Functional Interrogation of the AgRP Neural Circuits in Control of Appetite, Body Weight, and Behaviors

GLP-1, GIP, and Glucagon Agonists for Obesity Treatment: A Hunger Perspective

For centuries, increasingly sophisticated methods and approaches have been brought to bear to promote weight loss. Second only to the Holy Grail of research on aging, the idea of finding a single and simple way to lose weight has long preoccupied the minds of laymen and scientists alike. The effects of obesity are far-reaching and not to be minimized; the need for more effective treatments is obvious. Is there a single silver bullet that addresses this issue without effort on the part of the individual? The answer to this question has been one of the most elusive and sought-after in modern history. Now and then, a miraculous discovery propagates the illusion that a simple solution is possible. Now there are designer drugs that seem to accomplish the task: we can lose weight without effort using mono, dual, and triple agonists of receptors for glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and glucagon. There are, however, fundamental biological principles that raise intriguing questions about these therapies beyond the currently reported side-effects. This perspective reflects upon these issues from the angle of complex goal-oriented behaviors, and systemic and cellular metabolism associated with satiety and hunger.

Effects of non-nutritive sweeteners on growth and intestinal health by regulating hypothalamic RNA profile and ileum microbiota in guinea pigs

BACKGROUND

Non-nutritive sweeteners (NNS) are commonly used in sweetened foods and beverages; however their role in metabolic regulation is still not clear. In this experiment, we used guinea pigs as an animal model to study the effect of NNS on body growth and intestinal health by modifying gut microbiota and hypothalamus-related proteins.

RESULTS

For a 28-day feeding experiment a total of 40 guinea pigs were randomly divided into four groups, one control (CN) group and three treatments, in which three NNS were added to the diet: rebaudioside A (RA, 330 mg kg-1), sodium saccharin (SS, 800 mg kg-1), and sucralose (TGS, 167 mg kg-1), respectively. The TGS group exhibited significantly reduced food consumption in comparison with the CN group (P < 0.05) whereas the RA group showed increased food consumption in comparison with the CN group (P < 0.05). Notably, Taste receptor type 1 subunit 2 (T1R2) expression in the hypothalamus was significantly higher in the RA group than in the CN group (P < 0.05). The mRNA expressions of appetite-stimulated genes arouti-related neuropeptide (AGRP), neuropeptide Y (NPY), and thyroid stimulating hormone (TSHB) were significantly higher than those in the CN group (P < 0.05) but mRNA expressions of appetite-suppressed genes tryptophan hydroxylase 2(THP2) were significantly lower in the TGS group (P < 0.05). Furthermore, NNS in the guinea pig diets (RA, SS, TGS) significantly increased the relative abundance of Muribaculaceae but decreased the relative abundance of Clostridia_vadin BB60 in comparison with the CN group (P < 0.05). We also found that dietary supplementation with RA also significantly altered the relative abundance of Lactobacillus.

CONCLUSION

Our finding confirmed that dietary supplementation with RA and TGS affected body growth and intestinal health by modulating hypothalamic RNA profiles and ileum microbiota, suggesting that NNS should be included in guinea-pig feeding. © 2024 Society of Chemical Industry.

The regulatory effects of second-generation antipsychotics on lipid metabolism: Potential mechanisms mediated by the gut microbiota and therapeutic implications

Second-generation antipsychotics (SGAs) are the mainstay of treatment for schizophrenia and other neuropsychiatric diseases but cause a high risk of disruption to lipid metabolism, which is an intractable therapeutic challenge worldwide. Although the exact mechanisms underlying this lipid disturbance are complex, an increasing body of evidence has suggested the involvement of the gut microbiota in SGA-induced lipid dysregulation since SGA treatment may alter the abundance and composition of the intestinal microflora. The subsequent effects involve the generation of different categories of signaling molecules by gut microbes such as endogenous cannabinoids, cholesterol, short-chain fatty acids (SCFAs), bile acids (BAs), and gut hormones that regulate lipid metabolism. On the one hand, these signaling molecules can directly activate the vagus nerve or be transported into the brain to influence appetite via the gut-brain axis. On the other hand, these molecules can also regulate related lipid metabolism via peripheral signaling pathways. Interestingly, therapeutic strategies directly targeting the gut microbiota and related metabolites seem to have promising efficacy in the treatment of SGA-induced lipid disturbances. Thus, this review provides a comprehensive understanding of how SGAs can induce disturbances in lipid metabolism by altering the gut microbiota.

