TGR5 signalling promotes mitochondrial fission and beige remodelling of white adipose tissue

Increased dietary protein stimulates amino acid catabolism via the gut microbiota and secondary bile acid production

Excess amino acids from a protein-rich diet are mainly catabolized in the liver. However, it is still unclear to what extent the gut microbiota may be involved in the mechanisms governing this catabolism. Therefore, the aim of this study was to investigate whether consumption of different dietary protein concentrations induces changes in the taxonomy of the gut microbiota, which may contribute to the regulation of hepatic amino acid catabolism. Consumption of a high-protein diet caused overexpression of HIF-1α in the colon and increase in mitochondrial activity, creating a more anaerobic environment that was associated with changes in the taxonomy of the gut microbiota promoting an increase in the synthesis of secondary bile acids, increased secretion of pancreatic glucagon. This effect was demonstrated in pancreatic islets, where secondary bile acids stimulated the expression of the PC2 enzyme that promotes glucagon formation. The increase in circulating glucagon was associated with an induction of the expression of hepatic amino acid-degrading enzymes, an effect attenuated by antibiotics. Thus, high protein intake in mice and humans induced the increase of different species in the gut microbiota with the capacity to produce secondary bile acids leading to an increase in secondary bile acids and glucagon levels, promoting amino acid catabolism.

Pharmacological and physiological activation of TGR5 in the NTS lowers food intake by enhancing leptin-STAT3 signaling

Feeding increases plasma bile acid levels while the nucleus of the solitary tract (NTS) and area postrema (AP) of the brain detect changes in hormones to regulate feeding. However, whether an increase in bile acids activates Takeda G protein-coupled receptor 5 (TGR5) in the NTS and/or AP to lower feeding through a negative feedback pathway is unknown. Here, we discover that infusion of TGR5 agonist CCDC in the NTS of male rats lowered food intake without causing conditional taste avoidance in short-term high fat (HF) fed male rats in association with HF-induced increase in TGR5 expression in the NTS. In contrast, CCDC infusion into the AP failed to lower food intake in HF rats with a reduction in TGR5 expression in the AP. CCDC infusion in the NTS activates TGR5 to reverse HF-induced leptin resistance by enhancing a leptin-leptin receptor-STAT3 signaling axis selectively in the NTS to lower feeding. Finally, metabolomic analysis indicated that HF impaired a refeeding-induced rise of endogenous TGR5 ligand deoxycholic acid in the plasma and subsequently in the NTS in association with hyperphagia, while direct infusion of deoxycholic acid in the NTS of HF rats activated TGR5 to lower feeding and enhanced leptin-STAT3 signaling, thereby altogether demonstrating physiological and pharmacological activation of TGR5 in the NTS regulates food intake. In summary, we discover that an activation of TGR5 in the NTS enhances leptin-STAT3 signaling to lower food intake. Our findings highlight the potential of targeting TGR5 to reverse leptin resistance in the NTS.

Unraveling the gut microbiota's role in obesity: key metabolites, microbial species, and therapeutic insights

Obesity, characterized by excessive fat accumulation, stems from an imbalance between energy intake and expenditure, with the gut microbiota playing a crucial role. This review highlights how gut microbiota influences metabolic pathways, inflammation, and adipose tissue regulation in obesity. Specific bacteria and metabolites, such as lipopolysaccharides (LPS) and short-chain fatty acids (SCFAs), modulate gut permeability, inflammation, and energy harvest, impacting obesity development. Certain gut bacteria, including Clostridium XIVb, Dorea spp., Enterobacter cloacae, and Collinsella aerofaciens, promote obesity by increasing energy harvest, gut permeability, and inflammatory response through LPS translocation into the bloodstream. Conversely, beneficial bacteria like Akkermansia muciniphila, Lactobacillus spp., and Bifidobacterium spp. enhance gut barrier integrity, regulate SCFA production, and modulate fasting-induced adipose factor, which collectively support metabolic health by reducing fat storage and inflammation. Metabolites such as SCFAs (acetate, propionate, and butyrate) interact with G-protein coupled receptors to regulate lipid metabolism and promote the browning of white adipose tissue (WAT), thus enhancing thermogenesis and energy expenditure. However, LPS contributes to insulin resistance and fat accumulation, highlighting the dual roles of these microbial metabolites in both supporting and disrupting metabolic function. Therapeutic interventions targeting gut microbiota, such as promoting WAT browning and activating brown adipose tissue (BAT), hold promise for obesity management. However, personalized approaches are necessary due to individual microbiome variability. Further research is essential to translate these insights into microbiota-based clinical therapies.

Crosstalk Between Bile Acids and Intestinal Epithelium: Multidimensional Roles of Farnesoid X Receptor and Takeda G Protein Receptor 5

Bile acids and their corresponding intestinal epithelial receptors, the farnesoid X receptor (FXR), the G protein-coupled bile acid receptor (TGR5), play crucial roles in the physiological and pathological processes of intestinal epithelial cells. These acids and receptors are involved in the regulation of intestinal absorption, signal transduction, cellular proliferation and repair, cellular senescence, energy metabolism, and the modulation of gut microbiota. A comprehensive literature search was conducted using PubMed, employing keywords such as bile acid, bile acid receptor, FXR (nr1h4), TGR5 (gpbar1), intestinal epithelial cells, proliferation, differentiation, senescence, energy metabolism, gut microbiota, inflammatory bowel disease (IBD), colorectal cancer (CRC), and irritable bowel syndrome (IBS), with a focus on publications available in English. This review examines the diverse effects of bile acid signaling and bile receptor pathways on the proliferation, differentiation, senescence, and energy metabolism of intestinal epithelial cells. Additionally, it explores the interactions between bile acids, their receptors, and the microbiota, as well as the implications of these interactions for host health, particularly in relation to prevalent intestinal diseases. Finally, the review highlights the importance of developing highly specific ligands for FXR and TGR5 receptors in the context of metabolic and intestinal disorders.

Bile acid metabolism in type 2 diabetes mellitus

Type 2 diabetes mellitus is a complex disorder associated with insulin resistance and hyperinsulinaemia that is insufficient to maintain normal glucose metabolism. Changes in insulin signalling and insulin levels are thought to directly explain many of the metabolic abnormalities that occur in diabetes mellitus, such as impaired glucose disposal. However, molecules that are directly affected by abnormal insulin signalling might subsequently go on to cause secondary metabolic effects that contribute to the pathology of type 2 diabetes mellitus. In the past several years, evidence has linked insulin resistance with the concentration, composition and distribution of bile acids. As bile acids are known to regulate glucose metabolism, lipid metabolism and energy balance, these findings suggest that bile acids are potential mediators of metabolic distress in type 2 diabetes mellitus. In this Review, we highlight advances in our understanding of the complex regulation of bile acids during insulin resistance, as well as how bile acids contribute to metabolic control.

TGR5 Activation by Dietary Bioactives and Related Improvement in Mitochondrial Function for Alleviating Diabetes and Associated Complications

Takeda G protein-coupled receptor 5 (TGR5), also known as G protein-coupled bile acid receptor 1 (GPBAR1), is a cell surface receptor involved in key physiological processes, including glucose homeostasis and energy metabolism. Recent research has focused on the role of TGR5 activation in preventing or treating diabetes while also highlighting its potential impact on the progression of diabetic complications. Functional foods and edible plants have emerged as valuable sources of natural compounds that can activate TGR5, offering potential therapeutic benefits for diabetes management. Despite growing interest, studies on the activation of TGR5 by dietary bioactive compounds remain scattered. This Review aims to provide a comprehensive analysis of how dietary bioactives act as potential agents for TGR5 activation in managing diabetes and its complications. It explores the mechanisms of TGR5 activation through both direct agonistic effects and indirect pathways via modulation of the gut microbiota and bile acid metabolism.

