Faculty Profiles - KAWACHI Hiroshi

Angiotensin II receptor blockade inhibits acute glomerular injuries with the alteration of receptor expression Reviewed

Akiko Mii, Akira Shimizu, Yukinari Masuda, Masamichi Ishizaki, Hiroshi Kawachi, Yasuhiko Iino, Yasuo Katayama, Yuh Fukuda

LABORATORY INVESTIGATION 89 ( 2 ) 164 - 177 2009.2

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

Angiotensin II receptor blockade (ARB) suppresses the progression of chronic kidney disease. However, the re-noprotective effect of ARB in the active phase of glomerulonephritis (GN) has not been evaluated in detail. We examined the alteration of angiotensin II receptors' expression and the action of ARB on acute glomerular injuries in GN. Thy-1 GN was induced in rats that were divided into three groups (n = 7, in each group); high dose ( 3 mg/kg/day) or low dose (0.3 mg/kg/day) olmesartan (Thy-1 GN+HD- or LD-ARB group), and vehicle (Thy-1 GN group). Renal function and histopathology were assessed by week 2. In the Thy-1 GN group, diffuse mesangiolysis and focal aneurysmal ballooning developed by day 3. Marked mesangial proliferation and activation progressed with glomerular epithelial injury. We confirmed that both angiotensin II type 1 receptor (AT1R) and type 2 receptor (AT2R) were expressed on glomerular endothelial, mesangial, epithelial cells, and macrophages, and increased 7 days after disease induction. However, ARB treatment caused a decrease in AT1R and a further increase in AT2R expression in glomeruli. ARB prevented capillary destruction and preserved eNOS expression after diffuse mesangiolysis. Mesangial proliferation and activation was suppressed markedly with low levels of PDGF-B expression. Glomerular desmin expression, which is a marker for injured glomerular epithelial cells, was diminished significantly with retained expression of nephrin and podoplanin. Glomerular macrophage infiltration was also inhibited. Proteinuria was suppressed significantly. Furthermore, these effects of ARB showed dose dependency. These results provide insights that ARB affects individual glomerular cells and macrophages through angiotensin II receptors, with the alteration of both AT1R and AT2R expressions, and leads to inhibition of the acute destructive and proliferative glomerular lesions in GN. Laboratory Investigation ( 2009) 89, 164-177; doi:10.1038/labinvest.2008.128; published online 12 January 2009

DOI： 10.1038/labinvest.2008.128

[Basic research for kidney disease].

Kawachi Hiroshi

Nihon Jinzo Gakkai Shi 51 ( 1 ) 7 - 12 2009

Dissociation of NEPH1 from nephrin is involved in development of a rat model of focal segmental glomerulosclerosis Reviewed

Yasuhiro Otaki, Naoko Miyauchi, Mutsumi Higa, Akira Takada, Takeshi Kuroda, Fumitake Gejyo, Fujio Shimizu, Hiroshi Kawachi

American Journal of Physiology - Renal Physiology 295 ( 5 ) F1376 - F1387 2008.11

Language：English Publishing type：Research paper (scientific journal) Publisher：5

Focal segmental glomerulosclerosis (FSGS) is a disease showing severe proteinuria, and the disease progresses to end-stage kidney failure in many cases. However, the pathogenic mechanism of FSGS is not well understood. The slit diaphragm (SD), which bridges the neighboring foot processes of glomerular epithelial cells, is understood to function as a barrier of the glomerular capillary wall. To investigate the role of SD dysfunction in the development of FSGS, we analyzed the expression of SD-associated molecules in rat adriamycin-induced nephropathy, a mimic of FSGS. The staining of the SD molecules nephrin, podocin, and NEPH1 had already shifted to a discontinuous dotlike pattern at the initiation phase of the disease, when neither proteinuria nor any morphological alterations were detected yet. The alteration of NEPH1 expression was the most evident among the molecules examined, and NEPH1 was dissociated from nephrin at the initiation phase. On day 28, when severe proteinuria was detected and sclerotic changes were already observed, alteration of the expressions of nephrin, podocin, and NEPH1 worsened, but no alteration in the expression of other SD-associated molecules or other podocyte molecules was detected. It is postulated that the dissociation of NEPH1 from nephrin initiates proteinuria and that the SD alteration restricted in these molecules plays a critical role in the development of sclerotic changes in FSGS. Copyright © 2008 the American Physiological Society.

