Npp1 promotes atherosclerosis in ApoE knockout mice

Abstract

Objective Ecto-Nucleotide Pyrophosphatase/Phosphodiesterase 1 (NPP1) generates inorganic pyrophosphate (PPi), a physiologic inhibitor of hydroxyapatite deposition. In a previous study, we found NPP1 expression to be inversely correlated with the degree of atherosclerotic plaque calcification. Moreover, function-impairing mutations of ENPP1, the gene encoding for NPP1, are associated with severe, artery tunica media calcification and myointimal hyperplasia with infantile onset in humans. NPP1 and PPi have the potential to modulate atherogenesis by regulating arterial smooth muscle cell (SMC) differentiation and function, including increase of pro-atherogenic osteopontin (OPN) expression. Hence, this study tested the hypothesis that NPP1 deficiency modulates both atherogenesis and atherosclerotic intimal plaque calcification. Methods and Results Npp1/ApoE double deficient mice were generated by crossing mice bearing the ttw allele of Enpp1 (that encodes a truncation mutation) with ApoE null mice and fed with high fat/high cholesterol atherogenic diet. Atherosclerotic lesion area and calcification were examined at 13, 18, 23 and 28 weeks of age. The aortic SMCs isolated from both ttw/ttw ApoE−/− and ttw/+ ApoE−/− mice demonstrated decreased Opn expression. The 28 weeks old ttw/ttw ApoE−/− and ttw/+ ApoE−/− had significantly smaller atherosclerotic lesions compared with wild type congenic ApoE−/− mice. Only ttw/ttw but not ttw/+ mice developed artery media calcification. Furthermore in ttw/+ mice, there was a tendency towards increased plaque calcification compared to ApoE−/− mice without Npp1 deficiency. Conclusion We conclude that Npp1 promotes atherosclerosis, potentially mediated by Opn expression in ApoE knockout mice.

Genetic mapping and exome sequencing identify 2 mutations associated with stroke protection in pediatric patients with sickle cell anemia

“…35,36 Lower levels of PP i are the main cause of the arterial calcification in patients with calcification of infancy and in the respective mouse models of defective ENPP1. [36][37][38] In contrast, increased levels of PP i are known to inhibit vascular calcification. 39 The ENPP1 K173Q mutation identified in this study has previously been shown to affect intracellular ENPP1 activity and serum ENPP1 enzyme levels.…”

Juxta-articular joint-capsule mineralization in CD73 deficient mice: Similarities to patients withNT5Emutations

“…3 At the same time, P i can serve as a pro-mineralization factor, particularly in the context of increased inorganic phosphate/ pyrophosphate (P i /PP i ) ratio. 4 In 2004, 3 research groups independently generated knock out mice by targeted disruption of the mouse Nt5e, the gene encoding CD73. [5][6][7] These mice were subsequently characterized to show altered thromboregulation and augmented vascular inflammatory response, lack of CD73 was shown to promote arteriogenesis, and the Nt5e ¡/¡ mice manifested with fulminant vascular leakage during hypoxia.…”

Role of CD73 and extracellular adenosine in disease

“…Increased TNAP activity could certainly clear pyrophosphate generated by ENPP1 and might mimic outcomes of the more severe form of vascular calcification noted in generalized arterial calcification of infancy; the latter characterized by mutations in ENPP1 and low generation rates of pyrophosphate ab initio [3]. Although deletion of Enpp1 in mice models disease in infancy with soft tissue and arterial medial calcification associated with ectopic osteochondral differentiation [16][17][18], it seems that Cd73 deletion in mice does not result in similar phenotypes [16,[18][19][20]. The authors are to be congratulated on this important clinical discovery.…”