Role of lipids in killing mycobacteria by macrophages: evidence for NF-κB-dependent and -independent killing induced by different lipids

Abstract

SummaryWe have shown that several lipids can modulate the macrophage innate immune response against mycobacteria and enhance their killing. Since NF-kB is required for mycobacterial killing, we tested the ability of lipids to activate NF-kB in uninfected macrophages and those infected with mycobacteria. In uninfected cells, sphingomyelin (SM), phosphatidylinositol-4-phosphate (PIP) and arachidonic acid (AA) enhanced NF-kB activation and the cell surface expression of CD69, a macrophage activation marker regulated by NF-kB. Sphingosine (Sph), sphingosine-1-phosphate (S1P), diacylglycerol (DAG), eicosapentanoic acid (EPA) and phosphatidyl choline (PC) failed to activate either NF-kB or CD69. Ceramide (Cer) activated CD69 expression without activating NF-kB. In Mycobacterium smegmatis-infected cells, NF-kB was transiently activated in a manner that was enhanced by SM, PIP and AA. In contrast Mycobacterium avium mostly repressed NF-kB activation and only SM and AA could induce its partial activation. While lipids that activate NF-kB in uninfected cells tend to kill mycobacteria in macrophages Sph and S1P failed to activate NF-kB under most conditions but nevertheless enhanced killing of M. smegmatis, M. avium and M. tuberculosis H37Rv. Our results argue that both NF-kB-dependent and -independent mechanisms are involved in macrophage killing of mycobacteria and that both mechanisms can be enhanced by selected lipids.

Comprehensive Proteomic and Metabolomic Signatures of Nontypeable Haemophilus influenzae-Induced Acute Otitis Media Reveal Bacterial Aerobic Respiration in an Immunosuppressed Environment

“…Reduction in the content of PC aa in the gastrointestinal mucosae leads to increased invasion of pathogens (118). PC aa derivatives in the plasma membrane inhibit actin polymerization, inhibit phagosomal actin assembly, stimulate Mycobacterium survival in phagosomes, and increase nitric oxide production (78,118,119). These PC aa functions are also complementary with the proposed increase in actin rearrangements suggested by the proteomics analysis (Fig.…”

Regulation of macrophage function by sphingosine-1-phosphate

“…Although extracellular application of S1P would suggest a receptor-mediated mechanism in mycobacterial killing, the concentrations of S1P showing significant effects in this study were generally high (45 mM) thus, opening the possibility that effects could also be mediated by membrane-surpassed S1P or by activation of nonspecific receptors (Shikata et al 2003). Nevertheless, the mycobacteriocidal effect of exogenously added S1P was later confirmed at doses of 100 nM (Gutierrez et al 2009). Interestingly, S1P did not activate nuclear factorkB (NF-kB) to kill intracellular pathogens, although inducing an altered cytosolic distribution pattern of p65.…”

“…Interestingly, S1P did not activate nuclear factorkB (NF-kB) to kill intracellular pathogens, although inducing an altered cytosolic distribution pattern of p65. In comparison to unstimulated macrophages, p65 colocalized with cortical actin after S1P treatment (Gutierrez et al 2009). This might be a way to prevent NF-kB activation, as suggested previously (Zhu et al 1998).…”

Mucosal Protection by Phosphatidylcholine

“…The mechanism of action of PC is not entirely clear, but there is evidence that via PC, the p65 subunit can interact with F-actin and, thus, prevent NF-ĸB activation [32,33]. …”