Propagation and culture of renal fibroblasts

Hypoxia Promotes the Expression of ADAM9 by Tubular Epithelial Cells, Which Enhances Transforming Growth Factor β1 Activation and Promotes Tissue Fibrosis in Patients With Lupus Nephritis

OBJECTIVE

Enhanced expression of transforming growth factor (TGF) β in the kidneys of patients with lupus nephritis (LN) can lead to progressive fibrosis, resulting in end-organ damage. ADAM9 activates TGFβ1 by cleaving the latency-associated peptide (LAP). We hypothesized that ADAM9 in the kidney may accelerate fibrogenesis by activating TGFβ1.

METHODS

We assessed the expression of ADAM9 in the kidneys of mice and humans who were lupus prone. In vitro experiments were conducted using tubular epithelial cells (TECs) isolated from mice and explored the mechanisms responsible for the up-regulation of ADAM9 and the subsequent activation of TGFβ1. To assess the role of ADAM9 in the development of tubular-intestinal fibrosis in individuals with LN, we generated MRL/lpr mice who were Adam9 deficient.

RESULTS

ADAM9 was highly expressed in tubules from MRL/lpr mice. The transcription factor hypoxia-inducible factor-1α was found to promote the transcription of ADAM9 in TECs. TECs from mice who were Adam9 deficient and exposed to the hypoxia mimetic agent dimethyloxalylglycine failed to cleave the LAP to produce bioactive TGFβ1 from latent TGFβ1. Coculture of TECs from mice who were Adam9 deficient with fibroblasts in the presence of dimethyloxalylglycine and latent TGFβ1 produced decreased amounts of type I collagen and α-smooth muscle actin (SMA) by fibroblasts. MRL/lpr mice who were Adam9 deficient showed reduced interstitial fibrosis. At the translational level, ADAM9 expression in tissues and urine of patients with LN was found to increase.

CONCLUSION

Hypoxia promotes the expression of ADAM9 by TECs, which is responsible for the development of interstitial fibrosis in patients with LN by enhancing the TGFβ1 activation, which promotes fibroblasts to produce collagen and α-SMA.

Myofibroblast depletion reduces kidney cyst growth and fibrosis in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) involves the development and persistent growth of fluid filled kidney cysts. In a recent study, we showed that ADPKD kidney cyst epithelial cells can stimulate the proliferation and differentiation of peri-cystic myofibroblasts. Although dense myofibroblast populations are often found surrounding kidney cysts, their role in cyst enlargement or fibrosis in ADPKD is unclear. To clarify this, we examined the effect of myofibroblast depletion in the Pkd1RC/RC (RC/RC) mouse model of ADPKD. RC/RC;αSMAtk mice that use the ganciclovir-thymidine kinase system to selectively deplete α-smooth muscle actin expressing myofibroblasts were generated. Ganciclovir treatment for four weeks depleted myofibroblasts, reduced kidney fibrosis and preserved kidney function in these mice. Importantly, myofibroblast depletion significantly reduced cyst growth and cyst epithelial cell proliferation in RC/RC;αSMAtk mouse kidneys. Similar ganciclovir treatment did not alter cyst growth or fibrosis in wild-type or RC/RC littermates. In vitro, co-culture with myofibroblasts from the kidneys of patients with ADPKD increased 3D microcyst growth of human ADPKD cyst epithelial cells. Treatment with conditioned culture media from ADPKD kidney myofibroblasts increased microcyst growth and cell proliferation of ADPKD cyst epithelial cells. Further examination of ADPKD myofibroblast conditioned media showed high levels of protease inhibitors including PAI1, TIMP1 and 2, NGAL and TFPI-2, and treatment with recombinant PAI1 and TIMP1 increased ADPKD cyst epithelial cell proliferation in vitro. Thus, our findings show that myofibroblasts directly promote cyst epithelial cell proliferation, cyst growth and fibrosis in ADPKD kidneys, and their targeting could be a novel therapeutic strategy to treat PKD.

IL-15 Prevents Renal Fibrosis by Inhibiting Collagen Synthesis: A New Pathway in Chronic Kidney Disease?

