Bone formation during fracture repair inevitably initiates within or around extravascular deposits of a fibrin-rich matrix. In addition to a central role in hemostasis, fibrin is thought to enhance bone repair by supporting inflammatory and mesenchymal progenitor egress into the zone of injury. However, given that a failure of efficient fibrin clearance can impede normal wound repair, the precise contribution of fibrin to bone fracture repair, whether supportive or detrimental, is unknown. Here, we employed mice with genetically and pharmacologically imposed deficits in the fibrin precursor fibrinogen and fibrin-degrading plasminogen to explore the hypothesis that fibrin is vital to the initiation of fracture repair, but impaired fibrin clearance results in derangements in bone fracture repair. In contrast to our hypothesis, fibrin was entirely dispensable for long-bone fracture repair, as healing fractures in fibrinogen-deficient mice were indistinguishable from those in control animals. However, failure to clear fibrin from the fracture site in plasminogen-deficient mice severely impaired fracture vascularization, precluded bone union, and resulted in robust heterotopic ossification. Pharmacological fibrinogen depletion in plasminogen-deficient animals restored a normal pattern of fracture repair and substantially limited heterotopic ossification. Fibrin is therefore not essential for fracture repair, but inefficient fibrinolysis decreases endochondral angiogenesis and ossification, thereby inhibiting fracture repair.
Masato Yuasa, Nicholas A. Mignemi, Jeffry S. Nyman, Craig L. Duvall, Herbert S. Schwartz, Atsushi Okawa, Toshitaka Yoshii, Gourab Bhattacharjee, Chenguang Zhao, Jesse E. Bible, William T. Obremskey, Matthew J. Flick, Jay L. Degen, Joey V. Barnett, Justin M.M. Cates, Jonathan G. Schoenecker
Chronic kidney disease is characterized by interstitial fibrosis and proliferation of scar-secreting myofibroblasts, ultimately leading to end-stage renal disease. The hedgehog (Hh) pathway transcriptional effectors GLI1 and GLI2 are expressed in myofibroblast progenitors; however, the role of these effectors during fibrogenesis is poorly understood. Here, we demonstrated that GLI2, but not GLI1, drives myofibroblast cell-cycle progression in cultured mesenchymal stem cell–like progenitors. In animals exposed to unilateral ureteral obstruction, Hh pathway suppression by expression of the GLI3 repressor in GLI1+ myofibroblast progenitors limited kidney fibrosis. Myofibroblast-specific deletion of
Rafael Kramann, Susanne V. Fleig, Rebekka K. Schneider, Steven L. Fabian, Derek P. DiRocco, Omar Maarouf, Janewit Wongboonsin, Yoichiro Ikeda, Dirk Heckl, Steven L. Chang, Helmut G. Rennke, Sushrut S. Waikar, Benjamin D. Humphreys
Macrophages (Mø) are integral in ischemia/reperfusion injury–incited (I/R-incited) acute kidney injury (AKI) that leads to fibrosis and chronic kidney disease (CKD). IL-34 and CSF-1 share a receptor (c-FMS), and both cytokines mediate Mø survival and proliferation but also have distinct features. CSF-1 is central to kidney repair and destruction. We tested the hypothesis that IL-34–dependent, Mø-mediated mechanisms promote persistent ischemia-incited AKI that worsens subsequent CKD. In renal I/R, the time-related magnitude of Mø-mediated AKI and subsequent CKD were markedly reduced in IL-34–deficient mice compared with controls. IL-34, c-FMS, and a second IL-34 receptor, protein-tyrosine phosphatase ζ (PTP-ζ) were upregulated in the kidney after I/R. IL-34 was generated by tubular epithelial cells (TECs) and promoted Mø-mediated TEC destruction during AKI that worsened subsequent CKD via 2 distinct mechanisms: enhanced intrarenal Mø proliferation and elevated BM myeloid cell proliferation, which increases circulating monocytes that are drawn into the kidney by chemokines. CSF-1 expression in TECs did not compensate for IL-34 deficiency. In patients, kidney transplants subject to I/R expressed IL-34, c-FMS, and PTP−ζ in TECs during AKI that increased with advancing injury. Moreover, IL-34 expression increased, along with more enduring ischemia in donor kidneys. In conclusion, IL-34-dependent, Mø-mediated, CSF-1 nonredundant mechanisms promote persistent ischemia-incited AKI that worsens subsequent CKD.
