TGR5 activation suppressed S1P/S1P2 signaling and resisted high glucose-induced fibrosis in glomerular mesangial cells

Bioactive metabolites: A clue to the link between MASLD and CKD?

Metabolites produced as intermediaries or end-products of microbial metabolism provide crucial signals for health and diseases, such as metabolic dysfunction-associated steatotic liver disease (MASLD). These metabolites include products of the bacterial metabolism of dietary substrates, modification of host molecules (such as bile acids [BAs], trimethylamine-N-oxide, and short-chain fatty acids), or products directly derived from bacteria. Recent studies have provided new insights into the association between MASLD and the risk of developing chronic kidney disease (CKD). Furthermore, alterations in microbiota composition and metabolite profiles, notably altered BAs, have been described in studies investigating the association between MASLD and the risk of CKD. This narrative review discusses alterations of specific classes of metabolites, BAs, fructose, vitamin D, and microbiota composition that may be implicated in the link between MASLD and CKD.

Protective effect of UDCA against IL-11- induced cardiac fibrosis is mediated by TGR5 signalling

Introduction

Cardiac fibrosis occurs in a wide range of cardiac diseases and is characterised by the transdifferentiation of cardiac fibroblasts into myofibroblasts these cells produce large quantities of extracellular matrix, resulting in myocardial scar. The profibrotic process is multi-factorial, meaning identification of effective treatments has been limited. The antifibrotic effect of the bile acid ursodeoxycholic acid (UDCA) is established in cases of liver fibrosis however its mechanism and role in cardiac fibrosis is less well understood.

Methods

In this study, we used cellular models of cardiac fibrosis and living myocardial slices to characterise the macroscopic and cellular responses of the myocardium to UDCA treatment. We complemented this approach by conducting RNA-seq on cardiac fibroblasts isolated from dilated cardiomyopathy patients. This allowed us to gain insights into the mechanism of action and explore whether the IL-11 and TGFβ/WWP2 profibrotic networks are influenced by UDCA. Finally, we used fibroblasts from a TGR5 KO mouse to confirm the mechanism of action.

Results and discussion

We found that UDCA reduced myofibroblast markers in rat and human fibroblasts and in living myocardial slices, indicating its antifibrotic action. Furthermore, we demonstrated that the treatment of UDCA successfully reversed the profibrotic IL-11 and TGFβ/WWP2 gene networks. We also show that TGR5 is the most highly expressed UDCA receptor in cardiac fibroblasts. Utilising cells isolated from a TGR5 knock-out mouse, we identified that the antifibrotic effect of UDCA is attenuated in the KO fibroblasts. This study combines cellular studies with RNA-seq and state-of-the-art living myocardial slices to offer new perspectives on cardiac fibrosis. Our data confirm that TGR5 agonists, such as UDCA, offer a unique pathway of action for the treatment of cardiac fibrosis. Medicines for cardiac fibrosis have been slow to clinic and have the potential to be used in the treatment of multiple cardiac diseases. UDCA is well tolerated in the treatment of other diseases, indicating it is an excellent candidate for further in-human trials.

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.

Role of Bile Acid Receptors in the Development and Function of Diabetic Nephropathy

Diabetic nephropathy (DN) is a prevalent microvascular complication that occurs often in individuals with diabetes. It significantly raises the mortality rate of affected patients. Therefore, there is an urgent need to identify therapeutic targets for controlling and preventing the occurrence and development of DN. Bile acids (BAs) are now recognized as intricate metabolic integrators and signaling molecules. The activation of BAs has great promise as a therapeutic approach for preventing DN, renal damage caused by obesity, and nephrosclerosis. The nuclear receptors (NRs), farnesoid X receptor (FXR), pregnane X receptor (PXR), vitamin D receptor (VDR); and the G protein-coupled BA receptor, Takeda G-protein-coupled receptor 5 (TGR5) have important functions in controlling lipid, glucose, and energy metabolism, inflammation, as well as drug metabolism and detoxification. Over the past 10 years, there has been advancement in comprehending the biology and processes of BA receptors in the kidney, as well as in the creation of targeted BA receptor agonists. In this review, we discuss the role of BA receptors, FXR, PXR, VDR, and TGR5 in DN and their role in renal physiology, as well as the development and application of agonists that activate BA receptors for the treatment of kidney diseases.

Intestinal flora and bile acid interactions impact the progression of diabetic kidney disease

In recent years, with the rapid development of omics technologies, researchers have shown that interactions between the intestinal flora and bile acids are closely related to the progression of diabetic kidney disease (DKD). By regulating bile acid metabolism and receptor expression, the intestinal flora affects host metabolism, impacts the immune system, and exacerbates kidney injury in DKD patients. To explore interactions among the gut flora, bile acids and DKD, as well as the related mechanisms, in depth, in this paper, we review the existing literature on correlations among the gut flora, bile acids and DKD. This review also summarizes the efficacy of bile acids and their receptors as well as traditional Chinese medicines in the treatment of DKD and highlights the unique advantages of bile acid receptors in DKD treatment. This paper is expected to reveal a new and important potential strategy for the clinical treatment of DKD.

