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Abdalrahman T, Dubuis L, Green J, Davies N, Franz T. Cellular mechanosensitivity to substrate stiffness decreases with increasing dissimilarity to cell stiffness. Biomech Model Mechanobiol 2017; 16:2063-2075. [PMID: 28733924 DOI: 10.1007/s10237-017-0938-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2017] [Accepted: 07/11/2017] [Indexed: 01/07/2023]
Abstract
Computational modelling has received increasing attention to investigate multi-scale coupled problems in micro-heterogeneous biological structures such as cells. In the current study, we investigated for a single cell the effects of (1) different cell-substrate attachment (2) and different substrate modulus [Formula: see text] on intracellular deformations. A fibroblast was geometrically reconstructed from confocal micrographs. Finite element models of the cell on a planar substrate were developed. Intracellular deformations due to substrate stretch of [Formula: see text], were assessed for: (1) cell-substrate attachment implemented as full basal contact (FC) and 124 focal adhesions (FA), respectively, and [Formula: see text]140 KPa and (2) [Formula: see text], 140, 1000, and 10,000 KPa, respectively, and FA attachment. The largest strains in cytosol, nucleus and cell membrane were higher for FC (1.35[Formula: see text], 0.235[Formula: see text] and 0.6[Formula: see text]) than for FA attachment (0.0952[Formula: see text], 0.0472[Formula: see text] and 0.05[Formula: see text]). For increasing [Formula: see text], the largest maximum principal strain was 4.4[Formula: see text], 5[Formula: see text], 5.3[Formula: see text] and 5.3[Formula: see text] in the membrane, 9.5[Formula: see text], 1.1[Formula: see text], 1.2[Formula: see text] and 1.2[Formula: see text] in the cytosol, and 4.5[Formula: see text], 5.3[Formula: see text], 5.7[Formula: see text] and 5.7[Formula: see text] in the nucleus. The results show (1) the importance of representing FA in cell models and (2) higher cellular mechanical sensitivity for substrate stiffness changes in the range of cell stiffness. The latter indicates that matching substrate stiffness to cell stiffness, and moderate variation of the former is very effective for controlled variation of cell deformation. The developed methodology is useful for parametric studies on cellular mechanics to obtain quantitative data of subcellular strains and stresses that cannot easily be measured experimentally.
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Affiliation(s)
- Tamer Abdalrahman
- Division of Biomedical Engineering, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Observatory, South Africa
| | - Laura Dubuis
- Division of Biomedical Engineering, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Observatory, South Africa
| | - Jason Green
- Cardiovascular Research Unit, Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town, Observatory, South Africa
| | - Neil Davies
- Cardiovascular Research Unit, Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town, Observatory, South Africa
| | - Thomas Franz
- Division of Biomedical Engineering, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Observatory, South Africa. .,Bioengineering Science Research Group, Engineering Sciences, Faculty of Engineering and the Environment, University of Southampton, Southampton, UK.
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52
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Long KR, Shipman KE, Rbaibi Y, Menshikova EV, Ritov VB, Eshbach ML, Jiang Y, Jackson EK, Baty CJ, Weisz OA. Proximal tubule apical endocytosis is modulated by fluid shear stress via an mTOR-dependent pathway. Mol Biol Cell 2017; 28:2508-2517. [PMID: 28720662 PMCID: PMC5597323 DOI: 10.1091/mbc.e17-04-0211] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Revised: 07/07/2017] [Accepted: 07/13/2017] [Indexed: 12/02/2022] Open
Abstract
Kidney proximal tubule cells cultured under shear stress become remarkably well differentiated and endocytic capacity is rapidly tuned in response to acute changes in shear stress. The results have implications for understanding how proximal tubule function is regulated acutely by daily variations in glomerular filtration rate. Cells lining the proximal tubule (PT) have unique membrane specializations that are required to maintain the high-capacity ion transport and endocytic functions of this nephron segment. PT cells in vivo acutely regulate ion transport in response to changes in glomerular filtration rate (GFR) to maintain glomerulotubular balance. PT cells in culture up-regulate endocytic capacity in response to acute changes in fluid shear stress (FSS); however, it is not known whether GFR modulates PT endocytosis to enable maximally efficient uptake of filtered proteins in vivo. Here, we show that cells cultured under continuous FSS develop an expanded apical endocytic pathway and increased endocytic capacity and lysosomal biogenesis. Furthermore, endocytic capacity in fully differentiated cells is rapidly modulated by changes in FSS. PT cells exposed to continuous FSS also acquired an extensive brush border and basolateral membrane invaginations resembling those observed in vivo. Culture under suboptimal levels of FSS led to intermediate phenotypes, suggesting a threshold effect. Cells exposed to FSS expressed higher levels of key proteins necessary for PT function, including ion transporters, receptors, and membrane-trafficking machinery, and increased adenine nucleotide levels. Inhibition of the mechanistic target of rapamycin (mTOR) using rapamycin prevented the increase in cellular energy levels, lysosomal biogenesis, and endocytic uptake, suggesting that these represent a coordinated differentiation program. In contrast, rapamycin did not prevent the FSS-induced increase in Na+/K+-ATPase levels. Our data suggest that rapid tuning of the endocytic response by changes in FSS may contribute to glomerulotubular balance in vivo. Moreover, FSS provides an essential stimulus in the differentiation of PT cells via separate pathways that up-regulate endocytosis and ion transport capacity. Variations in FSS may also contribute to the maturation of PT cells during kidney development and during repair after kidney injury.
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Affiliation(s)
- Kimberly R Long
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Katherine E Shipman
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Youssef Rbaibi
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Elizabeth V Menshikova
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Vladimir B Ritov
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Megan L Eshbach
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Yu Jiang
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Edwin K Jackson
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Catherine J Baty
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Ora A Weisz
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
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53
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Stretch-induced actomyosin contraction in epithelial tubes: Mechanotransduction pathways for tubular homeostasis. Semin Cell Dev Biol 2017; 71:146-152. [PMID: 28610943 DOI: 10.1016/j.semcdb.2017.05.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2017] [Accepted: 05/24/2017] [Indexed: 02/08/2023]
Abstract
Many tissues in our body have a tubular shape and are constantly exposed to various stresses. Luminal pressure imposes tension on the epithelial and myoepithelial or smooth muscle cells surrounding the lumen of the tubes. Contractile forces generated by actomyosin assemblies within these cells oppose the luminal pressure and must be calibrated to maintain tube diameter homeostasis and tissue integrity. In this review, we discuss mechanotransduction pathways that can lead from sensation of cell stretch to activation of actomyosin contractility, providing rapid mechanochemical feedback for proper tubular tissue function.
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54
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Eshbach ML, Kaur A, Rbaibi Y, Tejero J, Weisz OA. Hemoglobin inhibits albumin uptake by proximal tubule cells: implications for sickle cell disease. Am J Physiol Cell Physiol 2017; 312:C733-C740. [PMID: 28356267 PMCID: PMC5494590 DOI: 10.1152/ajpcell.00021.2017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Revised: 03/10/2017] [Accepted: 03/28/2017] [Indexed: 11/22/2022]
Abstract
Proximal tubule (PT) dysfunction, including tubular proteinuria, is a significant complication in young sickle cell disease (SCD) that can eventually lead to chronic kidney disease. Hemoglobin (Hb) dimers released from red blood cells upon hemolysis are filtered into the kidney and internalized by megalin/cubilin receptors into PT cells. The PT is especially sensitive to heme toxicity, and tubular dysfunction in SCD is thought to result from prolonged exposure to filtered Hb. Here we show that concentrations of Hb predicted to enter the tubule lumen during hemolytic crisis competitively inhibit the uptake of another megalin/cubilin ligand (albumin) by PT cells. These effects were independent of heme reduction state. The Glu7Val mutant of Hb that causes SCD was equally effective at inhibiting albumin uptake compared with wild-type Hb. Addition of the Hb scavenger haptoglobin (Hpt) restored albumin uptake in the presence of Hb, suggesting that Hpt binding to the Hb αβ dimer-dimer interface interferes with Hb binding to megalin/cubilin. BLAST searches and structural modeling analyses revealed regions of similarity between Hb and albumin that map to this region and may represent sites of Hb interaction with megalin/cubilin. Our studies suggest that impaired endocytosis of megalin/cubilin ligands, rather than heme toxicity, may be the cause of tubular proteinuria in SCD patients. Additionally, loss of these filtered proteins into the urine may contribute to the extra-renal pathogenesis of SCD.
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Affiliation(s)
- Megan L Eshbach
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania; and
| | - Amandeep Kaur
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania; and
| | - Youssef Rbaibi
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania; and
| | - Jesús Tejero
- Division of Pulmonary, Allergy and Critical Care Medicine, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Ora A Weisz
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania; and
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55
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Wang T, Weinbaum S, Weinstein AM. Regulation of glomerulotubular balance: flow-activated proximal tubule function. Pflugers Arch 2017; 469:643-654. [PMID: 28271233 DOI: 10.1007/s00424-017-1960-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Revised: 02/15/2017] [Accepted: 02/17/2017] [Indexed: 12/23/2022]
Abstract
The purpose of this review is to summarize our knowledge and understanding of the physiological importance and the mechanisms underlying flow-activated proximal tubule transport. Since the earliest micropuncture studies of mammalian proximal tubule, it has been recognized that tubular flow is an important regulator of sodium, potassium, and acid-base transport in the kidney. Increased fluid flow stimulates Na+ and HCO3- absorption in the proximal tubule via stimulation of Na/H-exchanger isoform 3 (NHE3) and H+-ATPase. In the proximal tubule, brush border microvilli are the major flow sensors, which experience changes in hydrodynamic drag and bending moment as luminal flow velocity changes and which transmit the force of altered flow to cytoskeletal structures within the cell. The signal to NHE3 depends upon the integrity of the actin cytoskeleton; the signal to the H+-ATPase depends upon microtubules. We have demonstrated that alterations in fluid drag impact tubule function by modulating ion transporter availability within the brush border membrane of the proximal tubule. Beyond that, there is evidence that transporter activity within the peritubular membrane is also modulated by luminal flow. Secondary messengers that regulate the flow-mediated tubule function have also been delineated. Dopamine blunts the responsiveness of proximal tubule transporters to changes in luminal flow velocity, while a DA1 antagonist increases flow sensitivity of solute reabsorption. IP3 receptor-mediated intracellular Ca2+ signaling is critical to transduction of microvillus drag. In this review, we summarize our findings of the regulatory mechanism of flow-mediated Na+ and HCO3- transport in the proximal tubule and review available information about flow sensing and regulatory mechanism of glomerulotubular balance.
