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Shimada BK, Pomozi V, Zoll J, Kuo S, Martin L, Le Saux O. ABCC6, Pyrophosphate and Ectopic Calcification: Therapeutic Solutions. Int J Mol Sci 2021; 22:ijms22094555. [PMID: 33925341 PMCID: PMC8123679 DOI: 10.3390/ijms22094555] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Revised: 04/20/2021] [Accepted: 04/21/2021] [Indexed: 12/11/2022] Open
Abstract
Pathological (ectopic) mineralization of soft tissues occurs during aging, in several common conditions such as diabetes, hypercholesterolemia, and renal failure and in certain genetic disorders. Pseudoxanthoma elasticum (PXE), a multi-organ disease affecting dermal, ocular, and cardiovascular tissues, is a model for ectopic mineralization disorders. ABCC6 dysfunction is the primary cause of PXE, but also some cases of generalized arterial calcification of infancy (GACI). ABCC6 deficiency in mice underlies an inducible dystrophic cardiac calcification phenotype (DCC). These calcification diseases are part of a spectrum of mineralization disorders that also includes Calcification of Joints and Arteries (CALJA). Since the identification of ABCC6 as the “PXE gene” and the development of several animal models (mice, rat, and zebrafish), there has been significant progress in our understanding of the molecular genetics, the clinical phenotypes, and pathogenesis of these diseases, which share similarities with more common conditions with abnormal calcification. ABCC6 facilitates the cellular efflux of ATP, which is rapidly converted into inorganic pyrophosphate (PPi) and adenosine by the ectonucleotidases NPP1 and CD73 (NT5E). PPi is a potent endogenous inhibitor of calcification, whereas adenosine indirectly contributes to calcification inhibition by suppressing the synthesis of tissue non-specific alkaline phosphatase (TNAP). At present, therapies only exist to alleviate symptoms for both PXE and GACI; however, extensive studies have resulted in several novel approaches to treating PXE and GACI. This review seeks to summarize the role of ABCC6 in ectopic calcification in PXE and other calcification disorders, and discuss therapeutic strategies targeting various proteins in the pathway (ABCC6, NPP1, and TNAP) and direct inhibition of calcification via supplementation by various compounds.
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Affiliation(s)
- Briana K Shimada
- Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, HI 96817, USA
| | - Viola Pomozi
- Institute of Enzymology, RCNS, Hungarian Academy of Sciences, 1117 Budapest, Hungary
| | - Janna Zoll
- Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, HI 96817, USA
| | - Sheree Kuo
- Department of Pediatrics, Kapi'olani Medical Center for Women and Children, University of Hawaii, Honolulu, HI 96826, USA
| | - Ludovic Martin
- PXE Consultation Center, MAGEC Reference Center for Rare Skin Diseases, Angers University Hospital, 49100 Angers, France
- BNMI, CNRS 6214/INSERM 1083, University Bretagne-Loire, 49100 Angers, France
| | - Olivier Le Saux
- Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, HI 96817, USA
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Molecular Genetics and Modifier Genes in Pseudoxanthoma Elasticum, a Heritable Multisystem Ectopic Mineralization Disorder. J Invest Dermatol 2020; 141:1148-1156. [PMID: 33341249 DOI: 10.1016/j.jid.2020.10.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Revised: 10/19/2020] [Accepted: 10/23/2020] [Indexed: 01/08/2023]
Abstract
In the past two decades, there has been great progress in identifying the molecular basis and pathomechanistic details in pseudoxanthoma elasticum (PXE), a heritable multisystem ectopic mineralization disorder. Although the identification of pathogenic variants in ABCC6 has been critical for understanding the disease process, genetic modifiers have been disclosed that explain the phenotypic heterogeneity of PXE. Adding to the genetic complexity of PXE are PXE-like phenotypes caused by pathogenic variants in other ectopic mineralization-associated genes. This review summarizes the current knowledge of the genetics and candidate modifier genes in PXE, a multifactorial disease at the genome-environment interface.
