Phosphorylation of Dynamin-related protein1 (Drp1) represents an important regulatory mechanism for mitochondrial fission. Here we established the role of Drp1 Serine 600 (S600) phosphorylation on mitochondrial fission in vivo, and assessed the functional consequences of targeted elimination of the Drp1S600 phosphorylation site in progression of diabetic nephropathy (DN). We generated a knockin mouse in which S600 was mutated to alanine (Drp1S600A). We found that diabetic Drp1S600A mice exhibited improved biochemical and histological features of DN along with reduced mitochondrial fission and diminished mitochondrial ROS in vivo. Importantly, we observed that the effect of Drp1S600 phosphorylation on mitochondrial fission in the diabetic milieu was stimulus- but not cell type-dependent. Mechanistically, we showed that mitochondrial fission in high glucose conditions occurs through concomitant binding of phospho-Drp1S600 with mitochondrial fission factor (Mff) and actin-related protein 3 (Arp3), ultimately leading to accumulation of F-actin and Drp1 on the mitochondria. Taken together, these findings establish that a single phosphorylation site in Drp1 can regulate mitochondrial fission and progression of DN in vivo, and highlight the stimulus-specific consequences of Drp1S600 phosphorylation on mitochondrial dynamics.
Daniel L. Galvan, Jianyin Long, Nathanael Green, Benny H. Chang, Jamie S. Lin, Paul T. Schumacker, Luan D. Truong, Paul Overbeek, Farhad R. Danesh
Because of the less than robust response to therapy and impact on choice of optimal chemotherapy and prognosis, chronic kidney disease has drawn attention in the treatment of multiple myeloma, a malignant hematologic disorder that can produce significant amounts of monoclonal immunoglobulin free light chains. These low molecular weight proteins are relatively freely filtered through the glomerulus and are reabsorbed by the proximal tubule. The present study demonstrated that during the process of metabolism of immunoglobulin free light chains, reactive oxygen species activated the Signal Transducer and Activator of Transcription 1 (STAT1) pathway in proximal tubule epithelium. STAT1 activation served as the seminal signaling molecule that produced the pro-inflammatory molecule, Interleukin-1β, as well as the pro-fibrotic agent, Transforming Growth Factor-β, by this portion of the nephron. These effects occurred in vivo and were produced specifically by the generation of hydrogen peroxide by the VL domain of the light chain. To the extent that the experiments reflect the human condition, these studies offered new insights into the pathogenesis of progressive kidney failure in the setting of lymphoproliferative disorders, such as multiple myeloma, that feature increased circulating levels of monoclonal immunoglobulin fragments that require metabolism by the kidney.
Wei-Zhong Ying, Xingsheng Li, Sunil Rangarajan, Wenguang Feng, Lisa M. Curtis, Paul W. Sanders
Increased urinary oxalate excretion (hyperoxaluria) promotes the formation of calcium oxalate crystals. Monogenic diseases due to hepatic enzymes deficiency result in chronic hyperoxaluria, promoting end-stage renal disease in children and young adults. Ethylene glycol poisoning also results in hyperoxaluria promoting acute renal failure and frequently death. Stiripentol is an antiepileptic drug used to treat children affected by Dravet syndrome, possibly by inhibiting neuronal lactate dehydrogenase 5 isoenzyme. As this isoenzyme is also the last step of hepatic oxalate production, we hypothesized that Stiripentol would potentially reduce hepatic oxalate production and urine oxalate excretion. In vitro, Stiripentol decreased in a dose-dependent manner the synthesis of oxalate by hepatocytes. In vivo, Stiripentol oral administration reduced significantly urine oxalate excretion in rats. Stiripentol protected kidneys against calcium oxalate crystal deposits in acute ethylene glycol intoxication and chronic calcium oxalate nephropathy models. In both models, Stiripentol improved significantly renal function. Patients affected by Dravet syndrome and treated with Stiripentol had a lower urine oxalate excretion than control patients. A young girl affected by severe type I hyperoxaluria received Stiripentol for several weeks: urine oxalate excretion decreased by two-thirds. Stiripentol is a promising potential therapy against genetic hyperoxaluria and ethylene glycol poisoning.
