Antagonistic activities of glucagon and insulin control metabolism in mammals, and disruption of this balance underlies diabetes pathogenesis. Insulin-producing cells (IPCs) in the brain of insects such as Drosophila also regulate serum glucose, but it remains unclear whether insulin is the sole hormonal regulator of glucose homeostasis and whether mechanisms of glucose-sensing and response in IPCs resemble those in pancreatic islets. Here we show, by targeted cell ablation, that Drosophila corpora cardiaca (CC) cells of the ring gland are also essential for larval glucose homeostasis. Unlike IPCs, CC cells express Drosophila cognates of sulphonylurea receptor (Sur) and potassium channel (Ir), proteins that comprise ATP-sensitive potassium channels regulating hormone secretion by islets and other mammalian glucose-sensing cells. They also produce adipokinetic hormone, a polypeptide with glucagon-like functions. Glucose regulation by CC cells is impaired by exposure to sulphonylureas, drugs that target the Sur subunit. Furthermore, ubiquitous expression of an akh transgene reverses the effect of CC ablation on serum glucose. Thus, Drosophila CC cells are crucial regulators of glucose homeostasis and they use glucose-sensing and response mechanisms similar to islet cells.
"The ion channel involved in the action of Phote-HrTH on the crop muscle contractions is probably the potassium channel. The K ATP channel has also been shown to govern the release of AKH in the CC, thus regulating concentrations of circulating glucose in the hemolymph of D. melanogaster (Kim and Rulifson, 2004). It has been shown, but not published that tetraethylammonium, a known potassium channel blocker, applied to the in vitro crop bioassay of P. regina and, several other known channel blockers significantly reduced crop lobe (P5) contractions (Stoffolano et al., 2013). "
[Show abstract][Hide abstract] ABSTRACT: Phote-HrTH (Phormia terraenovae hypertrehalosemic hormone) has been demonstrated in the Diptera to be involved in flight metabolism, reproduction, and diapause. Each of these events needs the hormone’s action and requirement for carbohydrates is the common denominator. In Diptera, carbohydrates are taken up during feeding by action of the cibarial pump and are then stored in the crop. Using adult Phormia regina, both a bioassay and electrophysiological recordings show that Phote-HrTH slows down or inhibits the crop lobe muscles (P5) and, at the same time, stimulates the muscles of the pump 4 (P4) involved in pushing fluids out of the crop and up into the midgut for digestion. The EC50 for P4 was in the nanomolar range while the IC50 for P5 was 1.4-75.1 pM. The effect of Phote-HrTH on P4/5 suggests that the peptide is important in coordinating the two pumps, which are involved in moving carbohydrates up into the midgut for digestion. The adult crop organ is an essential storage organ for carbohydrates and now should be considered an important structure capable of delivering nutrients to the midgut for digestion.
"In Drosophila, sugar homeostasis is often associated with the AKH and insulin signaling, whereas insulin signaling is also modulated by proteins and amino acids in the diet (Brogiolo et al., 2001; Buch et al., 2008; Kim and Rulifson, 2004; Lee and Park, 2004; Rulifson et al., 2002). Recently, Bai and colleagues have showed that Daw expression is modulated by insulin signaling and identified Daw as a target of dFOXO (Bai et al., 2013), raising the possibility that glucose repression may be similarly affected by insulin signaling. "
[Show abstract][Hide abstract] ABSTRACT: Organisms need to assess their nutritional state and adapt their digestive capacity to the demands for various nutrients. Modulation of digestive enzyme production represents a rational step to regulate nutriment uptake. However, the role of digestion in nutrient homeostasis has been largely neglected. In this study, we analyzed the mechanism underlying glucose repression of digestive enzymes in the adult Drosophila midgut. We demonstrate that glucose represses the expression of many carbohydrases and lipases. Our data reveal that the consumption of nutritious sugars stimulates the secretion of the transforming growth factor β (TGF-β) ligand, Dawdle, from the fat body. Dawdle then acts via circulation to activate TGF-β/Activin signaling in the midgut, culminating in the repression of digestive enzymes that are highly expressed during starvation. Thus, our study not only identifies a mechanism that couples sugar sensing with digestive enzyme expression but points to an important role of TGF-β/Activin signaling in sugar metabolism.
"AKHs comprise a family of peptide hormones that are synthesized, stored and released predominantly by neurosecretory cells of the corpora cardiaca (CC), neuroendocrine glands connected to the brain (Gäde et al. 1997). The most widely recognized action of the AKH family of peptides is their role for mobilizing carbohydrates , lipids and the amino acid proline from reserves to support the extreme energetic demands of insect flight (Gäde and Auerswald 2003; Gäde 2004), but recent physiological and genetic studies in Drosophila melanogaster and Bombyx mori suggest that AKHs may also play roles in nutrient homeostasis, particularly blood sugar regulation (Satake et al. 2000; Kim and Rulifson 2004; Isabel et al. 2005). However, evidence of the involvement of AKH in diapause metabolism is currently limited to one study (Socha and Kodrík 1999). "
[Show abstract][Hide abstract] ABSTRACT: The presence and potential role of adiponectin- and resistin-like peptides in mobilizing free lipids of hemolymph during over-wintering was studied in females of the European solitary red mason bee Osmia bicornis L. (Hymenoptera: Megachilidae). The levels of both peptides (as demonstrated both by RIA/ELISA and Western blots) were highest in fat body tissue homogenates during early pre-wintering (September) followed by a gradual and significant decline during wintering and post-wintering months (November–March).
There was a gradual reduction of the lipid levels in hemolymph and adiponectin-like and resistin-like peptide content in fat body. Thus, the total lipid content in hemolymph and the adiponectin-like and resistin-like peptides in fat body homogenates was positively correlated. Our experiments also demonstrated that injections of various concentrations of fat body extracts as well as various doses of adiponectin and resistin increased the
lipid levels in hemolymph in O. bicornis females at the three different periods of over-wintering time. In particular, injections of fat body extract and adiponectin resulted in the strongest mobilization of lipids especially in the first two periods of over-wintering: pre-wintering and wintering. Resistin also elicited an increase of lipid levels in hemolymph, but its effectiveness was lower compared to fat body extract and
adiponectin. Taken together, our results strongly suggest the presence of adiponectin-like and resistin-like peptides in the fat body of O. bicornis and postulate a dynamic physiological role for these peptides during the process of over-wintering.
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