Akihiro Shimizu

The Jikei University School of Medicine, Edo, Tōkyō, Japan

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Publications (5)25.97 Total impact

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    ABSTRACT: NFE2-related factor 2 (Nrf2) is a master regulatory transcription factor for antioxidant genes. Inhibition of its adaptor protein, Kelch-like ECH-associated protein 1 (Keap1), activates Nrf2. Podocyte injury triggers the progressive deterioration of glomerular damage toward glomerulosclerosis. We examined whether modulation of the Keap1-Nrf2 system has an impact on this process. Nrf2 null-mutant (KO) and Keap1 hypomorphic knockdown (KD) mice were crossed with NEP25 mice, in which podocyte-specific injury can be induced by an immunotoxin. Thiobarbituric acid reactive substances, 8-hydroxydeoxyguanosine and phosphorylated JNK were increased in the injured NEP25 kidney. Real-time PCR revealed that Keap1 KD upregulated Nrf2 target genes, including Gclc, Gclm, Gstp1, Gstp2 and Nqo1 in the glomerulus. However, podocyte injury did not upregulate these genes in Keap1 wild-type mice, nor did it further increase the expression of those genes in Keap1 KD mice. Three weeks after the induction of podocyte injury, glomerulosclerosis was considerably more attenuated in Keap1 KD mice than in control mice (median sclerosis index, 0.27 versus 3.03, on a 0-4 scale). Keap1 KD mice also showed considerably preserved nephrin staining (median index, 6.76 versus 0.91, on a 0-8 scale) and decreased glomeruli containing desmin-positive injured podocytes (median percentage, 24.5% versus 85.8%), along with a decrease in mRNAs for Fn1, Tgfb1, Col4a4 and Col1a2. Thus, podocyte injury cannot effectively activate Nrf2, but Nrf2 activation by Keap1 knockdown attenuates glomerulosclerosis. These results indicate that the Nrf2-Keap1 system is a promising drug target for the treatment of chronic kidney diseases.
    Nephrology Dialysis Transplantation 02/2014; · 3.37 Impact Factor
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    ABSTRACT: Recent studies have reported that podocytes are postnatally generated from progenitor cells localized in Bowman's capsule or in the bone marrow. In the present study, we investigated whether or not podocyte regeneration is important in the repair of injured glomeruli after mild podocyte injury in mice. Mild podocyte injury was induced in NEP25 mice (n = 8) by injecting an immunotoxin, LMB2 (0.625 ng/g body weight). Control mice, not injured by LMB2 injection (n = 7) was used as a comparison. Proliferating cells were labeled by continuous infusion of bromodeoxyuridine (BrdU). Podocytes, identified by nephrin, WT1 or podocin staining, that had incorporated BrdU were enumerated 4 weeks later. A total of 742 corpuscles were inspected in serial sections stained for BrdU and nephrin; 19% showed sclerosis. BrdU(+) cells were observed in both the glomeruli and Bowman's capsules, averaging 2.5 ± 3.1 in non-sclerotic corpuscles and 7.0 ± 5.8 in sclerotic corpuscles. Only one BrdU(+) cell was also positive for nephrin. Another cell, localized at a position consistent with its potential identification as a podocyte, was nephrin negative but had incorporated BrdU. WT1 staining similarly revealed that only two nuclei were doubly positive for BrdU and WT1. Additional 1676 corpuscles were inspected by double staining for BrdU and podocin; none were doubly positive. Podocytes are not replenished by proliferation of endogenous progenitor cells in mice with glomerular injury.
    Nephrology Dialysis Transplantation 12/2013; · 3.37 Impact Factor
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    ABSTRACT: Angiotensin II content in the kidney is much higher than in the plasma, and it increases more in kidney diseases through an uncertain mechanism. Because the kidney abundantly expresses angiotensinogen mRNA, transcriptional dysregulation of angiotensinogen within the kidney is one potential cause of increased renal angiotensin II in the setting of disease. Here, we observed that kidney-specific angiotensinogen knockout mice had levels of renal angiotensinogen protein and angiotensin II that were similar to those levels of control mice. In contrast, liver-specific knockout of angiotensinogen nearly abolished plasma and renal angiotensinogen protein and renal tissue angiotensin II. Immunohistochemical analysis in mosaic proximal tubules of megalin knockout mice revealed that angiotensinogen