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

miR-455-3p regulates lymphangiogenesis in silicosis by regulating VEGF-C/VEGFR3

Silicosis is a disease characterized by lung inflammation and fibrosis caused by long-term inhalation of free silicon dioxide (SiO2). Recent studies have found that a large number of lymphatic hyperplasia occurs during the occurrence and development of silicosis. miRNAs play an important role in lymphangiogenesis. However, the regulation and mechanism of miRNAs on lymphangiogenesis in silicosis remain unclear. In this study, lymphangiogenesis was observed in silicosis rats, and VEGF-C-targeted miRNAs were screened, and the effect of miRNAs on the formation of human lymphatic endothelial cells (HLECs) tubular structure was investigated in vitro. The results showed that SiO2 promoted the expressions of Collagen Ι and α-SMA, TNF-α, IL-6 and VEGF-C increased first and then decreased, and promoted the formation of lymphatic vessels. Bioinformatics methods screened miR-455-3p for targeted binding to VEGF-C, and dual luciferase reporter genes confirmed VEGF-C as the target gene of miR-455-3p, and miR-455-3p was down-regulated in the lung tissue of silicosis rats. Transfection of miR-455-3p Inhibitors down-regulated the expression level of miR-455-3p and up-regulated the expression levels of VEGF-C and VEGFR-3 in HLECs, enhanced migration ability and increased tube formation. Transfection of miR-455-3p Mimics showed an opposite trend. These results suggest that miR-455-3p further regulates the tubular structure formation of HLECs by regulating VEGF-C/VEGFR3. Therefore, targeting miR-455-3p may provide a new therapeutic strategy for SiO2-induced silicosis injury.

Chronic environmental hypoxia attenuates innate immunity activation and renal injury in two CKD models

Tissue hypoxia has been pointed out as a major pathogenic factor in chronic kidney disease (CKD). However, epidemiological and experimental evidence inconsistent with this notion has been described. We have previously reported that chronic exposure to low ambient Po2 promoted no renal injury in normal rats and in rats with 5/6 renal ablation (Nx) unexpectedly attenuated renal injury. In the present study, we investigated whether chronic exposure to low ambient Po2 would also be renoprotective in two additional models of CKD: adenine (ADE) excess and chronic nitric oxide (NO) inhibition. In both models, normobaric ambient hypoxia attenuated the development of renal injury and inflammation. In addition, renal hypoxia limited the activation of NF-κB and NOD-like receptor family pyrin domain containing 3 inflammasome cascades as well as oxidative stress and intrarenal infiltration by angiotensin II-positive cells. Renal activation of hypoxia-inducible factor (HIF)-2α, along with other adaptive mechanisms to hypoxia, may have contributed to these renoprotective effects. The present findings may contribute to unravel the pathogenesis of CKD and to the development of innovative strategies to arrest its progression.NEW & NOTEWORTHY Hypoxia is regarded as a major pathogenic factor in chronic kidney disease (CKD). In disagreement with this view, we show here that sustained exposure to low ambient Po2 lessened kidney injury and inflammation in two CKD models: adenine (ADE) excess and chronic nitric oxide (NO) inhibition. Together with our previous findings in the remnant kidney, these observations indicate that local changes elicited by hypoxia may exert renoprotection in CKD, raising the prospect of novel therapeutic strategies for this disease.

The role of cellular crosstalk in the progression of diabetic nephropathy

Diabetic nephropathy (DN) is one of the most common complications of diabetes, and its main manifestations are progressive proteinuria and abnormal renal function, which eventually develops end stage renal disease (ESRD). The pathogenesis of DN is complex and involves many signaling pathways and molecules, including metabolic disorders, genetic factors, oxidative stress, inflammation, and microcirculatory abnormalities strategies. With the development of medical experimental techniques, such as single-cell transcriptome sequencing and single-cell proteomics, the pathological alterations caused by kidney cell interactions have attracted more and more attention. Here, we reviewed the characteristics and related mechanisms of crosstalk among kidney cells podocytes, endothelial cells, mesangial cells, pericytes, and immune cells during the development and progression of DN and highlighted its potential therapeutic effects.

The density of renal lymphatics correlates with clinical outcomes in IgA nephropathy

Introduction

IgA nephropathy (IgAN) is the most common primary glomerulonephritis (GN) worldwide. The disease course fluctuates, and the most important challenge is the considerable variation in the time lag between diagnosis and the development of a hard clinical end point, such as end-stage kidney disease (ESKD). The reaction of renal tissue to damage resembles the common wound-healing response. One part of this repair in IgAN is the expansion of lymphatic vessels known as lymphangiogenesis. The aim of this work was to establish the prognostic value of the density of lymphatic vessels in the renal biopsy at the time of diagnosis, for predicting the risk of ESKD in a Spanish cohort of patients with IgAN.

Methods

We performed a retrospective multicenter study of 76 patients with IgAN. The end point of the study was progression to ESKD. The morphometric analysis of lymphatic vessels was performed on tissue sections stained with antipodoplanin antibody.

Results

Density of lymphatic vessels was significantly higher in patients with IgAN with mesangial hypercellularity >50%, segmental sclerosis, higher degrees of interstitial fibrosis, and tubular atrophy. Patients with more lymphatic vessels had significantly higher values of proteinuria and lower estimated glomerular filtration rate (eGFR). A density of lymphatic vessels ≥8 per mm² was associated with a significantly higher rate of progression to ESKD at 3 years from biopsy. After adjustment for the International IgAN prediction score, at the multivariate logistic regression, high density of lymphatic vessels (≥8 per mm²) remained significantly associated with a higher rate of early progression to ESKD.

Conclusion

This study contributes to the understanding of the natural history of the progression to ESKD in patients with IgAN revealing the density of lymphatics vessels may optimize the prognostic value of the International IgA predicting tool to calculate the risk of ESKD, favoring the evaluation of new targeted therapies.

RNA sequencing reveals induction of specific renal inflammatory pathways in a rat model of malignant hypertension

In malignant hypertension, far more severe kidney injury occurs than in the "benign" form of the disease. The role of high blood pressure and the renin-angiotensin-aldosterone system is well recognized, but the pathogenesis of the renal injury of malignant hypertension (MH) remains incompletely understood. Using the rat model of two-kidney, one-clip renovascular hypertension in which some but not all animals develop MH, we performed a transcriptomic analysis of gene expression by RNA sequencing to identify transcriptional changes in the kidney cortex specific for MH. Differential gene expression was assessed in three groups: MH, non-malignant hypertension (NMH), and normotensive, sham-operated controls. To distinguish MH from NMH, we considered two factors: weight loss and typical renovascular lesions. Mean blood pressure measured intraarterially was elevated in MH (220 ± 6.5 mmHg) as well as in NMH (192 ± 6.4 mmHg), compared to controls (119 ± 1.7 mmHg, p < 0.05). Eight hundred eighty-six genes were exclusively regulated in MH only. Principal component analysis revealed a separated clustering of the three groups. The data pointed to an upregulation of many inflammatory mechanisms in MH including pathways which previously attracted relatively little attention in the setting of hypertensive kidney injury: Transcripts from all three complement activation pathways were upregulated in MH compared to NMH but not in NMH compared with controls; immunohistochemistry confirmed complement deposition in MH exclusively. The expression of chemokines attracting neutrophil granulocytes (CXCL6) and infiltration of myeloperoxidase-positive cells were increased only in MH rats. The data suggest that these pathways, especially complement deposition, may contribute to kidney injury under MH. KEY MESSAGES: The most severe hypertension-induced kidney injury occurs in malignant hypertension. In a rat model of malignant hypertension, we assessed transcriptional responses in the kidney exposed to high blood pressure. A broad stimulation of inflammatory mechanisms was observed, but a few specific pathways were activated only in the malignant form of the disease, notably activation of the complement cascades. Complement inhibitors may alleviate the thrombotic microangiopathy of malignant hypertension even in the absence of primary complement abnormalities.

