Nephrology
Abstract
Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in PKD1 or PKD2, which encode polycystin-1 (PC1) and polycystin-2 (PC2) respectively. These proteins are thought to form a signaling complex that can flux cations including calcium. One of the earliest symptoms in ADPKD is a decline in the concentrating ability of the kidneys, occurring prior to cyst formation. We reasoned that hyperosmolality stimulates the polycystin complex, and that the loss of this function impairs water reabsorption. We found that hyperosmolality resulted in the phosphorylation of a microtubule associated protein 4 (MAP4) in a PC1-dependent manner which then elicited ER-localized PC2 calcium signals. ER-localized PC2 hyperosmotic calcium signals were required for trafficking of the water channel aquaporin (AQP2). Pre-cystic PC1-KO and PC2-KO murine kidneys had cytosolic localized AQP2, and diluted urine compared to their respective controls. Kidney tissue sections from ADPKD patients showed decreased AQP2 apical membrane localization in cystic and non-cystic tubules. Our study demonstrates that osmolality is a physiological stimulus of the polycystin complex, and loss of polycystin osmosensing results in impaired water reabsorption via AQP2. This likely contributes to the declined concentrating ability of the kidneys and high circulating vasopressin levels in ADPKD patients.
Authors
Karla M. Márquez-Nogueras, Ryne M. Knutila, Virdjinija Vuchkovska, Charlie Yang, Patricia Outeda, Darren P. Wallace, Ivana Y. Kuo
Abstract
Transforming growth factor beta (TGF-β) signaling is the master modulator of renal fibrosis. However, targeting drugs have failed to prevent the progression of chronic kidney disease (CKD) in clinical trials due to the extensive biological regulation of TGF-β signaling. It is necessary to investigate the precise downstream mechanisms of TGF-β signaling that regulate renal fibrosis. In this study, we found that PR-domain containing 16 (PRDM16) expression in human renal tubular epithelial cells was markedly reduced by TGF-β. Mechanistically, activated Smad3 induced by TGF-β interacted with the cofactor H-Ras and bound to the promoter of PRDM16, downregulating its transcription. Tubular-specific knockout of PRDM16 promoted renal fibrosis in models of unilateral ureteral occlusion (UUO) and unilateral ischemia-reperfusion injury (UIRI) by exacerbating mitochondrial dysfunction. In vitro, PRDM16 blocked TGF-β-induced mitochondrial injury and lipid deposition by upregulating Peroxisome Proliferator-Activated Receptor Gamma Coactivator-1α (PGC-1α). Delivery of the exogenous PRDM16 gene preserved renal function and ameliorated the progression of renal fibrosis by protecting mitochondrial function. We report PRDM16 as a novel downstream target of TGF-β signaling that attenuates renal fibrosis by safeguarding tubular mitochondrial function.
Authors
Qian Yuan, Ben Tang, Yuting Zhu, Chao Wan, Yaru Xie, Yajuan Xie, Cheng Wan, Hua Su, Youhua Liu, Chun Zhang
Low‐intensity pulsed ultrasound stimulation to treat renal fibrosis through inhibiting tubular IL-1R
Abstract
Low-intensity pulsed ultrasound stimulation (LIPUS) has become increasingly appreciated for its therapeutic effect on kidney diseases. However, its role and biological mechanism in treating chronic kidney disease (CKD) remain poorly defined. Here, we revealed that LIPUS was applied in a safe range with an intensity of 25-315 mW/cm2. Daily LIPUS at an intensity of 315 mW/cm2 ameliorated ischemia-reperfusion (IR)-induced tubular injury and renal fibrosis, accompanied by the remarkable downregulation of IL-1R. Transcriptome sequencing showed that LIPUS significantly down-regulated IL-1R and its downstream genes in IL-1β-stimulated IR-injured mice. LIPUS effectively reversed IL-1β-induced tubular injury and reduced the production of profibrotic cytokines by down-regulating IL-1R in vivo and in vitro. Renal proximal tubule-specific Il1r1 knockout mice exhibited milder renal tubular injury and fibrosis after IR injury. However, LIPUS did not ameliorate IR injury in proximal tubule-specific Il1r1 knockout mice. Collectively, daily LIPUS at an intensity of 315 mW/cm2 relieves IR-induced tubular injury and fibrosis, potentially through down-regulating tubular IL-1R.
