Age-related decline in label-retaining tubular cells: implication for reduced regenerative capacity after injury in the aging kidney

Recovery after acute kidney injury is impaired in the elderly, but the precise mechanism for such age-related incompetence remains unclear. By in vivo bromodeoxyuridine (BrdU) labeling, renal progenitor cells (label-retaining cells; LRCs) were identified in tubules of normal rat kidney and were shown to be the origin of proliferating cells after injury. In the present study, the involvement of LRCs in the age-related decline of tubular recovery after injury was examined. After 1 wk of BrdU labeling followed by a 2-wk chase period, ischemia-reperfusion injury was induced in 7-wk-, 7-mo-, and 12-mo-old rats. Age-related decreases in DNA synthesis and cell proliferation in renal tubules after injury were found. The number of LRCs also significantly declined with age. At 24 h after reperfusion, the number of LRCs significantly increased in all ages of rats tested. There was no significant difference in the ratio of LRC division among rats of different ages. The area of the rat endothelial cell antigen (RECA)-1-positive capillary network declined with age. When renal tubules isolated from rats treated with BrdU label were cocultured with human umbilical vein endothelial cells (HUVEC), the number of LRCs significantly increased compared with tubules cultured without HUVEC. These data suggest that the reduced capacity of tubular regeneration in the aging kidney is partly explained by the shortage of LRC reserves. The size of the LRC pool might be regulated by the surrounding peritubular capillary network.

Enhancement of in vitro human tubulogenesis by endothelial cell-derived factors: implications for in vivo tubular regeneration after injury

Renal proximal tubular epithelium can regenerate after various insults. To examine whether the tubular repair process is regulated by surrounding peritubular capillaries, we established an in vitro human tubulogenesis model that mimics in vivo tubular regeneration after injury. In this model, HGF, a potent renotropic factor, dose dependently induced tubular structures in human renal proximal tubular epithelial cells cultured in gels. Consistent with regenerating tubular cells after injury, HGF-induced tubular structures expressed a developmental gene, Pax-2, and a mesenchymal marker, vimentin, and formed a lumen with aquaporin-1 expression. Electron microscopic analysis showed the presence of microvilli on the apical site of the lumen, suggesting that these structures are morphologically equivalent to renal tubules in vivo. When cocultured with human umbilical vein endothelial cells (HUVEC), HGF-induced tubular formation was significantly enhanced. This could not be reproduced by the addition of VEGF, basic FGF, or PDGF. Protein array revealed that HUVEC produced various matrix metalloproteinases (MMPs). The stimulatory effects of coculture with HUVEC or HUVEC-derived conditional medium were almost completely abolished by addition of the tissue inhibitor of metalloproteinase (TIMP)-1 or TIMP-2. These data suggest that endothelial cell-derived factors including MMPs play a critical role in tubulogenesis and imply a potential role of peritubular capillary endothelium as a source of factor(s) required for tubular recovery after injury.

Effects of proteasome inhibitors on rat renal fibrosis in vitro and in vivo

AIM

Transforming growth factor-β (TGF-β) is involved in renal tubulointerstitial fibrosis. Recently, the ubiquitin proteasome system was shown to participate in the TGF-β signalling pathway. The aim of this study was to examine the effects of proteasome inhibitors on TGF-β-induced transformation of renal fibroblasts and tubular epithelial cells in vitro and on unilateral ureteral obstruction (UUO) in vivo.

METHODS

Rat renal fibroblasts NRK-49F cells and tubular epithelial cells, NRK-52E, were treated with TGF-β in the presence or absence of a proteasome inhibitor, MG132 or lactacystin. Rats were subjected to UUO and received MG132 i.p. for 7 days.

