Lymphatic microvessels in the rat remnant kidney model of renal fibrosis: aminopeptidase p and podoplanin are discriminatory markers for endothelial cells of blood and lymphatic vessels

Effects of nitric oxide on renal interstitial fibrosis in rats with unilateral ureteral obstruction

AIMS

It is well recognized that microvascular injury is a major determinant of renal fibrosis. Mounting evidence shows that nitric oxide (NO) plays an important role in angiogenesis. Therefore, we investigated to the effects of NO on kidney angiogenesis and renal fibrosis.

METHODS

In the present study, a unilateral ureteral obstruction (UUO) model was established with L-arginine (L-Arg, 1 g/dl) and N-nitro-L-arginine methyl ester (L-NAME, 5 mg/dl) serving as interference factors. We investigated the alteration of NO concentration with spectrophotometry, peritubular capillary (PTC) density with aminopeptidase P (JG12) immunohistochemical staining, and the expression of vascular endothelial growth factor (VEGF), endothelial nitric oxide synthase (eNOS), hypoxia inducible factor-1α (HIF-1α) and transforming growth factor-β1 (TGF-β1) with immunohistochemical staining and Western blotting at weeks 2, 3 and 4.

KEY FINDINGS

Our findings showed that the expressions of VEGF, eNOS and PTC density were significantly decreased in rats with UUO, which was accompanied by a progressive increase in HIF-1α, TGF-β1 and an area of renal interstitial fibrosis. The administration of L-Arg promoted the synthesis of NO and significantly elevated the expressions of VEGF, eNOS and PTC density with the conspicuous loss of HIF-1α and TGF-β1 expressions and ultimately ameliorated renal fibrosis, which was markedly aggravated by L-NAME administration.

SIGNIFICANCE

These findings demonstrate that NO appears to play an important role in kidney angiogenesis and in slowing the progression of renal interstitial fibrosis, which suggests that NO may serve as a novel therapeutic strategy for preventing renal fibrosis as well as fibrosis in other organs.

Restoring the renal microvasculature to treat chronic kidney disease

Chronic kidney disease is characterized by progressive loss of the renal microvasculature, which leads to local areas of hypoxia and induction of profibrotic responses, scarring and deterioration of renal function. Revascularization alone might be sufficient to restore kidney function and regenerate the structure of the diseased kidney. For revascularization to be successful, however, the underlying disease process needs to be halted or alleviated and there must remain a sufficient number of surviving nephron units that can serve as a scaffold for kidney regeneration. This Perspectives article describes how revascularization might be achieved using vascular growth factors or adoptive transfer of endothelial progenitor cells and provides a brief outline of the studies performed to date. An overview of how therapeutic strategies targeting the microvasculature could be enhanced in the future is also presented.

Transforming growth factor-β induces vascular endothelial growth factor-C expression leading to lymphangiogenesis in rat unilateral ureteral obstruction

Inflammation is recognized as an important contributor to lymphangiogenesis; however, in tubulointerstitial lesions in human chronic kidney diseases, this process is better correlated with the presence of myofibroblasts rather than macrophages. As little is known about the interaction between lymphangiogenesis and renal fibrosis, we utilized the rat unilateral ureteral obstruction model to analyze inflammation, fibrosis, lymphangiogenesis, and growth factor expression. Additionally, we determined the relationship between vascular endothelial growth factor-C (VEGF-C), an inducer of lymphangiogenesis, and the profibrotic factor, transforming growth factor-β1 (TGF-β1). The expression of both TGF-β1 and VEGF-C was detected in tubular epithelial and mononuclear cells, and gradually increased, peaking 14 days after ureteral obstruction. The kinetics and localization of VEGF-C were similar to those of TGF-β1, and the expression of these growth factors and lymphangiogenesis were linked with the progression of fibrosis. VEGF-C expression was upregulated by TGF-β1 in cultured proximal tubular epithelial cells, collecting duct cells, and macrophages. Both in vitro and in vivo, the induction of VEGF-C along with the overall appearance of lymphatics in vivo was specifically suppressed by the TGF-β type I receptor inhibitor LY364947. Thus, TGF-β1 induces VEGF-C expression, which leads to lymphangiogenesis.

