Expression of monocyte chemoattractant protein-1 in proximal tubular epithelial cells in a rat model of progressive kidney failure

Impairment of kidney function in various types of glomerular disease is associated with tubulointerstitial changes. Monocyte chemoattractant protein-1 (MCP-1) is up-regulated in the tubulointerstitium and in the glomeruli in many human and experimental kidney disorders. We investigated the localization of MCP-1 expression in a rat model of progressive kidney failure. Male Wistar rats were subjected to subtotal nephrectomy (n = 30) or sham surgery (n = 30). Immunohistochemistry with immunoelectron microscopy and in situ hybridization were used to examine the expression of MCP-1 protein and messenger ribonucleic acid (mRNA) in the kidney, respectively. MCP-1 protein and mRNA were hardly detected in both glomeruli and tubulointerstitium of control rats. However, in the rats subjected to nephrectomy, MCP-1 expression was increased in the tubular cells of the remnant kidney, accompanied by significant macrophage infiltration. MCP-1 was observed mainly in the proximal tubular cells and only weakly in distal tubular cells. No significant expression of MCP-1 protein or mRNA was noted in the glomeruli. Immunoelectron microscopy showed the presence of MCP-1 in the rough endoplasmic reticulum of proximal tubular cells, confirming that MCP-1 is produced in proximal tubular cells. MCP-1 was also observed in endocytic vesicles adjacent to the brush border of proximal tubular cells, suggesting incorporation of MCP-1 from the tubular lumen. Our findings indicate localized expression of MCP-1 in proximal tubular cells in the remnant kidney and suggest that MCP-1 in proximal tubular cells is involved in tubulointerstitial damage in chronic kidney failure associated with glomerular hypertension.     

Immunopathology of renal disease

The reviewed information implicates immune mechanisms in a variety of renal glomerular and tubulointerstitial diseases. Antibodies reactive with intrinsic structural or planted endogenous or exogenous antigens, and with circulating endogenous or exogenous antigens can initiate inflammatory capillary injury by localization in glomerular capillary tufts or along tubular basement membranes. This results in activation of mediator systems, including complement, neutrophils and other leukocytes, amines, peptides, and proteases, which result in vascular and tissue alterations. In some instances, nonimmune activation of complement (for instance, by the properdin system) and other mediators of vascular injury may be involved. A role of cellularly mediated immunologic injury in glomerular disease is not clear and remains the subject of considerable current research. More clearly, there is involvement of lymphocytes in tubulointerstitial and interstitial diseases as well as allograft rejection reactions. A rich armamentarium of in-vitro immunologic tests for specific antibodies, immune-complexes, serum complement levels, and renal tissue analysis provides opportunity for enhanced precision of diagnosis and monitoring progress of disease or treatment. Unfortunately, at the present time, there are not many effective therapies specific for most renal glomerular diseases; perhaps in the future better identification of offending environmental or host antigens will result in more effective prevention and treatment. Application of knowledge concerning renal glomerular diseases to the study of hypersensitivity induced tubulointerstitial injury has resulted in increasing understanding of the pathogenesis of interstitial inflammatory disease of the kidney.     

Kidney VISTA prevents IFN-γ/IL-9 axis–mediated tubulointerstitial fibrosis after acute glomerular injury

Severe glomerular injury ultimately leads to tubulointerstitial fibrosis that determines patient outcome, but the immunological molecules connecting these processes remain undetermined. The present study addressed whether V-domain Ig suppressor of T cell activation (VISTA), constitutively expressed in kidney macrophages, plays a protective role in tubulointerstitial fibrotic transformation after acute antibody-mediated glomerulonephritis. After acute glomerular injury using nephrotoxic serum, tubules in the VISTA-deficient (Vsir–/–) kidney suffered more damage than those in WT kidneys. When interstitial immune cells were examined, the contact frequency of macrophages with infiltrated T cells increased and the immunometabolic features of T cells changed to showing high oxidative phosphorylation and fatty acid metabolism and overproduction of IFN-γ. The Vsir–/– parenchymal tissue cells responded to this altered milieu of interstitial immune cells as more IL-9 was produced, which augmented tubulointerstitial fibrosis. Blocking antibodies against IFN-γ and IL-9 protected the above pathological process in VISTA-depleted conditions. In human samples with acute glomerular injury (e.g., antineutrophil cytoplasmic autoantibody vasculitis), high VISTA expression in tubulointerstitial immune cells was associated with low tubulointerstitial fibrosis and good prognosis. Therefore, VISTA is a sentinel protein expressed in kidney macrophages that prevents tubulointerstitial fibrosis via the IFN-γ/IL-9 axis after acute antibody-mediated glomerular injury.     

