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A mutation in Ampd2 is associated with nephrotic syndrome and hypercholesterolemia in mice.

Helmering J, Juan T, Li CM, Chhoa M, Baron W, Gyuris T, Richards WG, Turk JR, Lawrence J, Cosgrove PA, Busby J, Kim KW, Kaufman SA, Cummings C, Carlson G, Véniant MM, Lloyd DJ - Lipids Health Dis (2014)

Bottom Line: We identify the third gene as Ampd2, a liver isoform of AMP Deaminase (Ampd), a central component of energy and purine metabolism pathways.The causative mutation was a guanine-to-thymine transversion resulting in an A341S conversion in Ampd2.Metabolomic analysis confirmed an increase in hepatic AMP levels and a decrease in allantoin levels consistent with Ampd2 deficiency, and increases in campesterol and β-sitosterol.

View Article: PubMed Central - PubMed

Affiliation: Department of Metabolic Disorders, Amgen Inc, One Amgen Center Dr, Thousand Oaks, CA 91320, USA. dlloyd@amgen.com.

ABSTRACT

Background: Previously, we identified three loci affecting HDL-cholesterol levels in a screen for ENU-induced mutations in mice and discovered two mutated genes. We sought to identify the third mutated gene and further characterize the mouse phenotype.

Methods: We engaged, DNA sequencing, gene expression profiling, western blotting, lipoprotein characterization, metabolomics assessment, histology and electron microscopy in mouse tissues.

Results: We identify the third gene as Ampd2, a liver isoform of AMP Deaminase (Ampd), a central component of energy and purine metabolism pathways. The causative mutation was a guanine-to-thymine transversion resulting in an A341S conversion in Ampd2. Ampd2 homozygous mutant mice exhibit a labile hypercholesterolemia phenotype, peaking around 9 weeks of age (251 mg/dL vs. wildtype control at 138 mg/dL), and was evidenced by marked increases in HDL, VLDL and LDL. In an attempt to determine the molecular connection between Ampd2 dysfunction and hypercholesterolemia, we analyzed hepatic gene expression and found the downregulation of Ldlr, Hmgcs and Insig1 and upregulation of Cyp7A1 genes. Metabolomic analysis confirmed an increase in hepatic AMP levels and a decrease in allantoin levels consistent with Ampd2 deficiency, and increases in campesterol and β-sitosterol. Additionally, nephrotic syndrome was observed in the mutant mice, through proteinuria, kidney histology and effacement and blebbing of podocyte foot processes by electron microscopy.

Conclusion: In summary we describe the discovery of a novel genetic mouse model of combined transient nephrotic syndrome and hypercholesterolemia, resembling the human disorder.

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Related in: MedlinePlus

Hepatic AMP, ADP, and ATP levels inAmpd2+/+andAmpd2m/mmice. Hepatic AMP, ADP, and ATP levels were determined by HPLC. Open bars represent AMP; solid bars - ADP and hatched bars - ATP. Statistical analysis was carried out by unpaired two-tailed t-tests, * p <0.05 vs. Ampd2+/+.
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Fig4: Hepatic AMP, ADP, and ATP levels inAmpd2+/+andAmpd2m/mmice. Hepatic AMP, ADP, and ATP levels were determined by HPLC. Open bars represent AMP; solid bars - ADP and hatched bars - ATP. Statistical analysis was carried out by unpaired two-tailed t-tests, * p <0.05 vs. Ampd2+/+.

Mentions: We engaged metabolomics to assist in determining the mechanism of hypercholesterolemia in Ampd2m/m mice. Liver and plasma from 9-week old Ampd2+/+ and Ampd2m/m mice were collected for metabolite analysis. These analyses confirmed the cholesterol phenotype of the Ampd2m/m mice in both plasma and liver samples (Additional file 1: Table S1). Additionally cholesterol esters were elevated up to 5 fold. Allantoin, the terminal metabolite in the purine degradation pathway was significantly reduced in the livers from Ampd2m/m mice (Additional file 1: Table S1). The upstream metabolites AMP and ATP were significantly increased in Ampd2m/m mice (Additional file 1: Table S1 and Figure 4). Metabolomic analysis also demonstrated significant increases in plasma plant sterols including campesterol and β-sitosterol.Figure 4


A mutation in Ampd2 is associated with nephrotic syndrome and hypercholesterolemia in mice.