Decoding TGR5: A comprehensive review of its impact on cerebral diseases

Currently, unraveling the enigmatic realm of drug targets for cerebral disorders poses a formidable challenge. Takeda G protein-coupled receptor 5 (TGR5), also known as G protein-coupled bile acid receptor 1, is a specific bile acid receptor. Widely distributed across various tissues, TGR5 orchestrates a myriad of biological functions encompassing inflammation, energy metabolism, fatty acid metabolism, immune responses, cellular proliferation, apoptosis, and beyond. Alongside its well-documented implications in liver diseases, obesity, type 2 diabetes, tumors, and cardiovascular diseases, a growing body of evidence accentuates the pivotal role of TGR5 in cerebral diseases. Thus, this comprehensive review aimed to scrutinize the current insights into the pathological mechanisms involving TGR5 in cerebral diseases, while contemplating its potential as a promising therapeutic target for cerebral diseases.

Polyzwitterion-branched polycholic acid nanocarriers based oral delivery insulin for long-term glucose and metabolic regulation in diabetes mellitus

Diabetes represents a global health crisis that necessitates advancements in prevention, treatment, and management. Beyond glucose regulation, addressing weight management and associated complications is imperative. This study introduces an oral nanoparticle formulation designed to simultaneously control blood glucose, obesity, and metabolic dysfunction. These nanoparticles, based on poly (zwitterion-cholic acid), incorporate a polyzwitterion component to enhance permeation through the mucus layer and prolong drug residence. Furthermore, bile acid polymers not only regulate lipid metabolism but also ameliorate obesity-associated inflammation in adipose and liver tissues. In vivo experiments demonstrated significant hypoglycemic effects in healthy, type I diabetic, and type II diabetic mice. Notably, the nanocarriers significantly reduced body weight gain, ameliorated inflammation in adipose and liver tissues, and modulated lipid metabolism in the liver of db/db mice. Our study elucidates a comprehensive strategy for addressing glycemic control and diabetes-related complications, offering a promising approach for diabetes prevention and treatment.

4-hydroxybenzoic acid induces browning of white adipose tissue through the AMPK-DRP1 pathway in HFD-induced obese mice

BACKGROUND

Beige adipocytes have physiological functions similar to brown adipocytes, which are available to increase energy expenditure through uncoupling protein 1 (UCP1) within mitochondria. Recently, many studies showed white adipocytes can undergo remodeling into beige adipocytes, called "browning", by increasing fusion and fission events referred to as mitochondrial dynamics.

PURPOSE

In this study, we aimed to investigate the browning effects of 4-hydroxybenzoic acid (4-HA), one of the major compounds of black raspberries.

METHODS

We examined the mechanism underlying the browning properties of 4-HA focusing on UCP1-dependent non-shivering thermogenesis in 3T3-L1 white adipocytes, high-fat diet (HFD)-induced obese male C57BL/6J mice, and cold-exposed male C57BL/6J mice.

RESULTS

4-HA treatment elevates browning markers such as UCP1, T-Box transcription factor 1, and PR domain containing 16, mitochondrial function factors like oxidative phosphorylation complex as well as mitochondrial dynamic-related factors like phosphorylated dynamin-related protein 1 (p-DRP1), DRP1, and mitofusin 1 in 3T3-L1 white adipocytes, which were also confirmed in inguinal white adipose tissue (iWAT) of HFD-induced obese mice. Mdivi-1 blocked the increased DRP1-mediated mitochondrial fission by 4-HA, and even the browning effect of 4-HA was abolished. Furthermore, 4-HA increased AMP-activated protein kinase (AMPK) in both the 3T3-L1 white adipocytes and iWAT of HFD-induced obese mice. Inhibition of AMPK with Compound C also blocked the 4-HA-induced mitochondrial fission and browning effect.

CONCLUSIONS

4-HA induces the browning of white adipocytes into beige adipocytes by regulating the DRP1-mediated mitochondrial dynamics through AMPK. These findings suggest that 4-HA could serve as a therapeutic candidate for obesity and related metabolic disorders.

Resveratrol stimulates brown of white adipose via regulating ERK/DRP1-mediated mitochondrial fission and improves systemic glucose homeostasis

PURPOSE

Diabetes mellitus and metabolic homeostasis disorders may benefit from white adipose tissue (WAT) browning, which is associated with mitochondrial fission. Resveratrol, a dietary polyphenol, exhibits beneficial effects against abnormalities related to metabolic diseases. However, it remains unknown whether resveratrol contributes to WAT browning by regulating mitochondrial fission.

METHODS

We administered resveratrol (0.4% mixed with control) to db/db mice for 12 weeks, measuring body weight, oral glucose tolerance, insulin tolerance, and histological changes. The uncoupling protein 1 (UCP1) and dynamin-related protein 1 (DRP1) expressions in the epididymal WAT were assessed via immunoblotting.

RESULTS

We found that resveratrol improved systemic glucose homeostasis and insulin resistance in db/db mice, which was associated with increased UCP1 in epididymal WAT. Resveratrol-treated mice exhibited more fragmented mitochondria and increased phosphorylation of DRP1 in the epididymal WAT of the db/db mice. These results were further confirmed in vitro, where resveratrol induced extracellular signal-regulated kinase (ERK) signaling activation, leading to phosphorylation of DRP1 at the S616 site (p-DRP1S616) and mitochondrial fission, which was reversed by an ERK inhibitor in 3T3-L1 adipocytes.

CONCLUSION

Resveratrol plays a role in regulating the phosphorylation of ERK and DRP1, resulting in the promotion of beige cells with epididymal WAT and the improvement of glucose homeostasis. Our present study provides novel insights into the potential mechanism of resveratrol-mediated effects on WAT browning, suggesting that it is, at least in part, mediated through ERK/DRP1-mediated mitochondrial fission.

TGR5 receptors in SF1-expressing neurons of the ventromedial hypothalamus regulate glucose homeostasis

OBJECTIVE

Steroidogenic factor-1 (SF1) neurons of the ventromedial hypothalamus play key roles in the regulation of food intake, body weight and glucose metabolism. The bile acid receptor Takeda G protein-coupled receptor 5 (TGR5) is expressed in the hypothalamus, where it determines some of the actions of bile acids on food intake and body weight through still poorly defined neuronal mechanisms. Here, we examined the role of TGR5 in SF1 neurons in the regulation of energy balance and glucose metabolism.

METHODS

We used a genetic approach combined with metabolic phenotyping and molecular analyses to establish the effect of TGR5 deletion in SF1 neurons on meal pattern, body weight, body composition, energy expenditure and use of energy substrates as well as on possible changes in glucose handling and insulin sensitivity.

RESULTS

Our findings reveal that TGR5 in SF1 neurons does not play a major role in the regulation of food intake or body weight under standard chow, but it is involved in the adaptive feeding response to the acute exposure to cold or to a hypercaloric, high-fat diet, without changes in energy expenditure. Notably, TGR5 in SF1 neurons hinder glucose metabolism, since deletion of the receptor improves whole-body glucose uptake through heightened insulin signaling in the hypothalamus and in the brown adipose tissue.

CONCLUSIONS

TGR5 in SF1 neurons favours satiety by differently modifying the meal pattern in response to specific metabolic cues. These studies also reveal a novel key function for TGR5 in SF1 neurons in the regulation of whole-body insulin sensitivity, providing new insight into the role played by neuronal TGR5 in the regulation of metabolism.

Crosstalk between fat tissue and muscle, brain, liver, and heart in obesity: cellular and molecular perspectives

A high-fat diet and physical inactivity are key contributors to obesity, predisposing individuals to various chronic diseases, such as cardiovascular disease and diabetes, which involve multiple organs and tissues. To better understand the role of multi-organ interaction mechanisms in the rising incidence of obesity and its associated chronic conditions, treatment and prevention strategies are being extensively investigated. This review examines the signaling mechanisms between different tissues and organs, with a particular focus on the crosstalk between adipose tissue and the muscle, brain, liver, and heart, and potentially offers new strategies for the treatment and management of obesity and its complications.