Kidney dendritic cell activation is required for progression of renal disease in a mouse model of glomerular injury

The progression of kidney disease to renal failure correlates with infiltration of mononuclear immune cells into the tubulointerstitium. These infiltrates contain macrophages, DCs, and T cells, but the role of each cell type in disease progression is unclear. To investigate the underlying immune mechanisms, we generated transgenic mice that selectively expressed the model antigens ovalbumin and hen egg lysozyme in glomerular podocytes (NOH mice). Coinjection of ovalbumin-specific transgenic CD8⁺ CTLs and CD4⁺ Th cells into NOH mice resulted in periglomerular mononuclear infiltrates and inflammation of parietal epithelial cells, similar to lesions frequently observed in human chronic glomerulonephritis. Repetitive T cell injections aggravated infiltration and caused progression to structural and functional kidney damage after 4 weeks. Mechanistic analysis revealed that DCs in renal lymph nodes constitutively cross-presented ovalbumin and activated CTLs. These CTLs released further ovalbumin for CTL activation in the lymph nodes and for simultaneous presentation to Th cells by distinct DC subsets residing in the kidney tubulointerstitium. Crosstalk between tubulointerstitial DCs and Th cells resulted in intrarenal cytokine and chemokine production and in recruitment of more CTLs, monocyte-derived DCs, and macrophages. The importance of DCs was established by the fact that DC depletion rapidly resolved established kidney immunopathology. These findings demonstrate that glomerular antigen–specific CTLs and Th cells can jointly induce renal immunopathology and identify kidney DCs as a mechanistic link between glomerular injury and the progression of kidney disease.     

Mechanisms in remodeling of the kidney

Representative remodeling of the kidney in CKD includes development of glomerulosclerosis and tubulointerstitial fibrosis. Injury to glomerular endothelium, mesangium, or podocyte can induce glomerulosclerosis, although recent studies have focused on a role of podocytes due to its lack of proliferation. Development of tubulointerstitial fibrosis is multi-factorial, and includes proteinuria, chronic hypoxia, activation of the intra-renal renin-angiotensin system, imbalance of matrix production and protease activity, and epithelial-mesenchymal transdifferentiation. Optimal remodeling may induce restoration of normal kidney structure, and some potential candidates of resident renal stem cells have been proposed. Development of therapeutic approaches targeting final common pathways will open a new avenue in management of patients with CKD.     

Drug-induced renal failure: a focus on tubulointerstitial disease

Therapeutic agents induce acute renal failure (ARF) by promoting various types of injury to the kidney. Acute interstitial nephritis (AIN) develops from medications that incite an allergic reaction, leading to interstitial inflammation and tubular damage. Acute tubular necrosis (ATN) is a dose-dependent process that develops from direct toxicity on tubular epithelia, typically in the absence of inflammation. Additional, less common patterns of drug-induced renal injury include osmotic nephropathy, crystal nephropathy, and acute nephrocalcinosis. This review focuses on the multitude of patterns of drug-induced renal failure due to tubulointerstitial disease.     

Anti–microRNA-21 oligonucleotides prevent Alport nephropathy progression by stimulating metabolic pathways

