Hepatocyte growth factor: a regulator of extracellular matrix genes in mouse mesangial cells

Renal fibrosis as a hallmark of diabetic kidney disease: Potential role of targeting transforming growth factor-beta (TGF-β) and related molecules

INTRODUCTION

Diabetic kidney disease (DKD) is the most common cause of end-stage renal disease (ESRD) worldwide. Currently, there is no effective treatment to completely prevent DKD progression to ESRD. Renal fibrosis and inflammation are the major pathological features of DKD, being pursued as potential therapeutic targets for DKD.

AREAS COVERED

Inflammation and renal fibrosis are involved in the pathogenesis of DKD. Anti-inflammatory drugs have been developed to combat DKD but without efficacy demonstrated. Thus, we have focused on the mechanisms of TGF-β-induced renal fibrosis in DKD, as well as discussing the important molecules influencing the TGF-β signaling pathway and their potential development into new pharmacotherapies, rather than targeting the ligand TGF-β and/or its receptors, such options include Smads, microRNAs, histone deacetylases, connective tissue growth factor, bone morphogenetic protein 7, hepatocyte growth factor, and cell division autoantigen 1.

EXPERT OPINION

TGF-β is a critical driver of renal fibrosis in DKD. Molecules that modulate TGF-β signaling rather than TGF-β itself are potentially superior targets to safely combat DKD. A comprehensive elucidation of the pathogenesis of DKD is important, which requires a better model system and access to clinical samples via collaboration between basic and clinical researchers.

Inflammation in kidney repair: Mechanism and therapeutic potential

The kidney has a remarkable ability of repair after acute kidney injury (AKI). However, when injury is severe or persistent, the repair is incomplete or maladaptive and may lead to chronic kidney disease (CKD). Maladaptive kidney repair involves multiple cell types and multifactorial processes, of which inflammation is a key component. In the process of inflammation, there is a bidirectional interplay between kidney parenchymal cells and the immune system. The extensive and complex crosstalk between renal tubular epithelial cells and interstitial cells, including immune cells, fibroblasts, and endothelial cells, governs the repair and recovery of the injured kidney. Further research in this field is imperative for the discovery of biomarkers and promising therapeutic targets for kidney repair. In this review, we summarize the latest progress in the immune response and inflammation during maladaptive kidney repair, analyzing the interaction between immune cells and intrinsic kidney cells, pointing out the potentialities of inflammation-related pathways as therapeutic targets, and discussing the challenges and future research prospects in this field.

Inflammatory Mediators and Renal Fibrosis

Renal inflammation is the initial, healthy response to renal injury. However, prolonged inflammation promotes the fibrosis process, which leads to chronic pathology and eventually end-stage kidney disease. There are two major sources of inflammatory cells: first, bone marrow-derived leukocytes that include neutrophils, macrophages, fibrocytes and mast cells, and second, locally activated kidney cells such as mesangial cells, podocytes, tubular epithelial cells, endothelial cells and fibroblasts. These activated cells produce many profibrotic cytokines and growth factors that cause accumulation and activation of myofibroblasts, and enhance the production of the extracellular matrix. In particular, activated macrophages are key mediators that drive acute inflammation into chronic kidney disease. They produce large amounts of profibrotic factors and modify the microenvironment via a paracrine effect, and they also transdifferentiate to myofibroblasts directly, although the origin of myofibroblasts in the fibrosing kidney remains controversial. Collectively, understanding inflammatory cell functions and mechanisms during renal fibrosis is paramount to improving diagnosis and treatment of chronic kidney disease.

Cellular and molecular mechanisms of kidney fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. It is considered as the underlying pathological process of chronic kidney disease (CKD), which affects more than 10% of world population and for which treatment options are limited. Renal fibrosis is defined by excessive deposition of extracellular matrix, which disrupts and replaces the functional parenchyma that leads to organ failure. Kidney's histological structure can be divided into three main compartments, all of which can be affected by fibrosis, specifically termed glomerulosclerosis in glomeruli, interstitial fibrosis in tubulointerstitium and arteriosclerosis and perivascular fibrosis in vasculature. In this review, we summarized the different appearance, cellular origin and major emerging processes and mediators of fibrosis in each compartment. We also depicted and discussed the challenges in translation of anti-fibrotic treatment to clinical practice and discuss possible solutions and future directions.

