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Masaomi Nangaku

Publications and source records attributed to Masaomi Nangaku.

At least 19 recordsLinked to original sources
PubMed2006

DAF/Crry double deficiency in mice exacerbates nephrotoxic serum-induced proteinuria despite markedly reduced systemic complement activity.

Decay-accelerating factor (DAF) and complement receptor 1-related gene/protein y (Crry) are two membrane-anchored complement regulatory proteins in rodent. Although both proteins are broadly distributed and exert complement regulation at the same steps of the complement cascade, DAF knockout mice are viable whereas Crry knockout mice die in utero as a result of maternal complement attack. The latter outcome has prevented the dissection of overlapping functions of DAF and Crry in adult mouse tissues in vivo. By crossing female DAF(-/-)/Crry(-/-)/C3(-/-) mice with male DAF(-/-)/Crry(+/-)/C3(+/-) mice, we circumvented maternal complement attack during fetal development and generated viable DAF(-/-)/Crry(-/-)/C3(+/-) mice to address the consequence of DAF/Crry double deficiency. DAF(-/-)/Crry(-/-)/C3(+/-) mice were born at the expected frequency and survived to adulthood. However, they were found to have greatly reduced systemic complement activity due, at least in part, to spontaneous C3 activation and consumption. Plasma C3 proteins in DAF(-/-)/Crry(-/-)/C3(+/-) mice were 30% of that of wild-type mice, and serum complement activity, as assessed by zymosan and immune complex C3 opsonization assays, was 90% reduced in DAF(-/-)/Crry(-/-)/C3(+/-) mice. Remarkably, despite greatly reduced systemic complement activity, DAF(-/-)/Crry(-/-)/C3(+/-) mice developed more severe proteinuria after induction of nephrotoxic serum nephritis as compared with DAF(-/-)/Crry(+/-)/C3(+/-) and DAF(-/-)/Crry(-/-)/C3(-/-) littermate controls. The results highlight the critical and overlapping role of Crry and DAF in vivo in preventing complement activation and tissue injury.

Animals↗
PubMed2006

High glucose blunts vascular endothelial growth factor response to hypoxia via the oxidative stress-regulated hypoxia-inducible factor/hypoxia-responsible element pathway.

Vascular endothelial growth factor (VEGF) is an important survival factor for endothelial cells in hypoxic environments. High glucose regulates certain aspects of VEGF expression in various cell types, including proximal tubular cells. Thus, ambient glucose levels may modulate the progression of chronic kidney disease, especially diabetic nephropathy. Immortalized rat proximal tubular cells (IRPTC) were cultured for 24 h under hypoxic conditions (1% O(2)), with or without high d-glucose (25 mM), or with or without high l-glucose (25 mM). Controls included culture in normoxic conditions and normal d-glucose (5.5 mM). VEGF mRNA expression was assessed by real-time quantitative PCR, and VEGF protein in the supernatant was assessed by ELISA. Hypoxia increased VEGF expression. This response was significantly blunted by high d-glucose (1.98 +/- 0.11- versus 2.65 +/- 0.27-fold increase for VEGF mRNA expression, 252.8 +/- 14.7 versus 324.0 +/- 11.5 pg/10(5) cells for VEGF protein; P < 0.05 both) but not by high l-glucose. It is interesting that hydrogen peroxide also blunted this response, whereas alpha-tocopherol restored the VEGF response to hypoxia in the presence of high d-glucose. For determination of involvement of the hypoxia-inducible factor (HIF)/hypoxia-responsible element (HRE) pathway, IRPTC that were stably transfected with HRE-luciferase were cultured under the previous conditions. High d-glucose also reduced luciferase activity under hypoxia, whereas alpha-tocopherol restored activity. In vivo experiments using streptozotocin-induced diabetic rats confirmed that hyperglycemia blunted HIF-HRE pathway activation. Insulin treatment restored activation of the HIF-HRE pathway in streptozotocin-induced diabetic rats. In conclusion, high glucose blunts VEGF response to hypoxia in IRPTC. This effect is mediated by the oxidative stress-regulated HIF-HRE pathway.

Animals↗
PubMed2006

Pathogenesis of renal anemia.

Anemia is a common complication of chronic kidney disease. Although mechanisms involved in the pathogenesis of renal anemia include chronic inflammation, iron deficiency, and shortened half-life of erythrocytes, the primary cause is deficiency of erythropoietin (EPO). Serum EPO levels in patients with chronic kidney disease are usually within the normal range and thus fail to show an appropriate increase with decreasing hemoglobin levels, as found in nonrenal anemias. Studies elucidating the regulation of EPO expression led to the identification of the hypoxia inducible factor-hypoxia responsive element system. However, despite much progress in understanding the molecular mechanisms through which cells can sense oxygen availability and translate this information into altered gene expression, the reason why EPO production is inappropriately low in diseased kidneys remains incompletely understood. Both alterations in the function of EPO-producing cells and perturbations of the oxygen-sensing mechanism in the kidney may contribute. As with other anemias, the consequences of renal anemia are a moderate decrease in tissue oxygen tensions and counterregulatory mechanisms that maintain total oxygen consumption, including a persistent increase in cardiac output.

