Activation of FXR protects against renal fibrosis via suppressing Smad3 expression

Bile acid metabolism in health and ageing-related diseases

Bile acids (BAs) have surpassed their traditional roles as lipid solubilizers and regulators of BA homeostasis to emerge as important signalling molecules. Recent research has revealed a connection between microbial dysbiosis and metabolism disruption of BAs, which in turn impacts ageing-related diseases. The human BAs pool is primarily composed of primary BAs and their conjugates, with a smaller proportion consisting of secondary BAs. These different BAs exert complex effects on health and ageing-related diseases through several key nuclear receptors, such as farnesoid X receptor and Takeda G protein-coupled receptor 5. However, the underlying molecular mechanisms of these effects are still debated. Therefore, the modulation of signalling pathways by regulating synthesis and composition of BAs represents an interesting and novel direction for potential therapies of ageing-related diseases. This review provides an overview of synthesis and transportion of BAs in the healthy body, emphasizing its dependence on microbial community metabolic capacity. Additionally, the review also explores how ageing and ageing-related diseases affect metabolism and composition of BAs. Understanding BA metabolism network and the impact of their nuclear receptors, such as farnesoid X receptor and G protein-coupled receptor 5 agonists, paves the way for developing therapeutic agents for targeting BA metabolism in various ageing-related diseases, such as metabolic disorder, hepatic injury, cardiovascular disease, renal damage and neurodegenerative disease.

The renal apical sodium-dependent bile acid transporter expression rescue attenuates renal damage in diabetic nephropathy via farnesoid X receptor activation

AIM

Bile acids (BA) function as signalling molecules regulating glucose-lipid homeostasis and energy expenditure. However, the expression of the apical sodium-dependent bile acid transporter (ASBT) in the kidney, responsible for renal BA reabsorption, is downregulated in patients with diabetic kidney disease (DKD). Using the db/db mouse model of DKD, this study aimed to investigate the effects of rescuing ASBT expression via adeno-associated virus-mediated delivery of ASBT (AAVASBT) on kidney protection.

METHODS

Six-week-old male db/db mice received an intraparenchymal injection of AAVASBT at a dose of 1 × 1011 viral genomes (vg)/animal and were subsequently fed a chow diet for 2 weeks. Male db/m mice served as controls. For drug treatment, daily intraperitoneal (i.p.) injections of the farnesoid X receptor (FXR) antagonist guggulsterone (GS, 10 mg/kg) were administered one day after initiating the experiment.

RESULTS

AAVASBT treatment rescued renal ASBT expression and reduced the urinary BA output in db/db mice. AAVASBT treatment activated kidney mitochondrial biogenesis and ameliorated renal impairment associated with diabetes by activating FXR. In addition, the injection of FXR antagonist GS in DKD mice would reverse these beneficial effects by AAVASBT treatment.

CONCLUSION

Our work indicated that restoring renal ASBT expression slowed the course of DKD via activating FXR. FXR activation stimulates mitochondrial biogenesis while reducing renal oxidative stress and lipid build up, indicating FXR activation's crucial role in preventing DKD. These findings further suggest that the maintenance of renal BA reabsorption could be a viable treatment for DKD.

Activation of farnesoid X receptor retards expansion of renal collecting duct cell-derived cysts via inhibition of CFTR-mediated Cl- secretion

The transcription factor farnesoid X receptor (FXR) regulates energy metabolism. Specifically, FXR functions to regulate cystic fibrosis transmembrane conductance regulator (CFTR)-mediated Cl- secretion in intestinal epithelial cells. Therefore, this study aimed to investigate the role of FXR in CFTR-mediated Cl- secretion in renal tubular cells and to further elucidate its effects on renal cyst formation and growth. CFTR-mediated Cl- transport was evaluated via short-circuit current (ISC) measurements in Madin-Darby canine kidney (MDCK) cell monolayers and primary rat inner medullary collecting duct cells. The role of FXR in renal cyst formation and growth was determined by the MDCK cell-derived cyst model. Incubation with synthesized (GW4064) and endogenous (CDCA) FXR ligands reduced CFTR-mediated Cl- secretion in a concentration- and time-dependent manner. The inhibitory effect of FXR ligands was not due to the result of reduced cell viability and was attenuated by cotreatment with an FXR antagonist. FXR activation significantly decreased CFTR protein but not its mRNA. In addition, FXR activation inhibited CFTR-mediated Cl- secretion in primary renal collecting duct cells. FXR activation decreased ouabain-sensitive ISC without altering Na+-K+-ATPase mRNA and protein levels. Furthermore, FXR activation significantly reduced the number of cysts and renal cyst expansion. These inhibitory effects were correlated with a decrease in the expression of protein synthesis regulators mammalian target of rapamycin/S6 kinase. This study shows that FXR activation inhibits Cl- secretion in renal cells via inhibition of CFTR expression and retards renal cyst formation and growth. The discoveries point to a physiological role of FXR in the regulation of CFTR and a potential therapeutic application in polycystic kidney disease treatment.NEW & NOTEWORTHY The present study reveals that farnesoid X receptor (FXR) activation reduces microcyst formation and enlargement. This inhibitory effect of FXR activation is involved with decreased cell proliferation and cystic fibrosis transmembrane conductance regulator-mediated Cl- secretion in renal collecting duct cells. FXR might represent a novel target for the treatment of autosomal dominant polycystic kidney disease.

Dual soluble epoxide hydrolase inhibitor - farnesoid X receptor agonist interventional treatment attenuates renal inflammation and fibrosis

Introduction

Renal fibrosis associated with inflammation is a critical pathophysiological event in chronic kidney disease (CKD). We have developed DM509 which acts concurrently as a farnesoid X receptor agonist and a soluble epoxide hydrolase inhibitor and investigated DM509 efficacy as an interventional treatment using the unilateral ureteral obstruction (UUO) mouse model.

Methods

Male mice went through either UUO or sham surgery. Interventional DM509 treatment (10mg/kg/d) was started three days after UUO induction and continued for 7 days. Plasma and kidney tissue were collected at the end of the experimental protocol.

Results

UUO mice demonstrated marked renal fibrosis with higher kidney hydroxyproline content and collagen positive area. Interventional DM509 treatment reduced hydroxyproline content by 41% and collagen positive area by 65%. Renal inflammation was evident in UUO mice with elevated MCP-1, CD45-positive immune cell positive infiltration, and profibrotic inflammatory gene expression. DM509 treatment reduced renal inflammation in UUO mice. Renal fibrosis in UUO was associated with epithelial-to-mesenchymal transition (EMT) and DM509 treatment reduced EMT. UUO mice also had tubular epithelial barrier injury with increased renal KIM-1, NGAL expression. DM509 reduced tubular injury markers by 25-50% and maintained tubular epithelial integrity in UUO mice. Vascular inflammation was evident in UUO mice with 9 to 20-fold higher ICAM and VCAM gene expression which was reduced by 40-50% with DM509 treatment. Peritubular vascular density was reduced by 35% in UUO mice and DM509 prevented vascular loss.

Discussion

Interventional treatment with DM509 reduced renal fibrosis and inflammation in UUO mice demonstrating that DM509 is a promising drug that combats renal epithelial and vascular pathological events associated with progression of CKD.