Biologically active lipids in the regulation of lymphangiogenesis in disease states

Lymphatic vessels have crucial roles in the regulation of interstitial fluids, immune surveillance, and the absorption of dietary fat in the intestine. Lymphatic function is also closely related to the pathogenesis of various disease states such as inflammation, lymphedema, endometriosis, liver dysfunction, and tumor metastasis. Lymphangiogenesis, the formation of new lymphatic vessels from pre-existing lymphatic vessels, is a critical determinant in the above conditions. Although the effect of growth factors on lymphangiogenesis is well-characterized, and biologically active lipids are known to affect smooth muscle contractility and vasoaction, there is accumulating evidence that biologically active lipids are also important inducers of growth factors and cytokines that regulate lymphangiogenesis. This review discusses recent advances in our understanding of biologically active lipids, including arachidonic acid metabolites, sphingosine 1-phosphate, and lysophosphatidic acid, as regulators of lymphangiogenesis, and the emerging importance of the lymphangiogenesis as a therapeutic target.

The lymphatics in kidney health and disease

The mammalian vascular system consists of two networks: the blood vascular system and the lymphatic vascular system. Throughout the body, the lymphatic system contributes to homeostatic mechanisms by draining extravasated interstitial fluid and facilitating the trafficking and activation of immune cells. In the kidney, lymphatic vessels exist mainly in the kidney cortex. In the medulla, the ascending vasa recta represent a hybrid lymphatic-like vessel that performs lymphatic-like roles in interstitial fluid reabsorption. Although the lymphatic network is mainly derived from the venous system, evidence supports the existence of lymphatic beds that are of non-venous origin. Following their development and maturation, lymphatic vessel density remains relatively stable; however, these vessels undergo dynamic functional changes to meet tissue demands. Additionally, new lymphatic growth, or lymphangiogenesis, can be induced by pathological conditions such as tissue injury, interstitial fluid overload, hyperglycaemia and inflammation. Lymphangiogenesis is also associated with conditions such as polycystic kidney disease, hypertension, ultrafiltration failure and transplant rejection. Although lymphangiogenesis has protective functions in clearing accumulated fluid and immune cells, the kidney lymphatics may also propagate an inflammatory feedback loop, exacerbating inflammation and fibrosis. Greater understanding of lymphatic biology, including the developmental origin and function of the lymphatics and their response to pathogenic stimuli, may aid the development of new therapeutic agents that target the lymphatic system.

Xanthine oxidoreductase inhibitor topiroxostat ameliorates podocyte injury by inhibiting the reduction of nephrin and podoplanin

BACKGROUND

Topiroxostat, an inhibitor of xanthine oxidoreductase (XOR) was shown to reduce urinary albumin excretion of hyperuricemic patients with chronic kidney disease. However, its pharmacological mechanism is not well understood. In this study, we examined the effects of topiroxostat on glomerular podocytes. Podocyte is characterized by foot process and a unique cell-cell junction slit diaphragm functioning as a final barrier to prevent proteinuria.

METHODS

The effects of topiroxostat on the expressions of podocyte functional molecules were analysed in db/db mice, a diabetic nephropathy model, anti-nephrin antibody-induced rat podocyte injury model and cultured podocytes treated with adriamycin.

RESULTS

Topiroxostat treatment ameliorated albuminuria in db/db mice. The expression of desmin, a podocyte injury marker was increased, and nephrin and podocin, key molecules of slit diaphragm, and podoplanin, an essential molecule in maintaining foot process were downregulated in db/db mice. Topiroxostat treatment prevented the alterations in the expressions of these molecules in db/db mice. XOR activity in kidney was increased in rats with anti-nephrin antibody-induced podocyte injury. Topiroxostat treatment reduced XOR activity and restored the decreased expression of nephrin, podocin and podoplanin in the podocyte injury. Furthermore, topiroxostat enhanced the expression of podoplanin in injured human cultured podocytes.

CONCLUSIONS

Podocyte injury was evident in db/db mice. Topiroxostat ameliorated albuminuria in diabetic nephropathy model by preventing podocyte injury. Increase of XOR activity in kidney contributes to development of podocyte injury caused by stimulation to slit diaphragm. Topiroxostat has an effect to stabilize slit diaphragm and foot processes by inhibiting the reduction of nephrin, podocin and podoplanin.

Xanthine oxidoreductase inhibitor topiroxostat ameliorates podocyte injury by inhibiting the reduction of nephrin and podoplanin

BACKGROUND

Topiroxostat, an inhibitor of xanthine oxidoreductase (XOR) was shown to reduce urinary albumin excretion of hyperuricemic patients with chronic kidney disease. However, its pharmacological mechanism is not well understood. In this study, we examined the effects of topiroxostat on glomerular podocytes. Podocyte is characterized by foot process and a unique cell-cell junction slit diaphragm functioning as a final barrier to prevent proteinuria.

METHODS

The effects of topiroxostat on the expressions of podocyte functional molecules were analysed in db/db mice, a diabetic nephropathy model, anti-nephrin antibody-induced rat podocyte injury model and cultured podocytes treated with adriamycin.

RESULTS

Topiroxostat treatment ameliorated albuminuria in db/db mice. The expression of desmin, a podocyte injury marker was increased, and nephrin and podocin, key molecules of slit diaphragm, and podoplanin, an essential molecule in maintaining foot process were downregulated in db/db mice. Topiroxostat treatment prevented the alterations in the expressions of these molecules in db/db mice. XOR activity in kidney was increased in rats with anti-nephrin antibody-induced podocyte injury. Topiroxostat treatment reduced XOR activity and restored the decreased expression of nephrin, podocin and podoplanin in the podocyte injury. Furthermore, topiroxostat enhanced the expression of podoplanin in injured human cultured podocytes.

CONCLUSIONS

Podocyte injury was evident in db/db mice. Topiroxostat ameliorated albuminuria in diabetic nephropathy model by preventing podocyte injury. Increase of XOR activity in kidney contributes to development of podocyte injury caused by stimulation to slit diaphragm. Topiroxostat has an effect to stabilize slit diaphragm and foot processes by inhibiting the reduction of nephrin, podocin and podoplanin.

Adenosine A1 Receptor Deficiency Aggravates Extracellular Matrix Accumulation in Diabetic Nephropathy through Disturbance of Peritubular Microenvironment

BACKGROUND

We previously observed that adenosine A1 receptor (A1AR) had a protective role in proximal tubular megalin loss associated with albuminuria in diabetic nephropathy (DN). In this study, we aimed to explore the role of A1AR in the fibrosis progression of DN.

METHODS

We collected DN patients' samples and established a streptozotocin-induced diabetes model in wild-type (WT) and A1AR-deficient (A1AR^-/-) mice. The location and expression of CD34, PDGFRβ, and A1AR were detected in kidney tissue samples from DN patients by immunofluorescent and immunohistochemical staining. We also analyzed the expression of TGFβ, collagen (I, III, and IV), α-SMA, and PDGFRβ using immunohistochemistry in WT and A1AR^-/- mice. CD34 and podoplanin expression were analyzed by Western blotting and immunohistochemical staining in mice, respectively. Human renal proximal tubular epithelial cells (HK2) were cultured in medium containing high glucose and A1AR agonist as well as antagonist.

RESULTS

In DN patients, the expression of PDGFRβ was higher with the loss of CD34. The location of PDGFRβ and TGFβ was near to each other. The A1AR, which was colocalized with CD34 partly, was also upregulated in DN patients. In WT-DN mice, obvious albuminuria and renal pathological leisure were observed. In A1AR^-/- DN mice, more severe renal tubular interstitial fibrosis and more extracellular matrix deposition were observed, with lower CD34 expression and pronounced increase of PDGFRβ. In HK2 cells, high glucose stimulated the epithelial-mesenchymal transition (EMT) process, which was inhibited by A1AR agonist.

CONCLUSION

A1AR played a critical role in protecting the tubulointerstitial fibrosis process in DN by regulation of the peritubular microenvironment.

Hydrogen promotes the activation of Cu, Zn superoxide dismutase in a rat corneal alkali-burn model

AIM

To investigate the effects of hydrogen (H₂) on Cu, Zn superoxide dismutase (SOD1) activation in a rat model of corneal alkali burn.

