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Updated: Jun 2, 2026
Isolation and In Vitro Culture of Murine and Human Alveolar Macrophages
Published on: April 20, 2018
PTEN limits alveolar macrophage function against Pseudomonas aeruginosa after bone marrow transplantation
Leah L N Hubbard1, Carol A Wilke, Eric S White
1Department of Internal Medicine, Division of Pulmonary and Critical Care Medicine, USA. bmoore@umich.edu
Abstract:
Hematopoietic stem cell transplant patients are susceptible to infection despite cellular reconstitution. In a murine model of syngeneic bone marrow transplantation (BMT), we previously reported that BMT mice have impaired host defense against Pseudomonas aeruginosa pneumonia due to overproduction of (PG)E(2) in lung. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is an effector in the PGE(2) signaling pathway that negatively regulates alveolar macrophage (AM) phagocytosis and bacterial killing. Therefore, examined whether overproduction of PGE(2) after BMT inhibits AM host defense by up-regulating PTEN phosphatase activity. We found that PTEN activity is elevated in BMT AMs in response to increased PGE(2) signaling and that pharmacological inhibition of PTEN activity in BMT AMs fully restores phagocytosis of serum-opsonized P. aeruginosa but only partially restores phagocytosis of nonopsonized P. aeruginosa. In wild-type mice transplanted with myeloid-specific conditional PTEN knockout (PTEN CKO) bone marrow, bacterial clearance is improved after challenge with P. aeruginosa pneumonia. Furthermore, PTEN CKO BMT AMs display improved TNF-α production and enhanced phagocytosis and killing of serum-opsonized P. aeruginosa despite overproduction of PGE(2). However, AM phagocytosis of nonopsonized P. aeruginosa is only partially restored in the absence of PTEN after BMT. This may be related to elevated AM expression of IL-1 receptor-associated kinase (IRAK)-M, a molecule previously identified in the PGE(2) signaling pathway to inhibit AM phagocytosis of nonopsonized bacteria. These data suggest that PGE(2) signaling up-regulates IRAK-M independently of PTEN and that these molecules differentially inhibit opsonized and nonopsonized phagocytosis of P. aeruginosa.
Insights
Hematopoietic stem cell transplant recipients have weakened defenses against Pseudomonas aeruginosa pneumonia. Targeting PTEN (phosphatase and tensin homolog deleted on chromosome 10) enhances alveolar macrophage function, improving bacterial clearance.
Area of Science:
- Immunology
- Microbiology
- Transplantation
Background:
- Hematopoietic stem cell transplant (HSCT) patients remain vulnerable to infections, including Pseudomonas aeruginosa pneumonia, even after immune reconstitution.
- Previous studies in murine models demonstrated that bone marrow transplantation (BMT) impairs host defense against P. aeruginosa due to elevated lung prostaglandin E2 (PGE2) production.
- Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is identified as a key regulator in the PGE2 signaling pathway, negatively impacting alveolar macrophage (AM) phagocytosis and bacterial killing.
Purpose of the Study:
- To investigate whether elevated PGE2 production post-BMT inhibits AM-mediated host defense by increasing PTEN phosphatase activity.
- To determine the role of PTEN in AM phagocytosis and bacterial clearance of P. aeruginosa following BMT.
- To explore the differential effects of PTEN inhibition on the phagocytosis of opsonized versus non-opsonized P. aeruginosa.
Main Methods:
- Murine model of syngeneic bone marrow transplantation (BMT).
- Assessment of PTEN phosphatase activity in alveolar macrophages (AMs) from BMT mice.
- Pharmacological inhibition of PTEN activity in BMT AMs.
- Utilized myeloid-specific conditional PTEN knockout (PTEN CKO) bone marrow in wild-type mice undergoing BMT.
- Quantification of bacterial clearance and TNF-α production in response to P. aeruginosa challenge.
- Analysis of IL-1 receptor-associated kinase (IRAK)-M expression in AMs.
Main Results:
- PTEN activity was significantly elevated in AMs from BMT mice, correlating with increased PGE2 signaling.
- Pharmacological inhibition of PTEN fully restored phagocytosis of serum-opsonized P. aeruginosa but only partially restored non-opsonized P. aeruginosa by BMT AMs.
- BMT with PTEN CKO bone marrow improved bacterial clearance and enhanced phagocytosis and killing of opsonized P. aeruginosa, despite elevated PGE2.
- Elevated IRAK-M expression in PTEN CKO BMT AMs was observed, suggesting independent regulation by PGE2 and a role in limiting non-opsonized bacterial phagocytosis.
Conclusions:
- PGE2 signaling up-regulates PTEN activity in AMs post-BMT, impairing host defense against P. aeruginosa.
- PTEN inhibition partially restores AM phagocytosis of non-opsonized P. aeruginosa, suggesting other inhibitory pathways are involved.
- PGE2 also up-regulates IRAK-M independently of PTEN, contributing to the impaired clearance of non-opsonized bacteria, highlighting differential mechanisms affecting bacterial clearance post-transplant.