RESULTS

In cultured renal cells, both MG132 and lactacystin inhibited TGF-β-induced α-smooth muscle actin (α-SMA) protein expression according to both western blotting and immunofluorescent study results. MG132 also suppressed TGF-β-induced mRNA expression of α-SMA and upregulation of Smad-response element reporter activity. However, MG132 did not inhibit TGF-β-induced phosphorylation and nuclear translocation of Smad2. In contrast, MG132 increased the protein level of Smad co-repressor SnoN, demonstrating that SnoN is one of the target molecules by which MG132 blocks the TGF-β signalling pathway. Although the proteasome inhibitor suppressed TGF-β-induced transformation of cultured fibroblasts and tubular epithelial cells, MG132 treatment did not ameliorate tubulointerstitial fibrosis in the rat UUO model.

CONCLUSION

Proteasome inhibitors attenuate TGF-β signalling by blocking Smad signal transduction in vitro, but do not inhibit renal interstitial fibrosis in vivo.

Efficacy and safety of tacrolimus for induction therapy in patients with active lupus nephritis

After the completion of a double-blind placebo-controlled trial, tacrolimus (TAC) was approved for the treatment of lupus nephritis (LN) in Japan. However, the approved maximal dose, 3 mg/day, is almost half the dose used for induction therapy outside Japan. In this study, we retrospectively evaluated the efficacy and safety of low-dose TAC (≤3 mg/day) for induction therapy in 13 adult patients (2 men and 11 women) with active LN. Eight patients were treated for LN flares. Twelve patients underwent renal biopsies: 8 with class IV, 2 with class III + V, 1 with class IV + V, and 1 with class V renal histology, according to the International Society of Nephrology/Renal Pathology Society (ISN/RPS) classification. The mean initial doses of prednisone and TAC were 34.6 ± 14.5 and 2.7 ± 0.6 mg/day, respectively. All the patients achieved a complete remission (CR) at 7.7 ± 6.7 months (mean ± SD) after the last administration of TAC, except for 2 patients who discontinued TAC treatment; 1 because of worsening systemic lupus erythematosus and 1 because of hypertension. Two patients experienced a flare-up after achieving CR. The mean blood TAC concentration 12 h after the last administration (C12) was significantly lower among the patients with flare-ups than among those with a sustained CR (1.5 ± 1.5 vs. 5.1 ± 1.9 ng/mL, P = 0.034). These data showed that low-dose TAC was effective for induction therapy in patients with active LN, although a lower TAC concentration may be associated with a poor outcome.

Nestin is a novel marker for renal tubulointerstitial injury in immunoglobulin A nephropathy

AIM

Nestin, an intermediate filament originally identified as a marker of neural progenitor cells, is transiently expressed in endothelial cells and tubuloepithelial cells during kidney development. However, in adult kidneys, podocytes are the only cells that express nestin. In this study, we examined tubulointerstitial nestin expression in human glomerulonephritis.

METHODS

Renal biopsy specimens obtained from 41 adult patients with immunoglobulin (Ig)A nephropathy were studied. Nestin expression was determined by immunohistochemical staining and estimated by digital image analysis. To identify the phenotype of nestin-positive cells, a double immunofluorescent study was performed for nestin and CD34 (a marker for endothelial cells) or alpha-smooth muscle actin (alpha-SMA, a marker for myofibroblasts).

RESULTS

In normal kidney, nestin expression was restricted to the podocytes and was not detected in tubular cells and tubulointerstitial cells. In contrast, increased nestin expression was observed at tubulointerstitial areas of IgA nephropathy. The degree of tubulointerstitial nestin expression was positively correlated with tubulointerstitial fibrosis (r = 0.546, P < 0.001). The double immunofluorescent study showed that most nestin-positive cells in the interstitium were co-stained with CD34 or alpha-SMA, suggesting that peritubular endothelial cells and tubulointerstitial myofibroblasts express nestin during the progression of tubulointerstitial injury. In addition, strong nestin expression was associated with deterioration of renal function.

CONCLUSION

Nestin expression is associated with tubulointerstitial injury and predicts renal prognosis in IgA nephropathy. Nestin could be a new marker for peritubular endothelial cell injury and tubulointerstitial fibrosis.

