High content analysis of granuloma histology and neutrophilic inflammation in adult zebrafish infected with Mycobacterium marinum

Modeling nontuberculous mycobacterial infections in zebrafish

The incidence of infections due to nontuberculous mycobacteria (NTM) has increased rapidly in recent years, surpassing tuberculosis in developed countries. Due to inherent antimicrobial resistance, NTM infections are particularly difficult to treat with low cure rates. There is an urgent need to understand NTM pathogenesis and to develop novel therapeutic approaches for the treatment of NTM diseases. Zebrafish have emerged as an excellent animal model due to genetic amenability and optical transparency during embryonic development, allowing spatiotemporal visualization of host-pathogen interactions. Furthermore, adult zebrafish possess fully functional innate and adaptive immunity and recapitulate important pathophysiological hallmarks of mycobacterial infection. Here, we report recent breakthroughs in understanding the hallmarks of NTM infections using the zebrafish model.

Treatment of infection-induced vascular pathologies is protective against persistent rough morphotype Mycobacterium abscessus infection in zebrafish

Mycobacterium abscessus infections are of increasing global prevalence and are often difficult to treat due to complex antibiotic resistance profiles. While there are similarities between the pathogenesis of M. abscessus and tuberculous mycobacteria, including granuloma formation and stromal remodelling, there are distinct molecular differences at the host-pathogen interface. Here we have used a zebrafish-M. abscessus model and host-directed therapies that were previously identified in the zebrafish-M. marinum model to identify potential host-directed therapies against M. abscessus infection. We find efficacy of anti-angiogenic and vascular normalizing therapies against rough M. abscessus infection, but no effect of anti-platelet drugs.

Inhibition of infection-induced vascular permeability modulates host leukocyte recruitment to Mycobacterium marinum granulomas in zebrafish

Mycobacterial granuloma formation involves significant stromal remodeling including the growth of leaky, granuloma-associated vasculature. These permeable blood vessels aid mycobacterial growth, as antiangiogenic or vascular normalizing therapies are beneficial host-directed therapies in preclinical models of tuberculosis across host-mycobacterial pairings. Using the zebrafish-Mycobacterium marinum infection model, we demonstrate that vascular normalization by inhibition of vascular endothelial protein tyrosine phosphatase (VE-PTP) decreases granuloma hypoxia, the opposite effect of hypoxia-inducing antiangiogenic therapy. Inhibition of VE-PTP decreased neutrophil recruitment to granulomas in adult and larval zebrafish, and decreased the proportion of neutrophils that extravasated distal to granulomas. Furthermore, VE-PTP inhibition increased the accumulation of T cells at M. marinum granulomas. Our study provides evidence that, similar to the effect in solid tumors, vascular normalization during mycobacterial infection increases the T cell:neutrophil ratio in lesions which may be correlates of protective immunity.

Adaptation to an amoeba host drives selection of virulence-associated traits in Vibrio cholerae

Predation by heterotrophic protists drives the emergence of adaptive traits in bacteria, and often these traits lead to altered interactions with hosts and persistence in the environment. Here we studied adaptation of the cholera pathogen, Vibrio cholerae during long-term co-incubation with the protist host, Acanthamoeba castellanii. We determined phenotypic and genotypic changes associated with long-term intra-amoebal host adaptation and how this impacts pathogen survival and fitness. We showed that adaptation to the amoeba host leads to temporal changes in multiple phenotypic traits in V. cholerae that facilitate increased survival and competitive fitness in amoeba. Genome sequencing and mutational analysis revealed that these altered lifestyles were linked to non-synonymous mutations in conserved regions of the flagellar transcriptional regulator, flrA. Additionally, the mutations resulted in enhanced colonisation in zebrafish, establishing a link between adaptation of V. cholerae to amoeba predation and enhanced environmental persistence. Our results show that pressure imposed by amoeba on V. cholerae selects for flrA mutations that serves as a key driver for adaptation. Importantly, this study provides evidence that adaptive traits that evolve in pathogens in response to environmental predatory pressure impact the colonisation of eukaryotic organisms by these pathogens.

Analgesic, anti-inflammatory and acute oral toxicity profile of leaf and bark extracts of Albizia procera

Background

Pain and inflammation are associatory events in cancer, diabetes, cardiovascular diseases, arthritis and other chronic diseases. Corticosteroids, non-steroidal anti-inflammatory drugs exert potential side effects on long term use. This study was aimed to investigate the acute oral toxicity, anti-inflammatory and analgesic activities of leaf and bark extracts of Albizia procera in experimental animal models.

Methods

Ethyl acetate, ethanol, and hydroalcoholic extracts of Albizia procera (leaf and bark) were subjected for acute oral toxicity, anti-inflammatory and analgesic screening. Carrageenan and cotton pellet granuloma models were used to assess acute and chronic anti-inflammatory effects, respectively. Intraplanar formalin test was used to assess the analgesic activity.

