Abstract
Nutrient-sensing mechanisms in animals’ sense available nutrients to generate a physiological regulatory response involving absorption, digestion, and regulation of food intake and to maintain glucose and energy homeostasis. During nutrient sensing via the gastrointestinal tract, nutrients interact with receptors on the enteroendocrine cells in the gut, which in return respond by secreting various hormones. Sensing of nutrients by the gut plays a critical role in transmitting food-related signals to the brain and other tissues informing the composition of ingested food to digestive processes. These signals modulate feeding behaviors, food intake, metabolism, insulin secretion, and energy balance. The increasing significance of fly genetics with the availability of a vast toolbox for studying physiological function, expression of chemosensory receptors, and monitoring the gene expression in specific cells of the intestine makes the fly gut the most useful tissue for studying the nutrient-sensing mechanisms. In this review, we emphasize on the role of Drosophila gut in nutrient-sensing to maintain metabolic homeostasis and gut-brain cross talk using endocrine and neuronal signaling pathways stimulated by internal state or the consumption of various dietary nutrients. Overall, this review will be useful in understanding the post-ingestive nutrient-sensing mechanisms having a physiological and pathological impact on health and diseases.
Highlights
Nutrients are simple organic molecules that, after digestion, are engaged in biochemical reactions that produce energy in animals
Intestinal physiology in Drosophila is modulated by extrinsic hormones that are released by endocrine glands such as the ring gland in the brain ((Drosophila insulin-like peptide (DILP), adipokinetic hormone (Akh), Ast-A, sNPF, neuropeptide F (NPF), corazonin (Crz), leucokinin (Lk)) [60–65] or the fat body ((DILP, unpaired 2 (Upd2), CCHa2)) [66–68]
RNA sequencing, direct optogenetics activation of gustatory receptors, molecular neurogenetics, and behavioral assays provide the complex cellular composition of a real intestine and opportunities to assess various cell types and their physiological roles compared to the mammalian system at a single-cell level
Summary
Nutrients are simple organic molecules that, after digestion, are engaged in biochemical reactions that produce energy in animals. The part of the nervous system located in an animal’s gut involved in digestion and absorption of nutrients is known as the enteric nervous system (ENS). It is a lesser-explored system compared to the central nervous system (CNS) in human health and diseases. The bidirectional communication between the brain and digestive tract are interesting avenues to explore post-ingestive mechanisms, especially nutrient sensing via gut in health and disease. We are discussing the importance of the gut in nutrient sensing (digestive/absorptive functions), its neural connectivity with the brain, as well as its role in regulating food preferences by using inter-organ signaling, and its role in various diseases. The compiled understanding of nutrient sensing by the gut could lead to the discovery of physiologically significant intestinal nutrition sensors and the development of new therapeutic targets for diabetes, obesity, aging, neurodegenerative diseases, and GI illnesses
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