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1.
Can J Ophthalmol ; 2024 May 27.
Article in English | MEDLINE | ID: mdl-38815959

ABSTRACT

OBJECTIVE: To compare clinical outcomes of combined pars plana vitrectomy (PPV) and secondary scleral fixation of an intraocular lens (IOL) using Gore-Tex suture versus flanged intrascleral haptic fixation (FIHF) using double needles. DESIGN: Single-centre retrospective cohort series. PARTICIPANTS: Eyes undergoing PPV with simultaneous scleral fixation of an IOL. METHOD: Eyes that underwent fixation of a Bausch & Lomb Akreos AO60 or enVista MX60E IOL using Gore-Tex suture or a Tecnis ZA9003 or Zeiss CT LUCIA 602 IOL using FIHF were included. The primary outcome was change from baseline visual acuity to postoperative month 3. Secondary outcomes included deviation from refractive target aim and rates of postoperative complications. RESULTS: Seventy-nine eyes of 72 patients were included. Mean (±SD) follow-up was 16 ± 10.5 months (range, 4.5-45.2 months). Fifty-three eyes (67.1%) underwent Gore-Tex suture fixation, and 26 eyes (32.9%) underwent FIHF. Across all eyes, mean visual acuity improved from 1.30 ± 0.74 logMAR (20/399 Snellen equivalent) preoperatively to 0.36 ± 0.36 logMAR (20/45 Snellen equivalent) at 3 months (p < 0.001). No difference in visual acuity at month 3 was noted between the 2 techniques (p = 0.34). Mean deviation from refractive target aim was not significantly different between the Gore-Tex and FIHF groups (+0.14 ± 1.33 D vs -0.16 ± 0.88 D; p = 0.45). Reoperation rates were similar between groups (2 of 53 eyes in the Gore-Tex group vs 3 of 26 eyes in the FIHF group; p = 0.32). CONCLUSION: Combined PPV and scleral fixation of IOLs with Gore-Tex suture and FIHF resulted in similar improvements in visual acuity. No significant differences in refractive outcome and postoperative complication profiles were noted.

2.
bioRxiv ; 2024 Jan 10.
Article in English | MEDLINE | ID: mdl-38260455

ABSTRACT

Epigenetic control of cellular transcription and phenotype is influenced by changes in the cellular microenvironment, yet how mechanical cues from these microenvironments precisely influence epigenetic state to regulate transcription remains largely unmapped. Here, we combine genome-wide epigenome profiling, epigenome editing, and phenotypic and single-cell RNA-seq CRISPR screening to identify a new class of genomic enhancers that responds to the mechanical microenvironment. These 'mechanoenhancers' could be active on either soft or stiff extracellular matrix contexts, and regulated transcription to influence critical cell functions including apoptosis, mechanotransduction, proliferation, and migration. Epigenetic editing of mechanoenhancers on rigid materials tuned gene expression to levels observed on softer materials, thereby reprogramming the cellular response to the mechanical microenvironment. These editing approaches may enable the precise alteration of mechanically-driven disease states.

3.
bioRxiv ; 2024 Jan 11.
Article in English | MEDLINE | ID: mdl-38260589

ABSTRACT

The ability of cells to sense and respond to mechanical forces is critical in many physiological and pathological processes. However, the mechanisms by which forces affect protein function inside cells remain unclear. Motivated by in vitro demonstrations of fluorescent proteins (FPs) undergoing reversible mechanical switching of fluorescence, we investigated if force-sensitive changes in FP function could be visualized in cells. Guided by a computational model of FP mechanical switching, we develop a formalism for its detection in Förster resonance energy transfer (FRET)-based biosensors and demonstrate its occurrence in cellulo in a synthetic actin-crosslinker and the mechanical linker protein vinculin. We find that in cellulo mechanical switching is reversible and altered by manipulation of cellular force generation as well as force-sensitive bond dynamics of the biosensor. Together, this work describes a new framework for assessing FP mechanical stability and provides a means of probing force-sensitive protein function inside cells. MOTIVATION: The ability of cells to sense mechanical forces is critical in developmental, physiological, and pathological processes. Cells sense mechanical cues via force-induced alterations in protein structure and function, but elucidation of the molecular mechanisms is hindered by the lack of approaches to directly probe the effect of forces on protein structure and function inside cells. Motivated by in vitro observations of reversible fluorescent protein mechanical switching, we developed an approach for detecting fluorescent protein mechanical switching in cellulo . This enables the visualization of force-sensitive protein function inside living cells.