METHODS

In each rat, one cornea was subjected to alkali exposure. Physiological saline (saline group) or H₂-dissolved saline (H₂ group) was instilled continuously on the cornea for 5min before and after alkali exposure. Inflammatory cells, neovascularization, and cytoplasmic SOD1 levels were evaluated immunohistochemically in enucleated eyes from both groups. Three-dimensional ultrastructural tissue changes in the eyes were analyzed using low-vacuum scanning electron microscopy.

RESULTS

The numbers of both inflammatory and vascular endothelial cells were significantly reduced in the corneas of the H₂ group (P<0.01). Furthermore, H₂ treatment increased both cytoplasmic SOD1 levels (P<0.01) and activity in corneal epithelial cells (P<0.01). Notably, the SOD1 activity level in the H₂ group was approximately 2.5-fold greater than that in the saline group.

CONCLUSION

H₂ treatment suppresses inflammation and neovascularization in the injured cornea and indirectly suppresses oxidative insult to the cornea by upregulating the SOD1 enzyme protein level and activity.

Peroxisome Proliferator-Activated Receptor Beta/Delta Agonist Suppresses Inflammation and Promotes Neovascularization

The effects of peroxisome proliferator-activated receptor (PPAR)β/δ ophthalmic solution were investigated in a rat corneal alkali burn model. After alkali injury, GW501516 (PPARβ/δ agonist) or vehicle ophthalmic solution was topically instilled onto the rat’s cornea twice a day until day 7. Pathological findings were evaluated, and real-time reverse transcription polymerase chain reaction was performed. GW501516 strongly suppressed infiltration of neutrophils and pan-macrophages, and reduced the mRNA expression of interleukin-6, interleukin-1β, tumor necrosis factor alpha, and nuclear factor-kappa B. On the other hand, GW501516 promoted infiltration of M2 macrophages, infiltration of vascular endothelial cells associated with neovascularization in the wounded area, and expression of vascular endothelial growth factor A mRNA. However, 7-day administration of GW501516 did not promote neovascularization in uninjured normal corneas. Thus, the PPARβ/δ ligand suppressed inflammation and promoted neovascularization in the corneal wound healing process. These results will help to elucidate the role of PPARβ/δ in the field of ophthalmology.

Combination of Peroxisome Proliferator-Activated Receptor (PPAR) Alpha and Gamma Agonists Prevents Corneal Inflammation and Neovascularization in a Rat Alkali Burn Model

Peroxisome proliferator-activated receptor alpha (PPARα) and gamma (PPARγ) agonists have anti-inflammatory and anti-neovascularization effects, but few reports have tested the combination of PPARα and PPARγ agonists. In this study, we investigated the therapeutic effects of ophthalmic solutions of agonists of PPARα, PPARγ, and the combination in a rat corneal alkali burn model. After alkali injury, an ophthalmic solution of 0.05% fenofibrate (PPARα group), 0.1% pioglitazone (PPARγ group), 0.05% fenofibrate + 0.1% pioglitazone (PPARα+γ group), or vehicle (vehicle group) was topically instilled onto the rat’s cornea twice a day. After instillation, upregulation was seen of PPAR mRNA corresponding to each agonist group. Administration of agonists for PPARα, PPARγ, and PPARα+γ suppressed inflammatory cells, neovascularization, and fibrotic changes. In addition, the PPARγ agonist upregulated M2 macrophages, which contributed to wound healing, whereas the PPARα agonist suppressed immature blood vessels in the early phase. Administration of PPARα+γ agonists showed therapeutic effects in corneal wound healing, combining the characteristics of both PPARα and PPARγ agonists. The results indicate that the combination of PPARα and γ agonists may be a new therapeutic strategy.

Observation of Corneal Wound Healing and Angiogenesis Using Low-Vacuum Scanning Electron Microscopy

Purpose

Wound healing processes in a rat corneal alkali burn model were observed using low-vacuum scanning electron microscopy (LV-SEM), a new observation method that can use paraffin sections for light microscopic immunostaining.

Methods

Injured cornea was observed under immunohistochemistry, LV-SEM, and transmission electron microscopy. In LV-SEM, periodic acid-methenamine silver staining was used to observe collagen and platinum blue staining was used to observe vascular endothelial cells. Analyses of the messenger RNA expression involved in neovascularization processes after wound creation were also performed.

Results

LV-SEM depicted progression of corneal wound healing in a stereoscopic fashion. In neovascularization processes after wound creation, LV-SEM with osmification clearly demonstrated detachment of pericytes from the vascular endothelial cells, in association with up-regulation of angiopoietin-2 messenger RNA expression.

Conclusions

LV-SEM enables high magnification observation of paraffin sections used for immunohistochemistry. LV-SEM provides easy, detailed observations and offers a promising new observational modality in the field of ophthalmology.

Translational Relevance

High magnification analysis was easily available using LV-SEM with conventional paraffin sections for light microscopy.

Beyond a Passive Conduit: Implications of Lymphatic Biology for Kidney Diseases

The kidney contains a network of lymphatic vessels that clear fluid, small molecules, and cells from the renal interstitium. Through modulating immune responses and via crosstalk with surrounding renal cells, lymphatic vessels have been implicated in the progression and maintenance of kidney disease. In this Review, we provide an overview of the development, structure, and function of lymphatic vessels in the healthy adult kidney. We then highlight the contributions of lymphatic vessels to multiple forms of renal pathology, emphasizing CKD, transplant rejection, and polycystic kidney disease and discuss strategies to target renal lymphatics using genetic and pharmacologic approaches. Overall, we argue the case for lymphatics playing a fundamental role in renal physiology and pathology and treatments modulating these vessels having therapeutic potential across the spectrum of kidney disease.

Endothelial-epithelial communication in polycystic kidney disease: Role of vascular endothelial growth factor signalling

Whereas targeting the cyst epithelium and its molecular machinery has been the prevailing clinical strategy for polycystic kidney disease, the endothelium, including blood vasculature and lymphatics, is emerging as an important player in this disorder. In this Review, we provide an overview of the structural and functional alterations to blood vasculature and lymphatic vessels in the polycystic kidney. We also discuss evidence for vascular endothelial growth factor signalling, otherwise critical for endothelial cell development and maintenance, as being a fundamental molecular pathway in polycystic kidney disease and a potential therapeutic target for modulating cyst expansion.

Effect of Calcitriol on the Renal Microvasculature Differentiation Disturbances Induced by AT1 Blockade During Nephrogenesis in Rats

Alterations in the renal vasculature during fetal programming can cause disturbances in renal structure and function that persist into adulthood. Calcitriol can affect cellular differentiation and proliferation, and promote endothelial cell maintenance, each of which is a key event in nephrogenesis. Calcitriol is a negative endocrine regulator of the renin gene. Rats exposed to renin-angiotensin system (RAS) antagonists during lactation have been shown to develop renal disorders, which demonstrated that the RAS may play an important role in mammalian kidney development. We evaluated the effects of calcitriol administration on losartan [angiotensin II receptor antagonist (ANGII), AT₁]-induced changes in renal differentiation in rats during lactation. Rats treated with losartan showed alterations in renal function and structure that persisted into adulthood. These disruptions included hydronephrosis, papillary atrophy, endothelial dysfunction, and aberrant endothelial structure. These changes were mitigated by treatment with calcitriol. The results of our study showed that animals exposed to AT₁ blockade during lactation exhibited altered renal microvasculature differentiation in adulthood that was attenuated by treatment with calcitriol.

