Transcriptome profiling of zebrafish infected with Streptococcus suis

Host-pathogen interactions made transparent with the zebrafish model

The zebrafish holds much promise as a high-throughput drug screening model for immune-related diseases, including inflammatory and infectious diseases and cancer. This is due to the excellent possibilities for in vivo imaging in combination with advanced tools for genomic and large scale mutant analysis. The context of the embryo’s developing immune system makes it possible to study the contribution of different immune cell types to disease progression. Furthermore, due to the temporal separation of innate immunity from adaptive responses, zebrafish embryos and larvae are particularly useful for dissecting the innate host factors involved in pathology. Recent studies have underscored the remarkable similarity of the zebrafish and human immune systems, which is important for biomedical applications. This review is focused on the use of zebrafish as a model for infectious diseases, with emphasis on bacterial pathogens. Following a brief overview of the zebrafish immune system and the tools and methods used to study host-pathogen interactions in zebrafish, we discuss the current knowledge on receptors and downstream signaling components that are involved in the zebrafish embryo’s innate immune response. We summarize recent insights gained from the use of bacterial infection models, particularly the Mycobacterium marinum model, that illustrate the potential of the zebrafish model for high-throughput antimicrobial drug screening.

Infectious disease modeling and innate immune function in zebrafish embryos

The major cell types of the innate immune system, macrophages and neutrophils, develop during the first two days of zebrafish embryogenesis. The interaction of these immune cells with pathogenic microbes can excellently be traced in the optically transparent zebrafish embryos. Various tools and methods have recently been developed for visualizing and isolating the zebrafish embryonic innate immune cells, for establishing infections by different micro-injection techniques, and for analyzing the host innate immune response following microbial recognition. Here we provide practical guidelines for the application of these methodologies and review the current state of the art in zebrafish infectious disease research.

Microarray analyses of THP-1 cells infected with Streptococcus suis serotype 2

Streptococcus suis serotype 2 (S. suis 2) is a pathogen responsible for several diseases in both pigs and humans. To gain more insight into the pathogenesis of this organism, an oligonucleotide (oligo)-based microarray was used to investigate gene expression changes in human monocytic cells (THP-1) in response to exposure to S. suis 2 strain SC19. A total of 328 differentially expressed genes were identified. These differentially expressed genes belonged to a variety of functional categories, including genes involved in apoptosis, immunity, signal transduction, chemokine production and the ubiquitin-proteasome system. Our findings can be of interest for future research.

Gene expression of conditioned locomotion and context-specific locomotor sensitization controlled by morphine-associated environment

The nucleus accumbens (NAc) is involved in contextual drug associations, which might be particularly important for environmental cue-induced relapse to drug seeking. In the present study, rats were first administered repeated morphine for 5 days (5 mg/kg, i.p.) in a contextually paired and unpaired design. After reexposure to the morphine-associated environment, which induced conditioned locomotor activity in the morphine-paired group, we performed a rat 27k 70-mer oligo array to profile gene expression in the NAc. One hundred fifty-five upregulated and 88 downregulated genes were found in the paired group compared with the unpaired group. Eight gene transcripts were then selected to confirm their alterations by quantitative real-time polymerase chain reaction (qRT-PCR). The identified genes generally play important roles in neuroactive receptor-ligand interactions, synapse plasticity, ion transport, and protein phosphorylation. Furthermore, the expression of the eight selected genes that were identified and confirmed to show significant fold changes in the first microarray experiment were again measured with qRT-PCR after morphine challenge (2 mg/kg, i.p.). As expected, 2 mg/kg morphine-induced context-specific sensitization. Meanwhile, mRNA expression of the selected genes showed marked upregulation in the morphine-paired group compared with the unpaired and acute groups. These results suggest that alterations in the expression of the identified genes in the NAc may contribute to the neuroplasticity underlying contextual cue-induced relapse to drug use.