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A chronic high-cholesterol diet paradoxically suppresses hepatic CYP7A1 expression in FVB/NJ mice.

ABSTRACT: Cholesterol 7?-hydroxylase (CYP7A1) encodes for the rate-limiting step in the conversion of cholesterol to bile acids in the liver. In response to acute cholesterol feeding, mice upregulate CYP7A1 via stimulation of the liver X receptor (LXR) ?. However, the effect of a chronic high-cholesterol diet on hepatic CYP7A1 expression in mice is unknown. We demonstrate that chronic cholesterol feeding (0.2% or 1.25% w/w cholesterol for 12 weeks) in FVB/NJ mice results in a >60% suppression of hepatic CYP7A1 expression associated with a >2-fold increase in hepatic cholesterol content. In contrast, acute cholesterol feeding induces a >3-fold upregulation of hepatic CYP7A1 expression. We show that chronic, but not acute, cholesterol feeding increases the expression of hepatic inflammatory cytokines, tumor necrosis factor (TNF)?, and interleukin (IL)-1?, which are known to suppress hepatic CYP7A1 expression. Chronic cholesterol feeding also results in activation of the mitogen activated protein (MAP) kinases, c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). Furthermore, we demonstrate in vitro that suppression of CYP7A1 by TNF? and IL-1? is dependent on JNK and ERK signaling. We conclude that chronic high-cholesterol feeding suppresses CYP7A1 expression in mice. We propose that chronic cholesterol feeding induces inflammatory cytokine activation and liver damage, which leads to suppression of CYP7A1 via activation of JNK and ERK signaling pathways.

SUBMITTER: Henkel AS

PROVIDER: S-EPMC3023549 | biostudies-literature | 2011 Feb

REPOSITORIES: biostudies-literature

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A chronic high-cholesterol diet paradoxically suppresses hepatic CYP7A1 expression in FVB/NJ mice.

Henkel Anne S AS Anderson Kristy A KA Dewey Amanda M AM Kavesh Mark H MH Green Richard M RM

Journal of lipid research 20101120 2

Cholesterol 7α-hydroxylase (CYP7A1) encodes for the rate-limiting step in the conversion of cholesterol to bile acids in the liver. In response to acute cholesterol feeding, mice upregulate CYP7A1 via stimulation of the liver X receptor (LXR) α. However, the effect of a chronic high-cholesterol diet on hepatic CYP7A1 expression in mice is unknown. We demonstrate that chronic cholesterol feeding (0.2% or 1.25% w/w cholesterol for 12 weeks) in FVB/NJ mice results in a >60% suppression of hepatic C ...[more]

PMID: 21097822

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Project description:Noise-induced hearing loss (NIHL) affects millions of people worldwide and presents a large social and personal burden. Pharmacological activation of SIRT3, a regulator of the mitochondrial oxidative stress response, has a protective effect on hearing thresholds after traumatic noise damage in mice. In contrast, the role of endogenously activated SIRT3 in hearing recovery has not been established. Here we tested the hypothesis that SIRT3 is required in mice for recovery of auditory thresholds after a noise exposure that confers a temporary threshold shift (TTS). SIRT3-specific immunoreactivity is present in outer hair cells, around the post-synaptic regions of inner hair cells, and faintly within inner hair cells. Prior to noise exposure, homozygous Sirt3-KO mice have slightly but significantly higher thresholds than their wild-type littermates measured by the auditory brainstem response (ABR), but not by distortion product otoacoustic emissions (DPOAE). Moreover, homozygous Sirt3-KO mice display a significant reduction in the progression of their peak 1 amplitude at higher frequencies prior to noise exposure. After exposure to a single sub-traumatic noise dose that does not permanently reduce cochlear function, compromise cell survival, or damage synaptic structures in wild-type mice, there was no difference in hearing function between the two genotypes, measured by ABR and DPOAE. The numbers of hair cells and auditory synapses were similar in both genotypes before and after noise exposure. These loss-of-function studies complement previously published gain-of-function studies and help refine our understanding of SIRT3's role in cochlear homeostasis under different damage paradigms. They suggest that SIRT3 may promote spiral ganglion neuron function. They imply that cellular mechanisms of homeostasis, in addition to the mitochondrial oxidative stress response, act to restore hearing after TTS. Finally, we present a novel application of a biomedical statistical analysis for identifying changes between peak 1 amplitude progressions in ABR waveforms after damage.

Dataset Information

A chronic high-cholesterol diet paradoxically suppresses hepatic CYP7A1 expression in FVB/NJ mice.

Publications

A chronic high-cholesterol diet paradoxically suppresses hepatic CYP7A1 expression in FVB/NJ mice.

Similar Datasets

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