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Cadmium (Cd2+) is a toxic and non-essential divalent metal ion in eukaryotic cells. Cells can only be targeted by Cd2+ if it hijacks physiological high-affinity entry pathways, which transport essential divalent metal ions in a process termed “ionic and molecular mimicry”. Hence, “free” Cd2+ ions and Cd2+ complexed with small organic molecules are transported across cellular membranes via ion channels, carriers and ATP hydrolyzing pumps, whereas receptor-mediated endocytosis (RME) internalizes Cd2+-protein complexes. Only Cd2+ transport pathways validated by stringent methodology, namely electrophysiology, 109Cd2+ tracer studies, inductively coupled plasma mass spectrometry, atomic absorption spectroscopy, Cd2+-sensitive fluorescent dyes, or specific ligand binding and internalization assays for RME are reviewed whereas indirect correlative studies are excluded. At toxicologically relevant concentrations in the submicromolar range, Cd2+ permeates voltage-dependent Ca2+ channels (“T-type” CaV3.1, CatSper), transient receptor potential (TRP) channels (TRPA1, TRPV5/6, TRPML1), solute carriers (SLCs) (DMT1/SLC11A2, ZIP8/SLC39A8, ZIP14/SLC39A14), amino acid/cystine transporters (SLC7A9/SLC3A1, SLC7A9/SLC7A13), and Cd2+-protein complexes are endocytosed by the lipocalin-2/NGAL receptor SLC22A17. Cd2+ transport via the mitochondrial Ca2+ uniporter, ATPases ABCC1/2/5 and transferrin receptor 1 is likely but requires further evidence. Cd2+ flux occurs through the influx carrier OCT2/SLC22A2, efflux MATE proteins SLC47A1/A2, the efflux ATPase ABCB1, and RME of Cd2+-metallothionein by the receptor megalin (low density lipoprotein receptor-related protein 2, LRP2):cubilin albeit at high concentrations thus questioning their relevance in Cd2+ loading. Which Cd2+-protein complexes are internalized by megalin:cubilin in vivo still needs to be determined. A stringent conservative and reductionist approach is mandatory to verify relevance of transport pathways for Cd2+ toxicity and to overcome dissemination of unsubstantiated conjectures.

The ABCA3 lipid transporter is located in the limiting membrane of lamellar bodies (LBs) in type-II-pneumocytes. Mutations within the ABCA3 gene may functionally impair the transporter, causing lung diseases in newborns, children and adults. Assays to quantify volume and lipid filling of the LBs on the level of the vesicular structures and thereby assess the function of ABCA3 are still lacking. In the present study human influenza haemagglutinin- (HA-) tagged wild type and mutant ABCA3 proteins were stably expressed in lung A549 cells. Fluorescently-labelled TopFluor phosphatidylcholine (TopF-PC) incorporated in surfactant-like liposomes was delivered to the cells and visualized by confocal microscopy. Subsequently, a comprehensive image analysis method was applied to quantify volume and fluorescence intensity of TopF-PC in ABCA3-HA-positive vesicles. TopF-PC accumulated within the vesicles in a time and concentration-dependent manner, whereas the volume remained unchanged, suggesting active transport into preformed ABCA3 containing vesicles. Furthermore, this finding was supported by a decrease of the fluorescence intensity within the vesicles when either the ATPase of the transporter was inhibited by vanadate, or when a disease-causing mutation (K1388N) close to the ABCA3-nucleotide binding domain 2 was introduced. Conversely, a mutation (E292V) located in the first cytoplasmic loop of ABCA3 did not significantly affect lipid transport, but rather resulted in smaller vesicles. In addition to these findings, the assay used in this work for analysing the PC-lipid transport into ABCA3 positive vesicles will be useful to screen for compounds susceptible to restore function in mutated ABCA3 protein.