4.
Proc Natl Acad Sci U S A ; 120(50): e2316456120, 2023 Dec 12.
Article in English | MEDLINE | ID: mdl-38055737

ABSTRACT

The ability of cells to move in a mechanically coupled, coordinated manner, referred to as collective cell migration, is central to many developmental, physiological, and pathophysiological processes. Limited understanding of how mechanical forces and biochemical regulation interact to affect coupling has been a major obstacle to unravelling the underlying mechanisms. Focusing on the linker protein vinculin, we use a suite of Förster resonance energy transfer-based biosensors to probe its mechanical functions and biochemical regulation, revealing a switch that toggles vinculin between loadable and unloadable states. Perturbation of the switch causes covarying changes in cell speed and coordination, suggesting alteration of the friction within the system. Molecular scale modelling reveals that increasing levels of loadable vinculin increases friction, due to engagement of self-stabilizing catch bonds. Together, this work reveals a regulatory switch for controlling cell coupling and describes a paradigm for relating biochemical regulation, altered mechanical properties, and changes in cell behaviors.


Subject(s)
Fluorescence Resonance Energy Transfer , Mechanical Phenomena , Vinculin/metabolism , Cell Movement/physiology , Cell Adhesion/physiology
5.
Nat Commun ; 14(1): 8300, 2023 Dec 14.
Article in English | MEDLINE | ID: mdl-38097542

ABSTRACT

The ability of cells and tissues to respond differentially to mechanical forces applied in distinct directions is mediated by the ability of load-bearing proteins to preferentially maintain physical linkages in certain directions. However, the molecular basis and biological consequences of directional force-sensitive binding remain unclear. Vinculin (Vcn) is a load-bearing linker protein that exhibits directional catch bonding due to interactions between the Vcn tail domain (Vt) and filamentous (F)-actin. We developed a computational approach to predict Vcn residues involved in directional catch bonding and produced a set of associated Vcn variants with unaltered Vt structure, actin binding, or phospholipid interactions. Incorporation of the variants did not affect Vcn activation but reduced Vcn loading and altered exchange dynamics, consistent with the loss of directional catch bonding. Expression of Vcn variants perturbed the coordination of subcellular structures and cell migration, establishing key cellular functions for Vcn directional catch bonding.


Subject(s)
Actin Cytoskeleton , Actins , Actins/metabolism , Vinculin/genetics , Actin Cytoskeleton/metabolism , Cell Movement , Protein Binding
6.
J Acad Ophthalmol (2017) ; 15(2): e197-e203, 2023 Jul.
Article in English | MEDLINE | ID: mdl-37706000

ABSTRACT

Purpose Despite easing restrictions on social distancing and travel since the beginning of coronavirus disease 2019 pandemic, virtual interviews remain a widely used format for ophthalmology fellowship interviews. This study aims to evaluate the relative benefits and drawbacks of in-person versus virtual interviews during a cycle where both formats were prevalent. Methods A prospective cross-sectional study surveyed all fellowship applicants ( N = 311) who applied to Wills Eye Hospital and Bascom Palmer Eye Institute during the 2022 to 2023 application cycle. Results A total of 59 (19%) applicants responded to the survey, with the majority being male (53.0%) and between the ages of 20 and 35 (91.3%). There was no statistically significant difference between the number of virtual and in-person interviews attended or the total number of interviews attended. The highest ranked limitations of the virtual interview process were limited exposure to details of the program structure, limited opportunity to exhibit applicants' strengths to the program, and limited exposure to the fellows. The highest ranked strengths were less pressure during interviews, greater scheduling flexibility, and ability to interview at more fellowship programs. The highest ranked limitations of the in-person interview process were more pressure during interviews, inability to interview at all desired fellowship programs, and decreased scheduling flexibility. The highest ranked strengths based on median rankings were greater exposure to details of the program structure, greater ability to exhibit an applicant's strengths to the program, and greater exposure to the geographic location/city. Conclusion While both in-person and virtual interviews have their own benefits and limitations, virtual interviews appear to be more cost-effective and time-efficient while in-person interviews provide better opportunities to assess program fit and culture. A hybrid format that combines the ideal aspects of both formats may be an optimal solution.

