The renal (myo-)fibroblast: a heterogeneous group of cells

Renal fibrosis is a central pathological process in kidneys of patients with chronic kidney disease (CKD). Identification of effective treatments that halt or reverse fibrosis would be beneficial for most, if not all, CKD patients. Key to this is an understanding of fibrogenesis, including the principal responsible cells, the renal fibroblasts. It is in part due to their inconspicuous appearance that it was believed that there might not be much more to a fibroblast than a simple interstitial mesenchymal cell which makes up the organ stroma. The so-called 'renal fibroblasts' are a heterogeneous population of mesenchymal cells with various essential functions during kidney development and in adult life. Still, remarkable uncertainties exist in the nomenclature of renal mesenchymal cells-or renal fibroblasts-and molecular characterization remains poor. The embryonic origin of fibroblasts is unclear as well, although some studies point to a neural crest origin of these cells. The renal myofibroblasts appear de novo in renal fibrosis, originating from renal fibroblasts. Myofibroblasts most likely represent a stressed and dedifferentiated phenotype of fibroblasts. We have only just begun to appreciate that renal fibroblasts are anything but simple renal interstitial cells.     

Tranilast attenuates structural and functional aspects of renal injury in the remnant kidney model

Pathologic fibrosis is a key feature of progressive renal disease that correlates closely with kidney dysfunction and in which the prosclerotic growth factor TGF-beta has been consistently implicated. Tranilast (n-[3,4-dimethoxycinnamoyl] anthranilic acid), an antifibrotic agent that is used to treat hypertrophic scars and scleroderma, has also been shown to inhibit TGF-beta-induced extracellular matrix synthesis in a range of cell types, including those of renal origin. Therefore, the effects of tranilast on kidney fibrosis and dysfunction were examined in the subtotal nephrectomy model of progressive renal injury. Subtotal nephrectomy led to proteinuria and renal dysfunction in association with glomerulosclerosis, tubulointerstitial fibrosis, and macrophage accumulation. Despite persistent hypertension, treatment with tranilast led to a reduction in albuminuria (61.7 (x)/(/) 1.2 versus 20.5 (x)/(/) 1.3 mg/d; P < 0.01) and plasma creatinine (0.16 versus 0.08 mmol/L; P < 0.01) in subtotally nephrectomized rats. In addition, features suggestive of TGF-beta activation, including glomerulosclerosis, tubulointerstitial fibrosis, tubular atrophy, and macrophage accumulation, all were significantly attenuated by tranilast in association with evidence of reduced TGF-beta signaling in vivo. In the context of a recent pilot study in humans, the findings of the present report suggest that tranilast may provide a novel strategy for the treatment of progressive kidney disease characterized by fibrotic scarring.     

Donor and Recipient Origin of Mesenchymal and Endothelial Cells in Chronic Renal Allograft Remodeling

Chronic transplant dysfunction (CTD) is the leading cause for limited kidney graft survival. Renal CTD is characterized by interstitial and vascular remodeling leading to interstitial fibrosis, tubular atrophy and transplant vasculopathy (TV). The origin of cells and pathogenesis of interstitial and vascular remodeling are still unknown. To study graft-versus-recipient origin of interstitial myofibroblasts, vascular smooth muscle cells (SMCs) and endothelial cells (ECs), we here describe a new rat model for renal CTD using Dark Agouti kidney donors and R26 human placental alkaline phosphatase transgenic Fischer344 recipients. This model showed the development of CTD within 12 weeks after transplantation. In interstitial remodeling, both graft- and recipient-derived cells contributed to a similar extent to the accumulation of myofibroblasts. In arteries with TV, we observed graft origin of neointimal SMCs and ECs, whereas in peritubular and glomerular capillaries, we detected recipient EC chimerism. These data indicate that, within the interstitial and vascular compartments of the transplanted kidney, myofibroblasts, SMCs and ECs involved in chronic remodeling are derived from different sources and suggest distinct pathogenetic mechanisms within the renal compartments.     

