Nephrology
Abstract
The role of the renal organic anion transporters OAT1 (also known as SLC22A6, originally identified as NKT) and OAT3 (also known as SLC22A8) in chronic kidney disease (CKD) remains poorly understood. This is particularly so from the viewpoint of residual proximal tubular secretion, a key adaptive mechanism to deal with protein-bound uremic toxins in CKD. Using the subtotal nephrectomy (STN) model, plasma metabolites accumulating in STN rats treated with and without the OAT inhibitor, probenecid, were identified. Comparisons with metabolomics data from Oat1-KO and Oat3-KO mice support the centrality of the OATs in residual tubular secretion of uremic solutes, such as indoxyl sulfate, kynurenate, and anthranilate. Overlapping our data with those of published metabolomics data regarding gut microbiome–derived uremic solutes — which can have dual roles in signaling and toxicity — indicates that OATs play a critical role in determining their plasma levels in CKD. Thus, the OATs, along with other SLC and ABC drug transporters, are critical to the movement of uremic solutes across tissues and into various body fluids, consistent with the remote sensing and signaling theory. The data support a role for OATs in modulating remote interorganismal and interorgan communication (gut microbiota–blood-liver-kidney-urine). The results also have implications for understanding drug-metabolite interactions involving uremic toxins.
Authors
Kevin T. Bush, Prabhleen Singh, Sanjay K. Nigam
Abstract
BK channels are expressed in intercalated (ICs) and principal (PCs) cells in the cortical collecting duct (CCD) of the mammalian kidney and have been proposed to be responsible for flow-induced K+ secretion (FIKS) and K+ adaptation. To examine the IC-specific role of BK channels, we generated a mouse with targeted disruption of the pore-forming BK alpha subunit (BKα) in ICs (IC-BKα-KO). Whole cell charybdotoxin (ChTX)-sensitive K+ currents were readily detected in control ICs, but largely absent in ICs of IC-BKα-KO mice. When placed on a high K+ (HK) diet for 13 days, blood [K+] was significantly greater in IC-BKα-KO mice vs. controls in males only, although urinary K+ excretion rates following isotonic volume expansion were similar in males and females. FIKS was present in microperfused CCDs isolated from controls, but was absent in IC-BKα-KO CCDs of both sexes. Also, flow-stimulated ENaC-mediated Na+ absorption was greater in CCDs from female IC-BKα-KO mice than in CCDs from males. Our results confirm a critical role of IC BK channels in FIKS. Sex contributes to the capacity for adaptation to a HK diet in IC-BKα-KO mice.
Authors
Rolando Carrisoza-Gaytan, Evan C. Ray, Daniel Flores, Allison L. Marciszyn, Peng Wu, Leah Liu, Arohan R. Subramanya, WenHui Wang, Shaohu Sheng, Lubika J. Nkashama, Jingxin Chen, Edwin K. Jackson, Stephanie M. Mutchler, Szilvia Heja, Donald E. Kohan, Lisa M. Satlin, Thomas R. Kleyman
Abstract
C5a is a potent inflammatory mediator, which binds C5aR1 and C5aR2. Although pathogenic roles of C5a/C5aR1 axis in inflammatory disorders are well-documented, the roles for C5a/C5aR2 axis in inflammatory disorders and underlying mechanisms remain unclear. Here, we show that C5a/C5aR2 axis contributes to renal inflammation and tissue damage in a mouse model of acute pyelonephritis. Compared with WT littermates, C5ar2-/- mice had significantly reduced renal inflammation, tubular damage and renal bacterial load following bladder inoculation with uropathogenic E coli. The decrease in inflammatory responses in the kidney of C5ar2-/- mice was correlated with reduced intrarenal levels of high mobility group box 1 protein (HMGB1), NLRP3 inflammasome components, cleaved caspase-1 and IL-1β. In vitro, C5a stimulation of macrophages from C5ar1-/- mice (lacking C5aR1 but expressing C5aR2) led to significant upregulation of HMGB1 release, NLRP3/caspase-1 inflammasome activation and IL-1β secretion. Furthermore, blockade of HMGB1 significantly reduced C5a-mediated upregulation of NLRP3/caspase-1 inflammasome activation and IL-1β secretion in the macrophages, implying a HMGB1-dependent upregulation of NLRP3/caspase-1 inflammasome activation in macrophages. Our findings demonstrate a pathogenic role for C5a/C5aR2 axis in renal injury following renal infection and suggest that C5a/C5aR2 axis contributes to renal inflammation and tissue damage through up-regulation of HMGB1 and NLRP3/caspase-1 inflammasome.
