Hongwei Yu, PhD
Professor
Phone: (304) 696-7356
yuh@marshall.edu

Research Interests

My research focuses on two areas: lung infections in Cystic Fibrosis and the role of segmented filamentous bacteria (SFB) in the gut immunity.

CYSTIC FIBROSIS BIOFILMS

The major cause of morbidity and mortality in patients with Cystic Fibrosis is chronic lung infections with the bacterial pathogen, Pseudomonas aeruginosa. During the course of infection, this bacterium overproduces a capsular polysaccharide called alginate. The overproduction of alginate is a marker for chronic infections and responsible for the disease progression. The goal of our research is to prevent the development of chronic infections by controlling the molecular mechanisms that govern alginate regulation. Alginate is negatively regulated by the transmembrane protein MucA. There are two molecular mechanisms by which P. aeruginosa regulates the production of alginate. The first is through the activation of the intramembrane proteases, and the second is through mutations in mucA. Previously we found that induction of a small envelope protein can activate the alginate biosynthetic pathway in the strains with a wild type mucA (Refs. 2 and 10). Additionally, we determined that increasing the activities of a specific protease, alginate overproduction can also be stably induced in strains with only a cytoplasmic portion of MucA (Refs. 3 and 9). These strains provide model systems for a pathway-based screen for potential biofilm inhibitors. Our ultimate goal is to develop therapeutics that target biofilm formation for clinical trials.

MODELING LUNG INFECTIONS

To investigate how the host defenses react to lung colonization by P. aeruginosa, we used a whole-body exposure system which nebulizes bacterial suspension in micron-size droplets (Ref. 12). Using this model, we previously screened 11 inbred mouse strains for the susceptibility to lung infection by P. aeruginosa PAO1. Mouse strain DBA/2 is hypersensitive to colonization and develops acute pneumonia as characterized by the alveolar exudate and edema formation coupled with specific induction of IL-17, monocyte chemotactic protein (MCP)-1 and vascular endothelial growth factor (VEGF) in the lung tissues (Ref. 11). Analysis of the antibacterial function of bone marrow derived naïve macrophages between the sensitive DBA/2 and the resistant C57BL/6 mice revealed that the macrophages of DBA/2 can perform phagocytosis, but the ingestion does not lead to the elimination of P. aeruginosa PAO1 (Figure 1). The goal of this project is to better understand the etiology of lung infections for the development of novel therapeutics.



Figure 1. DBA/2 naive macrophages have reduced bactericidal activity compared to C57BL/6. Epifluorescent images of naïve macrophages produced by bone marrow progenitor cells after a 20 min exposure to GFP-labeled P. aeruginosa PAO1. C57BL/6 macrophages are able to control P. aeruginosa growth significantly better (* = p<0.05, ANOVA, Student’s t test, Holm’s method) than DBA/2 macrophages for up to five hours of exposure. The control represents medium inoculated with bacteria in the absence of macrophages. Data plotted is the mean of three experiment. SEGMENTED FILAMENTOUS BACTERIA (SFB)

Gut microbiota, a bacterial community made up of 500-1,000 different species, are important to human health. Within microbiota, there is a morphologically-distinct, symbiotic member known as segmented filamentous bacteria (SFB). SFB is an anaerobic, spore-forming Gram-positive bacterium that plays a vital role in the development of the immune system in mice. More specifically, SFB has been shown to attach to the apical epithelium of the small intestine to induce the interleukin-17-producing T helper (TH17) cells. TH17 cells are important for protection against intestinal pathogens, as well as maintaining gut homeostasis. However, little is known about the role of SFB in humans. Recently, we found that SFB colonization occurs early in human life, followed by an age-associated decrease in overall abundance (Ref. 6). We observed that the majority of 7 to 12 mo.-old Chinese infants carry SFB. However, SFB was not detected in older children (>3 years old). The presence of SFB in American children has never been investigated. We are currently conducting a survey to examine the prevalence of SFB in healthy American children, and determine if a correlation exists between SFB and various pediatric gastrointestinal tract (GI) diseases