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ß-adrenergic stimulation increases macrophage CD14 expression and E. coli phagocytosis through PKA signaling mechanisms.

ABSTRACT: CD14 is a glycoprotein that binds bacterial LPS in MØ. It is an essential component of the phagocytic system and is increased in septic shock. Critical injury and sepsis result in elevated endogenous CA levels. CAs have a significant impact on MØ inflammatory functions. We tested the hypothesis that ?-adrenergic stimulation regulates CD14 expression and bacterial phagocytosis in BMØ. Murine BMØ stimulated with isoproterenol (>8 h) induced a dose-dependent increase in cell surface CD14 expression. Specific PKA inhibitor (H-89) and gene-silencing (siRNA) studies demonstrated the role of cAMP-dependent PKA in mediating this response. In addition, we observed a correlation between an isoproterenol-mediated increase in CD14 expression and live Escherichia coli uptake in BMØ. Further, the essential role of CD14 in an isoproterenol-mediated increase in E. coli uptake was highlighted from experiments using CD14(-/-) mice. Moreover, the dose response of isoproterenol stimulation to CD14 expression and E. coli phagocytosis overlapped with similar EC50. Additionally, isoproterenol-mediated E. coli phagocytosis was prevented by H-89, suggesting that ?-adrenergic stimulus in BMØ increases CD14 expression and live E. coli phagocytosis through a common signaling pathway. Our studies indicate the potential impact of ?-adrenergic agents on important innate immune functions.

SUBMITTER: Muthu K

PROVIDER: S-EPMC2974431 | biostudies-literature | 2010 Oct

REPOSITORIES: biostudies-literature

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ß-adrenergic stimulation increases macrophage CD14 expression and E. coli phagocytosis through PKA signaling mechanisms.

Muthu Kuzhali K He Li-K LK Szilagyi Andrea A Strotmon Patrick P Gamelli Richard L RL Shankar Ravi R

Journal of leukocyte biology 20100719 4

CD14 is a glycoprotein that binds bacterial LPS in MØ. It is an essential component of the phagocytic system and is increased in septic shock. Critical injury and sepsis result in elevated endogenous CA levels. CAs have a significant impact on MØ inflammatory functions. We tested the hypothesis that β-adrenergic stimulation regulates CD14 expression and bacterial phagocytosis in BMØ. Murine BMØ stimulated with isoproterenol (>8 h) induced a dose-dependent increase in cell surface CD14 expression ...[more]

PMID: 20643814

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Project description:Acute lung injury (ALI) is a common clinical emergency and all‑trans retinoic acid (ATRA) can alleviate organ injury. Therefore, the present study investigated the role of ATRA in ALI. Lipopolysaccharide (LPS)‑induced ALI rats were treated with ATRA and the arterial partial pressure of oxygen (PaO2), lung wet/dry weight (W/D) ratio and protein content in the bronchial alveolar lavage fluid (BALF) were measured to evaluate the effect of ATRA on ALI rats. Alveolar macrophages were isolated from the BALF. The phagocytic function of macrophages was detected using the chicken erythrocyte phagocytosis method and flow cytometry. The viability of macrophages was measured using a Cell Counting Kit‑8 assay, and apoptosis was analyzed using a TUNEL assay and flow cytometry. The expression levels of Toll‑like receptor 4 (TLR4) and cluster of differentiation (CD)14 on the macrophage membrane were detected by immunofluorescence staining. The protein levels of TLR4, CD14, phosphorylated (p)‑65, p65, p‑IκBα and IκBα were analyzed using western blotting. The concentrations of IL‑6, IL‑1β and macrophage inflammatory protein‑2 in the plasma of rats were detected by ELISA. Macrophages were treated with IAXO‑102 (TLR4 inhibitor) to verify the involvement of CD14/TLR4 in the effect of ATRA on ALI. ATRA provided protection against LPS‑induced ALI, as evidenced by the increased PaO2 and reduced lung W/D ratio and protein content in the BALF. ATRA enhanced macrophage phagocytosis and viability and reduced apoptosis and inflammation in ALI rats. Mechanically, ATRA inhibited CD14 and TLR4 expression and NF‑κB pathway activation. ATRA enhanced macrophage phagocytosis and reduced inflammation by inhibiting the CD14/TLR4‑NF‑κB pathway in LPS‑induced ALI. In summary, ATRA inactivated the NF‑κB pathway by inhibiting the expression of CD14/TLR4 receptor in the alveolar macrophages of rats, thus enhancing the phagocytic function of macrophages in ALI rats, improving the activity of macrophages, inhibiting apoptosis, reducing the levels of inflammatory factors, and consequently playing a protective role in ALI model rats. This study may offer novel insights for the clinical management of ALI.

Project description:Enterotoxigenic E. coli (ETEC) are endemic in low-resource settings and cause robust secretory diarrheal disease in children less than five years of age. ETEC cause secretory diarrhea by producing the heat-stable (ST) and/or heat-labile (LT) enterotoxins. Recent studies have shown that ETEC can be carried asymptomatically in children and adults, but how ETEC subvert mucosal immunity to establish intestinal residency remains unclear. Macrophages are innate immune cells that can be exploited by enteric pathogens to evade mucosal immunity, so we interrogated the ability of ETEC and other E. coli pathovars to survive within macrophages. Using gentamicin protection assays, we show that ETEC H10407 is phagocytosed more readily than other ETEC and non-ETEC isolates. Furthermore, we demonstrate that ETEC H10407, at high bacterial burdens, causes nitrite accumulation in macrophages, which is indicative of a proinflammatory macrophage nitric oxide killing response. However, at low bacterial burdens, ETEC H10407 remains viable within macrophages for an extended period without nitrite accumulation. We demonstrate that LT, but not ST, intoxication decreases the number of ETEC phagocytosed by macrophages. Furthermore, we now show that macrophages exposed simultaneously to LPS and LT produce IL-33, which is a cytokine implicated in promoting macrophage alternative activation, iron recycling, and intestinal repair. Lastly, iron restriction using deferoxamine induces IL-33 receptor (IL-33R) expression and allows ETEC to escape macrophages. Altogether, these data demonstrate that LT provides ETEC with the ability to decrease the perceived ETEC burden and suppresses the initiation of inflammation. Furthermore, these data suggest that host IL-33/IL-33R signaling may augment pathways that promote iron restriction to facilitate ETEC escape from macrophages. These data could help explain novel mechanisms of immune subversion that may contribute to asymptomatic ETEC carriage.

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ß-adrenergic stimulation increases macrophage CD14 expression and E. coli phagocytosis through PKA signaling mechanisms.

Publications

ß-adrenergic stimulation increases macrophage CD14 expression and E. coli phagocytosis through PKA signaling mechanisms.

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