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Walshe T.E.,Schepens Eye Research Institute | Dela Paz N.G.,Schepens Eye Research Institute | Dela Paz N.G.,La Jolla Bioengineering Institute | D'Amore P.A.,Schepens Eye Research Institute
Arteriosclerosis, Thrombosis, and Vascular Biology | Year: 2013

OBJECTIVE-: Vascular endothelial cells (ECs) are continuously exposed to blood flow that contributes to the maintenance of vessel structure and function; however, the effect of hemodynamic forces on transforming growth factor-β (TGF-β) signaling in the endothelium is poorly described. We examined the potential role of TGF-β signaling in mediating the protective effects of shear stress on ECs. APPROACH AND RESULTS-: Human umbilical vein ECs (HUVECs) exposed to shear stress were compared with cells grown under static conditions. Signaling through the TGF-β receptor ALK5 was inhibited with SB525334. Cells were examined for morphological changes and harvested for analysis by real-time polymerase chain reaction, Western blot analysis, apoptosis, proliferation, and immunocytochemistry. Shear stress resulted in ALK5-dependent alignment of HUVECs as well as attenuation of apoptosis and proliferation compared with static controls. Shear stress led to an ALK5-dependent increase in TGF-β3 and Krüppel-like factor 2, phosphorylation of endothelial NO synthase, and NO release. Addition of the NO donor S-nitroso-N- acetylpenicillamine rescued the cells from apoptosis attributable to ALK5 inhibition under shear stress. Knockdown of TGF-β3, but not TGF-β1, disrupted the HUVEC monolayer and prevented the induction of Krüppel-like factor 2 by shear. CONCLUSIONS-: Shear stress of HUVECs induces TGF-β3 signaling and subsequent activation of Krüppel-like factor 2 and NO, and represents a novel role for TGF-β3 in the maintenance of HUVEC homeostasis in a hemodynamic environment. © 2013 American Heart Association, Inc.

Kwon R.Y.,La Jolla Bioengineering Institute | Meays D.R.,La Jolla Bioengineering Institute | Tang W.J.,San Diego State University | Frangos J.A.,La Jolla Bioengineering Institute
Journal of Bone and Mineral Research | Year: 2010

Interstitial fluid flow (IFF) has been widely hypothesized to mediate skeletal adaptation to mechanical loading. Although a large body of in vitro evidence has demonstrated that fluid flow stimulates osteogenic and antiresorptive responses in bone cells, there is much less in vivo evidence that IFF mediates loading-induced skeletal adaptation. This is due in large part to the challenges associated with decoupling IFF from matrix strain. In this study we describe a novel microfluidic system for generating dynamic intramedullary pressure (ImP) and IFF within the femurs of alert mice. By quantifying fluorescence recovery after photobleaching (FRAP) within individual lacunae, we show that microfluidic generation of dynamic ImP significantly increases IFF within the lacunocanalicular system. In addition, we demonstrate that dynamic pressure loading of the intramedullary compartment for 3 minutes per day significantly eliminates losses in trabecular and cortical bone mineral density in hindlimb suspended mice, enhances trabecular and cortical structural integrity, and increases endosteal bone formation rate. Unlike previously developed modalities for enhancing IFF in vivo, this is the first model that allows direct and dynamic modulation of ImP and skeletal IFF within mice. Given the large number of genetic tools for manipulating the mouse genome, this model is expected to serve as a powerful investigative tool in elucidating the role of IFF in skeletal adaptation to mechanical loading and molecular mechanisms mediating this process. © 2010 American Society for Bone and Mineral Research.

