Objective: Stroke is a sexually dimorphic disease. A growing body of literature from both clinical and experimental studies suggests that the outcomes after stroke differ in males versus females. Peripheral immune cells play a key role in stroke outcomes and also show sexual dimorphism. However, general immunosuppression has not shown an overall benefit in stroke patients. Therefore, identifying novel targets to improve stroke outcomes are urgently needed. P2X4 receptors (P2X4R) and P2X7 receptors (P2X7R) are the predominant subtypes expressed on immune and neural cells. The P2X7R and P2X4R interact and may physically associate with each other. Recent evidence demonstrates that P2X4R is necessary for the pro-inflammatory function of P2X7R. The goal of this study is to test the hypothesis that genetic deletion of P2X4R in myeloid immune cells impacts on stroke outcome and that such outcome differs in males vs. female mice.
Methods: P2X4R myeloid knockout mice and wild type littermates of both sexes (∼20-25g; C57BL/6), were randomized and subjected to right middle cerebral artery occlusion (MCAO-90min) followed by 3 days of reperfusion. At 72h after stroke mice were perfused and infarcts were quantified from 30μicron cut cresyl violet stained sections. The effect of myeloid P2X4R deletion on chronic functional recovery was assessed with neurological scores, corner test, Open field and the novel object recognition test. Data are expressed as mean±sem. ANOVA was performed and a P < .05 was set for statistical significance.
Results: A significant neuroprotective effect is seen in P2X4R KO compared to WT females (Cortex 36.1±1.5 vs 27.5±4.7; Striatum 67.4±1.5 vs 56.3±7.0; Total 34.8±1.6 vs 26.9±2.8. P<.05; n=7KO, 9WT). Ongoing studies in P2X4R KO ovariectomized females will determine if these sex specific effects are dependent on hormones (estrogen).
Conclusions: There is a sex-specific effect of immune cell P2X4R deletion. Myeloid specific deletion of P2X4R protects females from ischemia/reperfusion injury but has no salutary effect in males. This is the first study to demonstrate a deleterious effect of myeloid P2X4R on stroke outcomes. These initial findings implicate myeloid P2X4 as a novel therapeutic approach to improve ischemic outcomes in females.