Oligomycin A induces autophagy in the IPLB-LdFB insect cell line

The Over-Irradiation Metabolite Derivative, 24-Hydroxylumister-ol3, Reduces UV-Induced Damage in Skin

The hormonal form of vitamin D₃, 1,25(OH)₂D₃, reduces UV-induced DNA damage. UV exposure initiates pre-vitamin D₃ production in the skin, and continued UV exposure photoisomerizes pre-vitamin D₃ to produce "over-irradiation products" such as lumisterol₃ (L₃). Cytochrome P450 side-chain cleavage enzyme (CYP11A1) in skin catalyzes the conversion of L₃ to produce three main derivatives: 24-hydroxy-L₃ [24(OH)L₃], 22-hydroxy-L₃ [22(OH)L₃], and 20,22-dihydroxy-L₃ [20,22(OH)L₃]. The current study investigated the photoprotective properties of the major over-irradiation metabolite, 24(OH)L₃, in human primary keratinocytes and human skin explants. The results indicated that treatment immediately after UV with either 24(OH)L₃ or 1,25(OH)₂D₃ reduced UV-induced cyclobutane pyrimidine dimers and oxidative DNA damage, with similar concentration response curves in keratinocytes, although in skin explants, 1,25(OH)₂D₃ was more potent. The reductions in DNA damage by both compounds were, at least in part, the result of increased DNA repair through increased energy availability via increased glycolysis, as well as increased DNA damage recognition proteins in the nucleotide excision repair pathway. Reductions in UV-induced DNA photolesions by either compound occurred in the presence of lower reactive oxygen species. The results indicated that under in vitro and ex vivo conditions, 24(OH)L₃ provided photoprotection against UV damage similar to that of 1,25(OH)₂D₃.

Advances in the Immune Regulatory Role of Non-Coding RNAs (miRNAs and lncRNAs) in Insect-Pathogen Interactions

Insects are by far the most abundant and diverse living organisms on earth and are frequently prone to microbial attacks. In other to counteract and overcome microbial invasions, insects have in an evolutionary way conserved and developed immune defense mechanisms such as Toll, immune deficiency (Imd), and JAK/STAT signaling pathways leading to the expression of antimicrobial peptides. These pathways have accessory immune effector mechanisms, such as phagocytosis, encapsulation, melanization, nodulation, RNA interference (RNAi), lysis, autophagy, and apoptosis. However, pathogens evolved strategies that circumvent host immune response following infections, which may have helped insects further sophisticate their immune response mechanisms. The involvement of ncRNAs in insect immunity is undeniable, and several excellent studies or reviews have investigated and described their roles in various insects. However, the functional analyses of ncRNAs in insects upon pathogen attacks are not exhaustive as novel ncRNAs are being increasingly discovered in those organisms. This article gives an overview of the main insect signaling pathways and effector mechanisms activated by pathogen invaders and summarizes the latest findings of the immune modulation role of both insect- and pathogen-encoded ncRNAs, especially miRNAs and lncRNAs during insect–pathogen crosstalk.

Mitochondrial dysfunction triggers the pathogenesis of Parkinson's disease in neuronal C/EBPβ transgenic mice

Respiratory chain complex I deficiency elicits mitochondrial dysfunction and reactive oxidative species (ROS), which plays a crucial role in Parkinson's disease (PD) pathogenesis. However, it remains unclear whether the impairment in other complexes in the mitochondrial oxidative phosphorylation chain is also sufficient to trigger PD onset. Here we show that inhibition of Complex II or III in the electron transport chain (ETC) induces the motor disorder and PD pathologies in neuronal Thy1-C/EBPβ transgenic mice. Through a cell-based screening of mitochondrial respiratory chain inhibitors, we identified TTFA (complex II inhibitor) and Atovaquone (complex III inhibitor), which robustly block the oxidative phosphorylation functions, strongly escalate ROS, and activate C/EBPβ/AEP pathway that triggers dopaminergic neuronal cell death. Oral administration of these inhibitors to Thy1-C/EBPβ mice elicits constipation and motor defects, associated with Lewy body-like inclusions. Deletion of SDHD (Succinate dehydrogenase) gene from the complex II in the Substantia Nigra of Thy1-C/EBPβ mice triggers ROS and PD pathologies, resulting in motor disorders. Hence, our findings demonstrate that mitochondrial ETC inactivation triggers PD pathogenesis via activating C/EBPβ/AEP pathway.