Fibroblasts in kidney fibrosis emerge via endothelial-to-mesenchymal transition

Fibroblasts are key mediators of fibrosis in the kidney and other organs, but their origin during fibrosis is still not completely clear. Activated fibroblasts likely arise from resident quiescent fibroblasts via epithelial-to-mesenchymal transition and from the bone marrow. Here, we demonstrate that endothelial cells also contribute to the emergence of fibroblasts during kidney fibrosis via the process of endothelial-to-mesenchymal transition (EndMT). We examined the contribution of EndMT to renal fibrosis in three mouse models of chronic kidney disease: (1) Unilateral ureteral obstructive nephropathy, (2) streptozotocin-induced diabetic nephropathy, and (3) a model of Alport renal disease. Approximately 30 to 50% of fibroblasts coexpressed the endothelial marker CD31 and markers of fibroblasts and myofibroblasts such as fibroblast specific protein-1 and alpha-smooth muscle actin. Endothelial lineage tracing using Tie2-Cre;R26R-stop-EYFP transgenic mice further confirmed the presence of EndMT-derived fibroblasts. Collectively, our results demonstrate that EndMT contributes to the accumulation of activated fibroblasts and myofibroblasts in kidney fibrosis and suggest that targeting EndMT might have therapeutic potential.     

PAI-1 deficiency attenuates the fibrogenic response to ureteral obstruction

BACKGROUND: Progressive renal disease is characterized by the induction of plasminogen activator inhibitor-1 (PAI-1), suggesting that impaired activity of the renal plasmin cascade may play a role in renal fibrosis. METHODS: To test this hypothesis, the severity of renal fibrosis caused by unilateral ureteral obstruction (UUO) was compared in PAI-1 wild-type (+/+) and PAI-1 deficient (-/-) mice. The extent of interstitial inflammation and fibrosis, renal plasminogen activator and plasmin activity, and renal expression of profibrotic genes was evaluated after 3, 7, and 14 days of UUO. RESULTS: Renal PAI-1 mRNA levels increased 8- to 16-fold in the +/+ mice after UUO surgery, and PAI-1 protein was detected in kidney homogenates. Interstitial fibrosis was significantly attenuated in -/- mice compared with +/+ mice at day 7 and day 14, based on the interstitial area stained with picrosirius red and total kidney collagen content. However, neither the mean renal plasminogen activator nor plasmin activities were increased in -/- mice compared with +/+ mice. The number of interstitial macrophages were significantly lower in the -/- mice three and seven days after UUO; interstitial myofibroblasts were significantly fewer at three days. At the same time points, this altered interstitial cellularity was associated with a significant reduction in renal mRNA levels for transforming growth factor-beta and procollagens alpha 1(I) and alpha 1(III). CONCLUSIONS: These studies establish an important fibrogenic role for PAI-1 in the renal fibrogenic response. The results demonstrate that one important fibrosis-promoting function of PAI-1 is its role in the recruitment of fibrosis-inducing cells, including myofibroblasts and macrophages.     

The origin of interstitial myofibroblasts in chronic kidney disease

Chronic kidney diseases (CKD), independent of their primary cause, lead to progressive, irreversible loss of functional renal parenchyma. Renal pathology in CKD is characterized by tubulointerstitial fibrosis with excessive matrix deposition produced by myofibroblasts. Because blocking the formation of these scar-forming cells represents a logical therapeutic target for patients with progressive fibrotic kidney disease, the origin of renal myofibroblasts is a subject of intense investigation. Although the traditional view holds that resident fibroblasts are the myofibroblast precursor, for the last 10 years, injured epithelial cells have been thought to directly contribute to the myofibroblast pool by the process of epithelial-to-mesenchymal transition (EMT). The recent application of genetic fate mapping techniques in mouse fibrosis models has provided new insights into the cell hierarchies in fibrotic kidney disease and results cast doubt on the concept that EMT is a source of myofibroblast recruitment in vivo, but rather point to the resident pericyte/perivascular fibroblast as the myofibroblast progenitor pool. This review will highlight recent findings arguing against EMT as a direct contributor to the kidney myofibroblast population and review the use of genetic fate mapping to elucidate the cellular mechanisms of kidney homeostasis and disease.     

Fibrosis and evidence for epithelial-mesenchymal transition in the kidneys of patients with staghorn calculi

Study Type – Therapy (case control) Level of Evidence 2b What’s known on the subject? and What does the study add? It has been shown that patients with nephrolithiasis did not have normal kidney function (retrospective study). Renal inflammation and fibrosis have been shown in kidney biopsies of nephrolithiasis patients, particularly those with brushite and cystine stones. No pathological change in kidney biopsies of patients with idiopathical calcium oxalate stone is noted. Our cross‐sectional study of patients with large kidney stone formation (mostly staghorn stones) shows that the patients have reduced overall kidney function regardless of stone type, and robust signs of inflammation and fibrosis are observed in stone‐containing renal tissues. Reduced kidney function is closely associated with the degree of renal fibrosis. This is the first study demonstrating that renal tubular cells in stone‐baring kidneys are undergoing epithelial‐mesenchymal transition, and TGF‐β₁ is overproduced in these mesenchymalized cells.

