Wnt pathway regulation in chronic renal allograft damage

Loss of Klotho contributes to kidney injury by derepression of Wnt/β-catenin signaling

Aging is an independent risk factor for CKD, but the molecular mechanisms that link aging and CKD are not well understood. The antiaging protein Klotho may be an endogenous antagonist of Wnt/β-catenin signaling, which promotes fibrogenesis, suggesting that loss of Klotho may contribute to CKD through increased Wnt/β-catenin activity. Here, normal adult kidneys highly expressed Klotho in the tubular epithelium, but various models of nephropathy exhibited markedly less expression of Klotho. Loss of Klotho was closely associated with increased β-catenin in the diseased kidneys, suggesting an inverse correlation between Klotho and canonical Wnt signaling. In vitro, both full-length and secreted Klotho bound to multiple Wnts, including Wnt1, Wnt4, and Wnt7a. Klotho repressed gene transcription induced by Wnt but not by active β-catenin. Furthermore, Klotho blocked Wnt-triggered activation and nuclear translocation of β-catenin, as well as the expression of its target genes in tubular epithelial cells. Investigating potential mediators of Klotho loss in CKD, we found that TGF-β1 suppressed Klotho expression and concomitantly activated β-catenin; conversely, overexpression of Klotho abolished fibrogenic effects of TGF-β1. In two mouse models of CKD induced by unilateral ureteral obstruction or adriamycin, in vivo expression of secreted Klotho inhibited the activation of renal β-catenin and expression of its target genes. Secreted Klotho also suppressed myofibroblast activation, reduced matrix expression, and ameliorated renal fibrosis. Taken together, these results suggest that Klotho is an antagonist of endogenous Wnt/β-catenin activity; therefore, loss of Klotho may contribute to kidney injury by releasing the repression of pathogenic Wnt/β-catenin signaling.

Kidney tubular β-catenin signaling controls interstitial fibroblast fate via epithelial-mesenchymal communication

Activation of β-catenin, the principal mediator of canonical Wnt signaling, is a common pathologic finding in a wide variety of chronic kidney diseases (CKD). While β-catenin is induced predominantly in renal tubular epithelium in CKD, surprisingly, depletion of tubular β-catenin had little effect on the severity of renal fibrosis. Interestingly, less apoptosis was detected in interstitial fibroblasts in knockout mice, which was accompanied by a decreased expression of Bax and Fas ligand (FasL). Tubule-specific knockout of β-catenin diminished renal induction of matrix metalloproteinase (MMP-7), which induced FasL expression in interstitial fibroblasts and potentiated fibroblast apoptosis in vitro. These results demonstrate that loss of tubular β-catenin resulted in enhanced interstitial fibroblast survival due to decreased MMP-7 expression. Our studies uncover a novel role of the tubular β-catenin/MMP-7 axis in controlling the fate of interstitial fibroblasts via epithelial-mesenchymal communication.

Inhibition of WISE preserves renal allograft function

Wnt-modulator in surface ectoderm (WISE) is a secreted modulator of Wnt signaling expressed in the adult kidney. Activation of Wnt signaling has been observed in renal transplants developing interstitial fibrosis and tubular atrophy; however, whether WISE contributes to chronic changes is not well understood. Here, we found moderate to high expression of WISE mRNA in a rat model of renal transplantation and in kidneys from normal rats. Treatment with a neutralizing antibody against WISE improved proteinuria and graft function, which correlated with higher levels of β-catenin protein in kidney allografts. In addition, treatment with the anti-WISE antibody reduced infiltration of CD68(+) macrophages and CD8(+) T cells, attenuated glomerular and interstitial injury, and decreased biomarkers of renal injury. This treatment reduced expression of genes involved in immune responses and in fibrogenic pathways. In summary, WISE contributes to renal dysfunction by promoting tubular atrophy and interstitial fibrosis.

