Nephrology
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
Abstract
Adult renal proximal tubules are composed of terminally differentiated epithelial cells that exhibit few signs of proliferation over time. However, upon acute kidney injury (AKI), surviving epithelial cells can re-enter the mitotic cycle and express genes and proteins coincident with a dedifferentiated, more embryonic phenotype. While a stable, terminally differentiated cellular phenotype is thought to be maintained, at least in part, by epigenetic imprints that impart both active and repressive histone marks, it is unclear whether regenerating cells after injury need to replicate such marks to recover. To test whether renal epithelial cell regeneration is dependent on histone H3K4 methylation, we generated a mouse model that deleted the Paxip1 gene in mature renal proximal tubules. Paxip1 encodes the adaptor protein PTIP, which is part of an Mll3/4 histone H3K4 methyltransferase complex and is essential for embryonic development. Mice with PTIP deletions in the adult kidney proximal tubules were viable and fertile. Upon acute kidney injury, such mice failed to regenerate damaged tubules leading to scarring and interstitial fibrosis. The inability to repair damage was likely due to a failure to re-enter mitosis and reactivate regulatory genes such as Sox9, which is necessary for epithelial cell regeneration. PTIP deletion reduced histone H3K4 methylation in uninjured adult kidneys but did not significantly affect function or the expression of epithelial specific markers. A transient decrease in trimethylation was also observed in controls after AKI but returned to normal after repair. Strikingly, cell lineage tracing revealed that surviving PTIP mutant cells could alter their phenotype and lose epithelial markers. These data demonstrate that PTIP and associated MLL3/4 mediated histone methylation are needed for regenerating proximal tubules and to maintain or reestablish the cellular epithelial phenotype.
Authors
Abdul Soofi, Ana P. Kutschat, Mohammad H. Azam, Ann M. Laszczyk, Gregory R. Dressler
Abstract
BACKGROUND. Mitochondrial dysfunction, a proposed mechanism of COPD pathogenesis, is associated with the leakage of mitochondrial DNA (mtDNA), which may be detected extracellularly in various bodily fluids. Despite evidence for the increased prevalence of chronic kidney disease in COPD subjects and for mitochondrial dysfunction in the kidneys of murine COPD models, whether urine mtDNA (u-mtDNA) associates with measures of disease severity in COPD is unknown. METHODS. Cell-free u-mtDNA, defined as copy number of mitochondrially-encoded NADH dehydrogenase-1 (MTND1) gene, was measured by real-time quantitative PCR and normalized to urine creatinine in cell-free urine samples from participants in the Subpopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS) cohort. Urine albumin/creatinine ratios (UACR) were measured in the same samples. Associations between u-mtDNA and UACR and clinical disease parameters, including FEV1 % predicted, clinical measures of exercise tolerance, respiratory symptom burden, and chest CT measures of lung structure were examined. RESULTS. U-mtDNA and UACR levels were measured in never smokers (n = 64), smokers without airflow obstruction (n = 109), participants with mild/moderate COPD (n = 142), and participants with severe COPD (n = 168). U-mtDNA was associated with increased respiratory symptom burden, especially among smokers without COPD. Significant sex differences in u-mtDNA levels were observed with females having higher u-mtDNA levels across all study subgroups. U-mtDNA associated with worse spirometry and CT emphysema in males only, and worse respiratory symptoms in females only. Similar associations were not found with UACR. CONCLUSION. U-mtDNA levels may help to identify distinct clinical phenotypes and underlying pathobiological differences in males versus females with COPD.
Authors
William Z. Zhang, Michelle C. Rice, Katherine L. Hoffman, Clara Oromendia, Igor Barjaktarevic, J. Michael Wells, Annette T. Hastie, Wassim W. Labaki, Christopher B. Cooper, Alejandro P. Comellas, Gerard J. Criner, Jerry A. Krishnan, Robert Paine III, Nadia N. Hansel, Russell P. Bowler, R. Graham Barr, Stephen P. Peters, Prescott G. Woodruff, Jeffrey L. Curtis, Meilan K. Han, Karla V. Ballman, Fernando J. Martinez, Augustine M.K. Choi, Kiichi Nakahira, Suzanne M. Cloonan, Mary E. Choi
Abstract
Proteinuric chronic kidney disease (CKD) remains a major health problem worldwide. While the progression of primary glomerular disease to induce tubulointerstitial lesions is well established, the effect of tubular injury to trigger glomerular damage is poorly understood. We hypothesized that injured tubules secrete mediators that adversely affect glomerular health. To test this, we utilized conditional knockout mice with tubule-specific ablation of β-catenin (Ksp-β-cat-/-), and subjected them to chronic angiotensin II (Ang II) infusion or adriamycin. Compared to control mice, Ksp-β-cat-/- mice were dramatically protected from proteinuria and glomerular damage. Matrix metalloproteinase-7 (MMP-7), a downstream target of β-catenin, was upregulated in treated control mice, but this induction was blunted in the Ksp-β-cat-/- littermates. Incubation of isolated glomeruli with MMP-7 ex vivo led to nephrin depletion and impaired glomerular permeability. Furthermore, MMP-7 specifically and directly degraded nephrin in cultured glomeruli or cell-free systems, and this effect was dependent on its proteolytic activity. In vivo, expression or infusion of exogenous MMP-7 caused proteinuria, and genetic ablation of MMP-7 protected mice from Ang II-induced proteinuria and glomerular injury. Collectively, these results demonstrate that beta-catenin-driven MMP-7 release from renal tubules promotes glomerular injury via direct degradation of the key slit diaphragm protein nephrin.
Authors
Roderick J. Tan, Yingjian Li, Brittney M. Rush, Débora Malta Cerqueira, Dong Zhou, Haiyan Fu, Jacqueline Ho, Donna Beer Stolz, Youhua Liu
Abstract
Although oxidative stress plays central roles in postischemic renal injury, region-specific alterations in energy and redox metabolism caused by short-duration ischemia remain unknown. Imaging mass spectrometry enabled us to reveal spatial heterogeneity of energy and redox metabolites in the postischemic murine kidney. After 10-minute ischemia and 24-hour reperfusion (10mIR), in the cortex and outer stripes of the outer medulla, ATP substantially decreased, but not in the inner stripes of the outer medulla and inner medulla. 10mIR caused renal injury with elevation of fractional excretion of sodium, although histological damage by oxidative stress was limited. Ischemia-induced NADH elevation in the cortex indicated prolonged production of reactive oxygen species by xanthine oxidase (XOD). However, consumption of reduced glutathione after reperfusion suggested the amelioration of oxidative stress. An XOD inhibitor, febuxostat, which blocks the degradation pathway of adenine nucleotides, promoted ATP recovery and exerted renoprotective effects in the postischemic kidney. Because effects of febuxostat were canceled by silencing of the hypoxanthine phosphoribosyl transferase 1 gene in cultured tubular cells, mechanisms for the renoprotective effects appear to involve the purine salvage pathway, which uses hypoxanthine to resynthesize adenine nucleotides, including ATP. These findings suggest a novel therapeutic approach for acute ischemia/reperfusion renal injury with febuxostat through salvaging high-energy adenine nucleotides.
Authors
Kentaro Fujii, Akiko Kubo, Kazutoshi Miyashita, Masaaki Sato, Aika Hagiwara, Hiroyuki Inoue, Masaki Ryuzaki, Masanori Tamaki, Takako Hishiki, Noriyo Hayakawa, Yasuaki Kabe, Hiroshi Itoh, Makoto Suematsu
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