Nephrology
Abstract
Atrial natriuretic peptide (ANP), encoded by Nppa, is a vasodilatory hormone that promotes salt excretion. Genome-wide association studies identified Nppa as a causative factor of blood pressure development, and in humans, ANP levels were suggested as an indicator of salt sensitivity. This study aimed to provide insights into the effects of ANP on cardiorenal function in salt-sensitive hypertension. To address this question, hypertension was induced in SSNPPA-/- (knockout of Nppa in the Dahl Salt-Sensitive (SS) rat background) or SSWT (wild type Dahl SS) rats by a high salt diet challenge (HS, 4% NaCl for 21 days). Chronic infusion of ANP in SSWT rats attenuated the increase in blood pressure and cardiorenal damage. Overall, SSNPPA-/- strain demonstrated higher blood pressure and intensified cardiac fibrosis (with no changes in ejection fraction) compared to SSWT rats. Furthermore, SSNPPA-/- rats exhibited kidney hypertrophy and higher glomerular injury scores, reduced diuresis, and lower sodium and chloride excretion than SSWT when fed a HS diet. Additionally, the activity of epithelial Na+ channel (ENaC) was found to be increased in the collecting ducts of the SSNPPA-/- rats. Taken together, these data show promise for the therapeutic benefits of ANP and ANP-increasing drugs for treating salt-sensitive hypertension.
Authors
Daria V. Ilatovskaya, Vladislav Levchenko, Kristen Winsor, Gregory R. Blass, Denisha R. Spires, Elizaveta Sarsenova, Iuliia Polina, Adrian Zietara, Mark Paterson, Alison J. Kriegel, Alexander Staruschenko
Abstract
In this investigation, a potentially novel signaling pathway in gentamicin-induced acute kidney injury—worsened by overexpression of proximal tubular enzyme, myo-inositol oxygenase (MIOX)—was elucidated. WT, MIOX-transgenic (MIOX-Tg), and MIOX-KO mice were used. Gentamicin was administered to induce tubular injury. MIOX-Tg mice had severe tubular lesions associated with increased serum creatinine and proteinuria. Lesions were relatively mild, with no rise in serum creatinine and no albuminuria in MIOX-KO mice. Transfection of HK-2 cells with MIOX-pcDNA led to increased gentamicin-induced reactive oxygen species (ROS). Marked increase of ROS-mediated lipid hydroperoxidation was noted in MIOX-Tg mice, as assessed by 4-HNE staining. This was associated with increased expression of arachidonate 12-lipoxygenase (ALOX-12) and generation of 12-hydroxyeicosatetraenoic acid (12-HETE). In addition, notable monocyte/macrophage influx, upregulation of NF-κB and inflammatory cytokines, and apoptosis was observed in MIOX-Tg mice. Treatment of cells with ALOX-12 siRNA abolished gentamicin-mediated induction of cytokines and 12-HETE generation. HETE-12 treatment promoted this effect, along with upregulation of various signaling kinases and activation of GPCR31. Similarly, treatment of cells or mice with the ALOX-12 inhibitor ML355 attenuated inflammatory response, kinase signaling cascade, and albuminuria. Collectively, these studies highlight a potentially novel mechanism (i.e., the ROS/ALOX-12/12-HETE/GPR31 signaling axis) relevant to gentamicin-induced nephrotoxicity modulated by MIOX.
Authors
Isha Sharma, Yingjun Liao, Xiaoping Zheng, Yashpal S. Kanwar
Abstract
The importance of healthy mitochondrial function is implicated in the prevention of chronic/diabetic kidney diseases (CKD/DKD). Sex differences also play an important role in DKD. Our previous studies revealed that mitochondrial substrate overload (modeled by homozygous deletion of carnitine acetyl-transferase – CrAT) in proximal tubules causes renal injury. Here we demonstrate the importance of intact mitochondrial substrate efflux by titrating the amount of overload through the generation of a heterozygous CrAT knockout model (“PT-CrATHET” mouse). Intriguingly, these animals developed renal injury similarly to their homozygous counterparts. Mitochondria were structurally and functionally impaired in both sexes. Transcriptomic analyses, however, revealed striking sex differences. Male mice shut down fatty acid oxidation and several other metabolism-related pathways. Females had a significantly weaker transcriptional response in metabolism but activation of inflammatory pathways was prominent. Proximal tubular cells from PT-CrATHET mice of both sexes exhibited a shift towards a more glycolytic phenotype, but females were still able to oxidize fatty acid-based substrates. Our results demonstrate that maintaining mitochondrial substrate metabolism balance is crucial to satisfy proximal tubular energy demand. Our findings have potentially broad implications as both the glycolytic shift and the sexual dimorphisms discovered herein offer new modalities for future interventions for treating kidney disease.