Fluorescent microangiography is a novel and widely applicable technique for delineating the renal microvasculature

Rarefaction of the renal microvasculature correlates with declining kidney function. However, current technologies commonly used for its evaluation are limited by their reliance on endothelial cell antigen expression and assessment in two dimensions. We set out to establish a widely applicable and unbiased optical sectioning method to enable three dimensional imaging and reconstruction of the renal microvessels based on their luminal filling. The kidneys of subtotally nephrectomized (SNx) rats and their sham-operated counterparts were subjected to either routine two-dimensional immunohistochemistry or the novel technique of fluorescent microangiography (FMA). The latter was achieved by perfusion of the kidney with an agarose suspension of fluorescent polystyrene microspheres followed by optical sectioning of 200 µm thick cross-sections using a confocal microscope. The fluorescent microangiography method enabled the three-dimensional reconstruction of virtual microvascular casts and confirmed a reduction in both glomerular and peritubular capillary density in the kidneys of SNx rats, despite an overall increase in glomerular volume. FMA is an uncomplicated technique for evaluating the renal microvasculature that circumvents many of the limitations imposed by conventional analysis of two-dimensional tissue sections.

ARB treatment prevents the decrease in endothelial progenitor cells and the loss of renal microvasculature in remnant kidney

BACKGROUND

Endothelial progenitor cells (EPCs) are involved in endothelium turnover and play a role in renal capillary repair. Since angiotensin II has been shown to negatively affect EPCs and blockade of angiotensin II decreases the progression of renal diseases, we investigated the effects of losartan on EPCs and renal endothelial cells in remnant kidney.

METHODS

Sprague-Dawley rats were randomized to receive losartan (25 mg/kg/day) or solvent for 15 weeks after 5/6 nephrectomy. Peripheral blood CD34+ EPCs were counted and the number of CD31+ endothelial colonies was determined. Glomerular and tubulointerstitial capillary endothelial cells were assessed and vascular endothelial growth factor (VEGF) and thrombospondin (TSP-1) expression were determined.

RESULTS

EPCs and the number of endothelial colonies were significantly reduced in 5/6 nephrectomized rats, which was associated with a decrease in glomerular and tubulointerstitial endothelial cells, a decrease in VEGF and an increase in TSP-1 expression. Losartan treatment largely prevented changes in both EPCs and remnant kidney.

CONCLUSION

The gradual loss of renal capillaries in remnant kidney was associated with decreased EPCs and endothelial colonies, hindering capillary endothelial repair in remnant kidney. Losartan treatment largely prevented the loss of EPCs and preserved renal endothelial cells, which may be part of the mechanism of how it contributes to renal protection.

Expression of lymphatic endothelium-specific hyaluronan receptor LYVE-1 in the developing mouse kidney

Our knowledge of the embryonic development of the lymphatic vessels within the kidney is limited. The aim of this study was to establish the time of appearance and the distribution of intra-renal lymphatic vessels in the developing mouse kidney by using the lymphatic marker, LYVE-1. Kidneys from embryonic day 12 (E12) to E18, from neonates at post-natal day 1 (P1) to P21, and from adults were studied. In the adult mouse kidney, LYVE-1 was expressed mainly in the lymphatic endothelial cells (LECs) and in a subset of endothelial cells in the glomerular capillaries. However, in the developing mouse kidney, LYVE-1 was also expressed transiently in F4/80(+)/CD11b(-) immature macrophages/dendritic cells and in the developing renal vein. LYVE-1(+) lymphatic vessels connected with extra-renal lymphatics were detected in the kidney at E13. F4/80(+)/CD11b(-)/LYVE-1(+) immature macrophages/dendritic cells appeared prior to the appearance of LYVE-1(+) renal lymphatic vessels and were closely intermingled or even formed part of the lymphatic vascular wall. Prox1 was expressed only in the LYVE-1(+) LECs from fetus to adult-hood, but not in LYVE-1(+) endothelial cells of the developing renal vein and macrophages/dendritic cells. Thus, lymphatic vessels of the kidney might originate by extension of extra-renal lymphatics through an active branching process possibly associated with F4/80(+)/CD11b(-)/LYVE-1(+) macrophages/dendritic cells.

Renal fibrosis: novel insights into mechanisms and therapeutic targets

Renal fibrosis is the common end point of virtually all progressive kidney diseases. Renal fibrosis should not be viewed as a simple and uniform 'scar', but rather as a dynamic system that involves extracellular matrix components and many, if not all, renal and infiltrating cell types. The involved cells exhibit enormous plasticity or phenotypic variability-a fact that we are only beginning to appreciate. Only a detailed understanding of the underlying mechanisms of renal fibrosis can facilitate the development of effective treatments. In this Review, we discuss the most recent advances in renal, or more specifically, tubulointerstitial fibrosis. Novel mechanisms as well as potential treatment targets based on different cell types are described. Problems that continue to plague the field are also discussed, including specific therapeutic targeting of the kidney, the development of improved diagnostic methods to assess renal fibrosis and the shortcomings of available animal models.

