Tubules are the major site of M-CSF production in experimental kidney disease: correlation with local macrophage proliferation

Genetic variants of interferon-response factor 5 are associated with the incidence of chronic kidney disease: the D.E.S.I.R. study

Inflammation has been associated with renal diseases. The Interferon Regulatory Factor (IRF)-5 is a key transcription factor in the pro-inflammatory polarization of M1-like macrophages. GWAS have reported that the IRF5 locus is associated with autoimmune diseases and with the estimated glomerular filtration rate (eGFR). We study whether allelic variations in IRF5 are associated with the incidence of chronic kidney disease (CKD) in a general population. We genotyped eleven IRF5 SNPs in the French D.E.S.I.R. cohort from the general population (n = 4820). Associations of SNPs with baseline renal parameters were assessed. Data were analyzed for three endpoints during a 9-year follow-up, incidence of:at least stage 3 CKD, the KDIGO criterion "certain drop in eGFR", and incidence of micro/macro albuminuria. In the cross-sectional analysis, rs10954213 and rs10954214 were associated with eGFR and rs1874328 with urinary albumin/creatinine ratio (ACR). Rs3807306, rs11761199, rs78658945, rs1874328, rs10954213 and rs11770589 were associated with the incidence of stage 3 CKD in multi-adjusted models. Rs4731532, rs3807306, and rs11761199 were associated with the incidence of CKD defined by the KDIGO. Rs4731532, rs3807306, rs11761199 and rs79288514 were associated with the incidence of micro/macro albuminuria. Our results support the hypothesis of the importance of IRF5 mediated macrophage polarization in the etiology of CKD.

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.

Myeloid PFKFB3-mediated glycolysis promotes kidney fibrosis

Excessive renal fibrosis is a common pathology in progressive chronic kidney diseases. Inflammatory injury and aberrant repair processes contribute to the development of kidney fibrosis. Myeloid cells, particularly monocytes/macrophages, play a crucial role in kidney fibrosis by releasing their proinflammatory cytokines and extracellular matrix components such as collagen and fibronectin into the microenvironment of the injured kidney. Numerous signaling pathways have been identified in relation to these activities. However, the involvement of metabolic pathways in myeloid cell functions during the development of renal fibrosis remains understudied. In our study, we initially reanalyzed single-cell RNA sequencing data of renal myeloid cells from Dr. Denby's group and observed an increased gene expression in glycolytic pathway in myeloid cells that are critical for renal inflammation and fibrosis. To investigate the role of myeloid glycolysis in renal fibrosis, we utilized a model of unilateral ureteral obstruction in mice deficient of Pfkfb3, an activator of glycolysis, in myeloid cells (Pfkfb3 ΔMϕ ) and their wild type littermates (Pfkfb3 WT). We observed a significant reduction in fibrosis in the obstructive kidneys of Pfkfb3 ΔMϕ mice compared to Pfkfb3 WT mice. This was accompanied by a substantial decrease in macrophage infiltration, as well as a decrease of M1 and M2 macrophages and a suppression of macrophage to obtain myofibroblast phenotype in the obstructive kidneys of Pfkfb3 ΔMϕ mice. Mechanistic studies indicate that glycolytic metabolites stabilize HIF1α, leading to alterations in macrophage phenotype that contribute to renal fibrosis. In conclusion, our study implicates that targeting myeloid glycolysis represents a novel approach to inhibit renal fibrosis.

The contribution of the immune system to genitourinary fibrosis

Fibrotic diseases of the genitourinary tract are devastating and incompletely understood pathologies. These diseases include urethral and ureteral strictures, retroperitoneal fibrosis, and Peyronie's disease. They can contribute to obstructive uropathy and sexual dysfunction. Poor understanding of the pathophysiology of these diseases severely limits our ability to prevent and treat them. Genitourinary fibrotic diseases likely represent related pathologies that share common underlying mechanisms involving wound healing in response to injury. These diseases share the common feature of extracellular matrix abnormalities-such as collagen deposition, transforming growth factor-β accumulation, and dysregulation of collagen maturation-leading to abnormal tissue stiffness. Given the association of many of these diseases with autoimmunity, a systemic pro-inflammatory state likely contributes to their associated fibrogenesis. Herein, we explore the immunologic contribution to fibrogenesis in several fibrotic diseases of the genitourinary system. Better understanding how the immune system contributes to fibrosis in these diseases may improve prevention and therapeutic strategies and elucidate the functions of immunologic contributors to fibrosis in general.

The Role of Myeloid Cells in Acute Kidney Injury and Kidney Repair

AKI remains highly prevalent, yet no optimal therapy is available to prevent it or promote recovery after initial insult. Experimental studies have demonstrated that both innate and adaptive immune responses play a central role during AKI. In response to injury, myeloid cells are first recruited and activated on the basis of specific signals from the damaged microenvironment. The subsequent recruitment and activation state of the immune cells depends on the stage of injury and recovery, reflecting a dynamic and diverse spectrum of immunophenotypes. In this review, we highlight our current understanding of the mechanisms by which myeloid cells contribute to injury, repair, and fibrosis after AKI.

A therapeutic oxygen carrier isolated from Arenicola marina decreased P. gingivalis induced inflammation and tissue destruction

The control of inflammation and infection is crucial for periodontal wound healing and regeneration. M101, an oxygen carrier derived from Arenicola marina, was tested for its anti-inflammatory and anti-infectious potential based on its anti-oxidative and tissue oxygenation properties. In vitro, no cytotoxicity was observed in oral epithelial cells (EC) treated with M101. M101 (1 g/L) reduced significantly the gene expression of pro-inflammatory markers such as TNF-α, NF-κΒ and RANKL in P. gingivalis-LPS stimulated and P. gingivalis-infected EC. The proteome array revealed significant down-regulation of pro-inflammatory cytokines (IL-1β and IL-8) and chemokine ligands (RANTES and IP-10), and upregulation of pro-healing mediators (PDGF-BB, TGF-β1, IL-10, IL-2, IL-4, IL-11 and IL-15) and, extracellular and immune modulators (TIMP-2, M-CSF and ICAM-1). M101 significantly increased the gene expression of Resolvin-E1 receptor. Furthermore, M101 treatment reduced P. gingivalis biofilm growth over glass surface, observed with live/dead analysis and by decreased P. gingivalis 16 s rRNA expression (51.7%) (p < 0.05). In mice, M101 reduced the clinical abscess size (50.2%) in P. gingivalis-induced calvarial lesion concomitant with a decreased inflammatory score evaluated through histomorphometric analysis, thus, improving soft tissue and bone healing response. Therefore, M101 may be a novel therapeutic agent that could be beneficial in the management of P. gingivalis associated diseases.

