Mycoplasma genitalium Protein of Adhesion Suppresses T Cell Activation via CypA-CaN-NFAT Pathway.

Mycoplasma genitalium is a prokaryotic microorganism that causes urogenital tract infections. M. genitalium protein of adhesion (MgPa) was essential for M. genitalium attachment and subsequent invasion into host cells. Our prior research confirmed that Cyclophilin A (CypA) was the binding receptor for MgPa and MgPa-CypA interaction can lead to the production of inflammatory cytokines. In this study, we revealed that the recombinant MgPa (rMgPa) could inhibit the CaN-NFAT signaling pathway to reduce the level of IFN-γ, IL-2, CD25, and CD69 in Jurkat cells by binding to the CypA receptor. Moreover, rMgPa inhibited the expressions of IFN-γ, IL-2, CD25, and CD69 in primary mouse T cells. Likewise, the expressions of these T cells activation-related molecules in CypA-siRNA-transfected cells and CypA-/- mouse primary T cell was strengthened by rMgPa. These findings showed that rMgPa suppressed T cell activation by downregulating the CypA-CaN-NFAT pathway, and as a result, acted as an immunosuppressive agent. IMPORTANCE Mycoplasma genitalium is a sexually transmitted bacterium that can co-infect with other infections and causes nongonococcal urethritis in males, cervicitis, pelvic inflammatory disease, premature birth, and ectopic pregnancy in women. The adhesion protein of M. genitalium (MgPa) is the primary virulence factor in the complicated pathogenicity of M. genitalium. This research proved that MgPa could interact with host cell Cyclophilin A (CypA) and prevent T cell activation by inhibiting Calcineurin (CaN) phosphorylation and NFAT nuclear translocation, which clarified the immunosuppression mechanism of M. genitalium to host T cells. Therefore, this study can provide a new idea that CypA can be used for a therapeutic or prophylactic target for M. genitalium infection.

Vimentin Is an Attachment Receptor for Mycoplasma pneumoniae P1 Protein.

Mycoplasma pneumoniae is the most common pathogen causing respiratory tract infection, and the P1 protein on its adhesion organelle plays a crucial role during the pathogenic process. Currently, there are many studies on P1 and receptors on host cells, but the adhesion mechanism of P1 protein is still unclear. In this study, a modified virus overlay protein binding assay (VOPBA) and liquid chromatography-mass spectrometry (LC-MS) were performed to screen for proteins that specifically bind to the region near the carboxyl terminus of the recombinant P1 protein (rP1-C). The interaction between rP1-C and vimentin or ß-4-tubulin were confirmed by far-Western blotting and coimmunoprecipitation. Results verified that vimentin and ß-4-tubulin were mainly distributed on the cell membrane and cytoplasm of human bronchial epithelial (BEAS-2B) cells, but only vimentin could interact with rP1-C. The results of the adhesion and adhesion inhibition assays indicated that the adhesion of M. pneumoniae and rP1-C to cells could be partly inhibited by vimentin and its antibody. When vimentin was downregulated with the corresponding small interfering RNA (siRNA) or overexpressed in BEAS-2B cells, the adhesion of M. pneumoniae and rP1-C to cells was decreased or increased, respectively, which indicated that vimentin was closely associated with the adhesion of M. pneumoniae and rP1-C to BEAS-2B cells. Our results demonstrate that vimentin could be a receptor on human bronchial epithelial cells for the P1 protein and plays an essential role in the adhesion of M. pneumoniae to cells, which may clarify the pathogenesis of M. pneumoniae. IMPORTANCE Mycoplasma pneumoniae is the most common pathogen causing respiratory tract infection, and the P1 protein on its adhesion organelle plays a crucial role during the pathogenic process. A variety of experiments, including enzyme-linked immunosorbent assay (ELISA), coimmunoprecipitation, adhesion, and adhesion inhibition assay, have demonstrated that the M. pneumoniae P1 protein can interact with vimentin, that the adhesion of M. pneumoniae and recombinant P1 protein to BEAS-2B cells was affected by the expression level of vimentin. This provides a new idea for the prevention and treatment of Mycoplasma pneumoniae infection.