OBJECTIVES

? To quantify fibrotic lesions in renal tissues obtained from patients with large calculi and to evaluate association with renal function. ? Presence of epithelial‐mesenchymal transition (EMT) in stone‐containing renal tissues was investigated.

PATIENTS, SUBJECTS AND METHODS

? In all, 50 patients with nephrolithiasis with large calculi and matched healthy controls (37) were recruited. ? Plasma creatinine (Cr) and corrected Cr clearance (CCr) were determined in all subjects. ? Of the 50 patients, 38 had renal tissue available for histological analysis. Fibrosis was assessed by Masson’s trichrome staining. Co‐expression of epithelial cytokeratins and mesenchymal markers [α‐smooth muscle actin (αSMA) and vimentin] in renal tubular cells was detected by dual immunofluorescence staining. ? Expression of fibronectin, transforming growth factor β₁ (TGF‐β₁) and CD68 were investigated.

RESULTS

? Overall, the kidney function of the patients was significantly reduced, indicated by increased plasma Cr and decreased corrected CCr compared with healthy controls. ? Inflammation grading in renal tissues of the patients was correlated with the percentage of the fibrotic area. Renal fibrosis was inversely correlated with renal function. ? Cytokeratins co‐expressed with αSMA and vimentin were found in nephrolithiatic renal tubular cells, and these cells strongly expressed fibronectin and TGF‐β₁. ? Infiltration of CD68‐positive cells was a common finding in the inflamed renal sections.

CONCLUSIONS

? Kidneys of large stone‐forming patients had robust signs of inflammation and fibrosis, and there was a close correlation of renal fibrosis with renal dysfunction. ? This is the first study to show evidence for renal tubular cells showing signs of EMT in large stone‐containing kidneys. Plausibly, TGF‐β₁ triggers EMT, which at least in part contributes to large stone‐induced renal fibrosis.     

Hepatocyte growth factor: renotropic role and potential therapeutics for renal diseases

Hepatocyte growth factor (HGF), a ligand for the c-Met receptor tyrosine kinase, has mitogenic, motogenic, anti-apoptotic, and morphogenic (for example, induction of branching tubulogenesis) activities for renal tubular cells, while it has angiogenic and angioprotective actions for endothelial cells. Stromal cells such as mesangial cells, endothelial cells, and macrophages are sources of renal HGF; thus, HGF mediates epithelial-stromal and endothelial-mesangial interactions in the kidney. In response to acute renal injury, the expression of HGF increases in the injured kidney and in distant intact organs such as the lung and spleen. Locally and systemically increased HGF supports renal regeneration, possibly not only by enhancing cell growth but also by promoting morphogenesis of renal tissue. During progression of chronic renal failure/renal fibrosis, the expression of HGF decreases in a manner reciprocal to the increase in expression of transforming growth factor-beta (TGF-beta), a key player in tissue fibrosis. A decrease in endogenous HGF, as well as increase in TGF-beta, augments susceptibility to the onset of chronic renal failure/renal fibrosis. On the other hand, supplements of exogenous HGF have preventive and therapeutic effects in cases of acute and chronic renal failure/renal fibrosis in laboratory animals. HGF prevents epithelial cell death and enhances regeneration and remodeling of renal tissue with injury or fibrosis. A renotropic system underlies the vital potential of the kidney to regenerate, while an impaired renotropic system may confer susceptibility to the onset of renal diseases. Thus, HGF supplementation may be one therapeutic strategy to treat subjects with renal diseases, as it enhances the intrinsic ability of the kidney to regenerate.     

Biology of the renal pericyte

Pericytes are cells of mesenchymal origin that are intimately involved in the development and stabilization of vascular networks. Novel studies of their role in inflammation have identified that pericytes are not only major contributors to the activated matrix depositing myofibroblast populations seen in progressive renal fibrosis but perhaps even more importantly, the detachment of renal pericytes from the vasculature contributes to the microvasculature rarefaction and subsequent hypoxia associated with chronic kidney disease. In this review, our current understanding of the functioning of renal pericytes will be considered and set in the context of the wider literature that is currently available on this neglected population of cells.     