MicroRNA-21 (miR-21) contributes to the pathogenesis of fibrogenic diseases in multiple organs, including the kidneys, potentially by silencing metabolic pathways that are critical for cellular ATP generation, ROS production, and inflammatory signaling. Here, we developed highly specific oligonucleotides that distribute to the kidney and inhibit miR-21 function when administered subcutaneously and evaluated the therapeutic potential of these anti–miR-21 oligonucleotides in chronic kidney disease. In a murine model of Alport nephropathy, miR-21 silencing did not produce any adverse effects and resulted in substantially milder kidney disease, with minimal albuminuria and dysfunction, compared with vehicle-treated mice. miR-21 silencing dramatically improved survival of Alport mice and reduced histological end points, including glomerulosclerosis, interstitial fibrosis, tubular injury, and inflammation. Anti–miR-21 enhanced PPARα/retinoid X receptor (PPARα/RXR) activity and downstream signaling pathways in glomerular, tubular, and interstitial cells. Moreover, miR-21 silencing enhanced mitochondrial function, which reduced mitochondrial ROS production and thus preserved tubular functions. Inhibition of miR-21 was protective against TGF-β–induced fibrogenesis and inflammation in glomerular and interstitial cells, likely as the result of enhanced PPARα/RXR activity and improved mitochondrial function. Together, these results demonstrate that inhibition of miR-21 represents a potential therapeutic strategy for chronic kidney diseases including Alport nephropathy.     

Electroporation-mediated HGF gene transfection protected the kidney against graft injury

The annual rate of kidney graft loss caused by chronic allograft nephropathy (CAN) has not improved over the past decade. Recent reports suggest that acute renal ischemia results in development of CAN. The goal of the present study was to assess the renoprotective potential and safety of hepatocyte growth factor (HGF) gene transfer using a porcine kidney transplant warm ischemia injury model. Following left porcine kidney removal, 10 min of warm ischemic injury was intentionally induced. Next, the HGF expression vector or vehicle was infused into the renal artery with the renal vein clamped ex vivo, and electric pulses were discharged using bathtub-type electrodes. Kidney grafts were then transplanted after removing the right kidney. Histopathological examination of vehicle-transfected kidney transplant revealed initial tubular injury followed by tubulointerstitial fibrosis. In contrast, HGF-transfected kidneys showed no initial tubular damage and no interstitial fibrosis at 6 months post-transplant. We conclude that electroporation-mediated ex vivo HGF gene transfection protects the kidney against graft injury in a porcine model.     

Mechanisms of tubulo-interstitiaI injury in progressive renal diseases

Abstract. A vast amount of evidence, based upon human renal biopsy material, indicates that the presence of tubular atrophy and interstitial fibrosis is a better indicator of outcome of renal function than is the extent of glomerular sclerosis. The pathophysiological basis for this surprising fact has not been adequately addressed. In this review we point out that the systemic hypertension which accompanies most forms of chronic renal disease could impact adversely upon the vasodilated interstitial vascular compartment which, together with a component of primary capillary injury related to the disease process, could cause progressive obliteration of particular capillaries. This would initiate a process of chronic tubular ischaemia ultimately leading to tubular atrophy. Since tubular cells have been shown to produce an array of cytokines and growth factors which modulate fibroblast proliferation, extracellular matrix production and chemo-attracts for infiltrating cells, it is further proposed that it is the tubular injury which initiates the deleterious cascade of events. Tubular injury may be aggravated by the filtration of potentially 'noxious' molecules through the diseased glomerulus and by infiltrating cells. As the vascular bed into which glomerular blood flow empties is progressively obliterated, glomerular function declines and renal failure advances in relation to the degree of tubulo-interstitial fibrosis.     

Uremic toxins overload accelerates renal damage in a rat model of chronic renal failure