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Affiliation(s)
- Tong Wang
- Department of Cellular and Molecular Physiology, Yale University, 333 Cedar Street, New Haven, CT, 06520, USA.
| | - Sheldon Weinbaum
- Department of Biomedical Engineering, City College of New York, CUNY, New York, NY, USA
| | - Alan M Weinstein
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, NY, USA
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56
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Fluid shear stress-induced TGF-β/ALK5 signaling in renal epithelial cells is modulated by MEK1/2. Cell Mol Life Sci 2017; 74:2283-2298. [PMID: 28168444 PMCID: PMC5425503 DOI: 10.1007/s00018-017-2460-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Revised: 01/06/2017] [Accepted: 01/09/2017] [Indexed: 12/14/2022]
Abstract
Renal tubular epithelial cells are exposed to mechanical forces due to fluid flow shear stress within the lumen of the nephron. These cells respond by activation of mechano-sensors located at the plasma membrane or the primary cilium, having crucial roles in maintenance of cellular homeostasis and signaling. In this paper, we applied fluid shear stress to study TGF-β signaling in renal epithelial cells with and without expression of the Pkd1-gene, encoding a mechano-sensor mutated in polycystic kidney disease. TGF-β signaling modulates cell proliferation, differentiation, apoptosis, and fibrotic deposition, cellular programs that are altered in renal cystic epithelia. SMAD2/3-mediated signaling was activated by fluid flow, both in wild-type and Pkd1−/− cells. This was characterized by phosphorylation and nuclear accumulation of p-SMAD2/3, as well as altered expression of downstream target genes and epithelial-to-mesenchymal transition markers. This response was still present after cilia ablation. An inhibitor of upstream type-I-receptors, ALK4/ALK5/ALK7, as well as TGF-β-neutralizing antibodies effectively blocked SMAD2/3 activity. In contrast, an activin-ligand trap was ineffective, indicating that increased autocrine TGF-β signaling is involved. To study potential involvement of MAPK/ERK signaling, cells were treated with a MEK1/2 inhibitor. Surprisingly, fluid flow-induced expression of most SMAD2/3 targets was further enhanced upon MEK inhibition. We conclude that fluid shear stress induces autocrine TGF-β/ALK5-induced target gene expression in renal epithelial cells, which is partially restrained by MEK1/2-mediated signaling.
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57
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Mohammed SG, Arjona FJ, Latta F, Bindels RJM, Roepman R, Hoenderop JGJ. Fluid shear stress increases transepithelial transport of Ca
2+
in ciliated distal convoluted and connecting tubule cells. FASEB J 2017; 31:1796-1806. [DOI: 10.1096/fj.201600687rrr] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Accepted: 01/03/2017] [Indexed: 11/11/2022]
Affiliation(s)
- Sami G. Mohammed
- Department of PhysiologyRadboud Institute for Molecular Life SciencesRadboud University Medical CenterNijmegenThe Netherlands
| | - Francisco J. Arjona
- Department of PhysiologyRadboud Institute for Molecular Life SciencesRadboud University Medical CenterNijmegenThe Netherlands
| | - Femke Latta
- Department of PhysiologyRadboud Institute for Molecular Life SciencesRadboud University Medical CenterNijmegenThe Netherlands
| | - René J. M. Bindels
- Department of PhysiologyRadboud Institute for Molecular Life SciencesRadboud University Medical CenterNijmegenThe Netherlands
| | - Ronald Roepman
- Department of Human GeneticsRadboud Institute for Molecular Life SciencesRadboud University Medical CenterNijmegenThe Netherlands
| | - Joost G. J. Hoenderop
- Department of PhysiologyRadboud Institute for Molecular Life SciencesRadboud University Medical CenterNijmegenThe Netherlands
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58
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Abstract
Microfluidics is an interdisciplinary field intersecting many areas in engineering. Utilizing a combination of physics, chemistry, biology, and biotechnology, along with practical applications for designing devices that use low volumes of fluids to achieve high-throughput screening, is a major goal in microfluidics. Microfluidic approaches allow the study of cells growth and differentiation using a variety of conditions including control of fluid flow that generates shear stress. Recently, Piezo1 channels were shown to respond to fluid shear stress and are crucial for vascular development. This channel is ideal for studying fluid shear stress applied to cells using microfluidic devices. We have developed an approach that allows us to analyze the role of Piezo channels on any given cell and serves as a high-throughput screen for drug discovery. We show that this approach can provide detailed information about the inhibitors of Piezo channels.
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59
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Hyperfiltration-associated biomechanical forces in glomerular injury and response: Potential role for eicosanoids. Prostaglandins Other Lipid Mediat 2017; 132:59-68. [PMID: 28108282 DOI: 10.1016/j.prostaglandins.2017.01.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Revised: 12/22/2016] [Accepted: 01/10/2017] [Indexed: 12/29/2022]
Abstract
Hyperfiltration is a well-known risk factor in progressive loss of renal function in chronic kidney disease (CKD) secondary to various diseases. A reduced number of functional nephrons due to congenital or acquired cause(s) results in hyperfiltration in the remnant kidney. Hyperfiltration-associated increase in biomechanical forces, namely pressure-induced tensile stress and fluid flow-induced shear stress (FFSS) determine cellular injury and response. We believe the current treatment of CKD yields limited success because it largely attenuates pressure-induced tensile stress changes but not the effect of FFSS on podocytes. Studies on glomerular podocytes, tubular epithelial cells and bone osteocytes provide evidence for a significant role of COX-2 generated PGE2 and its receptors in response to tensile stress and FFSS. Preliminary observations show increased urinary PGE2 in children born with a solitary kidney. FFSS-induced COX2-PGE2-EP2 signaling provides an opportunity to identify targets and, for developing novel agents to complement currently available treatment.
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60
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Shi S, Carattino MD. Expression and Analysis of Flow-regulated Ion Channels in Xenopus Oocytes. Bio Protoc 2017; 7:e2224. [PMID: 28670605 DOI: 10.21769/bioprotoc.2224] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
Abstract
Mechanically-gated ion channels play key roles in mechanotransduction, a process that translates physical forces into biological signals. Epithelial and endothelial cells are exposed to laminar shear stress (LSS), a tangential force exerted by flowing fluids against the wall of vessels and epithelia. The protocol outlined herein has been used to examine the response of ion channels expressed in Xenopus oocytes to LSS (Hoger et al., 2002; Carattino et al., 2004; Shi et al., 2006). The Xenopus oocyte is a reliable system that allows for the expression and chemical modification of ion channels and regulatory proteins (George et al., 1989; Palmer et al., 1990; Sheng et al., 2001; Carattino et al., 2003). Therefore, this technique is suitable for studying the molecular mechanisms that allow flow-activated channels to respond to LSS.
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Affiliation(s)
- Shujie Shi
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Marcelo D Carattino
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania.,Department of Cell Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
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61
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Verma D, Meng F, Sachs F, Hua SZ. Flow-induced focal adhesion remodeling mediated by local cytoskeletal stresses and reorganization. Cell Adh Migr 2016; 9:432-40. [PMID: 26418333 DOI: 10.1080/19336918.2015.1089379] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Cells respond to fluid shear stress through dynamic processes involving changes in actomyosin and other cytoskeletal stresses, remodeling of cell adhesions, and cytoskeleton reorganization. In this study we simultaneously measured focal adhesion dynamics and cytoskeletal stress and reorganization in MDCK cells under fluid shear stress. The measurements used co-expression of fluorescently labeled paxillin and force sensitive FRET probes of α-actinin. A shear stress of 0.74 dyn/cm(2) for 3 hours caused redistribution of cytoskeletal tension and significant focal adhesion remodeling. The fate of focal adhesions is determined by the stress state and stability of the linked actin stress fibers. In the interior of the cell, the mature focal adhesions disassembled within 35-40 min under flow and stress fibers disintegrated. Near the cell periphery, the focal adhesions anchoring the stress fibers perpendicular to the cell periphery disassembled, while focal adhesions associated with peripheral fibers sustained. The diminishing focal adhesions are coupled with local cytoskeletal stress release and actin stress fiber disassembly whereas sustaining peripheral focal adhesions are coupled with an increase in stress and enhancement of actin bundles. The results show that flow induced formation of peripheral actin bundles provides a favorable environment for focal adhesion remodeling along the cell periphery. Under such condition, new FAs were observed along the cell edge under flow. Our results suggest that the remodeling of FAs in epithelial cells under flow is orchestrated by actin cytoskeletal stress redistribution and structural reorganization.
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Affiliation(s)
- Deepika Verma
- b Department of Mechanical and Aerospace Engineering ; SUNY-Buffalo ; Buffalo , NY USA
| | - Fanjie Meng
- a Department of Physiology and Biophysics ; SUNY-Buffalo , Buffalo , NY USA
| | - Frederick Sachs
- a Department of Physiology and Biophysics ; SUNY-Buffalo , Buffalo , NY USA
| | - Susan Z Hua
- a Department of Physiology and Biophysics ; SUNY-Buffalo , Buffalo , NY USA.,b Department of Mechanical and Aerospace Engineering ; SUNY-Buffalo ; Buffalo , NY USA
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62
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Chevtchik NV, Fedecostante M, Jansen J, Mihajlovic M, Wilmer M, Rüth M, Masereeuw R, Stamatialis D. Upscaling of a living membrane for bioartificial kidney device. Eur J Pharmacol 2016; 790:28-35. [PMID: 27395800 DOI: 10.1016/j.ejphar.2016.07.009] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Revised: 06/24/2016] [Accepted: 07/06/2016] [Indexed: 12/01/2022]
Abstract
The limited removal of metabolic waste products in dialyzed kidney patients leads to high morbidity and mortality. One powerful solution for a more complete removal of those metabolites might be offered by a bioartificial kidney device (BAK), which contains a hybrid "living membrane" with functional proximal tubule epithelial cells (PTEC). These cells are supported by an artificial functionalized hollow fiber membrane (HFM) and are able to actively remove the waste products. In our earlier studies, conditionally immortalized human PTEC (ciPTEC) showed to express functional organic cationic transporter 2 (OCT2) when seeded on small size flat or hollow fiber polyethersulfone (PES) membranes. Here, an upscaled "living membrane" is presented. We developed and assessed the functionality of modules containing three commercially available MicroPES HFM supporting ciPTEC. The HFM were optimally coated with L-Dopa and collagen IV to support a uniform and tight monolayer formation of matured ciPTEC under static culturing conditions. Both abundant expression of zonula occludens-1 (ZO-1) protein and limited diffusion of FITC-inulin confirm a clear barrier function of the monolayer. Furthermore, the uptake of 4-(4-(dimethylamino)styryl)-N-methylpyridinium iodide (ASP+), a fluorescent OCT2 substrate, was studied in absence and presence of known OCT inhibitors, such as cimetidine and a cationic uremic solutes mixture. The ASP+ uptake by the living upscaled membrane was decreased by 60% in the presence of either inhibitor, proving the active function of OCT2. In conclusion, this study presents a successful upscaling of a living membrane with active organic cation transport as a support for BAK device.
