Local macrophage and myofibroblast proliferation in progressive renal injury in the rat remnant kidney

Proliferation of monocytes and macrophages in homeostasis, infection, injury, and disease

Monocytes (Mo) and macrophages (Mφ) play important roles in the function of tissues, organs, and systems of all animals during homeostasis, infection, injury, and disease. For decades, conventional wisdom has dictated that Mo and Mφ are end-stage cells that do not proliferate and that Mφ accumulation in tissues is the result of infiltration of Mo from the blood and subsequent differentiation to Mφ. However, reports from the early 1900s to the present describe evidence of Mo and Mφ proliferation in different tissues and contexts. The purpose of this review is to summarize both historical and current evidence for the contribution of Mφ proliferation to their accumulation in different tissues during homeostasis, infection, injury, and disease. Mφ proliferate in different organs and tissues, including skin, peritoneum, lung, heart, aorta, kidney, liver, pancreas, brain, spinal cord, eye, adipose tissue, and uterus, and in different species including mouse, rat, rabbit, and human. Mφ can proliferate at different stages of differentiation with infiltrating Mo-like cells proliferating in certain inflammatory contexts (e.g. skin wounding, kidney injury, bladder and liver infection) and mature resident Mφ proliferating in other inflammatory contexts (e.g. nematode infection, acetaminophen liver injury) and during homeostasis. The pathways involved in stimulating Mφ proliferation also may be context dependent, with different cytokines and transcription factors implicated in different studies. Although Mφ are known to proliferate in health, injury, and disease, much remains to be learned about the regulation of Mφ proliferation in different contexts and its impact on the homeostasis, injury, and repair of different organs and tissues.

The Advances of Single-Cell RNA-Seq in Kidney Immunology

Kidney diseases are highly prevalent and treatment is costly. Immune cells play important roles in kidney diseases; however, it has been challenging to investigate the contribution of each cell type in kidney pathophysiology. Recently, the development of single-cell sequencing technology has allowed the extensive study of immune cells in blood, secondary lymphoid tissues, kidney biopsy and urine samples, helping researchers generate a comprehensive immune cell atlas for various kidney diseases. Here, we discuss several recent studies using scRNA-seq technology to explore the immune-related kidney diseases, including lupus nephritis, diabetic kidney disease, IgA nephropathy, and anti-neutrophil cytoplasmic antibody-associated glomerulonephritis. Application of scRNA-seq successfully defined the transcriptome profiles of resident and infiltrating immune cells, as well as the intracellular communication networks between immune and adjacent cells. In addition, the discovery of similar immune cells in blood and urine suggests the possibility of examining kidney immunity without biopsy. In conclusion, these immune cell atlases will increase our understanding of kidney immunology and contribute to novel therapeutics for patients with kidney diseases.

Macrophage polarization in chronic kidney disease: a balancing act between renal recovery and decline?

Macrophages are heterogenous cells of the innate immune system that can fluidly modulate their phenotype to respond to their local microenvironment. They are found throughout the renal compartments, where they contribute to homeostasis and function. However, renal injury activates molecular pathways that initially stimulate differentiation of macrophages into a proinflammatory M1 phenotype. Later in the course of healing, abundant apoptotic debris and anti-inflammatory cytokines induce the production of anti-inflammatory M2 macrophages, which contribute to tissue regeneration and repair. Thus, the dynamic balance of M1 and M2 populations may outline the burden of inflammation and process of tissue repair that define renal outcomes, which has been the impetus for therapeutic efforts targeting macrophages. This review will discuss the role of these phenotypes in the progression of chronic renal injury, potential pathogenic mechanisms, and the promise of macrophage-based therapeutic applications for chronic kidney disease.

Radiation Nephropathy in a Nonhuman Primate Model of Partial-Body Irradiation With Minimal Bone Marrow Sparing-Part 2: Histopathology, Mediators, and Mechanisms

Male rhesus macaques were subjected to partial-body irradiation at 10, 11, or 12 Gy with 5% bone marrow protection. Animals were euthanized when dictated by prospectively determined clinical parameters or at approximately 180 d following irradiation. Histological sections of kidney were stained with hematoxylin and eosin as well as a battery of histochemical and immunohistochemical stains. Histopathological alterations were centered on glomerular changes and fibrosis of glomeruli and the interstitial compartment. These changes were first noted in animals necropsied approximately 100 d postirradiation and continued in animals necropsied through the observation period. Glomerular changes included congestion, thrombosis, erythrocyte degeneration, capillary tuft dilation, fibrin deposition, altered quantity and dispersion pattern of von Willebrand factor, increased mesangial matrix, and mesangial deposits of material that stained positively with periodic acid-Schiff staining. Areas of interstitial and glomerular fibrosis, as demonstrated by Masson's trichrome staining, were topographically associated with increased immunohistochemical staining for connective tissue growth factor, alpha smooth muscle actin, and collagen 1, but there was little staining for transforming growth factor beta. Fibrotic glomeruli had reduced microvascularity as demonstrated by reduced CD31 immunohistochemical staining. Vascular congestion was commonly noted in the region of the corticomedullary junction, and proteinaceous casts were commonly noted in cortical and medullary tubules. Longitudinal analysis of histopathological alterations provided evidence defining the latency, severity, and progression of delayed radiation-induced kidney injury.

Macrophages: versatile players in renal inflammation and fibrosis

Macrophages have important roles in immune surveillance and in the maintenance of kidney homeostasis; their response to renal injury varies enormously depending on the nature and duration of the insult. Macrophages can adopt a variety of phenotypes: at one extreme, M1 pro-inflammatory cells contribute to infection clearance but can also promote renal injury; at the other extreme, M2 anti-inflammatory cells have a reparative phenotype and can contribute to the resolution phase of the response to injury. In addition, bone marrow monocytes can differentiate into myeloid-derived suppressor cells that can regulate T cell immunity in the kidney. However, macrophages can also promote renal fibrosis, a major driver of progression to end-stage renal disease, and the CD206⁺ subset of M2 macrophages is strongly associated with renal fibrosis in both human and experimental diseases. Myofibroblasts are important contributors to renal fibrosis and recent studies provide evidence that macrophages recruited from the bone marrow can transition directly into myofibroblasts within the injured kidney. This process is termed macrophage-to-myofibroblast transition (MMT) and is driven by transforming growth factor-β1 (TGFβ1)-Smad3 signalling via a Src-centric regulatory network. MMT may serve as a key checkpoint for the progression of chronic inflammation into pathogenic fibrosis.

Inflammatory Mediators and Renal Fibrosis

Renal inflammation is the initial, healthy response to renal injury. However, prolonged inflammation promotes the fibrosis process, which leads to chronic pathology and eventually end-stage kidney disease. There are two major sources of inflammatory cells: first, bone marrow-derived leukocytes that include neutrophils, macrophages, fibrocytes and mast cells, and second, locally activated kidney cells such as mesangial cells, podocytes, tubular epithelial cells, endothelial cells and fibroblasts. These activated cells produce many profibrotic cytokines and growth factors that cause accumulation and activation of myofibroblasts, and enhance the production of the extracellular matrix. In particular, activated macrophages are key mediators that drive acute inflammation into chronic kidney disease. They produce large amounts of profibrotic factors and modify the microenvironment via a paracrine effect, and they also transdifferentiate to myofibroblasts directly, although the origin of myofibroblasts in the fibrosing kidney remains controversial. Collectively, understanding inflammatory cell functions and mechanisms during renal fibrosis is paramount to improving diagnosis and treatment of chronic kidney disease.

Treatment with lecinoxoids attenuates focal and segmental glomerulosclerosis development in nephrectomized rats

Focal segmental glomerulosclerosis (FSGS) is a scarring process associated with chronic low‐grade inflammation ascribed to toll‐like receptor (TLR) activation and monocyte migration. We developed synthetic, small‐molecule lecinoxoids, VB‐201 and VB‐703, that differentially inhibit TLR‐2‐ and TLR‐4‐mediated activation and monocyte migration. The efficacy of anti‐inflammatory lecinoxoid treatment on FSGS development was explored using a 5/6 nephrectomy rat model. Five‐sixths of nephrectomized rats were treated with lecinoxoids VB‐201, VB‐703 or PBS, for 7 weeks. Upon sacrifice, albumin/creatinine ratio, glomerulosclerosis, fibrosis‐related gene expression and the number of glomerular and interstitial monocyte were evaluated. Treatment of nephrectomized rats with lecinoxoids ameliorated glomerulosclerosis. The percentage of damaged glomeruli, glomerular sclerosis and glomeruli fibrotic score was significantly reduced following VB‐201 and VB‐703 treatment. VB‐703 attenuated the expression of fibrosis hallmark genes collagen, fibronectin (FN) and transforming growth factor β (TGF‐β) in kidneys and improved albumin/creatinine ratio with higher efficacy than did VB‐201, but only VB‐201 significantly reduced the number of glomerular and interstitial monocytes. These results indicate that treatment with TLR‐2, and more prominently, TLR‐4 antagonizing lecinoxioids, is sufficient to significantly inhibit FSGS. Moreover, inhibiting monocyte migration can also contribute to treatment of FSGS. Our data demonstrate that targeting TLR‐2‐TLR‐4 and/or monocyte migration directly affects the priming phase of fibrosis and may consequently perturb disease parthogenesis.