Authors
Ting Zhang, Kun-yi Wu, Ning Ma, Lin-ling Wei, Malgorzata A. Garstka, Wuding Zhou, Ke Li
Abstract
Renal cysts are the defining feature of autosomal dominant polycystic kidney disease (ADPKD); however, the substantial interstitial inflammation is an often-overlooked aspect of this disorder. Recent studies suggest that immune cells in the cyst microenvironment impact ADPKD progression. Here we report that microRNAs (miRNAs) are new molecular signals in this crosstalk. We found that miR-214 and its host long non-coding RNA Dnm3os are upregulated in orthologous ADPKD mouse models and cystic kidneys from humans with ADPKD. In situ hybridization revealed that interstitial cells in the cyst microenvironment are the primary source of miR-214. While genetic deletion of miR-214 does not affect kidney development or homeostasis, surprisingly, its inhibition in Pkd2 and Pkd1 mutant mice aggravates cyst growth. Mechanistically, the pro-inflammatory TLR4/INF-γ/STAT1 pathways transactivate the miR-214 host gene. miR-214, in turn as a negative feedback loop, directly inhibits Tlr4. Accordingly, miR-214 deletion is associated with increased Tlr4 expression and enhanced peri-cystic macrophage accumulation. Thus, miR-214 upregulation is a compensatory protective response in the cyst microenvironment that restrains inflammation and cyst growth.
Authors
Ronak Lakhia, Matanel Yheskel, Andrea Flaten, Harini Ramalingam, Karam Aboudehen, Silvia Ferrè, Laurence M. Biggers, Abheepsa Mishra, Christopher Paul Chaney, Darren P. Wallace, Thomas Carroll, Peter Igarashi, Vishal Patel
Abstract
The maintenance of functional independence is the top priority of patients with chronic kidney disease (CKD). Defects in mitochondrial energetics may compromise physical performance and independence. We investigated associations of the presence and severity of kidney disease with in vivo muscle energetics and the association of muscle energetics with physical performance. We performed measures of in vivo leg and hand muscle mitochondrial capacity (ATPmax) and resting ATP turnover (ATPflux) using 31phosphorus magnetic resonance spectroscopy and oxygen uptake (O2 uptake) by optical spectroscopy in 77 people (53 participants with CKD and 24 controls). We measured physical performance using the 6-minute walk test. Participants with CKD had a median estimated glomerular filtration rate (eGFR) of 33 ml/min per 1.73 m2. Participants with CKD had a –0.19 mM/s lower leg ATPmax compared with controls but no difference in hand ATPmax. Resting O2 uptake was higher in CKD compared with controls, despite no difference in ATPflux. ATPmax correlated with eGFR and serum bicarbonate among participants with GFR <60. ATPmax of the hand and leg correlated with 6-minute walking distance. The presence and severity of CKD associate with muscle mitochondrial capacity. Dysfunction of muscle mitochondrial energetics may contribute to reduced physical performance in CKD.
