Monocytes may promote myofibroblast accumulation and apoptosis in Alport renal fibrosis

NDRG2 alleviates photoreceptor apoptosis by regulating the STAT3/TIMP3/MMP pathway in mice with retinal degenerative disease

Photoreceptor apoptosis is the main pathological feature of retinal degenerative diseases; however, the underlying molecular mechanism has not been elucidated. Recent studies have shown that N-myc downstream regulated gene 2 (NDRG2) exerts a neuroprotective effect on the brain and spinal cord. In addition, our previous studies have confirmed that NDRG2 is expressed in mouse retinal photoreceptors and counteracts N-methyl-N-nitrosourea (MNU)-induced apoptosis. However, the underlying molecular mechanism remains unclear. In this study, we observed that the expression of NDRG2 was not only significantly inhibited in photoreceptors after MNU treatment but also after hydrogen peroxide treatment, and photoreceptor apoptosis was alleviated or aggravated after overexpression or knockdown of NDRG2 in the 661W photoreceptor cell line, respectively. The apoptosis inhibitor Z-VAD-FMK rescued photoreceptor apoptosis induced by MNU after NDRG2 knockdown. Next, we screened and identified tissue inhibitor of metalloproteinases 3 (TIMP3) as the downstream molecule of NDRG2 in 661W cells by using quantitative real-time polymerase chain reaction. TIMP3 exerts a neuroprotective effect by inhibiting the expression of matrix metalloproteinases (MMPs). Subsequently, we found that signal transducer and activator of transcription 3 (STAT3) mediated the NDRG2-associated regulation of TIMP3. Finally, we overexpressed NDRG2 in mouse retinal tissues by intravitreally injecting an adeno-associated virus with mouse NDRG2 in vivo. Results showed that NDRG2 upregulated the expression of phospho-STAT3 (p-STAT3) and TIMP3, while suppressing MNU-induced photoreceptor apoptosis and MMP expression. Our findings revealed how NDRG2 regulates the STAT3/TIMP3/MMP pathway and uncovered the molecular mechanism underlying its neuroprotective effect on mouse retinal photoreceptors.

Molecular and Cellular Mechanisms Underlying the Initiation and Progression of Alport Glomerular Pathology

Alport syndrome results from a myriad of variants in the COL4A3, COL4A4, or COL4A5 genes that encode type IV (basement membrane) collagens. Unlike type IV collagen α1(IV)₂α2(IV)₁ heterotrimers, which are ubiquitous in basement membranes, α3/α4/α5 have a limited tissue distribution. The absence of these basement membrane networks causes pathologies in some, but not all these tissues. Primarily the kidney glomerulus, the stria vascularis of the inner ear, the lens, and the retina as well as a rare link with aortic aneurisms. Defects in the glomerular basement membranes results in delayed onset and progressive focal segmental glomerulosclerosis ultimately requiring the patient to undergo dialysis and if accessible, kidney transplant. The lifespan of patients with Alport syndrome is ultimately significantly shortened. This review addresses the consequences of the altered glomerular basement membrane composition in Alport syndrome with specific emphasis on the mechanisms underlying initiation and progression of glomerular pathology.

Intravital imaging reveals glomerular capillary distension and endothelial and immune cell activation early in Alport syndrome

Alport syndrome (AS) is a genetic disorder caused by mutations in type IV collagen that lead to defective glomerular basement membrane, glomerular filtration barrier (GFB) damage, and progressive chronic kidney disease. While the genetic basis of AS is well known, the molecular and cellular mechanistic details of disease pathogenesis have been elusive, hindering the development of mechanism-based therapies. Here, we performed intravital multiphoton imaging of the local kidney tissue microenvironment in a X-linked AS mouse model to directly visualize the major drivers of AS pathology. Severely distended glomerular capillaries and aneurysms were found accompanied by numerous microthrombi, increased glomerular endothelial surface layer (glycocalyx) and immune cell homing, GFB albumin leakage, glomerulosclerosis, and interstitial fibrosis by 5 months of age, with an intermediate phenotype at 2 months. Renal histology in mouse or patient tissues largely failed to detect capillary aberrations. Treatment of AS mice with hyaluronidase or the ACE inhibitor enalapril reduced the excess glomerular endothelial glycocalyx and blocked immune cell homing and GFB albumin leakage. This study identified central roles of glomerular mechanical forces and endothelial and immune cell activation early in AS, which could be therapeutically targeted to reduce mechanical strain and local tissue inflammation and improve kidney function.

Tripartite motif-containing 35 (TRIM35) is up-regulated in UUO-induced renal fibrosis animal model

Renal fibrosis has been recognized as a serious health threat in the world because of the high cost of treatment and poor prognosis. However, the molecular mechanism of renal fibrosis is still largely unknown. In this study, we aimed at illustrating the role of TRIM35 in the renal fibrosis process. A UUO mouse model and a TGF-β1-induced tubulointerstitial fibrosis model were constructed for the research of renal fibrosis at animal and cell level, respectively. Hematoxylin-eosin and Masson staining were used for visualizing the pathological change. qRT-PCR, Western blot analysis and immunohistochemical staining were used to detect the expression of fibrosis-associated proteins and TRIM35. The results showed that, after the modeling, the expressions of α-SMA, Collagen I, Collagen III, Fibronectin and Snail1 were up-regulated, while the expression of E-cadherin was down-regulated, indicating the successful construction of animal and cell models. More importantly, TRIM35 was proved to be up-regulated in both animal and cell models. Therefore, this study demonstrates the potential promotional effect of TRIM35 in the renal fibrosis process, which may prove to be a new biomarker for the diagnosis and development of new treatments of renal fibrosis.

