Localization of transforming growth factor-beta and latent transforming growth factor-beta binding protein in rat kidney

Diverse Role of TGF-β in Kidney Disease

Inflammation and fibrosis are two pathological features of chronic kidney disease (CKD). Transforming growth factor-β (TGF-β) has been long considered as a key mediator of renal fibrosis. In addition, TGF-β also acts as a potent anti-inflammatory cytokine that negatively regulates renal inflammation. Thus, blockade of TGF-β inhibits renal fibrosis while promoting inflammation, revealing a diverse role for TGF-β in CKD. It is now well documented that TGF-β1 activates its downstream signaling molecules such as Smad3 and Smad3-dependent non-coding RNAs to transcriptionally and differentially regulate renal inflammation and fibrosis, which is negatively regulated by Smad7. Therefore, treatments by rebalancing Smad3/Smad7 signaling or by specifically targeting Smad3-dependent non-coding RNAs that regulate renal fibrosis or inflammation could be a better therapeutic approach. In this review, the paradoxical functions and underlying mechanisms by which TGF-β1 regulates in renal inflammation and fibrosis are discussed and novel therapeutic strategies for kidney disease by targeting downstream TGF-β/Smad signaling and transcriptomes are highlighted.

Protective outcomes of low-dose doxycycline on renal function of Wistar rats subjected to acute ischemia/reperfusion injury

Renal ischemia-reperfusion injury (IRI) is a major cause of acute renal failure. Doxycycline (Dc) belongs to the tetracycline-class of antibiotics with demonstrated beneficial molecular effects in the brain and heart, mainly through matrix metalloproteinases inhibition (MMP). However, Dc protection of renal function has not been demonstrated. We determined whether low doses of Dc would prevent decreases in glomerular filtration rate (GFR) and maintain tubular Na⁺ handling in Wistar rats subjected to kidney I/R. Male Wistar rats underwent bilateral kidney ischemia for 30min followed by 24h reperfusion (I/R). Doxycycline (1, 3, and 10mg/kg, i.p.) was administered 2h before surgery. Untreated I/R rats showed a 250% increase in urine volume and proteinuria, a 60% reduction in GFR, accumulation of urea-nitrogen in the blood, and a 60% decrease in the fractional Na⁺ excretion due to unbalanced Na⁺ transporter activity. Treatment with Dc 3mg/kg maintained control levels of urine volume, proteinuria, GFR, blood urea-nitrogen, fractional Na⁺ excretion, and equilibrated Na⁺ transporter activities. The Dc protection effects on renal function were associated with kidney structure preservation and prevention of TGFβ and fibronectin deposition. In vitro, total MMP activity was augmented in I/R and inhibited by 25 and 50μM Dc. In vivo, I/R augmented MMP-2 and -9 protein content without changing their activities. Doxycycline treatment downregulated total MMP activity and MMP-2 and -9 protein content. Our results suggest that treatment with low dose Dc protects from IRI, thereby preserving kidney function.

The role of transforming growth factor β1 in the regulation of blood pressure

Although human association studies suggest a link between polymorphisms in the gene encoding transforming growth factor (TGF) β1 and differing blood pressure levels, a causative mechanism for this correlation remains elusive. Recently we have generated a series of mice with graded expression of TGFβ1, ranging from approximately 10% to 300% compared to normal. We have found that blood pressure and plasma volume are negatively regulated by TGFβ1. Of note, the 10% hypomorph exhibits primary aldosteronism and markedly impaired urinary excretion of water and electrolytes. We here review previous literature highlighting the importance of TGFβ signaling as a natriuretic system, which we postulate is a causative mechanism explaining how polymorphisms in TGFβ1 could influence blood pressure levels.

Detection of Bcl-2 mRNA and its product in the glomerular podocytes of the normal rat kidney

Podocyte apoptosis underlies podocytepenia leading to glomerulosclerosis. An apoptosis inhibitory protein Bcl-2 is expressed in the podocytes in the early stage of nephrogenesis and downregulated in the maturing stage of human fetal kidneys. Recent studies reported changed localization and expression of Bcl-2 in the renal glomeruli under the pathologic conditions. This study aimed to confirm in situ localization of Bcl-2 mRNA and its product in the glomeruli, and to demonstrate the local expression of Bcl-2 mRNA in normal rat glomeruli. Paraffin sections of the kidneys from normal male Wistar rats were immunostained by anti-Bcl-2 monoclonal antibody. The localization of Bcl-2 mRNA in the glomeruli was evaluated by in situ hybridization. The glomeruli were dissected from frozen sections of the kidneys with the laser microdissection (LMD) system. Total RNA extracted from 10, 100 or 200 dissected glomeruli was used for reverse-transcription polymerase chain reaction (RT-PCR) and real-time PCR. Bcl-2 mRNA and its product were detected in the podocytes but barely in the mesangial cells. In RT-PCR, the specific-sized bands of Bcl-2 from 100 or 200 dissected glomeruli were clearly observed. Real-time PCR for Bcl-2 showed that cDNA from 100 or 200 dissected glomeruli became amplified at 36 or 33cycles, respectively. Bcl-2 is expressed in the glomerular podocytes of the normal rat kidney and quantitative analysis of Bcl-2 mRNA in the renal glomeruli is possible using the LMD technique.

Expression of transforming growth factor-beta1 limits renal ischemia-reperfusion injury

BACKGROUND

Renal ischemia-reperfusion injury (IRI) largely contributes to kidney transplant dysfunction and acute kidney injury, but its pathogenesis is not fully understood. In this study, the role of transforming growth factor (TGF)-beta1 in renal IRI is investigated using TGF-beta1 deficient mice.

METHOD

Human renal tubular epithelial cells (TEC) line (HK-2) was used as an in vitro model, and cell apoptosis was determined by flow cytometric analysis. Renal IRI was induced in mice by clamping renal vein and artery for 45 min at 32 degrees C.

RESULTS

Here, we showed that in cultures of HK-2 cells, TGF-beta1 expression was up-regulated by tumor necrosis factor (TNF)-alpha. Neutralization of TGF-beta1 activity increased both spontaneous and TNF-alpha-mediated apoptosis, and knockdown of TGF-beta1 expression increased the sensitivity of cell apoptosis to TNF-alpha. In a mouse model of renal IRI, a deficiency in TGF-beta1 expression increased the severity of renal injury, as indicated by more severe renal tubular damage, higher levels of serum creatinine or blood urea nitrogen in TGF-beta1 deficient mice as compared with those in wild-type controls. Further experiments showed that the antiapoptosis of TGF-beta1 correlated with up-regulation of Bcl-2 in kidney cells.

CONCLUSION

Expression of TGF-beta1 in TECs, potentially induced by proinflammatory TNF-alpha, renders TECs resistance to cell death. In mice, TGF-beta1 deficiency results in more prone to IRI. These data imply that TGF-beta1 may act as a feedback survival factor in the resistance to kidney injury and maintenance of epithelium homeostasis.

Do changes in transglutaminase activity alter latent transforming growth factor beta activation in experimental diabetic nephropathy?

BACKGROUND

Diabetic nephropathy is the leading cause of end-stage kidney failure worldwide. It is characterized by excessive extracellular matrix accumulation. Transforming growth factor beta 1 (TGF-β1) is a fibrogenic cytokine playing a major role in the healing process and scarring by regulating extracellular matrix turnover, cell proliferation and epithelial mesanchymal transdifferentiation. Newly synthesized TGF-β is released as a latent, biologically inactive complex. The cross-linking of the large latent TGF-β to the extracellular matrix by transglutaminase 2 (TG2) is one of the key mechanisms of recruitment and activation of this cytokine. TG2 is an enzyme catalyzing an acyl transfer reaction leading to the formation of a stable ε(γ-glutamyl)-lysine cross-link between peptides.

METHODS

To investigate if changes in TG activity can modulate TGF-β1 activation, we used the mink lung cell bioassay to assess TGF-β activity in the streptozotocin model of diabetic nephropathy treated with TG inhibitor NTU281 and in TG2 overexpressing opossum kidney (OK) proximal tubular epithelial cells.

