Nephrology; Nephrotic Syndrome; Physiology; Proteinuria; Podocytes; Glomerular Filtration Barrier
Our laboratory is interested in defining the mechanism of proteinuria by studying podocytes, which are specialized cells that line the capillary loops and play a key role in maintenance of the glomerular filtration barrier. We have identified a network of proteins that bind directly or indirectly to proteins that human genetic studies have implicated to be causal for nephrotic syndrome. Through mice genetics, loss of specific proteins in this network has demonstrated severe proteinuria, and podocyte foot process effacement. By utilizing fluorescently tagged proteins,we have visualized that these proteins lie at the interface of endocytosis and the actin cytoskeleton, and are implicated in controlling the formation and maintenance of the glomerular filtration barrier.
Specialized Terms: Podocytes; Glomerular Filtration Barrier
Extensive Research Description
My research in Dr. Lloyd Cantley’s laboratory (Professor of Internal Medicine at Yale University) had focused on hepatocyte growth factor (HGF), a secreted protein that plays important roles in epithelial morphogenesis, mitogenesis, and motogenesis. We made the novel discovery that paxillin functions as a scaffolding protein that regulates the HGF-dependent activation of ERK at focal adhesions. In a follow-up study, we demonstrated that paxillin itself is a substrate to ERK-dependent phosphorylation, which recruits FAK and Rac and is necessary for HGF-dependent tubulogenesis. These findings were published as two first-authored papers in Molecular Cell and are important because they elucidate the mechanism by which HGF regulates focal adhesion turnover, which is essential for cell spreading and morphogenesis. More generally, they explain how compartmentalization of MAP kinase signaling is achieved through local activation on scaffolding proteins, such as paxillin. In a third study we observed that during in vitro tubulogenesis, the cells located in the middle of the tubules appeared well differentiated whereas cells located at the ends had a mesenchymal appearance. We discovered that cell confluency modulates the responsiveness to HGF through its effects on the activation of Akt and beta-catenin. These findings were published in MCB and are relevant to the mechanism of tubular regeneration after acute kidney injury, which we hypothesize involves HGF-stimulated cell spreading, proliferation, and dedifferentiation
After starting my own laboratory, we have focused on podocytes, the specialized epithelial cells that maintain the glomerular filtration barrier, and are critical targets in proteinuric disorders such as diabetic nephropathy. My current research in podocyte biology is concentrated in two areas.
One interest lies in the further understanding of cell-matrix biology in his study of podocytes. When podocytes are injured, the foot processes undergo a term known as effacement, where the cells collapse losing cell-cell junction proteins resulting in proteinuria. A mechanisms of podocytes undergoing foot process effacement likely requires cell spreading and motility which requires turnover of focal adhesion proteins, which acts as a“glue” to keep cells attached to its matrix. To further address this hypothesis, a key focal adhesion protein, FAK, was conditionally deleted in podocytes taking advantage of mice genetics. Generation of these mice resulted in resistance to proteinuria induced by various injury models. Moreover, as FDA approved FAK inhibitors are available, through collaboration with Novartis Pharmaceuticals, treatment of mice with FAK inhibitors during injury significantly reduced proteinuria and histological kidney injury.
My second interest in podocyte biology is to evaluate the importance of various interacting partners of known human disease causing mutations that result in nephrotic syndrome. Currently, we have identified a network of proteins that bind directly or indirectly to proteins that human genetic studies have implicated to be causal for nephrotic syndrome. Through mice genetics, loss of specific proteins in this network has demonstrated severe proteinuria, and podocyte foot process effacement. Through collaboration with Dr. Pietro De Camilli, we have found that these network of proteins lie at the interface of endocytosis and the actin cytoskeleton and now are in the process of expanding our understanding by determining critical factors that are being endocytosed in the podocytes. Hopefully these fundamental findings will lead to therapeutic targets in the treatment of nephrotic syndrome in the future.
The future directions of my lab are to further understand cell-matrix biology and endocytosis in podocytes by using mice genetic models of disease. Moreover, we are in the process of obtaining human samples to discover novel disease mutations, which may lead to further understanding of disease processes leading to nephrotic syndrome.