Lymphangiogenesis, myeloid cells and inflammation

The lymphatic system is essential for the maintenance of tissue fluid balance, immune surveillance and the absorption of fatty acids in the gastrointestinal tract. The lymphatic circulation is also a key player in disease processes such as cancer metastasis, lymphedema and various inflammatory disorders. With the identification of specific growth factors for lymphatic endothelial cells and markers that distinguish blood and lymphatic vessels, as well as the development of in vivo imaging technologies that provide new tools to examine the lymphatic drainage function in real time, many advancements have been made in lymphatic vascular research during the past few years. Despite these significant achievements, our understanding of the role of lymphatics in disease processes other than cancer metastasis is still rather limited. The current review will focus on the recent progress made in studies of lymphatics in inflammatory disorders.

Lymphatics in idiopathic pulmonary fibrosis: new insights into an old disease

The lymphatic vasculature plays a key role in tissue homeostasis and immune surveillance. There is mounting evidence of a role for the lymphatic circulation and for newly formed lymphatic vessels in the pathogenesis of lung disease. Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, debilitating lung disease. In IPF, the lung parenchyma undergoes extensive remodeling. This review focuses on the current knowledge and understanding of the pathogenesis of IPF, and recent evidence of the involvement of lymphangiogenesis in lung injury and repair and the molecular and cellular pathways leading to the development of lymphatic vasculature.

The goddess of the waters

The renal lymphatic system is cardinal in circulatory physiology and immunology. Sakamoto et al. report that lymphatic angiogenesis is increased in tubulointerstitial lesions in human chronic renal disease and correlates with tissue damage. Moreover, lymphatic growth was associated with vascular endothelial growth factor-C (VEGF-C) expression in mononuclear and tubular epithelial cells. Diabetic nephropathy had the highest level of VEGF-C and the most extensive lymphangiogenesis. The data suggest that lymphangiogenesis is a common feature in the progression of tubulointerstitial fibrosis.

The definition of fibrogenic processes in fibroblastic foci of idiopathic pulmonary fibrosis based on morphometric quantification of extracellular matrices

There is limited information regarding the process of tissue remodeling in fibroblastic foci associated with idiopathic pulmonary fibrosis. The aim of this study was to identify the different pathologic stages of tissue remodeling in fibroblastic foci based on the histopathologic differences in the glycosaminoglycan distribution and collagen deposition. In addition, we also aimed at clarifying the stage-specific characteristics by taking into consideration the expression pattern of matrix metalloproteinase and angiogenesis. Lung biopsies of 16 patients with idiopathic pulmonary fibrosis were used. The presence of glycosaminoglycans was detected by Alcian blue staining, and type I collagen was detected by immunohistochemical analysis with a primary antibody specific to the cross-linked carboxyterminal telopeptide of type I collagen. The fibroblastic foci characterized by the expression intensity of Alcian blue and telopeptide of type I collagen were divided into 3 groups, namely, Alcian blue(+)telopeptide of type I collagen(weak), Alcian blue(+)telopeptide of type I collagen(+), and Alcian blue(weak)telopeptide of type I collagen(+); consequently, 3 new stages were defined--stages I, II, and III, respectively. A significant inverse correlation was observed between the area densities of Alcian blue(+) and telopeptide of type I collagen(+) in fibroblastic foci. Stage I was characterized by the expression of matrix metalloproteinase-2 and tissue inhibitor of matrix metalloprotease-2 in fibroblasts and the overlying epithelium of fibroblastic foci, and also the absence of capillary angiogenesis. In contrast, the expression of these proteins was attenuated in stage III, except for that of matrix metalloproteinase-2 in fibroblasts. In stages II and III, capillary angiogenesis was observed. Lymphangiogenesis was undetected in all the 3 stages. Thus, pathologic staging helps understand the roles of the factors involved in tissue remodeling in idiopathic pulmonary fibrosis.

