TGR5 suppresses high glucose-induced upregulation of fibronectin and transforming growth factor-β1 in rat glomerular mesangial cells by inhibiting RhoA/ROCK signaling

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.

Indole-3-carboxaldehyde alleviates cisplatin-induced acute kidney injury in mice by improving mitochondrial dysfunction via PKA activation

Cisplatin (DDP) is widely used in the treatment of cancer as a chemotherapeutic drug. However, its severe nephrotoxicity limits the extensive application of cisplatin, which is characterized by injury and apoptosis of renal tubular epithelial cells. This study aimed to reveal the protective effect and its underlying mechanism of Indole-3-carboxaldehyde (IC) against DDP-induced AKI in mice and NRK-52E cells pretreated with PKA antagonist (H-89). Here, we reported that IC improved renal artery blood flow velocity and renal function related indicators, attenuated renal pathological changes, which were confirmed by the results of HE staining and PASM staining. Meanwhile, IC inhibited the levels of inflammatory factors, oxidative stress, CTR1, OCT2, and the levels of autophagy and apoptosis. Mitochondrial dysfunction was significantly improved as observed by TEM. To clarify the potential mechanism, NRK-52E cells induced by DDP was used and the results proved that H-89 could blocked the improvement with IC effectively in vitro. Our findings showed that IC has the potential to treat cisplatin-induced AKI, and its role in protecting the kidney was closely related to activating PKA, inhibiting autophagy and apoptosis, improving mitochondrial function, which could provide a theoretical basis for the development of new clinical drugs.

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.

LncRNA NEAT1 accelerates renal fibrosis progression via targeting miR-31 and modulating RhoA/ROCK signal pathway

Renal fibrosis is the final pathway for chronic kidney disease to end-stage renal failure. Noncoding RNAs have been reported to play a crucial role in renal fibrosis. Here, the effects of long noncoding RNA (lncRNA) nuclear-enriched abundant transcript 1 (NEAT1) and miR-31 on renal fibrosis and their regulatory mechanism were evaluated. RT-qPCR was used to assess NEAT1, miR-31, and RhoA levels. Western blot was performed to analyze the expression of fibrosis markers, RhoA, rho-related kinase (ROCK1), and connective tissue growth factor (CTGF). RNA immunoprecipitation (RIP), fluorescence in situ hybridization (FISH), and luciferase reporter assays verified the interaction between miR-31 and NEAT1 or RhoA. Renal fibrosis and injury were observed by Masson and hematoxylin and eosin (H&E) staining. The expression level of inflammatory cytokines was detected by ELISA. Immunohistochemistry (IHC) was performed to examine the expression levels of α-smooth muscle actin (α-SMA) and RhoA in renal tissues. We showed that NEAT1 was highly expressed, whereas miR-31 was decreased in renal fibrosis. NEAT1 was found to directly bind miR-31 to positively regulate RhoA expression. Furthermore, NEAT1 silencing inhibited renal fibrosis and inflammation and suppressed the RhoA/ROCK1 signaling pathway. However, knockdown of miR-31 could reverse these effects. NEAT1 silencing or overexpression of miR-31 alleviated renal fibrosis in vivo. In conclusion, NEAT1 accelerates renal fibrosis progression via negative regulation of miR-31 and the activation of RhoA/ROCK1 pathway, thereby upregulating the expression level of CTGF, providing a theoretical basis for treatment and prognostic evaluation of renal fibrosis.

Differential Fibrotic Response of Muscle Fibroblasts, Myoblasts, and Myotubes to Cholic and Deoxycholic Acids

Fibrosis is a condition characterized by an increase in the components of the extracellular matrix (ECM). In skeletal muscle, the cells that participate in the synthesis of ECM are fibroblasts, myoblasts, and myotubes. These cells respond to soluble factors that increase ECM. Fibrosis is a phenomenon that develops in conditions of chronic inflammation, extensive lesions, or chronic diseases. A pathological condition with muscle weakness and increased bile acids (BA) in the blood is cholestatic chronic liver diseases (CCLD). Skeletal muscle expresses the membrane receptor for BA called TGR5. To date, muscle fibrosis in CCLD has not been evaluated. This study aims to assess whether BA can induce a fibrotic condition in muscle fibroblasts, myoblasts, and myotubes. The cells were incubated with deoxycholic (DCA) and cholic (CA) acids, and fibronectin protein levels were evaluated by Western blot. In muscle fibroblasts, both DCA and CA induced an increase in fibronectin protein levels. The same response was found in fibroblasts when activating TGR5 with the specific receptor agonist (INT-777). Interestingly, DCA reduced fibronectin protein levels in both myoblasts and myotubes, while CA did not show changes in fibronectin protein levels in myoblasts and myotubes. These results suggest that DCA and CA can induce a fibrotic phenotype in muscle-derived fibroblasts. On the other hand, DCA decreased the fibronectin in myoblasts and myotubes, whereas CA did not show any effect in these cell populations. Our results show that BA has different effects depending on the cell population to be analyzed.