Chronic kidney disease (CKD), secondary to renal fibrogenesis, is a public health burden. The activation of interstitial myofibroblasts and excessive production of extracellular matrix (ECM) proteins are major events leading to end-stage kidney disease. Recently, interleukin-15 (IL-15) has been implicated in fibrosis protection in several organs, with little evidence in the kidney. Since endogenous IL-15 expression decreased in nephrectomized human allografts evolving toward fibrosis and kidneys in the unilateral ureteral obstruction (UUO) model, we explored IL-15's renoprotective role by pharmologically delivering IL-15 coupled or not with its soluble receptor IL-15Rα. Despite the lack of effects on myofibroblast accumulation, both IL-15 treatments prevented tubulointerstitial fibrosis (TIF) in UUO as characterized by reduced collagen and fibronectin deposition. Moreover, IL-15 treatments inhibited collagen and fibronectin secretion by transforming growth factor-β (TGF-β)-treated primary myofibroblast cultures, demonstrating that the antifibrotic effect of IL-15 in UUO acts, in part, through a direct inhibition of ECM synthesis by myofibroblasts. In addition, IL-15 treatments resulted in decreased expression of monocyte chemoattractant protein 1 (MCP-1) and subsequent macrophage infiltration in UUO. Taken together, our study highlights a major role of IL-15 on myofibroblasts and macrophages, two main effector cells in renal fibrosis, demonstrating that IL-15 may represent a new therapeutic option for CKD.

The tyrosine-kinase inhibitor Nintedanib ameliorates autosomal-dominant polycystic kidney disease

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease and is characterized by progressive growth of fluid-filled cysts. Growth factors binding to receptor tyrosine kinases (RTKs) stimulate cell proliferation and cyst growth in PKD. Nintedanib, a triple RTK inhibitor, targets the vascular endothelial growth-factor receptor (VEGFR), platelet-derived growth-factor receptor (PDGFR), and fibroblast growth-factor receptor (FGFR), and is an approved drug for the treatment of non-small-cell lung carcinoma and idiopathic lung fibrosis. To determine if RTK inhibition using nintedanib can slow ADPKD progression, we tested its effect on human ADPKD renal cyst epithelial cells and myofibroblasts in vitro, and on Pkd1f/fPkhd1Cre and Pkd1RC/RC, orthologous mouse models of ADPKD. Nintedanib significantly inhibited cell proliferation and in vitro cyst growth of human ADPKD renal cyst epithelial cells, and cell viability and migration of human ADPKD renal myofibroblasts. Consistently, nintedanib treatment significantly reduced kidney-to-body-weight ratio, renal cystic index, cystic epithelial cell proliferation, and blood-urea nitrogen levels in both the Pkd1f/fPkhd1Cre and Pkd1RC/RC mice. There was a corresponding reduction in ERK, AKT, STAT3, and mTOR activity and expression of proproliferative factors, including Yes-associated protein (YAP), c-Myc, and Cyclin D1. Nintedanib treatment significantly reduced fibrosis in Pkd1RC/RC mice, but did not affect renal fibrosis in Pkd1f/fPkhd1Cre mice. Overall, these results suggest that nintedanib may be repurposed to effectively slow cyst growth in ADPKD.

Human Liver Stem Cell Derived Extracellular Vesicles Alleviate Kidney Fibrosis by Interfering with the β-Catenin Pathway through miR29b

Human liver stem-cell-derived extracellular vesicles (HLSC-EVs) exhibit therapeutic properties in various pre-clinical models of kidney injury. We previously reported an overall improvement in kidney function following treatment with HLSC-EVs in a model of aristolochic acid nephropathy (AAN). Here, we provide evidence that HLSC-EVs exert anti-fibrotic effects by interfering with β-catenin signalling. A mouse model of AAN and an in vitro pro-fibrotic model were used. The β-catenin mRNA and protein expression, together with the pro-fibrotic markers α-SMA and collagen 1, were evaluated in vivo and in vitro following treatment with HLSC-EVs. Expression and functional analysis of miR29b was performed in vitro following HLSC-EV treatments through loss-of-function experiments. Results showed that expression of β-catenin was amplified both in vivo and in vitro, and β-catenin gene silencing in fibroblasts prevented AA-induced up-regulation of pro-fibrotic genes, revealing that β-catenin is an important factor in fibroblast activation. Treatment with HLSC-EVs caused increased expression of miR29b, which was significantly inhibited in the presence of α-amanitin. The suppression of the miR29b function with a selective inhibitor abolished the anti-fibrotic effects of HLSC-EVs, resulting in the up-regulation of β-catenin and pro-fibrotic α-Sma and collagen type 1 genes. Together, these data suggest a novel HLSC-EV-dependent regulatory mechanism in which β-catenin is down regulated by HLSC-EVs-induced miR29b expression.