NF-ĸB axis in diabetic neuropathy, cardiomyopathy and nephropathy: A roadmap from molecular intervention to therapeutic strategies

Diabetes mellitus (DM) is a metabolic illness defined by elevated blood glucose levels, mediating various tissue alterations, including the dysfunction of vital organs. Diabetes mellitus (DM) can lead to many consequences that specifically affect the brain, heart, and kidneys. These issues are known as neuropathy, cardiomyopathy, and nephropathy, respectively. Inflammation is acknowledged as a pivotal biological mechanism that contributes to the development of various diabetes consequences. NF-κB modulates inflammation and the immune system at the cellular level. Its abnormal regulation has been identified in several clinical situations, including cancer, inflammatory bowel illnesses, cardiovascular diseases, and Diabetes Mellitus (DM). The purpose of this review is to evaluate the potential impact of NF-κB on complications associated with DM. Enhanced NF-κB activity promotes inflammation, resulting in cellular harm and compromised organ performance. Phytochemicals, which are therapeutic molecules, can potentially decline the NF-κB level, therefore alleviating inflammation and the progression of problems correlated with DM. More importantly, the regulation of NF-κB can be influenced by various factors, such as TLR4 in DM. Highlighting these factors can facilitate the development of novel therapies in the future.

Lipid metabolism disorder in diabetic kidney disease

Diabetic kidney disease (DKD), a significant complication associated with diabetes mellitus, presents limited treatment options. The progression of DKD is marked by substantial lipid disturbances, including alterations in triglycerides, cholesterol, sphingolipids, phospholipids, lipid droplets, and bile acids (BAs). Altered lipid metabolism serves as a crucial pathogenic mechanism in DKD, potentially intertwined with cellular ferroptosis, lipophagy, lipid metabolism reprogramming, and immune modulation of gut microbiota (thus impacting the liver-kidney axis). The elucidation of these mechanisms opens new potential therapeutic pathways for DKD management. This research explores the link between lipid metabolism disruptions and DKD onset.

TGR5 signalling in heart and brain injuries: focus on metabolic and ischaemic mechanisms

The heart and brain are the core organs of the circulation and central nervous system, respectively, and play an important role in maintaining normal physiological functions. Early neuronal and cardiac damage affects organ function. The relationship between the heart and brain is being continuously investigated. Evidence-based medicine has revealed the concept of the "heart- brain axis," which may provide new therapeutic strategies for certain diseases. Takeda protein-coupled receptor 5 (TGR5) is a metabolic regulator involved in energy homeostasis, bile acid homeostasis, and glucose and lipid metabolism. Inflammation is critical for the development and regeneration of the heart and brain during metabolic diseases. Herein, we discuss the role of TGR5 as a metabolic regulator of heart and brain development and injury to facilitate new therapeutic strategies for metabolic and ischemic diseases of the heart and brain.

Mitochondrial oxidative damage reprograms lipid metabolism of renal tubular epithelial cells in the diabetic kidney

The functional and structural changes in the proximal tubule play an important role in the occurrence and development of diabetic kidney disease (DKD). Diabetes-induced metabolic changes, including lipid metabolism reprogramming, are reported to lead to changes in the state of tubular epithelial cells (TECs), and among all the disturbances in metabolism, mitochondria serve as central regulators. Mitochondrial dysfunction, accompanied by increased production of mitochondrial reactive oxygen species (mtROS), is considered one of the primary factors causing diabetic tubular injury. Most studies have discussed how altered metabolic flux drives mitochondrial oxidative stress during DKD. In the present study, we focused on targeting mitochondrial damage as an upstream factor in metabolic abnormalities under diabetic conditions in TECs. Using SS31, a tetrapeptide that protects the mitochondrial cristae structure, we demonstrated that mitochondrial oxidative damage contributes to TEC injury and lipid peroxidation caused by lipid accumulation. Mitochondria protected using SS31 significantly reversed the decreased expression of key enzymes and regulators of fatty acid oxidation (FAO), but had no obvious effect on major glucose metabolic rate-limiting enzymes. Mitochondrial oxidative stress facilitated renal Sphingosine-1-phosphate (S1P) deposition and SS31 limited the elevated Acer1, S1pr1 and SPHK1 activity, and the decreased Spns2 expression. These data suggest a role of mitochondrial oxidative damage in unbalanced lipid metabolism, including lipid droplet (LD) formulation, lipid peroxidation, and impaired FAO and sphingolipid homeostasis in DKD. An in vitro study demonstrated that high glucose drove elevated expression of cytosolic phospholipase A2 (cPLA2), which, in turn, was responsible for the altered lipid metabolism, including LD generation and S1P accumulation, in HK-2 cells. A mitochondria-targeted antioxidant inhibited the activation of cPLA2f isoforms. Taken together, these findings identify mechanistic links between mitochondrial oxidative metabolism and reprogrammed lipid metabolism in diabetic TECs, and provide further evidence for the nephroprotective effects of SS31 via influencing metabolic pathways.

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.

The degradation of TGR5 mediated by Smurf1 contributes to diabetic nephropathy

The multiple roles of TGR5 in the regulation of glucose metabolism, inflammation, and oxidative stress have drawn attention as therapeutic candidates for diabetes-related kidney disease. However, diabetes induces downregulation of renal TGR5 protein expression, and the regulatory mechanisms have not been clarified. Here, we identify that Smurf1, an E3 ubiquitin ligase, is a critical interactor of TGR5 and mediates the ubiquitination and proteasomal degradation of TGR5 under high glucose stimulation in glomerular mesangial cells. Genetic deficiency of Smurf1 restores TGR5 protein expression and attenuates renal injuries in diabetic mice. Mechanistically, Smurf1 interacts with the TGR5 ICL2 region by its HECT domain and induces K11/K48-linked polyubiquitination of TGR5 at K306 residue. Moreover, restoration of TGR5 protects db/db mice from diabetic nephropathy. These observations elucidate the critical role of Smurf1 in regulating TGR5 stability, suggesting that pharmacological targeting of the interaction between Smurf1 and TGR5 could serve as a promising therapeutic strategy against diabetic nephropathy.

