The pathogenesis of cachexia in patients with uremia is unknown. We tested the hypothesis that uremia-associated cachexia is caused by leptin signaling through the hypothalamic melanocortin receptor 4 (MC4-R). We performed either subtotal nephrectomy (N) or sham operations in WT, leptin receptor–deficient (db/db), and MC4-R knockout (MC4-RKO) mice. The animals were on 17% protein diets, and none of the uremic animals were acidotic. WT-N mice produced a classic syndrome of cachexia characterized by decreased food intake, increased metabolic rate, and loss of lean body mass. Corrected leptin levels were elevated. db/db mice and MC4-RKO mice resisted the cachexic effects of uremia on weight gain, body composition, and metabolic rate. Likewise, treatment of WT mice with intracranial agouti-related peptide reversed the cachexic effects of uremia on appetite, weight gain, body composition, and metabolic rate. Gene expression of ubiquitin C and proteasome subunits C2, C3, and C9 was not changed in the uremic animals, suggesting that other pathways are involved in this model of nonacidotic uremic cachexia. The results of this study suggest that elevated circulating levels of cytokines such as leptin may be an important cause of uremia-associated cachexia via signaling through the central melanocortin system.
Wai Cheung, Pin X. Yu, Brian M. Little, Roger D. Cone, Daniel L. Marks, Robert H. Mak
TNF is essential for the development of glomerulonephritis, an immune-mediated disorder that is a major cause of renal failure worldwide. However, TNF has proinflammatory and immunosuppressive properties that may segregate at the level of the 2 TNF receptors (TNFRs), TNFR1 and TNFR2. TNFR1-deficient mice subjected to immune complex–mediated glomerulonephritis developed less proteinuria and glomerular injury, and fewer renal leukocyte infiltrates at early time points after disease induction, and this was associated with a reduced systemic immune response to nephrotoxic rabbit IgG. However, proteinuria and renal pathology were similar to those in wild-type controls at later time points, when lack of TNFR1 resulted in excessive renal T cell accumulation and an associated reduction in apoptosis of these cells. In sharp contrast, TNFR2-deficient mice were completely protected from glomerulonephritis at all time points, despite an intact systemic immune response. TNFR2 was induced on glomerular endothelial cells of nephritic kidneys, and TNFR2 expression on intrinsic cells, but not leukocytes, was essential for glomerulonephritis and glomerular complement deposition. Thus, TNFR1 promotes systemic immune responses and renal T cell death, while intrinsic cell TNFR2 plays a critical role in complement-dependent tissue injury. Therefore, therapeutic blockade specifically of TNFR2 may be a promising strategy in the treatment of immune-mediated glomerulonephritis.
Volker Vielhauer, George Stavrakis, Tanya N. Mayadas
Autosomal dominant polycystic kidney disease (ADPKD) is the most common human monogenic genetic disorder and is characterized by progressive bilateral renal cysts and the development of renal insufficiency. The cystogenesis of ADPKD is believed to be a monoclonal proliferation of PKD-deficient (PKD–/–) renal tubular epithelial cells. To define the function of Pkd1, we generated chimeric mice by aggregation of Pkd1–/– ES cells and Pkd1+/+ morulae from ROSA26 mice. As occurs in humans with ADPKD, these mice developed cysts in the kidney, liver, and pancreas. Surprisingly, the cyst epithelia of the kidney were composed of both Pkd1–/– and Pkd1+/+ renal tubular epithelial cells in the early stages of cystogenesis. Pkd1–/– cyst epithelial cells changed in shape from cuboidal to flat and replaced Pkd1+/+ cyst epithelial cells lost by JNK-mediated apoptosis in intermediate stages. In late-stage cysts, Pkd1–/– cells continued immortalized proliferation with downregulation of p53. These results provide a novel understanding of the cystogenesis of ADPKD patients. Furthermore, immortalized proliferation without induction of p53 was frequently observed in 3T3-type culture of mouse embryonic fibroblasts from Pkd1–/– mice. Thus, Pkd1 plays a role in preventing immortalized proliferation of renal tubular epithelial cells through the induction of p53 and activation of JNK.