RESULTS

Application of the site-directed TG inhibitor NTU281 caused a 25% reduction in kidney levels of active TGF-β1. Specific upregulation of TG2 in OK proximal tubular epithelial cells increased latent TGF-β recruitment and activation by 20.7% and 19.7%, respectively, in co-cultures with latent TGF-β binding protein producing fibroblasts.

CONCLUSIONS

Regulation of TG2 directly influences the level of active TGF-β1, and thus, TG inhibition may exert a renoprotective effect by targeting not only a direct extracellular matrix deposition but also TGF-β1 activation and recruitment.

Role of triglyceride-rich lipoproteins in diabetic nephropathy

Diabetic nephropathy is an increasingly important cause of morbidity and mortality worldwide. A large body of evidence suggests that dyslipidemia has an important role in the progression of kidney disease in patients with diabetes. Lipids may induce renal injury by stimulating TGF-beta, thereby inducing the production of reactive oxygen species and causing damage to the glomeruli and glomerular glycocalyx. Findings from basic and clinical studies strongly suggest that excess amounts of a variety of lipoproteins and lipids worsens diabetes-associated microvascular and macrovascular disease, increases glomerular injury, increases tubulointerstitial fibrosis, and accelerates the progression of diabetic nephropathy. The increasing prevalence of obesity, type 2 diabetes mellitus, and diabetic nephropathy means that interventions that can interrupt the pathophysiological cascade of events induced by lipoproteins and lipids could enable major life and cost savings. This Review discusses the structural, cellular, and microscopic findings associated with diabetic nephropathy and the influence of lipoproteins, specifically triglyceride-rich lipoproteins (TGRLs), on the development and perpetuation of diabetic nephropathy. Some of the accepted and hypothesized mechanisms of renal injury relating to TGRLs are also described.

Effect of RAS inhibition on TGF-β, renal function and structure in experimentally induced diabetic hypertensive nephropathy rats

OBJECTIVE

Transforming growth factor-β (TGF-β) implicated in the pathogenesis of diabetic nephropathy. Hence, developing agents that antagonize fibrogenic signals is a critical issue facing researchers.

MATERIAL AND METHODS

Fifty rats were allocated to five groups: 1=control rats, 2=diabetic hypertensive rats 3=diabetic hypertensive rats treated with spironolactone, 4=diabetic hypertensive rats treated with moexpril, 5=diabetic hypertensive rats treated with both spironolactone and moexpril. Measurement of TGF-β, aldosterone, creatinine and ACE. Degree of fibrosis was calculated.

RESULTS

Serum creatinine, mean arterial blood pressure (MAP), aldosterone, ACE, TGF-β and renal fibrosis increased significantly in untreated diabetic hypertensive rats compared with control rats. Administration of spironolactone, moexpril, or both decreased these changes.

CONCLUSIONS

Addition of the spironolactone to moexpril was more effective in reducing fibrosis and improvement of renal function than monotherapy with either drug, possibly due to a dual inhibitory effect on the RAS, and thus suppression of TGF-β.

Increased TG2 expression can result in induction of transforming growth factor beta1, causing increased synthesis and deposition of matrix proteins, which can be regulated by nitric oxide

In fibrotic conditions increases in TG2 activity has been linked to an increase in the deposition of extracellular matrix proteins. Using TG2 transfected Swiss 3T3 fibroblasts expressing TG2 under the control of the tetracycline-regulated inducible promoter, we demonstrate that induction of TG2 not only stimulates an increase in collagen and fibronectin deposition but also an increase in the expression of these proteins. Increased TG2 expression in these fibroblasts led to NF-kappaB activation, resulting in the increased expression of transforming growth factor (TGF) beta(1). In addition, cells overexpressing TG2 demonstrated an increase in biologically active TGFbeta(1) in the extracellular environment. A specific site-directed inhibitor of TG abolished the NF-kappaB and TGFbeta1 activation and the subsequent elevation in the synthesis and deposition of extracellular matrix proteins, confirming that this process depends on the induction of transglutaminase activity. Treatment of TG2-induced fibroblasts with nontoxic doses of nitric oxide donor S-nitroso-N-acetylpenicillamine resulted in decreased TG2 activity and apprehension of the inactive enzyme on the cell surface. This was paralleled by a reduction in activation of NF-kappaB and TGFbeta(1) production with a subsequent decrease in collagen expression and deposition. These findings support a role for NO in the regulation of TG2 function in the extracellular environment.

Modulation of tissue transglutaminase in tubular epithelial cells alters extracellular matrix levels: a potential mechanism of tissue scarring

The up-regulation and trafficking of tissue transglutaminase (TG2) by tubular epithelial cells (TEC) has been implicated in the development of kidney scarring. TG2 catalyses the crosslinking of proteins via the formation of highly stable epsilon(gamma-glutamyl) lysine bonds. We have proposed that TG2 may contribute to kidney scarring by accelerating extracellular matrix (ECM) deposition and by stabilising the ECM against proteolytic decay. To investigate this, we have studied ECM metabolism in Opossum kidney (OK) TEC induced to over-express TG2 by stable transfection and in tubular cells isolated from TG2 knockout mice. Increasing the expression of TG2 led to increased extracellular TG2 activity (p<0.05), elevated epsilon(gamma-glutamyl) lysine crosslinking in the ECM and higher levels of ECM collagen per cell by (3)H-proline labelling. Immunofluorescence demonstrated that this was attributable to increased collagen III and IV levels. Higher TG2 levels were associated with an accelerated collagen deposition rate and a reduced ECM breakdown by matrix metalloproteinases (MMPs). In contrast, a lack of TG2 was associated with reduced epsilon(gamma-glutamyl) lysine crosslinking in the ECM, causing reduced ECM collagen levels and lower ECM per cell. We report that TG2 contributes to ECM accumulation primarily by accelerating collagen deposition, but also by altering the susceptibility of the tubular ECM to decay. These findings support a role for TG2 in the expansion of the ECM associated with kidney scarring.

Association of donor inflammation- and apoptosis-related genotypes and delayed allograft function after kidney transplantation

BACKGROUND

Delayed renal allograft survival (delayed graft function [DGF]) after deceased donor kidney transplantation is associated with an increased risk of allograft loss. Inflammatory response and apoptosis are associated with increased risk of DGF.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

We first recruited 616 recipients of kidneys from 512 deceased kidney donors, and donor DNA was genotyped. These recipients, who were included in a prospective cohort study of 9 transplant centers in the Delaware Valley region, had their DGF outcome obtained through medical record abstraction. We then identified the recipient (n = 349) of the contralateral deceased kidney donor, if not part of the cohort, through the US Renal Data System registry. The final cohort consisted of 965 recipients of deceased donor kidneys from 512 donors.

PREDICTORS

Donor single-nucleotide polymorphisms in genes for tumor necrosis factor alpha (TNF), transforming growth factor beta1 (TGFB1), interleukin 10 (IL10), p53 (TP53), and heme oxygenase 1 (HMOX1).

OUTCOMES

DGF, defined as the need for dialysis therapy in the first week posttransplantation. Secondary outcomes included acute rejection and estimated glomerular filtration rate.

MEASUREMENTS

Information for DGF, acute rejection, and estimated glomerular filtration rate for recipients in the Delaware Valley Cohort was obtained through medical record abstraction. For other recipients, information for DGF was obtained from United Network for Organ Sharing forms and Centers for Medicare & Medicaid Services claims in the US Renal Data System registry.

RESULTS

No association was detected between the TGFB1, IL10, TP53, and HMOX1 genes and DGF. The G allele of the TNF polymorphism rs3093662 was associated with DGF in an adjusted analysis (odds ratio, 1.85 compared with A allele; 95% confidence interval, 1.16 to 2.96; P = 0.01). However, this association did not achieve statistical significance after adjusting for multiple comparisons.

LIMITATIONS

Inadequate sample size for infrequent genotypes and multiple comparisons.

CONCLUSION

Because of the low frequency of donor single-nucleotide polymorphisms of interest, a larger sample size and replication are necessary to confirm these findings on the association of donor genotypes with DGF.

