Hemizygous deletion of CTGF/CCN2 does not suffice to prevent fibrosis of the severely injured kidney

Generation of Conditional KO Mice of CCN2 and Its Function in the Kidney

CCN2 has been shown to be closely involved in the progression of renal fibrosis, indicating the potential of CCN2 inhibition as a therapeutic target. Although the examination of the renal disease phenotypes of adult CCN2 knockout mice has yielded valuable scientific insights, perinatal death has limited studies of CCN2 in vivo. Conditional knockout technology has become widely used to delete genes in the target cell populations or time points using cell-specific Cre recombinase-expressing mice. Therefore, several lines of CCN2-floxed mice have been developed to assess the functional role of CCN2 in adult mice.CCN2 levels are elevated in renal fibrosis and proliferative glomerulonephritis, making them suitable disease models for assessing the effects of CCN2 deletion on the kidney. Renal fibrosis is characterized by glomerulosclerosis and tubulointerstitial fibrosis and transforming growth factor-β. CCN2 is increased in fibrosis and modulates a number of downstream signaling pathways involved in the fibrogenic properties of TGF-β. Unilateral ureteral obstruction is one of the most widely used models of renal tubulointerstitial fibrosis. In addition, anti-glomerular basement membrane antibody glomerulonephritis has become the most widely used model for evaluating the effect of increased renal CCN2 expression. Herein, we describe the construction of CCN2-floxed mice and inducible systemic CCN2 conditional knockout mice and methods for the operation of unilateral ureteral obstruction and the induction of anti-glomerular basement membrane antibody glomerulonephritis.

Cellular communication network 2 (connective tissue growth factor) aggravates acute DNA damage and subsequent DNA damage response-senescence-fibrosis following kidney ischemia reperfusion injury

Chronic allograft dysfunction with progressive fibrosis of unknown cause remains a major issue after kidney transplantation, characterized by ischemia-reperfusion injury (IRI). One hypothesis to account for this is that spontaneous progressive tubulointerstitial fibrosis following IRI is driven by cellular senescence evolving from a prolonged, unresolved DNA damage response (DDR). Since cellular communication network factor 2 ((CCN2), formerly called connective tissue growth factor), an established mediator of kidney fibrosis, is also involved in senescence-associated pathways, we investigated the relation between CCN2 and cellular senescence following kidney transplantation. Tubular CCN2 overexpression was found to be associated with DDR, loss of kidney function and tubulointerstitial fibrosis in both the early and the late phase in human kidney allograft biopsies. Consistently, CCN2 deficient mice developed reduced senescence and tubulointerstitial fibrosis in the late phase; six weeks after experimental IRI. Moreover, tubular DDR markers and plasma urea were less elevated in CCN2 knockout than in wild-type mice. Finally, CCN2 administration or overexpression in epithelial cells induced upregulation of tubular senescence-associated genes including p21, while silencing of CCN2 alleviated DDR induced by anoxia-reoxygenation injury in cultured proximal tubule epithelial cells. Thus, our observations indicate that inhibition of CCN2 can mitigate IRI-induced acute kidney injury, DNA damage, and the subsequent DDR-senescence-fibrosis sequence. Hence, targeting CCN2 might help to protect the kidney from transplantation-associated post-IRI chronic kidney dysfunction.

Vaccination against connective tissue growth factor attenuates the development of renal fibrosis

There is a critical need for efficient treatment of chronic kidney disease (CKD). Renal fibrosis is a final common pathway to end-stage renal disease independent of the underlying etiology, and connective tissue growth factor (CTGF) is a well-recognized profibrotic factor in fibrosis of various organ systems. Here, we developed a novel peptide vaccine against CTGF to attenuate the development of renal fibrosis. Three inoculations with this CTGF vaccine at 2-week intervals elicited antibodies specifically binding to human full-length CTGF, and the antigen-specific serum IgG antibody titers were maintained for > 30 weeks. The efficacy of the CTGF vaccine on renal fibrosis was evaluated in adenine-induced CKD and unilateral ureteral obstruction (UUO) murine models. In adenine-induced CKD model, immunization with the CTGF vaccine attenuated renal interstitial fibrosis. Vaccinated mice showed low levels of serum creatinine and urea nitrogen and low urine albumin–creatinine ratio compared with vehicle-treated mice. In UUO model, the CTGF vaccination also suppressed the onset of renal fibrosis. In an in vitro study, CTGF vaccine-elicited IgG antibodies efficiently suppressed CTGF-induced- and transforming growth factor-β-induced α-smooth muscle actin expression in kidney fibroblasts. These results demonstrate that the CTGF vaccine is a promising strategy to attenuate the development of renal fibrosis.

