Vesicles in the Flow: How Endothelium Communicates Vascular Danger in Atherosclerosis

Introduction

Atherosclerosis develops preferentially at arterial sites exposed to disturbed flow, such as bifurcations and curvatures, where endothelial cells experience oscillatory or low shear stress (1). These hemodynamic conditions promote endothelial activation, inflammation, and the recruitment of circulating monocytes (2-5), initiating the cascade of events that ultimately leads to plaque formation. While the importance of endothelial mechanotransduction in atherogenesis has long been recognised, the mechanisms by which hemodynamic signals are communicated to immune cells remain incompletely understood. In recent years, extracellular vesicles (EVs) have emerged as critical mediators of intercellular communication within the vascular wall, carrying proteins, lipids, and nucleic acids that influence vascular inflammation and remodeling (6-7).

Background

Endothelial-derived extracellular vesicles (EEVs) are increasingly recognised as biomarkers and potential effectors of vascular dysfunction (8). Elevated circulating EV levels have been described in patients with cardiovascular disease, reflecting endothelial activation and injury (8-10). However, the influence of local hemodynamic forces on EEV secretion and their functional consequences for immune cell behavior has remained largely unexplored. Understanding how disturbed flow shapes EEV-mediated signaling could therefore provide important insights into the early mechanisms driving atherosclerosis.

Key findings

In this context, the study by Hou and colleagues (11) provides compelling mechanistic evidence linking disturbed flow, EEV secretion, and inflammatory macrophage polarisation. Using complementary in vivo and in vitro models, the authors demonstrate that endothelial cells exposed to disturbed flow release significantly higher numbers of extracellular vesicles compared with cells exposed to laminar shear stress. These findings were confirmed in a mouse model of disturbed flow induced by partial carotid artery ligation, where increased EV accumulation was observed in regions prone to atherosclerotic lesion formation.

Mechanistically, the authors identify activation of the MAPK signaling pathway as a key mediator translating mechanical cues into EEVs secretion. Disturbed flow increased the expression of upstream MAPK components, including Ras and Raf1, and enhanced ERK (extracellular signal-regulated kinase) phosphorylation in endothelial cells. Pharmacological inhibition of MAPK signaling significantly reduced EEVs release even under disturbed flow conditions, suggesting that this pathway plays a central role in mechanotransduction leading to EV production.

Biological effects and mechanistic insights 

Importantly, the study extends beyond the characterisation of EEVs release to examine their biological effects on immune cells involved in atherogenesis. Endothelial EVs generated under disturbed flow promoted adhesion of monocytes to the endothelial layer and enhanced their trans-endothelial migration. More strikingly, these EVs induced inflammatory polarisation of macrophages, shifting them from an anti-inflammatory M2 phenotype towards a pro-inflammatory M1 phenotype. This transition was revealed by increased expression of inflammatory markers such as CD86 and CD80 and reduced expression of the M2 marker CD206, consistent with enhanced inflammatory activity.

Clinical implications and future directions

These findings highlight EEV-mediated communication as an important mechanism linking endothelial mechanobiology with immune activation during early atherogenesis. By promoting inflammatory macrophage polarisation, disturbed flow–derived EEVs may amplify vascular inflammation and accelerate plaque development. Interestingly, the authors report that these EEVs did not induce phenotypic switching of vascular smooth muscle cells (contractile to synthetic), suggesting that their primary effects may occur during the early inflammatory stages of atherosclerosis rather than during later plaque remodeling.

From a broader perspective, this work contributes to a growing body of literature emphasising the role of extracellular vesicles as mediators of vascular cross-talk. EVs can integrate mechanical, metabolic, and inflammatory signals and deliver them to target cells within the vascular wall or circulation. In the context of disturbed flow, EVs may therefore function as “mechanotransduction messengers,” translating hemodynamic forces into immune responses that drive lesion formation.

The study also raises intriguing questions about the molecular cargo responsible for these pro-inflammatory effects. Although the authors demonstrate functional consequences of EV exposure, the specific microRNAs, proteins, or lipids contained within disturbed flow–derived EVs have yet to be fully characterised. Previous studies suggest that laminar shear stress can induce anti-inflammatory microRNAs in endothelial EVs, whereas disturbed flow may favor a pro-inflammatory cargo profile. Defining these molecular signatures could provide new insights into the regulation of vascular inflammation and identify potential therapeutic targets.

Another notable implication concerns the growing interest in EVs as biomarkers of vascular disease. If disturbed flow enhances the release of pro-atherogenic endothelial EVs, circulating EV profiles might reflect the hemodynamic environment within arteries and provide early indicators of vascular risk before overt plaque formation becomes detectable.

Study limitations 

Despite its strengths, several limitations should be acknowledged. The study relies primarily on experimental models, and the translational relevance of these findings in human atherosclerosis remains to be confirmed. In addition, while MAPK inhibition reduced EV secretion, targeting this pathway in vivo may have broad biological effects beyond EV regulation. Future studies will therefore be needed to determine whether more selective strategies can modulate EV-mediated signaling without disrupting essential endothelial functions.

Overall, the work by Hou et al. provides important mechanistic insight into how hemodynamic forces influence intercellular communication within the vascular wall. By identifying endothelial EVs as key mediators linking disturbed flow to inflammatory macrophage polarisation, this study advances our understanding of the early cellular events that promote atherosclerosis. These findings reinforce the concept that vascular biology cannot be understood solely through individual cell types, but rather through dynamic communication networks shaped by the local hemodynamic environment.
As interest in extracellular vesicles continues to grow, integrating mechanobiology, immunology, and vascular physiology will likely reveal new opportunities for both diagnostic and therapeutic innovation in cardiovascular disease.