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Tseng MH, Konrad M, Ding JJ, Lin SH. Clinical and Genetic Approach to Renal Hypomagnesemia. Biomed J 2021; 45:74-87. [PMID: 34767995 PMCID: PMC9133307 DOI: 10.1016/j.bj.2021.11.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Revised: 11/01/2021] [Accepted: 11/03/2021] [Indexed: 12/03/2022] Open
Abstract
Magnesium (Mg2+) is an important intracellular cation and essential to maintain cell function including cell proliferation, immunity, cellular energy metabolism, protein and nucleic acid synthesis, and regulation of ion channels. Consequences of hypomagnesemia affecting multiple organs can be in overt or subtle presentations. Besides detailed history and complete physical examination, the assessment of urinary Mg2+ excretion is help to differentiate renal from extra-renal (gastrointestinal, tissue sequestration, and shifting) causes of hypomagnesemia. Renal hypomagnesemia can be caused by an increased glomerular filtration and impaired reabsorption in proximal tubular cells, thick ascending limb of the loop of Henle or distal convoluted tubules. A combination of renal Mg2+ wasting, familial history, age of onset, associated features, and exclusion of acquired etiologies point to inherited forms of renal hypomagnesemia. Based on clinical phenotypes, its definite genetic diagnosis can be simply grouped into specific, uncertain, and unknown gene mutations with a priority of genetic approach methods. An unequivocal molecular diagnosis could allow for prediction of clinical outcome, providing genetic counseling, avoiding unnecessary studies or interventions, and possibly uncovering the pathogenic mechanism. Given numerous identified genes responsible for Mg2+ transport in renal hypomagnesemia over the past two decades, several potential and specific molecular and cellular therapeutic strategies to correct hypomagnesemia are promising.
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Affiliation(s)
- Min-Hua Tseng
- Division of Nephrology, Department of Pediatrics, Chang Gung Memorial Hospital and Chang Gung University, Taoyuan, Taiwan; Department of Pediatrics, Xiamen Chang Gung Hospital, China
| | - Martin Konrad
- Department of General Pediatrics, University Children's Hospital Münster, Münster, Germany
| | - Jhao-Jhuang Ding
- Department of Pediatrics, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan
| | - Shih-Hua Lin
- Division of Nephrology, Department of Medicine, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan.
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Ataluren-Promising Therapeutic Premature Termination Codon Readthrough Frontrunner. Pharmaceuticals (Basel) 2021; 14:ph14080785. [PMID: 34451881 PMCID: PMC8398184 DOI: 10.3390/ph14080785] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2021] [Revised: 07/30/2021] [Accepted: 08/06/2021] [Indexed: 02/08/2023] Open
Abstract
Around 12% of hereditary disease-causing mutations are in-frame nonsense mutations. The expression of genes containing nonsense mutations potentially leads to the production of truncated proteins with residual or virtually no function. However, the translation of transcripts containing premature stop codons resulting in full-length protein expression can be achieved using readthrough agents. Among them, only ataluren was approved in several countries to treat nonsense mutation Duchenne muscular dystrophy (DMD) patients. This review summarizes ataluren’s journey from its identification, via first in vitro activity experiments, to clinical trials in DMD, cystic fibrosis, and aniridia. Additionally, data on its pharmacokinetics and mechanism of action are presented. The range of diseases with underlying nonsense mutations is described for which ataluren therapy seems to be promising. What is more, experiments in which ataluren did not show its readthrough activity are also included, and reasons for their failures are discussed.
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Salerno EE, Patel SP, Marshall A, Marshall J, Alsufayan T, Mballo CSA, Quade BN, Parker MD. Extrarenal Signs of Proximal Renal Tubular Acidosis Persist in Nonacidemic Nbce1b/c-Null Mice. J Am Soc Nephrol 2019; 30:979-989. [PMID: 31040187 DOI: 10.1681/asn.2018050545] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Accepted: 03/05/2019] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND The SLC4A4 gene encodes electrogenic sodium bicarbonate cotransporter 1 (NBCe1). Inheritance of recessive mutations in SLC4A4 causes proximal renal tubular acidosis (pRTA), a disease characterized by metabolic acidosis, growth retardation, ocular abnormalities, and often dental abnormalities. Mouse models of pRTA exhibit acidemia, corneal edema, weak dental enamel, impacted colons, nutritional defects, and a general failure to thrive, rarely surviving beyond weaning. Alkali therapy remains the preferred treatment for pRTA, but it is unclear which nonrenal signs are secondary to acidemia and which are a direct consequence of NBCe1 loss from nonrenal sites (such as the eye and enamel organ) and therefore require separate therapy. SLC4A4 encodes three major NBCe1 variants: NBCe1-A, NBCe1-B, and NBCe1-C. NBCe1-A is expressed in proximal tubule epithelia; its dysfunction causes the plasma bicarbonate insufficiency that underlies acidemia. NBCe1-B and NBCe1-C exhibit a broad extra-proximal-tubular distribution. METHODS To explore the consequences of Nbce1b/c loss in the absence of acidemia, we engineered a novel strain of Nbce1b/c-null mice and assessed them for signs of pRTA. RESULTS Nbce1b/c-null mice have normal blood pH, but exhibit increased mortality, growth retardation, corneal edema, and tooth enamel defects. CONCLUSIONS The correction of pRTA-related acidemia should not be considered a panacea for all signs of pRTA. The phenotype of Nbce1b/c-null mice highlights the physiologic importance of NBCe1 variants expressed beyond the proximal tubular epithelia and potential limitations of pH correction by alkali therapy in pRTA. It also suggests a novel genetic locus for corneal dystrophy and enamel hypomineralization without acidemia.