Cadmium (Cd2+) in the environment is a significant health hazard. Chronic low Cd2+ exposure mainly results from food and tobacco smoking and causes kidney damage, predominantly in the proximal tubule. Blood Cd2+ binds to thiol-containing high (e.g., albumin, transferrin) and low molecular weight proteins (e.g., the high-affinity metal-binding protein metallothionein, &beta, 2-microglobulin, &alpha, 1-microglobulin and lipocalin-2). These plasma proteins reach the glomerular filtrate and are endocytosed at the proximal tubule via the multiligand receptor complex megalin:cubilin. The current dogma of chronic Cd2+ nephrotoxicity claims that Cd2+-metallothionein endocytosed via megalin:cubilin causes renal damage. However, a thorough study of the literature strongly argues for revision of this model for various reasons, mainly: (i) It relied on studies with unusually high Cd2+-metallothionein concentrations, (ii) the KD of megalin for metallothionein is ~105-times higher than (Cd2+)-metallothionein plasma concentrations. Here we investigated the uptake and toxicity of ultrafiltrated Cd2+-binding protein ligands that are endocytosed via megalin:cubilin in the proximal tubule. Metallothionein, &beta, 1-microglobulin, lipocalin-2, albumin and transferrin were investigated, both as apo- and Cd2+-protein complexes, in a rat proximal tubule cell line (WKPT-0293 Cl.2) expressing megalin:cubilin at low passage, but is lost at high passage. Uptake was determined by fluorescence microscopy and toxicity by MTT cell viability assay. Apo-proteins in low and high passage cells as well as Cd2+-protein complexes in megalin:cubilin deficient high passage cells did not affect cell viability. The data prove Cd2+-metallothionein is not toxic, even at &gt, 100-fold physiological metallothionein concentrations in the primary filtrate. Rather, Cd2+-&beta, 2-microglobulin, Cd2+-albumin and Cd2+-lipocalin-2 at concentrations present in the primary filtrate are taken up by low passage proximal tubule cells and cause toxicity. They are therefore likely candidates of Cd2+-protein complexes damaging the proximal tubule via megalin:cubilin at concentrations found in the ultrafiltrate.

Background Knowledge about the clinical spectrum of lung disease caused by variations in the ATP binding cassette subfamily A member 3 (ABCA3) gene is limited. Here we describe genotype-phenotype correlations in a European cohort. Methods We retrospectively analysed baseline and outcome characteristics of 40 patients with two disease-causing ABCA3 mutations collected between 2001 and 2015. Results Of 22 homozygous (15 male) and 18 compound heterozygous patients (3 male), 37 presented with neonatal respiratory distress syndrome as term babies. At follow-up, two major phenotypes are documented: patients with (1) early lethal mutations subdivided into (1a) dying within the first 6 months or (1b) before the age of 5 years, and (2) patients with prolonged survival into childhood, adolescence or adulthood. Patients with null/null mutations predicting complete ABCA3 deficiency died within the 1st weeks to months of life, while those with null/other or other/other mutations had a more variable presentation and outcome. Treatment with exogenous surfactant, systemic steroids, hydroxychloroquine and whole lung lavages had apparent but many times transient effects in individual subjects. Conclusions Overall long-term (>5 years) survival of subjects with two disease-causing ABCA3 mutations was

ABCA3 is a surfactant lipid transporter in the limiting membrane of lamellar bodies in alveolar type II cells. Mutations in the ATP-binding cassette, sub-family A (ABC1), member 3 (ABCA3) gene cause respiratory distress syndrome in newborns, and chronic interstitial lung disease in children and adults. ABCA3 belongs to the class of full ABC transporters, which are supposed to be functional in their monomeric forms. Although other family members e.g., ABCA1 and ABCC7 have been shown to function as oligomers, the oligomerization state of ABCA3 is unknown. In the present study, the oligomerization of ABCA3 was investigated in cell lysates and crude membrane preparations from transiently and stably transfected 293 cells using blue native PAGE (BN-PAGE), gel filtration and co-immunoprecipitation. Additionally, homooligomerization was examined in vivo in cells using bioluminescence resonance energy transfer (BRET). Using BN-PAGE and gel filtration, we demonstrate that non-denatured ABCA3 exists in different oligomeric forms, with monomers (45%) and tetramers (30%) being the most abundant forms. Furthermore, we also show the existence of 20% dimers and 5% trimers. BRET analyses verified intermolecular interactions in vivo. Our results also demonstrated that the arrest of ABCA3 in the endoplasmic reticulum (ER), either through drug treatment or induced by mutations in ABCA3, inhibited the propensity of the protein to form dimers. Based on our results, we suggest that transporter oligomerization is crucial for ABCA3 function and that a disruption of oligomerization due to mutations represents a novel pathomechanism in ABCA3-associated lung disease.

