Time course of cytokine mRNA expression in kidneys of rats with unilateral ureteral obstruction

Obstructive nephropathy and molecular pathophysiology of renal interstitial fibrosis

The kidneys play a key role in maintaining total body homeostasis. The complexity of this task is reflected in the unique architecture of the organ. Ureteral obstruction greatly affects renal physiology by altering hemodynamics, changing glomerular filtration and renal metabolism, and inducing architectural malformations of the kidney parenchyma, most importantly renal fibrosis. Persisting pathological changes lead to chronic kidney disease, which currently affects ∼10% of the global population and is one of the major causes of death worldwide. Studies on the consequences of ureteral obstruction date back to the 1800s. Even today, experimental unilateral ureteral obstruction (UUO) remains the standard model for tubulointerstitial fibrosis. However, the model has certain limitations when it comes to studying tubular injury and repair, as well as a limited potential for human translation. Nevertheless, ureteral obstruction has provided the scientific community with a wealth of knowledge on renal (patho)physiology. With the introduction of advanced omics techniques, the classical UUO model has remained relevant to this day and has been instrumental in understanding renal fibrosis at the molecular, genomic, and cellular levels. This review details key concepts and recent advances in the understanding of obstructive nephropathy, highlighting the pathophysiological hallmarks responsible for the functional and architectural changes induced by ureteral obstruction, with a special emphasis on renal fibrosis.

Cold Shock Domain Protein DbpA Orchestrates Tubular Cell Damage and Interstitial Fibrosis in Inflammatory Kidney Disease

DNA-binding protein A (DbpA) belongs to the Y-box family of cold shock domain proteins that exert transcriptional and translational activities in the cell via their ability to bind and regulate mRNA. To investigate the role of DbpA in kidney disease, we utilized the murine unilateral ureter obstruction (UUO) model, which recapitulates many features of obstructive nephropathy seen in humans. We observed that DbpA protein expression is induced within the renal interstitium following disease induction. Compared with wild-type animals, obstructed kidneys from Ybx3-deficient mice are protected from tissue injury, with a significant reduction in the number of infiltrating immune cells as well as in extracellular matrix deposition. RNAseq data from UUO kidneys show that Ybx3 is expressed by activated fibroblasts, which reside within the renal interstitium. Our data support a role for DbpA in orchestrating renal fibrosis and suggest that strategies targeting DbpA may be a therapeutic option to slow disease progression.

The Role of Connexin 43 in Renal Disease: Insights from In Vivo Models of Experimental Nephropathy

Renal disease is a major public health challenge since its prevalence has continuously increased over the last decades. At the end stage, extrarenal replacement therapy and transplantation remain the only treatments currently available. To understand how the disease progresses, further knowledge of its pathophysiology is needed. For this purpose, experimental models, using mainly rodents, have been developed to unravel the mechanisms involved in the initiation and progression of renal disease, as well as to identify potential targets for therapy. The gap junction protein connexin 43 has recently been identified as a novel player in the development of kidney disease. Its expression has been found to be altered in many types of human renal pathologies, as well as in different animal models, contributing to the activation of inflammatory and fibrotic processes that lead to renal damage. Furthermore, Cx43 genetic, pharmacogenetic, or pharmacological inhibition preserved renal function and structure. This review summarizes the existing advances on the role of this protein in renal diseases, based mainly on different in vivo animal models of acute and chronic renal diseases.

ASK1/p38 signaling in renal tubular epithelial cells promotes renal fibrosis in the mouse obstructed kidney

