Autophagy in Tenebrio molitor Immunity: Conserved Antimicrobial Functions in Insect Defenses

Abstract

The yellow mealworm beetle (Tenebrio molitor) has been exploited as an experimental model to unravel the intricacies of cellular and humoral immunity against pathogenic infections. Studies on this insect model have provided valuable insights into the phenotypic plasticity of immune defenses against parasites and pathogens. It has thus been possible to characterize the hemocoelic defenses of T. molitor that rely on the recognition of non-self-components of pathogens by pattern recognition receptors (PRRs). The subsequent signaling cascade activating pathways such as the NF-κB controlled by Toll and IMD pathways lead to the synthesis of antimicrobial peptides (AMPs), onset of hemocyte-driven phagocytosis, and activation of the prophenoloxidase cascade regulating the process of melanization. Nevertheless, the activation of autophagy-mediated defenses of T. molitor against the facultative intracellular gram-positive bacterium Listeria monocytogenes provides clear evidence of the existence of a cross-talk between autophagy and the IMD pathway. Moreover, the identification of several autophagy-related genes (Atgs) in T. molitor transcriptome and expressed sequence tag (EST) databases has contributed to the understanding of the autophagy-signaling cascade triggered by L. monocytogenes challenge. Providing further evidence of the cross-talk hypothesis, TmRelish has been shown to be required not only for regulating the synthesis of AMPs through the PGRP-LE/IMD pathway activation but also for the expression of Atgs in T. molitor larvae following L. monocytogenes challenge. Notably, L. monocytogenes can stimulate the T. molitor innate immune system by producing molecules recognized by the multifunctional PRR (TmPGRP-LE), which stimulates intracellular activation of the IMD pathway and autophagy. Considering the conservation of autophagy components involved in combating intracellular pathogens, it will be interesting to extrapolate a dynamic cross-talk model of immune activation. This review summarizes the most significant findings on the regulation of autophagy in T. molitor during L. monocytogenes infection and on the role of the innate immunity machinery, including the NF-κB pathway, in the control of pathogenic load.

Identification of a Novel Densovirus in Aphid, and Uncovering the Possible Antiviral Process During Its Infection

“…Hence, the underlying mechanisms resistant to microbes in aphids are fascinated. In this study, KEGG enriched results show that the intrinsic antiviral mechanism in insects, such as autophagy pathway is also activated subjected to SmDV ( 52 – 54 ). The results of gene-concept network show that five significantly upregulated DEGs are shared in seven KEGG pathways, which probably be the other potential antiviral pathways in aphids.…”

Immune Defense Mechanism of Reticulitermes chinensis Snyder (Blattodea: Isoptera) against Serratia marcescens Bizio

“…In many organisms, endocytosis plays a housekeeping role and prevents the entry of foreign microbes [ 28 ]. Autophagy is an important pathway for insects to degrade dysfunctional cell components and eliminate the invaders [ 29 ]. We identified some cellular immune pathways from the top 20 enriched KEGG terms, such as endocytosis, lysosome, autophagy, and phagosome ( Figure 1 C).…”

Current Status of Immune Deficiency Pathway in Tenebrio molitor Innate Immunity

“…Another pathway that supposedly interacts with Imd signaling is autophagy, a conserved cellular mechanism that maintains homeostasis by eliminating dysfunctional cellular components and intracellular pathogens mediating its delivery to the lysosomes ( 63 , 64 ). PGRP-LE recognizes the intracellular pathogen Listeria and induces autophagy ( 64 ).…”

“…This was briefly addressed in a study wherein silencing of Tm Relish in T. molitor larvae decreased the mRNA levels of Tm Atg1 in the fat bodies and hemocytes subsequent to Listeria infection ( 47 ). This proposes a cross-talk between Listeria -induced autophagy and Imd pathway in T. molitor ( 63 ).…”