BACKGROUND: Children's interstitial lung diseases (chlLD) comprise a broad spectrum of diseases. Besides the genetically defined surfactant dysfunction disorders, most entities pathologically involve the alveolar surfactant region, possibly affecting the surfactant proteins SP-B and SP-C. Therefore, our objective was to determine the value of quantitation of SP-B and SP-C levels in bronchoalveolar lavage fluid (BALF) for the diagnosis of chlLD. METHODS: Levels of SP-B and SP-C in BALF from 302 children with chlLD and in controls were quantified using western blotting. In a subset, single-nucleotide polymorphisms (SNPs) in the SFTPC promoter were genotyped by direct sequencing. RESULTS: While a lack of dimeric SP-B was found only in the sole subject with hereditary SP-B deficiency, low or absent SP-C was observed not only in surfactant dysfunction disorders but also in patients with other diffuse parenchymal lung diseases pathogenetically related to the alveolar surfactant region. Genetic analysis of the SFTPC promoter showed association of a single SNP with SP-C level. CONCLUSION: SP-B levels may be used for screening for SP-B deficiency, while low SP-C levels may point out diseases caused by mutations in TTF1, SFTPC, ABCA3, and likely in other genes involved in surfactant metabolism that remain to be identified. We conclude that measurement of levels of SP-B and SP-C was useful for the differential diagnosis of chlLD, and for the precise molecular diagnosis, sequencing of the genes is necessary.

Diffuse parenchymal lung diseases (DPLDs) are characterized by chronic inflammation and fibrotic remodeling of the interstitial tissue. A small fraction of DPLD cases can be genetically defined by mutations in certain genes, with ABCA3 being the gene most commonly affected. However, the pathomechanisms underlying ABCA3-induced DPLD are far from clear. To investigate whether ABCA3 plays a role in cellular cholesterol homeostasis, phospholipids, free cholesterol, and cholesteryl esters were quantified in cells stably expressing ABCA3 using mass spectrometry. Cellular free cholesterol and lipid droplets were visualized by filipin or oil red staining, respectively. Expression of SREBP regulated genes was measured using qPCR. Cell viability was assessed using the XTT assay. We found that wild type ABCA3 reduces cellular free cholesterol levels, induces the SREBP pathway, and renders cells more resistant to loading with exogenous cholesterol. Moreover, ABCA3 mutations found in patients with DPLD interfere with this protective effect of ABCA3, resulting in free cholesterol induced cell death. We conclude that ABCA3 plays a previously unrecognized role in the regulation of cellular cholesterol levels. Accumulation of free cholesterol as a result of a loss of ABCA3 export function represents a novel pathomechanism in ABCA3-induced DPLD.

Patients with interstitial lung disease due to surfactant protein C (SFTPC) mutations are rare and not well characterised.We report on all subjects collected over a 15-year period in the kids-lung register with interstitial lung disease and a provenSFTPCmutation. We analysed clinical courses, interventions and outcomes, as well as histopathological and radiological interrelations.17 patients (seven male) were followed over a median of 3 years (range 0.3–19). All patients were heterozygous carriers of autosomal dominantSFTPCmutations. Three mutations (p.L101P, p.E191 K and p.E191*) have not been described before in the context of surfactant protein C deficiency. Patients with alterations in the BRICHOS domain of the protein (amino acids 94–197) presented earlier. At follow-up, one patient was healthy (2 years), six patients were “sick-better” (2.8 years, range 0.8–19), seven patients were “sick-same” (6.5 years, 1.3–15.8) and three patients were “sick-worse” (0.3 years, 0.3–16.9). Radiological findings changed from ground-glass to increasing signs of fibrosis and cyst formation with increasing age. Empiric treatments had variable effects, also in patients with the same genotype.Prospective studies with randomised interventions are urgently needed and can best be performed in the framework of international registers.

Introduction: ABCA3 is a lipid transporter expressed in alveolar type II pneumocytes. It is involved in the transport of phospholipids into lamellar bodies (LBs) and is therefore essential for the assembly of pulmonary surfactant and LB biogenesis. Mutations in the ABCA3 gene display a common genetic cause for respiratory distress syndrome in newborns and interstitial lung disease in children. Aim: As ABCA3 shares several features with CFTR (ABCC7), small molecules that are able to correct mutated CFTR proteins were tested for ABCA3 mutations. Methods: A549 cells stably expressing HA-tagged wildtype ABCA3 or variants Q215K, M760R, A1046E, K1388N, or G1421R, were treated with a range of different correctors to identify molecules that are able to restore ABCA3 processing and function. Cells were analyzed in regard to ABCA3 protein pattern in Western blotting and immunofluorescence. Activity of corrected ABCA3 protein was quantified using a lipid transport assay with TopFluor-conjugated phosphatidylcholine. Results: Two of the tested correctors restored processing of all ABCA3 variants except for M760R and led to a WT-like appearance of mutated protein in Western blotting and immunofluorescence. Lipid transport into ABCA3-HA-positive vesicles was increased by corrector treatment for WT ABCA3 and all variants except for M760R. Conclusion: The identification of molecules with the ability to correct processing and function of mutated ABCA3 proteins are an important step towards the development of drugs for the treatment of children suffering from respiratory distress syndrome or interstitial lung disease.