Androgen-Influenced Polarization of Activin A-Producing Macrophages Accompanies Post-pyelonephritic Renal Scarring

Ascending bacterial pyelonephritis, a form of urinary tract infection (UTI) that can result in hospitalization, sepsis, and other complications, occurs in ~250,000 US patients annually; uropathogenic Escherichia coli (UPEC) cause a large majority of these infections. Although UTIs are primarily a disease of women, acute pyelonephritis in males is associated with increased mortality and morbidity, including renal scarring, and end-stage renal disease. Preclinical models of UTI have only recently allowed investigation of sex and sex-hormone effects on pathogenesis. We previously demonstrated that renal scarring after experimental UPEC pyelonephritis is augmented by androgen exposure; testosterone exposure increases both the severity of pyelonephritis and the degree of renal scarring in both male and female mice. Activin A is an important driver of scarring in non-infectious renal injury, as well as a mediator of macrophage polarization. In this work, we investigated how androgen exposure influences immune cell recruitment to the UPEC-infected kidney and how cell-specific activin A production affects post-pyelonephritic scar formation. Compared with vehicle-treated females, androgenized mice exhibited reduced bacterial clearance from the kidney, despite robust myeloid cell recruitment that continued to increase as infection progressed. Infected kidneys from androgenized mice harbored more alternatively activated (M2) macrophages than vehicle-treated mice, reflecting an earlier shift from a pro-inflammatory (M1) phenotype. Androgen exposure also led to a sharp increase in activin A-producing myeloid cells in the infected kidney, as well as decreased levels of follistatin (which normally antagonizes activin action). As a result, infection in androgenized mice featured prolonged polarization of macrophages toward a pro-fibrotic M2a phenotype, accompanied by an increase in M2a-associated cytokines. These data indicate that androgen enhancement of UTI severity and resulting scar formation is related to augmented local activin A production and corresponding promotion of M2a macrophage polarization.

ROCK Inhibition May Stop Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease and is strongly associated with cardiovascular mortality. Given the pandemic of obesity and diabetes, the elucidation of the molecular underpinnings of DKD and establishment of effective therapy are urgently required. Studies over the past decade have identified the activated renin-angiotensin system (RAS) and hemodynamic changes as important therapeutic targets. However, given the residual risk observed in patients treated with RAS inhibitors and/or sodium glucose co-transporter 2 inhibitors, the involvement of other molecular machinery is likely, and the elucidation of such pathways represents fertile ground for the development of novel strategies. Rho-kinase (ROCK) is a serine/threonine kinase that is under the control of small GTPase protein Rho. Many fundamental cellular processes, including migration, proliferation, and survival are orchestrated by ROCK through a mechanism involving cytoskeletal reorganization. From a pathological standpoint, several analyses provide compelling evidence supporting the hypothesis that ROCK is an important regulator of DKD that is highly pertinent to cardiovascular disease. In cell-based studies, ROCK is activated in response to a diverse array of external stimuli associated with diabetes, and renal ROCK activity is elevated in the context of type 1 and 2 diabetes. Experimental studies have demonstrated the efficacy of pharmacological or genetic inhibition of ROCK in the prevention of diabetes-related histological and functional abnormalities in the kidney. Through a bird’s eye view of ROCK in renal biology, the present review provides a conceptual framework that may be widely applicable to the pathological processes of multiple organs and illustrate novel therapeutic promise in diabetology.

The Impact of Versatile Macrophage Functions on Acute Kidney Injury and Its Outcomes

Acute kidney injury (AKI) is a common and devastating clinical condition with a high morbidity and mortality rate and is associated with a rapid decline of kidney function mostly resulting from the injury of proximal tubules. AKI is typically accompanied by inflammation and immune activation and involves macrophages (Mϕ) from the beginning: The inflamed kidney recruits “classically” activated (M1) Mϕ, which are initially poised to destroy potential pathogens, exacerbating inflammation. Of note, they soon turn into “alternatively” activated (M2) Mϕ and promote immunosuppression and tissue regeneration. Based on their roles in kidney recovery, there is a growing interest to use M2 Mϕ and Mϕ-modulating agents therapeutically against AKI. However, it is pertinent to note that the clinical translation of Mϕ-based therapies needs to be critically reviewed and questioned since Mϕ are functionally plastic with versatile roles in AKI and some Mϕ functions are detrimental to the kidney during AKI. In this review, we discuss the current state of knowledge on the biology of different Mϕ subtypes during AKI and, especially, on their role in AKI and assess the impact of versatile Mϕ functions on AKI based on the findings from translational AKI studies.

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.

Granulocyte macrophage-colony stimulating factor: A key modulator of renal mononuclear phagocyte plasticity

Macrophage-colony stimulating factor (M-CSF) and granulocyte macrophage-colony stimulating factor (GM-CSF) play key roles in the differentiation of macrophages and dendritic cells (DCs). We examined the effect of treatment with M-CSF-containing macrophage medium or GM-CSF-containing DC medium upon the phenotype of murine bone marrow-derived macrophages and DCs. Culture of macrophages for 5 days in DC medium reduced F4/80 expression and increased CD11c expression with cells effectively stimulating T cell proliferation in a mixed lymphocyte reaction. DC medium treatment of macrophages significantly reduced phagocytosis of both apoptotic cells and latex beads and strongly induced the expression of the chemokine receptor CCR7 known to be involved in DC trafficking to lymph nodes. Lysates of obstructed murine kidneys expressed both M-CSF and GM-CSF though M-CSF expression was dominant (M-CSF:GM-CSF ratio ∼30:1). However, combination treatment with both M-CSF and GM-CSF (ratio 30:1) indicated that small amounts of GM-CSF skewed macrophages towards a DC-like phenotype. To determine whether macrophage phenotype might be modulated in vivo we tracked CD45.1⁺ bone marrow-derived macrophages intravenously administered to CD45.2⁺ mice with unilateral ureteric obstruction. Flow cytometry of enzyme dissociated kidneys harvested 3 days later indicated CD11c and MHC Class II upregulation by adoptively transferred CD45.1⁺ cells with CD45.1⁺ cells evident in draining renal lymph nodes. Our data suggests that GM-CSF modulates mononuclear phagocyte plasticity, which likely promotes resolution of injury and healing in the injured kidney.