Successful treatment of lipoprotein glomerulopathy in a daughter and a mother using niceritrol

We report two patients, a daughter and a mother, with lipoprotein glomerulopathy (LPG) who were successfully treated with niceritrol. Both patients carried a mutation in the apolipoprotein E (apoE) gene known as ApoE Tokyo/Maebashi. The daughter was found to have proteinuria at the age of 4 years. Four years later, she was diagnosed as having LPG based on a renal biopsy. She was treated with several medications including pravastatin, ethyl icosapentate, enalapril, warfarin and cyclophosphamide, all of which failed to reduce her proteinuria. At the age of 17 years, she exhibited an increase in proteinuria and a decline in renal function, despite ongoing treatment with pravastatin and enalapril. After switching from pravastatin to niceritrol, a marked reduction in the proteinuria and an improvement in renal function were observed. Her mother was found to have proteinuria at the age of 57 years and was diagnosed as having LPG based on a renal biopsy. She was also treated with niceritrol, resulting in an improvement in her proteinuria and renal function. These cases suggest that niceritrol might be a useful therapeutic option for LPG.

Effectiveness of oral iron to manage anemia in long-term hemodialysis patients with the use of ultrapure dialysate

The aim of this study was to evaluate the effectiveness of oral iron to manage anemia in long-term hemodialysis (HD) patients using ultrapure dialysate. This study was prospectively conducted on 23 patients (11 males and 12 females; median age 60 years, range 35-81) who underwent HD in our hospital from March to September 2007. The patients were randomly assigned to two treatment groups. The first group of 11 patients received ferrous fumarate 305 mg per oral tablet once a day, while the second group of 12 patients received infusions of 50 mg iron in a 0.9% sodium chloride solution. At the end of the 6-month treatment, patients receiving oral iron and intravenous iron had a significant increase in transferrin saturation from baseline (20.1±8.9 to 29.7±7.2; p=0.011 and 17.4±6.1 to 33.7±8.6; p=0.0001, respectively) and ferritin (32.6±15.4 to 115.4±28.2; p=0.0001 and 57.8±26.7 to 183.5±47.5; p=0.0002, respectively). In both groups, hemoglobin, hematocrit and dry weight were increased, but did not reach statistical significance. Moreover, both groups showed a significant reduction in the mean weekly erythropoietin dose from baseline (5,590.9±1,513.6 to 3,727.3±1,618.1; p=0.011 and 6,775.8±2,292.2 to 4,375.0±2,473.7; p=0.027, respectively). Oral iron is indeed as effective as intravenous iron in managing anemia in HD patients using ultrapure dialysate.

Pro32Thr polymorphism of inosine triphosphate pyrophosphatase gene predicts efficacy of low-dose azathioprine for patients with systemic lupus erythematosus

We evaluated the relationship between the efficacy of low-dose azathioprine (AZA) therapy and the inosine triphosphate pyrophosphatase (ITPA) 94C>A (Pro32Thr) polymorphism in patients with systemic lupus erythematosus (SLE). We performed a multiple regression analysis to assess the influence of various factors on the reduction in SLE disease activity index (SLEDAI) scores. The ITPA 94C>A polymorphism had the highest correlation with the change in SLEDAI score (r = 0.354, P = 0.006).

Fluvastatin prevents podocyte injury in a murine model of HIV-associated nephropathy

BACKGROUND

Recent studies have reported that statins have renoprotective effects, independent from lowering plasma cholesterol. In this study, we examined whether statins were beneficial in a murine model of HIV-associated nephropathy (HIVAN).

METHODS

We used conditional transgenic mice that express one of the HIV-1 accessory genes, vpr, selectively in podocytes using podocin promoter and the Tet-on system. These mice develop aggressive collapsing focal segmental glomerular sclerosis with massive proteinuria and deterioration of renal function within 4 weeks following heminephrectomy and doxycycline administration. Fluvastatin was administrated simultaneously with doxycycline, and the effect was compared with untreated controls after 4 weeks.