Human Liver Stem Cell-Derived Extracellular Vesicles Prevent Aristolochic Acid-Induced Kidney Fibrosis

With limited therapeutic intervention in preventing the progression to end-stage renal disease, chronic kidney disease (CKD) remains a global health-care burden. Aristolochic acid (AA) induced nephropathy is a model of CKD characterised by inflammation, tubular injury, and interstitial fibrosis. Human liver stem cell-derived extracellular vesicles (HLSC-EVs) have been reported to exhibit therapeutic properties in various disease models including acute kidney injury. In the present study, we aimed to investigate the effects of HLSC-EVs on tubular regeneration and interstitial fibrosis in an AA-induced mouse model of CKD. NSG mice were injected with HLSC-EVs 3 days after administering AA on a weekly basis for 4 weeks. Mice injected with AA significantly lost weight over the 4-week period. Deterioration in kidney function was also observed. Histology was performed to evaluate tubular necrosis, interstitial fibrosis, as well as infiltration of inflammatory cells/fibroblasts. Kidneys were also subjected to gene array analyses to evaluate regulation of microRNAs (miRNAs) and pro-fibrotic genes. The effect of HLSC-EVs was also tested in vitro to assess pro-fibrotic gene regulation in fibroblasts cocultured with AA pretreated tubular epithelial cells. Histological analyses showed that treatment with HLSC-EVs significantly reduced tubular necrosis, interstitial fibrosis, infiltration of CD45 cells and fibroblasts, which were all elevated during AA induced injury. At a molecular level, HLSC-EVs significantly inhibited the upregulation of the pro-fibrotic genes α-Sma, Tgfb1, and Col1a1 in vivo and in vitro. Fibrosis gene array analyses revealed an upregulation of 35 pro-fibrotic genes in AA injured mice. Treatment with HLSC-EVs downregulated 14 pro-fibrotic genes in total, out of which, 5 were upregulated in mice injured with AA. Analyses of the total mouse miRnome identified several miRNAs involved in the regulation of fibrotic pathways, which were found to be modulated post-treatment with HLSC-EVs. These results indicate that HLSC-EVs play a regenerative role in CKD possibly through the regulation of genes and miRNAs that are activated during the progression of the disease.

Inactivation of MAP3K7 in FOXD1-expressing cells results in loss of mesangial PDGFRΒ and juvenile kidney scarring

Transforming growth factor-β (TGFβ) plays a central role in renal scarring, controlling extracellular matrix deposition by interstitial cells and mesangial cells. TGFβ signals through Smad and mitogen-activated protein kinase (MAPK) pathways. To understand the role of MAPK in interstitial and mesangial cells, we genetically inactivated TGFβ-activated kinase-1 ( Map3k7) using Foxd1^+/cre. Embryonic kidney development was unperturbed in mutants, but spontaneous scarring of the kidney ensued during the first postnatal week, with retention of embryonic nephrogenic rests and accumulation of collagen IV in the mesangium. MAPK signaling in the mesangium of mutant mice was skewed, with depressed p38 but elevated c-Jun NH₂-terminal kinase (JNK) activation at postnatal day 3. Despite normal expression of platelet-derived growth factor receptor-β (PDGFRβ) in the mesangium of mutants at birth, expression was lost concomitantly with the increase in JNK activation, and studies in isolated mesangial cells revealed that JNK negatively regulates Pdgfrβ. In summary, we show that MAP3K7 balances MAPK signaling in mesangial cells, suppressing postnatal JNK activation. We propose that the balance of MAPK signaling is essential for appropriate postnatal regulation of mesangial PDGFRβ expression.