Gut microbiota and bile acids: Metabolic interactions and impacts on diabetic kidney disease

The intestinal microbiota comprises approximately 1013-1014 species of bacteria and plays a crucial role in host metabolism by facilitating various chemical reactions. Secondary bile acids (BAs) are key metabolites produced by gut microbiota.Initially synthesized by the liver, BA undergoes structural modifications through the activity of various intestinal microbiota enzymes, including eukaryotic, bacterial, and archaeal enzymes. These modified BA then activate specific receptors that regulate multiple metabolic pathways in the host, such as lipid and glucose metabolism, energy balance, inflammatory response, and cell proliferation and death. Recent attention has been given to intestinal flora disorders in diabetic kidney disease (DKD), where activation of BA receptors has shown promise in alleviating diabetic kidney damage by modulating renal lipid metabolism and mitochondrial production. Imbalances in the intestinal flora can influence the progression of DKD through the regulation of bile acid and its receptor pathways. This review aims to propose a mechanism involving the gut-BA-diabetes and nephropathy axes with the goal of optimizing new strategies for treating DKD.

Bile acid is a responsible host factor for high-fat diet-induced gut microbiota alterations in rats: proof of the "bile acid hypothesis"

High-fat diet (HFD)-induced alterations in gut microbiota may be associated with host pathophysiology, prompting increased interest in elucidating their causal relationships. However, the mechanisms by which HFDs induce these alterations require further clarification. Our previous study using cholic acid (CA)-fed rats suggested that bile acid drives the HFD-induced microbiota alterations as a host factor, a concept termed the "bile acid hypothesis". We analyzed the alterations in the cecal microbiota and bile acid composition in HFD-fed rats and compared the results with those of rats on a CA-supplemented diet. In both cases, the concentrations of total bile acids, including highly bactericidal deoxycholic acid (DCA), increased, concomitant with the increases in the Firmicutes (Bacillota)/Bacteroidetes (Bacteroidota) ratio. Operational taxonomic units (OTUs), accounting for 63.39% of the cecal microbiota of control rats, showed a significant correlation with the total bile acid concentration in HFD-fed rats. A DCA sensitivity test conducted in Firmicutes isolates, corresponding to the predominant OTUs from the HFD-fed rats, exhibited significantly higher DCA resistance compared with Bacteroidetes. The top 12 most abundant OTUs of Firmicutes and Bacteroidetes showing positive or negative correlations with the total bile acid concentration were selected from the HFD-fed rats, and their dynamics were compared with those in the CA-fed rats. Of the 24 OTUs, 18, which constituted 48.28% of the cecal population in the control rats, were altered in the same direction (increase or decrease) in the HFD- and CA-supplemented diet groups. Therefore, approximately half of the cecal populations in the control rats were affected by bile acids, substantiating the bile acid hypothesis microbiologically and quantitatively.

Targeting TGR5 to mitigate liver fibrosis: Inhibition of hepatic stellate cell activation through modulation of mitochondrial fission

Chronic hepatitis B virus (HBV) infection continues to be a prominent cause of liver fibrosis and end-stage liver disease in China, necessitating the development of effective therapeutic strategies. This study investigated the potential of targeting TGR5 to alleviate liver fibrosis by impeding the activation of hepatic stellate cells (HSCs), which play a pivotal role in fibrotic progression. Using the human hepatic stellate cell line LX-2 overexpressing hepatitis B virus X protein (HBX), this study revealed that TGR5 activation through INT-777 inhibits HBX-induced LX-2 cell activation, thereby ameliorating liver fibrosis, which is associated with the attenuation of mitochondrial fission and introduces a novel regulatory pathway in liver fibrosis. Additional experiments with mitochondrial fission inducers and inhibitors confirm the crucial role of mitochondrial dynamics in TGR5-mediated effects. In vivo studies using TGR5 knockout mice substantiate these findings, demonstrating exacerbated fibrosis in the absence of TGR5 and its alleviation with the mitochondrial fission inhibitor Mdivi-1. Overall, this study provides insights into TGR5-mediated regulation of liver fibrosis through the modulation of mitochondrial fission in HSCs, suggesting potential therapeutic strategies for liver fibrosis intervention.

Bile Acid Signaling in Metabolic and Inflammatory Diseases and Drug Development

Bile acids are the end products of cholesterol catabolism. Hepatic bile acid synthesis accounts for a major fraction of daily cholesterol turnover in humans. Biliary secretion of bile acids generates bile flow and facilitates biliary secretion of lipids, endogenous metabolites, and xenobiotics. In intestine, bile acids facilitate the digestion and absorption of dietary lipids and fat-soluble vitamins. Through activation of nuclear receptors and G protein-coupled receptors and interaction with gut microbiome, bile acids critically regulate host metabolism and innate and adaptive immunity and are involved in the pathogenesis of cholestasis, metabolic dysfunction-associated steatotic liver disease, alcohol-associated liver disease, type-2 diabetes, and inflammatory bowel diseases. Bile acids and their derivatives have been developed as potential therapeutic agents for treating chronic metabolic and inflammatory liver diseases and gastrointestinal disorders. SIGNIFICANCE STATEMENT: Bile acids facilitate biliary cholesterol solubilization and dietary lipid absorption, regulate host metabolism and immunity, and modulate gut microbiome. Targeting bile acid metabolism and signaling holds promise for treating metabolic and inflammatory diseases.

Shengmai San formula alleviates high-fat diet-induced obesity in mice through gut microbiota-derived bile acid promotion of M2 macrophage polarization and thermogenesis

BACKGROUND

Shengmai San Formula (SMS) is a traditional Chinese medicine (TCM) that has been used to treat wasting-thirst regarded as diabetes mellitus, which occurs disproportionately in obese patients. Therefore, we investigated whether SMS could be used to treat obesity, and explored possible mechanisms by which it might improve glucose and fat metabolism.

METHODS

To investigate the effects of SMS on a high-fat diet (HFD)-induced obesity (DIO) model, we studied glucose metabolism via glucose tolerance testing (GTT) and insulin tolerance testing (ITT). Browning of white adipose tissue (WAT) was evaluated using H&E staining, along with browning-related gene and protein expression. Changes in bile acid (BA) levels in serum, liver, ileum, and inguinal white adipose tissue were detected by Ultra performance liquid chromatography tandem quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). In addition, antimicrobial mixture (ABX) and fecal microbial transplantation (FMT) experiments were used to verify the role of gut flora in the effects produced by SMS on HFD-induced obesity model.

RESULTS

SMS ameliorated diet-induced dyslipidemia in a dose-dependent manner and reduced glucose intolerance and insulin resistance in DIO mice, helping to restore energy metabolism homeostasis. SMS significantly altered the structure of intestinal microbiome composition, decreasing the abundance of Lactobacillus carrying bile salt hydrolase (BSH) enzymes and thereby increasing the level of conjugated BAs in the blood, ileum, and iWAT. Increased TCA content promoted the secretion of Slit3 from M2 macrophages in iWAT, which activates the protein kinase A/calmodulin-dependent protein kinase II (PKA/CaMKII) signaling pathway in sympathetic neurons via the roundabouts receptor 1(ROBO1). This pathway promotes the synthesis and release of norepinephrine (NE), inducing cyclic adenosine monophosphate (cAMP) release in adipose tissue that activates the cyclic adenosine monophosphate/protein kinase A/phosphorylated hormone-sensitive lipase (cAMP/PKA/pHSL) pathway and enhances WAT browning. ABX treatment eliminated SMS effects on glucose and lipid metabolism in DIO mice, whereas glucose and lipid metabolism in obese mice improved following SMS-FMT and increased the level of serum bile acids.

CONCLUSION

SMS affects intestinal flora and bile acid composition in vivo and increased TCA promotes M2 macrophage polarization and Slit3 release in adipose tissue. This induces NE release and increases WAT browning in obese mice, which may be a mechanism by which SMS could be used to treat obesity.