Analyzing the role of podocyte cell-matrix interactions
Analyzing the role of podocyte endocytosis
Podocyte-associated talin1 is critical for glomerular filtration barrier maintenance.
Podocyte-associated talin1 is critical for glomerular filtration barrier maintenance. Tian X, Kim JJ, Monkley SM, Gotoh N, Nandez R, Soda K, Inoue K, Balkin DM, Hassan H, Son SH, Lee Y, Moeckel G, Calderwood DA, Holzman LB, Critchley DR, Zent R, Reiser J, Ishibe S. J Clin Invest. 2014 Mar 3;124(3):1098-113. doi: 10.1172/JCI69778. Epub 2014 Feb 17.
Role of dynamin, synaptojanin, and endophilin in podocyte foot processes.
Role of dynamin, synaptojanin, and endophilin in podocyte foot processes. Soda K, Balkin DM, Ferguson SM, Paradise S, Milosevic I, Giovedi S, Volpicelli-Daley L, Tian X, Wu Y, Ma H, Son SH, Zheng R, Moeckel G, Cremona O, Holzman LB, De Camilli P, Ishibe S. J Clin Invest. 2012 Dec 3;122(12):4401-11. doi: 10.1172/JCI65289. Epub 2012 Nov 26.
Inhibition of podocyte FAK protects against proteinuria and foot process effacement.
Ma, H, Togawa, A, Soda,K, Zhang,J, Lee,S, Ma,M, Yu,J, Ardito, Czyzyk,J, Diggs,J, Joly, D, Hatakeyama, S, Kawahara, E, Holzman, L, Guan, J.L, and Ishibe, S. J Am Soc Nephrol. 2010 Jul;21(7):1145-56. doi: 10.1681/ASN.2009090991. Epub 2010 Jun 3.
Deletion of the Met receptor in the collecting duct decreases renal repair following ureteral obstruction.
Ma, H, Saenko, M, Opuko, A, Togawa, A, Soda,K, Marlier, A, Moeckel, G, Cantley, LG and Ishibe, S Deletion of the Met receptor in the collecting duct decreases renal repair following ureteral obstruction Kidney International Kidney Int. 2009 Oct;76(8):868-76.
Full List of PubMed Publications
- Inoue K, Balkin DM, Liu L, Nandez R, Wu Y, Tian X, Wang T, Nussbaum R, De Camilli P, Ishibe S: Kidney Tubular Ablation of Ocrl/Inpp5b Phenocopies Lowe Syndrome Tubulopathy. J Am Soc Nephrol. 2017 May; 2016 Nov 28. PMID: 27895154
- Beckerman P, Bi-Karchin J, Park AS, Qiu C, Dummer PD, Soomro I, Boustany-Kari CM, Pullen SS, Miner JH, Hu CA, Rohacs T, Inoue K, Ishibe S, Saleem MA, Palmer MB, Cuervo AM, Kopp JB, Susztak K: Transgenic expression of human APOL1 risk variants in podocytes induces kidney disease in mice. Nat Med. 2017 Apr; 2017 Feb 20. PMID: 28218918
- Tian X, Ishibe S: Targeting the podocyte cytoskeleton: from pathogenesis to therapy in proteinuric kidney disease. Nephrol Dial Transplant. 2016 Oct; 2016 Mar 10. PMID: 26968197
- Hassan H, Tian X, Inoue K, Chai N, Liu C, Soda K, Moeckel G, Tufro A, Lee AH, Somlo S, Fedeles S, Ishibe S: Essential Role of X-Box Binding Protein-1 during Endoplasmic Reticulum Stress in Podocytes. J Am Soc Nephrol. 2016 Apr; 2015 Aug 24. PMID: 26303067
- Inoue K, Ishibe S: Podocyte endocytosis in the regulation of the glomerular filtration barrier. Am J Physiol Renal Physiol. 2015 Sep 1; 2015 Jun 17. PMID: 26084928
- Soda K, Ishibe S: The function of endocytosis in podocytes. Curr Opin Nephrol Hypertens. 2013 Jul. PMID: 23703394
