Endothelial dysfunction in aortic aneurysm and dissection pathogenesis

Summary

Aortic aneurysm and dissection (AAD) represent catastrophic vascular conditions with high mortality rates. Currently, non-surgical therapeutic options remain limited, while surgical intervention entails significant risk. As the second most common aortic disease after atherosclerosis and the ninth leading cause of death worldwide, aortic dissection involves separation of the parietal layer caused by intimal tear or intramural hemorrhage. Endothelial dysfunction is an important participant and amplifier in the early onset of AAD. Most cases begin with intimal injury in which endothelial injury plays a contributing role and are characterized by increased permeability, inflammatory infiltration, and disrupted intercellular junctions. This process compromises vessel wall integrity and initiates a complex cascade of reactions that ultimately lead to AAD. Therefore, discussing the localization of the role of endothelial cells in the early stage of aortic disease, and based on this analysis of possible therapeutic targets and directions, is of great significance for understanding the initial events associated with AAD.

Cardiovascular medicine; Integrative aspects of cell biology; Specialized functions of cells

Introduction

Aortic aneurysm (AA) is defined as a permanent aortic dilation exceeding 50% of the normal vessel diameter. Although frequently asymptomatic for extended periods, AA can lead to catastrophic complications, including acute rupture or dissection.^1,2 Current estimates place AA incidence at 2.79 cases per 100,000 individuals.¹ Similarly, aortic dissection (AD), characterized by the separation of aortic wall layers, exhibits high morbidity and mortality. In the United States, AD mortality reached 21.3 cases per million in 2019,³ reflecting a seven-year upward trend mirrored globally.^3,4 Established risk factors include smoking, male sex, and hypertension.⁵ Anatomically, AD is categorized using the Stanford classification: type A involves the ascending aorta or aortic arch, while type B originates in the descending aorta. Since 1970, the gold standard for type A dissection has been intimal tear excision followed by graft replacement.^6,7,8 Although emergency surgery has improved survival, postoperative in-hospital mortality remains high, at approximately 25%.⁷ Conversely, managing simple type B dissection remains controversial. Conservative pharmacological management fails to reverse structural wall changes, and alternative interventions face significant technical hurdles^6,9,10,11,12 Given these limitations, exploring novel therapeutic targets and management protocols for AA/AD progression is imperative.

AA/AD pathogenesis involves multi-factorial drivers, including hemodynamic disturbances, vascular inflammation, metabolic disorders, and vascular smooth muscle cell (VSMC) dysfunction.^{13,14,15,16,17,18} Evidence suggests that most AD cases originate from intimal damage.^19,20 Disrupted endothelial cell (EC) junctions increase permeability and promote inflammation, ultimately compromising vascular wall integrity and precipitating AD.²¹ Consequently, investigating endothelial dysfunction in AA/AD remains essential. Long regarded as a passive semi-permeable barrier since their characterization in 1865, ECs have emerged as a focal point of active research only since the 1970s^22,23 As the innermost arterial lining, ECs secrete a glycoprotein basement membrane to sequester blood from surrounding tissues, while the luminal surface maintains direct contact with the circulation (Figure 1).²³ Under injury or hypoxia, local ECs initiate angiogenesis via coordinated vascular sprouting.^24,25,26 Beyond serving as a physical barrier, ECs function as mechanotransducers through the glycocalyx (GCX),^27,28 which is vital for peripheral tissue homeostasis.²⁹ Activation of GCX by blood components regulates vasoconstriction and oxygen distribution.²³ Effective blood supply regulation necessitates precise coordination between ECs and VSMCs.³⁰ By sensing hemodynamic shifts and blood-borne signals, ECs maintain vascular homeostasis while modulating vasoconstriction and vasodilation (Figure 1).^{23,31,32,33,34}

Figure 1.

Fundamental vascular EC functions are essential for maintaining vascular homeostasis

In response to tissue hypoxia or injury, ECs secrete pro-angiogenic molecules to facilitate neovascularization. The endothelial GCX serves as a protective barrier against viral and bacterial pathogens while sequestering circulating proteins. Furthermore, EC mechanosensors and chemoreceptors detect blood-borne signals to modulate vascular tone, including contraction and vasodilation.

As established, most AA/AD cases originate from intimal loss. ECs, as the primary intimal component, play a fundamental role in preserving vascular integrity.³⁵ Therefore, exploring endothelial dysfunction in AA/AD through recent advancements and novel insights is crucial. This review focuses on the molecular mechanisms governing EC involvement in AA/AD and its associated complications. Furthermore, promising diagnostic strategies and therapeutic directions derived from these mechanisms are summarized.

Endothelial barrier and mechanotransduction

Junctional complexes

Adherens junctions, centered on VE-cadherin and associated catenins, stabilize cell-cell adhesion and mitigate paracellular leakage. Tight junction components further restrict permeability, particularly within specialized vascular beds. Additionally, Platelet endothelial cell adhesion molecule-1 (PECAM-1) and other junction-associated molecules facilitate leukocyte transmigration and junctional remodeling during inflammation. Consequently, junctional disruption increases permeability, enabling immune cell extravasation and exposing the media to blood-borne mediators.^36,37

Endothelial GCX and surface sensing

The endothelial GCX serves as both a permeability barrier and a mechanosensor. GCX degradation correlates with increased leukocyte adhesion and aberrant shear stress signaling.³⁸

Shear stress-responsive programs

Hemodynamic forces dictate EC phenotypes. Disturbed flow triggers inflammatory activation, whereas physiological laminar shear maintains an anti-inflammatory, nitric oxide-producing state. This protective phenotype is mediated by shear-responsive transcriptional programs, including KLF family factors and Endothelial nitric oxide synthase (eNOS) signaling (Figure 2).³⁹

Figure 2.

Temporal endothelial inflammatory network in aortic dissection

Early endothelial injury induced by factors such as disturbed flow, hypertension, angiotensin II, and oxidative stress disrupts endothelial integrity and activates inflammatory signaling pathways. Activated endothelial cells promote cytokine production, immune cell recruitment, endothelium-VSMC interactions, intimal ECM degradation, and intimal degeneration. In turn, it triggers the phenotypic switch of vascular smooth muscle cells in the media, which eventually leads to intimal tear, false lumen formation, aortic dissection progression, and systemic complications.

