Analysis of MMP2 promoter polymorphisms in patients with pseudoxanthoma elasticum

Novel Genetic Microvascular Dysplasia Causing Hypoperfusion of Cardiac, Renal, and Cerebral Circulation

BACKGROUND

Microvascular disorders represent an uncommon site of tissue hypo-perfusion and damage. Various genetic and acquired causes can be involved. A 65-year-old man was admitted because of refractory angina, which he had had since the age of 30 years, micro-hematuria, and recurrent transitory ischemic attacks from the age of 64.

METHODS

Hematochemical studies, ECG, Holter monitoring, 2D-echo, cardiac magnetic resonance (CMR), CTA of cerebral vessels, endomyocardial coronary angiography, and kidney biopsy processes were undertaken. Gene mutation analysis was conducted using next-generation sequencing, which included more than 5000 genes associated with inherited diseases.

RESULTS

Hematochemical findings were unremarkable. The ECG, Holter, 2D-echo, and CTA of brain vessels were normal. Cerebral magnetic resonance showed the presence of multiple small foci of ischemia. Coronary and ventricular angiography showed normal arteries with remarkably slow flow and multiple biventricular micro-aneurysms. At the endomyocardial biopsy, five of seven arterioles presented severe lumen obstruction due to hypertrophy and disarray of the muscular coat. Similarly, obstructed pre-glomerular arteries with glomerular sclerosis were seen at the renal biopsy. Genetics identified mutations in the ABCC6, MMP2, and XYLT1 genes, which play pivotal roles in the extracellular matrix.

CONCLUSION

This study described a new genetic microvascular obstructive disease causing progressive hypo-perfusion of the human brain, heart, and kidney.

Matrix Metalloproteinases Contribute to the Calcification Phenotype in Pseudoxanthoma Elasticum

Ectopic calcification and dysregulated extracellular matrix remodeling are prominent hallmarks of the complex heterogenous pathobiochemistry of pseudoxanthoma elasticum (PXE). The disease arises from mutations in ABCC6, an ATP-binding cassette transporter expressed predominantly in the liver. Neither its substrate nor the mechanisms by which it contributes to PXE are completely understood. The fibroblasts isolated from PXE patients and Abcc6-/- mice were subjected to RNA sequencing. A group of matrix metalloproteinases (MMPs) clustering on human chromosome 11q21-23, respectively, murine chromosome 9, was found to be overexpressed. A real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay and immunofluorescent staining confirmed these findings. The induction of calcification by CaCl2 resulted in the elevated expression of selected MMPs. On this basis, the influence of the MMP inhibitor Marimastat (BB-2516) on calcification was assessed. PXE fibroblasts (PXEFs) exhibited a pro-calcification phenotype basally. PXEF and normal human dermal fibroblasts responded with calcium deposit accumulation and the induced expression of osteopontin to the addition of Marimastat to the calcifying medium. The raised MMP expression in PXEFs and during cultivation with calcium indicates a correlation of ECM remodeling and ectopic calcification in PXE pathobiochemistry. We assume that MMPs make elastic fibers accessible to controlled, potentially osteopontin-dependent calcium deposition under calcifying conditions.

Molecular Genetics and Modifier Genes in Pseudoxanthoma Elasticum, a Heritable Multisystem Ectopic Mineralization Disorder

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.

Early arterial calcification does not correlate with bone loss in pseudoxanthoma elasticum

BACKGROUND AND AIMS

Pseudoxanthoma elasticum (PXE; OMIM 264800, prevalence 1/25,000 to 1/50,000) is an autosomal recessive multisystem disease due to deficiency in ABCC6, an ATP-binding cassette, sub-family C transporter. The PXE phenotype is mainly characterized by progressive ectopic calcification of connective tissues (namely skin, retinal Bruch's membrane and peripheral arteries) but the impact of PXE on bone structure is currently unknown. The present study sought to investigate bone mineralization and its potential link with vascular calcification in a large cohort of PXE patients with inherited mutations of the ABCC6 gene.

METHODS AND RESULTS

96 patients (61 women) matching the PXE criteria participated in this study. Their clinical history and status and bone biological markers were collected. Bone mineral density (BMD) was measured by dual energy X-ray absorptiometry and expressed as T- and Z-scores. Osteoporotic fractures were identified by X-ray, and coronary (CAC) and lower limb arterial calcification (LLAC) scores were determined by CT scan.