FGF23 activates injury-primed renal fibroblasts via FGFR4-dependent signalling and enhancement of TGF-β autoinduction

Bone-derived fibroblast growth factor 23 (FGF23) is an important endocrine regulator of mineral homeostasis with effects transduced by cognate FGF receptor (FGFR)1-α-Klotho complexes. Circulating FGF23 levels rise precipitously in patients with kidney disease and portend worse renal and cardiovascular outcomes. De novo expression of FGF23 has been found in the heart and kidney following injury but its significance remains unclear. Studies showing that exposure to chronically high FGF23 concentrations activates hypertrophic gene programs in the cardiomyocyte has spawned intense interest in other pathological off-target effects of FGF23 excess. In the kidney, observational evidence points to a concordance of ectopic renal FGF23 expression and the activation of local transforming growth factor (TGF)-β signalling. Although we have previously shown that FGF23 activates injury-primed renal fibroblasts in vitro, our understanding of the mechanism underpinning these effects was incomplete. Here we show that in the absence of α-Klotho, FGF23 augments pro-fibrotic signalling cascades in injury-primed renal fibroblasts via activation of FGFR4 and upregulation of the calcium transporter, transient receptor potential cation channel 6. The resultant rise in intracellular calcium and production of mitochondrial reactive oxygen species induced expression of NFAT responsive-genes and enhanced TGF-β1 autoinduction through non-canonical JNK-dependent pathways. Reconstitution with transmembrane α-Klotho, or its soluble ectodomain, restored classical Egr signalling and antagonised FGF23-driven myofibroblast differentiation. Thus, renal FGF23 may amplify local myofibroblast activation in injury and perpetuate pro-fibrotic signalling. These findings strengthen the rationale for exploring therapeutic inhibition of FGFR4 or restoration of α-Klotho as upstream regulators of off-target FGF23 effects.

Yap/Taz Deletion in Gli+ Cell-Derived Myofibroblasts Attenuates Fibrosis

In damaged kidneys, increased extracellular matrix (ECM) and tissue stiffness stimulate kidney fibrosis through incompletely characterized molecular mechanisms. The transcriptional coactivators yes-associated protein (Yap) and transcriptional coactivator with PDZ-binding motif (Taz) function as mechanosensors in cancer cells and have been implicated in the regulation of myofibroblasts in the kidney. We hypothesized that the development of kidney fibrosis depends on Yap-induced activation and proliferation of kidney fibroblasts. In mice, Yap expression increased in renal fibroblasts after unilateral ureteral obstruction (UUO), in association with worsening of interstitial fibrosis. In cultured fibroblasts, inhibition of Yap/Taz signaling blocked TGF-β1-induced fibroblast-to-myofibroblast transformation and ECM production, whereas constitutive activation of Yap promoted fibroblast transformation and ECM production even in the absence of TGF-β1. Moreover, in the absence of TGF-β1, fibroblasts seeded on a stiffened ECM transformed into myofibroblasts in a process dependent on the activation of Yap. In mice with UUO, the Yap inhibitor verteporfin reduced interstitial fibrosis. Furthermore, Gli1⁺ cell-specific knockout of Yap/Taz in mice suppressed UUO-induced ECM deposition, myofibroblast accumulation, and interstitial fibrosis. In a UUO-release model, induction of Gli1⁺ cell-specific Yap/Taz knockout partially reversed the development of interstitial fibrosis. Thus, in the kidney, Yap is a tissue mechanosensor that can be activated by ECM and transforms fibroblasts into myofibroblasts; the interaction of Yap/Taz and ECM forms a feed-forward loop resulting in kidney fibrosis. Identifying mechanisms that interrupt this profibrotic cycle could lead to the development of anti-fibrosis therapy.