DOI： 10.1152/ajprenal.00075.2008

Activated macrophages down-regulate podocyte nephrin and podocin expression via stress-activated protein kinases Reviewed

Yohei Ikezumi, Toshiaki Suzuki, Tamaki Karasaw, Hiroshi Kawachi, David J. Nikolic-Paterson, Makoto Uchiyam

BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS 376 ( 4 ) 706 - 711 2008.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE

The development of proteinuria and glomerulosclerosis in kidney disease is associated with podocyte damage, including down-regulation of nephrin and podocin. Macrophages are known to induce renal injury, but the mechanisms involved are not fully understood. This study examined macrophage-mediated podocyte damage. Conditioned media (CM) from activated macrophages caused a 50-60% reduction in nephrin and podocin nnRNA and protein expression in cultured mouse podocytes and rat glomeruli. This was abolished by a neutralizing anti-TNF alpha antibody. The addition of recombinant TNF alpha to podocytes OF glomeruli caused a comparable reduction in podocyte nephrin and podocin expression to that of macrophage CM. Inhibition of c-Jun amino terminal kinase (JNK) or p38 kinase abolished the TNF alpha-induced reduction in nephrin and podocin expression. This study demonstrates that activated macrophages can induce podocyte injury via a TNF alpha-JNK/p38-dependent mechanism. This may explain, in part, the protective effects of JNK and p38 blockade in experimental kidney disease. (C) 2008 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.bbrc.2008.09.049

Selective loss of podoplanin protein expression accompanies proteinuria and precedes alterations in podocyte morphology in a spontaneous proteinuric rat model Reviewed

Klaas Koop, Michael Eikmans, Markus Wehland, Hans Baelde, Daphne Ijpelaar, Reinhold Kreutz, Hiroshi Kawachi, Dontscho Kerjaschki, Emile de Heer, Jan Anthonie Bruijn

AMERICAN JOURNAL OF PATHOLOGY 173 ( 2 ) 315 - 326 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER SOC INVESTIGATIVE PATHOLOGY, INC

To evaluate changes during the development of proteinuria, podocyte morphology and protein expression were evaluated in spontaneously proteinuric, Dahl salt-sensitive (Dahl SS) rats. Dahl SS rats on a low-salt diet were compared with spontaneously hypertensive rats (SHR) at age 2, 4, 6, 8, and 10 weeks. Blood pressure, urinary protein excretion, urinary albumin excretion, and podocyte morphology were evaluated. In addition, the expression of 11 podocyte-related proteins was determined by analyzing protein and mRNA levels. in Dahl SS rats, proteinuria became evident around week 5, increasing thereafter. SHR rats remained non-proteinuric. Dahl SS rats showed widespread foot process effacement at 10 weeks. At:58 weeks, expression and distribution of the podocyte proteins was similar between the two strains, except for the protein podoplanin. At 4 weeks, podoplanin began decreasing in the glomeruli of Dahl SS rats in a focal and segmental fashion. Podoplanin loss increased progressively and correlated with albuminuria (r = 0.8, P < 0.001). Double labeling experiments revealed increased expression of the podocyte stress marker desmin in glomerular areas where podoplanin was lost. Dahl SS rats did not show podoplanin gene mutations or decreased mRNA expression. Thus, podocyte morphology and the expression and distribution of most podocyte-specific proteins were normal in young Dahl SS rats, despite marked proteinuria. Our study suggests that decreased expression of podoplanin plays a role in the decrease of glomerular permselectivity.

DOI： 10.2353/ajpath.2008.080063

Rosuvastatin is additive to high-dose candesartan in slowing progression of experimental mesangioproliferative glomerulosclerosis Reviewed

Stephanie Krämer, Susanne Kron, Yingrui Wang-Rosenke, Tanja Loof, Dmytro Khadzhynov, Stanislao Morgera, Hiroshi Kawachi, Fujio Shimizu, Sebastian Martini, Hans-H. Neumayer, Harm Peters

American Journal of Physiology - Renal Physiology 294 ( 4 ) F801 - F811 2008.4

Language：English Publishing type：Research paper (scientific journal)