Uremic toxins have been suggested to promote progression of chronic renal failure by damaging tubular cells. Previous in vitro studies have indicated that some uremic toxins induce oxidative stress and activate NF-kappaB to upregulate plasminogen activator inhibitor-1 in tubular cells. These mechanisms may promote tubulointerstitial fibrosis. The present study examined whether uremic toxins induce glomerular and tubulointerstitial damage in vivo. Two uremic toxins, hippuric acid (HA) or indoleacetic acid (IAA), were tested in two independent experiments (HA-treated rats vs. non-HA-treated controls, IAA-treated rats vs. non-IAA-treated controls). The uremic toxins were administered to subtotally nephrectomized rats. Renal functions were measured periodically and glomerular sclerosis and interstitial fibrosis were examined at the end of the experimental period (18 and 24 weeks, respectively, after subtotal nephrectomy for HA and IAA treatments). Glomerular filtration rate (inulin clearance) at the end of the study period was significantly lower in uremic toxin-treated rats than in control rats (HA-treated rats: 0.090 +/- 0.004 ml/min/100 g body weight vs. non-HA-treated controls: 0.125 +/- 0.013, IAA-treated rats: 0.068 +/- 0.006 versus non-IAA-treated controls: 0.100 +/- 0.013; both p < 0.05). Beta-N-acetyl-glucoseamidase excretion was significantly higher in uremic toxin-treated rats than in control rats (HA-treated: 0.55 +/- 0.05 U/day vs. control: 0.39 +/- 0.04 at week 18, IAA-treated: 0.35 +/- 0.02 vs. control: 0.26 +/- 0.07 at week 16; both p < 0.05). Glomerular sclerosis index was significantly higher in uremic toxin-treated rats than in control rats (HA-treated: 0.85 +/- 0.16 versus control: 0.48 +/- 0.10, IAA-treated: 1.13 +/- 0.25 vs. control: 0.57 +/- 0.10; both p < 0.05). Significant enlargement of interstitial fibrosis was observed in indoleacetic acid-treated rats. These results indicate that overload of uremic toxins accelerates the loss of kidney function, glomerular sclerosis and tubulointerstitial injury in a rat model of chronic renal failure. The present study suggests the potential benefit of early intervention to remove various uremic toxins in delaying the onset of end-stage renal failure in patients with progressive renal disease.     

Hypoxia promotes fibrogenesis in vivo via HIF-1 stimulation of epithelial-to-mesenchymal transition

Hypoxia has been proposed as an important microenvironmental factor in the development of tissue fibrosis; however, the underlying mechanisms are not well defined. To examine the role of hypoxia-inducible factor-1 (HIF-1), a key mediator of cellular adaptation to hypoxia, in the development of fibrosis in mice, we inactivated Hif-1alpha in primary renal epithelial cells and in proximal tubules of kidneys subjected to unilateral ureteral obstruction (UUO) using Cre-loxP-mediated gene targeting. We found that Hif-1alpha enhanced epithelial-to-mesenchymal transition (EMT) in vitro and induced epithelial cell migration through upregulation of lysyl oxidase genes. Genetic ablation of epithelial Hif-1alpha inhibited the development of tubulointerstitial fibrosis in UUO kidneys, which was associated with decreased interstitial collagen deposition, decreased inflammatory cell infiltration, and a reduction in the number of fibroblast-specific protein-1-expressing (FSP-1-expressing) interstitial cells. Furthermore, we demonstrate that increased renal HIF-1alpha expression is associated with tubulointerstitial injury in patients with chronic kidney disease. Thus, we provide clinical and genetic evidence that activation of HIF-1 signaling in renal epithelial cells is associated with the development of chronic renal disease and may promote fibrogenesis by increasing expression of extracellular matrix-modifying factors and lysyl oxidase genes and by facilitating EMT.     

急性肾损伤后慢性肾脏病发病机制及其诊治进展

急性肾损伤后常出现肾小管间质纤维化等慢性肾脏病表现,甚至进展至终末期肾病,发病机制包括小管上皮细胞适应不良性修复、免疫炎症过度反应、毛细血管稀疏、氧化应激等。随着人们对急性肾损伤后慢性化转归机制的深入认识,近年来相关的干预新靶点和新策略相继问世,展示了人类攻克急性肾损伤预后不良的良好前景。     

Statin therapy in patients with chronic kidney disease: to use or not to use

Dyslipdemia is a common complication of chronic kidney disease (CKD) and contributes to high cardiovascular morbidity and mortality of CKD patients. Experimental studies have demonstrated that lipids induce glomerular and tubulointerstitial injury and that lipid-lowering treatments ameliorate renal injury. Therapy with statins not only has the potential to lower cardiovascular morbidity and mortality in patients with CKD but also to slow progression of renal disease. Whereas the guidelines for treatment of hyperlipidaemia in nonrenal patients are based on prospective, randomized, placebo-controlled mega-trials, such data are not available for CKD patients. This review outlines the limited information currently available on the effect of statins among patients with CKD and summarizes the ongoing randomized trials designed to address this question.     