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Venkatachalam K, Chennamsetty K. Elastosis perforans serpiginosa in a case of pseudoxanthoma elasticum: A rare association. Indian Dermatol Online J 2016; 7:103-6. [PMID: 27057491 PMCID: PMC4804577 DOI: 10.4103/2229-5178.178078] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Elastosis perforans serpiginosa (EPS), characterized by transepidermal elimination of fragmented elastic fibers, clinically presents as hyperkeratotic papules. EPS is classified into three types: (1) Idiopathic; (2) reactive, with associated connective tissue diseases such as pseudoxanthoma elasticum (PXE), Ehlers–Danlos syndrome, cutis laxa, Marfan syndrome, osteogenesis imperfecta, Down's syndrome; (3) the one that is induced by D-penicillamine. A rare association of EPS with PXE, which is primarily a defect of transmembrane transporter protein with accumulation of certain metabolic compounds and secondary calcification of elastic fibers has been documented in the literature. We report a case of PXE with associated lesions that were histopathologically compatible with EPS.
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Affiliation(s)
- Konakanchi Venkatachalam
- Department of Dermatology, Venereology and Leprosy, Andhra Medical College, Visakhapatnam, Andhra Pradesh, India
| | - Kavya Chennamsetty
- Department of Dermatology, Venereology and Leprosy, Andhra Medical College, Visakhapatnam, Andhra Pradesh, India
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Oztas Z, Karadeniz C, Afrashi F, Nalcaci S, Yaman B. Minor trauma resulting in subretinal haemorrhage with choroidal rupture: a case of subtle pseudoxanthoma elasticum in a child. Clin Exp Optom 2016; 99:84-6. [PMID: 26875857 DOI: 10.1111/cxo.12275] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2014] [Revised: 09/11/2014] [Accepted: 12/10/2014] [Indexed: 11/29/2022] Open
Affiliation(s)
- Zafer Oztas
- Department of Ophthalmology, School of Medicine, Ege University, Izmir, Turkey.
| | - Cem Karadeniz
- Department of Pediatric Cardiology, Izmir Dr Behçet Uz Children's Hospital, Izmir, Turkey
| | - Filiz Afrashi
- Department of Ophthalmology, School of Medicine, Ege University, Izmir, Turkey
| | - Serhad Nalcaci
- Department of Ophthalmology, School of Medicine, Ege University, Izmir, Turkey
| | - Banu Yaman
- Department of Pathology, School of Medicine, Ege University, Izmir, Turkey
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Zhang Z, Liu X. Pseudoxanthoma elasticum. Med J Aust 2014; 201:544. [PMID: 25358583 DOI: 10.5694/mja14.00247] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2014] [Accepted: 06/26/2014] [Indexed: 11/17/2022]
Affiliation(s)
- Zhenying Zhang
- Dermatology, University of Hong Kong - Shenzhen Hospital, Shenzhen, Guangdong, China.
| | - Xiaoming Liu
- Dermatology, University of Hong Kong - Shenzhen Hospital, Shenzhen, Guangdong, China
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Aerts C, De Keyser C, Leys A. Visual loss and presumed pseudoxanthoma elasticum confirmed with genetic analysis but not with skin examination and biopsies. GMS OPHTHALMOLOGY CASES 2011; 1:Doc03. [PMID: 27625925 PMCID: PMC5015608 DOI: 10.3205/oc000003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE Case report of a patient with angioid streaks, peau d'orange, comet tail lesions, choroidal neovascularisation and presumed pseudoxanthoma elasticum (PXE). PXE was confirmed by gene analysis but not by skin biopsies. METHODS Case report of a patient with angioid streaks identified at age 21 and follow-up till age 43 with repeated fluorescein angiography (FA) and optical coherence tomography (OCT). Dermatologic examination, skin biopsies and genetical analysis performed to confirm suspected diagnosis of PXE. RESULTS At age 43, no specific skin lesions were identified and 3 biopsies could not confirm PXE. Genetic analysis showed a homozygous mutation in the ABCC6 gene and confirmed the diagnosis of PXE. CONCLUSIONS This case illustrates that in patients with angioid streaks having strong ocular indicators of PXE, confirmation of PXE can be obtained not only with dermatologic examination and skin biopsies, but also with genetic analysis. PXE associated mutations can be detected occasionally in biopsy negative patients and for this reason are extremely helpful in confirming a suspected diagnosis.