Osteopontin deficiency ameliorates Alport pathology by preventing tubular metabolic deficits

Alport syndrome is a rare hereditary renal disorder with no etiologic therapy. We found that osteopontin (OPN) is highly expressed in the renal tubules of the Alport mouse and plays a causative pathological role. OPN genetic deletion ameliorated albuminuria, hypertension, tubulointerstitial proliferation, renal apoptosis, and hearing and visual deficits in the Alport mouse. In Alport renal tubules we found extensive cholesterol accumulation and increased protein expression of dynamin-3 (DNM3) and LDL receptor (LDLR) in addition to dysmorphic mitochondria with defective bioenergetics. Increased pathological cholesterol influx was confirmed by a remarkably increased uptake of injected DiI-LDL cholesterol by Alport renal tubules, and by the improved lifespan of the Alport mice when crossed with the Ldlr-/- mice with defective cholesterol influx. Moreover, OPN-deficient Alport mice demonstrated significant reduction of DNM3 and LDLR expression. In human renal epithelial cells, overexpressing DNM3 resulted in elevated LDLR protein expression and defective mitochondrial respiration. Our results suggest a potentially new pathway in Alport pathology where tubular OPN causes DNM3- and LDLR-mediated enhanced cholesterol influx and impaired mitochondrial respiration.

Inhibition of penile tunica albuginea myofibroblasts activity by adipose-derived stem cells

The activation of tunica albuginea myofibroblasts (MFs) serves an essential role in Peyronie's disease (PD). Increasing evidence has reported that adipose tissue-derived stem cells (ADSCs) have been demonstrated to attenuate the symptoms of PD in animal models. However, the mechanisms of the antifibrotic effects of ADSCs in PD remain to be fully elucidated. In the present study, the inhibitory effects and possible mechanism of ADSCs on the activation of MFs derived from rat penile tunica albuginea were investigated. ADSCs were obtained from the paratesticular fat of Sprague Dawley rats. MFs were transformed from rat penile tunica albuginea fibroblasts through stimulation with 5 ng/ml tumor growth factor-β1. Transwell cell cultures were adopted for co-culture of ADSCs and MFs. Western blot analysis was used to assess changes in the expression levels of α smooth muscle actin (αSMA), collagen I, phosphorylated (p)-SMAD family member 2 (Smad2), Smad2, ras homolog family member A (RhoA), Rho associated coiled-coil containing protein kinase (ROCK)1 and ROCK2, caspase3, caspase9, and matrix metalloproteinases (MMPs). Collagen gel assays were used to assess cell contractility. Additionally, the concentration of hydroxyproline in the culture medium was detected using commercially available kits. It was demonstrated that ADSCs reduced the expression of αSMA and collagen I of MFs. Furthermore, p-Smad2, RhoA, ROCK1 and ROCK2 expression was significantly reduced in the MFs+ADSCs group compared with that in the MFs-only culture, while the expression of MMPs (MMP2, MMP3, MMP9 and MMP13) and caspases (caspase3 and caspase9) was upregulated. In addition, ADSCs were able to downregulate the concentration of hydroxyproline in the culture medium of MFs and reverse the contraction of MFs. Collectively, these results suggested that ADSCs inhibited the activation of MFs, decreased collagen production, and suppressed the contraction of myofibroblasts, via Smad and RhoA/ROCK signaling pathways. Furthermore, ADSCs reduced the deposition of collagen and promoted the apoptosis of MFs via MMPs, and caspases. Accordingly, the application of ADSCs may provide a novel therapeutic strategy for PD.

Bromide supplementation exacerbated the renal dysfunction, injury and fibrosis in a mouse model of Alport syndrome

A seminal study recently demonstrated that bromide (Br-) has a critical function in the assembly of type IV collagen in basement membrane (BM), and suggested that Br- supplementation has therapeutic potential for BM diseases. Because salts of bromide (KBr and NaBr) have been used as antiepileptic drugs for several decades, repositioning of Br- for BM diseases is probable. However, the effects of Br- on glomerular basement membrane (GBM) disease such as Alport syndrome (AS) and its impact on the kidney are still unknown. In this study, we administered daily for 16 weeks 75 mg/kg or 250 mg/kg (within clinical dosage) NaBr or NaCl (control) via drinking water to 6-week-old AS mice (mouse model of X-linked AS). Treatment with 75 mg/kg NaBr had no effect on AS progression. Surprisingly, compared with 250 mg/kg NaCl, 250 mg/kg NaBr exacerbated the progressive proteinuria and increased the serum creatinine and blood urea nitrogen in AS mice. Histological analysis revealed that glomerular injury, renal inflammation and fibrosis were exacerbated in mice treated with 250 mg/kg NaBr compared with NaCl. The expressions of renal injury markers (Lcn2, Lysozyme), matrix metalloproteinase (Mmp-12), pro-inflammatory cytokines (Il-6, Il-8, Tnf-α, Il-1β) and pro-fibrotic genes (Tgf-β, Col1a1, α-Sma) were also exacerbated by 250 mg/kg NaBr treatment. Notably, the exacerbating effects of Br- were not observed in wild-type mice. These findings suggest that Br- supplementation needs to be carefully evaluated for real positive health benefits and for the absence of adverse side effects especially in GBM diseases such as AS.

Association between Monocyte Count and Risk of Incident CKD and Progression to ESRD

BACKGROUND AND OBJECTIVES

Experimental evidence suggests a role for monocytes in the biology of kidney disease progression; however, whether monocyte count is associated with risk of incident CKD, CKD progression, and ESRD has not been examined in large epidemiologic studies.