Rosuvastatin is additive to high-dose candesartan in slowing progression of experimental mesangioproliferative glomerulosclerosis (GS). Progressive mesangioproliferative glomerulonephritis, mostly IgA nephropathy, is a major cause of end-stage kidney disease worldwide. In a chronic-progressive model of mesangioproliferative GS, we tested the renoprotective efficacy of rosuvastatin alone and in combination with a high-dose of the AT1 blocker candesartan. Treatment was started 1 wk after disease induction (anti-thy1 antibody injection into uninephrectomized rats) and continued until week 20. Tubulointerstitial expression of the key fibrosis mediator transforming growth factor (TGF)-β served as the main marker of disease progression. Compared with the untreated GS rats (475 ± 52 pg/ml), tubulointerstitial TGF-β1 protein expression was significantly reduced by both single therapies (rosuvastatin -47%, candesartan -51%, P &lt
0.01). Tubulointerstitial matrix accumulation (matrix score in GS: 64 ± 7%) was relatively reduced by -45 and -52%, respectively (P &lt
0.01). The combination of rosuvastatin and candesartan had significantly greater effects on tubulointerstitial TGF-β1 expression (-82% vs. GS) and matrix accumulation (-83% vs. GS) (P &lt
0.001 vs. GS, P &lt
0.05 vs. single therapy) than either drug alone. Similar additive beneficial effects were observed for renal fibronectin and tissue inhibitor of metalloproteinase-1 expression, cell proliferation, macrophage infiltration, proteinuria, and kidney function. In conclusion, rosuvastatin limits the progressive course of anti-thy1-induced GS toward chronic tubulointerstitial fibrosis and renal insufficiency to a degree comparable to the one achieved by a high dose of the AT1 antagonist candesartan. Combined treatment yields significantly greater actions on renal TGF-β overexpression and matrix accumulation, cell proliferation, and macrophage infiltration. The results suggest that rosuvastatin and an AT 1 blocker independently interfere with separate key pathways involved in the progression of chronic mesangioproliferative GS. Copyright © 2008 the American Physiological Society.

DOI： 10.1152/ajprenal.00148.2007

Use of mizoribine as a rescue drug for steroid-resistant pediatric IgA nephropathy Reviewed

Yohei Ikezumi, Toshiaki Suzuki, Tamaki Karasawa, Hiroshi Kawachi, David J. Nikolic-Paterson, Makoto Uchiyama

PEDIATRIC NEPHROLOGY 23 ( 4 ) 645 - 650 2008.4

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

Recent clinical trials have shown a beneficial effect of mizoribine (Miz), an immunosuppressive drug, in the treatment of new-onset pediatric IgA nephropathy (IgAN). In this study, we evaluated the efficacy of Miz treatment in three children with established steroid-resistant IgAN. The patients had IgAN featuring persistent proteinuria and diffuse mesangial proliferation and had failed to respond to 2 years of treatment with prednisolone. Based upon the second biopsy results, patients were given methylprednisolone (mPSL) pulse therapy that induced a transient reduction in proteinuria, which was reversed when the mPSL dose was tapered. Miz therapy was then instigated in place of pulse mPSL. All three patients showed a substantial reduction in proteinuria and resolution of hematuria within 5 months. A follow-up biopsy in two of the patients showed a substantial reduction in the severity of glomerular lesions and a decrease in the number of activated macrophages. In conclusion, Miz therapy was found to be a safe and effective therapy in three cases of steroid-resistant pediatric IgAN. The ability of Miz to reduce the number of activated macrophages may be an important mechanism by which this drug ameliorated renal disease in these patients.

DOI： 10.1007/s00467-007-0664-2

Eplerenone potentiates the antiproteinuric effects of enalapril in experimental nephrotic syndrome Reviewed

Farid Nakhoul, Eliyahu Khankin, Afif Yaccob, Hiroshi Kawachi, Tony Karram, Huda Awaad, Nakhoul Nakhoul, Aaron Hoffman, Zaid Abassi

American Journal of Physiology - Renal Physiology 294 ( 3 ) F628 - F637 2008.3

Language：English Publishing type：Research paper (scientific journal)