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Affiliation(s)
- Carolien Aerts
- Department of Dermatology, University Hospitals Leuven, Leuven, Belgium
| | | | - Anita Leys
- Department of Ophthalmology, University Hospitals Leuven, Leuven, Belgium,*To whom correspondence should be addressed: Anita Leys, Department of Ophthalmology, University Hospitals Leuven, Kapucijnenvoer 33, 3000 Leuven, Belgium, E-mail:
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Uitto J, Bercovitch L, Terry SF, Terry PF. Pseudoxanthoma elasticum: progress in diagnostics and research towards treatment : Summary of the 2010 PXE International Research Meeting. Am J Med Genet A 2011; 155A:1517-26. [PMID: 21671388 PMCID: PMC3121926 DOI: 10.1002/ajmg.a.34067] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Accepted: 03/25/2011] [Indexed: 11/07/2022]
Abstract
Pseudoxanthoma elasticum (PXE), a prototypic heritable disorder with ectopic mineralization, manifests with characteristic skin findings, ocular involvement, and cardiovascular problems. The classic forms of PXE are due to loss-of-function mutations in the ABCC6 gene, which encodes ABCC6, a putative transmembrane efflux transporter expressed primarily in the liver. While considerable progress has recently been made in understanding the molecular genetics and pathomechanisms of PXE, no effective or specific treatment is currently available for this disorder. PXE International, the premiere patient advocacy organization, organized a workshop in November 2010 to assess the current state of diagnostics and research to develop an agenda towards treatment of PXE. This overview summarizes the progress in PXE research, with emphasis on molecular therapies for this, currently intractable, disorder.
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Affiliation(s)
- Jouni Uitto
- Department of Dermatology and Cutaneous Biology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
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Larusso J, Ringpfeil F, Uitto J. Pseudoxanthoma elasticum: a streamlined, ethnicity-based mutation detection strategy. Clin Transl Sci 2011; 3:295-8. [PMID: 21167005 DOI: 10.1111/j.1752-8062.2010.00243.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Pseudoxanthoma elasticum (PXE), an autosomal recessive multisystem disorder, is caused by mutations in the ABCC6 gene, and approximately 300 distinct mutations representing >1000 mutant alleles have been disclosed thus far. Few population-based studies have reported mutational hotspots in some geographic areas. In this study, we attempted to correlate recurring mutations with the individuals' ethnic origin. Specifically, we plotted our international database of 70 families from distinct or mixed ethnic backgrounds against their mutations. The frequent p.R1141X mutation was distributed widely across Europe, while deletion of exons 23-29 (del23-29) was encountered in Northern Europe and in Northern Mediterranean countries. p.R1138W may be a marker for French descent, evidenced by its presence also in French Canadians. The splice site transition mutation 3736-1G→A was seen in the neighboring countries Greece and Turkey, whereas 2542 delG occurs only in the Japanese. Two mutations seem to be present worldwide without evidence of a founder effect, p.Q378X and p.R1339C, suggesting the presence of mutational hotspots. Knowledge of this distribution will allow us to streamline mutation screening through a targeted, stepwise approach when the ethnicity of a patient is known. This will facilitate the identification of individuals at risk, improving their care to prevent ophthalmological and vascular disease.
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Affiliation(s)
- Jennifer Larusso
- Department of Dermatology and Cutaneous Biology, Jefferson Medical College, and Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania, USA
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Georgalas I, Tservakis I, Papaconstaninou D, Kardara M, Koutsandrea C, Ladas I. Pseudoxanthoma elasticum, ocular manifestations, complications and treatment. Clin Exp Optom 2010; 94:169-80. [PMID: 21198842 DOI: 10.1111/j.1444-0938.2010.00559.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Pseudoxanthoma elasticum (PXE), also known as Groenblad syndrome, is an inherited disorder characterised by mineralisation and fragmentation of elastic fibres in a number of organs including the skin, eyes and arterial blood vessels. The clinical manifestations of PXE centre on three major organ systems: skin, cardiovascular system and the eyes. This review focuses on the ocular manifestations of pseudoxanthoma elasticum, namely, peau d'orange, angioid streaks and choroidal neovascularisation, the clinical course of patients, the diagnostic approaches and current therapeutic strategies, such as laser photocoagulation whether transpupillary thermotherapy or photodynamic therapy, macular translocation surgery and anti-vascular endothelial growth factor treatment.
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Affiliation(s)
- Ilias Georgalas
- Department of Ophthalmology, G Gennimatas Hospital of Athens, NHS, University of Athens, Athens, Greece.