Antifibrotic Effects of Hepatocyte Growth Factor on Endothelial-to-Mesenchymal Transition via Transforming Growth Factor-Beta1 (TGF-β1)/Smad and Akt/mTOR/P70S6K Signaling Pathways

Background

The related mechanisms involved in allograft interstitial fibrosis and chronic allograft dysfunction (CAD), following renal transplant, remain largely unknown. Here, we explored the role of hepatocyte growth factor (HGF) treatment on the endothelial-to-mesenchymal transition (EndMT) as a new way to target and prevent kidney fibrosis and improve outcomes for renal transplant recipients.

Method/Material

We extracted proteins and mRNAs from human umbilical vein endothelial cells (HUVECs) and human renal glomerular endothelial cells (HRGECs) treated with transforming growth factor-beta1 (TGF-β1) and/or varying doses of HGF, and assessed the effect of HGF on the EndMT using western blotting, qRT-PCR, and ELISA assays. We utilized cell motility and migration assays to evaluate cell movement, and applied western blotting to assess the mechanism by which TGF-β1 induced the EndMT.

Results

HGF significantly attenuated the development of TGF-β1-induced EndMT in a concentration-dependent way, and weakened the abilities of motility and migration of both HUVECs and HRGECs. Moreover, our results reveal that the antifibrotic effect of HGF on the EndMT was associated with the TGF-β/Smad and Akt/mTOR/p70S6K signaling pathways.

Conclusions

Our study suggests that HGF treatment significantly attenuates the development of EndMT induced by TGF-β1 via the TGFβ/Smad and Akt/mTOR/P70S6K signaling, which provides novel insights into the prevention and treatment of interstitial fibrosis and CAD following renal transplant.

Scatter Factors in renal disease: Dr. Jeckyll and Mr. Hyde?

The Scatter Factors are two homologous proteins, named Scatter Factor/Hepatocyte Growth Factor and Macrophage Stimulating Protein. Their receptors are the products of two oncogenes, Met and Ron, respectively. The Scatter Factors induce movement, stimulate proliferation, regulate apoptosis and are morphogenic, i.e. operate an integrated program that seems tailored to drive organ development and to regenerate injured tissues. On the other hand, Scatter Factors may be responsible for pathologic tissue remodeling, infiltration of inflammatory cells, and tumor growth and diffusion. The review describes the involvement of Scatter Factors in renal disease, including acute renal failure, glomerulonephritis, chronic fibrosing nephropathies, dialysis, renal transplantation and renal tumors, and discusses the double-faced role of Scatter Factors, that play either a protective or a pathogenic role.

Phenotypic transitions and fibrosis in diabetic nephropathy

The cause of renal fibrosis in diabetic nephropathy is widely believed to be phenotypic switching of fibroblasts to an activated state. However, emerging evidence suggests that diabetes also alters the phenotype of normal, non-fibroblast kidney cells, such as mesangial cells, tubular epithelial cells, and bone marrow-derived progenitors. Experiments have shown that cytokines, high glucose, and advanced glycation end products induce profibrotic changes in kidney cell phenotype by the processes of myofibroblast transdifferentiation and epithelial-mesenchymal transition. As a result, differentiated kidney cells become reprogrammed to secrete and accumulate extracellular matrix. This revised view implies that inhibiting phenotypic transitions in nonfibroblasts might limit fibrosis in diabetic nephropathy.

Hepatocyte growth factor: new arsenal in the fights against renal fibrosis?

Hepatocyte growth factor (HGF) has emerged as a potent, endogenous antifibrotic factor that shows an impressive efficacy in ameliorating tissue fibrosis in a wide variety of animal models. Herrero-Fresneda et al. provide new evidence demonstrating that intramuscular injection of HGF gene reduces mortality, inflammation, and renal fibrosis in chronic allograft nephropathy.

