Why insects do not biosynthesize cholesterol

Authors: HAAS, ERIC - Creighton University; KIM, YONGGYN - Andong National University; Stanley, David

Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2022
Publication Date: 11/13/2022
Citation: Haas, E., Kim, Y., Stanley, D.W. 2022. Why insects do not biosynthesize cholesterol. Archives of Insect Biochemistry and Physiology. https://doi.org/10.1002/arch.21983.
DOI: https://doi.org/10.1002/arch.21983

Interpretive Summary: A small proportion of insect species are very harmful to humans and animals by directly transmitting diseases such as malaria, by severely limiting crop production and by application of environmentally damaging insecticides. Scientists around the world are working to develop novel pest insect management technologies that will support production of crops to nourish a growing human population far into the future. Developing modern insect pest management programs requires steadily increasing knowledge of insect biology. Here, we report new knowledge on insect nutritional requirements for growth and reproduction. It has been known for decades that insects require dietary cholesterol because they lack the genes required to make it. In this paper, we report that virtually all invertebrate animals, including shrimp, lobster and other invertebrate food animals, similarly require dietary cholesterol. This far broader understanding of the insect need for dietary cholesterol will be used by scientists around the world in designing research programs meant to manage pest insects without harming many highly valuable invertebrate food animals.

Technical Abstract: Two aspects of insect lipid biochemistry differ from the mammalian background. In one aspect, nearly a hundred years ago scientists demonstrated that the polyunsaturated fatty acid, linoleic acid (LA; 18:2n-6) is an essential nutrient in the diets of all mammals that have been studied in that regard. An unknown number of insect species are able to biosynthesize LA de novo. Some species take the biosynthesized LA into fatty acid elongation/desaturation pathways to produce other polyunsaturated fatty acids, 18:3n-6, 20:3n-6 and 20:4n-6. A couple of species use the de novo produced LA to biosynthesize prostaglandins and other eicosanoids, short-lived signal moieties that mediate important physiological actions in immunity and reproduction. Insects differ from mammals, also, in their lack of genes that encode enzymes acting in biosynthesis of cholesterol. Insects require dietary cholesterol to meet their needs in cellular, physiological, developmental and reproductive needs. Looking at a broader view of invertebrate biochemistry, virtually most protostomes lost all or most genes involved in cholesterol biosynthesis. The massive gene loss occurred during the Ediacaran Period, which lasted 96 million years, from the end of the Cryogenian Period (635 million years ago; MYA) to the beginning of the Cambrian Period (538.6 MYA). The key point here is that the inability to biosynthesize cholesterol is not limited to insects; it occurs in virtually all protostomes. We address the protostome need to acquire exogenous sterols.