Ectopic calcification in pseudoxanthoma elasticum responds to inhibition of tissue-nonspecific alkaline phosphatase

Sci Transl Med. 2017 Jun 7;9(393):eaal1669. doi: 10.1126/scitranslmed.aal1669.

Abstract

Biallelic mutations in ABCC6 cause pseudoxanthoma elasticum (PXE), a disease characterized by calcification in the skin, eyes, and blood vessels. The function of ATP-binding cassette C6 (ABCC6) and the pathogenesis of PXE remain unclear. We used mouse models and patient fibroblasts to demonstrate genetic interaction and shared biochemical and cellular mechanisms underlying ectopic calcification in PXE and related disorders caused by defined perturbations in extracellular adenosine 5'-triphosphate catabolism. Under osteogenic culture conditions, ABCC6 mutant cells calcified, suggesting a provoked cell-autonomous defect. Using a conditional Abcc6 knockout mouse model, we excluded the prevailing pathogenic hypothesis that singularly invokes failure of hepatic secretion of an endocrine inhibitor of calcification. Instead, deficiency of Abcc6 in both local and distant cells was necessary to achieve the early onset and penetrant ectopic calcification observed upon constitutive gene targeting. ABCC6 mutant cells additionally had increased expression and activity of tissue-nonspecific alkaline phosphatase (TNAP), an enzyme that degrades pyrophosphate, a major inhibitor of calcification. A selective and orally bioavailable TNAP inhibitor prevented calcification in ABCC6 mutant cells in vitro and attenuated both the development and progression of calcification in Abcc6-/- mice in vivo, without the deleterious effects on bone associated with other proposed treatment strategies.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, N.I.H., Intramural

MeSH terms

  • ATP-Binding Cassette Transporters / metabolism
  • Adenosine Triphosphate / metabolism
  • Alkaline Phosphatase / antagonists & inhibitors*
  • Alkaline Phosphatase / metabolism
  • Animals
  • Calcinosis / complications*
  • Calcinosis / enzymology*
  • Crosses, Genetic
  • Disease Models, Animal
  • Epistasis, Genetic
  • Extracellular Space / metabolism
  • Female
  • Fibroblasts / metabolism
  • Gene Deletion
  • Humans
  • Liver / metabolism
  • Male
  • Mice
  • Mice, Mutant Strains
  • Models, Biological
  • Multidrug Resistance-Associated Proteins / genetics
  • Mutation / genetics
  • Osteogenesis
  • Phenotype
  • Phosphoric Diester Hydrolases / metabolism
  • Pseudoxanthoma Elasticum / complications*
  • Pseudoxanthoma Elasticum / enzymology*
  • Pyrophosphatases / metabolism

Substances

  • ABCC6 protein, human
  • ATP-Binding Cassette Transporters
  • Abcc6 protein, mouse
  • Multidrug Resistance-Associated Proteins
  • Adenosine Triphosphate
  • Alkaline Phosphatase
  • alkaline phosphatase 2, mouse
  • Phosphoric Diester Hydrolases
  • ectonucleotide pyrophosphatase phosphodiesterase 1
  • Pyrophosphatases