Tamm-Horsfall protein in Balkan endemic nephropathy

It is suggested that Tamm-Horsfall protein, a specific renal glycoprotein, may be involved in the pathogenesis of some renal diseases. In cadmium nephropathy and Fanconi syndrome (primary tubular diseases of the kidney) an increased excretion rate of Tamm-Horsfall protein has been observed. Balkan endemic nephropathy is a chronic tubulointerstitial disease of unknown etiology, most probably a primary disease of the kidney tubules with secondary reaction of the interstitial tissue. Investigation of Tamm-Horsfall proteinuria in Balkan endemic nephropathy has shown that subjects living in the area where this condition is prevalent have a significantly higher Tamm-Horsfall protein /creatinine ratio than those living in the control area where the condition has not been observed. Differences in this ratio among diseased, suspect and subjects "at risk" were not observed, despite differences in their glomerular filtration rates. But excretion of Tamm-Horsfall protein per litre of glomerular filtrate was significantly different among diseased, suspect and subjects "at risk" and significantly higher compared to control subjects. a relatively significant correlation was obtained between Tamm-Horsfall protein excretion rate and glomerular filtration rate as measured by creatinine clearance in both control and subjects living in the area of Balkan endemic nephropathy. Determination of Tamm-Horsfall protein in urine together with determination of proteinuria by electrophoresis on cellulose acetate membranes as a screening procedure, and by SDS -electrophoresis in polyacrylamide gell may be useful laboratory tests in detecting this nephropathy.     

Development of experimental model of chronic pyelonephritis with Escherichia coli O75:K5:H-bearing Dr fimbriae: mutation in the dra region prevented tubulointerstitial nephritis.

Escherichia coli that express Dr fimbriae and related adhesins recognize the common receptor decay accelerating factor. E. coli strains that express adhesins of the Dr family were postulated to be associated with cystitis (30-50%), pregnancy-associated pyelonephritis (30%), and chronic diarrhea (50%). In this study, we investigated the hypothesis that E. coli renal interstitial binding mediated by the Dr adhesin may be important for the development of chronic pyelonephritis. An insertional dra mutant, E. coli DR14, of the clinical E. coli isolate IH11128 bearing Dr fimbriae, was constructed and used to characterize persistence of infection and interstitial tropism in an experimental model of ascending pyelonephritis. Quantitative cultures of kidney homogenates indicated that Dr hemagglutinin positive (Dr+) E. coli IH11128 established a 1-yr colonization of renal tissue. In the Dr hemagglutinin negative (Dr-) group, 50% of animals cleared infection within 20 wk and 100% between 32 to 52 wk. Dr+ E. coli colonized the renal interstitium. Significant histological changes corresponding to tubulointerstitial nephritis including interstitial inflammation, fibrosis, and tubular atrophy were found in the kidney tissue of the Dr+ but not the Dr- group. A substantial amount of fimbrial antigen was detected in the parenchymal regions affected by interstitial inflammation and fibrosis. The obtained results are consistent with the hypothesis that mutation within the dra region, affecting E. coli binding to tubular basement membranes, prevented renal interstitial tropism and the development of the changes characteristically seen in tubulointerstitial nephritis.     

Chronic tubulointerstitial nephritis and renal insufficiency associated with long-term "subtherapeutic" gentamicin

To determine whether long-term "subtherapeutic" concentrations of aminoglycoside produce chronic tubulointerstitial nephropathy, Fisher rats were given gentamicin, 20 mg/kg/day, for up to 6 months via indwelling osmotic infusion pumps. Studies included renal histology, autoradiographic quantitation of renal cell tritiated thymidine uptake, renal function and renal cortical gentamicin assay. Acute proximal tubular injury, without tubular necrosis, followed by recovery, occurred during the first month. Subsequently only mild, nonprogressive tubulointerstitial changes and a twofold increase in tubular cell turnover were observed. Inulin clearance fell more than 50% during the 6 months of treatment compared with 10% in age-matched controls. Serum creatinine and creatinine clearance overestimated glomerular filtration rate during treatment and did not distinguish treated animals from controls. During the month after 6 months of gentamicin, tubular microcystic changes and active tubulointerstitial nephritis developed, with a continued fall in inulin clearance. In summary, gentamicin, in "subtherapeutic" doses, produces mild chronic tubulointerstitial nephritis with progressive renal failure. Cessation of treatment is associated with microcystic and inflammatory changes, suggesting that the renal response to tubular injury can be dissociated from the amount of toxin in the renal cortex. Keeping serum aminoglycoside levels below accepted therapeutic range for 6 months did not preclude nephrotoxicity.     