DESIGN, SETTINGS, PARTICIPANTS, & MEASUREMENTS

We built a longitudinal observational cohort of 1,594,700 United States veterans with at least one eGFR during fiscal year 2004 (date of last eGFR during this period designated time zero) and no prior history of ESRD, dialysis, or kidney transplant. Cohort participants were followed until September 30, 2013 or death. Monocyte count closest to and before time zero was categorized in quartiles: quartile 1, >0.00 to ≤0.40 thousand cells per cubic millimeter (k/cmm); quartile 2, >0.40 to ≤0.55 k/cmm; quartile 3, >0.55 to ≤0.70 k/cmm; and quartile 4, >0.70 k/cmm. Survival models were built to examine the association between monocyte count and risk of incident eGFR<60 ml/min per 1.73 m2, risk of incident CKD, and risk of CKD progression defined as doubling of serum creatinine, eGFR decline ≥30%, or the composite outcome of ESRD, dialysis, or renal transplantation.

RESULTS

Over a median follow-up of 9.2 years (interquartile range, 8.3-9.4); in adjusted survival models, there was a graded association between monocyte counts and risk of renal outcomes. Compared with quartile 1, quartile 4 was associated with higher risk of incident eGFR<60 ml/min per 1.73 m2 (hazard ratio, 1.13; 95% confidence interval, 1.12 to 1.14) and risk of incident CKD (hazard ratio, 1.15; 95% confidence interval, 1.13 to 1.16). Quartile 4 was associated with higher risk of doubling of serum creatinine (hazard ratio, 1.22; 95% confidence interval, 1.20 to 1.24), ≥30% eGFR decline (hazard ratio, 1.18; 95% confidence interval, 1.17 to 1.19), and the composite renal end point (hazard ratio, 1.19; 95% confidence interval, 1.16 to 1.22). Cubic spline analyses of the relationship between monocyte count levels and renal outcomes showed a linear relationship, in which risk was higher with higher monocyte count. Results were robust to changes in sensitivity analyses.

CONCLUSIONS

Our results show a significant association between higher monocyte count and risks of incident CKD and CKD progression to ESRD.

Collagen IV diseases: A focus on the glomerular basement membrane in Alport syndrome

Alport syndrome is the result of mutations in any of three type IV collagen genes, COL4A3, COL4A4, or COL4A5. Because the three collagen chains form heterotrimers, there is an absence of all three proteins in the basement membranes where they are expressed. In the glomerulus, the mature glomerular basement membrane type IV collagen network, normally comprised of two separate networks, α3(IV)/α4(IV)/α5(IV) and α1(IV)/α2(IV), is comprised entirely of collagen α1(IV)/α2. This review addresses the current state of our knowledge regarding the consequence of this change in basement membrane composition, including both the direct, via collagen receptor binding, and indirect, regarding influences on glomerular biomechanics. The state of our current understanding regarding mechanisms of glomerular disease initiation and progression will be examined, as will the current state of the art regarding emergent therapeutic approaches to slow or arrest glomerular disease in Alport patients.

Collagen IV diseases: A focus on the glomerular basement membrane in Alport syndrome

Alport syndrome is the result of mutations in any of three type IV collagen genes, COL4A3, COL4A4, or COL4A5. Because the three collagen chains form heterotrimers, there is an absence of all three proteins in the basement membranes where they are expressed. In the glomerulus, the mature glomerular basement membrane type IV collagen network, normally comprised of two separate networks, α3(IV)/α4(IV)/α5(IV) and α1(IV)/α2(IV), is comprised entirely of collagen α1(IV)/α2. This review addresses the current state of our knowledge regarding the consequence of this change in basement membrane composition, including both the direct, via collagen receptor binding, and indirect, regarding influences on glomerular biomechanics. The state of our current understanding regarding mechanisms of glomerular disease initiation and progression will be examined, as will the current state of the art regarding emergent therapeutic approaches to slow or arrest glomerular disease in Alport patients.

Progression of Alport Kidney Disease in Col4a3 Knock Out Mice Is Independent of Sex or Macrophage Depletion by Clodronate Treatment

Alport syndrome is a genetic disease of collagen IV (α3, 4, 5) resulting in renal failure. This study was designed to investigate sex-phenotype correlations and evaluate the contribution of macrophage infiltration to disease progression using Col4a3 knock out (Col4a3KO) mice, an established genetic model of autosomal recessive Alport syndrome. No sex differences in the evolution of body mass loss, renal pathology, biomarkers of tubular damage KIM-1 and NGAL, or deterioration of kidney function were observed during the life span of Col4a3KO mice. These findings confirm that, similar to human autosomal recessive Alport syndrome, female and male Col4a3KO mice develop renal failure at the same age and with similar severity. The specific contribution of macrophage infiltration to Alport disease, one of the prominent features of the disease in human and Col4a3KO mice, remains unknown. This study shows that depletion of kidney macrophages in Col4a3KO male mice by administration of clodronate liposomes, prior to clinical onset of disease and throughout the study period, does not protect the mice from renal failure and interstitial fibrosis, nor delay disease progression. These results suggest that therapy targeting macrophage recruitment to kidney is unlikely to be effective as treatment of Alport syndrome.

Effects of mycophenolate mofetil on kidney function and phosphorylation status of renal proteins in Alport COL4A3-deficient mice

Background

We investigated the effects of mycophenolate mofetil (MMF) on kidney function and on protein phosphorylation in a mouse model for the human Alport syndrome.

Methods

COL4A3-deficient (COL4A3−/−) mice were randomly allocated to receive a placebo (PLC COL4A3−/−) or MMF treatment (MMF COL4A3−/−). Wild type mice (WT) were used as controls. Changes in serum creatinine, total protein and blood urea nitrogen (BUN), concentrations of mycophenolic acid (MPA) and its glucuronide metabolite (MPAG), serum protein electrophoresis, urine dipstick chemistry and sediment were measured. Changes in the phosphorylation status of renal proteins and histology were analyzed.