Stress-activated kinases p38 MAPK and JNK promote renal fibrosis; however, how the pathways by which these kinases are activated in kidney disease remain poorly defined. Apoptosis signal-regulating kinase 1 (ASK1/MAPKKK5) is a member of the MAPKKK family that can induce activation of p38 and JNK. The present study examined whether ASK1 induces p38/JNK activation and renal fibrosis in unilateral ureteric obstruction (UUO) using wild-type (WT) and Ask1-deficient ( Ask1−/−) mice. Basal p38 and JNK activation in WT kidneys was increased three- to fivefold in day 7 UUO mice in association with renal fibrosis. In contrast, there was no increase in p38 activation in Ask1−/− UUO mice, whereas JNK activation was only partially increased. The progressive increase in kidney collagen (hydroxyproline) content seen on days 7 and 12 of UUO in WT mice was significantly reduced in Ask1−/− UUO mice in association with reduced α-smooth muscle actin-positive myofibroblast accumulation. However, cultured WT and Ask1−/− renal fibroblasts showed equivalent proliferation and matrix production, indicating that ASK1 acts indirectly on fibroblasts. Tubular epithelial cells are the main site of p38 activation in the obstructed kidney. Angiotensin II and H2O2, but not IL-1 or lipopolysaccharide, induced p38 activation and upregulation of transforming growth factor-β1, platelet-derived growth factor-B, and monocyte chemoattractant protein-1 production was suppressed in Ask1−/− tubular epithelial cells. In addition, macrophage accumulation was significantly inhibited in Ask1−/− UUO mice. In conclusion, ASK1 is an important upstream activator of p38 and JNK signaling in the obstructed kidney, and ASK1 is a potential therapeutic target in renal fibrosis.

Targeting connexin 43 protects against the progression of experimental chronic kidney disease in mice

Excessive recruitment of monocytes and progression of fibrosis are hallmarks of chronic kidney disease (CKD). Recently we reported that the expression of connexin 43 (Cx43) was upregulated in the kidney during experimental nephropathy. To investigate the role of Cx43 in the progression of CKD, we interbred RenTg mice, a genetic model of hypertension-induced CKD, with Cx43+/- mice. The renal cortex of 5-month-old RenTgCx43+/- mice showed a marked decrease of cell adhesion markers leading to reduced monocyte infiltration and interstitial renal fibrosis compared with their littermates. In addition, functional and histological parameters such as albuminuria and glomerulosclerosis were ameliorated in RenTgCx43+/- mice. Interestingly, treatment with Cx43 antisense produced remarkable improvement of renal function and structure in 1-year-old RenTg mice. Similar results were found in Cx43+/- or wild-type mice treated with Cx43 antisense after obstructive nephropathy. Furthermore, in these mice, Cx43 antisense attenuated E-cadherin downregulation and phosphorylation of the transcription factor Sp1 by the ERK pathway resulting in decreased transcription of type I collagen gene. Interestingly, Cx43-specific blocking peptide inhibited monocyte adhesion in activated endothelium and profibrotic pathways in tubular cells. Cx43 was highly increased in biopsies of patients with CKD. Thus, Cx43 may represent a new therapeutic target against the progression of CKD.

Antifibrotic effects of pirfenidone in rat proximal tubular epithelial cells

OBJECTIVE

Renal fibrosis is a common cause of renal dysfunction with chronic kidney disease. We previously investigated the renoprotective effects of the antifibrotic agent pirfenidone in a rat model of subtotal nephrectomy. Here, we further evaluated the antifibrotic effects of pirfenidone in rat proximal tubular epithelial cells.

METHODS

NRK52E cells were incubated in a medium containing either transforming growth factor (TGF)-β1 (3 ng/mL) or platelet-derived growth factor (PDGF)-BB (5 Ang/mL) or both, with or without pirfenidone (0.1-1 mmol/L), for 24 h to assess mRNA expression, for 48 h to assess protein production, and for 1 h or various time (5-120 min) to assess phosphorylation of signal kinase.

RESULTS

TGF-β1, a key mediator in renal fibrosis, induced increases in the mRNA expression of various profibrotic factors and extracellular matrix, including plasminogen activator inhibitor type 1 (PAI-1), fibronectin, type 1 collagen, and connective tissue growth factor (CTGF)-increases which pirfenidone significantly inhibited. Specifically, pirfenidone potently inhibited TGF-β1-induced increases in the mRNA expression and protein secretion of PAI-1, an effect mediated, at least in part, via the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling. Further, PDGF-BB, which has been implicated in renal interstitial fibrosis, potently activated PAI-1 expression under TGF-β1 stimulation, and pirfenidone significantly inhibited TGF-β1- and PDGF-BB-induced increases in PAI-1 expression.