Toll-like receptor-4 deficiency alleviates chronic intermittent hypoxia-induced renal injury, inflammation, and fibrosis

BACKGROUND

Obstructive sleep apnea (OSA)-associated chronic kidney disease is mainly caused by chronic intermittent hypoxia (CIH) triggered renal damage. This study aims to investigate the role of toll-like receptor-4 (TLR4) in underlying mechanism involved chronic intermittent hypoxia (CIH)-induced renal damage.

METHODS

C57BL/6J mice with normal TLR4 (TLR4 WT) or deficient TLR4 (TLR4 KO) were divided into four groups and exposed to normal air (NA) and CIH: TLR4 WT + NA, TLR4 KO + NA, TLR4 WT + CIH, and TLR4 KO + CIH. CIH lasted for 8 h/day and 7 days/week for 6 weeks. Renal injury and inflammation were evaluated by histology and ELISA. Renal tubular apoptosis, macrophages, and fibroblasts recruitment were determined by TUNEL assay, immunofluorescence, and western blot.

RESULTS

In response to CIH, TLR4 deficiency alleviated renal histological injury, renal dysfunction, and fibrosis. TLR4 deficiency ameliorated renal dysfunction (serum BUN and creatinine) and tubular endothelial apoptosis determined by immunofluorescence staining of CD31 and TUNEL, and western blot of apoptotic protein (caspase-3, c-caspase-3, and Bax/Bcl-2 ratio). Furthermore, we also found TLR4 deficiency abrogated CIH-induced macrophages (CD68) and fibroblasts (α-SMA) recruitment, further reducing expression of extra-cellular matrix protein (collagen I and collagen IV) and inflammatory cytokines release (IL-6, TNF-α, and MCP-1). Finally, we used immunohistochemistry to demonstrate that TLR4 deficiency attenuated increased expression of MyD88 and NF-kB p65 after CIH treatment.

CONCLUSIONS

Our data suggest that TLR4 plays a vital role in CIH-induced renal injury, inflammation and fibrosis, and inhibition of TLR4 probably provides a therapeutic potential for CIH-induced kidney damage.

NLRP3 inflammasome inhibition ameliorates tubulointerstitial injury in the remnant kidney model

Recent studies suggest that NLRP3 inflammasome activation is involved in the pathogenesis of chronic kidney disease (CKD). Allopurinol (ALLO) inhibits xanthine oxidase (XOD) activity, and, consequently, reduces the production of uric acid (UA) and reactive oxygen species (ROS), both of which can activate the NLRP3 pathway. Thus, ALLO can contribute to slow the progression of CKD. We investigated whether inhibition of XOD by ALLO reduces NLRP3 activation and renal injury in the 5/6 renal ablation (Nx) model. Adult male Munich-Wistar rats underwent Nx and were subdivided into the following two groups: Nx, receiving vehicle only, and Nx + ALLO, Nx rats given ALLO, 36 mg/Kg/day in drinking water. Rats undergoing sham operation were studied as controls (C). Sixty days after surgery, Nx rats exhibited marked albuminuria, creatinine retention, and hypertension, as well as glomerulosclerosis, tubular injury, and cortical interstitial expansion/inflammation/fibrosis. Such changes were accompanied by increased XOD activity and UA renal levels, associated with augmented heme oxigenase-1 and reduced superoxide dismutase-2 renal contents. Both the NF-κB and NLRP3 signaling pathways were activated in Nx. ALLO normalized both XOD activity and the parameters of oxidative stress. ALLO also attenuated hypertension and promoted selective tubulointerstitial protection, reducing urinary NGAL and cortical interstitial injury/inflammation. ALLO reduced renal NLRP3 activation, without interfering with the NF-κB pathway. These observations indicate that the tubulointerstitial antiinflammatory and antifibrotic effects of ALLO in the Nx model involve inhibition of the NLRP3 pathway, and reinforce the view that ALLO can contribute to arrest or slow the progression of CKD.

Nitrolipids in kidney physiology and disease

The kidneys are vital organs responsible for maintaining body fluid homeostasis within proper physiologic ranges. Kidney disease is an epidemic clinical problem causing significant morbidity and mortality, and current treatments are limited to renin-angiotensin system blockade or renal replacement therapy for the majority of affected individuals. There is a critical, unmet need for novel pharmacological agents to improve the outcome of patients with kidney disease. Nitro-oleic acid (NO2-OA) is an endogenously generated electrophilic compound with the capacity to modify thiols in proteins, altering their function. The most important targets appear to be the Keap1/Nrf2 and NF-κB pathways, which have widespread effects on antioxidant, detoxifying, and inflammatory responses in cells and tissues. Through these and potentially additional protective actions, NO2-OA may be capable of preserving or enhancing kidney function in acute and chronic kidney diseases.

Multiple Mechanisms are Involved in Salt-Sensitive Hypertension-Induced Renal Injury and Interstitial Fibrosis

Salt-sensitive hypertension (SSHT) leads to kidney interstitial fibrosis. However, the potential mechanisms leading to renal fibrosis have not been well investigated. In present study, Dahl salt-sensitive (DS) rats were divided into three groups: normal salt diet (DSN), high salt diet (DSH) and high salt diet treated with hydrochlorothiazide (HCTZ) (DSH + HCTZ). A significant increase in systolic blood pressure (SBP) was observed 3 weeks after initiating the high salt diet, and marked histological alterations were observed in DSH rats. DSH rats showed obvious podocyte injury, peritubular capillary (PTC) loss, macrophage infiltration, and changes in apoptosis and cell proliferation. Moreover, Wnt/β-catenin signaling was significantly activated in DSH rats. However, HCTZ administration attenuated these changes with decreased SBP. In addition, increased renal and urinary Wnt4 expression was detected with time in DSH rats and was closely correlated with histopathological alterations. Furthermore, these alterations were also confirmed by clinical study. In conclusion, the present study provides novel insight into the mechanisms related to PTC loss, macrophage infiltration and Wnt/β-catenin signaling in SSHT-induced renal injury and fibrosis. Therefore, multi-target therapeutic strategies may be the most effective in preventing these pathological processes. Moreover, urinary Wnt4 may be a noninvasive biomarker for monitoring renal injury after hypertension.

Renoprotective effect of a combination of garlic and telmisartan against ischemia/reperfusion-induced kidney injury in obese rats

Obesity enhances the frequency and severity of acute kidney injury (AKI). Telmisartan pre-treatment was used experimentally in the amelioration of ischemia/reperfusion (IR)-induced AKI. However, there is a lack of evidence regarding its beneficial effects on AKI in obese animals. The present study, therefore, aimed to explore the protective effects of garlic and/or telmisartan against renal damage induced by unilateral IR in obese rats. Meloxicam was used as a standard anti-inflammatory agent. Prophylactic oral administration of meloxicam (3 mg kg(-1)), garlic (500 mg kg(-1)) and/or telmisartan (5 and 10 mg kg(-1)) for 4 wk protected against renal function deterioration induced by IR in obese rats. Both doses of telmisartan significantly reduced serum total cholesterol and triacyglycerol levels as well as peri-renal adipocytes size and renal fibrosis. Renal nuclear factor-kappa B immunoreactivity, tumor necrosis factor-alpha content as well as interleukin-10, adiponectin receptor 1 and macrophages (M1, M2) polarization markers (CD11c, CD206) mRNA expressions were down-regulated in ischemic kidney tissues and white adipose tissues around them by all treatments. Moreover, garlic, telmisartan and their combinations significantly suppressed oxidative stress in renal ischemic tissues. Histological picture was also improved by these treatments. Interestingly, the combinations provided a greater protection than their monotherapy in a dose-dependent manner. We suppose that this combination may be a promising prophylactic regimen for managing AKI in case of obesity. Thus, future experimental and clinical large-scale studies are necessary.

Mycophenolate mofetil combined with prednisone for diffuse proliferative lupus nephritis: a histopathological study

Mycophenolate mofetil (MMF) is a potential new treatment for diffuse proliferative lupus nephritis. This study examines the clinical and histopathological effects, and potential mechanisms, of combination MMF/prednisone therapy in diffuse proliferative lupus nephritis. Nine patients with diffuse proliferative lupus nephritis confirmed by renal biopsy received MMF/prednisone for six months when repeat biopsies were performed. Clinical and histopathological parameters of activity and chronicity were studied. Collagens were detected by Sirus red staining; leucocyte phenotype, osteopontin (OPN), fibrinectin (FN), a-smooth muscle actin (a-SMA) and TGF-b1 were detected by immunohistochemistry. The changes of clinical and histopathologic parameters were assessed and compared to histopathologic indicators. Eight of the nine patients achieved clinical remission; renal function deteriorated in one. Histopathological activity indices reduced significantly (9.56 + 2.83 versus 5.22 + 1.86, P < 0.01); however, the chronicity indices did not change (3.56 + 1.42 versus 3.22 + 1.20). T-cell and monocyte/macrophage infiltration, OPN expression and the percentage of proliferative cells in both glomerulus and tubulo-interstitiumdecreased significantly. Other features of chronic lesions, except for glomerular collagen deposition, did not change. In conclusion, MMF/prednisone therapy was effective for our patients with proliferative lupus nephritis. The active inflammatory lesions could be ameliorated through reduction of lymphocyte and monocyte/macrophage infiltration, inhibition of cell proliferation and downregulation of adhesive molecules. However, the chronic fibrotic lesions could not be significantly reduced.

