Nephrology
Abstract
Histone deacetylase (HDAC) enzymes regulate transcription through epigenetic modification of chromatin structure, but their specific functions in the kidney remain elusive. We discovered that the human kidney expresses class I HDACs. Kidney medullary-specific inhibition of class I HDACs in the rat during high salt feeding results in hypertension, polyuria, hypokalemia, and nitric oxide (NO) deficiency. Three new, inducible murine models were used to determine that HDAC1 and HDAC2 in the kidney epithelium are necessary for maintaining epithelial integrity and maintaining fluid-electrolyte balance during increased dietary sodium intake. Moreover, single nucleus RNA sequencing determined that epithelial HDAC1 and HDAC2 are necessary for expression of many sodium or water transporters and channels. In performing a systematic review and meta-analysis of serious adverse events associated with clinical HDAC inhibitor use, we found that HDAC inhibitors increased the odds ratio of experiencing fluid-electrolyte disorders such as hypokalemia. This study provides insight on the mechanisms of potential serious adverse events with HDAC inhibitors, which may be fatal to critically ill patients. In conclusion, kidney tubular HDACs provide a link between the environment, such as consumption of high salt diets, with regulation of homeostatic mechanisms to remain in fluid-electrolyte balance.
Authors
Kelly A. Hyndman, Joshua S. Speed, Luciano D. Mendoza, John Allan, Jackson Colson, Randee Sedaka, Chunhua Jin, Hyun Jun Jung, Samir El-Dahr, David Pollock, Jennifer Pollock.
Abstract
Mutations in PKD1 (encoding for Polycystin-1, PC1) are found in 80-85% of patients with ADPKD. We tested the hypothesis that changes in actin dynamics result from PKD1 mutations through dysregulation of compartmentalised centrosomal RhoA signalling mediated by specific RhoGAP (ARHGAP) proteins resulting in the complex cellular cystic phenotype. Initial studies revealed that the actin cytoskeleton was highly disorganised in PKD1 patient-derived cells and was associated with an increase in total and centrosomal RhoA activation and ROCK signalling. Using cilia length as a phenotypic readout for centrosomal RhoA activity, we identified ARHGAP5, 29, 35 as essential regulators of ciliation in normal human renal tubular cells. Importantly, a specific decrease in centrosomal ARHGAP35 was observed in PKD1 null cells using a centrosome-targeted proximity ligation assay and by immunofluorescence labelling. Finally, we demonstrate that another ROCK inhibitor (hydroxyfasudil) reduced cyst expansion in both human PKD1 3D cyst assays and an inducible Pkd1 mouse model. In summary, we report a novel interaction between PC1 and ARHGAP35 in the regulation of centrosomal RhoA activation and ROCK signalling. Targeting the RhoA/ROCK pathway inhibited cyst formation in vitro and in vivo indicating its relevance to ADPKD pathogenesis and for developing new therapies to inhibit cyst initiation.
Authors
Andrew J. Streets, Philipp P. Prosseda, Albert C.M. Ong
Abstract
The epithelial filtration slit is a crucial component of the glomerular capillary membrane, which is essential for maintaining glomerular filtration function. Though chronic kidney diseases are an immense clinical problem, the mechanisms through which structural alterations reduce glomerular water filtration have not yet been understood completely. To investigate the mechanisms underlying filtration function loss, we studied rats with spontaneously occurring progressive kidney disease, either treated with angiotensin II antagonist or untreated, combining high-resolution electron microscopy of the glomerular capillary wall with theoretical water filtration modeling. Under pathological conditions, epithelial filtration pores and the extension of the subpodocyte space were larger than in normal controls. Numerical analyses indicated that these ultrastructural changes increased hydraulic resistance of the glomerular capillary wall by extending coverage of the filtration barrier by the subpodocyte space, with the changes in hydrodynamic forces acting on podocytes likely being responsible for their detachment. Angiotensin II inhibition normalized the subpodocyte space’s hydraulic resistance, restored mechanical podocyte load, and preserved CD151–α3 integrin complex assembly, improving podocyte adherence and survival. Our results show that ultrastructural changes in podocytes are major determinants of the hydraulic resistance of the glomerular capillary wall and highlight the mechanism of podocyte loss in kidney disease progression, as well as the mechanisms underlying angiotensin II inhibition.
