Endothelial cells secrete small extracellular vesicles bidirectionally containing distinct cargo to uniquely reprogram vascular cells in the circulation and vessel wall
Authors: Raju Sneha , Botts Steven R. , Blaser Mark , Prajapati Kamalben , Ho Tse Wing Winnie , Ching Crizza , Galant Natalie J , Fiddes Lindsey , Wu Ruilin , Clift Cassandra L. , Pham Tan , Lee Warren L , Singh Sasha A , Aikawa Elena , Fish Jason E , Howe Kathryn L 
Published: April 2023

Rationale: Extracellular vesicles (EVs) contain bioactive cargo including microRNAs (miRNAs) and proteins that are released by cells as a form of cell-cell communication. Endothelial cells (ECs) form the innermost lining of all blood vessels and thereby interface with cells in the circulation as well as cells residing in the vascular wall. It is unknown whether ECs have the capacity to release EVs capable of governing recipient cells within two separate compartments, and how this is affected by endothelial activation commonly seen in atheroprone regions.

Objective: Given their boundary location, we propose that ECs utilize bidirectional release of distinct EV cargo in quiescent and activated states to communicate with cells within the circulation and blood vessel wall.

Methods and Results: EVs were isolated from primary human aortic endothelial cells (ECs) (+/- IL-1β activation), quantified, and analysed by miRNA transcriptomics and proteomics. Compared to quiescent ECs, activated ECs increased EV release, with miRNA and protein cargo that were related to atherosclerosis. RNA sequencing of EV-treated monocytes and smooth muscle cells (SMCs) revealed that EVs from activated ECs altered pathways that were pro-inflammatory and atherogenic. Apical and basolateral EV release was assessed using ECs on transwells. ECs released more EVs apically, which increased with activation. Apical and basolateral EV cargo contained distinct transcriptomes and proteomes that were altered by EC activation. Notably, basolateral EC-EVs displayed greater changes in the EV secretome, with pathways specific to atherosclerosis.In silicoanalysis determined that compartment-specific cargo released by the apical and basolateral surfaces of ECs can reprogram monocytes and SMCs, respectively.

Conclusions: The demonstration that ECs are capable of polarized EV cargo loading and directional EV secretion reveals a novel paradigm for endothelial communication, which may ultimately enhance our ability to design endothelial-based therapeutics for cardiovascular diseases such as atherosclerosis where ECs are persistently activated.

Non-standard Abbreviations and Acronyms

cryo-EM

cryogenic electron microscopy

EC

endothelial cell

EV

extracellular vesicle

GO

gene ontology

HAEC

human aortic endothelial cell

SMC

human aortic vascular smooth muscle cell

IL-1β

interleukin 1 beta

KEGG

Kyoto encyclopedia of genes and genomes

LC-MS

label-free liquid-chromatography mass spectrometry

MVB

multivesicular body

miRNA

microRNA

RNAseq

RNA sequencing

TEM

transmission electron microscopy

TIRF

total interal reflection fluorescence microscopy

miRNA

microRNA

Graphical abstract: Polarized endothelial extracellular vesicle communication with luminal and abluminal vascular cells

Endothelial cell small extracellular vesicle (EC-EV) release from apical (luminal) and basolateral (abluminal) surfaces in quiescence and after endothelial activation. Quiescent EC-EVs are depicted in blue (bright blue=apical, light blue=basolateral), while activated EC-EVs are depicted in red (bright red=apical, light red=basolateral). Luminal monocyte is represented in purple with upregulation of pro-inflammatory transcripts (bright purple) after uptake of activated EC-EVs from the apical surface, compared to uptake of quiescent apical EC-EVs (light purple). Basolateral EC-EVs are taken up by an abluminal resident smooth muscle cell depicted in yellow. Smooth muscle cell uptake of activated basolateral EC-EVs with upregulation of pro-inflammatory/pro-atherogenic transcripts (bright yellow), as compared to uptake of quiescent EC-EVs (light yellow).