Farnesoid X receptor prevents neutrophil extracellular traps via reduced sphingosine-1-phosphate in chronic kidney disease

Farnesoid X receptor (FXR) activation reduces renal inflammation, but the underlying mechanisms remain elusive. Neutrophil extracellular traps (NETs) are webs of DNA formed when neutrophils undergo specialized programmed cell death (NETosis). The signaling lipid sphingosine-1-phosphate (S1P) stimulates NETosis via its receptor on neutrophils. Here, we identify FXR as a negative regulator of NETosis via repressing S1P signaling. We determined the effects of the FXR agonist obeticholic acid (OCA) in mouse models of adenosine phosphoribosyltransferase (APRT) deficiency and Alport syndrome, both genetic disorders that cause chronic kidney disease. Renal FXR activity is greatly reduced in both models, and FXR agonism reduces disease severity. Renal NETosis and sphingosine kinase 1 (Sphk1) expression are increased in diseased mice, and they are reduced by OCA in both models. Genetic deletion of FXR increases Sphk1 expression, and Sphk1 expression correlates with NETosis. Importantly, kidney S1P levels in Alport mice are two-fold higher than controls, and FXR agonism restores them back to baseline. Short-term inhibition of sphingosine synthesis in Alport mice with severe kidney disease reverses NETosis, establishing a causal relationship between S1P signaling and renal NETosis. Finally, extensive NETosis is present in human Alport kidney biopsies (six male, nine female), and NETosis severity correlates with clinical markers of kidney disease. This suggests the potential clinical relevance of the newly identified FXR-S1P-NETosis pathway. In summary, FXR agonism represses kidney Sphk1 expression. This inhibits renal S1P signaling, thereby reducing neutrophilic inflammation and NETosis.NEW & NOTEWORTHY Many preclinical studies have shown that the farnesoid X receptor (FXR) reduces renal inflammation, but the mechanism is poorly understood. This report identifies FXR as a novel regulator of neutrophilic inflammation and NETosis via the inhibition of sphingosine-1-phosphate signaling. Additionally, NETosis severity in human Alport kidney biopsies correlates with clinical markers of kidney disease. A better understanding of this signaling axis may lead to novel treatments that prevent renal inflammation and chronic kidney disease.

Bile Acid Network and Vascular Calcification-Associated Diseases: Unraveling the Intricate Connections and Therapeutic Potential

Bile acids play a crucial role in promoting intestinal nutrient absorption and biliary cholesterol excretion, thereby protecting the liver from cholesterol accumulation and bile acid toxicity. Additionally, bile acids can bind to specific nuclear and membrane receptors to regulate energy expenditure and specific functions of particular tissues. Vascular calcification refers to the pathological process of calcium-phosphate deposition in blood vessel walls, which serves as an independent predictor for cardiovascular adverse events. In addition to aging, this pathological change is associated with aging-related diseases such as atherosclerosis, hypertension, chronic kidney disease, diabetes mellitus, and osteoporosis. Emerging evidence suggests a close association between the bile acid network and these aforementioned vascular calcification-associated conditions. Several bile acids have been proven to participate in calcium-phosphate metabolism, affecting the transdifferentiation of vascular smooth muscle cells and thus influencing vascular calcification. Targeting the bile acid network shows potential for ameliorating these diseases and their concomitant vascular calcification by regulating pathways such as energy metabolism, inflammatory response, oxidative stress, and cell differentiation. Here, we present a summary of the metabolism and functions of the bile acid network and aim to provide insights into the current research on the profound connections between the bile acid network and these vascular calcification-associated diseases, as well as the therapeutic potential.

Kidney lipid dysmetabolism and lipid droplet accumulation in chronic kidney disease

Chronic kidney disease (CKD) is a global health problem with rising incidence and prevalence. Among several pathogenetic mechanisms responsible for disease progression, lipid accumulation in the kidney parenchyma might drive inflammation and fibrosis, as has been described in fatty liver diseases. Lipids and their metabolites have several important structural and functional roles, as they are constituents of cell and organelle membranes, serve as signalling molecules and are used for energy production. However, although lipids can be stored in lipid droplets to maintain lipid homeostasis, lipid accumulation can become pathogenic. Understanding the mechanisms linking kidney parenchymal lipid accumulation to CKD of metabolic or non-metabolic origin is challenging, owing to the tremendous variety of lipid species and their functional diversity across different parenchymal cells. Nonetheless, multiple research reports have begun to emphasize the effect of dysregulated kidney lipid metabolism in CKD progression. For example, altered cholesterol and fatty acid metabolism contribute to glomerular and tubular cell injury. Newly developed lipid-targeting agents are being tested in clinical trials in CKD, raising expectations for further therapeutic development in this field.

YAP/TAZ: Molecular pathway and disease therapy

The Yes-associated protein and its transcriptional coactivator with PDZ-binding motif (YAP/TAZ) are two homologous transcriptional coactivators that lie at the center of a key regulatory network of Hippo, Wnt, GPCR, estrogen, mechanical, and metabolism signaling. YAP/TAZ influences the expressions of downstream genes and proteins as well as enzyme activity in metabolic cycles, cell proliferation, inflammatory factor expression, and the transdifferentiation of fibroblasts into myofibroblasts. YAP/TAZ can also be regulated through epigenetic regulation and posttranslational modifications. Consequently, the regulatory function of these mechanisms implicates YAP/TAZ in the pathogenesis of metabolism-related diseases, atherosclerosis, fibrosis, and the delicate equilibrium between cancer progression and organ regeneration. As such, there arises a pressing need for thorough investigation of YAP/TAZ in clinical settings. In this paper, we aim to elucidate the signaling pathways that regulate YAP/TAZ and explore the mechanisms of YAP/TAZ-induce diseases and their potential therapeutic interventions. Furthermore, we summarize the current clinical studies investigating treatments targeting YAP/TAZ. We also address the limitations of existing research on YAP/TAZ and propose future directions for research. In conclusion, this review aims to provide fresh insights into the signaling mediated by YAP/TAZ and identify potential therapeutic targets to present innovative solutions to overcome the challenges associated with YAP/TAZ.

Regulon analysis identifies protective FXR and CREB5 in proximal tubules in early diabetic kidney disease

Diabetic kidney disease (DKD) is the most common complication of diabetes mellitus and a leading cause of kidney failure worldwide. Despite its prevalence, the mechanisms underlying early kidney damage in DKD remain poorly understood. In this study, we used single nucleus RNA-seq to construct gene regulatory networks (GRNs) in the kidney cortex of patients with early DKD. By comparing these networks with those of healthy controls, we identify cell type-specific changes in genetic regulation associated with diabetic status. The regulon activities of FXR (NR1H4) and CREB5 were found to be upregulated in kidney proximal convoluted tubule epithelial cells (PCTs), which were validated using immunofluorescence staining in kidney biopsies from DKD patients. In vitro experiments using cultured HK2 cells showed that FXR and CREB5 protected cells from apoptosis and epithelial-mesenchymal transition. Our findings suggest that FXR and CREB5 may be promising targets for early intervention in patients with DKD.