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Affiliation(s)
| | - Sangita P Patel
- Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York.,State University of New York Eye Institute, Buffalo, New York; and.,Research and Ophthalmology Services, VA Western New York Healthcare System, Buffalo, New York
| | | | | | | | | | | | - Mark D Parker
- Departments of Physiology and Biophysics and .,Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York.,State University of New York Eye Institute, Buffalo, New York; and
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Horita S, Nakamura M, Suzuki M, Satoh N, Suzuki A, Homma Y, Nangaku M. The role of renal proximal tubule transport in the regulation of blood pressure. Kidney Res Clin Pract 2017; 36:12-21. [PMID: 28428931 PMCID: PMC5331971 DOI: 10.23876/j.krcp.2017.36.1.12] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2016] [Revised: 10/18/2016] [Accepted: 12/05/2016] [Indexed: 12/15/2022] Open
Abstract
The electrogenic sodium/bicarbonate cotransporter 1 (NBCe1) on the basolateral side of the renal proximal tubule plays a pivotal role in systemic acid-base homeostasis. Mutations in the gene encoding NBCe1 cause severe proximal renal tubular acidosis accompanied by other extrarenal symptoms. The proximal tubule reabsorbs most of the sodium filtered in the glomerulus, contributing to the regulation of plasma volume and blood pressure. NBCe1 and other sodium transporters in the proximal tubule are regulated by hormones, such as angiotensin II and insulin. Angiotensin II is probably the most important stimulator of sodium reabsorption. Proximal tubule AT1A receptor is crucial for the systemic pressor effect of angiotensin II. In rodents and rabbits, the effect on proximal tubule NBCe1 is biphasic; at low concentration, angiotensin II stimulates NBCe1 via PKC/cAMP/ERK, whereas at high concentration, it inhibits NBCe1 via NO/cGMP/cGKII. In contrast, in human proximal tubule, angiotensin II has a dose-dependent monophasic stimulatory effect via NO/cGMP/ERK. Insulin stimulates the proximal tubule sodium transport, which is IRS2-dependent. We found that in insulin resistance and overt diabetic nephropathy, stimulatory effect of insulin on proximal tubule transport was preserved. Our results suggest that the preserved stimulation of the proximal tubule enhances sodium reabsorption, contributing to the pathogenesis of hypertension with metabolic syndrome. We describe recent findings regarding the role of proximal tubule transport in the regulation of blood pressure, focusing on the effects of angiotensin II and insulin.
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Affiliation(s)
- Shoko Horita
- Department of Nephrology and Endocrinology, The University of Tokyo Hospital, Tokyo, Japan
| | - Motonobu Nakamura
- Department of Nephrology and Endocrinology, The University of Tokyo Hospital, Tokyo, Japan
| | - Masashi Suzuki
- Department of Nephrology and Endocrinology, The University of Tokyo Hospital, Tokyo, Japan
| | - Nobuhiko Satoh
- Department of Nephrology and Endocrinology, The University of Tokyo Hospital, Tokyo, Japan
| | - Atsushi Suzuki
- Department of Nephrology and Endocrinology, The University of Tokyo Hospital, Tokyo, Japan
| | - Yukio Homma
- Department of Urology, The University of Tokyo Hospital, Tokyo, Japan
| | - Masaomi Nangaku
- Department of Nephrology and Endocrinology, The University of Tokyo Hospital, Tokyo, Japan
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Myers EJ, Yuan L, Felmlee MA, Lin YY, Jiang Y, Pei Y, Wang O, Li M, Xing XP, Marshall A, Xia WB, Parker MD. A novel mutant Na + /HCO3 - cotransporter NBCe1 in a case of compound-heterozygous inheritance of proximal renal tubular acidosis. J Physiol 2016; 594:6267-6286. [PMID: 27338124 DOI: 10.1113/jp272252] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 06/08/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The inheritance of two defective alleles of SLC4A4, the gene that encodes the widely-expressed electrogenic sodium bicarbonate cotransporter NBCe1, results in the bicarbonate-wasting disease proximal renal tubular acidosis (pRTA). In the present study, we report the first case of compound-heterozygous inheritance of pRTA (p.Arg510His/p.Gln913Arg) in an individual with low blood pH, blindness and neurological signs that resemble transient ischaemic attacks. We employ fluorescence microscopy on non-polarized (human embryonic kidney) and polarized (Madin-Darby canine kidney) renal cell lines and electrophysiology on Xenopus oocytes to characterize the mutant transporters (R510H and Q913R). Both mutant transporters exhibit enhanced intracellular retention in renal cells, an observation that probably explains the HCO3- transport deficit in the individual. Both mutants retain a close-to-normal per molecule Na+ /HCO3- cotransport activity in Xenopus oocytes, suggesting that they are suitable candidates for folding-correction therapy. However, Q913R expression is uniquely associated with a depolarizing, HCO3- independent, Cl- -conductance in oocytes that could have pathological consequences if expressed in the cells of patients. ABSTRACT Proximal renal tubular acidosis (pRTA) is a rare, recessively-inherited disease characterized by abnormally acidic blood, blindness, as well as below average height and weight. pRTA is typically associated with homozygous mutation of the solute carrier 4 family gene SLC4A4. SLC4A4 encodes the electrogenic sodium bicarbonate cotransporter NBCe1, a membrane protein that acts to maintain intracellular and plasma pH. We present the first description of a case of compound-heterozygous inheritance of pRTA. The individual has inherited two mutations in NBCe1: p.Arg510His (R510H) and p.Gln913Arg (Q913R), one from each parent. In addition to the usual features of pRTA, the patient exhibits unusual signs, such as muscle spasms and fever. We have recreated these mutant transporters for expression in model systems. We find that both of the mutant proteins exhibit substantial intracellular retention when expressed in mammalian renal cell lines. When expressed in Xenopus oocytes, we find that the R510H and Q913R-mutant NBCe1 molecules exhibit apparently normal Na+ /HCO3- cotransport activity but that Q913R is associated with an unusual HCO3- independent anion-leak. We conclude that a reduced accumulation of NBCe1 protein in the basolateral membrane of proximal-tubule epithelia is the most probable cause of pRTA in this case. We further note that the Q913R-associated anion-leak could itself be pathogenic if expressed in the plasma membrane of mammalian cells, compromising the benefit of strategies aiming to enhance mutant NBCe1 accumulation in the plasma membrane.
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Affiliation(s)
- Evan J Myers
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA
| | - Lu Yuan
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Melanie A Felmlee
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA.,Department of Pharmaceutics and Medicinal Chemistry, Thomas J. Long School of Pharmacy and Health Sciences, University of the Pacific, Stockton, California, USA
| | - Yuan-Yuan Lin
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Yan Jiang
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Yu Pei
- Department of Endocrinology, Chinese People's Army General Hospital, Beijing, China
| | - Ou Wang
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Mei Li
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Xiao-Ping Xing
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Aniko Marshall
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA
| | - Wei-Bo Xia
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China.
| | - Mark D Parker
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA. .,Department of Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA. .,State University of New York Eye Institutes, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA.
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Namgoong JH, Bertoni C. Clinical potential of ataluren in the treatment of Duchenne muscular dystrophy. Degener Neurol Neuromuscul Dis 2016; 6:37-48. [PMID: 30050367 PMCID: PMC6053089 DOI: 10.2147/dnnd.s71808] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Duchenne muscular dystrophy (DMD) is an autosomal dominant, X-linked neuromuscular disorder caused by mutations in dystrophin, one of the largest genes known to date. Dystrophin gene mutations are generally transmitted from the mother to male offspring and can occur throughout the coding length of the gene. The majority of the methodologies aimed at treating the disorder have focused on restoring a shorter, although partially functional, dystrophin protein. The approach has the potential of converting a severe DMD phenotype into a milder form of the disease known as Becker muscular dystrophy. Others have focused on ameliorating the disease by targeting secondary pathologies such as inflammation or loss of regeneration. Of great potential is the development of strategies that are capable of restoring full-length dystrophin expression due to their ability to produce a normal, fully functional protein. Among these strategies, the use of read-through compounds (RTCs) that could be administered orally represents an ideal option. Gentamicin has been previously tested in clinical trials for DMD with limited or no success, and its use in the clinic has been dismissed due to issues of toxicity and lack of clear benefits to patients. More recently, new RTCs have been identified and tested in animal models for DMD. This review will focus on one of those RTCs known as ataluren that has now completed Phase III clinical studies for DMD and at providing an overview of the different stages that have led to its clinical development for the disease. The impact that this new drug may have on DMD and its future perspectives will also be described, with an emphasis on the importance of further assessing the clinical benefits of this molecule in patients as it becomes available on the market in different countries.
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Affiliation(s)
- John Hyun Namgoong
- Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA,
| | - Carmen Bertoni
- Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA,
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