Download 2015 department of medicine research day

2015 DEPARTMENT OF MEDICINE RESEARCH DAY
Title of Poster: Genome-wide association analysis of liver fibrosis in mice identifies a
novel fibrosis susceptibility locus on chromosome 13
Presenter: Simon W. Beaven
Division: Digestive Diseases
☒Faculty ☐Fellow ☐Resident ☐Post-doc Research Fellow ☐Graduate Student ☐Medical Student ☐Other
Principal Investigator/Mentor: Simon W. Beaven Co-Investigators: Iina Tuominen, Kevin Wroblewski, Mete Civelek,
Kara Clerkin, Ashot Asaryan, Sara Haroutunian, Samuel French, Calvin Pan, Brian W. Parks, Margarete Mehrabian, Clara
Magyar, Aldons J Lusis
Thematic Poster Category: Infections, Injury and Repair, Inflammation, Host Defense, Immunology, Hemostasis and
Atherosclerosis
Abstract
Background and Aims: Liver fibrosis, characterized by excess deposition of collagen within the
hepatic parenchyma, is a multifactorial trait that develops in response to all types of chronic liver
injury, including fatty liver (NAFLD/NASH), viral hepatitis (B & C), and alcohol abuse. The Hybrid
Mouse Diversity Panel (HMDP) is a collection of 100 genetically distinct mouse strains that can be used
to model diseases, including liver fibrosis, for genome-wide association analysis. Our aim was to
characterize the genetic background of liver fibrosis in the HMDP strains subjected to chemicallyinduced liver damage.
Methods: Chronic liver injury was induced by serial carbon tetrachloride (CCl 4) injections twice weekly
for six weeks. A total of 437 CCl4-treated (1-9 mice per strain) and 256 vehicle-treated (1-7 per
strain) mice were harvested for liver histology and gene expression. Liver sections were stained with
picrosirius red as a specific marker of pathologic fibrillar collagen. Slides were digitally scanned at 20x
magnification. Using Definiens Tissue Studio, we designed an algorithm to quantify fibrosis as the
collagen proportionate area % (CPA%) of the whole section, excluding normal vascular wall and liver
capsular collagen. This algorithm was designed in conjunction with a pathologist at UCLA. The
association of 208,514 single nucleotide polymorphisms (SNPs) to CPA% was analyzed using a linear
mixed model that has previously been shown to allow correction for population structure, which is
extensive in mice. Liver gene expression was studied with quantitative PCR.
Results: Variation in fibrosis was broad between resistant and susceptible mouse strains, with
estimated heritability of 39%. The mean CPA% ranged from 0.28 to 3.33 in the CCl 4-treated mice. A
locus on chromosome 13, with a peak SNP identified as rs36783842, reached genome-wide
significance in the association analysis (P=1.78 x 10-7). Conditioning on this SNP identified a 3.5 Mb
region containing 17 protein-coding genes that where further analyzed for differences in liver
expression. Of the twelve genes that were expressed in the liver, only one gene, Stard3nl, was
significantly downregulated in the ten most fibrosis-susceptible strains, compared with all the other
strains (P=0.0002 in CCl4-treated mice).
Conclusions: This is the largest genome-wide association study of liver fibrosis in mice. By using
CPA% as a robust quantitative measure, we identified a novel pro-fibrotic locus that influences the
differences in fibrosis susceptibility in the 100 mouse strains of the HMDP. Ongoing work aims to test
the causative role of Stard3nl in fibrosis. Our results also demonstrate significant heritability of the
trait, define automated CPA% as an unbiased quantitative measure for fibrosis, and provide a road
map for rational strain selection when testing anti-fibrotic drugs.