The development of hepatic steatosis depends on the presence of liver-innervating parasympathetic cholinergic neurons in mice fed a high-fat diet

Hepatic lipid metabolism is regulated by the autonomic nervous system of the liver, with the sympathetic innervation being extensively studied, while the parasympathetic efferent innervation is less understood despite its potential importance. In this study, we investigate the consequences of disrupted brain-liver communication on hepatic lipid metabolism in mice exposed to obesogenic conditions. We found that a subset of hepatocytes and cholangiocytes are innervated by parasympathetic nerve terminals originating from the dorsal motor nucleus of the vagus. The elimination of the brain-liver axis by deleting parasympathetic cholinergic neurons innervating the liver prevents hepatic steatosis and promotes browning of inguinal white adipose tissue (ingWAT). The loss of liver-innervating cholinergic neurons increases hepatic Cyp7b1 expression and fasting serum bile acid levels. Furthermore, knockdown of the G protein-coupled bile acid receptor 1 gene in ingWAT reverses the beneficial effects of the loss of liver-innervating cholinergic neurons, leading to the reappearance of hepatic steatosis. Deleting liver-innervating cholinergic neurons has a small but significant effect on body weight, which is accompanied by an increase in energy expenditure. Taken together, these data suggest that targeting the parasympathetic cholinergic innervation of the liver is a potential therapeutic approach for enhancing hepatic lipid metabolism in obesity and diabetes.

The development of hepatic steatosis depends on the presence of liver-innervating parasympathetic cholinergic neurons in mice fed a high-fat diet

Hepatic lipid metabolism is regulated by the autonomic nervous system of the liver, with the sympathetic innervation being extensively studied, while the parasympathetic efferent innervation is less understood despite its potential importance. In this study, we investigate the consequences of disrupted brain-liver communication on hepatic lipid metabolism in mice exposed to obesogenic conditions. We found that a subset of hepatocytes and cholangiocytes are innervated by parasympathetic nerve terminals originating from the dorsal motor nucleus of the vagus. The elimination of the brain-liver axis by deleting parasympathetic cholinergic neurons innervating the liver prevents hepatic steatosis and promotes browning of inguinal white adipose tissue (ingWAT). The loss of liver-innervating cholinergic neurons increases hepatic Cyp7b1 expression and fasting serum bile acid levels. Furthermore, knockdown of the G protein-coupled bile acid receptor 1 gene in ingWAT reverses the beneficial effects of the loss of liver-innervating cholinergic neurons, leading to the reappearance of hepatic steatosis. Deleting liver-innervating cholinergic neurons has a small but significant effect on body weight, which is accompanied by an increase in energy expenditure. Taken together, these data suggest that targeting the parasympathetic cholinergic innervation of the liver is a potential therapeutic approach for enhancing hepatic lipid metabolism in obesity and diabetes.

The role of botanical triterpenoids and steroids in bile acid metabolism, transport, and signaling: Pharmacological and toxicological implications

Bile acids (BAs) are synthesized by the host liver from cholesterol and are delivered to the intestine, where they undergo further metabolism by gut microbes and circulate between the liver and intestines through various transporters. They serve to emulsify dietary lipids and act as signaling molecules, regulating the host's metabolism and immune homeostasis through specific receptors. Therefore, disruptions in BA metabolism, transport, and signaling are closely associated with cholestasis, metabolic disorders, autoimmune diseases, and others. Botanical triterpenoids and steroids share structural similarities with BAs, and they have been found to modulate BA metabolism, transport, and signaling, potentially exerting pharmacological or toxicological effects. Here, we have updated the research progress on BA, with a particular emphasis on new-found microbial BAs. Additionally, the latest advancements in targeting BA metabolism and signaling for disease treatment are highlighted. Subsequently, the roles of botanical triterpenoids in BA metabolism, transport, and signaling are examined, analyzing their potential pharmacological, toxicological, or drug interaction effects through these mechanisms. Finally, a research paradigm is proposed that utilizes the gut microbiota as a link to interpret the role of these important natural products in BA signaling.

Bile acid profiles and mRNA abundance of bile acid-related genes in adipose tissue of dairy cows with high versus normal body condition

Besides their lipid-digestive role, bile acids (BA) influence overall energy homeostasis, such as glucose and lipid metabolism. We hypothesized that BA along with their receptors, regulatory enzymes, and transporters are present in subcutaneous adipose tissue (scAT). In addition, we hypothesized that their mRNA abundance varies with the body condition of dairy cows around calving. Therefore, we analyzed BA in serum and scAT as well as the mRNA abundance of BA-related enzymes, transporters, and receptors in scAT during the transition period in cows with different body conditions around calving. In a previously established animal model, 38 German Holstein cows were divided into either a high (HBCS; n = 19) or normal BCS (NBCS; n = 19) group based on their BCS and back-fat thickness (BFT). Cows were fed different diets to achieve the targeted differences in BCS and BFT (NBCS: BCS <3.5, BFT <1.2 cm; HBCS: BCS >3.75, BFT >1.4 cm) until dry-off at 7 wk antepartum. During the dry period and subsequent lactation, both groups were fed the same diets according to their energy demands. Using a targeted metabolomics approach via liquid chromatography-electrospray ionization-MS /MS, BA were analyzed in serum and scAT at wk -7, 1, 3, and 12 relative to parturition. In serum, 15 BA were observed: cholic acid (CA), chenodeoxycholic acid (CDCA), glycocholic acid (GCA), taurocholic acid (TCA), glycochenodeoxycholic acid (GCDCA), taurochenodeoxycholic acid, deoxycholic acid (DCA), lithocholic acid, glycodeoxycholic acid (GDCA), glycolithocholic acid, taurodeoxycholic acid, taurolithocholic acid, β-muricholic acid, tauromuricholic acid (sum of α and β), and glycoursodeoxycholic acid, whereas in scAT 7 BA were detected: CA, GCA, TCA, GCDCA, taurochenodeoxycholic acid, GDCA, and taurodeoxycholic acid. In serum and scAT samples, the primary BA CA and its conjugate GCA were predominantly detected. Increasing serum concentrations of CA, CDCA, TCA, GCA, GCDCA, DCA, and β-muricholic acid with the onset of lactation might be related to the increasing DMI after parturition. Furthermore, serum concentrations of CA, CDCA, GCA, DCA, GCDCA, TCA, lithocholic acid, and GDCA were lower in HBCS cows compared with NBCS cows, concomitant with increased lipolysis in HBCS cows. The correlation between CA in serum and scAT may point to the transport of CA across cell membranes. Overall, the findings of the present study suggest a potential role of BA in lipid metabolism depending on the body condition of periparturient dairy cows.

Yin-Yang control of energy balance by lipids in the hypothalamus: The endocannabinoids vs bile acids case

Obesity is a chronic and debilitating disorder that originates from alterations in energy-sensing brain circuits controlling body weight gain and food intake. The dysregulated syntheses and actions of lipid mediators in the hypothalamus induce weight gain and overfeeding, but the molecular and cellular underpinnings of these alterations remain elusive. In response to changes in the nutritional status, different lipid sensing pathways in the hypothalamus direct body energy needs in a Yin-Yang model. Endocannabinoids orchestrate the crosstalk between hypothalamic circuits and the sympathetic nervous system to promote food intake and energy accumulation during fasting, whereas bile acids act on the same top-down axis to reduce energy intake and possibly storage after the meal. In obesity, the bioavailability and downstream cellular actions of endocannabinoids and bile acids are altered in hypothalamic neurons involved in body weight and metabolic control. Thus, the onset and progression of this disease might result from an imbalance in hypothalamic sensing of multiple lipid signals, which are possibly integrated by common molecular nodes. In this viewpoint, we discuss a possible model that explains how bile acids and endocannabinoids may exert their effects on energy balance regulation via interconnected mechanisms at the level of the hypothalamic neuronal circuits. Therefore, we propose a new conceptual framework for understanding and treating central mechanisms of maladaptive lipid action in obesity.

