Modulation of lipid profile by secretory phospholipase A2 group IIA: Verification with a transgenic mouse model

We previously demonstrated a positive relation of secretory phospholipase A2 group IIA (sPLA2-IIA) with circulating high-density lipoprotein cholesterol (HDL-C) in patients with coronary artery disease, and sPLA2-IIA increased cholesterol efflux in THP-1 cells through peroxisome proliferator-activated receptor-γ (PPAR-γ)/liver X receptor α/ATP-binding cassette transporter A1 (ABCA1) signaling pathway. The aim of the present study was to examine the role of sPLA2-IIA over-expression on lipid profile in a transgenic mouse model. Fifteen apoE-/- and C57BL/7 female mice received bone marrow transplantation from transgenic SPLA2-IIA mice, and treated with specific PPAR-γ inhibitor GW9662. High fat diet was given after one week of bone marrow transplantation, and animals were sacrificed after twelve weeks. Immunohistochemical staining showed over-expression of sPLA2-IIA protein in the lung and spleen. The circulating level of HDL-C, but not that of low-density lipoprotein cholesterol (LDL-C), total cholesterol, or total triglyceride, was increased by sPLA2-IIA over-expression, and was subsequently reversed by GW9662 treatment. Over-expression of sPLA2-IIA resulted in augmented expression of cholesterol transporter ABCA1 at mRNA level in the aortas, and at protein level in macrophages, co-localized with macrophage specific antigen CD68. GW9662 exerted potent inhibitory effects on sPLA2-IIA-induced ABCA1 expression. Conclusively, we demonstrated the effects of sPLA2-IIA on circulating HDL-C level and the expression of ABCA1, possibly through regulation of PPAR-γ signaling in transgenic mouse model, that is in concert with the conditions in patients with coronary artery disease.

Doxorubicin inhibits cholesterol efflux through the miR-33/ABCA1 pathway

Doxorubicin (DOX) is extensively used for the treatment of kinds of cancers, and cardiovascular toxicity is one of the side effects. However, it is unclear whether DOX causes impairment of cardiac function by promoting atherosclerosis. Thus, we investigated the role of DOX in regulating the lipid deposition of macrophages and its molecular mechanism. RAW 264.7 cell line was stimulated with DOX in the presence or absence of low-density lipoprotein (LDL). We found that DOX increased miR-33 and reduced ATP binding cassette transporter A1 (ABCA1) protein. Moreover, cholesterol efflux was suppressed by DOX, which was more efficient under a high-cholesterol condition. After transfecting mimics or inhibitors of miR-33 into cells, ABCA1 protein was respectively decreased and increased, and intracellular lipid accumulation was correspondingly regulated. Overall, DOX suppresses the expression of ABCA1 protein by upregulating miR-33, promoting an intracellular lipid deposition in macrophages, which is a sign of early atherosclerosis. This provides new insights for clinical observation and evaluation of the side effects of DOX.

Di-n-butyl phthalate promotes lipid accumulation via the miR200c-5p-ABCA1 pathway in THP-1 macrophages

Di-n-butyl phthalate (DBP) is ubiquitously in the environment and has been detected in almost all of human bodies. Few data could be found about the effects of DBP on cardiovascular system, though its reproductive toxicities have been studied extensively. This study aimed to explore the effects of DBP on lipid metabolism, a key step during the formation of atherosclerosis, since DBP was recently reported to be associated with atherosclerosis. THP-1 macrophages were employed and exposed to various levels of DBP (10^-8, 10^-7, 10^-6, 10^-5 and 10^-4 mol/L) or DMSO as control. Lipid accumulation was determined by detection of cellular total cholesterol, free cholesterol, cholesterol ester and content of lipid drops. Expressions of mRNA/miRNAs and proteins were measured by qRT-PCR and western blotting, respectively. Bioinformatic analysis and dual luciferase reporter assay were used to analyze the combination between miR200c-5p and ATP-binding cassette transporter A1 (ABCA1). Cholesterol efflux assay was executed to study the inhibitory effects of DBP on cholesterol efflux capability. Results revealed that DBP at 10^-7 mol/L prompted THP-1 macrophages lipid accumulation by inhibiting cholesterol efflux via suppressing ABCA1 expression. In addition, a non-linear inverted U-shaped relationship between DBP and lipid accumulation could be observed. Moreover, miR200c-5p could directly targets to ABCA1 3'UTR and modulate ABCA1 expression. Besides, downregulation of ABCA1 expression and reduction of lipid efflux induced by DBP were due to the miR200c-5p upregulation. Collectively, these data suggested that DBP at levels relative to human exposure could increase lipid accumulation in THP-1 macrophages by decreasing cholesterol efflux through miR200c-5p-ABCA1, then potentiate the formation of atherosclerosis.

ABCA1 and metabolic syndrome; a review of the ABCA1 role in HDL-VLDL production, insulin-glucose homeostasis, inflammation and obesity

ATP-binding cassette transporter A1 (ABCA1) is an integral cell-membrane protein that mediates the rate-limiting step of high density lipoprotein (HDL) biogenesis and suppression of inflammation by triggering a number of signaling pathways via interacting with an apolipoprotein acceptor. The hepatic ABCA1 is involved in regulation of very low density lipoprotein (VLDL) production by affecting the apolipoprotein B trafficking and lipidation of VLDL particles. This protein is involved in protecting the function of pancreatic β-cells and insulin secretion by cholesterol homeostasis. Adipose tissue lipolysis is associated with ABCA1 activity. This transporter is involved in controlling obesity and insulin sensitivity by regulating triglyceride (TG) lipolysis and influencing on adiponectin, visfatin, leptin, and GLUT4 genes expression. The ABCA1 of skeletal muscle cells play a role in increasing the glucose uptake by enhancing the Akt phosphorylation and transferring GLUT4 to the plasma membrane. Abnormal status of ABCA1-regulated phenotypes is observed in metabolic syndrome. This syndrome is associated with the occurrence of many diseases. This review is a summary of the role of ABCA1 in HDL and VLDL production, homeostasis of insulin and glucose, suppression of inflammation and obesity controlling to provide a better insight into the association of this protein with metabolic syndrome.

Akt isoform-dependent regulation of ATP-Binding cassette A1 expression by apolipoprotein E

We previously reported that apolipoprotein E (apoE) upregulates ATP-binding cassette transporter A1 (ABCA1) transcription through phosphatidylinositol 3-kinase (PI3K). Here we demonstrate that treatment of murine macrophages with human apoE3 enhanced Akt phosphorylation, and upregulated ABCA1 protein and mRNA expression. Inhibition of PI3K weakened apoE3-induced Akt phosphorylation, and ABCA1 protein and mRNA increase. In contrast, inhibition of Akt only diminished apoE-induced ABCA1 protein but not the mRNA level. Suppression of protein synthesis did not erase the ability of apoE3 to increase ABCA1 protein level. Further, apoE3 increased the resistance of ABCA1 protein to calpain-mediated degradation without affecting calpain activity. Treatment of macrophages with apoE3 selectively enhanced the phosphorylation of Akt1 and Akt2, but not Akt3. Knockdown of Akt1 or Akt2 increased and decreased ABCA1 protein level, respectively; while overexpression of these Akt isoenzymes caused changes in ABCA1 protein level opposite to those induced by knockdown of the corresponding Akt. These data imply that apoE3 guards against calpain-mediated ABCA1 degradation through Akt2.