7.
Dev Cell ; 58(6): 522-534.e7, 2023 03 27.
Article in English | MEDLINE | ID: mdl-36924770

ABSTRACT

Mechanosensitive processes often rely on adhesion structures to strengthen, or mature, in response to applied loads. However, a limited understanding of how the molecular tensions that are experienced by a particular protein affect the recruitment of other proteins represents a major obstacle in the way of deciphering molecular mechanisms that underlie mechanosensitive processes. Here, we describe an imaging-based technique, termed fluorescence-tension co-localization (FTC), for studying molecular-tension-sensitive protein recruitment inside cells. Guided by discrete time Markov chain simulations of protein recruitment, we integrate immunofluorescence labeling, molecular tension sensors, and machine learning to determine the sensitivity, specificity, and context dependence of molecular-tension-sensitive protein recruitment. The application of FTC to the mechanical linker protein vinculin in mouse embryonic fibroblasts reveals constitutive and context-specific molecular-tension-sensitive protein recruitment that varies with adhesion maturation. FTC overcomes limitations associated with the alteration of numerous proteins during the manipulation of cell contractility, providing molecularly specific insights into tension-sensitive protein recruitment.


Subject(s)
Fibroblasts , Focal Adhesions , Animals , Mice , Focal Adhesions/metabolism , Fibroblasts/metabolism , Vinculin/metabolism , Cell Adhesion/physiology
8.
bioRxiv ; 2023 Jan 14.
Article in English | MEDLINE | ID: mdl-36711698

ABSTRACT

Collective cell migration (CCM) plays important roles in development, physiological, and pathological processes. A key feature of CCM is the dynamic mechanical coupling between cells, which enables both long-range coordination and local rearrangements. This coupling requires the ability of cell adhesions to adapt to forces. Recent efforts have identified key proteins and implicated cellular-scale mechanical properties, but how key proteins give rise to these larger-scale mechanical processes is unclear. Using force-sensitive biosensors, cell migration assays, and molecular clutch models, we sought a molecular understanding of adhesion strengthening that could bridge this gap. We found that the mechanical linker protein vinculin bears substantial loads at AJs, FAs, and in the cytoplasm during epithelial sheet migration, and we identified a switch-like residue on vinculin that regulates its conformation and loading at the AJs during CCM. In vinculin KO-rescue, this switch jointly controlled the speed and coupling length-scale of CCM, which suggested changes in adhesion-based friction. To test this, we developed molecularly detailed friction clutch models of the FA and AJ. They show that open, loaded vinculin increases friction in adhesive structures, with larger affects observed in AJs. Thus, this work elucidates how load-bearing linker proteins can be regulated to alter mechanical properties of cells and enable rapid tuning of mechanical coupling in CCM.

9.
Res Sq ; 2023 Jan 12.
Article in English | MEDLINE | ID: mdl-36711743

ABSTRACT

The ability of cells and tissues to differentially resist or adapt to mechanical forces applied in distinct directions is mediated by the ability of load-bearing proteins to preferentially maintain physical linkages in certain directions. However, the molecular basis and biological consequences of directional force-sensitive binding are unclear. Vinculin (Vcn) is a load-bearing linker protein that exhibits directional catch bonding due to interactions between the Vcn tail domain (Vt) and filamentous (F)-actin. We developed a computational approach to predict Vcn residues involved in directional catch bonding and produced a set of associated Vcn variants with unaltered Vt structure, actin binding, or phospholipid interactions. Incorporation of these variants into Vcn biosensors did not perturb Vcn conformation, but reduced Vcn loading consistent with loss of directional catch bonding. Expression of Vcn variants perturbed the coalignment of FAs and F-actin and directed cell migration, establishing key cellular functions for Vcn directional catch bonding.