Knowledge about the clinical spectrum of lung disease caused by variations in the ATP binding cassette subfamily A member 3 (ABCA3) gene is limited. Here we describe genotype-phenotype correlations in a European cohort.We retrospectively analysed baseline and outcome characteristics of 40 patients with two disease-causing ABCA3 mutations collected between 2001 and 2015.Of 22 homozygous (15 male) and 18 compound heterozygous patients (3 male), 37 presented with neonatal respiratory distress syndrome as term babies. At follow-up, two major phenotypes are documented: patients with (1) early lethal mutations subdivided into (1a) dying within the first 6 months or (1b) before the age of 5 years, and (2) patients with prolonged survival into childhood, adolescence or adulthood. Patients with null/null mutations predicting complete ABCA3 deficiency died within the 1st weeks to months of life, while those with null/other or other/other mutations had a more variable presentation and outcome. Treatment with exogenous surfactant, systemic steroids, hydroxychloroquine and whole lung lavages had apparent but many times transient effects in individual subjects.Overall long-term (5 years) survival of subjects with two disease-causing ABCA3 mutations was20%. Response to therapies needs to be ascertained in randomised controlled trials.

Background Pseudoxanthoma elasticum (PXE) is a rare hereditary disorder predominantly affecting the skin, the eyes and the cardiovascular system. The disease is caused by mutations in the ABCC6 gene and characterized by ectopic calcification and extracellular matrix (ECM) alterations. Matrix metalloproteinases (MMPs) play a pivotal role in the process of ECM remodeling and are likely implied in PXE pathology. The aim of the present study was to investigate the association of single nucleotide polymorphisms (SNPs) in the promoter of the MMP2 gene, and PXE. Methods We evaluated the allelic distribution of five SNPs in the MMP2 promoter in DNA samples from 168 German patients affected by PXE and in 168 healthy, age- and sex-matched control subjects using restriction fragment length polymorphism analysis. Results The alleles c.-1575G, c.-1306C, and c.-790T were more abundant in the PXE patients' group. Furthermore, the haplotype GCTCG was significantly associated with PXE (OR 1.56, 95% CI 1.14–2.12, Pcorrected = 0.026). Conclusions Our results may indicate an involvement of MMP2 in the pathology of PXE. The promoter polymorphisms associated with PXE may lead to increased MMP2 expression and thereby contribute to the elevated proteolytic activity observed in PXE in vitro and in vivo.

Pseudoxanthoma elasticum (PXE) is a heritable disorder affecting the skin, eyes and cardiovascular system. It is caused by mutations in the ABCC6 gene and its clinical picture is highly variable. PXE often leads to severe visual impairment due to the development of choroidal neovascularisation (CNV). CNV in PXE-associated retinopathy is believed to be mediated by the action of vascular endothelial growth factor (VEGF). The objective of the present study was to evaluate a possible impact of variations in the VEGFA gene on ocular manifestations of PXE. For this purpose, we evaluated the distribution of 10 single nucleotide polymorphisms (SNPs) in the promoter and coding region of the VEGFA gene in DNA samples from 163 German patients affected by PXE and in 163 healthy control subjects. Haplotype analysis of SNPs c.-1540A>C, c.-460C>T, c.-152G>A, c.405C>G, c.674C>T, c.1032C>T, c.4618C>T and c.5092C>A revealed that the haplotype CTGGCCCC was associated with PXE (OR 2.05, 95% CI 1.33-3.15, P(corrected) = 0.01). Furthermore, five SNPs showed significant association with severe retinopathy. The most significant single SNP association was c.-460C>T (OR 3.83, 95% CI 2.01-7.31, P(corrected) = 0.0003). Logistic regression analysis identified the c.-460T and the c.674C alleles as independent risk factors for development of severe retinopathy. Our findings suggest an involvement of VEGF in the pathogenesis of ocular PXE manifestations. VEGF gene polymorphisms might prove useful as prognostic markers for the development of PXE-associated retinopathy and permit earlier therapeutic intervention in order to prevent loss of central vision, one of the most devastating consequences of this disease.