A robust, accurate, sensitive LC-MS/MS method to measure indoxyl sulfate, validated for plasma and kidney cells

Proximal tubular damage is an important prognostic determinant in various chronic kidney diseases (CKDs). Currently available diagnostic methods do not allow for early disease detection and are neither efficient. Indoxyl sulfate (IS) is an endogenous metabolite and protein-bound uremic toxin that is eliminated via renal secretion, but accumulates in plasma during tubular dysfunction. Therefore, it may be suitable as a tubular function marker. To evaluate this, a fast bioanalytical method was developed and validated for IS in various species and a kidney cell line using LC-MS/MS. An isotope-labeled IS potassium salt as an internal standard and acetonitrile (ACN) as a protein precipitant were used for sample pretreatment. The analyte was separated on a Polaris 3 C18-A column by gradient elution using 0.1% formic acid in water and ACN, and detected by negative electrospray ionization in selected reaction monitoring mode. The within-day (≤ 4.0%) and between-day (≤ 4.3%) precisions and accuracies (97.7 to 107.3%) were within the acceptable range. The analyte showed sufficient stability at all conditions investigated. Finally, applying this assay, significantly higher plasma and lower urine concentrations of IS were observed in mice with diabetic nephropathy with tubular damage, which encourages validation toward its use as a biomarker.

Connective Tissue Growth Factor Single Nucleotide Polymorphisms in (Familial) Pulmonary Fibrosis and Connective Tissue Disease Associated Interstitial Lung Disease

PURPOSE

Connective tissue growth factor (CTGF) is an important mediator in fibrotic disease. Single nucleotide polymorphisms (SNPs) in CTGF have been found to be associated with different fibrotic diseases and CTGF protein was found to be upregulated in lung tissue, bronchoalveolar lavage cells, and plasma of idiopathic pulmonary fibrosis (IPF) patients. We investigated whether genetic variants predispose to sporadic IPF (spIPF), familial pulmonary fibrosis (FPF), and connective tissue disease associated ILD (CTD-ILD).

METHODS

In total, 294 patients with spIPF and 294 healthy individuals were genotyped for CTGF rs12526196, rs9402373, rs6918698, and rs9399005. For replication of CTGF rs6918698 findings in pulmonary fibrosis, 128 patients with FPF, 125 with CTD-ILD, and an independent control cohort of 130 individuals were included. Lung tissue of 6 IPF patients was stained for CTGF to assess pulmonary localization.

RESULTS

Of the four SNPs, only the minor allele frequency (MAF) of CTGF rs6918698 deviated between spIPF (MAF 0.41) and controls (MAF 0.47; OR 0.774 (0.615-0.975); p = 0.030). Further comparison of CTGF rs6918698G showed a difference between FPF (MAF 0.33) and controls (MAF 0.48; OR 0.545 (0.382-0.778); p = 0.001), but not with CTD-ILD. CTGF was localized in alveolar and bronchiolar epithelium, alveolar macrophages, myofibroblasts and endothelium and highly expressed in the basal cell layer of sandwich foci.

CONCLUSION

CTGF rs6918698G associates with spIPF and with FPF, but not with CTD-ILD in a Dutch cohort. CTGF is localized in lung tissue involved in IPF pathogenesis. Further research into the role of this SNP on CTGF expression and fibrogenesis is warranted.

The decisive role of molecular pathology in presumed somatic metastases of type II testicular germ cell tumors: report of 2 cases

Background

Molecular diagnostics can be decisive in the differential diagnosis between a somatic metastasis of type II testicular germ cell tumor (TGCT) or a second primary carcinoma. This is in line with recent recommendations from the International Society of Urological Pathology, based on an international survey which showed that molecular testing is currently only performed by a minority of urological pathologists.

Case presentations

This case report illustrates the necessity of molecular testing in two patients with a history of type II TGCT and a metastatic (retro) peritoneal carcinoma years later. The genetic hallmark of type II TGCT, chromosome 12p gain, was studied by fluorescence in situ hybridization and whole genome methylation profiling in case 1, and by single nucleotide polymorphism (SNP)-array in case 2. Next generation sequencing (NGS) was used to further explore clonality between the primary TGCT and peritoneal metastasis in case 2. In case 1, chromosome 12p gain was found in the primary type II TGCT and in the acinar cell carcinoma of the metastatic malignancy. In case 2, SNP array showed 12p gain in the epithelial component of the primary teratomatous TGCT but not in the peritoneal adenocarcinoma. Furthermore, NGS showed no mutations in the primary teratomatous TGCT but a KRAS and GNAS mutation in the peritoneal adenocarcinoma, suggestive of an appendicular origin.