Wnt6 regulates epithelial cell differentiation and is dysregulated in renal fibrosis

Diabetic nephropathy is the most common microvascular complication of diabetes mellitus, manifesting as mesangial expansion, glomerular basement membrane thickening, glomerular sclerosis, and progressive tubulointerstitial fibrosis leading to end-stage renal disease. Here we describe the functional characterization of Wnt6, whose expression is progressively lost in diabetic nephropathy and animal models of acute tubular injury and renal fibrosis. We have shown prominent Wnt6 and frizzled 7 (FzD7) expression in the mesonephros of the developing mouse kidney, suggesting a role for Wnt6 in epithelialization. Importantly, TCF/Lef reporter activity is also prominent in the mesonephros. Analysis of Wnt family members in human renal biopsies identified differential expression of Wnt6, correlating with severity of the disease. In animal models of tubular injury and fibrosis, loss of Wnt6 was evident. Wnt6 signals through the canonical pathway in renal epithelial cells as evidenced by increased phosphorylation of GSK3β (Ser9), nuclear accumulation of β-catenin and increased TCF/Lef transcriptional activity. FzD7 was identified as a putative receptor of Wnt6. In vitro Wnt6 expression leads to de novo tubulogenesis in renal epithelial cells grown in three-dimensional culture. Importantly, Wnt6 rescued epithelial cell dedifferentiation in response to transforming growth factor-β (TGF-β); Wnt6 reversed TGF-β-mediated increases in vimentin and loss of epithelial phenotype. Wnt6 inhibited TGF-β-mediated p65-NF-κB nuclear translocation, highlighting cross talk between the two pathways. The critical role of NF-κB in the regulation of vimentin expression was confirmed in both p65(-/-) and IKKα/β(-/-) embryonic fibroblasts. We propose that Wnt6 is involved in epithelialization and loss of Wnt6 expression contributes to the pathogenesis of renal fibrosis.

Delivery of microRNA-146a with polyethylenimine nanoparticles inhibits renal fibrosis in vivo

Renal fibrosis is the final common pathway leading to end-stage renal disease. Although microRNA (miR) was recently shown to be involved in the development of renal fibrosis, few studies have focused on the effects on renal fibrosis of exogenous miR delivered in an in vivo therapeutic setting. The study reported here investigated the effects of miR-146a delivery using polyethylenimine nanoparticles (PEI-NPs) on renal fibrosis in vivo. PEI-NPs bearing miR-146 or control-miR (nitrogen/phosphate ratio: 6) were injected into the tail vein of a mouse model of renal fibrosis induced by unilateral ureteral obstruction. PEI-NPs bearing miR-146 significantly enhanced miR-146a expression in the obstructed kidney compared with the control group, while inhibiting the renal fibrosis area, expression of alpha-smooth muscle actin, and infiltration of F4/80-positive macrophages into the obstructed kidney. In addition, PEI-NPs bearing miR-146a inhibited the transforming growth factor beta 1–Smad and tumor necrosis factor receptor-associated factor 6–nuclear factor kappa B signaling pathways. Control-miR-PEI-NPs did not show any of these effects. These results suggest that the delivery of miR-146a attenuated renal fibrosis by inhibiting pro-fibrotic and inflammatory signaling pathways and that the delivery of appropriate miRs may be a therapeutic option for preventing renal fibrosis in vivo.

Biotin amelioration of nephrotoxicity in streptozotocin-induced diabetic mice

The current study was carried out to investigate the protective role of biotin in kidney injury and oxidative stress in diabetic mice type 1. Male Swiss albino mice were randomly divided into 3 groups. Control group received saline. Diabetes type 1 was induced in second and third groups by intraperitoneal injection of streptozotocin as a single dose (150 mg/kg). Second group remained as the untreated diabetic group and the third group received 15 mg/kg daily oral dose of biotin for 12 successive days. Biochemical results showed significant elevation in blood glucose and urea levels in both diabetic groups. Also, there is an increase in glomerular areas and decrease in glomerular cellularity in both diabetic groups. Histopathological results showed severe alterations in the untreated diabetic group represented by distorted glomeruli, inflammatory cells, and giant macrophages. In addition, there was an intense immune-reaction response toward acrolein indicator of oxidative damage. Upon biotin administration of diabetic mice, the above mentioned histopathological changes were reduced and also acroline reaction of oxidative damage was diminished. Our findings prove that biotin has a protective role against streptozotocin-induced oxidative damage in kidneys of laboratory mice.

Brazilian red propolis attenuates hypertension and renal damage in 5/6 renal ablation model

The pathogenic role of inflammation and oxidative stress in chronic kidney disease (CKD) is well known. Anti-inflammatories and antioxidant drugs has demonstrated significant renoprotection in experimental nephropathies. Moreover, the inclusion of natural antioxidants derived from food and herbal extracts (such as polyphenols, curcumin and lycopene) as an adjuvant therapy for slowing CKD progression has been largely tested. Brazilian propolis is a honeybee product, whose anti-inflammatory, antimicrobial and antioxidant effects have been widely shown in models of sepsis, cancer, skin irritation and liver fibrosis. Furthermore, previous studies demonstrated that this compound promotes vasodilation and reduces hypertension. However, potential renoprotective effects of propolis in CKD have never been investigated. The aim of this study was to evaluate the effects of a subtype of Brazilian propolis, the Red Propolis (RP), in the 5/6 renal ablation model (Nx). Adult male Wistar rats underwent Nx and were divided into untreated (Nx) and RP-treated (Nx+RP) groups, after 30 days of surgery; when rats already exhibited marked hypertension and proteinuria. Animals were observed for 90 days from the surgery day, when Nx+RP group showed significant reduction of hypertension, proteinuria, serum creatinine retention, glomerulosclerosis, renal macrophage infiltration and oxidative stress, compared to age-matched untreated Nx rats, which worsened progressively over time. In conclusion, RP treatment attenuated hypertension and structural renal damage in Nx model. Reduction of renal inflammation and oxidative stress could be a plausible mechanism to explain this renoprotection.

Macrophages promote renal fibrosis through direct and indirect mechanisms

There is a close spatial and temporal relationship between macrophage accumulation and active renal fibrosis in human and experimental kidney disease. Different subtypes of macrophages have been identified. Pro-inflammatory M1-type macrophages can cause acute tissue injury, whereas pro-fibrotic M2-type macrophages can drive the fibrotic response during ongoing tissue injury. Macrophages induce fibrosis through the recruitment, proliferation, and activation of fibroblasts. In addition, there is accumulating evidence that supports a direct fibrotic role for macrophages via transition into myofibroblasts in a process termed macrophage–myofibroblast transition (MMT). Co-expression of macrophage and myofibroblast antigens identifies the MMT process both in human and experimental fibrotic kidney disease. This co-expression identifies a bone marrow–derived monocyte/macrophage source for a substantial proportion of the myofibroblast population present during renal fibrosis. This postulated MMT pathway represents a new mechanism linking macrophage-rich acute inflammation with the progression to myofibroblast accumulation and renal fibrosis. Further studies are required to identify the molecular mechanisms regulating the MMT process, which macrophage populations can undergo MMT, and to define the functional contribution of MMT to active collagen deposition during renal fibrosis.

Injured kidney endothelium is only marginally repopulated by cells of extrarenal origin

The role of bone marrow marrow-derived cells after kidney endothelial injury is controversial. In this study, we investigated if and to what extent extrarenal cells incorporate into kidney endothelium after acute as well as during chronic endothelial injury. Fischer F-344 wt (wild type) rat kidney grafts were transplanted into R26- hPAP (human placental alkaline phosphatase) transgenic Fischer F-344 recipient rats to allow identification of extrarenal cells by specific antibody staining. A severe model of renal thrombotic microangiopathy was induced via graft perfusion with antiglomerular endothelial cell (GEN) antibody and resulted in eradication of 85% of the glomerular and 69% of the peritubular endothelium (GEN group). At week 4 after injury, renal endothelial healing as well as recovery of the kidney function was seen. Endothelial chimerism was evaluated by double staining for hPAP and endothelial markers RECA-1 or JG-12. Just 0.25% of the glomerular and 0.1% of the peritubular endothelium was recipient derived. In a second experiment, chronic endothelial injury was induced by combination of kidney transplantation with 5/6 nephrectomy (5/6 Nx group). After 14 wk, only 0.86% of the peritubular and 0.05% of the glomerular endothelium was of recipient origin. In summary, despite demonstration of extensive damage and loss as well as excellent regeneration, just a minority of extrarenal cells were incorporated into kidney endothelium in rat models of acute and chronic renal endothelial cell injury. Our results highlight that kidney endothelial regeneration after specific and severe injury is almost exclusively of renal origin.