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Affiliation(s)
- Natalia Vladimirovna Chevtchik
- Department of Biomaterials Science and Technology, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands
| | - Michele Fedecostante
- Department of Pharmaceutical Sciences, UIPS Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands
| | - Jitske Jansen
- Department of Pharmaceutical Sciences, UIPS Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands
| | - Milos Mihajlovic
- Department of Pharmaceutical Sciences, UIPS Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands
| | - Martijn Wilmer
- Department of Pharmacology and Toxicology, Radboud Institute for Molecular Life Sciences, Radboudumc, Nijmegen, The Netherlands
| | - Marieke Rüth
- eXcorLab GmbH, Industrie Center Obernburg, Obernburg, Germany
| | - Rosalinde Masereeuw
- Department of Pharmaceutical Sciences, UIPS Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands
| | - Dimitrios Stamatialis
- Department of Biomaterials Science and Technology, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands.
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63
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Obesity-related glomerulopathy: clinical and pathologic characteristics and pathogenesis. Nat Rev Nephrol 2016; 12:453-71. [PMID: 27263398 DOI: 10.1038/nrneph.2016.75] [Citation(s) in RCA: 425] [Impact Index Per Article: 53.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The prevalence of obesity-related glomerulopathy is increasing in parallel with the worldwide obesity epidemic. Glomerular hypertrophy and adaptive focal segmental glomerulosclerosis define the condition pathologically. The glomerulus enlarges in response to obesity-induced increases in glomerular filtration rate, renal plasma flow, filtration fraction and tubular sodium reabsorption. Normal insulin/phosphatidylinositol 3-kinase/Akt and mTOR signalling are critical for podocyte hypertrophy and adaptation. Adipokines and ectopic lipid accumulation in the kidney promote insulin resistance of podocytes and maladaptive responses to cope with the mechanical forces of renal hyperfiltration. Although most patients have stable or slowly progressive proteinuria, up to one-third develop progressive renal failure and end-stage renal disease. Renin-angiotensin-aldosterone blockade is effective in the short-term but weight loss by hypocaloric diet or bariatric surgery has induced more consistent and dramatic antiproteinuric effects and reversal of hyperfiltration. Altered fatty acid and cholesterol metabolism are increasingly recognized as key mediators of renal lipid accumulation, inflammation, oxidative stress and fibrosis. Newer therapies directed to lipid metabolism, including SREBP antagonists, PPARα agonists, FXR and TGR5 agonists, and LXR agonists, hold therapeutic promise.
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64
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Orhon I, Dupont N, Zaidan M, Boitez V, Burtin M, Schmitt A, Capiod T, Viau A, Beau I, Kuehn EW, Friedlander G, Terzi F, Codogno P. Primary-cilium-dependent autophagy controls epithelial cell volume in response to fluid flow. Nat Cell Biol 2016; 18:657-67. [PMID: 27214279 DOI: 10.1038/ncb3360] [Citation(s) in RCA: 110] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Accepted: 04/18/2016] [Indexed: 12/31/2022]
Abstract
Autophagy is an adaptation mechanism that is vital for cellular homeostasis in response to various stress conditions. Previous reports indicate that there is a functional interaction between the primary cilium (PC) and autophagy. The PC, a microtubule-based structure present at the surface of numerous cell types, is a mechanical sensor. Here we show that autophagy induced by fluid flow regulates kidney epithelial cell volume in vitro and in vivo. PC ablation blocked autophagy induction and cell-volume regulation. In addition, inhibition of autophagy in ciliated cells impaired the flow-dependent regulation of cell volume. PC-dependent autophagy can be triggered either by mTOR inhibition or a mechanism dependent on the polycystin 2 channel. Only the LKB1-AMPK-mTOR signalling pathway was required for the flow-dependent regulation of cell volume by autophagy. These findings suggest that therapies regulating autophagy should be considered in developing treatments for PC-related diseases.
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Affiliation(s)
- Idil Orhon
- Institut Necker Enfants-Malades (INEM), INSERM U1151-CNRS UMR 8253, Université Paris Descartes-Sorbonne Paris Cité, Paris F-75993, France
| | - Nicolas Dupont
- Institut Necker Enfants-Malades (INEM), INSERM U1151-CNRS UMR 8253, Université Paris Descartes-Sorbonne Paris Cité, Paris F-75993, France
| | - Mohamad Zaidan
- Institut Necker Enfants-Malades (INEM), INSERM U1151-CNRS UMR 8253, Université Paris Descartes-Sorbonne Paris Cité, Paris F-75993, France
| | - Valérie Boitez
- Institut Necker Enfants-Malades (INEM), INSERM U1151-CNRS UMR 8253, Université Paris Descartes-Sorbonne Paris Cité, Paris F-75993, France
| | - Martine Burtin
- Institut Necker Enfants-Malades (INEM), INSERM U1151-CNRS UMR 8253, Université Paris Descartes-Sorbonne Paris Cité, Paris F-75993, France
| | - Alain Schmitt
- Institut Cochin, INSERM U1016-CNRS UMR 8104, Université Paris Descartes-Sorbonne Paris Cité, Paris F-75014, France
| | - Thierry Capiod
- Institut Necker Enfants-Malades (INEM), INSERM U1151-CNRS UMR 8253, Université Paris Descartes-Sorbonne Paris Cité, Paris F-75993, France
| | - Amandine Viau
- Department of Nephrology, University Medical Center, Albert-Ludwig-University of Freiburg, D-79106 Freiburg, Germany
| | - Isabelle Beau
- INSERM UMR 1185, Université Paris-Sud 11, Kremlin-Bicêtre F-94276, France
| | - E Wolfgang Kuehn
- Department of Nephrology, University Medical Center, Albert-Ludwig-University of Freiburg, D-79106 Freiburg, Germany.,Center for Biological Signaling Studies (bioss), Albert-Ludwig-University, D-79104 Freiburg, Germany
| | - Gérard Friedlander
- Institut Necker Enfants-Malades (INEM), INSERM U1151-CNRS UMR 8253, Université Paris Descartes-Sorbonne Paris Cité, Paris F-75993, France
| | - Fabiola Terzi
- Institut Necker Enfants-Malades (INEM), INSERM U1151-CNRS UMR 8253, Université Paris Descartes-Sorbonne Paris Cité, Paris F-75993, France
| | - Patrice Codogno
- Institut Necker Enfants-Malades (INEM), INSERM U1151-CNRS UMR 8253, Université Paris Descartes-Sorbonne Paris Cité, Paris F-75993, France
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65
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Piezo1-dependent regulation of urinary osmolarity. Pflugers Arch 2016; 468:1197-1206. [DOI: 10.1007/s00424-016-1811-z] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Revised: 03/13/2016] [Accepted: 03/15/2016] [Indexed: 12/13/2022]
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Abstract
PURPOSE OF REVIEW The proximal tubule plays a critical role in the reabsorption of ions, solutes and low molecular weight proteins from the glomerular filtrate. Although the proximal tubule has long been known to acutely modulate ion reabsorption in response to changes in flow rates of the glomerular filtrate, it has only recently been discovered that proximal tubule cells can similarly adjust endocytic capacity in response to flow. This review synthesizes our current understanding of mechanosensitive regulation of endocytic capacity in proximal tubule epithelia and highlights areas of opportunity for future investigations. RECENT FINDINGS Recent studies have reported that the endocytic capacity of proximal tubule cells is dramatically increased upon exposure to flow and the accompanying fluid shear stress. Modulation of this pathway is dependent on increases in intracellular calcium initiated by bending of the primary cilium, and also requires purinergic receptor activation that is mediated by release of extracellular ATP. This article summarizes what is currently known about the signaling cascade that transduces changes in flow into alterations in endocytosis. We discuss the implications of this newly described regulatory pathway with respect to our understanding of protein retrieval by the kidney under normal conditions, and in diseases that present with low molecular weight proteinuria. SUMMARY Primary cilia act as mechanotransducers that modulate apical endocytic capacity in proximal tubule cells in response to changes in fluid shear stress.
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67
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Schillers H, Medalsy I, Hu S, Slade AL, Shaw JE. PeakForce Tapping resolves individual microvilli on living cells. J Mol Recognit 2016; 29:95-101. [PMID: 26414320 PMCID: PMC5054848 DOI: 10.1002/jmr.2510] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Revised: 08/17/2015] [Accepted: 08/18/2015] [Indexed: 12/18/2022]
Abstract
Microvilli are a common structure found on epithelial cells that increase the apical surface thus enhancing the transmembrane transport capacity and also serve as one of the cell's mechanosensors. These structures are composed of microfilaments and cytoplasm, covered by plasma membrane. Epithelial cell function is usually coupled to the density of microvilli and its individual size illustrated by diseases, in which microvilli degradation causes malabsorption and diarrhea. Atomic force microscopy (AFM) has been widely used to study the topography and morphology of living cells. Visualizing soft and flexible structures such as microvilli on the apical surface of a live cell has been very challenging because the native microvilli structures are displaced and deformed by the interaction with the probe. PeakForce Tapping® is an AFM imaging mode, which allows reducing tip-sample interactions in time (microseconds) and controlling force in the low pico-Newton range. Data acquisition of this mode was optimized by using a newly developed PeakForce QNM-Live Cell probe, having a short cantilever with a 17-µm-long tip that minimizes hydrodynamic effects between the cantilever and the sample surface. In this paper, we have demonstrated for the first time the visualization of the microvilli on living kidney cells with AFM using PeakForce Tapping. The structures observed display a force dependence representing either the whole microvilli or just the tips of the microvilli layer. Together, PeakForce Tapping allows force control in the low pico-Newton range and enables the visualization of very soft and flexible structures on living cells under physiological conditions.