Endothelial inflammatory activation in AA/AD

Ang-II

Angiotensin II (Ang-II) plays a central role in various cardiovascular diseases, including AA/AD, and is frequently utilized to establish experimental animal models.^40,41 Previous research has demonstrated that Ang-II promotes endothelial inflammation by modulating ET-1, interleukin 6 (IL-6), and matrix metalloproteinase 9 (MMP-9).^42,43 Specifically, Ang-II binds to the angiotensin type 1 receptor (AT1R) to stimulate Yes-associated protein (YAP) phosphorylation, thereby inducing endothelial inflammation.⁴⁴ Recent studies have further confirmed that Ang-II-activated phospho-YAP promotes M1 macrophage polarization and adhesion, exacerbating the inflammatory response.⁴⁵ These findings reiterate that Ang-II-induced endothelial inflammation significantly drives AA/AD onset and progression.

Furthermore, this discussion explores Ang-II-induced endothelial inflammation in AD-associated acute lung injury (ALI). With an incidence exceeding 30%, ALI remains a major cause of mortality in patients with AD.⁴⁶ In ALI pathogenesis, Ang-II predominantly targets pulmonary microvascular endothelial cells (PMVECs), modulating both inflammatory signaling and vascular permeability.^47,48,49 Consequently, elucidating the role of ECs in AD-associated ALI is essential, as recent evidence links AD-induced ALI closely to PMVEC dysfunction.^46,50 Earlier studies have suggested that VE-cadherin promotes EC adhesion by forming complex molecular assemblies.^51,52,53 In PMVECs, VE-cadherin is phosphorylated at Y685 under physiological conditions; however, Ang-II induction triggers rapid dephosphorylation at this site.⁵⁴ This Y685 phosphorylation shift has been linked to altered vascular permeability, a process potentially regulated by Src kinase.^55,56 Src kinase inhibitors further downregulate pY685-VE-cadherin levels, suggesting that Src kinase participates in Ang-II-induced dephosphorylation. Following Ang-II stimulation, PMVEC contraction, cytoskeletal rearrangement, and pY685-VE-cadherin dephosphorylation occur rapidly, ultimately aggravating AD-associated ALI.^54,57,58 Monocyte chemoattractant protein-1 (MCP-1) also contributes to AD-related ALI by promoting monocyte aggregation and migration.^58,59 Ang-II can stimulate the expression of p-IκBα and p-p65 in PMVECs, activating the NF-κB signaling pathway⁵⁰ and increasing MCP-1 levels, which further intensifies the inflammatory response through macrophage recruitment.^50,60 Conversely, the MCP-1 inhibitor bindarit decreases the expressions of caspase-3 and B lymphoblastoma-2 gene-associated X protein (Bax) while upregulating B cell lymphoma 2 (Bcl-2), thereby inhibiting Ang-II-induced PMVEC apoptosis and delaying ALI progression.⁵⁰

These findings highlight the pathogenic influence of Ang-II on endothelial function in both AD and its associated ALI,⁶¹ the latter of which warrants further investigation given its high fatality rate.

NF-κB

Bioinformatics analysis identifies FKBP11 as a crucial factor in AD pathogenesis.⁶² As a member of the peptidyl-proline cis-trans isomerase family, FKBP11 is predominantly expressed in ECs. Cellular studies have revealed that FKBP11 facilitates p65 phosphorylation and NF-κB dimer formation, thereby activating the NF-κB-p65 signaling pathway. This activation prompts ECs to release pro-inflammatory cytokines, which enhance circulating monocyte migration and activation to drive inflammation.⁶² Furthermore, high endothelial FKBP11 expression increases the levels of macrophage-derived matrix metalloproteinases (MMPs), particularly MMP9.⁶² These findings confirm that endothelial FKBP11 simultaneously stimulates endothelial inflammation via NF-κB signaling and propagates localized inflammation through macrophage recruitment.⁶² This process likely involves MMP-mediated extracellular matrix (ECM) degradation, especially by MMP9, which eliminates barriers to macrophage migration and compromises vascular wall integrity, ultimately contributing to AD progression^62,63,64 (Figure 2).

Platelet involvement in inflammation and abdominal aortic cardiovascular disease is well established.^65,66,67,68 CD40L serves as a critical link between platelet function and vascular pathology, triggering EC inflammation via platelet activation^69,70,71. ECs also express CD40, the cognate receptor for CD40L.⁶⁵ Lu et al. found that the interaction between CD40 and CD40L significantly elevates inflammatory cytokines, including IL-1β, IL-2, IL-6, and TNF-α,⁷² suggesting that CD40-CD40L signaling facilitates AD development through inflammatory pathways. Research further confirms that the interaction between CD40L-expressing platelets and CD40-expressing ECs transforms CD40L into its soluble form.⁷³ While the CD40-CD40L complex activates the NF-κB signaling pathway to drive endothelial inflammation, soluble CD40L appears to lose this pro-inflammatory stimulatory capacity (Figure 2).⁷⁴

The phosphatidylinositol 3-kinase (PI3K)-protein kinase B (PKB/AKT) pathway participates in various pathologies.^{75,76,77,78,79} In AA/AD, PI3K phosphorylation modulates NF-κB nuclear translocation by accelerating AKT phosphorylation, thereby stimulating endothelial inflammation. Senkyunolide I (SEI) antagonizes the production of various inflammatory cytokines (ICAM-1, VCAM-1, TNF-α, and IL-6) by inhibiting PI3K phosphorylation⁷⁹ (Figure 2).

In conclusion, the NF-κB signaling pathway remains central to AA/AD-related endothelial inflammation. FKBP11 facilitates pathway activation by promoting NF-κB dimer formation and nuclear translocation. The CD40-CD40L interaction regulates this pathway via platelet activation, while the PI3K-AKT axis is critically involved in the nuclear translocation required for NF-κB activation.