Nephrotic syndrome (NS) is a clinical state characterized by massive proteinuria and edema. It is believed that nephrin and podocin are involved in the development of proteinuria. The proteinuria and effects of eplerenone alone or combined with enalapril on nephrin/podocin abundance in rats with NS have not yet been studied. Therefore, the present study was designed to examine the early (beginning 2 days before NS induction) and late (beginning 2 wk after NS induction) effects of eplerenone and enalapril, alone or combined, on proteinuria and nephrin/podocin abundance in rats with adriamycin-induced NS. Adriamycin caused a significant increase in daily protein excretion (U prV
from 26.96 ± 3.43 to 958.57 ± 56.7 mg/day, P &lt
0.001) and cumulative proteinuria [from 900.33 ± 135.5 to 22,490.62 ± 931.26 mg (P &lt
0.001)] during 6 wk. Early treatment with enalapril significantly decreased UprV from 958.6 ± 56.7 to 600.31 ± 65.13 mg/day (P &lt
0.001) and cumulative proteinuria to 12,842.37 ± 1,798.17 mg/6 wk (P &lt
0.001). Similarly, early treatment with eplerenone produced a profound antiproteinuric effect: UprV decreased from 958.57 ± 56.7 to 593.38 ± 21.83 mg/day, P &lt
0.001, and cumulative proteinuria to 16,601.84 ± 1,334.31 mg/6 wk
P &lt
0.001. An additive effect was obtained when enalapril and eplerenone were combined: U prV decreased from 958.57 ± 56.69 to 424.17 ± 38.54 mg/day, P &lt
0.001, and cumulative protein excretion declined to 10,252.88 ± 1,011.3 mg/6 wk, P &lt
0.001. These antiproteinuric effects were associated with substantial preservation of glomerular nephrin and podocin. In contrast, late treatment with either enalapril or eplerenone alone or combined mildly decreased UprV and cumulative proteinuria. Thus pretreatment with eplerenone or enalapril is effective in reducing daily and cumulative protein excretion and preservation of nephrin/podocin. More profound antiproteinuric effects were obtained when enalapril and eplerenone were combined. Copyright © 2008 the American Physiological Society.

DOI： 10.1152/ajprenal.00524.2007

Low-dose mTOR inhibition by rapamycin attenuates progression in anti-thy1-induced chronic glomerulosclerosis of the rat Reviewed

Stephanie Krämer, Yingrui Wang-Rosenke, Valeska Scholl, Eva Binder, Tanja Loof, Dmytro Khadzhynov, Hiroshi Kawachi, Fujio Shimizu, Fritz Diekmann, Klemens Budde, Hans-H. Neumayer, Harm Peters

American Journal of Physiology - Renal Physiology 294 ( 2 ) F440 - F449 2008.2

Language：English Publishing type：Research paper (scientific journal)

Treatment options in human mesangioproliferative glomerulonephritis/ sclerosis, mostly IgA nephropathy, are limited. Progressive mesangioproliferative nephropathy represents a major cause of end-stage kidney disease. The present study explores the efficacy of low-dose mTOR inhibition by rapamycin in a chronic-progressive model of mesangioproliferative glomerulosclerosis (cGS). cGS was induced by high-dose anti-thy1 antibody injection into uninephrectomized rats. Rapamycin administration (2.5 mg·kg-1·body wt-1) was started 10 days after antibody injection and continued until week 20. cGS was characterized by advancing proteinuria, increased blood pressure, marked tubulointerstitial and glomerular fibrosis, cell proliferation and round cell infiltration, and impaired renal function. Kruskal-Wallis and Mann-Whitney U-tests were used for statistical analysis. The course of chronic anti-thy1-induced glomerulosclerosis was significantly attenuated by low-dose rapamycin treatment. In week 20, this was demonstrated by improvements in proteinuria (-38%), systolic blood pressure (-16 mmHg), tubulointerstitial and glomerular histological matrix accumulation (-61 and -24%), transforming growth factor-β1 overexpression (-41 and -47%), collagen I deposition (-53 and -65%), cell proliferation (-90 and -76%), and leukocyte number (macrophages -52 and -53%
lymphocytes -58 and 51%), respectively. Rapamycin improved renal function as well (blood creatinine -0.68 mg/dl, urea -66.7 mg/day, and creatinine clearance +0.13 ml·min -1·100 g body wt-1). In conclusion, low-dose mTOR inhibition by rapamycin limits the progressive course of anti-thy1-induced renal disease toward chronic glomerulosclerosis, tubulointerstitial fibrosis, and renal insufficiency. Renoprotection by rapamycin involved significant beneficial effects on multiple key pathways in the progression of chronic renal disease, i.e., proteinuria, extracellular matrix accumulation, renal cell proliferation, and inflammatory cell infiltration. Copyright © 2008 the American Physiological Society.