GPCR-mediated regulation of beige adipocyte formation: Implications for obesity and metabolic health

Obesity and its associated complications pose a significant burden on health. The non-shivering thermogenesis (NST) and metabolic capacity properties of brown adipose tissue (BAT), which are distinct from those of white adipose tissue (WAT), in combating obesity and its related metabolic diseases has been well documented. However, beige adipose tissue, the third and relatively novel type of adipose tissue, which emerges in extensive presence of WAT and shares similar favorable metabolic properties with BAT, has garnered considerable attention in recent years. In this review, we focused on the role of G protein-coupled receptors (GPCRs), the largest receptor family and the most successful class of drug targets in humans, in the induction of beige adipocytes. More importantly, we highlight researchers' clinical treatment attempts to ameliorate obesity and other related metabolic diseases through the formation and activation of beige adipose tissue. In summary, this review provides valuable insights into the formation of beige adipose tissue and the involvement of GPCRs, based on the latest advancements in scientific research.

Bile Acids as Emerging Players at the Intersection of Steatotic Liver Disease and Cardiovascular Diseases

Affecting approximately 25% of the global population, steatotic liver disease (SLD) poses a significant health concern. SLD ranges from simple steatosis to metabolic dysfunction-associated steatohepatitis and fibrosis with a risk of severe liver complications such as cirrhosis and hepatocellular carcinoma. SLD is associated with obesity, atherogenic dyslipidaemia, and insulin resistance, increasing cardiovascular risks. As such, identifying SLD is vital for cardiovascular disease (CVD) prevention and treatment. Bile acids (BAs) have critical roles in lipid digestion and are signalling molecules regulating glucose and lipid metabolism and influencing gut microbiota balance. BAs have been identified as critical mediators in cardiovascular health, influencing vascular tone, cholesterol homeostasis, and inflammatory responses. The cardio-protective or harmful effects of BAs depend on their concentration and composition in circulation. The effects of certain BAs occur through the activation of a group of receptors, which reduce atherosclerosis and modulate cardiac functions. Thus, manipulating BA receptors could offer new avenues for treating not only liver diseases but also CVDs linked to metabolic dysfunctions. In conclusion, this review discusses the intricate interplay between BAs, metabolic pathways, and hepatic and extrahepatic diseases. We also highlight the necessity for further research to improve our understanding of how modifying BA characteristics affects or ameliorates disease.

Genipin improves obesity through promoting bile secretion and changing bile acids composition in diet-induced obese rats

OBJECTIVES

Bile acids (BAs), as signaling molecules to regulate metabolism, have received considerable attention. Genipin is an iridoid compound extracted from Fructus Gradeniae, which has been shown to relieve adiposity and metabolic syndrome. Here, we investigated the mechanism of genipin counteracting obesity and its relationship with BAs signals in diet-induced obese (DIO) rats.

METHODS

The DIO rats were received intraperitoneal injections of genipin for 10 days. The body weight, visceral fat, lipid metabolism in the liver, thermogenic genes expressions in brown fat, BAs metabolism and signals, and key enzymes for BAs synthesis were determined.

KEY FINDINGS

Genipin inhibited fat synthesis and promoted lipolysis in the liver, and upregulated thermogenic gene expressions in brown adipose tissue of DIO rats. Genipin increased bile flow rate and upregulated the expressions of aquaporin 8 and the transporters of BAs in liver. Furthermore, genipin changed BAs composition by promoting alternative pathways and inhibiting classical pathways for BAs synthesis and upregulated the expressions of bile acid receptors synchronously.

CONCLUSIONS

These results suggest that genipin ameliorate obesity through BAs-mediated signaling pathways.

Fructose induces hepatic steatosis in adolescent mice linked to the disorders of lipid metabolism, bile acid metabolism, and autophagy

The effects of excessive fructose intake on the development and progression of metabolic disorders have received widespread attention. However, the deleterious effects of fructose on the development of hepatic metabolic disease in adolescents and its potential mechanisms are not fully understood. In this study, we investigated the effects of isocaloric fructose-rich diets on the liver of adolescent mice. The results showed that fructose-rich diets had no effect on the development of obesity in the adolescent mice, but did induce hepatic lipid accumulation. Besides, we found that fructose-rich diets promoted hepatic inflammatory responses and oxidative stress in adolescent mice, which may be associated with activation of the NLRP3 inflammasome and inhibition of the Nrf2 pathway. Furthermore, our results showed that fructose-rich diets caused disturbances in hepatic lipid metabolism and bile acid metabolism, as well as endoplasmic reticulum stress and autophagy dysfunction. Finally, we found that the intestinal barrier function was impaired in the mice fed fructose-rich diets. In conclusion, our study demonstrates that dietary high fructose induces hepatic metabolic disorders in adolescent mice. These findings provide a theoretical foundation for fully understanding the effects of high fructose intake on the development of hepatic metabolic diseases during adolescence.

TGR5 deficiency in excitatory neurons ameliorates Alzheimer's pathology by regulating APP processing

Bile acids (BAs) metabolism has a significant impact on the pathogenesis of Alzheimer's disease (AD). We found that deoxycholic acid (DCA) increased in brains of AD mice at an early stage. The enhanced production of DCA induces the up-regulation of the bile acid receptor Takeda G protein-coupled receptor (TGR5), which is also specifically increased in neurons of AD mouse brains at an early stage. The accumulation of exogenous DCA impairs cognitive function in wild-type mice, but not in TGR5 knockout mice. This suggests that TGR5 is the primary receptor mediating these effects of DCA. Furthermore, excitatory neuron-specific knockout of TGR5 ameliorates Aβ pathology and cognition impairments in AD mice. The underlying mechanism linking TGR5 and AD pathology relies on the downstream effectors of TGR5 and the APP production, which is succinctly concluded as a "p-STAT3-APH1-γ-secretase" signaling pathway. Our studies identified the critical role of TGR5 in the pathological development of AD.

Inhibition of fatty acid uptake by TGR5 prevents diabetic cardiomyopathy

Diabetic cardiomyopathy is characterized by myocardial lipid accumulation and cardiac dysfunction. Bile acid metabolism is known to play a crucial role in cardiovascular and metabolic diseases. Takeda G-protein-coupled receptor 5 (TGR5), a major bile acid receptor, has been implicated in metabolic regulation and myocardial protection. However, the precise involvement of the bile acid-TGR5 pathway in maintaining cardiometabolic homeostasis remains unclear. Here we show decreased plasma bile acid levels in both male and female participants with diabetic myocardial injury. Additionally, we observe increased myocardial lipid accumulation and cardiac dysfunction in cardiomyocyte-specific TGR5-deleted mice (both male and female) subjected to a high-fat diet and streptozotocin treatment or bred on the diabetic db/db genetic background. Further investigation reveals that TGR5 deletion enhances cardiac fatty acid uptake, resulting in lipid accumulation. Mechanistically, TGR5 deletion promotes localization of CD36 on the plasma membrane through the upregulation of CD36 palmitoylation mediated by the palmitoyl acyltransferase DHHC4. Our findings indicate that the TGR5-DHHC4 pathway regulates cardiac fatty acid uptake, which highlights the therapeutic potential of targeting TGR5 in the management of diabetic cardiomyopathy.

Effects of intestine-specific deletion of FGF15 on the development of fatty liver disease with vertical sleeve gastrectomy

BACKGROUND

Vertical sleeve gastrectomy (SGx) is a type of bariatric surgery to treat morbid obesity and metabolic dysfunction-associated steatotic liver disease (MASLD). The molecular mechanisms of SGx to improve MASLD are unclear, but increased bile acids (BAs) and FGF19 (mouse FGF15) were observed. FGF15/19 is expressed in the ileum in response to BAs and is critical in not only suppressing BA synthesis in the liver but also promoting energy expenditure. We hypothesized the reduction of obesity and resolution of MASLD by SGx may be mediated by FGF15/19.

METHODS

First, we conducted hepatic gene expression analysis in obese patients undergoing SGx, with the results showing increased expression of FGF19 in obese patients' livers. Next, we used wild-type and intestine-specific Fgf15 knockout mice (Fgf15ile-/-) to determine the effects of FGF15 deficiency on improving the metabolic effects.

