Chronic kidney disease is a leading cause of death in the United States. Tubulointerstitial fibrosis (TIF) is considered the final common pathway leading to end-stage renal disease (ESRD). Here, we used pharmacologic, genetic, in vivo, and in vitro experiments to show that activation of the Notch pathway in tubular epithelial cells (TECs) in patients and in mouse models of TIF plays a role in TIF development. Expression of Notch in renal TECs was found to be both necessary and sufficient for TIF development. Genetic deletion of the Notch pathway in TECs reduced renal fibrosis. Consistent with this, TEC-specific expression of active Notch1 caused rapid development of TIF. Pharmacologic inhibition of Notch activation using a γ-secretase inhibitor ameliorated TIF. In summary, our experiments establish that epithelial injury and Notch signaling play key roles in fibrosis development and indicate that Notch blockade may be a therapeutic strategy to reduce fibrosis and ESRD development.
Bernhard Bielesz, Yasemin Sirin, Han Si, Thiruvur Niranjan, Antje Gruenwald, Seonho Ahn, Hideki Kato, James Pullman, Manfred Gessler, Volker H. Haase, Katalin Susztak
Mechanisms of progression of chronic kidney disease (CKD), a major health care burden, are poorly understood. EGFR stimulates CKD progression, but the molecular networks that mediate its biological effects remain unknown. We recently showed that the severity of renal lesions after nephron reduction varied substantially among mouse strains and required activation of EGFR. Here, we utilized two mouse strains that react differently to nephron reduction — FVB/N mice, which develop severe renal lesions, and B6D2F1 mice, which are resistant to early deterioration — coupled with genome-wide expression to elucidate the molecular nature of CKD progression. Our results showed that lipocalin 2 (Lcn2, also known as neutrophil gelatinase–associated lipocalin [NGAL]), the most highly upregulated gene in the FVB/N strain, was not simply a marker of renal lesions, but an active player in disease progression. In fact, the severity of renal lesions was dramatically reduced in Lcn2–/– mice. We discovered that Lcn2 expression increased upon EGFR activation and that Lcn2 mediated its mitogenic effect during renal deterioration. EGFR inhibition prevented Lcn2 upregulation and lesion development in mice expressing a dominant negative EGFR isoform, and hypoxia-inducible factor 1α (Hif-1α) was crucially required for EGFR-induced Lcn2 overexpression. Consistent with this, cell proliferation was dramatically reduced in Lcn2–/– mice. These data are relevant to human CKD, as we found that LCN2 was increased particularly in patients who rapidly progressed to end-stage renal failure. Together our results uncover what we believe to be a novel function for Lcn2 and a critical pathway leading to progressive renal failure and cystogenesis.
Amandine Viau, Khalil El Karoui, Denise Laouari, Martine Burtin, Clément Nguyen, Kiyoshi Mori, Evangéline Pillebout, Thorsten Berger, Tak Wah Mak, Bertrand Knebelmann, Gérard Friedlander, Jonathan Barasch, Fabiola Terzi
Dense deposit disease (DDD) is a severe renal disease characterized by accumulation of electron-dense material in the mesangium and glomerular basement membrane. Previously, DDD has been associated with deficiency of factor H (fH), a plasma regulator of the alternative pathway (AP) of complement activation, and studies in animal models have linked pathogenesis to the massive complement factor 3 (C3) activation caused by this deficiency. Here, we identified a unique DDD pedigree that associates disease with a mutation in the C3 gene. Mutant C3923ΔDG, which lacks 2 amino acids, could not be cleaved to C3b by the AP C3-convertase and was therefore the predominant circulating C3 protein in the patients. However, upon activation to C3b by proteases, or to C3(H2O) by spontaneous thioester hydrolysis, C3923ΔDG generated an active AP C3-convertase that was regulated normally by decay accelerating factor (DAF) but was resistant to decay by fH. Moreover, activated C3b923ΔDG and C3(H2O)923ΔDG were resistant to proteolysis by factor I (fI) in the presence of fH, but were efficiently inactivated in the presence of membrane cofactor protein (MCP). These characteristics cause a fluid phase–restricted AP dysregulation in the patients that continuously activated and consumed C3 produced by the normal C3 allele. These findings expose structural requirements in C3 that are critical for recognition of the substrate C3 by the AP C3-convertase and for the regulatory activities of fH, DAF, and MCP, all of which have implications for therapeutic developments.