Anemia↗
PubMed2006

Hypoxia and expression of hypoxia-inducible factor in the aging kidney.

Renal senescence is characterized by interstitial fibrosis and loss of peritubular capillaries. In this study, we provided evidence of tubulointerstitial hypoxia and the operation of hypoxia-inducible factor (HIF) in the aging kidney. Using two distinct methods, pimonidazole immunostaining and the expression of the "hypoxia-responsive" reporter of the transgenic rats, we identified the age-related expansion of hypoxia in all areas of the kidney. Expansion was most prominent in the cortex. Clusters of hypoxic tubules were observed in the superficial cortical zones, areas adjacent to the outer nephrons and expanded in the medullary rays. The degree of hypoxia was positively correlated with the age-related tubulointerstitial injury (R(2) = 0.88, p <.01), which was associated with the upregulation of HIF-regulated genes, such as vascular endothelial growth factor (VEGF) and glucose transporter-1 (GLUT1) (real-time polymerase chain reaction). These findings point to the involvement of hypoxia and highlight the pathological relevance of HIF and its target genes in the aging kidney.

Aging↗
PubMed2006

A severe diabetic nephropathy model with early development of nodule-like lesions induced by megsin overexpression in RAGE/iNOS transgenic mice.

Many factors are involved in the pathogenesis of diabetic nephropathy. A single gene abnormality may be prerequisite but insufficient to the disease to manifest. It is therefore only when a second or sometimes a third damage is associated that the consequences of pathogenic phenotypes become evident. We generated the triple transgenic mice overexpressing megsin (a novel glomerular-specific serpin), a receptor for advanced glycation end products (RAGE), and inducible nitric oxide synthase (iNOS). Compared with the single- or two-gene transgenic mice, the triple transgenic mice developed, at an early age (16 weeks), severe albuminuria and renal damage with all of the characteristics of human diabetic nephropathy (i.e., glomerular hypertrophy, diffuse mesangial expansion, inflammatory cell infiltration, and interstitial fibrosis). Interestingly, 30-40% of glomeruli exhibit nodule-like lesions. Oxidative and carbonyl stress makers (pentosidine, N(epsilon)-carboxymethyllysine, and 8-hydroxy-deoxyguanosine) were significantly higher in the triple transgenic mice. The iNOS transgenic mice have a diabetes phenotype, the renal consequences of which are moot, and the superimposition of RAGE leads to more conspicuous manifestations. By additional overexpression of megsin, a gene known to be involved in mesangial proliferation and expansion, these local consequences become dramatically manifest and approximate those observed in human pathology. This multiple hit approach is of interest in consideration of the sequential events during development of diabetic nephropathy.

Animals↗
PubMed2005

Chronic hypoxia and tubulointerstitial injury: a final common pathway to end-stage renal failure.

Recent studies emphasize the role of chronic hypoxia in the tubulointerstitium as a final common pathway to end-stage renal failure. When advanced, tubulointerstitial damage is associated with the loss of peritubular capillaries. Associated interstitial fibrosis impairs oxygen diffusion and supply to tubular and interstitial cells. Hypoxia of tubular cells leads to apoptosis or epithelial-mesenchymal transdifferentiation. This in turn exacerbates fibrosis of the kidney and subsequent chronic hypoxia, setting in train a vicious cycle whose end point is ESRD. A number of mechanisms that induce tubulointerstitial hypoxia at an early stage have been identified. Glomerular injury and vasoconstriction of efferent arterioles as a result of imbalances in vasoactive substances decrease postglomerular peritubular capillary blood flow. Angiotensin II not only constricts efferent arterioles but, via its induction of oxidative stress, also hampers the efficient utilization of oxygen in tubular cells. Relative hypoxia in the kidney also results from increased metabolic demand in tubular cells. Furthermore, renal anemia hinders oxygen delivery. These factors can affect the kidney before the appearance of significant pathologic changes in the vasculature and predispose the kidney to tubulointerstitial injury. Therapeutic approaches that target the chronic hypoxia should prove effective against a broad range of renal diseases. Current modalities include the improvement of anemia with erythropoietin, the preservation of peritubular capillary blood flow by blockade of the renin-angiotensin system, and the use of antioxidants. Recent studies have elucidated the mechanism of hypoxia-induced transcription, namely that prolyl hydroxylase regulates hypoxia-inducible factor. This has given hope for the development of novel therapeutic approaches against this final common pathway.