Conclusions

Without the molecular data, both cases would have been regarded as a metastatic TGCT with development of somatic-type malignancy, which appeared a wrong diagnosis for case 2. These cases demonstrate the importance of molecular methods as an adjunct in today’s pathology practice.

Interleukin-22 Attenuated Renal Tubular Injury in Aristolochic Acid Nephropathy via Suppressing Activation of NLRP3 Inflammasome

Aristolochic acid nephropathy (AAN), as a rapidly progressive interstitial nephropathy due to excessive ingestion of aristolochia herbal medications, has recently raised considerable concerns among clinicians and researchers as its underlying pathogenic mechanisms are largely unclear. In the current study, we identified NLRP3 inflammasome activation as a novel pathological mechanism of AAN. We found that NLRP3 inflammasome was aberrantly activated both in vivo and in vitro after AA exposure. Blockade of IL-1β and NLRP3 inflammasome activation by IL-1Ra significantly attenuated renal tubular injury and function loss in AA-induced nephropathy. Moreover, NLRP3 or Caspase-1 deficiency protected against renal injury in the mouse model of acute AAN, suggesting that the NLRP3 signaling pathway was probably involved in the pathogenesis of AAN. We also found that administration of IL-22 could markedly attenuate renal tubular injury in AAN. Notably, IL-22 intervention significantly alleviated renal fibrosis and dysfunction in AA-induced nephropathy. Furthermore, IL-22 largely inhibited renal activation of NLRP3 inflammasome in AA-induced nephropathy. These results indicated that IL-22 ameliorated renal tubular injury in AAN through suppression of NLRP3 inflammasome activation. In summary, this study identified renal activation of NLRP3 inflammasome as a novel mechanism underlying the pathogenesis of AAN, thus providing a potential therapeutic strategy for AAN based on suppression of NLRP3 inflammasome activation.

CTGF in kidney fibrosis and glomerulonephritis

Background

Glomerulonephritis, which causes inflammation in glomeruli, is a common cause of end-stage renal failure. Severe and prolonged inflammation can damage glomeruli and lead to kidney fibrosis. Connective tissue growth factor (CTGF) is a member of the CCN matricellular protein family, consisting of four domains, that regulates the signaling of other growth factors and promotes kidney fibrosis.

Main body of the abstract

CTGF can simultaneously interact with several factors with its four domains. The microenvironment differs depending on the types of cells and tissues and differentiation stages of these cells. The diverse biological actions of CTGF on various types of cells and tissues depend on this difference in microenvironment. In the kidney, CTGF is expressed at low levels in normal condition and its expression is upregulated by kidney fibrosis. CTGF expression is known to be upregulated in the extra-capillary and mesangial lesions of glomerulonephritis in human kidney biopsy samples. In addition to involvement in fibrosis, CTGF modulates the expression of inflammatory mediators, including cytokines and chemokines, through distinct signaling pathways, in various cell systems. In anti-glomerular basement membrane (GBM) glomerulonephritis, systemic CTGF knockout (Rosa-CTGF cKO) mice exhibit 50% reduction of proteinuria and decreased crescent formation and mesangial expansion compared with control mice. In addition to fibrotic markers, the glomerular mRNA expression of Ccl2 is increased in the control mice with anti-GBM glomerulonephritis, and this increase is reduced in Rosa-CTGF cKO mice with nephritis. Accumulation of MAC2-positive cells in glomeruli is also reduced in Rosa-CTGF cKO mice. These results suggest that CTGF may be required for the upregulation of Ccl2 expression not only in anti-GBM glomerulonephritis but also in other types of glomerulonephritis, such as IgA nephropathy; CTGF expression and accumulation of macrophages in the mesangial area have been documented in these glomerular diseases. CTGF induces the expression of inflammatory mediators and promotes cell adhesion.

Short conclusion

CTGF plays an important role in the development of glomerulonephritis by inducing the inflammatory process. CTGF is a potentiate target for the treatment of glomerulonephritis.

Endothelin A receptor blocker and calcimimetic in the adenine rat model of chronic renal insufficiency

BACKGROUND

We studied whether endothelin receptor antagonist and calcimimetic treatments influence renal damage and kidney renin-angiotensin (RA) components in adenine-induced chronic renal insufficiency (CRI).

