On February 15, 2024, the Xuan ouYang research group from the State Key Laboratory of Pathogenic Microbiology Biosafety (Chinese People's Liberation Army Academy of Military Medical Sciences) published online in the Microbilogy Journal of Spectrum a research paper entitled "TRIM56-mediated production of type I interferon inhibits intracellular replication of Rickettsia rickettsii. The study used granuloman organisms to knock out the TRIM56 gene in HeLa cells and THP-1 acute monocytic cell lines to obtain homozygous knockout cell lines HeLa trim56-/-(Item no: LM010125) and THP-1 trim56-/-(Item no: LM010058), and found that TRIM56 has a role in the innate immune response to intracellular Rickettsia bacterial infection, providing new evidence for Rocky Mountain mottled fever (RMSF, also known as rickettsial spotted fever) treatment provides a new target.

Frontier

spotted fever group (SFG) Rickettsia Richettsia is a kind of intracellular bacteria, which is mainly transmitted by ticks. Among them, highly pathogenic Rickettsia R. conorii can cause Rocky Mountain Mountain spotted fever (RMSF). Studies have shown that host cells such as human THP-1 macrophages, murine bone marrow-derived macrophages (BMDMs), and human microvascular endothelial cells (HMECs) secrete type I interferon (IFN-I) during Rickettsia infection. Human THP-1 macrophages infected with Richettsia produce varying levels of interferon-β(IFN-β) and inhibit the replication of rickettsiae. At the same time, BMDM cells infected with Rickettsia R. parkeri can mediate IFN-β production by DNA sensor cGAS, induce the expression of interferon regulatory factor IRF5, and upregulate the expression of genes encoding guanylate binding protein and inducible nitric oxide synthase, thereby inhibiting the replication of R. parkeri. Highly pathogenic Rickettsial R. conorii infected HMECs likewise secrete IFN-β and inhibit its replication. However, the effect of IFN-I on host cells infected with highly pathogenic Rickettsia remains unclear. In addition, host TRIM56 protein, as a restriction factor for a variety of viruses, is involved in IFN-I signaling pathways. TRIM56 can stimulate RIG-I and MDA5 innate immune receptors, thereby regulating the inflammatory response to regulate the inflammatory response. However, the mechanism of TRIM56's antibacterial action, especially on rickettsiae, is not clear.

research method

In order to study the effect of TRIM56 on the replication of rickettsia bacteria, the authors examined the infection of rickettsia after silencing TRIM56 gene and overexpressing plasmid pcDNA3.1-hTRIM56-HA(pcTRIM56) in HeLa cells, quantified rickettsia DNA using qPCR, and found that silencing TRIM56 promoted the replication of rickettsia, and overexpression had bacteriostatic effect. Built with Granular OrganismsKnockout of trim56-/-gene in HeLa and THP-1 cellsIt was found with high levels of Rickettsia. These findings demonstrate that TRIM56 exerts an inhibitory effect on the replication of rickettsia in cells.

Previous studies have shown that IFN-β produces a strong dose-dependent restriction on the growth of rickettsia R. parkeri in mouse bone marrow-derived macrophages. TRIM56 is involved in the initiation of innate antiviral immune responses, including IFN responses. To investigate the effect of TRIM56 on rickettsia-induced IFN-β responses, we analyzed IFN-β transcript levels in rickettsia-infected wild-type (WT) and trim56-/- HeLa cells and THP-1 cells. The mRNA levels of IFN-β in wild-type cells were found to be significantly elevated after infection. At the same time, the expression level of IFN-β was increased by transfection of TRIM56 full-length plasmid. Therefore, it is speculated that TRIM56 can affect the secretion of IFN-β after Rickettsial infection. Subsequently, WT and trim56-/- THP-1 cells differentiated from PMA(phorbol 12-myristate 13-acetate) were treated with IFN-β (200 ng/mL) for 48 hours, and rickettsia was significantly reduced in IFN-β-treated WT and trim56-/- THP-1 cells compared to the untreated group. Taken together, the above results indicate that the absence of TRIM56 specifically inhibits the transcription and secretion of IFN-β, thereby promoting the intracellular replication of rickettsia.

Conclusion     

References

1. Parola P, Paddock CD, Socolovschi C, Labruna MB, Mediannikov O, Kernif T, Abdad MY, Stenos J, Bitam I, Fournier PE, Raoult D. 2013. Update on tick-borne rickettsioses around the world: a geographic approach. Clin Microbiol Rev26:657-702.

2. Curto P, Santa C, Cortes L, Manadas B, Simões I. 2021. Spotted fever group Rickettsia trigger species-specific alterations in macrophage proteome signatures with different impacts in host innate inflammatory responses. Microbiol Spectr 9: e0081421.

3. Cheng R, Zhou C, Zhao M, Zhang S, Wan W, Yu Y, Wen B, Jiao J, Xiong X, Xu Q, OuYang X.0.TRIM56-mediated production of type I interferon inhibits intracellular replication of Rickettsia rickettsii. Microbiol Spectr0:e03695-23.https://doi.org/10.1128/spectrum.03695-23