RESULTS

SGx improved metabolic endpoints in both genotypes, evidenced by decreased obesity, improved glucose tolerance, and reduced MASLD progression. However, Fgf15ile-/- mice showed better improvement compared to wild-type mice after SGx, suggesting that other mediators than FGF15 are also responsible for the beneficial effects of FGF15 deficiency. Further gene expression analysis in brown adipose tissue suggests increased thermogenesis.

CONCLUSIONS

FGF15 deficiency, the larger BA pool and higher levels of secondary BAs may increase energy expenditure in extrahepatic tissues, which may be responsible for improved metabolic functions following SGx.

Update on the development of TGR5 agonists for human diseases

The G protein-coupled bile acid receptor 1 (GPBAR1) or TGR5 is widely distributed across organs, including the small intestine, stomach, liver, spleen, and gallbladder. Many studies have established strong correlations between TGR5 and glucose homeostasis, energy metabolism, immune-inflammatory responses, and gastrointestinal functions. These results indicate that TGR5 has a significant impact on the progression of tumor development and metabolic disorders such as diabetes mellitus and obesity. Targeting TGR5 represents an encouraging therapeutic approach for treating associated human ailments. Notably, the GLP-1 receptor has shown exceptional efficacy in clinical settings for diabetes management and weight loss promotion. Currently, numerous TGR5 agonists have been identified through natural product-based approaches and virtual screening methods, with some successfully progressing to clinical trials. This review summarizes the intricate relationships between TGR5 and various diseases emphasizing recent advancements in research on TGR5 agonists, including their structural characteristics, design tactics, and biological activities. We anticipate that this meticulous review could facilitate the expedited discovery and optimization of novel TGR5 agonists.

The Hepatokine Orosomucoid 2 Mediates Beneficial Metabolic Effects of Bile Acids

Bile acids (BAs) are pleiotropic regulators of metabolism. Elevated levels of hepatic and circulating BAs improve energy metabolism in peripheral organs, but the precise mechanisms underlying the metabolic benefits and harm still need to be fully understood. In the current study, we identified orosomucoid 2 (ORM2) as a liver-secreted hormone (i.e., hepatokine) induced by BAs and investigated its role in BA-induced metabolic improvements in mouse models of diet-induced obesity. Contrary to our expectation, under a high-fat diet (HFD), our Orm2 knockout (Orm2-KO) exhibited a lean phenotype compared with C57BL/6J control, partly due to the increased energy expenditure. However, when challenged with a HFD supplemented with cholic acid, Orm2-KO eliminated the antiobesity effect of BAs, indicating that ORM2 governs BA-induced metabolic improvements. Moreover, hepatic ORM2 overexpression partially replicated BA effects by enhancing insulin sensitivity. Mechanistically, ORM2 suppressed interferon-γ/STAT1 activities in inguinal white adipose tissue depots, forming the basis for anti-inflammatory effects of BAs and improving glucose homeostasis. In conclusion, our study provides new insights into the molecular mechanisms of BA-induced liver-adipose cross talk through ORM2 induction.

ARTICLE HIGHLIGHTS

Bile acid signaling in the regulation of whole body metabolic and immunological homeostasis

Bile acids (BAs) play a crucial role in nutrient absorption and act as key regulators of lipid and glucose metabolism and immune homeostasis. Through the enterohepatic circulation, BAs are synthesized, metabolized, and reabsorbed, with a portion entering the vascular circulation and distributing systemically. This allows BAs to interact with receptors in all major organs, leading to organ-organ interactions that regulate both local and global metabolic processes, as well as the immune system. This review focuses on the whole-body effects of BA-mediated metabolic and immunological regulation, including in the brain, heart, liver, intestine, eyes, skin, adipose tissue, and muscle. Targeting BA synthesis and receptor signaling is a promising strategy for the development of novel therapies for various diseases throughout the body.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

The role of bile acid receptor TGR5 in regulating inflammatory signalling

Takeda G protein-coupled receptor 5 (TGR5) is a bile acid receptor, and its role in regulating metabolism after binding with bile acids has been established. Since the immune response depends on metabolism to provide biomolecules and energy to cope with challenging conditions, emerging evidence reveals the regulatory effects of TGR5 on the immune response. An in-depth understanding of the effect of TGR5 on immune regulation can help us disentangle the interaction of metabolism and immune response, accelerating the development of TGR5 as a therapeutic target. Herein, we reviewed more than 200 articles published in the last 20 years in PubMed, to discuss the roles of TGR5 in regulating inflammatory response, the molecular mechanism, as well as existing problems. Particularly, its anti-inflammation effect is emphasized.

The bile-gut axis and metabolic consequences of cholecystectomy

Cholelithiasis and cholecystitis affect individuals of all ages and are often treated by surgical removal of the gallbladder (cholecystectomy), which is considered a safe, low-risk procedure. Nevertheless, recent findings show that bile and its regulated storage and excretion may have important metabolic effects and that cholecystectomy is associated with several metabolic diseases postoperatively. Bile acids have long been known as emulsifiers essential to the assimilation of lipids and absorption of lipid-soluble vitamins, but more recently, they have also been reported to act as metabolic signaling agents. The nuclear receptor, farnesoid X receptor (FXR), and the G protein-coupled membrane receptor, Takeda G protein-coupled receptor 5 (TGR5), are specific to bile acids. Through activation of these receptors, bile acids control numerous metabolic functions. Cholecystectomy affects the storage and excretion of bile acids, which in turn may influence the activation of FXR and TGR5 and their effects on metabolism including processes leading to metabolic conditions such as metabolic dysfunction-associated steatotic liver disease and metabolic syndrome. Here, with the aim of elucidating mechanisms behind cholecystectomy-associated dysmetabolism, we review studies potentially linking cholecystectomy and bile acid-mediated metabolic effects and discuss possible pathophysiological mechanisms behind cholecystectomy-associated dysmetabolism.

Discovery of betulinic acid derivatives as gut-restricted TGR5 agonists: Balancing the potency and physicochemical properties

The pleiotropic effects of TGR5 make it an appealing target for intervention of metabolic and inflammatory disorders, but systemic activation of TGR5 faces challenges of on-target side effects, especially gallbladder filling. Gut-restricted agonists were proved to be sufficient to circumvent these side effects, but extremely low systemic exposure may not be effective in activating TGR5 since it is located on the basolateral membrane. Herein, to balance potency and physicochemical properties, a series of gut-restricted TGR5 agonists with diversified kinetophores had been designed and synthesized. Compound 22-Na exhibited significant antidiabetic effect, and showed favorable gallbladder safety after 7 days of oral administration in humanized TGR5H88Y mice, confirming that gut-restricted agonism of TGR5 is a viable strategy to alleviate systemic target-related effects.

Gut microbiota in overweight and obesity: crosstalk with adipose tissue

Overweight and obesity are characterized by excessive fat mass accumulation produced when energy intake exceeds energy expenditure. One plausible way to control energy expenditure is to modulate thermogenic pathways in white adipose tissue (WAT) and/or brown adipose tissue (BAT). Among the different environmental factors capable of influencing host metabolism and energy balance, the gut microbiota is now considered a key player. Following pioneering studies showing that mice lacking gut microbes (that is, germ-free mice) or depleted of their gut microbiota (that is, using antibiotics) developed less adipose tissue, numerous studies have investigated the complex interactions existing between gut bacteria, some of their membrane components (that is, lipopolysaccharides), and their metabolites (that is, short-chain fatty acids, endocannabinoids, bile acids, aryl hydrocarbon receptor ligands and tryptophan derivatives) as well as their contribution to the browning and/or beiging of WAT and changes in BAT activity. In this Review, we discuss the general physiology of both WAT and BAT. Subsequently, we introduce how gut bacteria and different microbiota-derived metabolites, their receptors and signalling pathways can regulate the development of adipose tissue and its metabolic capacities. Finally, we describe the key challenges in moving from bench to bedside by presenting specific key examples.