A Computer Model of Oxygen Dynamics in the Cortex of the Rat Kidney at the Cell-Tissue Level

The renal cortex drives renal function. Hypoxia/reoxygenation are primary factors in ischemia-reperfusion (IR) injuries, but renal oxygenation per se is complex and awaits full elucidation. Few mathematical models address this issue: none captures cortical tissue heterogeneity. Using agent-based modeling, we develop the first model of cortical oxygenation at the cell-tissue level (RCM), based on first principles and careful bibliographical analysis. Entirely parameterized with Rat data, RCM is a morphometrically equivalent 2D-slice of cortical tissue, featuring peritubular capillaries (PTC), tubules and interstitium. It implements hemoglobin/O2 binding-release, oxygen diffusion, and consumption, as well as capillary and tubular flows. Inputs are renal blood flow RBF and PO2 feeds; output is average tissue PO2 (tPO2). After verification and sensitivity analysis, RCM was validated at steady-state (tPO2 37.7 ± 2.2 vs. 36.9 ± 6 mmHg) and under transients (ischemic oxygen half-time: 4.5 ± 2.5 vs. 2.3 ± 0.5 s in situ). Simulations confirm that PO2 is largely independent of RBF, except at low values. They suggest that, at least in the proximal tubule, the luminal flow dominantly contributes to oxygen delivery, while the contribution of capillaries increases under partial ischemia. Before addressing IR-induced injuries, upcoming developments include ATP production, adaptation to minutes-hours scale, and segmental and regional specification.

Lymphangiogenesis in a mouse model of renal transplant rejection extends life span of the recipients

Renal allograft rejection can be prevented by immunological tolerance, which may be associated with de novo formed lymphatic vessels in the donor kidney after transplantation in man. A suitable mouse model of renal allograft rejection in which lymphangiogenesis can be deliberately induced in the graft is critical for elucidating the mechanisms responsible for the association between attenuated transplant rejection and abundance of lymphatic vessels. Here we describe the development of a novel mouse model of rapid renal transplant rejection in which transgenic induction of lymphangiogenesis in the immune-incompatible graft greatly extends its survival time. Thus, our novel approach may facilitate exploitation of lymphangiogenesis in the grafted organ.

Lymphangiogenesis in kidney and lymph node mediates renal inflammation and fibrosis

Lymphangiogenesis is associated with chronic kidney disease (CKD) and occurs following kidney transplant. Here, we demonstrate that expanding lymphatic vessels (LVs) in kidneys and corresponding renal draining lymph nodes (RDLNs) play critical roles in promoting intrarenal inflammation and fibrosis following renal injury. Our studies show that lymphangiogenesis in the kidney and RDLN is driven by proliferation of preexisting lymphatic endothelium expressing the essential C-C chemokine ligand 21 (CCL21). New injury-induced LVs also express CCL21, stimulating recruitment of more CCR7⁺ dendritic cells (DCs) and lymphocytes into both RDLNs and spleen, resulting in a systemic lymphocyte expansion. Injury-induced intrarenal inflammation and fibrosis could be attenuated by blocking the recruitment of CCR7⁺ cells into RDLN and spleen or inhibiting lymphangiogenesis. Elucidating the role of lymphangiogenesis in promoting intrarenal inflammation and fibrosis provides a key insight that can facilitate the development of novel therapeutic strategies to prevent progression of CKD-associated fibrosis.

Lymphatic Function in Autoimmune Diseases

Lymphatic vessels are critical for clearing fluid and inflammatory cells from inflamed tissues and also have roles in immune tolerance. Given the functional association of the lymphatics with the immune system, lymphatic dysfunction may contribute to the pathophysiology of rheumatic autoimmune diseases. Here we review the current understanding of the role of lymphatics in the autoimmune diseases rheumatoid arthritis, scleroderma, lupus, and dermatomyositis and consider the possibility that manual therapies such as massage and acupuncture may be useful in improving lymphatic function in autoimmune diseases.

Attenuated Lymphatic Proliferation Ameliorates Diabetic Nephropathy and High-Fat Diet-Induced Renal Lipotoxicity

Lymphangiogenesis occurs in response to renal injury and is correlated with interstitial fibrosis. Diabetes- and high-fat diet (HFD)-induced intrarenal lipotoxicity and their relationships with lymphangiogenesis are not established. We used PPARα agonist, fenofibrate, to unravel the linkage between lipotoxicity and lymphangiogenesis. Eight-week-old male C57BLKS/J db/db mice and HFD Spontaneously hypertensive rats (SHRs) were fed fenofibrate for 12 weeks. HK-2 and RAW264.7 cells were used to investigate their lymphangiogenic capacity in relation to lipotoxicity. Fenofibrate improved intrarenal lipotoxicity by increasing expression of PPARα and phosphorylation of AMPK. Lymphatic proliferation was attenuated; expression of lymphatic endothelial hyaluronan receptor-1 (LYVE-1), podoplanin, vascular endothelial growth factor-C (VEGF-C), and vascular endothelial growth factor receptor-3 (VEGFR-3) was decreased. In parallel, extent of tubulointerstitial fibrosis, apoptosis and inflammatory cell infiltration was reduced. In HK2 cells, palmitate- and high glucose-induced over expression of lymphatic makers was diminished by fenofibrate via activation of PPARα-AMPK-pACC signaling. Enhanced expression of M1 phenotype in RAW264.7 cells correlated with increased lymphatic growth. A causal relationship between lipotoxicity and lymphatic proliferation with a cellular link to macrophage activation can be speculated; pro-inflammatory M1 type macrophage is involved in the development of lymphangiogenesis through stimulation of VEGF-C and by its transdifferentiation into lymphatic endothelial cells.

Angiopoietin-1 Promotes the Integrity of Neovascularization in the Subcutaneous Matrigel of Type 1 Diabetic Rats

Objective

This study aimed to investigate the effects of Ang-1 on neovascularization of diabetic organs by subcutaneous Matrigel angiogenesis model, established in type 1 diabetic rats.

Methods

Ang-1 adenoviral vector was constructed. The rat model was established by STZ and divided into four group. The Matrigel was inserted subcutaneously into the abdominal cavity of rats at 8 weeks, the treatment group was injected with Ang-1 adenovirus vector via tail vein, and the rats were sacrificed at 10 weeks. Neovascularization of Matrigel was observed with transmission electron microscopy. The marker of vascular endothelial cell and pericyte were detected by immunofluorescence. Immunohistochemical detection of the neovascular endothelial junction protein was performed. RT-PCR was used to determine protein expression of neovascular in Matrigel.

Results

Vascular cavity-like structure could be seen in subcutaneous Matrigel of diabetic rats, and the cavity was filled with a lot of red blood cells. Transmission electron microscopy showed that neovascular endothelial structure of the Matrigel was incomplete, while the Ang-1 treatment group had more vascular cavity-like structures, intact vascular endothelial structure, and reduced inflammatory cell infiltration in Matrigel. Additionally, the integrity of vascularization improved, and the marker of pericyte and the cell tight junctions protein was upregulated in Ang-1 treatment group.

Conclusion

Hyperglycemia could induce pathological angiogenesis in subcutaneous Matrigel of diabetic rats, and Ang-1 could upregulate the expression of intercellular junction protein in subcutaneous Matrigel of diabetic rats and promote the integrity of neovascularization in the subcutaneous Matrigel of diabetic rats.

Low-energy extracorporeal shock wave ameliorates ischemic acute kidney injury in rats

BACKGROUND

Low-energy extracorporeal shock wave (SW) improves ventricular function in ischemic cardiomyopathy through the upregulation of vascular endothelial growth factor (VEGF). VEGF is known to play important roles in acute kidney injury (AKI), and the present study investigates the efficacy of SW for AKI by renal ischemia-reperfusion (I/R) injury.

METHODS

Male 8-week-old Sprague-Dawley rats were divided into the following groups: SW-treated I/R group (I/R-SW), untreated I/R group (I/R), and Sham group. To induce I/R, the left renal pedicles were clamped for 45 min. The I/R-SW group was treated with SW to both kidneys on the immediate postoperative period (day 0), days 1, 2, 7, 8, 9, 14, 15, and 16. Rats were killed on day 2 and day 20 to determine histology, renal function, and Vegf family mRNA expression.

RESULTS

Plasma creatinine on day 2 was significantly lower in the I/R-SW group than in the I/R group. Light microscopy revealed significantly lower tubular injury scores for the outer medulla in the I/R-SW group than in the I/R group. Podoplanin-positive lymphatic vessels were significantly increased in the left (affected side) outer medulla in the I/R-SW group on day 20. The expression levels of Vegf in the right (intact side) cortex were significantly higher in the I/R-SW group than in the I/R group on day 2.