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Affiliation(s)
- Hermann Schillers
- Institute of Physiology II, University of Münster, Robert-Koch-Str. 27b, Münster, 48149, Germany
| | - Izhar Medalsy
- Bruker Nano Surfaces Division, 112 Robin Hill Rd, Santa Barbara, CA, 93117, USA
| | - Shuiqing Hu
- Bruker Nano Surfaces Division, 112 Robin Hill Rd, Santa Barbara, CA, 93117, USA
| | - Andrea L Slade
- Bruker Nano Surfaces Division, 112 Robin Hill Rd, Santa Barbara, CA, 93117, USA
| | - James E Shaw
- Bruker Nano Surfaces Division, 112 Robin Hill Rd, Santa Barbara, CA, 93117, USA
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68
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Du Z, Duan Y, Yan Q, Weinbaum S, Weinstein AM, Wang T. Flow-activated proximal tubule function underlies glomerulotubular balance. THE KITASATO MEDICAL JOURNAL 2016; 46:105-117. [PMID: 31105444 PMCID: PMC6519745] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Flow-modulated salt and water transport in proximal tubules has been recognized for more than four decades. Recent work has made major progress in defining the underlying cellular mechanisms. First, we demonstrated that perfusion-absorption balance is present in the isolated perfused proximal tubule of the mouse kidney, and thus is independent of neuronal control and systemic hormonal regulation. In proximal tubule, higher axial flow rates stimulate sodium and bicarbonate absorption by increased apical membrane Na+/H+-transporter and H-ATPase activity. It is also evident that fluid shear stress stimulates Na+/H+ exchanger isoform 3 (NHE3) exocytosis and trafficking to the apical membrane of the proximal tubule cells. Second, experimental data and modeling calculations provide strong evidence that brush border microvilli function as flow sensors in the proximal tubule. Flow-induced changes of proximal tubule absorption depend on the changes of torque (bending moment) on the microvilli, and that an intact actin cytoskeleton is required to transduce signals from the brush border to cell and alter transport activity, NHE3 expression and trafficking. Third, the increased NHE3 exocytosis by dopamine blockers enhanced tubule sensitivity to torque, and the IP3 receptor-mediated intracellular Ca2+ signaling is a critical step in transduction of fluid drag on microvillus drag tips in modulating Na+ and HCO3 - transport. Finally, in all of our experimental studies, flow-dependent transport in mouse tubules was achieved with virtually no change in tubule cell volume. Our model calculations suggest that this observation is strong evidence for proportional luminal and peritubular effects of flow on transporter density.
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Affiliation(s)
- Zhaopeng Du
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT
| | - Yi Duan
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, NY
| | - QingShang Yan
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT
| | - Sheldon Weinbaum
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, NY
| | - Alan M. Weinstein
- Department of Biomedical Engineering, City College of New York, of the City University of New York, NY
| | - Tong Wang
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT
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69
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Carrisoza-Gaytan R, Carattino MD, Kleyman TR, Satlin LM. An unexpected journey: conceptual evolution of mechanoregulated potassium transport in the distal nephron. Am J Physiol Cell Physiol 2015; 310:C243-59. [PMID: 26632600 DOI: 10.1152/ajpcell.00328.2015] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Flow-induced K secretion (FIKS) in the aldosterone-sensitive distal nephron (ASDN) is mediated by large-conductance, Ca(2+)/stretch-activated BK channels composed of pore-forming α-subunits (BKα) and accessory β-subunits. This channel also plays a critical role in the renal adaptation to dietary K loading. Within the ASDN, the cortical collecting duct (CCD) is a major site for the final renal regulation of K homeostasis. Principal cells in the ASDN possess a single apical cilium whereas the surfaces of adjacent intercalated cells, devoid of cilia, are decorated with abundant microvilli and microplicae. Increases in tubular (urinary) flow rate, induced by volume expansion, diuretics, or a high K diet, subject CCD cells to hydrodynamic forces (fluid shear stress, circumferential stretch, and drag/torque on apical cilia and presumably microvilli/microplicae) that are transduced into increases in principal (PC) and intercalated (IC) cell cytoplasmic Ca(2+) concentration that activate apical voltage-, stretch- and Ca(2+)-activated BK channels, which mediate FIKS. This review summarizes studies by ourselves and others that have led to the evolving picture that the BK channel is localized in a macromolecular complex at the apical membrane, composed of mechanosensitive apical Ca(2+) channels and a variety of kinases/phosphatases as well as other signaling molecules anchored to the cytoskeleton, and that an increase in tubular fluid flow rate leads to IC- and PC-specific responses determined, in large part, by the cell-specific composition of the BK channels.
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Affiliation(s)
| | - Marcelo D Carattino
- Renal-Electrolyte Division, Department of Medicine, Pittsburgh, Pennsylvania
| | - Thomas R Kleyman
- Renal-Electrolyte Division, Department of Medicine, Pittsburgh, Pennsylvania
| | - Lisa M Satlin
- Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, New York; and
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70
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Raghavan V, Weisz OA. Discerning the role of mechanosensors in regulating proximal tubule function. Am J Physiol Renal Physiol 2015; 310:F1-5. [PMID: 26662200 DOI: 10.1152/ajprenal.00373.2015] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
All cells in the body experience external mechanical forces such as shear stress and stretch. These forces are sensed by specialized structures in the cell known as mechanosensors. Cells lining the proximal tubule (PT) of the kidney are continuously exposed to variations in flow rates of the glomerular ultrafiltrate, which manifest as changes in axial shear stress and radial stretch. Studies suggest that these cells respond acutely to variations in flow by modulating their ion transport and endocytic functions to maintain glomerulotubular balance. Conceptually, changes in the axial shear stress in the PT could be sensed by three known structures, namely, the microvilli, the glycocalyx, and primary cilia. The orthogonal component of the force produced by flow exhibits as radial stretch and can cause expansion of the tubule. Forces of stretch are transduced by integrins, by stretch-activated channels, and by cell-cell contacts. This review summarizes our current understanding of flow sensing in PT epithelia, discusses challenges in dissecting the role of individual flow sensors in the mechanosensitive responses, and identifies potential areas of opportunity for new study.
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Affiliation(s)
- Venkatesan Raghavan
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Ora A Weisz
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
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71
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Tomilin V, Mamenko M, Zaika O, Pochynyuk O. Role of renal TRP channels in physiology and pathology. Semin Immunopathol 2015; 38:371-83. [PMID: 26385481 DOI: 10.1007/s00281-015-0527-z] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Accepted: 09/04/2015] [Indexed: 01/05/2023]
Abstract
Kidneys critically contribute to the maintenance of whole-body homeostasis by governing water and electrolyte balance, controlling extracellular fluid volume, plasma osmolality, and blood pressure. Renal function is regulated by numerous systemic endocrine and local mechanical stimuli. Kidneys possess a complex network of membrane receptors, transporters, and ion channels which allows responding to this wide array of signaling inputs in an integrative manner. Transient receptor potential (TRP) channel family members with diverse modes of activation, varied permeation properties, and capability to integrate multiple downstream signals are pivotal molecular determinants of renal function all along the nephron. This review summarizes experimental data on the role of TRP channels in a healthy mammalian kidney and discusses their involvement in renal pathologies.
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Affiliation(s)
- Viktor Tomilin
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, 6431 Fannin, Houston, TX, 77030, USA.,Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russian Federation
| | - Mykola Mamenko
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, 6431 Fannin, Houston, TX, 77030, USA
| | - Oleg Zaika
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, 6431 Fannin, Houston, TX, 77030, USA
| | - Oleh Pochynyuk
- Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, 6431 Fannin, Houston, TX, 77030, USA.
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72
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Schophuizen CM, De Napoli IE, Jansen J, Teixeira S, Wilmer MJ, Hoenderop JG, Van den Heuvel LP, Masereeuw R, Stamatialis D. Development of a living membrane comprising a functional human renal proximal tubule cell monolayer on polyethersulfone polymeric membrane. Acta Biomater 2015; 14:22-32. [PMID: 25527093 DOI: 10.1016/j.actbio.2014.12.002] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 11/22/2014] [Accepted: 12/02/2014] [Indexed: 10/24/2022]
Abstract
The need for improved renal replacement therapies has stimulated innovative research for the development of a cell-based renal assist device. A key requirement for such a device is the formation of a "living membrane", consisting of a tight kidney cell monolayer with preserved functional organic ion transporters on a suitable artificial membrane surface. In this work, we applied a unique conditionally immortalized proximal tubule epithelial cell (ciPTEC) line with an optimized coating strategy on polyethersulfone (PES) membranes to develop a living membrane with a functional proximal tubule epithelial cell layer. PES membranes were coated with combinations of 3,4-dihydroxy-l-phenylalanine and human collagen IV (Coll IV). The optimal coating time and concentrations were determined to achieve retention of vital blood components while preserving high water transport and optimal ciPTEC adhesion. The ciPTEC monolayers obtained were examined through immunocytochemistry to detect zona occludens 1 tight junction proteins. Reproducible monolayers were formed when using a combination of 2 mg ml(-1) 3,4-dihydroxy-l-phenylalanine (4 min coating, 1h dissolution) and 25 μg ml(-1) Coll IV (4 min coating). The successful transport of (14)C-creatinine through the developed living membrane system was used as an indication for organic cation transporter functionality. The addition of metformin or cimetidine significantly reduced the creatinine transepithelial flux, indicating active creatinine uptake in ciPTECs, most likely mediated by the organic cation transporter, OCT2 (SLC22A2). In conclusion, this study shows the successful development of a living membrane consisting of a reproducible ciPTEC monolayer on PES membranes, an important step towards the development of a bioartificial kidney.
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73
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Mamenko M, Zaika O, Boukelmoune N, O'Neil RG, Pochynyuk O. Deciphering physiological role of the mechanosensitive TRPV4 channel in the distal nephron. Am J Physiol Renal Physiol 2015; 308:F275-86. [PMID: 25503733 PMCID: PMC4329491 DOI: 10.1152/ajprenal.00485.2014] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 12/08/2014] [Indexed: 12/14/2022] Open
Abstract
Long-standing experimental evidence suggests that epithelial cells in the renal tubule are able to sense osmotic and pressure gradients caused by alterations in ultrafiltrate flow by elevating intracellular Ca(2+) concentration. These responses are viewed as critical regulators of a variety of processes ranging from transport of water and solutes to cellular growth and differentiation. A loss in the ability to sense mechanical stimuli has been implicated in numerous pathologies associated with systemic imbalance of electrolytes and to the development of polycystic kidney disease. The molecular mechanisms conferring mechanosensitive properties to epithelial tubular cells involve activation of transient receptor potential (TRP) channels, such as TRPV4, allowing direct Ca(2+) influx to increase intracellular Ca(2+) concentration. In this review, we critically analyze the current evidence about signaling determinants of TRPV4 activation by luminal flow in the distal nephron and discuss how dysfunction of this mechanism contributes to the progression of polycystic kidney disease. We also review the physiological relevance of TRPV4-based mechanosensitivity in controlling flow-dependent K(+) secretion in the distal renal tubule.