METHODS

Male Wistar rats (n = 80) were divided into 5 groups for 12 weeks: control (n = 12), 0.3% adenine (Ade; n = 20), Ade + 50 mg/kg/day sitaxentan (n = 16), Ade + 20 mg/kg/day cinacalcet (n = 16), and Ade + sitaxentan + cinacalcet (n = 16). Blood pressure (BP) was measured using tail-cuff, kidney histology was examined, and RA components measured using RT-qPCR.

RESULTS

Adenine caused tubulointerstitial damage with severe CRI, anemia, hyperphosphatemia, 1.8-fold increase in urinary calcium excretion, and 3.5-fold and 18-fold increases in plasma creatinine and PTH, respectively. Sitaxentan alleviated tubular atrophy, while sitaxentan + cinacalcet combination reduced interstitial inflammation, tubular dilatation and atrophy in adenine-rats. Adenine diet did not influence kidney angiotensin converting enzyme (ACE) and AT₄ receptor mRNA, but reduced mRNA of renin, AT_1a, AT₂, (pro)renin receptor and Mas to 40-60%, and suppressed ACE2 to 6% of that in controls. Sitaxentan reduced BP by 8 mmHg, creatinine, urea, and phosphate concentrations by 16-24%, and PTH by 42%. Cinacalcet did not influence BP or creatinine, but reduced PTH by 84%, and increased hemoglobin by 28% in adenine-rats. The treatments further reduced renin mRNA by 40%, while combined treatment normalized plasma PTH, urinary calcium, and increased ACE2 mRNA 2.5-fold versus the Ade group (p < 0.001).

CONCLUSIONS

In adenine-induced interstitial nephritis, sitaxentan improved renal function and tubular atrophy. Sitaxentan and cinacalcet reduced kidney renin mRNA by 40%, while their combination alleviated tubulointerstitial damage and urinary calcium loss, and increased kidney tissue ACE2 mRNA.

Connective tissue growth factor regulates fibrosis-associated renal lymphangiogenesis

Lymphangiogenesis is correlated with the degree of renal interstitial fibrosis. Pro-fibrotic transforming growth factor β induces VEGF-C production, the main driver of lymphangiogenesis. Connective tissue growth factor (CTGF) is an important determinant of fibrotic tissue remodeling, but its possible involvement in lymphangiogenesis has not been explored. We found prominent lymphangiogenesis during tubulointerstitial fibrosis to be associated with increased expression of CTGF and VEGF-C in human obstructed nephropathy as well as in diabetic kidney disease. Using CTGF knockout mice, we investigated the involvement of CTGF in development of fibrosis and associated lymphangiogenesis in obstructive nephropathy. The increase of lymphatic vessels and VEGF-C in obstructed kidneys was significantly reduced in CTGF knockout compared to wild-type mice. Also in mouse kidneys subjected to ischemia-reperfusion injury, CTGF knockdown was associated with reduced lymphangiogenesis. In vitro, CTGF induced VEGF-C production in HK-2 cells, while CTGF siRNA suppressed transforming growth factor β1-induced VEGF-C upregulation. Furthermore, surface plasmon resonance analysis showed that CTGF and VEGF-C directly interact. Interestingly, VEGF-C-induced capillary-like tube formation by human lymphatic endothelial cells was suppressed by full-length CTGF but not by naturally occurring proteolytic CTGF fragments. Thus, CTGF is significantly involved in fibrosis-associated renal lymphangiogenesis through regulation of, and direct interaction with, VEGF-C.

Tubulointerstitial expression and urinary excretion of connective tissue growth factor 3 months after renal transplantation predict interstitial fibrosis and tubular atrophy at 5 years in a retrospective cohort analysis

Connective tissue growth factor (CTGF) is an important mediator of renal allograft fibrosis, and urinary CTGF (CTGFu) levels correlate with the development of human allograft interstitial fibrosis. We evaluated the predictive value of CTGF protein expression in 160 kidney transplant recipients with paired protocol biopsies at 3 months and 5 years after transplantation. At month 3 and year 1, CTGFu was measured using ELISA, and biopsies were immunohistochemically stained for CTGF, with semiquantitative scoring of tubulointerstitial CTGF-positive area (CTGFti). Predictors of interstitial fibrosis and tubular atrophy (IF/TA) severity at 5 years were donor age [OR 1.05 (1.02-1.08), P = 0.001], female donor [OR 0.40 (0.18-0.90), P = 0.026], induction therapy [OR 2.76 (1.10-6.89), P = 0.030], and CTGFti >10% at month 3 [OR 2.72 (1.20-6.15), P = 0.016]. In subgroups of patients with little histologic damage at 3 months [either ci score 0 (n = 119), IF/TA score ≤1 (n = 123), or absence of IF/TA, interstitial inflammation, and tubulitis (n = 45)], consistent predictors of progression of chronic histologic damage by 5 years were donor age, induction therapy, CTGFti >10%, and CTGFu. These results suggest that, even in patients with favorable histology at 3 months, significant CTGF expression is often present which may predict accelerated accumulation of histologic damage.

