TGF-beta and regulation of interstitial nephritis

Kidney aging--inevitable or preventable?

The aging process affects all organs, including the kidneys. As part of this process, progressive scarring and a measurable decline in renal function occur in most people over time. The improved understanding of the processes that can lead to and/or hasten scarring and loss of renal function over time parallels advances in our understanding of the aging process. Clinical factors, including hypertension, diabetes mellitus, obesity, abnormal lipid levels and vitamin D deficiency, have been associated with increasing renal sclerosis with age. In addition, tissue factors such as angiotensin II, advanced glycation end products, oxidative stress and Klotho are associated with renal aging. These associations and possible interventions, including the control of blood pressure, blood sugar, weight, diet and calorie restriction might make renal aging more preventable than inevitable.

Histopathological and ultrastructural effects of Losartan on embryonic rat kidney

The aim of our study was to investigate the histopathological, immunohistochemical and ultrastructural effects of Losartan (a selective angiotensin II type-1 receptor blocker) on renal development in rats. Twelve pregnant rats were divided into control and experimental groups. In the experimental group, Losartan (10 mg/kg/day) was given via nasogastric tube, between the sixth day of implantation and time of sacrifice on embryonic days 18 and 20. All formalin-fixed, paraffin wax-embedded renal tissue sections were stained with hematoxylin and eosin or labelled for binding of primary antibodies against transforming growth factor-beta (TGF-beta 1,-2,-3) using an avidin-biotin-peroxidase method. For electron microscopic examination, samples were fixed with glutaraldehyde and osmium tetroxide and embedded in araldite. Glomerular basement membrane (GBM) thickness was measured and compared using an unpaired t-test. Angiotensin II type-1 receptor antagonism by Losartan inhibited renal growth and delayed nephron maturation. Increased immunoreactivity of TGF-beta's was observed in developing nephron precursors and interstitial cells in the experimental group. Electron microscopical examination showed that thickening of the GBM was normal in the control group but an irregular thickening was seen in the experimental group (p < 0.001). It was also seen that epithelial cells of developing tubules underwent apoptosis in the experimental group. Thus, renal development in rats seems to depend on an intact renin-angiotensin system.

Regulation of inducible class II MHC, costimulatory molecules, and cytokine expression in TGF-beta1 knockout renal epithelial cells: effect of exogenous TGF-beta1

As reports of mice genetically deficient for TGF-beta1 demonstrated aberrant renal class II MHC expression, we investigated inducible class II MHC expression on renal tubular epithelial cells derived from TGF-beta1 knockout (-/-) and wild-type (+/+) mice. IFN-gamma markedly upregulated class II MHC (I-A(b)) expression in both (-/-) and (+/+) tubular epithelial cells. Coincubation studies of (+/+) and (-/-) tubular epithelial cells with IFN-gamma+LPS, or pretreatment of these cells with TGF-beta1, revealed inhibition of IFN-gamma-induced I-A(b) mRNA and cell surface expression that occurred via a decrease in class II transactivator gene expression in both (+/+) and (-/-) tubular epithelial cells. In addition, ICAM-1 was constitutively expressed on both (+/+) and (-/-) tubular epithelial cells and was upregulated by IFN-gamma or IFN-gamma+LPS. ICAM-1 expression in (+/+) and (-/-) tubular epithelial cells, however, was decreased by TGF-beta1. Parallel analysis evaluating B7-1 expression detected low levels of B7-1 in unstimulated (+/+) and (-/-) tubular epithelial cells that were increased by IFN-gamma, LPS, and IFN-gamma+LPS. IFN-gamma+LPS-mediated upregulation of B7-1 was also blocked by pretreatment with TGF-beta1. Cytokine analysis detected significantly higher levels of TNF-alpha and MIP-1alpha mRNA in all treated (-/-) preparations than in (+/+) tubular epithelial cell controls. These studies demonstrate normal patterns of class II MHC, ICAM-1, and B7 expression in TGF-beta1 (-/-) tubular epithelial cells in response to IFN-gamma, LPS, and TGF-beta1. Upregulated cytokine expression at baseline and in response to proinflammatory mediators is apparent in (-/-) tubular epithelial cells, however, and suggests that dysregulation of cytokine expression in inflammatory responses may be a primary event in multifocal inflammation observed in TGF-beta1-deficient animals.

Potential methods to prevent interstitial fibrosis in renal disease

Almost all forms of end stage renal disease (ESRD) are characterised by progressive interstitial fibrosis and tubular atrophy. Since most forms of chronic renal failure are initiated by inflammatory processes, anti-inflammatory strategies can be successful, if initiated early, in preventing progression of the disease process. Unfortunately, in most cases the disease is only detected clinically following robust progression of interstitial fibrosis. In these patients, control of secondary risk factors, such as hypertension and hyperglycaemia, can slow the progression rate but cannot stop the process completely. Certainly, ACE inhibitors remain the mainstay of preserving renal function. However, additional therapies are needed for the effective treatment of progressive renal fibrosis. A number of compounds have shown some very potent antifibrotic properties in vitro and in vivo, and are currently undergoing further evaluation. This review discusses the most promising among them. However, few of the therapeutic agents discussed here have been tested clinically. Studies evaluating the potential of a number of these have just commenced whereas for many others clinical use is still many years away. However, some very promising reagents may enhance our clinical arsenal within a relatively short period of time.