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Affiliation(s)
- M Mamenko
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, Texas
| | - O Zaika
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, Texas
| | - N Boukelmoune
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, Texas
| | - R G O'Neil
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, Texas
| | - O Pochynyuk
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, Texas
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74
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Du Z, Weinbaum S, Weinstein AM, Wang T. Regulation of glomerulotubular balance. III. Implication of cytosolic calcium in flow-dependent proximal tubule transport. Am J Physiol Renal Physiol 2015; 308:F839-47. [PMID: 25651568 DOI: 10.1152/ajprenal.00601.2014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Accepted: 01/25/2015] [Indexed: 11/22/2022] Open
Abstract
In the proximal tubule, axial flow (drag on brush-border microvilli) stimulates Na(+) and HCO3 (-) reabsorption by modulating both Na/H exchanger 3 (NHE3) and H-ATPase activity, a process critical to glomerulotubular balance. We have also demonstrated that blocking the angiotensin II receptor decreases baseline transport, but preserves the flow effect; dopamine leaves baseline fluxes intact, but abrogates the flow effect. In the current work, we provide evidence implicating cytosolic calcium in flow-dependent transport. Mouse proximal tubules were microperfused in vitro at perfusion rates of 5 and 20 nl/min, and reabsorption of fluid (Jv) and HCO3 (-) (JHCO3) were measured. We examined the effect of high luminal Ca(2+) (5 mM), 0 mM Ca(2+), the Ca(2+) chelator BAPTA-AM, the inositol 1,4,5-trisphosphate (IP3) receptor antagonist 2-aminoethoxydiphenyl borate (2-APB), and the Ca-ATPase inhibitor thapsigargin. In control tubules, increasing perfusion rate from 5 to 20 nl/min increased Jv by 62% and JHCO3 by 104%. With respect to Na(+) reabsorption, high luminal Ca(2+) decreased transport at low flow, but preserved the flow-induced increase; low luminal Ca(2+) had little impact; both BAPTA and 2-APB had no effect on baseline flux, but abrogated the flow effect; thapsigargin decreased baseline flow, leaving the flow effect intact. With respect to HCO3 (-) reabsorption, high luminal Ca(2+) decreased transport at low flow and mildly diminished the flow-induced increase; low luminal Ca(2+) had little impact; both BAPTA and 2-APB had no effect on baseline flux, but abrogated the flow effect. These data implicate IP3 receptor-mediated intracellular Ca(2+) signaling as a critical step in transduction of microvillous drag to modulate Na(+) and HCO3 (-) transport.
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Affiliation(s)
- Zhaopeng Du
- Department of Cellular and Molecular Physiology, Yale University, New Haven, Connecticut
| | - Sheldon Weinbaum
- Department of Biomedical Engineering, City College of New York, CUNY, New York, New York; and
| | - Alan M Weinstein
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, New York
| | - Tong Wang
- Department of Cellular and Molecular Physiology, Yale University, New Haven, Connecticut;
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75
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Honoré E, Martins JR, Penton D, Patel A, Demolombe S. The Piezo Mechanosensitive Ion Channels: May the Force Be with You! Rev Physiol Biochem Pharmacol 2015; 169:25-41. [DOI: 10.1007/112_2015_26] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
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76
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Pluznick JL, Caplan MJ. Chemical and Physical Sensors in the Regulation of Renal Function. Clin J Am Soc Nephrol 2014; 10:1626-35. [PMID: 25280495 DOI: 10.2215/cjn.00730114] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
In order to assess the status of the volume and composition of the body fluid compartment, the kidney monitors a wide variety of chemical and physical parameters. It has recently become clear that the kidney's sensory capacity extends well beyond its ability to sense ion concentrations in the forming urine. The kidney also keeps track of organic metabolites derived from a surprising variety of sources and uses a complex interplay of physical and chemical sensing mechanisms to measure the rate of fluid flow in the nephron. Recent research has provided new insights into the nature of these sensory mechanisms and their relevance to renal function.
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Affiliation(s)
- Jennifer L Pluznick
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and
| | - Michael J Caplan
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
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77
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Cabral PD, Garvin JL. TRPV4 activation mediates flow-induced nitric oxide production in the rat thick ascending limb. Am J Physiol Renal Physiol 2014; 307:F666-72. [PMID: 24966090 DOI: 10.1152/ajprenal.00619.2013] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Nitric oxide (NO) regulates renal function. Luminal flow stimulates NO production in the thick ascending limb (TAL). Transient receptor potential vanilloid 4 (TRPV4) is a mechano-sensitive channel activated by luminal flow in different types of cells. We hypothesized that TRPV4 mediates flow-induced NO production in the rat TAL. We measured NO production in isolated, perfused rat TALs using the fluorescent dye DAF FM. Increasing luminal flow from 0 to 20 nl/min stimulated NO from 8 ± 3 to 45 ± 12 arbitrary units (AU)/min (n = 5; P < 0.05). The TRPV4 antagonists, ruthenium red (15 μmol/l) and RN 1734 (10 μmol/l), blocked flow-induced NO production. Also, luminal flow did not increase NO production in the absence of extracellular calcium. We also studied the effect of luminal flow on NO production in TALs transduced with a TRPV4shRNA. In nontransduced TALs luminal flow increased NO production by 47 ± 17 AU/min (P < 0.05; n = 5). Similar to nontransduced TALs, luminal flow increased NO production by 39 ± 11 AU/min (P < 0.03; n = 5) in TALs transduced with a control negative sequence-shRNA while in TRPV4shRNA-transduced TALs, luminal flow did not increase NO production (Δ10 ± 15 AU/min; n = 5). We then tested the effect of two different TRPV4 agonists on NO production in the absence of luminal flow. 4α-Phorbol 12,13-didecanoate (1 μmol/l) enhanced NO production by 60 ± 11 AU/min (P < 0.002; n = 7) and GSK1016790A (10 ηmol/l) increased NO production by 52 ± 15 AU/min (P < 0.03; n = 5). GSK1016790A (10 ηmol/l) did not stimulate NO production in TRPV4shRNA-transduced TALs. We conclude that activation of TRPV4 channels mediates flow-induced NO production in the rat TAL.
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Affiliation(s)
- Pablo D Cabral
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio; and Universidad de Buenos Aires, Facultad de Medicina, Ciudad Autónoma de Buenos Aires, Buenos Aires, Argentina
| | - Jeffrey L Garvin
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio; and
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78
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Carrisoza-Gaytan R, Liu Y, Flores D, Else C, Lee HG, Rhodes G, Sandoval RM, Kleyman TR, Lee FYI, Molitoris B, Satlin LM, Rohatgi R. Effects of biomechanical forces on signaling in the cortical collecting duct (CCD). Am J Physiol Renal Physiol 2014; 307:F195-204. [PMID: 24872319 DOI: 10.1152/ajprenal.00634.2013] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
An increase in tubular fluid flow rate (TFF) stimulates Na reabsorption and K secretion in the cortical collecting duct (CCD) and subjects cells therein to biomechanical forces including fluid shear stress (FSS) and circumferential stretch (CS). Intracellular MAPK and extracellular autocrine/paracrine PGE2 signaling regulate cation transport in the CCD and, at least in other systems, are affected by biomechanical forces. We hypothesized that FSS and CS differentially affect MAPK signaling and PGE2 release to modulate cation transport in the CCD. To validate that CS is a physiological force in vivo, we applied the intravital microscopic approach to rodent kidneys in vivo to show that saline or furosemide injection led to a 46.5 ± 2.0 or 170 ± 32% increase, respectively, in distal tubular diameter. Next, murine CCD (mpkCCD) cells were grown on glass or silicone coated with collagen type IV and subjected to 0 or 0.4 dyne/cm(2) of FSS or 10% CS, respectively, forces chosen based on prior biomechanical modeling of ex vivo microperfused CCDs. Cells exposed to FSS expressed an approximately twofold greater abundance of phospho(p)-ERK and p-p38 vs. static cells, while CS did not alter p-p38 and p-ERK expression compared with unstretched controls. FSS induced whereas CS reduced PGE2 release by ∼40%. In conclusion, FSS and CS differentially affect ERK and p38 activation and PGE2 release in a cell culture model of the CD. We speculate that TFF differentially regulates biomechanical signaling and, in turn, cation transport in the CCD.
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Affiliation(s)
| | - Yu Liu
- Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, New York
| | - Daniel Flores
- Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, New York; Department of Medicine, James J. Peters Veterans Affairs Medical Center, New York, New York
| | - Cindy Else
- Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, New York
| | - Heon Goo Lee
- Department of Orthopedics, Robert Carroll and Jane Chace Carroll Laboratories, Columbia College of Physicians and Surgeons, New York, New York
| | - George Rhodes
- Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; and
| | - Ruben M Sandoval
- Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; and
| | - Thomas R Kleyman
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Francis Young-In Lee
- Department of Orthopedics, Robert Carroll and Jane Chace Carroll Laboratories, Columbia College of Physicians and Surgeons, New York, New York
| | - Bruce Molitoris
- Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana; and
| | - Lisa M Satlin
- Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, New York; Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, New York
| | - Rajeev Rohatgi
- Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, New York; Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, New York; Department of Medicine, James J. Peters Veterans Affairs Medical Center, New York, New York;
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79
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Shear stress-dependent regulation of apical endocytosis in renal proximal tubule cells mediated by primary cilia. Proc Natl Acad Sci U S A 2014; 111:8506-11. [PMID: 24912170 DOI: 10.1073/pnas.1402195111] [Citation(s) in RCA: 110] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The kidney has an extraordinary ability to maintain stable fractional solute and fluid reabsorption over a wide range of glomerular filtration rates (GFRs). Internalization of filtered low molecular weight proteins, vitamins, hormones, and other small molecules is mediated by the proximal tubule (PT) multiligand receptors megalin and cubilin. Changes in GFR and the accompanying fluid shear stress (FSS) modulate acute changes in PT ion transport thought to be mediated by microvillar bending. We found that FSS also affects apical endocytosis in PT cells. Exposure of immortalized PT cell lines to physiologically relevant levels of FSS led to dramatically increased internalization of the megalin-cubilin ligand albumin as well as the fluid phase marker dextran. FSS-stimulated apical endocytosis was initiated between 15 and 30 min postinduction of FSS, occurred via a clathrin- and dynamin-dependent pathway, and was rapidly reversed upon removing the FSS. Exposure to FSS also caused a rapid elevation in intracellular Ca(2+) [Ca(2+)]i, which was not observed in deciliated cells, upon treatment with BAPTA-AM, or upon inclusion of apyrase in the perfusion medium. Strikingly, deciliation, BAPTA-AM, and apyrase also blocked the flow-dependent increase in endocytosis. Moreover, addition of ATP bypassed the need for FSS in enhancing endocytic capacity. Our studies suggest that increased [Ca(2+)]i and purinergic signaling in response to FSS-dependent ciliary bending triggers a rapid and reversible increase in apical endocytosis that contributes to the efficient retrieval of filtered proteins in the PT.