Inhibition of prostasin expression by TGF-beta1 in renal epithelial cells

BACKGROUND

Prostasin has been shown to be involved in the regulation of sodium handling in the kidney. TGF-beta1 has been demonstrated to suppress alphaENaC expression and sodium uptake. Therefore, we hypothesized that TGF-beta1 may regulate prostasin expression to modulate sodium reabsorption in the kidney.

METHODS

To determine if TGF-beta1 has an effect on prostasin expression, we isolated 2.9 kb of the rat prostasin promoter, and measured its transcriptional activity with a luciferase assay in mouse cortical collecting duct cell line (M-1). The effect of TGF-beta1 on the mRNA and protein abundance of prostasin, and amiloride-sensitive (22)Na uptake was determined.

RESULTS

Treatment of M-1 cells with 20 ng/mL of TGF-beta1 for 24 hours significantly decreased the promoter activity by 50 +/- 1%, and the inhibitory effect was dose dependent over the range of 0.1 to 20 ng/mL. We identified a 50 bp region (-410 to -360) containing c-Rel-like sequence in prostasin promoter that is responsible for the TGF-beta1-mediated inhibition, and found that TGF-beta1 increases IkappaBalpha expression in M-1 cells. TGF-beta1 reduced endogenous prostasin mRNA and protein expression in M-1 cells by 50 +/- 12% and 44 +/- 12%, respectively, and the amiloride-sensitive (22)Na uptake by 35.9 +/- 4.8%.

CONCLUSION

Our findings indicate the possibility that TGF-beta1 transcriptionally inhibits prostasin expression by the induction of IkappaBalpha and the subsequent inhibition of NF-kappaB/Rel activity in M-1 cells, and also suggest the possibility that TGF-beta1 might inhibit sodium reabsorption through a reduction in prostasin expression and subsequent inhibition of ENaC activity.

Diverse effects of long-term treatment with imidapril and irbesartan on cell growth signal, apoptosis and collagen type I expression in the left ventricle of spontaneously hypertensive rats

To compare diverse effects of angiotensin II type 1 receptor antagonists (irbesartan) and angiotensin converting enzyme inhibitors (imidapril) on left ventricular remodeling in spontaneously hypertensive rats (SHR). Thirty male SHR were randomly divided into three groups: SHR-IR (treated with irbesartan, 50 mg/kg), SHR-IM (imidapril, 3 mg/kg), SHR-C (placebo). Ten male Wistar Kyoto rats (WKY) treated with placebo acted as the control. All treatments were administered once daily from 14 to 27 weeks of age. Imidapril and irbesartan have the similar inhibitor effects on blood pressure and left ventricular mass indexes in SHR. Despite both drugs suppressed ERK-1 protein expression, decreased cardiomyocytes apoptosis index, blocked collagen type I deposition, reduced TGF-beta(1) gene expression in SHR, imidapril elicits a stronger inhibitory effect. Irbesartan had little effect on MKP-1 protein expression, but imidapril decreased it significantly. As a result, the ERK-1/MKP-1 ratio in SHR-IR was significantly greater than that in SHR-IM (P < 0.05). These results suggest that the balance between MKP-1 and ERKs in myocardial tissue is important for cardiac cell proliferation and growth. They also indicate that the similar efficacy of antihypertensive treatment in reducing blood pressure does not predict the similar capacity to control the individual facet of left ventricular remodeling. Irbesartan is more effective in regressing the homeostasis between ERK-1 and MKP-1, however imidapril is superior in suppressing apoptosis and collagen synthesis in cardiac tissue.

Mesenteric artery remodeling and effects of imidapril and irbesartan on it in spontaneously hypertensive rats

AIM: To investigate the remodeling of mesenteric artery and the expression of TGF-β₁, c-Jun in mesenteric artery and effects of imidapril and irbesartan on the remodeling in spontaneously hypertensive rats (SHR).

METHODS: Thirty SHR (male/female, 21/9), aged 13 wk, were randomly divided into 3 groups (7 male rats and 3 female rats each group): SHR group, imidapril group (imidapril 3 mg/kg·d was given in drinking water for 14 wk), and irbesartan group (irbesartan 50 mg/kg·d was given in drinking water foe 14 wk). Ten homogenous Wistar Kyoto rats, 5 males and 5 females, weighing 206 ± 49 g, were selected as normal control group (WKY group). Systolic pressure was measured on day 1, 2, 4, 6, 8, 10, 12 and 14 during the experiment and the rats were killed at the end of the experiment. Angiotensin II (Ang II) level in plasma and mesenteric arteries was measured by radioimmunoassay. The morphology of the secondary branches of mesenteric artery were examined by light microscopy and electron microscopy. Reverse transcription polymerase chain reaction (RT-PCR) was used to detect the expression of transforming growth factor TGF-β₁ and c-Jun mRNA.

RESULTS: Compared with imidapril group and irbesartan group, the blood pressure was remarkably increased in SHR group. Ang II level in plasma and mesenteric arteries in SHR group was the same or lower than that in WKY group, and was higher in irbesartan group and lower in imidapril group. The remodeling of mesenteric arteries in SHR group was mostly obvious among the 4 groups. The ratio of TGF-β₁ absorbed light value to GAPDH absorbed light value in the SHR group was 0.887 ± 0.019, which was significantly higher than that in WKY group, imidapril group, and irbesartan group with the ratios of 0.780 ± 0.018, 0.803 ± 0.005, and 0.847 ± 0.017, respectively (P < 0.01). Ang II level in plasma and mesenteric arteries in imidapril group was significantly lower than that in irbesartan group (P < 0.05). The c-Jun absorbed light value/GAPDH absorbed light value of mesenteric arteries in the SHR group was 0.850 ± 0.015, which was significantly higher than that in the WKY, imidapril, and irbesartan groups (0.582 ± 0.013, 0.743 ± 0.012, and 0.789 ± 0.013, respectively, P < 0.01), and was significantly lower in imidapril group than in irbesartan group (P < 0.05).

CONCLUSION: Imidapril and irbesartan can not only control blood pressure but also inhibit mesenteric arteries remodeling and mRNA expression of TGF-β₁, c-Jun in SHR. Imidapril is more effective than irbesartan.

Antisense oligonucleotide against 47-kDa heat shock protein (Hsp47) inhibits wound-induced enhancement of collagen production

It is well known that excessive collagen synthesis during the wound-healing process causes scar formation. Our recent in-vivo study indicates that antisense treatment against 47-kDa heat shock protein (Hsp47), a collagen-specific molecular chaperone, relieves scar formation following skin wounds in rats [Wang et al., Plast. Reconstr. Surg., in press]. In order to understand the mechanism of this phenomenon, we examined the effects of antisense treatment on the expression of mRNAs and proteins of Hsp47 and collagens in fibroblasts derived from wounded rat tongues. Hsp47 and procollagen alpha1(I) and alpha1(III) mRNAs were consistently increased after wounding and were maximal at day 5 post-injury. Treatment with antisense oligonucleotide against Hsp47 efficiently blocked the production of procollagen alpha2(I) and alpha1(III) proteins, but had little effect on their mRNA levels. Therefore, we conclude that antisense oligonucleotide against Hsp47 inhibits the production of procollagen type I and III proteins in fibroblasts derived from wounded tongues, overcoming the increase in their mRNAs.

Expression of TGF-beta-induced matrix protein betaig-h3 is up-regulated in the diabetic rat kidney and human proximal tubular epithelial cells treated with high glucose

BACKGROUND

betaig-h3 is an extracellular matrix protein whose expression in several cell types is greatly increased by transforming growth factor-beta (TGF-beta). TGF-beta is believed to be involved in the development of diabetic nephropathy and thus we have assessed the possibility that betaig-h3 may be a downstream molecule in this pathogenic process.

METHODS

Immunoblotting and immunohistochemistry were done using an antibody against mouse betaig-h3 protein. betaig-h3 and TGF-beta concentrations were measured by enzyme-linked immunosorbent assay (ELISA). Cell adhesion and migration were assessed by measuring activity of N-acetyl-beta-d-glucosaminidase and using a transwell plate, respectively.

