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The role of Mcl-1 in S. aureus-induced cytoprotection of infected macrophages.

Koziel J, Kmiecik K, Chmiest D, Maresz K, Mizgalska D, Maciag-Gudowska A, Mydel P, Potempa J - Mediators Inflamm. (2013)

Bottom Line: Consistent with this, we proved a crucial role of Mcl-1 in S. aureus-induced cytoprotection, since silencing of MCL1 by siRNA profoundly reversed the cytoprotection of infected cells leading to apoptosis.Increased MCL1 expression in infected cells was associated with enhanced NFκB activation and subsequent IL-6 secretion, since the inhibition of both NFκB and IL-6 signalling pathways abrogated Mcl-1 induction and cytoprotection.Finally, we confirmed our observation in vivo in murine model of septic arthritis showing the association between the severity of arthritis and Mcl-1 expression.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Ul. Gronostajowa 7, 30-387 Kraków, Poland. joanna.koziel@uj.edu.pl

ABSTRACT
As a facultative intracellular pathogen, Staphylococcus aureus invades macrophages and then promotes the cytoprotection of infected cells thus stabilizing safe niche for silent persistence. This process occurs through the upregulation of crucial antiapoptotic genes, in particular, myeloid cell leukemia-1 (MCL-1). Here, we investigated the underlying mechanism and signal transduction pathways leading to increased MCL-1 expression in infected macrophages. Live S. aureus not only stimulated de novo synthesis of Mcl-1, but also prolonged the stability of this antiapoptotic protein. Consistent with this, we proved a crucial role of Mcl-1 in S. aureus-induced cytoprotection, since silencing of MCL1 by siRNA profoundly reversed the cytoprotection of infected cells leading to apoptosis. Increased MCL1 expression in infected cells was associated with enhanced NFκB activation and subsequent IL-6 secretion, since the inhibition of both NFκB and IL-6 signalling pathways abrogated Mcl-1 induction and cytoprotection. Finally, we confirmed our observation in vivo in murine model of septic arthritis showing the association between the severity of arthritis and Mcl-1 expression. Therefore, we propose that S. aureus is hijacking the Mcl-1-dependent inhibition of apoptosis to prevent the elimination of infected host cells, thus allowing the intracellular persistence of the pathogen, its dissemination by infected macrophages, and the progression of staphylococci diseases.

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Exposure to S. aureus triggers Mcl-1 production in vivo. (a) Immunoblot reveals increase in Mcl-1 expression in inflamed joints derived from three individual S. aureus-infected mice (Sa) in comparison to noninfected animals (Veh.). A representative immunoblot from three separate experiments is shown. (b) The expression of Mcl-1 in joints correlates with infection score and bacterial load determined as described in Section 2. Data represents Mcl-1 levels in noninfected (Veh.; n = 6) and S. aureus-infected (Sa; n = 6) animals, obtained by densitometric analyses of western blots.
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fig3: Exposure to S. aureus triggers Mcl-1 production in vivo. (a) Immunoblot reveals increase in Mcl-1 expression in inflamed joints derived from three individual S. aureus-infected mice (Sa) in comparison to noninfected animals (Veh.). A representative immunoblot from three separate experiments is shown. (b) The expression of Mcl-1 in joints correlates with infection score and bacterial load determined as described in Section 2. Data represents Mcl-1 levels in noninfected (Veh.; n = 6) and S. aureus-infected (Sa; n = 6) animals, obtained by densitometric analyses of western blots.

Mentions: S. aureus is the causative agent in about 60% of nongonococcal bacterial arthritis cases, a disease characterized among others by robust influx of macrophages and their sustain activation in joints [15, 16]. Therefore, we determined Mcl-1 expression in inflamed joints in the previously established murine model of S. aureus arthritis [17]. To this end DBA1 mice were injected i.v. with 5 × 107 CFU, a dose causing a low mortality rate (see Supplementary Figure 1(a) in Supplementary Material available online at http://dx.doi.org/10.1155/2013/427021). At day 8 after injection all animals showed clear symptoms of arthritis (Supplementary Figure 1(b)). Bacteriological examination of joints, spleen, and kidneys revealed the abundant load of S. aureus in 100% of mice (Supplementary Figure 1(c)). This finding correlates with inflammatory response manifested by IL-6 secretion (Supplementary Figure 1(d)) and splenomegaly (data not shown). Further investigation of the relationship between both clinical and bacteriological signs of arthritis and Mcl-1 expression in joints revealed the significant association (Figures 3(a) and 3(b)). We found Mcl-1 expression being significantly upregulated in S. aureus-positive joints (32.83 ± 7.94-fold above the control level) in comparison to noninfected tissues (4.29 ± 0.82-fold above the control level, P < 0.001). Furthermore, we also observed positive association between the Mcl-1 expression level and bacterial load in joints. This indicates that S. aureus induced Mcl-1 expression also in vivo in the inflamed tissue.


