Molecular mechanisms of selective autophagy in Drosophila

Preventing excessive autophagy protects from the pathology of mtDNA mutations in Drosophila melanogaster

Aberration of mitochondrial function is a shared feature of many human pathologies, characterised by changes in metabolic flux, cellular energetics, morphology, composition, and dynamics of the mitochondrial network. While some of these changes serve as compensatory mechanisms to maintain cellular homeostasis, their chronic activation can permanently affect cellular metabolism and signalling, ultimately impairing cell function. Here, we use a Drosophila melanogaster model expressing a proofreading-deficient mtDNA polymerase (POLγexo-) in a genetic screen to find genes that mitigate the harmful accumulation of mtDNA mutations. We identify critical pathways associated with nutrient sensing, insulin signalling, mitochondrial protein import, and autophagy that can rescue the lethal phenotype of the POLγexo- flies. Rescued flies, hemizygous for dilp1, atg2, tim14 or melted, normalise their autophagic flux and proteasome function and adapt their metabolism. Mutation frequencies remain high with the exception of melted-rescued flies, suggesting that melted may act early in development. Treating POLγexo- larvae with the autophagy activator rapamycin aggravates their lethal phenotype, highlighting that excessive autophagy can significantly contribute to the pathophysiology of mitochondrial diseases. Moreover, we show that the nucleation process of autophagy is a critical target for intervention.

Highlighting roles of autophagy in human diseases: a perspective from single-cell RNA sequencing analyses

Autophagy, the lysosome-driven breakdown of intracellular components, is pivotal in regulating eukaryotic cellular processes and maintaining homeostasis, making it physiologically important even under normal conditions. Cellular mechanisms involving autophagy include the response to nutrient deprivation, intracellular quality control, early development, and cell differentiation. Despite its established health significance, the role of autophagy in cancer and other diseases remains complex and not fully understood. A comprehensive understanding of autophagy is crucial to facilitate the development of novel therapies and drugs that can protect and improve human health. High-throughput technologies, such as single-cell RNA sequencing (scRNA-seq), have enabled researchers to study transcriptional landscapes at single-cell resolution, significantly advancing our knowledge of autophagy pathways across diverse physiological and pathological contexts. This review discusses the latest advances in scRNA-seq for autophagy research and highlights its potential in the molecular characterization of various diseases.

A Ketogenic Diet Affects Gut Microbiota by Regulating Gut Microbiota and Promoting Hippocampal TRHR Expression to Combat Seizures

With the persistent challenge that epilepsy presents to therapeutic avenues, the study seeks to decipher the effects of the ketogenic diet (KD) on gut microbiota and subsequent epileptic outcomes. Mouse fecal samples from distinct KD and control diet (CD) cohorts underwent 16S rRNA sequencing. Differential genes of epileptic mice under these diets were sourced from the GEO database. The study melded in vivo and in vitro techniques to explore the nuanced interactions between KD, gut microbiota, and hippocampal TRHR dynamics. The KD regimen was found to result in a notable reduction in gut microbiota diversity when compared to the CD groups. Distinctive microbial strains, which are hypothesised to interact with epilepsy through G protein-coupled receptors, were spotlighted. In vivo, explorations affirmed that gut microbiota as central to KD's anti-epileptic efficacy. Of 211 distinguished genes, the neuroactive ligand-receptor interaction pathway was underscored, particularly emphasizing TRHR and TRH. Clinical observations revealed a surge in hippocampal TRHR and TRH expressions influenced by KD, mirroring shifts in neuronal discharges. The KD, leveraging gut microbiota alterations, amplifies hippocampal TRHR expression. This finding provides a novel intervention strategy to reduce seizures.