Wang L.,U.S. National Institute of Standards and Technology | Bigos M.,Stanford University | Nolan J.P.,La Jolla Bioengineering Institute
Cytometry Part A | Year: 2012

Results from a standardization study cosponsored by the International Society for Advancement of Cytometry (ISAC) and the US National Institute of Standards and Technology (NIST) are reported. The study evaluated the variability of assigning intensity values to fluorophore standard beads by bead manufacturers and the variability of cross calibrating the standard beads to stained polymer beads (hard-dyed beads) using different flow cytometers. Hard dyed beads are generally not spectrally matched to the fluorophores used to stain cells, and spectral response varies among flow cytometers. Thus if hard dyed beads are used as fluorescence calibrators, one expects calibration for specific fluorophores (e.g., FITC or PE) to vary among different instruments. Using standard beads surface-stained with specific fluorophores (FITC, PE, APC, and Pacific Blue™), the study compared the measured intensity of fluorophore standard beads to that of hard dyed beads through cross calibration on 133 different flow cytometers. Using robust CV as a measure of variability, the variation of cross calibrated values was typically 20% or more for a particular hard dyed bead in a specific detection channel. The variation across different instrument models was often greater than the variation within a particular instrument model. As a separate part of the study, NIST and four bead manufacturers used a NIST supplied protocol and calibrated fluorophore solution standards to assign intensity values to the fluorophore beads. Values assigned to the reference beads by different groups varied by orders of magnitude in most cases, reflecting differences in instrumentation used to perform the calibration. The study concluded that the use of any spectrally unmatched hard dyed bead as a general fluorescence calibrator must be verified and characterized for every particular instrument model. Close interaction between bead manufacturers and NIST is recommended to have reliable and uniformly assigned fluorescence standard beads. © 2012 International Society for Advancement of Cytometry.

Melchior B.,La Jolla Bioengineering Institute | Frangos J.A.,La Jolla Bioengineering Institute
American Journal of Physiology - Cell Physiology | Year: 2012

Disturbed flow patterns, including reversal in flow direction, are key factors in the development of dysfunctional endothelial cells (ECs) and atherosclerotic lesions. An almost immediate response of ECs to fluid shear stress is the increase in cytosolic calcium concentration ([Ca 2+] i). Whether the source of [Ca 2+] i is extracellular, released from Ca 2+ intracellular stores, or both is still undefined, though it is likely dependent on the nature of forces involved. We have previously shown that a change in flow direction (retrograde flow) on a flow-adapted endothelial monolayer induces the remodeling of the cell-cell junction along with a dramatic [Ca 2+] i burst compared with cells exposed to unidirectional or orthograde flow. The heterotrimeric G protein-α q and 11 subunit (Gα q/11) is a likely candidate in effecting shear-induced increases in [Ca 2+] i since its expression is enriched at the junction and has been previously shown to be activated within seconds after onset of flow. In flowadapted human ECs, we have investigated to what extent the Gα q/11 pathway mediates calcium dynamics after reversal in flow direction. We observed that the elapsed time to peak [Ca 2+] i response to a 10 dyn/cm 2 retrograde shear stress was increased by 11 s in cells silenced with small interfering RNA directed against Gα q/11. A similar lag in [Ca 2+] i transient was observed after cells were treated with the phospholipase C (PLC)-βγ inhibitor, U-73122, or the phosphatidylinositol-specific PLC inhibitor, edelfosine, compared with controls. Lower levels of inositol 1,4,5-trisphosphate accumulation seconds after the onset of flow correlated with the increased lag in [Ca 2+] i responses observed with the different treatments. In addition, inhibition of the inositol 1,4,5-trisphosphate receptor entirely abrogated flow-induced [Ca 2+] i. Taken together, our results identify the Gα q/11-PLC pathway as the initial trigger for retrograde flowinduced endoplasmic reticulum calcium store release, thereby offering a novel approach to regulating EC dysfunctions in regions subjected to the reversal of blood flow. © 2012 the American Physiological Society.