Results

MMF influenced kidney function and protein phosphorylation. Serum creatinine and BUN were lower in MMF treated compared to PLC treated COL4A3−/− mice. Serum albumin and alpha-1 globulins were significantly decreased while serum creatinine, alpha-2 globulins, urine dipstick protein, leukocyte esterase, hemoglobin and red blood cells were all increased in both COL4A3−/− groups compared to WT. Differential 2DE-gel analysis identified six phosphorylated kidney protein spots that were significantly altered by MMF.

Conclusions

These data suggest that the MMF treatment in this murine model moderately improved kidney function and reversed the phosphorylation status of six renal phosphoprotein spots to that seen in WT mice.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-014-0056-z) contains supplementary material, which is available to authorized users.

An update on the pathomechanisms and future therapies of Alport syndrome

Alport Syndrome (AS) is an inherited progressive disease that is caused by mutations of the genes encoding the key collagen chains, α3, α4, and α5, which are necessary for the composition of collagen type IV to form a robust glomerular basement membrane (GBM), capable of withstanding the significant biomechanical strain to which the glomerulus is subjected. Progressive loss of the filtration barrier allows excessive proteinuria, which ultimately leads to end-stage kidney disease (ESKD). The evidence for a beneficial renoprotective effect of renin-angiotensin-aldosterone system (RAAS) blockade by angiotensin-converting enzyme (ACE) inhibition and/or angiotensin receptor blockers (ARBs) is well established in AS and recent evidence has shown that it can significantly delay the time to onset of renal replacement therapy and ESKD. Future potential treatments of AS disease progression are evaluated in this review.

Renal protective effects of aliskiren beyond its antihypertensive property in a mouse model of progressive fibrosis

BACKGROUND

The direct renin inhibitor aliskiren is known to exhibit a strong antihypertensive effect. However, the organoprotective potential of aliskiren beyond its antihypertensive properties is less clear. This study investigates the antifibrotic nephroprotective effects of aliskiren in a nonhypertensive mouse model for progressive renal fibrosis.

METHODS

COL4A3(-/-) mice received aliskiren via osmotic minipumps. Placebo-treated animals served as controls. Therapy was initiated in 6-week-old animals already showing renal damage (proteinuria ~1 g/l, starting renal fibrosis) and lasted for 4 weeks. Six animals were sacrificed after 9.5 weeks; serum urea and proteinuria were measured. Kidneys were further investigated using histological, immunohistological, and western blot techniques. Survival until end-stage renal failure was monitored in the remaining animals.

RESULTS

COL4A3(-/-) mice did not develop hypertension. Aliskiren serum levels were in the therapeutic range (288 ± 44 ng/ml). Therapy significantly prolonged lifespan until death from renal failure by 18% compared with placebo-treated controls (78.6 ± 8.2 vs. 66.6 ± 4.9 days, P < 0.05). Similarly, therapy reduced the amount of proteinuria and serum urea. Compared with placebo-treated controls, the accumulation of extracellular matrix and renal scarring and the levels of transforming growth factor-β (TGFβ) and connective tissue growth factor (CTGF) were decreased in treated mice.

CONCLUSIONS

Despite the late onset of therapy, our results indicate nephroprotective effects of the renin inhibitor aliskiren beyond its antihypertensive property in this animal model of progressive renal fibrosis. In addition to the recognized antihypertensive action of aliskiren, its antifibrotic, antiproteinuric effects demonstrated in the present study indicate that aliskiren may have potential as an important therapeutic option for chronic fibrotic diseases in humans.

Macrophages and renal fibrosis

Renal fibrosis is a key determinant of the progression of renal disease irrespective of the original cause and thus can be regarded as a final common pathway that dictates eventual outcome. The development of renal fibrosis involves many cellular and molecular mediators including leukocytes, myofibroblasts, cytokines, and growth factors, as well as metalloproteinases and their endogenous inhibitors. Study of experimental and human renal disease has shown the involvement of macrophages in renal fibrosis resulting from diverse disease processes. Recent work exploring the nature of both circulating monocytes and tissue macrophages has highlighted their multifaceted phenotype and this impacts their role in renal fibrosis in vivo. In this review we outline the key players in the fibrotic response of the injured kidney and discuss the role of monocytes and macrophages in renal scarring.

Collagen XIII induced in vascular endothelium mediates alpha1beta1 integrin-dependent transmigration of monocytes in renal fibrosis

Alport syndrome is a common hereditary basement membrane disorder caused by mutations in the collagen IV α3, α4, or α5 genes that results in progressive glomerular and interstitial renal disease. Interstitial monocytes that accumulate in the renal cortex from Alport mice are immunopositive for integrin α1β1, while only a small fraction of circulating monocytes are immunopositive for this integrin. We surmised that such a disparity might be due to the selective recruitment of α1β1-positive monocytes. In this study, we report the identification of collagen XIII as a ligand that facilitates this selective recruitment of α1β1 integrin-positive monocytes. Collagen XIII is absent in the vascular endothelium from normal renal cortex and abundant in Alport renal cortex. Neutralizing antibodies against the binding site in collagen XIII for α1β1 integrin selectively block VLA1-positive monocyte migration in transwell assays. Injection of these antibodies into Alport mice slows monocyte recruitment and protects against renal fibrosis. Thus, the induction of collagen XIII in endothelial cells of Alport kidneys mediates the selective recruitment of α1β1 integrin-positive monocytes and may potentially serve as a therapeutic target for inflammatory diseases in which lymphocyte/monocyte recruitment involves the interaction with α1β1 integrin.