Transcriptome analysis of renal ischemia/reperfusion injury and its modulation by ischemic pre-conditioning or hemin treatment

Ischemia/reperfusion injury (IRI) is a leading cause of acute renal failure. The definition of the molecular mechanisms involved in renal IRI and counter protection promoted by ischemic pre-conditioning (IPC) or Hemin treatment is an important milestone that needs to be accomplished in this research area. We examined, through an oligonucleotide microarray protocol, the renal differential transcriptome profiles of mice submitted to IRI, IPC and Hemin treatment. After identifying the profiles of differentially expressed genes observed for each comparison, we carried out functional enrichment analysis to reveal transcripts putatively involved in potential relevant biological processes and signaling pathways. The most relevant processes found in these comparisons were stress, apoptosis, cell differentiation, angiogenesis, focal adhesion, ECM-receptor interaction, ion transport, angiogenesis, mitosis and cell cycle, inflammatory response, olfactory transduction and regulation of actin cytoskeleton. In addition, the most important overrepresented pathways were MAPK, ErbB, JAK/STAT, Toll and Nod like receptors, Angiotensin II, Arachidonic acid metabolism, Wnt and coagulation cascade. Also, new insights were gained about the underlying protection mechanisms against renal IRI promoted by IPC and Hemin treatment. Venn diagram analysis allowed us to uncover common and exclusively differentially expressed genes between these two protective maneuvers, underscoring potential common and exclusive biological functions regulated in each case. In summary, IPC exclusively regulated the expression of genes belonging to stress, protein modification and apoptosis, highlighting the role of IPC in controlling exacerbated stress response. Treatment with the Hmox1 inducer Hemin, in turn, exclusively regulated the expression of genes associated with cell differentiation, metabolic pathways, cell cycle, mitosis, development, regulation of actin cytoskeleton and arachidonic acid metabolism, suggesting a pleiotropic effect for Hemin. These findings improve the biological understanding of how the kidney behaves after IRI. They also illustrate some possible underlying molecular mechanisms involved in kidney protection observed with IPC or Hemin treatment maneuvers.

Tubule-specific ablation of endogenous β-catenin aggravates acute kidney injury in mice

β-Catenin is a unique intracellular protein functioning as an integral component of the cell-cell adherens complex and a principal signaling protein mediating canonical Wnt signaling. Little is known about its function in adult kidneys in the normal physiologic state or after acute kidney injury (AKI). To study this, we generated conditional knockout mice in which the β-catenin gene was specifically disrupted in renal tubules (Ksp-β-cat-/-). These mice were phenotypically normal with no appreciable defects in kidney morphology and function. In the absence of β-catenin, γ-catenin functionally substituted for it in E-cadherin binding, thereby sustaining the integrity of epithelial adherens junctions in the kidneys. In AKI induced by ischemia reperfusion or folic acid, the loss of tubular β-catenin substantially aggravated renal lesions. Compared with controls, Ksp-β-cat-/- mice displayed higher mortality, elevated serum creatinine, and more severe morphologic injury. Consistently, apoptosis was more prevalent in kidneys of the knockout mice, which was accompanied by increased expression of p53 and Bax, and decreased phosphorylated Akt and survivin. In vitro activation of β-catenin by Wnt1 or stabilization of β-catenin protected tubular epithelial cells from apoptosis, activated Akt, induced survivin, and repressed p53 and Bax expression. Hence, endogenous β-catenin is pivotal for renal tubular protection after AKI by promoting cell survival through multiple mechanisms.