Abnormal lymphangiogenesis in idiopathic pulmonary fibrosis with insights into cellular and molecular mechanisms

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, debilitating respiratory disease whose pathogenesis is poorly understood. In IPF, the lung parenchyma undergoes extensive remodeling. We hypothesized that lymphangiogenesis is part of lung remodeling and sought to characterize pathways leading to lymphangiogenesis in IPF. We found that the diameter of lymphatic vessels in alveolar spaces in IPF lung tissue correlated with disease severity, suggesting that the alveolar microenvironment plays a role in the lymphangiogenic process. In bronchoalveolar lavage fluid (BALF) from subjects with IPF, we found short-fragment hyaluronic acid, which induced migration and proliferation of lymphatic endothelial cells (LECs), processes required for lymphatic vessel formation. To determine the origin of LECs in IPF, we isolated macrophages from the alveolar spaces; CD11b(+) macrophages from subjects with IPF, but not those from healthy volunteers, formed lymphatic-like vessels in vitro. Our findings demonstrate that in the alveolar microenvironment of IPF, soluble factors such as short-fragment hyaluronic acid and cells such as CD11b(+) macrophages contribute to lymphangiogenesis. These results improve our understanding of lymphangiogenesis and tissue remodeling in IPF and perhaps other fibrotic diseases as well.

Lymphatic vessels develop during tubulointerstitial fibrosis

Recent progress with specific markers of lymphatic vessel endothelium allowed recognition of lymphangiogenic events in various disease states; however, there is little information concerning this process in human chronic renal diseases. To determine this we measured expression of the lymphatic marker D2-40 and vascular endothelial growth factor-C (VEGF-C), a major growth factor in lymphangiogenesis, in 124 human renal biopsy specimens. In the kidneys of control subjects and in uninjured areas of pathologic specimens, lymphatic vessels were detected only around the arcuate and interlobular arteries. An increase in the number of lymphatic vessels was found at the site of tubulointerstitial lesions correlating with the degree of tissue damage and more strongly correlating with areas of fibrosis than inflammation. On serial sections, lymphatic vessel proliferation was found in the tubulointerstitial area at the site of tuft adhesions to Bowman's capsule. Lymphatic growth was associated with VEGF-C expression in inflammatory mononuclear cells and tubular epithelial cells, mainly of proximal tubules. Lymphangiogenesis and VEGF-C expression was elevated in diabetic nephropathy in comparison to other renal diseases. Our results indicate that lymphangiogenesis is a common feature in the progression of the tubulointerstitial fibrosis.

Characterization of lymphangiogenesis in various stages of idiopathic diffuse alveolar damage

In pulmonary fibrosis, an abnormal healing process, is believed to be involved in the damage to lung tissue. This process has not been correlated with lymphangiogenesis, which has garnered current interest in relation to wound healing. The aim of the present study was to clarify the characteristics of lymphangiogenesis in pulmonary fibrosis associated with idiopathic diffuse alveolar damage. Formalin-fixed and paraffin-embedded lung tissues from 13 autopsy cases with idiopathic diffuse alveolar damage were used. Antibodies specific to CD34 and D2-40 were used to detect blood vessels and lymphatics, respectively, and immunohistochemical examinations and morphometry analyses were performed. The standardized density of capillaries was increased significantly in the exudative stage of diffuse alveolar damage, whereas that of the lymphatics remained unchanged. In the proliferative stage, new lymphatics emerged, primarily in the intra-alveolar fibrotic lesions where capillaries were absent. In the fibrotic stage, in which the lung was shrunken, as revealed by the elevated density of pulmonary arteries, the standardized density of capillaries was reduced significantly. The standardized area density of the interstitium was elevated in the proliferative stage and subsequently reduced in the fibrotic stage. Three-dimensional reconstruction of images revealed that some new lymphatics lacked connection to existing lymphatics. During the progression of diffuse alveolar damage, lymphangiogenesis occurs independent of capillary angiogenesis.

Glomerular hypertrophy precedes albuminuria and segmental loss of podoplanin in podocytes in Munich-Wistar-Frömter rats

