Reconceptualizing Endothelial-to-mesenchymal transition in atherosclerosis: Signaling pathways and prospective targeting strategies

Abstract

Background: The modification of endothelial cells (ECs) biological function under pathogenic conditions leads to the expression of mesenchymal stromal cells (MSCs) markers, defined as endothelial-to-mesenchymal transition (EndMT). Invisible in onset and slow in progression, atherosclerosis (AS) is a potential contributor to various atherosclerotic cardiovascular diseases (ASCVD). By triggering AS, EndMT, the "initiator" of AS, induces the progression of ASCVD such as coronary atherosclerotic heart disease (CHD) and ischemic cerebrovascular disease (ICD), with serious clinical complications such as myocardial infarction (MI) and stroke. In-depth research of the pathomechanisms of EndMT and identification of potential targeted therapeutic strategies hold considerable research value for the prevention and treatment of ASCVD-associated with delayed EndMT. Although previous studies have progressively unraveled the complexity of EndMT and its pathogenicity triggered by alterations in vascular microenvironmental factors, systematic descriptions of the most recent pathogenic roles of EndMT in the progression of AS, targeted therapeutic strategies, and their future research directions are scarce.

Aim of review: We aim to provide new researchers with comprehensive knowledge of EndMT in AS. We exhaustively review the latest research advancements in the field and provide a theoretical basis for investigating EndMT, a biological process with sophisticated mechanisms.

Key scientific concepts of review: This review summarized that altered hemodynamics with microenvironmental crosstalk consisting of inflammatory responses or glycolysis, oxidative stress, lactate or acetyl-CoA (Ac-CoA), fatty acid oxidation (FAO), intracellular iron overload, and transcription factors, including ELK1 and STAT3, modulate the EndMT and affect AS progression. In addition, we provide new paradigms for the development of promising therapeutic agents against these disease-causing processes and indicate promising directions and challenges that need to be addressed to elucidate the EndMT process.

Keywords: Atherosclerosis; Cytokines; Endothelial-to-mesenchymal transition; Fatty acid oxidation; Glycolysis; Hemodynamic; Inflammatory microenvironment; Iron homeostasis; Transcription factors.

Graphical abstract

Fig. 1

EndMT assessment criteria. 1) ECs are activated and adherent junctions dissociate resulting in lipid accumulation in the vessel wall. The expression of endothelial markers such as VE-cadherin, CD31 and von Willebrand factor (vWF)is reduced. 2) The expression of mesenchymal markers such as alpha smooth muscle actin (α-SMA), N-cadherin, and transgelin (SN22α) is acquired. 3) The incorporation of transcription factors such as ELK1, STAT3, KLF2/4, FOXs, OCT4, ZEB1/2, SMADs, and SNAI. 4) Distinctive phenotypic changes in EndMT include transformation from a cobblestone-like appearance to a spindle shape and intercellular junctions replaced by fibrous tissue. Scale bar, 100 μm.

Fig. 2

Transcriptional regulatory networks of pro-EndMT. Pro-EndMT transcription factors serve as a giant family, typically represented by ELK1, STAT3, KLF2/4, FOXs, SNAI, TWIST1, SMADs and ZEB1. EndMT triggers endothelial dysfunction and increases vascular permeability, leading to the invasion of lipids, metabolic wastes, cytokines, and other pathological substances into the sub-vascular and triggering cardiovascular lesions. Meanwhile, distinctive phenotypic changes in EndMT include the loss of EC morphology, intercellular tight junctions, and acquisition of migration. BMPR1A induced ID2 to interact with ZEB1, which in turn downregulated Tgfbr2 transcription and inhibited TGF-β-induced EndMT. ELK1 undergoes a cytoplasmic-nuclear translocation that upregulates the transcription of Bach1, which subsequently upregulates the transcription of Snai1 and leads to the expression of α-SMA, which in turn induces EndMT. Phosphorylated STAT3 upregulates Snai transcription. By trans-activating miR-483 and consequently decreasing the expression of CTGF, KLF4 inhibits EndMT. By contrast, miR-10b inhibits KLF4. HDAC3/HD3α/AKT1 complex activates TGF-β2 signaling and induces EndMT. HDAC7 binds and down-regulates transcriptional activation of MMP10 by myocyte enhancer factor-2 (MEF2), which in turn inhibits EndMT.

Fig. 3

Major metabolic processes exerting pro-EndMT in atherosclerosis. Glycolysis involving glucose and mitochondrial metabolism of pyruvate, a product of glycolysis, to Acetyl-CoA (Ac-CoA) in a manner dependent on the activity of acyl-CoA synthetase short-chain family member 1/2 (ACSS1/2) enhances transforming growth factor beta (TGF-β) signaling and induces EndMT in a positive feedback manner. Ac-CoA produced in the cytoplasm dependent on citrate acid and ATP-citrate lyase (ACLY) activity inhibits EndMT. Ac-CoA carboxylase 1/2 (ACC1/2) prevents protein modification by acetylation by mediating the conversion of cytoplasmic Ac-CoA to malonyl-CoA, which in turn decreases Ac-CoA levels. Acetylation modifications inhibit the activity of ACSS1 and ACSS2, whereas SIRT3 and SIRT1, located in the mitochondria and cytoplasm, respectively, mediate the deacetylation of ACSS1 and ACSS2, thereby restoring their biological functions. Oscillatory shear stress (OSS) induced sterol regulatory element binding protein 2 (SREBP2) upregulates 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) transcription. Activated PFKFB3 is in a glycolysis-dependent manner, leading to the inactivation of the transcriptional co-repressor C-terminal binding protein 1 (CTBP1) or forkhead box P1 (FOXP1). Lactate enhances the affinity binding of CBP/p300 to Snail family transcriptional repressor 1 (SNAI1) and lactylated SNAI1 via monocarboxylate transporter (MCT), which in turn activated the TGF-β/SMAD2 axis resulting in endothelial dysfunction and EndMT. Laminar shear stress (LSS) activates the MEKK3/MEK5/ERK5 axis by enhancing the interaction between heart-of-glass 1 (HEG1) and krev interaction trapped protein 1 (KRIT1), thereby up-regulating Klf2/4 transcription and activating downstream molecules, EndMT is then suppressed.