Histones: The critical players in innate immunity.

The highly conserved histones in different species seem to represent a very ancient and universal innate host defense system against microorganisms in the biological world. Histones are the essential part of nuclear matter and act as a control switch for DNA transcription. However, histones are also found in the cytoplasm, cell membranes, and extracellular fluid, where they function as host defenses and promote inflammatory responses. In some cases, extracellular histones can act as damage-associated molecular patterns (DAMPs) and bind to pattern recognition receptors (PRRs), thereby triggering innate immune responses and causing initial organ damage. Histones and their fragments serve as antimicrobial peptides (AMPs) to directly eliminate bacteria, viruses, fungi, and parasites in vitro and in vivo. Histones are also involved in phagocytes-related innate immune response as components of neutrophil extracellular traps (NETs), neutrophil activators, and plasminogen receptors. In addition, as a considerable part of epigenetic regulation, histone modifications play a vital role in regulating the innate immune response and expression of corresponding defense genes. Here, we review the regulatory role of histones in innate immune response, which provides a new strategy for the development of antibiotics and the use of histones as therapeutic targets for inflammatory diseases, sepsis, autoimmune diseases, and COVID-19.

Insight into the Pathogenic Mechanism of Mycoplasma pneumoniae.

Mycoplasma pneumoniae, an obligate parasitic pathogen without cell wall, can cause severe upper and lower respiratory tract symptoms. It is the pathogen of human bronchitis and walking pneumonia, and named community-acquired pneumonia. In addition to severe respiratory symptoms, there are clinical extrapulmonary manifestations in the skin, brain, kidney, musculoskeletal, digestive system, and even blood system after M. pneumoniae infection. Hereby, we comprehensively summarized and reviewed the intrapulmonary and extrapulmonary pathogenesis of M. pneumoniae infection. The pathogenesis of related respiratory symptoms caused by M. pneumoniae is mainly adhesion damage, direct damage including nutrient predation, invasion and toxin, cytokine induced inflammation damage and immune evasion effect. The pathogenesis of extrapulmonary manifestations includes direct damage mediated by invasion and inflammatory factors, indirect damage caused by host immune response, and vascular occlusion. The intrapulmonary and extrapulmonary pathogenic mechanisms of M. pneumoniae infection are independent and interrelated, and have certain commonalities. In fact, the pathogenic mechanisms of M. pneumoniae are complicated, and the specific content is still not completely clear, further researches are necessary for determining the detailed pathogenesis of M. pneumoniae. This review can provide certain guidance for the effective prevention and treatment of M. pneumoniae infection.

The genome and antigen proteome analysis of Spiroplasma mirum.

Spiroplasma mirum, small motile wall-less bacteria, was originally isolated from a rabbit tick and had the ability to infect newborn mice and caused cataracts. In this study, the whole genome and antigen proteins of S. mirum were comparative analyzed and investigated. Glycolysis, pentose phosphate pathway, arginine metabolism, nucleotide biosynthesis, and citrate fermentation were found in S. mirum, while trichloroacetic acid, fatty acids metabolism, phospholipid biosynthesis, terpenoid biosynthesis, lactose-specific PTS, and cofactors synthesis were completely absent. The Sec systems of S. mirum consist of SecA, SecE, SecDF, SecG, SecY, and YidC. Signal peptidase II was identified in S. mirum, but no signal peptidase I. The relative gene order in S. mirum is largely conserved. Genome analysis of available species in Mollicutes revealed that they shared only 84 proteins. S. mirum genome has 381 pseudogenes, accounting for 31.6% of total protein-coding genes. This is the evidence that spiroplasma genome is under an ongoing genome reduction. Immunoproteomics, a new scientific technique combining proteomics and immunological analytical methods, provided the direction of our research on S. mirum. We identified 49 proteins and 11 proteins (9 proteins in common) in S. mirum by anti-S. mirum serum and negative serum, respectively. Forty proteins in S. mirum were identified in relation to the virulence. All these proteins may play key roles in the pathogeny and can be used in the future for diagnoses and prevention.