Anemia↗
PubMed2005

Renoprotective properties of angiotensin receptor blockers beyond blood pressure lowering.

Clinical studies have demonstrated that some antihypertensive agents provide renoprotection independent of BP lowering. Recent in vitro and in vivo studies evaluated the mechanisms involved in this protection. First, the in vitro effects of several angiotensin II type 1 receptor blockers (ARB), calcium channel blockers (CCB), and beta blockers (BB) on various mediators were compared: Formation of pentosidine (an advanced glycation end product), hydroxyl radical-induced formation of o-tyrosine, and transition metals-induced oxidation of ascorbic acid (the Fenton reaction). All of the six tested ARB but neither the six CCB nor the nine BB inhibited pentosidine formation. ARB, as well as BB but not CCB, inhibited hydroxyl radicals-mediated o-tyrosine formation. ARB but neither BB nor CCB inhibited efficiently transition metals-catalyzed oxidation of ascorbic acid. Second, the in vivo consequences for the kidney of these various in vitro effects were evaluated. Hypertensive, type 2 diabetic rats with nephropathy, SHR/NDmcr-cp, were given for 20 wk either olmesartan (ARB) or nifedipine (CCB), or atenolol (BB). Despite similar BP reduction, only ARB significantly reduced proteinuria and prevented glomerular and tubulointerstitial damage (mesangial activation, podocyte injury, tubulointerstitial injury, and inflammatory cell infiltration). It is interesting that only ARB prevented abnormal iron deposition in the interstitium, corrected chronic hypoxia, reduced expressions of heme oxygenase and p47phox (a subunit of NADPHoxidase), and inhibited pentosidine formation (which correlates well with proteinuria). These observations confirm unique renoprotective properties of ARB, independent of BP lowering but related to decreased oxidative stress (hydroxyl radicals scavenging and inhibition of the Fenton reaction), correction of chronic hypoxia, and inhibition of advanced glycation end product formation and of abnormal iron deposition. These benefits of ARB may contribute to the renoprotection observed beyond BP lowering.

Analysis of Variance↗
PubMed2005

Enhanced erythropoiesis mediated by activation of the renin-angiotensin system via angiotensin II type 1a receptor.

Although clinical and experimental studies have long suggested a role for the renin-angiotensin system (RAS) in the regulation of erythropoiesis, the molecular basis of this role has not been well understood. We report here that transgenic mice carrying both the human renin and human angiotensinogen genes displayed persistent erythrocytosis as well as hypertension. To identify the receptor molecule responsible for this phenotype, we introduced both transgenes into the AT1a receptor null background and found that the hematocrit level in the compound mice was restored to the normal level. Angiotensin II has been shown to influence erythropoiesis by two means, up-regulation of erythropoietin levels and direct stimulation of erythroid progenitor cells. Thus, we conducted bone marrow transplantation experiments and clarified that AT1a receptors on bone marrow-derived cells were dispensable for RAS-dependent erythrocytosis. Plasma erythropoietin levels and kidney erythropoietin mRNA expression in the double transgenic mice were significantly increased compared with those of the wild-type control, while the elevated plasma erythropoietin levels were significantly attenuated in the compound mice. These results provide clear genetic evidence that activated RAS enhances erythropoiesis through the AT1a receptor of kidney cells and that this effect is mediated by the elevation of plasma erythropoietin levels in vivo.

Angiotensin II↗
PubMed2005

In a type 2 diabetic nephropathy rat model, the improvement of obesity by a low calorie diet reduces oxidative/carbonyl stress and prevents diabetic nephropathy.

BACKGROUND: The present study has been undertaken to unravel the critical factors involved in the progression of diabetic nephropathy (DN). METHODS: A unique type 2 diabetic rat model with a wide range of metabolic derangements and hypertension has been utilized, the spontaneously hypertensive/NIH-corpulent rat SHR/NDmcr-cp(cp/cp). It develops histologically evident glomerular injury and tubulointerstitial damage, including mesangial activation, podocyte injury, and inflammatory cell infiltration in the tubulointerstitium. RESULTS: A low calorie diet for 22 weeks significantly improves obesity, proteinuria and renal morphological alterations. The correction of renal injury is independent of blood pressure control. Obesity correction, although partial, normalizes the renal content of pentosidine taken as a marker of oxidative stress and advanced glycation end products (AGEs). This occurs despite the fact that, in this model, improvement of glucose control and hyperlipidaemia is limited. Proteinuria and body weight are highly correlated with renal pentosidine content, while proteinuria and body weight are also correlated with each other. Diabetic renal injury is thus inhibited by a low calorie diet with an attendant reduction of oxidative stress and AGE formation, despite sustained hypertension. CONCLUSION: The present findings suggest a direct role of obesity in the generation of a localized oxidative stress and AGE formation, directly responsible for DN.