FGF23 is synthesised locally by renal tubules and activates injury-primed fibroblasts

In kidney disease, higher circulating levels of the mineral-regulating hormone fibroblast growth factor (FGF)-23 are predictive of disease progression but direct pathogenic effects on the kidney are unknown. We sought evidence of local renal synthesis in response to unilateral ureteric obstruction in the mouse, and pro-fibrotic actions of FGF23 on the fibroblast in vitro. Acute tubulointerstitial injury due to unilateral ureteric obstruction stimulated renal FGF23 synthesis by tubules, and downregulated inactivating proprotein convertases, without effects on systemic mineral metabolism. In vitro, FGF23 had divergent effects on fibroblast activation in cells derived from normal and obstructed kidneys. While FGF23 failed to stimulate fibrogenesis in normal fibroblasts, in those primed by injury, FGF23 induced pro-fibrotic signalling cascades via activation of TGF-β pathways. Effects were independent of α-klotho. Tubule-derived FGF23 may amplify myofibroblast activation in acute renal injury, and might provide a novel therapeutic target in renal fibrosis.

Epigenetic Modifications to H3K9 in Renal Tubulointerstitial Cells after Unilateral Ureteric Obstruction and TGF-β1 Stimulation

Introduction: Epigenetic regulation of fibrogenesis through post-translational histone modifications (marks) may be a key determinant of progression in renal disease. In this study, we examined the distribution and acquisition of histone 3 Lysine 9 (H3K9) marks after injury and stimulation with the pro-fibrotic cytokine TGF-β1. Our focus was on their presence in activated fibroblasts (myofibroblasts) and epithelial cells (epithelial-mesenchymal transition).

Methods and Results: Immunofluorescent microscopy was used to examine global H3K9 acetylation (H3K9Ac) and tri-methylation (H3K9Me3) after unilateral ureteric obstruction (UUO) in mice. Confocal, super resolution microscopy and flow cytometry were used to determine the in vitro effect of TGF-β1 on structural arrangement of these marks, and their relationship with α-smooth muscle actin (αSMA) expression, a marker of myofibroblasts and early EMT. The number of individual histone marks was increased 10 days after UUO (p < 0.05 vs. control), with both marks clearly seen in various cell types including proximal tubules and myofibroblasts. Sub-nuclear microscopy in primary rat renal fibroblasts and a proximal tubule cell line (NRK-52e) showed that H3K9Ac was co-localized with phosphorylated-Ser2 RNA polymerase II (pRNAPol II), while H3K9Me3 was not, consistent with permissive and repressive effects on gene expression respectively. In both cell types H3K9Ac was diffusely distributed throughout the nucleus, while H3K9Me3 was found in compartments resembling the nucleolus, and in the case of the fibroblast, also juxtapositioned with the nuclear membrane. TGF-β1 had no effect on H3K9Ac marks in either cell, but resulted in a redistribution of H3K9Me3 within the fibroblast nucleus. This was unrelated to any change in mitogenesis, but was associated with increased αSMA expression.

Conclusion: These findings highlight why it is important to consider the epigenetics of each cell individually, because whilst no overall enrichment occurred, renal myofibroblast differentiation was accompanied by distinct changes in histone mark arrangements.

Instructive Role of the Microenvironment in Preventing Renal Fibrosis

Accumulation of myofibroblasts is a hallmark of renal fibrosis. A significant proportion of myofibroblasts has been reported to originate via endothelial‐mesenchymal transition. We initially hypothesized that exposing myofibroblasts to the extract of endothelial progenitor cells (EPCs) could reverse this transition. Indeed, in vitro treatment of transforming growth factor‐β1 (TGF‐β1)‐activated fibroblasts with EPC extract prevented expression of α‐smooth muscle actin (α‐SMA); however, it did not enhance expression of endothelial markers. In two distinct models of renal fibrosis—unilateral ureteral obstruction and chronic phase of folic acid‐induced nephropathy—subcapsular injection of EPC extract to the kidney prevented and reversed accumulation of α‐SMA‐positive myofibroblasts and reduced fibrosis. Screening the composition of EPC extract for cytokines revealed that it is enriched in leukemia inhibitory factor (LIF) and vascular endothelial growth factor. Only LIF was capable of reducing fibroblast‐to‐myofibroblast transition of TGF‐β1‐activated fibroblasts. In vivo subcapsular administration of LIF reduced the number of myofibroblasts and improved the density of peritubular capillaries; however, it did not reduce the degree of fibrosis. A receptor‐independent ligand for the gp130/STAT3 pathway, hyper‐interleukin‐6 (hyper‐IL‐6), not only induced a robust downstream increase in pluripotency factors Nanog and c‐Myc but also exhibited a powerful antifibrotic effect. In conclusion, EPC extract prevented and reversed fibroblast‐to‐myofibroblast transition and renal fibrosis. The component of EPC extract, LIF, was capable of preventing development of the contractile phenotype of activated fibroblasts but did not eliminate TGF‐β1‐induced collagen synthesis in cultured fibroblasts and models of renal fibrosis, whereas a receptor‐independent gp130/STAT3 agonist, hyper‐IL‐6, prevented fibrosis. In summary, these studies, through the evolution from EPC extract to LIF and then to hyper‐IL‐6, demonstrate the instructive role of microenvironmental cues and may provide in the future a facile strategy to prevent and reverse renal fibrosis. Stem Cells Translational Medicine2017;6:992–1005