Obesity in CKD

Metabolic syndrome, characterized by truncal obesity, hypertriglyceridemia, elevated blood pressure, and insulin resistance, is recognized increasingly as a major risk factor for kidney disease and also is a common feature of patients who are on dialysis. Obesity is considered a major generator of metabolic syndrome. Early in the course of obesity-initiated metabolic syndrome, structural and functional changes similar to diabetic kidney disease occur. Previous studies examined the histologic and functional changes that occur in the kidney in the early stages of obesity caused by a high-fat diet. They reported that a high-fat diet caused increased arterial pressure, hyperinsulinemia, activation of the renin-angiotensin system, glomerular hyperfiltration, and structural changes in the kidney that may be the precursors of more severe glomerular injury associated with prolonged obesity. Among several factors causing renal injury, Rho-kinase also plays an important role in the pathogenesis of obesity-related renal disease. We further propose that perinephric adipose tissues could be a source of inflammatory chemokines, which acts in concert with the renal Rho-kinase stimulated in situ to exacerbate renal inflammation. In this review, we note the mechanisms inducing chronic kidney disease (CKD) by obesity, especially the relation between insulin resistance and CKD.     

The Role of Toll-Like Receptor 2 in Inflammation and Fibrosis during Progressive Renal Injury

Tissue fibrosis and chronic inflammation are common causes of progressive organ damage, including progressive renal disease, leading to loss of physiological functions. Recently, it was shown that Toll-like receptor 2 (TLR2) is expressed in the kidney and activated by endogenous danger signals. The expression and function of TLR2 during renal fibrosis and chronic inflammation has however not yet been elucidated. Therefore, we studied TLR2 expression in human and murine progressive renal diseases and explored its role by inducing obstructive nephropathy in TLR2^−/− or TLR2^+/+ mice. We found that TLR2 is markedly upregulated on tubular and tubulointerstitial cells in patients with chronic renal injury. In mice with obstructive nephropathy, renal injury was associated with a marked upregulation and change in distribution of TLR2 and upregulation of murine TLR2 danger ligands Gp96, biglycan, and HMGB1. Notably, TLR2 enhanced inflammation as reflected by a significantly reduced influx of neutrophils and production of chemokines and TGF-β in kidneys of TLR2^−/− mice compared with TLR2^+/+ animals. Although, the obstructed kidneys of TLR2^−/− mice had less interstitial myofibroblasts in the later phase of obstructive nephropathy, tubular injury and renal matrix accumulation was similar in both mouse strains. Together, these data demonstrate that TLR2 can initiate renal inflammation during progressive renal injury and that the absence of TLR2 does not affect the development of chronic renal injury and fibrosis.     

整合素连接激酶和α-平滑肌肌动蛋白在肾间质纤维化动物模型中的表达及意义

摘要] 目的：探讨整合素连接激酶(ILK)和α-平滑肌肌动蛋白(α- SMA)在肾间质纤维化中的作用及意义。方法： 通过结扎单侧输尿管建立大鼠肾间质纤维化模型，随机分为假手术组、模型组和对照组，术后1、3、7、14d处死各组大鼠，取梗阻侧肾做HE、PAS及Masson染色，并用免疫组化方法检测ILK和α- SMA的表达；RT-PCR检测ILK的mRNA表达。结果：ILK主要表达于病变肾小管上皮细胞和一些肾间质细胞胞浆,并且随间质病变的加重,表达量增加,范围增大。 在正常组织中，α－SMA仅表达于血管壁。但在损害间质中，可见它表达于损害的肾小管上皮细胞和间质细胞,且随着损害程度的加重而增加。ILK、α- SMA 与间质纤维化程度呈正相关，其在间质中的表达量也成正相关。结论: 随着间质病变程度的加重, ILK、α－SMA的表达量明显增加，说明与肾间质纤维化的形成有密切关系。