Animals↗
PubMed2005

Protection of endothelial cells by dextran sulfate in rats with thrombotic microangiopathy.

The characteristic features of thrombotic microangiopathy (TMA) include glomerular and peritubular capillary endothelial cell injury in association with loss of heparan sulfate proteoglycans on the cell surface and thrombus formation, followed by subsequent ischemic tubulointerstitial damage. It therefore was hypothesized that dextran sulfate (DXS) may protect the kidney against endothelial damage in a model of TMA. TMA was induced in rats by renal artery perfusion of an antiglomerular endothelial antibody, followed by the administration of DXS or vehicle. Renal damage was assessed by histologic analysis and measurements of blood urea nitrogen and creatinine. Whereas control rats developed severe renal failure with extensive glomerular and tubular injury, administration of DXS significantly protected renal function and preserved the glomerular endothelium and peritubular capillaries. The beneficial effect of DXS could be attributed to the ability of DXS to protect endothelial cells from coagulation and complement activation, as demonstrated by the histologic analysis. In addition, binding of the administered DXS to the surface of the glomerular endothelium was confirmed in TMA rats, suggesting that DXS acts as a "repair coat" of injured glomerular endothelium. In conclusion, DXS protects the kidney from experimental TMA. This protection may be mediated by DXS's binding directly to the surface of glomerular endothelium and amelioration of coagulation, complement activation, and cellular matrix loss.

Animals↗
PubMed2005

Hypoxia-inducible factor modulates tubular cell survival in cisplatin nephrotoxicity.

Hypoxia-inducible factor (HIF)-1 is a transcription factor mediating cellular response to hypoxia. Although it is expressed in tubular cells of the ischemic kidney, its functional role is not fully clarified in the pathological context. In this study, we investigated a role of HIF in tubular cell apoptosis induced by cisplatin. HIF-1alpha was expressed in tubular cells in the outer medulla 3 days after cisplatin (6 mg/kg) administration. With the in vivo administration of cobalt to activate HIF, the number of apoptotic renal tubular cells became much smaller in the outer medulla, compared with the vehicle group. We also examined the functional role of HIF-1 in vitro using immortalized rat proximal tubular cells (IRPTC). In hypoxia, IRPTC that express dominant-negative (dn) HIF-1alpha showed impaired survival in cisplatin injury at variable doses (25-100 microM, 24 h), which was not obvious in normoxia. The observed difference in cell viability in hypoxia was associated with the increased number of apoptotic cells in dnHIF-1alpha clones (Hoechst 33258 staining). Studies on intracellular signaling revealed that the degree of cytochrome c release, dissipation of mitochondrial membrane potentials, and caspase-9 activity were all more prominent in dnHIF-1alpha clones than in control IRPTC, pointing to the accelerated signaling of mitochondrial pathways. We propose that HIF-1 mediates cytoprotection against cisplatin injury in hypoxic renal tubular cells, by reducing the number of apoptotic cells through stabilization of mitochondrial membrane integrity and suppression of apoptosis signaling. A possibility was suggested that activation of HIF-1 could be a new promising therapeutic target for hypoxic renal diseases.

Animals↗
PubMed2005

Cellular response to injury in membranous nephropathy.

The pathogenesis of membranous nephropathy (MN) involves in situ formation of subepithelial immune deposits that produce glomerular injury by damaging and/or activating podocytes through complement-dependent processes. C5b-9 formation and insertion into podocyte cell membranes causes glomerular injury in MN. C5b-9 in sublytic quantities stimulates podocytes to produce proteases, oxidants, prostanoids, extracellular matrix components, and cytokines including TGF-beta. C5b-9 also causes alterations of the cytoskeleton that lead to abnormal distribution of slit diaphragm protein and detachment of viable podocytes that are shed into Bowman's space. These events result in disruption of the functional integrity of the glomerular basement membrane and the protein filtration barrier of podocytes with subsequent development of massive proteinuria. Complement components in proteinuric urine also induce tubular epithelial cell injury and mediate progressive interstitial disease in MN. Measurements of urinary C5b-9 or podocyte excretion in the urine may be useful in the diagnosis of MN and as measures of disease activity and response to therapy. Recent studies of cell-cycle proteins and DNA damage in podocytes have clarified why podocytes fail to proliferate in response to C5b-9-mediated injury and podocyte loss in MN, resulting in the development of glomerular sclerosis and renal failure. Improved understanding of the role of complement in the pathogenesis of MN and of the cellular response to C5b-9 attack creates several new opportunities for therapeutic intervention that may benefit patients with MN in the future.

Complement Membrane Attack Complex↗