The Anti-fibrotic Actions of Relaxin Are Mediated Through a NO-sGC-cGMP-Dependent Pathway in Renal Myofibroblasts In Vitro and Enhanced by the NO Donor, Diethylamine NONOate

INTRODUCTION

The anti-fibrotic hormone, relaxin, has been inferred to disrupt transforming growth factor (TGF)-β1/Smad2 phosphorylation (pSmad2) signal transduction and promote collagen-degrading gelatinase activity via a nitric oxide (NO)-dependent pathway. Here, we determined the extent to which NO, soluble guanylate cyclase (sGC) and cyclic guanosine monophosphate (cGMP) were directly involved in the anti-fibrotic actions of relaxin using a selective NO scavenger and sGC inhibitor, and comparing and combining relaxin's effects with that of an NO donor.

METHODS AND RESULTS

Primary renal cortical myofibroblasts isolated from injured rat kidneys were treated with human recombinant relaxin (RLX; 16.8 nM), the NO donor, diethylamine NONOate (DEA/NO; 0.5-5 μM) or the combined effects of RLX (16.8 nM) and DEA/NO (5 μM) over 72 h. The effects of RLX (16.8 nM) and DEA/NO (5 μM) were also evaluated in the presence of the NO scavenger, hydroxocobalamin (HXC; 100 μM) or sGC inhibitor, ODQ (5 μM) over 72 h. Furthermore, the effects of RLX (30 nM), DEA/NO (5 μM) and RLX (30 nM) + DEA/NO (5 μM) on cGMP levels were directly measured, in the presence or absence of ODQ (5 μM). Changes in matrix metalloproteinase (MMP)-2, MMP-9 (cell media), pSmad2 and α-smooth muscle actin (α-SMA; a measure myofibroblast differentiation) (cell layer) were assessed by gelatin zymography and Western blotting, respectively. At the highest concentration tested, both RLX and DEA/NO promoted MMP-2 and MMP-9 levels by 25-33%, while inhibiting pSmad2 and α-SMA expression by up to 50% (all p < 0.05 vs. untreated and vehicle-treated cells). However, 5μM of DEA/NO was required to produce the effects seen with 16.8 nM of RLX over 72 h. The anti-fibrotic effects of RLX or DEA/NO alone were completely abrogated by HXC and ODQ (both p < 0.01 vs. RLX alone or DEA/NO alone), but were significantly enhanced when added in combination (all p < 0.05 vs. RLX alone). Additionally, the direct cGMP-promoting effects of RLX, DEA/NO and RLX+DEA/NO (which all increased cGMP levels by 12-16-fold over basal levels; all p < 0.01 vs. vehicle-treated cells) were significantly inhibited by pre-treatment of ODQ (all p < 0.05 vs. the respective treatments alone).

CONCLUSION

These findings confirmed that RLX mediates its TGF-β1-inhibitory and gelatinase-promoting effects via a NO-sGC-cGMP-dependent pathway, which was additively augmented by co-administration of DEA/NO.

