Novel ENU-Induced Point Mutation in Scavenger Receptor Class B, Member 1, Results in Liver Specific Loss of SCARB1 Protein

Ioannis M Stylianou,Beverly Paigen,Daniel J Rader,Sara K Vanorman,Karen L Svenson,John S Millar,Yanina Langle,Pieter H Reitsma

doi:10.1371/journal.pone.0006521

Abstract

Cardiovascular disease (CVD) is the largest cause of premature death in human populations throughout the world. Circulating plasma lipid levels, specifically high levels of LDL or low levels of HDL, are predictive of susceptibility to CVD. The scavenger receptor class B member 1 (SCARB1) is the primary receptor for the selective uptake of HDL cholesterol by liver and steroidogenic tissues. Hepatic SCARB1 influences plasma HDL-cholesterol levels and is vital for reverse cholesterol transport. Here we describe the mapping of a novel N-ethyl-N-nitrosourea (ENU) induced point mutation in the Scarb1 gene identified in a C57BL/6J background. The mutation is located in a highly conserved amino acid in the extracellular loop and leads to the conversion of an isoleucine to an asparagine (I179N). Homozygous mutant mice express normal Scarb1 mRNA levels and are fertile. SCARB1 protein levels are markedly reduced in liver (∼90%), but not in steroidogenic tissues. This leads to ∼70% increased plasma HDL levels due to reduced HDL cholesteryl ester selective uptake. Pdzk1 knockout mice have liver-specific reduction of SCARB1 protein as does this mutant; however, in vitro analysis of the mutation indicates that the regulation of SCARB1 protein in this mutant is independent of PDZK1. This new Scarb1 model may help further our understanding of post-translational and tissue-specific regulation of SCARB1 that may aid the important clinical goal of raising functional HDL.

Highlights

Cardiovascular disease (CVD) is the largest cause of premature death in human populations throughout the world
At 8 weeks of age, while consuming standard laboratory chow, a male G3 animal, the founder of the mutant strain discussed in this report, showed an 44% increase in total plasma cholesterol (117 and 168 mg/dL for control and mutant respectively) and a 73% increase in plasma HDL cholesterol (73 and 133 mg/dL for control and mutant respectively) which exceed 2.5 standard sex separately and N for each genotype-sex group
Further mapping, using a combination of intercrosses between backcross animals and continued backcrossing of selected recombinants, yielded 334 total progeny and reduced the genomic location to a 2.1 Mb interval (LOD = 49.5, D5Mit160 - D5Mit214). This region contains approximately 20 genes, including an obvious candidate Scarb1 based on its known role in HDL metabolism (Figure 1B)

Summary

Introduction

Cardiovascular disease (CVD) is the largest cause of premature death in human populations throughout the world. It has long been known that circulating plasma lipid levels, high levels of LDL or low levels of HDL, are predictive of susceptibility to CVD. Knockout Scarb12/2 mice have elevated HDL cholesterol levels, reduced selective HDLcholesterol clearance, decreased bile cholesterol concentration and secretion, and reduced reverse cholesterol transport (RCT) [6,7,8,9,10]. Disruption of Scarb in chow-fed Apoe-deficient (Scarb1/Apoe double KO [dKO] mice) or Western diet-fed LDL receptor-deficient (Scarb1/Ldlr dKO) mice develop markedly accelerated atherosclerosis [8,11,12], demonstrating that elevated HDL and its atheroprotective effects are dissociated when reverse cholesterol transport (RCT) is impaired

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Results

Conclusion