Jea-Hyun Baek, Rui Zeng, Julia Weinmann-Menke, M. Todd Valerius, Yukihiro Wada, Amrendra K. Ajay, Marco Colonna, Vicki R. Kelley
Kidney size adaptively increases as mammals grow and in response to the loss of 1 kidney. It is not clear how kidneys size themselves or if the processes that adapt kidney mass to lean body mass also mediate renal hypertrophy following unilateral nephrectomy (UNX). Here, we demonstrated that mice harboring a proximal tubule–specific deletion of
Jian-Kang Chen, Kojiro Nagai, Jianchun Chen, David Plieth, Masayo Hino, Jinxian Xu, Feng Sha, T. Alp Ikizler, C. Chad Quarles, David W. Threadgill, Eric G. Neilson, Raymond C. Harris
Steroid-resistant nephrotic syndrome (SRNS) is a frequent cause of progressive renal function decline and affects millions of people. In a recent study, 30% of SRNS cases evaluated were the result of monogenic mutations in 1 of 27 different genes. Here, using homozygosity mapping and whole-exome sequencing, we identified recessive mutations in
Heon Yung Gee, Fujian Zhang, Shazia Ashraf, Stefan Kohl, Carolin E. Sadowski, Virginia Vega-Warner, Weibin Zhou, Svjetlana Lovric, Humphrey Fang, Margaret Nettleton, Jun-yi Zhu, Julia Hoefele, Lutz T. Weber, Ludmila Podracka, Andrej Boor, Henry Fehrenbach, Jeffrey W. Innis, Joseph Washburn, Shawn Levy, Richard P. Lifton, Edgar A. Otto, Zhe Han, Friedhelm Hildebrandt
Autosomal dominant polycystic kidney disease (ADPKD) is characterized by renal cyst formation, inflammation, and fibrosis. Macrophages infiltrate cystic kidneys, but the role of these and other inflammatory factors in disease progression are poorly understood. Here, we identified macrophage migration inhibitory factor (MIF) as an important regulator of cyst growth in ADPKD. MIF was upregulated in cyst-lining epithelial cells in polycysitn-1–deficient murine kidneys and accumulated in cyst fluid of human ADPKD kidneys. MIF promoted cystic epithelial cell proliferation by activating ERK, mTOR, and Rb/E2F pathways and by increasing glucose uptake and ATP production, which inhibited AMP-activated protein kinase signaling. MIF also regulated cystic renal epithelial cell apoptosis through p53-dependent signaling. In polycystin-1–deficient mice, MIF was required for recruitment and retention of renal macrophages, which promoted cyst expansion, and
Li Chen, Xia Zhou, Lucy X. Fan, Ying Yao, Katherine I. Swenson-Fields, Mihaela Gadjeva, Darren P. Wallace, Dorien J.M. Peters, Alan Yu, Jared J. Grantham, Xiaogang Li
Podocytes are specialized epithelial cells in the kidney glomerulus that play important structural and functional roles in maintaining the filtration barrier. Nephrotic syndrome results from a breakdown of the kidney filtration barrier and is associated with proteinuria, hyperlipidemia, and edema. Additionally, podocytes undergo changes in morphology and internalize plasma proteins in response to this disorder. Here, we used fluid-phase tracers in murine models and determined that podocytes actively internalize fluid from the plasma and that the rate of internalization is increased when the filtration barrier is disrupted. In cultured podocytes, the presence of free fatty acids (FFAs) associated with serum albumin stimulated macropinocytosis through a pathway that involves FFA receptors, the Gβ/Gγ complex, and RAC1. Moreover, mice with elevated levels of plasma FFAs as the result of a high-fat diet were more susceptible to Adriamycin-induced proteinuria than were animals on standard chow. Together, these results support a model in which podocytes sense the disruption of the filtration barrier via FFAs bound to albumin and respond by enhancing fluid-phase uptake. The response to FFAs may function in the development of nephrotic syndrome by amplifying the effects of proteinuria.
Jun-Jae Chung, Tobias B. Huber, Markus Gödel, George Jarad, Björn Hartleben, Christopher Kwoh, Alexander Keil, Aleksey Karpitskiy, Jiancheng Hu, Christine J. Huh, Marina Cella, Richard W. Gross, Jeffrey H. Miner, Andrey S. Shaw
Thiazide diuretics are used to treat hypertension; however, compensatory processes in the kidney can limit antihypertensive responses to this class of drugs. Here, we evaluated compensatory pathways in SPAK kinase–deficient mice, which are unable to activate the thiazide-sensitive sodium chloride cotransporter NCC (encoded by
P. Richard Grimm, Yoskaly Lazo-Fernandez, Eric Delpire, Susan M. Wall, Susan G. Dorsey, Edward J. Weinman, Richard Coleman, James B. Wade, Paul A. Welling
Miguel Verbitsky, Simone Sanna-Cherchi, David A. Fasel, Brynn Levy, Krzysztof Kiryluk, Matthias Wuttke, Alison G. Abraham, Frederick Kaskel, Anna Köttgen, Bradley A. Warady, Susan L. Furth, Craig S. Wong, Ali G. Gharavi
The HSP40 cochaperone SEC63 is associated with the SEC61 translocon complex in the ER. Mutations in the gene encoding SEC63 cause polycystic liver disease in humans; however, it is not clear how altered SEC63 influences disease manifestations. In mice, loss of SEC63 induces cyst formation both in liver and kidney as the result of reduced polycystin-1 (PC1). Here we report that inactivation of SEC63 induces an unfolded protein response (UPR) pathway that is protective against cyst formation. Specifically, using murine genetic models, we determined that SEC63 deficiency selectively activates the IRE1α-XBP1 branch of UPR and that SEC63 exists in a complex with PC1. Concomitant inactivation of both SEC63 and XBP1 exacerbated the polycystic kidney phenotype in mice by markedly suppressing cleavage at the G protein–coupled receptor proteolysis site (GPS) in PC1. Enforced expression of spliced XBP1 (XBP1s) enhanced GPS cleavage of PC1 in SEC63-deficient cells, and XBP1 overexpression in vivo ameliorated cystic disease in a murine model with reduced PC1 function that is unrelated to SEC63 inactivation. Collectively, the findings show that SEC63 function regulates IRE1α/XBP1 activation, SEC63 and XBP1 are required for GPS cleavage and maturation of PC1, and activation of XBP1 can protect against polycystic disease in the setting of impaired biogenesis of PC1.
Sorin V. Fedeles, Jae-Seon So, Amol Shrikhande, Seung Hun Lee, Anna-Rachel Gallagher, Christina E. Barkauskas, Stefan Somlo, Ann-Hwee Lee