Effects of dehydroepiandrosterone on G6PD activity and chitin synthesis in Hyphantria cunea larvae

Objective This study investigated the inhibitory effect of dehydroepiandrosterone (DHEA) on glucose-6-phosphate dehydrogenase (G6PD) activity and the pentose phosphate pathway (PPP) in larvae of Hyphantria cunea, a major agricultural and forestry pest, further examining the role of the PPP in larval growth, development, and chitin biosynthesis.

Method The HcG6PD gene was cloned from Hyphantria cunea, and the amino acid composition, physicochemical properties and structural characteristics of HcG6PD were analyzed by bioinformatics software. The expression pattern of HcG6PD at different developmental stages was analyzed by RT-qPCR. The G6PD activity, the expression levels of key genes and intermediate product content in PPP in the 5th instar larvae of H. cunea were measured after treating with DHEA. Meanwhile, the inhibitory effect of DHEA on G6PD and PPP was analyzed. To evaluate the effects of G6PD inhibition on chitin synthesis, the relative expression levels of key genes in the chitin synthesis pathway and the chitin content in epidermis of the 5th instar H. cunea larvae were determined. Meanwhile, chitin in the epidermis was stained after treating with DHEA.

Result (1) After treating the 5th instar larvae with DHEA for 72 hours, the activity of G6PD significantly decreased, and the transcriptional levels of the key genes of PPP (HcG6PD, Hc6PGD, Hc6PGL) were only 18%, 17%, and 13% of control, respectively. The content of fructose-6-phosphoric acid (F6P) of key genes of PPP was only 0.18 times of control. (2) DHEA treatment led to the obstruction of larval growth and molting. After treating with DHEA for 72 hours, the mass gain of the 5th instar larvae was only 13% of control, and the molting time of larvae was delayed by approximately 4.8 days compared with control. (3) The transcription levels of key genes (HcGNA, HcPAGM, HcUAP, HcCHSA) in chitin synthesis pathway of the 5th instar H. cunea larvae were inhibited by DHEA. This inhibition led to a reduction in epidermal chitin content, which was only 27% of control, as well as a thinning of epidermal chitin structure.

Conclusion DHEA significantly inhibites the PPP metabolic pathway in H. cunea larvae by suppressing G6PD activity, reducing the transcriptional levels of Hc6PGL and Hc6PGD, and the content of F6P. The inhibition of G6PD activity and PPP induced by DHEA significantly depresses the growth and development, and the epidermal chitin biosynthesis in H. cunea larvae.