Low density lipoprotein receptor-related protein 1 expression correlates with cholesteryl ester accumulation in the myocardium of ischemic cardiomyopathy patients

Abstract

Our hypothesis was that overexpression of certain lipoprotein receptors might be related to lipid accumulation in the human ischemic myocardium. Intramyocardial lipid overload contributes to contractile dysfunction and arrhythmias in cardiomyopathy. Thus, the purpose of this study was to assess the effect of hypercholesterolemic LDL and hypertrigliceridemic VLDL dose on LRP1 expression in cardiomyocytes, as well as the potential correlation between LRP1 expression and neutral lipid accumulation in the left ventricle tissue from ischemic cardiomyopathy patients. Cell culture experiments include control and LRP1-deficient cardiomyocytes exposed to lipoproteins under normoxic and hypoxic conditions. Explanted hearts from 18 ICM patients and eight non-diseased hearts (CNT) were included. Low density lipoprotein receptor-related protein 1 (LRP1), very low density lipoprotein receptor (VLDLR) and low density lipoprotein receptor (LDLR) expression was analyzed by real time PCR and Western blotting. Cholesteryl ester (CE), triglyceride (TG) and free cholesterol (FC) content was assess by thin layer chromatography following lipid extraction. Western blotting experiments showed that protein levels of LRP1, VLDLR and HIF-1α were significantly upregulated in ischemic hearts. Immunohistochemistry and confocal microscopy analysis showed that LRP1 and HIF-1α were upregulated in cardiomyocytes of ICM patients. In vitro studies showed that VLDL, LDL and hypoxia exerted an upregulatory effect on LRP1 expression and that LRP1 played a major role in cholesteryl ester accumulation from lipoproteins in cardiomyocytes. Myocardial CE accumulation strongly correlated with LRP1 levels in ischemic hearts. Taken together, our results suggest that LRP1 upregulation is key for myocardial cholesterol ester accumulation in ischemic human hearts and that LRP1 may be a target to prevent the deleterious effects of myocardial cholesterol accumulation in ischemic cardiomyopathy.

Aggregated Low-Density Lipoprotein Induces LRP1 Stabilization Through E3 Ubiquitin Ligase CHFR Downregulation in Human Vascular Smooth Muscle Cells

“…Our group reported that LRP1 is upregulated at transcriptional level by hypercholesterolemia through sterol regulatory element-binding proteins (SREBP) downregulation in human VSMC, [8][9][10] and by hypoxia through hypoxia-inducible factor 1α upregulation in human VSMC 11 and cardiomyocytes. 12,13 Other groups have reported that insulin promotes the presence of LRP1 in the plasma membrane without influencing mRNA expression levels. 14,15 LRP1 cellular turnover is regulated by the ubiquitinproteasome system, 16 an important mechanism for targeting membrane proteins to destruction, and therefore key in the modulation of protein levels.…”

Lipoproteins: A Source of Cardiac Lipids

“…However, there are no data indicating a role for LRP1 in cardiac lipid metabolism under normal conditions. Treatment of isolated cardiomyocytes with increasing doses of LDL and VLDL in normoxic conditions led to increased levels of VLDLr and LRP1 expression, while LDLr expression did not change [ 82 ]. When LRP1 was knocked down in isolated cardiomyocytes that were treated with LDL, cholesteryl ester uptake continued although at a signifi cantly slower rate [ 82 ].…”

“…This may involve the VLDLr [ 74 ], although changes in cardiac lipid uptake and accumulation during ischemia might be model specifi c. In one report, myocardial infarction in mice led to a marked increase in expression of VLDLr and accumulation of intracellular lipids; this was prevented by with VLDLr defi ciency [ 74 ]. Increased VLDLr expression levels due to ischemia may be driven by hypoxia-inducible factor (HIF)-1α, which is elevated in ischemic hearts [ 82 ] and is a positive regulator of VLDLr expression [ 74 , 117 ]. However, in rat models of low-fl ow ischemia cardiac FA uptake and TG content were reduced [ 118 ].…”

“…siRNA-mediated knock-down of LRP1 prevented hypoxia-induced VLDL-cholesteryl ester uptake in isolated neonatal rat ventricular myocytes and a mouse cardiomyocyte cell line [ 37 ]. LRP1 protein expression levels increase in patients with ischemic cardiomyopathy [ 82 ].…”

“…Increased LRP-1 expression occurs in ischemic cardiomyopathy patients [ 82 ] who have increased cardiac TG and cholesterol, as well as in isolated cardiomyocytes during hypoxia [ 37 ]. siRNA-mediated knock-down of LRP1 prevented hypoxia-induced VLDL-cholesteryl ester uptake in isolated neonatal rat ventricular myocytes and a mouse cardiomyocyte cell line [ 37 ].…”