Glutamine enhances sucrose taste through a gut microbiota-gut-brain axis in Drosophila.

AIMS: Amino acids (AAs) are known to play important roles in various physiological functions. However, their effect on sweet taste perception remains largely unknown. MAIN METHODS: We used Drosophila to evaluate the effect of each AA on sucrose taste perception. Individual AA was supplemented into diets and male flies were fed on these diets for 6 days. The proboscis extension response (PER) assay was applied to assess the sucrose taste sensitivity of treated flies. We further utilized the RNA-seq and germ-free (GF) flies to reveal the underlying mechanisms of sucrose taste sensitization induced by glutamine (Gln). KEY FINDINGS: We found that supplementation of Gln into diets significantly enhances sucrose taste sensitivity. This sucrose taste sensitization is dependent on gut microbiota and requires a specific gut bacterium Acetobacter tropicalis (A. tropicalis). We further found that CNMamide (CNMa) in the gut and CNMa receptor (CNMaR) in dopaminergic neurons are required for increased sucrose taste sensitivity by Gln diet. Finally, we demonstrated that a gut microbiota-gut-brain axis is required for Gln-induced sucrose taste sensitization. SIGNIFICANCE: These findings can advance understanding of the complex interplay between host physiology, dietary factors, and gut microbiota.

Natural compounds as obesity pharmacotherapies.

Obesity has become a serious global public health problem, affecting over 988 million people worldwide. Nevertheless, current pharmacotherapies have proven inadequate. Natural compounds have garnered significant attention due to their potential antiobesity effects. Over the past three decades, ca. 50 natural compounds have been evaluated for the preventive and/or therapeutic effects on obesity in animals and humans. However, variations in the antiobesity efficacies among these natural compounds have been substantial, owing to differences in experimental designs, including variations in animal models, dosages, treatment durations, and administration methods. The feasibility of employing these natural compounds as pharmacotherapies for obesity remained uncertain. In this review, we systematically summarized the antiobesity efficacy and mechanisms of action of each natural compound in animal models. This comprehensive review furnishes valuable insights for the development of antiobesity medications based on natural compounds.

Nutritional geometry framework of sucrose taste in Drosophila.

Dietary protein (P) and carbohydrate (C) have a major impact on the sweet taste sensation. However, it remains unclear whether the balance of P and C influences the sweet taste sensitivity. Here, we use the nutritional geometry framework (NGF) to address the interaction of protein and carbohydrates on sweet taste using Drosophila as a model. Our results reveal that high-protein, low-carbohydrate (HPLC) diets sensitize to sweet taste and low-protein, high-carbohydrate (LPHC) diets desensitize sweet taste in both male and female flies. We further investigate the underlying mechanisms of the effects of two diets on sweet taste using RNA sequencing. When compared to the LPHC diet, the mRNA expression of genes involved in the metabolism of glycine, serine, and threonine is significantly upregulated in the HPLC diet group, suggesting these amino acids may mediate sweet taste perception. We further find that sweet sensitization occurs in flies fed with the LPHC diet supplemented with serine and threonine. Our study demonstrates that sucrose taste sensitivity is affected by the balance of dietary protein and carbohydrates possibly through changes in serine and threonine.

Branched chain amino acids impact health and lifespan indirectly via amino acid balance and appetite control.

Elevated branched chain amino acids (BCAAs) are associated with obesity and insulin resistance. How long-term dietary BCAAs impact late-life health and lifespan is unknown. Here, we show that when dietary BCAAs are varied against a fixed, isocaloric macronutrient background, long-term exposure to high BCAA diets leads to hyperphagia, obesity and reduced lifespan. These effects are not due to elevated BCAA per se or hepatic mTOR activation, but rather due to a shift in the relative quantity of dietary BCAAs and other AAs, notably tryptophan and threonine. Increasing the ratio of BCAAs to these AAs resulted in hyperphagia and is associated with central serotonin depletion. Preventing hyperphagia by calorie restriction or pair-feeding averts the health costs of a high BCAA diet. Our data highlight a role for amino acid quality in energy balance and show that health costs of chronic high BCAA intakes need not be due to intrinsic toxicity but, rather, a consequence of hyperphagia driven by AA imbalance.

Sucralose Promotes Food Intake through NPY and a Neuronal Fasting Response.

Non-nutritive sweeteners like sucralose are consumed by billions of people. While animal and human studies have demonstrated a link between synthetic sweetener consumption and metabolic dysregulation, the mechanisms responsible remain unknown. Here we use a diet supplemented with sucralose to investigate the long-term effects of sweet/energy imbalance. In flies, chronic sweet/energy imbalance promoted hyperactivity, insomnia, glucose intolerance, enhanced sweet taste perception, and a sustained increase in food and calories consumed, effects that are reversed upon sucralose removal. Mechanistically, this response was mapped to the ancient insulin, catecholamine, and NPF/NPY systems and the energy sensor AMPK, which together comprise a novel neuronal starvation response pathway. Interestingly, chronic sweet/energy imbalance promoted increased food intake in mammals as well, and this also occurs through an NPY-dependent mechanism. Together, our data show that chronic consumption of a sweet/energy imbalanced diet triggers a conserved neuronal fasting response and increases the motivation to eat.