title: Mono-allelic and bi-allelic ENPP1 deficiency promote post-injury neointimal hyperplasia associated with increased C/EBP homologous protein expression.
abstract: OBJECTIVE
  Bi-allelic function-inactivating ENPP1 mutations cause artery media calcification (AMC) with associated severe myointimal hyperplasia in generalized arterial calcification of infancy (GACI), whereas mono-allelic ENPP1 deficiency is phenotypically normal. Here, we tested if ENPP1 deficiency promotes abnormal vascular smooth muscle cell (VSMC)-driven responses to injury, with or without calcification. The ER stress mediator C/EBP homologous protein (CHOP) affects neointimal hyperplasia and atherosclerosis, and has paradoxical effects on bone formation. Hence, we assessed relationships between ENPP1 and CHOP in VSMCs.
  
  
  METHODS
  We studied ENPP1-deficient mice and control littermates subjected to left carotid artery ligation, and isolated and studied VSMCs from these and Chop-/- mice, or with CHOP siRNA treatment.
  
  
  RESULTS
  Normal Enpp1-/+ mice, in addition to Enpp1-/- mice prior to AMC development, had accelerated neointimal hyperplasia in response to carotid artery ligation at 7-8 weeks age. Neointimal hyperplasia was linked with robust artery media CHOP expression in situ, but with marked AMC only in injured Enpp1-/- arteries. Cultured, ENPP1-deficient and CHOP-deficient VSMCs had increased migration and proliferation to PDGF. Cultured Chop-/- VSMCs demonstrated increased Pi donor-induced calcification. CHOP was significantly increased in Pi donor treated Enpp1-/- and Enpp1-/+ cultured VSMCs. CHOP siRNA treatment of Enpp1-/- VSMCs increased calcification, associated with elevated expression of tissue nonspecific alkaline phosphatase and the master osteoblastic transcription factor RUNX2.
  
  
  CONCLUSIONS
  Both mono-allelic and bi-allelic ENPP1 deficiency promote dysregulated VSMC function, with robust lesion CHOP expression and enhanced neointimal hyperplasia after injury in vivo, but marked post-injury calcification limited to Enpp1-/- mice. Intimal hyperplasia in GACI appears regulated by biologic effects of ENPP1 deficiency other than calcification, including ER stress. VSMC CHOP excess in ENPP1 deficiency may primarily function to limit VSMC calcification.
authors: San Diego VA Healthcare System and Department of Medicine, University of California, 111K, 3350 La Jolla Village Dr., San Diego, CA 92161, USA.
authors: Ramon L
authors: RL
authors: Serrano
authors: San Diego VA Healthcare System and Department of Medicine, University of California, 111K, 3350 La Jolla Village Dr., San Diego, CA 92161, USA.
authors: Weifang
authors: W
authors: Yu
authors: San Diego VA Healthcare System and Department of Medicine, University of California, 111K, 3350 La Jolla Village Dr., San Diego, CA 92161, USA. Electronic address: rterkeltaub@ucsd.edu.
authors: Robert
authors: R
authors: Terkeltaub
mesh_terms: D000469:Alkaline Phosphatase / Q000096:biosynthesis / Q000235:genetics; D000483:Alleles; D000818:Animals; D016893:Carotid Stenosis / Q000378:metabolism / Q000473:pathology*; D002454:Cell Differentiation; D050659:Core Binding Factor Alpha 1 Subunit / Q000096:biosynthesis / Q000235:genetics; D004195:Disease Models, Animal; D005838:Genotype; D006965:Hyperplasia; D008026:Ligation; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D032389:Myocytes, Smooth Muscle / Q000378:metabolism / Q000473:pathology*; D058426:Neointima / Q000503:physiopathology*; D010727:Phosphoric Diester Hydrolases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D011755:Pyrophosphatases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D051742:Transcription Factor CHOP / Q000096:biosynthesis* / Q000172:deficiency / Q000235:genetics; D017539:Tunica Intima / Q000293:injuries* / Q000473:pathology; D017540:Tunica Media / Q000473:pathology; D056811:Unfolded Protein Response / Q000502:physiology; D061205:Vascular Calcification / Q000209:etiology / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; C493716:Runx2 protein, mouse; D051742:Transcription Factor CHOP; C510878:ALPL protein, mouse; D000469:Alkaline Phosphatase; D010727:Phosphoric Diester Hydrolases; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; D011755:Pyrophosphatases
keywords: Artery media calcification; CHOP; ER stress; Generalized arterial calcification of infancy; Unfolded protein response