IL-33-sST2 axis

The IL-33-sST2 (soluble suppression of tumorigenicity 2 receptor) axis holds significant prognostic value in cardiovascular diseases, including AD.⁸⁰ IL-33 directly drives EC inflammation by stimulating the release of pro-inflammatory cytokines and intensifying leukocyte-EC adhesion.^81,82 Additionally, IL-33 upregulates vascular cell adhesion molecule-1 (VCAM-1) and induces the secretion of chemoattractants, such as CXCL1 and CCL2,^82,83 to further recruit leukocytes (Figure 3). Evidence further suggests that IL-33 induces shifts in vascular permeability and aberrant angiogenesis during inflammation—pathological features closely linked to AD pathogenesis.^{84,85,86,87,88,89,90,91} Plasma sST2, an ST2 isoform secreted by ECs and immune cells, functions as a decoy receptor to sequester extracellular IL-33.⁸⁰ Notably, the IL-33-sST2 axis and Ang-II induce EC inflammation in AD through distinct mechanisms. While Ang-II serves as a primary driver of initial EC dysfunction, IL-33-sST2 signaling typically arises secondary to early EC damage, primarily acting to amplify the inflammatory response.^40,41,84,85 While Ang-II-mediated responses reflect the intimal barrier’s reaction to pathological environments, the IL-33-sST2 axis represents an inflammatory amplification loop. By recruiting additional immune cells, this axis compromises adjacent EC integrity and exacerbates mural inflammation. Consequently, the IL-33-sST2 axis plays a critical pathogenic role in AD, with sST2 levels serving as a vital clinical biomarker for emergency AD diagnosis.^{92,93,94,95,96,97}

Figure 3.

S-nitrosylation of PLS3 accelerates EC migration

The conversion of endothelial PLS3 to PLS3-SNO facilitates the assembly of a molecular complex with cofilin and plectin. This interaction disrupts endothelial cell-to-cell junctions and promotes actin filament-mediated migration, which ultimately exacerbates EC loss in the pathogenesis of AD.

Oxidative stress (NOX2-ROS-CypA axis)

In AD pathogenesis, NADPH oxidase 2 (NOX2) drives the production of endothelial reactive oxygen species (ROS), which stimulate EC inflammation while simultaneously triggering ERK1/2 phosphorylation in VSMCs via cyclophilin A (CypA).¹⁹ As a core member of the NADPH oxidase family, NOX2 serves as a predominant cellular ROS source.⁹⁸ ROS are defined as highly reactive, oxygen-containing molecules generated by aerobic organisms during the metabolism of molecular oxygen. Notably, elevated ROS production within ECs alone suffices to upregulate pro-inflammatory cytokines and facilitate leukocyte recruitment,¹⁹ marking a state of EC activation that propagates localized inflammation through ROS-mediated signaling. Furthermore, NOX2 triggers the secretion of CypA. As a highly conserved, ROS-sensitive immunophilin, extracellular CypA promotes inflammatory cell infiltration and modulates ERK1/2 phosphorylation, thereby exacerbating VSMC dysfunction and AD progression. Research also implicates the STAT3-CypA and CypA-FoxO1 pathways in mediating EC inflammation and apoptosis, indicating that CypA concurrently intensifies EC damage and stimulates VSMC activation. Crucially, ECs are the primary source of CypA, expressing CypA at 10-fold higher levels than VSMCs.¹⁹ Because NOX2-induced EC activation precedes CypA-mediated ERK1/2 signaling in VSMCs, ROS-driven VSMC injury in AD likely originates from these initial endothelial activation events.

EC-VSMC interaction

In AD pathogenesis, the interaction between ECs and VSMCs follows a sequential trajectory: unidirectional initiation followed by a positive feedback loop. NOX2-induced ROS generation in ECs not only triggers direct endothelial inflammation but also stimulates robust CypA secretion, reaching levels 10-fold higher than those observed in VSMCs.⁹⁹ Through paracrine signaling, CypA targets CD147 receptors on the VSMC surface to activate ERK1/2 phosphorylation.⁹⁹ This activation subsequently induces VSMC inflammation, phenotypic switching, and apoptosis, ultimately leading to medial destruction and AD formation.¹⁰⁰ In a reciprocal feedback loop, CypA exacerbates EC injury via the STAT3 and FoxO1 pathways, while the recruitment of inflammatory cells further amplifies this signaling network. This establishes a vicious cycle involving ECs, VSMCs, and infiltrating immune cells.^101,102 Crucially, ECs serve as the initiators of these pathological signals, VSMCs act as the downstream executors, and CypA functions as the primary paracrine mediator. Additionally, alternative intercellular communication modes, including exosomes and direct cell contact, such as Notch signaling, may converge with this axis to drive AD progression.

Endothelial stress and death programs

Pyroptosis (TLR4-NLRP3-caspase-1)

Lipopolysaccharide (LPS)-binding protein (LBP) serves as a primary carrier for LPS, facilitating inflammatory responses via its N-terminal domain.^103,104 Upon entering circulation, the LPS-LBP complex binds to the CD14 receptor and activates Toll-like receptor 4 (TLR4)-expressing ECs to induce an inflammatory response.^103,105,106 Simultaneously, a TLR4-expressing macrophage subset is activated.^103,105 TLR4 signaling triggers the caspase-1-associated endothelial pyroptosis pathway by stimulating the NLRP3 inflammasome assembly in the pyrin-domain protein 3 (NLRP3).¹⁰⁷ This activation leads to EC loss and accelerates AD progression.¹⁰³ Notably, clinical stool tests suggest that the LPS involved in this process originates from gut microbiota.¹⁰³

Non-coding RNAs linking EC apoptosis/ferroptosis to AD

Studies have shown that abnormal apoptosis is found in various cardiovascular pathologies.^{108,109,110,111,112} While AD research has historically focused on VSMC apoptosis,^109,113,114 emerging evidence highlights the critical role of EC apoptosis. miR-27a, a microRNA highly expressed in ECs, has emerged as a key regulator of AD development.^{115,116,117,118} Studies have confirmed that miR-27a is downregulated in AD, which alleviates its inherent inhibitory effect on EC apoptosis.¹¹⁶ Sun et al. used bioinformatics analysis and identified Fas-associated death domain (FADD) protein as the primary downstream target of miR-27a.¹¹⁶ Reduced miR-27a levels allow FADD to interact with the Fas death domain, initiating the extrinsic apoptotic pathway and compromising vascular wall integrity.^119,120 Although caspase-3 and caspase-8 levels increase during this process,¹¹⁶ miR-27a specifically modulates EC apoptosis via FADD signaling.