Hepatocyte Growth Factor Gene Therapy Slows Down the Progression of Diabetic Nephropathy in db/db Mice

BACKGROUND

Effect of hepatocyte growth factor (HGF) has scarcely been determined on diabetic nephropathy.

METHODS

Adenovirus encoding human HGF gene or LacZ gene (as the control) was injected into the hindlimb muscles of the C57BL/KsJ-db/db (db/db) mice at the age of 12 weeks, a model of genetic diabetes. Diabetic nephropathy was then evaluated at the age of 24 weeks.

RESULTS

The urine volume and albumin excretion progressively decreased in the control, whereas they remained unchanged in the HGF-treated group during the 12-week follow-up. The HGF gene therapy did not affect glucose metabolism. However, it resulted in a better renal function as evaluated by creatinine clearance (Ccr) than the control; Ccr was progressively worsened in controls (0.14 +/- 0.02 liters/day) whereas unchanged in the HGF gene-treated group (0.38 +/- 0.09 liters/day, p < 0.05). Kidneys of the HGF gene-treated mice showed glomeruli with greater area and cell population, smaller glomerular sclerotic index, and less fibrosis in both glomeruli and renal tubules, where apoptotic rate of glomerular endothelial cells and that of tubular epithelial cells were significantly decreased. TGF-beta1 expression was significantly decreased in kidneys of the HGF gene-treated group. Finally, the HGF treatment significantly improved the long-term survival of db/db mice.

CONCLUSIONS

The HGF gene delivery thus appeared to slow down the aggravation of diabetic nephropathy in db/db mice by attenuating progression from the hyperfiltration phase into the sclerotic phase through antiapoptotic and antifibrotic actions. The present findings suggest that the HGF gene delivery can be a novel therapeutic approach against diabetic nephropathy.

Oxidized LDL inhibit hepatocyte growth factor synthesis in coronary smooth muscle cells

Hepatocyte growth factor (HGF) is a potent regeneration factor for endothelial and epithelial cells, and has also been shown to modulate extracellular matrix synthesis and matrix metalloproteinase activity in renal epithelial cells and tumor cells. Controversial results have been published concerning the possible role of HGF in the pathogenesis of coronary atherosclerosis. In this study, we have investigated the effect of oxidized low density lipoproteins (LDL) and elevated glucose concentrations on HGF synthesis in cultured human coronary artery smooth muscle cells. In addition, we have studied whether HGF modulates the release of extracellular matrix, extracellular matrix metalloproteinase inducer (EMMPRIN) and matrix metalloproteinases (MMP) by coronary artery smooth muscle cells. Oxidized LDL (1-10 microg/ml) induced a significant dose-dependent decrease of HGF release and a concomitant decrease of HGF mRNA expression, whereas native LDL and elevated glucose concentrations induced no significant changes of HGF synthesis. Incubation of cultured human coronary smooth muscle cells with human HGF (1-100 ng/ml) did not significantly alter cell migration and collagen I, fibronectin, EMMPRIN, MMP-1, MMP-2 and MMP-9 release. In summary, our results provide evidence that HGF does not promote coronary plaque growth or plaque destabilization. Regarding the fact that HGF is a potent endothelial cell regeneration factor, the observed downregulation of HGF synthesis by oxidized LDL supports the concept that HGF might be a protective factor in coronary atherosclerosis and that a decrease rather than an increase of HGF synthesis might promote coronary atherosclerosis.

Experimental strategies to reverse chronic renal disease

Progression of chronic nephropathies still represents a major challenge for clinical nephrologists. Specific therapies that prevent patients from requiring dialysis or transplantation are still not available. However, recent experimental studies have demonstrated that regression of advanced lesions in the kidney can be achieved. This review summarizes the recent therapeutic advances using experimental models that might translate into novel human therapies to prevent, or significantly delay, requirement of renal replacement therapy.