RESULTS

44% of the women were menopausal. Osteopenia was disclosed in 46% (17 women) while 23% (9 women) exhibited osteoporosis, 3 with severe osteoporosis. Fractures of an osteoporotic nature were authenticated in 3 patients (1 woman). Markers of bone remodelling processes (CTX, BSAP and osteocalcin) were within the normal range for our laboratory standards. Severe vitamin D deficiency (<25nmol/L) was found in 15%, while 51% exhibited no vitamin D deficiency (vitamin D≥50nmol/L). LLAC and CAC scores were significantly higher in the patients with a low T- and/or Z-score, although this difference disappeared in multivariate analysis with age as a confounding factor. There was no significant difference in LLAC and CAC between PXE patients with and without osteoporotic fractures. There was no statistically significant association between BMD, LLAC and CAC and any of the bone remodelling factors.

CONCLUSIONS

This is the first report on the bone mineralization process in PXE patients. Our data shows that PXE patients are not markedly prone to exaggerated bone demineralization and fracture risk, and prevalence of osteoporosis remains within the normal range for the general population. Furthermore, the relationships between LLAC, but not CAC, and BMD with age are similar to those observed in the general population. Therefore, despite its pivotal role in ectopic calcification, ABCC6 deficiency does not interfere with the bone-vascular axis. The lack of PXE-related disturbances between BMD and arterial calcification also supports vitamin D supplementation in PXE patients with vitamin D deficiency. ClinicalTrials.gov Identifier: NCT01446393.

Can APOE and MTHFR polymorphisms have an influence on the severity of cardiovascular manifestations in Italian Pseudoxanthoma elasticum affected patients?

Background

The clinical phenotype of Pseudoxanthoma elasticum (PXE) affected patients, although progressive with age, is very heterogeneous, even in the presence of identical ABCC6 mutations, thus suggesting the occurrence of modifier genes. Beside typical skin manifestations, the cardiovascular (CV) system, and especially the peripheral vasculature, is frequently and prematurely compromised.

Methods and results

A cohort of 119 Italian PXE patients has been characterized for apolipoprotein E (APOE) and methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms by PCR. The severity of the clinical phenotype has been quantified according to the Phenodex PXE International score system. Statistical analysis (chi² test, odd ratio, regression analysis, analysis of variance) were done by GraphPad. Data demonstrate that the frequency of APOE alleles is similar in PXE patients and in healthy subjects and that the allelic variant E2 confers a protection against the age-related increase of CV manifestations. By contrast, PXE patients are characterized by high frequency of the MTHFR-T677T polymorphism. With age, CV manifestations in T677T, but also in C677T, patients are more severe than those associated with the C677C genotype. Interestingly, compound heterozygosity for C677T and A1298C polymorphisms is present in 70% of PXE patients.

Conclusions

PXE patients may be screened for these polymorphisms in order to support clinicians for a better management of disease-associated CV complications.

The ABCC6 transporter: what lessons can be learnt from other ATP-binding cassette transporters?

ABC transporters represent a large family of ATP-driven transmembrane transporters involved in uni- or bidirectional transfer of a large variety of substrates. Divided in seven families, they represent 48 transporter proteins, several of which have been associated with human disease. Among the latter is ABCC6, a unidirectional exporter protein primarily expressed in liver and kidney. ABCC6 deficiency has been shown to cause the ectopic mineralization disorder pseudoxanthoma elasticum (PXE), characterized by calcification and fragmentation of elastic fibers, resulting in oculocutaneous and cardiovascular symptoms. Unique in the group of connective tissue disorders, the pathophysiological relation between the ABCC6 transporter and ectopic mineralization in PXE remains enigmatic, not in the least because of lack of knowledge on the substrate(s) of ABCC6 and its unusual expression pattern. Because many features, including structure and transport mechanism, are shared by many ABC transporters, it is worthwhile to evaluate if and to what extent the knowledge on the physiology and pathophysiology of these other transporters may provide useful clues toward understanding the (patho)physiological role of ABCC6 and how its deficiency may be dealt with.

Characterization of cardiovascular involvement in pseudoxanthoma elasticum families

OBJECTIVE

Pseudoxanthoma elasticum (PXE) is an autosomal recessive connective tissue disorder with involvement of the skin, the retina, and the cardiovascular system. Cardiovascular involvement is mainly characterized by mineralization and fragmentation of elastic fibers of blood vessels and premature atherosclerosis. We conducted an ultrasound study to investigate the cardiovascular phenotype and to propose recommendations for the management of patients with PXE and heterozygous ABCC6 mutation carriers.