10.
Front Bioeng Biotechnol ; 10: 837619, 2022.
Article in English | MEDLINE | ID: mdl-35299636

ABSTRACT

Meniscus injuries are highly prevalent, and both meniscus injury and subsequent surgery are linked to the development of post-traumatic osteoarthritis (PTOA). Although the pathogenesis of PTOA remains poorly understood, the inflammatory cytokine IL-1 is elevated in synovial fluid following acute knee injuries and causes degradation of meniscus tissue and inhibits meniscus repair. Dynamic mechanical compression of meniscus tissue improves integrative meniscus repair in the presence of IL-1 and dynamic tensile strain modulates the response of meniscus cells to IL-1. Despite the promising observed effects of physiologic mechanical loading on suppressing inflammatory responses of meniscus cells, there is a lack of knowledge on the global effects of loading on meniscus transcriptomic profiles. In this study, we compared two established models of physiologic mechanical stimulation, dynamic compression of tissue explants and cyclic tensile stretch of isolated meniscus cells, to identify conserved responses to mechanical loading. RNA sequencing was performed on loaded and unloaded meniscus tissue or isolated cells from inner and outer zones, with and without IL-1. Overall, results from both models showed significant modulation of inflammation-related pathways with mechanical stimulation. Anti-inflammatory effects of loading were well-conserved between the tissue compression and cell stretch models for inner zone; however, the cell stretch model resulted in a larger number of differentially regulated genes. Our findings on the global transcriptomic profiles of two models of mechanical stimulation lay the groundwork for future mechanistic studies of meniscus mechanotransduction, which may lead to the discovery of novel therapeutic targets for the treatment of meniscus injuries.

12.
Theranostics ; 11(12): 6090-6104, 2021.
Article in English | MEDLINE | ID: mdl-33897901

ABSTRACT

Therapeutic ultrasound or shockwave has shown its great potential to stimulate neural and muscle tissue, where cavitation microbubble induced Ca2+ signaling is believed to play an important role. However, the pertinent mechanisms are unknown, especially at the single-cell level. Particularly, it is still a major challenge to get a comprehensive understanding of the effect of potential mechanosensitive molecular players on the cellular responses, including mechanosensitive ion channels, purinergic signaling and integrin ligation by extracellular matrix. Methods: Here, laser-induced cavitation microbubble was used to stimulate individual HEK293T cells either genetically knocked out or expressing Piezo1 ion channels with different normalized bubble-cell distance. Ca2+ signaling and potential membrane poration were evaluated with a real-time fluorescence imaging system. Integrin-binding microbeads were attached to the apical surface of the cells at mild cavitation conditions, where the effect of Piezo1, P2X receptors and integrin ligation on single cell intracellular Ca2+ signaling was assessed. Results: Ca2+ responses were rare at normalized cell-bubble distances that avoided membrane poration, even with overexpression of Piezo1, but could be increased in frequency to 42% of cells by attaching integrin-binding beads. We identified key molecular players in the bead-enhanced Ca2+ response: increased integrin ligation by substrate ECM triggered ATP release and activation of P2X-but not Piezo1-ion channels. The resultant Ca2+ influx caused dynamic changes in cell spread area. Conclusion: This approach to safely eliciting a Ca2+ response with cavitation microbubbles and the uncovered mechanism by which increased integrin-ligation mediates ATP release and Ca2+ signaling will inform new strategies to stimulate tissues with ultrasound and shockwaves.


Subject(s)
Calcium Signaling/physiology , Calcium/metabolism , Integrins/metabolism , Adenosine Triphosphate/metabolism , Cell Line , Extracellular Matrix/metabolism , HEK293 Cells , Humans , Ion Channels/metabolism , Microbubbles
13.
J Acad Ophthalmol (2017) ; 13(2): e102-e107, 2021 Jul.
Article in English | MEDLINE | ID: mdl-37388849