The roles of gut microbiota and its metabolites in diabetic nephropathy

Diabetic nephropathy (DN) is a severe microvascular complication of diabetes, which increases the risk of renal failure and causes a high global disease burden. Due to the lack of sustainable treatment, DN has become the primary cause of end-stage renal disease worldwide. Gut microbiota and its metabolites exert critical regulatory functions in maintaining host health and are associated with many pathogenesis of aging-related chronic diseases. Currently, the theory gut-kidney axis has opened a novel angle to understand the relationship between gut microbiota and multiple kidney diseases. In recent years, accumulating evidence has revealed that the gut microbiota and their metabolites play an essential role in the pathophysiologic processes of DN through the gut-kidney axis. In this review, we summarize the current investigations of gut microbiota and microbial metabolites involvement in the progression of DN, and further discuss the potential gut microbiota-targeted therapeutic approaches for DN.

Bibliometric visualization analysis of gut-kidney axis from 2003 to 2022

Background: The gut-kidney axis refers to the interaction between the gastrointestinal tract and the kidneys, and its disorders have become increasingly important in the development of kidney diseases. The aim of this study is to identify current research hotspots in the field of the gut-kidney axis from 2003 to 2022 and provide guidance for future research in this field. Methods: We collected relevant literature on the gut-kidney axis from the Web of Science Core Collection (WoSCC) database and conducted bibliometric and visualization analyses using biblioshiny in R-Studio and VOSviewer (version 1.6.16). Results: A total of 3,900 documents were retrieved from the WoSCC database. The publications have shown rapid expansion since 2011, with the greatest research hotspot emerging due to the concept of the "intestinal-renal syndrome," first proposed by Meijers. The most relevant journals were in the field of diet and metabolism, such as Nutrients. The United States and China were the most influential countries, and the most active institute was the University of California San Diego. Author analysis revealed that Denise Mafra, Nosratola D. Vaziri, Fouque, and Denis made great contributions in different aspects of the field. Clustering analysis of the keywords found that important research priorities were "immunity," "inflammation," "metabolism," and "urinary toxin," reflecting the basis of research in the field. Current research frontiers in the field include "hyperuricemia," "gut microbiota," "diabetes," "trimethylamine n-oxide," "iga nephropathy," "acute kidney injury," "chronic kidney disease," "inflammation," all of which necessitate further investigation. Conclusion: This study presents a comprehensive bibliometric analysis and offers an up-to-date outlook on the research related to the gut-kidney axis, with a specific emphasis on the present state of intercommunication between gut microbiota and kidney diseases in this field. This perspective may assist researchers in selecting appropriate journals and partners, and help to gain a deeper understanding of the field's hotspots and frontiers, thereby promoting future research.

Relaxin elicits renoprotective actions accompanied by increasing bile acid levels in streptozotocin-induced diabetic mice

BACKGROUND

The peptide hormone relaxin has potent anti-fibrotic and anti-inflammatory properties in various organs, including the kidneys. However, the protective effects of relaxin in the context of diabetic kidney complications remain controversial. Here, we aimed to evaluate the effects of relaxin treatment on key markers of kidney fibrosis, oxidative stress, and inflammation and their subsequent impact on bile acid metabolism in the streptozotocin-induced diabetes mouse model.

METHODS AND RESULTS

Male mice were randomly allocated to placebo-treated control, placebo-treated diabetes or relaxin-treated diabetes groups (0.5 mg/kg/d, final 2 weeks of diabetes). After 12 weeks of diabetes or sham, the kidney cortex was harvested for metabolomic and gene expression analyses. Diabetic mice exhibited significant hyperglycaemia and increased circulating levels of creatine, hypoxanthine and trimethylamine N-oxide in the plasma. This was accompanied by increased expression of key markers of oxidative stress (Txnip), inflammation (Ccl2 and Il6) and fibrosis (Col1a1, Mmp2 and Fn1) in the diabetic kidney cortex. Relaxin treatment for the final 2 weeks of diabetes significantly reduced these key markers of renal fibrosis, inflammation, and oxidative stress in diabetic mice. Furthermore, relaxin treatment significantly increased the levels of bile acid metabolites, deoxycholic acid and sodium glycodeoxycholic acid, which may in part contribute to the renoprotective action of relaxin in diabetes.

CONCLUSION

In summary, this study shows the therapeutic potential of relaxin and that it may be used as an adjunctive treatment for diabetic kidney complications.

The role of TGR5 as an onco-immunological biomarker in tumor staging and prognosis by encompassing the tumor microenvironment

The relationship between G protein–coupled bile acid receptor 1 (TGR5, GPBAR1) and, specifically, cancer has been studied in in vivo and in vitro experiments, but there is still a lack of pan-cancer analysis to understand the prognostic significance and functioning mechanism of TGR5 in different cancer-driving oncogenic processes. Here, we used Gene Expression Integration, Human Protein Atlas, and The Cancer Genome Atlas (TCGA) to perform a pan-cancer analysis of the role of TGR5 in all 33 tumors. In all TCGA tumors, the TGR5 gene expression has been assessed, and we found that the high TGR5 gene expression in most cancers is associated with poor prognosis of overall survival for cancers such as glioblastoma multiforme (p = 0.0048), kidney renal papillary cell carcinoma (p = 0.033), lower grade glioma (p = 0.0028), thymoma (p = 0.048), and uveal melanoma (p = 0.004), and then the lower expression of TGR5 was linked with poor prognosis in cervical squamous cell carcinoma and endocervical adenocarcinoma (p = 0.014), malignant mesothelioma (MESO) (p = 0.048), sarcoma (p = 0.018), and skin cutaneous melanoma (p = 0.0085). The TGR5 expression was linked with the immune infiltration level of the macrophage M2_TIDE and was also associated with DNA methylation in ovarian and breast cancers. The regulation of hormone secretion, Rap1 pathway, osteoclast differentiation, and bile acid pathway was involved in the functional mechanism of TGR5. Besides, gene expressions were different in different tumors detected by RT-PCR, and cell activity experiments have also found that TGR5 can increase the activity of renal cell carcinoma and reduce the activity of skin cancer and osteosarcoma cells. In this investigation, the aim was to assess the comprehensive overview of the oncogenic roles of TGR5 in all TCGA tumors using pan-analysis.