Enhanced mobilization of bone marrow cells does not ameliorate renal fibrosis.

BACKGROUND: The plasticity of bone marrow-derived stem cells, also comprising haematopoietic stem cells, has been shown to extend to renal epithelial lineages. Yet, the low rate of their contribution to the injured kidney has led to questions regarding their significance in tissue repair after acute injury. We describe here the effect of stem cell mobilization therapy on the progression of renal fibrosis in a mouse model of chronic obstructive nephropathy. METHODS: Mice were subjected to unilateral ureter obstruction (UUO) and treated with stem cell factor (SCF) and granulocyte-colony stimulating factor (G-CSF) or saline. Circulating cells were analysed by flow cytometry; labelled bone marrow c-KIT(HIGH) cells were injected into animals subjected to UUO. Granulocytes, macrophages, cellular proliferation or apoptosis and myofibroblasts were detected by immunostaining. Collagen deposition was determined by measuring renal hydroxyproline contents. Cytokine levels were measured by ELISA. RESULTS: SCF/G-CSF treatment of mice induced significant haematopoietic stem and progenitor cell mobilization from the bone marrow. Although these cells are able to migrate to the obstructed kidney, they did not influence renal damage, fibrosis and inflammatory cell influx. CONCLUSIONS: Although SCF/G-CSF treatment significantly enhanced the availability of haematopoietic stem cells to the obstructed kidney, the progression of renal fibrosis could not be delayed or halted. Our results indicate that effective stem cell mobilization does not alter renal fibrosis.     

Renal expression of trefoil factor 3 mRNA in association with tubulointerstitial fibrosis in IgA nephropathy

Aim

Trefoil factor 3 (TFF3) is a small peptide that is involved in mucosal protection. TFF3 is widely expressed in multiple tissues including kidney tissue. Previous studies have reported that the levels of urinary TFF3 are significantly increased in patients with chronic kidney disease. The aim of this study is to detect the TFF3 mRNA in kidney and elucidate the relationship between renal TFF3 mRNA and tubulointerstitial fibrosis in IgA nephropathy (IgAN).

Methods

We investigated the renal mRNA expression of TFF3 by real‐time PCR analysis in biopsy specimens from patients with IgAN, other glomerulonephritis (OGN) and minor glomerular abnormalities (MGA). We also determined the renal localization of TFF3 and the levels of urinary TFF3 by immunostaining and ELISA, respectively.

Results

The renal TFF3 mRNA expression was significantly associated with the urinary TFF3 secretion and the tubulointerstitial fibrosis score in the IgAN group alone. Immunostaining of the renal specimen of IgAN patients revealed that TFF3 is located in the renal tubular epithelial cells. The locations were almost the same as those that showed uromodulin positivity; specifically, the thick ascending limb (TAL) of the loop of Henle and the early portion of the distal tubule. The urinary TFF3 levels were positively correlated with the levels of urinary biomarkers of tubulointerstitial injury in such patients.

Conclusion

Renal TFF3 mRNA is associated with renal tubulointerstitial fibrosis in IgAN patients. The TFF3 located in the renal tubular epithelial cells may play a role in the progression of tubulointerstitial fibrosis in IgAN patients.     

Role of the endothelial-to-mesenchymal transition in renal fibrosis of chronic kidney disease

All types of progressive chronic kidney disease (CKD) inevitably induce renal fibrosis, the hallmark of which is the activation and accumulation of a large number of matrix-producing fibroblasts or myofibroblasts. The activated fibroblasts or myofibroblasts are derived from diverse origins, such as residential fibroblasts, vascular pericytes, epithelial-to-mesenchymal transition (EMT), and bone marrow (circulating fibrocytes). Recently, endothelial-to-mesenchymal transition (EndMT) or endothelial-to-myofibroblast transition has also been suggested to promote fibrosis and is recognized as a novel mechanism for the generation of myofibroblasts. Similar to EMT, during EndMT, endothelial cells lose their adhesion and apical–basal polarity to form highly invasive, migratory, spindle-shaped, elongated mesenchymal cells. More importantly, biochemical changes accompany these distinct changes in cell polarity and morphology, including the decreased expression of endothelial markers and the acquisition of mesenchymal markers. This review highlights evidence supporting the important role of EndMT in the development of renal fibrosis in CKD and its underlying mechanisms, including novel biological significance of microRNA regulation.     

