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Chlamydia psittaci Plasmid-Encoded CPSIT_P7 Elicits Inflammatory Response in Human Monocytes via TLR4/Mal/MyD88/NF-κB
Qian Chen1,2, Yumeng Li1,3, Xiaoliang Yan1
1Institution of Pathogenic Biology, Hengyang Medical College, University of South China, Hunan Provincial Key Laboratory for Special Pathogens Prevention and Control, Hunan Province Cooperative Innovation Center for Molecular Target New Drug Study, University of South China, Hengyang, China.
Abstract:
The chlamydial plasmid, an essential virulence factor, encodes plasmid proteins that play important roles in chlamydial infection and the corresponding immune response. However, the virulence factors and the molecular mechanisms of Chlamydia psittaci are not well understood. In the present study, we investigated the roles and mechanisms of the plasmid-encoded protein CPSIT_P7 of C. psittaci in regulating the inflammatory response in THP-1 cells (human monocytic leukemia cell line). Based on cytokine arrays, CPSIT_P7 induces the expression of interleukin-6 (IL-6), interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1) in THP-1 cells. Moreover, the expression levels of IL-6, IL-8, and MCP-1 stimulated by CPSIT_P7 declined after silencing of the Toll-like receptor 4 (TLR4) gene using small interfering RNA and transfection of a dominant negative plasmid encoding TLR4 (pZERO-hTLR4). We further demonstrated that transfection with the dominant negative plasmid encoding MyD88 (pDeNy-hMyD88) and the dominant negative plasmid encoding Mal (pDeNy-hMal) could also abrogate the expression of the corresponding proteins. Western blot and immunofluorescence assay results showed that CPSIT_P7 could activate nuclear factor κB (NF-κB) signaling pathways in THP-1 cells. Altogether, our results indicate that the CPSIT_P7 induces the TLR4/Mal/MyD88/NF-κB signaling axis and therefore contributes to the inflammatory cytokine response.
Insights
The chlamydial plasmid protein CPSIT_P7 triggers an inflammatory response by activating the Toll-like receptor 4 (TLR4) pathway. This pathway involves Mal, MyD88, and NF-κB, leading to increased cytokine production.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- The chlamydial plasmid is crucial for virulence, but its encoded proteins' roles in infection and immune response are unclear.
- Understanding virulence factors and molecular mechanisms of *Chlamydia psittaci* is essential.
Purpose of the Study:
- To investigate the role of plasmid-encoded protein CPSIT_P7 from *C. psittaci* in regulating inflammatory responses.
- To elucidate the molecular mechanisms by which CPSIT_P7 influences inflammation in human monocytic cells.
Main Methods:
- Utilized cytokine arrays to assess protein-induced cytokine expression in THP-1 cells.
- Employed small interfering RNA (siRNA) and dominant-negative plasmids to silence or inhibit Toll-like receptor 4 (TLR4), Mal, and MyD88.
- Applied Western blot and immunofluorescence assays to analyze nuclear factor κB (NF-κB) pathway activation.
Main Results:
- CPSIT_P7 significantly induced the expression of interleukin-6 (IL-6), interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1) in THP-1 cells.
- Silencing TLR4, Mal, or MyD88 abrogated CPSIT_P7-induced cytokine expression.
- CPSIT_P7 was shown to activate the NF-κB signaling pathway.
Conclusions:
- CPSIT_P7 induces inflammatory cytokine production through the TLR4/Mal/MyD88/NF-κB signaling axis.
- This pathway activation by CPSIT_P7 contributes to the inflammatory cytokine response during *Chlamydia psittaci* infection.
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