Molecular characterization and functional analysis of duck IKKα

Epidemiology, genetic diversity, and evolutionary dynamics of Tembusu virus

Tembusu virus (TMUV) is an emerging pathogenic flavivirus associated with acute egg-drop and fatal encephalitis in domestic waterfowl. Since its initial identification in mosquitoes in 1955, TMUV has been confirmed to infect ducks, pigeons, sparrows, geese, and chickens, posing a significant threat to the poultry industry. Here, we sequenced two DTMUV strains isolated in 2019 and systematically investigated the possible origin, genetic relationships, evolutionary dynamics, and transmission patterns of TMUV based on complete virus genome sequences in the public database. We found that TMUV can be divided into four major clusters: TMUV, cluster 1, cluster 2, and cluster 3. Interestingly, we found that cluster 2.2 (within cluster 2) is the most commonly involved in interspecies transmission events, and subcluster 2.1.2 (within cluster 2.1) is currently the most prevalent cluster circulating in Asia. Notably, we also identified three positively selected sites in the E and NS1 proteins, which may be involved in virus replication, immune evasion, and host adaptation. Finally, phylogeographic analysis revealed that cluster dispersal originated in Southeast Asia and that short-distance transmission events have occurred frequently. Altogether, these data provide novel insights into the evolution and dispersal of TMUV, facilitating the development of rapid diagnostics, vaccines, and therapeutics against TMUV infection.

Evolution of RNA sensing receptors in birds

Birds are important hosts for many RNA viruses, including influenza A virus, Newcastle disease virus, West Nile virus and coronaviruses. Innate defense against RNA viruses in birds involves detection of viral RNA by pattern recognition receptors. Several receptors of different classes are involved, such as endosomal toll-like receptors and cytoplasmic retinoic acid-inducible gene I-like receptors, and their downstream adaptor proteins. The function of these receptors and their antagonism by viruses is well established in mammals; however, this has received less attention in birds. These receptors have been characterized in a few bird species, and the completion of avian genomes will permit study of their evolution. For each receptor, functional work has established ligand specificity and activation by viral infection. Engagement of adaptors, regulation by modulators and the supramolecular organization of proteins required for activation are incompletely understood in both mammals and birds. These receptors bind conserved nucleic acid agonists such as single- or double-stranded RNA and generally show purifying selection, particularly the ligand binding regions. However, in birds, these receptors and adaptors differ between species, and between individuals, suggesting that they are under selection for diversification over time. Avian receptors and signalling pathways, like their mammalian counterparts, are targets for antagonism by a variety of viruses, intent on escape from innate immune responses.

Characterization of duck IκB kinase β involved in innate immunity

IκB kinase β (IKKβ), a catalytic subunit of the IKK complex, is involved in a wide array of biological processes, particularly in inflammation and innate immunity. Although extensive studies have been carried out to explore the roles of mammalian IKKβs in innate immune response, the function of IKKβ in avian innate immunity is largely unknown. Here, we cloned and characterized the duck IKKβ (duIKKβ) gene for the first time. DuIKKβ encoded 755 amino acids and displayed high sequence similarity to pseudopodoces and haliaeetus IKKβs. DuIKKβ transcripts were widely distributed in all tested tissues, especially with high expression in the thymus and bursa of Fabricius. Overexpression of duIKKβ promoted NF-κB activation and initiated the downstream cytokines expression including IFN-β, ZAP, PKR, IL-8, and CCL5 in duck embryo fibroblasts. Furthermore, knockdown of endogenous duIKKβ significantly reduced LPS-, poly(I:C)- or SeV-induced NF-κB activation. Finally, we demonstrated that duIKKβ showed antiviral activity against Duck Tembusu virus infection. Our findings provide insights into the roles of duIKKβ in avian innate immunity.

Redox Homeostasis in Poultry: Regulatory Roles of NF-κB

Redox biology is a very quickly developing area of modern biological sciences, and roles of redox homeostasis in health and disease have recently received tremendous attention. There are a range of redox pairs in the cells/tissues responsible for redox homeostasis maintenance/regulation. In general, all redox elements are interconnected and regulated by various means, including antioxidant and vitagene networks. The redox status is responsible for maintenance of cell signaling and cell stress adaptation. Physiological roles of redox homeostasis maintenance in avian species, including poultry, have received limited attention and are poorly characterized. However, for the last 5 years, this topic attracted much attention, and a range of publications covered some related aspects. In fact, transcription factor Nrf2 was shown to be a master regulator of antioxidant defenses via activation of various vitagenes and other protective molecules to maintain redox homeostasis in cells/tissues. It was shown that Nrf2 is closely related to another transcription factor, namely, NF-κB, responsible for control of inflammation; however, its roles in poultry have not yet been characterized. Therefore, the aim of this review is to describe a current view on NF-κB functioning in poultry with a specific emphasis to its nutritional modulation under various stress conditions. In particular, on the one hand, it has been shown that, in many stress conditions in poultry, NF-κB activation can lead to increased synthesis of proinflammatory cytokines leading to systemic inflammation. On the other hand, there are a range of nutrients/supplements that can downregulate NF-κB and decrease the negative consequences of stress-related disturbances in redox homeostasis. In general, vitagene-NF-κB interactions in relation to redox balance homeostasis, immunity, and gut health in poultry production await further research.