The bacterial cell envelope is a protective barrier at the frontline of bacterial interaction with the environment, and its integrity is regulated by various stress response systems. The Rcs (regulator of capsule synthesis) system, a non-orthodox two-component regulatory system (TCS) found in many members of the Enterobacteriaceae family, is one of the envelope stress response pathways. The Rcs system can sense envelope damage or defects and regulate the transcriptome to counteract stress, which is particularly important for the survival and virulence of pathogenic bacteria. In this review, we summarize the roles of the Rcs system in envelope stress responses (ESRs) and virulence regulation. We discuss the environmental and intrinsic sources of envelope stress that cause activation of the Rcs system with an emphasis on the role of RcsF in detection of envelope stress and signal transduction. Finally, the different regulation mechanisms governing the Rcs system's control of virulence in several common pathogens are introduced. This review highlights the important role of the Rcs system in the environmental adaptation of bacteria and provides a theoretical basis for the development of new strategies for control, prevention, and treatment of bacterial infections.

SOX9 (Sex-determining region Y Box 9) is a well-characterized transcription factor that is a marker for progenitor cells in various tissues. In the liver, cells delineated by SOX9 are responsible for regenerating liver parenchyma when cell proliferation is impaired following chronic injury. However, whether these SOX9⁺ cells play a role in liver carcinogenesis has not been fully understood, although high SOX9 expression has been linked to poor survival outcome in liver cancer patients. To address this question, we developed a liver cancer mouse model (Pten^loxP/loxP; Sox9-Cre^ERT+; R26R^YFP) where tumor suppressor Pten (phosphatase and tensin homolog deleted on chromosome ten) is deleted in SOX9⁺ cells following tamoxifen injection. In this paper, we employ lineage-tracing to demonstrate the tumorigenicity potential of the Pten^-, SOX9⁺ cells. We show that these cells are capable of giving rise to mixed-lineage tumors that manifest features of both hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (CCA). Our results suggest that PTEN loss induces the transformation of SOX9⁺ cells. We further show that to activate these transformed SOX9⁺ cells, the presence of liver injury is crucial. Liver injury, induced by hepatotoxin 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) or high-fat diet (HFD), substantially increases tumor incidence and accelerates liver carcinogenesis from SOX9⁺ cells in Pten null mice but not in control mice. We further examine the mechanisms underlying tumor formation in this model to show that concurrent with the induction of niche signal (i.e., Wnt signaling), liver injury significantly stimulates the expansion of tumor-initiating cells (TICs). Together, these data show that (1) SOX9⁺ cells have the potential to become TICs following the primary transformation (i.e. Pten deletion) and that (2) liver injury is necessary for promoting the activation and proliferation of transformed SOX9⁺ cells, resulting in the genesis of mixed-lineage liver tumors.

Chronic inflammatory disorders are thought to arise due to an interplay between predisposing host genetics and environmental factors. For example, the onset of inflammatory bowel disease is associated with enteric proteobacterial infection, yet the mechanistic basis for this association is unclear. We have shown previously that genetic defiency in TLR1 promotes acute enteric infection by the proteobacteria Yersinia enterocolitica. Examining that model further, we uncovered an altered cellular immune response that promotes the recruitment of neutrophils which in turn increases metabolism of the respiratory electron acceptor tetrathionate by Yersinia. These events drive permanent alterations in anti-commensal immunity, microbiota composition, and chronic inflammation, which persist long after Yersinia clearence. Deletion of the bacterial genes involved in tetrathionate respiration or treatment using targeted probiotics could prevent microbiota alterations and inflammation. Thus, acute infection can drive long term immune and microbiota alterations leading to chronic inflammatory disease in genetically predisposed individuals.

BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is a chronic and fatal pulmonary interstitial disease that usually occurs in the elderly. The senescence of alveolar epithelial cells (AECs) is an important mechanism of IPF. The AECs of patients with IPF have lower expression of peroxisome proliferator-activated receptor-γ coactivator-1 alpha (PGC-1α), which has been shown to play an important role in maintaining mitochondrial morphology and energy metabolism. This study sought to explore the mechanism by which ZLN005 improves mitochondrial function by upregulating PGC-1α to protect AECs from aging. METHODS: Western blot was used to detect the expression of PGC-1α, mitochondrial synthesis protein nuclear respiratory factor-1 (NRF-1), and p21WAF1 in the lung tissue of the IPF patients and the mice with bleomycin (BLM)-induced pulmonary fibrosis. A549 cells and mice AEC2 cells were treated with hydrogen peroxide (H2O2) to construct cell senescence models. Cell senescence was detected by senescence-associated beta-galactosidase staining. The mitochondrial respiratory function was measured, including the adenosine triphosphate (ATP) generation, reactive oxygen species (ROS) level, changes in cell membrane potential, and energy metabolism. Using lentivirus as a vector and using gene editing technology to over express (upPGC-1α) and knockdown PGC-1α (shPGC-1α) in the A549 cells. The PGC-1α agonist ZLN005 was used to pretreat the A549 and shPGC-1α A549 cells, and cell aging and mitochondrial respiratory function were observed. RESULTS: The Western blot and immunofluorescence assays showed that the expression of PGC-1α and NRF-1 was decreased in the lung tissues of the IPF patients and BLM-induced mice pulmonary fibrosis model, while the expression of p21WAF1 was increased. The results of the immunofluorescence and mitochondrial function experiments also indicated that the expression of PGC-1α and mitochondrial synthesis protein NRF-1 were decreased in the senescent cells. Further, the mitochondrial morphology was abnormal and the mitochondrial function was impaired. PGC-1α was involved in the AEC senescence by regulating mitochondrial morphology and function. Treatment with the agonist of PGC-1α (i.e., ZLN005) blocked the H2O2-induced cell senescence by enhancing the expression of PGC-1α. CONCLUSIONS: These results provide preliminary insights into the potential clinical application of ZLN005 as a novel therapeutic agent for the treatment of IPF.