Fl1sa^A/J
QTL Variant Detail

Summary

• QTL variant: Fl1sa^A/J
• Name: fatty liver 1 in SMXA; A/J
• MGI ID: MGI:3723476
• QTL: Fl1sa Location: unknown Genetic Position: Chr12, cM position of peak correlated region/allele: 13.69 cM
• QTL Note: genome coordinates based on the marker associated with the peak LOD score

Variant origin

• Strain of Specimen: A/J

Variant description

• Allele Type: QTL
• Mutation: Undefined
• Mutation details: This allele confers increased liver weight, liver total lipid content, and liver triglycerides compared to SM/JNshm. (J:124974)

Expression

In Structures Affected by this Mutation:

1 anatomical structure(s)

Notes

Candidate Genes

J:240255

The SMXA-5 mouse is an animal model of high-fat diet-induced fatty liver. The major QTL for fatty liver, Fl1sa on chromosome 12, was previously identified in a SM/J SMXA-5 intercross. The SMXA-5 genome consists of the SM/J and A/J genomes, and the A/J allele of Fl1sa is the fatty liver-susceptibility allele. The existence of the responsible genes for fatty liver within Fl1sa was confirmed in A/J-Chr 12^SM/J consomic mice. [J:124974].

The aim of the current study was to identify candidate genes for Fl1sa, and to investigate whether the identified genes affect the lipid metabolism.

To identify candidate genes for Fl1sa, DNA microarray analysis was performed using the livers of A/J-Chr 12^SM/J and A/J mice that were fed a high-fat diet. The mRNA levels of three genes (Iah1, Rrm2, Prkd1) in the chromosomal region of Fl1sa were significantly different between the strains.

Iah1 mRNA levels in the liver, kidney, and lung were significantly higher in

A/J-Chr 12^SM/J mice than in A/J mice. The hepatic Iah1 mRNA level in A/J-Chr 12^SM/J mice was 3.2-fold higher than that in A/J mice. A stable cell line expressing the mouse Iah1 protein in mouse hepatoma Hepa1-6 cells was constructed. Overexpression of Iah1 in Hepa1-6 cells suppressed the mRNA levels of Cd36 and Dgat2, genes which play important roles in triglyceride synthesis and lipid metabolism.

J:244215

Nonalcoholic fatty liver disease (NAFLD) is a multifactorial disease caused by interactions between environmental and genetic factors.

It was previously determined that SMXA-5 mice develop severe fatty liver on a high fat diet, although parental SM/J and A/J mice were resistant to fatty liver. Quantitative trait analysis using (SM/J x SMxA-5)F2 intercrossed mice identified a significant QTL, Fl1sa (fatty liver 1 in SMXA), for liver weight, liver triglyceride and total lipid content on centromere-53.06 Mb of mouse Chromosome 12. The A/J allele at Fl1sa was associated with the fatty liver. [J:124974] In a subsequent study using the livers from A/J-Chr 12^SM/J consomic and A/J mice that were fed a high fat diet three candidate genes were identified, Iah1, Rrm2 and Prkd1 using DNA microarray analysis. [J: 240255]

The goal of the current study was to narrow the previously identified Fl1sa region by genetic dissection using novel congenic mice to identify candidate genes within the narrowed Fl1sa region. Two strains of congenic mice, A.SM-(centromere - D12Mit85)/J (R2) and A.SM-(D12Mit85-D12Mit112)/J (R3), were constructed from parental A/J and A/JChr 12 ^SM/J. Microsatellite markers and SNPs were used for the genotyping of R2 and R3 genomic DNA. Physical positions were taken from GRCm38.P4. The lipid accumulation in the respective livers was analyzed. As the liver triglyceride content in R2 and R3 congenic mice was significantly lower than in A/J mice.

Male A/J, A/J-Chr12^SM/J, R2 and R3 mice were fed standard chow until 6 weeks of age and thereafter fed a high fat diet from 6 to 13 weeks of age. At 13 weeks of age all mice were sacrificed after a 4 hour fast. The liver and white adipose tissue (subcutaneous fat, epididymal fat, mesenteric fat and retroperitoneal fat) were harvested and weighed. Blood sample were collected to measure serum lipids. Serum triglyceride, cholesterol and hepatic triglyceride content were measured. Whole transcripts from epididymal fats were measured using a Mouse Genome ST 2.0 array.

Liver triglyceride content was significantly lower in A/J-Chr 12^SM/J, R2 and R3 mice compared with that of A/J mice. Liver triglyceride and liver total lipid in R2 and R3 mice showed intermediate values between those of A/J and A/J-Chr 12 ^SM/J mice. The results suggested that the genes responsible for fatty liver existed in the SM/J region in strain R2 (centromere-29.20 Mb) and in the SM/J region in strain R3 (29.20-46.75 Mb) of Chromosome 12, Fig 1.

Subsequently, in both of the narrowed Fl1sa regions microarray analysis of liver and epididymal fat from A/J and A/J-Chr 12 ^SM/J mice was performed in an attempt to identify candidate genes. Significant differences in gene expression levels in epididymal fat analysis were confirmed in 6 candidate genes: Ntsr2, Zfp125, Gdap10, Nrcam, Stxbp6 and Nova1 between the two strains.