Focal segmental glomerulosclerosis (FSGS) is a common cause of end-stage renal disease. Albuminuria is a risk factor for FSGS and is influenced by environmental, genetic, and sex-specific factors. Podocytes play a central role in the development of albuminuria, but the precise relationship between early glomerular and podocyte-associated damage and albuminuria is unclear. Furthermore, experimental findings demonstrate a sex difference in development of albuminuria and FSGS. We investigated the early glomerular changes in male Munich-Wistar-Frömter (MWF) rats, which spontaneously develop albuminuria, and male albuminuria-resistant spontaneously hypertensive rats (SHR). In addition, since female MWF rats are protected from overt proteinuria and progressive renal disease, we compared the phenotypic changes in podocytes during early development of albuminuria in male and female MWF rats. In male MWF rats, glomerular hypertrophy preceded the onset of albuminuria and was greater than in male SHR. Albuminuria developed starting at 6 wk of age and coincided with focal and segmental loss of podoplanin, increased expression of desmin, entrapment of albumin in affected podocytes, and focal and segmental foot process effacement at the ultrastructural level. Other podocyte-associated molecules, such as nephrin and zonula occludens 1, were unaffected. Early glomerular hypertrophy and podocyte damage did not differ between male and female MWF rats. Our data show for the first time that albuminuria in male and female MWF rats is preceded by glomerular hypertrophy and accompanied by focal and segmental loss of podoplanin when FSGS was not yet present.

Changes in the rat subcutaneous connective tissue after saline and histamine injection in relation to fluid storage and excretion

An experimental design was developed for morphometric analysis of the subcutaneous connective tissue after the subcutaneous injection of 0.1 ml of saline or a histamine solution (0.01, 0.1 or 1% histamine dihydrochloride in saline). The subcutaneous connective tissue of 4-week-old rats, originally 170.0 +/- 13.6 mum in thickness, swelled 5.2-fold at 15 min, 3.0-fold at 2 h, and 1.2-fold at 6 h after the injection of saline. The total cross sectional area of both blood and lymphatic vessels increased when compared to that at pre-injection (0.0186 +/- 0.0030 mm(2) in 6-mm-long specimen), 1.4-fold at 15 min, 2.2-fold at 2 h, and 1.1-fold at 6 h post-injection, while the total number of these vessels increased 1.1-fold at 2 h. The total cross sectional area of lymphatic vessels (0.0006 +/- 0.0002 mm(2) in 6-mm-long specimen) alone surged 7.7-fold at 15 min, 4.8-fold at 2 h, and 7.3-fold at 6 h. Collagen fibers were respectively highly, moderately, and mildly disorganized in arrangement at 15 min, 2 h, and 6 h after the saline injection. Histamine elicited an earlier, longer, and more pronounced vasodilatation, particularly at high concentrations. The transvascular permeability of Evans blue increased depending on the concentration of histamine. These findings indicate that the subcutaneous connective tissue has the ability to expand and store a considerable amount of fluid and reversibly returns to normal steady-state conditions by increasing fluid excretion into the blood and lymphatic vessels. It was also strongly suggested that the blood vessels are deeply involved in the excretion and volume regulation of the tissue fluid.

How to control lymphangiogenesis: a novel role for rapamycin

Analysis of the lymphatic microvasculature has become possible only recently by the discovery of novel proteins specifically expressed in lymphatic endothelial cells only. Therapeutic manipulation of de novo lymphangiogenesis might become clinically relevant in the future in diverse situations, such as renal transplant rejection. In this issue Huber et al. demonstrate that rapamycin acts as an efficient inhibitor of lymphangiogenesis.

The contribution of B cells to renal interstitial inflammation

Local B-cell infiltrates play a role in tissue fibrosis, neolymphangiogenesis, and renal allograft survival. We sought to characterize the B-cell infiltrates, factors involved in B-cell recruitment, and lymphangiogenesis in renal interstitial injury (ie, acute and chronic interstitial nephritis and chronic IgA nephropathy). CD20-positive B cells formed a prominent part of the interstitial infiltrating cells. Together with CD3-positive T cells, the CD20-positive B cells formed larger nodular structures. CD10-positive pre-B cells were rare, and the majority were mature CD27-positive B cells. Proliferating B cells were detected within nodular infiltrates. The level of mRNA expression of the chemokine CXCL13 was increased and correlated with CD20 mRNA in the tubulointerstitial space. CXCL13 protein was predominantly found at sites of nodular infiltrates, in association with CXCR5-positive B cells. Furthermore, sites of chronic interstitial inflammation were associated with a high number of lymphatic vessels. B-cell infiltrates form a prominent part of the interstitial infiltrates both in primary interstitial lesions and in IgA nephropathy. CXCR5-positive B cells might be recruited via the chemokine CXCL13 and seem to contribute to the formation of intrarenal lymphoid follicle-like structures. These might represent an intrarenal immune system.

