Strain background modifies phenotypes in the ATP8B1-deficient mouse

Abstract

Background: Mutations in ATP8B1 (FIC1) underlie cases of cholestatic disease, ranging from chronic and progressive (progressive familial intrahepatic cholestasis) to intermittent (benign recurrent intrahepatic cholestasis). The ATP8B1-deficient mouse serves as an animal model of human ATP8B1 deficiency.

Methodology/principal findings: We investigated the effect of genetic background on phenotypes of ATP8B1-deficient and wild-type mice, using C57Bl/6 (B6), 129, and (B6-129) F1 strain backgrounds. B6 background resulted in greater abnormalities in ATP8B1-deficient mice than did 129 and/or F1 background. ATP8B1-deficient pups of B6 background gained less weight. In adult ATP8B1-deficient mice at baseline, those of B6 background had lower serum cholesterol levels, higher serum alkaline phosphatase levels, and larger livers. After challenge with cholate-supplemented diet, these mice exhibited higher serum alkaline phosphatase and bilirubin levels, greater weight loss and larger livers. ATP8B1-deficient phenotypes in mice of F1 and 129 backgrounds are usually similar, suggesting that susceptibility to manifestations of ATP8B1 deficiency may be recessive. We also detected differences in hepatobiliary phenotypes between wild-type mice of differing strains.

Conclusions/significance: Our results indicate that the ATP8B1-deficient mouse in a B6 background may be a better model of human ATP8B1 deficiency and highlight the importance of informed background strain selection for mouse models of liver disease.

Figure 1. ATP8B1 mutant B6 mice exhibit slower weight gain during the nursing period.

Pup weight in WT and ATP8B1 mutant mice of B6, 129, and F₁ backgrounds at: A) mid-nursing period (∼day 10) and B) weaning. Weights of mutant pups were normalized to those of WT and heterozygote littermates; means and SEM are shown. Range of N's: a) B6 (n = 14−56), 129 (n = 23−57), and F₁ (n = 70−136) and b) B6 (n = 12−53), 129 (n = 23−58), and F₁ (n = 50−138).

Figure 2. ATP8B1 mutant B6 mice lose substantial weight upon cholate feeding.

Weight change per day in WT (A) and ATP8B1 mutant (B) mice of B6, 129, and F₁ backgrounds after feeding of control (grey) or cholate (black) diet for 4–8 days; means and SEM are shown. N's for cholate diet: B6 (n = 8−13), 129 (n = 18−35), and F₁ (n = 13−18); and control diet: B6 (n = 5−9), 129 (n = 22−29), and F₁ (n = 11−16).

Figure 3. Atp8b1 mutation results in lowered serum cholesterol and increased serum alkaline phosphatase (sALP) levels in B6 mice.

Serum cholesterol and alkaline phosphatase levels in WT (A, C) and mutant (B, D) mice of B6, 129, and F₁ backgrounds at baseline (light grey) and after feeding of cholate (black) or control (medium grey) diet for 4–8 days; means and SEM are shown. N's at baseline: B6 (n = 7−15), 129 (n = 42−66), and F₁ (n = 21−36); N's for cholate diet: B6 (n = 5−12), 129 (n = 15−29), and F₁ (n = 6−19) and for control diet: B6 (n = 5−12), 129 (n = 18−29), and F₁ (n = 11−18).

Figure 4. Serum bilirubin concentration increases in ATP8B1 mutant mice upon cholate feeding.

Proportion of WT (A) and ATP8B1 mutant (B) mice of B6, 129, and F₁ backgrounds with normal (light grey), moderately elevated (medium grey), and highly elevated (black) serum bilirubin levels in after feeding cholate or control diet for 4–8 days. N's for cholate diet: B6 (n = 5−8), 129 (n = 30−31), and F₁ (n = 13−25); and control diet: B6 (n = 10−13), 129 (n = 39−48), and F₁ (n = 18−23).

Figure 5. Serum Bile salts levels are higher in ATP8B1 mutant mice.

Serum bile salt levels in WT (A) and Atp8b1 mutant (B) mice of B6, 129, and F₁ backgrounds at baseline (light grey) and after feeding of cholate (black) or control (medium grey) diet for 4–8 days; means and SEM are shown. N's at baseline: B6 (n = 9−15), 129 (n = 48−43), and F₁ (n = 43−45). N's for cholate diet: B6 (n = 7−13), 129 (n = 18−35), and F₁ (n = 13−18); and control diet: B6 (n = 5−9), 129 (n = 22−29), and F₁ (n = 11−16).

Figure 6. Composition of gallbladder bile after feeding of cholate-supplemented diet is influenced by ATP8B1 mutation and strain.

Bile cholesterol, phospholipid, and bile salt levels in WT (A, C, & E) and ATP8B1 mutant (B, D, & F) mice of B6, 129, and F₁ backgrounds after feeding of cholate diet for 4–8 days; means and SEM are shown. N's: B6 (n = 11−19), 129 (n = 39−52), and F₁ (n = 19−22).

Figure 7. ATP8B1 mutant B6 mice have larger livers than mutant 129 mice.

Liver weight as a proportion of final body weight in WT (A) and ATP8B1 mutant (B) mice of B6, 129, and F1 backgrounds after feeding of cholate (black) or control (grey) diet for 4–8 days; means and SEM are shown. N's for cholate diet: B6 (n = 7−13), 129 (n = 18−35), and F1 (n = 13−18); and control diet: B6 (n = 5−9), 129 (n = 22−29), and F1 (n = 11−16).

Figure 8. Hepatic levels of triglycerides and cholesterol are influenced by diet and Atp8b1 mutation.

Hepatic triglycerides and cholesterol in WT (A, C, E, and G) and mutant (B, D, F, and H) mice of B6, 129, and F1 background after cholate (black) and control (grey) diet for 4–8 days; mean and SEM are shown. N's for cholate diet: B6 (n = 4−10), 129 (n = 8−20), and F1 (n = 4−9); and control diet: B6 (n = 4−11), 129 (8−19), F1 (n = 4−8).