ABSTRACT

Objective This study aimed to evaluate the experiences and preferences of ophthalmology fellowship applicants utilizing a virtual interview format. Design Present study is a cross-sectional study. Subjects All fellowship applicants to Wills Eye Hospital during 2020 to 2021 application cycle were included. Methods A nonvalidated, online survey was conducted, and surveys were distributed at the conclusion of the interview process after rank list submission. Main Outcome Measures Applicant demographics, application submissions, interview experiences, financial considerations, and suggestions for improvement of the virtual interview process were the primary outcomes of this cross-sectional study. Results Survey responses were received from 68 fellowship applicants (34% response rate). Thirty (44%) applicants preferred in-person interviews, 25 (36%) preferred virtual interviews, and 13 (19%) would like to prefer the option to choose either. Fifty-five of 68 (80%) applicants attended the same range of interviews for which they received interview invitations. Reduced costs were reported as the highest ranked strength of virtual interviews in 44 (65%) applicants, with a majority of respondents (68%) spending less than U.S. $250 throughout the entire process. The highest ranked limitation for virtual interviews was limited exposure to the culture/environment of the program in 20 (29%) respondents. On a scale of 0 to 100, the mean (standard deviation [SD]) satisfaction level with the fellowship application process was 74.6 (18.3) and mean (SD) perceived effectiveness levels of virtual interviews was 67.4 (20.4). Conclusion Respondents were generally satisfied with virtual interviews and noted reduced costs and increased ability to attend more fellowship interviews as the strengths of the virtual interview format. Limited exposure to the culture/environment of the program was cited as the most important limitation.

14.
Cytometry A ; 99(4): 407-416, 2021 04.
Article in English | MEDLINE | ID: mdl-32700451

ABSTRACT

FÓ§rster (or fluorescence) resonance energy transfer (FRET) is a quantifiable energy transfer in which a donor fluorophore nonradiatively transfers its excitation energy to an acceptor fluorophore. A change in FRET efficiency indicates a change of proximity and environment of these fluorophores, which enables the study of intermolecular interactions. Measurement of FRET efficiency using the sensitized emission method requires a donor-acceptor calibrated system. One of these calibration factors named the G factor, which depends on instrument parameters related to the donor and acceptor measurement channels and on the fluorophores quantum efficiencies, can be determined in several different ways and allows for conversion of the raw donor and acceptor emission signals to FRET efficiency. However, the calculated value of the G factor from experimental data can fluctuate significantly depending on the chosen experimental method and the size of the sample. In this technical note, we extend the results of Gates et al. (Cytometry Part A 95A (2018) 201-213) by refining the calibration method used for calibration of FRET from image pixel data. Instead of using the pixel histograms of two constructs with high and low FRET efficiency to determine the G factor, we use pixel histogram data from one construct of known efficiency. We validate this method by determining the G factor with the same constructs developed and used by Gates et al. and comparing the results from the two approaches. While the two approaches are equivalent theoretically, we demonstrate that the use of a single construct with known efficiency provides a more precise experimental measurement of the G factor that can be attained by collecting a smaller number of images. © 2020 International Society for Advancement of Cytometry.


Subject(s)
Fluorescence Resonance Energy Transfer , Fluorescent Dyes , Calibration
15.
Dev Cell ; 54(1): 60-74.e7, 2020 07 06.
Article in English | MEDLINE | ID: mdl-32585132

ABSTRACT

Basement membranes (BMs) are supramolecular matrices built on laminin and type IV collagen networks that provide structural and signaling support to tissues. BM complexity, however, has hindered an understanding of its formation, dynamics, and regulation. Using genome editing, we tagged 29 BM matrix components and receptors in C. elegans with mNeonGreen. Here, we report a common template that initiates BM formation, which rapidly diversifies during tissue differentiation. Through photobleaching studies, we show that BMs are not static-surprisingly, many matrix proteins move within the laminin and collagen scaffoldings. Finally, quantitative imaging, conditional knockdown, and optical highlighting indicate that papilin, a poorly studied glycoprotein, is the most abundant component in the gonadal BM, where it facilitates type IV collagen removal during BM expansion and tissue growth. Together, this work introduces methods for holistic investigation of BM regulation and reveals that BMs are highly dynamic and capable of rapid change to support tissues.