Wnt/β-Catenin Signaling: a Promising New Target for Fibrosis Diseases

Wnt/β-catenin signaling is involved in virtually every aspect of embryonic development and also controls homeostatic self-renewal in a number of adult tissues. Recently, emerging evidence from researches of organ fibrosis suggest that sustained Wnt/β-catenin pathway reactivation is linked to the pathogenesis of fibrotic disorders. Here we focus on Wnt/β-catenin-related pathogenic effects in different organs, such as lung fibrosis, liver fibrosis, skin fibrosis and renal fibrosis. Additionally, Wnt/β-catenin signaling works in a combinatorial manner with TGF-β signaling in the process of fibrosis, and TGF-β signaling can induce expression of Wnt/β-catenin superfamily members and vice versa. Moreover, network analysis, based on pathway databases, revealed that key factors in the Wnt pathway were targeted by some differentially expressed microRNAs detected in fibrosis diseases. These findings demonstrated the crosstalks between Wnt/β-catenin pathway and TGF-β signalings, and microRNAs, highlighting the role of Wnts in organ fibrogenesis. Most importantly, nowadays there is a variety of Wnt pathway inhibitors which give us the potential therapeutic feasibility, modulation of the Wnt pathway may, therefore, present as a suitable and promising therapeutic strategy in the future.

Sonic hedgehog signaling mediates epithelial-mesenchymal communication and promotes renal fibrosis

Sonic hedgehog (Shh) signaling is a developmental signal cascade that plays an essential role in regulating embryogenesis and tissue homeostasis. Here, we investigated the potential role of Shh signaling in renal interstitial fibrogenesis. Ureteral obstruction induced Shh, predominantly in the renal tubular epithelium of the fibrotic kidneys. Using Gli1(lacZ) knock-in mice, we identified renal interstitial fibroblasts as Shh-responding cells. In cultured renal fibroblasts, recombinant Shh protein activated Gli1 and induced α-smooth muscle actin (α-SMA), desmin, fibronectin, and collagen I expression, suggesting that Shh signaling promotes myofibroblast activation and matrix production. Blockade of Shh signaling with cyclopamine abolished the Shh-mediated induction of Gli1, Snail1, α-SMA, fibronectin, and collagen I. In vivo, the kidneys of Gli1-deficient mice were protected against the development of interstitial fibrosis after obstructive injury. In wild-type mice, cyclopamine did not affect renal Shh expression but did inhibit induction of Gli1, Snail1, and α-SMA. In addition, cyclopamine reduced matrix expression and mitigated fibrotic lesions. These results suggest that tubule-derived Shh mediates epithelial-mesenchymal communication by targeting interstitial fibroblasts after kidney injury. We conclude that Shh/Gli1 signaling plays a critical role in promoting fibroblast activation, production of extracellular matrix, and development of renal interstitial fibrosis.

Matrix metalloproteinase-7 as a surrogate marker predicts renal Wnt/β-catenin activity in CKD

A variety of chronic kidney diseases exhibit reactivation of Wnt/β-catenin signaling. In some tissues, β-catenin transcriptionally regulates matrix metalloproteinase-7 (MMP-7), but the association between MMP-7 and Wnt/β-catenin signaling in chronic kidney disease is unknown. Here, in mouse models of both obstructive nephropathy and focal segmental glomerulosclerosis (adriamycin nephropathy), we observed upregulation of MMP-7 mRNA and protein in a time-dependent manner. The pattern and extent of MMP-7 induction were positively associated with Wnt/β-catenin signaling in these models. Activation of β-catenin through ectopic expression of Wnt1 promoted MMP-7 expression in vivo, whereas delivery of the gene encoding the endogenous Wnt antagonist Dickkopf-1 abolished its induction. Levels of MMP-7 protein detected in the urine correlated with renal Wnt/β-catenin activity. Pharmacologic blockade of Wnt/β-catenin signaling by paricalcitol inhibited MMP-7 expression in diseased kidneys and reduced the levels detected in the urine. In vitro, β-catenin activation induced the expression and secretion of MMP-7 and promoted the binding of T cell factor to the MMP-7 promoter in kidney epithelial cells. We also observed higher levels of MMP-7 expression, which correlated with β-catenin, in kidney tissue from patients with various nephropathies. In summary, levels of renal MMP-7 correlate with Wnt/β-catenin activity, and urinary MMP-7 may be a noninvasive biomarker of this profibrotic signaling in the kidney.