Hepatocyte growth factor in kidney fibrosis: therapeutic potential and mechanisms of action

Hepatocyte growth factor (HGF) is a pleiotropic factor that plays an imperative role in tubular repair and regeneration after acute renal injury. Growing evidence indicates that HGF is also an endogenous renoprotective factor that possesses a potent antifibrotic ability. HGF prevents the initiation and progression of chronic renal fibrosis and inhibits transforming growth factor (TGF)-beta(1) expression in a wide variety of animal models. In vitro, HGF counteracts the action of TGF-beta(1) in different types of kidney cells, resulting in blockade of the myofibroblastic activation from interstitial fibroblasts and glomerular mesangial cells, as well as inhibition of the mesenchymal transition from tubular epithelial cells. Recent studies reveal that HGF antagonizes the profibrotic actions of TGF-beta(1) by intercepting Smad signal transduction through diverse mechanisms. In interstitial fibroblasts, HGF blocks activated Smad-2/3 nuclear translocation, whereas it specifically upregulates the expression of the Smad transcriptional corepressor SnoN in tubular epithelial cells. In glomerular mesangial cells, HGF stabilizes another Smad corepressor, TGIF, by preventing it from degradation. Smad corepressors bind to activated Smad-2/3 and sequester their ability to transcriptionally activate TGF-beta target genes. This article reviews recent advances in our understanding of the cellular and molecular mechanisms underlying HGF inhibition of renal fibrosis.

Regression of advanced diabetic nephropathy by hepatocyte growth factor gene therapy in rats

Diabetic nephropathy is the main cause of end-stage renal disease requiring dialysis in developed countries. In this study, we demonstrated the therapeutic effect of hepatocyte growth factor (HGF) on advanced rather than early diabetic nephropathy using a rat model of streptozotocin-induced diabetes. Early diabetic nephropathy (16 weeks after induction of diabetes) was characterized by albuminuria, hyperfiltration, and glomerular hypertrophy, whereas advanced diabetic nephropathy showed prominent transforming growth factor (TGF)-beta1 upregulation, mesangial expansion, and glomerulosclerosis. An SP1017-formulated human HGF (hHGF) plasmid was administered by intramuscular injection combined with electroporation over a 30-day follow-up in rats with early and advanced diabetic nephropathy. hHGF gene therapy upregulated endogenous rat HGF in the diabetic kidney (rat HGF by RT-PCR was threefold higher than in diabetic rats without therapy). hHGF gene therapy did not improve functional or morphologic abnormalities in early diabetic nephropathy. hHGF gene therapy reduced albuminuria and induced strong regression of mesangial expansion and glomerulosclerosis in advanced diabetic nephropathy. These findings were associated with suppression of renal TGF-beta1 and mesangial connective tissue growth factor (CTGF) upregulation, inhibition of renal tissue inhibitor of metalloproteinase (TIMP)-1 expression, and reduction of renal interstitial myofibroblasts. In conclusion, our results suggest that hHGF gene therapy may be considered as an innovative therapeutic strategy to treat advanced diabetic nephropathy.

Hepatocyte growth factor ameliorates progression of interstitial fibrosis in rats with established renal injury

BACKGROUND

Hepatocyte growth factor (HGF) has been reported to prevent injury in several models of renal disease; however, whether HGF can also retard progression of established renal disease is not known.

METHODS

The aim of the present study was to examine the effects of HGF on progression of chronic renal disease in rats with remnant kidneys and established injury. Studies were performed in rats that underwent subtotal nephrectomy, were observed for two weeks without therapy, and then randomized to receive HGF or vehicle by continuous infusion for an additional two weeks.

RESULTS

HGF administration was associated with a reduction in morphologic evidence of interstitial, but not glomerular injury. The beneficial effects of HGF were not associated with reductions in the expression of transforming growth factor-beta (TGF-beta), or in the extent epithelial cell apoptosis or transdifferentiation. Rather, HGF appeared to induce fibrinolytic pathways by increasing expression of metalloproteinase-9 (MMP-9) and decreasing levels of plasminogen activator inhibitor-1 (PAI-1) and tissue inhibitor of metalloproteinase-1 (TIMP-2). HGF administration was also associated with an apparent increase in renal endothelin production and a significant reduction in glomerular capillary pressure.