Subject(s)
Basement Membrane/metabolism , Extracellular Matrix/metabolism , Animals , Caenorhabditis elegans , Caenorhabditis elegans Proteins/genetics , Caenorhabditis elegans Proteins/metabolism , Collagen/genetics , Collagen/metabolism , Laminin/genetics , Laminin/metabolism , Motion
16.
J Biomed Opt ; 24(12): 1-11, 2019 12.
Article in English | MEDLINE | ID: mdl-31884745

ABSTRACT

We demonstrate the possibility of measuring FRET efficiency with a low-cost frequency-domain fluorescence lifetime imaging microscope (FD-FLIM). The system utilizes single-frequency-modulated excitation, which enables the use of cost-effective laser sources and electronics, simplification of data acquisition and analysis, and a dual-channel detection capability. Following calibration with coumarin 6, we measured the apparent donor lifetime in mTFP1-mVenus FRET standards expressed in living cells. We evaluated the system's sensitivity by differentiating the short and long lifetimes of mTFP1 corresponding to the known standards' high and low FRET efficiency, respectively. Furthermore, we show that the lifetime of the vinculin tension sensor, VinTS, at focal adhesions (2.30 ± 0.16 ns) is significantly (p < 10 - 6) longer than the lifetime of the unloaded TSMod probe (2.02 ± 0.16 ns). The pixel dwell time was 6.8 µs for samples expressing the FRET standards, with signal typically an order of magnitude higher than VinTS. The apparent FRET efficiency (EFRETapp) of the standards, calculated from the measured apparent lifetime, was linearly related to their known FRET efficiency by a factor of 0.92 to 0.99 (R2 = 0.98). This relationship serves as a calibration curve to convert apparent FRET to true FRET and circumvent the need to measure multiexponential lifetime decays. This approach yielded a FRET efficiency of 18% to 19.5%, for VinTS, in agreement with published values. Taken together, our results demonstrate a cost-effective, fast, and sensitive FD-FLIM approach with the potential to facilitate applications of FLIM in mechanobiology and FRET-based biosensing.


Subject(s)
Fluorescence Resonance Energy Transfer/methods , Microscopy, Fluorescence/methods , Molecular Probes/chemistry , Animals , Cell Line , Equipment Design , Fluorescence Resonance Energy Transfer/instrumentation , Focal Adhesions/physiology , Image Processing, Computer-Assisted , Mice , Microscopy, Fluorescence/instrumentation , Signal Processing, Computer-Assisted , Vinculin/chemistry
17.
Biophys J ; 117(9): 1692-1701, 2019 11 05.
Article in English | MEDLINE | ID: mdl-31623884

ABSTRACT

During metastasis, cancer cells navigate through a spatially heterogeneous extracellular matrix (ECM). Physical properties of ECM, including the degree of confinement, influence cell migration behavior. Here, utilizing in vitro three-dimensional collagen microtracks, we demonstrate that cell-ECM interactions, specifically the degree of spatial confinement, regulate migratory behavior. We found that cells migrate faster when they are fully confined, contacting all four walls (top, bottom, and two sides) of a collagen microtrack, compared with cells that are partially confined, contacting less than four walls. When fully confined, cells exhibit fewer but larger vinculin-containing adhesions and create greater strains in the surrounding matrix directed toward the cell body. In contrast, partially confined cells develop a more elongated morphology with smaller but significantly more vinculin-containing adhesions and displace the surrounding matrix less than fully confined cells. The resulting effect of increasing cell contractility via Rho activation is dependent on the number of walls with which the cell is in contact. Although matrix strains increase in both fully and partially confined cells, cells that are partially confined increase speed, whereas those in full confinement decrease speed. Together, these results suggest that the degree of cell-ECM contact during confined migration is a key determinant of speed, morphology, and cell-generated substrate strains during motility, and these factors may work in tandem to facilitate metastatic cell migration.


Subject(s)
Cell Movement , Extracellular Matrix/metabolism , Cell Line, Tumor , Cell Size , Cell-Matrix Junctions/metabolism , Enzyme Activation , Focal Adhesions/metabolism , Humans , Vinculin/metabolism , rho GTP-Binding Proteins/metabolism
18.
J Cell Sci ; 132(17)2019 09 02.
Article in English | MEDLINE | ID: mdl-31391240

