CoA protects against the deleterious effects of caloric overload in Drosophila

We developed a Drosophila model of T2D in which high sugar (HS) feeding leads to insulin resistance. In this model, adipose TG storage is protective against fatty acid toxicity and diabetes. Initial biochemical and gene expression studies suggested that deficiency in CoA might underlie reduced TG synthesis in animals during chronic HS feeding. Focusing on the Drosophila fat body (FB), which is specialized for TG storage and lipolysis, we undertook a series of experiments to test the hypothesis that CoA could protect against the deleterious effects of caloric overload. Quantitative metabolomics revealed a reduction in substrate availability for CoA synthesis in the face of an HS diet. Further reducing CoA synthetic capacity by expressing FB-specific RNAi targeting pantothenate kinase (PK orfumble) or phosphopantothenoylcysteine synthase (PPCS) exacerbated HS-diet-induced accumulation of FFAs. Dietary supplementation with pantothenic acid (vitamin B5, a precursor of CoA) was able to ameliorate HS-diet-induced FFA accumulation and hyperglycemia while increasing TG synthesis. Taken together, our data support a model where free CoA is required to support fatty acid esterification and to protect against the toxicity of HS diets

Similar effects of high-fructose and high-glucose feeding in a Drosophila model of obesity and diabetes

As in mammals, high-sucrose diets lead to obesity and insulin resistance in the model organism Drosophila melanogaster (called Drosophila hereafter). To explore the relative contributions of glucose and fructose, sucrose’s component monosaccharides, we compared their effects on larval physiology. Both sugars exhibited similar effects to sucrose, leading to obesity and hyperglycemia. There were no striking differences resulting from larvae fed high glucose versus high fructose. Some small but statistically significant differences in weight and gene expression were observed that suggest Drosophila is a promising model system for understanding monosaccharide-specific effects on metabolic homeostasis.</div

Effect of dietary additives on intestinal permeability in both Drosophila and a human cell co-culture

Increased intestinal barrier permeability has been correlated with aging and disease, including type 2 diabetes, Crohn's disease, celiac disease, multiple sclerosis and irritable bowel syndrome. The prevalence of these ailments has risen together with an increase in industrial food processing and food additive consumption. Additives, including sugar, metal oxide nanoparticles, surfactants and sodium chloride, have all been suggested to increase intestinal permeability. We used two complementary model systems to examine the effects of food additives on gut barrier function: a Drosophila in vivo model and an in vitro human cell co-culture model. Of the additives tested, intestinal permeability was increased most dramatically by high sugar. High sugar also increased feeding but reduced gut and overall animal size. We also examined how food additives affected the activity of a gut mucosal defense factor, intestinal alkaline phosphatase (IAP), which fluctuates with bacterial load and affects intestinal permeability. We found that high sugar reduced IAP activity in both models. Artificial manipulation of the microbiome influenced gut permeability in both models, revealing a complex relationship between the two. This study extends previous work in flies and humans showing that diet can play a role in the health of the gut barrier. Moreover, simple models can be used to study mechanisms underlying the effects of diet on gut permeability and function. This article has an associated First Person interview with the first author of the paper

A high-sugar diet produces obesity and insulin resistance in wild-type Drosophila

SUMMARY Insulin-resistant, ‘type 2’ diabetes (T2D) results from a complex interplay between genes and environment. In particular, both caloric excess and obesity are strongly associated with T2D across many genetic backgrounds. To gain insights into how dietary excess affects insulin resistance, we studied the simple model organism Drosophila melanogaster. Larvae reared on a high-sugar diet were hyperglycemic, insulin resistant and accumulated fat – hallmarks of T2D – compared with those reared on control diets. Excess dietary sugars, but not fats or proteins, elicited insulin-resistant phenotypes. Expression of genes involved in lipogenesis, gluconeogenesis and β-oxidation was upregulated in high-sugar-fed larvae, as were FOXO targets, consistent with known mechanisms of insulin resistance in humans. These data establish a novel Drosophila model of diet-induced insulin resistance that bears strong similarity to the pathophysiology of T2D in humans

A <em>Drosophila</em> Model of High Sugar Diet-Induced Cardiomyopathy

<div><p>Diets high in carbohydrates have long been linked to progressive heart dysfunction, yet the mechanisms by which chronic high sugar leads to heart failure remain poorly understood. Here we combine diet, genetics, and physiology to establish an adult <em>Drosophila melanogaster</em> model of chronic high sugar-induced heart disease. We demonstrate deterioration of heart function accompanied by fibrosis-like collagen accumulation, insulin signaling defects, and fat accumulation. The result was a shorter life span that was more severe in the presence of reduced insulin and P38 signaling. We provide evidence of a role for hexosamine flux, a metabolic pathway accessed by glucose. Increased hexosamine flux led to heart function defects and structural damage; conversely, cardiac-specific reduction of pathway activity prevented sugar-induced heart dysfunction. Our data establish <em>Drosophila</em> as a useful system for exploring specific aspects of diet-induced heart dysfunction and emphasize enzymes within the hexosamine biosynthetic pathway as candidate therapeutic targets.</p> </div

<i>Drosophila</i> model of diabetic cardiomyopathy.