Pseudoxanthoma elasticum (PXE, OMIM 177850 and 264800) is a rare heritable disorder predominantly affecting the skin, the eyes and the vascular system. The disease is caused by mutations in the ABCC6 gene and is characterized by calcification and extracellular matrix remodeling, including alterations of the vessel walls. Here, we investigated the cell adhesion molecules ICAM-1 in PXE patients.Soluble ICAM-1 was determined in 58 non-consanguineous PXE patients by quantitative sandwich enzyme immunoassay. The allelic frequencies of the ICAM-1 variant p.K469E were analyzed in patients and age- and sex-matched controls.Soluble ICAM-1 levels were significantly elevated in male and female PXE patients (p0.02 and p0.001, respectively). In addition, the ICAM-1 concentration correlated with the ABCC6 gene status of the PXE patients. The ICAM variant p.K469E genotypes were not different in PXE patients and age- and sex-matched controls.Our data show for the first time increased ICAM-1 concentrations in PXE patients, potentially due to the chronic oxidative stress and elevated protease activity followed by extracellular matrix remodeling which have been previously observed in PXE patients.

Interstitial lung diseases (ILD) comprise disorders of mostly unknown cause. Among the few molecularly defined entities, mutations in the gene encoding the ATP-binding cassette (ABC), subfamily A, member 3 (ABCA3) lipid transporter represent the main cause of inherited surfactant dysfunction disorders, a subgroup of ILD. Whereas many cases are reported, specific methods to functionally define such mutations are rarely presented.In this study, we exemplarily utilized a set of molecular tools to characterize the mutation K1388N, which had been identified in a patient suffering from ILD with lethal outcome. We also aimed to correlate in vitro and ex vivo findings.We found that presence of the K1388N mutation did not affect protein expression, but resulted in an altered protein processing and a functional impairment of ABCA3. This was demonstrated by decreased dipalmitoyl-phosphatidylcholine (PC 32:0) content and malformed lamellar bodies in cells transfected with the K1388N variant as compared to controls.Here we present a set of tools useful for categorizing different ABCA3 mutations according to their impact upon ABCA3 activity. Knowledge of the molecular defects and close correlation of in vitro and ex vivo data will allow us to define groups of mutations that can be targeted by small molecule correctors for restoring impaired ABCA3 transporter in the future. Pediatr Pulmonol. 2016;51:1284-1294. © 2016 Wiley Periodicals, Inc.

Background: ABCA3 is an ATP-dependent lipid transporter involved in surfactant production and is located in the limiting membrane of lamellar bodies (LB) in type II pneumocytes. Mutations within the ABCA3-gene cause respiratory distress syndrome in newborns and chronic interstitial lung diseases in children and adults. In order to develop correctors that can rescue mutant ABCA3, a reliable method is needed to measure ABCA3 transport activity. Methods: Liposomes of surfactant-like composition were prepared and fluorescent Top-Fluor-Phosphatidylcholine (TopF-PC) was incorporated. A549 cells stably expressing ABCA3-HA were incubated with these liposomes. ATP-dependence of transport was evaluated using an ATPase-inhibitor. Cells were imaged using confocal laser scanning microscopy and fluorescence intensity was analysed using the Fiji-Plugin Particle_in_cell-3D , which has been modified for the analysis of vesicular transport. Results: We show that TopF-PC fluorescence can be used to estimate the amount of lipids present in single LBs. Moreover, we found differences in the TopF-PC fluorescence intensity between wild type-cells and cells expressing mutations, which are supposed to be functional ones. We were able to demonstrate an increase of fluorescence in the LBs over different time slots from 0 to 72 hours. In concordance with active transport of TopF-PC by ABCA3, we found a decrease in ABCA3-function after treatment with the ATPase-inhibitor. Summary: This method presents an important step towards a functional assay to analyse transport of lipids by ABCA3 and its impairment by mutations. The assay will enable us to identify correctors, which can improve lipid transport function of mutated ABCA3.