Lymphatic neoangiogenesis in human renal allografts: results from sequential protocol biopsies

Neoangiogenesis of lymphatic vessels may be important for the cellular immune response in renal transplants. To determine the prevalence and chronology of lymph vessel proliferation and its relation to cellular infiltrates and allograft function, we analyzed sequential protocol biopsies (n = 162), taken at 6, 12 and 26 weeks after transplantation. Biopsies were stained with an antibody against podoplanin and lymphatic vessel density was quantified per square millimeter. The prevalence of lymph vessel-positive biopsies and the lymph vessel density were similar at 6, 12 and 26 weeks after transplantation. Biopsies with acute cellular rejection showed no significantly different lymph vessel density compared to those below the threshold for acute rejection or chronic allograft nephropathy. While lymphatic neoangiogenesis was equally prevalent in biopsies with and without infiltrates, the lymph vessel density was significantly higher in areas with cellular infiltrates than in areas without. Graft function at 1 year after transplantation was better in cases with lymph vessels in their infiltrates compared to cases with lymph vessel-free infiltrates. In conclusion, lymphangiogenesis not only shows a clear association with cellular infiltrates but might also have an impact on the pathogenicity of these cellular infiltrates.

Anti-inflammatory effect of hepatocyte growth factor in chronic kidney disease: targeting the inflamed vascular endothelium

Recent studies show that hepatocyte growth factor (HGF) has potent anti-inflammatory effects in multiple animal models of disease in various organ systems, including the kidney, suggesting that HGF may suppress a common proinflammatory process. The aim of this study was to examine the molecular mechanism of HGF's anti-inflammatory actions in a model of chronic kidney disease. Beginning 2 wk after subtotal nephrectomy, rats received a continuous infusion of recombinant HGF, neutralization of endogenous HGF by daily injection of an anti-HGF antibody, or preimmune IgG for an additional 2 wk. The effects on inflammation and injury were examined. HGF administration ameliorated whereas neutralizing endogenous HGF worsened renal inflammation in remnant kidneys. This was accompanied by parallel alterations in endothelial activation and inflammation, marked respectively by de novo E-selectin expression in renal vascular endothelium and leukocyte adhesion to endothelium. In vitro, HGF abrogated monocyte adhesion to TNF-alpha-activated endothelial monolayers and suppressed endothelial expression of E-selectin, which depended on NF-kappaB signaling. In addition, HGF suppressed NF-kappaB reporter gene activity that was induced by TNF-alpha and counteracted TNF-alpha-elicited NF-kappaB interaction with kappaB elements at the E-selectin gene level. Dissection of the NF-kappaB signaling cascade revealed that suppression of NF-kappaB depended on HGF's inhibitory action on NF-kappaB and IkappaB phosphorylation and IkappaB degradation. In vivo, continuous infusion of exogenous HGF markedly diminished sequestration of circulating fluorescence-labeled macrophages in the remnant kidney, mimicking the action of an E-selectin blocking antibody. These findings suggest that HGF has potent and direct anti-inflammatory effects on the basis of suppression of NF-kappaB activation and downstream endothelial inflammation.

Everolimus inhibits glomerular endothelial cell proliferation and VEGF, but not long-term recovery in experimental thrombotic microangiopathy

BACKGROUND

Everolimus is a potent immunosuppressant used in renal transplant therapy, but its effects on renal endothelial cell regeneration after injury are unknown. The effects of an everolimus therapy were investigated in a model of renal thrombotic microangiopathy (TMA) with specific endothelial cell (EC) injury in the rat in vivo as well as in glomerular ECs in vitro.

METHODS

During the early regenerative phase (day 3) of the renal microvascular injury model in vivo, everolimus inhibited glomerular EC proliferation by up to 60% compared with vehicle-treated rats, whereas apoptosis was not different in these groups. This decreased EC proliferation was associated with an enhanced deposition of fibrin in everolimus treated animals on day 3. In cultured glomerular endothelial cells, everolimus effectively and dose dependently inhibited cellular proliferation. This anti-proliferative effect was associated with a reduced phosphorylation of the p70S6 kinase and reduction of the pro-angiogenic factor VEGF in glomeruli in vivo and in cultured podocytes in vitro.

RESULTS

Despite the prolonged EC repair and in contrast to the anti-Thy1 nephritis model, everolimus therapy did not disturb the long-term repair reaction in this thrombotic microangiopathy model.

CONCLUSION

Everolimus is anti-proliferative for glomerular EC in vitro and in vivo and does not seem to have detrimental long-term effects in experimental renal TMA, when only the glomerular endothelium, but not the mesangium is severely injured.