The gut microbe Bacteroides fragilis ameliorates renal fibrosis in mice

Renal fibrosis is an inevitable outcome of various manifestations of progressive chronic kidney diseases (CKD). The need for efficacious treatment regimen against renal fibrosis can therefore not be overemphasized. Here we show a novel protective role of Bacteroides fragilis (B. fragilis) in renal fibrosis in mice. We demonstrate decreased abundance of B. fragilis in the feces of CKD patients and unilateral ureteral obstruction (UUO) mice. Oral administration of live B. fragilis attenuates renal fibrosis in UUO and adenine mice models. Increased lipopolysaccharide (LPS) levels are decreased after B. fragilis administration. Results of metabolomics and proteomics studies show decreased level of 1,5-anhydroglucitol (1,5-AG), a substrate of SGLT2, which increases after B. fragilis administration via enhancement of renal SGLT2 expression. 1,5-AG is an agonist of TGR5 that attenuates renal fibrosis by inhibiting oxidative stress and inflammation. Madecassoside, a natural product found via in vitro screening promotes B. fragilis growth and remarkably ameliorates renal fibrosis. Our findings reveal the ameliorative role of B. fragilis in renal fibrosis via decreasing LPS and increasing 1,5-AG levels.

The role and mechanisms of gut microbiota in diabetic nephropathy, diabetic retinopathy and cardiovascular diseases

Type 2 diabetes mellitus (T2DM) and T2DM-related complications [such as retinopathy, nephropathy, and cardiovascular diseases (CVDs)] are the most prevalent metabolic diseases. Intriguingly, overwhelming findings have shown a strong association of the gut microbiome with the etiology of these diseases, including the role of aberrant gut bacterial metabolites, increased intestinal permeability, and pathogenic immune function affecting host metabolism. Thus, deciphering the specific microbiota, metabolites, and the related mechanisms to T2DM-related complications by combined analyses of metagenomics and metabolomics data can lead to an innovative strategy for the treatment of these diseases. Accordingly, this review highlights the advanced knowledge about the characteristics of the gut microbiota in T2DM-related complications and how it can be associated with the pathogenesis of these diseases. Also, recent studies providing a new perspective on microbiota-targeted therapies are included.

Identification of Hub Genes Involved in Tubulointerstitial Injury in Diabetic Nephropathy by Bioinformatics Analysis and Experiment Verification

Diabetic nephropathy (DN) is the most important cause of end-stage renal disease with a poorer prognosis and high economic burdens of medical treatments. It is of great research value and clinical significance to explore potential gene targets of renal tubulointerstitial lesions in DN. To properly identify key genes associated with tubulointerstitial injury of DN, we initially performed a weighted gene coexpression network analysis of the dataset to screen out two nonconserved gene modules (dark orange and dark red). The regulation of oxidative stress-induced intrinsic apoptotic signaling pathway, PI3K-Akt signaling pathway, p38MAPK cascade, and Th1 and Th2 cell differentiation were primarily included in Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of these two modules. Next, 199 differentially expressed genes (DEGs) were identified via the limma package. Then, the GO annotation and KEGG pathways of the DEGs were primarily enriched in extracellular matrix (ECM) organization, epithelial cell migration, cell adhesion molecules (CAMs), NF-kappa B signaling pathway, and ECM-receptor interaction. Gene set enrichment analysis showed that in the DN group, the interaction of ECM-receptor, CAMs, the interaction of cytokine-cytokine receptor, and complement and coagulation cascade pathways were significantly activated. Eleven key genes, including ALB, ANXA1, ANXA2, C3, CCL2, CLU, EGF, FOS, PLG, TIMP1, and VCAM1, were selected by constructing a protein-protein interaction network, and expression validation, ECM-related pathways, and glomerular filtration rate correlation analysis were performed in the validated dataset. The upregulated expression of hub genes ANXA2 and FOS was verified by real-time quantitative PCR in HK-2 cells treated with high glucose. This study revealed potential regulatory mechanisms of renal tubulointerstitial damage and highlighted the crucial role of extracellular matrix in DN, which may promote the identification of new biomarkers and therapeutic targets.

Renal Farnesoid X Receptor improves high fructose-induced salt-sensitive hypertension in mice by inhibiting DNM3 to promote nitro oxide production

OBJECTIVE

Farnesoid X Receptor (FXR) is highly expressed in renal tubules, activation of which attenuates renal injury by suppressing inflammation and fibrosis. However, whether renal FXR contributes to the regulation of blood pressure (BP) is poorly understood. This study aimed to investigate the anti-hypertensive effect of renal FXR on high-fructose-induced salt-sensitive hypertension and underlying mechanism.