Authors
Andrea Remuzzi, Sara Conti, Bogdan Ene-Iordache, Susanna Tomasoni, Paola Rizzo, Ariela Benigni, Giuseppe Remuzzi
Abstract
Background: A treatment option for ADPKD has highlighted the need to identify rapidly progressive patients. Kidney size/age and genotype have predictive power for renal outcomes, but their relative and additive value, plus associated trajectories of disease progression, are not well defined. Methods: The value of genotypic and/or kidney imaging data (Mayo Imaging Class) to predict the time to functional (end stage kidney disease; ESKD, or decline in estimated glomerular filtration rate; eGFR) or structural (increase in height adjusted total kidney volume; htTKV) outcomes were evaluated in a Mayo Clinic PKD1/PKD2 population; and eGFR and htTKV trajectories from 20-65 years of age modeled and independently validated in similarly defined CRISP and HALT PKD patients. Results: Both genotypic and imaging groups strongly predicted ESKD and eGFR endpoints, with genotype improving the imaging predictions, and vice versa; a multivariate model had strong discriminatory power (C statistic = 0.845). However, imaging but not genotypic groups predicted htTKV growth, although more severe genotypic and imaging groups had larger kidneys at a young age. The trajectory of eGFR decline was linear from baseline in the most severe genotypic and imaging groups, but curvilinear in milder groups. Imaging class trajectories differentiated htTKV growth rates; severe classes had rapid early growth and large kidneys but growth later slowed. Conclusions: The value of imaging, genotypic, and combined data to identify rapidly progressive patients was demonstrated, and reference values for clinical trials provided. Our data indicates that differences in kidney growth rates before adulthood significantly define patients with severe disease. Funding: NIDDK grants: Mayo DK058816, DK090728; CRISP DK056943, DK056956, DK056957, DK056961; HALT PKD DK062410, DK062408, DK062402, DK082230, DK062411, DK062401.
Authors
Sravanthi Lavu, Lisa E. Vaughan, Sarah R. Senum, Timothy L. Kline, Arlene B. Chapman, Ronald D. Perrone, Michal Mrug, William E. Braun, Theodore I. Steinman, Frederic F. Rahbari-Oskoui, Godela M. Brosnahan, Kyongtae T. Bae, Douglas Landsittel, Fouad T. Chebib, Alan S. L. Yu, Vicente E. Torres, Peter C. Harris
Abstract
Kidney disease is one of the most devastating complications of diabetes, and tubular atrophy predicts diabetic kidney disease (DKD) progression to end stage renal disease. We have proposed that fatty acids bound to albumin contribute to tubular atrophy by inducing lipotoxicity, following filtration across damaged glomeruli, and subsequent proximal tubule reabsorption by a fatty acid transport protein-2 (FATP2)-dependent mechanism. To address this possibility, genetic (Leprdb/db eNOS-/-) and induced (high fat diet plus low dose streptozotocin) mouse models of obesity and DKD, were bred with global FATP2 gene (Slc27a2)-deleted mice, and then phenotyped. DKD-prone mice with the Slc27a2-/- genotype demonstrated normalization of glomerular filtration rate, reduced albuminuria, improved kidney histopathology, and longer lifespan compared to diabetic Slc27a2+/+ mice. Genetic and induced DKD-prone Slc27a2-/- mice also exhibited markedly reduced fasting plasma glucose, with mean values approaching euglycemia, despite increased obesity and decreased physical activity. Glucose lowering in DKD-prone Slc27a2-/- mice was accompanied by beta-cell hyperplasia and sustained insulin secretion. Together, our data indicate that FATP2 uniquely regulates DKD pathogenesis by a combined lipotoxicity and glucotoxicity (glucolipotoxicity) mechanism.