Haemocyte-mediated immunity in insects: Cells, processes and associated components in the fight against pathogens and parasites

The host defence of insects includes a combination of cellular and humoral responses. The cellular arm of the insect innate immune system includes mechanisms that are directly mediated by haemocytes (e.g., phagocytosis, nodulation and encapsulation). In addition, melanization accompanying coagulation, clot formation and wound healing, nodulation and encapsulation processes leads to the formation of cytotoxic redox-cycling melanin precursors and reactive oxygen and nitrogen species. However, demarcation between cellular and humoral immune reactions as two distinct categories is not straightforward. This is because many humoral factors affect haemocyte functions and haemocytes themselves are an important source of many humoral molecules. There is also a considerable overlap between cellular and humoral immune functions that span from recognition of foreign intruders to clot formation. Here, we review these immune reactions starting with the cellular mechanisms that limit haemolymph loss and participate in wound healing and clot formation and advancing to cellular functions that are critical in restricting pathogen movement and replication. This information is important because it highlights that insect cellular immunity is controlled by a multilayered system, different components of which are activated by different pathogens or during the different stages of the infection.

Curcumin-induced autophagy and nucleophagy in Spodoptera frugiperda Sf9 insect cells occur via PI3K/AKT/TOR pathways

Compounds from plants or microbes are important resources for new natural pesticides against a wide variety of pests. The growing attention on the role of autophagy (type II cell death) in regulation of insect toxicology has propelled researchers to investigate autophagic cell death pathways. Our previous study proved that the cytotoxic effect of curcumin in Spodoptera frugiperda cells is regulated by autophagy. However, the signaling pathways and molecular mechanisms had not been determined. The current study elucidates curcumin inhibition of survival signaling by blocking the activation of PI3K/AKT/TOR pathways to induce autophagy in S. frugiperda cells. The result demonstrates that nucleophagy associated with cell death following the curcumin treatment. Following the curcumin treatment, Atg8/LC3 immunostaining in both nucleus and cytoplasm was markedly increased. Further, messenger RNA expression level of Atg8 and Atg1 genes regulation by curcumin was examined using quantitative reverse transcription polymerase chain reaction, and the result exhibited increased level of expression after curcumin treatment in a time-dependent manner. Our current study provides new insights to the autophagy occurring via PI3K/AKT/TOR pathways in S. frugiperda Sf9 insect cells induced by curcumin. Taken together, our results show for the first time that curcumin induced nucleophagy in lepidopteron insect cell line.

Natural β-carboline alkaloids regulate the PI3K/Akt/mTOR pathway and induce autophagy in insect Sf9 cells

The β-carboline alkaloids are a large group of naturally occurring and synthetic indole alkaloids with remarkable pharmacological properties. Furthermore, these alkaloids have also been reported to be effective agents for controlling many pests and plant pathogenic nematodes. However, studies on these potential insecticidal components are scarce. The previous finding that these bioactive compounds can induce programmed cell death in cancer cell lines provided a new insight for exploration of their toxicological mechanisms on insects. In the present study, the cytotoxicity of five natural harmala alkaloids was measured, and the autophagy-inducing effect was confirmed in the Spodoptera frugiperda Sf9 cultured cell line. The results demonstrated that these alkaloids inhibited the proliferation of Sf9 cells in a dose- and time-dependent manner, and the unsaturated β-carboline alkaloids, harmine and harmol, exhibited stronger autophagy induction activity based on monodansylcadaverineand LysoTracker Red staining. Many autophagy-related genes were increased after β-carbolines treatment at the RNA level, and the protein expression of Sf-Atg8 was also confirmed to increase after treatment. In addition, the primary autophagic signaling pathway, the PI3K/Akt/mTOR pathway, was altered during the procedure. Furthermore, experiments with special inhibitors and activators were performed to confirm the effect of β-carbolines on this pathway. The results suggested that the PI3K/Akt/mTOR pathway primarily regulated harmine-induced autophagy in insect cells, and this finding may potentially benefit the application of these promising bioactivity components.

