxoproline (instead of the normal substrate, gamma-glutamyl cysteine) and the 5-oxoproline is converted into glutamate by the ATP-dependant enzyme, 5-oxoprolinase. Thus, in cysteine-limiting conditions, glutamate is cycled back into glutamate via 5-oxoproline at the cost of two ATP molecules without production of glutathione and is the cause of the decreased levels of glutathione synthesis, as well as the ATP depletion observed in these cells. The model is also compatible with the differences seen in the human patients and the mouse model of cystinosis, where renal failure is not observed.
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Affiliation(s)
- Akhilesh Kumar
- Institute of Microbial Technology, Sector 39-A, Chandigarh 160 036, India
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13
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Sansanwal P, Kambham N, Sarwal MM. Caspase-4 may play a role in loss of proximal tubules and renal injury in nephropathic cystinosis. Pediatr Nephrol 2010; 25:105-9. [PMID: 19705160 DOI: 10.1007/s00467-009-1289-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2009] [Revised: 07/09/2009] [Accepted: 07/14/2009] [Indexed: 11/27/2022]
Abstract
Nephropathic cystinosis is characterized clinically by generalized proximal renal tubular dysfunction, renal Fanconi Syndrome and progressive renal failure. Glomerular-proximal tubule disconnection has been noted in renal biopsies from patients with nephropathic cystinosis. In vitro studies performed in cystinotic fibroblasts and renal proximal tubular cells support a role for apoptosis of the glomerulotubular junction, and we have further extended these studies to human native cystinotic kidney specimens. We performed semi-quantitative analysis of tubular density in kidney biopsies from patients with nephropathic cystinosis and demonstrated a significant reduction (p=0.0003) in the number of proximal tubules in the kidney tissue of patients with cystinosis compared to normal kidneys and kidneys with other causes of renal injury; this reduction appears to be associated with the over-expression of caspase-4. This study provides the first quantitative evidence of a loss of proximal tubules in nephropathic cystinosis and suggests a possible role of caspase-4 in the apoptotic loss of proximal tubular cells. Further work is needed to elucidate if this injury mechanism may be causative for the progression of renal functional decline in nephropathic cystinosis.
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Affiliation(s)
- Poonam Sansanwal
- Department of Pediatrics, Stanford University, G306, 300 Pasteur Drive, Stanford, CA 94304, USA
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14
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Sansanwal P, Yen B, Gahl WA, Ma Y, Ying L, Wong LJC, Sarwal MM. Mitochondrial autophagy promotes cellular injury in nephropathic cystinosis. J Am Soc Nephrol 2009; 21:272-83. [PMID: 19959713 DOI: 10.1681/asn.2009040383] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
The molecular and cellular mechanisms underlying nephropathic cystinosis, which exhibits generalized proximal tubular dysfunction and progressive renal failure, remain largely unknown. Renal biopsies from patients with this disorder can reveal abnormally large mitochondria, but the relevance of this and other ultrastructural abnormalities is unclear. We studied the ultrastructure of fibroblasts and renal proximal tubular epithelial cells from patients with three clinical variants of cystinosis: Nephropathic, intermediate, and ocular. Electron microscopy revealed the presence of morphologically abnormal mitochondria and abnormal patterns of mitochondrial autophagy (mitophagy) with a high number of autophagic vacuoles and fewer mitochondria (P < 0.02) in nephropathic cystinosis. In addition, we observed increased apoptosis in renal proximal tubular epithelial cells, greater expression of LC3-II/LC3-I (microtubule-associated protein 1 light chain 3), and significantly more autophagosomes in the nephropathic variant. The autophagy inhibitor 3-methyl adenine rescued cell death in cystinotic cells. Cystinotic cells had increased levels of beclin-1 and aberrant mitochondrial function with a significant decrease in ATP generation and an increase in reactive oxygen species. This study provides ultrastructural and functional evidence of abnormal mitophagy in nephropathic cystinosis, which may contribute to the renal Fanconi syndrome and progressive renal injury.
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Affiliation(s)
- Poonam Sansanwal
- Department of Pediatrics, G306, 300 Pasteur Drive, Stanford, CA 94304, USA
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