Abstract
Sterols, especially cholesterol (Chl), are fundamental for animal survival. Insects lacking the ability to synthesize Chl are sterol auxotrophic animals and utilize dietary Chl and phytosterols to survive. The sterols obtained from a diet are distributed to the tissues; however, sterol homeostasis in insect tissues remains to be elucidated. This study sought to understand the sterol characteristics of insect tissues through detailed sterol quantification and statistics. The combination of sterol quantification using liquid chromatography tandem mass spectrometry (LC-MS/MS) and principal component analysis (PCA) revealed tissue-specific sterol characteristics in the silkworm, Bombyx mori, a phytophagous insect. We found that insect tissues have tissue-intrinsic sterol profiles. The brain has a unique sterol composition as compared to other tissues—high concentration of Chl and less accumulation of phytosterols. Other tissues also have intrinsic sterol characteristics, which when defined by dietary sterols or Chl metabolites, indicate preference for a sterol and consistently manage their own sterol homeostasis. Though most tissues never change sterol profiles during development, the brain drastically changes its sterol profile at the wandering stage, indicating that it could alter sterol composition in preparation for metamorphosis. These results suggest the existence of tissue- and sterol-specific systems for sterol homeostasis in insects.
Highlights
IntroductionThe main sterol is cholesterol (Chl), which is a necessary component of cell membranes [1], a material of steroid hormones [2], and a ligand for the Hedgehog signaling process [3,4]
Sterol is an essential lipid for living organisms
These tissues contained both Chl and phytosterols. Though these tissues contained large amounts of Chl, its accumulation index in common sterols in the prothoracic glands (PGs) and Malpighian tubules were lower than that of the brain (Figure 3). These results indicate that most silkworm tissues incorporate and maintain Chl and phytosterols, but the brain may cause its enlargement during the final instar development, maintaining a certain ratio of range to fit brain sizes
Summary
The main sterol is cholesterol (Chl), which is a necessary component of cell membranes [1], a material of steroid hormones [2], and a ligand for the Hedgehog signaling process [3,4]. Most animals synthesize Chl from acetyl-CoA with sequential enzymatic reactions in all tissues, mainly liver, adrenal gland, brain, ovary, and testis [5]. Chl is predominantly synthesized in the liver, while accumulation of Chl is notable in the brain [6,7]. The breakdown of Chl homeostasis results in severe disease. Excessive accumulation of Chl induces atherosclerotic cardiovascular disease and Alzheimer’s disease [8,9,10,11]. The maintenance of Chl homeostasis is essential for animal survival
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