METHODS

Hypertension was induced in male C57BL/6 mice by 20% fructose in drinking water with 4% sodium chloride in diet (HFS) for 8 weeks. The effects of FXR on NO production were estimated in vitro and in vivo.

RESULTS

Compared with control, HFS intake elevated BP, enhanced renal injury and reduced renal NO levels as well as FXR expression in the kidney of mice. In the mouse renal collecting duct cells mIMCD-K2, FXR agonists promoted NO production by enhancing the expression of neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS), whereas this effect was diminished by fxr knockdown. We further found that Dynamin 3 (DNM3), a binding protein with nNOS in the renal medulla, was inhibited by FXR and its deficiency elevated NO production in mIMCD-K2 cells. In HFS-fed mice, renal fxr overexpression significantly attenuated hypertension and renal fibrosis, regulated the expression of DNM3/nNOS/iNOS, and increased renal NO levels.

CONCLUSION

Our results demonstrated that renal FXR prevents HFS-induced hypertension by inhibiting DNM3 to promote NO production. These findings provide insights into the role and potential mechanism of renal FXR for the treatment of hypertension.

Lower bile acids as an independent risk factor for renal outcomes in patients with type 2 diabetes mellitus and biopsy-proven diabetic kidney disease

AIMS

Abnormalities of glucolipid metabolism are critical mechanisms involved in the progression of diabetic kidney disease (DKD). Bile acids have an essential role in regulating glucolipid metabolism. This study investigated the clinicopathological characteristics of DKD patients with different bile acid levels and explored the relationship between bile acids and renal outcomes of DKD patients.

METHODS

We retrospectively reviewed and evaluated the histopathological features and clinical features of our cohort of 184 patients with type 2 diabetes mellitus and biopsy-proven DKD. Patients were divided into the lower bile acids group (≤2.8 mmol/L) and higher bile acids group (>2.8 mmol/L) based on the cutoff value of bile acids obtained using the time-dependent receiver-operating characteristic curve. Renal outcomes were defined as end-stage renal disease (ESRD). The influence of bile acids on renal outcomes and correlations between bile acids and clinicopathological indicators were evaluated.

RESULTS

Bile acids were positively correlated with age (r = 0.152; P = 0.040) and serum albumin (r = 0.148; P = 0.045) and negatively correlated with total cholesterol (r = -0.151; P = 0.041) and glomerular class (r = -0.164; P =0.027). During follow-up, 64 of 184 patients (34.78%) experienced progression to ESRD. Lower levels of proteinuria, serum albumin, and bile acids were independently associated with an increased risk of ESRD (hazard ratio, R=5.319; 95% confidence interval, 1.208-23.425).

CONCLUSIONS

Bile acids are an independent risk factor for adverse renal outcomes of DKD patients. The serum level of bile acids should be maintained at more than 2.8 mmol/L in DKD patients. Bile acid analogs or their downstream signaling pathway agonists may offer a promising strategy for treating DKD.

Hirudin, a thrombin inhibitor, attenuates TGF-β-induced fibrosis in renal proximal tubular epithelial cells by inhibition of protease-activated receptor 1 expression via S1P/S1PR2/S1PR3 signaling

Renal interstitial fibrosis (RIF) is the final common outcome of numerous chronic kidney diseases, contributing to end-stage renal disease. Hirudin, a thrombin inhibitor, has attracted increased attention as a potential treatment approach for renal fibrosis. The present study aimed to investigate the molecular mechanism underlying the effect of hirudin on fibrosis in renal proximal tubular epithelial cells. An in vivo mouse RIF model established using unilateral ureteral obstruction (UUO) and an in vitro of RIF using the renal tubular epithelial cell line HK-2 treated with TGF-β were used. Expressions of sphingosine-1-phosphate (S1P) receptors (S1PR)1-4 and protease-activated receptor 1 (PAR1) were measured by reverse transcription-quantitative PCR and western blotting in mice with UUO and TGF-β induced HK-2 cells. Western blotting was used to detect the expression of N-cadherin, Slug, E-cadherin, Collagen IV, fibronectin, MMP9 and monocyte chemoattractant protein-1. Immunofluorescence staining was conducted to measure α-SMA level expression. The results demonstrated that the expression levels of S1PR1, S1PR2, S1PR3, S1PR4 and PAR1 were upregulated in both TGF-β-induced HK-2 cells and renal tissues from mice with unilateral ureteral ligation. Notably, hirudin inhibited TGF-β-induced PAR1, S1PR2 and S1PR3 upregulation in both HK-2 cells and renal tissues. Additionally, the inhibition of S1PR2 and S1PR3 resulted in PAR1 downregulation. Furthermore, treatment with S1P and PAR1 agonists abolished the effect of hirudin on the expression of EMT, fibrosis-related proteins and monocyte chemoattractant protein 1. In conclusion, hirudin attenuated TGF-β-induced fibrosis in proximal renal tubular epithelial HK-2 cells by inhibiting PAR1 expression via the S1P/S1PR2/S1PR3 signaling pathway. Therefore, hirudin may be considered as a promising therapeutic agent for RIF.

Roles of Gut Microbial Metabolites in Diabetic Kidney Disease

Diabetes is a highly prevalent metabolic disease that has emerged as a global challenge due to its increasing prevalence and lack of sustainable treatment. Diabetic kidney disease (DKD), which is one of the most frequent and severe microvascular complications of diabetes, is difficult to treat with contemporary glucose-lowering medications. The gut microbiota plays an important role in human health and disease, and its metabolites have both beneficial and harmful effects on vital physiological processes. In this review, we summarize the current findings regarding the role of gut microbial metabolites in the development and progression of DKD, which will help us better understand the possible mechanisms of DKD and explore potential therapeutic approaches for DKD.

