Investigation of juvenile hormone analogue, fenoxycarb, effect on programmed cell death of fat body in Galleria mellonella (Lepidoptera: Pyralidae)

Insect fat body is a special tissue that proteins, carbohydrates and lipids are synthesized, stored, metabolized, detoxification processes are carried out. Functions of the fat body that undertakes the tasks of the liver and fat tissue in the vertebra alone, are regulated by the endocrine system. During metamorphosis, it enters a major change process and "remodeling". While larval fat body cells are being removed by programmed cell death, new fat body cells that adapt to adult life multiply and develop from stem cells. In this study, primarily, key features of programmed cell death during the remodeling process during the larval-pupal metamorphosis of Galleria mellonella fat body were analyzed. Secondly, during the fat body remodeling process, the role of juvenile hormone was tried to be elucidated by applying a juvenile hormone analogue, fenoxycarb. Specific markers of apoptosis during degeneration of larval fat body cells were investigated by morphological observations, TUNEL method and measurement of caspase 3 enzyme activity spectrophotometrically. Transmission electron microscopy studies and spectrophotometric measurement of acid phosphatase activity were performed for the analysis of autophagic cell death. EcR B1 protein, an ecdysone receptor isoform, was determined by western blot for analysis of the link between fat body tissue remodeling process and steroid hormone ecdysone. The results indicate that the degeneration process of larval fat body cells is largely accomplished by autophagic cell death. Fenoxycarb application caused extra larval molting in the last instar larvae. It was determined that in the 5 μg fenoxycarb application group, removal of the larval fat body cells by programmed cell death was prevented, and thus the remodeling process in the fat body was not performed. This result revealed the inhibitory effect of juvenile hormone on fat body remodeling. During the metamorphosis of the control group and the 5 μg fenoxycarb-treated group larvae and pupae, the high presence of ecdysone receptor B1 by western blotting demonstrates that it plays a role in the autophagic cell death in larval fat body cells through the EcR-B1 isoform of ecdysone.