Expression levels of TGF-β1 and CTGF are associated with the severity of Duchenne muscular dystrophy

The present study aimed to analyze the association of transforming growth factor-β1 (TGF-β1) and connective tissue growth factor (CTGF) expression levels in skeletal muscle with the clinical manifestation of Duchenne muscular dystrophy (DMD). A total of 18 cases of DMD, which were confirmed by routine pathological diagnosis were recruited into the present study, along with 8 subjects who suffered from acute trauma but did not present any neuromuscular diseases and were enrolled as the healthy controls. Immunohistochemical staining was used to detect the expression levels of CTGF and TGF-β1 in muscle biopsy specimens. Furthermore, Spearman rank correlation analysis was conducted among the expression levels of CTGF and TGF-β1, age, clinical severity and pathological severity in DMD patients. The immunohistochemical staining results revealed that the expression levels of CTGF and TGF-β1 were significantly increased in the DMD group compared with those in the control group (P<0.05). These levels were not found to be significantly correlated with the onset age (P>0.05), but there was a significant correlation with the degree of pathology and clinical severity (P<0.05). In conclusion, an upregulated expression of CTGF and TGF-β1 was revealed in the skeletal muscle of DMD patients, which were in positive correlation with the degree of pathology and clinical severity. These two factors may be involved in the pathophysiology of fibrosis in DMD.

Design and Analysis of CCN Gene Activity Using CCN Knockout Mice Containing LacZ Reporters

Two developments have greatly facilitated the construction of CCN mutant mouse strains. The first is the availability of modified embryonic stem (ES) cells and mice developed through several large-scale government-sponsored research programs. The second is the advent of CRISPR/Cas9 technology. In this chapter, we describe the available mouse strains generated by gene targeting techniques and the CCN targeting vectors and genetically modified ES cells that are available for the generation of CCN mutant mice. Many of these mutant mouse lines and ES cells carry a β-galactosidase reporter that can be used to track CCN expression, facilitating phenotypic analysis and revealing new sites of CCN action. Therefore, we also describe a method for β-galactosidase staining.

Production and Analysis of Conditional KO Mice of CCN2 in Kidney

CCN2 has been shown to be closely involved in the progression of renal fibrosis, indicating the potential of CCN2 inhibition as a therapeutic target. Although the examination of the phenotypes of adult CCN2 knockout mice with renal diseases has yielded valuable scientific insights, perinatal death has limited studies of CCN2 in vivo. Conditional knockout technology has become widely used for the deletion of genes in the desired cell populations and time points through the use of cell-specific Cre recombinase-expressing mice. Accordingly, several lines of CCN2 floxed mice have been developed for the assessment of the functional role of CCN2 in adult mice.CCN2 levels are increased in renal fibrosis and proliferative glomerulonephritis, which represent good disease models for evaluating the effects of CCN2 deletion on the kidney. Of these, anti-glomerular basement membrane antibody glomerulonephritis has become the most widely used model for evaluating the effect of increased renal CCN2 expression. Herein, we describe the construction of CCN2 floxed mice and inducible systemic CCN2 conditional knockout mice and methods for the induction of anti-glomerular basement membrane antibody glomerulonephritis.

CCN2 reduction mediates protective effects of BMP7 treatment in obstructive nephropathy

Treatment with rhBMP7 exerts profound protective effects in a wide variety of experimental models of renal disease. However, little is known about how these protective effects are mediated, and which cells in the kidney are targeted by exogenous rhBMP7 treatment. To determine if rhBMP7 increases glomerular and tubulointerstitial canonical BMP signaling, we performed Unilateral Ureteral Obstruction (UUO, a widely used obstructive nephropathy model) in mice reporting transcriptional activity downstream of canonical BMP signaling by the expression of GFP under the BMP Responsive Element of the Id1 promoter (BRE:gfp mice). We also analysed the impact of rhBMP7 treatment on severity of the UUO phenotype, on TGFβ signaling, and on expression of CCN2 (CTGF). Despite profound protective effects with respect to morphological damage, macrophage infiltration, and fibrosis, no significant difference in GFP-expression was observed upon rhBMP7 administration. Also TGFβ signalling was similar in rhBMP7 and vehicle treated mice, but CCN2 expression in obstructed kidneys was significantly reduced by rhBMP7 treatment. Of note, in heterozygous CCN2 mice (CCN2+/−) treatment with rhBMP7 did not (further) reduce the severity of kidney damage in the UUO-model. These data suggest that protection against obstructive nephropathy by exogenous rhBMP7 treatment relies primarily on non-canonical BMP signaling, and may be mediated in large part by downregulation of CCN2 expression.