Bioinformatics analysis further suggests that miR-1909-5p, a non-coding RNA, regulates cellular ferroptosis.^121,122 Clinical studies showed significantly elevated miR-1909-5p expression in ECs among AD patients, which positively correlates with nicotine stimulation.¹²³ This aligns with findings that nicotine modulates EC inflammation and adhesion, thereby accelerating aortic disease progression.¹²⁴ miR-1909-5p inhibits the expression of glutathione peroxidase 4 (GPX4), promoting ferroptosis in ECs and subsequent AD induction.¹²³ Mechanistically, miR-1909-5p likely neutralizes GPX4-mediated reduction of glutathione-dependent lipid hydroperoxides into lipid alcohols,^{125,126,127,128} stripping ECs of endogenous ferroptotic protection. Consequently, accelerated endothelial ferroptosis exacerbates aortic intimal damage. This research highlights how nicotine diminishes GPX4-mediated defenses to precipitate ferroptosis in AD.

Mitochondrial apoptosis (Bcl-2/Bax-caspase-3)

In AD, Bax in ECs activates caspase-3 by altering mitochondrial outer membrane permeability, thereby initiating apoptosis. Bax upregulation may correlate with PI3K/AKT pathway activation. Conversely, Bcl-2 utilizes its unique hydrophobic structure to bind to the Bax BH3 domain, sequestering pro-apoptotic properties and antagonizing apoptosis.^79,129,130 Caspase-3, existing as an inactive dimer, requires cleavage by initiator caspases for its activation.¹³¹ Consequently, inhibiting the classical Bcl-2/Bax apoptotic pathway preserves endothelial functional integrity in AD.

Endothelial migration/denudation and endothelial repair

Cell migration significantly influences the pathogenesis of cardiovascular diseases.¹²⁰ Pan et al. identified PLS3 as a specific target of S-nitrosylation (SNO), noting that PLS3 is highly abundant in ECs and that PLS3-SNO levels are markedly elevated in thoracic AD. The mechanism by which PLS3 -SNO promotes EC migration involves cofilin and pectin.¹³² Cofilin, a recognized actin regulator, drives cell migration upon dephosphorylation; however, its role in AD-related endothelial dysfunction is a recent discovery.¹³³ Plectin interacts with the cytoskeleton to maintain intracellular structural stability and peripheral cell junctions.¹³⁴ Enhanced migration mediated by PLS3-SNO likely stems from increased motile forces and compromised junctional integrity. Pan et al. further demonstrated that PLS3-SNO forms a complex with plectin and cofilin, which promotes EC migration and tube formation while simultaneously weakening cell-to-cell junctions. Notably, this effect is partially mitigated by PLS3 denitrosylation.¹³² INOS plays a vital role in regulating this PLS3-SNO-dependent cofilin/F-actin pathway,^135,136,137 consistent with evidence that Ang II-induced ECs activate Inducible nitric oxide synthase (iNOS), which is essential for maintaining endothelial function and NO-dependent SNO (Figure 3).^135,136

Platelet factor 4 (PF4), a tetrameric protein, is implicated in various platelet-related pathologies.¹³⁸ PF4 predominantly influences ECs by inhibiting migration through interactions with heparan sulfate (HS), suggesting a protective role of the endothelial barrier during AA/AD. This mechanism likely involves HS binding because HSase, a reagent that removes surface HS, neutralizes PF4-mediated inhibition of EC invasion without affecting other induction conditions such as Ang II.¹³⁹ HS is critical for activating the fibroblast growth factor (FGF)-FGF receptor (FGFR) axis by forming HS proteoglycan coreceptors.¹⁴⁰ The FGF-FGFR axis is involved in numerous pathological conditions and facilitates vascular regeneration while maintaining EC stability by regulating molecules including transforming growth factor β (TGF-β) and TGF-βR1.^141,142 Notably, PF4 diminishes EC migration by inhibiting the FGF-FGFR axis, potentially involving various cell adhesion molecules (CAMs). Additionally, studies have indicated that PF4 inhibits the phosphorylation of ERK1/2, P38, and AKT (Ser473) within ECs under AA/AD contexts, though whether this indicates the direct suppression of inflammatory pathways remains unverified.¹³⁹

In conclusion, research by Pan et al. provides detailed evidence that PLS3-SNO accelerates EC migration in AD. While PF4 inhibits EC migration specifically through HS interactions, its potential role in suppressing EC inflammation in AD requires further validation. Current evidence suggests that the targeted inhibition of endothelial migration preserves barrier integrity. In AA/AD environments, this inhibitory effect helps maintain the structural stability of the aortic wall, potentially reducing disease incidence or delaying progression.

Endothelial cell ERS and AA/AD

Recent studies have demonstrated that endoplasmic reticulum stress (ERS) significantly contributes to AA/AD pathogenesis. The HDAC1 (histone deacetylase 1–nucleosome remodeling)-ZEB2 (zinc finger E-box-binding homeobox 2)-NuRD (deacetylase) complex stimulates ERS by inhibiting the expression of endothelial cystathionine γ lyase (CSE) and subsequently weakening the S-sulfhydration of protein disulfide isomerase (PDI-SSH). Mechanistically, this complex represses the transcription of CTH, the gene encoding CSE. While the CSE-H2S axis is vital for maintaining endothelial homeostasis,^20,143 H2S serves as a versatile signaling molecule that regulates vascular tone, inflammation, and angiogenesis.^20,144 Furthermore, H2S is essential for protein S-sulfhydration via the sulfur transfer pathway.^20,145 Reduced H2S levels impair the PDI-SSH, which activates the protein kinase RNA-like endoplasmic reticulum kinase (PERK) signaling pathway and precipitates endothelial ERS.²⁰