Modulation of Wnt and Hedgehog signaling pathways is linked to retinoic acid-induced amelioration of chronic allograft dysfunction

Chronic renal allograft damage (CAD) is manifested by a smoldering inflammatory process that leads to transplant glomerulopathy, diffuse interstitial fibrosis and tubular atrophy with loss of tubular structures. Using a Fischer 344 (RT1lvl) to Lewis (RT1l) rat renal allograft model, transcriptomic profiling and pathway mapping, we have previously shown that dynamic dysregulation of the Wnt signaling pathways may underlie progressive CAD. Retinoic acid, an important regulator of differentiation during vertebrate embryogenesis, can moderate the damage observed in this experimental model of CAD. We show here that subsets of the Hedgehog (Hh) and canonical Wnt signaling pathways are linked to the pathophysiology of progressive fibrosis, loss of cilia in epithelia and chronic dysfunction. Oral treatment with 13cis retinoic acid (13cRA) was found to selectively ameliorate the dysregulation of the Hh and canonical Wnt pathways associated with CAD, and lead to a general preservation of cilial structures. Interplay between these pathways helps explain the therapeutic effects of retinoic acid treatment in CAD, and suggests future targets for moderating chronic fibrosing organ damage.

Canonical Wnt/β-catenin signaling mediates transforming growth factor-β1-driven podocyte injury and proteinuria

Transforming growth factor-β1 (TGF-β1) upregulation occurs in virtually all chronic kidney diseases and is associated with podocyte injury and proteinuria; however, the mechanisms contributing to this in vivo are ambiguous. In vitro, incubation of podocytes with TGF-β1 induced Wnt1 expression, β-catenin activation, and stimulated the expression of Wnt/β-catenin downstream target genes. Ectopic expression of Wnt1 or β-catenin mimicked TGF-β1, induced Snail1, and suppressed nephrin expression. The Wnt antagonist, Dickkopf-1, blocked TGF-β1-induced β-catenin activation, Snail1 induction, and nephrin suppression. In vivo, ectopic expression of TGF-β1 induced Wnt1 expression, activated β-catenin, and upregulated Wnt target genes such as Snail1, MMP-7, MMP-9, desmin, Fsp1, and PAI-1 in mouse glomeruli, leading to podocyte injury and albuminuria. Consistently, concomitant expression of Dickkopf-1 gene abolished β-catenin activation, inhibited TGF-β1-triggered Wnt target gene expression, and mitigated albuminuria. Thus, canonical Wnt/β-catenin signaling mediates TGF-β1-driven podocyte injury and proteinuria. These studies suggest that Wnt/β-catenin signaling may be exploited as a therapeutic target for the treatment of proteinuric kidney diseases.

Delayed graft function in the kidney transplant

Acute kidney injury occurs with kidney transplantation and too frequently progresses to the clinical diagnosis of delayed graft function (DGF). Poor kidney function in the first week of graft life is detrimental to the longevity of the allograft. Challenges to understand the root cause of DGF include several pathologic contributors derived from the donor (ischemic injury, inflammatory signaling) and recipient (reperfusion injury, the innate immune response and the adaptive immune response). Progressive demand for renal allografts has generated new organ categories that continue to carry high risk for DGF for deceased donor organ transplantation. New therapies seek to subdue the inflammatory response in organs with high likelihood to benefit from intervention. Future success in suppressing the development of DGF will require a concerted effort to anticipate and treat tissue injury throughout the arc of the transplantation process.

Molecular evaluation of renal biopsies: a search for predictive and prognostic markers in lupus nephritis

The therapeutic management of patients with lupus nephritis (LN) remains a major challenge. The availability of biomarkers that accurately predict renal flares, response to immunosuppressive treatment and risk of progression to end-stage renal disease would allow the more effective use of currently available immunosuppression, with less toxicity. The molecular analysis of renal biopsy samples provides direct insights into pathologic processes in LN, and constitutes a valuable approach to discover biomarkers that may be used to improve the outcome of LN patients. Reich et al. recently described a method for simultaneously detecting multiple mRNA transcripts in archived formalin-fixed renal biopsy samples. The authors identify three transcripts (EGF, MMP7 and COL1A1) that relate to pathological indices of kidney injury and function.