Inhibitory effect of TGF-β1 on NO production in peritoneal macrophages from collagen-induced arthritis rats involving the LPS-TLR4 pathway

Transforming growth factor-β1 (TGF-β1) is critical in controlling inflammatory responses and the prevention of autoimmune diseases. Although the effect of TGF-β1 on macrophages from normal mice or rats has been established, little attention has been paid to its effect on disease conditions. In the present study, we investigated the regulatory effect, and possible mechanism, of TGF-β1 exposure on the secretion of nitric oxide (NO) in peritoneal macrophages (PMΦ) obtained from collagen-induced arthritis (CIA) rats. The CIA model was established by immunizing the emulsion of collagen type II and incomplete Freund's adjuvant (IFA) in Wistar rats. PMΦ were incubated with TGF-β1 (5 ng/ml) for 36 h and the supernatant, and cell mRNA and protein were collected. NO concentration was determined using an NO assay kit. The mRNA expression of inducible nitric oxide synthase (iNOS) and Toll-like receptor 4 (TLR4) was determined using reverse transcription-polymerase chain reaction (RT-PCR). The protein expression of iNOS was tested with western blot analysis. The expression of membrane TLR4 was determined by flow cytometry. We discovered that the secretion of NO from the PMΦ of CIA rats increased compared with normal rats. TGF-β1 significantly inhibited the production of NO in the PMΦ from CIA rats. iNOS mRNA and protein expression in the PMΦ from CIA rats may be suppressed by TGF-β1. TLR4 mRNA and protein expression in PMΦ from CIA rats were upregulated with LPS stimulation and treatment with TGF-β1 inhibited their expression. These results demonstrated that TGF-β1 inhibited lipopolysaccharide (LPS)-induced NO production in the PMΦ from CIA rats, which may be due to the inhibition of the LPS-TLR4 signaling pathway.

Seliciclib inhibits renal hypertrophy but not fibrosis in the rat following subtotal nephrectomy

BACKGROUND

5/6 subtotal nephrectomy (SNx) is a non-immune stimulus used to induce renal fibrosis. The ability of seliciclib, a cyclin-dependent kinase inhibitor, to reduce kidney hypertrophy and extracellular matrix (ECM) deposition has been examined in the SNx rat.

METHODS

Wistar rats were subjected to SNx under isoflurane anaesthesia. The acute effect of seliciclib 28 mg/kg (5 days) on compensatory renal growth (CRG), kidney protein and DNA was determined. In chronic studies albuminuria, hypertension and GFR were monitored. Ki67, apoptag and α-smooth muscle actin were determined by immunohistochemistry together with Masson's trichrome staining. The effect of a maximum non-hypotensive dose of seliciclib 28 mg/kg (8 weeks) was determined.

RESULTS

Acutely, the remnant kidney developed CRG. Seliciclib 28 mg/kg inhibited both CRG by 45% and increased kidney protein by 48% without affecting increased kidney DNA. Chronically, SNx rats developed albuminuria, hypertension, low GFR with increased tubulointerstitial cell proliferation, apoptosis, myofibroblast accumulation and enhanced ECM deposition. Seliciclib 28 mg/kg (8 weeks) had no effect on either renal function or renal pathology. Plasma concentrations of seliciclib exceeded 5 µM throughout the study.

CONCLUSIONS

Despite inhibition of early renal hypertrophy, a maximum non-hypotensive dose of seliciclib 28 mg/kg had no impact on the progression of kidney fibrosis in the SNx rat.

Proximal tubule angiotensin AT2 receptors mediate an anti-inflammatory response via interleukin-10: role in renoprotection in obese rats

The angiotensin type 2 receptor (AT2R) has been shown to lower inflammation in the kidney. However, the role of the anti-inflammatory cytokine interleukin (IL)-10 in AT2R-mediated attenuation of inflammation has not been elucidated. We hypothesized that AT2R activation is renoprotective by directly increasing the levels of anti-inflammatory cytokine IL-10 in the kidney via nitric oxide (NO) signaling. For in vitro studies, the human proximal tubule epithelial cell-line (human kidney-2 [HK-2]) was activated with lipopolysaccharide (10 μg/mL) and AT2R agonist C21 (1 μmol/L) for 24 hours, and media cytokine levels were assessed. Lipopolysaccharide modestly downregulated AT2R expression. Treatment with C21 lowered lipopolysaccharide-induced levels of both tumor necrosis factor-α and IL-6, but increased IL-10 levels. Treatment with neutralizing IL-10 antibody (1 μg/mL) or NO synthase inhibitor L-NAME (1 mmol/L) abolished this effect. For in vivo studies, prehypertensive obese Zucker rats and age-matched lean Zucker rats were treated for 2 weeks with C21 (300 μg/kg per day, IP) and AT2R antagonist (PD123319; 50 μg/kg per minute, SC infusion). Compared with lean Zucker rats, obese Zucker rats had higher levels of renal AT2R expression, tumor necrosis factor-α, and IL-6. C21 treatment decreased levels of tumor necrosis factor-α by 75% and IL-6 by 60%. Conversely, PD treatment lowered the renal IL-10 levels in obese Zucker rats by ≈60%. Renal morphometry revealed increased mesangial matrix expansion and glomerular macrophage infiltration, which was improved by C21 treatment in obese Zucker rats. Our findings suggest that proximal tubule AT2R activation is anti-inflammatory by increasing IL-10 production, which is largely NO dependent and thus offers renoprotection by preventing early inflammation-induced renal injury in obesity.

The antihypertensive actions of statins: modulation by salt intake

Hydroxy methyl glutaryl CoA inhibitors (statins) are the agents most frequently used to reduce elevated serum cholesterol. In addition to their cholesterol lowering effects, statins also have nonlipid lowering pleiotropic properties. These include reducing oxidative stress, renin-angiotensin and endothelin synthesis and activity, and improving nitric oxide (NO) synthesis and availability. Thus, one would predict that statins might be able to exert an antihypertensive effect. Experimental models bear out the blood pressure lowering effects but the data from clinical trials have been inconsistent perhaps due to inappropriate experimental designs, sample size, blood pressure measurement techniques etc. Moreover, although experimental models strongly suggest a role for salt intake in the potential antihypertensive responses to statins, available clinical trials fail to report salt intake in the studied populations. The statins' antihypertensive effects remain an unsettled hypothesis and calls for a large clinical trial at a wide range of doses and a controlled salt intake. Statins meanwhile remain as a excellent option to control high cholesterol and in tissue injury prevention.

Ischemia/reperfusion-induced renal failure in rats as a model for evaluating cell therapies

Chronic renal failure is a devastating disease that leads to a multitude of complications. Cell therapy has emerged as a potential treatment modality for renal failure. However, efficacy testing on systemic renal function has been challenging due to the limited availability of reliable models that are fully characterized. In this study, we investigated the possibility of using renal ischemia/reperfusion (I/R) injury as a viable model for testing cell therapies. We examined functional and pathological changes in rat kidneys that were exposed to different ischemia times. Male Lewis rats were divided into five groups. Renal failure was induced by clamping both renal pedicles for combinations of 60, 75, and 90 min, followed by reperfusion. Age-matched healthy rats served as controls. Blood was collected at regular intervals for serum chemistry, and kidneys were harvested at the same intervals for histomorphological assessment. Serum creatinine levels of the animals with I/R injury increased significantly after 3 days and returned to normal levels at 4 weeks. Histologically, kidney tissue showed progressive glomerular and tubular deterioration with varying degrees of fibrosis. Animals exposed to 75- and 90-min ischemia combination times consistently generated more severe injury than the 60-min ischemia period. However, these groups resulted in a high mortality rate. A model in which one kidney is exposed to a shorter ischemia time (60 or 90 min) resulted in sustained renal damage with a lower mortality rate. This study shows that kidneys exposed to I/R result in renal tissue damage as well as decreased renal function. This model can be used to study both the short-term and longer-term effects of kidney disease by varying the length of the ischemic time. In particular, the use of longer ischemic times (75 and 90 min) could be used to study new therapies for acute renal disease, whereas shorter ischemic times (60 min) could be used to study therapies for chronic renal insufficiency.

Upregulation of nestin in proximal tubules may participate in cell migration during renal repair

The characteristics of renal tubular progenitor/precursor cells and the role of renal tubule regeneration in the repair of remnant kidneys (RKs) after nephrectomy are not well known. In the present study of a murine model of subtotal nephrectomy, we used immunofluorescence (IF), immunoblot analysis, and in situ hybridization methods to demonstrate that nestin expression was transiently upregulated in tubule cells near the incision edges of RKs. The nestin-positive tubules were immature proximal tubules that colabeled with lotus tetragonolobus agglutinin but not with markers of mature tubules (aquaporin-1, Tamm-Horsfall protein, and aquaporin-2). In addition, many of the nestin-expressing tubule cells were actively proliferative cells, as indicated by colabeling with bromodeoxyuridine. Double-label IF and immunoblot analysis also showed that the upregulation of tubular nestin was associated with enhanced transforming growth factor-β1 (TGF-β1) expression in the incision edge of RKs but not α-smooth muscle actin, which is a marker of fibrosis. In cultured human kidney proximal tubule cells (HKC), immunoblot analysis indicated that TGF-β1 induced nestin expression and loss of E-cadherin expression, suggesting an association of nestin expression and cellular dedifferentiation. Knockdown of nestin expression by a short hairpin RNA-containing plasmid led to decreased migration of HKC cells that were induced by TGF-β1. Taken together, our results suggest that the tubule repair that occurs during the recovery process following nephrectomy may involve TGF-β1-induced nestin expression in immature renal proximal tubule cells and the promotion of renal cell migration.

