Beet armyworm caterpillars producing prostaglandin dehydrogenase and reductase (left), lacking prostaglandin dehydrogenase (centre) and lacking prostaglandin reductase (right). Photo credit: Yonggyun Kim.

Beet armyworm caterpillars producing prostaglandin dehydrogenase and reductase (left), lacking prostaglandin dehydrogenase (centre) and lacking prostaglandin reductase (right). Photo credit: Yonggyun Kim.

Life is all about striking the right balance. Too little of some substances can be disastrous for the body, while a surfeit can have equally devastating consequences. Hitting a happy intermediate between the production and destruction of key chemicals is essential for health and wellbeing. Prostaglandins are a vital group of hormones that regulate biological processes ranging from reproduction to maintaining a healthy immune system in animals from mammals to insects. However, if the equilibrium between prostaglandin production and destruction is disturbed, the immune system can run amok, wreaking a wide variety of damage. ‘To prevent excessive prostaglandins, there must be effective breakdown’, says Yonggyun Kim from Andong National University, Korea, explaining that the biological processes that reduce prostaglandin levels in mammals are reasonably well understood. However, little was known about the process in insects. ‘The beet armyworm (Spodoptera exigua) has often been used to study insect prostaglandins in the past’, says Kim, who teamed up with Shabbir Ahmed to find out how the agricultural pest disposes of prostaglandins from its body.

Knowing that mammals use two enzymes – a prostaglandin dehydrogenase and a reductase enzyme – to break down the essential hormones, Shabbir searched the moth's genome for evidence of the enzymes and found two genes that could encode the elusive proteins. However, Kim needed direct evidence that the genes were producing mRNA – which could, in turn, be translated into the key proteins – in the insects’ bodies. Scrutinising a range of tissues from the caterpillar and adult moths, Shabbir and Kim found that the insects were capable of producing the necessary mRNA for the enzymes. In addition, the insects ramped up mRNA expression of the two genes when they experienced a fake infection. The duo also noticed that the insects increased mRNA expression of genes associated with prostaglandin synthesis before activating the genes that clear the hormone from the insects’ bodies, when it needs to turn down its immune system.

But how would the caterpillars cope if Kim and Shabbir disabled the dehydrogenase and reductase mRNAs, leaving the insects unable to produce the enzymes necessary to remove prostaglandin hormones from their bodies? This time the insects’ immune systems went into fatal overdrive, producing colossal quantities of melanin – which would usually fight off an infection – before the insect died.

Kim admits that this is the first of many studies looking into the mechanisms that the beet armyworm uses to control prostaglandin levels in their bodies. ‘We need to demonstrate that the dehydrogenase and reductase gene products degrade active prostaglandins’, says Kim. However, he is optimistic that his discovery could help to develop new insecticides to target the annoying crop-devouring pest. ‘I want to design specific compounds to inhibit the insect prostaglandin dehydrogenase and reductase enzyme activities’, says Kim, hopefully.

Ahmed
,
S.
and
Kim
,
Y.
(
2020
).
Prostaglandin catabolism in Spodoptera exigua, a lepidopteran insect
.
J. Exp. Biol.
223
,
jeb233221
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