Agouti-related peptide neuronal silencing overcomes delayed puberty in neonatally underfed male mice

Agouti-related peptide (AgRP) neurons are thought to indirectly regulate the activity of hypothalamic gonadotrophin-releasing hormone neurons which control fertility. AgRP neurons also drive caloric intake and are modulated by metabolically-relevant hormones, providing a link to the hypothalamic-pituitary-gonadal axis. In mice expressing Cre-dependant designer receptors (DREADDs) in AgRP neurons, we activated or silenced these neurons in vivo using the synthetic ligand clozapine-N-oxide (CNO) to observe the effect of AgRP neuron activity on timing of puberty. To validate these animals, we chronically treated both stimulatory (hM3Dq) and inhibitory (hM4Di) DREADD × AgRP-Cre mice with CNO, observing a pronounced increase and decrease of food intake, respectively, consistent with the known orexigenic effects of these neurons. RNAscope was performed to visually confirm the activation of AgRP neurons. Puberty onset was assessed in males and females. There was no effect on preputial separation in males or vaginal opening and first oestrus in females after CNO treatment from day 26 to 30 to chronically modulate AgRP neurons. Next, to determine whether the delay in puberty onset occurring in response to neonatal underfeeding could be overcome by inhibiting AgRP neuronal activity, mice were raised in large (neonatally underfed) or normal litter sizes. The delay in puberty from underfeeding was completely reversed in CNO-treated AgRP-hM4Di male mice. These data highlight the inhibitory role of AgRP neurons to delay puberty onset when undernutrition occurs during the neonatal period, at least in male mice. TRAIL REGISTRATION NUMBER: JNE-22-0081-OA.R2.

AgRP neuronal activity across feeding-related behaviours

AgRP neurons trigger one of the most potent orexigenic responses and are both necessary and sufficient for feeding. Recent technical advances for monitoring in vivo neuronal activity have revisited a previously well-established model of AgRP neurons' feeding regulatory effects. Our current understanding of AgRP neurons has increased in complexity and revealed a fine-tuned regulation of their activity dynamics across the whole sequence of feeding-related behaviours. This review focuses on recent studies that refined and re-evaluated our understanding of the regulatory principles and behavioural effects of AgRP circuits. We aim to cover major discoveries on the dynamic regulation of AgRP neuronal activity by exteroceptive and interoceptive food-related cues, their pleiotropic effects in feeding and whole-body homeostasis, and the associated AgRP circuits. The function and regulation of AgRP neuron will be sequentially discussed across the temporal series of behavioural and physiological changes occurring during the appetitive (food craving and foraging), the anticipatory (discovery of food-predicting cues), and the consummatory/post-ingestive phase of feeding (calorie ingestion).

Drinking Water with Saccharin Sodium Alters the Microbiota-Gut-Hypothalamus Axis in Guinea Pig

The effects of saccharin, as a type of sweetener additive, on the metabolism and development of mammals are still controversial. Our previous research revealed that saccharin sodium (SS) promoted the feed intake and growth of guinea pigs. In this experiment, we used the guinea pig model to study the physiological effect of SS in the microbiota-gut-hypothalamus axis. Adding 1.5 mM SS to drinking water increased the serum level of glucose, followed by the improvement in the morphology and barrier function of the ileal villus, such as SS supplementation which increased the villus height and villus height/crypt depth ratio. Saccharin sodium (SS) treatment activated the sweet receptor signaling in the ileum and altered GHRP hormone secretion. In the hypothalamus of SS and control (CN) group, RNA-seq identified 1370 differently expressed genes (796 upregulated, 574 downregulated), enriching into the taste signaling transduction, and neuroactive ligand-receptor interaction. LEfSe analysis suggested that Lactobacillaceae-Lactobacillus was the microbe with significantly increased abundance of ileum microorganisms in the SS-treated group, while Brevinema-Andersonii and Erysipelotrichaceae-Ilebacterium were the microbes with significantly increased abundance of the control. Furthermore, SS treatment significantly enhanced the functions of chemoheterotrophy and fermentation of ileal microflora compared to the CN group. Accordingly, SS treatment increased levels of lactic acid and short-chain fatty acids (acetic acid, propionic acid and N-valeric acid) in the ileal digesta. In summary, drinking water with 1.5 mM SS activated sweet receptor signaling in the gut and altered GHRP hormone secretion, followed by the taste signaling transduction in the hypothalamus.