Targeted inhibition of β-catenin/CBP signaling ameliorates renal interstitial fibrosis

Because fibrotic kidneys exhibit aberrant activation of β-catenin signaling, this pathway may be a potential target for antifibrotic therapy. In this study, we examined the effects of β-catenin activation on tubular epithelial-mesenchymal transition (EMT) in vitro and evaluated the therapeutic efficacy of the peptidomimetic small molecule ICG-001, which specifically disrupts β-catenin-mediated gene transcription, in obstructive nephropathy. In vitro, ectopic expression of stabilized β-catenin in tubular epithelial (HKC-8) cells suppressed E-cadherin and induced Snail1, fibronectin, and plasminogen activator inhibitor-1 (PAI-1) expression. ICG-001 suppressed β-catenin-driven gene transcription in a dose-dependent manner and abolished TGF-β1-induced expression of Snail1, PAI-1, collagen I, fibronectin, and α-smooth muscle actin (α-SMA). This antifibrotic effect of ICG-001 did not involve disruption of Smad signaling. In the unilateral ureteral obstruction model, ICG-001 ameliorated renal interstitial fibrosis and suppressed renal expression of fibronectin, collagen I, collagen III, α-SMA, PAI-1, fibroblast-specific protein-1, Snail1, and Snail2. Late administration of ICG-001 also effectively attenuated fibrotic lesions in obstructive nephropathy. In conclusion, inhibiting β-catenin signaling may be an effective approach to the treatment of fibrotic kidney diseases.

Wnt-signaling pathways in progressive renal fibrosis

INTRODUCTION

The prevention and potential reversal of interstitial fibrosis is a central strategy for the treatment of progressive renal disease. This strategy requires a better understanding of the underlying pathophysiologic processes involved in progressive renal fibrosis.

AREAS COVERED

The developmental processes in which Wnt (combination of 'wingless' and 'INT')/frizzled signaling is involved is discussed in this review, including cell fate determination, cell polarity, tissue patterning and control of cell proliferation. These pathways are also active in the adult where they play key roles in the maintenance of tissue homeostasis, wound repair and chronic tissue damage.

EXPERT OPINION

Wnt biology helps to control cell polarity, moderates cell proliferation and underlies other processes linked to renal homeostasis. Reactivation and dysregulation of the Wnt pathways underlie chronic fibrosis and progressive renal failure. Wnt signaling is, however, context-dependent: the pathways are complex and undergo many levels of cross-talk with other regulatory systems and regulatory pathways. On one hand, this may help to explain the positive effects of Wnt-signaling blockades seen in some animal models of chronic renal damage and, on the other, this suggests that it may be difficult to predict how modifications of the Wnt pathway may influence a process.

Suppression of chronic damage in renal allografts by Liver X receptor (LXR) activation relevant contribution of macrophage LXRα

Liver X receptors (LXR)-α,β regulate intracellular cholesterol homeostasis and inhibit inflammatory gene expression. We studied the effects of the LXRα,β-agonist GW3965 on acute and chronic organ damage in the F344-LEW rat kidney transplantation model. In addition, to gain LXR isoform and cell-specific insights BALB/c kidneys were transplanted into mice with macrophage overexpression of LXRα (mLXRα-tg) and evaluated 7 and 42 days after transplantation. After 56 days GW3965 improved significantly function and morphology of rat kidney allografts by substantial reduction of mononuclear cell infiltrate and fibrosis; in vitro GW3965 reduced inflammatory activity of bone marrow-derived macrophages (BMDMs) and alloreactivity of T cells. Kidneys transplanted into mLXRα-tg mice were also protected from development of chronic allograft dysfunction. Similarly to GW3965-activated BMDMs, mLXRα-tg macrophages secreted significantly less monocyte chemoattractant protein 1 and macrophage inflammatory protein 1β. Interestingly, 7 days after transplantation, when the total number of intragraft macrophages did not differ, evidently more arginase 1- and mannose receptor C type 1-positive cells were found in LXR rat and mice kidney allografts; in vitro both LXR activation by GW3965 and mLXRα overexpression accentuated the induction of alternative activation of BMDMs by IL-4/IL-13, suggesting an additional mechanism by LXRs to prevent graft damage. The results highlight the relevance of macrophage LXRα in allograft rejection and prevention of fibrosis.

