title: Comparing expression and activity of PCSK9 in SPRET/EiJ and C57BL/6J mouse strains shows lack of correlation with plasma cholesterol.
abstract: OBJECTIVE
  Low-density lipoprotein receptor (LDLR) and proprotein convertase subtilisin/kexin type 9 (PCSK9) are opposing regulators of plasma LDL-cholesterol levels. The PCSK9 gene exhibits many single or compound polymorphisms within or among mammalian species. This is case between the SPRET/EiJ (SPRET) and C57BL/6J (B6) mouse strains. We examined whether these polymorphisms could be associated with differential expression and activity of their respective PCSK9 molecules.
  
  
  METHODS
  Liver expression of LDLR and PCSK9 transcripts were assessed by RT-PCR, and that of their corresponding proteins by immunoblotting. Purified recombinant PCSK9 proteins were assayed for their ability to degrade LDLR.Pcsk9gene proximal promoters were tested for activation of a luciferase reporter gene.
  
  
  RESULTS
  SPRET and B6 mice carried comparable levels of plasma cholesterol in spite of the fact that SPRET mice expressed less PCSK9 and more LDLR in liver. There were indels and single-base differences between theirPcsk9cDNA and promoter sequences. Ex vivo, SPRET PCSK9 protein was less secreted but was more active at degrading LDLR. Its gene promoter was more active at driving expression of the luciferase reporter.
  
  
  CONCLUSIONS
  Collectively, these results suggest that, compared to the B6 mouse, the SPRET mouse may represent an example of absence of direct correlation between PCSK9 and cholesterol levels in plasma, due to genetic variations leading to reduced secretion of PCSK9 associated with greater LDLR-degrading activity.
authors.affiliation: Functional Endoproteolysis Laboratory, Clinical Research Institute of Montreal, 110 avenue des Pins Ouest, Montreal, Quebec H2W 1R7, Canada.
authors.forename: Francine
authors.initials: F
authors.lastname: Sirois
authors.affiliation: Functional Endoproteolysis Laboratory, Clinical Research Institute of Montreal, 110 avenue des Pins Ouest, Montreal, Quebec H2W 1R7, Canada; Chronic Disease Program, Ottawa Hospital Research Institute, 725 Parkdale Avenue, Ottawa, Ontario K1Y 4E9, Canada; Department of Biochemistry, Microbiology, and Immunology, Faculty of Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada.
authors.forename: Michel
authors.initials: M
authors.lastname: Chrétien
authors.affiliation: Functional Endoproteolysis Laboratory, Clinical Research Institute of Montreal, 110 avenue des Pins Ouest, Montreal, Quebec H2W 1R7, Canada; Chronic Disease Program, Ottawa Hospital Research Institute, 725 Parkdale Avenue, Ottawa, Ontario K1Y 4E9, Canada; Department of Biochemistry, Microbiology, and Immunology, Faculty of Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada.
authors.forename: Majambu
authors.initials: M
authors.lastname: Mbikay
keywords: Cholesterol; Genetic variation; LDLR; Lipoprotein; Mus spretus; PCSK9; Promoter