Potential Therapeutic Targets of Obesity-Related Glomerulopathy

The global increase of obesity parallels the obesity-related glomerulopathy (ORG) epidemic. The purpose of this review is to emphasize the potential therapeutic targets of ORG as well as the corresponding possible mechanisms. We systematically identified surveys, reports, and published studies that included data for the purpose of this review and did literature analysis. Under circumstance of obesity, weight loss, and renin-angiotensin-aldosterone blockade are the most studied therapies, effective to induce antiproteinuric effects and reversal of hyperfiltration in ORG. Glucagon-like peptide-1-based therapies led to improvement in proteinuria. Newer therapies directed to lipid metabolism, including farnesoid X receptor and takeda G protein-coupled receptor 5 agonists, peroxisome proliferator-activated receptor α agonists, hold therapeutic promise. Prevention and treatments of obesity and ORG are of great importance.

TGR5 activation attenuates neuroinflammation via Pellino3 inhibition of caspase-8/NLRP3 after middle cerebral artery occlusion in rats

BACKGROUND

Nucleotide-binding oligomerization domain-like receptor pyrin domain-containing protein 3 (NLRP3) plays an important role in mediating inflammatory responses during ischemic stroke. Bile acid receptor Takeda-G-protein-receptor-5 (TGR5) has been identified as an important component in regulating brain inflammatory responses. In this study, we investigated the mechanism of TGR5 in alleviating neuroinflammation after middle cerebral artery occlusion (MCAO).

METHODS

Sprague-Dawley rats were subjected to MCAO and TGR5 agonist INT777 was administered intranasally 1 h after MCAO. Small interfering RNAs (siRNA) targeting TGR5 and Pellino3 were administered through intracerebroventricular injection 48 h before MCAO. Infarct volumes and neurologic scores were evaluated, and ELISA, flow cytometry, immunofluorescence staining, immunoblotting, and co-immunoprecipitation were used for the evaluations.

RESULTS

Endogenous TGR5 and Pellino3 levels increased after MCAO. TGR5 activation by INT777 significantly decreased pro-inflammatory cytokine, cleaved caspase-8, and NLRP3 levels, thereby reducing brain infarctions; both short- and long-term neurobehavioral assessments showed improvements. Ischemic damage induced the interaction of TGR5 with Pellino3. Knockdown of either TGR5 or Pellino3 increased the accumulation of cleaved caspase-8 and NLRP3, aggravated cerebral impairments, and abolished the anti-inflammatory effects of INT777 after MCAO.

CONCLUSIONS

TGR5 activation attenuated brain injury by inhibiting neuroinflammation after MCAO, which could be mediated by Pellino3 inhibition of caspase-8/NLRP3.

Suppression of Th17 cell differentiation via sphingosine-1-phosphate receptor 2 by cinnamaldehyde can ameliorate ulcerative colitis

Ulcerative colitis (UC) is chronic disease characterized by diffuse inflammation of the mucosa of the colon and rectum. Although the etiology is unknown, dysregulation of the intestinal mucosal immune system is closely related to UC. Cinnamaldehyde (CA) is a major active compound from cinnamon, is known as its anti-inflammatory and antibacterial. However, little research focused on its regulatory function on immune cells in UC. Therefore, we set out to explore the modulating effects of CA on immune cells in UC. We found that CA reduced the progression of colitis through controlling the production of proinflammatory cytokines and inhibiting the proportion of Th17 cells. Furthermore, the liquid chromatography-mass spectrometry (LC-MS) method was employed for analyzing and differentiating metabolites, data showed that sphingolipid pathway has a great influence on the effect of CA on UC. Meanwhile, sphingosine-1-phosphate receptor 2 (S1P2) and Rho-GTP protein levels were downregulated in colonic tissues after CA treatment. Moreover, in vitro assays showed that CA inhibited Th17 cell differentiation and downregulated of S1P2 and Rho-GTP signaling. Notably, we found that treatment with S1P2 antagonist (JTE-013) weakened the inhibitory effect of CA on Th17 cells. Furthermore, S1P2 deficiency (S1P2-/-) blocked the effect of CA on Th17 cell differentiation. In addition, CA can also improve inflammation via lncRNA H19 and MIAT. To sum up, this study provides clear evidence that CA can ameliorate ulcerative colitis through suppressing Th17 cells via S1P2 pathway and regulating lncRNA H19 and MIAT, which further supports S1P2 as a potential drug target for immunity-mediated UC.

Role and significance of bile acid membrane receptor GPBAR1 in pathogenesis of obstructive jaundice

GPBAR1 is the first confirmed G protein coupled bile acid membrane receptor, which is widely expressed in the liver, gallbladder, kidney, intestine, and the nervous and cardiovascular systems. During the development of obstructive jaundice (OJ), GPBAR1 is activated by bile acid signal and mediates different signal transduction pathways, thus playing a corresponding role in the pathogenesis of OJ. GPBAR1 may be a potential therapeutic target for the treatment of OJ by controlling inflammation, regulating the function of bile duct epithelial barrier, inhibiting renal oxidative stress, and regulating intestinal mucosal barrier and intestinal flora, pruritus and sensory disturbance, and cardiovascular function. This article reviews the role and signficance of GPBAR1 in the pathogenesis of OJ.