Increased chymase-positive mast cells in children with crescentic glomerulonephritis

Mast cell-derived chymase is an angiotensin II-forming enzyme that appears to be involved in tubulointerstitial fibrosis in the kidneys. Previous studies have shown that the level of chymase increases in grafted kidneys after rejection and in adult patients with diabetic nephropathy. However, the significance of chymase in children with renal diseases has not been investigated. Using immunohistochemistry, we have investigated chymase expression in biopsy samples of renal tissue from 104 children with kidney diseases, including rapidly progressive crescentic glomerulonephritis (n?=?3), diabetic nephropathy (n?=?2), allografted kidney (n?=?3), membranoproliferative glomerulonephritis (n?=?6), immunoglobulin A nephropathy (n?=?33) and Henoch–Schönlein purpura nephritis (n?=?23). Increased numbers of chymase-positive mast cells were observed in the renal cortex of all three patients with crescentic glomerulonephritis (mean 26.0/mm²; range 19.3–36.8/mm²). Chymase-positive cells were also observed in the renal biopsy of an allografted kidney and in those from children with diabetic nephropathy. The mean number of chymase-positive cells in renal tissue samples characterized by each renal disease was significantly correlated with the mean intensity of the interstitial fibrosis in that same tissue sample (Spearman’s rank correlation test p?=?0.0013; rank correlation coefficient ?0.84). These findings suggest that mast cell-derived chymase plays an important role in juvenile crescentic glomerulonephritis.     

Blockage of tubular epithelial to myofibroblast transition by hepatocyte growth factor prevents renal interstitial fibrosis.

Activation of alpha-smooth muscle actin-positive myofibroblast cells is a key event in the progression of chronic renal diseases that leads to end-stage renal failure. Although the origin of these myofibroblasts in the kidney remains uncertain, emerging evidence suggests that renal myofibroblasts may derive from tubular epithelial cells by a process of epithelial to mesenchymal transition. It was demonstrated that hepatocyte growth factor (HGF) exhibited a remarkable ability to block this phenotypic transition both in vitro and in vivo. HGF abrogated the alpha-smooth muscle actin expression and E-cadherin depression triggered by transforming growth factor-beta1 in tubular epithelial cells in a dose-dependent manner. HGF also blocked morphologic transformation of tubular epithelial cells and inhibited the expression and extracellular deposition of fibronectin. In a mouse model of renal fibrosis disease induced by unilateral ureteral obstruction, transforming growth factor-beta type I receptor expression was specifically increased in renal tubules, and myofibroblastically phenotypic transition of the tubules was evident in vivo. Remarkably, injections of exogenous HGF blocked myofibroblast activation and drastically prevented renal interstitial fibrosis in the obstructed kidneys. These results suggest that tubular epithelial to myofibroblast conversion may play an important role in the pathogenesis of renal fibrosis and that blocking this phenotypic transition could provide a novel therapeutic strategy for the treatment of fibrotic diseases.     

Smad7 gene therapy ameliorates an autoimmune crescentic glomerulonephritis in mice

Autoimmune crescentic glomerulonephritis is characterized by severe immune response with glomerular crescentic formation and fibrosis in the kidney. Recent studies indicate that overexpression of renal Smad7 attenuates both renal fibrosis and inflammation in rat remnant kidney. However, little attention has been paid to the potential role of TGF-beta/Smad signaling in autoimmune kidney disease. This study tested the hypothesis that blocking TGF-beta signaling by overexpression of Smad7 may have a therapeutic effect in a mouse model of autoimmune crescentic glomerulonephritis that was induced in C57BL/6 x DBA/2J F1 hybrid mice by giving DBA/2J donor lymphocytes. Smad7 gene was transfected into the kidney using the ultrasound-microbubble-mediated system. Results showed that overexpression of Smad7 blocked both renal fibrosis and inflammatory pathways in terms of Smad2/3 and NF-kappaB activation (P < 0.01), thereby inhibiting alpha-smooth muscle actin; collagen I, III, and IV accumulation; and expression of inflammatory cytokines (IL-1beta and IL-6), adhesion molecule/chemokine (intercellular adhesion molecule-1, monocyte chemoattractant protein-1), and inducible nitric oxide synthase (all P < 0.01). Leukocyte infiltration (CD4(+) cells and macrophages) was also suppressed (P < 0.005). Severe histologic damage (glomerular crescent formation and tubulointerstitial injury) and functional injury including proteinuria were significantly improved (all P < 0.05). This study provides important evidence that overexpression of Smad7 may have therapeutic potential for autoimmune kidney disease.     