In AD, the IL-6 levels reflect systemic inflammation and are closely associated with clinical outcomes.¹⁴⁶ Beyond its inflammatory role, IL-6 induces iron overload and ERS in ECs. Recent single-cell sequencing data reveal that the IL-6-IL-6 receptor (IL-6R) complex activates the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway in ECs, thereby upregulating hypoxia-inducible factor 1α (HIF-1α) expression.¹⁴⁷ HIF-1α subsequently stimulates the transcription of bivalent metal transporter 1 (DMT1). While HIF-1α expression depends on JAK-STAT signaling and is further modulated by hypoxic microenvironments, it directly regulates DMT1 transcription without feedback onto the JAK-STAT axis.^147,148 Specifically, HIF-1α enhances DMT1 expression by increasing the transcriptional volume, rather than through mRNA stabilization. Although intracellular DMT1 typically maintains equilibrium via the IRP/IRE system based on iron availability, this balance shifts in AD as HIF-1α gains transcriptional dominance.^149,150 Given that DMT1 facilitates cellular iron uptake, its overexpression disrupts endothelial iron homeostasis, ultimately exacerbating ERS under AD conditions.¹⁵¹

ECM and endothelial dysfunction in AA/AD

The ECM provides the essential structural framework for cellular processes,¹⁵² and maintaining ECM integrity is fundamental to aortic homeostasis.¹⁵³ Unsaturated fatty acids, such as oleic acid (OA) and linoleic acid (LA), are stored within membrane phospholipids and mobilized by phospholipase A2 (PLA2) enzymes.¹⁵⁴ While initial hypotheses proposed that higher OA consumption correlates with reduced cardiovascular risk,¹⁵⁵ Watanabe et al. demonstrated that the knockdown of group V sPLA2 (PLA2-V) actually exacerbates AA/AD development.¹⁵⁴ As a phospholipase, PLA2-V mobilizes endogenous lipids; specifically, it upregulates OA and LA mobilization by hydrolyzing phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in Ang-II-induced murine ECs.¹⁵⁴ OA and LA appear to counteract AA/AD by stimulating lysyl oxidase (LOX) expression and inhibiting GATA-binding protein 3 (GATA3) induction.¹⁵⁴ Conversely, LOX deficiency, frequently induced by β-aminopropionitrile monofumarate (BAPN) in experimental models, increases susceptibility to AA/AD.¹⁵⁶ GATA3 downregulates LOX, an enzyme that normally prevents AA/AD by maintaining ECM functionality.¹⁵⁷ Meanwhile, OA and LA have been shown to mitigate ERS, which would otherwise downregulate LOX and upregulate GATA3.^157,158 Notably, while TGF-β1 also upregulates LOX, the effects of OA and LA appear to function independently of both TGF-β1 and fatty acid receptors.^154,159 Finally, Watanabe et al. effectively prevented the development of AA/AD in PLA2-V-knockdown mice by administering exogenous diets enriched with OA or LA. These findings raise the intriguing possibility that targeted dietary interventions could offer protective benefits against AA/AD, a hypothesis that warrants further clinical and experimental validation. Although Watanabe et al. did not directly elucidate the specific ECM-related mechanisms, they integrated the lipid-regulating function of sPLA2-V with established ECM research, effectively linking endothelial dysfunction to ECM stability in the context of AA/AD.

Single-cell and spatial transcriptomics

Single-cell RNA sequencing (scRNA-seq) has revolutionized the understanding of EC heterogeneity in AA and AD. This systematic review examines these advancements across three dimensions: endothelial heterogeneity, phenotypic transitions, and spatial transcriptomics.

EC subsets in human and mouse AA models

Yang et al. utilized scRNA-seq to identify four functionally distinct EC subsets in an AngII- and high-salt-induced mouse AA model.¹⁶⁰ These subpopulations include c11 (Fn1⁺ mesenchymal ECs, characterizing mesenchymal transition), c12(Cd36⁺ lipid metabolism-like ECs, regulation of lipid metabolism), c13 (Lrg1⁺ activated ECs, reflecting inflammatory activation), and c17 (Mmrn1⁺ lymphoid ECs, exhibiting lymphatic characteristics). These subsets undergo dynamic proportional shifts during AA development. Notably, a significant expansion of mesenchymal-like ECs suggests that endothelial-to-mesenchymal transition (EndMT) represents a pivotal event in AA pathogenesis.¹⁶⁰

Time-specific cellular profiles of human AD

Luo et al. conducted scRNA-seq analysis on 14 human ascending aorta samples, including 4 acute, 3 subacute, and 2 chronic patients with Stanford type A aortic dissection (STAAD), alongside 5 controls, to construct a comprehensive spatiotemporal cellular atlas.¹⁶¹ The heterogeneity of ECs exhibited dynamic shifts corresponding to disease stages. During the acute phase, ECs demonstrated robust inflammatory activation and enhanced immune cell interactions, whereas ECs in the subacute and chronic phases primarily mediated vascular repair and remodeling.¹⁶¹ Ligand-receptor analysis revealed extensive inflammation-related communication between ECs and immune populations, specifically macrophages and T cells.¹⁶¹ Furthermore, the crosstalk between ECs and smooth muscle cells appears to be fundamentally driven by EndMT-related signaling pathways, such as TGF-β.

