Abstracts (complete list) - Wissenschaft Online

Michael Schramm, Ulrike Karow, Albert Haas, Martin Krönke, Olaf Utermöhlen
Effects of Acid SphingoMyelinase on listeriocidal activiy of
macrophages
Deficiency in the enzyme acid sphingomyelinase (ASMase) impairs the capacity of
macrophages to kill intracellular bacteria, e.g. Listeria monocytogenes. Here, we
analyzed the impact of deficiency in ASMase on antibacterial effector mechanisms in
macrophages.
The classical antibacterial effector mechanisms, i.e. generation of antimicrobial reactive
oxygen and nitrogen intermediates, was not altered in ASMase-deficient (ASMase -/- )
compared to wild type macrophages. In contrast, maturation of phagosomes containing
either vital Listeria monocytogenes or heat killed L. monocytogenes (HKLM) was
significantly impaired as indicated by reduced colocalization of bacteria with the
lysosomal marker protein lamp1 in ASMase -/- macrophages. Both vital L.
monocytogenes and HKLM showed a significantly prolonged colocalization with the late
phagosomal marker protein mannose-6-phosphate receptor. Thus, maturation of late
phagosomes containing L. monocytogenes into bactericidal phagolysosomes is impaired
in ASMase -/- macrophages. Consistently, the transfer of lysosomal fluid phase markers
into phagosomes containing HKLM was significantly reduced in ASMase -/- macrophages.
The transfer of lysosomal cargo of high molecluar weight was more impaired than that
of low molecular weight. Transfer of cathepsin D, a lysosomal protease involved in
bacterial degradation, from lysosomes to phagosomes containing L. monocytogenes was
markedly reduced in ASMase -/- compared to wild type cells. The reduced transfer of
lysosomal contents into phagosomes containing L. monocytogenes suggests that
ASMase regulates the fusion of phagosomes with lysosomes which is essentially
required for elimination of bacteria.