protein was incorporated selectively in megalin-intact cells of the proximal tubule, indicating that the proximal tubule reabsorbs filtered angiotensinogen through megalin. Disruption of the filtration barrier in a transgenic mouse model of podocyte-selective injury increased renal angiotensin II content and markedly increased both tubular and urinary angiotensinogen protein without an increase in renal renin activity, supporting the dependency of renal angiotensin II generation on filtered angiotensinogen. Taken together, these data suggest that liver-derived angiotensinogen is the primary source of renal angiotensinogen protein and angiotensin II. Furthermore, an abnormal increase in the permeability of the glomerular capillary wall to angiotensinogen, which characterizes proteinuric kidney diseases, enhances the synthesis of renal angiotensin II.
    Journal of the American Society of Nephrology 04/2012; 23(7):1181-9. · 8.99 Impact Factor
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    ABSTRACT: Angiotensin I-converting enzyme inhibitors and angiotensin receptor blockers protect podocytes more effectively than other anti-hypertensive drugs. Transgenic rats overexpressing angiotensin II Type 1 (AT1) receptor selectively in podocytes have been shown to develop glomerulosclerosis. The prevailing hypothesis is that angiotensin II has a capacity of directly acting on the AT1 receptor of podocytes to induce injury. We therefore investigated the mechanism of reno-protective effect of AT1 receptor in a mouse model of HIV-1 nephropathy. We generated transgenic mice carrying the HIV-1 gene (control/HIV-1) or both HIV-1 gene and podocyte-selectively nullified AT1 gene (AT1KO/HIV-1). In these mice, we measured urinary protein or albumin excretion and performed histological analysis. At 8 months of age, AT1KO/HIV-1 (n = 13) and control/HIV-1 (n = 15) mice were statistically indistinguishable with respect to urinary albumin/creatinine ratio (median 2.5 versus 9.1 mg/mg), glomerulosclerosis (median 0.63 versus 0.45 on 0-4 scale) and downregulation of nephrin (median 6.90 versus 7.02 on 0-8 scale). In contrast to the observed lack of effect of podocyte-specific AT1KO, systemic AT1 inhibition with AT1 blocker (ARB) significantly attenuated proteinuria and glomerulosclerosis in HIV-1 mice. These results indicate that the protective effect of ARB is mediated through its receptors on cells other than podocytes, such as efferent arteriolar smooth muscle cells.
    Nephrology Dialysis Transplantation 03/2012; 27(8):3169-75. · 3.37 Impact Factor
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    ABSTRACT: In the present study, we tested the hypothesis that the renoprotective effect of an angiotensin receptor blocker depends on the angiotensin II type 1 (AT(1)) receptor on podocytes. For this purpose, we generated podocyte-specific knockout mice for the AT(1) gene (Agtr1a) and crossed with NEP25, in which selective podocyte injury can be induced by immunotoxin, anti-Tac(Fv)-PE38. Four weeks after the addition of anti-Tac(Fv)-PE38, urinary albumin:creatinine ratio was not attenuated in Agtr1a knockout/NEP25 mice (n=18) compared with that in control NEP25 mice (n=13; 8.08+/-2.41 in knockout versus 4.84+/-0.73 in control). Both strains of mice showed similar degrees of sclerosis (0.66+/-0.17 versus 0.82+/-0.27 on a 0 to 4 scale) and downregulation of nephrin (5.78+/-0.45 versus 5.65+/-0.58 on a 0 to 8 scale). In contrast, AT(1) antagonist or an angiotensin I-converting enzyme inhibitor, but not hydralazine, remarkably attenuated proteinuria and sclerosis in NEP25 mice. Moreover, continuous angiotensin II infusion induced microalbuminuria similarly in both Agtr1a knockout and wild-type mice. Thus, angiotensin inhibition can protect podocytes and prevent the development of glomerulosclerosis independent of podocyte AT(1). Possible mechanisms include inhibitory effects on AT(1) of other cells or through mechanisms independent of AT(1). Our study further demonstrates that measures that directly affect only nonpodocyte cells can have beneficial effects even when sclerosis is triggered by podocyte-specific injury.
    Hypertension 02/2010; 55(4):967-73. · 6.87 Impact Factor

Publication Stats

38 Citations
193 Views
25.97 Total Impact Points

Institutions

  • 2012–2013
    • The Jikei University School of Medicine
      • • Division of Kidney and Hypertension
      • • Department of Internal Medicine H
      Edo, Tōkyō, Japan