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80
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Burnstock G, Evans LC, Bailey MA. Purinergic signalling in the kidney in health and disease. Purinergic Signal 2014; 10:71-101. [PMID: 24265071 PMCID: PMC3944043 DOI: 10.1007/s11302-013-9400-5] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 10/24/2013] [Indexed: 12/21/2022] Open
Abstract
The involvement of purinergic signalling in kidney physiology and pathophysiology is rapidly gaining recognition and this is a comprehensive review of early and recent publications in the field. Purinergic signalling involvement is described in several important intrarenal regulatory mechanisms, including tuboglomerular feedback, the autoregulatory response of the glomerular and extraglomerular microcirculation and the control of renin release. Furthermore, purinergic signalling influences water and electrolyte transport in all segments of the renal tubule. Reports about purine- and pyrimidine-mediated actions in diseases of the kidney, including polycystic kidney disease, nephritis, diabetes, hypertension and nephrotoxicant injury are covered and possible purinergic therapeutic strategies discussed.
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Affiliation(s)
- Geoffrey Burnstock
- Autonomic Neuroscience Centre, University College Medical School, Rowland Hill Street, London, NW3 2PF, UK,
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81
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Gildea JJ, Shah IT, Van Sciver RE, Israel JA, Enzensperger C, McGrath HE, Jose PA, Felder RA. The cooperative roles of the dopamine receptors, D1R and D5R, on the regulation of renal sodium transport. Kidney Int 2014; 86:118-26. [PMID: 24552847 PMCID: PMC4077925 DOI: 10.1038/ki.2014.5] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2013] [Revised: 11/27/2013] [Accepted: 12/12/2013] [Indexed: 02/07/2023]
Abstract
Determining the individual roles of the two dopamine D1-like receptors (D1R and D5R) on sodium transport in the human renal proximal tubule has been complicated by their structural and functional similarity. Here we used a novel D5R-selective antagonist (LE-PM436) and D1R or D5R-specific gene silencing to determine second messenger coupling pathways and heterologous receptor interaction between the two receptors. D1R and D5R co-localized in renal proximal tubule cells and physically interact, as determined by co-immunoprecipitation and FRET microscopy. Stimulation of renal proximal tubule cells with fenoldopam (D1R/D5R agonist) led to both adenylyl cyclase and phospholipase C (PLC) activation using real-time FRET biosensors ICUE3 and CYPHR, respectively. Fenoldopam increased cAMP accumulation and PLC activity and inhibited both NHE3 and NaKATPase activities. LE-PM436 and D5R siRNA blocked the fenoldopam-stimulated PLC pathway but not cAMP accumulation, while D1R siRNA blocked both fenoldopam-stimulated cAMP accumulation and PLC signaling. Either D1R or D5R siRNA, or LE-PM436 blocked the fenoldopam dependent inhibition of sodium transport. Further studies using the cAMP-selective D1R/D5R agonist SKF83822 and PLC-selective D1R/D5R agonist SKF83959 confirmed the cooperative influence of the two pathways on sodium transport. Thus, D1R and D5R interact in the inhibition of NHE3 and NaKATPase activity, the D1R primarily by cAMP, while the D1R/D5R heteromer modulates the D1R effect through a PLC pathway.
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Affiliation(s)
- John J Gildea
- The University of Virginia Health System, Department of Pathology, Charlottesville, Virginia, USA
| | - Ishan T Shah
- The University of Virginia Health System, Department of Pathology, Charlottesville, Virginia, USA
| | - Robert E Van Sciver
- The University of Virginia Health System, Department of Pathology, Charlottesville, Virginia, USA
| | - Jonathan A Israel
- The University of Virginia Health System, Department of Pathology, Charlottesville, Virginia, USA
| | - Christoph Enzensperger
- Institut für Pharmazie, Lehrstuhl für Pharmazeutische/Medizinische Chemie, Friedrich-Schiller-Universität Jena, Jena, Germany
| | - Helen E McGrath
- The University of Virginia Health System, Department of Pathology, Charlottesville, Virginia, USA
| | - Pedro A Jose
- University of Maryland School of Medicine, Departments of Medicine and Physiology, Baltimore, Maryland, USA
| | - Robin A Felder
- The University of Virginia Health System, Department of Pathology, Charlottesville, Virginia, USA
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82
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Zhang Z, Lin H, Cao C, Payne K, Pallone TL. Descending vasa recta endothelial cells and pericytes form mural syncytia. Am J Physiol Renal Physiol 2013; 306:F751-63. [PMID: 24381184 DOI: 10.1152/ajprenal.00470.2013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Using patch clamp, we induced depolarization of descending vasa recta (DVR) pericytes or endothelia and tested whether it was conducted to distant cells. Membrane potential was measured with the fluorescent voltage dye di-8-ANEPPS or with a second patch-clamp electrode. Depolarization of an endothelial cell induced responses in other endothelia within a millisecond and was slowed by gap junction blockade with heptanol. Endothelial response to pericyte depolarization was poor, implying high-resistance myo-endothelial coupling. In contrast, dual patch clamp of neighboring pericytes revealed syncytial coupling. At high sampling rate, the spread of depolarization between pericytes and endothelia occurred in 9 ± 2 or 12 ± 2 μs, respectively. Heptanol (2 mM) increased the overall input resistance of the pericyte layer to current flow and prevented transmission of depolarization between neighboring cells. The fluorescent tracer Lucifer yellow (LY), when introduced through ruptured patches, spread between neighboring endothelia in 1 to 7 s, depending on location of the flanking cell. LY diffused to endothelial cells on the ipsilateral but not contralateral side of the DVR wall and minimally between pericytes. We conclude that both DVR pericytes and endothelia are part of individual syncytia. The rate of conduction of membrane potential exceeds that for diffusion of hydrophilic molecules by orders of magnitude. Gap junction coupling of adjacent endothelial cells may be spatially oriented to favor longitudinal transmission along the DVR axis.
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Affiliation(s)
- Zhong Zhang
- Div. of Nephrology, N3W143, 22 S. Greene St., UMMS, Baltimore, MD 21201.
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83
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Grabias BM, Konstantopoulos K. The physical basis of renal fibrosis: effects of altered hydrodynamic forces on kidney homeostasis. Am J Physiol Renal Physiol 2013; 306:F473-85. [PMID: 24352503 DOI: 10.1152/ajprenal.00503.2013] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Healthy kidneys are continuously exposed to an array of physical forces as they filter the blood: shear stress along the inner lumen of the tubules, distension of the tubular walls in response to changing fluid pressures, and bending moments along both the cilia and microvilli of individual epithelial cells that comprise the tubules. Dysregulation of kidney homeostasis via underlying medical conditions such as hypertension, diabetes, or glomerulonephritis fundamentally elevates the magnitudes of each principle force in the kidney and leads to fibrotic scarring and eventual loss of organ function. The purpose of this review is to summarize the progress made characterizing the response of kidney cells to pathological levels of mechanical stimuli. In particular, we examine important, mechanically responsive signaling cascades and explore fundamental changes in renal cell homeostasis after cyclic strain or fluid shear stress exposure. Elucidating the effects of these disease-related mechanical imbalances on endogenous signaling events in kidney cells presents a unique opportunity to better understand the fibrotic process.
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Affiliation(s)
- Bryan M Grabias
- Dept. of Chemical and Biomolecular Engineering, The Johns Hopkins Univ., New Engineering Bldg. 114, 3400 N. Charles St., Baltimore, MD 21218.
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84
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Abstract
Morphogenesis is the remarkable process by which cells self-assemble into complex tissues and organs that exhibit specialized form and function during embryological development. Many of the genes and chemical cues that mediate tissue and organ formation have been identified; however, these signals alone are not sufficient to explain how tissues and organs are constructed that exhibit their unique material properties and three-dimensional forms. Here, we review work that has revealed the central role that physical forces and extracellular matrix mechanics play in the control of cell fate switching, pattern formation, and tissue development in the embryo and how these same mechanical signals contribute to tissue homeostasis and developmental control throughout adult life.
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Affiliation(s)
- Tadanori Mammoto
- Vascular Biology Program, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115;
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85
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Abstract
Serotonin (5-hydroxytryptamine, 5-HT) is a very simple molecule that plays key roles in complex communication mechanisms within the animal body. In the mammary glands, serotonin biosynthesis and secretion are induced in response to dilation of the alveolar spaces. Since its discovery several years ago, mammary 5-HT has been demonstrated to perform two homeostatic functions. First, serotonin regulates lactation and initiates the transition into the earliest phases of involution. Second, serotonin is a local signal that induces parathyroid hormone-related peptide (PTHrP), which allows the mammary gland to drive the mobilization of calcium from the skeleton. These processes use different receptor types, 5-HT7 and 5-HT2, respectively. In this review, we provide synthetic perspectives on the fundamental processes of lactation homeostasis and the adaptation of calcium homeostasis for lactation. We analyze the role of the intrinsic serotonin system in the physiological regulation of the mammary glands. We also consider the importance of the mammary serotonin system in pathologies and therapies associated with lactation and breast cancer.
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Affiliation(s)
- Nelson D Horseman
- Department of Molecular and Cellular Physiology, Systems Biology and Physiology Program, University of Cincinnati, Cincinnati, Ohio 45208;
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86
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Peyronnet R, Martins JR, Duprat F, Demolombe S, Arhatte M, Jodar M, Tauc M, Duranton C, Paulais M, Teulon J, Honoré E, Patel A. Piezo1-dependent stretch-activated channels are inhibited by Polycystin-2 in renal tubular epithelial cells. EMBO Rep 2013; 14:1143-8. [PMID: 24157948 DOI: 10.1038/embor.2013.170] [Citation(s) in RCA: 113] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Revised: 10/07/2013] [Accepted: 10/07/2013] [Indexed: 01/07/2023] Open
Abstract
Mechanical forces associated with fluid flow and/or circumferential stretch are sensed by renal epithelial cells and contribute to both adaptive or disease states. Non-selective stretch-activated ion channels (SACs), characterized by a lack of inactivation and a remarkably slow deactivation, are active at the basolateral side of renal proximal convoluted tubules. Knockdown of Piezo1 strongly reduces SAC activity in proximal convoluted tubule epithelial cells. Similarly, overexpression of Polycystin-2 (PC2) or, to a greater extent its pathogenic mutant PC2-740X, impairs native SACs. Moreover, PC2 inhibits exogenous Piezo1 SAC activity. PC2 coimmunoprecipitates with Piezo1 and deletion of its N-terminal domain prevents both this interaction and inhibition of SAC activity. These findings indicate that renal SACs depend on Piezo1, but are critically conditioned by PC2.
