ABCC6
Multidrug resistance-associated protein 6 (ATP-binding cassette sub-family C member 6) (Anthracycline resistance-associated protein) (Multi-specific organic anion transporter E) (MOAT-E) [ARA] [MRP6]
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The molecular processes of aging are very heterogenic and not fully understood. Studies on rare progeria syndromes, which display an accelerated progression of physiological aging, can help to get a better understanding. Pseudoxanthoma elasticum (PXE) caused by mutations in the [i]ATP-binding cassette sub-family C member 6[/i] ([i]ABCC6[/i]) gene shares some molecular characteristics with such premature aging diseases. Thus, this is the first study trying to broaden the knowledge of aging processes in PXE patients. In this study, we investigated aging associated biomarkers in primary human dermal fibroblasts and sera from PXE patients compared to healthy controls. Determination of serum concentrations of the aging biomarkers eotaxin-1 (CCL11), growth differentiation factor 11 (GDF11) and insulin-like growth factor 1 (IGF1) showed no significant differences between PXE patients and healthy controls. Insulin-like growth factor binding protein 3 (IGFBP3) showed a significant increase in serum concentrations of PXE patients older than 45 years compared to the appropriate control group. Tissue specific gene expression of GDF11 and IGFBP3 were significantly decreased in fibroblasts from PXE patients compared to normal human dermal fibroblasts (NHDF). IGFBP3 protein concentration in supernatants of fibroblasts from PXE patients were decreased compared to NHDF but did not reach statistical significance due to potential gender specific variations. The minor changes in concentration of circulating aging biomarkers in sera of PXE patients and the significant aberrant tissue specific expression seen for selected factors in PXE fibroblasts, suggests a link between ABCC6 deficiency and accelerated aging processes in affected peripheral tissues of PXE patients.
Keywords
- CCL11
- GDF11
- IGF1
- IGFBP
- aging
- pseudoxanthoma elasticum
Pseudoxanthoma elasticum (PXE) is characterized by progressive ectopic mineralization of elastic fibers in dermal, ocular and vascular tissues. No effective treatment exists. It is caused by inactivating mutations in the gene encoding for the ATP-binding cassette, sub-family C member 6 transporter (ABCC6), which is mainly expressed in the liver. The ABCC6 substrate (s) and the PXE pathomechanism remain unknown. Recent studies have shown that overexpression of ABCC6 in HEK293 cells results in efflux of ATP, which is rapidly converted into nucleoside monophosphates and pyrophosphate (PPi). Since the latter inhibits mineralization, it was proposed that the absence of circulating PPi in PXE patients results in the characteristic ectopic mineralization. These studies also demonstrated that the presence of ABCC6 modifies cell secretory activity and suggested that ABCC6 can change the cell phenotype. Stable [i]ABCC6[/i] knockdown HepG2 clones were generated using small hairpin RNA (shRNA) technology. The intracellular glutathione and ROS levels were determined. Experiments using cell cycle analysis, real-time PCR and western blot were performed on genes involved in the senescence phenotype. To shed light on the physiological role of ABCC6, we focused on the phenotype of HepG2 cells that lack ABCC6 activity. Interestingly, we found that [i]ABCC6[/i] knockdown HepG2 cells show: 1) intracellular reductive stress; 2) cell cycle arrest in G1 phase; 3) upregulation of p21 p53 independent; and 4) downregulation of lamin A/C. These findings show that the absence of ABCC6 profoundly changes the HepG2 phenotype, suggesting that the PXE syndrome is a complex metabolic disease that is not exclusively related to the absence of pyrophosphate in the bloodstream.
MeSH Terms
- Cellular Senescence
- Cyclin-Dependent Kinase Inhibitor p21
- G1 Phase Cell Cycle Checkpoints
- Gene Knockout Techniques
- Hep G2 Cells
- Humans
- Multidrug Resistance-Associated Proteins
- Oxidative Stress
- Pseudoxanthoma Elasticum
- Up-Regulation
Keywords
- ABCC6
- Cell cycle
- Reductive stress
- Senescence
Pseudoxanthoma elasticum (PXE), a rare genetic disease caused by mutations in the ABCC6 gene, is characterized by progressive calcification of elastic fibers in the skin, eyes, and the cardiovascular system. The pathomechanism of the mineralization is still obscure. Several hypotheses have been proposed, one of them suggesting a role for fibroblasts in controlling the amount and the quality of the calcified extracellular matrix. This hypothesis raises the question whether changes in mesenchymal cells are the cause and/or the consequences of the calcification process. In this study, fibroblasts were isolated and cultured from Abcc6( / ) and Abcc6(-/-) mice of different ages to investigate parameters known to be associated with the phenotype of fibroblasts from PXE patients. Results demonstrate that a few changes (Ank and Opn downregulation) are already present before the occurrence of calcification. By contrast, a modification of other parameters (intracellular O2- content, Tnap activity, and Bmp2 upregulation) can be observed in Abcc6(-/-) mice after the onset of tissue mineralization. These data suggest that in the Abcc6(-/-) genotype, dermal fibroblasts actively contribute to changes that promote matrix calcification and that these cells can be further modulated with time by the calcified environment, thus contributing to the age-dependent progression of the disease.
MeSH Terms
- ATP-Binding Cassette Transporters
- Aging
- Animals
- Calcinosis
- Cell Proliferation
- Cells, Cultured
- Dermis
- Disease Models, Animal
- Disease Progression
- Elastic Tissue
- Extracellular Matrix
- Fibroblasts
- Mice
- Mice, Knockout
- Multidrug Resistance-Associated Proteins
- Pseudoxanthoma Elasticum
- Reactive Oxygen Species
Pseudoxanthoma elasticum (PXE), a rare heritable disorder caused by mutations of the ABCC6 gene, is characterized by fragmentation and mineralization of elastic fibres. We determined the extent of degradation of elastin by measuring and comparing the amount of desmosines in plasma and urine of PXE patients, healthy carriers and normal subjects. Using capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) we measured the amount of desmosines in the urine of 46 individuals (14 PXE patients, 17 healthy carriers and 15 controls) and in the plasma of 56 subjects (18 PXE patients, 23 healthy carriers and 15 controls). Pseudoxanthoma elasticum patients and carriers were identified by clinical, structural and molecular biology analyses. The urinary excretion of desmosines was two-fold higher in PXE patients than in controls (P < 0.01); the values for healthy carriers were intermediate between those of PXE patients and controls. A very similar trend between patients and their relatives was observed for plasma desmosines. There was a significant correlation between the amount of the desmosines in plasma and urine. Moreover, a positive correlation was observed between urinary desmosine content and age of the patients as well as between urinary desmosine content and severity of clinical manifestations. Both the urinary and plasma desmosine concentrations indicate that elastin degradation is higher in PXE patients and, to a lesser extent, in healthy carriers than in normal subjects. Data seem to indicate that the amount of elastin breakdown products correlates with the age of patients as well as with the severity of the disease.
MeSH Terms
- Adult
- Aging
- Desmosine
- Electrophoresis, Capillary
- Female
- Heterozygote
- Humans
- Linear Models
- Male
- Middle Aged
- Pseudoxanthoma Elasticum
- Severity of Illness Index