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Köblös G, Andrikovics H, Prohászka Z, Tordai A, Váradi A, Arányi T. The R1141X loss-of-function mutation of the ABCC6 gene is a strong genetic risk factor for coronary artery disease. Genet Test Mol Biomarkers 2010; 14:75-8. [PMID: 19929409 DOI: 10.1089/gtmb.2009.0094] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Loss-of-function mutations of ABCC6 cause pseudoxanthoma elasticum (PXE). This Mendelian disorder is characterized by elastic calcification leading to dermal, ocular, and cardiovascular symptoms like coronary artery disease (CAD) and stroke. Although PXE is a recessive disease, microscopic dermal lesions, serum alterations, and higher anecdotal incidence of stroke or CAD among carriers were reported. Here we investigated the association of the c.3421C>T loss-of-function mutation of ABCC6 and CAD and stroke. A previous study demonstrated the association of the c.3421C>T mutation with CAD; however, the frequency found in the control population was unexpectedly high, contradicting, thus, the prevalence of PXE. In the present study, genomic DNA from 749 healthy blood donors was used as control, while 363 and 361 patients suffering from stroke and CAD were investigated, respectively. One carrier was found in our control group, which is in accordance with the reported prevalence of this mutation. No significant association was found between carrier status and stroke in our cohort. In contrast, a significant association of carrier status and CAD was observed (5/361 carriers: p = 0.016, odds ratio [OR] = 10.5). We propose that carriers of ABCC6 loss-of-function mutations benefit from CAD prevention therapy.
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Affiliation(s)
- Gabriella Köblös
- Institute of Enzymology, Hungarian Academy of Sciences, Budapest, Hungary
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de Boussac H, Ratajewski M, Sachrajda I, Köblös G, Tordai A, Pulaski L, Buday L, Váradi A, Arányi T. The ERK1/2-hepatocyte nuclear factor 4alpha axis regulates human ABCC6 gene expression in hepatocytes. J Biol Chem 2010; 285:22800-8. [PMID: 20463007 DOI: 10.1074/jbc.m110.105593] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
ABCC6 mutations are responsible for the development of pseudoxanthoma elasticum, a rare recessive disease characterized by calcification of elastic fibers. Although ABCC6 is mainly expressed in the liver the disease has dermatologic, ocular, and cardiovascular symptoms. We investigated the transcriptional regulation of the gene and observed that hepatocyte growth factor (HGF) inhibits its expression in HepG2 cells via the activation of ERK1/2. Similarly, other factors activating the cascade also inhibited ABCC6 expression. We identified the ERK1/2 response element in the proximal promoter by luciferase reporter gene assays. This site overlapped with a region conferring the tissue-specific expression pattern to the gene and with a putative hepatocyte nuclear factor 4alpha (HNF4alpha) binding site. We demonstrated that HNF4alpha regulates the expression of ABCC6, acts through the putative binding site, and determines its cell type-specific expression. We also showed that HNF4alpha is inhibited by the activation of the ERK1/2 cascade. In conclusion we describe here the first regulatory pathway of ABCC6 expression showing that the ERK1/2-HNF4alpha axis has an important role in regulation of the gene.
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Affiliation(s)
- Hugues de Boussac
- Institute of Enzymology, Hungarian Academy of Sciences, Karolina ut 29, 1113 Budapest, Hungary
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Abstract
Pseudoxanthoma elasticum (PXE), a prototypic heritable disorder with ectopic mineralization, manifests with characteristic skin findings, ocular involvement and cardiovascular problems, with considerable morbidity and mortality. The classic forms of PXE are due to loss-of-function mutations in the ABCC6 gene, which encodes ABCC6, a transmembrane efflux transporter expressed primarily in the liver. Several lines of evidence suggest that PXE is a primary metabolic disorder, which in the absence of ABCC6 transporter activity, displays reduced plasma anti-mineralization capacity due to reduced fetuin-A and matrix gla-protein (MGP) levels. MGP requires to be activated by gamma-glutamyl carboxylation, a vitamin K-dependent reaction, to serve in an anti-mineralization role in the peripheral connective tissue cells. Although the molecules transported from the hepatocytes to circulation by ABCC6 in vivo remain unidentified, it has been hypothesized that a critical vitamin K derivative, such as reduced vitamin K conjugated with glutathione, is secreted to circulation physiologically, but not in the absence of ABCC6 transporter activity. As a result, activation of MGP by gamma-glutamyl carboxylase is diminished, allowing slow yet progressive mineralization of connective tissues characteristic of PXE. Understanding of the pathomechanistic details of PXE provides a basis for the development of targeted molecular therapies for this currently intractable disease.
