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Acinetobacter baumannii outer membrane protein A induces autophagy in bone marrow-derived dendritic cells involving

Hongyi Tan¹, Liyan Cao²

¹Department of Pulmonary and Critical Care Medicine, Huizhou Central People's Hospital, Guangdong Medical University, Huizhou, China.

Immunity, Inflammation and Disease

|April 27, 2023

Abstract

Background:

Outer membrane protein A (OmpA) is the major virulence factor of Acinetobacter baumannii and plays a wide role in the pathogenesis and antimicrobial resistance of A. baumannii. Dendritic cells (DCs) are the most effective antigen-presenting cells and play a crucial role in regulating the immune response to multiple antigens and immune sentries. We aimed to study the role and molecular mechanisms of OmpA-induced mouse bone marrow-derived dendritic cells (BMDCs) autophagy in the immune response of A. baumannii.

Methods:

First, purified A. baumannii OmpA was assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blot. OmpA effect on BMDCs viability was evaluated by MTT assay. BMDCs were pretreated with autophagy inhibitor chloroquine or transfected with overexpression plasmids (oe-NC or oe-PI3K). Then BMDCs apoptosis, inflammatory cytokines, protein kinase B (PI3K)/mammalian target of rapamycin (mTOR) pathway, and autophagy-related factors levels were evaluated.

Results:

SDS-PAGE and western blot verified the successful purification of OmpA. BMDCs viability repressed gradually with the increase of OmpA concentration. OmpA treatment of BMDCs led to apoptosis and inflammation in BMDCs. OmpA caused incomplete autophagy in BMDCs, and light chain 3 (LC3), Beclin1, P62, and LC3II/I levels were significantly elevated with the increase of the time and concentration of OmpA treatment. Chloroquine reversed OmpA effects on autophagy in BMDCs, that was, LC3, Beclin1, and LC3II/I levels were reduced, while P62 level was elevated. Furthermore, chloroquine reversed OmpA effects on apoptosis and inflammation in BMDCs. PI3K/mTOR pathway-related factor expression was affected by OmpA treatment of BMDCs. After overexpression of PI3K, these effects were reversed.

Conclusions:

A. baumannii OmpA induced autophagy in BMDCs involving the PI3K/mTOR pathway. Our study may provide a novel therapeutic target and theoretical basis for treating infections caused by A. baumannii.

Insights

Acinetobacter baumannii outer membrane protein A (OmpA) triggers autophagy in dendritic cells via the PI3K/mTOR pathway, offering a potential target for treating bacterial infections.

Area of Science:

Immunology
Microbiology
Cell Biology

Background:

Outer membrane protein A (OmpA) is a key virulence factor in Acinetobacter baumannii, contributing to pathogenesis and antibiotic resistance.
Dendritic cells (DCs) are crucial antigen-presenting cells that orchestrate immune responses.
Understanding OmpA's interaction with DCs is vital for developing effective treatments.

Purpose of the Study:

To investigate the role of OmpA in inducing autophagy in mouse bone marrow-derived dendritic cells (BMDCs).
To elucidate the molecular mechanisms underlying OmpA-induced autophagy in the context of A. baumannii infection.
To explore the implications for immune response modulation and therapeutic strategies.

Main Methods:

Purification and verification of Acinetobacter baumannii OmpA using SDS-PAGE and Western blot.
Assessment of OmpA's impact on BMDC viability (MTT assay) and apoptosis.
Evaluation of autophagy markers (LC3, Beclin1, P62), inflammatory cytokines, and the PI3K/mTOR pathway, with and without autophagy inhibitors (chloroquine) or PI3K overexpression.

Main Results:

OmpA treatment reduced BMDC viability and induced apoptosis and inflammation.
OmpA triggered incomplete autophagy, evidenced by altered levels of LC3, Beclin1, and P62.
Autophagy inhibition or PI3K overexpression reversed OmpA's effects on apoptosis, inflammation, and autophagy.
OmpA modulated the PI3K/mTOR pathway, influencing autophagy induction.

Conclusions:

Acinetobacter baumannii OmpA induces autophagy in dendritic cells through the PI3K/mTOR signaling pathway.
This OmpA-induced autophagy plays a significant role in the immune response to A. baumannii.
The findings suggest OmpA as a potential therapeutic target for A. baumannii infections.

Read full analysis

Keywords:

Acinetobacter baumannii BMDCs OmpA PI3K/mTOR pathway autophagy

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