Ecdysterone and an analogue of juvenile hormone on the autophagy in the cells of fat body of mamestra brassicae

Abstract

The effect of ecdysterone and a juvenile hormone analogue (JHa) on autophagy and heterophagy was investigated in the fat body cells of the last larval instar of Mamestra brassicae. In the course of normal development autophagic vacuoles and protein granules of heterophagic origin begin to accumulate in these cells, on the 4th and 5th day of the last larval stage respectively. When ecdysterone (10 mug/g body weight) was administered to the larvae for 24 h either on the 1st or on the 2nd day of the last larval stage, autophagic and heterophagic vacuoles appeared in the cells as early as on the 2nd or 3rd days. Autophagy was also observed in the cells of one-or two-day-old last larval fat body after a 5 h incubation in a medium containing 10 mug/ml ecdysterone, in vitro. Ligation of the last thoracic segment resulted in inhibition of metamorphic changes in the fat body lobules of the isolated abdomen. Injection of 10 mug ecdysterone into the isolated abdomen resulted in an appearence of autophagic vacuoles in these cells, too. JHa treatment, when started on the 2nd or 3rd day of the last larval stage, inhibited both auto- and heterophagy and the fat bodies maintained their larval character. Treatment started on the 4th or 5th day proved either ineffective or lethal. It is concluded that the auto- and heterophagy taking place in the larval fat body cells are stimulated by ecdysterone and inhibited by JHa. Experiments performed in vitro or on ligated animals in vivo provided evidence for a direct action of ecdysterone at the cellular level.