Pyruvate dehydrogenase alleviates macrophage autophagy in Hcy-induced ApoE–/– mice

Abstract

Macrophages play a protective role in atherosclerosis, whereas homocysteine (Hcy) is recognized as an independent risk factor for atherosclerosis. Defects in macrophage autophagy contribute to the formation of atherosclerotic plaques, and dysregulated energy metabolism is closely linked to the process of autophagy. However, the regulation of macrophage autophagy by pyruvate dehydrogenase (PDH), a key component of the PDH complex involved in energy and metabolic homeostasis, remains poorly understood in the context of atherosclerosis induced by Hcy. In our study, proteomic profiling identifies 748 upregulated proteins and 760 downregulated proteins in Hcy-treated macrophages. KEGG pathway analysis reveals significant enrichment of differentially expressed proteins in metabolism-related pathways, including those related to the biosynthesis of amino acids, carbon metabolism, and glycolysis/gluconeogenesis. Additionally, we explore the role of PDH in mediating Hcy-induced atherosclerosis in ApoE–/– mice. The results show a marked reduction in PDH expression and activity in Hcy-treated macrophages, leading to impaired autophagy. Notably, PDH activation enhances the assembly of the autophagy initiator ULK1-FIP200-Atg13 complex through the modulation of the AMPK/mTOR signaling pathway, suggesting a potential therapeutic target for Hcy-induced atherosclerosis.

1. Introduction

Atherosclerosis is a major cause of many cardiovascular diseases and is strongly associated with global mortality and morbidity [1,2]. Numerous studies have identified homocysteine (Hcy) as an independent risk factor for atherosclerosis, as it induces endothelial dysfunction, abnormal proliferation of vascular smooth muscle cells, and other pathological changes [3,4]. Previous research has shown that inflammation increases in macrophages as plaque progresses, highlighting the critical role of macrophages in the development of atherosclerotic lesions [5]. However, the underlying mechanisms by which macrophages contribute to Hcy-induced atherosclerosis remain unclear.

Autophagy is an evolutionarily conserved process that sequesters excess, aged, or damaged cytoplasmic material and delivers it to lysosomes for degradation. Efficient autophagy clears damaged organelles and proteins resulting from cellular stress and damage. It also degrades cholesterol ingested by macrophages before it is effluxed, thereby preventing lipid accumulation and foam cell formation in atherosclerosis [6,7]. However, defects in autophagy have been associated with an increased risk of specific cardiovascular disorders in laboratory animals [8,9]. For example, dysregulated autophagy can contribute to ischaemia‒reperfusion injury and postmyocardial infarction [10–12]. Moreover, Yang et al. [13] demonstrated that Hcy could accelerate hepatocyte autophagy by upregulating TFEB through DNMT3b-mediated DNA hypomethylation. Autophagy is regulated by the AMPK/mTOR/ULK1 signaling pathway [14,15], and ULK1 is activated by serine-threonine protein kinases and forms a complex with ATG13 and FIP200, initiating autophagy [16]. These findings underscore the need for further research to elucidate the mechanisms of autophagy in Hcy-induced atherosclerosis.

Numerous studies have demonstrated that glycolysis and the mitochondrial tricarboxylic acid (TCA) cycle are involved in various pathological processes of cardiovascular diseases, including endothelial dysfunction, inflammation, vascular smooth muscle cell proliferation, and thrombosis following plaque rupture [17,18]. Pyruvate dehydrogenase (PDH), a key rate-limiting enzyme that catalyzes irreversible oxidative decarboxylation of pyruvate, links glycolysis with the TCA cycle and oxidative phosphorylation and regulates its activity to ensure the balance of cellular energy metabolism [19]. Recent studies have highlighted the relationship between PDH activity and several malignancies, such as colorectal cancer and renal cancer [20,21]. In addition to cancer, PDH dysfunction has been implicated in cardiovascular diseases, including hypertension, myocarditis, and type 2 diabetes [22,23]. Additionally, Sojeong et al. [24] reported that PDH deficiency resulted in a reduction in the number of double-positive T-cell progenitor cells, which contributed to leukemia development.