Authors
Bryan Kestenbaum, Jorge Gamboa, Sophia Liu, Amir S. Ali, Eric Shankland, Thomas Jue, Cecilia Giulivi, Lucas R. Smith, Jonathan Himmelfarb, Ian H. de Boer, Kevin Conley, Baback Roshanravan
Abstract
Renal activation of the complement system has been described in patients with diabetic nephropathy (DN), although its pathological relevance is still ill-defined. Here, we studied whether glomerular C3a, generated by uncontrolled complement activation, promotes podocyte damage, leading to proteinuria and renal injury in mice with type 2 diabetes. BTBR ob/ob mice exhibited podocyte loss, albuminuria, and glomerular injury accompanied by C3 deposits and increased C3a and C3a receptor (C3aR) levels. Decreased glomerular nephrin and α-actinin4 expression, coupled with integrin-linked kinase induction, were also observed. Treatment of DN mice with a C3aR antagonist enhanced podocyte density and preserved their phenotype, limiting proteinuria and glomerular injury. Mechanistically, ultrastructural and functional mitochondrial alterations, accompanied by downregulation of antioxidant superoxide dismutase 2 (SOD2) and increased protein oxidation, occurred in podocytes and were normalized by C3aR blockade. In cultured podocytes, C3a induced cAMP-dependent mitochondrial fragmentation. Alterations of mitochondrial membrane potential, SOD2 expression, and energetic metabolism were also found in response to C3a. Notably, C3a-induced podocyte motility was inhibited by SS-31, a peptide with mitochondrial protective effects. These data indicate that C3a blockade represents a potentially novel therapeutic strategy in DN for preserving podocyte integrity through the maintenance of mitochondrial functions.
Authors
Marina Morigi, Luca Perico, Daniela Corna, Monica Locatelli, Paola Cassis, Claudia Elisa Carminati, Silvia Bolognini, Carlamaria Zoja, Giuseppe Remuzzi, Ariela Benigni, Simona Buelli
Abstract
To define cellular mechanisms underlying kidney function and failure, the Kidney Precision Medicine Project (KPMP) analyzes biopsy tissue in a multi-center research network to build cell-level process maps of kidney. This study aimed to establish a single cell RNA sequencing strategy to use cell level transcriptional profiles from kidney biopsies in KPMP to define molecular subtypes in glomerular diseases.Using multiple sources of adult human kidney reference tissue samples, 22,268 single cell profiles passed KPMP quality control parameters. Unbiased clustering resulted in 31 distinct cell clusters that were linked to kidney and immune cell types using specific cell markers. Focusing on endothelial cell phenotypes, in silico and in situ hybridization methods assigned three discrete endothelial cell clusters to distinct renal vascular beds. Transcripts defining glomerular endothelial cell (GEC) were evaluated in biopsies from patients with ten different glomerular diseases in the NEPTUNE and ERCB cohort studies. Highest GEC scores were observed in patients with focal segmental glomerulosclerosis (FSGS). Molecular endothelial signatures suggested two distinct FSGS patient subgroups with alpha-2 macroglobulin (A2M) as a key downstream mediator of the endothelial cell phenotype. Finally, glomerular A2M transcript levels associated with lower proteinuria remission rates, linking endothelial function with long-term outcome in FSGS.
Authors
Rajasree Menon, Edgar A. Otto, Paul J. Hoover, Sean Eddy, Laura H. Mariani, Bradley Godfrey, Celine C. Berthier, Felix Eichinger, Lalita Subramanian, Jennifer L. Harder, Wenjun Ju, Viji Nair, Maria Larkina, Abhijit S. Naik, Jinghui Luo, sanjay jain, Rachel Sealfon, Olga G. Troyanskaya, Nir Hacohen, Jeffrey B. Hodgin, Matthias Kretzler
Abstract
Acute kidney injury (AKI) and chronic kidney diseases are associated with high mortality and morbidity. Although the underlying mechanisms determining the transition from acute to chronic injury are not completely understood, immune-mediated processes are critical in renal injury. We have performed a comparison of 2 mouse models leading to either kidney regeneration or fibrosis. Using global gene expression profiling we could identify immune-related pathways accounting for the majority of the observed transcriptional changes during fibrosis. Unbiased examination of the immune cell composition, using single-cell RNA sequencing, revealed major changes in tissue-resident macrophages and T cells. Following injury, there was a marked increase in tissue-resident IL-33R+ and IL-2Ra+ regulatory T cells (Tregs). Expansion of this population before injury protected the kidney from injury and fibrosis. Transcriptional profiling of Tregs showed a differential upregulation of regenerative and proangiogenic pathways during regeneration, whereas in the fibrotic environment they expressed markers of hyperactivation and fibrosis. Our data point to a hitherto underappreciated plasticity in Treg function within the same tissue, dictated by environmental cues. Overall, we provide a detailed cellular and molecular characterization of the immunological changes during kidney injury, regeneration, and fibrosis.