Discovery of the First-in-Class Intestinal Restricted FXR and FABP1 Dual Modulator ZLY28 for the Treatment of Nonalcoholic Fatty Liver Disease

The prevalence of nonalcoholic steatohepatitis (NASH) is increasing rapidly worldwide, and NASH has become a serious problem for human health. Recently, the selective activation of the intestinal farnesoid X receptor (FXR) was considered as a more promising strategy for the treatment of NASH with lesser side effects due to reduced systemic exposure. Moreover, the inhibition of intestinal fatty acid binding protein 1 (FABP1) alleviated obesity and NASH by reducing dietary fatty acid uptake. In this study, the first-in-class intestinal restricted FXR and FABP1 dual-target modulator ZLY28 was discovered by comprehensive multiparameter optimization studies. The reduced systemic exposure of ZLY28 might provide better safety by decreasing the on- and off-target side effects in vivo. In NASH mice, ZLY28 exerted robust anti-NASH effects by inhibiting FABP1 and activating the FXR-FGF15 signaling pathway in the ileum. With the above attractive efficacy and preliminary safety profiles, ZLY28 is worthy of further evaluation as a novel anti-NASH agent.

FXR inhibition may protect from SARS-CoV-2 infection by reducing ACE2

Preventing SARS-CoV-2 infection by modulating viral host receptors, such as angiotensin-converting enzyme 2 (ACE2)1, could represent a new chemoprophylactic approach for COVID-19 that complements vaccination2,3. However, the mechanisms that control the expression of ACE2 remain unclear. Here we show that the farnesoid X receptor (FXR) is a direct regulator of ACE2 transcription in several tissues affected by COVID-19, including the gastrointestinal and respiratory systems. We then use the over-the-counter compound z-guggulsterone and the off-patent drug ursodeoxycholic acid (UDCA) to reduce FXR signalling and downregulate ACE2 in human lung, cholangiocyte and intestinal organoids and in the corresponding tissues in mice and hamsters. We show that the UDCA-mediated downregulation of ACE2 reduces susceptibility to SARS-CoV-2 infection in vitro, in vivo and in human lungs and livers perfused ex situ. Furthermore, we reveal that UDCA reduces the expression of ACE2 in the nasal epithelium in humans. Finally, we identify a correlation between UDCA treatment and positive clinical outcomes after SARS-CoV-2 infection using retrospective registry data, and confirm these findings in an independent validation cohort of recipients of liver transplants. In conclusion, we show that FXR has a role in controlling ACE2 expression and provide evidence that modulation of this pathway could be beneficial for reducing SARS-CoV-2 infection, paving the way for future clinical trials.

The programming of kidney injury in offspring affected by maternal overweight and obesity: role of lipid accumulation, inflammation, oxidative stress, and fibrosis in the kidneys of offspring

Maternal overweight and obesity are considered important factors affecting fetal development with many potential consequences for offspring after delivery, including the increased risk of obesity and diabetes mellitus. Maternal obesity promotes adiposity in the offspring by increasing fat deposition and expansion in the body of the offspring. The expansion of adipose tissue changes adipokine levels, including a decrease in adiponectin and an increase in leptin. In addition to changes in adipokine levels, there are also increases in pro-inflammatory cytokines, pro-fibrotic cytokines, and reactive oxygen species, leading to oxidative stress in the offspring. These contribute to the promotion of insulin resistance in offspring, which is associated with kidney injury. Interestingly, maternal obesity can also promote renal lipid accumulation, which could activate inflammatory processes and promote renal oxidative stress and renal fibrosis. These alterations in the kidneys of the offspring imply that a mother being overweight/obese can program the development of kidney disease in offspring. This review will discuss the effects of a mother being overweight or obese on their offspring and the consequences with regard to the kidneys of their offspring. With a focus on the molecular mechanisms, including renal inflammation, renal oxidative stress, renal fibrosis, and renal lipid metabolism in offspring born to overweight and obese mothers, the causative mechanisms and perspective of these conditions will be included.

Diminished Tubule Epithelial Farnesoid X Receptor Expression Exacerbates Inflammation and Fibrosis Response in Aged Rat Kidney

The age-associated functional decline of the kidney is accompanied by structural changes including glomerular sclerosis and interstitial fibrosis. Aging kidneys also exhibit increased vulnerability in stressful environmental conditions. In this study, we assessed the differences in responses between young and aged animals to folic acid (FA)-induced renal fibrosis. To monitor the effects of aging on FA-induced kidney fibrosis, we administered FA (250 mg/kg) to young (6-month old) and aged (20-month old) rats. The development of severe fibrosis was only detected in aged rat kidneys, which was accompanied by increased kidney injury and inflammation. Furthermore, we found that FA-treated aged rats had significantly lower farnesoid X receptor (FXR) expression in the tubular epithelial cells than the rats not treated with FA. Interestingly, the extent of inflammation was severe in the kidneys of aged rat, where the FXR expression was low. To explore the role of FXR in kidney inflammation, in vitro studies were performed using NRK52E kidney tubule epithelial cells. NF-κB activation by lipopolysaccharide treatment induces chemokine production in NRK52E cells. The activation of FXR by obeticholic acid significantly reduced the transcriptional activity of NF-κB and chemokine production. In contrast, FXR knockdown increased LPS-induced chemokine production in NRK52E cells. Finally, FXR-knockout mice that were administered FA showed increased inflammation and severe fibrosis. In summary, we demonstrated that diminished FXR expression in the epithelial cells of the renal tubules exacerbated the fibrotic response in aged rat kidneys by upregulating pro-inflammatory NF-κB activation.

Role of FXR in Renal Physiology and Kidney Diseases

Farnesoid X receptor, also known as the bile acid receptor, belongs to the nuclear receptor (NR) superfamily of ligand-regulated transcription factors, which performs its functions by regulating the transcription of target genes. FXR is highly expressed in the liver, small intestine, kidney and adrenal gland, maintaining homeostasis of bile acid, glucose and lipids by regulating a diverse array of target genes. It also participates in several pathophysiological processes, such as inflammation, immune responses and fibrosis. The kidney is a key organ that manages water and solute homeostasis for the whole body, and kidney injury or dysfunction is associated with high morbidity and mortality. In the kidney, FXR plays an important role in renal water reabsorption and is thought to perform protective functions in acute kidney disease and chronic kidney disease, especially diabetic kidney disease. In this review, we summarize the recent advances in the understanding of the physiological and pathophysiological function of FXR in the kidney.

EDP-297: A novel, farnesoid X receptor agonist-Results of a phase I study in healthy subjects

EDP-297 is a farnesoid X receptor agonist under development for treating nonalcoholic steatohepatitis. The pharmacokinetic (PK), pharmacodynamic (PD), food effect, and safety were evaluated in a single ascending dose (SAD) and multiple ascending dose (MAD) phase I study. Healthy subjects received single EDP-297 doses of 20-600 μg or once daily doses of 5-90 μg for 14 days. Safety, PKs, and PDs were assessed, including fibroblast growth factor 19 (FGF-19) and 7-α-hydroxy-4-cholesten-3-one (C4). Among 82 subjects, EDP-297 was generally well-tolerated. Pruritus was observed in four subjects in the SAD phase and seven subjects in the MAD phase; four severe cases occurred at 90 μg in the MAD phase, including one that led to drug discontinuation. A grade 2 elevation in alanine aminotransferase occurred with 90 μg. Mean lipid values remained within normal range. Plasma exposures of EDP-297 increased with SADs and MADs, with mean half-life following multiple doses of 9-12.5 h. No food effect was observed. Mean FGF-19 increased and C4 decreased up to 95% and 92%, respectively. EDP-297 was generally well-tolerated up to 60 μg MAD, with linear PKs suitable for once daily oral dosing, target engagement, and no food effect.

