title: Loss of equilibrative nucleoside transporter 1 in mice leads to progressive ectopic mineralization of spinal tissues resembling diffuse idiopathic skeletal hyperostosis in humans.
abstract: Diffuse idiopathic skeletal hyperostosis (DISH) is a noninflammatory spondyloarthropathy, characterized by ectopic calcification of spinal tissues. Symptoms include spine pain and stiffness, and in severe cases dysphagia and spinal cord compression. The etiology of DISH is unknown and there are no specific treatments. Recent studies have suggested a role for purine metabolism in the regulation of biomineralization. Equilibrative nucleoside transporter 1 (ENT1) transfers hydrophilic nucleosides, such as adenosine, across the plasma membrane. In mice lacking ENT1, we observed the development of calcified lesions resembling DISH. By 12 months of age, ENT1(-/-) mice exhibited signs of spine stiffness, hind limb dysfunction, and paralysis. Micro-computed tomography (µCT) revealed ectopic mineralization of paraspinal tissues in the cervical-thoracic region at 2 months of age, which extended to the lumbar and caudal regions with advancing age. Energy-dispersive X-ray microanalysis of lesions revealed a high content of calcium and phosphorus with a ratio similar to that of cortical bone. At 12 months of age, histological examination of ENT1(-/-) mice revealed large, irregular accumulations of eosinophilic material in paraspinal ligaments and entheses, intervertebral discs, and sternocostal articulations. There was no evidence of mineralization in appendicular joints or blood vessels, indicating specificity for the axial skeleton. Plasma adenosine levels were significantly greater in ENT1(-/-) mice than in wild-type, consistent with loss of ENT1--a primary adenosine uptake pathway. There was a significant reduction in the expression of Enpp1, Ank, and Alpl in intervertebral discs from ENT1(-/-) mice compared to wild-type mice. Elevated plasma levels of inorganic pyrophosphate in ENT1(-/-) mice indicated generalized disruption of pyrophosphate homeostasis. This is the first report of a role for ENT1 in regulating the calcification of soft tissues. Moreover, ENT1(-/-) mice may be a useful model for investigating pathogenesis and evaluating therapeutics for the prevention of mineralization in DISH and related disorders.
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON, Canada.
authors.forename: Sumeeta
authors.initials: S
authors.lastname: Warraich
authors.forename: Derek B J
authors.initials: DB
authors.lastname: Bone
authors.forename: Diana
authors.initials: D
authors.lastname: Quinonez
authors.forename: Hisataka
authors.initials: H
authors.lastname: Ii
authors.forename: Doo-Sup
authors.initials: DS
authors.lastname: Choi
authors.forename: David W
authors.initials: DW
authors.lastname: Holdsworth
authors.forename: Maria
authors.initials: M
authors.lastname: Drangova
authors.forename: S Jeffrey
authors.initials: SJ
authors.lastname: Dixon
authors.forename: Cheryle A
authors.initials: CA
authors.lastname: Séguin
authors.forename: James R
authors.initials: JR
authors.lastname: Hammond
mesh_terms: D000818:Animals; D002113:Calcification, Physiologic; D033721:Equilibrative Nucleoside Transporter 1 / Q000235:genetics / Q000502:physiology*; D015870:Gene Expression; D004057:Hyperostosis, Diffuse Idiopathic Skeletal / Q000473:pathology*; D051379:Mice; D008810:Mice, Inbred C57BL; D013052:Spectrometry, X-Ray Emission; D013131:Spine / Q000473:pathology*; D014057:Tomography, X-Ray Computed
chemical_list: D033721:Equilibrative Nucleoside Transporter 1; C498476:SLC29A1 protein, mouse