The second plenary session at ISEV 2021 was presented by Chantal Boulanger, senior research professor and director at the French National Health and Medical Research Institute, INSERM. During the talk, Boulanger discussed fascinating insights on extracellular vesicles (EVs) and cardiovascular disorders, including data from her work at the Paris-Cardiovascular Research Center. Her group has documented associations between circulating microparticles and endothelial dysfunction, using cell culture studies, mouse models, and studies of human tissues and biofluids.
Erythrocyte-derived EVs induce arterial spasms in myeloproliferative neoplasm
Boulanger began the presentation by highlighting findings that have helped spur interest in EVs and their role in cardiovascular disease; for example, circulating EVs from patients with cardiovascular diseases can downregulate endothelial nitric oxide synthase and increase the production of reactive oxygen species, leading to increased vasospasms and a reduction in endothelial athero-protective properties.
These observations, in a roundabout way, led the group to study diseases of the bone marrow and blood; in particular, a group of blood cancers called myeloproliferative neoplasms. Interestingly, these conditions – even though they do not cause any obstruction to coronary arteries – are associated with a high prevalence of acute coronary syndrome. Myeloproliferative neoplasms include polycythemia vera, essential thrombocythemia, and primary myelofibrosis, all of which are associated with a mutation in a gene that encodes a protein kinase called JAK2 (Janus kinase 2). The JAK2V617F mutation leads to constitutive activation of the growth factor receptor and downstream pathways, which ultimately results in myeloid cell proliferation. In this context, the group placed a particular focus on EVs with a diameter of 0.1-1 μm, or 100-1000 nm, which they refer to as ‘microvesicles.’
Investigations into microvesicles and myeloproliferative neoplasms led to study published in 2020 in the Journal of Clinical Investigation<super-script>1<super-script>, from which a few key findings were shared:
- In vitro, aortas from wild-type mice show a greater contractile response to vasoactive drug phenylephrine when exposed to microvesicles from patients with the JAK2V617F mutation.
- Erythrocyte-derived microvesicles derived from mice with the JAK2V617F mutation induce this increased contractile response in mouse arteries, in vitro. This response is not observed when vesicles derived from platelets or monocytes are administered.
- The increased contractile response to phenylephrine is also observed in vivo; greater contraction is observed in the femoral artery of mice given an intravenous bolus of erythrocyte-derived microvesicles.
- Proteomic analysis of proteins from erythrocyte-derived microvesicles identified alterations that may confer a pro-oxidant phenotype, including increased expression of myeloperoxidase. Pharmacological inhibition of myeloperoxidase suppressed their effect on oxidative stress, implying a potential role for myeloperoxidase in conferring the observed effect of erythrocyte-derived microvesicles from JAK2V617F mice.
EVs and myocardial infarction
In the second part of the presentation, Boulanger highlighted major findings and papers related to EVs and myocardial infarction (MI, commonly known as a heart attack) including:
- The first hint that circulating vesicles were higher in patients with MI<super-script>2<super-script> and evidence showing that these vesicles were rich in endothelial markers
- Vesicle concentration is positively associated with the extent of injury of the myocardium in humans<super-script>3 <super-script>
- Increased EV concentration observed 24 hours after myocardial infarction induced in mice; levels had returned to baseline after four days<super-script>3 <super-script>
- Increased levels of VCAM1 in vesicles in mice after MI, an adhesion protein expressed in activated endothelial cells<super-script>3 <super-script>
- Intravenous administration of endothelial EVs isolated in vitro can mobilise monocytes from the spleen in mice<super-script>3 <super-script>
- Endothelial EVs rescue ischemia-reperfusion injury in a human heart-on-a-chip model. A lesser fraction of dead cells was observed when the reperfusion injury was applied in the presence of endothelial EVs. Cardiomyocyte contraction was higher in the presence of endothelial EVs, both during ischemia and after recovery<super-script>4 <super-script>
Isolating EVs from heart tissue after myocardial infarction
After highlighting a review on endothelial cell-cardiomyocyte cross talk in heart development and disease,<super-script>5<super-script> Boulanger discussed the isolation of EVs from heart tissue of mice after MI. Here, small and large EVs were characterised using tunable resistive pulse sensing (TRPS, specifically the qNano by Izon Science), electron microscopy, western blot and flow cytometry analysis <super-script>6,7<super-script> which revealed a transient increase of large and small EVs in cardiac tissue after MI. Interestingly, this was not observed after MI in diabetic mice7 and ongoing work is aiming to determine whether this lack of EV accumulation is due to increased release from cardiac tissue into the circulation.
Boulanger also highlighted two soon-to-be-published articles which can now be found in the European Heart Journal (one research article<super-script>8<super-script> and one editorial piece authored by Boulanger<super-script>9<super-script>) which expand further on the driving factors of EV release from cardiomyocytes. The recent study by Anselmo et al.<super-script>8<super-script> focused on cardiomyocyte-derived vesicles in patients with ischaemic myocardium and identified higher concentrations of circulating CD172-positive EVs to be associated with a more favourable prognosis.
Altogether, these findings imply a role for EVs in cardiovascular function, and raise many questions about their mechanisms, clearance, and prognostic value.