RESULTS

Fluvastatin at 10 mg/kg/day significantly decreased urinary albumin excretion (87 versus 11 mg/day, P < 0.01) and glomerular sclerosis (2.4 versus 1.0, P < 0.01, assessed by semi-quantitative scoring: 0-4). Fluvastatin also decreased serum creatinine and total cholesterol, but these differences were not statistically significant (0.36 versus 0.32 mg/dl, P = 0.35; 492 versus 378 mg/dl, P = 0.11, respectively). Phenotypic changes in podocytes, as indicated by the downregulation of nephrin, Wilms' tumour 1 and synaptopodin, along with upregulation of proliferating cell nuclear antigen, were attenuated by fluvastatin, suggesting its protective effects against podocyte injuries. In cultured podocytes, angiotensin II treatment decreased nephrin expression to 13% of basal levels, which was reversed to 58% by adding fluvastatin.

CONCLUSIONS

In conclusion, fluvastatin was effective in treating experimental HIVAN. The beneficial effect of this drug might be caused, in part, by preserving nephrin expression in podocytes against angiotensin II-mediated injury.

Expression of IL-19 and its receptors in RA: potential role for synovial hyperplasia formation

OBJECTIVE

IL-19 is a novel cytokine of the IL-10 family. In this study, we sought to examine whether IL-19 plays a role in the pathogenesis of RA.

METHODS

Expression of IL-19, IL-20 receptor 1 (IL-20R1) and IL-20R2 was examined by RT-PCR and immunohistochemical analysis in rheumatoid synovium. The effects of IL-19 on synovial cells established from rheumatoid synovium (RASCs), with regard to IL-6 production and signal transducers and activators of transcription3 (STAT3) activation, were examined by ELISA and western blot analysis, respectively. The effect of IL-19 on RASC apoptosis was examined by Hoechst staining, flow cytometry analysis of annexin V binding and caspase-3 activity.

RESULTS

IL-19, IL-20R1 and IL-20R2 mRNA were detected by RT-PCR in synovial tissues from RA patients. Immunohistochemical analysis showed IL-19 was predominantly expressed in the hyperplastic lining layers of RA synovial tissues. The majority of IL-19-positive cells were vimentin-positive and CD68-positive synovial cells, serving as markers of fibroblasts and macrophages, respectively. IL-20R1 and IL-20R2 (IL-20Rs) were expressed in both the lining and sublining layers of RA synovium. In RASC, IL-19 was induced by lipopolysaccharide stimulation and constitutive expression of IL-20Rs was observed, suggesting IL-19 has an autocrine action. In terms of this function, IL-19 induced STAT3 activation and increased IL-6 production by RASC above the medium control. Moreover, IL-19 significantly reduced RASC apoptosis induced by serum starvation.

CONCLUSIONS

These data suggest that IL-19, produced by synovial cells, promotes joint inflammation in RA by inducing IL-6 production and decreasing synovial cell apoptosis.

[Efficacy of steroid pulse therapy in patients with IgA nephropathy and impaired renal function]

OBJECTIVE

In the current study, we evaluated the efficacy of methylprednisolone (MP) pulse therapy in IgA nephropathy (IgAN) patients with established renal function impairment.

PATIENTS AND METHODS

We retrospectively analyzed the effect of MP pulse therapy in patients with histologically active IgAN (8 males, 12 females) whose estimated glomerular filtration rate was less than 60 mL/min/1.73 m2 (33.4 +/- 13.1, mean +/- SD). The efficacy of the MP pulse therapy was analyzed by calculating the regression coefficients (dL/mg/month) from the slopes of the 1/serum creatinine (Cr), urine protein/creatinine ratio (g/g x Cr), and the estimated interval from the pulse therapy to dialysis (that is, for Cr to reach 8 mg/dL, as calculated from the slope of 1/Cr) or the actual interval.