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Affiliation(s)
- Jouni Uitto
- Department of Dermatology and Cutaneous Biology, Jefferson Medical College and Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, PA 19107, USA.
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Overexpression of fetuin-a counteracts ectopic mineralization in a mouse model of pseudoxanthoma elasticum (abcc6(-/-)). J Invest Dermatol 2010; 130:1288-96. [PMID: 20090764 DOI: 10.1038/jid.2009.423] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The pathologic hallmark of pseudoxanthoma elasticum (PXE) is ectopic mineralization of soft connective tissues. Recent studies have suggested that PXE is a metabolic disease, and perturbations in a number of circulatory factors have been postulated. One of them is fetuin-A, a 60-kDa glycoprotein synthesized in the liver and secreted into blood. Observations in targeted mutant mice (Ahsg(-/-)) and in cell culture model systems have shown that fetuin-A is a powerful anti-mineralization factor in circulation, and the serum levels of fetuin-A in patients with PXE as well as in a mouse model of PXE (Abcc6(-/-)) have been shown to be reduced by up to 30%. In this study, we tested the hypothesis that overexpression of fetuin-A in Abcc6(-/-) mice counteracts the ectopic mineralization. Delivery of an expression construct containing full-length mouse fetuin-A complementary DNA (cDNA), linked to a His-tag, to the liver of these mice resulted in elevated serum levels of this protein. As a consequence, soft tissue mineralization, which is a characteristic of Abcc6(-/-) mice, was reduced by approximately 70% at 12 weeks of age, but the effect was transient when examined 4 weeks later. The results suggest that normalization of serum fetuin-A, either through gene therapy approaches or by direct protein delivery to the circulation, may offer strategies for treating PXE and perhaps other heritable disorders of soft tissue mineralization.
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Affiliation(s)
- Robb Marchione
- Department of Dermatology and Cutaneous Surgery, University of Miami Miller School of Medicine, Miami, Florida, USA
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Fülöp K, Barna L, Symmons O, Závodszky P, Váradi A. Clustering of disease-causing mutations on the domain-domain interfaces of ABCC6. Biochem Biophys Res Commun 2009; 379:706-9. [PMID: 19133228 DOI: 10.1016/j.bbrc.2008.12.142] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2008] [Accepted: 12/15/2008] [Indexed: 10/21/2022]
Abstract
Mutations in ABCC6 are responsible for pseudoxanthoma elasticum (PXE), a rare genetic disease affecting the elastic tissues of the body. ABCC6 encodes a 1503 amino acid long ABC transporter, ABCC6/MRP6. The functional link between the impaired activity of the protein and the disease is not known. We have built a homology model of this transporter, and analyzed the distribution of the known 119 missense PXE-associated mutations within the predicted structure. Significant clustering of the missense mutations has been found at complex domain-domain interfaces: at the transmission interface that involves four intracellular loops and the two ABC domains as well as at the ABC-ABC interacting surfaces. The mutations affecting these regions are 2.75 and 3.53-fold more frequent than the average mutational rate along the transporter protein sequence. These data provide a genetic proof of the importance of these domain-domain interactions in the ABCC6 transporter.
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Affiliation(s)
- Krisztina Fülöp
- Institute of Enzymology, Hungarian Academy of Sciences, Karolina ut 29, Budapest, Hungary
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LaRusso J, Li Q, Jiang Q, Uitto J. Elevated dietary magnesium prevents connective tissue mineralization in a mouse model of pseudoxanthoma elasticum (Abcc6(-/-)). J Invest Dermatol 2009; 129:1388-94. [PMID: 19122649 DOI: 10.1038/jid.2008.391] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Pseudoxanthoma elasticum (PXE) is an autosomal recessive multisystem disorder characterized by ectopic connective tissue mineralization, with clinical manifestations primarily in the skin, eyes, and cardiovascular system. There is considerable, both intra- and interfamilial, variability in the spectrum of phenotypic presentation. Previous studies have suggested that mineral content of the diet may modify the severity of the clinical phenotype in PXE. In this study, we utilized a targeted mutant mouse (Abcc6(-/-)) as a model system for PXE. We examined the effects of changes in dietary phosphate and magnesium on the mineralization process using calcification of the connective tissue capsule surrounding the vibrissae as an early phenotypic biomarker. Mice placed on custom-designed diets either high or low in phosphate did not show changes in mineralization, which was similar to that noted in Abcc6(-/-) mice on control diet. However, mice placed on diet enriched in magnesium (fivefold) showed no evidence of connective tissue mineralization in this mouse model of PXE. The inhibitory capacity of magnesium was confirmed in a cell-based mineralization assay system in vitro. Collectively, our observations suggest that assessment of dietary magnesium in patients with PXE may be warranted.