A novel role for farnesoid X receptor in the bile acid-mediated intestinal glucose homeostasis

The farnesoid X receptor (FXR), as a bile acid (BA) sensor, plays an important role in the regulation of lipid metabolism. However, the effects and underlying molecular mechanisms of FXR on intestinal glucose homeostasis remain elusive. Herein, we demonstrated that FXR and glucose transporter 2 (GLUT2) are essential for BA‐mediated glucose homeostasis in the intestine. BA‐activated FXR enhanced glucose uptake in intestinal epithelial cells by increasing the expression of GLUT2, which depended on ERK1/2 phosphorylation via S1PR2. However, it also reduced the cell energy generation via inhibition of oxidative phosphorylation, which is crucial for intestinal glucose transport. Moreover, BA‐activated FXR signalling potently inhibited specific glucose flux through the intestinal epithelium to the circulation, which reduced the increase in blood glucose levels in mice following oral glucose administration. This trend was supported by the changed ratio of GLUT2 to SGLT1 in the brush border membrane (BBM), including especially decreased GLUT2 abundance in the BBM. Furthermore, impaired intestinal FXR signalling was observed in the patients with intestinal bile acid deficiency (IBAD). These findings uncover a novel function by which FXR sustains the intestinal glucose homeostasis and provide a rationale for FXR agonists in the treatment of IBAD‐related hyperglycaemia.

Gentiopicroside activates the bile acid receptor Gpbar1 (TGR5) to repress NF-kappaB pathway and ameliorate diabetic nephropathy

Our previous studies indicated that the G-protein-coupled bile acid receptor, Gpbar1 (TGR5), inhibits inflammation by inhibiting the NF-κB signalling pathway, eventually attenuating diabetic nephropathy (DN). Gentiopicroside (GPS), the main active secoiridoid glycoside of Gentiana manshurica Kitagawa, has been demonstrated to inhibit inflammation in various diseases via inhibiting the inflammatory signalling pathways. However, whether GPS inhibits the NF-κB signalling pathway by activating TGR5 and regulates the pathological progression of diabetic renal fibrosis requires further investigation. In this study, we found that GPS significantly reversed the downregulation of TGR5 and inhibited the overproduction of fibronectin (FN), transforming growth factor β1 (TGF-β1), intercellular adhesion molecule-1 (ICAM-1) and vascular adhesion molecule-1 (VCAM-1) in glomerular mesangial cells (GMCs) exposed to high glucose (HG). Additionally, GPS prevented the phosphorylation and degradation of IκBα, and subsequently inhibited the activation of the NF-κB signalling pathway. Further investigation found that GPS enhanced the stabilization of IκBα by promoting the interaction of β-arrestin2 with IκBα via TGR5 activation, which contributed to the inhibition of NF-κB signalling pathway. Importantly, the depletion of TGR5 blocked the inhibition of the NF-κB signalling pathway and reversed the downregulation of FN, ICAM-1, VCAM-1 and TGF-β1 by GPS in HG-induced GMCs. Moreover, GPS increased the TGR5 protein levels and promoted the interaction between IκBα and β-arrestin2, thereby inhibiting the reduction of IκBα and blocked NF-κB p65 nuclear translocation in the kidneys of STZ-induced diabetic mice. Collectively, these data suggested that GPS regulates the TGR5-β-arrestin2-NF-κB signalling pathway to prevent inflammation in the kidneys of diabetic mice, and ultimately ameliorates the pathological progression of diabetic renal fibrosis.

Apolipoprotein M suppresses the phenotypes of IgA nephropathy in hyper-IgA mice

Because the association between sphingosine 1-phosphate (S1P)/apolipoprotein M (ApoM) and chronic kidney diseases has not been established, we investigated the involvement of S1P/ApoM in the phenotypes of IgA nephropathy in hyper-IgA (HIGA) mice. The overexpression of ApoM in adenoviral gene transfer ameliorated the phenotypes of IgA nephropathy in HIGA mice, whereas the knockdown of ApoM with siRNA caused deterioration. When ApoM-overexpressing HIGA mice were treated with VPC23019, an antagonist against S1P receptor 1 (S1P1) and 3 (S1P3), we observed that the protective effects of ApoM were reversed, whereas JTE013, an antagonist against S1P2, did not inhibit the effects. We also found that S1P bound to albumin accelerated the proliferation of MES13 cells and the fibrotic changes of HK2 cells, which were inhibited by JTE013, whereas S1P bound to ApoM suppressed these changes, which were inhibited by VPC23019. These results suggest that S1P bound to ApoM possesses properties protective against the phenotypes of IgA nephropathy through S1P1 and S1P3, whereas S1P bound to albumin exerts deteriorating effects through S1P2. ApoM may be useful as a therapeutic target to treat or retard the progression of IgA nephropathy.-Kurano, M., Tsuneyama, K., Morimoto, Y., Nishikawa, M., Yatomi, Y. Apolipoprotein M suppresses the phenotypes of IgA nephropathy in hyper-IgA mice.

Obstructive jaundice induced kidney damage is mediated by down-regulation of bile acid receptors FXR and TGR5

AIM

To investigate the changes in the expression of bile acid receptors FXR and TGR5 in obstructive jaundice (OJ) induced renal injury.

METHODS

Twelve male Sprague-Dawley rats were randomly divided into two groups to undergo either sham operation (CON) or bile duct ligation (BDL). The animals were operated by surgical ligation of the common bile duct to establish an OJ model. Two weeks post operation, serum samples were collected to assess renal associated biochemical markers including alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bile acid (TBA), total bilirubin (TBIL), direct bilirubin (DBIL), serum urea nitrogen (BUN), creatinine (Cr), and uric acid (UA). In addition, the urine of the rats was collected for urine chemistry analysis. Transcription and translation of FXR and TGR5 genes were detected by qRT-PCR and Western blot, respectively. Tissue sections of the kidneys were stained with hematoxylin and eosin (HE) and examined for microscopically pathological changes.

