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Jönsson ÅLM, Hilberg O, Simonsen U, Christensen JH, Bendstrup E. New insights in the genetic variant spectrum of SLC34A2 in pulmonary alveolar microlithiasis; a systematic review. Orphanet J Rare Dis 2023; 18:130. [PMID: 37259144 DOI: 10.1186/s13023-023-02712-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Accepted: 04/30/2023] [Indexed: 06/02/2023] Open
Abstract
Pulmonary alveolar microlithiasis (PAM) is a rare autosomal recessive lung disease caused by variants in the SLC34A2 gene encoding the sodium-dependent phosphate transport protein 2B, NaPi-2b. PAM is characterized by deposition of calcium phosphate crystals in the alveoli. Onset and clinical course vary considerably; some patients remain asymptomatic while others develop severe respiratory failure with a significant symptom burden and compromised survival. It is likely that PAM is under-reported due to lack of recognition, misdiagnosis, and mild clinical presentation. Most patients are genetically uncharacterized as the diagnostic confirmation of PAM has traditionally not included a genetic analysis. Genetic testing may in the future be the preferred tool for diagnostics instead of invasive methods. This systematic review aims to provide an overview of the growing knowledge of PAM genetics. Rare variants in SLC34A2 are found in almost all genetically tested patients. So far, 34 allelic variants have been identified in at least 68 patients. A majority of these are present in the homozygous state; however, a few are found in the compound heterozygous form. Most of the allelic variants involve only a single nucleotide. Half of the variants are either nonsense or frameshifts, resulting in premature termination of the protein or decay of the mRNA. There is currently no cure for PAM, and the only effective treatment is lung transplantation. Management is mainly symptomatic, but an improved understanding of the underlying pathophysiology will hopefully result in development of targeted treatment options. More standardized data on PAM patients, including a genetic diagnosis covering larger international populations, would support the design and implementation of clinical studies to the benefit of patients. Further genetic characterization and understanding of how the molecular changes influence disease phenotype will hopefully allow earlier diagnosis and treatment of the disease in the future.
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Affiliation(s)
- Åsa Lina M Jönsson
- Department of Clinical Genetics, Aarhus University Hospital, Aarhus, Denmark.
- Department of Biomedicine, Aarhus University, Aarhus, Denmark.
| | - Ole Hilberg
- Department of Regional Health Research, University of Southern Denmark, Odense, Denmark.
- Department of Medicine, Lillebaelt Hospital, Vejle, Denmark.
| | - Ulf Simonsen
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | | | - Elisabeth Bendstrup
- Centre for Rare Lung Diseases, Department of Respiratory Diseases and Allergy, Aarhus University Hospital, Aarhus, Denmark
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Ding M, Zhang Q, Zhang M, Jiang X, Wang M, Ni L, Gong W, Huang B, Chen J. Phosphate Overload Stimulates Inflammatory Reaction via PiT-1 and Induces Vascular Calcification in Uremia. J Ren Nutr 2021; 32:178-188. [PMID: 34688540 DOI: 10.1053/j.jrn.2021.03.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 01/27/2021] [Accepted: 03/20/2021] [Indexed: 11/11/2022] Open
Abstract
OBJECTIVE Vascular calcification (VC) is an important risk factor for cardiovascular disease in maintenance hemodialysis (MHD) patients. Hyperphosphatemia and microinflammation statement are known major contributors to the development of VC; however, the mechanisms are unknown. The aims of this study were to explore the risk factors of VC in MHD patients and to explore whether high phosphate could increase the secretion of inflammatory cytokines via PiT-1 in monocytes. METHODS A cross-sectional study was conducted on 65 MHD patients to assess the relevance of coronary artery calcification (CAC), inflammatory factors, serum phosphate, and sodium-dependent phosphate cotransporter (NPT) mRNA expression of peripheral blood mononuclear cells (PBMCs). Multivariate logistic regression analysis was used to analyze the predictors of CAC. The calcification effects of high phosphate (HP), TNF-α, and supernatants of healthy human monocytes treated with HP were further evaluated in cultured HASMCs. RESULTS Diabetes, longer dialysis vintage, higher serum TNF-α levels, and PiT-1 mRNA expression of PBMCs) were independent risk factors of CAC in MHD patients. The mRNA levels of PiT-1 in PBMCs were positively correlated with serum phosphate, CAC scores, and Pit-2 mRNA levels of PBMCs. The expressions of TNF-α, IL-6, and PiT-1 in human monocytes were significantly increased in a dose-dependent manner after treatment with HP, which was subsequently inhibited by NPT antagonist phosphonoformic acid. Neither TNF-α alone nor supernatants of monocytes stimulated with HP promoted the expression of osteopontin and Runt-related transcription factor 2 (Runx2) or caused mineralization in human aortic smooth muscle cells, but combined with HP intervention, the calcification effects were markedly increased in human aortic smooth muscle cells and ameliorated by phosphonoformic acid treatment. CONCLUSION Hyperphosphatemia directly increased the synthesis and secretion of TNF-α by monocytes may via PiT-1 pathway, resulting in elevated systemic inflammatory response, which may further aggravate VC induced by phosphate overload in MHD patients.
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Affiliation(s)
- Minwen Ding
- Division of Nephrology, National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, Shanghai, China
| | - Qian Zhang
- Division of Nephrology, National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, Shanghai, China
| | - Minmin Zhang
- Division of Nephrology, National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, Shanghai, China
| | - Xinxin Jiang
- Division of Nephrology, National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, Shanghai, China
| | - Mengjing Wang
- Division of Nephrology, National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, Shanghai, China
| | - Li Ni
- Division of Nephrology, National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, Shanghai, China
| | - Wen Gong
- Division of Nephrology, National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, Shanghai, China
| | - Bihong Huang
- Division of Nephrology, National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, Shanghai, China
| | - Jing Chen
- Division of Nephrology, National Clinical Research Center for Aging and Medicine, Huashan Hospital, Fudan University, Shanghai, China.