Results

All the extracts of Albizia procera were found to be well-tolerated up to 2000 mg/kg in female rats. Ethanolic leaf (ETLE) and bark (ETBE) of Albizia procera showed anti-inflammatory actions. But, only ETBE produced significant protection in chronic inflammation and analgesic activity.

Conclusion

In summary, Albizia procera possess significant anti-inflammatory and analgesic properties. This study adds evidence on the traditional use of Albizia procera plant for treating painful inflammatory disorders.

Rough and smooth variants of Mycobacterium abscessus are differentially controlled by host immunity during chronic infection of adult zebrafish

Prevalence of Mycobacterium abscessus infections is increasing in patients with respiratory comorbidities. After initial colonisation, M. abscessus smooth colony (S) variants can undergo an irreversible genetic switch into highly inflammatory, rough colony (R) variants, often associated with a decline in pulmonary function. Here, we use an adult zebrafish model of chronic infection with R and S variants to study M. abscessus pathogenesis in the context of fully functioning host immunity. We show that infection with an R variant causes an inflammatory immune response that drives necrotic granuloma formation through host TNF signalling, mediated by the tnfa, tnfr1 and tnfr2 gene products. T cell-dependent immunity is stronger against the R variant early in infection, and regulatory T cells associate with R variant granulomas and limit bacterial growth. In comparison, an S variant proliferates to high burdens but appears to be controlled by TNF-dependent innate immunity early during infection, resulting in delayed granuloma formation. Thus, our work demonstrates the applicability of adult zebrafish to model persistent M. abscessus infection, and illustrates differences in the immunopathogenesis induced by R and S variants during granulomatous infection.

The pathogen Mycobacterium abscessus can switch from a smooth colony form (S) into a highly inflammatory, rough colony form (R) during infection. Here, Kam et al. use an adult zebrafish model of M. abscessus chronic infection to illustrate differences in the immunopathogenesis induced by R and S variants.

Zebrafish Heme Oxygenase 1a Is Necessary for Normal Development and Macrophage Migration

Heme oxygenase function is highly conserved between vertebrates where it plays important roles in normal embryonic development and controls oxidative stress. Expression of the zebrafish heme oxygenase 1 genes is known to be responsive to oxidative stress suggesting a conserved physiological function. In this study, we generate a knockout allele of zebrafish hmox1a and characterize the effects of hmox1a and hmox1b loss on embryonic development. We find that loss of hmox1a or hmox1b causes developmental defects in only a minority of embryos, in contrast to Hmox1 gene deletions in mice that cause loss of most embryos. Using a tail wound inflammation assay we find a conserved role for hmox1a, but not hmox1b, in normal macrophage migration to the wound site. Together our results indicate that zebrafish hmox1a has clearly a partitioned role from hmox1b that is more consistent with conserved functions of mammalian Heme oxygenase 1.

Haem oxygenase limits Mycobacterium marinum infection-induced detrimental ferrostatin-sensitive cell death in zebrafish

Iron homeostasis is essential for both sides of the host-pathogen interface. Restricting access of iron slows bacterial growth while iron is also a necessary cofactor for host immunity. Haem oxygenase 1 (HMOX1) is a critical regulator of iron homeostasis that catalyses the liberation of iron during degradation of haem. It is also a stress-responsive protein that can be rapidly upregulated and confers protection to the host. Although a protective role of HMOX1 has been demonstrated in a variety of diseases, the role of HMOX1 in Mycobacterium tuberculosis infection is equivocal across experiments with different host-pathogen combinations. Here, we use the natural host-pathogen pairing of the zebrafish-Mycobacterium marinum infection platform to study the role of zebrafish haem oxygenase in mycobacterial infection. We identify zebrafish Hmox1a as the relevant functional paralog of mammalian HMOX1 and demonstrate a conserved role for Hmox1a in protecting the host from M. marinum infection. Using genetic and chemical tools, we show zebrafish Hmox1a protects the host against M. marinum infection by reducing infection-induced iron accumulation and ferrostatin-sensitive cell death.

Zebrafish as an alternative animal model in human and animal vaccination research

Much of medical research relies on animal models to deepen knowledge of the causes of animal and human diseases, as well as to enable the development of innovative therapies. Despite rodents being the most widely used research model worldwide, in recent decades, the use of the zebrafish (Danio rerio) model has exponentially been adopted among the scientific community. This is because such a small tropical freshwater teleost fish has crucial genetic, anatomical and physiological homology with mammals. Therefore, zebrafish constitutes an excellent experimental model for behavioral, genetic and toxicological studies which unravels the mechanism of various human diseases. Furthermore, it serves well to test new therapeutic agents, such as the safety of new vaccines. The aim of this review was to provide a systematic literature review on the most recent studies carried out on the topic. It presents numerous advantages of this type of animal model in tests of efficacy and safety of both animal and human vaccines, thus highlighting gains in time and cost reduction of research and analyzes.