Marine Le Dudal, Lea Huguet, Joëlle Perez, Sophie Vandermeersch, Elise Bouderlique, Ellie Tang, Carole Martori, Nicole Chemaly, Rima Nabbout, Jean-Philippe Haymann, Vincent Frochot, Laurent Baud, Georges Deschênes, Michel Daudon, Emmanuel Letavernier
Acute kidney injury (AKI) can lead to chronic kidney disease (CKD) if injury is severe and/or repair is incomplete. However, the pathogenesis of CKD following renal ischemic injury is not fully understood. Capillary rarefaction and tubular hypoxia are common findings during the AKI to CKD transition. We investigated the tubular stress response to hypoxia and demonstrated that a stress responsive transcription factor, FoxO3, was regulated by prolyl hydroxylase. Hypoxia inhibited FoxO3 prolyl hydroxylation and FoxO3 degradation, thus leading to FoxO3 accumulation and activation in tubular cells. Hypoxia-activated Hif-1α contributed to FoxO3 activation and functioned to protect kidneys, as tubular deletion of Hif-1α decreased hypoxia-induced FoxO3 activation, and resulted in more severe tubular injury and interstitial fibrosis following ischemic injury. Strikingly, tubular deletion of FoxO3 during the AKI to CKD transition aggravated renal structural and functional damage leading to a more profound CKD phenotype. We showed that tubular deletion of FoxO3 resulted in decreased autophagic response and increased oxidative injury, which may explain renal protection by FoxO3. Our study indicates that in the hypoxic kidney, stress responsive transcription factors can be activated for adaptions to counteract hypoxic insults, thus attenuating CKD development.
Ling Li, Huimin Kang, Qing Zhang, Vivette D. D'Agati, Qais Al-Awqati, Fangming Lin
We identified 2 genes, histone deacetylase 1 (HDAC1) and HDAC2, contributing to the pathogenesis of proteinuric kidney diseases, the leading cause of end-stage kidney disease. mRNA expression profiling from proteinuric mouse glomeruli was linked to Connectivity Map databases, identifying HDAC1 and HDAC2 with the differentially expressed gene set reversible by HDAC inhibitors. In numerous progressive glomerular disease models, treatment with valproic acid (a class I HDAC inhibitor) or SAHA (a pan-HDAC inhibitor) mitigated the degree of proteinuria and glomerulosclerosis, leading to a striking increase in survival. Podocyte HDAC1 and HDAC2 activities were increased in mice podocytopathy models, and podocyte-associated Hdac1 and Hdac2 genetic ablation improved proteinuria and glomerulosclerosis. Podocyte early growth response 1 (EGR1) was increased in proteinuric patients and mice in an HDAC1- and HDAC2-dependent manner. Loss of EGR1 in mice reduced proteinuria and glomerulosclerosis. Longitudinal analysis of the multicenter Veterans Aging Cohort Study demonstrated a 30% reduction in mean annual loss of estimated glomerular filtration rate, and this effect was more pronounced in proteinuric patients receiving valproic acid. These results strongly suggest that inhibition of HDAC1 and HDAC2 activities may suppress the progression of human proteinuric kidney diseases through the regulation of EGR1.