Saori Nishio, Masahiko Hatano, Michio Nagata, Shigeo Horie, Takao Koike, Takeshi Tokuhisa, Toshio Mochizuki
Neutrophil gelatinase–associated lipocalin (Ngal), also known as siderocalin, forms a complex with iron-binding siderophores (Ngal:siderophore:Fe). This complex converts renal progenitors into epithelial tubules. In this study, we tested the hypothesis that Ngal:siderophore:Fe protects adult kidney epithelial cells or accelerates their recovery from damage. Using a mouse model of severe renal failure, ischemia-reperfusion injury, we show that a single dose of Ngal (10 μg), introduced during the initial phase of the disease, dramatically protects the kidney and mitigates azotemia. Ngal activity depends on delivery of the protein and its siderophore to the proximal tubule. Iron must also be delivered, since blockade of the siderophore with gallium inhibits the rescue from ischemia. The Ngal:siderophore:Fe complex upregulates heme oxygenase-1, a protective enzyme, preserves proximal tubule N-cadherin, and inhibits cell death. Because mouse urine contains an Ngal-dependent siderophore-like activity, endogenous Ngal might also play a protective role. Indeed, Ngal is highly accumulated in the human kidney cortical tubules and in the blood and urine after nephrotoxic and ischemic injury. We reveal what we believe to be a novel pathway of iron traffic that is activated in human and mouse renal diseases, and it provides a unique method for their treatment.
Kiyoshi Mori, H. Thomas Lee, Dana Rapoport, Ian R. Drexler, Kirk Foster, Jun Yang, Kai M. Schmidt-Ott, Xia Chen, Jau Yi Li, Stacey Weiss, Jaya Mishra, Faisal H. Cheema, Glenn Markowitz, Takayoshi Suganami, Kazutomo Sawai, Masashi Mukoyama, Cheryl Kunis, Vivette D’Agati, Prasad Devarajan, Jonathan Barasch
Veronique Chauvet, Xin Tian, Herve Husson, David H. Grimm, Tong Wang, Thomas Hieseberger, Peter Igarashi, Anton M. Bennett, Oxana Ibraghimov-Beskrovnaya, Stefan Somlo, Michael J. Caplan
Jorma Wartiovaara, Lars-Göran Öfverstedt, Jamshid Khoshnoodi, Jingjing Zhang, Eetu Mäkelä, Sara Sandin, Vesas Ruotsalainen, R. Holland Cheng, Hannu Jalanko, Ulf Skoglund, Karl Tryggvason
Polycystin-1, which is encoded by a gene that is mutated in autosomal dominant polycystic kidney disease (ADPKD), is involved in cell-matrix interactions as well as in ciliary signaling. The precise mechanisms by which it functions, however, remain unclear. Here we find that polycystin-1 undergoes a proteolytic cleavage that releases its C-terminal tail (CTT), which enters the nucleus and initiates signaling processes. The cleavage occurs in vivo in association with alterations in mechanical stimuli. Polycystin-2, the product of the second gene mutated in ADPKD, modulates the signaling properties of the polycystin-1 CTT. These data reveal a novel pathway by which polycystin-1 transmits messages directly to the nucleus.