Regulation of endothelin-1 and transforming growth factor-beta1 production in cultured proximal tubular cells by albumin and heparan sulphate glycosaminoglycans

BACKGROUND

Both endothelin-1 (ET-1) and transforming growth factor beta 1 (TGF-beta1) have been implicated in the progression of interstitial fibrosis. In the present study we enquired if albumin influences the production of these factors in cultured human proximal tubular epithelial cells (PTEC) and if heparan sulphate glycosaminoglycans (HS-GAG) can inhibit this production.

METHODS

ET-1 and TGF-beta1 production in supernatants of PTEC was measured by RIA and ELISA respectively. In addition semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) was performed to study differences in ET-1 and TGF-beta1 mRNA expression. To demonstrate ET-1 or TGF-beta1 binding to heparin or HS-GAG, binding studies by means of dot blot analysis were carried out.

RESULTS

TGF-beta1 and ET-1 were both produced in different concentrations, depending on the PTEC culture tested. Human serum albumin (HSA) up-regulated the production of both factors in a time and dose dependent fashion. The production of these factors was inhibited by heparin under basal and stimulatory conditions. ET-1 production was only inhibited by HS-GAG with a high degree of sulphation. For the inhibition of TGF-beta1 production, the sulphation of HS-GAG was less critical. TGF-beta1, but not ET-1 mRNA expression was inhibited by HS-GAG. Inhibition of sulphation of cell surface HS-GAG resulted in the inhibition of ET-1 but not TGF-beta1 production. Both factors were able to bind to HS-GAG, although this required different amounts of HS-GAG sulphation for each factor.

CONCLUSIONS

Our data demonstrate that in PTEC the release of pro-fibrogenic factors can be inhibited by HS-GAG. This may explain to some extent the beneficial effect of heparin in the treatment of interstitial fibrosis.

Evidence that furin is an authentic transforming growth factor-beta1-converting enzyme

Transforming growth factor (TGF)-beta1 plays an essential role in cell growth and differentiation. It is also considered as a gatekeeper of immune homeostasis with gene disruption leading to autoimmune and inflammatory diseases. TGF-beta1 is produced as an inactive precursor polypeptide that can be efficiently secreted but correct proteolytic cleavage is an essential step for its activation. Assessment of the cleavage site has revealed a unique R-H-R-R sequence reminiscent of proprotein convertase (PC) recognition motifs and has previously demonstrated that this PC-like cleavage site is correctly cleaved by furin, a member of the PC family. Here we report that among PC members, furin more closely satisfies the requirements needed to fulfill the role of a genuine TGF-beta1 convertase. Even though six members of the PC family have the ability to cleave TGF-beta1, ectopic expression of alpha(1)-antitrypsin Portland (alpha(1)-AT-PDX), a potent furin inhibitor, blocked 80% of TGF-beta1 processing mediated by endogenous enzymes as demonstrated in an in vitro digestion assay. Genetic complementation of a furin-deficient LoVo cell line with the wild-type gene restores the production of mature and bioactivable TGF-beta1. Moreover, both furin and TGF-beta are coordinately expressed and regulated in vitro and in vivo in the hematopoietic and immune system, an important tissue target. These results demonstrate for the first time that furin is an authentic and adaptive TGF-beta1-converting enzyme whereas other members of the PC family might substitute or supplement furin activity. Our study advances our comprehension of the complexity of the TGF-beta system and should facilitate the development of therapeutically useful TGF-beta inhibitors.

Renal tubulointerstitial fibrosis. New thoughts on its development and progression

Current investigation of the pathogenesis of tubulointerstitial injury indicates that both interstitial fibroblasts and renal tubular epithelial cells promote extracellular matrix accumulation. Moreover, two peptides--TGF-beta and angiotensin II--produced locally or delivered in the circulation, appear to play a central role in renal fibrosis. Pharmacologic amelioration of renal fibrosis may require methods directed at multiple factors involved in the fibrotic process, including angiotensin II, TGF-beta, and the proliferation and activation of interstitial fibroblasts.

Angiotensin stimulates TGF-beta1 and clusterin in the hydronephrotic neonatal rat kidney

Unilateral ureteral obstruction (UUO) induces activation of the renin-angiotensin system and upregulation of transforming growth factor-beta1 (TGF-beta1; a cytokine modulating cellular adhesion and fibrogenesis) and clusterin (a glycoprotein produced in response to cellular injury). This study was designed to examine the regulation of renal TGF-beta1 and clusterin by ANG II in the neonatal rat. Animals were subjected to UUO in the first 2 days of life, and renal TGF-beta1 and clusterin mRNA were measured 3 days later. Rats were divided into treatment groups receiving saline vehicle, ANG, losartan (AT(1) receptor inhibitor), or PD-123319 (AT(2) receptor inhibitor). ANG stimulated renal TGF-beta1 expression via AT(1) receptors, a response similar to that in the adult. In contrast, clusterin expression was stimulated via AT(2) receptors, a response differing from that in the adult, in which ANG inhibits clusterin expression via AT(1) receptors. We speculate that the unique response of the neonatal hydronephrotic kidney to ANG II is due to the preponderance of AT(2) receptors in the developing kidney.

New insights into the pathogenesis of interstitial nephritis

Emerging data on the role of interstitial inflammation in progressive renal disease are redefining our understanding of the pathogenic mechanisms of chronic kidney damage. Recent experimental evidence emphasizes the role for both immune and non-immune mechanisms in interstitial nephritis. New observations regarding maneuvers that downregulate such injurious renal responses may direct further studies that develop new therapeutic modalities.