Alpha hemolysin of of E.coli induces the activation of erythrocytes calpains

FERNANDA CARRIZO-VELASQUEZ; SABINA M. MATÉ.; LAURA BAKÁS; VANESA S. HERLAX

Salto

Congreso; Latin American Crosstalk in Biophysics and Physiology.; 2015

LAFeBS (Latin American Federation of Biophysical Societies) y la seccional Biofísica de la Sociedad Uruguaya de Biociencias (SBF.uy), el Comité Organizador del VIII Curso PosLatAm y Congreso SBF.uy/SAB 2015

Uropathogenic strains of E. coli deliver the toxin alpha-hemolysin (HlyA) to optimize the host environment for the spread of infection. It was reported that at high concentrations, the toxin forms pores in eukaryotic membranes, leading to cell lysis, while lower concentrations have appeared to interfere with host-cell?signaling pathways causing cell death by apoptosis. Nevertheless, what is not clear is how often HlyA reaches levels that are high enough to lyse host target cells during the course of an infection. In the present investigation we demonstrate that a low toxin concentration induces the suicidal death of erythrocytes (eryptosis), the major cell type present in blood. Eryptosis is triggered both by an increment in intracellular calcium and by ceramide. Since we have previously demonstrated that a low concentration of HlyA induces an increase in intraerythrocyte calcium1, in the present experiments we have shown that this ion activates calpains. Furthermore, by mass spectroscopy, we demonstrated that calpains hydrolyze skeleton proteins such as spectrin, ankyrin, protein 4.1 and the electrophoretic Band-3 species, thus resulting in morphologic changes in the erythrocytes. We furthermore observed that a low toxin concentration induced the activation of endogenous sphingomyelinases that in turn increased the amount of ceramide in erythrocyte membranes. Both spectrin proteolysis and ceramide formation may cause the exposure of phosphatidylserine on the membrane so as to trigger a macrophage engulfment of the erythrocyte. By this means eryptosis may be an advantageous mechanism for removing defective erythrocytes before hemolysis.