Single-Cell Chromatin and Gene-Regulatory Dynamics of Mouse Nephron Progenitors

BACKGROUND

We reasoned that unraveling the dynamic changes in accessibility of genomic regulatory elements and gene expression at single-cell resolution will inform the basic mechanisms of nephrogenesis.

METHODS

We performed single-cell ATAC-seq and RNA-seq both individually (Singleomes; Six2GFPcells) and jointly in the same cells (Multiomes; kidneys) to generate integrated chromatin and transcriptional maps in mouse embryonic and neonatal nephron progenitor cells (NPCs).

RESULTS

WWe demonstrate that singleomes and multiomes are comparable in assigning most cell states, identification of new cell type markers, and defining the transcription factors driving cell identity. However, multiomes are more precise in defining the progenitor population. Multiomes identified a "pioneer" bHLH/Fox motif signature in NPCs. Moreover, we identified a subset of Fox factors exhibiting high chromatin activity in podocytes. One of these Fox factors, Foxp1, is important for nephrogenesis. Key nephrogenic factors are distinguished by strong correlation between linked generegulatory elements and gene expression.

CONCLUSION

Mapping the regulatory landscape at single-cell resolution informs the regulatory hierarchy of nephrogenesis. Paired single-cell epigenomes and transcriptomes of nephron progenitors should provide a foundation to understand prenatal programming, regeneration following injury, and ex vivo nephrogenesis.

Knockout of farnesoid X receptor gene aggravates cisplatin-induced kidney injury

OBJECTIVES

Farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily of ligand activated transcription factors and belongs to bile acid receptor. Studies have shown that the expression of FXR in renal tissue can reduce renal injury via regulation of glucose and lipid metabolism, inhibition of inflammatory response, reduction of oxidative stress and renal fibrosis. However, it is unclear whether FXR is involved in autophagy in renal diseases. This study aims to investigate the role of FXR in cisplatin-induced acute renal injury and whether its mechanism is related to autophagy regulation.

METHODS

Twelve male WT or FXR-KO mice at 12 weeks were randomly divided into a WT group, a WT+cisplatin group, a FXR-KO group, and a FXR-KO+cisplatin group, with 6 mice in each group. The WT+cisplatin group and the FXR-KO+cisplatin group were intraperitoneally injected with cisplatin (20 mg/kg), and the WT group and the FXR-KO group were intraperitoneally injected with equal volume of cisplatin solvent. Seventy-two hours later, the mice were killed and blood and renal tissue samples were collected. The levels of SCr and BUN were detected by immunoturbidimetry. After the staining, the pathological changes of renal tissue were observed under optical microscope. The protein levels of LC3 and p62 were detected by Western blotting and immunohistochemistry. The clearance of damaged mitochondria and the accumulation of lysosomal substrate were observed under electron microscope. The apoptosis of renal tubular epithelial cells was detected by TUNEL.

RESULTS

Compared with the WT group or the FXR-KO group, both SCr and BUN levels in the WT+cisplatin group or the FXR-KO+cisplatin group were significantly increased (P<0.01 or P<0.001), and SCr and BUN levels in the FXR-KO+cisplatin group were significantly higher than those in the WT+cisplatin group (both P<0.05). Under the light microscope, there were no obvious pathological changes in the renal tissue of mice in the WT group and the FXR-KO group. Both the WT+cisplatin group and the FXR-KO+cisplatin group had vacuolar or granular degeneration of renal tubular epithelial cells, flat cells, lumen expansion, brush edge falling off, and even exposed basement membrane and tubular formation. The scores of renal tubular injury in the WT+cisplatin group and the FXR-KO+cisplatin group were significantly higher than those in the WT group and the FXR-KO group, respectively (both P<0.001), and the score in the FXR-KO+cisplatin group was significantly higher than that in the WT+cisplatin group (P<0.05). Under the transmission electron microscope, the mitochondria of mouse tubular epithelial cell in the WT+cisplatin group and the FXR-KO+cisplatin group was swollen, round, vacuolated, cristae broken or disappeared; the lysosome was uneven and high-density clumps, and the change was more obvious in the FXR-KO+cisplatin group. Western blotting showed that the ratio of LC3-II to LC3-I was decreased and the expression of p62 was increased in the WT+cisplatin group compared with the WT group and the FXR-KO+cisplatin group compared with FXR-KO group (P<0.05 or P<0.01); compared with the FXR-KO group, the ratio of LC3-II to LC3-I was decreased and the expression of p62 was increased significantly in the FXR-KO+cisplatin group (both P<0.05). Immunohistochemistry results showed that the expression of total LC3 and p62 in renal cortex of the WT+cisplatin group and the FXR-KO+cisplatin group was increased significantly, especially in the FXR-KO+cisplatin group. TUNEL results showed that the mice in the WT group and the FXR-KO group had negative staining or only a few apoptotic tubular epithelial cells, and the number of apoptotic cells in the WT+cisplatin group and the FXR-KO+cisplatin group were increased. The apoptosis rates of renal tubular epithelial cells in the WT+cisplatin group and the FXR-KO+cisplatin group were significantly higher than those in the WT group and the FXR-KO group, respectively (both P<0.001), and the apoptosis rate in the FXR-KO+cisplatin group was significantly higher than that in the WT+cisplatin group (P<0.05).

CONCLUSIONS

Knockout of FXR gene aggravates cisplatin induced acute renal injury, and its mechanism may be related to inhibiting autophagy and promoting apoptosis.

Nuclear receptors in renal health and disease

As a major social and economic burden for the healthcare system, kidney diseases contribute to the constant increase of worldwide deaths. A deeper understanding of the underlying mechanisms governing the etiology, development and progression of kidney diseases may help to identify potential therapeutic targets. As a superfamily of ligand-dependent transcription factors, nuclear receptors (NRs) are critical for the maintenance of normal renal function and their dysfunction is associated with a variety of kidney diseases. Increasing evidence suggests that ligands for NRs protect patients from renal ischemia/reperfusion (I/R) injury, drug-induced acute kidney injury (AKI), diabetic nephropathy (DN), renal fibrosis and kidney cancers. In the past decade, some breakthroughs have been made for the translation of NR ligands into clinical use. This review summarizes the current understanding of several important NRs in renal physiology and pathophysiology and discusses recent findings and applications of NR ligands in the management of kidney diseases.

