Fibroblasts from patients affected by Pseudoxanthoma elasticum exhibit an altered PPi metabolism and are more responsive to pro-calcifying stimuli.
BACKGROUND
Pseudoxanthoma elasticum (PXE) is a genetic disorder characterized by progressive calcification of soft connective tissues. The pathogenesis is still hard to pin down. In PXE dermal fibroblasts, in addition to impaired carboxylation of the vitamin K-dependent inhibitor matrix Gla protein (MGP), we have also demonstrated an up-regulation of alkaline phosphatase activity. In the light of these data we have suggested that both calcium and phosphate metabolism might be locally altered, both pathways acting in synergy on the occurrence of matrix calcification.


OBJECTIVE
This study aims to better explore if cultured PXE fibroblasts, compared to control cells, exhibit a modified inorganic pyrophosphate (PPi) metabolism and are more responsive to pro-calcifying stimuli.


METHODS
Primary human dermal fibroblasts isolated from healthy individuals and from PXE patients were cultured for different time points in standard and in pro-calcifying media. The expression of ANKH/ANKH, ENPP1/PC1, ALPL/TNAP, SPP1/OPN was evaluated by qRT-PCR and Western blot, respectively. TNAP activity was measured by spectrophotometric analyses, whereas calcification was investigated by light and electron microscopy as well as by micro-analytical techniques.


RESULTS
In the presence of pro-calcifying stimuli, dermal fibroblasts alter their phenotype favouring matrix mineralization. In particular, ENPP1/PC1 and SPP1/OPN expression, as well as TNAP activity, was differently expressed in control and in PXE fibroblasts. Moreover, in pathologic cells the ratio between factors favouring and reducing PPi availability exhibits a more pronounced shift towards a pro-calcifying balance.


CONCLUSIONS
PXE fibroblasts are more susceptible to pro-calcifying stimuli and in these cells an altered PPi metabolism contributes to matrix calcification.
Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.
Federica
F
Boraldi
Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.
Giulia
G
Annovi
Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.
Angelica
A
Bartolomeo
Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy. Electronic address: daniela.quaglino@unimore.it.
Daniela
D
Quaglino
D000328:Adult; D000469:Alkaline Phosphatase / Q000378:metabolism; D002114:Calcinosis / Q000150:complications / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D017931:DNA Primers; D011756:Diphosphates / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D008855:Microscopy, Electron, Scanning; D008875:Middle Aged; D011561:Pseudoxanthoma Elasticum / Q000378:metabolism* / Q000473:pathology; D012867:Skin / Q000378:metabolism; D013052:Spectrometry, X-Ray Emission; D015854:Up-Regulation; D000097568:Matrix Gla Protein
D000469:Alkaline Phosphatase; D002118:Calcium; D002135:Calcium-Binding Proteins; D017931:DNA Primers; D011756:Diphosphates; D016326:Extracellular Matrix Proteins; D000097568:Matrix Gla Protein; C107241:diphosphoric acid
Ectopic calcification; Fibroblasts; Pseudoxanthoma elasticum; Pyrophosphate