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Alexander RT, Dimke H. Molecular mechanisms underlying paracellular calcium and magnesium reabsorption in the proximal tubule and thick ascending limb. Ann N Y Acad Sci 2022; 1518:69-83. [PMID: 36200584 DOI: 10.1111/nyas.14909] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Calcium and magnesium are the most abundant divalent cations in the body. The plasma level is controlled by coordinated interaction between intestinal absorption, reabsorption in the kidney, and, for calcium at least, bone storage and exchange. The kidney adjusts urinary excretion of these ions in response to alterations in their systemic concentration. Free ionized and anion-complexed calcium and magnesium are filtered at the glomerulus. The majority (i.e., >85%) of filtered divalent cations are reabsorbed via paracellular pathways from the proximal tubule and thick ascending limb (TAL) of the loop of Henle. Interestingly, the largest fraction of filtered calcium is reabsorbed from the proximal tubule (65%), while the largest fraction of filtered magnesium is reclaimed from the TAL (60%). The paracellular pathways mediating these fluxes are composed of tight junctional pores formed by claudins. In the proximal tubule, claudin-2 and claudin-12 confer calcium permeability, while the exact identity of the magnesium pore remains to be determined. Claudin-16 and claudin-19 contribute to the calcium and magnesium permeable pathway in the TAL. In this review, we discuss the data supporting these conclusions and speculate as to why there is greater fractional calcium reabsorption from the proximal tubule and greater fractional magnesium reabsorption from the TAL.
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Affiliation(s)
- R Todd Alexander
- Departments of Physiology & Pediatrics, University of Alberta, Edmonton, Alberta, Canada.,Women's and Children's Health Institute, Edmonton, Alberta, Canada
| | - Henrik Dimke
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Demark.,Department of Nephrology, Odense University Hospital, Odense, Denmark
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Liu S, Abboud MI, John T, Mikhailov V, Hvinden I, Walsby-Tickle J, Liu X, Pettinati I, Cadoux-Hudson T, McCullagh JSO, Schofield CJ. Roles of metal ions in the selective inhibition of oncogenic variants of isocitrate dehydrogenase 1. Commun Biol 2021; 4:1243. [PMID: 34725432 PMCID: PMC8560763 DOI: 10.1038/s42003-021-02743-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2021] [Accepted: 10/04/2021] [Indexed: 12/29/2022] Open
Abstract
Cancer linked isocitrate dehydrogenase (IDH) 1 variants, notably R132H IDH1, manifest a 'gain-of-function' to reduce 2-oxoglutarate to 2-hydroxyglutarate. High-throughput screens have enabled clinically useful R132H IDH1 inhibitors, mostly allosteric binders at the dimer interface. We report investigations on roles of divalent metal ions in IDH substrate and inhibitor binding that rationalise this observation. Mg2+/Mn2+ ions enhance substrate binding to wt IDH1 and R132H IDH1, but with the former manifesting lower Mg2+/Mn2+ KMs. The isocitrate-Mg2+ complex is the preferred wt IDH1 substrate; with R132H IDH1, separate and weaker binding of 2-oxoglutarate and Mg2+ is preferred. Binding of R132H IDH1 inhibitors at the dimer interface weakens binding of active site Mg2+ complexes; their potency is affected by the Mg2+ concentration. Inhibitor selectivity for R132H IDH1 over wt IDH1 substantially arises from different stabilities of wt and R132H IDH1 substrate-Mg2+ complexes. The results reveal the importance of substrate-metal ion complexes in wt and R132H IDH1 catalysis and the basis for selective R132H IDH1 inhibition. Further studies on roles of metal ion complexes in TCA cycle and related metabolism, including from an evolutionary perspective, are of interest.
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Affiliation(s)
- Shuang Liu
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK
- Broad Institute of MIT and Harvard, 415 Main Street, Cambridge, MA, 02142, USA
| | - Martine I Abboud
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK
- Department of Natural Sciences, Lebanese American University, Byblos/Beirut, Lebanon
| | - Tobias John
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK
| | - Victor Mikhailov
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK
| | - Ingvild Hvinden
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK
| | - John Walsby-Tickle
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK
| | - Xiao Liu
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK
| | - Ilaria Pettinati
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK
| | - Tom Cadoux-Hudson
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK
| | - James S O McCullagh
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK
| | - Christopher J Schofield
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK.
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