Molecular and genetic aspects of guanylyl cyclase natriuretic peptide receptor-A in regulation of blood pressure and renal function

Natriuretic peptides (NPs) exert diverse effects on several biological and physiological systems, such as kidney function, neural and endocrine signaling, energy metabolism, and cardiovascular function, playing pivotal roles in the regulation of blood pressure (BP) and cardiac and vascular homeostasis. NPs are collectively known as anti-hypertensive hormones and their main functions are directed toward eliciting natriuretic/diuretic, vasorelaxant, anti-proliferative, anti-inflammatory, and anti-hypertrophic effects, thereby, regulating the fluid volume, BP, and renal and cardiovascular conditions. Interactions of NPs with their cognate receptors display a central role in all aspects of cellular, biochemical, and molecular mechanisms that govern physiology and pathophysiology of BP and cardiovascular events. Among the NPs atrial and brain natriuretic peptides (ANP and BNP) activate guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) and initiate intracellular signaling. The genetic disruption of Npr1 (encoding GC-A/NPRA) in mice exhibits high BP and hypertensive heart disease that is seen in untreated hypertensive subjects, including high BP and heart failure. There has been a surge of interest in the NPs and their receptors and a wealth of information have emerged in the last four decades, including molecular structure, signaling mechanisms, altered phenotypic characterization of transgenic and gene-targeted animal models, and genetic analyses in humans. The major goal of the present review is to emphasize and summarize the critical findings and recent discoveries regarding the molecular and genetic regulation of NPs, physiological metabolic functions, and the signaling of receptor GC-A/NPRA with emphasis on the BP regulation and renal and cardiovascular disorders.

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.

ASK1 inhibitor treatment suppresses p38/JNK signalling with reduced kidney inflammation and fibrosis in rat crescentic glomerulonephritis

Activation of p38 mitogen‐activated protein kinase (MAPK) and c‐Jun amino terminal kinase (JNK) is prominent in human crescentic glomerulonephritis. p38 and JNK inhibitors suppress crescentic disease in animal models; however, the upstream mechanisms inducing activation of these kinases in crescentic glomerulonephritis are unknown. We investigated the hypothesis that apoptosis signal‐regulating kinase 1 (ASK1/MAP3K5) promote p38/JNK activation and renal injury in models of nephrotoxic serum nephritis (NTN); acute glomerular injury in SD rats, and crescentic disease in WKY rats. Treatment with the selective ASK1 inhibitor, GS‐444217 or vehicle began 1 hour before nephrotoxic serum injection and continued until animals were killed on day 1 (SD rats) or 14 (WKY rats). NTN resulted in phosphorylation (activation) of p38 and c‐Jun in both models which was substantially reduced by ASK1 inhibitor treatment. In SD rats, GS‐444217 prevented proteinuria and glomerular thrombosis with suppression of macrophage activation on day 1 NTN. In WKY rats, GS‐444217 reduced crescent formation, prevented renal impairment and reduced proteinuria on day 14 NTN. Macrophage activation, T‐cell infiltration and renal fibrosis were also reduced by GS‐444217. In conclusion, GS‐444217 treatment inhibited p38/JNK activation and development of renal injury in rat NTN. ASK1 inhibitors may have therapeutic potential in rapidly progressive glomerulonephritis.

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.

Progression of chronic kidney disease: too much cellular talk causes damage

Tubulointerstitial fibrosis, tubular atrophy, and peritubular capillary rarefaction are major hallmarks of chronic kidney disease. The tubulointerstitium consists of multiple cell components including tubular epithelial, mesenchymal (fibroblasts and pericytes), endothelial, and inflammatory cells. Crosstalk among these cell components is a key component in the pathogenesis of this complex disease. After severe or recurrent injury, the renal tubular epithelial cells undergo changes in structure and cell cycle that are accompanied by altered expression and production of cytokines. These cytokines contribute to the initiation of the fibrotic response by favoring activation of fibroblasts, recruitment of inflammatory cells, and loss of endothelial cells. This review focuses on how augmented growth factor and cytokine production induces epithelial crosstalk with cells in the interstitium to promote progressive tubulointerstitial fibrosis after renal injury.

ISN Forefronts Symposium 2015: The Diverse Function of Macrophages in Renal Disease

Experimental and human studies indicate that macrophages play a key role within the diseased kidney and represent a target for novel therapies. This brief review outlines the involvement and nature of macrophages in renal disease and highlights the phenotypic plasticity of these cells and their responsiveness to the renal microenvironment.

Proximal tubule-derived colony stimulating factor-1 mediates polarization of renal macrophages and dendritic cells, and recovery in acute kidney injury

Infiltrating cells play an important role in both the development of and recovery from acute kidney injury (AKI). Macrophages and renal dendritic cells are of particular interest because they can exhibit distinctly different functional phenotypes, broadly characterized as proinflammatory (M1) or tissue reparative (M2). Resident renal macrophages and dendritic cells participate in recovery from AKI in response to either ischemia/reperfusion or a model of selective proximal tubule injury induced by diphtheria toxin-induced apoptosis in transgenic mice expressing the human diphtheria toxin receptor on proximal tubule cells. Colony Stimulating Factor-1 (CSF-1) is an important factor mediating the recovery from AKI, and CSF-1 can stimulate macrophage and dendritic cell proliferation and polarization during the recovery phase of AKI. The kidney, and specifically the proximal tubule, is a major source of intrarenal CSF-1 production in response to AKI. We induced selective deletion of proximal tubule CSF-1 to determine its role in expansion and proliferation of renal macrophages and dendritic cells and in recovery from AKI. In both models of AKI, there was decreased M2 polarization, delayed functional and structural recovery and increased tubulointerstitial fibrosis. Thus, intrarenal CSF-1 is an important mediator of macrophage/dendritic cell polarization and recovery from AKI.