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Abstract
Phosphate is an essential nutrient for life and is a critical component of bone formation, a major signaling molecule, and structural component of cell walls. Phosphate is also a component of high-energy compounds (i.e., AMP, ADP, and ATP) and essential for nucleic acid helical structure (i.e., RNA and DNA). Phosphate plays a central role in the process of mineralization, normal serum levels being associated with appropriate bone mineralization, while high and low serum levels are associated with soft tissue calcification. The serum concentration of phosphate and the total body content of phosphate are highly regulated, a process that is accomplished by the coordinated effort of two families of sodium-dependent transporter proteins. The three isoforms of the SLC34 family (SLC34A1-A3) show very restricted tissue expression and regulate intestinal absorption and renal excretion of phosphate. SLC34A2 also regulates the phosphate concentration in multiple lumen fluids including milk, saliva, pancreatic fluid, and surfactant. Both isoforms of the SLC20 family exhibit ubiquitous expression (with some variation as to which one or both are expressed), are regulated by ambient phosphate, and likely serve the phosphate needs of the individual cell. These proteins exhibit similarities to phosphate transporters in nonmammalian organisms. The proteins are nonredundant as mutations in each yield unique clinical presentations. Further research is essential to understand the function, regulation, and coordination of the various phosphate transporters, both the ones described in this review and the phosphate transporters involved in intracellular transport.
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Affiliation(s)
- Nati Hernando
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
| | - Kenneth Gagnon
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
| | - Eleanor Lederer
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
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Hernando N, Wagner CA. Mechanisms and Regulation of Intestinal Phosphate Absorption. Compr Physiol 2018; 8:1065-1090. [PMID: 29978897 DOI: 10.1002/cphy.c170024] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
States of hypo- and hyperphosphatemia have deleterious consequences including rickets/osteomalacia and renal/cardiovascular disease, respectively. Therefore, the maintenance of appropriate plasma levels of phosphate is an essential requirement for health. This control is executed by the collaborative action of intestine and kidney whose capacities to (re)absorb phosphate are regulated by a number of hormonal and metabolic factors, among them parathyroid hormone, fibroblast growth factor 23, 1,25(OH)2 vitamin D3 , and dietary phosphate. The molecular mechanisms responsible for the transepithelial transport of phosphate across enterocytes are only partially understood. Indeed, whereas renal reabsorption entirely relies on well-characterized active transport mechanisms of phosphate across the renal proximal epithelia, intestinal absorption proceeds via active and passive mechanisms, with the molecular identity of the passive component still unknown. The active absorption of phosphate depends mostly on the activity and expression of the sodium-dependent phosphate cotransporter NaPi-IIb (SLC34A2), which is highly regulated by many of the factors, mentioned earlier. Physiologically, the contribution of NaPi-IIb to the maintenance of phosphate balance appears to be mostly relevant during periods of low phosphate availability. Therefore, its role in individuals living in industrialized societies with high phosphate intake is probably less relevant. Importantly, small increases in plasma phosphate, even within normal range, associate with higher risk of cardiovascular disease. Therefore, therapeutic approaches to treat hyperphosphatemia, including dietary phosphate restriction and phosphate binders, aim at reducing intestinal absorption. Here we review the current state of research in the field. © 2017 American Physiological Society. Compr Physiol 8:1065-1090, 2018.
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Affiliation(s)
- Nati Hernando
- National Center for Competence in Research NCCR Kidney.CH, Institute of Physiology, University Zurich-Irchel, Zurich, Switzerland
| | - Carsten A Wagner
- National Center for Competence in Research NCCR Kidney.CH, Institute of Physiology, University Zurich-Irchel, Zurich, Switzerland
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Shobeiri N, Adams MA, Holden RM. Phosphate: an old bone molecule but new cardiovascular risk factor. Br J Clin Pharmacol 2014; 77:39-54. [PMID: 23506202 PMCID: PMC3895346 DOI: 10.1111/bcp.12117] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Accepted: 02/21/2013] [Indexed: 12/24/2022] Open
Abstract
Phosphate handling in the body is complex and involves hormones produced by the bone, the parathyroid gland and the kidneys. Phosphate is mostly found in hydroxyapatite. however recent evidence suggests that phosphate is also a signalling molecule associated with bone formation. Phosphate balance requires careful regulation of gut and kidney phosphate transporters, SLC34 transporter family, but phosphate signalling in osteoblasts and vascular smooth muscle cells is likely mediated by the SLC20 transporter family (PiT1 and PiT2). If not properly regulated, phosphate imblanace could lead to mineral disorders as well as vascular calcification. In chronic kidney disease-mineral bone disorder, hyperphosphataemia has been consistently associated with extra-osseous calcification and cardiovascular disease. This review focuses on the physiological mechanisms involved in phosphate balance and cell signalling (i.e. osteoblasts and vascular smooth muscle cells) as well as pathological consequences of hyperphosphataemia. Finally, conventional as well as new and experimental therapeutics in the treatment of hyperphosphataemia are explored.
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Affiliation(s)
- Navid Shobeiri
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, ON, Canada
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Takano M, Horiuchi T, Sasaki Y, Kato Y, Nagai J, Yumoto R. Expression and function of PEPT2 during transdifferentiation of alveolar epithelial cells. Life Sci 2013; 93:630-6. [DOI: 10.1016/j.lfs.2013.08.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Revised: 08/10/2013] [Accepted: 08/15/2013] [Indexed: 01/25/2023]
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