RESULTS

Immunohistochemistry revealed that betaig-h3 occurs mainly in the basement membrane of proximal tubules, particularly the S3 segment but also to lesser extents in the basement membranes of the cortical thick ascending limb cells and the parietal glomerular epithelial cells in Bowman's capsule. Immunoblotting revealed that approximately 68 kD bands were seen only in the cortex + the outer stripe of the outer medulla. Rats with streptozotocin (STZ)-induced diabetes exhibited a marked and sustained increase in renal betaig-h3 abundance. This was mirrored by urinary betaig-h3 levels. In vitro experiments with human primary renal proximal tubular epithelial cells revealed that their expression of betaig-h3 was greatly increased by either TGF-beta or glucose. High glucose levels also stimulated TGF-beta production by renal proximal tubular epithelial cells and the high glucose-induced betaig-h3 expression was almost completely blocked by anti-TGF-beta antibody. betaig-h3 mediated renal proximal tubular epithelial cells adhesion and migration.

CONCLUSION

betaig-h3 may be important in the development of diabetic nephropathy. Furthermore, the level of urinary betaig-h3 may be useful as an early marker reflecting disease onset and progression.

Collagen-binding heat shock protein HSP47 expression during healing of fetal skin wounds

Wounds in fetal animals are known to heal without scar formation, but the mechanism involved remains unclear. Scar tissue is characterized by disorganized collagen bundles. The 47-kDa heat shock protein (HSP47) is a molecular chaperone that specifically targets collagen processing. However, the role of HSP47 in scar formation is poorly understood. We studied the relation of HSP47 expression in skin to scar formation during fetal wound healing. Immunohistochemical analysis demonstrated HSP47-positive cells in the epidermal cell layer of fetal and neonatal rat skin and the absence of such cells in subcutaneous tissue. After induction of a wound on the back of fetal and neonatal rats, the message of collagen type I was increased only in neonatal skin but not in fetal skin. HSP47-positive cells consistently increased for 7 days after wound induction in neonatal rats. In contrast, HSP47-positive cells and HSP47 protein were unchanged in fetal rats. We conclude that the scarless healing of fetal skin wounds is related to lack of change in HSP47 expression. HSP47 may thus be an important determinant of scar formation during wound healing.

Quantification of TGF-beta1 mRNA along rat nephron in obstructive nephropathy

Unilateral ureteral obstruction (UUO) leads to interstitial fibrosis of the obstructed kidney, and transforming growth factor-beta1 (TGF-beta1) is thought to play an important role in this process. Although increased TGF-beta1 mRNA expression in the obstructed kidney has been demonstrated, the source of the increased TGF-beta1 remains to be elucidated. To determine the precise localization of TGF-beta1 in the obstructed kidney, we examined TGF-beta1 mRNA expression using in situ hybridization and competitive RT-PCR in rats with UUO. In situ hybridization demonstrated that TGF-beta1 mRNA expression was preferentially increased in tubular epithelial cells and to a lesser degree in infiltrating macrophages in obstructed kidneys. Quantitative analysis using competitive RT-PCR in microdissected nephron segments revealed that levels of TGF-beta1 mRNA in obstructed kidneys relative to control kidneys increased significantly in proximal tubules, thick ascending limbs of Henle, and distal convoluted tubules, whereas those in glomeruli and collecting ducts did not change significantly. Of the tubular segments, the proximal tubules appeared to predominantly contribute to increased TGF-beta1 mRNA. Our findings suggest that renal tubules, particularly proximal tubules, are the main contributors to increased TGF-beta1 mRNA expression in obstructed kidneys and to the subsequent interstitial fibrosis.

Recipient age and weight affect chronic renal allograft rejection in rats

Nephron doses and immune responses change with age. Therefore, age is a potential risk factor for graft survival after kidney transplantation. The aim of this study was to determine whether age-related differences are of importance for long-term outcomes after renal transplantation. Kidneys from Fisher 344 rats were orthotopically transplanted into nephrectomized Lewis rats. Kidneys were transplanted using donors and recipients of three age levels, i.e., young (8 wk of age), adult (16 wk of age), and old (40 wk of age). Rats were killed 24 wk after transplantation, and functional, morphologic, and molecular evaluations were performed. Recipient age, rather than donor age, determined graft survival rates. No significant correlation was observed between donor kidney weight on the day of transplantation and morphologic results. Advanced recipient age was associated with reduced creatinine clearance, more severe histologic injuries, including extended glomerular sclerosis, interstitial fibrosis, and vascular lesions, more pronounced cellular infiltration, and greater expression of transforming growth factor-beta and platelet-derived growth factor A and B chains. Although no significant correlation between donor age or kidney weight on the day of transplantation and morphologic results was observed, there was a significant correlation between recipient body weight on the day of transplantation and allograft injury. It is concluded that recipient age and weight affect chronic renal rejection. Renal allografts may benefit from young recipient age but may deteriorate in old recipients, suggesting effects of recipient functional demand on long-term outcomes.

A novel model to study renal myofibroblast formation in vitro

BACKGROUND

In chronic renal disease, the decrease of excretory renal function closely correlates with the extent of interstitial fibrosis. A common feature of interstitial fibrosis is the occurrence of myofibroblasts, which are regarded as the predominant cells in matrix synthesis. We studied the transformation of renal fibroblasts into myofibroblasts in vitro as a model to elucidate the mechanisms underlying this process.

METHODS

Primary cultures of freshly isolated rat inner medullary fibroblasts were established as reported previously. mRNA expression of myofibroblast markers and interstitial collagens was examined by Northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR). Phenotypic expression was investigated by immunolabeling. Endogenous transforming growth factor-beta (TGF-beta) production was inhibited by addition of a neutralizing antibody or by TGF-beta 1 antisense oligodeoxynucleotides (ODNs).

RESULTS

Initially and during the first 36 hours, primary culture cells expressed neither alpha-smooth muscle actin nor desmin mRNA. From day 2 of primary culture, we observed a strong increase in these mRNAs, as evaluated by RT-PCR, followed by the phenotypic expression of these myofibroblast markers. Collagen type I mRNA was first detectable from day 4 of primary culture and showed a strong increase in its expression level during the following days, with phenotypic expression predominantly in myofibroblasts. The transformation rate of fibroblasts to myofibroblasts largely decreased in cocultures with collecting duct cells. This effect could be reversed by reducing the seeding density. We examined in this system the effect of TGF-beta 1 to define further its putative fibrogenic activity. However, neither the addition of exogenous TGF-beta 1 nor the inhibition of endogenous TGF-beta production showed any significant effect on fibroblast transformation, suggesting that this cytokine exerts its effects at other levels or requires a cofactor.

CONCLUSIONS

We present a novel model to examine the de novo expression of myofibroblast markers and collagen type I in freshly isolated fibroblasts under defined conditions in primary culture. This model could provide a strategy for the molecular characterization of myofibroblast formation and the phenomena associated with this process.

Elastic fiber proteins in the glomerular mesangium in vivo and in cell culture

BACKGROUND

Glomerular capillaries of the mammalian kidney are exposed to high intraluminal hydrostatic pressures and require elastic constraint to maintain size, shape, and integrity. Previous morphological and functional studies indicated that the extracellular matrices of glomeruli, that is, basement membrane and mesangial matrix, contribute to glomerular resilience and mechanical stability. Immunofluorescence microscopy findings demonstrated elastic fiber components to be located in the renal vasculature, including glomeruli. The aim of this study was to clarify the exact glomerular localization, composition, and cellular production of these proteins.

METHODS

We examined the renal distribution of the elastic fiber proteins fibrillin-1, emilin, microfibril-associated glycoproteins (MAGPs) 1 and 2, latent transforming growth factor-binding protein-1 (LTBP-1), and elastin using immunohistology and immunoelectron microscopy of human, rat, and mouse kidneys. In mesangial cell cultures, we also studied the expression and extracellular deposition of such proteins by use of Northern blotting and immunocytochemistry.

RESULTS

Fibrillin-1, emilin, MAGPs 1 and 2, and LTBP-1 were present in glomeruli of mouse, rat, and human kidney, where they were located predominantly in the mesangial extracellular matrix underlying glomerular endothelium and basement membrane. Several of these proteins, as well as elastin, were also expressed in the renal vasculature. While elastin localized to the glomerular vascular pole in afferent and efferent arterioles extending to Bowman's capsule, it was not found in the glomerular capillary tuft. Cultured mesangial cells of rat, mouse, and human kidneys expressed mRNAs of fibrillin-1, emilin, MAGP-2, and elastin, and the respective proteins localized within and outside of mesangial cells, as shown by immunocytochemistry. mRNA expression of fibrillin-1, emilin, and elastin was strong in quiescent mesangial cells; their gene expression was further up-regulated by transforming growth factor-beta1, while it was transiently reduced when cells were exposed to mitogenic 10% fetal calf serum and platelet-derived growth factor.