Evaluation of biomarkers for in vitro prediction of drug-induced nephrotoxicity: comparison of HK-2, immortalized human proximal tubule epithelial, and primary cultures of human proximal tubular cells

There has been intensive effort to identify in vivo biomarkers that can be used to monitor drug-induced kidney damage and identify injury before significant impairment occurs. Kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and human macrophage colony stimulating factor (M-CSF) have been validated as urinary and plasma clinical biomarkers predictive of acute and chronic kidney injury and disease. Similar validation of a high throughput in vitro assay predictive of nephrotoxicity could potentially be implemented early in drug discovery lead optimization to reduce attrition at later stages of drug development. To assess these known in vivo biomarkers for their potential for in vitro screening of drug-induced nephrotoxicity, we selected a panel of nephrotoxic agents and examined their effects on the overexpression of nephrotoxicity biomarkers in immortalized (HK-2) and primary (commercially available and freshly in-house produced) human renal proximal tubule epithelial cells. Traditional cytotoxicity was contrasted with expression levels of KIM-1, NGAL, and M-CSF assessed using ELISA and real-time quantitative reverse transcription PCR. Traditional cytotoxicity assays and biomarker assays using HK-2 cells were both unsuitable for prediction of nephrotoxicity. However, increases in protein levels of KIM-1 and NGAL in primary cells were well correlated with dose levels of known nephrotoxic compounds, with limited correlation seen in M-CSF protein and mRNA levels. These results suggest that profiling compounds against primary cells with monitoring of biomarker protein levels may have potential as in vitro predictive assays of drug-induced nephrotoxicity.

Rho-kinase regulation of TNF-α-induced nuclear translocation of NF-κB RelA/p65 and M-CSF expression via p38 MAPK in mesangial cells

The small GTPase Rho and its downstream effector, Rho-associated coiled-coil containing protein kinase (Rho-kinase), regulate a number of cellular processes, including organization of the actin cytoskeleton, cell adhesion, and migration. While pharmacological inhibitors of Rho-kinase signaling are known to block renal inflammation, the molecular basis for this effect is unclear. Here, we provide evidence that proinflammatory TNF-α promotes mesangial expression of macrophage colony-stimulating factor (M-CSF), a key regulator for the growth and differentiation of mononuclear phagocytes, in a Rho-kinase-dependent manner. Consistent with this observation, TNF-α-mediated renal expression of M-CSF in insulin-resistant db/db mice was downregulated by Rho-kinase inhibition. Small interfering RNA-facilitated knockdown of Rho-kinase isoforms ROCK1 and ROCK2 indicated that both isoforms make comparable contributions to regulation of M-CSF expression in mesangial cells. From a mechanistic standpoint, Western blotting and EMSA showed that Rho-kinase and its downstream target p38 MAPK regulate nuclear translocation of NF-κB RelA/p65 and subsequent DNA binding activity, with no significant effects on IκBα degradation and RelA/p65 phosphorylation. Moreover, we showed that Rho-kinase-mediated cytoskeletal organization is required for the nuclear uptake of RelA/p65. Collectively, these findings identify Rho-kinase as a critical regulator of chemokine expression and macrophage proliferation.

Toll-like receptor 4-induced IL-22 accelerates kidney regeneration

AKI involves early Toll-like receptor (TLR)-driven immunopathology, and resolution of inflammation is needed for rapid regeneration of injured tubule cells. Notably, activation of TLRs also has been implicated in epithelial repair. We hypothesized that TLR signaling drives tubule regeneration after acute injury through the induction of certain ILs. Systematic screening in vitro identified IL-22 as a candidate proregeneratory factor in primary tubular cell recovery, and IL-22 deficiency or IL-22 blockade impaired post-ischemic tubular recovery after AKI in mice. Interstitial mononuclear cells, such as dendritic cells and macrophages, were the predominant source of IL-22 secretion, whereas IL-22 receptor was expressed by tubular epithelial cells exclusively. Depleting IL-22-producing cells during the healing phase impaired epithelial recovery, which could be rescued entirely by reconstituting mice with IL-22. In vitro, necrotic tubular cells and oxidative stress induced IL-22 secretion selectively through TLR4. Although TLR4 blockade during the early injury phase prevented tubular necrosis and AKI, TLR4 blockade during the healing phase suppressed IL-22 production and impaired kidney regeneration. Taken together, these results suggest that necrotic cell-derived TLR4 agonists activate intrarenal mononuclear cells to secrete IL-22, which accelerates tubular regeneration and recovery in AKI.

Macrophages contribute to cellular but not humoral mechanisms of acute rejection in rat renal allografts

BACKGROUND

Cells of the monocyte/macrophage lineage have been implicated as effectors in acute allograft rejection based on short-term depletion studies. However, the therapeutic potential of targeting monocyte/macrophages in acute rejection is unknown. We investigated the potential of a c-fms kinase inhibitor (fms-I) in acute renal allograft rejection.

METHODS

Lewis rats underwent bilateral nephrectomy and received an orthotopic Dark Agouti renal allograft. Recipients received fms-I or vehicle from the time of transplantation until being killed on day 5.

RESULTS

Vehicle-treated rats developed severe allograft rejection with massive macrophage and T-cell infiltration. In contrast, fms-I substantially inhibited renal allograft dysfunction and structural damage with abrogation of macrophage and dendritic cell infiltration but had only a minor effect on the T-cell infiltrate. However, fms-I suppressed T-cell activation within the allograft, whereas systemic T- and B-cell activation was not affected. In a longer-term study to assess therapeutic potential, fms-I-treated rats developed severe antibody-mediated rejection on day 8 after transplantation. These transplants exhibited features of antibody-mediated rejection including capillaritis with thrombosis, acute tubular injury, IgG and C4d deposition, and neutrophil infiltration and activation. Interestingly, T-cell activation within these rejecting allografts remained suppressed, indicating separation of T-cell and antibody-mediated rejection.

CONCLUSION

This study demonstrates the ability of c-fms kinase blockade to selectively deplete monocyte/macrophages in acute allograft rejection, although this did not result in significant prolongation of allograft survival. Furthermore, we identify contrasting roles for macrophages in cellular and humoral mechanisms of acute renal allograft rejection.