The significant mechanism and treatments of cell death in heatstroke

With global warming, extreme environmental heat is becoming a social issue of concern, which can cause adverse health results including heatstroke (HS). Severe heat stress is characterized by cell death of direct heat damage, excessive inflammatory responses, and coagulation disorders that can lead to multiple organ dysfunction (MODS) and even death. However, the significant pathophysiological mechanism and treatment of HS are still not fully clear. Various modes of cell death, including apoptosis, pyroptosis, ferroptosis, necroptosis and PANoptosis are involved in MODS induced by heatstroke. In this review, we summarized molecular mechanism, key transcriptional regulation as for HSF1, NRF2, NF-κB and PARP-1, and potential therapies of cell death resulting in CNS, liver, intestine, reproductive system and kidney injury induced by heat stress. Understanding the mechanism of cell death provides new targets to protect multi-organ function in HS.

Research progress in mechanism of anticancer action of shikonin targeting reactive oxygen species

Excessive buildup of highly reactive molecules can occur due to the generation and dysregulation of reactive oxygen species (ROS) and their associated signaling pathways. ROS have a dual function in cancer development, either leading to DNA mutations that promote the growth and dissemination of cancer cells, or triggering the death of cancer cells. Cancer cells strategically balance their fate by modulating ROS levels, activating pro-cancer signaling pathways, and suppressing antioxidant defenses. Consequently, targeting ROS has emerged as a promising strategy in cancer therapy. Shikonin and its derivatives, along with related drug carriers, can impact several signaling pathways by targeting components involved with oxidative stress to induce processes such as apoptosis, necroptosis, cell cycle arrest, autophagy, as well as modulation of ferroptosis. Moreover, they can increase the responsiveness of drug-resistant cells to chemotherapy drugs, based on the specific characteristics of ROS, as well as the kind and stage of cancer. This research explores the pro-cancer and anti-cancer impacts of ROS, summarize the mechanisms and research achievements of shikonin-targeted ROS in anti-cancer effects and provide suggestions for designing further anti-tumor experiments and undertaking further experimental and practical research.

Innate immune and proinflammatory signals activate the Hippo pathway via a Tak1-STRIPAK-Tao axis

The Hippo pathway controls developmental, homeostatic and regenerative tissue growth, and is frequently dysregulated in various diseases. Although this pathway can be activated by innate immune/inflammatory stimuli, the underlying mechanism is not fully understood. Here, we identify a conserved signaling cascade that leads to Hippo pathway activation by innate immune/inflammatory signals. We show that Tak1, a key kinase in innate immune/inflammatory signaling, activates the Hippo pathway by inducing the lysosomal degradation of Cka, an essential subunit of the STRIPAK PP2A complex that suppresses Hippo signaling. Suppression of STRIPAK results in the activation of Hippo pathway through Tao-Hpo signaling. We further show that Tak1-mediated Hippo signaling is involved in processes ranging from cell death to phagocytosis and innate immune memory. Our findings thus reveal a molecular connection between innate immune/inflammatory signaling and the evolutionally conserved Hippo pathway, thus contributing to our understanding of infectious, inflammatory and malignant diseases.

Atg8 family proteins, LIR/AIM motifs and other interaction modes

The Atg8 family of ubiquitin-like proteins play pivotal roles in autophagy and other processes involving vesicle fusion and transport where the lysosome/vacuole is the end station. Nuclear roles of Atg8 proteins are also emerging. Here, we review the structural and functional features of Atg8 family proteins and their protein-protein interaction modes in model organisms such as yeast, Arabidopsis, C. elegans and Drosophila to humans. Although varying in number of homologs, from one in yeast to seven in humans, and more than ten in some plants, there is a strong evolutionary conservation of structural features and interaction modes. The most prominent interaction mode is between the LC3 interacting region (LIR), also called Atg8 interacting motif (AIM), binding to the LIR docking site (LDS) in Atg8 homologs. There are variants of these motifs like "half-LIRs" and helical LIRs. We discuss details of the binding modes and how selectivity is achieved as well as the role of multivalent LIR-LDS interactions in selective autophagy. A number of LIR-LDS interactions are known to be regulated by phosphorylation. New methods to predict LIR motifs in proteins have emerged that will aid in discovery and analyses. There are also other interaction surfaces than the LDS becoming known where we presently lack detailed structural information, like the N-terminal arm region and the UIM-docking site (UDS). More interaction modes are likely to be discovered in future studies.