Loss of collagen-receptor DDR1 delays renal fibrosis in hereditary type IV collagen disease

Alport syndrome is a hereditary type IV collagen disease leading to progressive renal fibrosis, hearing loss and ocular changes. End stage renal failure usually develops during adolescence. COL4A3-/- mice serve as an animal model for progressive renal scarring in Alport syndrome. The present study evaluates the role of Discoidin Domain Receptor 1 (DDR1) in cell-matrix interaction involved in pathogenesis of Alport syndrome including renal inflammation and fibrosis. DDR1/COL4A3 Double-knockouts were compared to COL4A3-/- mice with 50% or 100% expression of DDR1, wildtype controls and to DDR1-/- COL4A3+/+ controls for over 6years. Double-knockouts lived 47% longer, mice with 50% DDR1 lived 29% longer and showed improved renal function (reduction in proteinuria and blood urea nitrogen) compared to animals with 100% DDR1 expression. Loss of DDR1 reduced proinflammatory, profibrotic cells via signaling of TGFbeta, CTGF, NFkappaB and IL-6 and decreased deposition of extracellular matrix. Immunogold-staining and in-situ hybridisation identified podocytes as major players in DDR1-mediated fibrosis and inflammation within the kidney. In summary, glomerular epithelial cells (podocytes) express DDR1. Loss of DDR1-expression in the kidney delayed renal fibrosis and inflammation in hereditary type IV collagen disease. This supports our hypothesis that podocyte-matrix interaction via collagen receptors plays an important part in progression of renal fibrosis in Alport disease. The blockade of collagen-receptor DDR1 might serve as an important new therapeutic concept in progressive fibrotic and inflammatory diseases in the future.

Loss of the BMP antagonist USAG-1 ameliorates disease in a mouse model of the progressive hereditary kidney disease Alport syndrome

The glomerular basement membrane (GBM) is a key component of the filtering unit in the kidney. Mutations involving any of the collagen IV genes (COL4A3, COL4A4, and COL4A5) affect GBM assembly and cause Alport syndrome, a progressive hereditary kidney disease with no definitive therapy. Previously, we have demonstrated that the bone morphogenetic protein (BMP) antagonist uterine sensitization-associated gene-1 (USAG-1) negatively regulates the renoprotective action of BMP-7 in a mouse model of tubular injury during acute renal failure. Here, we investigated the role of USAG-1 in renal function in Col4a3-/- mice, which model Alport syndrome. Ablation of Usag1 in Col4a3-/- mice led to substantial attenuation of disease progression, normalization of GBM ultrastructure, preservation of renal function, and extension of life span. Immunohistochemical analysis revealed that USAG-1 and BMP-7 colocalized in the macula densa in the distal tubules, lying in direct contact with glomerular mesangial cells. Furthermore, in cultured mesangial cells, BMP-7 attenuated and USAG-1 enhanced the expression of MMP-12, a protease that may contribute to GBM degradation. These data suggest that the pathogenetic role of USAG-1 in Col4a3-/- mice might involve crosstalk between kidney tubules and the glomerulus and that inhibition of USAG-1 may be a promising therapeutic approach for the treatment of Alport syndrome.

Ccl2/Mcp-1 blockade reduces glomerular and interstitial macrophages but does not ameliorate renal pathology in collagen4A3-deficient mice with autosomal recessive Alport nephropathy

Lack of the alpha3 or alpha4 chain of type IV collagen (COL4) causes autosomal recessive Alport nephropathy in humans and mice that is characterized by progressive glomerulosclerosis and tubulointerstitial disease. Renal pathology is associated with chemokine-mediated macrophage infiltrates but their contribution to the progression of Alport nephropathy is unclear. We found Ccl2 to be expressed in increasing amounts during the progression of nephropathy in Col4a3-deficient mice; hence, we blocked Ccl2 with anti-Ccl2 Spiegelmers, biostable L-enantiomeric RNA aptamers suitable for in vivo applications. Ccl2 blockade reduced the recruitment of ex vivo-labelled macrophages into kidneys of Col4a3-deficient mice. We therefore hypothesized that a prolonged course of Ccl2 blockade would reduce renal macrophage counts and prevent renal pathology in Col4a3-deficient mice. Groups of Col4a3-deficient mice received subcutaneous injections of either an anti-mCcl2 Spiegelmer or non-functional control Spiegelmer on alternate days, starting from day 21 or 42 of age. Glomerular and interstitial macrophage counts were found to be reduced with Ccl2 blockade by 50% and 30%, respectively. However, this was not associated with an improvement of glomerular pathology, interstitial pathology, or of overall survival of Col4a3-deficient mice. We conclude that Ccl2 mediates the recruitment of glomerular and interstitial macrophages but this mechanism does not contribute to the progression of Alport nephropathy in Col4a3-deficient mice.

Integrin alpha1beta1 regulates matrix metalloproteinases via P38 mitogen-activated protein kinase in mesangial cells: implications for Alport syndrome

Previous work has shown that integrin alpha1-null Alport mice exhibit attenuated glomerular disease with decreased matrix accumulation and live much longer than strain-matched Alport mice. However, the mechanism underlying this observation is unknown. Here we show that glomerular gelatinase expression, specifically matrix metalloproteinase-2 (MMP-2), MMP-9, and MMP-14, was significantly elevated in both integrin alpha1-null mice and integrin alpha1-null Alport mice relative to wild-type mice; however, only MMP-9 was elevated in glomeruli of Alport mice that express integrin alpha1. Similarly, cultured mesangial cells from alpha1-null mice showed elevated expression levels of all three MMPs, whereas mesangial cells from Alport mice show elevated expression levels of only MMP-9. In both glomeruli and cultured mesangial cells isolated from integrin alpha1-null mice, activation of the p38 and ERK branches of the mitogen-activated protein kinase pathway was also observed. The use of small molecule inhibitors demonstrated that the activation of the p38, but not ERK, pathway was linked to elevated MMP-2, -9, and -14 expression levels in mesangial cells from integrin alpha1-null mice. In contrast, elevated MMP-9 levels in mesangial cells from Alport mice were linked to ERK pathway activation. Blockade of gelatinase activity using a small molecule inhibitor (BAY-12-9566) ameliorated progression of proteinuria and restored the architecture of the glomerular basement membrane in alpha1 integrin-null Alport mice, suggesting that elevated gelatinase activity exacerbates glomerular disease progression in these mice.