Distinct responses of lung and liver macrophages to acute endotoxemia: role of toll-like receptor 4

Exposure to excessive quantities of bacterial-derived lipopolysaccharide (LPS) is associated with injury to the lung and the liver. Macrophages are thought to play a key role in the pathogenic response to LPS by releasing proinflammatory/cytotoxic mediators. Macrophage responses to LPS are mediated in large part by toll-like receptor 4 (TLR4). In the present studies we used C3H/HeJ mice, which possess a mutated nonfunctional TLR4, to examine its role in lung and liver macrophage responses to acute endotoxemia induced by LPS administration. Treatment of control C3H/HeOuJ mice with LPS (3 mg/ml, i.p.) was associated with a significant increase in the number of macrophages in both the lung and the liver. This was most prominent after 48 h, and was preceded by expression of proliferating cell nuclear antigen (PCNA), suggesting that macrophage proliferation contributes to the response. In liver, but not lung macrophages, LPS administration resulted in a rapid (within 3 h) increase in mRNA expression of Mn superoxide dismutase (SOD) and heme oxygenase-1 (HO-1), key enzymes in antioxidant defense. In contrast, HO-1 protein expression decreased 3 h after LPS administration in liver macrophages, while in lung macrophages it increased. mRNA expression of enzymes mediating the biosynthesis of eicosanoids, including cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase-1 (mPGES-1), but not 12/15-lipoxygenase (LOX), was upregulated in liver macrophages 3-24 h after LPS, with no effect on lung macrophages. However, COX-2 protein expression increased in both cell types. Loss of functional TLR4 significantly blunted the effects of LPS. Thus, no major changes were observed after LPS administration in the number of lung and liver macrophages recovered from TLR4 mutant mice, or on expression of PCNA. Increases in HO-1, MnSOD, COX-2 and PGES-1 mRNA expression in liver macrophages were also reduced in these mice. Conversely, in lung macrophages, loss of functional TLR4 resulted in increased expression of COX-2 protein and 12/15-LOX mRNA. These results demonstrate distinct lung and liver macrophage responses to acute endotoxemia are mediated, in part, by functional TLR4.

Differential macrophage programming in the tumor microenvironment

Of the multiple unique stromal cell types common to solid tumors, tumor-associated macrophages (TAMs) are significant for fostering tumor progression. The protumor properties of TAMs derive from regulation of angiogenic programming, production of soluble mediators that support proliferation, survival and invasion of malignant cells, and direct and indirect suppression of cytotoxic T cell activity. These varied activities are dependent on the polarization state of TAMs that is regulated in part by local concentrations of cytokines and chemokines, as well as varied interactions of TAMs with normal and degraded components of the extracellular matrix. Targeting molecular pathways regulating TAM polarization holds great promise for anticancer therapy.

Lupus nephritis: current update

Lupus nephritis is a major cause of morbidity and mortality in patients with systemic lupus erythematosus. The general consensus is that 60% of lupus patients will develop clinically relevant nephritis at some time in the course of their illness. Prompt recognition and treatment of renal disease is important, as early response to therapy is correlated with better outcome. The present review summarizes our current understanding of the pathogenic mechanisms underlying lupus nephritis and how the disease is currently diagnosed and treated.

c-fms blockade reverses glomerular macrophage infiltration and halts development of crescentic anti-GBM glomerulonephritis in the rat

Depletion and adoptive transfer studies have demonstrated that macrophages induce glomerular lesions in experimental anti-glomerular basement membrane (anti-GBM) glomerulonephritis. However, there is no current therapeutic strategy that can rapidly and selectively remove these cells from the glomerulus in order to halt disease development. This study examined whether inhibition of the receptor for macrophage colony-stimulating factor (known as c-fms), which is selectively expressed by monocyte/macrophages, can eliminate the macrophage infiltrate in a rat model of crescentic anti-GBM glomerulonephritis. Wistar-Kyoto rats were treated with 10 or 30 mg/kg bid of fms-I (a selective c-fms kinase inhibitor) from the time of anti-GBM serum injection until being killed 1, 5 or 14 days later. fms-I treatment had only a minor effect upon the glomerular macrophage infiltrate on day 1 and did not prevent the subsequent induction of proteinuria. However, fms-I treatment reduced the glomerular macrophage infiltrate by 60% at day 5 and completely reversed the macrophage infiltrate by day 14. In addition, fms-I treatment downregulated the glomerular expression of pro-inflammatory molecules (TNF-α, NOS2, MMP-12, CCL2 and IL-12) on days 1 and 5, suggesting a suppression of the macrophage M1-type response. Despite a significant early loss of glomerular podocytes, ongoing proteinuria and glomerular tuft adhesions to Bowman's capsule, the reversal of the macrophage infiltrate prevented the development of glomerulosclerosis, crescent formation, tubulointerstitial damage and renal dysfunction. In conclusion, this study has identified c-fms kinase inhibition as a selective approach to target infiltrating macrophages in acute glomerular injury, which may have therapeutic potential in rapidly progressive crescentic glomerulonephritis.

Macrophages in renal development, injury, and repair

Macrophages have long been regarded as classic mediators of innate immunity because of their production of proinflammatory cytokines and their ability to induce apoptotic cell death. As a result of such activities and the detrimental long-term effect of kidney inflammation, macrophages principally have been regarded as mediators of glomerular damage, tubular cell death, and the downstream fibrotic events leading to chronic kidney disease. Although this has been the accepted consequence of macrophage infiltration in kidney disease, macrophages also play a critical role in normal organ development, cell turnover, and recovery from injury in many organs, including the kidney. There is also a growing awareness that there is considerable heterogeneity of phenotype and function within the macrophage population and that a greater understanding of these different states of activation may result in the development of therapies specifically designed to capitalize on this variation in phenotype and cellular responses. In this review, we discuss the current understanding of induction and consequences of classic versus alternative macrophage activation and highlight what additional therapeutic options this may provide for the management of both acute and chronic kidney disease as well as renal cancer.

Macrophages and renal fibrosis

Renal fibrosis is a key determinant of the progression of renal disease irrespective of the original cause and thus can be regarded as a final common pathway that dictates eventual outcome. The development of renal fibrosis involves many cellular and molecular mediators including leukocytes, myofibroblasts, cytokines, and growth factors, as well as metalloproteinases and their endogenous inhibitors. Study of experimental and human renal disease has shown the involvement of macrophages in renal fibrosis resulting from diverse disease processes. Recent work exploring the nature of both circulating monocytes and tissue macrophages has highlighted their multifaceted phenotype and this impacts their role in renal fibrosis in vivo. In this review we outline the key players in the fibrotic response of the injured kidney and discuss the role of monocytes and macrophages in renal scarring.