Authors
Allison McCrimmon, Kerin M. Cahill, Claudia Kruger, Margaret E. Mangelli, Emily Bouffard, Timothy Dobroski, Kelly N. Michanczyk, Susan J. Burke, Robert C. Noland, Daria V. Ilatovskaya, Krisztian Stadler
Abstract
Kidney fibrosis is the final common pathway of progressive kidney diseases, the underlying mechanisms of which is not fully understood. The purpose of the current study is to investigate a role of Piezo1, a mechanosensitive nonselective cation channel, in kidney fibrosis. In human fibrotic kidneys, Piezo1 protein expression was markedly upregulated. The abundance of Piezo1 protein in kidneys of mice with UUO or with folic-acid treatment was significantly increased. Inhibition of Piezo1 with GsMTx4 markedly ameliorated UUO or folic acid-induced kidney fibrosis. Mechanical stretch, compression or stiffness induced Piezo1 activation and pro-fibrotic responses in human HK2 cells and primary cultured mouse proximal tubular cells (mPTCs), which were greatly prevented by inhibition or silence of Piezo1. TGFβ-1 induced increased Piezo1 expression and pro-fibrotic phenotypic alterations in HK2 cells and mPTCs, which was again markedly prevented by inhibition of Piezo1. Activation of Piezo1 by Yoda1, a Piezo1 agonist, caused calcium influx and profibrotic responses in HK2 cells and induced calpain2 activation, followed by talin1 cleavage and upregulation of integrinβ1. Also, Yoda1 promoted the link between ECM and integrinβ1. In conclusion, Piezo1 is involved in the progression of kidney fibrosis and pro-fibrotic alterations in renal proximal tubular cells, likely through activating calcium-calpain2-integrinβ1 pathway.
Authors
Xiaoduo Zhao, Yonglun Kong, Baien Liang, Jinhai Xu, Yu Lin, Nan Zhou, Jing Li, Bin Jiang, Jianding Cheng, Chunling Li, Weidong Wang
Abstract
The current strategy to detect acute injury of kidney tubular cells relies on changes in serum levels of creatinine. Yet serum creatinine (sCr) is a marker of both functional and pathological processes and does not specifically assay tubular injury. In addition, sCr may require days to reach diagnostic thresholds, yet tubular cells respond with programs of damage and repair within minutes or hours. To detect acute responses to clinically relevant stimuli, we created Rosa26-floxed-stop uracil phosphoribosyl-transferase (Uprt) expressing mice and inoculated 4-thiouracil (TU) to tag nascent RNA at selected time points. Cre-driven TU-tagged RNA was isolated from whole kidneys and demonstrated that volume depletion and ischemia induced different genetic programs. Even lineage related cell types expressed different genes in response to the two stressors. TU-tagging also demonstrated the transient nature of the responses. Because we placed Uprt in the ubiquitously active Rosa-26 locus, RNAs from many cell types can be tagged in vivo and their roles interrogated under various conditions. In short, TU labeling identifies stimulus-specific, cell-specific, and time-dependent acute responses that are otherwise difficult to detect with other technologies and are entirely obscured when sCr is the sole metric of kidney damage.