CONCLUSIONS

Taken together, these results suggest that TGF-β1 closely correlates with renal fibrosis in cooperation with several fibrosis-promoting molecules, such as PAI-1 and PDGF, in rat proximal tubular epithelial cells, and pirfenidone inhibits TGF-β1-induced fibrosis cascade and will therefore likely exert antifibrotic effects under pathological conditions.

Effect of the inosine 5'-monophosphate dehydrogenase inhibitor BMS-566419 on renal fibrosis in unilateral ureteral obstruction in rats

Chronic allograft nephropathy (CAN) is a major cause of late allograft loss. One morphological characteristic of CAN is renal interstitial fibrosis. Mycophenolate mofetil (MMF), the inosine 5'-monophosphate dehydrogenase (IMPDH) inhibitor, has been reported to attenuate the progression of renal interstitial fibrosis. However, the question of whether the newly synthesized IMPDH inhibitors with structures different from MMF have an antifibrotic effect remains unanswered. We evaluated the antifibrotic effects of BMS-566419, a chemically synthesized IMPDH inhibitor, using an experimental rat model, unilateral ureteral obstruction (UUO), in comparison with those of MMF. Expression levels of monocyte chemoattractant protein-1 (MCP-1) and transforming growth factor-beta1 (TGF-β1), which play important roles in UUO-induced renal fibrosis, were also investigated to determine the mechanism by which BMS-566419 affects the progression of renal fibrosis. After 14 days of UUO, interstitial fibrosis was frequently observed in the renal cortex of rats administered vehicle control. BMS-566419 by oral administration showed a significant and dose-dependent suppressive effect on UUO-induced renal fibrosis in histopathological experiments. BMS-566419 treatment also decreased collagen content, as indicated by hydroxyproline concentration, and the expression of collagen type 1 mRNA. BMS-566419 also decreased the expression of mRNA for both MCP-1 and TGF-β1. The antifibrotic effects of treatment with BMS-566419 at 60 mg/kg seemed comparable to those with MMF at 40 mg/kg. These results suggest that BMS-566419 and other chemically synthesized IMPDH inhibitors have beneficial pharmacological effects similar to those of MMF, and are potential pharmaceutical candidates in the treatment of fibrotic renal disease, including CAN.

Prevention of renal interstitial fibrosis via histone deacetylase inhibition in rats with unilateral ureteral obstruction

Acute rejection following renal transplantation has become manageable with the introduction of calcineurin inhibitors, FK506 and cyclosporine A. However, chronic allograft dysfunction accompanied by renal interstitial fibrosis, which induces graft loss, remains unresolved. Here, we evaluated the effect of FR276457, a pan-histone deacetylase (HDAC) inhibitor, on interstitial fibrosis in the injured kidneys of a rat model of unilateral ureteral obstruction. The injured kidneys, harvested on Day 14 following the operation, showed progression of interstitial fibrosis, increases of hydroxyproline contents, and mRNA expression of collagen type Ialpha1 and monocyte chemotactic protein 1 (MCP-1). However, these changes were found to be prevented with daily oral administration of FR276457. In addition, given that MCP-1 is believed to contribute to progressive fibrosis, we investigated the direct effect of FR276457 on MCP-1 production by activated THP-1 cells in vitro. Results showed that FR276457 administration decreased MCP-1 production in these cells in a concentration-dependent manner. Findings from the present study suggested that a pan-HDAC inhibitor may exert a prophylactic effect against renal interstitial fibrosis by inhibiting MCP-1 production.

