Relationship PPAR-PGE2 in chronic inflammation : an opportunity for preventing atherothrombosis ? – PPARolePGE2

Chronic inflammation of the arterial wall triggered by lipid deposition and their oxidation induces atherosclerosis. Atherothrombosis, the ultimate cause of most of cardiovascular events, is the occurrence of thrombosis at the surface of atherosclerotic plaques. Antiplatelet treatments inhibit thrombosis and myocardial infarction; however their efficiency is limited by their inhibiting effect on hemostasis and the risk of bleeding. We previously showed that prostaglandin E2 (PGE2) is produced in atherosclerotic plaques and aggravates atherothrombosis without impacting hemostasis. However, the pathway controlling the PGE2 production in atherosclerotic plaques is not described.
PPARs are nuclear receptors involved in mechanisms controlling action of other eicosanoids ; however their interaction with PGE2 is not clear. Clinical studies suggest that PPARg activation with rosiglitazone increases the risk of cardiovascular events; however these data are controversial.
Our global objective is to determine whether a functional pathway PPARg/PGE2 is functional in atherosclerotic plaques, and whether this pathway would allow modulating the PGE2 production in order to prevent atherothrombosis.
In our first aim, we will test pharmacologically and in vitro whether one PPAR can control PGE2 production in macrophages. Our preliminary results showed that rosiglitazone, a PPARg activator, increased the PGE2 production. We will test its specificity by repeating the same experiment in presence of a PPARg inhibitor. To confirm this approach, we will transfect macrophages with siRNA in order to inhibit PPARg expression in macrophages.
In our second objective, we will test whether the PPARg/PGE2 pathway is significant in vivo, in atherosclerotic plaques. We will measure the expression of PPARs in mature/old murine plaques; our preliminary data showed that expression of PPARg is largely predominant (over other PPARs). Mice will be given rosiglitazone in order to detect its impact on the PGE2 production in plaques. We will confirm our results using a conditional and inducible line of mice knocked-out for PPARg, because PPARg interferes with the plaque development.
Our third objective is aimed at exploring the role of PGE2 in plaque, since it might be either pro- or anti-inflammatory. We will examine whether PGE2 can “reprogram” macrophages so that they respond to inflammatory stimuli by producing anti-inflammatory mediators, such as LXA4. We will then assess the results in vivo by crossing mPGES-1 and ApoE-deficient mice. The double KO will be unable to produce PGE2, and the measure of their LXA4 production will indicate whether PGE2 has any role in its production.
In the last aim, we will test whether manipulating the PPARg/PGE2 pathway impacts atherothrombosis. If PGE2 has a resolutive role, inhibiting its production might render plaques unstable. We will thus study the effect of rosiglitazone on plaque vulnerability by histology and scanning electronic microscopy. We will finally study the rosiglitazone effect on atherothrombosis, using a model that we set up in our lab.
Our research program will establish whether PPARg controls the PGE2 production in atherosclerotic plaques, whether PGE2 is pro-inflammatory or resolutive, and will examine the rosiglitazone effects on the plaque (stability, thrombogenicity). The latter point is important in regard of the controversy about the cardiovascular effects of rosiglitazone, a molecule largely used in the treatment of mellitus diabetes. Our results might open new avenues in the field of atherothrombosis prevention.