Authors
Fernanda do Valle Duraes, Armelle Lafont, Martin Beibel, Kea Martin, Katy Darribat, Rachel Cuttat, Annick Waldt, Ulrike Naumann, Grazyna Wieczorek, Swann Gaulis, Sabina Pfister, Kirsten D. Mertz, Jianping Li, Guglielmo Roma, Max Warncke
Abstract
ADPKD is the most common genetic cause of end stage kidney disease (ESRD). The treatment options for ADPKD are limited. We observed an upregulation in several IGF-1 pathway genes in the kidney of the Pkd1RC/RC mice. Pregnancy-associated plasma protein-A (PAPP-A), a metalloproteinase which cleaves inhibitory insulin-like growth factor binding proteins (IGFBPs), increasing the local bioactivity of IGF-1 was highly induced in the kideny of ADPKD mice. PAPP-A levels were high in cystic fluid and kidneys of humans with ADPKD. Our studies further showed the PAPP-A transcription in ADPKD is mainly regulated through the cAMP/CREB/CBP/p300 pathways. Pappa deficiency effectively inhibited the development of cysts in Pkd1RC/RC model of ADPKD. The role of PAPP-A in cystic disease appears to be regulation of the IGF-1 pathway and cellular proliferation in the kidney. Finally, preclinical studies demonstrated that treatment with monoclonal antibody that blocks the proteolytic activity of PAPP-A against IGFBP4 ameliorated ADPKD cystic disease in vivo in Pkd1RC/RC mice and ex vivo in embryonic kidneys. These data clearly indicated that the PAPP-A/IGF-1 pathway plays an important role in the growth and expansion of cysts in ADPKD. Our findings introduce a new therapeutic strategy for ADPKD that is the inhibition of PAPP-A.
Authors
Sonu Kashyap, Kyaw Zaw Hein, Claudia C.S. Chini, Jorgo Lika, Gina M. Warner, Laurie K. Bale, Vicente E. Torres, Peter C. Harris, Claus Oxvig, Cheryl A. Conover, Eduardo N. Chini
Abstract
Lithium (Li) is the mainstay pharmacotherapeutic mood stabilizer in bipolar disorder. Its efficacious use is complicated by acute and chronic renal side effects, including nephrogenic diabetes insipidus (NDI) and progression to chronic kidney disease (CKD). The nuclear factor erythroid-derived 2–related factor 2 (Nrf2) pathway senses and coordinates cellular responses to oxidative and electrophilic stress. Here, we identify that graded genetic activation of Nrf2 protects against Li-induced NDI (Li-NDI) and volume wasting via an aquaporin 2–independent mechanism. Renal Nrf2 activity is differentially expressed on functional segments of the nephron, and its activation along the distal tubule and collecting duct directly modulates ion transporter expression, mimicking paradoxical effects of diuretics in mitigating Li-NDI. In addition, Nrf2 reduces cyclooxygenase expression and vasoactive prostaglandin biosynthesis. Pharmacologic activation of Nrf2 confers protective effects, confirming this pathway as a potentially novel druggable target for the prevention of acute and chronic renal sequelae of Li therapy.
Authors
Soma Jobbagy, Dario A. Vitturi, Sonia R. Salvatore, Maria F. Pires, Pascal Rowart, David R. Emlet, Mark Ross, Scott Hahn, Claudette St. Croix, Stacy G. Wendell, Arohan R. Subramanya, Adam C. Straub, Roderick J. Tan, Francisco J. Schopfer
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