Genistein alleviates renin-angiotensin system mediated vascular and kidney alterations in renovascular hypertensive rats

Genistein is a bioflavonoid mainly found in soybean. This study evaluated the effect of genistein on vascular dysfunction and kidney damage in two-kidney, one-clipped (2K1C) hypertensive rats. Male Sprague-Dawley-2K1C hypertensive rats were treated with genistein (40 or 80 mg/kg) or losartan 10 mg/kg (n = 8/group). Genistein reduced blood pressure, attenuated the increase in sympathetic nerve-mediated contractile response and endothelial dysfunction in the mesenteric vascular beds and aorta of 2K1C rats. Increases in the intensity of tyrosine hydroxylase (TH) in the mesentery and plasma norepinephrine (NE) were alleviated in the genistein-treated group. Genistein also improved renal dysfunction, hypertrophy of the non-clipped kidney (NCK) and atrophy of the clipped kidney (CK) in 2K1C rats. Upregulation of angiotensin II receptor type I (AT₁R), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit 4 (Nox4) and Bcl2-associated X protein (BAX) and downregulation of B-cell lymphoma 2 (Bcl2) protein found in CK were restored by genistein. It also suppressed the overexpression of AT₁R, transforming growth factor beta I (TGF-β1), smad2/3 and p-smad3 in NCK. Genistein reduced serum angiotensin converting enzyme (ACE) activity and plasma angiotensin II (Ang II) in 2K1C rats. Low levels of catalase activity as well as high levels of superoxide generation and malondialdehyde (MDA) in 2K1C rats were restored by genistein treatment. In conclusion, genistein suppressed renin-angiotensin system-mediated sympathetic activation and oxidative stress in 2K1C rats. It alleviated renal atrophy in CK via modulation of AT₁R/NADPH oxidase/Bcl-2/BAX pathways and hypertrophy in NCK via AT₁R/TGF-β1/smad-dependent signalling pathways.

Deoxycholic Acid and Risks of Cardiovascular Events, ESKD, and Mortality in CKD: The CRIC Study

Rationale & Objective

Elevated levels of deoxycholic acid (DCA) are associated with adverse outcomes and may contribute to vascular calcification in patients with chronic kidney disease (CKD). We tested the hypothesis that elevated levels of DCA were associated with increased risks of cardiovascular disease, CKD progression, and death in patients with CKD.

Study Design

Prospective observational cohort study.

Setting & Participants

We included 3,147 Chronic Renal Insufficiency Cohort study participants who had fasting DCA levels. The average age was 59 ± 11 years, 45.3% were women, 40.6% were African American, and the mean estimated glomerular filtration rate was 42.5 ± 16.0 mL/min/1.73 m².

Predictor

Fasting DCA levels in Chronic Renal Insufficiency Cohort study participants.

Outcomes

Risks of atherosclerotic and heart failure events, end-stage kidney disease (ESKD), and all-cause mortality.

Analytical Approach

We used Tobit regression to identify predictors of DCA levels. We used Cox regression to examine the association between fasting DCA levels and clinical outcomes.

Results

The strongest predictors of elevated DCA levels in adjusted models were increased age and nonuse of statins. The associations between log-transformed DCA levels and clinical outcomes were nonlinear. After adjustment, DCA levels above the median were independently associated with higher risks of ESKD (HR, 2.67; 95% CI, 1.51-4.74) and all-cause mortality (HR, 2.13; 95% CI, 1.25-3.64). DCA levels above the median were not associated with atherosclerotic and heart failure events, and DCA levels below the median were not associated with clinical outcomes.

Limitations

We were unable to measure DCA longitudinally or in urinary or fecal samples, and we were unable to measure other bile acids. We also could not measure many factors that affect DCA levels.

Conclusions

In 3,147 participants with CKD stages 2-4, DCA levels above the median were independently associated with ESKD and all-cause mortality.

A naturally occurring FXR agonist, alisol B 23-acetate, protects against renal ischemia-reperfusion injury

The ligand-activated nuclear receptor, farnesoid X receptor (FXR), plays a pivotal role in regulating renal function. Activation of FXR by its specific agonists exerts renoprotective action in animals with acute kidney injury (AKI). In the present study, we aimed to identify naturally occurring agonists of FXR with potential as therapeutic agents in renal ischemia-reperfusion injury. In vitro and in vivo FXR activation was determined by a dual-luciferase assay, docking analysis, site-directed mutagenesis, and whole kidney transcriptome analysis. Wild-type (WT) and FXR knockout (FXR-/-) mice were used to determine the effect of potential FXR agonist on renal ischemia-reperfusion injury (IRI). We found that alisol B 23-acetate (ABA), a major active triterpenoid extracted from Alismatis rhizoma, a well-known traditional Chinese medicine, can activate renal FXR and induce FXR downstream gene expression in mouse kidney. ABA treatment significantly attenuated renal ischemia-reperfusion-induced AKI in WT mice but not in FXR-/- mice. Our results demonstrate that ABA can activate renal FXR to exert renoprotection against ischemia-reperfusion injury-induced AKI. Therefore, ABA may represent a potential therapeutic agent in the treatment of ischemic AKI.NEW & NOTEWORTHY In the present study, we found that alisol B 23-acetate (ABA), an identified natural farnesoid X receptor (FXR) agonist from the well-known traditional Chinese medicine Alismatis rhizoma, protects against ischemic acute kidney injury (AKI) in an FXR-dependent manner, as reflected by improved renal function, reduced renal tubular apoptosis, ameliorated oxidative stress, and suppressed inflammatory factor expression. Therefore, ABA may have great potential as a novel therapeutic agent in the treatment of AKI in the future.

Nuclear Receptors and Transcription Factors in Obesity-Related Kidney Disease

Both obesity and chronic kidney disease are increasingly common causes of morbidity and mortality worldwide. Although obesity often co-exists with diabetes and hypertension, it has become clear over the past several decades that obesity is an independent cause of chronic kidney disease, termed obesity-related glomerulopathy. This review defines the attributes of obesity-related glomerulopathy and describes potential pharmacologic interventions. Interventions discussed include peroxisome proliferator-activated receptors, the farnesoid X receptor, the Takeda G-protein-coupled receptor 5, and the vitamin D receptor.

Multi-Target Drugs for Kidney Diseases

Kidney diseases such as AKI, CKD, and GN can lead to dialysis and the need for kidney transplantation. The pathologies for kidney diseases are extremely complex, progress at different rates, and involve several cell types and cell signaling pathways. Complex kidney diseases require therapeutics that can act on multiple targets. In the past 10 years, in silico design of drugs has allowed for multi-target drugs to progress quickly from concept to reality. Several multi-target drugs have been made successfully to target AA pathways and transcription factors for the treatment of inflammatory, fibrotic, and metabolic diseases. Multi-target drugs have also demonstrated great potential to treat diabetic nephropathy and fibrotic kidney disease. These drugs act by decreasing renal TGF-β signaling, inflammation, mitochondrial dysfunction, and oxidative stress. There are several other recently developed multi-target drugs that have yet to be tested for their ability to combat kidney diseases. Overall, there is excellent potential for multi-target drugs that act on several cell types and signaling pathways to treat kidney diseases.

Targeting Farnesoid X receptor (FXR) for developing novel therapeutics against cancer

Cancer is one of the lethal diseases that arise due to the molecular alterations in the cell. One of those alterations associated with cancer corresponds to differential expression of Farnesoid X receptor (FXR), a nuclear receptor regulating bile, cholesterol homeostasis, lipid, and glucose metabolism. FXR is known to regulate several diseases, including cancer and cardiovascular diseases, the two highly reported causes of mortality globally. Recent studies have shown the association of FXR overexpression with cancer development and progression in different types of cancers of breast, lung, pancreas, and oesophagus. It has also been associated with tissue-specific and cell-specific roles in various cancers. It has been shown to modulate several cell-signalling pathways such as EGFR/ERK, NF-κB, p38/MAPK, PI3K/AKT, Wnt/β-catenin, and JAK/STAT along with their targets such as caspases, MMPs, cyclins; tumour suppressor proteins like p53, C/EBPβ, and p-Rb; various cytokines; EMT markers; and many more. Therefore, FXR has high potential as novel biomarkers for the diagnosis, prognosis, and therapy of cancer. Thus, the present review focuses on the diverse role of FXR in different cancers and its agonists and antagonists.