Clinical translation: Biomarkers and therapeutic strategies

Computed tomography angiography (CTA) remains the gold standard for AD diagnosis; however, its universal application for all suspected cases is clinically unfeasible.⁴⁶ Molecular imaging, which integrates classical imaging with early pathological processes, offers significant potential for the early detection of thoracic AD. Consequently, identifying novel auxiliary diagnostic markers is essential. Lu et al. demonstrated that CD40L, acting as a CD40 ligand, mediates endothelial dysfunction and induces inflammation upon interaction with CD40-expressing ECs.²¹ Notably, abnormal CD40L expression in AD patients is detectable via blood tests, with circulating levels approximately 13 ng/mL higher than those in healthy individuals. Nevertheless, because CD40L is highly expressed across various cell types, its isolated use may lead to misdiagnosis. Furthermore, the specific mechanism of CD40L in AD remains elusive, and its potential as a definitive diagnostic standard requires further investigation.⁷² Thrombospondin-2 (TSP-2), an ECM protein primarily secreted by vascular innate cells, has also emerged as a potential biomarker. Qi et al. suggested that AngII stimulates TSP-2 expression, which is partially derived from ECs. Although TSP-2 is independently associated with AD and exhibits approximately 0.9-fold upregulation in patient sera,¹⁶² elevated TSP-2 levels also occur in other cardiovascular diseases.^{163,164,165,166} Current findings, thus, suggest that TSP-2 lacks sufficient specificity for predicting AD. Additionally, hyaluronan can serve as a nanocarrier targeting CD44 for site-specific delivery.¹⁶⁷ As a cell surface adhesion factor, CD44 exacerbates inflammation by facilitating leukocyte-EC adhesion. The involvement of CD44 in AD pathogenesis suggests that CD44-targeting molecules could detect early thoracic AD tendencies,¹⁶⁸ though this requires further clinical validation. Clinically, patients presenting with acute, severe chest pain due to AD remain highly susceptible to misdiagnosis. In a large retrospective study with a prospectively validated cohort, sST2 demonstrated superior diagnostic utility. Wang et al. examined plasma sST2 levels in over 1,300 patients with suspected AD, finding that sST2 was most elevated in acute cases. Within 24 h of symptom onset, sST2 outperformed traditional markers like D-dimer and cardiac troponin I (cTnI). Notably, sST2 levels below 35 ng/mL effectively rule out AD.⁹² Compared with D-dimer and troponin, the core advantage of sST2 in acute AD diagnosis lies in its direct link with the disease’s pathological process, resulting in higher diagnostic accuracy (improved area under the curve [AUC] values) within the initial 24-h window.⁹² This specificity allows clinicians to distinguish AD from other conditions presenting with chest pain, such as acute myocardial infarction, thereby addressing the poor specificity inherent in traditional indicators.⁹⁵ Furthermore, the high negative predictive value (NPV) of a threshold below 35 ng/mL reduces unnecessary CT angiography and optimizes emergency workflows.⁹² Integrating sST2, D-dimer, and clinical scoring systems like Aortic Dissection Detection Risk Score (ADD-RS) offers significant potential for the comprehensive management of aortic diseases. The primary advantage of combining sST2 and D-dimer with image-based scoring systems lies in precision management across the entire spectrum of aortic pathologies (including AAD) through complementary biological mechanisms and functional stratification. Specifically, the biological complementarity of sST2 and D-dimer underpins this integrated strategy: while D-dimer reflects intravascular thrombosis and fibrinolysis with high sensitivity but limited specificity, sST2 is a specific protein released directly by the aortic wall in response to shear stress-induced damage. Consequently, sST2 is more intimately linked to the pathological progression of AD, yielding a diagnostic accuracy within 24 h of onset (AUC = 0.97) that significantly surpasses that of D-dimer.^92,169,170 The synergistic use of these biomarkers not only enhances diagnostic sensitivity but also enables the fine differentiation of disease subtypes. For instance, in the differential diagnosis of Stanford type B aortic dissection (TBAD) and intramural hematoma (IMH), TBAD patients typically exhibit markedly elevated levels of sST2 or D-dimer alone. Conversely, IMH patients present with a simultaneous elevation and a strong positive correlation between these markers, suggesting distinct underlying pathophysiological mechanisms. Integrating clinical risk assessment tools, such as the ADD-RS, facilitates a transition from purely biological diagnosis to an integrated clinical decision-making framework. Wang et al. demonstrated that combining ADD-RS with D-dimer yields 90% sensitivity and a 96% NPV for excluding AD.¹⁶⁹ However, replacing D-dimer with sST2 (ADD-RS ≤ 1 + sST2 < 35 ng/mL) increases both sensitivity and NPV to 99%, with an AUC of 0.95, significantly outperforming the D-dimer combination (AUC = 0.87).^92,169,170 This proposed “three-step strategy,” which initiates with ADD-RS clinical prediction, followed by sST2 and D-dimer biological differentiation, and concludes with targeted imaging for high-risk cases, minimizes unnecessary CTA, radiation exposure, and healthcare costs. Simultaneously, this approach ensures exceptionally high exclusion safety while optimizing the diagnostic pathway for acute aortic syndrome. Given its rapid execution and cost effectiveness, this methodology holds substantial clinical value. Currently, sST2 is recognized as superior to existing diagnostic markers and stands as a primary candidate for future clinical integration, whereas other potential targets summarized in Table 1 remain largely within the mechanistic research phase.

Table 1.

Potential RC-related biomarkers for the early diagnosis of AD

Target	Signaling pathway	Sensitivity	Specificity	Reference
CD40L	CD40-CD40L	+	–	Han et al.72; Henn et al.73; Hachem et al.74
TSP-2	ANG-II-TSP-2	+	–	Qi et al.(162)
CD44	–	–	–	Orian-Rousseau et al.(167)
SST-2	IL-33-sST-2	++	++	Demyanets et al.82; Stojkovic et al.85; Wang et al.92

Note: “–” represents better than unknown, “+” represents better, and “++” represents better than the currently available methods.