Veronique Chauvet, Xin Tian, Herve Husson, David H. Grimm, Tong Wang, Thomas Hieseberger, Peter Igarashi, Anton M. Bennett, Oxana Ibraghimov-Beskrovnaya, Stefan Somlo, Michael J. Caplan
Nephrin is a key functional component of the slit diaphragm, the structurally unresolved molecular filter in renal glomerular capillaries. Abnormal nephrin or its absence results in severe proteinuria and loss of the slit diaphragm. The diaphragm is a thin extracellular membrane spanning the approximately 40-nm-wide filtration slit between podocyte foot processes covering the capillary surface. Using electron tomography, we show that the slit diaphragm comprises a network of winding molecular strands with pores the same size as or smaller than albumin molecules, as demonstrated in humans, rats, and mice. In the network, which is occasionally stratified, immunogold-nephrin antibodies labeled individually detectable globular cross strands, about 35 nm in length, lining the lateral elongated pores. The cross strands, emanating from both sides of the slit, contacted at the slit center but had free distal endings. Shorter strands associated with the cross strands were observed at their base. Immunolabeling of recombinant nephrin molecules on transfected cells and in vitrified solution corroborated the findings in kidney. Nephrin-deficient proteinuric patients with Finnish-type congenital nephrosis and nephrin-knockout mice had only narrow filtration slits that lacked the slit diaphragm network and the 35-nm-long strands but contained shorter molecular structures. The results suggest the direct involvement of nephrin molecules in constituting the macromolecule-retaining slit diaphragm and its pores.
Jorma Wartiovaara, Lars-Göran Öfverstedt, Jamshid Khoshnoodi, Jingjing Zhang, Eetu Mäkelä, Sara Sandin, Vesa Ruotsalainen, R. Holland Cheng, Hannu Jalanko, Ulf Skoglund, Karl Tryggvason
Idiopathic pulmonary fibrosis is a progressive and fatal fibrotic disease of the lungs with unclear etiology. Prior efforts to treat idiopathic pulmonary fibrosis that focused on anti-inflammatory therapy have not proven to be effective. Recent insight suggests that the pathogenesis is mediated through foci of dysregulated fibroblasts driven by profibrotic cytokine signaling. TGF-β and PDGF are 2 of the most potent of these cytokines. In the current study, we investigated the role of TGF-β–induced fibrosis mediated by activation of the Abelson (Abl) tyrosine kinase. Our data indicate that fibroblasts respond to TGF-β by stimulating c-Abl kinase activity independently of Smad2/3 phosphorylation or PDGFR activation. Moreover, inhibition of c-Abl by imatinib prevented TGF-β–induced ECM gene expression, morphologic transformation, and cell proliferation independently of any effect on Smad signaling. Further, using a mouse model of bleomycin-induced pulmonary fibrosis, we found a significant inhibition of lung fibrosis by imatinib. Thus, Abl family members represent common targets for the modulation of profibrotic cytokine signaling.
Craig E. Daniels, Mark C. Wilkes, Maryanne Edens, Ted J. Kottom, Stephen J. Murphy, Andrew H. Limper, Edward B. Leof
Many adult organs contain stem cells, which are pluripotent and are involved in organ maintenance and repair after injury. In situ, these cells often have a low cycling rate and locate in specialized regions (niches). To detect such cells in the kidney, we administered a pulse of the nucleotide bromodeoxyuridine (BrdU) to rat and mouse pups and, after a long (more than 2-month) chase, examined whether the kidney contained a population of low-cycling cells. We found that in the adult kidney, BrdU-retaining cells were very sparse except in the renal papilla, where they were numerous. During the repair phase of transient renal ischemia, these cells entered the cell cycle and the BrdU signal quickly disappeared from the papilla, despite the absence of apoptosis in this part of the kidney. In vitro isolation of renal papillary cells showed them to have a plastic phenotype that could be modulated by oxygen tension and that when injected into the renal cortex, they incorporated into the renal parenchyma. In addition, like other stem cells, papillary cells spontaneously formed spheres. Single-cell clones of these cells coexpressed mesenchymal and epithelial proteins and gave rise to myofibroblasts, cells expressing neuronal markers, and cells of uncharacterized phenotype. These data indicate that the renal papilla is a niche for adult kidney stem cells.
Juan A. Oliver, Omar Maarouf, Faisal H. Cheema, Timothy P. Martens, Qais Al-Awqati