Authors
Tian Huai Shen, Jacob Stauber, Katherine Xu, Alexandra Jacunski, Neal Paragas, Miriam Callahan, Run Banlengchit, Abraham D. Levitman, Beatriz Desanti de Oliveira, Andrew Beenken, Madeleine S. Grau, Edwin Mathieu, Qingyin Zhang, Yuanji Li, Tejashree Gopal, Nathaniel Askanase, Siddarth Arumugam, Sumit Mohan, Pamela I. Good, Jacob S. Stevens, Fangming Lin, Samuel K. Sia, Chyuan-Sheng Lin, Vivette D'Agati, Krzysztof Kiryluk, Nicholas P. Tatonetti, Jonathan Barasch
Abstract
Peroxisomes are specialized cellular organelles involved in a variety of metabolic processes. In humans, mutations leading to complete loss of peroxisomes cause multiorgan failure (Zellweger’s spectrum disorders, ZSD), including renal impairment. However, the (patho)physiological role of peroxisomes in the kidney remains unknown. We addressed the role of peroxisomes in renal function in mice with conditional ablation of peroxisomal biogenesis in the renal tubule (cKO mice). Functional analyses did not reveal any overt kidney phenotype in cKO mice. However, infant male cKO mice had lower body and kidney weights, and adult male cKO mice exhibited substantial reductions in kidney weight and kidney weight/body weight ratio. Stereological analysis showed an increase in mitochondria density in proximal tubule cells of cKO mice. Integrated transcriptome and metabolome analyses revealed profound reprogramming of a number of metabolic pathways, including metabolism of glutathione and biosynthesis/biotransformation of several major classes of lipids. Although this analysis suggested compensated oxidative stress, challenge with high-fat feeding did not induce significant renal impairments in cKO mice. We demonstrate that renal tubular peroxisomes are dispensable for normal renal function. Our data also suggest that renal impairments in patients with ZSD are of extrarenal origin.
Authors
Camille Ansermet, Gabriel Centeno, Sylvain Pradervand, Dusan Harmacek, Andy Garcia, Jean Daraspe, Sai Kocherlakota, Myriam Baes, Yohan Bignon, Dmitri Firsov
Abstract
Fibrotic diseases account for nearly half of all deaths in the developed world. Despite its importance, the pathogenesis of fibrosis remains poorly understood. Recently, the two mechanosensitive transcription cofactors YAP and TAZ have emerged as important profibrotic regulators in multiple murine tissues. Despite this growing recognition, a number of important questions remain unanswered, including which cell types require YAP/TAZ activation for fibrosis to occur and the time course of this activation. Here, we present a detailed analysis of the role that myofibroblast YAP and TAZ play in organ fibrosis and the kinetics of their activation. Using analyses of cells, as well as multiple murine and human tissues, we demonstrated that myofibroblast YAP and TAZ were activated early after organ injury and that this activation was sustained. We further demonstrated the critical importance of myofibroblast YAP/TAZ in driving progressive scarring in the kidney, lung, and liver, using multiple transgenic models in which YAP and TAZ were either deleted or hyperactivated. Taken together, these data establish the importance of early injury-induced myofibroblast YAP and TAZ activation as a key event driving fibrosis in multiple organs. This information should help guide the development of new antifibrotic YAP/TAZ inhibition strategies.
Authors
Xiaolin He, Monica F. Tolosa, Tianzhou Zhang, Santosh Kumar Goru, Luisa Ulloa Severino, Paraish S. Misra, Caitríona M. McEvoy, Lauren Caldwell, Stephen G. Szeto, Feng Gao, Xiaolan Chen, Cassandra Atin, Victoria Ki, Noah Vukosa, Catherine Hu, Johnny Zhang, Christopher Yip, Adriana Krizova, Jeffrey L. Wrana, Darren A. Yuen
Abstract
IgA nephropathy (IgAN) is a leading cause of kidney failure, yet little is known about the immunopathogenesis of this disease. IgAN is characterized by deposition of IgA in the kidney glomeruli, but the source and stimulus for IgA production is not known. Clinical and experimental data suggest a role for aberrant immune responses to mucosal microbiota in IgAN, and in some countries of high disease prevalence tonsillectomy is regarded as standard-of-care therapy. To evaluate the relationship between microbiota and mucosal immune responses we characterized the tonsil microbiota in patients with IgAN versus non-related household-matched control subjects and identified increased carriage of the genus Neisseria and elevated Neisseria-targeted serum IgA in IgAN cases. We reverse-translated these findings in experimental IgAN driven by BAFF overexpression in BAFF-transgenic mice, rendered susceptible to Neisseria infection by introduction of a humanized CEACAM-1 transgene (B x hC-Tg). Colonization of B x hC-Tg mice with Neisseria yielded augmented levels of systemic Neisseria-specific IgA. Using a custom ELISPOT assay, we discovered anti-Neisseria-specific IgA-secreting cells within in the kidneys of these mice. These findings suggest a role for cytokine-driven aberrant mucosal immune responses to oropharyngeal pathobionts such as Neisseria in the immunopathogenesis of IgAN. Furthermore, in the presence of excess BAFF, pathobiont-specific IgA can be produced in situ within the kidney.