Rubén Martínez-Barricarte, Meike Heurich, Francisco Valdes-Cañedo, Eduardo Vazquez-Martul, Eva Torreira, Tamara Montes, Agustín Tortajada, Sheila Pinto, Margarita Lopez-Trascasa, B. Paul Morgan, Oscar Llorca, Claire L. Harris, Santiago Rodríguez de Córdoba
Ammonia absorption by the medullary thick ascending limb of Henle’s loop (MTALH) is thought to be a critical step in renal ammonia handling and excretion in urine, in which it is the main acid component. Basolateral Na+/H+ exchangers have been proposed to play a role in ammonia efflux out of MTALH cells, which express 2 exchanger isoforms: Na+/H+ exchanger 1 (NHE1) and NHE4. Here, we investigated the role of NHE4 in urinary acid excretion and found that NHE4–/– mice exhibited compensated hyperchloremic metabolic acidosis, together with inappropriate urinary net acid excretion. When challenged with a 7-day HCl load, NHE4–/– mice were unable to increase their urinary ammonium and net acid excretion and displayed reduced ammonium medulla content compared with wild-type littermates. Both pharmacologic inhibition and genetic disruption of NHE4 caused a marked decrease in ammonia absorption by the MTALH. Finally, dietary induction of metabolic acidosis increased NHE4 mRNA expression in mouse MTALH cells and enhanced renal NHE4 activity in rats, as measured by in vitro microperfusion of MTALH. We therefore conclude that ammonia absorption by the MTALH requires the presence of NHE4 and that lack of NHE4 reduces the ability of MTALH epithelial cells to create the cortico-papillary gradient of NH3/NH4+ needed to excrete an acid load, contributing to systemic metabolic acidosis.
Soline Bourgeois, Leonie Van Meer, Bharath Wootla, May Bloch-Faure, Régine Chambrey, Gary E. Shull, Lara R. Gawenis, Pascal Houillier
Crescentic glomerulonephritis (CGN), which frequently results in acute and chronic kidney disease, is characterized by and dependent on glomerular infiltration by macrophages. The mannose receptor (MR) is a pattern recognition receptor implicated in the uptake of endogenous and microbial ligands by macrophages, mesangial cells (MCs), and selected endothelial cells. It is upregulated on alternatively activated macrophages (i.e., macrophages associated with tissue repair and humoral immunity) and involved in antigen presentation to T cells. We used the mouse model of nephrotoxic nephritis to investigate the role of MR in CGN. Our results demonstrate what we believe to be a novel role for MR in the promotion of CGN that is independent of adaptive immune responses. MR-deficient (Mr–/–) mice were protected from CGN despite generating humoral and T cell responses similar to those of WT mice, but they demonstrated diminished macrophage and MC Fc receptor–mediated (FcR-mediated) functions, including phagocytosis and Fc-mediated oxygen burst activity. Mr–/– MCs demonstrated augmented apoptosis compared with WT cells, and this was associated with diminished Akt phosphorylation. Macrophage interaction with apoptotic MCs induced a noninflammatory phenotype that was more marked in Mr–/– macrophages than in WT macrophages. Our results demonstrate that MR augments Fc-mediated function and promotes MC survival. We suggest that targeting MR may provide an alternative therapeutic approach in CGN while minimizing the impact on adaptive immune responses, which are affected by conventional immunosuppressive approaches.