Age-dependent shifts in renal response to injury relate to altered BMP6/CTGF expression and signaling

Age is associated with an increased prevalence of chronic kidney disease (CKD), which, through progressive tissue damage and fibrosis, ultimately leads to loss of kidney function. Although much effort is put into studying CKD development experimentally, age has rarely been taken into account. Therefore, we investigated the effect of age on the development of renal tissue damage and fibrosis in a mouse model of obstructive nephropathy (i.e., unilateral ureter obstruction; UUO). We observed that after 14 days, obstructed kidneys of old mice had more tubulointerstitial atrophic damage but less fibrosis than those of young mice. This was associated with reduced connective tissue growth factor (CTGF), and higher bone morphogenetic protein 6 (BMP6) expression and pSMAD1/5/8 signaling, while transforming growth factor-β expression and transcriptional activity were no different in obstructed kidneys of old and young mice. In vitro, CTGF bound to and inhibited BMP6 activity. In summary, our data suggest that in obstructive nephropathy atrophy increases and fibrosis decreases with age and that this relates to increased BMP signaling, most likely due to higher BMP6 and lower CTGF expression.

CTGF knockout does not affect cardiac hypertrophy and fibrosis formation upon chronic pressure overload

BACKGROUND

One of the main contributors to maladaptive cardiac remodeling is fibrosis. Connective tissue growth factor (CTGF), a matricellular protein that is secreted into the cardiac extracellular matrix by both cardiomyocytes and fibroblasts, is often associated with development of fibrosis. However, recent studies have questioned the role of CTGF as a pro-fibrotic factor. Therefore, we aimed to investigate the effect of CTGF on cardiac fibrosis, and on functional, structural, and electrophysiological parameters in a mouse model of CTGF knockout (KO) and chronic pressure overload.

METHODS AND RESULTS

A new mouse model of global conditional CTGF KO induced by tamoxifen-driven deletion of CTGF, was subjected to 16weeks of chronic pressure overload via transverse aortic constriction (TAC, control was sham surgery). CTGF KO TAC mice presented with hypertrophic hearts, and echocardiography revealed a decrease in contractility on a similar level as control TAC mice. Ex vivo epicardial mapping showed a low incidence of pacing-induced ventricular arrhythmias (2/12 in control TAC vs. 0/10 in CTGF KO TAC, n.s.) and a tendency towards recovery of the longitudinal conduction velocity of CTGF KO TAC hearts. Picrosirius Red staining on these hearts unveiled increased fibrosis at a similar level as control TAC hearts. Furthermore, genes related to fibrogenesis were also similarly upregulated in both TAC groups. Histological analysis revealed an increase in fibronectin and vimentin protein expression, a significant reduction in connexin43 (Cx43) protein expression, and no difference in NaV1.5 expression of CTGF KO ventricles as compared with sham treated animals.

CONCLUSION

Conditional CTGF inhibition failed to prevent TAC-induced cardiac fibrosis and hypertrophy. Additionally, no large differences were found in other parameters between CTGF KO and control TAC mice. With no profound effect of CTGF on fibrosis formation, other factors or pathways are likely responsible for fibrosis development.

Blockade of CCN4 attenuates CCl4-induced liver fibrosis

INTRODUCTION

CCN4, also termed WNT-inducible signaling pathway protein-1 (WISP-1), has important roles in inflammation and tissue injury. This study aimed to investigate the effect of CCN4 inhibition using monoclonal anti-CCN4 antibody (CCN4mAb) on the liver injury and fibrosis in a mouse model of liver fibrosis.

MATERIAL AND METHODS

The mouse liver fibrosis model was induced by carbon tetrachloride (CCl4). Mice received vehicle (saline/olive oil) by subcutaneous injection, CCl4 by subcutaneous injection or CCl4 (subcutaneous) plus CCN4mAb by subcutaneous injection. The pro-inflammatory and pro-fibrotic factors were determined by Western blot. The biochemistry and histopathology, collagen deposition and nuclear factor (NF)-κB activity were also assessed.