The role of farnesoid X receptor in metabolic diseases, and gastrointestinal and liver cancer

Farnesoid X receptor (FXR) is a ligand-activated transcription factor involved in the control of bile acid (BA) synthesis and enterohepatic circulation. FXR can influence glucose and lipid homeostasis. Hepatic FXR activation by obeticholic acid is currently used to treat primary biliary cholangitis. Late-stage clinical trials investigating the use of obeticholic acid in the treatment of nonalcoholic steatohepatitis are underway. Mouse models of metabolic disease have demonstrated that inhibition of intestinal FXR signalling reduces obesity, insulin resistance and fatty liver disease by modulation of hepatic and gut bacteria-mediated BA metabolism, and intestinal ceramide synthesis. FXR also has a role in the pathogenesis of gastrointestinal and liver cancers. Studies using tissue-specific and global Fxr-null mice have revealed that FXR acts as a suppressor of hepatocellular carcinoma, mainly through regulating BA homeostasis. Loss of whole-body FXR potentiates progression of spontaneous colorectal cancer, and obesity-induced BA imbalance promotes intestinal stem cell proliferation by suppressing intestinal FXR in Apc^min/+ mice. Owing to altered gut microbiota and FXR signalling, changes in overall BA levels and specific BA metabolites probably contribute to enterohepatic tumorigenesis. Modulating intestinal FXR signalling and altering BA metabolites are potential strategies for gastrointestinal and liver cancer prevention and treatment. In this Review, studies on the role of FXR in metabolic diseases and gastrointestinal and liver cancer are discussed, and the potential for development of targeted drugs are summarized.

The critical role of FXR is associated with the regulation of autophagy and apoptosis in the progression of AKI to CKD

Autophagy is important for cells to break down and recycle cellular proteins, remove damaged organelles, and especially, for recovery from acute kidney injury (AKI). Despite research on the role and cellular mechanism of autophagy in AKI, the role of autophagy in the progression to chronic kidney disease (CKD) remains poorly understood. Here, using farnesoid X receptor (FXR) knockout (KO) mice, we determined whether FXR prevents the progression of AKI to CKD after renal ischemic-reperfusion (such as I/R) injury through the regulation of renal autophagy and apoptosis. FXR regulated genes that participate in renal autophagy under feeding and fasting conditions, such as hepatic autophagy, and the activation of FXR by agonists, such as GW4064 and INT-747, attenuated the increased autophagy and apoptosis of hypoxia-induced human renal proximal tubule epithelial (HK2) cells. The expression levels of autophagy-related and apoptosis-related proteins in FXR KO mice were increased compared with those in wild-type (WT) mice. We also showed that the increase in reactive oxidative species (ROS) in hypoxia-treated HK2 cells was attenuated by treatment with FXR agonist or by FXR overexpression, and that the level of ROS was elevated in FXR-deficient cells and mice. At 28 days after I/R injury, the autophagy levels were still elevated in FXR KO mice, and the expression levels of fibrosis-related proteins and ROS deposits were higher than those in WT mice. In conclusion, the regulation of renal autophagy and apoptosis by FXR may be a therapeutic target for the early stages of kidney damage, and the progression of AKI to CKD.

Nuclear receptors in the kidney during health and disease

Over the last 30 years, nuclear receptors (NRs) have been increasingly recognized as key modulators of systemic homeostasis and as contributing factors in many diseases. In the kidney, NRs play numerous important roles in maintaining homeostasis-many of which continue to be unraveled. As "master regulators", these important transcription factors integrate and coordinate many renal processes such as circadian responses, lipid metabolism, fatty acid oxidation, glucose handling, and inflammatory responses. The use of recently-developed genetic tools and small molecule modulators have allowed for detailed studies of how renal NRs contribute to kidney homeostasis. Importantly, while NRs are intimately involved in proper kidney function, they are also implicated in a variety of renal diseases such as diabetes, acute kidney injury, and other conditions such as aging. In the last 10 years, our understanding of renal disease etiology and progression has been greatly shaped by knowledge regarding how NRs are dysregulated in these conditions. Importantly, NRs have also become attractive therapeutic targets for attenuation of renal diseases, and their modulation for this purpose has been the subject of intense investigation. Here, we review the role in health and disease of six key renal NRs including the peroxisome proliferator-activated receptors (PPAR), estrogen-related receptors (ERR), the farnesoid X receptors (FXR), estrogen receptors (ER), liver X receptors (LXR), and vitamin D receptors (VDR) with an emphasis on recent findings over the last decade. These NRs have generated a wealth of data over the last 10 years that demonstrate their crucial role in maintaining normal renal homeostasis as well as their capacity to modulate disease progression.

trans-Chalcone inhibits high-fat diet-induced disturbances in FXR/SREBP-1c/FAS and FXR/Smad-3 pathways in the kidney of rats

High-fat diet (HFD) intake is linked to chronic kidney disease. Farnesoid X receptor (FXR) controls the renal lipid metabolism and fibrosis. The purpose of the current study was to evaluate the possible impacts of trans-chalcone on HFD-induced changes in renal lipid metabolism and Smad-3 expression through the regulation of FXR expression. To this aim, 28 rats were randomly divided into control, chalcone, HFD, and HFD + chalcone groups. At the end of treatments, renal FXR, sterol regulatory element-binding protein (SREBP)-1c, fatty acid synthase (FAS), Smad-3, and neutrophil gelatinase-associated lipocalin (NGAL) expression levels were assayed. Moreover, insulin sensitivity check index (QUICKI) was calculated. trans-Chalcone significantly inhibited HFD-induced reduction of insulin sensitivity. Moreover, HFD decreased the FXR expression, and trans-chalcone reversed this change. trans-Chalcone also inhibited HFD-induced increases in expression levels of SREBP-1c, FAS, Smad-3, and NGAL. Therefore, trans-chalcone, as a renoprotective agent, inhibits HFD-induced disturbances in FXR/SREBP-1c/FAS and FXR/Smad-3 pathways. PRACTICAL APPLICATIONS: Non-alcoholic fatty liver disease and metabolic syndrome, two health concerns with increasing prevalence, are known as important risk factors for chronic kidney disease. The current study indicated the preventive effect of trans-chalcone administration on HFD-induced disturbances in renal FXR/SREBP-1c/FAS and FXR/Smad-3 pathways. According to these results, trans-chalcone can be regarded as a renoprotective functional food component that can protect individuals with metabolic syndrome against chronic renal disease.

Discovery, Structural Refinement and Therapeutic Potential of Farnesoid X Receptor Activators

Farnesoid X receptor acts as bile acid sensing transcription factor and has been identified as valuable molecular drug target to treat severe liver disorders, such as non-alcoholic steatohepatitis (NASH). Preclinical and clinical data indicate anti-fibrotic effects obtained with FXR activation that also appear promising for other fibrotic diseases beyond NASH. Strong efforts in FXR ligand discovery have yielded potent steroidal and non-steroidal FXR activators, some of which have been studied in clinical trials. While the structure–activity relationship of some FXR agonist frameworks have been studied extensively, the structural diversity of potent FXR activator chemotypes is still limited to a handful of well-studied compound classes. Together with safety concerns related to full therapeutic activation of FXR, this indicates the need for novel innovative FXR ligands with selective modulatory properties. This chapter evaluates FXR's value as drug target with emphasis on fibrotic diseases, analyses FXR ligand recognition and requirements and focuses on the discovery and structural refinement of leading FXR activator chemotypes.