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Affiliation(s)
- Rémi Peyronnet
- Institut de Pharmacologie Moléculaire et Cellulaire, LabEx ICST, UMR 7275 CNRS, Université de Nice Sophia Antipolis, Valbonne, France
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87
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Alber M, Maini PK, Niebur G. Biomedical modeling: the role of transport and mechanics. Bull Math Biol 2013; 75:1233-7. [PMID: 23888390 DOI: 10.1007/s11538-013-9873-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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88
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Gonzalez J, Essig M, Klein J, Caubet C, Dissard R, Bascands JL, Schanstra JP, Buffin-Meyer B. [Renal urinary shear stress: a novel actor in nephropathies]. Med Sci (Paris) 2013; 29:279-85. [PMID: 23544382 DOI: 10.1051/medsci/2013293014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The role of fluid shear stress is well established in vascular pathophysiology. However, urinary shear stress now also appears as a key mechanism in the regulation of renal function. In addition, there is a growing body of evidence showing that modified urinary shear stress is involved in the development of nephropathies. Therefore we review here the state-of-the-art on the pathophysiological roles of urinary shear stress.
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89
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Tissue mechanics and fibrosis. Biochim Biophys Acta Mol Basis Dis 2013; 1832:884-90. [PMID: 23434892 DOI: 10.1016/j.bbadis.2013.02.007] [Citation(s) in RCA: 248] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Accepted: 02/10/2013] [Indexed: 12/17/2022]
Abstract
Mechanical forces are essential to the development and progression of fibrosis, and are likely to be as important as soluble factors. These forces regulate the phenotype and proliferation of myofibroblasts and other cells in damaged tissues, the activation of growth factors, the structure and mechanics of the matrix, and, potentially, tissue patterning. Better understanding of the variety and magnitude of forces, the characteristics of those forces in biological tissues, and their impact on fibrosis in multiple tissues is needed and may lead to identification of important new therapeutic targets. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.
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90
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Abstract
PURPOSE OF REVIEW This review summarizes recent literature highlighting the roles of chemical and mechanical sensory receptors in renal function. RECENT FINDINGS Both chemoreceptors and mechanoreceptors play important roles in renal physiology; here, we discuss specific examples of both chemoreceptors and mechanoreceptors in the kidney. SUMMARY In order to maintain homeostasis, the kidney uses sensory receptors to assess the composition and rate of flow of the forming urine. Understanding the roles of these receptors will help us to better understand how the kidney functions both in health and in disease.
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91
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Verma D, Ye N, Meng F, Sachs F, Rahimzadeh J, Hua SZ. Interplay between cytoskeletal stresses and cell adaptation under chronic flow. PLoS One 2012; 7:e44167. [PMID: 23028495 PMCID: PMC3446919 DOI: 10.1371/journal.pone.0044167] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Accepted: 07/30/2012] [Indexed: 01/16/2023] Open
Abstract
Using stress sensitive FRET sensors we have measured cytoskeletal stresses in α-actinin and the associated reorganization of the actin cytoskeleton in cells subjected to chronic shear stress. We show that long-term shear stress reduces the average actinin stress and this effect is reversible with removal of flow. The flow-induced changes in cytoskeletal stresses are found to be dynamic, involving a transient decrease in stress (phase-I), a short-term increase (3–6 min) (Phase-II), followed by a longer-term decrease that reaches a minimum in ∼20 min (Phase-III), before saturating. These changes are accompanied by reorganization of the actin cytoskeleton from parallel F-actin bundles to peripheral bundles. Blocking mechanosensitive ion channels (MSCs) with Gd3+ and GsMTx4 (a specific inhibitor) eliminated the changes in cytoskeletal stress and the corresponding actin reorganization, indicating that Ca2+ permeable MSCs participate in the signaling cascades. This study shows that shear stress induced cell adaptation is mediated via MSCs.
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Affiliation(s)
- Deepika Verma
- Department of Mechanical and Aerospace Engineering, SUNY-Buffalo, Buffalo, New York, United States of America
| | - Nannan Ye
- Department of Mechanical and Aerospace Engineering, SUNY-Buffalo, Buffalo, New York, United States of America
| | - Fanjie Meng
- Department of Physiology and Biophysics, SUNY-Buffalo, Buffalo, New York, United States of America
| | - Frederick Sachs
- Department of Physiology and Biophysics, SUNY-Buffalo, Buffalo, New York, United States of America
| | - Jason Rahimzadeh
- Department of Mechanical and Aerospace Engineering, SUNY-Buffalo, Buffalo, New York, United States of America
| | - Susan Z. Hua
- Department of Physiology and Biophysics, SUNY-Buffalo, Buffalo, New York, United States of America
- Department of Mechanical and Aerospace Engineering, SUNY-Buffalo, Buffalo, New York, United States of America
- * E-mail:
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92
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Meng F, Sachs F. Orientation-based FRET sensor for real-time imaging of cellular forces. J Cell Sci 2012; 125:743-50. [PMID: 22389408 DOI: 10.1242/jcs.093104] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Mechanical stress is an unmapped source of free energy in cells. Mapping the stress fields in a heterogeneous time-dependent environment like that found in cells requires probes that are specific for different proteins and respond to biologically relevant forces with minimal disturbance to the host system. To meet these goals, we have designed a genetically encoded stress sensor with minimal volume and high sensitivity and dynamic range. The new FRET-based sensor, called cpstFRET, is designed to be modulated by the angles between the donor and acceptor rather than the distance between them. Relative to other probes, it is physically smaller and exhibits a greater dynamic range and sensitivity and expresses well. For in vivo testing, we measured stress gradients in time and space in non-erythroid spectrin in several different cell types and found that spectrin is under constitutive stress in some cells but not in others. Stresses appear to be generated by both F-actin and tubulin. The probe revealed, for the first time, that spectrin undergoes time-dependent force modulation during cell migration. cpstFRET can be employed in vitro, in vivo and in situ, and when incorporated into biologically expressed extracellular polymers such as collagen, it can report multidimensional stress fields.
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Affiliation(s)
- Fanjie Meng
- Center for Single Molecule Biophysics, Department of Physiology and Biophysics, The State University of New York at Buffalo, 3435 Main Street, Buffalo, NY 14214, USA
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93
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Du Z, Wan L, Yan Q, Weinbaum S, Weinstein AM, Wang T. Regulation of glomerulotubular balance: II: impact of angiotensin II on flow-dependent transport. Am J Physiol Renal Physiol 2012; 303:F1507-16. [PMID: 22952281 DOI: 10.1152/ajprenal.00277.2012] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Underlying glomerulotubular balance (GTB) is the impact of axial flow to regulate Na(+) and HCO(3)(-) transport by modulating Na(+)-H(+) exchanger 3 (NHE3) and H-ATPase activity. It is not known whether the cascade of events following a change in flow relies on local angiotensin (ANG II) generation or receptor availability. Mouse tubules were microperfused in vitro at flows of 5 and 20 nl/min, and net fluid (J(v)) and HCO(3)(-) (J(HCO3)) absorption and cell height were measured. Na(+) (J(Na)) and Cl(-) (J(Cl)) absorption and changes in microvillous torque were estimated. Raising flow increased Na(+) and HCO(3)(-) reabsorption but did not change either Cl(-) transport or cell volume. Losartan reduced absolute Na(+) and HCO(3)(-) absorption at both low and high flows but did not affect fractional flow-stimulated transport. Compared with controls, in AT(1a) knockout (KO) mouse tubules, 53% of flow-stimulated Na(+) absorption was abolished, but flow-stimulated HCO(3)(-) absorption was retained at similar levels. The remaining flow-stimulated J(HCO3) was eliminated by the H-ATPase inhibitor bafilomycin. Inhibition of the AT(2) receptor by PD123319 increased both J(Na) and J(HCO3) but did not affect flow-mediated fractional changes. NHE3 expression at the protein level was reduced in AT(1a) KO mice kidneys. We conclude that 1) although the AT(1a) receptor is necessary for flow to impact NHE3, the effect on H(+)-ATPase is independent of AT(1a); 2) the small flow-mediated changes in cell volume suggest a coordinate flow effect on both luminal and basolateral transporters; and 3) there is no evidence of flow-dependent Cl(-) transport, and thus no evidence for convective paracellular Cl(-) transport in mouse tubules.
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Affiliation(s)
- Zhaopeng Du
- Dept. of Cellular and Molecular Physiology, Yale School of Medicine, New Haven, CT 06520-8026, USA
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94
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Pirodda A, Cicero AFG, Borghi C. Kidney disease and inner ear impairment: a simpler and closer pathogenic analogy? Intern Emerg Med 2012; 7 Suppl 2:S93-5. [PMID: 21968512 DOI: 10.1007/s11739-011-0703-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/09/2011] [Accepted: 09/17/2011] [Indexed: 10/17/2022]
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95
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Flores D, Liu Y, Liu W, Satlin LM, Rohatgi R. Flow-induced prostaglandin E2 release regulates Na and K transport in the collecting duct. Am J Physiol Renal Physiol 2012; 303:F632-8. [PMID: 22696602 DOI: 10.1152/ajprenal.00169.2012] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Fluid shear stress (FSS) is a critical regulator of cation transport in the collecting duct (CD). High-dietary sodium (Na) consumption increases urine flow, Na excretion, and prostaglandin E(2) (PGE(2)) excretion. We hypothesize that increases in FSS elicited by increasing tubular flow rate induce the release of PGE(2) from renal epithelial cells into the extracellular compartment and regulate ion transport. Media retrieved from CD cells exposed to physiologic levels of FSS reveal several fold higher concentration of PGE(2) compared with static controls. Treatment of CD cells with either cyclooxygenase-1 (COX-1) or COX-2 inhibitors during exposure to FSS limited the increase in PGE(2) concentration to an equal extent, suggesting COX-1 and COX-2 contribute equally to FSS-induced PGE(2) release. Cytosolic phospholipase A2 (cPLA2), the principal enzyme that generates the COX substrate arachidonic acid, is regulated by mitogen-activated protein-kinase-dependent phosphorylation and intracellular Ca(2+) concentration ([Ca(2+)](i)), both signaling processes, of which, are activated by FSS. Inhibition of the ERK and p38 pathways reduced PGE(2) release by 53.3 ± 8.4 and 32.6 ± 11.3%, respectively, while antagonizing the JNK pathway had no effect. In addition, chelation of [Ca(2+)](i) limited the FSS-mediated increase in PGE(2) concentration by 47.5 ± 7.5% of that observed in untreated sheared cells. Sheared cells expressed greater phospho-cPLA2 protein abundance than static cells; however, COX-2 protein expression was unaffected (P = 0.064) by FSS. In microperfused CDs, COX inhibition enhanced flow-stimulated Na reabsorption and abolished flow-stimulated potassium (K) secretion, but did not affect ion transport at a slow flow rate, implicating that high tubular flow activates autocrine/paracrine PGE(2) release and, in turn, regulates flow-stimulated cation transport. In conclusion, FSS activates cPLA2 to generate PGE(2) that regulates flow-mediated Na and K transport in the native CD. We speculate that dietary sodium intake modulates tubular flow rate to regulate paracrine PGE(2) release and cation transport in the CD.