<p>(A) Ventral view of the heart tube. 3D structures are shown. The heart was stained for F-Actin with phalloidin (magenta) and for nuclei with DAPI; Cypher-GFP (green) labeled Z-lines of myofibers within cardiomyocytes. Arrowheads indicate the non-myocardial longitudinal muscle fibers, asterisks the alary muscles that support the heart, and arrows the abdominal muscles. (B) Dorsal view of the heart tube. Myocardial cells wrap in a circular fashion around the central cavity. Arrows show the ostia through which hemolymph from the abdomen enters into the heart tube and circulates. (C) HSD significantly reduced life span. <i>w¹¹¹⁸</i> male flies were raised in 0.15 M or 1.0 M sucrose diet, food was changed every 2–3 days, and flies were counted every 10 days. HSD-fed flies displayed decreased median life span, 10 days shorter than flies fed an LSD. Mean ± SE are shown; n = 50 total flies in two separate experiments. The estimated median life span of HSD flies was also expressed as the percentage of LSD flies (*p = 7.61E-08 by log rank test). See also <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003175#pgen.1003175.s001" target="_blank">Figure S1</a>. (D) Hemolymph glucose concentrations in 3-week-old, control and HSD-fed <i>w¹¹¹⁸</i> adult flies. n≥6. (E) Hemolymph trehalose concentrations in 3-week-old, control and high sucrose-fed <i>w¹¹¹⁸</i> adult flies. n≥6. (F) Bodies from <i>w¹¹¹⁸</i> adults fed LSD or HSD for 3 weeks were treated with insulin (1 µM) or vehicle and visualized using antibodies against <i>Drosophila</i> PO₄-Akt or Syntaxin. n = 10. Bands from Western blot experiments were quantified, and PO₄-Akt was normalized to Syntaxin as a loading control. (G) Total triglycerides (TAG) were assayed enzymatically in 3-week-old control and high sugar-fed <i>w¹¹¹⁸</i> adult flies, and normalized to weight. n≥12. Mean ± SE are shown. An unpaired, two-tailed t-test was used to derive p-values.</p

High sucrose shortened <i>Drosophila</i> life span and was associated with increased cardiac arrhythmia and heart deterioration.

<p>(A) Representative M-mode (5 seconds) from flies fed LSD and HSD. Three-week-old adults fed an HSD showed moderate cardiac arrhythmia; at six weeks arrhythmicity was increased. (B) Arrhythmia index obtained from <i>w¹¹¹⁸</i> flies fed LSD and HSD. Arrhythmias observed in M-mode can be quantified as arrhythmia index, which is the standard deviation of all heart periods in each record normalized to the median heart period for each fly. Mean ± SE are shown. At week three, a significant increase in arrhythmia index was observed in HSD fed flies (0.44) compared to low sucrose fed flies (0.16) (*P = 1.54E-17 by F-test). Arrhythmia index of six-week-old flies increased to 0.66 in HSD and 0.26 in low sucrose diet, respectively (*P = 6.01E-12 by F-test). Data are means ± SE. (C) Heart period of adult files fed low vs. high dietary sucrose. At three weeks of age, no difference was observed between HSD- and LSD-fed flies. Heart period was significantly increased at six weeks of age in both HSD- and LSD-fed flies (*P = 9.64E-06 and 1.44E-09, respectively, by t-test). Interestingly at six weeks of age, heart period of HSD-fed flies was shorter than that of low sucrose fed flies (*P = 0.015 by t-test). Data are means ± SE. (D) Fractional shortening of adult flies fed low <i>vs.</i> high dietary sucrose. At three weeks of age, no difference was observed between HSD- and LSD-fed flies; however, fractional shortening was significantly decreased in flies fed HSD- <i>vs.</i> LSD-fed (*P = 0.043 by t-test). Data are means ± SE. (E) Quantification of Pericardin level of adult heart by Western blot. Eight hearts from three-week-old LSD- and HSD-fed flies, respectively, were loaded. Pericardin level was detected by a monoclonal antibody against Pericardin, and normalized to Actin level. (F,G) Representative confocal images of three-week-old adult fly hearts expressing Cypher-GFP (posterior A2/anterior A3 segment) and stained with anti-Pericardin (magenta) antibody. Pericardin levels in hearts of flies fed an HSD were increased compared to those fed low sucrose. Note that Pericardin was detected in heart tissue but not abdominal muscles. See also <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003175#pgen.1003175.s004" target="_blank">Figure S4</a>. (H) Fly hearts from <i>w¹¹¹⁸</i> adults fed LSD or HSD were treated with insulin (2.5 µM) or vehicle and visualized using antibodies against <i>Drosophila</i> PO₄-Akt, PO₄-4EBP or Actin, showing the response of the heart to exogenous insulin challenge. n = 3. Bands from Western blot experiments were quantified, and PO₄-Akt and PO₄-4EBP were normalized to Actin as a loading control. The ratio of HSD fed flies was then normalized to that of LSD fed flies. PO₄-Akt and PO₄-4EBP level were 74.3% and 13.9%, respectively, in HSD-fed flies compared to LSD-fed flies (P = 0.049 and 0.0003, respectively, by t-test). (I) Heart accumulated triglycerides (TAG) were assayed enzymatically in 15 hearts from 3-week-old LSD- and HSD-fed <i>w¹¹¹⁸</i> adult flies, and normalized to protein level. n = 2. (P = 0.028 by t-test). See also <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003175#pgen.1003175.s004" target="_blank">Figure S4</a> and <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003175#pgen.1003175.s010" target="_blank">Videos S1</a>, <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003175#pgen.1003175.s011" target="_blank">S2</a>, <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003175#pgen.1003175.s012" target="_blank">S3</a>.</p