J:289414

Nonalcoholic fatty liver disease (NAFLD) is a pathological condition caused by excess triglyceride deposition in the liver. The SMXA-5 severe fatty liver mouse model has been established from the SM/J and A/J strains. To explore the genetic factors involved in fatty liver development in SMXA-5 mice, the authors had previously performed QTL analysis, using (SM/JSMXA-5)F2 intercross mice, and identified Fl1sa on Chromosome 12 (centromere-53.06 Mb) as a significant QTL for fatty liver.

Isoamyl acetate-hydrolyzing esterase 1 homolog (Iah1) was selected as the most likely candidate gene for Fl1sa. Iah1 gene expression in fatty liver-resistant A/J-12SM mice was significantly higher than in fatty liver-susceptible A/J mice. These data indicated that the Iah1 gene might be associated with fatty liver development. However, the function of murine Iah1 remains unknown.

Therefore, in this study, the authors created Iah1 knockout (KO) mice with two different backgrounds [C57BL/6N (B6) and A/J-12SM (A12)] to investigate the relationship between Iah1 and liver lipid accumulation. Liver triglyceride accumulation in Iah1-KO mice of B6 or A12 background did not differ from their respective Iah1-wild type mice under a high-fat diet. These results indicated that loss of Iah1 did not contribute to fatty liver.

On the other hand, adipose tissue dysfunction causes lipid accumulation in ectopic tissues (liver, skeletal muscle, and pancreas). To investigate the effect of Iah1 deficiency on white adipose tissue, the authors performed DNA microarray analysis of epididymal fat in Iah1-KO mice of A12 background. This result showed that Iah1 deficiency might decrease adipokines Sfrp4 and Metrnl gene expression in epididymal fat.

This study demonstrated that Iah1 deficiency did not cause liver lipid accumulation and that Iah1 was not a suitable candidate gene for Fl1sa.

Mapping and Phenotype information for this QTL, its variants and associated markers

J:124974

Linkage analysis was performed on 255 (SM/JNshm x SMXA-5/Nshm)F2 animals to identify genetic loci associated with fatty liver. Parental strain SMXA-5/Nshm is a recombinant inbred strain derived from SM/J and A/J. This strain exhibits moderately impaired glucose tolerance, mild obesity, and hyperinsulinemia. SMXA-5/Nshm also displays fatty liver on a short term high-fat diet. Progenitor strains SM/J and A/J are resistant to diet-induced fatty liver. F2 animals were placed on a high-fat diet for 7 weeks before phenotype analysis. A panel of 73 polymorphic markers was used for the genome scan.

A QTL designated Fl1sa (fatty liver 1 in SMXA) showed significant linkage to relative liver weight. This locus maps to 13 cM on mouse Chromosome 12 near D12Mit270 (LOD=8.8). Fl1sa explains 15% of the phenotypic variance and also exhibits significant linkage to liver total lipid content (LOD=7.7) and liver triglyceride content (LOD=3.7). A/J-derived alleles at Fl1sa confers increased liver weight, liver total lipids, and liver triglycerides. Fl1sa was confirmed in a consomic line (A/J-Chr 12^SM/J/Nshm) carrying the entire chromosome 12 derived from SM/J on an A/J genetic background. This line displays decreased liver weight, decreased liver total lipids and decreasedliver triglycerides as would be expected from SM/J-derived Fl1sa alleles. Lpin1 at 9 cM is a potential candidate gene for Fl1sa.

A QTL designated Fl2sa (fatty liver 2 in SMXA) showed significant linkage to liver total lipid concentration (LOD=4.1) and relative liverweight (LOD=3.9). This locus maps to mouse Chromosome 2 between D2Mit162 (51.4 cM) and D2Mit28 (78.2 cM). Homozygosity for A/J-derived alleles at Fl2sa confer increased liver lipids and liver weight compared to homozygosity for SM/JNshm-derived alleles.

Linkage to relative liver weight (LOD=2.5), total lipid content (LOD=2.7), and total cholesterol content (LOD=3.7) mapped to mouse Chromosome 17 between D17Mit29 (15.1 cM) and D17Mit68 (24.5 cM). Homozygosity for A/J-derived alleles at D17Mit29 confers increased liver total cholesterol content compared to SM/JNshm homozygotes.

Suggestive linkage to liver total cholesterol mapped to 32 cM on mouse Chromosome 2 near D2Mit156 (LOD=2.5). SM/JNshm-derived alleles confer increased liver cholesterol at this locus. Suggestive linkage to liver triglyceride contentmapped to 96 cM near D2Mit226 (LOD=2.1) with the heterozygous genotype conferring increased liver triglycerides compared to either A/J or SM/JNshm homozygous genotypes.

Suggestive linkage to liver total lipid concentration (LOD=2.1) and serum triglyceride concentration (LOD=2.4) mapped to 0.5 cM on mouse Chromosome 6 near D6Mit86.

Suggestive linkage to serum triglyceride concentration mapped to 56 cM on mouse Chromosome 8 near D8Mit166 (LOD=2).

Suggestive linkage to liver triglyceride content mapped to 35 cM on mouse Chromosome 10 near D10Mit15 (LOD=1.9).

Suggestive linkage to liver weight (LOD=2.1) and serum triglyceride content (LOD=2.1) mapped to 40 cM on mouse Chromosome 11 near D11Mit15.

References

• Original: J:124974 Kumazawa M, et al., Searching for genetic factors of fatty liver in SMXA-5 mice by quantitative trait loci analysis under a high-fat diet. J Lipid Res. 2007 Sep;48(9):2039-46
• All: 4 reference(s)