Helmering J, Juan T, Li CM, Chhoa M, Baron W, Gyuris T, Richards WG, Turk JR, Lawrence J, Cosgrove PA, Busby J, Kim KW, Kaufman SA, Cummings C, Carlson G, Véniant MM, Lloyd DJ - Lipids Health Dis (2014)

Hepatic AMP, ADP, and ATP levels inAmpd2+/+andAmpd2m/mmice. Hepatic AMP, ADP, and ATP levels were determined by HPLC. Open bars represent AMP; solid bars - ADP and hatched bars - ATP. Statistical analysis was carried out by unpaired two-tailed t-tests, * p <0.05 vs. Ampd2+/+.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4232700&req=5

Fig4: Hepatic AMP, ADP, and ATP levels inAmpd2+/+andAmpd2m/mmice. Hepatic AMP, ADP, and ATP levels were determined by HPLC. Open bars represent AMP; solid bars - ADP and hatched bars - ATP. Statistical analysis was carried out by unpaired two-tailed t-tests, * p <0.05 vs. Ampd2+/+.
Mentions: We engaged metabolomics to assist in determining the mechanism of hypercholesterolemia in Ampd2m/m mice. Liver and plasma from 9-week old Ampd2+/+ and Ampd2m/m mice were collected for metabolite analysis. These analyses confirmed the cholesterol phenotype of the Ampd2m/m mice in both plasma and liver samples (Additional file 1: Table S1). Additionally cholesterol esters were elevated up to 5 fold. Allantoin, the terminal metabolite in the purine degradation pathway was significantly reduced in the livers from Ampd2m/m mice (Additional file 1: Table S1). The upstream metabolites AMP and ATP were significantly increased in Ampd2m/m mice (Additional file 1: Table S1 and Figure 4). Metabolomic analysis also demonstrated significant increases in plasma plant sterols including campesterol and β-sitosterol.Figure 4

Bottom Line: We identify the third gene as Ampd2, a liver isoform of AMP Deaminase (Ampd), a central component of energy and purine metabolism pathways.The causative mutation was a guanine-to-thymine transversion resulting in an A341S conversion in Ampd2.Metabolomic analysis confirmed an increase in hepatic AMP levels and a decrease in allantoin levels consistent with Ampd2 deficiency, and increases in campesterol and β-sitosterol.

View Article: PubMed Central - PubMed

Affiliation: Department of Metabolic Disorders, Amgen Inc, One Amgen Center Dr, Thousand Oaks, CA 91320, USA. dlloyd@amgen.com.

ABSTRACT

Background: Previously, we identified three loci affecting HDL-cholesterol levels in a screen for ENU-induced mutations in mice and discovered two mutated genes. We sought to identify the third mutated gene and further characterize the mouse phenotype.

Methods: We engaged, DNA sequencing, gene expression profiling, western blotting, lipoprotein characterization, metabolomics assessment, histology and electron microscopy in mouse tissues.

Results: We identify the third gene as Ampd2, a liver isoform of AMP Deaminase (Ampd), a central component of energy and purine metabolism pathways. The causative mutation was a guanine-to-thymine transversion resulting in an A341S conversion in Ampd2. Ampd2 homozygous mutant mice exhibit a labile hypercholesterolemia phenotype, peaking around 9 weeks of age (251 mg/dL vs. wildtype control at 138 mg/dL), and was evidenced by marked increases in HDL, VLDL and LDL. In an attempt to determine the molecular connection between Ampd2 dysfunction and hypercholesterolemia, we analyzed hepatic gene expression and found the downregulation of Ldlr, Hmgcs and Insig1 and upregulation of Cyp7A1 genes. Metabolomic analysis confirmed an increase in hepatic AMP levels and a decrease in allantoin levels consistent with Ampd2 deficiency, and increases in campesterol and β-sitosterol. Additionally, nephrotic syndrome was observed in the mutant mice, through proteinuria, kidney histology and effacement and blebbing of podocyte foot processes by electron microscopy.

Conclusion: In summary we describe the discovery of a novel genetic mouse model of combined transient nephrotic syndrome and hypercholesterolemia, resembling the human disorder.

Show MeSH
Related in: MedlinePlus