Epithelial to mesenchymal transition as a biomarker in renal fibrosis: are we ready for the bedside?

Over the past two decades, the concept of the epithelial to mesenchymal transition (EMT) has been imported from embryology and oncology to fibrosis, particularly in the kidney. This interest in EMT in the context of renal fibrosis stems from observations of epithelial cells undergoing phenotypic changes reminiscent of fibroblasts. Whether EMT is actually a source of interstitial fibroblasts has been the subject of heated debate, and this controversy has caused physicians to neglect the value of EMT as a biomarker in renal fibrosis. In this review, we describe the evolution of the techniques used to detect EMT during fibrosing renal diseases, and what information they provide in the diagnosis of various renal diseases. Highlighting the great heterogeneity of these techniques and the need to standardize them, we warn against some misleading uses of EMT markers. We suggest using the association of vimentin and β-catenin for the diagnosis of EMT in renal pathology because it is both sensitive and prognostic, thus satisfying the properties required for a screening test. Finally, we discuss the potential interests to diagnose EMT for the comprehension of renal fibrosis and for clinical practice.

Pathways and promoter networks analysis provides systems topology for systems biology approaches

Systems-level approaches provide help in characterizing the complexity of renal disease. In this review, we illustrate, using a series of recent examples of integrative studies based on pathway analysis and promoter networks, how new techniques allow the analysis of the layout of complex systems and, through this, help answer questions related to renal disease processes. These technologies include the identification of regulatory pathways dysregulated in the context of renal disease, and techniques for studying promoter networks. Both approaches make use of technologies applied to large-scale transcriptomics, transcriptomic profiling by DNA microarrays, or next-generation sequencing.

Blockade of Wnt/β-catenin signaling by paricalcitol ameliorates proteinuria and kidney injury

Recent studies implicate Wnt/β-catenin signaling in podocyte dysfunction. Because vitamin D analogs can inhibit β-catenin in other tissues, we tested whether the vitamin D analog paricalcitol could ameliorate podocyte injury, proteinuria, and renal fibrosis in adriamycin (ADR) nephropathy. Compared with vehicle-treated controls, paricalcitol preserved expression of nephrin, podocin, and WT1; prevented proteinuria; and reduced glomerulosclerotic lesions induced by ADR. Paricalcitol also inhibited expression of proinflammatory cytokines, reduced renal infiltration of monocytes/macrophages, hampered activation of renal myofibroblasts, and suppressed expression of the fibrogenic TGF-β1, CTGF, fibronectin, and types I and III collagen. Selective suppression of renal Wnt4, Wnt7a, Wnt7b, and Wnt10a expression after ADR accompanied these renoprotective effects of paricalcitol. Significant upregulation of β-catenin, predominantly in podocytes and tubular epithelial cells, accompanied renal injury; paricalcitol largely abolished this induction of renal β-catenin and inhibited renal expression of Snail, a downstream effector of Wnt/β-catenin signaling. Administration of paricalcitol also ameliorated established proteinuria. In vitro, paricalcitol induced a physical interaction between the vitamin D receptor and β-catenin in podocytes, which led to suppression of β-catenin-mediated gene transcription. In summary, these findings suggest that paricalcitol prevents podocyte dysfunction, proteinuria, and kidney injury in adriamycin nephropathy by inhibiting Wnt/β-catenin signaling.