IN-1130, a novel transforming growth factor-β type I receptor kinase (ALK5) inhibitor, suppresses renal fibrosis in obstructive nephropathy

The transforming growth factor-beta (TGF-beta) plays a central role in the progression of renal fibrosis. TGF-beta transduces its signal through the activin receptor-like kinase (ALK)5. IN-1130, a novel small molecule ALK5 inhibitor, inhibited the purified kinase domain of ALK5-mediated Smad3 phosphorylation with an IC(50) value of 5.3 nM. IN-1130 proved to be highly selective in a panel of 27 serine/threonine and tyrosine kinases including p38alpha mitogen-activated protein kinase. We evaluated the efficacy of IN-1130 to block renal fibrogenesis induced by unilateral ureteral obstruction (UUO) in rats. Either vehicle (saline) or IN-1130 (10 and 20 mg/kg/day) was intraperitoneally administered to UUO rats for 7 and 14 days. Phosphorylated Smad2 (pSmad2) and markers of fibrosis were analyzed in kidney tissues. In UUO control kidneys, interstitial fibrosis including tubular atrophy, loss and dilation, inflammatory cell infiltration, and fibroblast cell proliferation was prominent. These morphological changes were notably reduced by IN-1130 treatment. IN-1130 decreased levels of TGF-beta1 messenger RNA (mRNA), type I collagen mRNA, and pSmad2, compared to UUO control rats. As determined by measuring the hydroxyproline content, total kidney collagen amount was increased in UUO control kidneys, but significantly reduced by IN-1130 treatment, which was comparable to results of histochemical staining for collagen. IN-1130 also suppressed the expression of alpha-smooth muscle actin (alpha-SMA) and fibronectin in UUO kidneys. Our results show that IN-1130 suppressed the fibrogenic process of UUO, further underscoring the potential clinical benefits of IN-1130 in the treatment of renal fibrosis.

The interaction of urinary tract infection and renal insufficiency

Urinary tract infections (UTIs) are among the most common infections caused by microorganisms, and pyelonephritis is the most severe infection of the urogenital tract. The risk of developing chronic renal insufficiency due to a UTI without other risk factors is low. The pathogenicity and virulence of the infective microorganisms as well as the efficiency of local or systemic defence mechanisms determine the course and severity of the disease. Virulence properties (adhesins, toxins, capsule, iron uptake) are encoded by genomic structures and the determination of virulence is influenced by the host situation. In renal insufficiency, a variety of quite different substances (uraemic toxins, betaine, amino acids, creatinine, urea, glucose) influence the microbial environment. Defence factors (Tamm-Horsfall protein, defensin, phagocytic activity of granulocytes) and underlying anatomical lesions as well as pre-existing renal disease determine the severity of UTI and the prognosis of renal insufficiency.

Imatinib mesylate blocks a non-Smad TGF-beta pathway and reduces renal fibrogenesis in vivo

Transforming growth factor-beta (TGF-beta) is the single most important cytokine promoting renal fibrogenesis. p21-activated kinase-2 (PAK2) and activation of abelson nonreceptor tyrosine kinase (c-abl) have been shown recently to be smad-independent, fibroblast-specific targets downstream of the activated TGF-beta receptor. In the current study we show that in cultured NRK49F-renal fibroblasts (but not in tubular or mesangial cells) TGF-beta similarly activates PAK2 as well as c-abl and induces cell proliferation. Inhibition of the c-abl kinase with imatinib mesylate prevents increased proliferation after TGF-beta addition without affecting PAK2. These in vitro findings were extended to rats with unilateral obstructive nephropathy, a disease model of TGF-beta-driven renal fibrogenesis. In obstructed kidneys, PAK2 and c-abl activity were increased but only c-abl activation was blocked by imatinib. Treatment with imatinib did not prevent renal interstitial infiltration of macrophages or phosphorylation and nuclear translocation of smad2/3 in obstructed kidneys. In contrast, imatinib substantially inhibited an increase in the number of interstitial fibroblasts and myofibroblasts and reduced the expression and interstitial accumulation of collagen type III, collagen type IV and fibronectin. These findings indicate that TGF-beta-induced activation of the nonreceptor c-abl tyrosine kinase regulates fibroblast proliferation and, by this means, is a costimulatory signal in TGF-beta-dependent renal fibrogenesis. Inhibition of c-abl activity with imatinib mesylate ameliorates experimental renal fibrosis in rats.