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Affiliation(s)
- Jennifer LaRusso
- Department of Dermatology and Cutaneous Biology, Jefferson Medical College, Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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Li Q, Jiang Q, Pfendner E, Váradi A, Uitto J. Pseudoxanthoma elasticum: clinical phenotypes, molecular genetics and putative pathomechanisms. Exp Dermatol 2009; 18:1-11. [PMID: 19054062 PMCID: PMC3349969 DOI: 10.1111/j.1600-0625.2008.00795.x] [Citation(s) in RCA: 110] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Pseudoxanthoma elasticum (PXE), a prototype of heritable multisystem disorders, is characterised by pathologic mineralisation of connective tissues, with primary clinical manifestations in the skin, eyes and the cardiovascular system. The causative gene was initially identified as ABCC6 which encodes an ABC transporter protein (ABCC6) expressed primarily in the liver and the kidneys. The critical role of ABCC6 in ectopic mineralisation has been confirmed by the development of Abcc6(-/-) knock-out mice which recapitulate the features of connective tissue mineralisation characteristic of PXE. Over 300 distinct loss-of-function mutations representative of over 1000 mutant alleles in ABCC6 have been identified by streamlined mutation detection strategies in this autosomal recessive disease. More recently, missense mutations in the GGCX gene, either in compound heterozygous state or digenic with a recurrent ABCC6 nonsense mutation (p.R1141X), have been identified in patients with PXE-like cutaneous findings and vitamin K-dependent coagulation factor deficiency. GGCX encodes a carboxylase which catalyses gamma-glutamyl carboxylation of coagulation factors as well as of matrix gla protein (MGP) which in fully carboxylated form serves as a systemic inhibitor of pathologic mineralisation. Collectively, these observations suggest the hypothesis that a consequence of loss-of-function mutations in the ABCC6 gene is the reduced vitamin K-dependent gamma-glutamyl carboxylation of MGP, with subsequent connective tissue mineralisation. Further progress in understanding the detailed pathomechanisms of PXE should provide novel strategies to counteract, and perhaps cure, this complex heritable disorder at the genome-environment interface.
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Affiliation(s)
- Qiaoli Li
- Departments of Dermatology and Cutaneous Biology, and Biochemistry and Molecular Biology, Jefferson Medical College, and Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, PA 19107, USA
| | - Qiujie Jiang
- Departments of Dermatology and Cutaneous Biology, and Biochemistry and Molecular Biology, Jefferson Medical College, and Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, PA 19107, USA
| | | | - András Váradi
- Institute of Enzymology, Hungarian Academy of Sciences, Budapest, Hungary
| | - Jouni Uitto
- Departments of Dermatology and Cutaneous Biology, and Biochemistry and Molecular Biology, Jefferson Medical College, and Jefferson Institute of Molecular Medicine, Thomas Jefferson University, Philadelphia, PA 19107, USA
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Abstract
Pseudoxanthoma elasticum (PXE) is a pleiotropic multisystem disorder affecting skin, eyes, and the cardiovascular system with progressive pathological mineralization. It is caused by mutations in the ABCC6 gene expressed primarily in the liver and kidneys, and at very low levels, if at all, in tissues affected by PXE. A question has arisen regarding the pathomechanism of PXE, particularly the "metabolic" versus the "PXE cell" hypotheses. We examined a murine PXE model (Abcc6(-/-)) by transplanting muzzle skin from knockout (KO) and wild-type (WT) mice onto the back of WT and KO mice using mineralization of the connective tissue capsule surrounding the vibrissae as an early phenotypic biomarker. Grafting of WT mouse muzzle skin onto the back of KO mice resulted in mineralization of vibrissae, whereas grafting KO mouse muzzle skin onto WT mice did not. Thus, these findings implicate circulatory factors as a critical component of the mineralization process. This mouse grafting model supports the notion that PXE is a systemic metabolic disorder with secondary mineralization of connective tissues and that the mineralization process can be countered or even reversed by changes in the homeostatic milieu.
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