Role of neutral sphingomyelinase in mycobacterial infections
Final Report Abstract
In the present grant we aimed to investigate the role of sphingolipids in BCG infections. Specifically, we studied (i) molecular mechanisms of the regulation of autophagy by the neutral sphingomyelinase after BCG infections, (ii) the topology of ceramide and identification of binding proteins of ceramide upon infection with BCG, (iii) the role of caveolin-1 in BCG infection, (iv) the role of neutral sphingomyelinase in the formation of granulomas and the regulation of integrin functions upon infections with BCG and (v) the role of sphingosine in BCG infections. We demonstrated an important role of the neutral sphingomyelinase-2 in BCG infection of macrophages leading via p38 and JNK to an activation of surface β1-integrin finally granuloma formation. Heterozygosity of neutral sphingomyelinase-2 or neutralization of β1- integrin with antibodies against β1-integrin prevented granuloma formation, and promoted killing of the bacteria in vitro and in vivo suggesting that neutral sphingomyelinase-2- mediated formation of granuloma is a protective niche for Mycobacteria during chronic infection. We further demonstrated that the neutral sphingomyelinase regulates activation of the acid sphingomyelinase and expression of caveolin-1 upon BCG infection and thereby signalling cascades leading to increased release of reactive oxygen species, upregulation of lysosomal v-ATPase, cathepsin D and BCG killing as well as autophagy and Rac-1 activation. Thus, the neutral sphingomyelinase regulates pathways (acid sphingomyelinase) that promote killing of the pathogen, but also provide a niche for the pathogen (granuloma formation). It remains to be determined how these outcomes are balanced. In addition to studies on the role of sphingomyelinase in BCG infections, we investigated the function of sphingosine in mycobacterial infections. We show that sphingosine functions as a novel natural defense mechanism in macrophages against mycobacterial infections. Infection of macrophages results in a very rapid, i.e. within minutes, release of sphingosine in macrophages. Sphingosine is released from infected macrophages and incorporated into BCG. Sphingosine induces a very rapid, i.e. within seconds to minutes, permeabilization of the bacterial membrane resulting in a loss of membrane potential and ATP and killing of the pathogen. While the endogenous release of sphingosine is sufficient to kill a low number of infecting BCG, but is overwhelmed by higher numbers of BCG, addition of exogenous sphingosine is able to kill BCG completely at concentrations between 5 µM and 10 µM, concentrations that are without adverse effects on the macrophages. Most importantly, inhalation of sphingosine is sufficient to eliminate BCG in the lung of mice in (sub-)chronic model of mycobacterial infection.
Publications
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Bioactive Lipids and Redox Signaling: Molecular mechanism and disease pathogenesis. Antioxid Redox Signal 2018;125:651-672
Li PL, Gulbins E
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Crosstalk between sphingomyelinases and reactive oxygen species in mycobacterial infection. Antioxid Redox Signal Antioxid Redox Signal 2018;28: 935-948
Wu Y, Gulbins E, Grassmé H
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Mycobacterial infection is promoted by neutral sphingomyelinase 2 regulating a signaling cascade leading to activation of β1-Integrin. Cell Physiol Biochem 2018;51:1815-1829
Wu Y, Li C, Riehle A, Pollmeier B, Gulbins E, Grassmé H
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The function of sphingomyelinases in mycobacterial infections. Biol Chem 2018; 399: 1125-1133
Wu Y, Gulbins E, Grassmé H
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Acid sphingomyelinase-ceramide system in bacterial infections. Cell Physiol Biochem 2019;52:280-301
Li C, Wang A, Wu Y, Gulbins E, Grassmé H, Zhao Z
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Acid sphingomyelinase contributes to the control of mycobacterial infection via a signaling cascade leading from reactive oxygen species to cathepsin D. Cells 9:E2406
Wu Y, Li C, Peng H, Swaidan A, Riehle A, Pollmeier B, Zhang Y, Gulbins E, Grassmé H