Nephrotoxicity of mercuric chloride, methylmercury and cinnabar-containing Zhu-Sha-An-Shen-Wan in rats

Cinnabar (HgS) is used in traditional medicines, and total Hg content is used for risk assessment of cinnabar-containing traditional medicines such as Zhu-Sha-An-Shen-Wan (ZSASW). Is ZSASW or cinnabar toxicologically similar to common mercurials? Adult Sprague-Dawley rats were gavaged with ZSASW (1.4 g/kg), cinnabar (0.2g/kg), HgCl(2) (0.02 g/kg), MeHg (0.001 g/kg), or saline daily for 60 days, and toxicity was determined. Animal body-weight gain was decreased by HgCl(2) and MeHg. Blood urea nitrogen (BUN) was increased by MeHg. Histology showed severe kidney injury following MeHg and HgCl(2) treatments, but mild after ZSASW and cinnabar. Renal Hg contents were markedly increased in the HgCl(2) and MeHg groups but were not elevated in the ZSASW and cinnabar groups. The expression of kidney injury molecule-1 was increased 50-fold by MeHg, 4-fold by HgCl(2), but was unaltered by ZSASW and cinnabar; the expression of matrilysin was increased 3-fold by MeHg. In contrast, the expression of N-cadherin was decreased by HgCl(2). Thus, ZSASW and cinnabar are much less nephrotoxic than HgCl(2) and MeHg, indicating that chemical forms of mercury underlie their disposition and toxicity.

Conjunctival transcriptome in scarring trachoma

Trachoma is a poorly understood immunofibrogenic disease process, initiated by Chlamydia trachomatis. Differences in conjunctival gene expression profiles between Ethiopians with trachomatous trichiasis (with [TTI] or without [TT] inflammation) and controls (C) were investigated to identify relevant host responses. Tarsal conjunctival swab samples were collected for RNA isolation and C. trachomatis PCR. Transcriptome-wide microarray experiments were conducted on 42 samples (TTI, n = 13; TT, n = 15; C, n =14). Specific results were confirmed by using multiplex quantitative reverse transcription-PCR for 16 mRNA targets in an independent collection of case-control samples: 386 case-control pairs (TTI, n = 244; TT, n = 142; C, n = 386). The gene expression profiles of cases were consistent with squamous metaplasia (keratins, SPRR), proinflammatory cytokine production (IL1β, CXCL5, and S100A7), and tissue remodeling (MMP7, MMP9, MMP12, and HAS3). There was no difference in the level of IFNγ between cases and controls. However, cases had increased INDO, NOS2A, and IL13RA2 and reduced IL13. C. trachomatis was detected in 1/772. Cases show evidence of ongoing inflammation and tissue remodeling, which were more marked where clinical inflammation was also present. Significantly, these processes appear to be active in the absence of current C. trachomatis infection. There was limited evidence of a T(H)1 response (INDO and NOS2A) and no association between a T(H)2 response and cases. The epithelium appears to be actively involved in late cicatricial stages of trachoma through the production of proinflammatory factors (IL1β, CXCL5, and S100A7). Longitudinal studies are needed to investigate which etiological factors and pathways are associated with progressive scarring and whether simply controlling chlamydial infection will halt progression in people with established cicatricial disease.

Plasminogen activator inhibitor-1 is a transcriptional target of the canonical pathway of Wnt/beta-catenin signaling

