Keeping your vascular integrity: What can we learn from fish?

The Zebrafish Antiapoptotic Protein BIRC2 Promotes Edwardsiella piscicida Infection by Inhibiting Caspases and Accumulating p53 in a p53 Transcription-Dependent and -Independent Manner

IAPs (inhibitors of apoptosis) are endogenous caspase inhibitors with multiple biological activities. In the present study, we show functional characteristics of antiapoptotic protein BIRC2 (cIAP1) in response to Edwardsiella piscicida infection. Overexpression of BIRC2 in zebrafish larvae promoted the proliferation of E. piscicida, leading to a decreased larvae survival. The expression levels of caspases including casp3, casp8, and casp9 were significantly inhibited by BIRC2 overexpression in the case of E. piscicida infection. Treatment of zebrafish larvae microinjected with BIRC2 with the caspase activator PAC-1 completely blocked the negative regulation of BIRC2 on the E. piscicida infection, with the reduced inhibition on the casp3 and without inhibition on casp8 and casp9. In contrast to the regulation of BIRC2 on the caspases, BIRC2 overexpression significantly induced the expression of p53, especially at 24 hpi. In addition to the cytoplasmic p53 expression, BIRC2 overexpression also induced the expression of the nuclear p53 protein. Further analysis demonstrated that BIRC2 could interact and colocalize with p53 in the cytoplasm. The numbers of E. piscicida in larvae overexpressed with BIRC2 and treated with pifithrin-μ (an inhibitor of mitochondrial p53) or pifithrin-α (an inhibitor of p53 transactivation) were lower than those of larvae without pifithrin-μ or pifithrin-α treatment. Critically, the p53 inactivators pifithrin-μ and pifithrin-α had no significant effect on larval survival, but completely rescued larval survival for zebrafish microinjected with BIRC2 in the case of E. piscicida infection. Collectively, the present study suggest that piscine BIRC2 is a negative regulator for antibacterial immune response in response to the E. piscicida infection via inhibiting caspases, and accumulating p53 in a p53 transcription-dependent and -independent manner.

Irf8 regulates the progression of myeloproliferative neoplasm-like syndrome via Mertk signaling in zebrafish

Interferon regulatory factor (IRF)-8 is a critical transcription factor involved in the pathogenesis of myeloid neoplasia. However, the underlying mechanisms in vivo are not well known. Investigation of irf8-mutant zebrafish in this study indicated that Irf8 is evolutionarily conserved as an essential neoplastic suppressor through tight control of the proliferation and longevity of myeloid cells. Surviving irf8 mutants quickly developed a myeloproliferative neoplasm (MPN)-like disease with enhanced output of the myeloid precursors, which recurred after transplantation. Multiple molecules presented notable alteration and Mertk signaling was aberrantly activated in the hematopoietic cells in irf8 mutants. Transgenic mertk overexpression in Tg(coro1a:mertk) zebrafish recapitulated the myeloid neoplasia-like syndrome in irf8 mutants. Moreover, functional interference with Mertk, via morpholino knockdown or genetic disruption, attenuated the myeloid expansion phenotype caused by Irf8 deficiency. Therefore, Mertk signaling is a critical downstream player in the Irf8-mediated regulation of the progression of myeloid neoplasia. Our study extends the understanding of the mechanisms underlying leukemogenesis.

Essential functional modules for pathogenic and defensive mechanisms in Candida albicans infections

The clinical and biological significance of the study of fungal pathogen Candida albicans (C. albicans) has markedly increased. However, the explicit pathogenic and invasive mechanisms of such host-pathogen interactions have not yet been fully elucidated. Therefore, the essential functional modules involved in C. albicans-zebrafish interactions were investigated in this study. Adopting a systems biology approach, the early-stage and late-stage protein-protein interaction (PPI) networks for both C. albicans and zebrafish were constructed. By comparing PPI networks at the early and late stages of the infection process, several critical functional modules were identified in both pathogenic and defensive mechanisms. Functional modules in C. albicans, like those involved in hyphal morphogenesis, ion and small molecule transport, protein secretion, and shifts in carbon utilization, were seen to play important roles in pathogen invasion and damage caused to host cells. Moreover, the functional modules in zebrafish, such as those involved in immune response, apoptosis mechanisms, ion transport, protein secretion, and hemostasis-related processes, were found to be significant as defensive mechanisms during C. albicans infection. The essential functional modules thus determined could provide insights into the molecular mechanisms of host-pathogen interactions during the infection process and thereby devise potential therapeutic strategies to treat C. albicans infection.

The synaptic proteins β-neurexin and neuroligin synergize with extracellular matrix-binding vascular endothelial growth factor a during zebrafish vascular development

OBJECTIVE

The goal of this study was to determine the in vivo functions of the synaptic proteins neurexins and neuroligins in embryonic vascular system development using zebrafish as animal model.

METHODS AND RESULTS

In the present study, we show that the knockdown of the α-form of neurexin 1a induces balance defects and reduced locomotory activity, whereas β-neurexin 1a and neuroligin 1 morphants present defects in sprouting angiogenesis and vascular remodeling, in particular in the caudal plexus and subintestinal vessels. Coinjection of low doses of morpholinos for β-neurexin 1a and neuroligin 1 together or in combination with morpholinos targeting the -heparin--binding isoforms of vascular endothelial growth factor A (encoded by the VEGFAb gene) recapitulates the observed abnormalities, suggesting synergistic activity of these molecules. Similar coinjection experiments with morpholinos, targeting the enzyme heparan sulfate 6-O-sulfotransferase 2, confirm the presence of a functional correlation between extracellular matrix maturation and β-neurexin 1a or neuroligin 1.

CONCLUSIONS

Our data represent the first in vivo evidence of the role of neurexin and neuroligin in embryonic blood vessel formation and provide insights into their mechanism of action.