CONCLUSIONS

These findings demonstrate that specific elastic fiber proteins are produced and secreted by mesangial cells. This process is regulated by growth factors. Their abundance in the extracellular matrix of the mesangium is in keeping with the concept that elastic fiber proteins contribute to the mechanical stability and elastic strength of the glomerular capillary tuft.

Growth factor expression in the osteophytes of the human femoral head in osteoarthritis

Osteoarthritis is characterized by marked osteophyte formation consisting of new cartilage and bone. Because several growth factors are known to be involved in chondrogenesis and osteogenesis, the expression of transforming growth factor-beta 1 and basic fibroblast growth factor in the osteophytes of the human femoral heads in osteoarthritis were examined. Transforming growth factor-beta 1 messenger ribonucleic acid was detected in the osteophytes by reverse transcription-polymerase chain reaction. All of the nine examined osteophytes expressed transforming growth factor-beta 1 messenger ribonucleic acid, whereas one of four osteoarthritic femoral heads and none of four osteonecrotic femoral heads expressed transforming growth factor-beta 1 messenger ribonucleic acid. The extent of transforming growth factor-beta 1 messenger ribonucleic acid expression varied among the osteophytes. Transforming growth factor-beta 1 or basic fibroblast growth factor was analyzed in osteophytes immunohistochemically. Transforming growth factor-beta 1 was localized in the superficial cells in the osteophyte cartilage, but it was scarcely detected in the superficial cells in the degenerative articular cartilage. Basic fibroblast growth factor was detected in the cells in the whole layer of osteophyte cartilage and in the articular cartilage. There was a difference in the localization, which suggests the different roles of transforming growth factor-beta 1 and basic fibroblast growth factor in bone and cartilage metabolism in osteophyte formation.

Effect of angiotensin-converting enzyme inhibition on growth factor mRNA in chronic renal allograft rejection in the rat

BACKGROUND

Despite considerable progress in immunosuppression, the incidence of chronic renal allograft rejection has not decreased. Recent studies have revealed that angiotensin-converting enzyme (ACE) inhibition ameliorates graft arteriosclerosis, glomerulosclerosis, and tubular atrophy. Moreover, it decreases systemic and glomerular capillary hydrostatic pressure in a rat kidney allograft model. We evaluated the effects of the ACE inhibitor enalapril on cytokine and growth factor expression in chronically rejecting rat kidney allografts.

METHODS

Kidneys of Fisher (F344) rats were orthotopically transplanted into Lewis (Lew) rats. To prevent acute rejection, cyclosporine A (1.5 mg/kg/day) was given to all recipients during the first 10 days after transplantation. Enalapril (60 mg/L) or vehicle was added to the drinking water 10 days after transplantation. Animals were harvested 20 weeks after transplantation for histologic and immunohistologic studies, as well as for evaluation of cytokine and growth factor mRNA by semiquantitative polymerase chain reaction.

RESULTS

Controls developed severe signs of chronic rejection, such as glomerular and vascular lesions, associated with a large number of infiltrating leukocytes. Enalapril-treated animals developed less proteinuria and other signs of chronic rejection. The mRNA levels of transforming growth factor-beta 1 (TGF-beta 1), platelet-derived growth factor A and B chain (PDGF A and B), insulin-like growth factor-I (IGF-I), interleukin-1 (IL-1), and monocyte chemoattractant protein-1 (MCP-1) were significantly reduced in the enalapril group and were most pronounced for IL-1 and PDGF A. In addition, we found an increased level of renal angiotensinogen mRNA after treatment with enalapril.

CONCLUSIONS

Treatment with enalapril attenuated the development of proteinuria, ameliorated morphological damage, decreased leukocyte infiltration, and prevented a rise in renal mRNA levels of growth factors and cytokines in kidney grafts in a rat model of chronic renal allograft rejection.

SDZ-RAD prevents manifestation of chronic rejection in rat renal allografts

BACKGROUND

Chronic rejection remains the most frequent cause of renal graft loss over the long term. However, effective treatment of this process is not yet available. SDZ-RAD (40-O-[2-hydroxyethyl]-rapamycin) is a new, orally active rapamycin derivative with potent immunosuppressive activity. We have examined the effects of SDZ-RAD in a well-established model of chronic renal allograft rejection in rats.

METHODS

Kidneys of Fisher (F334) rats were orthotopically transplanted into bilaterally nephrectomized Lewis recipients. To suppress an initial episode of acute rejection, rats were briefly treated with low doses of cyclosporine for the first 10 days. Thereafter they received either SDZ-RAD (0.5 mg/kg(day) or vehicle. At 24 weeks, functional evaluations were performed, kidneys were harvested, and histological, immunohistological, and reverse transcription-polymerase chain reaction evaluations were performed.

RESULTS

Animals treated with SDZ-RAD developed lower proteinuria and less glomerulosclerosis as compared with controls. Additionally SDZ-RAD reduced the infiltration of macrophages and lymphocytes and the expression of intercellular adhesion molecule-1, laminin, and fibronectin. Furthermore, we observed a reduced expression of growth factor mRNA (transforming growth factor-beta and platelet-derived growth factor-AA) in these animals.

CONCLUSION

Our results demonstrated that SDZ-RAD effectively ameliorates chronic renal allograft rejection in rats, probably mediated by suppression of growth factors.

Administration of antenatal glucocorticoids upregulates peptide growth factor gene expression in nitrofen-induced congenital diaphragmatic hernia in rats

BACKGROUND/PURPOSE

There is increasing evidence to suggest that various growth factors play a crucial role in fetal lung growth and morphogenesis. An array of peptide growth factors regulate cell proliferation, differentiation, and various other cell functions in the developing lung. The aim of this study was to investigate the effect of antenatal glucocorticoids administration on gene expression of basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF) and transforming growth factor (TGF)-beta1 in nitrofen-induced congenital diaphragmatic hernia (CDH) in rats.

METHODS

A CDH model was induced in pregnant rats after administration of nitrofen. Dexamethasone (Dex; 0.25 mg/kg) was given intraperitoneally on day 18.5 and 19.5 of gestation (term, day 22). Cesarean section was performed on day 21 of gestation. mRNA was extracted from left lung and reverse transcription-polymerase chain reaction (RT-PCR) was performed to evaluate mRNA expression of each growth factors. Relative levels of mRNA were expressed as a ratio of the band density divided by that of beta-actin, a housekeeping gene known to be expressed at a constant level.

RESULTS

Relative mRNA levels of bFGF and TGF-beta1 were decreased significantly in CDH lung compared with controls. Antenatal Dex treatment up-regulated gene expression of bFGF, PDGF, and TGF-beta1 in the hypoplastic CDH lung.

CONCLUSIONS

The authors' findings suggest that decreased gene expression of bFGF, PDGF, and TGF-beta1 in the CDH lung may suppress lung growth and development. Increased gene expression of bFGF, PDGF, and TGF-beta1 in Dex-treated lung suggests that antenatal glucocorticoid administration may accelerate fetal lung growth by up-regulating these growth factors.

Monocyte chemoattractant protein-1 mediates collagen deposition in experimental glomerulonephritis by transforming growth factor-beta

BACKGROUND

Monocyte chemoattractant protein-1 (MCP-1) plays a significant role in the recruitment of monocytes/macrophages in experimental glomerulonephritis (GN). Because recent evidence points to possible profibrogenic effects of leukocyte-derived factors in GN, this study was designed to evaluate the role of the chemokine MCP-1 in the fibrogenesis of experimental GN.

METHODS

Rats with an anti-thy-1-induced GN were treated with a neutralizing antiserum against MCP-1. Glomerular collagen type IV, as a marker of glomerular matrix deposition, was assessed by Northern and Western blotting and immunohistology. Transforming growth factor-beta (TGF-beta), an important mediator of this matrix expansion, was studied by Northern and Western blotting.