Soluble fibronectin induces chemokine gene expression in renal tubular epithelial cells

BACKGROUND

Increasing proteinuria in kidney disease is associated with an increased risk of renal failure. Urinary proteins such as albumin induce inflammatory signaling and gene expression in tubular epithelial cells (TECs). Fibronectin is an extracellular matrix protein that can exist in soluble form and is excreted in the urine of patients with glomerular disease.

METHODS

To explore the impact of soluble fibronectin on tubular epithelium, murine TECs were stimulated with soluble fibronectin and chemokine mRNA was determined by RNase protection assay.

RESULTS

Fibronectin induced the expression of inflammatory chemokine genes, including monocyte chemoattractant protein-1 (MCP-1) (CCL2) and macrophage inflammatory protein-2 (MIP-2) within 2 hours in a dose-dependent manner. Phosphorylation of Src family tyrosine kinases was also increased in TECs following exposure to fibronectin. Src tyrosine kinases were involved in the fibronectin activation of MCP-1 since the Src inhibitors SU6656 and PP2 effectively reduced the induction of this chemokine. Fibronectin also induced the phosphorylation of extracellular signal-regulated protein kinase (ERK1/2) within minutes in TECs. The ERK kinase (MEK1/2) inhibitor U0126 inhibited the fibronectin induction of MCP-1 mRNA suggesting that ERK1/2 was also involved in this inflammatory pathway. Furthermore, fibronectin also induced phosphorylation of IkappaBalpha within 20 minutes in TECs. The nuclear factor-kappaB (NF-kappaB) inhibitors N-acetyl-L-cysteine (NAC) and pyrrolidinecarbodithioic acid (PDTC) effectively blocked fibronectin induction of MCP-1 mRNA.

CONCLUSION

Soluble fibronectin activates MCP-1 gene expression in TECs via Src tyrosine kinases, ERK1/2 and NF-kappaB. These data provide further support to the concept that proteinuria per se contributes to the tubulointerstitial injury observed in glomerular disease.

Obstructive Uropathy in Mice and Humans: Potential Role for PDGF-D in the Progression of Tubulointerstitial Injury

ABSTRACT. Tubulointerstitial fibrosis is a major characteristic of progressive renal diseases. Platelet-derived growth factor (PDGF) is a family of growth regulatory molecules consisting of PDGF-A and -B, along with the newly discovered PDGF-C and -D. They signal through cell membrane receptors, PDGF receptor α (PDGF-Rα) and receptor β (PDGF-Rβ). Involvement of PDGF-B and PDGF-Rβ in the initiation and progression of renal fibrosis has been well documented. The authors studied the localization of PDGF ligands and receptors by immunohistochemistry, with emphasis on the role of PDGF-D in murine renal fibrosis induced by unilateral ureteral obstruction (UUO). In mice with UUO,de novoexpression of PDGF-D was detected in interstitial cells at day 4, which increased to maximal expression at day 14. Increased expression of PDGF-B by interstitial cells and in some tubules was observed after day 4. The diseased mice did not show augmentation of PDGF-A or PDGF-C proteins in the areas of fibrosis. PDGF-Rα and -Rβ protein expression was increased in interstitial cells after day 4 and reached maximal expression at day 14. Human renal nephrectomies (n= 10) of chronic obstructive nephropathy demonstrated similarde novoexpression of PDGF-D in interstitial cells, correlating with expression of PDGF-Rβ and PDGF-B, as it did in the murine model. These observations suggest that PDGF-D plays an important role in the pathogenesis of tubulointerstitial injury through binding of PDGF-Rβ in both human obstructive nephropathy and the corresponding murine model of UUO. E-mail: calp@u.washington.edu

An oral adsorbent downregulates renal expression of genes that promote interstitial inflammation and fibrosis in diabetic rats

BACKGROUND/AIMS

An oral adsorbent, AST-120, removes uremic toxins such as indoxyl sulfate, and delays the progression of renal failure. This study was designed to investigate the effects of AST-120 on the molecular basis of interstitial inflammation and fibrosis, using Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of non-insulin-dependent diabetes mellitus.

METHODS

Four weeks after unilateral nephrectomy, the uninephrectomized OLETF (1/2NxOLETF) rats were divided into two groups: AST-120-administered and control 1/2NxOLETF rats. After the administration of AST-120 for 48 weeks, we examined the effects of AST-120 on renal functional, pathological, and gene expressional changes.