Curcumin induces autophagic cell death in Spodoptera frugiperda cells

The increasing interest in the role of autophagy (type II cell death) in the regulation of insect toxicology has propelled study of investigating autophagic cell death pathways. Turmeric, the rhizome of the herb Curcuma longa (Mañjaḷ in Tamil, India and Jiānghuáng in Chinese) have been traditionally used for the pest control either alone or combination with other botanical pesticides. However, the mechanisms by which Curcuma longa or curcumin exerts cytotoxicity in pests are not well understood. In this study, we investigated the potency of Curcuma longa (curcumin) as a natural pesticide employing Sf9 insect line. Autophagy induction effect of curcumin on Spodoptera frugiperda (Sf9) cells was investigated using various techniques including cell proliferation assay, morphology analysis with inverted phase contrast microscope and Transmission Electron Microscope (TEM) analysis. Autophagy was evaluated using the fluorescent dye monodansylcadaverine (MDC). Cell death measurement was examined using 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) within the concentrations of 5-15μg/mL. Curcumin inhibited the growth of the Sf9 cells and induced autophagic cell death in a time and dose dependent manner. Staining the cells with MDC showed the presence of autophagic vacuoles while increased in a dose and time dependent manner. At the ultrastructural level transmission electron microscopy, cells revealed massive autophagy vacuole accumulation and absence of chromatin condensation. Protein expression levels of ATG8-I and ATG8-II, well-established markers of autophagy related protein were elevated in a time dependent manner after curcumin treatment. The present study proves that curcumin induces autophagic cell death in Sf9 insect cell line and this is the first report of cytotoxic effect of curcumin in insect cells and that will be utilized as natural pesticides in future.

The Drosophila effector caspase Dcp-1 regulates mitochondrial dynamics and autophagic flux via SesB

Increasing evidence reveals that a subset of proteins participates in both the autophagy and apoptosis pathways, and this intersection is important in normal physiological contexts and in pathological settings. In this paper, we show that the Drosophila effector caspase, Drosophila caspase 1 (Dcp-1), localizes within mitochondria and regulates mitochondrial morphology and autophagic flux. Loss of Dcp-1 led to mitochondrial elongation, increased levels of the mitochondrial adenine nucleotide translocase stress-sensitive B (SesB), increased adenosine triphosphate (ATP), and a reduction in autophagic flux. Moreover, we find that SesB suppresses autophagic flux during midoogenesis, identifying a novel negative regulator of autophagy. Reduced SesB activity or depletion of ATP by oligomycin A could rescue the autophagic defect in Dcp-1 loss-of-function flies, demonstrating that Dcp-1 promotes autophagy by negatively regulating SesB and ATP levels. Furthermore, we find that pro-Dcp-1 interacts with SesB in a nonproteolytic manner to regulate its stability. These data reveal a new mitochondrial-associated molecular link between nonapoptotic caspase function and autophagy regulation in vivo.

A molecular view of autophagy in Lepidoptera

Metamorphosis represents a critical phase in the development of holometabolous insects, during which the larval body is completely reorganized: in fact, most of the larval organs undergo remodeling or completely degenerate before the final structure of the adult insect is rebuilt. In the past, increasing evidence emerged concerning the intervention of autophagy and apoptosis in the cell death processes that occur in larval organs of Lepidoptera during metamorphosis, but a molecular characterization of these pathways was undertaken only in recent years. In addition to developmentally programmed autophagy, there is growing interest in starvation-induced autophagy. Therefore we are now entering a new era of research on autophagy that foreshadows clarification of the role and regulatory mechanisms underlying this self-digesting process in Lepidoptera. Given that some of the most important lepidopteran species of high economic importance, such as the silkworm, Bombyx mori, belong to this insect order, we expect that this information on autophagy will be fully exploited not only in basic research but also for practical applications.

Increased levels of reduced cytochrome b and mitophagy components are required to trigger nonspecific autophagy following induced mitochondrial dysfunction

Mitochondria are essential organelles producing most of the energy required for the cell. A selective autophagic process called mitophagy removes damaged mitochondria, which is critical for proper cellular homeostasis; dysfunctional mitochondria can generate excess reactive oxygen species that can further damage the organelle as well as other cellular components. Although proper cell physiology requires the maintenance of a healthy pool of mitochondria, little is known about the mechanism underlying the recognition and selection of damaged organelles. In this study, we investigated the cellular fate of mitochondria damaged by the action of respiratory inhibitors (antimycin A, myxothiazol, KCN) that act on mitochondrial respiratory complexes III and IV, but have different effects with regard to the production of reactive oxygen species and increased levels of reduced cytochromes. Antimycin A and potassium cyanide effectively induced nonspecific autophagy, but not mitophagy, in a wild-type strain of Saccharomyces cerevisiae; however, low or no autophagic activity was measured in strains deficient for genes that encode proteins involved in mitophagy, including ATG32, ATG11 and BCK1. These results provide evidence for a major role of specific mitophagy factors in the control of a general autophagic cellular response induced by mitochondrial alteration. Moreover, increased levels of reduced cytochrome b, one of the components of the respiratory chain, could be the first signal of this induction pathway.

