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HDL functionality is dependent on hepatocyte stress defense factors NRF1 and NRF2

ABSTRACT: High density lipoproteins (HDL) promote homeostasis and counteract stressful tissue damage that underlie cardiovascular and other diseases by mediating reverse cholesterol transport, reducing inflammation, and abrogating oxidative damage. However, metabolically stressful conditions associated with atherosclerosis can impair these effects. Hepatocytes play a major role in the genesis and maturation of circulating HDL. Liver stress elicits marked regulatory changes to circulating HDL abundance and composition, which affect its functionality. Mechanisms linking liver stress to HDL functionality are incompletely understood. In this study, we sought to determine whether stress defending transcription factors nuclear factor erythroid 2 related factor-1 (NRF1) and -2 (NRF2) promote hepatocyte production of functional HDL. Using genetically engineered mouse models briefly fed a mild metabolically stressful diet, we investigated the effect of hepatocyte-specific deletion of NRF1, NRF2, or both on circulating HDL cholesterol level, protein composition, and function. Combined deletion, but not single gene deletion, reduced HDL cholesterol content as well as the capacity of HDL to accept cholesterol efflux from cultured macrophages and to counteract tumor necrosis factor a-induced inflammatory effect on cultured endothelial cells. This coincided with substantial alteration to the circulating HDL proteome, which correlated with liver gene expression profiles of corresponding proteins. Altogether, our findings show complementary actions by hepatocyte NRF1 and NRF2 play a role in shaping HDL composition and promote production of functionally viable HDL. Consequently, our study illuminates the possibility that enhancing stress defense programming in the liver may improve atheroprotective and perhaps other health promoting actions of HDL.

INSTRUMENT(S): LTQ Orbitrap

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Hepatocyte, Liver

DISEASE(S): Cardiovascular System Disease

SUBMITTER: Sadhna Phanse

LAB HEAD: Scott Widenmaier, PhD

PROVIDER: PXD042103 | Pride | 2023-07-03

REPOSITORIES: Pride

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Project description:Despite considerable progress understanding genes that affect the HDL particle, its function, and cholesterol content, genes identified to date explain only a small percentage of the genetic variation. We used N-ethyl-N-nitrosourea mutagenesis in mice to discover novel genes that affect HDL cholesterol levels. Two mutant lines (Hlb218 and Hlb320) with low HDL cholesterol levels were established. Causal mutations in these lines were mapped using linkage analysis: For line Hlb218 within a 12 Mbp region on Chr 10; and for line Hlb320 within a 17 Mbp region on Chr 7. High-throughput sequencing of Hlb218 liver RNA identified a mutation in Pla2g12b. The transition of G to A leads to a cysteine to tyrosine change and most likely causes a loss of a disulfide bridge. Microarray analysis of Hlb320 liver RNA showed a 7-fold downregulation of Hpn; sequencing identified a mutation in the 3M-bM-^@M-2 splice site of exon 8. Northern blot confirmed lower mRNA expression level in Hlb320 and did not show a difference in splicing, suggesting that the mutation only affects the splicing rate. In addition to affecting HDL cholesterol, the mutated genes also lead to reduction in serum non-HDL cholesterol and triglyceride levels. Despite low HDL cholesterol levels, the mice from both mutant lines show similar atherosclerotic lesion sizes compared to control mice. These new mutant mouse models are valuable tools to further study the role of these genes, their affect on HDL cholesterol levels, and metabolism. Mutant mice were generated as part of The Jackson LaboratoryM-bM-^@M-^Ys Heart, Lung, Blood, and Sleep Disorder Mutagenesis Program by treating male C57BL/6J (B6) mice with N-ethyl-N-nitrosourea (ENU). Third generation (G3) mice were phenotyped to ensure capture of both dominant and recessive mutations. Two unique G3 animals with low HDL cholesterol levels were then used to establish new inbred lines (Hlb218 and Hlb320) by mating them with B6 mice and intercrossing the offspring with low HDL cholesterol for 7 generations. Livers from 3 Hlb218, 3 Hlb320 males, and 6 B6 male controls were obtained for gene expression analysis. The samples were randomized over Illumina Mouse-6 Expression 1.1 BeadChips .

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HDL functionality is dependent on hepatocyte stress defense factors NRF1 and NRF2

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