Macrophage signaling pathways: a novel target in renal disease

Monocytes/macrophages are a heterogeneous cell population that play a critical role in host defense and tissue homeostasis. However, macrophage activation during acute and chronic inflammation can result in macrophage-mediated renal injury in a variety of settings, including proliferative glomerulonephritis. Macrophages can be activated via a number of intracellular signaling pathways (eg, c-Jun amino terminal kinase, p38 mitogen-activated protein kinase, FcR/Syk, Janus kinase/signal transducer and activator of transcription) that induce production of mediators of renal injury. Thus, targeting selected macrophage signaling pathways is a potential therapeutic strategy to suppress macrophage-mediated renal injury while leaving intact the desirable macrophage functions of host defense and tissue repair.

Targeted disruption of guanylyl cyclase-A/natriuretic peptide receptor-A gene provokes renal fibrosis and remodeling in null mutant mice: role of proinflammatory cytokines

Binding of atrial and brain natriuretic peptides to guanylyl cyclase-A/natriuretic peptide receptor-A produces second messenger cGMP, which plays an important role in maintaining renal and cardiovascular homeostasis. Mice carrying a targeted disruption of the Npr1 gene coding for guanylyl cyclase-A/natriuretic peptide receptor-A exhibit changes that are similar to those that occur in untreated human hypertension, including elevated blood pressure, cardiac hypertrophy, and congestive heart failure. The objective of this study was to determine whether disruption of the Npr1 gene in mice provokes kidney fibrosis, remodeling, and derangement. We found that systemic disruption of the Npr1 gene causes increased renal tubular damage characterized by dilation, flattening of epithelium, and expansion of interstitial spaces in Npr1(-/-) (0-copy) mice. Significant increases occurred in the expression levels of TNF-α (4-fold), IL-6 (4.5-fold), and TGF-β1 (2-fold) in 0-copy null mutant mice compared with 2-copy wild-type mice. An increased epithelial-to-mesenchymal transition indicated by increased expression of α-smooth muscle actin, was observed in Npr1(-/-) mouse kidneys. Treatment with captopril and losartan showed a 38 and 46% attenuation in fibrosis and 30 and 42% reduction in α-smooth muscle actin immunoexpression, respectively, in 1-copy and 0-copy mice compared with 2-copy mice. Although bendroflumethiazide treatment did not show any effect. The present results demonstrate that the disruption of Npr1 gene activates proinflammatory cytokines leading to fibrosis, hypertrophic growth, and remodeling of the kidneys of mutant mice.

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.

Preventive and therapeutic effects of imatinib in Wistar-Kyoto rats with anti-glomerular basement membrane glomerulonephritis

Imatinib is a selective tyrosine kinase inhibitor that can block activity of the platelet-derived growth factor receptor (PDGFR) and that has immunomodulatory effects on various cell types. Here we measured the protective effects of imatinib in Wistar-Kyoto rats with nephrotoxic serum nephritis, a kidney disease model where CD8+ T cells and macrophages play pathogenetic roles. Groups of animals were given imatinib from one day before up to 13 days following induction of nephritis and from day 7 to 20 following disease induction. Compared to control rats, at each time point imatinib treatment caused significantly less proteinuria, lowered serum blood urea nitrogen and creatinine, and decreased the number of glomeruli with necrosis, crescents, and fibrin deposits. Imatinib-treated rats had a significant reduction in glomerular macrophage accumulation and reduced renal cortical PDGFR-beta and M-CSF receptor mRNA expression. Using colocalization we found that glomerular macrophages had reduced IL-1beta and MCP-1 protein expression. Late imatinib treatment significantly reduced proteinuria, serum blood urea nitrogen, and creatinine, and reversed renal histopathological changes. We show that imatinib has renoprotective and therapeutic properties and provide pre-clinical work that will need to be confirmed in patients with crescentic glomerulonephritis.

Targeting renal macrophage accumulation via c-fms kinase reduces tubular apoptosis but fails to modify progressive fibrosis in the obstructed rat kidney

The role of macrophages in promoting interstitial fibrosis in the obstructed kidney is controversial. Macrophage depletion studies in the unilateral ureter obstruction (UUO) model have produced opposing results, presumably reflecting the subtleties of the individual depletion methods used. To address this question, we targeted the macrophage colony-stimulating factor receptor, c-fms, which is uniquely expressed by cells of the monocyte/macrophage lineage. Administration of 5, 12.5, or 30 mg/kg (bid) of a selective inhibitor of c-fms kinase activity (fms-I) resulted in a dose-dependent inhibition of renal macrophage accumulation in the rat UUO model. This was due to inhibition of local macrophage proliferation in the obstructed kidney and, at higher doses, to depletion of circulating blood monocytes. To determine the contribution of macrophages to renal pathology in the obstructed kidney, groups of animals were treated with 30 mg/kg fms-I and killed 3, 7, or 14 days later. Complete inhibition of renal macrophage accumulation prevented upregulation of the macrophage-associated proinflammatory mediators, tumor necrosis factor (TNF)-alpha and matrix metalloproteinase-12, and significantly reduced tubular apoptosis. Macrophage depletion caused a minor reduction of interstitial myofibroblast accumulation and deposition of interstitial collagen IV at day 3, but no difference was seen in renal fibrosis on day 7 or 14. Similarly, the upregulation of collagen IV, fibronectin, transforming growth factor-beta1 and connective tissue growth factor mRNA levels on day 7 and 14 in the obstructed kidney was unaffected by macrophage depletion. In conclusion, c-fms blockade was shown to selectively prevent interstitial macrophage accumulation and to reduce tubular apoptosis in the obstructed kidney, but it had no significant impact on the development of interstitial fibrosis.