The farnesoid X receptor agonist EDP-305 reduces interstitial renal fibrosis in a mouse model of unilateral ureteral obstruction

Farnesoid X receptor (FXR) is a nuclear receptor that has emerged as a key regulator in the maintenance of hepatic steatosis, inflammation, and fibrosis. However, the role of FXR in renal fibrosis remains to be established. Here, we investigate the effects of the FXR agonist EDP-305 in a mouse model of tubulointerstitial fibrosis via unilateral ureteral obstruction (UUO). Male C57Bl/6 mice received a UUO on their left kidney. On postoperative d 4, mice received daily treatment by oral gavage with either vehicle control (0.5% methylcellulose) or 10 or 30 mg/kg EDP-305. All animals were euthanized on postoperative d 12. EDP-305 dose-dependently decreased macrophage infiltration as measured by the F4/80 staining area and proinflammatory cytokine gene expression. EDP-305 also dose-dependently reduced interstitial fibrosis as assessed by morphometric quantification of the collagen proportional area and kidney hydroxyproline levels. Finally, yes-associated protein (YAP) activation, a major driver of fibrosis, increased after UUO injury and was diminished by EDP-305 treatment. Consistently, EDP-305 decreased TGF-β1-induced YAP nuclear localization in human kidney 2 cells by increasing inhibitory YAP phosphorylation. YAP inhibition may be a novel antifibrotic mechanism of FXR agonism, and EDP-305 could be used to treat renal fibrosis.-Li, S., Ghoshal, S., Sojoodi, M., Arora, G., Masia, R., Erstad, D. J., Ferriera, D. S., Li, Y., Wang, G., Lanuti, M., Caravan, P., Or, Y. S., Jiang, L.-J., Tanabe, K. K., Fuchs, B. C. The farnesoid X receptor agonist EDP-305 reduces interstitial renal fibrosis in a mouse model of unilateral ureteral obstruction.

Protein O-GlcNAcylation Is Essential for the Maintenance of Renal Energy Homeostasis and Function via Lipolysis during Fasting and Diabetes

BACKGROUND

Energy metabolism in proximal tubular epithelial cells (PTECs) is unique, because ATP production largely depends on lipolysis in both the fed and fasting states. Furthermore, disruption of renal lipolysis is involved in the pathogenesis of diabetic tubulopathy. Emerging evidence suggests that protein O-GlcNAcylation, an intracellular nutrient-sensing system, may regulate a number of metabolic pathways according to changes in nutritional status. Although O-GlcNAcylation in PTECs has been demonstrated experimentally, its precise role in lipolysis in PTECs is unclear.

METHODS

To investigate the mechanism of renal lipolysis in PTECs-specifically, the role played by protein O-GlcNAcylation-we generated mice with PTECs deficient in O-GlcNAc transferase (Ogt). We analyzed their renal phenotypes during ad libitum feeding, after prolonged fasting, and after mice were fed a high-fat diet for 16 weeks to induce obesity and diabetes.

RESULTS

Although PTEC-specific Ogt-deficient mice lacked a marked renal phenotype during ad libitum feeding, after fasting 48 hours, they developed Fanconi syndrome-like abnormalities, PTEC apoptosis, and lower rates of renal lipolysis and ATP production. Proteomic analysis suggested that farnesoid X receptor-dependent upregulation of carboxylesterase-1 is involved in O-GlcNAcylation's regulation of lipolysis in fasted PTECs. PTEC-specific Ogt-deficient mice with diabetes induced by a high-fat diet developed severe tubular cell damage and enhanced lipotoxicity.

CONCLUSIONS

Protein O-GlcNAcylation is essential for renal lipolysis during prolonged fasting and offers PTECs significant protection against lipotoxicity in diabetes.

The farnesoid X receptor: a potential target for expanding the therapeutic arsenal against kidney disease

INTRODUCTION

Farnesoid X receptor (FXR) is a nuclear bile acid (BA) receptor widely distributed among tissues, a major sensor of BA levels, primary suppressor of hepatic BA synthesis and secondary regulator of lipid metabolism and inflammation. Chronic kidney disease is a common, multifactorial condition with metabolic and inflammatory causes and implications. An array of natural and synthetic FXR agonists has been developed, but not yet studied clinically in kidney disease. Areas covered: Following a summary of FXR's physiological functions in the kidney, we discuss its effects in renal disease with emphasis on chronic and acute kidney disease, chemotherapy-induced nephrotoxicity, and renal neoplasia. Most information is derived from animal models; no relevant clinical study has been conducted to date. Expert opinion: Most available preclinical data indicates a promising outlook for clinical research in this direction. We believe FXR agonism to be an auspicious approach to treating renal disease, considering that multifactorial diseases call for ideally wide-reaching therapies.

Genistein attenuates renal fibrosis in streptozotocin‑induced diabetic rats

The present study aimed to investigate the antifibrogenic effects of genistein (GEN) on the kidney in streptozotocin (STZ)-induced diabetic rats and to determine the associated mechanisms. Rats were randomized into four groups: Normal control (N), STZ (S), L (STZ + low-dose GEN) and H (STZ + high-dose GEN). After 8 weeks, the fasting blood glucose (FBG) level, the ratio of kidney weight to body weight (renal index), 24-h urine protein, blood urea nitrogen (BUN), serum creatinine (SCr), renal total antioxidant capacity (T-AOC), superoxide dismutase (SOD), lipid peroxidation (LPO), malondialdehyde (MDA) and hydroxyproline (Hyp) contents were measured. The histomorphology and ultrastructure of the kidney were also assessed. In addition, mRNA expression levels of transforming growth factor-β1 (TGF-β1) and protein expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), NAD(P)H:quinone oxidoreductase 1 (NQO1), TGF-β1, mothers against decapentaplegic homolog 3 (Smad3), phosphorylated (p)-Smad3 and collagen IV were estimated. Compared with group N, the levels of FBG, renal index, 24-h urine protein, BUN, SCr, LPO, MDA and Hyp were increased, whereas the levels of T-AOC and SOD were decreased in group S. The structure of renal tissue was damaged, and the expression of Nrf2, HO-1 and NQO1 were reduced, whereas the expression of TGF-β1, Smad3, p-Smad3 and collagen IV were increased in group S. Compared with group S, the aforementioned indices were improved in groups L and H. In conclusion, GEN exhibited reno-protective effects in diabetic rats and its mechanisms may be associated with the inhibition of oxidative stress by activating the Nrf2-HO-1/NQO1 pathway, and the alleviation of renal fibrosis by suppressing the TGF-β1/Smad3 pathway.