Cellular senescence limits regenerative capacity and allograft survival

Long-term graft survival after kidney transplantation remains unsatisfactory and unpredictable. Interstitial fibrosis and tubular atrophy are major contributors to late graft loss; features of tubular cell senescence, such as increased p16(INK4a) expression, associate with these tubulointerstitial changes, but it is unknown whether the relationship is causal. Here, loss of the INK4a locus in mice, which allows escape from p16(INK4a)-dependent senescence, significantly reduced interstitial fibrosis and tubular atrophy and associated with improved renal function, conservation of nephron mass, and transplant survival. Compared with wild-type controls, kidneys from INK4a(-/-) mice developed significantly less interstitial fibrosis and tubular atrophy after ischemia-reperfusion injury. Consistently, mice that received kidney transplants from INK4a/ARF(-/-) donors had significantly better survival 21 days after life-supporting kidney transplantation and developed less tubulointerstitial changes. This correlated with higher proliferative rates of tubular cells and significantly fewer senescent cells. Taken together, these data suggest a pathogenic role of renal cellular senescence in the development of interstitial fibrosis and tubular atrophy and kidney graft deterioration by preventing the recovery from injury. Inhibiting premature senescence could have therapeutic benefit in kidney transplantation but has to be balanced against the risks of suspending antitumor defenses.     

Matrilysin (MMP-7) expression in renal tubular damage: association with Wnt4

BACKGROUND: Matrilysin, a secreted matrix metalloproteinase and target gene of Wnt signaling, functions in epithelial repair and host defense, but no role in renal injury has been described. METHODS: Matrilysin expression was assessed in human kidney specimens by immunohistochemistry, and in experimental renal injury in mice by immunohistochemistry, Northern blotting, and RNase protection assays (RPA). A relationship to Wnt4, which is also induced in renal injury, was determined by RPA and in situ hybridization. RESULTS: Matrilysin was not detected in the normal human renal tubular epithelium by immunohistochemistry. However, prominent staining was detected in sections from autosomal-dominant polycystic kidney disease in the cyst lining epithelium, atrophic tubules, and cyst micropolyps, and from hydronephrosis in dilated and atrophic tubules. Matrilysin expression was also induced by acute folic acid nephropathy and unilateral ureteral obstruction (UUO) in the mouse, and expression increased as acute injury progressed to tubulointerstitial fibrosis. Matrilysin staining was primarily localized to epithelium of distal tubule/collecting duct origin in both human and murine renal disease. Wnt signaling can induce matrilysin expression, and we found that the pattern of matrilysin expression during progression of renal fibrosis in the mouse after UUO or folic acid nephropathy, and in the jck model of murine polycystic kidney disease, closely paralleled that of Wnt4. CONCLUSION: These observations suggest that matrilysin may have a role in renal tubular injury and progression of tubulointerstitial fibrosis, and that Wnt4 may regulate matrilysin expression in the kidney.     

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.     

Renal fibroblast-like cells in Goodpasture syndrome rats

BACKGROUND: The extent of renal fibrosis is the best predictor for functional outcomes in a variety of progressive renal diseases. Interstitial fibroblast-like cells (FbLCs) are presumably involved in the fibrotic process. However, such FbLCs have never been well characterized in the kidney. METHODS: We characterized renal FbLCs in the nephritic kidney (in which the number of FbLCs and extracellular matrix accumulation were significantly increased) with regards to their expression of phenotypic and functional markers using day 49 Goodpasture syndrome (GPS) rats. RESULTS: Within the renal cortical interstitium, there were a number of alpha-smooth muscle actin(+) (alpha-SMA(+)) FbLCs, negative for vimentin (VIM) and transforming growth factor-beta 1, and not equipped with well-developed rough endoplasmic reticulum and actin-stress fibers. All of these findings were incompatible with the typical features of granulation tissue alpha-SMA(+) myofibroblasts. On the other hand, FbLCs negative for alpha-SMA and VIM produced alpha1(I) procollagen in the nephritic kidney. CONCLUSION: A number of FbLC populations reside within the cortical interstitium of the kidney in GPS rats, each of which is likely to have developed independently in response to the local conditions of the nephritic kidney, contributing to renal fibrogenesis. Further studies are needed to clarify the key type of FbLC that orchestrates other members to produce renal fibrosis.