CONCLUSION

These findings suggest that HGF can retard progression of chronic renal disease even after injury is already established, primarily by promoting matrix degradation.

Suppressions of chronic glomerular injuries and TGF-β1production by HGF in attenuation of murine diabetic nephropathy

Diabetic nephropathy is now the leading cause of end-stage renal diseases, and glomerular sclerotic injury is an initial event that provokes renal dysfunction during processes of diabetes-linked kidney disease. Growing evidence shows that transforming growth factor-β1(TGF-β1) plays a key role in this process, especially in eliciting hypertrophy and matrix overaccumulation. Thus it is important to find a ligand system to antagonize the TGF-β1-mediated pathogenesis under high-glucose conditions. Herein, we provide evidence that hepatocyte growth factor (HGF) targets mesangial cells, suppresses TGF-β1production, and minimizes glomerular sclerotic changes, using streptozotocin-induced diabetic mice. In our murine model, glomerular sclerogenesis (such as tuft area expansion and collagen deposition) progressed between 6 and 10 wk after the induction of hyperglycemia, during a natural course of diabetic disease. Glomerular HGF expression levels in the diabetic kidney transiently increased but then declined below a basal level, with manifestation of glomerular sclerogenesis. When anti-HGF IgG was injected into mice for 2 wk (i.e., from weeks 4 to 6 after onset of hyperglycemia), these glomerular changes were significantly aggravated. When recombinant HGF was injected into the mice for 4 wk (i.e., between 6 and 10 wk following streptozotocin treatment), the progression of glomerular hypertrophy and sclerosis was almost completely inhibited, even though glucose levels remained unchanged (>500 mg/dl). Even more important, HGF repressed TGF-β1production in glomerular mesangial cells even under hyperglycemic conditions both in vitro and in vivo. Consequently, not only albuminuria but also tubulointerstitial fibrogenesis were attenuated by HGF. Overall, HGF therapy inhibited the onset of renal dysfunction in the diabetic mice. On the basis of these findings, we wish to emphasize that HGF plays physiological and therapeutic roles in blocking renal fibrogenesis during a course of diabetic nephropathy.

Large-scale search of SNPs for type 2 DM susceptibility genes in a Japanese population

The etiology of type 2 diabetes (DM) is polygenic. We investigated here genes and polymorphisms that associate with DM in the Japanese population. Single-nucleotide polymorphisms (SNPs) of 398 derived from 120 candidate genes were examined for association with DM in a population-based case-control study. The study group consisted of 148 cases and 227 controls recruited from Funagata, Japan. No evident subpopulation structure was detected for the tested population. The association tests were conducted with standard allele positivity tables (chi(2) tests) between SNP genotype frequency and case-control status. The independent association of the SNPs from serum triglyceride levels and body mass index was examined by multiple logistic regression analysis. A value of P<0.01 was accepted as statistically significant. Six genes (met proto-oncogene, ATP-binding cassette transporter A1, fatty acid binding protein 2, LDL receptor defect C complementing, aldolase B, and sulfonylurea receptor) were shown to be associated with DM.

Delayed administration of hepatocyte growth factor reduces renal fibrosis in obstructive nephropathy

Hepatocyte growth factor (HGF) is a renotropic protein that elicits antifibrogenic activity by preventing the activation of matrix-producing myofibroblast cells in animal models of chronic renal diseases. However, whether a delayed administration of HGF can still attenuate renal fibrosis remains uncertain. In this study, we examined the therapeutic potential of exogenous HGF on an established renal interstitial fibrosis induced by unilateral ureteral obstruction (UUO). Three days after UUO, the obstructed kidneys displayed interstitial fibrotic lesions with characteristic features of an established renal fibrosis, as manifested by myofibroblast activation, fibronectin overexpression, interstitial matrix deposition, and transforming growth factor-beta1 upregulation. Beginning at this time point, administration of recombinant HGF into mice by intravenous injections for 11 days markedly suppressed the progression of renal interstitial fibrosis. HGF significantly suppressed renal alpha-smooth muscle actin expression, total kidney collagen contents, interstitial matrix components, such as fibronectin, and renal expression of transforming growth factor-beta1 and its type I receptor. Compared with the starting point (3 days after UUO), HGF treatment largely blunted the progression of myofibroblast accumulation and collagen deposition but did not reverse it. Delayed administration of HGF also suppressed the myofibroblastic transdifferentiation from tubular epithelial cells in vitro, as demonstrated by a decline in alpha-smooth muscle actin and fibronectin expression. These results suggest that exogenous HGF exhibits potent therapeutic effects on retarding the progression of an established renal fibrosis.