RESULTS

All patients showed improved regression coefficients (-0.0214 +/- 0.00166 vs. 0.00236 +/- 0.00895, 1 year before vs. after treatment, p < 0.01). The severity of proteinuria decreased significantly from a mean urine protein/creatinine ratio of 2.9 +/- 1.7 before therapy to 1.1 +/- 0.8 (p < 0.01) at 6 months and 0.8 +/- 0.7(p < 0.01) at 12 months after therapy. Although 7 patients underwent dialysis, the average interval from pulse therapy to dialysis was prolonged from an estimated interval of 1.1 +/- 0.9 years to an actual interval of 4.1 +/- 3.5 years. Six patients showed positive regression coefficients at the last observation (4.1 +/- 3.0 years after therapy). The remaining 7 patients who had not undergone dialysis also showed prolongation of the estimated interval from pulse therapy to dialysis of 5.9 +/- 5.1 years before pulse therapy to 25.7 +/- 20.6 years at the final observation (4.9 +/- 3.5 years after therapy). No serious side effects were observed in any of the patients.

CONCLUSION

MP pulse therapy can slow the progression of renal deterioration in patients with active IgAN, even in those patients in whom renal function impairment has set in.

[Renal disease in multiple myeloma]

Renal involvement is common in multiple myeloma. Although several types of renal disease are observed, most of them are considered to be specifically related to monoclonal immunoglobulin light chains. Myeloma cast nephropathy is the most frequent and sometimes associated with acute renal failure. AL amyloidosis and monoclonal immunoglobulin deposit disease are often presented as a nephrotic syndrome. In this review, we describe the pathogenesis and diagnosis of these three renal diseases. We also focus on the treatment of renal disease in multiple myeloma, in the view points of the chemotherapy to reduce M-protein and the prevention to reduce the risks of promoting renal injury.

Angiotensin II provokes podocyte injury in murine model of HIV-associated nephropathy

Conditional transgenic mice that express one of the human immunodeficiency virus (HIV)-1 accessory genes, vpr, selectively in podocytes using a podocin promoter and a tetracycline-inducible system develop renal injuries similar to those of patients with HIV-associated nephropathy (HIVAN). We have shown that a heminephrectomy accelerates podocyte injury, which is alleviated by angiotensin II (ANG II) type 1 receptor blocker (ARB). The current study further explores the role of ANG II in the genesis of HIVAN in this murine model. With ANG II infusion, heavy proteinuria was observed at 1 wk after the initiation of doxycycline administration to induce vpr expression in podocytes. Severe morphological and phenotypical changes in the podocytes were observed at 2 wk, together with extensive glomerulosclerosis. Norepinephrine infusion, instead of ANG II, increased the systemic blood pressure to the same level as that achieved using ANG II. However, albuminuria and glomerular injury were modest in norepinephrine-infused mice. Treatment with an ARB, olmesartan, almost completely inhibited glomerular injury. In contrast, lowering the blood pressure with a vasodilator, hydralazine, partially decreased albuminuria but did not produce any histological changes. ANG II infusion alone without doxycycline resulted in a lower level of albuminuria and minimal histological changes. These data demonstrate that excessive ANG II accelerates vpr-induced podocyte injury in a mouse model of HIVAN.