Leukocytes in tubulointerstitial inflammation

The work of Lange-Sperandio et al in this issue explores the differential role of beta2 integrins in promoting the macrophage infiltration characteristic of the obstructed kidneys of neonatal mice. Future work is needed to define factors that regulate macrophage death within or emigration from the kidney as well as to explore strategies to modulate macrophage phenotype. This knowledge will assist the development of novel therapeutic agents to limit injury and promote tissue repair.

Induction of protective genes by cobalt ameliorates tubulointerstitial injury in the progressive Thy1 nephritis

BACKGROUND

We previously demonstrated that chronic hypoxia has pivotal roles in the progression of tubulointerstitial injury from the early stage of the uninephrectomized Thy1 nephritis model. We have also shown that pretreatment of cobalt confers renoprotection in the ischemia/reperfusion (I/R) injury, in association with the up-regulation of hypoxia-inducible factor (HIF)-regulated genes. Here, we tested the hypothesis that cobalt administration not only attenuates acute ischemic insult, but also ameliorates tubulointerstitial injury secondary to chronic hypoxia.

METHODS

We applied sustained cobalt treatment to the uninephrectomized Thy1 nephritis model at 3 to 5 weeks, when tubular hypoxia appeared. Histologic evaluation, including glomerular and peritubular capillary networks, was made at 8 weeks. HIF activation was confirmed by real-time polymerase chain reaction (PCR) analyses for HIF-regulated genes, such as erythropoietin (EPO), vascular endothelial growth factor (VEGF), and heme oxygenase 1 (HO-1). Up-regulation of HIF-1alpha and HIF-regulated genes was also verified by Western blotting analysis. To elucidate responsible mechanisms of cobalt in the amelioration of tubuloniterstitial injury, terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick end labeling (TUNEL) staining was conducted at 5 weeks. A combination therapy with angiotensin receptor blocker (ARB), olmesartan, was also challenged.

RESULTS

Although the intervention did not change glomerular structural damage or urinary protein excretion rate, tubulointerstitial injury was improved in cobalt-treated animals when compared with the vehicle-treated group. The amelioration was associated with the parallel up-regulation of renoprotective, HIF-regulated gene expression. TUNEL staining revealed that the number of apoptotic cells was reduced in the cortex by cobalt administration, suggesting that renoprotection was achieved partly through its antiapoptotic properties. Furthermore, it was demonstrated that cobalt treatment exerts additional renoprotective effects with the ARB treatment in this model.

CONCLUSION

Maneuvers to activate HIF in the ischemic tubulointerstitium will be a new direction to future therapeutic strategies.

Comparison of the diagnostic accuracy of lymphatic endothelium markers: Bayesian approach

Tumor lymphatic density is evaluated by means of specific lymphatic endothelium markers, and is a potential predictor of clinically meaningful outcomes. There are many claims on the postulated superiority of some of these markers to identify lymphatics, always in the absence of quantitative data. We therefore compared the diagnostic accuracy of the antibody against podoplanin and the commercially available D2-40, employing Bayesian statistics to account for the absence of a gold standard. We used the pan-endothelial marker CD34 to identify 23,542 distinct blood and lymphatic vessels in sections from 30 formalin-fixed, paraffin-embedded archival tissue blocks of head and neck squamous cell carcinoma specimens. We stained two adjacent sections with podoplanin and D2-40 and identified the continuum of each stained vessel in the sections with a comprehensive method. Overall, 1,864 vessels were stained with both markers, 119 only with podoplanin and 391 only with D2-40. Significantly more vessels with intraluminal red blood cells were stained with D2-40 compared to podoplanin (McNemar's P<0.0001). Both antibodies had extremely high specificity (99.7% (95% credible interval (CrI): 99.5-99.9%) and 98.8% (95% CrI: 98.3-99.5%) for podoplanin and D2-40, respectively) and very high sensitivity (92.6% (95% CrI: 86.1-97.9%) and 97.3% (95% CrI: 94.9-99.2%) for podoplanin and D2-40, respectively). Inferences were qualitatively similar when we took into account in the analyses the possibility that the two tests (antibodies) may be correlated. We calculated that 96.3% (95% CrI: 94.2-98.6%) of the vessels stained with podoplanin and 88.9% (95% CrI: 83.9-95.7%) of the vessels stained with D2-40 were truly lymphatics. These numbers were in agreement with the observed number of stained vessels without intraluminal red blood cells. Our results suggest that both antibodies are excellent lymphatic endothelium markers and that there may be little reason to prefer either of them in most settings.