Kazunori Inoue, Geliang Gan, Maria Ciarleglio, Yan Zhang, Xuefei Tian, Christopher E. Pedigo, Corey Cavanaugh, Janet Tate, Ying Wang, Elizabeth Cross, Marwin Groener, Nathan Chai, Zhen Wang, Amy Justice, Zhenhai Zhang, Chirag R. Parikh, Francis P. Wilson, Shuta Ishibe
Soluble urokinase receptor (suPAR) is a circulatory molecule that activates αvβ3 integrin on podocytes, causes foot process effacement, and contributes to proteinuric kidney disease. While active integrin can be targeted by antibodies and small molecules, endogenous inhibitors haven’t been discovered yet. Here we report a novel, renoprotective role for inducible costimulator (ICOS) ligand (ICOSL) in early kidney disease through its selective binding to podocyte αvβ3 integrin. Contrary to ICOSL’s immune-regulatory role, ICOSL in non-hematopoietic cells limited the activation of αvβ3 integrin. Specifically, ICOSL contains arginine-glycine-aspartate (RGD) motif, which allowed for a high affinity and selective binding to αvβ3 and modulation of podocyte adhesion. This binding was largely inhibited either by a synthetic RGD peptide or by a disrupted RGD sequence in ICOSL. ICOSL binding favored the active αvβ3 rather than the inactive form and showed little affinity for other integrins. Consistent with the rapid induction of podocyte ICOSL by inflammatory stimuli, glomerular ICOSL expression was increased in biopsies of early stage human proteinuric kidney diseases. Icosl deficiency in mice resulted in an increased susceptibility to proteinuria that was rescued by recombinant ICOSL. Our work identified a novel role for ICOSL, which serves as an endogenous αvβ3-selective antagonist to maintain glomerular filtration.
Kwi Hye Koh, Yanxia Cao, Steve Mangos, Nicholas J. Tardi, Ranadheer R. Dande, Ha Won Lee, Beata Samelko, Mehmet M. Altintas, Vincent P. Schmitz, Hyun Lee, Kamalika Mukherjee, Vasil Peev, David J. Cimbaluk, Jochen Reiser, Eunsil Hahm
Epithelial-mesenchymal transition (EMT) contributes significantly to interstitial matrix deposition in diabetic kidney disease (DKD). However, detection of EMT in kidney tissue is impracticable, and anti-EMT therapies have long been hindered. We reported that phosphatase and tensin homolog (PTEN) promoted transforming growth factor beta 1 (TGF-β), sonic hedgehog (SHH), connective tissue growth factor (CTGF), interleukin 6 (IL-6), and hyperglycemia-induced EMT when PTEN was modified by a MEX3C-catalyzed K27-linked polyubiquitination at lysine 80 (referred to as PTENK27-polyUb). Genetic inhibition of PTENK27-polyUb alleviated Col4a3 knockout–, folic acid–, and streptozotocin-induced (STZ-induced) kidney injury. Serum and urine PTENK27-polyUb concentrations were negatively correlated with glomerular filtration rate (GFR) for diabetic patients. Mechanistically, PTENK27-polyUb facilitated dephosphorylation and protein stabilization of TWIST, SNAI1, and YAP in renal epithelial cells, leading to enhanced EMT. We identified that a small molecule, triptolide, inhibited MEX3C-catalyzed PTENK27-polyUb and EMT of renal epithelial cells. Treatment with triptolide reduced TWIST, SNAI1, and YAP concurrently and improved kidney health in Col4a3 knockout–, folic acid–injured disease models and STZ-induced, BTBR ob/ob diabetic nephropathy models. Hence, we demonstrated the important role of PTENK27-polyUb in DKD and a promising therapeutic strategy that inhibited the progression of DKD.
Yajuan Li, Qingsong Hu, Chunlai Li, Ke Liang, Yu Xiang, Heidi Hsiao, Tina K. Nguyen, Peter K. Park, Sergey D. Egranov, Chandrashekar R. Ambati, Nagireddy Putluri, David H. Hawke, Leng Han, Mien-Chie Hung, Farhad R. Danesh, Liuqing Yang, Chunru Lin
Soluble urokinase plasminogen activator receptor (suPAR) is an immune-derived circulating signaling molecule that has been implicated in chronic kidney disease such as focal segmental glomerulosclerosis (FSGS). Typically, native uPAR (isoform 1) translates to a three-domain protein capable of binding and activating integrins, yet the function of additional isoforms generated by alternative splicing is unknown. Here, we characterized mouse uPAR isoform 2 (msuPAR2), encoding domain I and nearly one-half of domain II, as a dimer in solution, as revealed by 3D electron microscopy structural analysis. In vivo, msuPAR2 transgenic mice exhibited signs of severe renal disease characteristic of FSGS with proteinuria, loss of kidney function and glomerulosclerosis. Sequencing of the glomerular RNAs from msuPAR2-Tg mice revealed differentially expressed gene signature that includes upregulation of the suPAR receptor Itgb3, encoding β3 integrin. Crossing msuPAR2-transgenic mice with three different integrin β3 deficiency models rescued msuPAR2-mediated kidney function. Further analyses indicated a central role for β3 integrin and c-Src in msuPAR2 signaling and in human FSGS kidney biopsies. Administration of Src inhibitors reduced proteinuria in msuPAR2-transgenic mice. In conclusion, mouse uPAR isoform 2 may play an important role in certain forms of scarring kidney disease.