CONCLUSION

Shock wave ameliorated renal tubular injury and renal function in AKI model, through the stimulation of Vegf family expression and lymphangiogenesis. SW may be effective as a non-invasive treatment for ischemic AKI.

Renal Interstitial Lymphangiogenesis in Renal Fibrosis

The basic physiological functions of the lymphatic system include absorption of water and macromolecular substances in the interstitial fluid to maintain the fluid homeostasis, promoting the intestinal absorption of nutrients such as lipids and vitamins from food. Recent studies have found that lymphangiogenesis is associated with some pathological conditions, such as tumor metastasis, injury repair, and chronic inflammation. For a long time, the study of lymphatic vessels (LVs) has been stagnant because of the lack of lymphatic-specific cytology and molecular markers. Renal interstitial lymphangiogenesis is found in patients with chronic kidney disease (CKD) and a series of animal models of renal fibrosis. Intervention of the formation or maturation of LVs in renal tissue of CKD may reduce the drainage of inflammatory cells, attenuate chronic inflammation, delay the progression of renal fibrosis, and improve renal function. This review will summarize the latest findings on renal interstitial lymphangiogenesis in CKD.

VEGF-C attenuates renal damage in salt-sensitive hypertension

Salt-sensitive hypertension is a major risk factor for renal impairment leading to chronic kidney disease. High-salt diet leads to hypertonic skin interstitial volume retention enhancing the activation of the tonicity-responsive enhancer-binding protein (TonEBP) within macrophages leading to vascular endothelial growth factor C (VEGF-C) secretion and NOS3 modulation. This promotes skin lymphangiogenesis and blood pressure regulation. Whether VEGF-C administration enhances renal and skin lymphangiogenesis and attenuates renal damage in salt-sensitive hypertension remains to be elucidated. Hypertension was induced in BALB/c mice by a high-salt diet. VEGF-C was administered subcutaneously to high-salt-treated mice as well as control animals. Analyses of kidney injury, inflammation, fibrosis, and biochemical markers were performed in vivo. VEGF-C reduced plasma inflammatory markers in salt-treated mice. In addition, VEGF-C exhibited a renal anti-inflammatory effect with the induction of macrophage M2 phenotype, followed by reductions in interstitial fibrosis. Antioxidant enzymes within the kidney as well as urinary RNA/DNA damage markers were all revelatory of abolished oxidative stress under VEGF-C. Furthermore, VEGF-C decreased the urinary albumin/creatinine ratio and blood pressure as well as glomerular and tubular damages. These improvements were associated with enhanced TonEBP, NOS3, and lymphangiogenesis within the kidney and skin. Our data show that VEGF-C administration plays a major role in preserving renal histology and reducing blood pressure. VEGF-C might constitute an interesting potential therapeutic target for improving renal remodeling in salt-sensitive hypertension.

Roles of the TGF-β⁻VEGF-C Pathway in Fibrosis-Related Lymphangiogenesis

Lymphatic vessels drain excess tissue fluids to maintain the interstitial environment. Lymphatic capillaries develop during the progression of tissue fibrosis in various clinical and pathological situations, such as chronic kidney disease, peritoneal injury during peritoneal dialysis, tissue inflammation, and tumor progression. The role of fibrosis-related lymphangiogenesis appears to vary based on organ specificity and etiology. Signaling via vascular endothelial growth factor (VEGF)-C, VEGF-D, and VEGF receptor (VEGFR)-3 is a central molecular mechanism for lymphangiogenesis. Transforming growth factor-β (TGF-β) is a key player in tissue fibrosis. TGF-β induces peritoneal fibrosis in association with peritoneal dialysis, and also induces peritoneal neoangiogenesis through interaction with VEGF-A. On the other hand, TGF-β has a direct inhibitory effect on lymphatic endothelial cell growth. We proposed a possible mechanism of the TGF-β–VEGF-C pathway in which TGF-β promotes VEGF-C production in tubular epithelial cells, macrophages, and mesothelial cells, leading to lymphangiogenesis in renal and peritoneal fibrosis. Connective tissue growth factor (CTGF) is also involved in fibrosis-associated renal lymphangiogenesis through interaction with VEGF-C, in part by mediating TGF-β signaling. Further clarification of the mechanism might lead to the development of new therapeutic strategies to treat fibrotic diseases.

Cellular and molecular mechanisms of kidney fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. It is considered as the underlying pathological process of chronic kidney disease (CKD), which affects more than 10% of world population and for which treatment options are limited. Renal fibrosis is defined by excessive deposition of extracellular matrix, which disrupts and replaces the functional parenchyma that leads to organ failure. Kidney's histological structure can be divided into three main compartments, all of which can be affected by fibrosis, specifically termed glomerulosclerosis in glomeruli, interstitial fibrosis in tubulointerstitium and arteriosclerosis and perivascular fibrosis in vasculature. In this review, we summarized the different appearance, cellular origin and major emerging processes and mediators of fibrosis in each compartment. We also depicted and discussed the challenges in translation of anti-fibrotic treatment to clinical practice and discuss possible solutions and future directions.

Peroxisome proliferator-activated receptor alpha agonist suppresses neovascularization by reducing both vascular endothelial growth factor and angiopoietin-2 in corneal alkali burn

We investigated the effect of a peroxisome proliferator-activated receptor alpha (PPARα) agonist ophthalmic solution in wound healing using a rat corneal alkali burn model. After instillation of a selective agonist of PPARα, fenofibrate, onto the burned cornea, PPARα-positive cells were observed in vascular endothelial cells, and there was upregulation of mRNA of PPARα in corneal stroma. Fenofibrate suppressed expression of neutrophils and macrophages during the early phase, and development of neovascularization and myofibroblast generation during the late phase. Fenofibrate reduced not only mRNA expression of vascular endothelial growth factor-A but also angiopoietin-1 and angiopoietin-2. Furthermore, fenofibrate suppressed scar formation by reducing type III collagen expression. These data suggest that a PPARα agonist ophthalmic solution might be a new strategy for treating corneal wounds through not only anti-inflammatory effects but also by preventing neovascularization.

Dapagliflozin in focal segmental glomerulosclerosis: a combined human-rodent pilot study

Focal segmental glomerulosclerosis (FSGS) is an important cause of nondiabetic chronic kidney disease (CKD). Sodium-glucose cotransporter 2 inhibition (SGLT2i) therapy attenuates the progression of diabetic nephropathy, but it remains unclear whether SGLT2i provides renoprotection in nondiabetic CKD such as FSGS. The primary aim of this pilot study was to determine the effect of 8 wk of dapagliflozin on glomerular filtration rate (GFR) in humans and in experimental FSGS. Secondary end points were related to changes in renal hemodynamic function, proteinuria, and blood pressure (BP). GFR (inulin) and renal plasma flow (para-aminohippurate), proteinuria, and BP were measured in patients with FSGS ( n = 10), and similar parameters were measured in subtotally nephrectomized (SNx) rats. In response to dapagliflozin, changes in GFR, renal plasma flow, and 24-h urine protein excretion were not statistically significant in humans or rats. Systolic BP (SBP) decreased in SNx rats (196 ± 26 vs. 165 ± 33 mmHg; P < 0.001), whereas changes were not statistically significant in humans (SBP 112.7 ± 8.5 to 112.8 ± 11.2 mmHg, diastolic BP 71.8 ± 6.5 to 69.6 ± 8.4 mmHg; P = not significant), although hematocrit increased (0.40 ± 0.05 to 0.42 ± 0.05%; P = 0.03). In archival kidney tissue from a separate patient cohort, renal parenchymal SGLT2 mRNA expression was decreased in individuals with FSGS compared with controls. Short-term treatment with the SGLT2i dapagliflozin did not modify renal hemodynamic function or attenuate proteinuria in humans or in experimental FSGS. This may be related to downregulation of renal SGLT2 expression. Studies examining the impact of SGLT2i on markers of kidney disease in patients with other causes of nondiabetic CKD are needed.

Lymphangiogenesis guidance by paracrine and pericellular factors

This review by Vaahtomeri et al. discusses the mechanisms by which the lymphatic vasculature network is formed, remodeled, and adapted to physiological and pathological challenges. It describes how the lymphatic vasculature network is controlled by an intricate balance of growth factors and biomechanical cues.

