1) Extracellular vesicles and coronary artery disease
Membrane vesicles released in the extracellular space are composed of a lipid bilayer enclosing soluble cytosolic material and nuclear components. Extracellular vesicles include apoptotic bodies, exosomes, and microvesicles (also known previously as microparticles). Originating from different subcellular compartments, the role of extracellular vesicles as regulators of transfer of biological information, acting locally and remotely, is now acknowledged. Circulating vesicles released from platelets, erythrocytes, leukocytes, and endothelial cells contain potential valuable biological information for biomarker discovery in primary and secondary prevention of coronary artery disease. Extracellular vesicles also accumulate in human atherosclerotic plaques, where they affect major biological pathways, including inflammation, proliferation, thrombosis, calcification, and vasoactive responses. Extracellular vesicles also recapitulate the beneficial effect of stem cells to treat cardiac consequences of acute myocardial infarction, and now emerge as an attractive alternative to cell therapy, opening new avenues to vectorize biological information to target tissues. Although interest in microvesicles in the cardiovascular field emerged about 2 decades ago, that for extracellular vesicles, in particular exosomes, started to unfold a decade ago, opening new research and therapeutic avenues (Boulanger et al, Nature Review Cardiology 2017).
We previously observed an increased release of endothelial microvesicles in atheroprone conditions, mimicked by in vitro low shear stress (Vion et al, Circ Res 2013). We and others confirmed these in vitro results in heathly subjects. The release of endothelial microvesicles under low shear stress conditions resulted from an augmented Erk1/2 activity and an impaired nitric oxide release, but not from increased apoptosis.
We also quantified circulating endothelial microvesicles in the Framingham epidemiologic cohort to test the hypothesis that their levels correlate with subclinical and clinical vascular disease in this large, well-characterized human population. We observed an association with the presence of cardiometabolic risk factors, in particular dyslipidemia, underscoring the influence of high risk metabolic profiles on endothelial integrity (Amabile, Cheng et al. Eur. Heart Journal 2014).
We recently demonstrated that coronary artery ligation transiently increases large and small EV levels in a murine model of myocardial infarction, when compared to sham animals. Vesicles of similar diameter were also isolated from interventricular septum fragments obtained from patients undergoing extracorporeal circulation for aortic valve replacement. Vesicles locally generated after myocardial infarction originated mainly from endothelial cells and from cardiomyocytes. Large EVs were preferentially taken up by infiltrating monocytes, where they caused an increased release of chemokines and inflammatory cytokines, whereas small EVs and EVs isolated from sham animals were without effects. Taken altogether, these results highlight the paracrine crosstalk between cardiac inflammatory cells and endogenously released EVs following myocardial infarction (Loyer et al., Circ. Research 2018).
Arterial cardiovascular events are the leading cause of death in patients with JAK2V617F myeloproliferative neoplasms. However, their mechanisms are poorly understood. In our recent study (Poisson et al, J. Clinical Investigation 2020)., we observed that genetically modified mice developing JAK2V617F myeloproliferative neoplasms have a strong arterial contraction in response to vasoconstrictors that could account for arterial cardiovascular events observed in patients. We then investigated the mechanisms involved and demonstrated that microvesicles, i.e. cell debris, derived from red blood cells, and circulating in the blood of patients with JAK2V617F myeloproliferative neoplasms transfer a protein (myeloperoxidase) to endothelial cells thus increasing arterial response. We finally showed that treatments, including hydroxyurea and simvastatin, improved arterial response and could thus be attractive to prevent arterial cardiovascular events in patients with JAK2V617F myeloproliferative neoplasms
2) Microvesicles and liver diseases
Cirrhosis is the final stage of chronic damage to the liver. About 200’000 to 500’000 individuals in France have cirrhosis and this disease is responsible for 170 000 deaths per year in Europe.
Cirrhosis is associated with portal hypertension that leads to the major complications of this disease, namely ascites and gastrointestinal bleeding. Portal hypertension results from an increase in intrahepatic resistance together with an augmentation of portal blood flow due to splanchnic and systemic vasodilation.
In a pioneer study, we demonstrated that plasma microvesicles contribute to vascular impairment associated with cirrhosis and that hepatocyte microvesicle levels increase with the severity of cirrhosis. These results thus suggested that hepatocyte and leuko-endothelial microvesicles might be helpful biomarkers in patients with cirrhosis. (Rautou et al, Gastroenterology 2012; Lemoinne et al, Nature Rev. Hepato. Gastro 2014). We tested this hypothesis and performed the first prospective study investigating the interest of a large panel of plasma cell-derived microvesicles to predict mortality in patients with cirrhosis. We included 242 patients with cirrhosis (139 at Beaujon Hospital, Clichy France test cohort; 103 in Barcelona, Spain, validation cohort) and analyzed their plasma microvesicle levels. We demonstrated that hepatocyte microvesicle levels strongly improve prediction of 6-month mortality in patients with advanced chronic liver disease. Our results suggest that therapies associated with decreased levels of circulating hepatocyte microvesicle might be attractive strategies in patients with severe cirrhosis (Payance et al., Hepatology 2018; Inserm Press Release).
We also demonstrated the potential interest of plasma levels of cytokeratin-18 fragments as new reliable non-invasive markers of alcoholic hepatitis for the diagnosis of alcoholic hepatitis which requires a transjugular liver biopsy, a procedure not always readily accessible. (Bissonnette et al. Hepatology 2017)
3) Endothelial autophagy
Autophagy is a major intracellular recycling system that primarily acts as a protective mechanism by preventing cell death and senescence. Under basal conditions, autophagy controls organelle and protein quality to maintain cellular homeostasis. Under conditions of stress, autophagy acts as a survival mechanism, maintaining cellular integrity by regenerating metabolic precursors and clearing subcellular debris. Autophagy is implicated in an expanding list of diseases. Our work is focused on the role of autophagy in endothelial cells and its involvement in the pathophysiology of diseases related to metabolic syndrome (combination of obesity, insulin resistance or type 2 diabetes, dyslipidemia and hypertension).
Atherosclerosis is the arterial consequence of the metabolic syndrome. Atherosclerosis is an inflammatory disease of large arteries which preferentially develops in particular areas of the vasculature, where the blood flow is disturbed and exerts low shear stress, such as arterial bifurcations and curvatures. Conversely, areas exposed to high shear stress are protected from plaque development. We demonstrated that autophagy is activated in high shear stress areas and protects against atherosclerotic plaque formation (Vion, Kheloufi et al., PNAS 2017). Conversely, autophagic flux is blocked in atheroprone low shear stress areas. This defect is responsible for the preferential plaque formation in atheroprone low shear stress areas, by inducing an endothelial inflammatory, apoptotic, and senescent phenotype.
Nonalcoholic fatty liver disease (NAFLD) is the liver manifestation of the metabolic syndrome. NAFLD encompasses a spectrum of histological lesions ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) which includes, in addition to steatosis, hepatocellular injury, inflammation, and varying degree of fibrosis, and can progress to cirrhosis and liver cancer. We recently demonstrated that autophagy is defective in liver endothelial cells of patients with NASH and that this defect is induced by inflammatory mediators present in the portal blood of patients with metabolic syndrome (Figure).
We also demonstrated that deficiency in autophagy induces liver endothelial cell alterations responsible for liver inflammation, liver cell death and liver fibrosis, thus promoting NASH development ().
Altogether, our work demonstrates that autophagy is a key process involved in endothelial cell homeostasis in a metabolic syndrome setting in different vascular beds. Targeting endothelial autophagy is an attractive strategy for the management of metabolic syndrome related disorders.