DOI： 10.1152/ajprenal.00379.2007

IFN-inducible protein 10 (CXCL10) regulates tubular cell proliferation in renal ischemia-reperfusion injury

Kengo Furuichi, Takashi Wada, Shinji Kitajikma, Tadasi Toyama, Toshiya Okumura, Akinori Hara, Hiroshi Kawachi, Fujio Shimizu, Takeshi Sugaya, Naofumi Mukaida, Shosaku Narumi, Kouji Matsushima, Shuichi Kaneko

NEPHRON EXPERIMENTAL NEPHROLOGY 109 ( 1 ) C29 - C38 2008

Language：English Publishing type：Research paper (scientific journal) Publisher：KARGER

Although renal tubular cell proliferation after acute tubular necrosis is an important and essential response in the recovery of renal dysfunction in acute renal failure, the precise factors and mechanisms of tubular cell regeneration remain unclear. Here, we describe our studies using a neutralizing antibody (Ab) against interferon-inducible protein of 10 kDa (IP-10; CXCL10) that indicate a role for CXCL10 in tubular cell proliferation after renal ischemia-reperfusion injury. Tissue necrosis and interstitial infiltrating numbers were comparable between anti-CXCL10 Ab-treated and control mice treated with IgG at the 24 and 48 h time points after reperfusion. In contrast, the numbers of Ki67-positive proliferating tubular cells were significantly increased in anti-CXCL10 Ab-treated mice 48 h after reperfusion. In accordance with the in vivo findings, in vitro studies using murine tubular epithelial cells indicated an antiproliferative effect of CXCL10 upon the intensity of cell proliferation and the number of Ki67-positive cells. These data suggest that CXCL10 plays a role in the regulation of tubular cell proliferation following renal ischemia-reperfusion injury. Copyright (C) 2008 S. Karger AG, Basel.

DOI： 10.1159/000135675

Suppressive activity of pemirolast potassium, an antiallergic drug, on glomerulonephritis: Studies in glomerulonephritis model rats and in patients with chronic glomerulonephritis concurrently affected by allergic rhinitis Reviewed

Tomohito Gohda, Chisei Ra, Chieko Hamada, Toshinao Tsuge, Hiroshi Kawachi, Yasuhiko Tomino

Arzneimittel-Forschung/Drug Research 58 ( 1 ) 18 - 23 2008

Language：English Publishing type：Research paper (scientific journal)

Background: It is still difficult to manage chronic glomerulonephritis with corticosteroids because of safety concerns, especially for patients with mild symptoms and infants. Therefore, an alternative approach is greatly required. Pemirolast potassium (CAS 100299-08-9) is an antiallergic drug with high safety. Methods: Two glomerulonephritis rat models were prepared to examine the pharmacological actions of pemirolast potassium: one reversible model prepared with the anti-Thy-1 antibody, and another irreversible model by unilateral nephrectomy and with the anti-Thy-1 antibody. Pemirolast potassium was administered to 10 Japanese chronic glomerulonephritis patients concurrently affected by allergic rhinitis in order to examine its efficacy for mild proteinuria. Results: Pemirolast potassium 1 and 10 mg/kg markedly inhibited proteinuria in the reversible model. In the irreversible model, pemirolast potassium 3 mg/kg showed a significant decrease in the incidence of glomerulosclerosis. In chronic glomerulonephritis patients, pemirolast potassium, 10 mg twice daily, for 6 months, significantly reduced the severity of proteinuria. Conclusion: Our research suggested the efficacy of pemirolast potassium in glomerulonephritis. A well-controlled study is considered necessary to validate pemirolast potassium as a therapeutic drug for glomerulonephritis. © ECV Editio Cantor Verlag.

Decreased tyrosine phosphorylation of nephrin in rat and human nephrosis

K. Uchida, K. Suzuki, M. Iwamoto, H. Kawachi, M. Ohno, S. Horita, K. Nitta

Kidney International 73 ( 8 ) 926 - 932 2008

Language：English Publishing type：Research paper (scientific journal) Publisher：Nature Publishing Group

Phosphorylation of tyrosine residue (Y1204) of rat nephrin by Fyn kinase allows Nck adaptor protein binding to nephrin motifs, which include the phosphorylated tyrosine. This phosphorylation-dependent switch induces actin polymerization in a cell culture system. Here, we generated an antibody recognizing phosphorylated nephrin at the Nck binding sites pY1204 and pY1228 to determine the phosphorylation status of nephrin using a rat model of puromycin aminonucleoside-induced nephrosis. Changes in globular actin (G-actin) and filamentous actin (F-actin) contents in isolated glomeruli were measured by western blot. Before experimental nephrosis, both Y1204 and Y1228 were phosphorylated, and most of the actin was filamentous. Before the onset of overt proteinuria, however, phosphorylation of both Y1204 and Y1228 rapidly decreased and became almost undetectable. During this period, the amount of F-actin in glomeruli began to decrease, whereas G-actin increased. Phosphorylation of nephrin at Y1228 in glomeruli of patients with minimal change nephrosis was significantly decreased compared with that in normal glomeruli. Our study suggests that tyrosine phosphorylation of nephrin by regulating F-actin formation may be important for the maintenance of normal podocyte morphology and function. © 2008 International Society of Nephrology.