Authors
Zhimin Huang, Jiaxin Dong, Ziqi Fu, Li Li, Simeng liu, Lin Wu, Honglei Guo, Ao Bian, Kang Liu, Wei Sun, Changying Xing, Steven D. Crowley, Jiafa Ren, Xiangqing Kong, Huijuan Mao
Abstract
Acute kidney injury (AKI) is characterized by a rapid decline in renal function. In severe or recurrent cases, AKI can progress to chronic kidney disease (CKD), marked by renal inflammation and fibrosis. Despite the severity of these outcomes, early-stage diagnostic tools and pharmacological interventions for AKI-to-CKD progression remain limited. In this study, we examined circular RNA (circRNA) expression profiles in mouse renal cortex tissues 14 days post-ischemia/reperfusion (I/R) injury using circRNA sequencing. The renal biopsy samples of patients after AKI exhibited reduced CircNSD1 expression, which was inversely associated with inflammation and fibrosis. Overexpression of CircNSD1 attenuated ferroptosis in vivo and in vitro, while slowing AKI-to-CKD progression. Mechanistically, CircNSD1 downregulated ACSL4 and SlC39A14 expression through histone H3 lysine 36 (H3K36) methylation, a critical pathway regulating ferroptosis after AKI or hypoxia/reoxygenation (H/R) injury. Furthermore, we identified that CircNSD1 encoded a NSD1-916aa peptide, which may functionally contribute to its observed effect. Collectively, these findings demonstrated that CircNSD1 may serve as a diagnostic and therapeutic target for early detection of AKI-to-CKD transition.
Authors
Li Gao, Junsheng Zhang, Chaoyi Chen, Sai Zhu, Xianglong Wei, Guiqin Tang, Sheng Wang, Yukai Wang, Xinran Liu, Ling Jiang, Yonggui Wu
Abstract
Mutations in Cullin-3 (CUL3) cause hypertension (HTN). We examined the role of smooth muscle cell (SMC) CUL3 in the regulation of renin gene expression. Mice with SMC-specific CUL3 deletion (S-CUL3KO) developed severe HTN with paradoxically preserved levels of plasma angiotensin peptides and renal renin expression. Cre-recombinase was active in JG cells resulting in decreased CUL3 expression. We evaluated components of the renin cell baroreceptor and revealed preserved lamin A/C but decreased integrin β1 expression in S-CUL3KO. We hypothesized that Rab proteins are involved in integrin β1 downregulation. Silencing either Rab21 or Rab5 in CUL3-deficient HEK293 cells increased integrin β1 protein. Co-immunoprecipitation revealed a direct interaction between Rab5 and CUL3. CUL3-deficiency increased Rab5 suggesting it is regulated by a CUL3-mediated mechanism and that CUL3-deficiency results in loss of Rab protein turnover leading to enhanced integrin β1 internalization. We conclude that the loss of integrin β1 from juxtaglomerular cells impairs the mechanosensory function of the renin cell baroreceptor, which underlies the persistent renin expression observed in hypertensive S-CUL3KO mice. These findings provide insights into the molecular mechanisms of HTN, revealing that dysregulation of Rab proteins and integrin β1 in the kidney due to CUL3-deficiency contributes to the development of HTN.