RESULTS

The administration of AST-120 to the 1/2NxOLETF rats attenuated the progression of renal dysfunction, proteinuria, glomerular sclerosis, tubular injury, and interstitial inflammation and fibrosis. AST-120 significantly reduced renal expression of intercellular adhesion molecule (ICAM)-1, osteopontin, monocyte chemotactic protein (MCP)-1, and transforming growth factor (TGF)-beta1, as well as clusterin. All the five molecules were expressed mainly in tubular cells. AST-120 also decreased serum and urinary levels of indoxyl sulfate and the overload of indoxyl sulfate in tubular cells.

CONCLUSIONS

AST-120 ameliorates tubulointerstitial injury by reducing renal expression of ICAM-1, osteopontin, MCP-1, TGF-beta1 and clusterin in 1/2NxOLETF rats.

Enhanced chemokine response in experimental acute Escherichia coli pyelonephritis in IL-1beta-deficient mice

The aim of the present study was to investigate the effects of IL-1beta and Escherichia coli on the expression and secretion of MIP-2, the mouse equivalent to human IL-8, MCP-1 and RANTES in the kidneys of mice with acute pyelonephritis. Female Bki NMRI, as well as IL-1beta deficient mice and their wild-type littermates, were transurethrally infected with either E. coli CFT 073 or injected with NaCl 0.9% (w/v) and thereafter obstructed for 6 h. The Bki NMRI mice were killed at 0, 24, 48 h and 6 days and the IL-1beta-deficient mice at 48 h. Chemokine mRNA and protein levels peaked at 24 h for the tested chemokines with the mRNA expression localized in the tubular epithelial cells and for MIP-2 also in neutrophils. Obstruction per se, also induced a chemokine expression similar to E. coli infection although at a lower level. Interestingly, MIP-2 levels were higher in the IL-1beta deficient mice as compared with the wild-type littermates. Likewise, the inflammatory changes were more frequent and, when present, more widespread in the IL-1beta-deficient mice than in the wild-type mice. Stimulation of a human renal tubular epithelial cell line (HREC), A498 and of primary human mesangial cells (HMC) with the same bacterial antigen depicted gene expression of the same chemokines. A rapid release of IL-8 and MCP-1 was observed from both cell types. RANTES response was delayed both in the HREC and the HMC. We conclude that acute E. coli pyelonephritis induces a MIP-2/IL-8, MCP-1 and RANTES expression and secretion localized primarily to the epithelial cells and that this production is confirmed after in vitro stimulation with the same bacterial antigen of human epithelial and mesangial cells. Blockade of induction of chemokine response may thus be an attractive target for possible therapeutic intervention.

Secretion of cytokines by uroepithelial cells stimulated by Escherichia coli and Citrobacter spp

Urinary tract epithelial cells (T 24/83) are able to express interleukin (IL)-6, IL-8, platelet-derived growth factor (PDGF) and tumour necrosis factor-alpha, but not IL-1 beta, IL-2, IL-4 and IL-10 in response to an infection with uropathogenic bacteria. The process of cytokine secretion is time dependent, with a significant increase in the cytokine activity after 60 min. The expression of virulence factors of the bacteria does not seem to play a role. The interaction between bacterial products (e.g. lipopolysaccharide) and/or bacterial adhesion mediated by adhesins and specific receptor molecules of cell surfaces may be responsible for the activity of mediator protein expression in the epithelial cells. The release of PDGF and IL-8 was found to be higher when due to Escherichia coli HB 101 (rough form) than that caused by other bacterial strains. Citrobacter CB 3009 provoked the highest level of IL-6. The PDGF level correlated significantly with IL-6 and IL-8 values (P<0.001). There was a significant correlation between the time-dependent release of IL-6 and IL-8 (P<0.05). In epithelial cytokine response to bacterial infection, the reaction of the epithelial cells may modify themselves (e.g. internalization of bacteria) and the immuno-regulatory processes that are caused by infection and responsible for parenchymal injury.