Dual effect of methylprednsolone pulses on apoptosis of peripheral leukocytes in patients with renal diseases

It is well known that change in apoptosis may modulate the natural story of illness, and that many drugs may act through modulation of apoptosis, but the role of steroids in acting through apoptosis in different settings, including renal diseases, has still to be elucidated. We studied the in vivo effects of steroids by oral assumption (10 to 25 mg/deltacortene) or by intravenous pulses (300 to 1000 mg/dose) on apoptosis and cellular subsets of peripheral lymphocytes, by evaluating DNA-fragmentation and lymphocyte subsets in 79 subjects: 22 controls and 57 patients with various renal diseases (25 Lupus-GN, 19 membranous-GN (MGN), 6 rapidly progressive-GN (RPGN), 2 acute interstitial nephritis (AIN), 5 on chronic dialysis. Baseline apoptosis was present in 1/22 (4.5%) of controls, 3/25 (12%) SLE, 2/6 (33.3%) RPGN and 10/19 (52.6%) MGN. A significant decrease in CD3+CD8+ cell count and a significant increase of the CD3+CD4/CD3+CD8+ ratio were found in apoptosis-positive subjects. DNA fragmentation did not change after oral steroids, paralleling a 22 to 32% decrease in total lymphocytes. Following intravenous methylprednisolone pulses, a deeper drop of all lymphocyte subsets was observed, while DNA fragmentation turned from present to absent in 2 MGN, but not in 2 RPGN, and from absent to present in 1 ARF and 1 SLE, independently of the dosage. We demonstrated that the presence of apoptosis in renal diseases is associated with decreased CD3+CD8+ cell count. Furthermore, steroid intravenous pulses, besides inducing a profound decrease in lymphocyte subsets, do exert a dual effect on baseline leukocyte apoptosis, eventually leading to a reversal of baseline patterns, either turning from negative to positive or from positive to negative. Oral steroid therapy did not influence baseline apoptosis.

Nitric oxide is an important mediator of renal tubular epithelial cell death in vitro and in murine experimental hydronephrosis

Macrophages play a pivotal role in tissue injury and fibrosis during renal inflammation. Although macrophages may induce apoptosis of renal tubular epithelial cells, the mechanisms involved are unclear. We used a microscopically quantifiable co-culture assay to dissect the cytotoxic interaction between murine bone marrow-derived macrophages and Madin-Darby canine kidney cells and primary murine renal tubular epithelial cells. The induction of tubular cell apoptosis by cytokine-activated macrophages was reduced by inhibitors of nitric oxide synthase whereas tubular cell proliferation was unaffected. Furthermore, cytokine-activated macrophages derived from mice targeted for the deletion of inducible nitric oxide synthase were noncytotoxic. We then examined the role of nitric oxide in vivo by inhibiting inducible nitric oxide synthase in the model of murine experimental hydronephrosis. l-N(6)-(1-iminoethyl)-lysine was administered in the drinking water between days 5 and 7 after ureteric obstruction. Macrophage infiltration was comparable between groups, but treatment significantly inhibited tubular cell apoptosis at day 7. Tubular cell proliferation was unaffected. Inducible nitric oxide synthase blockade also reduced interstitial cell apoptosis and increased collagen III deposition. These data indicate that nitric oxide is a key mediator of macrophage-directed tubular cell apoptosis in vitro and in vivo and also modulates tubulointerstitial fibrosis.

Role for macrophage metalloelastase in glomerular basement membrane damage associated with alport syndrome

Alport syndrome is a glomerular basement membrane (GBM) disease caused by mutations in type IV collagen genes. A unique irregular thickening and thinning of the GBM characterizes the progressive glomerular pathology. The metabolic imbalances responsible for these GBM irregularities are not known. Here we show that macrophage metalloelastase (MMP-12) expression is >40-fold induced in glomeruli from Alport mice and is markedly induced in glomeruli of both humans and dogs with Alport syndrome. Treatment of Alport mice with MMI270 (CGS27023A), a broad spectrum MMP inhibitor that blocks MMP-12 activity, results in largely restored GBM ultrastructure and function. Treatment with BAY-129566, a broad spectrum MMP inhibitor that does not inhibit MMP-12, had no effect. We show that inhibition of CC chemokine receptor 2 (CCR2) receptor signaling with propagermanium blocks induction of MMP-12 mRNA and prevents GBM damage. CCR2 receptor is expressed in glomerular podocytes of Alport mice, suggesting MCP-1 activation of CCR2 on podocytes may underlie induction of MMP-12. These data indicate that the irregular GBM that characterizes Alport syndrome may be mediated, in part, by focal degradation of the GBM due to MMP dysregulation, in particular, MMP-12. Thus, MMP-12/CCR2 inhibitors may provide a novel and effective therapeutic stra-tegy for Alport glomerular disease.

Stage-specific action of matrix metalloproteinases influences progressive hereditary kidney disease

BACKGROUND

Glomerular basement membrane (GBM), a key component of the blood-filtration apparatus in the in the kidney, is formed through assembly of type IV collagen with laminins, nidogen, and sulfated proteoglycans. Mutations or deletions involving alpha3(IV), alpha4(IV), or alpha5(IV) chains of type IV collagen in the GBM have been identified as the cause for Alport syndrome in humans, a progressive hereditary kidney disease associated with deafness. The pathological mechanisms by which such mutations lead to eventual kidney failure are not completely understood.