Chenodeoxycholic Acid-Loaded Nanoparticles Are Sufficient to Decrease Adipocyte Size by Inducing Mitochondrial Function

Excess fat accumulation is not only associated with metabolic diseases but also negatively impacts physical appearance and emotional well-being. Bile acid, the body's natural emulsifier, is one of the few FDA-approved noninvasive therapeutic options for double chin (submental fat) reduction. Synthetic sodium deoxycholic acid (NaDCA) causes adipose cell lysis; however, its side effects include inflammation, bruising, and necrosis. Therefore, we investigated if an endogenous bile acid, chenodeoxycholic acid (CDCA), a well-known signaling molecule, can be beneficial without many of the untoward effects. We first generated CDCA-loaded nanoparticles to achieve sustained and localized delivery. Then, we injected them into the subcutaneous fat depot and monitored adipocyte size and mitochondrial function. Unlike NaDCA, CDCA did not cause cytolysis. Instead, we demonstrate that a single injection of CDCA-loaded nanoparticles into the subcutaneous fat reduced the adipocyte size by promoting fat burning and mitochondrial respiration, highlighting their potential for submental fat reduction.

Mechanism of action of the bile acid receptor TGR5 in obesity

G protein-coupled receptors (GPCRs) are a large family of membrane protein receptors, and Takeda G protein-coupled receptor 5 (TGR5) is a member of this family. As a membrane receptor, TGR5 is widely distributed in different parts of the human body and plays a vital role in regulating metabolism, including the processes of energy consumption, weight loss and blood glucose homeostasis. Recent studies have shown that TGR5 plays an important role in glucose and lipid metabolism disorders such as fatty liver, obesity and diabetes. With the global obesity situation becoming more and more serious, a comprehensive explanation of the mechanism of TGR5 and filling the gaps in knowledge concerning clinical ligand drugs are urgently needed. In this review, we mainly explain the anti-obesity mechanism of TGR5 to promote the further study of this target, and show the electron microscope structure of TGR5 and review recent studies on TGR5 ligands to illustrate the specific binding between TGR5 receptor binding sites and ligands, which can effectively provide new ideas for ligand research and promote drug research.

Giardia Antagonizes Beneficial Functions of Indigenous and Therapeutic Intestinal Bacteria during Malnutrition

Undernutrition in children commonly disrupts the structure and function of the small intestinal microbial community, leading to enteropathies, compromised metabolic health, and impaired growth and development. The mechanisms by which diet and microbes mediate the balance between commensal and pathogenic intestinal flora remain elusive. In a murine model of undernutrition, we investigated the direct interactions Giardia lamblia, a prevalent small intestinal pathogen, on indigenous microbiota and specifically on Lactobacillus strains known for their mucosal and growth homeostatic properties. Our research reveals that Giardia colonization shifts the balance of lactic acid bacteria, causing a relative decrease in Lactobacillus spp . and an increase in Bifidobacterium spp . This alteration corresponds with a decrease in multiple indicators of mucosal and nutritional homeostasis. Additionally, protein-deficient conditions coupled with Giardia infection exacerbate the rise of primary bile acids and susceptibility to bile acid-induced intestinal barrier damage. In epithelial cell monolayers, Lactobacillus spp . mitigated bile acid-induced permeability, showing strain-dependent protective effects. In vivo, L. plantarum, either alone or within a Lactobacillus spp consortium, facilitated growth in protein-deficient mice, an effect attenuated by Giardia , despite not inhibiting Lactobacillus colonization. These results highlight Giardia's potential role as a disruptor of probiotic functional activity, underscoring the imperative for further research into the complex interactions between parasites and bacteria under conditions of nutritional deficiency.

Bile salt signaling and bile salt-based therapies in cardiometabolic disease

Bile salts have an established role in the emulsification and intestinal absorption of dietary lipids, and their homeostasis is tightly controlled by various transporters and regulators in the enterohepatic circulation. Notably, emerging evidence points toward bile salts as major modulators of cardiometabolic disease (CMD), an umbrella disease of disorders affecting the heart and blood vessels that is caused by systemic metabolic diseases such as Type 2 diabetes mellitus (T2DM) and metabolic dysfunction-associated steatotic liver disease (MASLD), the latter encompassing also metabolic dysfunction-associated steatohepatitis (MASH). The underlying mechanisms of protective effects of bile salts are their hormonal properties, enabling them to exert versatile metabolic effects by activating various bile salt-responsive signaling receptors with the nuclear farnesoid X receptor (FXR) and the Takeda G-protein-coupled receptor 5 (TGR5) as most extensively investigated. Activation of FXR and TGR5 is involved in the regulation of glucose, lipid and energy metabolism, and inflammation. Bile salt-based therapies directly targeting FXR and TGR5 signaling have been evaluated for their therapeutic potential in CMD. More recently, therapeutics targeting bile salt transporters thereby modulating bile salt localization, dynamics, and signaling, have been developed and evaluated in CMD. Here, we discuss the current knowledge on the contribution of bile salt signaling in the pathogenesis of CMD and the potential of bile salt-based therapies for the treatment of CMD.

Mulberry leaves supplementation alters lipid metabolism and promotes fatty acid β oxidation in growing mutton sheep

Mulberry leaves (MLs) are an unconventional feed with fiber and various active ingredients, and are acknowledged as likely to regulate lipid metabolism, while the molecular mechanism remains undefined. Therefore, our objective was to define the role of MLs on the overall lipid metabolism. We conducted a feeding experiment of three groups on growing mutton sheep fed with dried mulberry leaves (DMLs), with fermented mulberry leaves (FMLs), or without MLs (as control). Analyses of transcriptome and widely target lipids demonstrated the addition of MLs triggered big perturbations in genes and metabolites related to glycerolipid, phospholipid, ether lipid, and sphingolipid metabolism. Additionally, the variations of the above lipids in the treatment of MLs possibly facilitate immunity enhancement of growing mutton sheep via the activation of complement and coagulation cascades. Furthermore, treatments with MLs could expedite proceedings of lipid degradation and fatty acid β oxidation in mitochondria, thereby to achieve the effect of lipid reduction. Besides, added DMLs also fuel fatty acid β-oxidation in peroxisomes and own much stronger lipolysis than added FMLs, possibly attributed to high fiber content in DMLs. These findings establish the novel lipid-lowering role and immune protection of MLs, which lays the foundation for the medicinal application of MLs.

Oleanolic acid promotes skeletal muscle fiber type transformation by activating TGR5-mediated CaN signaling pathway

In recent years, the impact of bile acids and their representative G protein-coupled bile acid receptor 1 Takeda-G-protein-receptor-5 (TGR5) signaling pathway on muscle function and metabolic health has gained considerable interest. Increasing the content of slow muscle fibers has been recognized as an effective strategy to improve metabolic health. Oleanolic acid (OA) is a naturally occurring triterpenoid compound derived from plants, which can activate TGR5. The aim of this study was to investigate the effect of OA and TGR5 on muscle fiber types and further explore the underlying TGR5-dependent mechanisms. In this study, mice were divided into three groups and dietary supplementation with 0, 50, or 100 mg/kg OA. In addition, C2C12 cells were treated with OA at concentrations of 0, 5, 10, and 20 µM. Our studies revealed that OA promoted the conversion of fast to slow muscle fibers. In addition, it was found that OA activated the TGR5-mediated calcineurin (CaN)/nuclear factor of activated T cells cytoplasmic 1 (NFATc1) signaling pathway. Further mechanistic investigations demonstrated that inhibiting TGR5 and CaN abolished the effects of OA on muscle fiber types transformation. In conclusion, this study found that OA promotes the transformation of fast muscle fibers to slow muscle fibers through the TGR5-mediated CaN/NFATc1 signaling pathway.