RESULTS

The induction of GN resulted in a significant increase of glomerular collagen type IV deposition and TGF-beta synthesis. The neutralization of MCP-1 significantly reduced the enhanced collagen type IV protein synthesis and deposition without affecting collagen mRNA expression. However, both the enhanced transcription and protein synthesis of TGF-beta were inhibited by anti-MCP-1 antiserum in nephritic animals.

CONCLUSIONS

In this model of GN, MCP-1 has a fibrogenic effect through the stimulation of TGF-beta. MCP-1 is thus not only important for the recruitment of inflammatory cells, but also mediates glomerular matrix accumulation.

The concept of glomerular self-defense

The balance between local offense factors and defense machinery determines the fate of tissue injury: progression or resolution. In glomerular research, the most interest has been on the offensive side, for example, the roles of leukocytes, platelets, complement, cytokines, eicosanoids, and oxygen radical intermediates. There has been little focus on the defensive side, which is responsible for the attenuation and resolution of disease. The aim of this review is to address possible mechanisms of local defense that may be exerted during glomerular injury. Cytokine inhibitors, proteinase inhibitors, complement regulatory proteins, anti-inflammatory cytokines, anti-inflammatory eicosanoids, antithrombotic molecules, and extracellular matrix proteins can participate in the extracellular and/or cell surface defense. Heat shock proteins, antioxidants, protein phosphatases, and cyclin kinase inhibitors may contribute to the intracellular defense. This article outlines how the glomerulus, when faced with injurious cells or exposed to pathogenic mediators, defends itself via the intrinsic machinery that is brought into play in resident glomerular cells.

Sex hormones and gender-related differences: their influence on chronic renal allograft rejection

BACKGROUND

Renal hemodynamics and immune responses differ between males and females. Thus, sex hormones and genetically determined gender differences may determine the process of chronic rejection to some extent.

METHODS

Female (F) or male (M) F344 kidneys were orthotopically transplanted into ovariectomized female Lewis recipients and were treated for 16 weeks with either estradiol, testosterone, or vehicle.

RESULTS

Testosterone treatment resulted in increased urinary protein excretion independently of the donor gender, as well as extended glomerular sclerosis, interstitial fibrosis, and severe vascular lesions. Additionally, mononuclear cell infiltration was most pronounced in these animals, in parallel to an increased expression of intercellular adhesion molecule-1 (ICAM-1), fibronectin, laminin, and transforming growth factor-beta (TGF-beta) in the grafts. Estradiol treatment resulted in an improved graft function, reduced glomerular sclerosis, and a diminished cellular infiltration, in parallel to a reduced ICAM-1, fibronectin, laminin, and TGF-beta expression. In animals treated with vehicle, the gender of the donor influenced the outcome. Grafts of male origin had good graft function and histology, whereas grafts from female donors developed severe proteinuria and glomerular, interstitial, and vascular damage.

CONCLUSIONS

These results suggest that a protective effect of estradiol on the progression of chronic rejection exists that is independent of donor gender. Additionally, a male kidney may benefit from the absence of testosterone, whereas the function of a female kidney deteriorates in the absence of estradiol.

Renal expression of transforming growth factor-beta inducible gene-h3 (beta ig-h3) in normal and diabetic rats

BACKGROUND

Transforming growth factor-beta (TGF-beta) has been implicated in the pathogenesis of a number of kidney diseases characterized by glomerulosclerosis and tubulointerstitial fibrosis. TGF-beta is secreted in a latent form requiring extracellular modification to become biologically active. TGF-beta inducible gene-h3 (beta ig-h3) is a recently identified TGF-beta-induced gene product. The present study sought to examine beta ig-h3 expression in normal and diabetic rats.

METHODS

Beta ig-h3, TGF-beta1 and alpha1 (IV) collagen gene expression were assessed by Northern blot analysis and in situ hybridization in 20 Sprague Dawley rats, randomly assigned to receive streptozotocin (diabetic, N = 11) or citrate buffer alone (control, N = 9) and sacrificed eight months later. The effect of exogenous TGF-beta1 on beta ig-h3 expression was also assessed in cultured proximal tubular cells.

RESULTS

In situ hybridization localized beta ig-h3 gene expression to the juxtaglomerular apparatus and the pars recta (S3 segment) of proximal tubules in both control and diabetic animals. Kidney TGF-beta 1, beta ig-h3 and alpha1 (IV) collagen mRNA from diabetic rats were increased two- to threefold compared with controls (P < 0.01). There was a significant correlation between TGF-beta1 and beta ig-h3 gene expression in kidneys from diabetic rats (r = 0.73, P = 0.01). In addition, beta ig-h3 mRNA increased in response to exogenous TGF-beta1 in a dose-dependent fashion in cultured proximal tubular cells.

CONCLUSION

These findings support the hypothesis that biologically active TGF-beta plays a pathogenetic role in diabetic kidney disease and suggest that beta ig-h3 may be a useful index of TGF-beta1 bioactivity in the kidney.

Dietary salt enhances glomerular endothelial nitric oxide synthase through TGF-beta1

Dietary salt controls production of nitric oxide (NO), a potent paracrine relaxation factor involved in glomerular filtration and salt excretion. We hypothesized that glomerular NO production was enhanced through endothelial nitric oxide synthase (NOS3). Rats in metabolic cages were studied after 4 days on 0.3% (Lo-salt) or 8.0% (Hi-salt) NaCl diet. Steady-state mRNA and protein levels of NOS3 and calcium-dependent NO production of isolated glomeruli from Hi-salt animals were greater than those values observed in glomeruli from Lo-salt rats. Because dietary salt enhanced glomerular production of transforming growth factor-beta1 (TGF-beta1) [W.-Z. Ying and P. W. Sanders. Am. J. Physiol. 274 (Renal Physiol. 43): F635-F641, 1998], studies were then conducted to examine the interaction between NOS3 and TGF-beta1. Glomerular steady-state levels of mRNA of NOS3 and TGF-beta1 directly correlated (r2 = 0. 946; P < 0.0001). A neutralizing antibody to TGF-beta reduced NOS3 protein and NO production in cultured glomeruli from Hi-salt animals to levels seen in the Lo-salt glomeruli. Thus dietary salt increased glomerular expression of TGF-beta1, which in turn augmented NO production through NOS3.

TGF-β1 as an Endogenous Defender Against Macrophage-Triggered Stromelysin Gene Expression in the Glomerulus

Recent investigation has indicated that TGF-β1, the macrophage (Mφ) deactivator, may attenuate Mφ-mediated acute glomerular injury. Using stromelysin as an indicator, this study investigated whether and how endogenous TGF-β1 modulates the glomerular cell activation triggered by Mφ. Rat mesangial cells were stably transfected with a cDNA encoding the active form of TGF-β1 and a cDNA coding for a dominant-negative mutant of the TGF-βR type II. Compared with mock-transfected cells, TGF-β1 transfectants exhibited blunted expression of stromelysin in response to the Mφ-derived, inflammatory cytokine IL-1β. In contrast, mesangial cells expressing the dominant-interfering TGF-βR showed enhanced expression of stromelysin in response to IL-1β, suggesting that endogenous TGF-β functions as an autocrine inhibitor of the IL-1 response. In isolated, normal rat glomeruli, externally added TGF-β1 suppressed the induction of stromelysin by mediators that were elaborated by activated Mφ. Similarly, when isolated, nephritic glomeruli producing the active form of TGF-β1 were stimulated by IL-1β or Mφ-conditioned medium, the induction of stromelysin was dramatically suppressed as compared with normal glomeruli. To investigate whether endogenous TGF-β1 affects the glomerular cell activation triggered by Mφ, a technique for adoptive Mφ transfer was used. LPS-stimulated reporter Mφ were transferred into either normal rat glomeruli or nephritic glomeruli expressing active TGF-β1. In the normal glomeruli, stromelysin expression was markedly induced in resident cells after the transfer of activated Mφ. This induction was substantially repressed in those glomeruli producing active TGF-β1. These results reinforce the idea that TGF-β1 is an endogenous defender that attenuates certain actions of infiltrating Mφ in the glomerulus.