Loss of peritubular capillaries in the development of chronic allograft nephropathy

BACKGROUND

Chronic allograft nephropathy (CAN) remains the most important cause of late renal graft loss. In this study, we examined the role of peritubular capillary (PTC) injury in the development of CAN.

METHODS

We studied renal biopsies (n = 79) obtained from grafts with CAN. PTC injury was examined morphologically by immunohistochemistry for CD34. These findings were correlated with interstitial fibrosis and graft dysfunction. Humoral immunity involved in CAN was studied by C4d staining.

RESULTS

The CAN cases in the present study included chronic rejection (CR) (n = 14, 17.8%) and C4d-positive chronic humoral rejection (CHR; n = 6, 42.9% in CR cases). Irrespective of CR, CHR, or other CAN, the development of CAN was characterized by injury to and loss of identifiable PTCs, accompanied with the development of interstitial fibrosis. In CR and CHR cases, the loss of PTCs was prominent and seemed to progress within a relatively short period after transplantation. A decrease in the number of PTCs significantly correlated with the development of interstitial fibrosis (r = -0.75, P < .001) and impairment of graft function (r = -0.69, P < .001).

CONCLUSIONS

Irrespective of whether CR, CHR, or other factors contribute to CAN, the processes involved in its development appear similar and are characterized by progressive injury and loss of PTCs, with the development of renal scarring. Immunohistochemistry for CD34 in human renal biopsies is a useful method for the detection of microvascular injury.

Aminopeptidase P isozyme expression in human tissues and peripheral blood mononuclear cell fractions

Aminopeptidase P (APP) isoforms specifically remove the N-terminal amino acid from peptides that have a proline residue in the second position. The mRNA levels of three different isoforms, each coded by a different gene, were determined in 16 human tissues and in peripheral blood mononuclear cell (PBMC) fractions by RT-PCR. The cytosolic isoform, APP1, and the cell surface membrane-bound isoform, APP2, are expressed in all of the human tissues and PBMC fractions examined. The very high expression of APP2 mRNA in kidney compared to other tissues was confirmed by enzyme activity measurements. Among the PBMC fractions, APP2 expression is highest in resting CD8(+) T cells, but decreases in these cells following their activation with phytohemagglutinin; in contrast, expression of APP2 increases in CD4(+) T cells upon activation. The third isoform, APP3, is a hypothetical protein identified by nucleotide sequencing. A detailed analysis of its amino acid sequence confirmed that the protein is an aminopeptidase P-like enzyme with greater similarity to Escherichia coli APP than to either APP1 or APP2. Two splice variants of APP3 exist, one of which is predicted to have a mitochondrial localization (APP3m) while the other is cytosolic (APP3c). Both forms are variably expressed in all of the human tissues and PBMC fractions examined.

Mechanisms of tubulointerstitial fibrosis

PURPOSE OF REVIEW

Tubulointerstitial fibrosis is the final common pathway to end-stage renal disease. Understanding the mechanisms of tubulointerstitial fibrosis is essential in establishing novel therapeutic strategies for the prevention or arrest of progressive kidney diseases. The present review focuses on a newly proposed mechanism of tubulointerstitial fibrosis, one that emphasizes the roles of epithelial-mesenchymal transition and cellular activation.

RECENT FINDINGS

Among the cells that accumulate in the renal interstitium, fibroblasts are the principal effectors mediating tubulointerstitial fibrosis. By contrast, the phagocytosis of extracellular matrix and apoptotic cells by macrophages may actually exert a beneficial effect. Interstitial fibroblasts are more heterogeneous than expected, and during renal fibrosis new fibroblasts are derived mainly through epithelial-mesenchymal transition. The intracellular signaling pathways leading to initiation of epithelial-mesenchymal transition remain largely unknown, though recent studies have identified beta-catenin and Smad3 activation of lymphoid enhancer factor, integrin-linked kinase, and small GTPases and mitogen-activated protein kinases as key components. Transforming growth factor-beta is believed to be a critical fibrogenic factor, but recent studies have also focused on transforming growth factor-beta independent pathways as mechanisms of tubulointerstitial fibrosis. As the mechanisms underlying tubulointerstitial fibrosis leading to epithelial-mesenchymal transition have been identified, so have cytokines that efficiently antagonize renal fibrosis, particularly bone morphogenic protein-7 and hepatocyte growth factor.

SUMMARY

In combination with traditional angiotensin converting enzyme inhibitors, newly identified cytokines may eventually form the basis for new therapeutic strategies aimed at inhibiting the progression of renal disease.