Konstantia-Maria Chavele, Luisa Martinez-Pomares, Jan Domin, Samantha Pemberton, Stuart M. Haslam, Anne Dell, H. Terence Cook, Charles D. Pusey, Siamon Gordon, Alan D. Salama
John F. O’Toole, Yangjian Liu, Erica E. Davis, Christopher J. Westlake, Massimo Attanasio, Edgar A. Otto, Dominik Seelow, Gudrun Nurnberg, Christian Becker, Matti Nuutinen, Mikko Kärppä, Jaakko Ignatius, Johanna Uusimaa, Salla Pakanen, Elisa Jaakkola, Lambertus P. van den Heuvel, Henry Fehrenbach, Roger Wiggins, Meera Goyal, Weibin Zhou, Matthias T.F. Wolf, Eric Wise, Juliana Helou, Susan J. Allen, Carlos A. Murga-Zamalloa, Shazia Ashraf, Moumita Chaki, Saskia Heeringa, Gil Chernin, Bethan E. Hoskins, Hassan Chaib, Joseph Gleeson, Takehiro Kusakabe, Takako Suzuki, R. Elwyn Isaac, Lynne M. Quarmby, Bryan Tennant, Hisashi Fujioka, Hannu Tuominen, Ilmo Hassinen, Hellevi Lohi, Judith L. van Houten, Agnes Rotig, John A. Sayer, Boris Rolinski, Peter Freisinger, Sethu M. Madhavan, Martina Herzer, Florence Madignier, Holger Prokisch, Peter Nurnberg, Peter K. Jackson, Hemant Khanna, Nicholas Katsanis, Friedhelm Hildebrandt
Injury and loss of podocytes are leading factors of glomerular disease and renal failure. The postmitotic podocyte is the primary glomerular target for toxic, immune, metabolic, and oxidant stress, but little is known about how this cell type copes with stress. Recently, autophagy has been identified as a major pathway that delivers damaged proteins and organelles to lysosomes in order to maintain cellular homeostasis. Here we report that podocytes exhibit an unusually high level of constitutive autophagy. Podocyte-specific deletion of autophagy-related 5 (Atg5) led to a glomerulopathy in aging mice that was accompanied by an accumulation of oxidized and ubiquitinated proteins, ER stress, and proteinuria. These changes resulted ultimately in podocyte loss and late-onset glomerulosclerosis. Analysis of pathophysiological conditions indicated that autophagy was substantially increased in glomeruli from mice with induced proteinuria and in glomeruli from patients with acquired proteinuric diseases. Further, mice lacking Atg5 in podocytes exhibited strongly increased susceptibility to models of glomerular disease. These findings highlight the importance of induced autophagy as a key homeostatic mechanism to maintain podocyte integrity. We postulate that constitutive and induced autophagy is a major protective mechanism against podocyte aging and glomerular injury, representing a putative target to ameliorate human glomerular disease and aging-related loss of renal function.
Björn Hartleben, Markus Gödel, Catherine Meyer-Schwesinger, Shuya Liu, Theresa Ulrich, Sven Köbler, Thorsten Wiech, Florian Grahammer, Sebastian J. Arnold, Maja T. Lindenmeyer, Clemens D. Cohen, Hermann Pavenstädt, Dontscho Kerjaschki, Noboru Mizushima, Andrey S. Shaw, Gerd Walz, Tobias B. Huber
Levels of the necessary nutrient vitamin C (ascorbate) are tightly regulated by intestinal absorption, tissue accumulation, and renal reabsorption and excretion. Ascorbate levels are controlled in part by regulation of transport through at least 2 sodium-dependent transporters: Slc23a1 and Slc23a2 (also known as Svct1 and Svct2, respectively). Previous work indicates that Slc23a2 is essential for viability in mice, but the roles of Slc23a1 for viability and in adult physiology have not been determined. To investigate the contributions of Slc23a1 to plasma and tissue ascorbate concentrations in vivo, we generated Slc23a1–/– mice. Compared with wild-type mice, Slc23a1–/– mice increased ascorbate fractional excretion up to 18-fold. Hepatic portal ascorbate accumulation was nearly abolished, whereas intestinal absorption was marginally affected. Both heterozygous and knockout pups born to Slc23a1–/– dams exhibited approximately 45% perinatal mortality, and this was associated with lower plasma ascorbate concentrations in dams and pups. Perinatal mortality of Slc23a1–/– pups born to Slc23a1–/– dams was prevented by ascorbate supplementation during pregnancy. Taken together, these data indicate that ascorbate provided by the dam influenced perinatal survival. Although Slc23a1–/– mice lost as much as 70% of their ascorbate body stores in urine daily, we observed an unanticipated compensatory increase in ascorbate synthesis. These findings indicate a key role for Slc23a1 in renal ascorbate absorption and perinatal survival and reveal regulation of vitamin C biosynthesis in mice.