Mitophagy: a process that adapts to the cell physiology

This focus makes a case that mitophagy is not a straightforward process obeying simple rules. It is a complex process through which the cell gets rid of both damaged and healthy untainted mitochondria to adjust their amount, and in accordance with cellular energy requirements. Several aspects of mitophagy have been described in both yeast and mammalian cells. They have revealed a number of discrepancies in the regulation of this process in the two eukaryotic models. Data have shown that mitophagy is a function of cell physiology. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Dual effects of silibinin treatment on autophagy-regulated dermal apoptosis retardation and epidermal apoptosis up-regulation in UVB-induced skin inflammation

Skin inflammation induced by ultraviolet B (UVB) radiation is characterized by migration and chemotaxis of inflammatory cells, epidermic thickening and erythema. Apoptosis and autophagy of epidermal and dermal cells are involved in its development through the adjustment of balance between cell survival and death. In this study, the role of balance between cell survival and apoptosis in dermis and epidermis in UVB-induced skin inflammation and the effect of autophagy on the balance were elucidated, and the protective mechanism of silibinin was investigated through the examination of the influence of autophagy activation or inhibition on erythema, migration, and chemotaxis of inflammatory cells as well as apoptosis adjustments. In UVB-irradiated controls, dermal apoptosis was retarded and the survival of inflammatory cells was promoted through the up-regulation of dermal autophagic level; epidermal apoptosis was increased through the down-regulation of epidermal autophagic level, causing migration and chemotaxis of neutrophils and mast cells as well as skin erythema. In silibinin-treated group (50 mg/kg/day for 4 days), dermal apoptosis was increased through inhibiting dermal autophagy; improper adjustment of epidermal apoptosis was attenuated through promoting epidermal autophagy, presenting dual effects on the balance between autophagy and apoptosis of epidermal and dermal cells and the protection.

Macroautophagy: the key ingredient to a healthy diet?

Dietary compounds can influence the risk of cancer and other diseases through diverse mechanisms which include the activation or inhibition of macroautophagy. Macroautophagy is a catabolic process for the lysosomal degradation and recycling of cytoplasmic constituents which has been implicated in several pathologies, including cancer and neurodegeneration. In some instances, macroautophagy acts to suppress tumor formation and neural degeneration. Thus, it may be feasible to design diets, supplements or therapeutics that can alter the level of macroautophagy within cells to prevent or treat disease. While critical questions still need to be answered before we can safely and effectively implement such a strategy, we provide here a review of the literature regarding dietary constituents that have a demonstrated macroautophagy-modulating function.

New insights into autophagic cell death in the gypsy moth Lymantria dispar: a proteomic approach

Autophagy is an evolutionary ancient process based on the activity of genes conserved from yeast to metazoan taxa. Whereas its role as a mechanism to provide energy during cell starvation is commonly accepted, debate continues about the occurrence of autophagy as a means specifically activated to achieve cell death. The IPLB-LdFB insect cell line, derived from the larval fat body of the lepidoptera Lymantria dispar, represents a suitable model to address this question, as both autophagic and apoptotic cell death can be induced by various stimuli. Using morphological and functional approaches, we have observed that the culture medium conditioned by IPLB-LdFB cells committed to death by the ATPase inhibitor oligomycin A stimulates autophagic cell death in untreated IPLB-LdFB cells. Moreover, proteomic analysis of the conditioned media suggests that, in IPLB-LdFB cells, oligomycin A promotes a shift towards lipid metabolism, increases oxidative stress and specifically directs the cells towards autophagic activity.

Amino acid regulation of autophagosome formation

Amino acids are not only substrates for various metabolic pathways, but can also serve as signaling molecules controlling signal transduction pathways. One of these signaling pathways is mTOR-dependent and is activated by amino acids (leucine in particular) in synergy with insulin. Activation of this pathway inhibits autophagy. Because activation of mTOR-mediated signaling also stimulates protein synthesis, it appears that protein synthesis and autophagic protein degradation are reciprocally controlled by the same signaling pathway. Recent developments indicate that amino acid-stimulated mTOR-dependent signaling is subject to complex regulation. The mechanism by which amino acids stimulate mTORdependent signaling (and other signaling pathways), and its molecular connection with the autophagic machinery, is still unknown.