Authors
Shenaz Khan, Robert J. Gaivin, Caroline Abramovich, Michael Boylan, Jorge Calles, Jeffrey R. Schelling
Abstract
Free light chains (FLCs) induce inflammatory pathways in proximal tubule cells (PTCs). The role of toll-like receptors (TLR) in these responses is unknown. Here we present findings on the role of TLRs in FLC-induced PTC injury. We exposed human kidney PTC cultures to κ and λ FLCs, and used cell supernatants and pellets for ELISA and gene expression studies. We also analyzed tissues from Stat1–/– and littermate control mice treated with daily intraperitoneal injections of a κ-FLC for 10 days. FLCs increased the expression of TLRs 2, 4, 6 via HMGB1, a damage-associated molecular pattern. Countering TLRs 2, 4, and 6 through GIT-27 or specific TLR-siRNAs reduced downstream cytokine responses. Blocking HMGB1 through siRNA or pharmacologic inhibition, or via STAT1 inhibition reduced FLC-induced TLRs 2, 4, and 6 expression. Blocking endocytosis of FLCs through silencing of megalin/cubilin, with bafilomycin-A1, or hypertonic sucrose attenuated FLC-induced cytokine responses in PTCs. Immunohistochemistry showed decreased TLR 4 and 6 expression in kidney sections from Stat1–/– mice compared to their littermate controls. PTCs exposed to FLCs released HMGB1, which induced TLRs 2, 4, 6 expression and downstream inflammation. Blocking FLCs’ endocytosis, Stat1 knock-down, HMGB1 inhibition, and TLR knock-down each rescued PTCs from FLC-induced injury.
Authors
Rohit Upadhyay, Wei-Zhong Ying, Zannatul Nasrin, Hana Safah, Edgar A. Jaimes, Wenguang Feng, Paul W. Sanders, Vecihi Batuman
Abstract
Apelin is a well-established mediator of survival and mitogenic signalling through apelin receptor (Aplnr) and have been implicated in various cancers, however little is known regarding Elabela (ELA/APELA) signalling, also mediated by Aplnr, and its role and the role of the conversion of its precursor proELA into mature ELA in cancer are unknown. Here we identify a function of mTORC1 signalling as an essential mediator of ELA that represses kidney tumour cells growth, migration and survival. Moreover, sunitinib and ELA show synergistic effect in repressing tumour growth and angiogenesis in mice. The use of site directed mutagenesis and pharmacologic experiments provide evidence that the alteration of the cleavage site of proELA by Furin induced improved ELA anti-tumorigenic activity. Finally, cohort of tumours and public data sets revealed that ELA is only repressed in the main human kidney cancer subtypes namely clear cell, papillary, and chromophobe renal cell carcinoma. While Aplnr is expressed by various kidney cells, ELA is generally expressed by epithelial cells. Collectively, these results show the tumour-suppressive role of mTORC1 signalling mediated by ELA and establish the potential use of ELA or derivatives in kidney cancers treatment.
Authors
Fabienne Soulet, Clement Bodineau, Katarzyna B. Hooks, Jean Descarpentrie, Isabel D. Alves, Marielle Dubreuil, Amandine Mouchard, Malaurie Eugenie, Jean-Luc Hoepffner, José Javier Lopez, Juan A. Rosado, Isabelle Soubeyran, Mercedes Tomé, Raúl V. Durán, Macha Nikolski, Bruno O. Villoutreix, Serge Evrard, Geraldine Siegfried, Abdel-Majid Khatib
Abstract
Chronic kidney disease is the main cause of mortality in patients with tuberous sclerosis complex disease (TSC). The mechanisms underlying TSC cystic kidney disease remain unclear with no available interventions to prevent cyst formation. Using targeted deletion of TSC1 in nephron progenitor cells, we showed that cysts in TSC1 null embryonic kidneys originate from injured proximal tubular cells with high mTOR complex 1 activity. Injection of rapamycin to pregnant mice inhibited the mTOR pathway and tubular cell proliferation in kidneys of TSC1 null offspring. Rapamycin also prevented renal cystogenesis and prolonged the life span of TSC newborns. Gene expression analysis of proximal tubule cells, identified sets of genes and pathways that were modified secondary to TSC1 deletion and rescued by rapamycin administration during nephrogenesis. Inflammation with mononuclear infiltration was observed in the cystic areas of TSC1 null kidneys. Dexamethasone administration during pregnancy decreased cyst formation not only by inhibiting the inflammatory response but also by interfering with the mTORC1 pathway. These results reveal novel mechanisms of cystogenesis in TSC disease and suggest new interventions prior to birth to ameliorate cystic disease in offspring.
