Regulation of intestinal LDLR by the LXR-IDOL axis

Jessica K Nelson,Suzanne A.E Van Wouw,Saskia Scheij,Nienke M Van Loon,Martina Moeton,Jenina Kingma,Roelof Ottenhoff,Noam Zelcer

doi:10.1016/j.atherosclerosis.2020.10.898

Jessica K Nelson, Suzanne A.E Van Wouw + Show 6 more

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https://doi.org/10.1016/j.atherosclerosis.2020.10.898

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Journal: Atherosclerosis	Publication Date: Nov 9, 2020
Citations: 13	License type: cc-by

Affiliation: Amsterdam University Medical Centers

Abstract

Background and aimsCholesterol metabolism is tightly regulated by transcriptional and post-transcriptional mechanisms. Accordingly, dysregulation of cholesterol metabolism is a major risk factor for the development of coronary artery disease and associated complications. In recent years, it has become apparent that next to the liver, the intestine plays a key role in systemic cholesterol metabolism by governing cholesterol absorption, secretion, and incorporation into lipoprotein particles. We have previously demonstrated that the Liver X receptor (LXR)-regulated E3 ubiquitin ligase inducible degrader of LDLR (IDOL) is a regulator of cholesterol uptake owing to its ability to promote the ubiquitylation of the low-density lipoprotein receptor (LDLR). However, whether the LXR-IDOL-LDLR axis regulates the LDLR in the intestine and whether this influences intestinal cholesterol homeostasis is not known. MethodsIn this study, we evaluated the role of the LXR-IDOL-LDLR axis in enterocyte cell models and in primary enterocytes isolated from Idol(−/−) and wild type mice. Furthermore, we studied the regulation of intestinal LDLR in Idol(−/−) and in wild type mice treated with the LXR agonist GW3965. Finally, we assessed ezetimibe-induced trans-intestinal cholesterol efflux in Idol(−/−) mice. ResultsWe show that in a wide range of intestinal cell lines LXR activation decreases LDLR protein abundance, cell surface occupancy, and LDL uptake in an IDOL-dependent manner. Similarly, we find that pharmacological dosing of C57BL6/N mice with the LXR agonist GW3965 increases Idol expression across the intestine with a concomitant reduction in Ldlr protein. Conversely, primary enterocytes isolated from Idol(−/−) mice have elevated Ldlr. To test whether these changes contribute to trans-intestinal cholesterol efflux, we measured fecal cholesterol in mice following ezetimibe dosing, but found no differences between Idol(−/−) and control mice in this setting. ConclusionsIn conclusion, our study establishes that the LXR-IDOL-LDLR axis is active in the intestine and is part of the molecular circuitry that maintains cholesterol homeostasis in enterocytes.

Highlights

Cholesterol is an essential component of eukaryotic cell membranes and a precursor for a variety of bioactive molecules
Sterol-depletion of these cells markedly induced the expression of the sterol regulatory element binding proteins (SREBPs) targets HMGCR and low-density lipoprotein receptor (LDLR) (Fig. 1B and C)
GW3965 had a limited effect on expression of these SREBP targets, and the slight cell- and gene-specific increase observed in their expression likely represents a homeostatic response to Liver X re ceptor (LXR) activation

Summary

Introduction

Cholesterol is an essential component of eukaryotic cell membranes and a precursor for a variety of bioactive molecules. Increased intracellular concentrations can be cytotoxic and elevated levels of atherogenic lipoproteins are an established risk factor for the develop ment of atherosclerosis It follows that understanding the basic mecha nisms that govern cholesterol metabolism is a prerequisite for further development of therapeutic strategies to treat dyslipidemia and improve lipid-lowering strategies. An alternative pathway for cholesterol loss referred to as trans intestinal cholesterol excretion (TICE) has been proposed [4,6] This process can be stimulated by ezetimibe [7,8], plant sterols [9,10] or with agonists stimulating Farnesoid X receptors [11], Liver. Primary enterocytes isolated from Idol(− /− ) mice have elevated Ldlr To test whether these changes contribute to trans-intestinal cholesterol efflux, we measured fecal cholesterol in mice following ezetimibe dosing, but found no differences between Idol(− /− ) and control mice in this setting. Conclusions: In conclusion, our study establishes that the LXR-IDOL-LDLR axis is active in the intestine and is part of the molecular circuitry that maintains cholesterol homeostasis in enterocytes

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Conclusion