Introduction: ABCA3 is a lipid transporter found in alveolar type II cells, where it localizes to the outer membrane of lamellar bodies which store surfactant. Mutations in the ABCA3 gene are the most common known genetic cause of respiratory distress syndrome in newborns and of late onset interstitial lung disease in children. Objectives and methods: WT ABCA3 cDNA fused to a HA-tag was cloned into the pT2HB SB expression vector. Clinical relevant mutations R208W, Q215K, R288K, E292V, M760R, G964D and K1388N were inserted by site-directed mutagenesis into the WT ABCA3 gene. Vectors were stably transfected into A549 cells with the “Sleeping Beauty” system based on transposition. The level of ABCA3 expression and processing was examined by quantitative PCR and immunoblot analysis. Subcellular protein localization was analyzed by immunofluorescence. Changes in total lipid composition within the different cell lines were investigated by mass spectrometry. Results: Immunoblot analyses of mutated ABCA3 revealed changes in protein processing compared to the wildtype. Furthermore we found that ABCA3 is localized mainly at the limiting membrane of CD63-positive vesicles, whereas Q215K and M760R showed a different localization pattern. Mass spectrometry analyzed indicated alteration of lipid composition. Conclusion: We have prepared and characterized cellular models with ABCA3 mutations in order to investigate specific mechanisms for restoring its wildtype function. Supported by “Deutsches Zentrum fur Lungenforschung“ (DZL) and „Deutsche Forschungsgemeinschaft“ (DFG).

Methionyl-tRNA synthetase (MARS) catalyzes the ligation of methionine to tRNA and is critical for protein biosynthesis. We identified biallelic missense mutations in MARS in a specific form of pediatric pulmonary alveolar proteinosis (PAP), a severe lung disorder that is prevalent on the island of Réunion and the molecular basis of which is unresolved. Mutations were found in 26 individuals from Réunion and nearby islands and in two families from other countries. Functional consequences of the mutated alleles were assessed by growth of wild-type and mutant strains and methionine-incorporation assays in yeast. Enzyme activity was attenuated in a liquid medium without methionine but could be restored by methionine supplementation. In summary, identification of a founder mutation in MARS led to the molecular definition of a specific type of PAP and will enable carrier screening in the affected community and possibly open new treatment opportunities.

Background Interstitial lung disease occurring in children is a condition characterized by high frequency of cases due to genetic aberrations of pulmonary surfactant homeostasis, that are also believed to be responsible of a fraction of familial pulmonary fibrosis. To our knowledge, ABCA3 gene was not previously reported as causative agent of fibrosis affecting both children and adults in the same kindred. Methods We investigated a large kindred in which two members, a girl whose interstitial lung disease was first recognized at age of 13, and an adult, showed a diffuse pulmonary fibrosis with marked differences in terms of morphology and imaging. An additional, asymptomatic family member was detected by genetic analysis. Surfactant abnormalities were investigated at biochemical, and genetic level, as well as by cell transfection experiments. Results Bronchoalveolar lavage fluid analysis of the patients revealed absence of surfactant protein C, whereas the gene sequence was normal. By contrast, sequence of the ABCA3 gene showed a novel homozygous G > A transition at nucleotide 2891, localized within exon 21, resulting in a glycine to aspartic acid change at codon 964. Interestingly, the lung specimens from the girl displayed a morphologic usual interstitial pneumonitis-like pattern, whereas the specimens from one of the two adult patients showed rather a non specific interstitial pneumonitis-like pattern. Conclusions We have detected a large kindred with a novel ABCA3 mutation likely causing interstitial lung fibrosis affecting either young and adult family members. We suggest that ABCA3 gene should be considered in genetic testing in the occurrence of familial pulmonary fibrosis.

Background Mutations in the gene encoding surfactant protein C (SP-C) cause familial and sporadic interstitial lung disease (ILD), which is associated with considerable morbidity and mortality. Unfortunately, effective therapeutic options are still lacking due to a very limited understanding of pathomechanisms. Knowledge of mutant SP-C proprotein (proSP-C) trafficking, processing, intracellular degradation and aggregation is a crucial prerequisite for the development of specific therapies to correct aberrant trafficking and processing of proSP-C and to hinder accumulation of cytotoxic aggregates. Materials and methods To identify possible starting points for therapeutic intervention, we stably transfected A549 alveolar epithelial cells with several proSP-C mutations previously found in patients suffering from ILD. Effects of mutant proSP-C were assessed by Western blotting, immunofluorescence and Congo red staining. Results A group of mutations (p.I73T, p.L110R, p.A116D and p.L188Q) resulted in aberrant proSP-C products, which were at least partially trafficked to lamellar bodies. Another group of mutations (p.P30L and p.P115L) was arrested in the endoplasmic reticulum (ER). Except for p.I73T, all mutations led to accumulation of intracellular Congo red–positive aggregates. Enhanced ER stress was detectable in none of these stably transfected cells. Conclusions Different SP-C mutations have unique consequences for alveolar epithelial cell biology. As these cannot be predicted based upon the localization of the mutation, our data emphasize the importance of studying individual mutations in detail in order to develop mutation-specific therapies.