Authors
Morris Nechama, Yaniv Makayes, Elad Resnick, Karen Meir, Oded Volovelsky
Abstract
Renal fibrosis features exaggerated inflammation, extracellular matrix (ECM) deposition, and peritubular capillary loss. We previously showed that IL-10 stimulates high molecular weight hyaluronan (HMW-HA) expression by fibroblasts, and we hypothesize that HMW-HA attenuates renal fibrosis by reducing inflammation and ECM remodeling. We studied the effects of IL-10 overexpression on HA production and scarring in mouse models of unilateral ureteral obstruction (UUO) and ischemia/reperfusion (I/R) to investigate whether IL-10 anti-fibrotic effects are HA-dependent. C57BL/6J mice were fed with the HA synthesis inhibitor, 4-methylumbelliferone (4-MU), prior to UUO. We observed that in vivo injury increased intratubular spaces, ECM deposition, and HA expression at day 7 and onwards. IL-10 overexpression reduced renal fibrosis in both models, promoted HMW-HA synthesis and stability in UUO, and regulated cell proliferation in I/R. 4-MU inhibited IL-10-driven anti-fibrotic effects, indicating that HMW-HA is necessary for cytokine-mediated reduction of fibrosis. We also found that IL-10 induces in vitro HMW-HA production by renal fibroblasts via STAT3-dependent upregulation of HA synthase 2. We propose that IL-10-induced HMW-HA synthesis plays cytoprotective and anti-fibrotic roles in kidney injury, thereby revealing an effective strategy to attenuate renal fibrosis in obstructive and ischemic pathologies.
Authors
Xinyi Wang, Swathi Balaji, Emily H. Steen, Alexander J. Blum, Hui Li, Christina K. Chan, Scott R. Manson, Thomas C. Lu, Meredith M. Rae, Paul F. Austin, Thomas N. Wight, Paul L. Bollyky, Jizhong Cheng, Sundeep G. Keswani
Abstract
Lupus nephritis, one of the most serious manifestations of systemic lupus erythematosus (SLE), has both a heterogeneous clinical and pathological presentation. For example, proliferative nephritis identifies a more aggressive disease class that requires immunosuppression. However, the current classification system relies on the static appearance of histopathological morphology which does not capture differences in the inflammatory response. Therefore, a biomarker grounded in the disease biology is needed to understand the molecular heterogeneity of lupus nephritis and identify immunologic mechanism and pathways. Here, we analyzed the patterns of 1000 urine protein biomarkers in 30 patients with active lupus nephritis. We found that patients stratify over a chemokine gradient inducible by interferon-gamma. Higher values identified patients with proliferative lupus nephritis. After integrating the urine proteomics with the single-cell transcriptomics of kidney biopsies, it was observed that the urinary chemokines defining the gradient were predominantly produced by infiltrating CD8 T cells, along with natural killer and myeloid cells. The urine chemokine gradient significantly correlated with the number of kidney-infiltrating CD8 cells. These findings suggest that urine proteomics can capture the complex biology of the kidney in lupus nephritis. Patient-specific pathways may be noninvasively tracked in the urine in real time, enabling diagnosis and personalized treatment.
Authors
Andrea Fava, Jill P. Buyon, Chandra Mohan, Ting Zhang, H. Michael Belmont, Peter Izmirly, Robert Clancy, Jose Monroy Trujillo, Derek M. Fine, Yuji Zhang, Laurence Magder, Deepak A. Rao, Arnon Arazi, Celine C. Berthier, Anne Davidson, Betty Diamond, Nir Hacohen, David Wofsy, William Apruzzese, The Accelerating Medicines Partnership, Soumya Raychaudhuri, Michelle Petri
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