METHODS AND FINDINGS

We showed that increased susceptibility of defective human Alport GBM to proteolytic degradation is mediated by three different matrix metalloproteinases (MMPs)--MMP-2, MMP-3, and MMP-9--which influence the progression of renal dysfunction in alpha3(IV)-/- mice, a model for human Alport syndrome. Genetic ablation of either MMP-2 or MMP-9, or both MMP-2 and MMP-9, led to compensatory up-regulation of other MMPs in the kidney glomerulus. Pharmacological ablation of enzymatic activity associated with multiple GBM-degrading MMPs, before the onset of proteinuria or GBM structural defects in the alpha3(IV)-/- mice, led to significant attenuation in disease progression associated with delayed proteinuria and marked extension in survival. In contrast, inhibition of MMPs after induction of proteinuria led to acceleration of disease associated with extensive interstitial fibrosis and early death of alpha3(IV)-/- mice.

CONCLUSIONS

These results suggest that preserving GBM/extracellular matrix integrity before the onset of proteinuria leads to significant disease protection, but if this window of opportunity is lost, MMP-inhibition at the later stages of Alport disease leads to accelerated glomerular and interstitial fibrosis. Our findings identify a crucial dual role for MMPs in the progression of Alport disease in alpha3(IV)-/- mice, with an early pathogenic function and a later protective action. Hence, we propose possible use of MMP-inhibitors as disease-preventive drugs for patients with Alport syndrome with identified genetic defects, before the onset of proteinuria.

Conditional ablation of macrophages halts progression of crescentic glomerulonephritis

The presence of macrophages in inflamed glomeruli of rat kidney correlates with proliferation and apoptosis of resident glomerular mesangial cells. We assessed the contribution of inflammatory macrophages to progressive renal injury in murine crescentic glomerulonephritis (GN). Using a novel transgenic mouse (CD11b-DTR) in which tissue macrophages can be specifically and selectively ablated by minute injections of diphtheria toxin, we depleted renal inflammatory macrophages through days 15 and 20 of progressive crescentic GN. Macrophage depletion reduced the number of glomerular crescents, improved renal function, and reduced proteinuria. Morphometric analysis of renal tubules and interstitium revealed a marked attenuation of tubular injury that was associated with reduced proliferation and apoptosis of tubular cells. The population of interstitial myofibroblasts decreased after macrophage depletion and interstitial fibrosis also decreased. In the presence of macrophages, interstitial myofibroblasts exhibited increased levels of both proliferation and apoptosis, suggesting that macrophages act to support a population of renal myofibroblasts in a high turnover state and in matrix deposition. Finally, deletion of macrophages reduced CD4 T cells in the diseased kidney. This study demonstrates that macrophages are key effectors of disease progression in crescentic GN, acting to regulate parenchymal cell populations by modulating both cell proliferation and apoptosis.

Progression of kidney disease: Blocking leukocyte recruitment with chemokine receptor CCR1 antagonists

Chronic kidney disease (CKD) is usually associated with interstitial leukocytic cell infiltrates, which may contribute to disease progression by production of proinflammatory, proapoptotic, and profibrotic mediators. Recruiting leukocytes into the kidney involves local expression of chemotactic cytokines, that is, chemokines, that interact with respective chemokine receptors on the leukocyte's outer surface. Thus, specific chemokine receptor antagonists may represent an attractive therapeutic concept to interfere with renal leukocyte recruitment. Among the proinflammatory chemokine receptors, chemokine receptor (CCR)-1 has nonredundant roles for leukocyte adhesion to activated vascular endothelium and for transendothelial migration. In fact, blocking CCR-1 with specific small-molecule antagonists was shown to retard progression in various types of rodent CKD models. Here we discuss the perspective of CCR-1 as a new potential target for the treatment of CKD.

Nephroprotection by antifibrotic and anti-inflammatory effects of the vasopeptidase inhibitor AVE7688

BACKGROUND

Chronic renal disease substantially increases the risk of cardiovascular events and death. Vasopeptidase inhibitors are known to show a strong antihypertensive effect. In the present study, we investigated the nephroprotective potential of the vasopeptidase inhibitor AVE7688 beyond its antihypertensive effects in a mouse model of progressive renal fibrosis.

METHODS

COL4A3 -/- mice received 25 mg AVE7688 per kg body weight. Treatment was initiated in week 4 (early) and week 7 (late). Eight mice per group were sacrificed after 7.5 or 9.5 weeks, and serum levels of urea, systemic blood pressure, and proteinuria were measured. Renal tissue was investigated by routine histology, electron microscopy, immunohistochemistry, and Western blotting. Lifespan until death from renal fibrosis was monitored.

RESULTS

Lifespan of treated mice increased by 143% (early therapy) and by 53% (late therapy) compared to untreated animals (172 +/- 19 vs. 109 +/- 15 vs. 71 +/- 6 days, P < 0.01). Untreated COL4A3 -/- mice did not develop severe hypertension (mean systolic blood pressure 116 +/- 14 vs. 111 +/- 9 mm Hg in wild-type mice), and both therapies mildly reduced systemic blood pressure (107 +/- 13 and 105 +/- 14 mm Hg, data not significant). AVE7688 decreased proteinuria from 12 +/- 3 g/L in untreated mice to 2 +/- 1 g/L (early) and to 4 +/- 1 g/L (late therapy, P < 0.05), as well as serum-urea from 247 +/- 27 to 57 +/- 10 and to 105 +/- 20 mmol/L (P < 0.05). Extent of fibrosis, inflammation, and profibrotic cytokines was reduced by AVE7688 therapy.

