The E. coli IbeA receptor Vimentin (Vim), in conjunction with its co-receptor PSF, plays an important role in the pathogenesis of neonatal sepsis and meningitis (NSM), which remains a major cause of death in newborns, especially in low-birth weight infants. The ibeA locus is able to modulate expression of several virulence factors (e.g., fim, ibeB, ompA and biofilm-associated genes) and predominantly contribute to E. coli K1-caused early-onset human NSM by inducing both pathogen penetration and polymorphonuclear neutrophil (PMN) transmigration (PMNT) across the blood-brain barrier (BBB), which consists mainly of brain microvascular endothelial cells (BMEC). Vim has emerged as an organizer of a number of critical proteins involved in cell adhesion/migration and cell signaling. Vim- and PSF-mediated signaling is required for IbeA-induced NF-kB activation, pathogen penetration and PMNT across the BBB, which are the three hallmark features of bacterial meningitis. Lipid rafts (LRs) serve as a signaling platform for Vim, PSF, ?7 nAChR (regulator of inflammation), and other signaling molecules (e.g., caveolin-1, ERK and CaM kinase II). Our recent studies have demonstrated for the first time that Vim and PSF cooperatively regulate IbeA+ E. coli K1-induced NF-kB signaling. Vim forms a complex with IkB, NF-kB and tubulins in the resting cells through its head domain (HD). Vim- mediated modulation of the ubiquitin proteasome system (UPS) is essential for NF-kB activation. IbeA is able to induce the IkB kinase (IKK) activation, dissociation of the Vim/IkB-NF-kB complex, and expression of Vim, ?7 nAChR and proinflammatory factors (PIFs). Nuclear translocation of NF-kB is correlated with increased PSF in the nucleus. Circulating BMECs (cBMEC) and endothelial progenitor cells (EPC) in the blood could be used as cell-based biomarkers for indexing of the CNS injury and for monitoring genome-wide expression signatures (GES) during NSM. Most importantly, we have shown that IbeA+ E. coli-induced NF-kB activation, bacterial invasion, PMNT and BBB permeability are significantly reduced in Vim KO (-/-) mice, which are consistent with the in vitro findings. Based on these results, we hypothesize that Vim- and PSF-induced signaling is a new paradigm in which microbial factors (e.g., IbeA) induce cytoplasmic activation and nuclear translocation of NF-kB through the formation of the initial signaling complexes with other signaling molecules (e.g., caveolin-1, PI3K, ERK, CaM kinase II and Rac1) in lipid rafts. Subsequent activation of the IKK/NF-kB pathway and eventual upregulation of Vim, ?7 nAChR and PIFs lead to CNS inflammation/BBB disorders, which can be detected by cBMEC/EPC-based approaches. Our hypothesis will be examined with the following specific aims: 1). Examine how Vim and PSF act in concert to modulate IbeA-induced NF-kB activation/translocation and how NF-kB subsequently up-regulates gene expression by defining Vim- and PSF-mediated signaling. 2). Determine how Vim and PSF contribute to IbeA-induced pathogen penetration and PMN transmigration across the BBB by SCP analysis of cBMEC and genetic blockage of Vim.
The E. coli IbeA receptor vimentin, in conjunction with its co-receptor PSF, plays an important role in the pathogenesis of neonatal sepsis and meningitis (NSM), which remains a major cause of death in newborns, especially in low-birth weight infants. The novelty and uniqueness of this proposal are the comprehensive studies on the disease-causing mechanisms responsible for the three interrelated hallmark features of bacterial meningitis: NFkB activation, bacterial invasion and white blood cell transmigration across the blood-brain barrier.
