Blunted apoptosis of erythrocytes in mice deficient in the heterotrimeric G-protein subunit Gαi2

Abstract

Putative functions of the heterotrimeric G-protein subunit Gαi2-dependent signaling include ion channel regulation, cell differentiation, proliferation and apoptosis. Erythrocytes may, similar to apoptosis of nucleated cells, undergo eryptosis, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine (PS) exposure. Eryptosis may be triggered by increased cytosolic Ca2+ activity and ceramide. In the present study, we show that Gαi2 is expressed in both murine and human erythrocytes and further examined the survival of erythrocytes drawn from Gαi2-deficient mice (Gαi2−/−) and corresponding wild-type mice (Gαi2+/+). Our data show that plasma erythropoietin levels, erythrocyte maturation markers, erythrocyte counts, hematocrit and hemoglobin concentration were similar in Gαi2−/− and Gαi2+/+ mice but the mean corpuscular volume was significantly larger in Gαi2−/− mice. Spontaneous PS exposure of circulating Gαi2−/− erythrocytes was significantly lower than that of circulating Gαi2+/+ erythrocytes. PS exposure was significantly lower in Gαi2−/− than in Gαi2+/+ erythrocytes following ex vivo exposure to hyperosmotic shock, bacterial sphingomyelinase or C6 ceramide. Erythrocyte Gαi2 deficiency further attenuated hyperosmotic shock-induced increase of cytosolic Ca2+ activity and cell shrinkage. Moreover, Gαi2−/− erythrocytes were more resistant to osmosensitive hemolysis as compared to Gαi2+/+ erythrocytes. In conclusion, Gαi2 deficiency in erythrocytes confers partial protection against suicidal cell death.

Stimulation of Erythrocyte Cell Membrane Scrambling by C-Reactive Protein

“…Cellular mechanisms triggering eryptosis include oxidative stress [2], increased cytosolic Ca 2+ activity ([Ca 2+ ] i ) [2], ceramide [5], energy depletion [2], caspases [2, 6, 7] and the G-protein subunit Gαi2 [8]. Moreover, eryptosis may be stimulated following activation of casein kinase 1α, Janus-activated kinase JAK3, protein kinase C, and/or p38 kinase [2].…”

Stimulation of Eryptosis by Afatinib

“…Hallmarks of eryptosis are cell shrinkage [61] and cell membrane scrambling with phosphatidylserine translocation to the cell surface [58]. Cellular mechanisms participating in the orchestration of eryptosis include increase of cytosolic Ca 2+ activity ([Ca 2+ ] i ) [58], ceramide [62], caspases [58,63,64], G-protein Galphai2 [65], casein kinase 1α [58], Janus-activated kinase JAK3 [58], protein kinase C [58], and p38 kinase [58]. Eryptosis is suppressed by AMP activated kinase AMPK [58], cGMP-dependent protein kinase [58], mitogen and stress activated kinase MSK1/2 [66], PAK2 kinase [58] and sorafenib/sunitinib sensitive kinases [58].…”

Inhibition of Suicidal Erythrocyte Death by Volasertib

“…by energy depletion [22], hyperosmotic shock [22], and oxidative stress [22]. Signaling mechanisms triggering eryptosis include increase of cytosolic Ca 2+ activity ([Ca 2+ ] i ) [22], ceramide [25], caspases [22,26,27], G-protein Gαi2 [28], casein kinase 1α [22], Janus-activated kinase JAK3 [22], protein kinase C [22], and p38 kinase [22]. Signaling mechanisms inhibiting eryptosis include the kinases AMPK [22], cGMP-dependent protein kinase [22], MSK1/2 [29], PAK2 [22] and sorafenib/sunitinib sensitive kinases [22].…”