Current AA/AD management primarily relies on surgical intervention. Beyond addressing risk factors like hypertension, a significant therapeutic gap exists due to the lack of effective conservative pharmacological treatments.¹⁷¹ Global research increasingly focuses on exploring non-surgical alternatives, which are often more patient acceptable. Preserving normal EC function is critical for resisting AA/AD development, making EC regulation a high-priority clinical target.¹⁵³ Animal studies have established the role of AngII-induced endothelial dysfunction in AD pathogenesis, verifying that the angiotensin receptor blocker telmisartan counteracts Ang II-induced inflammatory states.⁴⁵ However, whether other cardiovascular drugs inhibiting Ang-II-related pathways, such as empagliflozin, can similarly antagonize AA/AD remains unknown.¹⁷² Resveratrol (RSV), a plant-derived polyphenol with potent anti-inflammatory properties, confers vascular protection and delays aneurysm progression. In murine models, RSV reduced BAPN-induced AD incidence from 75% to 30% by inhibiting SIRT1-mediated EC inflammation, thereby resisting AD development.¹⁷³ If clinically validated, RSV or similar SIRT1 modulators could serve as low-cost, natural-source preventive supplements to mitigate aneurysm risk, address early-stage non-surgical treatment gaps, and delay the expansion of small aneurysms or dissections. Notably, human oral RSV exhibits extremely low bioavailability, making it difficult to achieve effective endothelial concentrations within the vascular endothelium.¹⁷⁴ Additionally, Piao et al. found that substance P (SP) mitigates early-stage aortic injury by inhibiting inflammation and promoting endothelial repair,¹⁷⁵ and SP research has reached clinical trial stages.¹⁷⁵ AT-1001, a protease-activated receptor 2 inhibitor, restores endothelial barrier function by repairing tight interendothelial junctions. This prevents false lumen expansion during early AD stages and protects VSMCs from damage. In animal models, AT-1001 treatment reduced BAPN-induced TAAD incidence from 87.5% to 37.5%, increased survival rates from 37.5% to 81.3%,¹⁷⁶ and mitigated ascending aortic diameter expansion. To effectively block the pathological process, AT-1001 must be administered during early disease stages before irreversible endothelial barrier damage occurs. Compared with other pharmacological interventions, AT-1001 administration is highly time sensitive because it prevents further endothelial damage at critical junctures to preserve vascular structural integrity. ER-associated microparticles (MPs) produced by VSMCs under mechanical stretching contribute to AD by inducing endothelial dysfunction. 4-PBA, an ERS inhibitor, alleviates this MP upregulation. In animal experiments, 4-PBA reduced aortic diameter and wall thickness in BAPN-treated mice by approximately 25% and 60%, respectively.¹⁷⁷ These findings suggest that 4-PBA holds significant promise for preventing AD and its devastating consequences, such as rupture. In animal models, 4-PBA significantly alleviates aortic dilation and wall thickening, demonstrating unique potential for preventing AD. Its established human safety profile further facilitates rapid clinical trial entry.^178,179,180 However, its current clinical value remains limited by etiological differences between animal models (BAPN-induced) and human dissections (primarily driven by hypertension and atherosclerosis), mismatched intervention timing (prevention versus treatment of established lesions), and unknown long-term high-dose risks. Consequently, current evidence is insufficient for immediate clinical application.¹⁷⁹ Nevertheless, 4-PBA represents a promising next-generation preventive candidate, particularly for high-risk genetic populations.¹⁷⁷ Rigorous verification in more relevant models and strict clinical trials are essential to confirm its efficacy and safety before routine clinical use can be recommended. Luo et al. demonstrated that the PDI S-sulfide 2S donor GYY4137 and entinostat restore PDI-SSH by inhibiting the assembly of the HDAC1-ZEB2-NuRD complex, thereby alleviating ERS and antagonizing AD development. In murine models, entinostat and GYY4137 reduced the incidence of AngII-induced AD from 80% to 10% and 20%, respectively.²⁰ Both agents decreased aortic diameter while mitigating elastic fiber degradation and interstitial fibrosis. However, transitioning these compounds into routine clinical practice requires substantial further development. Although the link between endothelial dysfunction and AD is well established, most research-derived targeted therapies remain in the theoretical stage. Currently, only 4-PBA possesses the potential for rapid clinical trial progression owing to its established safety profile, whereas other candidates face a more prolonged path toward clinical implementation. All potential therapeutic targets discussed are summarized in Table 2.

Table 2.

Potential RC-related biomarkers for the treatment of AD

Medicine	Target	Cellular activity	Reference
Telmisartan	ANG-II	inflammation	Wang et al.45
RSV	SIRT1	inflammation	Wang et al.173
SP	–	inflammation	Piao et al.175
AT-1001	BAPN	repairing the junction between ECs	Yang et al.176
4-PBA	MPs	mechanical traction between ECs	Jia et al.177
GYY4137	HDAC1-ZEB2-NuRD	ERS	Luo et al.20

Discussion and future directions

As a life-threatening clinical emergency, AA/AD holds immense research value. Vascular intimal injury, the initiating event in AA/AD, directly compromises vascular wall barrier function and exposes subendothelial structures to pathological hemodynamic forces.^181,182 This injury immediately triggers secondary hemodynamic responses, including local shear force disturbances and wall tension concentration, which subsequently activate MMPs, trigger inflammatory cascades, and prompt VSMC apoptosis.^183,184,185 These molecular and cellular responses further degrade elastic fibers and weaken the medial structure, leading to progressive mechanical deterioration. The compromised mechanical environment amplifies the abnormal impact of blood flow on the damaged area, establishing a self-reinforcing positive feedback loop of “injury-pathological blood flow-mural weakening-exacerbated injury.” This cycle significantly accelerates large aneurysm expansion or dissection detachment, ultimately leading to rapid disease progression toward rupture or fatal ischemic events. Given the challenges in early diagnosis and the associated poor prognosis, the prevention of AA/AD is paramount (Figure 4). Maintaining normal EC function remains crucial for inhibiting AA/AD occurrence.¹⁵³ Therefore, exploring endothelial dysfunction, including inflammation, cell migration, and apoptosis, is essential for advancing the understanding of AA/AD pathogenesis and guiding future clinical diagnosis and treatment.

Figure 4.

Multi-cellular and multi-scale endothelial mechanisms in aortic aneurysm/dissection

Hemodynamic stress and Ang II signaling trigger endothelial activation, inflammation, ECM degradation, cell migration, oxidative stress, and cell death, leading to intimal barrier failure. These endothelial-driven events promote VSMC phenotype switching, proteolytic enzyme secretion, medial degeneration, and progressive aortic structural damage.

Inflammation drives the onset and progression of cardiovascular diseases, with early-stage endothelial dysfunction playing a pivotal role. Endothelial-related inflammatory states both compromise barrier function and activate pro-inflammatory processes in VSMCs. For instance, endothelial-derived CypA triggers VSMC ERK1/2 phosphorylation, while VSMC depletion represents a primary factor for severe aortic injury during AD. Among various signaling axes, the NF-κB pathway appears central to AD-associated endothelial inflammation. Specifically, CD40L modulates this inflammation by activating NF-κB-mediated responses. Conversely, SIRT1 signaling inhibits AD-associated endothelial inflammatory responses, likely through the suppression of the NF-κB pathway. This aligns with reports that NF-κB signaling in AD predominantly localizes within the intima. Beyond aortic injury, the endothelial NF-κB pathway regulates lung microvascular EC apoptosis during ALI via MCP-1.