Nestin expression in the kidney with an obstructed ureter

Nestin is an intermediate filament protein originally identified in neuroepithelial stem cells. This cytoskeletal-associated protein is also expressed in some non-neuronal organs including renal tubular cells and glomerular endothelial cells during kidney development. Little is known, however, about nestin expression in the kidney during injury. In this study, we find nestin expression induced in renal tubular and interstitial myofibroblasts in the adult rat kidney following unilateral ureteral obstruction. The degree of nestin expression was well correlated with the degree of tubulointerstitial fibrosis. Immunohistochemical identification of specific nephron segments showed that nestin was primarily expressed by proximal tubules, partially by distal tubules and thick ascending limbs of Henle but not by collecting ducts. The nestin-positive tubular cells also expressed vimentin and heat-shock protein 47 (HSP47) suggesting these cells reverted to a mesenchymal phenotype. Not all vimentin- or HSP-expressing cells expressed nestin; however, suggesting that nestin is distinct from these conventional mesenchymal markers. Nestin expression was also found associated with phenotypical changes in cultured renal cells induced by hypoxia or transforming growth factor-beta. Nestin expression was located in hypoxic regions of the kidney with an obstructed ureter. Our results indicate that nestin could be a novel marker for tubulointerstitial injury.

Angiotensin II type 1 receptor blockade inhibits the development and progression of HIV-associated nephropathy in a mouse model

HIV-associated nephropathy (HIVAN) is characterized by a collapsed glomerular capillary tuft with hyperplasia and hypertrophy of podocytes. Recently generated were conditional transgenic mice (podocin/Vpr) that express one of the HIV-1 accessory genes, vpr, selectively in podocytes using podocin promoter and Tet-on system. These transgenic mice developed renal injury similar to HIVAN when treated with doxycycline for 8 to 12 wk. This study demonstrated that nephron reduction by heminephrectomy markedly enhanced phenotypic changes of podocytes and led to severe FSGS within 4 wk. Nephrotic-range proteinuria was observed already at 2 wk, together with dedifferentiation and dysregulation of podocytes, indicated by decreased expression of nephrin, synaptopodin, and Wilms' tumor 1 protein and increased expression of Ki-67. The acceleration of phenotypic changes of podocytes, proteinuria, and subsequent glomerulosclerosis by heminephrectomy was almost completely inhibited by angiotensin II type 1 receptor (AT1R) blocker olmesartan. In contrast, the renoprotective effect of the calcium channel antagonist azelnidipine was minimal, although it lowered systemic BP to the same level as olmesartan, demonstrating that the inhibitory effect of AT1R blocker was independent of systemic BP. Olmesartan also reduced proteinuria and prevented glomerulosclerosis even by the delayed treatment, which was initiated after the podocyte injury appeared. These data suggest that nephron reduction exaggerates podocyte injury and subsequent glomerulosclerosis, possibly through glomerular hypertension, in the mouse model of HIVAN. AT1R blockade could be beneficial in the treatment of HIVAN by ameliorating podocyte injury by avoiding the vicious cycle of nephron reduction and glomerular hypertension.

OXIDATIVE STRESS-DEPENDENT CONVERSION OF HYDROGEN SULFIDE TO SULFITE BY ACTIVATED NEUTROPHILS

Sulfite, which is known as a major constituent of volcanic gas, is endogenously produced in mammals, and its concentration in serum is increased in patients with pneumonia. It has been reported that sulfite is produced by oxidation from hydrogen sulfide (H2S) as an intermediate in the mammalian body. The objective of this study was to investigate the ability of reactive oxygen species from neutrophils to produce sulfite from H2S. Sulfite production from activated neutrophils stimulated with N-formyl-methionyl-leucyl-phenylalanine gradually increased with an increased concentration of sodium hydrosulfide (NaHS) in the medium. The production of sulfite was markedly suppressed with an NADPH oxidase inhibitor, diphenyleneiodonium. When NaHS was added to the supernatant of activated neutrophils, a significant amount of sulfite was synthesized in the test tubes. Furthermore, when a medium containing NaHS was incubated with a water-soluble radical initiator, 2,2'-azobis-(amidinopropane) dihydrochloride, sulfite was formed in the solution and this increase was markedly suppressed by ascorbic acid. Finally, we determined serum concentrations of sulfite and H2S in an in vivo model of neutrophil activation induced by systemic injection of lipopolysaccharide (LPS) into rats. We found a significant increase in serum sulfite and H2S after LPS injection. Importantly, coadministration of ascorbic acid with LPS further increased serum H2S but suppressed sulfite levels. This finding implies that oxidative stress-dependent conversion of H2S to sulfite might occur in vivo. Thus, the oxidation of H2S is a novel sulfite production pathway in the inflammatory condition, and this chemical synthesis might be responsible for the upregulation of sulfite production in inflammatory conditions such as pneumonia.