Chronic VEGF blockade worsens glomerular injury in the remnant kidney model

VEGF inhibition can promote renal vascular and parenchymal injury, causing proteinuria, hypertension and thrombotic microangiopathy. The mechanisms underlying these side effects are unclear. We investigated the renal effects of the administration, during 45 days, of sunitinib (Su), a VEGF receptor inhibitor, to rats with 5/6 renal ablation (Nx). Adult male Munich-Wistar rats were distributed among groups S+V, sham-operated rats receiving vehicle only; S+Su, S rats given Su, 4 mg/kg/day; Nx+V, Nx rats receiving V; and Nx+Su, Nx rats receiving Su. Su caused no change in Group S. Seven and 45 days after renal ablation, renal cortical interstitium was expanded, in association with rarefaction of peritubular capillaries. Su did not worsen hypertension, proteinuria or interstitial expansion, nor did it affect capillary rarefaction, suggesting little angiogenic activity in this model. Nx animals exhibited glomerulosclerosis (GS), which was aggravated by Su. This effect could not be explained by podocyte damage, nor could it be ascribed to tuft hypertrophy or hyperplasia. GS may have derived from organization of capillary microthrombi, frequently observed in Group Nx+Su. Treatment with Su did not reduce the fractional glomerular endothelial area, suggesting functional rather than structural cell injury. Chronic VEGF inhibition has little effect on normal rats, but can affect glomerular endothelium when renal damage is already present.

Response gene to complement 32 is essential for fibroblast activation in renal fibrosis

Response gene to complement 32 (RGC-32) is a downstream target of transforming growth factor-β (TGF-β). TGF-β is known to play a pathogenic role in renal fibrosis. In this study, we investigated RGC-32 function in renal fibrosis following unilateral ureteral obstruction (UUO) in mice, a model of progressive tubulointerstitial fibrosis. RGC-32 is normally expressed only in blood vessels of mouse kidney. However, UUO induces RGC-32 expression in renal interstitial cells at the early stage of kidney injury, suggesting that RGC-32 is involved in interstitial fibroblast activation. Indeed, expression of smooth muscle α-actin (α-SMA), an indicator of fibroblast activation, is limited to the interstitial cells at the early stage, and became apparent later in both interstitial and tubular cells. RGC-32 knockdown by shRNA significantly inhibits UUO-induced renal structural damage, α-SMA expression and collagen deposition, suggesting that RGC-32 is essential for the onset of renal interstitial fibrosis. In vitro studies indicate that RGC-32 mediates TGF-β-induced fibroblast activation. Mechanistically, RGC-32 interacts with Smad3 and enhances Smad3 binding to the Smad binding element in α-SMA promoter as demonstrated by DNA affinity assay. In the chromatin setting, Smad3, but not Smad2, binds to α-SMA promoter in fibroblasts. RGC-32 appears to be essential for Smad3 interaction with the promoters of fibroblast activation-related genes in vivo. Functionally, RGC-32 is crucial for Smad3-mediated α-SMA promoter activity. Taken together, we identify RGC-32 as a novel fibrogenic factor contributing to the pathogenesis of renal fibrosis through fibroblast activation.

Nilotinib attenuates renal injury and prolongs survival in chronic kidney disease

The tyrosine kinase inhibitor imatinib is beneficial in experimental renal diseases, but the effect of the new tyrosine kinase inhibitor nilotinib on the progression of renal failure is unknown. We administered either nilotinib or vehicle to Sprague-Dawley rats beginning 2 weeks after 5/6 nephrectomy (Nx) or laparotomy and continuing for 8 weeks. Serum creatinine levels were significantly lower in the nilotinib group after 6 and 8 weeks of treatment. Furthermore, nilotinib-treated rats had less proteinuria, attenuated glomerulosclerosis and tubulointerstitial damage, and reduced macrophage infiltration into the tubulointerstitium. Treatment with nilotinib also significantly decreased renal cortical expression of profibrogenic genes, such as IL-1β and monocyte chemotactic protein-1, which correlated closely with the tubulointerstitial damage score and ED1-positive macrophages score. In addition, nilotinib treatment significantly prolonged survival. Taken together, these results suggest that nilotinib may limit the progression of chronic kidney disease.

Progression of glomerular and tubular disease in pediatrics

Chronic kidney disease may be stimulated by many different etiologies, but its progression involves a common, yet complex, series of events that lead to the replacement of normal tissue with scar. These events include altered physiology within the kidney leading to abnormal hemodynamics, chronic hypoxia, inflammation, cellular dysfunction, and activation of fibrogenic biochemical pathways. The end result is the replacement of normal structures with extracellular matrix. Treatments presently are focused on delaying or preventing such progression, and are largely nonspecific. In pediatrics, such therapy is complicated further by pathophysiological issues that render children a unique population.

Pkd2 dosage influences cellular repair responses following ischemia-reperfusion injury

Autosomal dominant polycystic kidney disease (ADPKD) results from mutations in either PKD1 or PKD2 and accounts for 10% of all patients on renal replacement therapy. The kidney disease phenotype is primarily characterized by cyst formation, but there are also prominent interstitial changes (inflammation, apoptosis, proliferation, and fibrosis). Using a model of unilateral ischemia-reperfusion injury, we tested the hypothesis that Pkd2 heterozygous kidneys are more sensitive to injury and that this could lead to interstitial inflammation and fibrosis. Baseline tubular proliferation in heterozygous kidneys was twofold higher than in wild-type kidneys. The magnitude and duration of tubular and interstitial proliferative responses was consistently greater in injured heterozygous compared with wild-type kidneys at all time points. Conversely, tubular p21 expression in heterozygotes was lower at baseline and following injury at all time points. Significantly more neutrophils and macrophages were detected in injured Pkd2 heterozygous kidneys at 2 days, correlating with increased expression of the cytokines interleukin (IL)-1beta and keratinocyte-derived chemokine and resulting in interstitial fibrosis at 28 days. We conclude that Pkd2 dosage influences both susceptibility and nature of the repair responses following injury. Polycystin-2 is therefore likely to play multiple roles in regulating tubular cell viability, repair, and remodeling in the mature kidney.

Connective tissue growth factor stimulates renal cortical myofibroblast-like cell proliferation and matrix protein production

Myofibroblasts primarily contribute to the pathogenesis of renal interstitial fibrosis by unregulated cell proliferation and synthesis of excessive amounts of extracellular matrix (ECM) proteins. We used cultured myofibroblast-like cells obtained by outgrowth from explants of rat kidney cortex to study the effects and relevant signaling pathway of connective tissue growth factor (CTGF) on cell proliferation and ECM production. Exogenous CTGF stimulated proliferation of myofibroblast-like cells in a dose- and time-dependent manner. CTGF also increased the secretion of fibronectin and collagen I protein in the supernatant medium. Nevertheless, CTGF did not affect matrix-degrading metalloproteinases-2 and -9 activities in supernatant medium measured by gelatin zymography. CTGF induced activation of extracellular signal-regulated protein kinase (ERK)1/2 mitogen-activated protein kinase pathway as early as 5 minutes. Inhibition of ERK1/2 activation with PD98059 completely blocked CTGF-induced cell proliferation as well as secretion of fibronectin and collagen I protein. The above results indicate that CTGF triggers cell proliferation and production of ECM proteins in cultured myofibroblast-like cells through the ERK1/2 mitogen-activated protein kinase pathway.

Effect of dominant negative transforming growth factor-beta receptor type II on cytotoxic activity of RAW 264.7, a murine macrophage cell line

Transforming growth factor-beta (TGF-beta) is a potent suppressor of the immune system. In the present study, we investigated the effect of TGF-beta resistance on a murine macrophage cell line, RAW 264.7, by overexpressing a dominant negative TGF-beta receptor type II (TbetaRIIDN) construct. As expected, TbetaRIIDN-expressing RAW cells, designated as RAW-TbetaRIIDN, were resistant to TGF-beta signaling. When these cells were cocultured with the murine renal cell carcinoma cell line, Renca, a dramatic increase in apoptosis of Renca cells was observed. Simultaneously, elevated levels of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-alpha) in association with IFN-gamma were detected in RAW-TbetaRIIDN cells. When the effects of TNF-alpha and iNOS were neutralized through the use of neutralizing antibody and N(G)-methyl-L-arginine, respectively, the enhanced cytotoxicity of TbetaRIIDN-RAW cells was partially reversed. Taken together, these results show that TGF-beta-resistant RAW 264.7 murine macrophage cells have increased cytotoxic activity that is in part mediated by iNOS and TNF-alpha.