In vitro methods to monitor autophagy in Lepidoptera

Autophagy is attracting growing interest, especially in relation to increasing evidence of the importance of autophagic processes in animal development, as well as in human cancer progression. In holometabolous insects (i.e., that undergo four distinct life cycle stages, including embryo, larva, pupa and imago), such as flies, butterflies, bees and beetles, autophagy has been found to play a fundamental role in metamorphosis, and given the high degree of conservation of the genes and the basic mechanisms of autophagy, attention to these relatively simple models has increased significantly. Together with Drosophila, Lepidoptera larvae are among the most common invertebrate models in studies concerning the protective action of starvation-induced autophagy or the possible role of autophagy as a programmed cell death process. In this chapter, we provide experimental methods developed for, or applicable to, the study of the autophagic process in the IPLB-LdFB cell line derived from the fat body of the caterpillar of the gypsy moth, Lymantria dispar.

Oligomycin A and the IPLB-LdFB insect cell line: actin and mitochondrial responses

Oligomycin A, an inhibitor of mitochondrial ATP synthase, provokes simultaneous and different responses in IPLB-LdFB insect cell line. The oligomycin A treatment causes mitochondrial loss, increase in reactive oxygen species (ROS), destabilization/reorganization of the actin microfilaments and, finally, autophagic cell death. We speculate that oligomycin A affects the mitochondria and that the impairment of these organelles leads to the generation of ROS in quantities that exceed the antioxidant capacity of the cell. This in turn would lead to a feedback loop of increased mitochondrial impairment, amplification of ROS production and the removal of damaged organelles through autophagy.

Programmed cell death and stem cell differentiation are responsible for midgut replacement in Heliothis virescens during prepupal instar

We have analyzed midgut development during the fifth larval instar in the tobacco budworm Heliothis virescens. In prepupae, the midgut formed during larval instars undergoes a complete renewal process. This drastic remodeling of the alimentary canal involves the destruction of the old cells by programmed cell-death mechanisms (autophagy and apoptosis). Massive proliferation and differentiation of regenerative stem cells take place at the end of the fifth instar and give rise to a new fully functioning epithelium that is capable of digesting and absorbing nutrients and that is maintained throughout the subsequent pupal stage. Midgut replacement in H. virescens is achieved by a balance between this active proliferation process and cell-death mechanisms and is different from similar processes characterized in other insects.

Influence of glucose starvation on the pathway of death in insect cell line Sl: apoptosis follows autophagy

The relation between autophagy and apoptosis has not been clearly elucidated. Here, we reported that apoptosis followed autophagy in insect Spodoptera litura cells (Sl) undergoing glucose starvation. Sl cells have been adapted to Leibovitz-15 medium supplemented with glucose (1.0 g/l) and 5% fetal bovine serum (FBS), used for mammalian cell cultures. If glucose (1 g/l) or glutamine (1.6 g/l) had not been supplemented in L-15 medium with 5% FBS, Sl cells began to form many vacuoles and these vacuoles gradually enlarged in the cytoplasm, which were autophagic vacuoles. However, these large vacuoles began to disappear gradually after 48 h of glucose starvation, accompanied with remarkable apoptosis without apoptotic bodies, which was demonstrated by DNA fragmentation and activation of caspase-3-like. During glucose starvation, Sl cell ATP concentrations gradually decreased. Interestingly, if the conditioned L-15 medium without glucose was replaced with fresh L-15 medium supplemented with glucose or glutamine after the cultures had been starved seriously for 48 h or longer, the formation of apoptotic bodies was initiated. These data suggested that the partial depletion of cell ATP triggered apoptosis following autophagy in glucose-starved Sl cells and the formation of apoptotic bodies required higher level of ATP than DNA fragmentation and activation of caspase-3-like activity. Additionally, the disappearance of autophagic vacuoles, negative staining of neutral red, green staining of acridine orange and diffusion of acid phosphatase activity in Sl cells at the late stage of starvation (over 48 h) suggested that the dysfunction of lysosome was more likely to involve in apoptosis. The facts that Actinomycin D-induced apoptosis was partially inhibited and cyclosporin A, blocking the opening of mitochondrial permeability transition (MPT) pores, inhibited partially apoptosis in glucose-starved Sl cells, suggested the pathway of glucose starvation-induced apoptosis seemed to be different from that induced by actinomycin D and the opening of MPT pores on mitochondria probably involved in apoptosis triggered by glucose starvation, respectively.