Identification of novel inhibitors of the transforming growth factor beta1 (TGF-beta1) type 1 receptor (ALK5)

Screening of our internal compound collection for inhibitors of the transforming growth factor beta1 (TGF-beta1) type I receptor (ALK5) identified several hits. Optimization of the dihydropyrroloimidazole hit 2 by introduction of a 2-pyridine and 3,4-methylenedioxyphenyl group gave 7, a selective ALK5 inhibitor. With this information, optimization of the triarylimidazole hit 8 gave the selective inhibitor 14, which inhibits TGF-beta1-induced fibronectin mRNA formation while displaying no measurable cytotoxicity in the 48 h XTT assay.

Hepatocyte growth factor and the kidney

Hepatocyte growth factor (HGF) and its specific c-met receptor constitute a paired signaling system that plays an important role in renal development and in the maintenance of normal adult kidney structure and functions. HGF elicits potent mitogenic, motogenic, morphogenic, and antiapoptotic activities in renal tubular epithelial cells. The nature of these pleiotropic actions renders it to be specifically suited to preserve and to reconstitute the structural and functional integrity of renal tubules after acute renal injury. Emerging evidence also indicates that both endogenous and exogenous HGF are beneficial by inhibiting the onset and progression of chronic renal diseases in various animal models. Administration of exogenous HGF protein, or its gene, effectively inhibits the activation of matrix-producing myofibroblasts, attenuates extracellular matrix deposition and interstitial fibrosis, and suppresses profibrogenic cytokine transforming growth factor-beta1 and its type I receptor expression in vivo. Hence, although more studies are warranted to further clarify its role in various chronic renal fibrosis models, delivery of either HGF or its gene may hold promise as a novel therapeutic strategy for promoting initial protection and subsequently regenerative repair after acute insult, and for ameliorating renal fibrosis and kidney dysfunction in chronically diseased conditions.

Small proteoglycans in human diabetic nephropathy: discrepancy between glomerular expression and protein accumulation of decorin, biglycan, lumican, and fibromodulin

Small leucine-rich proteoglycans (SLRPs), for example, decorin, biglycan, fibromodulin, and lumican, are extracellular matrix organizers and binding partners of TGF-b. Decorin is also involved in growth control and angiogenesis. Hence, these proteoglycans are likely of importance in the pathogenesis of diabetic glomerulosclerosis. In normal kidney, SLRPs were preferentially expressed in the tubulointerstitium. Weak expression occurred in the mesangial matrix. Biglycan was expressed by glomerular endothelial cells and, together with fibromodulin, by distal tubular cells and in collecting ducts. In all stages of diabetic nephropathy, there was a marked up-regulation of the proteoglycans in tubulointerstitium and glomeruli. Decorin and lumican became expressed in tubuli. However, in glomeruli, overexpression was not mirrored by local proteoglycan accumulation except in advanced nephropathy. In severe glomerulosclerosis, increased decorin concentrations were found in plasma and urine, and urinary TGF-b/decorin complexes could be demonstrated indirectly. The failure to detect an increased glomerular proteoglycan quantity during the development of nephropathy could be explained by assuming that they are secreted into the mesangial matrix, but cleared via the vasculature or the urinary tract, in part as complexes with TGF-b. They could thereby counteract the vicious circle being characterized by increased TGF-b production and increased matrix deposition in diabetic nephropathy.