Suicidal death of erythrocytes in recurrent hemolytic uremic syndrome

Abstract

Hemolytic uremic syndrome (HUS) is characterized by hemolytic anemia with fragmented erythrocytes, thrombocytopenia, and acute renal failure. Lack of complement inactivating factor H predisposes to the development of atypical HUS. Little is known about mechanisms linking complement activation with loss of erythrocyte integrity during HUS. Recent studies disclosed that increased cytosolic Ca2+ activity and cellular ceramide trigger programmed erythrocyte death or eryptosis, characterized by cell shrinkage and phosphatidylserine exposure at the erythrocyte surface. In the present study, we investigated whether eryptosis occurs during the course of HUS. To this end, erythrocytes from healthy volunteers were exposed to plasma from a patient with severe idiopathic recurrent HUS secondary to factor H depletion. Phosphatidylserine exposure (Annexin binding), cell volume (forward scatter), cytosolic Ca2+ activity (Fluo3 fluorescence), and ceramide formation [anti-ceramide antibody and enzymatic (diacylgycerol kinase) analysis] were determined. Exposure of erythrocytes to plasma from the patient, but not to plasma from healthy individuals, triggered Annexin binding. The effect of plasma on erythrocyte Annexin binding was abolished by plasmapheresis or filtration at 30 kDa. It was paralleled by formation of ceramide and increase of cytosolic Ca2+ activity. Enhanced Annexin binding of erythrocytes from healthy individuals was observed after exposure to plasma from three other patients with HUS. The proeryptotic effect of patient plasma was mimicked by exposure to the Ca2+ ionophore ionomycin, and eryptosis was potentiated in the presence of cell membrane-permeable C6-ceramide. Furthermore, in vitro complement activation similarly triggered erythrocyte phosphatidylserine exposure, an effect which was blunted by the addition of factor H. In conclusion, our present observations disclose a novel, pathophysiological, factor-H dependent mechanism leading to injury of erythrocytes during the course of hemolytic uremic syndrome.

Monomeric CRP contributes to complement control in fluid phase and on cellular surfaces and increases phagocytosis by recruiting factor H

“…29 aHUS is also associated with enhanced apoptosis of erythrocytes and human endothelial cells. 30,31 The reduced mCRP interaction of aHUS-associated Factor H mutants (Figure 2c) suggests that under inflammatory conditions this reduced surface binding causes increased cellular damage and enhances inflammation.…”

Hemin-induced suicidal erythrocyte death

“…A wide variety of clinical disorders is known to stimulate eryptosis, including iron deficiency [36], phosphate depletion [6], hemolytic uremic syndrome [43], sepsis [35], malaria [10,37,38], or Wilson's disease [46]. Some of these diseases may cause eryptosis by stimulating the formation of hemin.…”

Critical Role of the C-Terminal Domains of Factor H in Regulating Complement Activation at Cell Surfaces

“…7, A and B) was observed when factor H-mediated cell surface control was inhibited by rH 19 -20, even when the function of the membranebound regulatory proteins was intact and when shear stress was absent. Interestingly, eryptosis, a pathophysiological mechanism of RBC death, has recently been shown in vitro to be linked to HUS, to be induced by complement activation, and may be factor H dependent (70). Studies defining the relative contribution of each of these mechanisms to erythrocyte destruction in aHUS are warranted.…”