RESULTS

Compared with the CON group, the protein and mRNA expression of FXR and TGR5 was significantly decreased in the kidneys of the BDL rats. HE staining revealed that the kidneys of the BDL rats had decreased glomerular density and the local epithelial cells of the tubules shed. Also, the small tube lacuna was expanded, accompanied with the presence of a large number of unstructured substances.

CONCLUSION

This in vivo study demonstrated significant down-regulation of the bile acid receptors FXR and TGR5 in the kidneys of OJ rats, suggesting their role in kidney damage.

Bile acid receptors and the kidney

PURPOSE OF REVIEW

Bile acids act as activating signals of endogenous renal receptors: the nuclear receptor farnesoid X receptor (FXR) and the membrane-bound G protein-coupled bile acid receptor 1 (GPBAR1, also known as TGR5). In recent years, bile acids have emerged as important for renal pathophysiology by activating FXR and TGR5 and transcription factors relevant for lipid, cholesterol and carbohydrate metabolism, as well as genes involved in inflammation and renal fibrosis.

RECENT FINDINGS

Activation of bile acid receptors has a promising therapeutic potential in prevention of diabetic nephropathy and obesity-induced renal damage, as well as in nephrosclerosis. During the past decade, progress has been made in understanding the biology and mechanisms of bile acid receptors in the kidney and in the development of specific bile acid receptor agonists.

SUMMARY

In this review, we discuss current knowledge on the roles of FXR and TGR5 in the physiology of the kidney and the latest advances made in development and characterization of bile acid analogues that activate bile acid receptors for treatment of renal disease.

TGR5 expression in normal kidney and renal neoplasms

BACKGROUND

The G protein-coupled bile acid receptor (TGR5) is a cell surface receptor which induces the production of intracellular cAMP and promotes epithelial-mesenchymal transition in gastric cancer cell lines. TGR5 is found in a wide variety of tissues including the kidney. However, the patterns of TGR5 expression have not been well characterized in physiologic kidney or renal neoplasms. We explore the expression of TGR5 in benign renal tissue and renal neoplasms and assess its utility as a diagnostic marker.

METHODS

Sixty-one renal cortical neoplasms from 2000 to 2014 were retrieved. TGR5 protein expression was examined by immunohistochemistry. TGR5 mRNA was also measured by real-time PCR.

RESULTS

In normal renal tissue, TGR5 was strongly positive in collecting ducts, distal convoluted tubules and thin loop of Henle. Proximal convoluted tubules showed absent or focal weak staining. In clear cell renal cell carcinomas (RCCs), 25 of 27 cases (92%) were negative for TGR5 (p < 0.001). TGR5 mRNA was also significantly decreased in clear cell RCCs, suggesting that decreased TGR5 protein expression may be attributable to the downregulation of TGR5 mRNA in these tumors. All 11 papillary RCCs expressed TGR5 with 45% (5/11) exhibiting moderate to strong staining. All chromophobe RCCs and oncocytomas were positive for TGR5 with weak to moderate staining. TGR5 mRNA expression in these tumors was similar to normal kidney. All urothelial carcinomas of the renal pelvis strongly expressed TGR5 including a poorly differentiated urothelial carcinoma with sarcomatoid features.

CONCLUSION

TGR5 is strongly expressed in collecting ducts, distal convoluted tubules and thin loop of Henle. TGR5 protein and mRNA expression were notably decreased in clear cell RCCs and may be helpful in differentiating these tumors from other RCCs.

The role of sphingosine 1-phosphate receptor 2 in bile-acid-induced cholangiocyte proliferation and cholestasis-induced liver injury in mice

Bile duct obstruction is a potent stimulus for cholangiocyte proliferation, especially for large cholangiocytes. Our previous studies reported that conjugated bile acids (CBAs) activate the protein kinase B (AKT) and extracellular signal-regulated kinase 1 and 2 (ERK1/2) signaling pathways through sphingosine 1-phosphate receptor (S1PR) 2 in hepatocytes and cholangiocarcinoma cells. It also has been reported that taurocholate (TCA) promotes large cholangiocyte proliferation and protects cholangiocytes from bile duct ligation (BDL)-induced apoptosis. However, the role of S1PR2 in bile-acid-mediated cholangiocyte proliferation and cholestatic liver injury has not been elucidated. Here, we report that S1PR2 is the predominant S1PR expressed in cholangiocytes. Both TCA- and sphingosine-1-phosphate (S1P)-induced activation of ERK1/2 and AKT were inhibited by JTE-013, a specific antagonist of S1PR2, in cholangiocytes. In addition, TCA- and S1P-induced cell proliferation and migration were inhibited by JTE-013 and a specific short hairpin RNA of S1PR2, as well as chemical inhibitors of ERK1/2 and AKT in mouse cholangiocytes. In BDL mice, expression of S1PR2 was up-regulated in whole liver and cholangiocytes. S1PR2 deficiency significantly reduced BDL-induced cholangiocyte proliferation and cholestatic injury, as indicated by significant reductions in inflammation and liver fibrosis in S1PR2 knockout mice. Treatment of BDL mice with JTE-013 significantly reduced total bile acid levels in serum and cholestatic liver injury.

CONCLUSION

This study suggests that CBA-induced activation of S1PR2-mediated signaling pathways plays a critical role in obstructive cholestasis and may represent a novel therapeutic target for cholestatic liver diseases. (Hepatology 2017;65:2005-2018).