Changli Wei, Jing Li, Brian D. Adair, Ke Zhu, Jian Cai, Michael Merchant, Beata Samelko, Zhongji Liao, Kwi Hye Koh, Nicholas J. Tardi, Ranadheer R. Dande, Shuangxin Liu, Jianchao Ma, Salvatore DiBartolo, Stefan Hägele, Vasil Peev, Salim S. Hayek, David J. Cimbaluk, Melissa Tracy, Jon B. Klein, Sanja Sever, Sanford J. Shattil, M. Amin Arnaout, Jochen Reiser
Atypical hemolytic uremic syndrome (aHUS) is frequently associated in humans with loss-of-function mutations in complement-regulating proteins or gain-of-function mutations in complement-activating proteins. Thus, aHUS provides an archetypal complement-mediated disease with which to model new therapeutic strategies and treatments. Herein, we show that, when transferred to mice, an aHUS-associated gain-of-function change (D1115N) to the complement-activation protein C3 results in aHUS. Homozygous C3 p.D1115N (C3KI) mice developed spontaneous chronic thrombotic microangiopathy together with hematuria, thrombocytopenia, elevated creatinine, and evidence of hemolysis. Mice with active disease had reduced plasma C3 with C3 fragment and C9 deposition within the kidney. Therapeutic blockade or genetic deletion of C5, a protein downstream of C3 in the complement cascade, protected homozygous C3KI mice from thrombotic microangiopathy and aHUS. Thus, our data provide in vivo modeling evidence that gain-of-function changes in complement C3 drive aHUS. They also show that long-term C5 deficiency is not accompanied by development of other renal complications (such as C3 glomerulopathy) despite sustained dysregulation of C3. Our results suggest that this preclinical model will allow testing of novel complement inhibitors with the aim of developing precisely targeted therapeutics that could have application in many complement-mediated diseases.
Kate Smith-Jackson, Yi Yang, Harriet Denton, Isabel Y. Pappworth, Katie Cooke, Paul N. Barlow, John P. Atkinson, M. Kathryn Liszewski, Matthew C. Pickering, David Kavanagh, H. Terence Cook, Kevin J. Marchbank
In response to viral pathogens, the host upregulates antiviral genes that suppress translation of viral mRNAs. However, induction of such antiviral responses may not be exclusive to viruses, as the pathways lie at the intersection of broad inflammatory networks that can also be induced by bacterial pathogens. Using a model of Gram-negative sepsis, we show that propagation of kidney damage initiated by a bacterial origin ultimately involves antiviral responses that result in host translation shutdown. We determined that activation of the eukaryotic translation initiation factor 2-α kinase 2/eukaryotic translation initiation factor 2α (Eif2ak2/Eif2α) axis is the key mediator of translation initiation block in late-phase sepsis. Reversal of this axis mitigated kidney injury. Furthermore, temporal profiling of the kidney translatome revealed that multiple genes involved in formation of the initiation complex were translationally altered during bacterial sepsis. Collectively, our findings imply that translation shutdown is indifferent to the specific initiating pathogen and is an important determinant of tissue injury in sepsis.
Takashi Hato, Bernhard Maier, Farooq Syed, Jered Myslinski, Amy Zollman, Zoya Plotkin, Michael T. Eadon, Pierre C. Dagher