Melchior B.,La Jolla Bioengineering Institute | Frangos J.A.,La Jolla Bioengineering Institute
American Journal of Physiology - Cell Physiology | Year: 2010

Atheroprone regions of the arterial circulation are characterized by time-varying, reversing, and oscillatory wall shear stress. Several in vivo and in vitro studies have demonstrated that flow reversal (retrograde flow) is atherogenic and proinflammatory. The molecular and structural basis for the sensitivity of the endothelium to flow direction, however, has yet to be determined. It has been hypothesized that the ability to sense flow direction is dependent on the direction of inclination of the interendothelial junction. Immunostaining of the mouse aorta revealed an inclination of the cell-cell junction by 13° in direction of flow in the descending aorta where flow is unidirectional. In contrast, polygonal cells of the inner curvature where flow is disturbed did not have any preferential inclination. Using a membrane specific dye, the angle of inclination of the junction was dynamically monitored using live cell confocal microscopy in confluent human endothelial cell monolayers. Upon application of shear the junctions began inclining within minutes to a final angle of 10° in direction of flow. Retrograde flow led to a reversal of junctional inclination. Flow-induced junctional inclination was shown to be independent of the cytoskeleton or glycocalyx. Additionally, within seconds, retrograde flow led to significantly higher intracellular calcium responses than orthograde flow. Together, these results show for the first time that the endothelial intercellular junction inclination is dynamically responsive to flow direction and confers the ability to endothelial cells to rapidly sense and adapt to flow direction. Copyright © 2010 the American Physiological Society.

Reddy A.S.,La Jolla Bioengineering Institute | Warshaviak D.T.,La Jolla Bioengineering Institute | Chachisvilis M.,La Jolla Bioengineering Institute
Biochimica et Biophysica Acta - Biomembranes | Year: 2012

Molecular dynamics simulations of a dioleoylphosphocholine (DOPC) lipid bilayer were performed to explore its mechanosensitivity. Variations in the bilayer properties, such as area per lipid, volume, thickness, hydration depth (HD), hydration thickness (HT), lateral diffusion coefficient, and changes in lipid structural order were computed in the membrane tension range 0 to 15 dyn/cm. We determined that an increase in membrane tension results in a decrease in the bilayer thickness and HD of ~ 5% and ~ 5.7% respectively, whereas area per lipid, volume, and HT/HD increased by 6.8%, 2.4%, and 5% respectively. The changes in lipid conformation and orientation were characterized using orientational (S2) and deuterium (SCD) order parameters. Upon increase of membrane tension both order parameters indicated an increase in lipid disorder by 10-20%, mostly in the tail end region of the hydrophobic chains. The effect of membrane tension on lipid lateral diffusion in the DOPC bilayer was analyzed on three different time scales corresponding to inertial motion, anomalous diffusion and normal diffusion. The results showed that lateral diffusion of lipid molecules is anomalous in nature due to the non-exponential distribution of waiting times. The anomalous and normal diffusion coefficients increased by 20% and 52% when the membrane tension changed from 0 to 15 dyn/cm, respectively. In conclusion, our studies showed that membrane tension causes relatively significant changes in the area per lipid, volume, polarity, membrane thickness, and fluidity of the membrane suggesting multiple mechanisms by which mechanical perturbation of the membrane could trigger mechanosensitive response in cells. © 2012 Elsevier B.V. All rights reserved.

Nolan J.P.,La Jolla Bioengineering Institute | Stoner S.A.,La Jolla Bioengineering Institute
Cytometry Part A | Year: 2013

The analysis of individual nanoparticles by flow cytometry involves the measurement of dim signals that are near the detection limits of the instrument. Discriminating the signal from particles of interest from that of background particles in buffers and from optical and electronic noise can be challenging, and requires careful consideration of the measurement approach, control experiments, and scrutiny of the resulting data. In applying this scrutiny, we have come to recognize an artifact that results from the inappropriate selection of the trigger channel threshold that might not be obvious to the casual user. When measuring dim signals close to the noise or background levels, it is intuitive and common for the operator to adjust the trigger threshold to minimize the "false triggers" acquired by the system, and then to run the unknown sample, interpreting the events detected above the background as measurements of individual particles. We show here that when this approach is used to measure particles whose signals fall below the trigger threshold, only coincident events are detected, producing erroneous measurements of both particle number and brightness. We suggest that in many cases, the analysis of dim nanoparticles is best achieved using a fluorescence channel for the trigger. © 2013 International Society for Advancement of Cytometry.