DOI： 10.1038/ki.2008.19

The mTOR inhibitor everolimus attenuates the time course of chronic anti-Thy1 nephritis in the rat

Sandra Wittmann, Christoph Daniel, Andrea Braun, Regina Vogelbacher, Fuijo Shimizu, Hiroshi Kawachi, Christian Hugo

NEPHRON EXPERIMENTAL NEPHROLOGY 108 ( 2 ) 45 - 56 2008

Language：English Publishing type：Research paper (scientific journal) Publisher：KARGER

Background: The antiproliferative immunosuppressant everolimus adversely affects the acute reversible anti-Thy1 nephritis model. We hypothesized that everolimus treatment started after the acute proliferative phase could even be beneficial in the chronic anti-Thy1 nephritis model in the rat. Methods: Chronic anti-Thy1 nephritis was induced by injection of the monoclonal antibody 1-22-3 in 20 male Sprague-Dawley rats 7 days after uninephrectomy. Two weeks after disease induction, rats were randomly treated with either everolimus or vehicle for 14 weeks. Changes in progression of renal disease were investigated by immunohistochemistry and real-time PCR 16 weeks after disease induction. Results: During chronic anti-Thy1 nephritis, the formation of focal segmental glomerulosclerosis lesions, the degree of interstitial fibrosis as well as the increase in proteinuria over 14 weeks was ameliorated by everolimus treatment. Increased glomerular hypertrophy observed in the vehicle-treated rats was completely prevented in the everolimus-treated nephritic rats. Increased glomerular fibronectin mRNA and protein as well as the renal influx of monocytes/macrophages was significantly reduced in the evero-limus group. Everolimus reduced the pro-angiogenic factor vascular endothelial growth factor (VEGF) and VEGF mRNA in glomeruli, while the transforming growth factor-beta signaling pathway was not affected. Conclusion: 'Late' start of everolimus treatment demonstrates beneficial effects on the time course of chronic anti-Thy1 nephritis. Copyright (C) 2008 S. Karger AG, Basel.

DOI： 10.1159/000116112

Nephrin mediates actin reorganization via phosphoinositide 3-kinase in podocytes

J. Zhu, N. Sun, L. Aoudjit, H. Li, H. Kawachi, S. Lemay, T. Takano

Kidney International 73 ( 5 ) 556 - 566 2008

Language：English Publishing type：Research paper (scientific journal) Publisher：Nature Publishing Group

Nephrin is a slit diaphragm protein critical for structural and functional integrity of visceral glomerular epithelial cells (podocytes) and is known to be tyrosine phosphorylated by Src family kinases. We studied the role of phosphoinositide 3-kinase (PI3K), activated via the phosphorylation of nephrin, in actin cytoskeletal reorganization of cultured rat podocytes. Phosphorylation of rat nephrin by the Fyn kinase markedly increased its interaction with a regulatory subunit of PI3K. Stable transfection of rat nephrin in the podocytes with podocin led to nephrin tyrosine phosphorylation, PI3K-dependent phosphorylation of Akt, increased Rac1 activity, and an altered actin cytoskeleton with decreased stress fibers and increased lamellipodia. These changes were reversed with an inhibitor of PI3K and not seen when the nephrin-mutant Y1152F replaced wild-type nephrin. Rac1 and Akt1 contributed to lamellipodia formation and decreased stress fibers, respectively. Finally, in the rat model of puromycin aminonucleoside nephrosis, nephrin tyrosine phosphorylation, nephrin-PI3K association, and glomerular Akt phosphorylation were all decreased. Our results suggest that PI3K is involved in nephrin-mediated actin reorganization in podocytes. Disturbed nephrin-PI3K interactions may contribute to abnormal podocyte morphology and proteinuria. © 2008 International Society of Nephrology.

DOI： 10.1038/sj.ki.5002691