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.

The Wnt Signaling Pathway in Diabetic Nephropathy

Diabetic nephropathy (DN) is a serious kidney-related complication of both type 1 and type 2 diabetes mellitus (T1DM, T2DM) and the second major cause of end-stage kidney disease. DN can lead to hypertension, edema, and proteinuria. In some cases, DN can even progress to kidney failure, a life-threatening condition. The precise etiology and pathogenesis of DN remain unknown, although multiple factors are believed to be involved. The main pathological manifestations of DN include mesangial expansion, thickening of the glomerular basement membrane, and podocyte injury. Eventually, these pathological manifestations will lead to glomerulosclerosis, thus affecting renal function. There is an urgent need to develop new strategies for the prevention and treatment of DN. Existing evidence shows that the Wnt signaling cascade plays a key role in regulating the development of DN. Previous studies focused on the role of the Wnt canonical signaling pathway in DN. Subsequently, accumulated evidence on the mechanism of the Wnt non-canonical signaling indicated that Wnt/Ca²⁺ and Wnt/PCP also have essential roles in the progression of DN. In this review, we summarize the specific mechanisms of Wnt signaling in the occurrence and development of DN in podocyte injury, mesangial cell injury, and renal fibrosis. Also, to elucidate the significance of the Wnt canonical pathway in the process of DN, we uncovered evidence supporting that both Wnt/PCP and Wnt/Ca²⁺ signaling are critical for DN development.

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.

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.

ROCK Inhibition May Stop Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease and is strongly associated with cardiovascular mortality. Given the pandemic of obesity and diabetes, the elucidation of the molecular underpinnings of DKD and establishment of effective therapy are urgently required. Studies over the past decade have identified the activated renin-angiotensin system (RAS) and hemodynamic changes as important therapeutic targets. However, given the residual risk observed in patients treated with RAS inhibitors and/or sodium glucose co-transporter 2 inhibitors, the involvement of other molecular machinery is likely, and the elucidation of such pathways represents fertile ground for the development of novel strategies. Rho-kinase (ROCK) is a serine/threonine kinase that is under the control of small GTPase protein Rho. Many fundamental cellular processes, including migration, proliferation, and survival are orchestrated by ROCK through a mechanism involving cytoskeletal reorganization. From a pathological standpoint, several analyses provide compelling evidence supporting the hypothesis that ROCK is an important regulator of DKD that is highly pertinent to cardiovascular disease. In cell-based studies, ROCK is activated in response to a diverse array of external stimuli associated with diabetes, and renal ROCK activity is elevated in the context of type 1 and 2 diabetes. Experimental studies have demonstrated the efficacy of pharmacological or genetic inhibition of ROCK in the prevention of diabetes-related histological and functional abnormalities in the kidney. Through a bird’s eye view of ROCK in renal biology, the present review provides a conceptual framework that may be widely applicable to the pathological processes of multiple organs and illustrate novel therapeutic promise in diabetology.

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.

Bile acid signaling in renal water regulation

Emerging evidence has shown that bile acids play important roles in renal physiology and diseases by activating two major receptors, the nuclear farnesoid X receptor (FXR) and the membrane G protein-coupled bile acid receptor-1 (Gpbar1; also known as TGR5). Both FXR and TGR5 have been identified in human and rodent kidneys, where they are deeply involved in renal water handling. In mice, FXR- or TGR5-related gene deficiency has been associated with reduced aquaporin-2 expression accompanied with impaired urinary concentration ability. In this mini-review, we briefly discuss the current understanding of FXR/TGR5 signaling in the kidneys, with a special focus on the regulation of aquaporin-2 expression by bile acids in the collecting ducts and its potential significance in disease conditions.

Mesangial Cells and Renal Fibrosis

The main cellular constituents in glomerular mesangium are mesangial cells, which account for approximately 30-40% of the total cells in the glomerulus. Together with the mesangial matrix, mesangial cells form the glomerular basement membrane (GBM) in the glomerulus, whose main function is to perform the filtration. Under the pathologic conditions, mesangial cells are activated, leading to hyperproliferation and excess extracellular matrix (ECM). Moreover, mesangial cells also secrete several kinds of inflammatory cytokines, adhesion molecules, chemokines, and enzymes, all of which participate in the process of renal glomerular fibrosis. During the past years, researchers have revealed the roles of mesangial cells and the associated signal pathways involved in renal fibrosis. In this section, we will discuss how mesangial cells are activated and its contributions to renal fibrosis, as well as the molecular mechanisms and novel anti-fibrotic agents. Full understanding of the contributions of mesangial cells to renal fibrosis will benefit the clinical drug developing.

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.