Plasminogen activator inhibitor-1 (PAI-1) is a multifunctional glycoprotein that plays a critical role in the pathogenesis of chronic kidney and cardiovascular diseases. Although transforming growth factor (TGF)-beta1 is a known inducer of PAI-1, how it controls PAI-1 expression remains enigmatic. Here we investigated the mechanism underlying TGF-beta1 regulation of PAI-1 in kidney tubular epithelial cells (HKC-8). Surprisingly, overexpression of Smad2 or Smad3 in HKC-8 cells blocked PAI-1 induction by TGF-beta1, whereas knockdown of them sensitized the cells to TGF-beta1 stimulation, suggesting that Smad signaling is not responsible for PAI-1 induction. Blockade of several TGF-beta1 downstream pathways such as p38 MAPK or JNK, but not phosphatidylinositol 3-kinase/Akt and ERK1/2, only partially inhibited PAI-1 expression. TGF-beta1 stimulated beta-catenin activation in tubular epithelial cells, and ectopic expression of beta-catenin induced PAI-1 expression, whereas inhibition of beta-catenin abolished its induction. A functional T cell factor/lymphoid enhancer-binding factor-binding site was identified in the promoter region of the PAI-1 gene, which interacted with T cell factor upon beta-catenin activation. Deletion or site-directed mutation of this site abolished PAI-1 response to beta-catenin or TGF-beta1 stimulation. Similarly, ectopic expression of Wnt1 also activated PAI-1 expression and promoter activity. In vivo, PAI-1 was induced in kidney tubular epithelia in obstructive nephropathy. Delivery of Wnt1 gene activated beta-catenin and promoted PAI-1 expression after obstructive injury, whereas blockade of Wnt/beta-catenin signaling by Dickkopf-1 gene inhibited PAI-1 induction. Collectively, these studies identify PAI-1 as a direct downstream target of Wnt/beta-catenin signaling and demonstrate that PAI-1 induction could play a role in mediating the fibrogenic action of this signaling.

Pathway-focused arrays reveal increased matrix metalloproteinase-7 (matrilysin) transcription in trachomatous trichiasis

PURPOSE

Several genes that are associated with protection from or susceptibility to trachomatous trichiasis (TT) have been identified through genetic association studies. Yet there have been few studies in which gene expression profiles were assessed in TT cases and disease-free controls. The purpose was to identify genes that are differentially expressed in the upper tarsal conjunctiva of subjects with TT.

METHOD

Pathway-focused gene arrays were used to screen conjunctival RNA expression of 226 gene transcripts of interest. The screening was followed by validation of differentially expressed genes by qRT-PCR on an independent set of samples. Three different techniques were then used to test for quantitative differences in the recovered conjunctival protein fraction.

RESULTS

Focused arrays identified a set of 13 differentially expressed genes. Validation by qRT-PCR confirmed differential expression in four of these genes (COL1A1, COL7A1, MMP7, and TLR6). Increased expression of MMP7 was the only consistent differentially regulated gene in the conjunctival samples of trichiasis subjects. MMP7 was present in isolated conjunctival proteins and in the tissue culture supernatants of peripheral blood lymphocytes after stimulation.

CONCLUSIONS

There is an imbalance in extracellular matrix turnover with minimal contribution of adaptive immune responses at this stage of trichiasis. There was little evidence of broad differential expression in genes characteristic of polar responses of adaptive T cells or macrophages. The control of the MMP7 response and its activity appears significant in the fibrotic changes observed in TT.

Wnt/beta-catenin signaling: a novel target for therapeutic intervention of fibrotic kidney disease

Fibrosis of epithelial parenchymal organs and end-stage organ failure, the final common pathway of many progressive chronic diseases including chronic kidney disease, continue to increase worldwide and are a major determinant of morbidity and mortality. Fibrosis is an active biosynthetic healing response initiated to protect the tissue from injury through the timed release of proteins but leads to serious tissue damage when it becomes independent from the initiating stimulus. Massive deposition of extracellular matrix by accumulation of myofibroblasts and disruption of the normal tissue architecture are characteristic of tissue fibrosis. The highly conserved Wnt/beta-catenin signaling pathway is essential to embryonic development in general and kidney morphogenesis in particular by regulating the expression of target genes, most often through the transcription factor T cell factor (TCF) and/or lymphoid enhancer factor (LEF). Emerging evidence from studies of renal fibrosis suggests that altered Wnt/beta-catenin signaling is linked to the pathogenesis of renal fibrosis. The renoprotective properties of some currently available drugs might be attributable in part to inhibition of Wnt signaling. The development of orally active Wnt modulators will provide a potentially important pharmacological tool for further investigating the role of Wnt/beta-catenin signaling and might offer a novel therapeutic strategy in renal fibrosis.