Microglia is a Key Player in the Reduction of Stroke Damage Promoted by the New Antithrombotic Agent Ticagrelor

Abstract

The ADP-responsive P2Y 12 receptor is expressed on both platelets and microglia. Clinical data show that ticagrelor, a direct-acting, reversibly binding P2Y 12 -receptor antagonist, reduces total cardiovascular events, including stroke. In our present study, we investigated the expression of P2Y 12 receptors and the effects of ticagrelor on brain injury in Sprague-Dawley rats subjected to a permanent middle cerebral artery occlusion (MCAo). Rats were treated per os with ticagrelor 3 mg/kg or vehicle at 10 minutes, 22, and 36 hours after MCAo and killed after 48 hours. Immunofluorescence analysis showed an ischemia-related modulation of the P2Y 12 receptor, which is constitutively expressed in Iba1 þ resting microglia. After MCAo, activated microglia was mainly concentrated around the lesion, with fewer cells present inside the ischemic core. Ticagrelor significantly attenuated the evolution of ischemic damage-evaluated by magnetic resonance imaging (MRI) at 2, 24, and 48 hours after MCAo-, the number of infiltrating cells expressing the microglia/monocyte marker ED-1, the cerebral expression of proinflammatory mediators (interleukin 1 (IL-1), monocyte chemoattractant protein 1 (MCP-1), nitric oxide synthase (iNOS)) and the associated neurologic impairment. In transgenic fluorescent reporter CX3CR1-green fluorescent protein (GFP) mice, 72 hours after MCAo, ticagrelor markedly reduced GFP þ microglia and both early and late infiltrating blood-borne cells. Finally, in primary cultured microglia, ticagrelor fully inhibited ADP-induced chemotaxis (Po0.01). Our results show that ticagrelor is protective against ischemia-induced cerebral injury and this effect is mediated, at least partly, by inhibition of P2Y 12 -mediated microglia activation and chemotaxis.

mTORC1 pathway disruption ameliorates brain inflammation following stroke via a shift in microglia phenotype from M1 type to M2 type

“…Following ischemia, astrocytes are activated, resulting in increased GFAP expression that is accompanied by characteristic structural and functional changes. Microglia play a crucial role as brain‐resident immune‐competent and phagocytic cells, serving as scavenger cells in the event of infection, inflammation, trauma, ischemia, and neurodegeneration (3, 6, 23, 37, 38). Once activated, normally ramified microglia undergo a major morphologic transformation, taking on an amoeboid shape, and then act as phagocytic cells, resulting in the secretion of various molecules.…”

“…These primary immune cells of the CNS act not only as the major inflammatory cell type in the brain, but also in a very important homeostatic role. Because of their association with infection, trauma, inflammation, ischemia, and degenerative disease processes of the CNS (3–5), microglia may be a therapeutic target (6). However, they play a dual role in ischemic brain damage (7).…”

Purinergic receptor P2RY12-dependent microglial closure of the injured blood–brain barrier

“…However, two prior studies have shown that P2RY12 antagonist administration after ischemia is beneficial: The first study induced global stroke in mice and reported that clopidogrel administered 5 min to 4 h after stroke reduced delayed neuronal loss after transient occlusion of the common carotid arteries (49). The second study exposed rats to occlusion of the middle cerebral artery followed by injection of ticagrelor (a reversible P2RY12 antagonist) 10 min to 36 h later (50). Both studies ascribed the apparent neuroprotective effect of P2RY12 inhibition to a suppression of the inflammatory response to ischemic cellular injury.…”

“…The typical patient takes clopidogrel for months or years before an ischemic event. By administering clopidogrel after the ischemic event, the two aforementioned studies (49,50) would not have been expected to achieve functional P2RY12 inhibition until several days after injury, long after the acute role of microglia in reannealing the BBB would have been accomplished. As such, the designs of these studies would have effectively eliminated any deleterious effects of clopidogrel at the time of acute injury.…”

Purinergic mechanisms in neuroinflammation: An update from molecules to behavior

“…Accordingly, the protective role of microglial P2Y 12 receptors against brain ischemia (Webster et al, 2013) or LPS induced sepsis (Liverani et al, 2014b) has been demonstrated. In the case of a more pronounced stroke model, however, the pro-inflammatory action of P2Y 12 receptor activation prevails and pharmacological blockade of the receptor in this case is protective (Gelosa et al, 2014). In addition to P2Y 12 receptor expression on microglia, oligodendrocytic expression may be an important marker of demyelinating lesions in the neuroinflammatory disease, ALS (Amadio et al, 2014).…”