RESULTS

Chronic CCl4 treatment caused liver injury and collagen accumulation. The expression levels of CCN4, pro-inflammatory and pro-fibrotic mediators as well as the activity of NF-κB were markedly increased. Treatment with CCN4mAb significantly inhibited CCl4-induced CCN4 expression, leading to attenuated CCl4-induced liver injury and the inflammatory response. CCN4 blockade also significantly reduced the formation of collagen in the liver and the expression of α-smooth muscle actin and transforming growth factor β1.

CONCLUSIONS

CCN4 inhibition by CCN4mAb in vivo significantly attenuated the CCl4-induced liver injury and the progression of liver fibrosis. CCN4 may represent a novel therapeutic target for liver injury and fibrosis.

Loss of tumour suppressor PTEN expression in renal injury initiates SMAD3- and p53-dependent fibrotic responses

Deregulation of the tumour suppressor PTEN occurs in lung and skin fibrosis and diabetic and ischaemic renal injury. However, the potential role of PTEN and associated mechanisms in the progression of kidney fibrosis is unknown. Tubular and interstitial PTEN expression was dramatically decreased in several models of renal injury, including aristolochic acid nephropathy (AAN), streptozotocin (STZ)-mediated injury and ureteral unilateral obstruction (UUO), correlating with Akt, p53 and SMAD3 activation and fibrosis. Stable silencing of PTEN in HK-2 human tubular epithelial cells induced dedifferentiation and CTGF, PAI-1, vimentin, α-SMA and fibronectin expression, compared to HK-2 cells expressing control shRNA. Furthermore, PTEN knockdown stimulated Akt, SMAD3 and p53(Ser15) phosphorylation, with an accompanying decrease in population density and an increase in epithelial G1 cell cycle arrest. SMAD3 or p53 gene silencing or pharmacological blockade partially suppressed fibrotic gene expression and relieved growth inhibition orchestrated by deficiency or inhibition of PTEN. Similarly, shRNA suppression of PAI-1 rescued the PTEN loss-associated epithelial proliferative arrest. Moreover, TGFβ1-initiated fibrotic gene expression is further enhanced by PTEN depletion. Combined TGFβ1 treatment and PTEN silencing potentiated epithelial cell death via p53-dependent pathways. Thus, PTEN loss initiates tubular dysfunction via SMAD3- and p53-mediated fibrotic gene induction, with accompanying PAI-1-dependent proliferative arrest, and cooperates with TGFβ1 to induce the expression of profibrotic genes and tubular apoptosis.

Therapeutic targets for treating fibrotic kidney diseases

Renal fibrosis is the hallmark of virtually all progressive kidney diseases and strongly correlates with the deterioration of kidney function. The renin-angiotensin-aldosterone system blockade is central to the current treatment of patients with chronic kidney disease (CKD) for the renoprotective effects aimed to prevent or slow progression to end-stage renal disease (ESRD). However, the incidence of CKD is still increasing, and there is a critical need for new therapeutics. Here, we review novel strategies targeting various components implicated in the fibrogenic pathway to inhibit or retard the loss of kidney function. We focus, in particular, on antifibrotic approaches that target transforming growth factor (TGF)-β1, a key mediator of kidney fibrosis, and exciting new data on the role of autophagy. Bone morphogenetic protein (BMP)-7 and connective tissue growth factor (CTGF) are highlighted as modulators of profibrotic TGF-β activity. BMP-7 has a protective role against TGF-β1 in kidney fibrosis, whereas CTGF enhances TGF-β-mediated fibrosis. We also discuss recent advances in the development of additional strategies for antifibrotic therapy. These include strategies targeting chemokine pathways via CC chemokine receptors 1 and 2 to modulate the inflammatory response, inhibition of phosphodiesterase to restore nitric oxide-cyclic 3',5'-guanosine monophosphate function, inhibition of nicotinamide adenine dinucleotide phosphate oxidase 1 and 4 to suppress reactive oxygen species production, and inhibition of endothelin 1 or tumor necrosis factor α to ameliorate progressive renal fibrosis. Furthermore, a brief overview of some of the biomarkers of kidney fibrosis is currently being explored that may improve the ability to monitor antifibrotic therapies. It is hoped that evidence based on the preclinical and clinical data discussed in this review leads to novel antifibrotic therapies effective in patients with CKD to prevent or delay progression to ESRD.