The adhesion protein of Mycoplasma genitalium inhibits urethral epithelial cell apoptosis through CypA-CD147 activating PI3K/ Akt/NF-κB pathway.

By interacting with the receptor on the host cells membrane, Mycoplasma genitalium, a prokaryotic bacterium primarily transmitted through sexual contact, can adhere to and even enter cells. The adhesion protein of M. genitalium (MgPa) plays a critical function in the adhering and subsequent invasion into host cells. Our prior studies verified that cyclophilin A (CypA) was the receptor of MgPa on human urethral epithelial cells (SV-HUC-1) membrane and could induce pro-inflammatory cytokines production through the CypA-CD147-ERK-NF-κB pathway. This research aims to understand how MgPa interacts with its membrane receptor CypA to cause apoptosis in host cells. We employed flow cytometry to see if MgPa prevents or enhances apoptosis of SV-HUC-1 cells. The apoptosis-related proteins such as Bax, caspase-3, and cleaved caspase-3 were assayed using Western blot. Results suggested that MgPa could inhibit the apoptosis of SV-HUC-1 cells. And we demonstrated that interference with the expression of CypA or CD147 significantly reversed the inhibitory effect of MgPa on SV-HUC-1 cells apoptosis, indicating that MgPa inhibited urothelial cells apoptosis through CypA/CD147. Furthermore, we discovered that MgPa regulates the PI3K/Akt/NF-κB pathway through CypA/CD147 to inhibit SV-HUC-1 cells apoptosis. Ultimately, the inhibitory effect of MgPa on the apoptosis of the urothelial epithelial cells extracted from CypA-knockout mice was validated by Annexin V/PI assay. The results corroborated that MgPa could also inhibit mouse urothelial epithelial cells apoptosis. In summary, we demonstrated that MgPa could inhibit SV-HUC-1 cells apoptosis via regulating the PI3K/Akt/NF-κB pathway through CypA/CD147, providing experimental evidence for elucidating the survival strategies of M. genitalium in host cells. KEY POINTS: • M. genitalium protein of adhesion inhibited human urethral epithelial cells apoptosis through CypA-CD147 activating the signal pathway of PI3K/Akt/NF-κB • The knockdown of CypA and CD147 could downregulate the M. genitalium -activated PI3K/Akt/NF-κB pathway in SV-HUC-1 cells • MgPa could inhibit the apoptosis of normal C57BL mouse primary urethral epithelial cells, but not for CypA-knockout C57BL mouse primary urethral epithelial cells.

Identification of histone H2B as a potential receptor for Mycoplasma genitalium protein of adhesion.

Mycoplasma genitalium, the smallest prokaryotic microorganism capable of independent replication, is increasingly recognized as a sexually transmitted pathogen. M. genitalium protein of adhesion (MgPa) plays a pivotal role in the process of M. genitalium adhesion to host cells. We previously identified cyclophilin A as a cellular receptor of MgPa using the virus overlay protein binding assay (VOPBA) together with liquid chromatography-mass spectrometry (LC-MS). In the current study, we have evaluated H2B as an alternative cellular receptor for MgPa since H2B was assigned the second higher score as a potential binding partner of MgPa in the VOPBA and LC-MS screen. It was found that recombinant MgPa specifically bind to H2B both in the SV-HUC-1 cell membrane and in form of a recombinant protein. H2B was detected throughout the SV-HUC-1 cells, including the cytoplasmic membrane, cytosol and nucleus. Importantly, H2B partially inhibited the adhesion of M. genitalium to SV-HUC-1 cells. Finally, H2B was both co-precipitated with recombinant MgPa and co-localized with M. genitalium and recombinant MgPa in SV-HUC-1 cells. The above observations suggest that H2B may act as a potential cellular receptor of MgPa for mediating M. genitalium adhesion to host cells.