Induction of microRNA hsa-let-7d-5p, and repression of HMGA2, contribute protection against lipid accumulation in macrophage ‘foam’ cells

Richard J. Lightbody, Janice M.W. Taylor, Yvonne Dempsie, Annette Graham*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Accumulation of excess cholesterol and cholesteryl ester in macrophage ‘foam’ cells within the arterial intima characterises early ‘fatty streak’ atherosclerotic lesions, and is accompanied by epigenetic changes, including altered expression of microRNA sequences which determine of gene and protein expression. This study established that exposure to lipoproteins, including acetylated LDL, induced macrophage expression of microRNA hsa-let-7d-5p, a sequence previously linked with tumour suppression, and repressed expression of one of its target genes, high mobility group AT hook 2 (HMGA2). A let-7d-5p mimic repressed expression of HMGA2 (18%; p<0.05) while a marked increase (2.9-fold; p<0.05) in expression of HMGA2 was noted in the presence of let-7d-5p inhibitor. Under these conditions, let-7d-5p mimic significantly (p<0.05) decreased total (10%), free (8%) and cholesteryl ester (21%) mass, while the inhibitor significantly (p<0.05) increased total (29%) and free cholesterol (29%) mass, compared with the relevant controls. Let-7d-5p inhibition significantly (p<0.05) increased endogenous biosynthesis of cholesterol (38%) and cholesteryl ester (39%) pools in macrophage ‘foam’ cells, without altering the cholesterol efflux pathway, or esterification of exogenous radiolabelled oleate. Let-7d-5p inhibition in sterol-loaded cells increased the level of HMGA2 protein (32%; p<0.05), while SiRNA knockdown of this protein (29%; p<0.05) resulted in a (21%; p<0.05) reduction in free cholesterol mass. Thus, induction of let-7d-5p, and repression of its target HMGA2, in macrophages is a protective response to the challenge of increased cholesterol influx into these cells; dysregulation of this response may contribute to atherosclerosis and other disorders such as cancer.
Original languageEnglish
Article number159005
Number of pages13
JournalBiochimica et Biophysica Acta (BBA) ‐ Molecular and Cell Biology of Lipids
Volume1866
Issue number11
Early online date16 Jul 2021
DOIs
Publication statusE-pub ahead of print - 16 Jul 2021

Keywords

  • atherosclerosis, macrophage ‘foam’ cell, cholesterol, microRNA, hsa-lethal(let)-7d-5p, high mobility group AT hook 2

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