The contribution of platelets to the maintenance of vascular integrity in inflammation does not depend on the platelet’s ability to form a hemostatic plug. At this point, very little is known about how platelets protect the inflamed vasculature. Recent studies, including mine, have identified a critical role for ITAM platelet signaling in the maintenance of vascular integrity at sites of inflammation. Surprisingly, the GPCR signaling, playing an instrumental role in platelet plug formation, is not required in supporting vascular integrity at sites of inflammation. Therefore, depending on the signaling pathway, platelets may release vasoactive factors, up to now not-defined, can prevent hemorrhage by strengthening EC barrier function or by dampening the inflammatory response. To answer that question, we performed in vitro studies in which platelets were incubated with neutrophils stimulated or not by TNFα 10ng/ml for 4hours. Peroxydase activity and reactive oxygen species were measured by fluorogenic substrates. We observed that although platelets are known to recruit leukocyte at sites of inflammation, they can also dampen neutrophil activation. We are currently performing experiments to further understand the exact platelet mechanisms involved. For that purpose, we will use platelets treated with different inhibitors (aspirin, P2Y12 inhibitor, anti GPVI…) and analyze neutrophil neutrophil response.
In parallel to the in vitro studies, we set up the in vivo model of intracranial aneurysm. For this purpose, I collaborated with Cyrille Orset at INSERM 919, University of Caen, France. I went to learn the model and implemented in my lab. It’s a finicky preclinical in-vivo animal model described by Nuki et al, analog to the clinical manifestation of the disease process. We implanted mice angiotensin pump to induce hypertension and then injected elastase into the cerebrospinal fluid are combined to induce intracranial aneurysm formation and rupture in mice monitored by MRI surgery. This model requires a lot of training and high skill level in microsurgery. Now, I am pretty confident with this model to further delineate the platelet mechanisms. Aside the learning curve of this model, I observed by immunohistology a thrombus in the aneurysmal sac highly enriched in platelets and leukocytes suggesting that platelets can play an instrumental role in this disease. I presented these results at seminars and open doors days in our laboratory. I also communicate this data through the class I am teaching at the University of Paris Diderot and at meetings (International Vascular Biology Meeting in Boston, European Congress on Hemostasis and Thrombosis in Den Hague and in Marseille 2018).