Mechanical stretch induces podocyte hypertrophy in vitro

BACKGROUND

Increased intraglomerular pressure is a final pathway toward glomerulosclerosis in systemic hypertension, diabetes, and focal segmental glomerulosclerosis (FSGS). Increased intraglomerular pressure causes stress-tension, or stretch, on resident glomerular cells. However, the effects of stretch on podocyte growth, and the mechanisms that underlie this, have not been elucidated.

METHODS

To test the hypothesis that stretch alters podocyte growth, cultured mouse podocytes were exposed to cyclic mechanical stretch created by vacuum; control cells were grown under similar conditions, but not exposed to stretch. Proliferation (cell cycle phases) and hypertrophy (forward light scatter) were measured in stretched and control podocytes by flow cytometry. The role of the cyclin-dependent kinase (CDK) inhibitors, p21 and p27, was examined by stretching podocytes isolated from p21 and p27 knockout (-/-) mice, and the role of specific signaling pathways was assessed by Western blot analysis and blocking studies.

RESULTS

Our results showed that stretch reduced cell cycle progression in wild-type and single p27-/- podocytes and induced hypertrophy in these cells in all phases of the cell cycle at 24, 48, and 72 hours. In contrast, stretch did not induce hypertrophy in single p21-/- and double p21/p27-/- podocytes. Stretch-induced hypertrophy required cell cycle entry, and was prevented by specifically blocking extracellular signal-regulated kinase 1/2 (Erk1/2) or Akt. Although stretch increased p38 activation, inhibition of this pathway had no effect on hypertrophy.

CONCLUSION

Mechanical stretch induces hypertrophy in podocytes in vitro in all phases of the cell cycle. This effect is cell cycle dependent, and requires p21, Erk1/2, and Akt. Stretch may play a role in podocyte injury when intraglomerular pressure is increased.

Fluvastatin reduces renal fibroblast proliferation and production of type III collagen: therapeutic implications for tubulointerstitial fibrosis

BACKGROUND

Accumulating evidence suggests that hydroxymethylglutaryl-CoA reductase inhibitors have many biological effects beyond reducing cholesterol synthesis. In a mouse model of renal interstitial fibrosis induced by unilateral ureteral obstruction, fluvastatin, one of the lipophilic hydroxymethylglutaryl-CoA reductase inhibitors, was shown to ameliorate fibrosis.

METHODS

In the present study, we examined the direct effects of fluvastatin on proliferation, matrix and growth factor production by rat kidney fibroblasts (NRK-49F cells).

RESULTS

Treatment with fluvastatin reduced proliferation of NRK-49F cells in a dose-dependent manner. The addition of mevalonate or geranylgeranyl pyrophosphate but not farnesyl pyrophosphate to the culture medium almost completely abolished the effect of fluvastatin. Moreover, fluvastatin treatment decreased the expression of activated Rho in NRK-49F cells suggesting that fluvastatin may decrease cell growth through blocking the activation of Rho. The majority of fluvastatin-treated cells were arrested at the G1 phase, associated with down-regulation of cyclin A and up-regulation of cyclin-dependent kinase inhibitor p27kip1, indicating that cell cycle modulation is an important mechanism. Fluvastatin significantly decreased messenger RNA expression of type III collagen and connective tissue growth factor.

CONCLUSIONS

Taken together, it is suggested that fluvastatin may prevent tubulointerstitial fibrosis in a variety of progressive renal diseases by inhibiting proliferation of interstitial fibroblasts and their matrix synthesis.