Epithelial-mesenchymal transition (EMT) of renal tubular cells in canine glomerulonephritis

Tubulo-interstitial fibrosis in dogs may result from primary injury to the interstitium or develop secondary to other renal diseases. As in human renal pathology, tubular epithelial cells (TEC) are believed to actively participate in the mechanisms of renal fibrosis. In this study, we examined the changes in the tubular epithelial component in two specific canine diseases. Immunohistochemistry showed the expression of the epithelial marker cytokeratin, the smooth muscle marker alpha-SMA, the mesenchymal marker vimentin and PCNA in 20 dogs with membranous glomerulonephritis and membrano-proliferative glomerulonephritis. Results showed that the loss of the epithelial marker in TEC was directly correlated to the grade of tubulo-interstitial disease present and independent of the type of glomerulonephritis. Varying degrees of vimentin positivity were detected in tubular epithelium in areas of inflammation, and low numbers of scattered alpha-SMA-positive cells were also observed. Immunohistochemistry showed that epithelial tubular cells lose their cytokeratin staining characteristics and transdifferentiate into cells exhibiting key mesenchymal immunophenotypic feature of vimentin-positive staining in both diseases investigated. The integrity of the tubular basement membrane is likely to be fundamental in maintaining the epithelial phenotype of TEC. Animal models provide opportunities for investigating the pathogenesis of renal fibrosis in humans.

Transfer of lymphocytes from mice with renal ischemia can induce albuminuria in naive mice: a possible mechanism linking early injury and progressive renal disease?

Severe ischemia-reperfusion injury (IRI) predisposes to long-term impairment in kidney function both in patients and experimentally through unknown mechanisms. Given emerging evidence implicating lymphocytes in the pathogenesis of early injury to kidney, liver, and lung after IRI, we hypothesized that kidney IRI would potentially release or expose normally sequestered antigens that would lead to proliferation of antigen-recognizing lymphocytes. This, in turn, would directly participate in progressive kidney injury. To test this hypothesis, we purified splenic lymphocytes from C57BL/6 mice with severe renal IRI or sham operation 6 wk postischemia and transferred these cells to normal mice. Donor mice with IRI had significant fibrosis and cellular inflammation. The recipient mice were followed for 6 or 12 wk. Donor lymphocytes were found to traffic into recipient kidney. Twelve weeks after transfer, kidneys from mice which received IRI-primed lymphocytes exhibited significantly increased urinary albumin excretion compared with lymphocytes from sham mice. Splenic CD3+, CD4+, CD3+CD25+, and CD4+CD44+ counts were significantly increased in mice after lymphocyte transfer from IRI mice vs. mice with lymphocytes from sham mice. These data demonstrate that lymphocytes from IRI mice can traffic to recipient kidney and directly mediate albuminuria. These data identify a novel mechanism by which initial kidney injury predisposes to long-term dysfunction and identify lymphocytes as potential therapeutic targets for progressive renal diseases.

Correlations of tissue macrophages and cytoskeletal protein expression with renal fibrosis in patients with diabetes mellitus

BACKGROUND

In clinicopathological studies of cellular remodeling in the progression of diabetic nephropathy, it has not been well described whether tissue macrophage numbers and the expression of two cytoskeletal proteins--alpha-smooth muscle actin (alphaSMA) and vimentin--correlate with the disease severity.

METHODS

Renal biopsy specimens from 23 patients with noninsulin-dependent diabetes mellitus (NIDDM) were examined by immunoperoxidase methods for CD68+ macrophages and alphaSMA and vimentin staining in paraffin-embedded samples. alphaSMA staining was evaluated in mesangial and interstitial myofibroblastic cells, and vimentin staining was evaluated in podocytes and mesangial and tubular cells.

RESULTS

Glomerular macrophage numbers were not correlated with any clinicopathological scores. However, the interstitial macrophage score was significantly correlated with serum creatinine (sCr) and strongly correlated with the interstitial fibrosis score. Both alphaSMA and vimentin were detectable in the mesangium, without significant correlation with each other. A positive correlation was observed between mesangial alphaSMA and urinary (u-) protein levels. In contrast, an inverse correlation was observed between levels of mesangial vimentin and u-protein. Mesangial alphaSMA, but not vimentin, showed a significant correlation with glomerular sclerosis. Podocytic vimentin levels tended to decrease in patients with higher sCr levels. The severity of interstitial peritubular alphaSMA was correlated strongly with interstitial macrophage proliferation and significantly with the interstitial fibrosis score.

CONCLUSIONS

The expression of mesangial alphaSMA may play a role in the progression of glomerular damage, while, on the other hand, newly acquired mesangial vimentin seems to be attenuated by heavy proteinuria. In addition, it was suggested that peritubular alphaSMA-positive myofibroblastic cells, in collaboration with interstitial macrophages, contribute to the progression of interstitial fibrosis in diabetic nephropathy.

Chronic inhibition of nuclear factor-kappaB attenuates renal injury in the 5/6 renal ablation model

Recent studies indicated that the nuclear transcription factor, NF-kappaB, activates a number of proinflammatory genes in subjects with progressive nephropathies. We investigated whether NF-kappaB inhibition limits progressive renal injury in the 5/6 renal ablation model (Nx). Adult male Munich-Wistar rats were subdivided in four groups: S (n = 16), subjected to sham operation; S+PDTC (n = 18), sham-operated rats receiving the NF-kappaB inhibitor pyrrolidine-dithiocarbamate (PDTC; 60 mg x kg(-1) x day(-1)) in drinking water; Nx (n = 16), Nx rats receiving vehicle only; and Nx+PDTC (n = 19), Nx rats given PDTC as above. Thirty days after renal ablation, Nx rats exhibited systemic and glomerular hypertension. Only the former was attenuated by PDTC treatment. Sixty days after renal ablation, Nx rats exhibited marked hypertension, albuminuria and creatinine retention, as well as glomerulosclerosis and cortical interstitial expansion/inflammation. Immunohistochemical analysis of Nx rats showed renal interstitial infiltration by macrophages and by cells staining positively for ANG II and its receptor, AT(1). Glomerular and interstitial cells expressing the p65 subunit of the NF-kappaB system were also found. PDTC treatment attenuated renal injury and inflammation, as well as the density of cells staining positively for the p65 subunit. Activation of the NF-kappaB system plays an important role in the pathogenesis of renal injury in the Nx model. Inhibition of this system may represent a new strategy to prevent the progression of chronic kidney disease.

Partial depletion of macrophages by ED7 reduces renal injury in Adriamycin nephropathy

BACKGROUND

Because macrophages are considered to be possible effectors of disease in Adriamycin (ADR) nephrosis, we hypothesized that depletion of macrophages might protect against the initiation of renal injury. In the present study, a monoclonal antibody (ED7) directed against CD11b/CD18 integrin, which is expressed by macrophages, was used to investigate the pathogenetic effects of macrophages in ADR nephropathy.

METHODS

Male Wistar rats were treated with ED7 antibody, starting 1 day prior to ADR (7.5 mg/kg) treatment, or 7 days post-ADR when overt proteinuria was established.

RESULTS

Circulating ED7-positive cells were reduced by approximately 30% in rats with ADR nephrosis by the ED7 antibody, while the number of macrophages in the renal cortex of ADR rats was reduced by nearly 50% with the ED7 treatment, whether administered before or after ADR. Creatinine clearance was significantly ameliorated by ED7 when commenced pre-ADR (P < 0.05), but not when commenced post-ADR (P = NS) in comparison to untreated ADR rats. However, proteinuria was not alleviated by either ED7 treatment. Morphometric analysis showed less glomerular sclerosis when ED7 was commenced pre-ADR compared with ADR alone (P < 0.01), but not when commenced post-ADR (P = NS). Tubular atrophy was reduced by ED7 when it was commenced pre-ADR (tubular cell height and tubular diameter: P < 0.01 and P < 0.001, respectively), as was interstitial expansion (P < 0.01) compared with ADR alone. Cortical macrophage infiltration was reduced by 50% compared with ADR alone by the ED7 commenced before or after ADR. The number of cortical CD4+ T cells fell with ED7 starting pre-ADR, but not with the ED7 treatment commencing after ADR.

CONCLUSION

Partial macrophage depletion starting before but not after ADR protected both renal function and structure in this model of chronic proteinuric renal disease.

Polarized Light (400–2000 nm) and Non-ablative Laser (685 nm): A Description of the Wound Healing Process Using Immunohistochemical Analysis

OBJECTIVE

This study aimed to describe, through morphologic and cytochemical analysis, the healing process of wounds submitted (or not) to laser therapy (lambda685 nm) or polarized light (lambda400-2000 nm).

BACKGROUND DATA

There are many reports on different effects of several types of phototherapies on the treatment of distinct conditions, amongst them, on wound healing. Laser therapy and the use of polarized light are still controversial despite successive reports on their positive effects on several biological processes.

METHODS

Thirty male Wistar rats, approximately 4 months old, were used, and standardized excisional wounds were created on their dorsum. The wounds were irradiated in four equidistant points with laser light or illuminated with polarized light, both with doses of 20 or 40 J/cm2. Group 1 acted as untreated controls. Animals were irradiated every 48 h during 7 days, starting immediately after surgery, and were humanely killed on the 8th post-operative day. Specimens were taken and routinely processed and stained with H&E, and for descriptive analysis of myofibroblasts and collagen fibers, the specimens were imunnomarked by smooth muscle alpha-actin and picrosirius stain.

