31 research outputs found
Computational modeling with forward and reverse engineering links signaling network and genomic regulatory responses: NF-ÎșB signaling-induced gene expression responses in inflammation
<p>Abstract</p> <p>Background</p> <p>Signal transduction is the major mechanism through which cells transmit external stimuli to evoke intracellular biochemical responses. Diverse cellular stimuli create a wide variety of transcription factor activities through signal transduction pathways, resulting in different gene expression patterns. Understanding the relationship between external stimuli and the corresponding cellular responses, as well as the subsequent effects on downstream genes, is a major challenge in systems biology. Thus, a systematic approach is needed to integrate experimental data and theoretical hypotheses to identify the physiological consequences of environmental stimuli.</p> <p>Results</p> <p>We proposed a systematic approach that combines forward and reverse engineering to link the signal transduction cascade with the gene responses. To demonstrate the feasibility of our strategy, we focused on linking the NF-ÎșB signaling pathway with the inflammatory gene regulatory responses because NF-ÎșB has long been recognized to play a crucial role in inflammation. We first utilized forward engineering (Hybrid Functional Petri Nets) to construct the NF-ÎșB signaling pathway and reverse engineering (Network Components Analysis) to build a gene regulatory network (GRN). Then, we demonstrated that the corresponding IKK profiles can be identified in the GRN and are consistent with the experimental validation of the IKK kinase assay. We found that the time-lapse gene expression of several cytokines and chemokines (TNF-α, IL-1, IL-6, CXCL1, CXCL2 and CCL3) is concordant with the NF-ÎșB activity profile, and these genes have stronger influence strength within the GRN. Such regulatory effects have highlighted the crucial roles of NF-ÎșB signaling in the acute inflammatory response and enhance our understanding of the systemic inflammatory response syndrome.</p> <p>Conclusion</p> <p>We successfully identified and distinguished the corresponding signaling profiles among three microarray datasets with different stimuli strengths. In our model, the crucial genes of the NF-ÎșB regulatory network were also identified to reflect the biological consequences of inflammation. With the experimental validation, our strategy is thus an effective solution to decipher cross-talk effects when attempting to integrate new kinetic parameters from other signal transduction pathways. The strategy also provides new insight for systems biology modeling to link any signal transduction pathways with the responses of downstream genes of interest.</p
System-wide Analysis of the T Cell Response
SummaryThe T cell receptor (TCR) controls the cellular adaptive immune response to antigens, but our understanding of TCR repertoire diversity and response to challenge is still incomplete. For example, TCR clones shared by different individuals with minimal alteration to germline gene sequences (public clones) are detectable in all vertebrates, but their significance is unknown. Although small in size, the zebrafish TCR repertoire is controlled by processes similar to those operating in mammals. Thus, we studied the zebrafish TCR repertoire and its response to stimulation with self and foreign antigens. We found that cross-reactive public TCRs dominate the T cell response, endowing a limited TCR repertoire with the ability to cope with diverse antigenic challenges. These features of vertebrate public TCRs might provide a mechanism for the rapid generation of protective T cell immunity, allowing a short temporal window for the development of more specific private T cell responses
Dynamic Transcript Profiling of Candida Albicans Infection in Zebrafish: a Pathogen-Host Interaction Study
Candida albicans is responsible for a number of life-threatening infections
and causes considerable morbidity and mortality in immunocompromised patients.