Lymphatic vessels are important for tissue fluid homeostasis, lipid absorption, and immune cell trafficking and are involved in the pathogenesis of several human diseases. The mechanisms by which the lymphatic vasculature network is formed, remodeled, and adapted to physiological and pathological challenges are controlled by an intricate balance of growth factor and biomechanical cues. These transduce signals for the readjustment of gene expression and lymphatic endothelial migration, proliferation, and differentiation. In this review, we describe several of these cues and how they are integrated for the generation of functional lymphatic vessel networks.

Lymphangiogenesis: fuel, smoke, or extinguisher of inflammation's fire?

Lymphangiogenesis is a recognized hallmark of inflammatory processes in tissues and organs as diverse as the skin, heart, bowel, and airways. In clinical and animal models wherein the signaling processes of lymphangiogenesis are manipulated, most studies demonstrate that an expanded lymphatic vasculature is necessary for the resolution of inflammation. The fundamental roles that lymphatics play in fluid clearance and immune cell trafficking from the periphery make these results seemingly obvious as a mechanism of alleviating locally inflamed environments: the lymphatics are simply providing a drain. Depending on the tissue site, lymphangiogenic mechanism, or induction timeframe, however, evidence shows that inflammation-associated lymphangiogenesis (IAL) may worsen the pathology. Recent studies have identified lymphatic endothelial cells themselves to be local regulators of immune cell activity and its consequential phenotypes - a more active role in inflammation regulation than previously thought. Indeed, results focusing on the immunocentric roles of peripheral lymphatic function have revealed that the basic drainage task of lymphatic vessels is a complex balance of locally processed and transported antigens as well as interstitial cytokine and immune cell signaling: an interplay that likely defines the function of IAL. This review will summarize the latest findings on how IAL impacts a series of disease states in various tissues in both preclinical models and clinical studies. This discussion will serve to highlight some emerging areas of lymphatic research in an attempt to answer the question relevant to an array of scientists and clinicians of whether IAL helps to fuel or extinguish inflammation. Impact statement Inflammatory progression is present in acute and chronic tissue pathologies throughout the body. Lymphatic vessels play physiological roles relevant to all medical fields as important regulators of fluid balance, immune cell trafficking, and immune identity. Lymphangiogenesis is often concurrent with inflammation and can potentially aide or worsen disease progression. How new lymphatic vessels impact inflammation and by which mechanism is an important consideration in current and future clinical therapies targeting inflammation and/or vasculogenesis. This review identifies, across a range of tissue-specific pathologies, the current understanding of inflammation-associated lymphangiogenesis in the progression or resolution of inflammation.

Exposure to placental ischemia impairs postpartum maternal renal and cardiac function in rats

Women with a history of preeclampsia (PE) have an increased risk to develop cardiovascular and renal diseases later in life, but the mechanisms underlying this effect are unknown. In rats, we assessed whether placental ischemia results in long-term effects on the maternal cardiovascular and renal systems using the reduced uterine perfusion pressure (RUPP) model for PE. Sprague-Dawley rats received either a Sham or RUPP operation at gestational day 14 The rats were followed for 8 wk after delivery (Sham n = 12, RUPP n = 21) at which time mean arterial pressure (MAP; conscious), 24-h albuminuria, glomerular filtration rate (GFR; transcutaneous, FITC-sinistrin), and cardiac function (Vevo 770 system) were assessed. Subsequently, all rats were euthanized for mesenteric artery vasorelaxation and histology of heart and kidney. At 8 wk after delivery, there was no difference in MAP and albuminuria. However, RUPP rats showed a significantly reduced GFR [2.61 ± 0.53 vs. 3.37 ± 0.74 ml/min; P = 0.01]. Ultrasound showed comparable cardiac structure, but RUPP rats had a lower left ventricular ejection fraction (62 ± 7 vs. 69 ± 10%; P = 0.04). Heart and kidney histology was not different between Sham or RUPP rats. Furthermore, there were no differences in endothelial-dependent or -independent vasorelaxation. We show that exposure to placental ischemia in rats is accompanied by functional disturbances in maternal renal and cardiac function 8 wk after a preeclamptic pregnancy. However, these changes were not dependent on differences in blood pressure, small artery vasorelaxation, or cardiac and renal structure at this time point postpartum.

Blood capillary rarefaction and lymphatic capillary neoangiogenesis are key contributors to renal allograft fibrosis in an ACE inhibition rat model

Chronic allograft fibrosis is the major cause of graft loss in kidney transplantation. Progression can only be reduced by inhibition of the renin-angiotensin system (RAS). We tested the hypothesis that the protection provided by angiotensin-converting enzyme (ACE) inhibition also decreases capillary rarefaction, lymphangiogenesis, and podocyte injury in allograft fibrosis. Fisher kidneys were transplanted into bilaterally nephrectomized Lewis rats treated with enalapril (60 mg/kg per day) (ACE inhibitor, ACEi) or vehicle. Proteinuria, blood urea nitrogen, and plasma creatinine were regularly assessed, and grafts were harvested for morphological and immunohistological analysis at various times up to 32 wk. In the vehicle group, many new lymphatic capillaries and severe and diffuse mononuclear infiltration of allografts were observed already 1 wk after transplantation. Lymphangiogenesis increased until week 4, by which time inflammatory infiltration became focal. Lymphatic capillaries were often located at sites of inflammation. Progressive interstitial fibrosis, glomerulosclerosis, capillary rarefaction, and proteinuria appeared later, at weeks 4-12 The number of lymphatic capillary cross sections strongly correlated with the interstitial fibrosis score. Podoplanin immunostaining, a marker of healthy podocytes, disappeared from inflamed or sclerotic glomerular areas. ACEi protected from lymphangiogenesis and associated inflammation, preserved glomerular podoplanin protein expression, and reduced glomerulosclerosis, proteinuria, tubulointerstitial fibrosis, and blood capillary rarefaction at 32 wk. In conclusion, ACEi considerably decreased and/or delayed both glomerulosclerosis and tubulointerstitial injury. Prevention of glomerular podoplanin loss and proteinuria could be attributed to the known intraglomerular pressure-lowering effects of ACEi. Reduction of lymphangiogenesis could contribute to amelioration of tubulointerstitial fibrosis and inflammatory infiltration after ACEi.

New Insights into the Effects of Chronic Kidney Failure and Dialysate Exposure on the Peritoneum

♦ INTRODUCTION: Chronic uremia and the exposure to dialysis solutions during peritoneal dialysis (PD) induce peritoneal alterations. Using a long-term peritoneal exposure model, we compared the effects of chronic kidney failure (CKD) itself and exposure to either a 'conventional' or a 'biocompatible' dialysis solution on peritoneal morphology and function. ♦ METHODS: Wistar rats (Harlan, Zeist, the Netherlands) were grouped into: normal kidney function (NKF), CKD induced by 70% nephrectomy, CKD receiving daily peritoneal infusions with 3.86% glucose Dianeal (CKDD), or Physioneal (both solutions from Baxter Healthcare, Castlebar, Ireland) (CKDP). At 16 weeks, a peritoneal function test was performed, and histology, ultrastructure, and hydroxyproline content of peritoneal tissue were assessed. ♦ RESULTS: Comparing CKD with NKF, peritoneal transport rates were higher, mesothelial cells (MC) displayed increased number of microvilli, blood and lymph vasculature expanded, vascular basal lamina appeared thicker, with limited areas of duplication, and fibrosis had developed. All alterations, except lymphangiogenesis, were enhanced by exposure to both dialysis fluids. Distinct MC alterations were observed in CKDD and CKDP, the latter displaying prominent basolateral protrusions. In addition, CKDP was associated with a trend towards less fibrosis compared to CKDD. ♦ CONCLUSIONS: Chronic kidney failure itself induced peritoneal alterations, which were in part augmented by exposure to glucose-based dialysis solutions. Overall, the conventional and biocompatible solutions had similar long-term effects on the peritoneum. Importantly, the latter may attenuate the development of fibrosis.