Authors
Daria Golosova, Gaurav Kumar, Ko-Ting Lu, Patricia C. Muskus Veitia, Ana Hantke Guixa, Kelsey K. Wackman, Eva M. Fekete, Daniel T. Brozoski, Justin L. Grobe, Maria Luisa S. Sequeira-Lopez, R. Ariel Gomez, Pablo Nakagawa, Curt D. Sigmund
Abstract
BACKGROUND While urinary biomarkers show promise in predicting diabetic kidney disease (DKD) progression, distal tubular markers remain understudied. We investigated the association of distal tubule markers, epidermal growth factor (EGF) and uromodulin (UMOD), with DKD progression in the Veterans Affairs Diabetes in Nephropathy (VA NEPHRON-D) clinical trial.METHODS. We used Cox regression models to evaluate the association between each biomarker and DKD progression and the relationship between change over time in biomarker and DKD progression. We used mixed models to investigate biomarker levels at baseline, 12 months, and over time and their relationships with longitudinal eGFR change.RESULTS. Participants (n = 1,116) had type 2 diabetes, urine albumin-to-creatinine ratio (UACR) ≥ 300 mg/g, and eGFR 30–89.9 mL/min/1.73 m2. Mean age was 65 years, mean eGFR was 56 (SD 19) mL/min/1.73 m2, and median UACR was 840 (IQR 424–1,780) mg/g. One hundred forty-four participants (13%) had DKD progression over a median follow-up of 2.2 (1.3–3.1) years. Higher baseline EGF and UMOD were independently associated with a lower risk of DKD progression (adjusted HR 0.68, 95% CI 0.47, 0.99 and 0.85, [0.75, 0.98] per 2-fold higher concentration of EGF and UMOD, respectively). Serial biomarker measurements were performed at baseline and 12 months, and a slower decline in biomarkers was associated with a lower risk of DKD progression when adjusted for baseline biomarker levels.CONCLUSION. Urinary EGF and UMOD may serve as valuable prognostic biomarkers in DKD.TRIAL REGISTRATION. ClinicalTrials.gov NCT00555217.FUNDING. NIH U01DK102730, U01DK103225, K23 DK118198, R01DK137087, U01DK103225, R37DK039773, U01DK114866, U01DK106962, U01DK129984, and R01DK093770; National Institute of Diabetes and Digestive and Kidney Diseases contract U01DK106965.
Authors
Christina L. Tamargo, Steven G. Coca, Heather Thiessen Philbrook, David G. Hu, Joachim H. Ix, Michael G. Shlipak, Linda F. Fried, Orlando M. Gutierrez, Sushrut S. Waikar, Sarah J. Schrauben, Jeffrey R. Schelling, Peter Ganz, Paul L. Kimmel, Jason H. Greenberg, Rajat Deo, Ayumi Takakura, Ramachandran S. Vasan, Joseph V. Bonventre, Chirag R. Parikh
Abstract
Podocytes are kidney glomerular cells that depend on rigorously regulated cytoskeleton components and integrins to form and maintain the so-called foot processes, apparatuses that attach podocytes to the glomerular basement membrane and connect them to neighboring podocytes. In diabetic kidney disease (DKD) these foot processes are effaced as a result of cytoskeleton dysregulation, a phenomenon that gradually reduces glomerular filtration. Cytoskeleton-associated protein 4 (CKAP4) is a known linker between the endoplasmic reticulum, integrins and microtubular cytoskeleton. Since CKAP4 gene expression is downregulated in glomeruli from DKD patients but not in other chronic kidney diseases, we hypothesized a role for CKAP4 in the mechanisms leading to foot process effacement (FPE) in DKD. CKAP4 mRNA reduction in podocytes in DKD was demonstrated in human kidney biopsies. Knockdown of CKAP4 in vivo in zebrafish resulted in edema, proteinuria and foot process effacement, all typical features of DKD. Knockdown of CKAP4 in vitro led to disruption of the actin cytoskeleton and of the microtubular orientation. Moreover, it caused a downregulation of several integrins. These findings indicate that CKAP4 is crucial for foot process dynamics of podocytes. Its reduction, unique to DKD, is mechanistically connected to the pathophysiological processes leading to podocyte FPE.
Authors
Roberto Boi, Emelie Lassén, Alva Johansson, Peidi Liu, Aditi Chaudhari, Ramesh Tati, Janina Müller-Deile, Mario Schiffer, Kerstin Ebefors, Jenny Nyström
Abstract
Kidney thick ascending limb cells reabsorb sodium, potassium, calcium, magnesium and contribute to urinary concentration. These cells are typically viewed as a single type that recycles potassium across the apical membrane and generates a lumen-positive transepithelial voltage driving calcium and magnesium reabsorption, although variability in potassium channel expression has been reported. Additionally, recent transcriptomic analyses suggest that different cell types exist along this segment, but classifications have varied and have not led to a new consensus model. We used immunolocalization, electrophysiology and enriched single nucleus RNA-Seq to identify thick ascending limb cell types in rat, mouse and human. We identified three major TAL cell types defined by expression of potassium channels and claudins. One has apical potassium channels, low basolateral potassium conductance, and is bordered by a monovalent cation-permeable claudin. A second lacks apical potassium channels, has high basolateral potassium conductance and is bordered by calcium- and magnesium-permeable claudins. A third type also lacks apical potassium channels and has high basolateral potassium conductance, but these cells are ringed by monovalent cation-permeable claudins. The recognition of diverse cell types may resolve longstanding questions about how solute transport can be modulated selectively and how disruption of these cells leads to human disease.