CONCLUSION

The results indicate a strong nephroprotective effect of the vasopeptidase inhibitor in this animal model of progressive renal fibrosis. Besides the antihypertensive action of AVE7688, its antifibrotic, anti-inflammatory, and antiproteinuric effects demonstrated in the present study may serve as an important therapeutic option for chronic inflammatory and fibrotic diseases in man.

Chemokine receptor CCR1: a new target for progressive kidney disease

Infiltrating leukocytes are thought to contribute to the progression of kidney disease. Locally produced chemokines guide circulating leukocytes into the kidney, which renders therapeutic blockade of respective chemokine receptors on the leukocyte surface as potential targets for the inhibition of renal leukocyte recruitment. By using mutant mice and specific antagonists, we found that chemokine receptor CCR1 has non-redundant functions for leukocyte adhesion to activated vascular endothelium and for transendothelial diapedesis. Most importantly, CCR1 blockade with a specific small molecule antagonist can improve injury in several types of progressive kidney disease models, even if treatment is initiated in advanced disease states. Identification of new targets may add to the therapeutic options in chronic kidney disease.

Matrix metalloproteinase dysregulation in the stria vascularis of mice with Alport syndrome: implications for capillary basement membrane pathology

Alport syndrome results from mutations in genes encoding collagen alpha3(IV), alpha4(IV), or alpha5(IV) and is characterized by progressive glomerular disease associated with a high-frequency sensorineural hearing loss. Earlier studies of a gene knockout mouse model for Alport syndrome noted thickening of strial capillary basement membranes in the cochlea, suggesting that the stria vascularis is the primary site of cochlear pathogenesis. Here we combine a novel cochlear microdissection technique with molecular analyses to illustrate significant quantitative alterations in strial expression of mRNAs encoding matrix metalloproteinases-2, -9, -12, and -14. Gelatin zymography of extracts from the stria vascularis confirmed these findings. Treatment of Alport mice with a small molecule inhibitor of these matrix metalloproteinases exacerbated strial capillary basement membrane thickening, demonstrating that alterations in basement membrane metabolism result in matrix accumulation in the strial capillary basement membranes. This is the first demonstration of true quantitative analysis of specific mRNAs for matrix metalloproteinases in a cochlear microcompartment. Further, these data suggest that the altered basement membrane composition in Alport stria influences the expression of genes involved in basement membrane metabolism.

Dysregulation of renal MMP-3 and MMP-7 in canine X-linked Alport syndrome

Matrix metalloproteinases (MMPs) play an important regulatory role in many biological and pathological processes and their specific role in Alport syndrome (AS) is not yet clearly defined. In this study, the naturally occurring canine X-linked AS was used to demonstrate a potential role for MMP-3 and MMP-7 in Alport renal pathogenesis. Recently, we demonstrated that the expression of MMP-2, MMP-9 and MMP-14 was upregulated in the renal cortex of dogs with a spontaneous form of XLAS. In the present study, we examined necropsy samples of renal cortex from normal and XLAS dogs for MMP-3 and MMP-7 as they have the potential to activate MMP-2 and MMP-9. Immunohistochemical analysis showed strong immunostaining for both MMP-3 and MMP-7 in the interstitial space of XLAS kidneys, while virtually no immunostaining was observed in similar fields from normal dogs. RT-PCR and casein zymography confirmed that both mRNA transcripts and activities of MMP-3 and MMP-7 are elevated in XLAS kidneys. The induction of these MMPs likely contributes to tissue destruction associated with the fibrogenic process, while augmenting the activation of MMP-2 and MMP-9 by MMP-3 and MMP-7 in XLAS. Thus, these data further implicate a role for the MMPs in progressive renal pathogenesis associated with AS.

Delayed chemokine receptor 1 blockade prolongs survival in collagen 4A3-deficient mice with Alport disease

Human Alport disease is caused by a lack of the alpha3-, 4-, or 5-chain of type IV collagen (COL4A). Affected humans and COL4A3-deficient mice develop glomerulosclerosis and progressive renal fibrosis in the presence of interstitial macrophages, but their contribution to disease progression is under debate. This question was addressed by treating COL4A3-deficient mice with BX471, an antagonist of chemokine receptor 1 (CCR1) that is known to block interstitial leukocyte recruitment. Treatment with BX471 from weeks 6 to 10 of life improved survival of COL4A3-deficient mice, associated with less interstitial macrophages, apoptotic tubular epithelial cells, tubular atrophy, interstitial fibrosis, and less globally sclerotic glomeruli. BX471 reduced total renal Cll5 mRNA expression by reducing the number of interstitial CCL5-positive cells in inflammatory cell infiltrates. Intravital microscopy of the cremaster muscle in male mice identified that BX471 or lack of CCR1 impaired leukocyte adhesion to activated vascular endothelium and transendothelial leukocyte migration, whereas leukocyte rolling and interstitial migration were not affected. Furthermore, in activated murine macrophages, BX471 completely blocked CCL3-induced CCL5 production. Thus, CCR1-mediated recruitment and local activation of macrophages contribute to disease progression in COL4A3-deficient mice. These data identify CCR1 as a potential therapeutic target for Alport disease or other progressive nephropathies associated with interstitial macrophage infiltrates.

Apoptosis in glomerulonephritis

Apoptosis is of fundamental importance and plays a key role in determining the outcome of glomerulonephritis. Under ideal circumstances,apoptosis deletes infiltrating leukocytes and excess numbers of resident cells that are surplus to requirements, thereby facilitating tissue remodeling and the restoration of normal tissue architecture. Apoptosis also has a darker side, however, and may be responsible for the deletion of critically important resident glomerular cells, resulting in hypocellular scarring and loss of renal function. Recent data indicate that glomerular cell apoptosis may be manipulated to improve outcome in experimental models of renal inflammation. It is hoped that further research will provide novel therapeutic strategies for patients with inflammatory glomerulonephritis.