Abstract
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, we had previously performed quantitative trait locus (QTL) analysis, using (SM/J×SMXA-5)F2 intercross mice, and identified Fl1sa on chromosome 12 (centromere-53.06 Mb) as a significant QTL for fatty liver. Furthermore, 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, we 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 hands, 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, we 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.
Highlights
Severe fatty liver in SMXA-5 mice is caused by a combination of multiple genes that are latent in the genomes of both A/J and SM/J mice
Systemic isoamyl acetate-hydrolyzing esterase 1 homolog (Iah1)-KO mice on a C57BL/6N background might have not have led to the development of multiple gene-induced fatty liver
Metrnl mRNA levels tended to be slightly decreased in KO mice on an A/J-12SM background (KO_A12) mice (p = 0.05), there were no significant changes in Secreted frizzled-related protein 4 (Sfrp4) mRNA levels in the retroperitoneal adipose tissue (Fig 5C). These results indicated that Iah1 deficiency in visceral white adipose tissue decreased Sfrp4 and Metrnl gene expression
Summary
The tm1a (Iah1tm1a (EUCOMM) Hmgu) mice were obtained from the European Conditional Mouse Mutagenesis Program (EUCOMM). The CAG-Cre [B6.Cg-Tg (CAG-Cre) CZ-MO2Osb] [10] mice were obtained from RIKEN BRC (Japan, RBRC01828). The tm1a mice had a C57BL/6NTac genetic background and had a heterozygous knockout-first allele with the loxP and Frt sites (http://www.mousephenotype.org/about-ikmc/eucomm) (S1 Fig) [11]. The CAG-Cre transgenic mice (C57BL/6NCrSlc genetic background) constitutively express the Cre recombinase gene under the control of a CAG promoter. To generate KO mice, the tm1a heterozygotes were crossed with CAG-Cre mice resulting in tm1b heterozygotes which were heterozygous for Cre (mate A in S1 Fig). To remove the Cre recombinase, the tm1b heterozygotes (Iah1tm1b/WT, Cre/WT) were crossed with mice which had the same genotype and the heterozygotes (Iah1tm1b/WT, WT/WT) without Cre were chosen (mate B in S1 Fig). The Iah1tm1b heterozygotes were intercrossed to generate Iah1WT/WT (wild type, WT_B6), Iah1tm1b/WT (heterozygous KO, Hetero), and Iah1tm1b/tm1b (homozygous KO, KO_B6)
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