Christopher P. Corpe, Hongbin Tu, Peter Eck, Jin Wang, Robert Faulhaber-Walter, Jurgen Schnermann, Sam Margolis, Sebastian Padayatty, He Sun, Yaohui Wang, Robert L. Nussbaum, Michael Graham Espey, Mark Levine
Urolithiasis, a condition in which stones are present in the urinary system, including the kidneys and bladder, is a poorly understood yet common disorder worldwide that leads to significant health care costs, morbidity, and work loss. Acetaminophen-induced liver damage is a major cause of death in patients with acute liver failure. Kidney and urinary stones and liver toxicity are disturbances linked to alterations in oxalate and sulfate homeostasis, respectively. The sulfate anion transporter–1 (Sat1; also known as Slc26a1) mediates epithelial transport of oxalate and sulfate, and its localization in the kidney, liver, and intestine suggests that it may play a role in oxalate and sulfate homeostasis. To determine the physiological roles of Sat1, we created Sat1–/– mice by gene disruption. These mice exhibited hyperoxaluria with hyperoxalemia, nephrocalcinosis, and calcium oxalate stones in their renal tubules and bladder. Sat1–/– mice also displayed hypersulfaturia, hyposulfatemia, and enhanced acetaminophen-induced liver toxicity. These data suggest that Sat1 regulates both oxalate and sulfate homeostasis and may be critical to the development of calcium oxalate urolithiasis and hepatotoxicity.
Paul A. Dawson, Christopher S. Russell, Soohyun Lee, Sarah C. McLeay, Jacobus M. van Dongen, David M. Cowley, Lorne A. Clarke, Daniel Markovich
The glomerular basement membrane (GBM) is a key component of the filtering unit in the kidney. Mutations involving any of the collagen IV genes (COL4A3, COL4A4, and COL4A5) affect GBM assembly and cause Alport syndrome, a progressive hereditary kidney disease with no definitive therapy. Previously, we have demonstrated that the bone morphogenetic protein (BMP) antagonist uterine sensitization–associated gene-1 (USAG-1) negatively regulates the renoprotective action of BMP-7 in a mouse model of tubular injury during acute renal failure. Here, we investigated the role of USAG-1 in renal function in Col4a3–/– mice, which model Alport syndrome. Ablation of Usag1 in Col4a3–/– mice led to substantial attenuation of disease progression, normalization of GBM ultrastructure, preservation of renal function, and extension of life span. Immunohistochemical analysis revealed that USAG-1 and BMP-7 colocalized in the macula densa in the distal tubules, lying in direct contact with glomerular mesangial cells. Furthermore, in cultured mesangial cells, BMP-7 attenuated and USAG-1 enhanced the expression of MMP-12, a protease that may contribute to GBM degradation. These data suggest that the pathogenetic role of USAG-1 in Col4a3–/– mice might involve crosstalk between kidney tubules and the glomerulus and that inhibition of USAG-1 may be a promising therapeutic approach for the treatment of Alport syndrome.
Mari Tanaka, Misako Asada, Atsuko Y. Higashi, Jin Nakamura, Akiko Oguchi, Mayumi Tomita, Sachiko Yamada, Nariaki Asada, Masayuki Takase, Tomohiko Okuda, Hiroshi Kawachi, Aris N. Economides, Elizabeth Robertson, Satoru Takahashi, Takeshi Sakurai, Roel Goldschmeding, Eri Muso, Atsushi Fukatsu, Toru Kita, Motoko Yanagita