Melchior B.,La Jolla Bioengineering Institute | Frangos J.A.,La Jolla Bioengineering Institute
Journal of Cellular Biochemistry | Year: 2014

Endothelial cells undergo a rapid cell-cell junction inclination following exposure to atheroprotective unidirectional flow. In contrast, atherosclerotic lesions correlate with a heterogeneous distribution of the junctional wall inclination in cells exposed to time-varying, reversing, and oscillatory flow as well as to low mean shear stress. However, the underlying biochemical events by which endothelial cells distinctively respond to unidirectional versus flow reversal remain unclear. Here, we show that the subcellular distribution of flow-induced Akt-1 phosphorylation in endothelial cells lining the mouse aorta varies depending on local hemodynamics. Activated Akt-1 accumulated in perinuclear areas of cells in regions predisposed to disturbed flow but were localized at the cell-cell junction in regions of high unidirectional laminar shear stress. In flow-adapted human endothelial cells, reversal in flow direction was associated within minutes with a subcellular concentration of phosphorylated Akt-1 at the upstream edge of cells. Interestingly, oscillatory flow (with a zero mean shear stress) failed to activate Akt-1, whereas a unidirectional pulsatile flow of similar amplitude induced an increase in Akt-1 phosphorylation. Finally, silencing of the G protein αq/11 subunit abrogated both flow-induced Akt-1 and GSK-3β activation. Together, these results characterize the existence of a Gαq/11-mediated Akt-1 signaling pathway that is dynamically responsive to flow direction, thereby offering a novel approach to regulating EC dysfunctions in regions subjected to flow reversal. © 2013 Wiley Periodicals, Inc. © 2013 Wiley Periodicals, Inc.

Warshaviak D.T.,La Jolla Bioengineering Institute | Muellner M.J.,La Jolla Bioengineering Institute | Chachisvilis M.,La Jolla Bioengineering Institute
Biochimica et Biophysica Acta - Biomembranes | Year: 2011

The dipole potential of lipid bilayer membrane controls the difference in permeability of the membrane to oppositely charged ions. We have combined molecular dynamics (MD) simulations and experimental studies to determine changes in electric field and electrostatic potential of 1,2-dioleoyl-sn- glycero-3-phosphocholine (DOPC) lipid bilayer in response to applied membrane tension. MD simulations based on CHARMM36 force field showed that electrostatic potential of DOPC bilayer decreases by ~ 45 mV in the physiologically relevant range of membrane tension values (0 to 15 dyn/cm). The electrostatic field exhibits a peak (~ 0.8 × 109 V/m) near the water/lipid interface which shifts by 0.9 Å towards the bilayer center at 15 dyn/cm. Maximum membrane tension of 15 dyn/cm caused 6.4% increase in area per lipid, 4.7% decrease in bilayer thickness and 1.4% increase in the volume of the bilayer. Dipole-potential sensitive fluorescent probes were used to detect membrane tension induced changes in DOPC vesicles exposed to osmotic stress. Experiments confirmed that dipole potential of DOPC bilayer decreases at higher membrane tensions. These results are suggestive of a potentially new mechanosensing mechanism by which mechanically induced structural changes in the lipid bilayer membrane could modulate the function of membrane proteins by altering electrostatic interactions and energetics of protein conformational states. © 2011 Elsevier B.V. All rights reserved.

Yeshiva University and La Jolla Bioengineering Institute | Date: 2013-05-01

Nanoparticles are provided that comprise S-nitrosothiol (SNO) groups covalently bonded to the nanoparticles and/or S-nitrosothiol containing molecules encapsulated within the nanoparticles, as well as methods of making and using the nanoparticles. The invention also provides methods of preparing nanoparticles comprising Snitrosothiol (SNO) groups covalently bonded to the nanoparticles, where the methods comprise a) providing a buffer solution comprising chitosan, polyethylene glycol, nitrite, glucose, and hydrolyzed 3-mercaptopropyltrimethoxysilane (MPTS); b) adding hydrolyzed tetramethoxysilane (TMOS) to the buffer solution to produce a sol-gel; and c) lyophilizing and ball milling the sol-gel to produce nanoparticles of a desired size.

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