Experimental inhibition of porcupine-mediated Wnt O-acylation attenuates kidney fibrosis

Activated Wnt signaling is critical in the pathogenesis of renal fibrosis, a final common pathway for most forms of chronic kidney disease. Therapeutic intervention by inhibition of individual Wnts or downstream Wnt/β-catenin signaling has been proposed, but these approaches do not interrupt the functions of all Wnts nor block non-canonical Wnt signaling pathways. Alternatively, an orally bioavailable small molecule, Wnt-C59, blocks the catalytic activity of the Wnt-acyl transferase porcupine, and thereby prevents secretion of all Wnt isoforms. We found that inhibiting porcupine dramatically attenuates kidney fibrosis in the murine unilateral ureteral obstruction model. Wnt-C59 treatment similarly blunts collagen mRNA expression in the obstructed kidney. Consistent with its actions to broadly arrest Wnt signaling, porcupine inhibition reduces expression of Wnt target genes and bolsters nuclear exclusion of β-catenin in the kidney following ureteral obstruction. Importantly, prevention of Wnt secretion by Wnt-C59 blunts expression of inflammatory cytokines in the obstructed kidney that otherwise provoke a positive feedback loop of Wnt expression in collagen-producing fibroblasts and epithelial cells. Thus, therapeutic targeting of porcupine abrogates kidney fibrosis not only by overcoming the redundancy of individual Wnt isoforms but also by preventing upstream cytokine-induced Wnt generation. These findings reveal a novel therapeutic maneuver to protect the kidney from fibrosis by interrupting a pathogenic crosstalk loop between locally generated inflammatory cytokines and the Wnt/β-catenin signaling pathway.

Propagation and Culture of Human Renal Fibroblasts

The renal fibroblast and phenotypically related myofibroblast are universally present in all forms of progressive kidney disease. The in vitro study of the fibroblast, its behavior, and factors affecting its activity is therefore key to understanding both its role and significance. In this protocol, we describe a reproducible method for selective propagation and culture of primary human renal fibroblasts from the human kidney cortex. Techniques for their isolation, subculture, characterization, and cryogenic storage and retrieval are described in detail.

Cannabinoid receptor 1 is a major mediator of renal fibrosis

Chronic kidney disease, secondary to renal fibrogenesis, is a burden on public health. There is a need to explore new therapeutic pathways to reduce renal fibrogenesis. To study this, we used unilateral ureteral obstruction (UUO) in mice as an experimental model of renal fibrosis and microarray analysis to compare gene expression in fibrotic and normal kidneys. The cannabinoid receptor 1 (CB1) was among the most upregulated genes in mice, and the main endogenous CB1 ligand (2-arachidonoylglycerol) was significantly increased in the fibrotic kidney. Interestingly, CB1 expression was highly increased in kidney biopsies of patients with IgA nephropathy, diabetes, and acute interstitial nephritis. Both genetic and pharmacological knockout of CB1 induced a profound reduction in renal fibrosis during UUO. While CB2 is also involved in renal fibrogenesis, it did not potentiate the role of CB1. CB1 expression was significantly increased in myofibroblasts, the main effector cells in renal fibrogenesis, upon TGF-β1 stimulation. The decrease in renal fibrosis during CB1 blockade could be explained by a direct action on myofibroblasts. CB1 blockade reduced collagen expression in vitro. Rimonabant, a selective CB1 endocannabinoid receptor antagonist, modulated the macrophage infiltrate responsible for renal fibrosis in UUO through a decrease in monocyte chemoattractant protein-1 synthesis. Thus, CB1 has a major role in the activation of myofibroblasts and may be a new target for treating chronic kidney disease.