- Soda K, Balkin DM, Ferguson SM, Paradise S, Milosevic I, Giovedi S, Volpicelli-Daley L, Tian X, Wu Y, Ma H, Son SH, Zheng R, Moeckel G, Cremona O, Holzman LB, De Camilli P, Ishibe S: Role of dynamin, synaptojanin, and endophilin in podocyte foot processes. J Clin Invest. 2012 Dec; 2012 Nov 26. PMID: 23187129
- Togawa A, Sfakianos J, Ishibe S, Suzuki S, Fujigaki Y, Kitagawa M, Mellman I, Cantley LG: Hepatocyte Growth Factor stimulated cell scattering requires ERK and Cdc42-dependent tight junction disassembly. Biochem Biophys Res Commun. 2010 Sep 17; 2010 Aug 20. PMID: 20728428
- Ma H, Togawa A, Soda K, Zhang J, Lee S, Ma M, Yu Z, Ardito T, Czyzyk J, Diggs L, Joly D, Hatakeyama S, Kawahara E, Holzman L, Guan JL, Ishibe S: Inhibition of podocyte FAK protects against proteinuria and foot process effacement. J Am Soc Nephrol. 2010 Jul; 2010 Jun 3. PMID: 20522532
- Ma H, Saenko M, Opuko A, Togawa A, Soda K, Marlier A, Moeckel GW, Cantley LG, Ishibe S: Deletion of the Met receptor in the collecting duct decreases renal repair following ureteral obstruction. Kidney Int. 2009 Oct; 2009 Aug 12. PMID: 19675527
- Ishibe S, Karihaloo A, Ma H, Zhang J, Marlier A, Mitobe M, Togawa A, Schmitt R, Czyczk J, Kashgarian M, Geller DS, Thorgeirsson SS, Cantley LG: Met and the epidermal growth factor receptor act cooperatively to regulate final nephron number and maintain collecting duct morphology. Development. 2009 Jan. PMID: 19103805
- Ishibe S, Cantley LG: Epithelial-mesenchymal-epithelial cycling in kidney repair. Curr Opin Nephrol Hypertens. 2008 Jul. PMID: 18660674
- Shibazaki S, Yu Z, Nishio S, Tian X, Thomson RB, Mitobe M, Louvi A, Velazquez H, Ishibe S, Cantley LG, Igarashi P, Somlo S: Cyst formation and activation of the extracellular regulated kinase pathway after kidney specific inactivation of Pkd1. Hum Mol Genet. 2008 Jun 1; 2008 Feb 7. PMID: 18263604
- Ishibe S, Haydu JE, Togawa A, Marlier A, Cantley LG: Cell confluence regulates hepatocyte growth factor-stimulated cell morphogenesis in a beta-catenin-dependent manner. Mol Cell Biol. 2006 Dec; 2006 Oct 9. PMID: 17030602
- Gwira JA, Wei F, Ishibe S, Ueland JM, Barasch J, Cantley LG: Expression of neutrophil gelatinase-associated lipocalin regulates epithelial morphogenesis in vitro. J Biol Chem. 2005 Mar 4; 2005 Jan 6. PMID: 15637066
- Ishibe S, Joly D, Liu ZX, Cantley LG: Paxillin serves as an ERK-regulated scaffold for coordinating FAK and Rac activation in epithelial morphogenesis. Mol Cell. 2004 Oct 22. PMID: 15494312
- Ishibe S, Peixoto AJ: Methods of assessment of volume status and intercompartmental fluid shifts in hemodialysis patients: implications in clinical practice. Semin Dial. 2004 Jan-Feb. PMID: 14717810
- Ishibe S, Joly D, Zhu X, Cantley LG: Phosphorylation-dependent paxillin-ERK association mediates hepatocyte growth factor-stimulated epithelial morphogenesis. Mol Cell. 2003 Nov. PMID: 14636584
- Perazella MA, Ishibe S, Perazella MA, Reilly RF: Nephrogenic fibrosing dermopathy: an unusual skin condition associated with kidney disease. Semin Dial. 2003 May-Jun. PMID: 12753692