International audience; ATP-binding cassette transporter A3 (ABCA3) is a lipid transporter active in lung alveolar epithelial type II cells (ATII) and is essential for their function as surfactant-producing cells. ABCA3 mutational defects cause respiratory distress in newborns and interstitial lung disease (ILD) in children. The molecular pathomechanisms are largely unknown; however, viral infections may initiate or aggravate ILDs. Here, we investigated the impact of the clinically relevant ABCA3 mutations, p.Q215K and p.E292V, by stable transfection of A549 lung epithelial cells. ABCA3 mutations strongly impaired expression of the ATII differentiation marker SP-C and the key epithelial cell adhesion proteins E-cadherin and zonula occludens-1. Concurrently, cells expressing ABCA3 mutation acquired mesenchymal features as observed by increased expression of SNAI1, MMP-2 and TGF-beta1, and elevated phosphorylation of Src. Infection with respiratory syncytial virus (RSV), the most common viral respiratory pathogen in small children, potentiated the observed mutational effects on loss of epithelial and acquisition of mesenchymal characteristics. In addition, RSV infection of cells harboring ABCA3 mutations resulted in a morphologic shift to a mesenchymal phenotype. We conclude that ABCA3 mutations, potentiated by RSV infection, induce loss of epithelial cell differentiation in ATII. Loss of key epithelial features may disturb the integrity of the alveolar epithelium, thereby comprising its functionality. We suggest the impairment of epithelial function as a mechanism by which ABCA3 mutations cause ILD.

Pseudoxanthoma elasticum (PXE) is a rare disorder predominantly affecting the skin, the eyes, and the cardiovascular system. The disease is caused by mutations in the ABCC6 gene and characterized by ectopic calcification and extracellular matrix (ECM) alterations. Matrix metalloproteinases (MMPs) play a pivotal role in the process of ECM remodeling. In the present study, we investigated matrix metalloproteinases MMP-2 and MMP-9 in PXE patients compared to healthy controls. We analyzed the serum concentrations of MMP-2 and MMP-9 in a cohort of 69 German PXE patients and in 69 healthy, age-, and sex-matched control subjects using commercially available ELISA assays. We found elevated concentrations of both MMPs in the sera of PXE patients. MMP-2 levels were significantly higher in patients than controls (231 +/- 5.89 vs 202 +/- 5.17 ng/ml, p = 0.0002), as were MMP-9 levels (841 +/- 65.9 vs 350 +/- 30.8 ng/ml, p0.0001). Our findings point to an involvement of matrix metalloproteinases in PXE pathology. ECM remodeling in PXE is reflected by elevated levels of circulating MMP-2 and MMP-9. Those MMPs might, therefore, be applicable as serum markers for the matrix-degradative process in PXE.

Mutations in the ABCC6 gene, encoding the multidrug resistance-associated protein 6 (MRP6), cause pseudoxanthoma elasticum (PXE). This heritable disorder leads to pathological alterations in connective tissues. The implication of MRP6 deficiency in PXE is still unknown. Moreover, nothing is known about a possible compensatory expression of other ATP binding-cassette (ABC) transporter proteins in MRP6-deficient cells. We investigated the gene expression profile of 47 ABC transporters in human dermal fibroblasts of healthy controls (n=2) and PXE patients (n=4) by TaqMan low-density array. The analysis revealed the expression of 37 ABC transporter genes in dermal fibroblasts. ABCC6 gene expression was not quantifiable in fibroblasts derived from PXE patients. Seven genes (ABCA6, ABCA9, ABCA10, ABCB5, ABCC2, ABCC9 and ABCD2) were induced, whereas the gene expression of one gene (ABCA3) was decreased, comparing controls and PXE patients (with at least twofold changes). We reanalyzed the gene expression of selected ABC transporters in a larger set of dermal fibroblasts from controls and PXE patients (n=6, each). Reanalysis showed high interindividual variability between samples, but confirmed the results obtained in the array analysis. The gene expression of ABC transporter genes, as well as lineage markers of PXE, was further examined after inhibition of ABCC6 gene expression by using specific small-interfering RNA. These experiments corroborated the observed gene expression alterations, most notably in the ABCA subclass (up to fourfold, P

