Peripheral-specific Y1 receptor antagonism increases thermogenesis and protects against diet-induced obesity

Obesity and related metabolic diseases arise from a chronic imbalance where energy intake surpasses energy expenditure. Current therapies primarily focus on appetite modulation, but these often have limited efficacy and significant side effects due to their central nervous system actions. Neuropeptide Y (NPY), a potent regulator of feeding and energy homeostasis, acts through various Y receptors. While central NPY signaling strongly influences both food intake and energy expenditure (primarily by inhibiting BAT thermogenesis and WAT browning), its central effects also impact mood and anxiety, limiting its therapeutic potential. However, NPY and its Y receptors are also widely expressed in peripheral tissues, including adipose tissue, pancreas, and liver, suggesting a direct role in local metabolic control. Although the function of peripheral Y-receptor signaling in metabolism is largely unknown, recent findings highlight the inhibitory effect of Y1R signaling on insulin secretion and the beneficial impact of peripheral Y1R knockdown on fat mass and lipid oxidation. This study hypothesizes that peripheral Y1R blockade could alleviate diet-induced obesity (DIO) and improve glucose metabolism. To test this, the researchers used in vivo models of selective Y1R antagonism and examined the effects ex vivo in human adipose tissue, utilizing the peripheral-acting Y1R antagonist BIBO3304.

Genetic studies have linked the Leu7/Pro polymorphism in the NPY gene to higher circulating NPY levels and obesity risk. Therefore, reducing NPYergic tone could be a therapeutic strategy. Previous research has demonstrated the role of central NPY in controlling BAT thermogenesis and WAT browning. However, central NPY also influences mood and anxiety, hindering its clinical application. The role of peripheral NPY signaling in metabolic control is largely unclear. Some studies have highlighted Y1R's inhibitory action on pancreatic beta-cell insulin secretion and the positive effects of reducing peripheral Y1R signaling on fat mass and lipid oxidation. This current work aims to build upon this limited knowledge to fully elucidate the specific role of peripheral Y1R on metabolic outcomes.

The study employed several in vivo models of selective Y1R antagonism and examined its effects ex vivo in primary human adipose tissues. Wild-type (WT) C57BL/6JAusb mice were fed either a chow diet or a high-fat diet (HFD) for 7 weeks. Y-receptor mRNA expression levels were examined in various metabolically important tissues (BAT, WATi, WATe, liver, and skeletal muscle). To assess the effects of peripheral Y1R antagonism, 8-week-old WT mice received either BIBO3304 or a vehicle jelly daily for 7 weeks while on chow or HFD. Body weight, body composition (DEXA), food intake, energy expenditure (indirect calorimetry), respiratory exchange ratio (RER), physical activity, body temperature (thermal camera), and glucose and insulin tolerance tests were performed. mRNA and protein levels of key thermogenic and lipogenic markers were assessed in BAT and WATi using qPCR and Western blotting. Adipocyte size and distribution were analyzed by H&E staining. To confirm the role of Y1R in adipocytes, an adult-onset inducible adipocyte-specific Y1R deletion mouse model (AdipoTMCre/+;Y1lox/lox) was generated. Finally, ex vivo experiments on primary human adipocytes were performed using BIBO3304, with or without [Leu31,Pro34]NPY (a Y1R agonist), to assess the effects on thermogenic gene expression. Western blotting was used to analyze p-CREB and p-ERK levels in BAT and WATi. In vivo Akt activity in BAT was monitored using multiphoton microscopy in Akt-FRET biosensor mice.

1. Y1R mRNA expression was significantly elevated in BAT and WATi of HFD-fed mice and in adipose tissue of obese humans compared to lean controls. 2. BIBO3304 treatment significantly reduced body weight gain and fat mass in HFD-fed mice without affecting food intake or physical activity, but with a substantial increase in energy expenditure. 3. BIBO3304 treatment significantly improved glucose tolerance in HFD-fed mice. 4. BIBO3304 treatment increased BAT and body temperature, indicating enhanced thermogenesis. 5. BIBO3304 treatment significantly increased UCP1 and other thermogenic markers (DIO2, PRDM16, PGC1α, CIDEA, EVA1, PDK4, NRG4, and β3R) in BAT, and increased UCP1 in WATi. 6. Adipocyte-specific Y1R deletion mimicked the effects of BIBO3304, reducing body weight gain and fat mass, and improving glucose tolerance. 7. BIBO3304 treatment increased p-CREB and p-ERK levels in BAT and WATi, suggesting the involvement of cAMP-CREB and MAPK-ERK pathways. 8. In vivo imaging showed that BIBO3304 enhanced Akt activity in BAT after glucose challenge. 9. Ex vivo studies on human adipocytes confirmed BIBO3304's ability to upregulate thermogenic gene expression.

This study provides strong evidence that peripheral Y1R signaling plays a critical role in regulating energy homeostasis and obesity development. Selective antagonism of peripheral Y1R, either pharmacologically or genetically, protects against diet-induced obesity by enhancing energy expenditure, primarily through increased thermogenesis in BAT and browning of WAT. The upregulation of UCP1 and other thermogenic markers suggests that Y1R antagonism activates pathways that promote mitochondrial activity and lipid oxidation. The improvement in glucose homeostasis is likely linked to enhanced insulin signaling in BAT, as evidenced by increased Akt activity. The study demonstrates that the effect of Y1R blockade is mediated, at least in part, by the cAMP-CREB and MAPK-ERK signaling pathways. The findings are conserved across species, as demonstrated by the ex vivo experiments on human adipocytes. These findings offer a novel therapeutic strategy for obesity and diabetes by targeting peripheral Y1R, potentially avoiding the central nervous system side effects associated with existing therapies.

This research strongly supports the critical role of peripheral Y1 receptor signaling in the development of diet-induced obesity. Selective antagonism of peripheral Y1R, either through pharmacological means (BIBO3304) or genetic deletion, effectively protects against obesity and improves glucose homeostasis. This effect is primarily mediated by enhanced thermogenesis and browning of adipose tissue, indicating that targeting peripheral Y1R could provide a safer and more effective treatment option for obesity and related metabolic disorders. Future research should focus on developing selective, non-brain-penetrable Y1R antagonists for clinical translation.

The study primarily used mouse models, and while human adipose tissue experiments confirmed some findings, further human studies are needed to validate the findings in humans and confirm safety and efficacy. The study focused primarily on adipose tissue, and the potential contribution of Y1R signaling in other peripheral tissues requires further investigation. The tamoxifen used in the genetic deletion model can have independent effects on weight gain, which needs to be considered when interpreting the results.