A perspective on anti-CCN2 therapy for chronic kidney disease

Kidney fibrosis is the common end point of chronic kidney disease independent of aetiology. Currently, no effective therapy exists to reduce kidney fibrosis. CCN2 appears to be an interesting candidate for anti-fibrotic drug targeting, because it holds a central position in the development of kidney fibrosis and interacts with a variety of factors that are involved in the fibrotic response, including transforming growth factor (TGF) β and Bone morphogenetic proteins. Although CCN2 modifies many pathways, it does not appear to have a membrane receptor of its own. Numerous experimental and clinical studies lowering CCN2 bioavailability have shown promising results with minimal adverse side effects. This review aims to provide an overview of the current state of CCN2 research with a focus on anti-fibrotic therapy.

Targeting CTGF, EGF and PDGF pathways to prevent progression of kidney disease

Chronic kidney disease (CKD) is a major health and economic burden with a rising incidence. During progression of CKD, the sustained release of proinflammatory and profibrotic cytokines and growth factors leads to an excessive accumulation of extracellular matrix. Transforming growth factor β (TGF-β) and angiotensin II are considered to be the two main driving forces in fibrotic development. Blockade of the renin-angiotensin-aldosterone system has become the mainstay therapy for preservation of kidney function, but this treatment is not sufficient to prevent progression of fibrosis and CKD. Several factors that induce fibrosis have been identified, not only by TGF-β-dependent mechanisms, but also by TGF-β-independent mechanisms. Among these factors are the (partially) TGF-β-independent profibrotic pathways involving connective tissue growth factor, epidermal growth factor and platelet-derived growth factor and their receptors. In this Review, we discuss the specific roles of these pathways, their interactions and preclinical evidence supporting their qualification as additional targets for novel antifibrotic therapies.

Key roles for the small leucine-rich proteoglycans in renal and pulmonary pathophysiology

BACKGROUND

Small leucine-rich proteoglycans (SLRPs) are molecules that have signaling roles in a multitude of biological processes. In this respect, SLRPs play key roles in the evolution of a variety of diseases throughout the human body.

SCOPE OF REVIEW

We will critically review current developments in the roles of SLRPs in several types of disease of the kidney and lungs. Particular emphasis will be given to the roles of decorin and biglycan, the best characterized members of the SLRP gene family.

MAJOR CONCLUSIONS

In both renal and pulmonary disorders, SLRPs are essential elements that regulate several pathophysiological processes including fibrosis, inflammation and tumor progression. Decorin has remarkable antifibrotic and antitumorigenic properties and is considered a valuable potential treatment of these diseases. Biglycan can modulate inflammatory processes in lung and renal inflammation and is a potential target in the treatment of inflammatory conditions.

GENERAL SIGNIFICANCE

SLRPs can serve as either treatment targets or as potential treatment in renal or lung disease. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Connective tissue growth factor (CTGF) expression modulates response to high glucose

Connective tissue growth factor (CTGF) is an important mediator of fibrosis; emerging evidence link changes in plasma and urinary CTGF levels to diabetic kidney disease. To further ascertain the role of CTGF in responses to high glucose, we assessed the consequence of 4 months of streptozotocin-induced diabetes in wild type (+/+) and CTGF heterozygous (+/−) mice. Subsequently, we studied the influence of glucose on gene expression and protein in mice embryonic fibroblasts (MEF) cells derived from wildtype and heterozygous mice. At study initiation, plasma glucose, creatinine, triglyceride and cholesterol levels were similar between non-diabetic CTGF+/+ and CTGF+/− mice. In the diabetic state, plasma glucose levels were increased in CTGF+/+ and CTGF+/− mice (28.2 3.3 mmol/L vs 27.0 3.1 mmol/L), plasma triglyceride levels were lower in CTGF+/− mice than in CTGF+/+ (0.7 0.2 mmol/L vs 0.5 0.1 mmol/L, p<0.05), but cholesterol was essentially unchanged in both groups. Plasma creatinine was higher in diabetic CTGF+/+ group (11.7±1.2 vs 7.9±0.6 µmol/L p<0.01), while urinary albumin excretion and mesangial expansion were reduced in diabetic CTGF+/− animals. Cortices from diabetic mice (both CTGF +/+ and CTGF +/−) manifested higher expression of CTGF and thrombospondin 1 (TSP1). Expression of nephrin was reduced in CTGF +/+ animals; this reduction was attenuated in CTGF+/− group. In cultured MEF from CTGF+/+ mice, glucose (25 mM) increased expression of pro-collagens 1, IV and XVIII as well as fibronectin and thrombospondin 1 (TSP1). In contrast, activation of these genes by high glucose was attenuated in CTGF+/− MEF. We conclude that induction of Ctgf mediates expression of extracellular matrix proteins in diabetic kidney. Thus, genetic variability in CTGF expression directly modulates the severity of diabetic nephropathy.