Dual rna-sequencing approach for dissecting nontypeable haemophilus influenzae and host cell transcriptomes

Abstract

Characterization of host-pathogen interactions is critical for the development of next-generation therapies and vaccines. Classical approaches involve the use of transformed cell lines and/or animal models which may not reflect the complexity and response of the human host. The Gram-negative bacterium nontypeable Haemophilus influenzae (NTHi) commonly resides as a commensal in the human nasopharynx from where it can disseminate to local organs to cause a wide spectrum of diseases including otitis media, chronic obstructive pulmonary disease, cystic fibrosis and bronchitis. Successful colonization by NTHi depends on its ability to adhere and adapt to the respiratory tract mucosa, which serves as a frontline defense against respiratory pathogens. In opportunistic infections, colonization is followed by either a paracellular route across the epithelial barrier or invasion of non-phagocytic and epithelial cells. However, the temporal events associated to a successful colonization are far from being fully characterized. Recent improvements in tissue engineering techniques including the development of differentiated primary cell cultures and organotypic 3D cellular models have significantly increased our understanding of microbial pathogenesis by providing physiologically relevant representations of human upper airway tissue. Bridging of these techniques with the currently available next-generation sequencing technologies is a conceptually novel approach for studying infection-linked transcriptome alterations in such systems. Massively parallel cDNA sequencing (RNA-seq) offers the possibility of comprehensive and simultaneous whole genome transcriptional profiling of both host and invading pathogen, and overcomes the existing technical and economical limitations of probe-dependent methods. Taking advantage of the technological advances, we reconstituted the ciliated human bronchial epithelium in vitro using primary bronchial epithelial cells to simultaneously monitor the infection-linked global changes in NTHi and infected host epithelia gene expression by dual RNA-sequencing (RNA-seq). Acquisition of a total of nearly 2,5 billion sequences allowed construction of high-resolution strand-specific transcriptome maps of NTHi during infection of host mucosal surface, and monitoring of metabolic as well as stress-induced host-adaptation strategies of this pathogen. The initial stage of colonization was characterized by the binding of NTHi to cilia. Temporal analysis of host mRNA signatures revealed consequent remodeling of target cell cytoskeleton and junction complexes elicited by bacterial infection, with a profound effect on intermediate filament network of bronchial epithelium. At later stage of infection when bacteria start to internalize, NTHi down-regulated the central metabolism and increased the expression of transporters indicating alterations in the bacterial metabolic regime due to the evolving substrate availability. Concurrently, the oxidative environment generated by infected cells instigated bacterial expression of stress-induced defense mechanisms including the transport of exogenous glutathione and the activation of the toxin-antitoxin system. Notably, as part of our screening for novel signatures of infection, we identified a global profile of noncoding transcripts that are candidate small RNAs regulated during human host infection in Haemophilus species. Our data by providing a robust and comprehensive catalogue of regulatory and adaptive responses reflecting the complex crosstalk between the host and invading pathogen, may provide important insights into NTHi pathogenesis and the development of efficacious preventive strategies.