P2X7-mediated alteration of membrane fluidity is associated with the late stages of age-related macular degeneration

We have shown defcits in monocyte phagocytosis from patients with age-related macular degeneration (AMD). Cell membrane fuidity is known to afect phagocytic capacity and leucocyte functionality more generally. Therefore, we examined membrane fuidity of peripheral blood leucocytes in human patients with AMD and in the P2X7 null mouse model of AMD using fow cytometry with a fuorescent probe for fuidity, TMA-DPH. The results showed that membrane fuidity was decreased in all leucocyte types of late AMD relative to healthy controls (HC) including monocytes, neutrophils and lymphocytes but this was not apparent in earlier stages of AMD. Further analysis of factors contributing to membrane fuidity indicated that pre-treatment of monocytes and lymphocytes with ATP greatly increased membrane fuidity in humans and mice. Evidence from P2X7 null mice and P2X7 antagonists confrmed that these ATP-driven increases in membrane fuidity were mediated by P2X7 but were not associated with the classic P2X7 functions of pore formation or phagocytosis. Analysis of P2X7 expression indicated that receptor levels were elevated in classic monocytes of late AMD patients, further suggesting the P2X7 may contribute to altered plasma membrane properties. Our findings identifed a novel biological function of P2X7 in modulating membrane fuidity of leucocytes and demonstrated reduced membrane fuidity in cellular changes associated with the late stage of AMD.