Cell-death mechanisms in the IPLB-LdFB insect cell line: a nuclear located Bcl-2-like molecule as a possible controller of 2-deoxy-D-ribose-mediated DNA fragmentation

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.

In vitro effect of cadmium and copper on separated blood leukocytes of Dicentrarchus labrax

The immunotoxic effects of heavy metals on blood leukocytes of sea bass (Dicentrarchus labrax) were examined. The cells, separated by a discontinuous Percoll-gradients, were exposed in vitro to various sublethal concentrations of cadmium and copper (10(-7)M, 10(-5)M, and 10(-3)M) and their immunotoxic effect was then evaluated by measuring neutral red uptake, MTT assay, DNA fragmentation and Hsp70 gene expression. First of all, we demonstrated that the cells treated in vitro could incorporate Cd and Cu. A relationship between heavy metal exposure and dose-time-dependent alterations in responses of leukocytes from blood was found for both metals, but copper was more immunotoxic than cadmium in all assays performed. A significant reduction in the cells׳ ability to uptake neutral red and viability by MTT assay was recorded, indicating that both cadmium and copper could change the membrane permeability, inducing cellular apoptosis when the concentration of metals reached 10(-3)M. The apoptotic effect may also explain the high level of cytotoxicity found when the leukocytes were exposed to higher concentration of metals. These results demonstrated that toxic effect of copper and cadmium affect on the mechanisms of cell-mediated immunity reducing the immune defences of the organism.

The role of cytochrome c on apoptosis induced by Anagrapha falcifera multiple nuclear polyhedrosis virus in insect Spodoptera litura cells

There are conflicting reports on the role of cytochrome c during insect apoptosis. Our previous studies have showed that cytochrome c released from the mitochondria was an early event by western blot analysis and caspase-3 activation was closely related to cytochrome c release during apoptosis induced by baculovirus in Spodoptera litura cells (Sl-1 cell line). In the present study, alteration in mitochondrial morphology was observed by transmission electron microscopy, and cytochrome c release from mitochondria in apoptotic Sl-1 cells induced with Anagrapha falcifera multiple nuclear polyhedrosis virus (AfMNPV) has further been confirmed by immunofluoresence staining protocol, suggesting that structural disruption of mitochondria and the release of cytochrome c are important events during Lepidoptera insect cell apoptosis. We also used Sl-1 cell-free extract system and the technique of RNA interference to further investigate the role of cytochrome c in apoptotic Sl-1 cells induced by AfMNPV. Caspase-3 activity in cell- free extracts supplemented with exogenous cytochrome c was determined and showed an increase with the extension of incubation time. DsRNA-mediated silencing of cytochrome c resulted in the inhibition of apoptosis and protected the cells from AfMNPV-induced cell death. Silencing of expression of cytochrome c had a remarkable effect on pro-caspase-3 and pro-caspase-9 activation and resulted in the reduction of caspase-3 and caspase-9 activity in Sl-1 cells undergoing apoptosis. Caspase-9 inhibitor could inhibit activation of pro-caspase-3, and the inhibition of the function of Apaf-1 with FSBA blocked apoptosis, hinting that Apaf-1 could be involved in Sl-1 cell apoptosis induced by AfMNPV. Taken together, these results strongly demonstrate that cytochrome c plays an important role in apoptotic signaling pathways in Lepidopteran insect cells.

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.

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.

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

Functional and morphological modifications in the IPLB-LdFB insect cell line were examined following a short treatment with a reversible inhibitor of mitochondrial ATP synthase, oligomycin A, and subsequent incubation for various times in oligomycin-A-free medium. Oncosis, apoptosis and autophagy at variable percentages were observed under the various experimental conditions. Together with oncotic and apoptotic pathways that lead directly to cell death, the insect cells responded to ATP depletion with autophagy. Our results revealed that, in most cases, autophagy failed to restore cellular homeostasis, probably because of a massive sequestration of mitochondria in autophagic vacuoles. This critical event was a "point of no return" and ultimately resulted in cell necrosis. However, cells with a misshapen body and nucleus resembling "resistant forms" were observed at the end of the experiments. Our findings indicate that oligomycin-A-induced autophagy can promote cell protection or cell destruction and is an open-ended process that can lead to survival or death depending on a combination of concomitant factors.