PEtN-Modified O-Antigen Enhances Shigella Pathogenesis by Promoting Epithelial Cell Invasion and Inhibiting Complement Binding.

Shigellosis poses an ongoing global public health threat. The presence and length of the O-antigen in lipopolysaccharide play critical roles in Shigella pathogenesis. The plasmid-mediated opt gene encodes a phosphoethanolamine (PEtN) transferase that catalyzes the addition of PEtN to the O-antigen of Shigella flexneri serotype X and Y strains, converting them into serotype Xv and Yv strains, respectively. Since 2002, these modified strains have become prevalent in China. Here we demonstrate that PEtN-mediated O-antigen modification in S. flexneri increase the severity of corneal infection in guinea pigs without any adaptive cost. This heightened virulence is associated with epithelial cell adhesion and invasion, as well as an enhanced inflammatory response of macrophage. Notably, PEtN addition allow S. flexneri to attenuate the binding of complement C3 and better resist phagocytosis, potentially contributing to the retention of S. flexneri in the host environment.

Inactivation of MST1/2 Controls Macrophage Polarization to Affect Macrophage-Related Disease via YAP and Non-YAP Mechanisms.

Macrophage polarization is a critical process that regulates in inflammation, pathogen defense, and tissue repair. Here we demonstrate that MST1/2, a core kinase of Hippo pathway and a recently identified regulator of inflammation, plays a significant role in promoting M2 polarization. We provide evidence that inhibition of MST1/2, achieved through either gene-knockout or pharmacological treatment, leads to increased M1 polarization in a YAP-dependent manner, resulting in the development of M1-associated inflammatory disorders. Moreover, MST1/2 inhibition also leads to a substantial reduction in M2 polarization, but this occurs through the STAT6 and MEK/ERK signaling. The STAT6 is independent of YAP, but MEK/ERK is dependent of YAP. Consistent with these observations, both MST1/2-conditional knockout mice and wild-type mice treated with XMU-MP-1, a chemical inhibitor of MST1/2, exhibited reduced M2-related renal fibrosis, while simultaneously displaying enhanced LPS-mediated inflammation and improved clearance of MCR3-modified gram-negative bacteria. These findings uncover a novel role of MST1/2 in regulating macrophage polarization and establish it as a potential therapeutic target for the treatment of macrophage-related fibrotic diseases.

MCR Expression Conferring Varied Fitness Costs on Host Bacteria and Affecting Bacteria Virulence.

Since the first report of the plasmid-mediated, colistin-resistant gene, mcr-1, nine mcr genes and their subvariants have been identified. The spreading scope of mcr-1~10 varies greatly, suggesting that mcr-1~10 may have different evolutionary advantages. Depending on MCR family phylogeny, mcr-6 is highly similar to mcr-1 and -2, and mcr-7~10 are highly similar to mcr-3 and -4. We compared the expression effects of MCR-1~5 on bacteria of common physiological background. The MCR-1-expressing strain showed better growth than did MCR-2~5-expressing strains in the presence of colistin. LIVE/DEAD staining analysis revealed that MCR-3~5 expression exerted more severe fitness burdens on bacteria than did MCR-1 and -2. Bacteria expressing MCRs except MCR-2 showed enhanced virulence with increased epithelial penetration ability determined by trans-well model (p < 0.05). Enhanced virulence was also observed in the Galleria mellonella model, which may have resulted from bacterial membrane damage and different levels of lipopolysaccharide (LPS) release due to MCR expression. Collectively, MCR-1-expressing strain showed the best survival advantage of MCR-1~5-expressing strains, which may partly explain the worldwide distribution of mcr-1. Our results suggested that MCR expression may cause increased bacterial virulence, which is alarming, and further attention will be needed to focus on the control of infectious diseases caused by mcr-carrying pathogens.