The role of Mcl-1 in S. aureus-induced cytoprotection of infected macrophages.

Koziel J, Kmiecik K, Chmiest D, Maresz K, Mizgalska D, Maciag-Gudowska A, Mydel P, Potempa J - Mediators Inflamm. (2013)

Exposure to S. aureus triggers Mcl-1 production in vivo. (a) Immunoblot reveals increase in Mcl-1 expression in inflamed joints derived from three individual S. aureus-infected mice (Sa) in comparison to noninfected animals (Veh.). A representative immunoblot from three separate experiments is shown. (b) The expression of Mcl-1 in joints correlates with infection score and bacterial load determined as described in Section 2. Data represents Mcl-1 levels in noninfected (Veh.; n = 6) and S. aureus-infected (Sa; n = 6) animals, obtained by densitometric analyses of western blots.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3569898&req=5

fig3: Exposure to S. aureus triggers Mcl-1 production in vivo. (a) Immunoblot reveals increase in Mcl-1 expression in inflamed joints derived from three individual S. aureus-infected mice (Sa) in comparison to noninfected animals (Veh.). A representative immunoblot from three separate experiments is shown. (b) The expression of Mcl-1 in joints correlates with infection score and bacterial load determined as described in Section 2. Data represents Mcl-1 levels in noninfected (Veh.; n = 6) and S. aureus-infected (Sa; n = 6) animals, obtained by densitometric analyses of western blots.
Mentions: S. aureus is the causative agent in about 60% of nongonococcal bacterial arthritis cases, a disease characterized among others by robust influx of macrophages and their sustain activation in joints [15, 16]. Therefore, we determined Mcl-1 expression in inflamed joints in the previously established murine model of S. aureus arthritis [17]. To this end DBA1 mice were injected i.v. with 5 × 107 CFU, a dose causing a low mortality rate (see Supplementary Figure 1(a) in Supplementary Material available online at http://dx.doi.org/10.1155/2013/427021). At day 8 after injection all animals showed clear symptoms of arthritis (Supplementary Figure 1(b)). Bacteriological examination of joints, spleen, and kidneys revealed the abundant load of S. aureus in 100% of mice (Supplementary Figure 1(c)). This finding correlates with inflammatory response manifested by IL-6 secretion (Supplementary Figure 1(d)) and splenomegaly (data not shown). Further investigation of the relationship between both clinical and bacteriological signs of arthritis and Mcl-1 expression in joints revealed the significant association (Figures 3(a) and 3(b)). We found Mcl-1 expression being significantly upregulated in S. aureus-positive joints (32.83 ± 7.94-fold above the control level) in comparison to noninfected tissues (4.29 ± 0.82-fold above the control level, P < 0.001). Furthermore, we also observed positive association between the Mcl-1 expression level and bacterial load in joints. This indicates that S. aureus induced Mcl-1 expression also in vivo in the inflamed tissue.

Bottom Line: Consistent with this, we proved a crucial role of Mcl-1 in S. aureus-induced cytoprotection, since silencing of MCL1 by siRNA profoundly reversed the cytoprotection of infected cells leading to apoptosis.Increased MCL1 expression in infected cells was associated with enhanced NFκB activation and subsequent IL-6 secretion, since the inhibition of both NFκB and IL-6 signalling pathways abrogated Mcl-1 induction and cytoprotection.Finally, we confirmed our observation in vivo in murine model of septic arthritis showing the association between the severity of arthritis and Mcl-1 expression.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Ul. Gronostajowa 7, 30-387 Kraków, Poland. joanna.koziel@uj.edu.pl

ABSTRACT
As a facultative intracellular pathogen, Staphylococcus aureus invades macrophages and then promotes the cytoprotection of infected cells thus stabilizing safe niche for silent persistence. This process occurs through the upregulation of crucial antiapoptotic genes, in particular, myeloid cell leukemia-1 (MCL-1). Here, we investigated the underlying mechanism and signal transduction pathways leading to increased MCL-1 expression in infected macrophages. Live S. aureus not only stimulated de novo synthesis of Mcl-1, but also prolonged the stability of this antiapoptotic protein. Consistent with this, we proved a crucial role of Mcl-1 in S. aureus-induced cytoprotection, since silencing of MCL1 by siRNA profoundly reversed the cytoprotection of infected cells leading to apoptosis. Increased MCL1 expression in infected cells was associated with enhanced NFκB activation and subsequent IL-6 secretion, since the inhibition of both NFκB and IL-6 signalling pathways abrogated Mcl-1 induction and cytoprotection. Finally, we confirmed our observation in vivo in murine model of septic arthritis showing the association between the severity of arthritis and Mcl-1 expression. Therefore, we propose that S. aureus is hijacking the Mcl-1-dependent inhibition of apoptosis to prevent the elimination of infected host cells, thus allowing the intracellular persistence of the pathogen, its dissemination by infected macrophages, and the progression of staphylococci diseases.

Show MeSH
Related in: MedlinePlus