Exploring the connection between autophagy and heat-stress tolerance in Drosophila melanogaster

Mechanisms aimed at recovering from heat-induced damages are closely associated with the ability of ectotherms to survive exposure to stressful temperatures. Autophagy, a ubiquitous stress-responsive catabolic process, has recently gained renewed attention as one of these mechanisms. By increasing the turnover of cellular structures as well as the clearance of long-lived protein and protein aggregates, the induction of autophagy has been linked to increased tolerance to a range of abiotic stressors in diverse ectothermic organisms. However, whether a link between autophagy and heat-tolerance exists in insect models remains unclear despite broad ecophysiological implications thereof. Here, we explored the putative association between autophagy and heat-tolerance using Drosophila melanogaster as a model. We hypothesized that (i) heat-stress would cause an increase of autophagy in flies' tissues, and (ii) rapamycin exposure would trigger a detectable autophagic response in adults and increase their heat-tolerance. In line with our hypothesis, we report that flies exposed to heat-stress present signs of protein aggregation and appear to trigger an autophagy-related homoeostatic response as a result. We further show that rapamycin feeding causes the systemic effect associated with target of rapamycin (TOR) inhibition, induces autophagy locally in the fly gut, and increases the heat-stress tolerance of individuals. These results argue in favour of a substantial contribution of autophagy to the heat-stress tolerance mechanisms of insects.

LC3-associated phagocytosis promotes glial degradation of axon debris after injury in Drosophila models

Glial engulfment of neuron-derived debris after trauma, during development, and in neurodegenerative diseases supports nervous system functions. However, mechanisms governing the efficiency of debris degradation in glia have remained largely unexplored. Here we show that LC3-associated phagocytosis (LAP), an engulfment pathway assisted by certain autophagy factors, promotes glial phagosome maturation in the Drosophila wing nerve. A LAP-specific subset of autophagy-related genes is required in glia for axon debris clearance, encoding members of the Atg8a (LC3) conjugation system and the Vps34 lipid kinase complex including UVRAG and Rubicon. Phagosomal Rubicon and Atg16 WD40 domain-dependent conjugation of Atg8a mediate proper breakdown of internalized axon fragments, and Rubicon overexpression in glia accelerates debris elimination. Finally, LAP promotes survival following traumatic brain injury. Our results reveal a role of glial LAP in the clearance of neuronal debris in vivo, with potential implications for the recovery of the injured nervous system.

LncRNA MEG3: Potential stock for precision treatment of cardiovascular diseases

The prevalence and mortality rates of cardiovascular diseases are increasing, and new treatment strategies are urgently needed. From the perspective of basic pathogenesis, the occurrence and development of cardiovascular diseases are related to inflammation, apoptosis, fibrosis and autophagy of cardiomyocytes, endothelial cells and other related cells. The involvement of maternally expressed gene 3 (MEG3) in human disease processes has been increasingly reported. P53 and PI3K/Akt are important pathways by which MEG3 participates in regulating cell apoptosis. MEG3 directly or competitively binds with miRNA to participate in apoptosis, inflammation, oxidative stress, endoplasmic reticulum stress, EMT and other processes. LncRNA MEG3 is mainly involved in malignant tumors, metabolic diseases, immune system diseases, cardiovascular and cerebrovascular diseases, etc., LncRNA MEG3 has a variety of pathological effects in cardiomyocytes, fibroblasts and endothelial cells and has great clinical application potential in the prevention and treatment of AS, MIRI, hypertension and HF. This paper will review the research progress of MEG3 in the aspects of mechanism of action, other systemic diseases and cardiovascular diseases, and point out its great potential in the prevention and treatment of cardiovascular diseases. lncRNAs also play a role in endothelial cells. In addition, lncRNA MEG3 has shown biomarker value, prognostic value and therapeutic response measurement in tumor diseases. We boldly speculate that MEG3 will play a role in the emerging discipline of tumor heart disease.

