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Dual Effects of Bisphosphonates on Ectopic Skin and Vascular Soft Tissue Mineralization versus Bone Microarchitecture in a Mouse Model of Generalized Arterial Calcification of Infancy.

ABSTRACT: Generalized arterial calcification of infancy is an intractable ectopic mineralization disorder caused by mutations in the ENPP1 gene, resulting in reduced plasma inorganic pyrophosphate (PPi) levels. We previously characterized the Enpp1(asj) mutant mouse as a model of generalized arterial calcification of infancy, and we have now explored the potential efficacy of bisphosphonates, nonhydrolyzable PPi analogs, in preventing ectopic mineralization in these mice. The mice were maintained on either basic diet (control) or diets containing etidronate or alendronate in three different concentrations (experimental). Considering low bioavailability of bisphosphonates when administered orally, subsequent studies tested the mice with subcutaneous injections of etidronate. The treatments were initiated at 4 weeks of age, and the degree of mineralization was assessed at 12 weeks of age by quantitation of calcium deposits in the muzzle skin containing dermal sheath of vibrissae and in aorta. We found that bisphosphonate treatments significantly reduced mineralization in skin and aorta. These changes in treated mice were accompanied with restoration of their bone microarchitecture, determined by microcomputed tomography. The inhibitory capacity of bisphosphonates, with mechanistic implications, was confirmed in a cell-based mineralization assay in vitro. Collectively, these results suggest that bisphosphonate treatment may be beneficial by a dual effect for preventing ectopic soft tissue mineralization while correcting decreased bone mineralization in generalized arterial calcification of infancy caused by ENPP1 mutations.

SUBMITTER: Li Q

PROVIDER: S-EPMC4731049 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature

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Dual Effects of Bisphosphonates on Ectopic Skin and Vascular Soft Tissue Mineralization versus Bone Microarchitecture in a Mouse Model of Generalized Arterial Calcification of Infancy.

Li Qiaoli Q Kingman Joshua J Sundberg John P JP Levine Michael A MA Uitto Jouni J

The Journal of investigative dermatology 20160101 1

Generalized arterial calcification of infancy is an intractable ectopic mineralization disorder caused by mutations in the ENPP1 gene, resulting in reduced plasma inorganic pyrophosphate (PPi) levels. We previously characterized the Enpp1(asj) mutant mouse as a model of generalized arterial calcification of infancy, and we have now explored the potential efficacy of bisphosphonates, nonhydrolyzable PPi analogs, in preventing ectopic mineralization in these mice. The mice were maintained on eithe ...[more]

PMID: 26763447

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Project description:Generalized arterial calcification of infancy (GACI) is a life-threatening disorder in young infants. Cardiovascular symptoms are usually apparent within the first month of life. The symptoms are caused by calcification of large and medium-sized arteries, including the aorta, coronary arteries, and renal arteries. Most of the patients die by 6 months of age because of heart failure. Recently, homozygous or compound heterozygous mutations for the ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) gene were reported as causative for the disorder. ENPP1 regulates extracellular inorganic pyrophosphate (PP(i)), a major inhibitor of extracellular matrix calcification. A newborn was diagnosed with GACI. The infant died at the age of 7 weeks of cardiac failure and the parents were referred to Molecular Biology and Cytogenetic lab for further workup. Cytogenetics analysis was performed on the parents, which showed normal karyotypes and mutational analysis for the ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) gene was also performed. The mutational analysis showed that both father and mother of the deceased infant were heterozygous carriers of the mutation c.749C>T (p.P250L) in exon 7 of ENPP1 and it was likely, that the deceased child carried the same mutation homozygous on both alleles and died of GACI resulting from this ENPP1 mutation. The couple was counseled and monitored for the second pregnancy. Amniocentesis was performed at 15 weeks of gestation for mutational analysis of the same gene in the second pregnancy. The analysis was negative for the parental mutations. One month after the birth of a healthy infant, peripheral blood was collected from the baby and sent for reconfirmation. The results again were negative for the mutation and the baby was on 6 months follow up and no major symptoms were seen. The parents of the child benefited enormously by learning about the disease much in advance and also its risk of recurrence. The main aim of this study is to emphasize on two aspects: (i) the importance of modern molecular techniques in diagnosis such a syndrome and (2) the difficulties faced by the physician to provide appropriate diagnosis and the adequate genetic counseling to the family without molecular facilities.

