Myeloid PTEN Promotes Inflammation but Impairs Bactericidal Activities during Murine Pneumococcal Pneumonia

Abstract

Phosphatidylinositol 3-kinase has been described as an essential signaling component involved in the chemotactic cell influx that is required to eliminate pathogens. At the same time, PI3K was reported to modulate the immune response, thus limiting the magnitude of acute inflammation. The precise role of the PI3K pathway and its endogenous antagonist phosphatase and tensin homolog deleted on chromosome 10 (PTEN) during clinically relevant bacterial infections is still poorly understood. Utilizing mice lacking myeloid cell-specific PTEN, we studied the impact of PTEN on the immune response to Streptococcus pneumoniae. Survival analysis disclosed that PTEN-deficient mice displayed less severe signs of disease and prolonged survival. The inflammatory response to S. pneumoniae was greatly reduced in macrophages in vitro and in vivo. Unexpectedly, neutrophil influx to the lungs was significantly impaired in animals lacking myeloid-cell PTEN, whereas the additional observation of improved phagocytosis by alveolar macrophages lacking PTEN ultimately resulted in unaltered lung CFUs following bacterial infection. Together, the absence of myeloid cell-associated PTEN and consecutively enhanced PI3K activity dampened pulmonary inflammation, reduced neutrophil influx, and augmented phagocytic properties of macrophages, which ultimately resulted in decreased tissue injury and improved survival during murine pneumococcal pneumonia.

Role for B-cell adapter for PI3K (BCAP) as a signaling adapter linking Toll-like receptors (TLRs) to serine/threonine kinases PI3K/Akt

“…Genetic evidence, however, suggests that PI3K activation is involved in dampening the proinflammatory profile of both macrophages and dendritic cells (20,21,32). To investigate if BCAP links TLR signaling and PI3K activation, we examined the phosphorylation status of the downstream kinase, Akt, following activation of TLR2, TLR4, and TLR9.…”

Toll-like receptors, signaling adapters and regulation of the pro-inflammatory response by PI3K

“…60,64,65 Consequently, in a pneumococcal pneumonia model, mice deficient for PTEN in the myeloid compartment have less Tnf, Il6 and Cxcl1 (also known as KC), but more Il10 in their bronchiolar lavage fluid. 66 This phenotype corresponded with increased phagocytosis and elimination of intracellular bacteria by alveolar macrophages infected in vitro with Streptococcus pneumonia. 66 In contrast, Kuroda, et al found a requisite role for PTEN in elimination of Leishmania parasites in vivo in a manner suggested to be dependent upon Tnf-mediated other studies advocated a role for PI3K in inhibiting the inflammatory response.…”

“…66 This phenotype corresponded with increased phagocytosis and elimination of intracellular bacteria by alveolar macrophages infected in vitro with Streptococcus pneumonia. 66 In contrast, Kuroda, et al found a requisite role for PTEN in elimination of Leishmania parasites in vivo in a manner suggested to be dependent upon Tnf-mediated other studies advocated a role for PI3K in inhibiting the inflammatory response. [5][6][7] These discrepancies may be incompletely explained by usage of different pharmacological inhibitors as well as non-standard dosages.…”

The functions of tumor suppressor PTEN in innate and adaptive immunity

“…75 In addition, it can enhance GKS3β activation and thus promote an inflammatory response to TLR agonists in macrophages. 73 Kamo et al 76 found that the knockdown of PTEN could promote AKT/β-catenin/Foxol signaling and could down-regulate TLR4 expression in mouse liver cells responding to ischemia/reperfusion injury. The same signaling pathway may also trigger highmobility group box 1-mediated innate immune response in acute lung injury.…”

“…Deletion of PTEN in myeloid cells could enhance macrophage phagocytosis, reduce pulmonary neutrophil influx, diminish TNF-α, increase IL-10 and improve survival after S. pneumonia infection. 73 In addition, PTEN acts as an important regulator of NK cell localization. Leong et al found that in an NK cellspecific Pten-deletion mouse model, there was a significant expansion of peripheral blood NK cells and the premature egress of NK cells from the bone marrow due to selective hyper-responsiveness to the blood localizing chemokine sphingosine 1-phosphate.…”