Origin of renal myofibroblasts in the model of unilateral ureter obstruction in the rat

Tubulo-interstitial fibrosis is a constant feature of chronic renal failure and it is suspected to contribute importantly to the deterioration of renal function. In the fibrotic kidney there exists, besides normal fibroblasts, a large population of myofibroblasts, which are supposedly responsible for the increased production of intercellular matrix. It has been proposed that myofibroblasts in chronic renal failure originate from the transformation of tubular cells via epithelial–mesenchymal transition (EMT) or from infiltration by bone marrow-derived precursors. Little attention has been paid to the possibility of a transformation of resident fibroblasts into myofibroblasts in renal fibrosis. Therefore we examined the fate of resident fibroblasts in the initial phase of renal fibrosis in the classical model of unilateral ureter obstruction (UUO) in the rat. Rats were perfusion-fixed on days 1, 2, 3 and 4 after ligature of the right ureter. Starting from 1 day of UUO an increasing expression of alpha-smooth muscle actin (αSMA) in resident fibroblasts was revealed by immunofluorescence and confirmed by the observation of bundles of microfilaments and webs of intermediate filaments in the electron microscope. Inversely, there was a decreased expression of 5′-nucleotidase (5′NT), a marker of renal cortical fibroblasts. The RER became more voluminous, suggesting an increased synthesis of matrix. Intercellular junctions, a characteristic feature of myofibroblasts, became more frequent. The mitotic activity in fibroblasts was strongly increased. Renal tubules underwent severe regressive changes but the cells retained their epithelial characteristics and there was no sign of EMT. In conclusion, after ureter ligature, resident peritubular fibroblasts proliferated and they showed progressive alterations, suggesting a transformation in myofibroblasts. Thus the resident fibroblasts likely play a central role in fibrosis in that model.

Functional assessment of the kidney from magnetic resonance and computed tomography renography: impulse retention approach to a multicompartment model

A three-compartment model is proposed for analyzing magnetic resonance renography (MRR) and computed tomography renography (CTR) data to derive clinically useful parameters such as glomerular filtration rate (GFR) and renal plasma flow (RPF). The model fits the convolution of the measured input and the predefined impulse retention functions to the measured tissue curves. A MRR study of 10 patients showed that relative root mean square errors by the model were significantly lower than errors for a previously reported three-compartmental model (11.6% +/- 4.9 vs 15.5% +/- 4.1; P < 0.001). GFR estimates correlated well with reference values by (99m)Tc-DTPA scintigraphy (correlation coefficient r = 0.82), and for RPF, r = 0.80. Parameter-sensitivity analysis and Monte Carlo simulation indicated that model parameters could be reliably identified. When the model was applied to CTR in five pigs, expected increases in RPF and GFR due to acetylcholine were detected with greater consistency than with the previous model. These results support the reliability and validity of the new model in computing GFR, RPF, and renal mean transit times from MR and CT data.

Dendritic cells in the kidney

Dendritic cells (DC) in nonlymphoid organs function at the crossroads of innate and adaptive immunity, self-tolerance, and tissue homeostasis. This review provides an overview of the study of DC in the kidney, tracing its history leading to the current knowledge of the origins, migration, and function of renal DC. Together, these studies suggest that renal DC play a critical role in the health and disease of the kidney, opening the way to direct targeting of renal DC for therapeutic benefit.

Tubulointerstitial macrophage accumulation is regulated by sequentially expressed osteopontin and macrophage colony-stimulating factor: implication for the role of atorvastatin

Infiltration and local proliferation are known factors that contribute to tubulointerstitial macrophage accumulation. This study explored the time course of these two contributors' roles as tubulointerstitial inflammation and fibrosis progressing, and evaluated the mechanisms of the protective effect of atorvastatin. Unilateral ureteral obstructive (UUO) rats were treated with atorvastatin (10 mg/Kg) or vehicle. Expression of osteopontin (OPN) and macrophage colony-stimulating factor (M-CSF) was evaluated by RT-PCR and immunohistochemistry. Immunohistochemistry staining of ED1 was used to assess macrophage accumulation in interstitium. Histological evaluation was performed to semiquantify tubulointerstitial fibrosis. The results showed that on day 3 after UUO operation, OPN expression significantly increased and positively correlated with the number of the interstitial ED1⁺ cells, while on day 10, M-CSF expression upregulated and correlated with interstitial ED1⁺ cells. In atorvastatin treatment group, the increments of these two factors were attenuated significantly at the two time points, respectively. ED1⁺ cell accumulation and fibrosis also ameliorated in the treatment group. For all the samples of UUO and treatment group on day 10, ED1⁺ cells also correlated with interstitial fibrosis scores. The results suggest that OPN may induce the early macrophage/monocyte infiltration and M-CSF may play an important role in regulating macrophage accumulation in later stage of UUO nephropathy. Statin treatment decreases interstitial inflammation and fibrosis, and this renoprotective effect may be mediated by downregulating the expression of OPN and M-CSF.

Distinct In Vivo Roles of Colony-Stimulating Factor-1 Isoforms in Renal Inflammation

CSF-1, the major regulator of macrophage (Mphi) development, has three biologically active isoforms: a membrane-spanning, cell surface glycoprotein, a secreted glycoprotein, and a secreted proteoglycan. We hypothesized that there are shared and unique roles of individual CSF-1 isoforms during renal inflammation. To test this, we evaluated transgenic mice only expressing the cell surface or precursors of the secreted CSF-1 isoforms for Mphi accumulation, activation, and Mphi-mediated tubular epithelial cell (TEC) apoptosis during unilateral ureteral obstruction. The only difference between secreted proteoglycan and secreted glycoprotein CSF-1 isoforms is the presence (proteoglycan) or absence (glycoprotein) of an 18-kDa chondroitin sulfate glycosaminoglycan. We report that 1) cell surface CSF-1 isoform is sufficient to restore Mphi accumulation, activation, and TEC apoptosis to wild-type levels and is substantially more effective than the secreted CSF-1 isoforms; 2) the chondroitin sulfate glycosaminoglycan facilitates Mphi accumulation, activation, and TEC apoptosis; 3) increasing the level of secreted proteoglycan CSF-1 in serum amplifies renal inflammation; and 4) cell-cell contact is required for Mphi to up-regulate CSF-1-dependent expression of IFN-gamma. Taken together, we have identified central roles for the cell surface CSF-1 and the chondroitin sulfate chain on secreted proteoglycan CSF-1 during renal inflammation.