RESULTS

Control specimens showed the presence of ulceration, hyperemia, discrete edema, intense, and diffuse inflammation, collagen deposition was irregular, and myofibroblasts were seen parallel to the wound margins. Wounds treated by laser therapy with a dose of 20 J/cm2 showed mild hyperemia, inflammation varied from moderate to intense, the number of fibroblasts was large, and the distribution of collagen fibers was more regular. Increasing the dose to 40 J/cm2 evidenced exuberant neovascularization, severe hyperemia, moderate to severe inflammation, large collagen deposition, and fewer myofibroblasts. On subjects illuminated with polarized light with a dose of 20 J/cm2, mild to moderate hyperemia was detectable, and collagen matrix was expressive and unevenly distributed; a larger number of myofibroblasts was present and no re-epithelialization was seen. Increasing the dose resulted in mild to moderate hyperemia, no re-epithelialization was seen, edema was discrete, and inflammation was moderate.

CONCLUSION

The use of 685-nm laser light or polarized light with a dose of 20 J/cm2 resulted in increased collagen deposition and better organization on healing wounds, and the number of myofibroblast was increased when polarized light is used.

An extremely high dose of losartan affords superior renoprotection in the remnant model

BACKGROUND

Rats subjected to 5/6 renal ablation (NX) exhibit large renal amounts of angiotensin II (Ang II) and of its main receptor, AT-1R. At previously used doses, AT-1R blockers (ARB) offer only partial renal protection. A possible explanation for this limited effect is that these doses are insufficient to block most of the abnormally expressed AT-1R. We investigated whether extremely high doses of the ARB, losartan (L), offer better protection than conventional doses in the NX model.

METHODS

Thirty days after NX, tail-cuff pressure (TCP), albuminuria (U(alb)V, mg/day), glomerulosclerosis index (GSI), fractional interstitial area (%INT), and macrophage infiltration (MO) were evaluated in a separate group (NX(pre)). The remaining rats were then subdivided among 4 groups: NX+V, receiving vehicle; NX+L50, treated with L, at the "conventional" dose of 50 mg/kg/day; NX+L500, receiving L, 500 mg/kg/day; and NX+HH, receiving hydrochlorothiazide and hydralazine to lower blood pressure to a similar extent as in group L500.

RESULTS

After a month of treatment, blood pressure and renal vascular resistance were lowest in group L500. Glomerular pressure was lowered by a similar extent by L50 and L500, while GFR was similar among groups. U(alb)V, TCP, and renal injury were only partially reduced by L50 120 days after renal ablation. By contrast, L500 arrested renal inflammation and glomerular/interstitial injury at pretreatment levels, and promoted regression of hypertension and U(alb)V, causing no apparent untoward effects.

CONCLUSION

The renal protection afforded by ARB in NX is dose dependent. Maximal protection may require doses several fold higher than those currently employed.

Mast cell infiltration associated with tubulointerstitial fibrosis in chronic Aristolochic Acid Nephropathy

Aristolochic Acid Nephropathy (AAN) is regarded as a kind of toxic nephropathy caused by the formation of DNA- aristolochic acid adducts in renal parenchymal cells. However, the underlying mechanisms driving the progression of renal interstitial fibrosis in AAN still remains unclear. This study aims to elucidate the role of some immunological factors, especially mast cells (MCs), in the pathogenesis of AAN. Sixteen patients with AAN were enrolled in this study, including five acute and 11 chronic AAN. Monoclonal antibodies against human tryptase, alpha smooth muscle actin (alpha-SMA), and CD68 were applied on serial sections, which were further counterstained with Periodic Acid-Schiff. It was found that massive tryptase-positive MCs were observed in the fibrotic areas in chronic AAN, especially around thickened tubular basement membranes where myofibroblasts accumulated too. In contrast, MCs infiltrated to a less extent in acute AAN, and were barely found in normal control kidneys. In chronic AAN, the number of MCs in the tubulointerstitium was positively correlated with the degree of renal fibrosis (r=0.64, P <0.05), but not with serum creatinine levels. Meanwhile, the recruitment of MCs into the renal interstitium is accompanied with local proliferation of myofibroblasts. Macrophages were not abundant, neither in acute nor in chronic AAN. Our findings show for the first time that mast cell infiltration seems to be associated with the progression of fibrosis in the renal tubulointerstitium in chronic AAN.

Transforming growth factor-beta and Smad signalling in kidney diseases

Extensive studies have demonstrated that transforming growth factor-beta (TGF-beta) plays an important role in the progression of renal diseases. TGF-beta exerts its biological functions mainly through its downstream signalling molecules, Smad2 and Smad3. It is now clear that Smad3 is critical for TGF-beta's pro-fibrotic effect, whereas the functions of Smad2 in fibrosis in response to TGF-beta still need to be determined. Our recent studies have demonstrated that Smad signalling is also a critical pathway for renal fibrosis induced by other pro-fibrotic factors, such as angiotensin II and advanced glycation end products (AGE). These pro-fibrotic factors can activate Smads directly and independently of TGF-beta. They can also cause renal fibrosis via the ERK/p38 MAP kinase-Smad signalling cross-talk pathway. In contrast, blockade of Smad2/3 activation by overexpression of an inhibitory Smad7 prevents collagen matrix production induced by TGF-beta, angiotensin II, high glucose and AGE and attenuates renal fibrosis in various animal models including rat obstructive kidney, remnant kidney and diabetic kidney diseases. Results from these studies indicate that Smad signalling is a key and final common pathway of renal fibrosis. In addition, TGF-beta has anti-inflammatory and immune-regulatory properties. Our most recent studies demonstrated that TGF-beta transgenic mice are protected against renal inflammation in mouse obstructive and diabetic models. Upregulation of renal Smad7, thereby blocking NF.kappaB activation via induction of IkappaBalpha, is a central mechanism by which TGF-beta inhibits renal inflammation. In conclusion, TGF-beta signals through Smad2/3 to mediate renal fibrosis, whereas induction of Smad7 inhibits renal fibrosis and inflammation. Thus, targeting Smad signalling by overexpression of Smad7 may have great therapeutic potential for kidney diseases.

Intercellular adhesion molecule-1 deficiency is protective against nephropathy in type 2 diabetic db/db mice

Diabetic nephropathy is a leading cause of end-stage renal failure and is a growing concern given the increasing incidence of type 2 diabetes. Diabetic nephropathy is associated with progressive kidney macrophage accumulation and experimental studies suggest that intercellular adhesion molecule (ICAM)-1 facilitates kidney macrophage recruitment during type 1 diabetes. To ascertain the importance of ICAM-1 in promoting type 2 diabetic nephropathy, the development of renal injury in ICAM-1 intact and deficient db/db mice with equivalent hyperglycemia and obesity between ages 2 and 8 mo was examined and compared with results with normal db/+ mice. Increases in albuminuria (11-fold), glomerular leukocytes (10-fold), and interstitial leukocytes (three-fold) consisting of predominantly CD68+ macrophages were identified at 8 mo in diabetic db/db mice compared with nondiabetic db/+ mice. In comparison to db/db mice, ICAM-1-deficient db/db mice had marked reductions in albuminuria at 6 mo (77% downward arrow) and 8 mo (85% downward arrow). There was also a significant decrease in glomerular (63% downward arrow) and interstitial (83% downward arrow) leukocytes in ICAM-1-deficient db/db mice, which were associated with reduced glomerular hypertrophy and hypercellularity and tubular damage. The development of renal fibrosis (expression of TGF-beta1, collagen IV, and interstitial alpha-smooth muscle actin) was also strikingly attenuated in the ICAM-1-deficient db/db mice. Additional in vitro studies showed that macrophage activation by high glucose or advanced glycation end products could promote ICAM-1 expression on tubular cells and macrophage production of active TGF-beta1. Thus, ICAM-1 appears to be a critical promoter of nephropathy in mouse type 2 diabetes by facilitating kidney macrophage recruitment.

C5b-9 regulates peritubular myofibroblast accumulation in experimental focal segmental glomerulosclerosis

BACKGROUND

In human focal segmental glomerulosclerosis (FSGS), the tubulointerstitial deposition of the complement (C5b-9) membrane attack complex is correlated with interstitial myofibroblast accumulation and proteinuria. Here, we hypothesized that C5b-9 formation regulates renal myofibroblast accumulation in Adriamycin nephropathy.

METHODS

Adriamycin nephropathy was induced in complement C6-sufficient (C6+) and C6-deficient (C6-) piebold viral glaxo (PVG) rats. Groups of animals (N= 7 to 8 each) were examined on days 21 and 42. A group of C6+ animals, injected with vehicle, served as the control group.