Hyaluronan-induced VEGF-C promotes fibrosis-induced lymphangiogenesis via Toll-like receptor 4-dependent signal pathway

Hyaluronan (HA), a component of the extracellular matrix, modulates cellular behavior including angiogenesis. However, little is known about the effect of HA on lymphangiogenesis in fibrosis model. In this study, we investigated the roles of HA in lymphangiogenesis of unilateral ureteral obstruction (UUO). We found that HA cooperated synergistically with vascular endothelial cell growth factor-C to stimulate capillary-like tube formation and increase migration of cells in a haptotaxis assay. Accumulation of HA in the cortical interstitial space was positively correlated with the number of lymphatic vessels after UUO. Depletion of macrophages with clodronate decreased UUO-induced HA accumulation and lymphangiogenesis. Additionally, hyaluronan synthase (HAS) mRNA expression and HA production were increased in bone marrow-derived macrophages upon stimulation with TGF-β1. Transfer of mHAS2 and mHAS3 knock-down CD11b-positive macrophages to SCID mice resulted in a partial decrease in UUO-induced lymphangiogenesis. HA increased expression of vascular endothelial cell growth factor-C in macrophages. Vascular endothelial cell growth factor-C expression and LYVE-1-positive lymphatic area was significantly lower in the UUO-kidney from TLR4 null mice than that from TLR4 wild-type mice. Collectively, these results suggest that HA increases lymphangiogenesis in renal fibrosis model and also stimulates vascular endothelial cell growth factor-C production from macrophages through Toll-like receptor 4-dependent signal pathway.

Alteration in the podoplanin-ezrin-cytoskeleton linkage is an important initiation event of the podocyte injury in puromycin aminonucleoside nephropathy, a mimic of minimal change nephrotic syndrome

Podoplanin was identified as a protein associated with the transformation of arborized foot processes of glomerular epithelial cells (podocytes) to flat feet. However, the function of podoplanin in the podocyte is not yet fully clarified. In this study, we analyzed the molecular nature of podoplanin, and its expression in rat nephrotic models and patients with minimal change nephrotic syndrome (MCNS). We demonstrated here that podoplanin has two forms: one contains abundant sialic acid and the other a lesser amount of sialic acid. Podoplanin bound ezrin to interact with the cytoskeleton. The silencing of podoplanin in cultured podocytes caused a change in the cell shape and the distribution of ezrin and actin. The expression of podoplanin was clearly reduced before the onset of proteinuria in puromycin aminonucleoside (PAN) nephropathy, a mimic of MCNS, and the decrease in the expression of podoplanin became more evident at the proteinuric stage. Podoplanin was detected in normal urine samples, and the amount of urinary podoplanin markedly increased on day 1 of PAN nephropathy. Urinary ezrin was also detected. The amount of the phosphorylated ezrin was reduced, while the amount of the podoplanin-interacting ezrin increased. The podoplanin expression was reduced in a patient with active-phase MCNS. It is conceivable that the alteration of the podoplanin-ezrin-cytoskeleton linkage is an important event of the podocyte injury in MCNS.

Renal allograft fibrosis: biology and therapeutic targets

Renal tubulointerstitial fibrosis is the final common pathway of progressive renal diseases. In allografts, it is assessed with tubular atrophy as interstitial fibrosis/tubular atrophy (IF/TA). IF/TA occurs in about 40% of kidney allografts at 3-6 months after transplantation, increasing to 65% at 2 years. The origin of renal fibrosis in the allograft is complex and includes donor-related factors, in particular in case of expanded criteria donors, ischemia-reperfusion injury, immune-mediated damage, recurrence of underlying diseases, hypertensive damage, nephrotoxicity of immunosuppressants, recurrent graft infections, postrenal obstruction, etc. Based largely on studies in the non-transplant setting, there is a large body of literature on the role of different cell types, be it intrinsic to the kidney or bone marrow derived, in mediating renal fibrosis, and the number of mediator systems contributing to fibrotic changes is growing steadily. Here we review the most important cellular processes and mediators involved in the progress of renal fibrosis, with a focus on the allograft situation, and discuss some of the challenges in translating experimental insights into clinical trials, in particular fibrosis biomarkers or imaging modalities.

Lymphangiogenesis in renal diseases: passive bystander or active participant?

Lymphatic vessels (LVs) are involved in a number of physiological and pathophysiological processes such as fluid homoeostasis, immune surveillance, and resolution of inflammation and wound healing. Lymphangiogenesis, the outgrowth of existing LVs and the formation of new ones, has received increasing attention over the past decade on account of its prominence in organ physiology and pathology, which has been enabled by the development of specific tools to study lymph vessel functions. Several studies have been devoted to renal lymphatic vasculature and lymphangiogenesis in kidney diseases, such as chronic renal transplant dysfunction, primary renal fibrotic disorders, proteinuria, diabetic nephropathy and renal inflammation. This review describes the most recent findings on lymphangiogenesis, with a specific focus on renal lymphangiogenesis and its impact on renal diseases. We suggest renal lymphatics as a possible target for therapeutic interventions in renal medicine to dampen tubulointerstitial tissue remodelling and improve renal functioning.

Identification of novel genes associated with renal tertiary lymphoid organ formation in aging mice

A hallmark of aging-related organ deterioration is a dysregulated immune response characterized by pathologic leukocyte infiltration of affected tissues. Mechanisms and genes involved are as yet unknown. To identify genes associated with aging-related renal infiltration, we analyzed kidneys from aged mice (≥20 strains) for infiltrating leukocytes followed by Haplotype Association Mapping (HAM) analysis. Immunohistochemistry revealed CD45⁺ cell clusters (predominantly T and B cells) in perivascular areas coinciding with PNAd⁺ high endothelial venules and podoplanin⁺ lymph vessels indicative of tertiary lymphoid organs. Cumulative cluster size increased with age (analyzed at 6, 12 and 20 months). Based on the presence or absence of clusters in male and female mice at 20 months, HAM analysis revealed significant associations with loci on Chr1, Chr2, Chr8 and Chr14 in male mice, and with loci on Chr4, Chr7, Chr13 and Chr14 in female mice. Wisp2 (Chr2) showed the strongest association (P = 5.00×10⁻¹³⁷) in male mice; Ctnnbip1 (P = 6.42×10⁻²⁶⁷) and Tnfrsf8 (P = 5.42×10⁻²⁴⁵) (both on Chr4) showed the strongest association in female mice. Both Wisp2 and Ctnnbip1 are part of the Wnt-signaling pathway and the encoded proteins were expressed within the tertiary lymphoid organs. In conclusion, this study revealed differential lymphocytic infiltration and tertiary lymphoid organ formation in aged mouse kidneys across different inbred mouse strains. HAM analysis identified candidate genes involved in the Wnt-signaling pathway that may be causally linked to tertiary lymphoid organ formation.

TGF-β1 promotes lymphangiogenesis during peritoneal fibrosis

Peritoneal fibrosis (PF) causes ultrafiltration failure (UFF) and is a complicating factor in long-term peritoneal dialysis. Lymphatic reabsorption also may contribute to UFF, but little is known about lymphangiogenesis in patients with UFF and peritonitis. We studied the role of the lymphangiogenesis mediator vascular endothelial growth factor-C (VEGF-C) in human dialysate effluents, peritoneal tissues, and peritoneal mesothelial cells (HPMCs). Dialysate VEGF-C concentration correlated positively with the dialysate-to-plasma ratio of creatinine (D/P Cr) and the dialysate TGF-β1 concentration. Peritoneal tissue from patients with UFF expressed higher levels of VEGF-C, lymphatic endothelial hyaluronan receptor-1 (LYVE-1), and podoplanin mRNA and contained more lymphatic vessels than tissue from patients without UFF. Furthermore, mesothelial cell and macrophage expression of VEGF-C increased in the peritoneal membranes of patients with UFF and peritonitis. In cultured mesothelial cells, TGF-β1 upregulated the expression of VEGF-C mRNA and protein, and this upregulation was suppressed by a TGF-β type I receptor (TGFβR-I) inhibitor. TGF-β1-induced upregulation of VEGF-C mRNA expression in cultured HPMCs correlated with the D/P Cr of the patient from whom the HPMCs were derived (P<0.001). Moreover, treatment with a TGFβR-I inhibitor suppressed the enhanced lymphangiogenesis and VEGF-C expression associated with fibrosis in a rat model of PF. These results suggest that lymphangiogenesis associates with fibrosis through the TGF-β-VEGF-C pathway.

