7-Ketocholesterol Induces Lipid Metabolic Reprogramming and Enhances Cholesterol Ester Accumulation in Cardiac Cells

Abstract

7-Ketocholesterol (7KCh) is a major oxidized cholesterol product abundant in lipoprotein deposits and atherosclerotic plaques. Our previous study has shown that 7KCh accumulates in erythrocytes of heart failure patients, and further investigation centered on how 7KCh may affect metabolism in cardiomyocytes. We applied metabolomics to study the metabolic changes in cardiac cell line HL-1 after treatment with 7KCh. Mevalonic acid (MVA) pathway-derived metabolites, such as farnesyl-pyrophosphate and geranylgeranyl-pyrophosphate, phospholipids, and triacylglycerols levels significantly declined, while the levels of lysophospholipids, such as lysophosphatidylcholines (lysoPCs) and lysophosphatidylethanolamines (lysoPEs), considerably increased in 7KCh-treated cells. Furthermore, the cholesterol content showed no significant change, but the production of cholesteryl esters was enhanced in the treated cells. To explore the possible mechanisms, we applied mRNA-sequencing (mRNA-seq) to study genes differentially expressed in 7KCh-treated cells. The transcriptomic analysis revealed that genes involved in lipid metabolic processes, including MVA biosynthesis and cholesterol transport and esterification, were differentially expressed in treated cells. Integrated analysis of both metabolomic and transcriptomic data suggests that 7KCh induces cholesteryl ester accumulation and reprogramming of lipid metabolism through altered transcription of such genes as sterol O-acyltransferase- and phospholipase A2-encoding genes. The 7KCh-induced reprogramming of lipid metabolism in cardiac cells may be implicated in the pathogenesis of cardiovascular diseases.

Malonyl-CoA Accumulation as a Compensatory Cytoprotective Mechanism in Cardiac Cells in Response to 7-Ketocholesterol-Induced Growth Retardation

“…The co-treatment with 7KCh and lovastatin reduced the HMG-CoA level by 94%. It is consistent with our previous finding that 7KCh represses the expression of Acat2 and Hmgcs1 genes [16], the products of which act upstream of HMGCR in the MVA pathway. Such a co-treatment caused a 54% decrease in the cell number (Figure 6B).…”

“…It has been found that the basal and maximum respiration and the spare respiratory capacity are reduced in the PHB-deficient cells, with impaired organization of the respiratory supercomplexes [24,25]. Consistent with such a notion, our previous study has shown that the Phb1, Phb2, Higd1a, and Higd2a transcript levels declined in the 7KCh-treated cells [16]. Prohibin 1 (PHB1) and 2 (PHB2) participate in the assembly of respiratory supercomplexes and the maintenance of their stability [26].…”

“…An additional point about the malonyl CoA-inhibited β-oxidation is noteworthy. Our previous study has revealed that fatty acids can be released from phosphatidylcholines by phospholipase A2, and are used for esterification [16]. The fatty acid molecules are spared from β-oxidation through the action of malonyl-CoA.…”

“…We have recently reported that a 7KCh treatment induced changes in the cholesterol and lipid metabolism of HL-1 cells [16]. The genes involved in mevalonic acid biosynthesis and the metabolism of fatty acids, triacylglycerides and ketone bodies were down-regulated, while those involved in cholesterol transport and esterification were up-regulated [16]. Intriguingly, 7KCh enhanced the transcription of the genes regulated by ATF4, which has been recently identified as a key regulator of mitochondrial stress [17].…”

“…Given the central roles of mitochondria in the metabolism, mitochondrial dysfunction is accompanied by the reprogramming of the metabolism in cardiomyocytes. We have recently reported that a 7KCh treatment induced changes in the cholesterol and lipid metabolism of HL-1 cells [16]. The genes involved in mevalonic acid biosynthesis and the metabolism of fatty acids, triacylglycerides and ketone bodies were down-regulated, while those involved in cholesterol transport and esterification were up-regulated [16].…”