Mycobacterial Infection is Promoted by Neutral Sphingomyelinase 2 Regulating a Signaling Cascade Leading to Activation of β1-Integrin

Abstract

Background/Aims: Mycobacteria-induced diseases, especially tuberculosis, cause more than 1 million deaths each year, which is higher than any other single bacterial pathogen. Neutral sphingomyelinase 2 (Nsm2) has been implied in many physiological processes and diseases, but the role of Nsm2 in pathogen-host interactions and mycobacterial infections has barely been studied. Methods: We investigated the role of the Nsm2/ceramide system in systemic infection of mice and murine macrophages with Mycobacterium bovis Bacillus Calmette-Guérin (BCG) as a model for mycobacterial infection. For in vitro assays we isolated bone marrow-derived macrophages from Wildtype mice or Nsm2-heterozygous and investigated the role of Nsm2 for macrophage migration/clustering as well as the involvement of p38 mitogen-activated protein kinases (p38K), c-Jun N-terminal kinase (JNK), β1-integrin and Rac1 activity by Western blot and microscopic studies. For in vivo assays we injected mice intravenously with BCG and analyzed infected tissues for the role of Nsm2-mediated activation of β1-integrin in granuloma formation and bacterial burden. Results: Our results reveal that BCG infection of macrophages results in rapid stimulation of Nsm2. Genetic and pharmacological studies demonstrate that Nsm2 stimulates a signaling cascade via p38K and JNK to an activation of surface β1-integrin and Rac1 that leads to the formation of granuloma-like macrophages clusters in vitro and granuloma in vivo. Heterozygosity of Nsm2 in macrophages or antibody-mediated neutralization of active b1-integrin reduced macrophage clusters in vitro and granuloma formation in vivo. Most importantly, Nsm2 heterozygosity or treatment with neutralizing antibodies against β1-integrin protected mice from systemic BCG infections and chronic infections of the liver and spleen. Conclusion: The findings indicate that the Nsm2/ ceramide system plays an important role in systemic infection of mice with mycobacteria by regulating a signaling cascade via p38K, JNK, b1-integrin and Rac1.

Rac1 as a Target to Treat Dysfunctions and Cancer of the Bladder

“…A BCG-induced enhanced expression of Rac1 has been reported in a study with infected macrophages, both in vitro and in vivo. The mycobacteria activated the p38K/JNK/b1-integrin/Rac1 signaling cascade in the frame of the infection [ 59 ].…”

Above the Matrix: Functional Roles for Apically Localized Integrins

“…However, there are many open questions that need to be considered. For instance, there have been a handful of in vivo studies focusing on apical integrin function (Walsh et al, 2015;Grassme et al, 2017;Wu et al, 2018;Liu et al, 2020) as compared with the majority of the literature which uses cultured cell models.…”

Role of Neutral Sphingomyelinase-2 (NSM 2) in the Control of T Cell Plasma Membrane Lipid Composition and Cholesterol Homeostasis

“…Being most abundant in brain, NSM2 is also ubiquitously expressed including cells of the immune system. The role of NSM2 in cytokine (IL1-β, TNF-α, and IFN-γ) induced inflammation and bacterial infections is well established (Shamseddine et al, 2015; Wu et al, 2018) as is its role in cytotoxic effects of cancer chemotherapeutics. However, the involvement in pathogenesis and perpetuation of human tumors seems to be tumor specific (Bhati et al, 2008; Kim et al, 2008; Henry et al, 2013).…”