Previous studies of C. albicans pathogenesis have suggested several steps must
occur before virulent infection, including early adhesion, invasion, and late
tissue damage. However, the mechanism that triggers C. albicans transformation
from yeast to hyphae form during infection has yet to be fully elucidated. This
study used a systems biology approach to investigate C. albicans infection in
zebrafish. The surviving fish were sampled at different post-infection time
points to obtain time-lapsed, genome-wide transcriptomic data from both
organisms, which were accompanied with in sync histological analyses. Principal
component analysis (PCA) was used to analyze the dynamic gene expression
profiles of significant variations in both C. albicans and zebrafish. The
results categorized C. albicans infection into three progressing phases:
adhesion, invasion, and damage. Such findings were highly supported by the
corresponding histological analysis. Furthermore, the dynamic interspecies
transcript profiling revealed that C. albicans activated its filamentous
formation during invasion and the iron scavenging functions during the damage
phases, whereas zebrafish ceased its iron homeostasis function following
massive hemorrhage during the later stages of infection. This was followed by
massive hemorrhaging toward the end stage of infection. Most of the immune
related genes were expressed as the infection progressed from invasion to the
damage phase. Such global, inter-species evidence of virulence-immune and iron
competition dynamics during C. albicans infection could be crucial in
understanding control fungal pathogenesis
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Type I interferons and microbial metabolites of tryptophan modulate astrocyte activity and CNS inflammation via the aryl hydrocarbon receptor
Astrocytes play important roles in the central nervous system (CNS) during health and disease. Through genome-wide analyses we detected a transcriptional response to type I interferons (IFN-I) in astrocytes during experimental CNS autoimmunity and also in CNS lesions from multiple sclerosis (MS) patients. IFN-I signaling in astrocytes reduces inflammation and experimental autoimmune encephalomyelitis (EAE) disease scores via the ligand-activated transcription factor aryl hydrocarbon receptor (AhR) and suppressor of cytokine signaling 2 (SOCS2). The anti-inflammatory effects of nasally administered IFN-ÎČ are partly mediated by AhR. Dietary tryptophan is metabolized by the gut microbiota into AhR agonists that act on astrocytes to limit CNS inflammation. EAE scores were increased following ampicillin treatment during the recovery phase, and CNS inflammation was reduced in antibiotic-treated mice by supplementation with the tryptophan metabolites indole, indoxyl-3-sulfate (I3S), indole-3-propionic acid (IPA) and indole-3-aldehyde (IAld), or the bacterial enzyme tryptophanase. In individuals with MS, the circulating levels of AhR agonists were decreased. These findings suggest that IFN-I produced in the CNS act in combination with metabolites derived from dietary tryptophan by the gut flora to activate AhR signaling in astrocytes and suppress CNS inflammation
Zebrafish as a Model Host for Candida albicans Infectionâż
In this work, the zebrafish model organism was developed to obtain a minivertebrate host system for a Candida albicans infection study. We demonstrated that C. albicans can colonize and invade zebrafish at multiple anatomical sites and kill the fish in a dose-dependent manner. Inside zebrafish, we monitored the progression of the C. albicans yeast-to-hypha transition by tracking morphogenesis, and we monitored the corresponding gene expression of the pathogen and the early host immune response. We performed a zebrafish survival assay with different C. albicans strains (SC5314, ATCC 10231, an hgc1 mutant, and a cph1/efg1 double mutant) to determine each strain's virulence, and the results were similar to findings reported in previous mouse model studies. Finally, using zebrafish embryos, we monitored C. albicans infection and visualized the interaction between pathogen and host myelomonocytic cells in vivo. Taken together, the results of this work demonstrate that zebrafish can be a useful host model to study C. albicans pathogenesis, and they highlight the advantages of using the zebrafish model in future invasive fungal research
Engineered bacteria producing arylâhydrocarbon receptor agonists protect against ethanolâinduced liver disease in mice
International audienceBackground and Purpose Gut bacteria metabolize tryptophan into indoles. Intestinal levels of the tryptophan metabolite indoleâ3âacetic acid are reduced in patients with alcoholâassociated hepatitis. Supplementation of indoleâ3âacetic acid protects against ethanolâinduced liver disease in mice. The aim of this study was to evaluate the effect of engineered bacteria producing indoles as Arylâhydrocarbon receptor (Ahr) agonists. Methods C57BL/6 mice were subjected to chronicâplusâbinge ethanol feeding and orally given PBS, control Escherichia coli Nissle 1917 (EcN) or engineered EcNâAhr. The effects of EcN and EcNâAhr were also examined in mice lacking Ahr in interleukin 22 (Il22)âproducing cells. ResultsThrough the deletion of endogenous genes trpR and tnaA , coupled with over expression of a feedbackâresistant tryptophan biosynthesis operon, EcNâAhr were engineered to overproduce tryptophan. Additional engineering allowed conversion of this tryptophan to indoles including indoleâ3âacetic acid and indoleâ3âlactic acid. EcNâAhr ameliorated ethanolâinduced liver disease in C57BL/6 mice. EcNâAhr upregulated intestinal gene expression of Cyp1a1 , Nrf2 , Il22 , Reg3b , and Reg3g , and increased Il22âexpressing type 3 innate lymphoid cells. In addition, EcNâAhr reduced translocation of bacteria to the liver. The beneficial effect of EcNâAhr was abrogated in mice lacking Ahr expression in Il22âproducing immune cells. ConclusionsOur findings indicate that tryptophan metabolites locally produced by engineered gut bacteria mitigate liver disease via Ahrâmediated activation in intestinal immune cells