Dicer deficiency in proximal tubules exacerbates renal injury and tubulointerstitial fibrosis and upregulates Smad2/3

Renal fibrosis is a common pathological feature in chronic kidney disease (CKD), including diabetic kidney disease (DKD) and obstructive nephropathy. Multiple microRNAs have been implicated in the pathogenesis of both DKD and obstructive nephropathy, although the overall role of microRNAs in tubular injury and renal fibrosis in CKD is unclear. Dicer (a key RNase III enzyme for microRNA biogenesis) was specifically ablated from kidney proximal tubules in mice via the Cre-lox system to deplete micoRNAs. Proximal tubular Dicer knockout (PT- Dicer KO) mice and wild-type (WT) littermates were subjected to streptozotocin (STZ) treatment to induce DKD or unilateral ureteral obstruction (UUO) to induce obstructive nephropathy. Renal hypertrophy, renal tubular apoptosis, kidney inflammation, and tubulointerstitial fibrosis were examined. Compared with WT mice, PT- Dicer KO mice showed more severe tubular injury and renal inflammation following STZ treatment. These mice also developed higher levels of tubolointerstitial fibrosis. Meanwhile, PT- Dicer KO mice had a significantly higher Smad2/3 expression in kidneys than WT mice (at 6 mo of age) in both control and STZ-treated mice. Similarly, UUO induced more severe renal injury, inflammation, and interstitial fibrosis in PT- Dicer KO mice than WT. Although we did not detect obvious Smad2/3 expression in sham-operated mice (2-3 mo old), significantly more Smad2/3 was induced in obstructed PT- Dicer KO kidneys. These results supported a protective role of Dicer-dependent microRNA synthesis in renal injury and fibrosis development in CKD, specifically in DKD and obstructive nephropathy. Depletion of Dicer and microRNAs may upregulate Smad2/3-related signaling pathway to enhance the progression of CKD.

Update on FXR Biology: Promising Therapeutic Target?

Farnesoid X receptor (FXR), a metabolic nuclear receptor, plays critical roles in the maintenance of systemic energy homeostasis and the integrity of many organs, including liver and intestine. It regulates bile acid, lipid, and glucose metabolism, and contributes to inter-organ communication, in particular the enterohepatic signaling pathway, through bile acids and fibroblast growth factor-15/19 (FGF-15/19). The metabolic effects of FXR are also involved in gut microbiota. In addition, FXR has various functions in the kidney, adipose tissue, pancreas, cardiovascular system, and tumorigenesis. Consequently, the deregulation of FXR may lead to abnormalities of specific organs and metabolic dysfunction, allowing the protein as an attractive therapeutic target for the management of liver and/or metabolic diseases. Indeed, many FXR agonists have been being developed and are under pre-clinical and clinical investigations. Although obeticholic acid (OCA) is one of the promising candidates, significant safety issues have remained. The effects of FXR modulation might be multifaceted according to tissue specificity, disease type, and/or energy status, suggesting the careful use of FXR agonists. This review summarizes the current knowledge of systemic FXR biology in various organs and the gut–liver axis, particularly regarding the recent advancement in these fields, and also provides pharmacological aspects of FXR modulation for rational therapeutic strategies and novel drug development.

Genetic contributions to lupus nephritis in a multi-ethnic cohort of systemic lupus erythematous patients

OBJECTIVE

African Americans, East Asians, and Hispanics with systemic lupus erythematous (SLE) are more likely to develop lupus nephritis (LN) than are SLE patients of European descent. The etiology of this difference is not clear, and this study was undertaken to investigate how genetic variants might explain this effect.

METHODS

In this cross-sectional study, 1244 SLE patients from multiethnic case collections were genotyped for 817,810 single-nucleotide polymorphisms (SNPs) across the genome. Continental genetic ancestry was estimated utilizing the program ADMIXTURE. Gene-based testing and pathway analysis was performed within each ethnic group and meta-analyzed across ethnicities. We also performed candidate SNP association tests with SNPs previously established as risk alleles for SLE, LN, and chronic kidney disease (CKD). Association testing and logistic regression models were performed with LN as the outcome, adjusted for continental ancestries, sex, disease duration, and age.

RESULTS

We studied 255 North European, 263 South European, 238 Hispanic, 224 African American and 264 East Asian SLE patients, of whom 606 had LN (48.7%). In genome-wide gene-based and candidate SNP analyses, we found distinct genes, pathways and established risk SNPs associated with LN for each ethnic group. Gene-based analyses showed significant associations between variation in ZNF546 (p = 1.0E-06), TRIM15 (p = 1.0E-06), and TRIMI0 (p = 1.0E-06) and LN among South Europeans, and TTC34 (p = 8.0E-06) was significantly associated with LN among Hispanics. The SNP rs8091180 in NFATC1 was associated with LN (OR 1.43, p = 3.3E-04) in the candidate SNP meta-analysis with the highest OR among African-Americans (OR 2.17, p = 0.0035).

CONCLUSION

Distinct genetic factors are associated with the risk of LN in SLE patients of different ethnicities. CKD risk alleles may play a role in the development of LN in addition to SLE-associated risk variants. These findings may further explain the clinical heterogeneity of LN risk and response to therapy observed between different ethnic groups.

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.

Role of Smad3 signaling in the epithelial‑mesenchymal transition of the lens epithelium following injury

Transforming growth factor-β (TGF-β) is important in the development of posterior capsule opacification (PCO), and inhibition of the TGF-β pathway may represent a novel method of treating PCO. Drosophila protein, mothers against decapentaplegic homolog 3 (Smad3) is a phosphorylated receptor-activated Smad required for the transmission of TGF-β signals. Smad3 knockout (KO) disturbs the activation of TGF-β signaling, thus inhibiting the onset of PCO. In the present study, lens epithelial cell (LEC) damage induced by extracapsular cataract extraction was simulated by puncture of the anterior capsule using a 26-gauge hypodermic needle. The effect of Smad3 in the trauma-induced epithelial-mesenchymal transition (EMT) of the lens epithelium in Smad3-KO and wild-type (WT) mice was then observed. The expression levels of EMT markers and extracellular matrix components were measured in the two groups by reverse transcription-quantitative polymerase chain reaction analysis, western blot analysis and immunofluorescence staining. Apoptosis was also detected in the punctured anterior capsule. The Smad3-KO mice exhibited lower expression levels of α-smooth muscle actin, lumican, osteopontin, fibronectin and collagen, compared with the WT mice. Additionally, the Smad3-KO mice exhibited a higher percentage of apoptotic cells than the WT mice. Smad3 signaling was associated with the induction of trauma-induced EMT, and Smad3 KO interfered with TGF-β signaling pathway activation, but did not completely inhibit the trauma-induced EMT in LECs. Therefore, Smad3 may be a target in the treatment of PCO and other fibrosis-related diseases.

Therapeutic pro-fibrogenic signaling pathways in fibroblasts

Myofibroblasts (MFs) play a critical role in the progression of chronic inflammatory and fibroproliferative diseases in different tissues/organs, whatever the etiology. Fibrosis is preceded and sustained by persistent injury and inflammatory response in a profibrogenic scenario involving mutual interactions, operated by several mediators and pathways, of MFs and related precursor cells with innate immunity cells and virtually any cell type in a defined tissue. These interactions, mediators and related signaling pathways are critical in initiating and perpetuating the differentiation of precursor cells into MFs that in different tissues share peculiar traits and phenotypic responses, including the ability to proliferate, produce ECM components, migrate and contribute to the modulation of inflammatory response and tissue angiogenesis. Literature studies related to liver, lung and kidney fibrosis have outlined a number of MF-related core regulatory fibrogenic signaling pathways conserved across these different organs and potentially targetable in order to develop effective antifibrotic therapeutic strategies.