RESULTS

C6+ and C6- rats with Adriamycin nephropathy had equivalent proteinuria. C5b-9 deposition was increased and present on the apical surface of proximal tubular epithelial cells (day 21 and 42) and peritubular region (day 42 only) in C6+ rats with Adriamycin nephropathy, and absent in C6- rats. Peritubular myofibroblast accumulation increased in a time-dependent manner in C6+ proteinuric rats (control 1.2 +/- 0.4; Adriamycin nephropathy day 21 11.0 +/- 0.7; Adriamycin nephropathy day 42 19.8 +/- 1.7 cells per high power field). In C6- rats this increase was blunted by 87% and 56% on days 21 and 42, respectively (P < 0.01), and was associated with reduced interstitial extracellular matrix (ECM) deposition. Tubulointerstitial injury, tubular vimentin and interstitial monocyte accumulation were also reduced in C6- rats with Adriamycin nephropathy on day 21, but not at day 42. In contrast, the increase in periglomerular myofibroblast accumulation and glomerulosclerosis in Adriamycin nephropathy were not altered by C6 deficiency.

CONCLUSION

These data suggest that glomerular ultrafiltration of complement components and the intratubular formation of C5b-9 is a specific promotor of peritubular myofibroblast accumulation in FSGS.

Multiple facets of macrophages in renal injury

Macrophage infiltration is a common feature of renal disease and their presence has been synonymous with tissue damage and progressive renal failure. More recently work has focused on the heterogeneity of macrophage activation and in particular their ability to curtail inflammation and restore normal function. This has led to the view that it is macrophage function rather than their number that is important in determining the outcome of inflammatory disease. This review will focus on the pathways that regulate macrophage infiltration and activation and how these could be manipulated to control renal inflammatory disease. In particular, the ability of specific cell surface receptors and intracellular signaling pathways to control macrophage activation and how macrophages can be genetically manipulated to develop properties that favor resolution over ongoing injury.

Cyclooxygenase-2 (COX-2) inhibition limits abnormal COX-2 expression and progressive injury in the remnant kidney

BACKGROUND

The pathogenesis of progressive nephropathies involves hemodynamic and inflammatory factors. In the 5/6 nephrectomy model, a selective increase of cyclooxygenase-2 (COX-2) expression was shown, whereas treatment with a nonsteroidal anti-inflammatory or a specific COX-2 inhibitor was renoprotective. We investigated in the 5/6 nephrectomy model (1) the renal distribution of COX-2; (2) the hemodynamic and cellular mechanisms by which chronic COX-2 inhibition prevents renal injury.

METHODS

After 5/6 nephrectomy, adult male Munich-Wistar rats were subdivided in two groups: 5/6 nephrectomy (N=20), receiving vehicle, and 5/6 nephrectomy + celecoxib (N=19), treated orally with the COX-2 inhibitor, celecoxib, 10 mg/kg/day. Untreated and treated (celecoxib) sham-operated rats were also studied. Renal hemodynamics were examined at 4 weeks, whereas renal morphologic/immunohistochemical studies were carried at 8 weeks.

RESULTS

At 4 weeks, 5/6 nephrectomy rats exhibited marked systemic and glomerular hypertension. Celecoxib attenuated both systemic and glomerular hypertension, without affecting glomerular filtration rate (GFR). At 8 weeks, glomerulosclerosis and interstitial expansion were evident in 5/6 nephrectomy rats, and markedly attenuated in 5/6 nephrectomy rats given celecoxib. In both sham-operated and 5/6 nephrectomy rats, COX-2 was expressed at the macula densa. The extent of COX-2 expression at the macula densa was nearly tripled by celecoxib, indicating the existence of a feedback mechanism. In 5/6 nephrectomy rats, COX-2 was also expressed in glomeruli, arterioles, and the cortical interstitium, mostly at inflamed or sclerosing areas. Celecoxib markedly attenuated renal injury, inflammation, and ectopic COX-2 expression in 5/6 nephrectomy rats.

CONCLUSION

Chronic COX-2 inhibition attenuated progressive nephropathy by reducing glomerular hypertension, renal inflammation, and ectopic COX-2 expression, indicating a complex contribution of COX-2 to progressive renal injury in 5/6 nephrectomy rats.

Advanced glycation end products induce tubular epithelial-myofibroblast transition through the RAGE-ERK1/2 MAP kinase signaling pathway

Advanced glycation end products (AGEs) have been shown to play a role in tubular epithelial-myofibroblast transdifferentiation (TEMT) in diabetic nephropathy, but the intracellular signaling pathway remains unknown. We report here that AGEs signal through the receptor for AGEs (RAGE) to induce TEMT, as determined by de novo expression of a mesenchymal marker (alpha-smooth muscle actin, alpha-SMA) and loss of epithelial marker (E-cadherin), directly through the MEK1-ERK1/2 MAP kinase pathway, which is TGF-beta independent. This is supported by the following findings: AGEs induced de novo alpha-SMA mRNA expression as early as 2 hours followed by a loss of E-cadherin before TGF-beta mRNA expression at 24 hours and occurred in the absence of TGF-beta and AGE-induced activation of ERK1/2 MAP kinase at 15 minutes and TEMT at 24 hours were completely blocked by a neutralizing RAGE antibody, a soluble RAGE receptor, an ERK1/2 MAP kinase inhibitor (PD98059), and DN-MEK1, but not by a neutralizing TGF-beta antibody. Thus, this study demonstrates that AGEs activate the RAGE-ERK1/2 MAP kinase pathway to mediate the early TEMT process. The findings from this study suggest that targeting the RAGE or the ERK MAP kinase pathway may provide new therapeutic strategies for diabetic nephropathy and shed new light on the pathogenesis of diabetic nephropathy.

Antifibrotic effect of the Chinese herbs, Astragalus mongholicus and Angelica sinensis, in a rat model of chronic puromycin aminonucleoside nephrosis

Nephrotic syndrome has long been treated in China with two herbs, Astragalus mongholicus and Angelica sinensis, which may have antifibrotic effects.

METHODS

Rats with chronic puromycin-induced nephrosis were treated with Astragalus and Angelica 3 mL/d (n = 7) or enalapril 10 mg/kg/d (n = 7). Normal control rats (n = 7) received saline rather than puromycin, and an untreated control group (n = 7) received puromycin but no treatment. After 12 weeks, stained sections of the glomerulus and tubulointerstitium were evaluated for injury. Immunohistochemistry staining measured extracellular matrix components, transforming growth factor-beta1 (TGFbeta1), osteopontin, ED-1-positive cells, and alpha-actin. TGFbeta1 mRNA was assessed by in situ hybridization. Renin, ACE activity, angiotensin, and aldosterone were measured by radioimmunoassay or colorimetry. In the untreated rats, chronic renal injury progressed to marked fibrosis at 12 weeks. Astragalus and Angelica significantly reduced deterioration of renal function and histologic damage. Expressions of type III and IV collagen, fibronectin, and laminin also decreased significantly. This anti-fibrotic effect was similar to that of enalapril. The herbs had no effect on the renin-angiotensin system but did reduce the number of ED-1-positive, and alpha-actin positive cells and expression of osteopontin compared to untreated controls. The combination of Astragalus and Angelica retarded the progression of renal fibrosis and deterioration of renal function with comparable effects of enalapril. These effects were not caused by blocking the intrarenal renin-angiotensin system, but associated with suppression of the overexpression of TGFbeta1 and osteopontin, reduction of infiltrating macrophages, and less activation of renal intrinsic cells [corrected].

Perturbed medullary tubulogenesis in neonatal rat exposed to renin-angiotensin system inhibition

BACKGROUND

Pharmacological interruption of the angiotensin II type-1 receptor (AT(1)) signalling during nephrogenesis in rats induces irreversible abnormalities in kidney morphology, comprising papillary atrophy and tubulointerstitial damage, which are characterized by tubular dilatation/atrophy and interstitial inflammation/fibrosis. This study determined the time course for development of tubular structural and inflammatory changes and possible cytokine production in the renal medulla of newborn rats exposed to angiotensin-converting enzyme (ACE) inhibition. Additionally, medullary expression of E-cadherin, a marker for tubular formation, was investigated in ACE-inhibited rats.

METHODS

Newborn rats were exposed (postnatal days 0-12) to ACE inhibitor enalapril and killed at days 1, 2, 4, 9 and 13. One kidney was used for morphological evaluation and the other for immunohistochemistry, using antibodies directed against monocytes/macrophages, T cells and E-cadherin on frozen sections. In a separate experiment, rats were treated for 9 days and had their kidneys processed for western immunoblot and immunohistochemistry, where antibodies directed against monocyte chemoattractant protein-1 (MCP-1) and tumour necrosis factor-alpha (TNF-alpha) were used on paraffin sections.

RESULTS

In renal medulla from enalapril-treated rats, volume fractions of tubular lumens and interstitium were increased from postnatal days 2 and 4, respectively, while that of tubular cells was decreased from 4 days of age. Concomitant loss and/or reduction in E-cadherin expression (from day 2) was observed in dilated medullary tubules of enalapril-treated rats. Furthermore, in the medulla of enalapril-treated rats, the increased number of ED2+ (resident macrophages) cells, followed by the increase in ED1+ (monocytes/macrophages) and CD4+ T cells, was observed at days 9 and 13, respectively. This was accompanied by increased medullary expression of TNF-alpha at day 9.

CONCLUSIONS

Neonatal ACE inhibition perturbs medullary tubulogenesis, as indicated by tubular dilatation and a lack of E-cadherin expression in these tubules. Macrophage/monocyte-mediated immune response is a secondary event, coincidentally associated with the up-regulation of TNF-alpha.