Leukocytes in tubulointerstitial inflammation

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

Evidence that inhibition of tubular cell apoptosis protects against renal damage and development of fibrosis following ureteric obstruction

Ureteric obstruction is frequently encountered in primary care urology and can lead to damage to the ipsilateral kidney. Relief of all types of obstruction generally leads to the normalization of any deterioration in renal function noted at diagnosis. However, some evidence from animal models suggests that obstruction can cause progressive deleterious effects on renal function and blood pressure control, especially in the presence of preexisting pathologies such as essential hypertension. The last 10 years have seen a proliferation of studies in rodents wherein complete unilateral ureteric obstruction has been used as a model of renal fibrosis. However, the relevance of the findings to human obstructive uropathy has, in many cases, not been the primary aim. In this review, we outline the major events linking damage to the renal parenchyma and cell death to the evolution of fibrosis following obstruction. Special focus is given to the role of apoptosis as a major cause of cell death during and post-complete ureteric obstruction. Several interventions that reduce tubular apoptosis are discussed in terms of their ability to prevent subsequent progression to end-organ damage and fibrosis.

Macrophages and progressive tubulointerstitial disease

Macrophages and progressive tubulointerstitial disease. In chronic renal disease, tubulointerstitial inflammation and injury is associated with infiltrating macrophages. As a consequence of primary injury, proteinuria, chronic hypoxia, and glomerular-derived cytokines may all differentially modulate the expression of factors that promote macrophage recruitment. In addition to adhesion molecules and chemokines, products of complement system and renin-angiotensin system activation may direct this process. Once present at interstitial sites, macrophages interact with resident cells and extracellular matrix to generate a proinflammatory microenvironment that amplifies tissues injury and promotes scarring. There is now increasing evidence for the efficacy of interventions directed against factors that recruit, activate, or are produced by macrophages. A detailed understanding of the biology of this area may lead to the further development of therapies that will improve the outcome of renal 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.

Macrophage accumulation and renal fibrosis are independent of macrophage migration inhibitory factor in mouse obstructive nephropathy

BACKGROUND AND AIM

The progression of renal injury, initiated by either an immune or non-immune insult, is closely associated with the accumulation of leucocytes and fibroblasts in the damaged kidney. Macrophage migration inhibitory factor (MIF) regulates leucocyte activation and fibroblast proliferation in vitro. Studies have identified a pathological role for MIF in immune-initiated renal injury in the rat. In this study, we examined the role of MIF in obstructive nephropathy, where renal injury is initiated by a non-immune insult.

METHODS AND RESULTS

Unilateral ureteric ligation was performed on MIF wildtype (+/+) and MIF deficient (-/-) mice. Groups of five mice were killed at days 0, 1, 5 or 10 after obstruction, and kidneys were examined via immunohistochemistry and northern blotting. In MIF +/+ mice, expression of the MIF protein increased in obstructed kidneys compared to normal control kidneys. Interstitial macrophage and T cell accumulation was significantly increased in obstructed kidneys at day 5 and 10, but was unaffected by MIF deficiency. Osteopontin and macrophage colony stimulating factor (M-CSF) mRNA expression in obstructed kidneys were equally increased in both genotypes, indicating that expression of these chemokines is not influenced by MIF. No difference was detected in the development of renal fibrosis in obstructed MIF +/+ and MIF -/- kidneys, as assessed by myofibroblast accumulation and proliferation and expression of profibrotic molecules (transforming growth factor-beta 1(TGF-beta1) and collagen).

CONCLUSION

These results demonstrate that MIF expression is increased in obstructive nephropathy without affecting kidney leucocyte accumulation or the development of renal fibrosis. This suggests that the progression of renal injury in obstructive nephropathy is independent of MIF.

Advanced glycation end-products and peritoneal sclerosis

Long-term continuous ambulatory peritoneal dialysis (CAPD) often causes peritoneal fibrosis and sclerosis with a loss of function, and some CAPD patients develop sclerosing encapsulating peritonitis. Glucose-based peritoneal dialysis fluids readily produce glucose degradation products by heat sterilization, and glucose degradation products accelerate the formation of advanced glycation end-products (AGE) in the peritoneal cavity. The accumulation of AGE is observed in peritoneal mesothelial and submesothelial layers in CAPD patients, accompanied by enhanced expression of various growth factors and peritoneal thickening. The expression of transforming growth factor-beta1 (TGF-beta1), macrophage-colony stimulating factor, and vascular endothelial growth factor (VEGF) is distributed in the peritoneum similarly to that of AGE. In CAPD patients with low ultrafiltration (UF) capacity, peritoneal membrane is thickened owing to an increase in the number of cells such as fibroblasts and macrophages and collagen in the submesothelial layer. AGE is detected in the fibroblasts and macrophages as well as degenerated collagen. These cells in the submucosal layer are almost positive for the receptor for AGE (RAGE) and uptake AGE. The intensity of AGE accumulation and the expression of growth factors are associated with the severity of UF impairment. In fact, the accumulation of AGE and the expression of growth factors are recognized most markedly in the peritoneum of CAPD patients with low UF and sclerosing encapsulating peritonitis. In conclusion, long-time CAPD with heat-sterilized peritoneal dialysis fluid promotes AGE accumulation in the peritoneal membrane and alteration in peritoneal cell function and dialysis quality, followed by peritoneal sclerosis, and, finally, sclerosing encapsulating peritonitis.

Serum levels of macrophage-colony stimulating factor (M-CSF): a marker of kidney allograft rejection

BACKGROUND

Macrophage-colony stimulating factor (M-CSF) is the principal factor for survival of monocytes and macrophages that play an important role in allograft rejection. We studied M-CSF serum levels during successful renal transplantation and acute graft rejection.

METHODS

A total of 114 kidney allograft recipients were assessed for M-CSF levels by enzyme-linked immunosorbent assay (ELISA).

RESULTS

M-CSF serum levels were elevated in pre-transplant haemodialysis patients (611+/-355 IU/ml vs 168+/-61 in normal controls, P<0.01). Following successful renal transplantation, M-CSF decreased in the first month, stabilizing at 257+/-222 IU/ml (not significantly different from normal controls) in 52 post-transplant stable patients. There was no correlation between M-CSF level and creatinine clearance. M-CSF levels increased significantly (2-5 times) during biopsy-proven acute rejection episodes in 20 of 25 patients. All rejection episodes were successfully treated and serum M-CSF decreased rapidly to pre-rejection levels in 17/20 patients. In contrast, in five patients with cyclosporin toxicity and four patients with other causes of allograft dysfunction, M-CSF serum levels did not change.

CONCLUSIONS

M-CSF serum level might be a specific marker of acute rejection. The source of increased production during rejection warrants further investigation, with infiltrating T cells and resident kidney cells being likely candidates.