RNAi-mediated silencing of the autophagy-related gene NlATG3 inhibits survival and fecundity of the brown planthopper, Nilaparvata lugens

BACKGROUND

The brown planthopper (BPH), Nilaparvata lugens, is a serious insect pest of rice. Autophagy and its related gene ATG3 play multiple roles in insects. However, information about the functions of ATG3 in BPH (NlATG3) is unavailable, and its potential as a target for pest control remains unclear.

RESULTS

RT-qPCR results showed a relatively low expression of NlATG3 in 1st-4th-instar nymphs, which increased through 9-day-old adults. The expression of NlATG3 increased continuously in 1-day-old through 5-day-old eggs, whereas it decreased thereafter. The mRNA level of NlATG3 was markedly higher in the ovary (1.16) and head (1.00) compared to the rest body parts of BPH adults. Injecting nymphs with dsNlATG3 at doses from 62.5 to 250 ng per insect had strong lethal effect upon them. For the 5th-instar nymphs, all individuals died within 5 days after receiving the dsNlATG3, and importantly, no individual successfully molted. Transmission electron microscopy revealed the new cuticle of nymphs injected with dsNlATG3 became loose and curved, which is clearly different from that of the control. Correspondingly, the obvious vesicles in epidermal cells disappeared after dsNlATG3-treatment. RNAi of NlATG3 significantly reduced the total number of eggs laid per female as well as the eggs' hatchability, especially in the dsNlATG3♀ × dsGFP♂ group, whose total number of eggs laid per female largely decreased by 80.4%, and whose eggs' hatchability was significantly reduced from 95.7% to zero, when compared with the control (dsGFP♀ × dsGFP♂).

CONCLUSION

NlATG3 is a promising target for developing RNAi-based insect management strategies. © 2021 Society of Chemical Industry.

Autophagy in major human diseases

Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

Novel insights into biodegradation, interaction, internalization and impacts of high-aspect-ratio TiO2 nanomaterials: A systematic in vivo study using Drosophila melanogaster

The elongated nature of the high-aspect-ratio nanomaterials (NMs) can help us to obtain valuable information on its biodegradation, physical interaction with target-cells, and internalization. Three different length nano-titanium have been studied using Drosophila, TEM, and different biological markers. Nano-titanium, regardless of its shape, was eroded and degraded just entering the gut lumen of the larvae. Results showed that the distinguished shape of nanowires helps to understand the interactions of NMs with the intestinal barrier. The peritrophic membrane, as the first defense line of the intestinal barrier, succeeded in the reservation of NMs, though the perpendicular particles of nanowires stabbing it, making pores, and permitting their translocation into intestinal cells. On the other side, the exposure to TiO₂NPs did not decrease egg-to-adult viability, but all its different shapes, especially nanowires, mediated a wide molecular response including changes of expression in genes involved in stress, antioxidant, repair, and physical interaction responses. All these changes concerning their ability to elevate ROS levels ultimately led to potential genotoxicity. So, the high aspect ratio NMs are efficient in understanding the outstanding issues of NMs exposure, but at the same time could induce genotoxic impact rather than the low aspect ones.

Infection of Mammals and Mosquitoes by Alphaviruses: Involvement of Cell Death

Alphaviruses, such as the chikungunya virus, are emerging and re-emerging viruses that pose a global public health threat. They are transmitted by blood-feeding arthropods, mainly mosquitoes, to humans and animals. Although alphaviruses cause debilitating diseases in mammalian hosts, it appears that they have no pathological effect on the mosquito vector. Alphavirus/host interactions are increasingly studied at cellular and molecular levels. While it seems clear that apoptosis plays a key role in some human pathologies, the role of cell death in determining the outcome of infections in mosquitoes remains to be fully understood. Here, we review the current knowledge on alphavirus-induced regulated cell death in hosts and vectors and the possible role they play in determining tolerance or resistance of mosquitoes.