Authors
Elissa G. Currie, Bryan Coburn, Elisa A. Porfilio, Ping Lam, Olga L. Rojas, Jan Novak, Stuart Yang, Raad B. Chowdhury, Lesley A. Ward, Pauline W. Wang, Khashayar Khaleghi, James An, Sarah Q. Crome, Michelle A. Hladunewich, Sean J. Barbour, Daniel C. Cattran, Rulan S. Parekh, Christoph Licht, Rohan John, Rupert Kaul, Kenneth Croitoru, Scott D. Gray-Owen, David S. Guttman, Jennifer L. Gommerman, Heather N. Reich
Abstract
Molecular chaperones are responsible for maintaining cellular homeostasis, and one such chaperone, GRP170, is an endoplasmic reticulum (ER) resident that oversees both protein biogenesis and quality control. We previously discovered that GRP170 regulates the degradation and assembly of the epithelial sodium channel (ENaC), which reabsorbs sodium in the distal nephron and thereby regulates salt-water homeostasis and blood pressure. To define the role of GRP170 and more generally molecular chaperones in kidney physiology, we developed an inducible, nephron-specific GRP170 knockout mouse. Here we show that GRP170 deficiency causes a dramatic phenotype: profound hypovolemia, hyperaldosteronemia, and dysregulation of ion homeostasis, all of which are associated with the loss of ENaC. Additionally, the GRP170 KO mouse exhibits hallmarks of acute kidney injury (AKI). We further demonstrate that the unfolded protein response (UPR) is activated in the GRP170 deficient mouse. Notably, the UPR is also activated in AKI when originating from various other etiologies, including ischemia, sepsis, glomerulonephritis, nephrotic syndrome, and transplant rejection. Our work establishes the central role of GRP170 in kidney homeostasis and directly links molecular chaperone function to kidney injury.
Authors
Aidan W. Porter, Diep N. Nguyen, Dennis R. Clayton, Wily G. Ruiz, Stephanie M. Mutchler, Evan C. Ray, Allison L. Marciszyn, Lubika J. Nkashama, Arohan R. Subramanya, Sebastien Gingras, Thomas R. Kleyman, Gerard Apodaca, Linda M. Hendershot, Jeffrey L. Brodsky, Teresa M. Buck
Abstract
Aristolochic acid (AA) is the causative nephrotoxic alkaloid in aristolochic acid nephropathy, which results in a tubulointerstitial fibrosis. AA causes direct proximal tubule damage. There is also an influx of macrophages, although their role in the pathogenesis is poorly understood. Here we demonstrate that AA directly stimulates migration, inflammation, and reactive oxygen species (ROS) production in macrophages ex vivo. Cells lacking interferon regulatory factor 4 (IRF4), a known regulator of macrophage migration and phenotype, had a reduced migratory response, though effects on ROS production and inflammation were preserved or increased relative to wild-type cells. Macrophage-specific IRF4 knockout mice were protected from both acute and chronic kidney effects of AA administration based on functional and histological analysis. Renal macrophages from kidneys of AA-treated macrophage-specific IRF4 knockout mice demonstrated increased apoptosis and ROS production compared with wildtype controls, indicating that AA directly polarizes macrophages to a promigratory and proinflammatory phenotype. However, knockout mice had reduced renal macrophage abundance following AA administration. While macrophages lacking IRF4 can adopt a proinflammatory phenotype upon AA exposure, their inability to migrate to the kidney and increased rates of apoptosis upon infiltration provide protection from AA in vivo. These results provide evidence of direct AA effects on macrophages in AAN and add to the growing body of evidence that supports a key role of IRF4 in modulating macrophage function in kidney injury.
Authors
Kensuke Sasaki, Andrew S. Terker, Jiaqi Tang, Shirong Cao, Juan Pablo Arroyo, Aolei Niu, Suwan Wang, Xiaofeng Fan, Yahua Zhang, Stephanie R. Bennett, Ming-zhi Zhang, Raymond C. Harris
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