Project description:In recent years it has become clear that, mechanistically, biomineralization is a process that has to be actively inhibited as a default state. This inhibition must be released in a rigidly controlled manner in order for mineralization to occur in skeletal elements and teeth. A central aspect of this concept is the tightly controlled balance between phosphate, a constituent of the biomineral hydroxyapatite, and pyrophosphate, a physiochemical inhibitor of mineralization. Here, we provide a detailed analysis of a zebrafish mutant, dragonfish (dgf), which is mutant for ectonucleoside pyrophosphatase/phosphodiesterase 1 (Enpp1), a protein that is crucial for supplying extracellular pyrophosphate. Generalized arterial calcification of infancy (GACI) is a fatal human disease, and the majority of cases are thought to be caused by mutations in ENPP1. Furthermore, some cases of pseudoxanthoma elasticum (PXE) have recently been linked to ENPP1. Similar to humans, we show here that zebrafish enpp1 mutants can develop ectopic calcifications in a variety of soft tissues - most notably in the skin, cartilage elements, the heart, intracranial space and the notochord sheet. Using transgenic reporter lines, we demonstrate that ectopic mineralizations in these tissues occur independently of the expression of typical osteoblast or cartilage markers. Intriguingly, we detect cells expressing the osteoclast markers Trap and CathepsinK at sites of ectopic calcification at time points when osteoclasts are not yet present in wild-type siblings. Treatment with the bisphosphonate etidronate rescues aspects of the dgf phenotype, and we detected deregulated expression of genes that are involved in phosphate homeostasis and mineralization, such as fgf23, npt2a, entpd5 and spp1 (also known as osteopontin). Employing a UAS-GalFF approach, we show that forced expression of enpp1 in blood vessels or the floorplate of mutant embryos is sufficient to rescue the notochord mineralization phenotype. This indicates that enpp1 can exert its function in tissues that are remote from its site of expression.

Project description:Background and importanceHearing loss (HL) has been sporadically described, but not well characterized, in Generalized Arterial Calcification of Infancy (GACI), a rare disease in which pathological calcification typically presents in infancy.ObjectivesThis study aims to describe the clinical audiologic and otologic features and potential etiology of hearing impairment in GACI and gain pathophysiological insight from a murine model of GACI.DesignCross-sectional cohort study of individuals with GACI. Murine ossicle micromorphology of the ENPP1asj/asj mutant compared to wild-type.SettingClinical research hospital; basic science laboratory.ParticipantsNineteen individuals with GACI who met clinical, biochemical, and genetic criteria for diagnosis.Main outcomes and measuresClinical, biochemical, and radiologic features associated with hearing status.ResultsPure-tone thresholds could be established in 15 (n = 30 ears) of the 19 patients who underwent audiological assessments. The prevalence of HL was 50% (15/30) of ears, with conductive HL in 80% and sensorineural HL in 20%. In terms of patients with HL (n = 8), seven patients had bilateral HL and one patient had unilateral HL. Degree of HL was mild to moderate for 87% of the 15 ears with hearing loss. Of those patients with sufficient pure-tone and middle ear function data, 80% (8/10) had audiometric configurations suggestive of ossicular chain dysfunction (OCD). Recurrent episodes of otitis media (ROM) requiring pressure-equalizing tube placement were common. In patients who underwent cranial CT, 54.5% (6/11) had auricular calcification. Quantitative backscattered electron imaging (qBEI) of murine ossicles supports an OCD component of auditory dysfunction in GACI, suggesting loss of ossicular osteocytes without initiation of bone remodeling.Conclusions and relevanceHearing loss is common in GACI; it is most often conductive, and mild to moderate in severity. The etiology of HL is likely multifactorial, involving dysfunction of the ossicular chain and/or recurrent otitis media. Clinically, this study highlights the importance of early audiologic and otologic evaluation in persons with GACI. Novel findings of high rates of OCD and ROM may inform management, and in cases of unclear HL etiology, dedicated temporal bone imaging should be considered.

Project description:It is very unusual to see evidence of arterial calcification in infants and children, and when detected, genetic disorders of calcium metabolism should be suspected. Generalized arterial calcification of infancy (GACI) is a hereditary disease, which is characterized by severe arterial calcification of medium sized arteries, mostly involving the media with marked intimal proliferation and ectopic mineralization of the extravascular tissues. It is caused by inactivating variants in genes encoding either ENPP1, in a majority of cases (70-75%), or ABCC6, in a minority (9-10%). Despite similar histologic appearances between ENPP1 and ABCC6 deficiencies, including arterial calcification, organ calcification, and cardiovascular calcification, mortality is higher in subjects carrying the ENPP1 versus ABCC6 variants (40% vs 10%, respectively). Overall mortality in individuals with GACI is high (55%) before the age of 6 months, with 24.4% dying in utero or being stillborn. Rare cases show spontaneous regression with age, while others who survive into adulthood often manifest musculoskeletal complications (osteoarthritis and interosseous membrane ossification), enthesis mineralization, and cervical spine fusion. Despite recent advances in the understanding of the genetic mechanisms underlying this disease, there is still no ideal therapy for the resolution of vascular calcification in GACI. Although bisphosphonates with anti-calcification properties have been commonly used for the treatment of CAGI, their benefit is controversial, with favorable results reported at one year and questionable benefit with delayed initiation of treatment. Enzyme replacement therapy with administration of recombinant form of ENPP1 prevents calcification and mortality, improves hypertension and cardiac function, and prevents intimal proliferation and osteomalacia in mouse models of ENPP1 deficiency. Therefore, newer treatments targeting genes are on the horizon. In this article, we review up to date knowledge of the understanding of GACI, its clinical, pathologic, and etiologic understanding and treatment in support of more comprehensive care of GACI patients.

Dataset Information

Dual Effects of Bisphosphonates on Ectopic Skin and Vascular Soft Tissue Mineralization versus Bone Microarchitecture in a Mouse Model of Generalized Arterial Calcification of Infancy.

Publications

Dual Effects of Bisphosphonates on Ectopic Skin and Vascular Soft Tissue Mineralization versus Bone Microarchitecture in a Mouse Model of Generalized Arterial Calcification of Infancy.

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