Proteinuria triggers renal lymphangiogenesis prior to the development of interstitial fibrosis

Proteinuria is an important cause of progressive tubulo-interstitial damage. Whether proteinuria could trigger a renal lymphangiogenic response has not been established. Moreover, the temporal relationship between development of fibrosis, inflammation and lymphangiogenesis in chronic progressive kidney disease is not clear yet. Therefore, we evaluated the time course of lymph vessel (LV) formation in relation to proteinuria and interstitial damage in a rat model of chronic unilateral adriamycin nephrosis. Proteinuria and kidneys were evaluated up to 30 weeks after induction of nephrosis. LVs were identified by podoplanin/VEGFR3 double staining. After 6 weeks proteinuria was well-established, without influx of interstitial macrophages and myofibroblasts, collagen deposition, osteopontin expression (tubular activation) or LV formation. At 12 weeks, a ∼3-fold increase in cortical LV density was found (p<0.001), gradually increasing over time. This corresponded with a significant increase in tubular osteopontin expression (p<0.01) and interstitial myofibroblast numbers (p<0.05), whereas collagen deposition and macrophage numbers were not yet increased. VEGF-C was mostly expressed by tubular cells rather than interstitial cells. Cultured tubular cells stimulated with FCS showed a dose-dependent increase in mRNA and protein expression of VEGF-C which was not observed by human albumin stimulation. We conclude that chronic proteinuria provoked lymphangiogenesis in temporal conjunction with tubular osteopontin expression and influx of myofibroblasts, that preceded interstitial fibrosis.

Hypoxia and hypoxia signaling in tissue repair and fibrosis

Following injury, vascular damage results in the loss of perfusion and consequent low oxygen tension (hypoxia) which may be exacerbated by a rapid influx of inflammatory and mesenchymal cells with high metabolic demands for oxygen. Changes in systemic and cellular oxygen concentrations induce tightly regulated response pathways that attempt to restore oxygen supply to cells and modulate cell function in hypoxic conditions. Most of these responses occur through the induction of the transcription factor hypoxia-inducible factor-1 (HIF-1) which regulates many processes needed for tissue repair during ischemia in the damaged tissue. HIF-1 transcriptionally upregulates expression of metabolic proteins (GLUT-1), adhesion proteins (integrins), soluble growth factors (TGF-β and VEGF), and extracellular matrix components (type I collagen and fibronectin), which enhance the repair process. For these reasons, HIF-1 is viewed as a positive regulator of wound healing and a potential regulator of organ repair and tissue fibrosis. Understanding the complex role of hypoxia in the loss of function in scarring tissues and biology of chronic wound, and organ repair will aid in the development of pharmaceutical agents that can redress the detrimental outcomes often seen in repair and scarring.

Vascular endothelial growth factor-C and -D are involved in lymphangiogenesis in mouse unilateral ureteral obstruction

Lymphatic remodeling in inflammation has been found in tracheal mycoplasma infection, human kidney transplant, skin inflammation, peritonitis, and corneal inflammation. Here we investigated lymphangiogenesis in fibrotic area in unilateral ureteral obstruction, a model of progressive renal fibrosis, and evaluated the roles of vascular endothelial growth factor (VEGF)-C and -D in the obstructed kidney. Compared to sham-operated mice, the number of LYVE-1-positive lymphatic vessels, the proliferation of LYVE-1-positive lymphatic endothelial cells, along with VEGF-C and -D mRNA expression were all significantly increased following ureteral obstruction. Depletion of macrophages with clodronate decreased lymphangiogenesis in the obstructed kidney. VEGF-C expression was higher in M2- than in M1-polarized macrophages from bone marrow-derived macrophages, and also increased in Raw 264.7 or renal proximal tubule cells by stimulation with TGF-β1 or TNF-α. VEGF-D reversed the inhibitory effect of TGF-β1 on VEGF-C-induced migration, capillary-like tube formation, and proliferation of human lymphatic endothelial cells. Additionally, the blockade of VEGF-C and VEGF-D signaling decreased obstruction-induced lymphangiogenesis. Thus, VEGF-C and VEGF-D are associated with lymphangiogenesis in the fibrotic kidney in a mouse model of ureteral obstruction.

Inflammatory lymphangiogenesis in a rat transplant model of interstitial fibrosis and tubular atrophy

We have previously reported de novo lymphangiogenesis in human renal allograft nephrectomy specimens that exhibited interstitial fibrosis and tubular atrophy (IFTA). This study examined whether a similar pathology developed in an experimental model of renal transplantation in the rat. Renal transplants were carried out in rats comprising both isografts (Lewis kidneys → Lewis rats) and allografts (Fisher kidneys → Lewis rats). Animals were immunosuppressed in the immediate postoperative period and sacrificed at 12 months. Experimental readouts included lymphatic vessel number and location, inflammatory cell infiltration, interstitial fibrosis, renal function, blood pressure and proteinuria. Rat allografts demonstrated the characteristic features of IFTA with increased macrophage and T cell infiltration and scattered B cells aggregates. Rat allografts exhibited impaired renal function and proteinuria. Although there was no difference in the number of perivascular lymphatic vessels, there was a striking 18-fold increase in the number of interstitial lymphatic vessels in renal allografts. Furthermore, the lymphatic vessel number correlated with the extent of interstitial fibrosis. This rat allograft model of IFTA demonstrates a marked increase in the number of interstitial lymphatic vessels and mirrors previous work in failing human renal allografts.

The role of lymphatics in renal inflammation

Progressive renal diseases are characterized by tubulointerstitial inflammatory cell recruitment, tubular atrophy and fibrosis. Various aspects of the recruitment of leukocytes have been extensively studied, but the exit routes (i.e. the lymphatic vessels and their biology) have only recently found attention. Similar to the recruitment of inflammatory cells, the exit is coordinated by an orchestrated interaction of chemotactic cytokines and adhesion molecules. During inflammatory injury, new routes are created by the de novo formation of lymphatic vessels, i.e. neolymphangiogenesis. These newly formed lymphatic vessels help to cope with the increase in interstitial fluid related to inflammation. Here, we review some aspects of lymphatic biology and the current knowledge about lymphatic vessels in renal inflammation.

Development of lymphatic vasculature and morphological characterization in rat kidney

BACKGROUND

The mechanisms and morphological characteristics of lymphatic vascular development in embryonic kidneys remain uncertain.

METHODS

We examined the distribution and characteristics of lymphatic vessels in developing rat kidneys using immunostaining for podoplanin, prox-1, Ki-67, type IV collagen (basement membrane: BM), and α-smooth muscle actin (αSMA: pericytes or mural cells). We also examined the expression of VEGF-C.

RESULTS

At embryonic day 17 (E17), podoplanin-positive lymphatic vessels were observed mainly in the kidney hilus. At E20, lymphatic vessels extended further into the developing kidneys along the interlobar vasculature. In 1-day-old pups (P1) to P20, lymphatic vessels appeared around the arcuate arteries and veins of the kidneys, with some reaching the developing cortex via interlobular vessels. In 8-week-old adult rats, lymphatic vessels were extensively distributed around the blood vasculature from the renal hilus to cortex. Only lymphatic capillaries lacking continuous BM and αSMA-positive cells were present within adult kidneys, with none observed in renal medulla. VEGF-C was upregulated in the developing kidneys and expressed mainly in tubules. Importantly, the developing lymphatic vessels were characterized by endothelial cells immunopositive for podoplanin, prox-1, and Ki-67, with no surrounding BM or αSMA-positive cells.

CONCLUSION

During nephrogenesis, lymphatic vessels extend from the renal hilus into the renal cortex along the renal blood vasculature. Podoplanin, prox-1, Ki-67, type IV collagen, and αSMA immunostaining can detect lymphatic vessels during lymphangiogenesis.