Activation of the Mitogen-Activated Protein Kinase Signaling Pathway Is Instrumental in Determining the Ability ofMycobacterium aviumto Grow in Murine Macrophages

Abstract

Of the two common morphotypes of Mycobacterium avium, designated smooth transparent (SmT) or smooth opaque (SmO), the SmO morphotype is avirulent, whereas the SmT morphotype is virulent. The role of the host macrophage in determining these different virulence phenotypes was analyzed using an in vitro model of macrophage infection. Initial studies confirmed previous reports of the increased ability of the SmT bacteria to grow in macrophages; this increased virulence correlated with reduced induction of inflammatory cytokines. Examination of the response of the mitogen-activated protein kinase (MAPK) pathway following infection with either morphotype revealed that all three members of the MAPK pathway were activated. Pharmacologic inhibition of either the extracellular signal-regulated kinase (ERK) or p38MAPK pathways resulted in distinct consequences for the growth of the two morphotypes. In particular, inhibition of the p38MAPK resulted in attenuated growth of the SmT morphotype, which correlated with reduced PGE2 production. Inhibition of cyclooxygenase 2 by indomethacin also inhibited growth of SmT, substantiating the role for PGE2 in promoting the growth of SmT. In contrast, SmO induction of the ERK pathway was increased compared with the SmT morphotype, and inhibition of ERK resulted in decreased TNF-α synthesis and enhanced SmO growth. Pharmacologic inhibitors of the MAPK pathway were present for only the first 4 h of infection and yet had consequences for bacterial growth at 7 days. Therefore, the data suggest that induction of the MAPK pathway during uptake of bacteria is instrumental in determining the eventual fate of the bacteria.

Macrophage’s Proinflammatory Response to a Mycobacterial Infection Is Dependent on Sphingosine Kinase-Mediated Activation of Phosphatidylinositol Phospholipase C, Protein Kinase C, ERK1/2, and Phosphatidylinositol 3-Kinase

“…PI3K is a conserved family of signaling molecules that are involved in regulating cellular proliferation and survival. Recent data suggest that the PI3K-Akt pathway is activated in macrophages upon mycobacterial infection or treatment with mycobacterial glycolipids (55)(56)(57). We show that PI3K activity, as defined by Akt phosphorylation, was activated at higher levels upon infection with M. smegmatis compared with M. avium-infected macrophages.…”

Extracellular Superoxide Dismutase in Macrophages Augments Bacterial Killing by Promoting Phagocytosis

“…28,29 Twenty-four hours before use, macrophages were washed and cultured with media lacking both antibiotics and L929 supplement. Peritoneal macrophages were isolated from the peritoneum via instillation and recovery of sterile PBS without calcium or magnesium.…”

“…28,29 Wild-type and EC-SOD KO cells and bacteria were incubated independently as controls. After 1 hour of incubation in a static tube, the bacteria remaining were cultured in Luria-Bertani agar using the pour plate method to determine the number of CFUs.…”

Endocytosis of Mycobacterium tuberculosis Heat Shock Protein 60 Is Required to Induce Interleukin-10 Production in Macrophages*

“…We and others have shown that p38 MAPK and ERK1/2 signalings are crucial in regulating the anti-inflammatory and pro-inflammatory cytokines in macrophages by mycobacterial components (38, 60 -67). It has been reported that activation of p38 MAPK plays a critical role for IL-10 production (62, 66), whereas TNF-␣ secretion is predominantly dependent on ERK1/2 activation in macrophages (11,61). Therefore, we compared the phosphorylation status of p38 MAPK and ERK1/2 in situations where Mtbhsp60 is endocytosed by interacting with TLR2 and thereby resulting in dominant production of IL-10 to situations where it is predominantly sequestered on the cell surface, like interactions with TLR4 or with TLR2 in the presence of MDC, resulting in increased production of TNF-␣.…”