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Affiliation(s)
- Daniel Flores
- The Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029, USA
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96
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Thompson WR, Rubin CT, Rubin J. Mechanical regulation of signaling pathways in bone. Gene 2012; 503:179-93. [PMID: 22575727 DOI: 10.1016/j.gene.2012.04.076] [Citation(s) in RCA: 268] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 03/20/2012] [Accepted: 04/22/2012] [Indexed: 12/21/2022]
Abstract
A wide range of cell types depend on mechanically induced signals to enable appropriate physiological responses. The skeleton is particularly dependent on mechanical information to guide the resident cell population towards adaptation, maintenance and repair. Research at the organ, tissue, cell and molecular levels has improved our understanding of how the skeleton can recognize the functional environment, and how these challenges are translated into cellular information that can site-specifically alter phenotype. This review first considers those cells within the skeleton that are responsive to mechanical signals, including osteoblasts, osteoclasts, osteocytes and osteoprogenitors. This is discussed in light of a range of experimental approaches that can vary parameters such as strain, fluid shear stress, and pressure. The identity of mechanoreceptor candidates is approached, with consideration of integrins, pericellular tethers, focal adhesions, ion channels, cadherins, connexins, and the plasma membrane including caveolar and non-caveolar lipid rafts and their influence on integral signaling protein interactions. Several mechanically regulated intracellular signaling cascades are detailed including activation of kinases (Akt, MAPK, FAK), β-catenin, GTPases, and calcium signaling events. While the interaction of bone cells with their mechanical environment is complex, an understanding of mechanical regulation of bone signaling is crucial to understanding bone physiology, the etiology of diseases such as osteoporosis, and to the development of interventions to improve bone strength.
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Affiliation(s)
- William R Thompson
- Department of Medicine, University of North Carolina, Chapel Hill, NC 27599, USA.
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97
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Du Z, Yan Q, Wan L, Weinbaum S, Weinstein AM, Wang T. Regulation of glomerulotubular balance. I. Impact of dopamine on flow-dependent transport. Am J Physiol Renal Physiol 2012; 303:F386-95. [PMID: 22552936 DOI: 10.1152/ajprenal.00531.2011] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
In response to volume expansion, locally generated dopamine decreases proximal tubule reabsorption by reducing both Na/H-exchanger 3 (NHE3) and Na-K-ATPase activity. We have previously demonstrated that mouse proximal tubules in vitro respond to changes in luminal flow with proportional changes in Na(+) and HCO(3)(-) reabsorption and have suggested that this observation underlies glomerulotubular balance. In the present work, we investigate the impact of dopamine on the sensitivity of reabsorptive fluxes to changes in luminal flow. Mouse proximal tubules were microperfused in vitro at low and high flow rates, and volume and HCO(3)(-) reabsorption (J(v) and J(HCO3)) were measured, while Na(+) and Cl(-) reabsorption (J(Na) and J(Cl)) were estimated. Raising luminal flow increased J(v), J(Na), and J(HCO3) but did not change J(Cl). Luminal dopamine did not change J(v), J(Na), and J(HCO3) at low flow rates but completely abolished the increments of Na(+) absorption by flow and partially inhibited the flow-stimulated HCO(3)(-) absorption. The remaining flow-stimulated HCO(3)(-) absorption was completely abolished by bafilomycin. The DA1 receptor blocker SCH23390 and the PKA inhibitor H89 blocked the effect of exogenous dopamine and produced a two to threefold increase in the sensitivity of proximal Na(+) reabsorption to luminal flow rate. Under the variety of perfusion conditions, changes in cell volume were small and did not always parallel changes in Na(+) transport. We conclude that 1) dopamine inhibits flow-stimulated NHE3 activity by activation of the DA1 receptor via a PKA-mediated mechanism; 2) dopamine has no effect on flow-stimulated H-ATPase activity; 3) there is no evidence of flow stimulation of Cl(-) reabsorption; and 4) the impact of dopamine is a coordinated modulation of both luminal and peritubular Na(+) transporters.
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Affiliation(s)
- Zhaopeng Du
- Department of Cellular and Molecular Physiology, Yale University, New Haven, CT 06520-8026, USA
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98
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Du J, Wong WY, Sun L, Huang Y, Yao X. Protein kinase G inhibits flow-induced Ca2+ entry into collecting duct cells. J Am Soc Nephrol 2012; 23:1172-80. [PMID: 22518003 DOI: 10.1681/asn.2011100972] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The renal cortical collecting duct (CCD) contributes to the maintenance of K(+) homeostasis by modulating renal K(+) secretion. Cytosolic Ca(2+) ([Ca(2+)](i)) mediates flow-induced K(+) secretion in the CCD, but the mechanisms regulating flow-induced Ca(2+) entry into renal epithelial cells are not well understood. Here, we found that atrial natriuretic peptide, nitric oxide, and cyclic guanosine monophosphate (cGMP) act through protein kinase G (PKG) to inhibit flow-induced increases in [Ca(2+)](i) in M1-CCD cells. Coimmunoprecipitation, double immunostaining, and functional studies identified heteromeric TRPV4-P2 channels as the mediators of flow-induced Ca(2+) entry into M1-CCD cells and HEK293 cells that were coexpressed with both TRPV4 and TRPP2. In these HEK293 cells, introducing point mutations at two putative PKG phosphorylation sites on TRPP2 abolished the ability of cGMP to inhibit flow-induced Ca(2+) entry. In addition, treating M1-CCD cells with fusion peptides that compete with the endogenous PKG phosphorylation sites on TRPP2 also abolished the cGMP-mediated inhibition of the flow-induced Ca(2+) entry. Taken together, these data suggest that heteromeric TRPV4-P2 channels mediate the flow-induced entry of Ca(2+) into collecting duct cells. Furthermore, substances such as atrial natriuretic peptide and nitric oxide, which increase cGMP, abrogate flow-induced Ca(2+) entry through PKG-mediated inhibition of these channels.
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Affiliation(s)
- Juan Du
- School of Biomedical Sciences, Chinese University of Hong Kong, China
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99
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Abstract
The central goal of this overview article is to summarize recent findings in renal epithelial transport,focusing chiefly on the connecting tubule (CNT) and the cortical collecting duct (CCD).Mammalian CCD and CNT are involved in fine-tuning of electrolyte and fluid balance through reabsorption and secretion. Specific transporters and channels mediate vectorial movements of water and solutes in these segments. Although only a small percent of the glomerular filtrate reaches the CNT and CCD, these segments are critical for water and electrolyte homeostasis since several hormones, for example, aldosterone and arginine vasopressin, exert their main effects in these nephron sites. Importantly, hormones regulate the function of the entire nephron and kidney by affecting channels and transporters in the CNT and CCD. Knowledge about the physiological and pathophysiological regulation of transport in the CNT and CCD and particular roles of specific channels/transporters has increased tremendously over the last two decades.Recent studies shed new light on several key questions concerning the regulation of renal transport.Precise distribution patterns of transport proteins in the CCD and CNT will be reviewed, and their physiological roles and mechanisms mediating ion transport in these segments will also be covered. Special emphasis will be given to pathophysiological conditions appearing as a result of abnormalities in renal transport in the CNT and CCD.
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Affiliation(s)
- Alexander Staruschenko
- Department of Physiology and Kidney Disease Center, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
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100
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Milner JS, Grol MW, Beaucage KL, Dixon SJ, Holdsworth DW. Finite-element modeling of viscoelastic cells during high-frequency cyclic strain. J Funct Biomater 2012; 3:209-24. [PMID: 24956525 PMCID: PMC4031015 DOI: 10.3390/jfb3010209] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2012] [Revised: 03/06/2012] [Accepted: 03/13/2012] [Indexed: 12/20/2022] Open
Abstract
Mechanotransduction refers to the mechanisms by which cells sense and respond to local loads and forces. The process of mechanotransduction plays an important role both in maintaining tissue viability and in remodeling to repair damage; moreover, it may be involved in the initiation and progression of diseases such as osteoarthritis and osteoporosis. An understanding of the mechanisms by which cells respond to surrounding tissue matrices or artificial biomaterials is crucial in regenerative medicine and in influencing cellular differentiation. Recent studies have shown that some cells may be most sensitive to low-amplitude, high-frequency (i.e., 1-100 Hz) mechanical stimulation. Advances in finite-element modeling have made it possible to simulate high-frequency mechanical loading of cells. We have developed a viscoelastic finite-element model of an osteoblastic cell (including cytoskeletal actin stress fibers), attached to an elastomeric membrane undergoing cyclic isotropic radial strain with a peak value of 1,000 µstrain. The results indicate that cells experience significant stress and strain amplification when undergoing high-frequency strain, with peak values of cytoplasmic strain five times higher at 45 Hz than at 1 Hz, and peak Von Mises stress in the nucleus increased by a factor of two. Focal stress and strain amplification in cells undergoing high-frequency mechanical stimulation may play an important role in mechanotransduction.
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Affiliation(s)
- Jaques S Milner
- Imaging Research Laboratory, Robarts Research Institute, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON N6A 5K8, Canada.
| | - Matthew W Grol
- Department of Anatomy and Cell Biology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON N6A 5C1, Canada.
| | - Kim L Beaucage
- Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON N6A 5C1, Canada.
| | - S Jeffrey Dixon
- Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON N6A 5C1, Canada.
| | - David W Holdsworth
- Imaging Research Laboratory, Robarts Research Institute, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON N6A 5K8, Canada.
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