Dietary salt modulates renal production of transforming growth factor-beta in rats

Transforming growth factors (TGF) are potent multifunctional polypeptides that are involved in renal function and glomerular sclerosis. We postulated that dietary salt modified renal production of TGF-beta. An increase in dietary salt produced sustained increases in steady-state levels of mRNA for TGF-beta 1, -beta 2, and -beta 3 in the rat kidney. While serum concentration of TGF-beta 1 did not change, the 8.0% NaCl diet increased urinary excretion of TGF-beta 1, indicating enhanced renal production was the source of TGF-beta 1. Increasing urinary flow rates with diuretics did not further increase synthesis of TGF-beta 1 in animals receiving the 8.0% NaCl diet. The 8.0% NaCl diet increased production of TGF-beta 1 in both glomeruli and tubules, although active TGF-beta 1 was secreted in greater amounts only from glomeruli. Enhanced glomerular production of both inactive and active TGF-beta 1 induced by the 8.0% NaCl diet was inhibited by tetraethylammonium (TEA) and not glybenclamide. Cardiac production of TGF-beta 1 also increased on the 8.0% NaCl diet but was not affected by TEA. The results demonstrated that increased dietary salt augmented glomerular TGF-beta production by a mechanism that included a TEA-sensitive potassium channel. Dietary salt, by facilitating glomerular expression of TGF-beta, may directly promote development of glomerulosclerosis.

Growth factors and the kidney in diabetes mellitus

Nephromegaly and mesangial matrix expansion observed in the diabetic kidney are all clues of a role of growth factors in the pathogenesis of these lesions. A growing body of evidence shows that changes in (1) insulin-like growth factor I regulation, and (2) the transforming growth factor beta loop exist in the kidney in the diabetic hypertrophic kidney and in diabetic glomerulosclerosis. However, other growth factors may be involved in some diabetic renal changes. The abnormalities in growth factor content and regulation, the role of growth factors in the diabetic kidney, and the effect of hyperglycemia and advanced glycosylation end products on growth factors in the kidney are reviewed.

Intracellular processing of transforming growth factor-beta in mesangial cells

Transforming growth factor beta 1 (TGF-beta 1) is a multifunctional regulator of cell-growth, differentiation and extracellular matrix formation in several physiological conditions. It plays a crucial role in the process of glomerulosclerosis. Mature TGF-beta 1 is secreted as a latent form associated with the latency associated peptide (LAP), and its activation occurs through the LAP cleavage. The intracellular localization and the mechanisms of activation of TGF-beta 1 protein have not been elucidated in the mesangial cell. In the present report we examined the intracellular processing from TGF-beta 1 precursor to the latent-TGF-beta 1 in cultured mesangial cells by immunocytochemistry, using three rabbit polyclonal antibodies directed against different epitopes of human TGF-beta 1. The anti-LAP-TGF-beta 1 precursor Ab stained mesangial cells in the perinuclear region and in the cytoplasm in the area corresponding to the rough endoplasmic reticulum; the anti-COOH-terminal fragment of TGF-beta 1 Ab reacted in the same area, in vesicular structures located in the cytoplasm and furthermore, in the mesangial cell clusters, so-called hillocks, with an extracellular pattern; the anti-NH2-terminal fragment of TGF-beta 1 Ab stained only large exocytotic vesicles at the periphery of the cytoplasma. Our investigations suggest a conformational rearrangement of pro-TGF-beta 1 molecule occurring between the rough endoplasmic reticulum and the TGF-beta 1 secretion and support the idea that in mesangial cells the activation of TGF-beta 1 occurs during the secretion process. In conclusion, the processing of TGF-beta 1 in mesangial cells seems to be similar to that one observed in other mesenchymal cells.

Inhibition of protein tyrosine kinases attenuates increases in expression of transforming growth factor-beta isoforms and their receptors following arterial injury

Transforming growth factor-beta 1 (TGF-beta 1) has been implicated in neointima formation in mechanically injured vessels and in restenosis after angioplasty. To further understand the significance of TGF-beta s in neointima formation, we examined the temporal expression of three TGF-beta isoforms (-beta 1, -beta 2, and -beta 3), their receptors (ALK-2, ALK-5, and T beta RII), and two putative TGF-beta responses (elevations in alpha v and beta 3 integrin mRNAs) in balloon catheter-injured rat carotid arteries and their dependency on tyrosine kinase activity. Using a standardized reverse transcriptase-polymerase chain reaction assay optimized to estimate mRNA levels, we observed distinct patterns of mRNA regulation for TGF-beta 1, -beta 2, and -beta 3 during the 48 hours immediately after injury, which were localized to the vessel's media. TGF-beta 1 mRNA increased 10-fold during this time while TGF-beta 3 mRNA also increased almost 2-fold. There were also increases in mRNAs encoding the TGF-beta type I receptors ALK-5 and ALK-2, as well as the type II receptor (T beta RII). Eight hours after the injury, mRNA levels for ALK-2 and ALK-5 were on average 2-fold higher; mRNA encoding the type II receptor increased approximately 3-fold by 24 hours. There were also associated increases in TGF-beta 1, TGF-beta 3, ALK-5, and T beta RII immunoreactive peptide levels. Peak increases in mRNAs for integrins alpha v and beta 3 averaged approximately 2-fold and 2.5-fold, respectively. Perivascular administration of the tyrosine kinase inhibitor genistein at the time of vessel injury markedly (> 85%) inhibited elevations in mRNAs encoding TGF-beta 1, TGF-beta 3, T beta RII, and the two integrins alpha v and beta 3, while application of its inactive chemically similar homologue daidzein did not prevent the injury-induced elevations in mRNA levels. Since the increases in integrins alpha v and beta 3 mRNA could be theoretically attributed to TGF-beta actions despite being dependent on tyrosine kinase activity, we examined whether the observed elevations in integrins alpha v and beta 3 were due to TGF-beta 1 secretion, using cultured rat carotid artery smooth muscle cells. TGF-beta 1 neutralizing antibodies specifically inhibited elevations in integrins alpha v and beta 3 mRNAs due to platelet-derived growth factor-BB and fibroblast growth factor-2. We conclude that multiple components of the TGF-beta system in vessels are activated following injury and influence expression of integrin receptors important for smooth muscle cell migration. Activation of the TGF-beta system appears to be highly dependent on tyrosine kinases.

Renal cell regeneration following oxidant exposure: inhibition by TGF-beta1 and stimulation by ascorbic acid

Renal proximal tubular cell (RPTC) monolayers exposed to the model oxidant tert-butylhydroperoxide (TBHP; 0.8 mM) for 1.5 hrs were 33 and 31% confluent after 1 and 4 days, respectively. Control monolayers remained 100% confluent throughout the experiment. Exogenous TGF-beta1 promoted monolayer deterioration by potentiating cellular death and suppressed EGF-stimulated regeneration of the RPTC monolayer. Net TGF-beta1 production in injured RPTC increased 1.7- and 3.2-fold on Days 1 and 2, respectively, and returned to control levels 4 days following TBHP treatment. An anti-TGF-beta antibody increased monolayer confluence to 50% and DNA content 1.3-fold 4 days after TBHP exposure. L-Ascorbic acid 2-phosphate (AscP) present only during the recovery period increased monolayer confluence to 67% but had no effect on RPTC proliferation, suggesting that AscP promoted monolayer regeneration by cellular migration/spreading. AscP present continuously had no effect on the extent of TBHP-induced injury but promoted regeneration of RPTC with increased monolayer confluence (1.8-fold) and DNA content (1.8-fold) and decreased cellular lysis by 52% 4 days following TBHP exposure. The results demonstrate that TBHP-induced injury increases net TGF-beta1 production in RPTC and that autocrine TGF-beta1 inhibits regeneration of the monolayer by potentiating cellular injury and monolayer deterioration. The data also show that AscP is not cytoprotective during TBHP exposure but promotes RPTC regeneration by stimulating proliferation and migration/spreading and decreasing cellular death during the recovery period.

