Abstract
Autophagy is an important process by which pathogens and damaged or unused organelles are eliminated. The role of autophagy in development and the immune response to pathogens is well established. Autophagy-related protein 8 (Atg8) is involved in the formation of the autophagosome and, with the help of the serine protease Atg4, mediates the delivery of both vesicles and the autophagosome to the vacuole. Here, we cloned the Aedes albopictus autophagy-related protein 8 (AaAtg8) gene and characterized its role in the innate immunity of the mosquito against microbial infections. AaAtg8 is comprised of an open reading frame (ORF) region of 357 bp encoding a polypeptide of 118 amino acid residues. A domain analysis of AaAtg8 revealed an Atg8 ubiquitin-like domain, Atg7/Atg4 interaction sites, and peptide binding sites. The AaAtg8 mRNA expression was high in the Malpighian tubules and heads of both sugar-fed and blood-fed adult female mosquitoes. The expression level of AaAtg8 mRNA increased in the midgut and abdominal carcass following being challenged with Listeria monocytogenes. To investigate the role of AaAtg8 in the innate immune responses of Ae. albopictus, AaAtg8 gene-silenced adult mosquitoes were challenged by injection or by being fed microorganisms in blood. High mortality rates were observed in mosquitoes in which AaAtg8 was silenced after challenges of microorganisms to the host by blood feeding. This suggests that Atg8-autophagy plays a critical role in the gut immunity in Ae. albopictus.
Highlights
Autophagy is a conserved mechanism among metazoans, wherein dysfunctional cellular components are degraded in-bulk by the lysosome
Through an RNA interference-based silencing assay, that Aedes albopictus autophagy-related protein 8 (AaAtg8)-depleted adult mosquitoes are more susceptible to L. monocytogenes infection
Increased susceptibility against bacterial feeding (Escherichia coli, Staphylococcus aureus, L. monocytogenes and Candida albicans) was observed in the dsAaAtg8-treated group, suggesting that autophagy plays a critical role in antibacterial gut immunity in Ae. albopictus
Summary
Autophagy is a conserved mechanism among metazoans, wherein dysfunctional cellular components are degraded in-bulk by the lysosome. Many infection models have considered the autophagy signaling pathway responsible for targeting pathogens for eventual degradation in autolysosomes [4,5]. An autophagosome comprising the sequestered cytoplasm and dysfunctional organelles is formed This autophagosome subsequently fuses with the vacuolar membrane and discards the autophagic contents. Earlier reports suggest that Atg regulates the size of the autophagosome in selective autophagy [8,15]. In this context, the Atg protein is considered a reliable biomarker for autophagy induction and progression [16,17]. Increased susceptibility against bacterial feeding (Escherichia coli, Staphylococcus aureus, L. monocytogenes and Candida albicans) was observed in the dsAaAtg8-treated group, suggesting that autophagy plays a critical role in antibacterial gut immunity in Ae. albopictus
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