APPROACH AND RESULTS

Thirty-two patients, 23 carriers, and 28 healthy volunteers underwent cardiac and vascular ultrasound studies. Cardiac imaging revealed left ventricular diastolic dysfunction in patients with PXE with a significantly prolonged deceleration time and lower septal early diastolic velocities of the mitral annulus compared with controls. Carriers also demonstrated significantly prolonged deceleration time. Carotid-to-femoral pulse wave velocity was significantly increased in patients with PXE when compared with carriers and controls. Vascular imaging revealed a high prevalence of peripheral artery disease in both patients and carriers and a significantly higher carotid intima-media thickness compared with controls.

CONCLUSIONS

The results of this study clearly demonstrate impaired left ventricular diastolic function, impairment of the elastic properties of the aorta, and a high prevalence of peripheral artery disease in patients with PXE. Carriers also seem to exhibit a cardiovascular phenotype with mainly mild diastolic dysfunction and accelerated atherosclerosis. Increased awareness for cardiovascular events in both patients and heterozygous carriers is warranted.

New insights into the pathogenesis of pseudoxanthoma elasticum and related soft tissue calcification disorders by identifying genetic interactions and modifiers

Screening of the adenosine triphosphate binding cassette transporter protein subfamily C member 6 gene (ABCC6) in pseudoxanthoma elasticum (PXE) revealed a mutation detection rate of approximately 87%. Although 25% of the unidentified disease alleles underlie deletions/insertions, there remain several PXE patients with no clear genotype. The recent identification of PXE-related diseases and the high intra-familiar and inter-individual clinical variability of PXE led to the assumption that secondary genetic co-factors exist. Here, we summarize current knowledge of the genetics underlying PXE and PXE-related disorders based on human and animal studies. Furthermore, we discuss the role of genetic interactions and modifier genes in PXE and PXE-related diseases characterized by soft tissue calcification.

Matrix metalloproteinases in health and disease: insights from dermatopathology

Matrix metalloproteinases, a group of over 26 zinc-dependent enzymes, share a similar structure to each other and functionally are capable of degrading almost every component of the extracellular matrix. They are essential to normal development during embryogenesis and extracellular matrix remodeling and, given this, understandably enough have been implicated in multiple pathologic processes that encompass the inflammatory and neoplastic spectrum of disease. This review attempts to define roles of matrix metalloproteinases of relevance in normal skin and to elucidate their roles in inflammatory dermatoses and benign and malignant neoplasms.

Fibroblast involvement in soft connective tissue calcification

Soft connective tissue calcification is not a passive process, but the consequence of metabolic changes of local mesenchymal cells that, depending on both genetic and environmental factors, alter the balance between pro- and anti-calcifying pathways. While the role of smooth muscle cells and pericytes in ectopic calcifications has been widely investigated, the involvement of fibroblasts is still elusive. Fibroblasts isolated from the dermis of pseudoxanthoma elasticum (PXE) patients and of patients exhibiting PXE-like clinical and histopathological findings offer an attractive model to investigate the mechanisms leading to the precipitation of mineral deposits within elastic fibers and to explore the influence of the genetic background and of the extracellular environment on fibroblast-associated calcifications, thus improving the knowledge on the role of mesenchymal cells on pathologic mineralization.

The vascular phenotype in Pseudoxanthoma elasticum and related disorders: contribution of a genetic disease to the understanding of vascular calcification

Vascular calcification is a complex and dynamic process occurring in various physiological conditions such as aging and exercise or in acquired metabolic disorders like diabetes or chronic renal insufficiency. Arterial calcifications are also observed in several genetic diseases revealing the important role of unbalanced or defective anti- or pro-calcifying factors. Pseudoxanthoma elasticum (PXE) is an inherited disease (OMIM 264800) characterized by elastic fiber fragmentation and calcification in various soft conjunctive tissues including the skin, eyes, and arterial media. The PXE disease results from mutations in the ABCC6 gene, encoding an ATP-binding cassette transporter primarily expressed in the liver, kidneys suggesting that it is a prototypic metabolic soft-tissue calcifying disease of genetic origin. The clinical expression of the PXE arterial disease is characterized by an increased risk for coronary (myocardial infarction), cerebral (aneurysm and stroke), and lower limb peripheral artery disease. However, the structural and functional changes in the arterial wall induced by PXE are still unexplained. The use of a recombinant mouse model inactivated for the Abcc6 gene is an important tool for the understanding of the PXE pathophysiology although the vascular impact in this model remains limited to date. Overlapping of the PXE phenotype with other inherited calcifying diseases could bring important informations to our comprehension of the PXE disease.

Pseudoxanthoma elasticum: progress in diagnostics and research towards treatment : Summary of the 2010 PXE International Research Meeting

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.