MicroRNA-22 is a master regulator of bone morphogenetic protein-7/6 homeostasis in the kidney

Accumulating evidence suggests that microRNAs (miRNAs) contribute to a myriad of kidney diseases. However, the regulatory role of miRNAs on the key molecules implicated in kidney fibrosis remains poorly understood. Bone morphogenetic protein-7 (BMP-7) and its related BMP-6 have recently emerged as key regulators of kidney fibrosis. Using the established unilateral ureteral obstruction (UUO) model of kidney fibrosis as our experimental model, we examined the regulatory role of miRNAs on BMP-7/6 signaling. By analyzing the potential miRNAs that target BMP-7/6 in silica, we identified miR-22 as a potent miRNA targeting BMP-7/6. We found that expression levels of BMP-7/6 were significantly elevated in the kidneys of the miR-22 null mouse. Importantly, mice with targeted deletion of miR-22 exhibited attenuated renal fibrosis in the UUO model. Consistent with these in vivo observations, primary renal fibroblast isolated from miR-22-deficient UUO mice demonstrated a significant increase in BMP-7/6 expression and their downstream targets. This phenotype could be rescued when cells were transfected with miR-22 mimics. Interestingly, we found that miR-22 and BMP-7/6 are in a regulatory feedback circuit, whereby not only miR-22 inhibits BMP-7/6, but miR-22 by itself is induced by BMP-7/6. Finally, we identified two BMP-responsive elements in the proximal region of miR-22 promoter. These findings identify miR-22 as a critical miRNA that contributes to renal fibrosis on the basis of its pivotal role on BMP signaling cascade.

Primary culture of human renal proximal tubule epithelial cells and interstitial fibroblasts

Renal physiology and pathology are complex systems that are best studied in whole living organisms. This, however, is often restricted by our desire to limit the number of animal experiments undertaken and to replace them with relevant in vitro models that can be used as surrogates for the system under test. Primary culture cells are derived directly from the relevant tissue and therefore correlate more closely with the system under examination. Although the tissue of origin is not always readily available for culture and cells may quickly change their phenotype after only a few passages, they can be used in many circumstances to validate results obtained from closely related cell lines and to confirm vital protein expression patterns. This chapter outlines methods by which proximal tubular epithelial cells and renal interstitial fibroblasts can be isolated and characterized from human renal nephrectomy tissue.

Fibrinogen, acting as a mitogen for tubulointerstitial fibroblasts, promotes renal fibrosis

Fibrinogen plays an important role in blood coagulation but its function extends far beyond blood clotting being involved in inflammation and repair. Besides these crucial functions it can also promote tissue fibrosis. To determine whether fibrinogen is involved in the development of renal tubulointerstitial fibrosis we utilized the profibrotic model of unilateral ureteral obstruction in fibrinogen-deficient mice. In the heterozygotes, obstruction was associated with a massive deposition of intrarenal fibrinogen. Fibrinogen deficiency provided significant protection from interstitial damage and tubular disruption, attenuated collagen accumulation, and greatly reduced de novo expression of α-smooth muscle actin in the obstructed kidney. While no differences were found in renal inflammatory cell infiltration, fibrinogen deficiency was associated with a significant reduction in interstitial cell proliferation, a hallmark of renal fibrosis. In vitro, fibrinogen directly stimulated renal fibroblast proliferation in a dose-dependent manner. This mitogenic effect of fibrinogen was mediated by at least three different cell surface receptors on renal fibroblasts: TLR2, TLR4, and ICAM-1. Thus, our study suggests that fibrinogen promotes renal fibrosis by triggering resident fibroblast proliferation.

CD248+ stromal cells are associated with progressive chronic kidney disease

Stromal fibroblasts are the primary cells of the kidney that produce fibrotic matrix. CD248 is a stromal marker expressed on fibroblasts and pericytes within the human kidney. Here, we tested whether CD248 expression in the kidney colocalizes with fibrosis and if it is associated with known determinants of chronic kidney disease (CKD). CD248 expression was located and quantified in situ by immunohistochemistry in kidney biopsies from 93 patients with IgA nephropathy and compared with 22 archived biopsies encompassing normal kidney tissue as control. In normal kidney tissue, CD248 was expressed by resident pericytes, stromal fibroblasts, and was upregulated in human CKD. The expression was linked to known determinants of renal progression. This relationship was maintained in a multivariate analysis with CD248 expression linked to renal survival. CD248 was expressed by a population of α-smooth muscle actin (SMA)(+) myofibroblasts and α-SMA(-) stromal cells but not expressed on CD45(+) leukocytes. Thus, CD248 defines a subset of stromal cells, including but not limited to some myofibroblasts, linked to albuminuria and tubulointerstitial damage during tissue remodeling in CKD.