VSMC loss significantly contributes to AA/AD-associated vascular wall damage. Critical communication between ECs and VSMCs¹⁸⁶ occurs through diverse mechanisms, including direct cell-to-cell contact, ECM interactions, and extracellular vesicles.^187,188,189 For instance, endothelial JAGGED1 initiates VSMC differentiation by activating Notch receptor 3 (NOTCH3) signaling through direct contact,¹⁹⁰ a phenomenon well documented in atherosclerosis but less explored in AD.¹⁸⁹ Recent findings highlight a close EC-VSMC association during AD progression; specifically, NOX2-associated endothelial inflammation accelerates VSMC activation via paracrine CypA secretion. Concurrently, CypA may stimulate STAT3 or FoxO1 signaling to exacerbate endothelial damage, indicating reciprocal EC-VSMC effects. Notably, VSMCs also secrete minor amounts of CypA. Furthermore, miR-27a inhibits VSMC migration while counteracting AD-related endothelial apoptosis by modulating EC-derived matrix metalloproteinase-20 (MMP20) and growth/differentiation factor 8 (GDF8).¹¹⁶ This regulation appears to involve indirect mechanisms, rather than direct cellular contact. Recent studies have begun to document the interactions between ECs and VSMCs within the framework of AD; however, most discoveries remain incidental and lack comprehensive exploration. Crucially, the role of endothelial dysfunction is highly context dependent, rather than a universal initiating event. In diseases driven by traditional risk factors, such as hypercholesterolemia and hyperglycemia in atherosclerosis, endothelial impairment often serves as the primary initiator.¹⁹¹ Conversely, in pathologies driven by intrinsic VSMC defects (such as ACTA2 mutations), ECM abnormalities (e.g., Marfan syndrome), or aberrant TGF-β pathways (such as hereditary hemorrhagic telangiectasia), endothelial dysfunction functions not as the root cause but as a secondary “trigger” or a central amplifier of disease progression. Regardless of the initial insult, once a lesion is established, endothelial dysfunction frequently propagates a vicious cycle characterized by persistent inflammation, hyperpermeability, and a procoagulant state, ultimately exacerbating clinical outcomes.^192,193,194

Currently, AA/AD diagnosis and treatment continue to rely on conventional methods; however, novel EC-targeted therapies are emerging. For instance, sST2 levels play a critical role in diagnosing acute AD within 24 h of chest pain onset. RSV, a plant-derived polyphenol, demonstrates significant efficacy in mitigating early AD-related endothelial inflammation, while 4-phenylbutyric acid (4-PBA) shows potential in preventing catastrophic AA/AD rupture.¹⁷⁷ Furthermore, endothelial progenitor cells (EPCs) hold considerable promise due to their capacity to differentiate into mature ECs and repair vascular damage, though their current recognition is primarily limited to their protective role during AD progression. ALI is a major yet often overlooked complication of AD that further diminishes patient prognosis through associated pulmonary infections and hypoxemia. While AD-associated ALI is closely linked to PMVEC damage, clear therapeutic strategies remain scarce. Consequently, the effectiveness of existing EC-targeted therapies in treating PMVEC damage within the context of AD remains uncertain.

Translating results from animal models of AADs into clinical therapies presents fundamental challenges.¹⁹⁵ The core issue involves a profound mismatch in the causal hierarchy and disease heterogeneity between animal models and human pathologies. Mechanistically, most models (such as those induced by Ang-II or elastase) utilize a single, potent pathogenic factor, like local enzyme perfusion or supra-physiological agonist doses, to rapidly trigger disease onset.¹⁹⁶ This differs sharply from the multi-factorial causal structure of human diseases, which involves genetic susceptibility, environmental exposures (e.g., smoking), hemodynamic disorders, and long-term, low-intensity age-related degeneration. Consequently, drugs targeting a single pathway often fail within heterogeneous patient populations. Regarding heterogeneity, human aortic diseases encompass various subtypes with distinct etiologies, anatomical locations (chest/abdomen), pathological types (degenerative aneurysms/aneurysm dissections), and progression speeds.¹⁹⁷ However, existing models typically simulate only one specific subtype, failing to capture extensive clinical heterogeneity. Therefore, drugs proving effective under homogeneous model conditions rarely replicate that success in real-world clinical settings characterized by mixed etiologies and diverse pathologies. Future translational success depends on abandoning “one-size-fits-all” modeling in favor of constructing systems that reflect diverse causal hierarchies and multi-dimensional heterogeneity. Furthermore, clinical trials should be stratified based on well-defined pathological and physiological subtypes.

AA/AD has garnered significant attention as a life-threatening aortic pathology. While the fundamental role of VSMCs in AA/AD has been extensively documented, research focusing on ECs has progressed relatively slowly. This work emphasizes the importance of ECs in AA/AD, particularly as initiating factors for early vascular structural damage and their underexplored interactions with VSMCs. Enhancing the endothelial barrier in predisposed patients may prevent the onset of this catastrophic disease. By disrupting detrimental EC-VSMC interactions through targeted therapies, pathological damage could potentially be confined to the intima, thereby improving clinical outcomes. However, developing a comprehensive understanding of endothelial involvement in AA/AD necessitates further research.

Conclusion

Endothelial dysfunction is increasingly being recognized as a cornerstone of the initiation and progression of AA/AD. Compromised barrier integrity and aberrant mechanotransduction drive intimal vulnerability, while Ang II/AT1R-NF-κB-mediated inflammation, oxidative/ER stress, programmed cell death (apoptosis/pyroptosis/ferroptosis), and maladaptive migration/denudation collectively amplify immune infiltration, medial degeneration, and ECM remodeling. This endothelial-centric framework facilitates the identification of circulating EC-related biomarkers for early risk stratification and underpins therapeutic strategies directed at preserving intercellular junctions, dampening pro-inflammatory signaling, and enhancing endothelial repair. Nevertheless, successful clinical translation necessitates robust evidence from early-stage human studies, rigorous testing of endothelial-specific causality, and standardized multi-center validation.

Data and code availability

The datasets analyzed during the current study are available in the PubMed database.

Author contributions

K.W. and Y.L. drafted the manuscript and prepared the figures; F.K. and H.H. prepared the tables; S.W., T.Y., and S.Y. revised the article. All remaining authors contributed to manuscript polishing and visualization. All authors have read and approved the final manuscript.

Declaration of interests

The authors declare no competing interests.