Chemotherapy failure was reported in treatment of retinoblastoma suggesting a role for ATP-binding cassette (ABC) proteins. Little is known about the expression pattern of ABC proteins in this cancer type. We investigated the gene expression profile of 47 ABC proteins in the human retinoblastoma cell line Y79 by TaqMan low-density array. Analysis revealed 31 ABC transporter genes expressed in this tumor cell line. Y79 cells demonstrate high gene expression of ABCA7, ABCA12, ABCB7, ABCB10, ABCC1, ABCC4, ABCD3, ABCE1, ABCF1, ABCF2, and ABCF3 (more than twofold compared to pooled RNA from different tissues). Moreover, we show that Y79 cells exhibit an active calcein efflux pointing to multidrug resistance protein (MRP)-like transporter activity. In summary, we present for the first time an ABC transporter gene expression profile in cells derived from retinoblastoma. Most of the highly expressed ABC transporter genes are typical markers of cancer cells and might exhibit potential targets for medical treatment of retinoblastoma.

Pseudoxanthoma elasticum (PXE) is a hereditary disorder predominantly affecting the eyes, the skin, and the vascular system. The subretinal neovascularization and retinal hemorrhages leading to the loss of central vision in PXE are similar to the process observed in age-related macular degeneration (AMD). The complement factor H (CFH) variant c.1277TC (p.Y402H) is a recently discovered risk factor for AMD. The aim of this study was to analyze whether this CFH variant is a secondary genetic risk factor for PXE. Therefore, the genotypes of CFH c.1277TC (p.Y402H) were determined in 189 German PXE patients and 189 age- and sex-matched controls. The allelic frequencies of the investigated variant did not differ between patients and controls. The frequencies were 33%, 56%, and 11% for wild-type, heterozygous, and homozygous genotypes in the PXE patients and 36%, 51%, and 13% in the control cohort, respectively. Further, no significant associations were identified when allele carriers were analyzed or after adjustment for sex, age, smoking, organ involvement, hypertension, or age at disease onset. No significant genotype-phenotype correlation was detected. In conclusion, our data reliably show that the CFH variant c.1277TC (p.Y402H) is not a genetic risk factor for PXE.

Objectives Recent studies have revealed the involvement of calcification inhibitory proteins in the pathogenesis of pseudoxanthoma elasticum (PXE). Design and methods We analyzed serum concentrations of the calcification inhibitor matrix Gla protein ( MGP ) in a large cohort of patients suffering from PXE ( n = 101), 34 first-degree relatives and 67 healthy controls. Moreover, we determined the distribution of the two MGP promoter polymorphisms c.-7G>A and c.-138T>C in the three cohorts. Results We found significantly lower total MGP concentrations in the sera of PXE patients compared to healthy controls ( p = 0.0002). Furthermore, higher serum MGP concentrations could be correlated with a later PXE onset. Analysis of MGP promoter polymorphism frequencies revealed one MGP haplotype to be a potential protective co-factor in PXE. Conclusions Our findings point to a role of the local calcification inhibitor MGP in PXE manifestation.

Background: Pseudoxanthoma elasticum (PXE) is a rare hereditary disorder characterized by progressive calcification and fragmentation of elastic fibers in connective tissues. PXE is caused by mutations in the ABCC6 gene, which encodes the membrane transporter multidrug resistance–associated protein 6. Chronic oxidative stress was recently suggested to play a crucial role in the pathogenesis of the disease. Our aim was to investigate the association of PXE with genetic variation in genes coding for antioxidant enzymes. Methods: We used restriction fragment length polymorphism and allele-specific PCR analyses to evaluate the distribution of single-nucleotide polymorphisms in the genes encoding catalase (CAT), superoxide dismutase 2 (SOD2), and glutathione peroxidase 1 (GPX1) in DNA samples from 117 German PXE patients and 117 healthy age- and sex-matched control individuals. Results: The investigated genetic variants had previously been shown to affect the activities of these antioxidant enzymes. We found a correlation between genotype and age of disease onset for polymorphisms in CAT (c.−262C>T), SOD2 (c.47C>T), and GPX1 (c.593C>T). Furthermore, the age of disease onset was inversely correlated with the number of mutated alleles, indicating a cumulative effect on the time of disease onset [mean (SD) age of 40.9 (13.6) years, 32.4 (16.3) years, and 25.7 (15.9) years for carriers of 0, 1–2, and >2 mutated alleles, respectively; P = 0.03]. Conclusion: Our findings demonstrate that increased oxidative stress due to activity-affecting polymorphisms in genes encoding antioxidant enzymes leads to earlier PXE onset.