Giardia antagonizes beneficial functions of indigenous and therapeutic intestinal bacteria during protein deficiency

Undernutrition in children commonly disrupts the structure and function of the small intestinal microbial community, leading to enteropathies, compromised metabolic health, and impaired growth and development. The mechanisms by which diet and microbes mediate the balance between commensal and pathogenic intestinal flora remain elusive. In a murine model of undernutrition, we investigated the direct interactions Giardia lamblia, a prevalent small intestinal pathogen, on indigenous microbiota and specifically on Lactobacillus strains known for their mucosal and growth homeostatic properties. Our research reveals that Giardia colonization shifts the balance of lactic acid bacteria, causing a relative decrease in Lactobacillus spp. and an increase in Bifidobacterium spp. This alteration corresponds with a decrease in multiple indicators of mucosal and nutritional homeostasis. Additionally, protein-deficient conditions coupled with Giardia infection exacerbate the rise of primary bile acids and susceptibility to bile acid-induced intestinal barrier damage. In epithelial cell monolayers, Lactobacillus spp. mitigated bile acid-induced permeability, showing strain-dependent protective effects. In vivo, L. plantarum, either alone or within a Lactobacillus spp consortium, facilitated growth in protein-deficient mice, an effect attenuated by Giardia, despite not inhibiting Lactobacillus colonization. These results highlight Giardia's potential role as a disruptor of probiotic functional activity, underscoring the imperative for further research into the complex interactions between parasites and bacteria under conditions of nutritional deficiency.

Physical exercise plays a role in rebalancing the bile acids of enterohepatic axis in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is considered as one of the most common diseases of lipid metabolism disorders, which is closely related to bile acids disorders and gut microbiota disorders. Bile acids are synthesized from cholesterol in the liver, and processed by gut microbiota in intestinal tract, and participate in metabolic regulation through the enterohepatic circulation. Bile acids not only promote the consumption and absorption of intestinal fat but also play an important role in biological metabolic signaling network, affecting fat metabolism and glucose metabolism. Studies have demonstrated that exercise plays an important role in regulating the composition and function of bile acid pool in enterohepatic axis, which maintains the homeostasis of the enterohepatic circulation and the health of the host gut microbiota. Exercise has been recommended by several health guidelines as the first-line intervention for patients with NAFLD. Can exercise alter bile acids through the microbiota in the enterohepatic axis? If so, regulating bile acids through exercise may be a promising treatment strategy for NAFLD. However, the specific mechanisms underlying this potential connection are largely unknown. Therefore, in this review, we tried to review the relationship among NAFLD, physical exercise, bile acids, and gut microbiota through the existing data and literature, highlighting the role of physical exercise in rebalancing bile acid and microbial dysbiosis.

Chemical exploration of TGR5 functional hot-spots: Synthesis and structure-activity relationships of C7- and C23-Substituted cholic acid derivatives

The activation of TGR5 bestows on bile acids the ability to modulate nongenomic signaling pathways, which are responsible of physiological actions including immunosuppressive and anti-inflammatory properties as well as the regulation of glucose metabolism and energy homeostasis. TGR5 agonists have therefore emerged in drug discovery and preclinical appraisals as promising compounds for the treatment of liver diseases and metabolic syndrome. In this study, we have been devising site-selected chemical modifications of the bile acid scaffold to provide novel chemical tools able to modulate the functions of TGR5 in different tissues. Biological results of the tested collection of semisynthetic cholic acid derivatives were used to extend the structure-activity relationships of TGR5 agonists and to clarify the molecular basis and functional role of TGR5 hot-spots in the receptor activation and selectivity. Some unexpected properties deriving from the molecular structure of bile acids have been unveiled as relevant to the receptor activation and may hence be used to design novel, selective and potent TGR5 agonists.

Time-restricted feeding alleviates metabolic implications of circadian disruption by regulating gut hormone release and brown fat activation

Individuals with rotating and night shift work are highly susceptible to developing metabolic disorders such as obesity and diabetes. This is primarily attributed to disruptions in the circadian rhythms caused by activities and irregular eating habits. Time-restricted feeding (tRF) limits the daily eating schedules and has been demonstrated to markedly improve several metabolic disorders. Although an intricate relationship exists between tRF and circadian rhythms, the underlying specific mechanism remains elusive. We used a sleep disruption device for activity interference and established a model of circadian rhythm disorder in mice with different genetic backgrounds. We found that circadian rhythm disruption led to abnormal hormone secretion in the gut and elevated insulin resistance. tRF improved metabolic abnormalities caused by circadian rhythm disruption, primarily by restoring the gut hormone secretion rhythm and activating brown fat thermogenesis. The crucial function of brown fat in tRF was confirmed using a mouse model with brown fat removal. We demonstrated that chenodeoxycholic acid (CDCA) effectively improved circadian rhythm disruption-induced metabolic disorders by restoring brown fat activation. Our findings demonstrate the potential benefits of CDCA in reversing metabolic disadvantages associated with irregular circadian rhythms.

Bile acid receptors and renal regulation of water homeostasis

The kidney is the key organ responsible for maintaining the body's water and electrolyte homeostasis. About 99% of the primary urine filtered from the Bowman's capsule is reabsorbed along various renal tubules every day, with only 1-2 L of urine excreted. Aquaporins (AQPs) play a vital role in water reabsorption in the kidney. Currently, a variety of molecules are found to be involved in the process of urine concentration by regulating the expression or activity of AQPs, such as antidiuretic hormone, renin-angiotensin-aldosterone system (RAAS), prostaglandin, and several nuclear receptors. As the main bile acid receptors, farnesoid X receptor (FXR) and membrane G protein-coupled bile acid receptor 1 (TGR5) play important roles in bile acid, glucose, lipid, and energy metabolism. In the kidney, FXR and TGR5 exhibit broad expression across all segments of renal tubules, and their activation holds significant therapeutic potential for numerous acute and chronic kidney diseases through alleviating renal lipid accumulation, inflammation, oxidative stress, and fibrosis. Emerging evidence has demonstrated that the genetic deletion of FXR or TGR5 exhibits increased basal urine output, suggesting that bile acid receptors play a critical role in urine concentration. Here, we briefly summarize the function of bile acid receptors in renal water reabsorption and urine concentration.

HDAC1 inhibits beige adipocyte-mediated thermogenesis through histone crotonylation of Pgc1a/Ucp1

Obesity, one of the most serious public health issues, is caused by the imbalance of energy intake and energy expenditure. Increasing energy expenditure via induction of adipose tissue browning has become an appealing strategy to treat obesity and associated metabolic complications. Although histone modifications have been confirmed to regulate cellular energy metabolism, the involved biochemical mechanism of thermogenesis in adipose tissue is not completely understood. Herein, we report that class I histone deacetylases (HDAC) inhibitor MS275 increased PGC1α/UCP1 protein levels in inguinal white adipose tissue (iWAT) concomitant with elevated energy expenditure, reduced obesity and ameliorated glucose tolerance compared to control littermates. H3K18cr and H3K18ac levels were elevated after MS275 treatment. MS275 also promoted the transcription of Pgc1α and Ucp1 by enhancing the enrichment of H3K18cr and H3K18ac in the Pgc1α/Ucp1 enhancer and promoter, with a notable increase in H3K18cr. Mechanistically, the deletion of Hdac1 in beige adipocyte increases H3K18cr levels in enhancers and promoters of Pgc1α and Ucp1 genes, regulated the chromosomal state, thereby affecting the transcription of Pgc1α/Ucp1. Taken together, HDAC1 inhibits beige adipocyte-mediated thermogenesis through histone crotonylation of Pgc1a/Ucp1. This finding may provide a therapeutic strategy through increasing energy expenditure in obesity and related metabolic disorders.

The emerging role of bile acids in white adipose tissue

The effects of bile acids (BAs) on liver, enteroendocrine function, small intestine, and brown adipose tissue have been described extensively. Outside the liver, BAs in the peripheral circulation system represent a specific but underappreciated physiological compartment. We discuss how systemic BAs can be regarded as specific steroidal hormones that act on white adipocytes, and suggest the name 'bilokines' ('bile hormones') for the specific FXR/TGR5 receptor interaction in adipocytes. Some BAs and their agonists regulate adipocyte differentiation, lipid accumulation, hypoxia, autophagy, adipokine and cytokine secretion, insulin signaling, and glucose uptake. BA signaling could provide a new therapeutic avenue for adipoflammation and metaflammation in visceral obesity, the causal mechanisms underlying insulin resistance and type 2 diabetes mellitus (T2D).