Authors
Hasan Demirci, Jessica P. Bahena-Lopez, Alina Smorodchenko, Xiao-Tong Su, Jonathan W. Nelson, Chao-Ling Yang, Joshua N. Curry, Xin-Peng Duan, Wen-Hui Wang, Yuliya Sharkovska, Ruisheng Liu, Duygu Elif Yilmaz, Catarina Quintanova, Katie Emberley, Ben Emery, Nina Himmerkus, Markus Bleich, David H. Ellison, Sebastian Bachmann
Abstract
Microvascular rarefaction substantially contributes to renal dysfunction following ischemia-reperfusion injury (IRI). We characterized the microRNA signature of extracellular vesicles (EVs) released during endothelial apoptosis to identify biomarkers and regulators of microvascular rarefaction and renal dysfunction. Using in vitro models and RNA-Seq, we found miR-423-5p, let-7b-5p, and let-7c-5p enriched in small EVs from apoptotic endothelial cells. In mouse models of renal IRI and a cohort of 51 patients who have undergone renal transplant with delayed graft function, serum miR-423-5p correlated with circulating EVs, while let-7b-5p and let-7c-5p were also present in free form. Early acute kidney injury saw increased serum miR-423-5p levels linked to small EVs with endothelial markers. Over time, higher serum miR-423-5p levels were associated with large EVs and correlated with greater renal microvascular density and reduced fibrosis. Microvascular density and fibrosis predicted renal function 3 years after transplantation. We explored miR-423-5p’s role in renal homeostasis, finding that its injection during renal IRI preserved microvascular density and inhibited fibrosis. Endothelial cells transfected with miR-423-5p showed enhanced resistance to apoptosis, increased migration, and angiogenesis. Localized miR-423-5p injection in hindlimb ischemia model accelerated revascularization. These findings position miR-423-5p as a predictor of renal microvascular rarefaction and fibrosis, highlighting potential strategies for preserving renal function.
Authors
Francis Migneault, Hyunyun Kim, Alice Doreille, Shanshan Lan, Alexis Gendron, Marie-Hélène Normand, Annie Karakeussian Rimbaud, Martin Dupont, Isabelle Bourdeau, Éric Bonneil, Julie Turgeon, Sylvie Dussault, Pierre Thibault, Mélanie Dieudé, Éric Boilard, Alain Rivard, Héloïse Cardinal, Marie-Josée Hébert
Abstract
Diabetic kidney disease (DKD) is the leading cause of end stage kidney disease. Kidney tubular cells have a high energy demand, dependent on fatty acid oxidation (FAO). Although carnitine is indispensable for FAO, the pathological role of carnitine deficiency in DKD is not fully understood. We showed here that ectopic lipid accumulation due to impaired FAO increased in patients with DKD and inversely correlated with renal function. OCTN2 deficient mice exhibited systemic carnitine deficiency with increased renal lipid accumulation. Cell death and inflammation were induced in OCTN2-deficient, but not wild-type tubular cells exposed to high salt and high glucose. Compared with SDT fatty rats, uninephrectomized SDT fatty rats fed with 0.3% NaCl had higher lipid accumulation and exhibited increased urinary albumin excretion with renal dysfunction and tubulointerstitial injury, all of which were ameliorated by L-carnitine supplementation via stimulating FAO and mitochondrial biogenesis. In our single-center randomized control trial with patients undergoing peritoneal dialysis, L-carnitine supplementation preserved residual renal function and increased urine volume, the latter of which was correlated with improvement of tubular injury. The present study demonstrates the pathological role of impairment of carnitine-induced FAO in DKD, suggesting that L-carnitine supplementation is a potent therapeutic strategy for this devastating disorder.
Authors
Sakuya Ito, Kensei Taguchi, Goh Kodama, Saori Kubo, Tomofumi Moriyama, Yuya Yamashita, Yunosuke Yokota, Yosuke Nakayama, Yusuke Kaida, Masami Shinohara, Kyoko Tashiro, Keisuke Ohta, Sho-ichi Yamagishi, Kei Fukami
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