The role of transglutaminase in the rat subtotal nephrectomy model of renal fibrosis

Tissue transglutaminase is a calcium-dependent enzyme that catalyzes the cross-linking of polypeptide chains, including those of extracellular matrix (ECM) proteins, through the formation of epsilon-(gamma-glutamyl) lysine bonds. This crosslinking leads to the formation of protein polymers that are highly resistant to degradation. As a consequence, the enzyme has been implicated in the deposition of ECM protein in fibrotic diseases such as pulmonary fibrosis and atherosclerosis. In this study, we have investigated the involvement of tissue transglutaminase in the development of kidney fibrosis in adult male Wistar rats submitted to subtotal nephrectomy (SNx). Groups of six rats were killed on days 7, 30, 90, and 120 after SNx. As previously described, these rats developed progressive glomerulosclerosis and tubulo-interstitial fibrosis. The tissue level of epsilon-(gamma-glutamyl) lysine cross-link (as determined by exhaustive proteolytic digestion followed by cation exchange chromatography) increased from 3.47+/- 0.94 (mean+/-SEM) in controls to 13.24+/-1.43 nmol/g protein 90 d after SNx, P </= 0.01. Levels of epsilon-(gamma-glutamyl) lysine cross-link correlated well with the renal fibrosis score throughout the 120 observation days (r = 0.78, P </= 0.01). Tissue homogenates showed no significant change in overall transglutaminase activity (14C putrescine incorporation assay) unless adjusted for the loss of viable tubule cells, when an increase from 5.77+/-0.35 to 13.93+/-4.21 U/mg DNA in cytosolic tissue transglutaminase activity was seen. This increase was supported by Western blot analysis, showing a parallel increase in renal tissue transglutaminase content. Immunohistochemistry demonstrated that this large increase in epsilon-(gamma-glutamyl) lysine cross-link and tissue transglutaminase took place predominantly in the cytoplasm of tubular cells, while immunofluorescence also showed low levels of the epsilon-(gamma-glutamyl) lysine cross-link in the extracellular renal interstitial space. The number of cells showing increases in tissue transglutaminase and its cross-link product, epsilon-(gamma-glutamyl) lysine appeared greater than those showing signs of typical apoptosis as determined by in situ end-labeling. This observed association between tissue transglutaminase, epsilon-(gamma-glutamyl) lysine cross-link, and renal tubulointerstitial scarring in rats submitted to SNx suggests that tissue transglutaminase may play an important role in the development of experimental renal fibrosis and the associated loss of tubule integrity.

Role of transforming growth factor-beta 1 in glomerulonephritis

The role of transforming growth factor-beta 1 (TGF-beta 1) in human glomerulonephritis is still poorly understood. The relationship between expression of TGF-beta 1 protein or TGF-beta 1 mRNA and tissue damage was investigated using the enzyme-antibody and in situ hybridization method in frozen slices of renal tissue from 30 patients: 25 with glomerulonephritis (18 with immunoglobulin A nephropathy; two with focal glomerulosclerosis, one with membranous nephropathy, one with crescentic glomerulonephritis and three with lupus nephritis) and five control patients with minimal change disease. The expression of TGF-beta 1 mRNA was high in sclerotic and proliferative glomeruli, as well as in the tubular epithelial cells within tubulointerstitial lesions. There was significant correlation between the severity of tissue damage in immunoglobulin A nephropathy and the presence of TGF-beta 1 protein and TGF-beta 1 mRNA. These findings suggest that TGF-beta 1 is involved in glomerulosclerosis and the development of tubulointerstitial lesions, indicating its potential importance in the progression and aggravation of immunoglobulin A nephropathy.

Mesangial cell-derived transforming growth factor-beta 1 reduces macrophage adhesiveness with consequent deactivation

Adhesion of macrophages is a crucial event that determines the number and function of macrophages at inflammatory sites. The aim of this study was to elucidate the role of mesangial cells in the regulation of macrophage adhesiveness. J774.2 macrophages were suspended in serial dilutions of mesangial cell conditioned medium (MC medium) and seeded on plastic tissue culture plates. MC medium did not affect the initial adhesion of macrophages but induced subsequent detachment in a concentration-dependent manner. A similar effect was observed when macrophages were plated on plastic coated with laminin, collagen type IV or Matrigel. The reduced adhesiveness was reversible, and cell viability was unaffected by MC medium, indicating that the effect is not due to cytotoxicity. Conditioned media from fibroblastic, epithelial and endothelial cell lines did not induce macrophage detachment. To identify the active component in MC medium, we examined the involvement of transforming growth factor-beta 1 (TGF-beta 1) in the process. Mesangial cells constitutively expressed TGF-beta 1 mRNA, and MC medium contained the active form of TGF-beta 1. Exogenously added TGF-beta 1 induced macrophage detachment in a dose-dependent manner, and an anti-TGF-beta 1 neutralizing antibody partially abolished the activity of MC medium, indicating the involvement of TGF-beta 1 as an active component. Compared to adherent cells, detached macrophages showed reduced mitogenic activity and blunted induction of IL-1 beta and IL-6 in response to lipopolysaccharide. These data demonstrate that TGF-beta 1 is a mesangial cell-derived factor that impairs adhesiveness of macrophages and confers blunted responses to a specific stimulus. These findings suggest one potential mechanism for macrophage clearance from inflamed glomeruli.

Role of endothelin as a mitogen in experimental glomerulonephritis in rats

Recent studies have revealed that endothelin-1 (ET-1) is a potent mitogen for mesangial cells in vitro. To determine whether ET-1 exerts the mitogenic action on mesangial cells in vivo, we examined the glomerular expression of ET-1 and its receptors in a rat model of mesangial proliferative glomerulonephritis and assessed the effect of a specific endothelin A (ET(A)) receptor antagonist, FR139317, on mesangial cell proliferation in this model. The levels of preproET-1 mRNA expression and ET-1 protein production in glomeruli increased markedly on days 4 and 7 after disease induction, and the levels changed in concordance with the glomerular cell proliferation. In contrast, the level of ET(A) receptor mRNA initially decreased on day 1, and thereafter increased on days 4 and 7. Administration of FR139317 to rats with experimental glomerulonephritis induced a significant reduction in mesangial cell proliferation. In addition, in situ hybridization of preproET-1 mRNA and double-immunolabeling of ED-1 and OX-7 in a mirror image section revealed that the principal cell expressing ET-1 in glomeruli were infiltrating macrophages on day 1, and they were replaced by mesangial cells on day 4. These findings indicate that ET-1 functions as a potent mitogen for mesangial cells in vivo in an autocrine or paracrine fashion.

Transfer of a mutated gene encoding active transforming growth factor-beta 1 suppresses mitogenesis and IL-1 response in the glomerulus

Using in vivo gene transfer, we examined the anti-inflammatory potential of transforming growth factor-beta 1 (TGF-beta 1) in the renal glomerulus. TGF-beta 1 cDNA, modified to allow for secretion of the active form of TGF-beta 1, was introduced into cultured rat mesangial cells. The responses of the established transfectants were examined in culture. In vitro, the transduced mesangial cells showed a reduced mitogenic response to fetal calf serum and were insensitive to induction of matrix metalloproteinase-9 (MMP-9) by the proinflammatory cytokine IL-1 beta. To examine whether glomeruli which express active TGF-beta 1 in vivo are insensitive to these same stimuli, TGF-beta transfectants were transferred into normal rat glomeruli via renal artery injection. After 24 hours, isolated glomeruli containing transfectants exhibited TGF-beta bioactivity, a reduced mitogenic response, and repressed expression of MMP-9 in response to IL-1 beta. We further examined the responses of these chimeric glomeruli to an in vivo mitogenic stimulus by transferring TGF-beta transfectants into glomeruli of kidneys one day after the induction of anti-Thy-1 nephritis. The mitogenic activity of isolated glomeruli was examined four days after the cell injection. Compared to unmodified or mock cell-containing glomeruli, the in vivo mitogenic activity of glomeruli containing TGF-beta transfectants was significantly repressed. Furthermore, cellular outgrowth from nephritic glomeruli expressing active TGF-beta 1 was also suppressed ex vivo compared to controls. These data indicate that TGF-beta 1 inhibits mitogenesis and IL-1 response of the glomerulus and may, in part, act as a potential early suppressor of glomerular inflammation.