Apolipoprotein M delays the development of atherosclerosis by regulating autophagy and mitochondrial function.

Background: Apolipoprotein M (ApoM), a protein component of lipoproteins, is closely related to the development of atherosclerosis, but the specific mechanism remains elusive. Mitochondrial DNA damage can contribute to atherosclerosis, so this study was designed to investigate whether ApoM influences the structure and function of mitochondria during the progression of atherosclerosis and to explore the underlying mechanism.

Methods: Atherosclerosis models were established in male ApoM-deficient (ApoM^-/- ) and wild-type (ApoM^+/+ ) C57BL/6 mice fed a high-fat diet (HFD), and the development of atherosclerosis was verified by en face analysis of the aorta and Masson's trichrome staining. We utilized transmission electron microscopy (TEM) to examine the ultrastructure of the aorta, its endothelial cells and EA.hy926 cells. Mass spectrometry-based lipidomics was performed to measure lipidomes in the serum and liver tissue of ApoM^{- /-} mice. In EA.hy926 cells, we modulated the levels of autophagy and ApoM expression, and investigated the mechanism by which ApoM influences the pathogenesis of atherosclerosis through western blotting, JC-1 staining, flow cytometry, and Seahorse extracellular flux analysis.

Results: In ApoM^-/- mice fed an HFD, atherosclerotic markers such as aortic lipid accumulation, fibrosis, endothelial cell oedema, and mitochondrial swelling were observed, indicating early atherosclerotic development. Lipidomic analysis revealed that ApoM deficiency might lead to impaired autophagy and mitochondrial dysfunction. In EA.hy926 cells, overexpression of ApoM not only activated autophagy but also improved mitochondrial structure. Moreover, ApoM decreased the mitochondrial membrane potential (ΔΨm) of EA.hy926 cells, which was further reduced by autophagy activation. Additionally, overexpression of ApoM in EA.hy926 cells, which have a low basal metabolism and primarily rely on glycolysis for energy, significantly reduced basal mitochondrial respiration and adenosine triphosphate (ATP) production, suggesting that ApoM can facilitate mitochondrial fission.

Conclusions: ApoM exerts atheroprotective effects by promoting autophagy and regulating mitochondrial dynamics, thereby maintaining mitochondrial integrity and function. This study provides novel insights into the mechanisms underlying the protective role of ApoM in atherosclerosis and highlights its potential as a therapeutic target for cardiovascular diseases.