ABSTRACT

How ion channels localize and distribute on the cell membrane remains incompletely understood. We show that interventions that vary cell adhesion proteins and cell size also affect the membrane current density of inward-rectifier K+ channels (Kir2.1; encoded by KCNJ2) and profoundly alter the action potential shape of excitable cells. By using micropatterning to manipulate the localization and size of focal adhesions (FAs) in single HEK293 cells engineered to stably express Kir2.1 channels or in neonatal rat cardiomyocytes, we establish a robust linear correlation between FA coverage and the amplitude of Kir2.1 current at both the local and whole-cell levels. Confocal microscopy showed that Kir2.1 channels accumulate in membrane proximal to FAs. Selective pharmacological inhibition of key mediators of protein trafficking and the spatially dependent alterations in the dynamics of Kir2.1 fluorescent recovery after photobleaching revealed that the Kir2.1 channels are transported to the cell membrane uniformly, but are preferentially internalized by endocytosis at sites that are distal from FAs. Based on these results, we propose adhesion-regulated membrane localization of ion channels as a fundamental mechanism of controlling cellular electrophysiology via mechanochemical signals, independent of the direct ion channel mechanogating.


Subject(s)
Integrins/metabolism , Ion Channel Gating/physiology , Membrane Potentials/physiology , Potassium Channels, Inwardly Rectifying/metabolism , Animals , Endocytosis , Female , HEK293 Cells , Humans , Rats , Rats, Sprague-Dawley
19.
Proc Natl Acad Sci U S A ; 116(6): 1992-1997, 2019 02 05.
Article in English | MEDLINE | ID: mdl-30674675

ABSTRACT

Microarchitectural cues drive aligned fibrillar collagen deposition in vivo and in biomaterial scaffolds, but the cell-signaling events that underlie this process are not well understood. Utilizing a multicellular patterning model system that allows for observation of intracellular signaling events during collagen matrix assembly, we investigated the role of calcium (Ca2+) signaling in human mesenchymal stem cells (MSCs) during this process. We observed spontaneous Ca2+ oscillations in MSCs during fibrillar collagen assembly, and hypothesized that the transient receptor potential vanilloid 4 (TRPV4) ion channel, a mechanosensitive Ca2+-permeable channel, may regulate this signaling. Inhibition of TRPV4 nearly abolished Ca2+ signaling at initial stages of collagen matrix assembly, while at later times had reduced but significant effects. Importantly, blocking TRPV4 activity dramatically reduced aligned collagen fibril assembly; conversely, activating TRPV4 accelerated aligned collagen formation. TRPV4-dependent Ca2+ oscillations were found to be independent of pattern shape or subpattern cell location, suggesting this signaling mechanism is necessary for aligned collagen formation but not sufficient in the absence of physical (microarchitectural) cues that force multicellular alignment. As cell-generated mechanical forces are known to be critical to the matrix assembly process, we examined the role of TRPV4-mediated Ca2+ signaling in force generated across the load-bearing focal adhesion protein vinculin within MSCs using an FRET-based tension sensor. Inhibiting TRPV4 decreased tensile force across vinculin, whereas TRPV4 activation caused a dynamic unloading and reloading of vinculin. Together, these findings suggest TRPV4 activity regulates forces at cell-matrix adhesions and is critical to aligned collagen matrix assembly by MSCs.


Subject(s)
Calcium Signaling/physiology , Collagen/biosynthesis , Mesenchymal Stem Cells/metabolism , TRPV Cation Channels/metabolism , Vinculin/metabolism , Bone Marrow Cells , Calcium , Cell-Matrix Junctions/metabolism , Cellular Microenvironment , Extracellular Matrix , Focal Adhesions , Humans
20.
Curr Opin Biomed Eng ; 12: 83-94, 2019 Dec.
Article in English | MEDLINE | ID: mdl-32864525

ABSTRACT

Nearly all cellular processes are sensitive to mechanical inputs, and this plays a major role in diverse physiological processes. Mechanical stimuli are thought to be primarily detected through force-induced changes in protein structure. Approximately a decade ago, molecular tension sensors were created to measure forces across proteins within cells. Since then, an impressive assortment of sensors has been created and provided key insights into mechanotransduction, but comparisons of measurements between various sensors are challenging. In this review, we discuss the different types of molecular tension sensors, provide a system of classification based on their molecular-scale mechanical properties, and highlight how new applications of these sensors are enabling measurements beyond the magnitude of tensile load. We suggest that an expanded understanding of the functionality of these sensors, as well as integration with other techniques, will lead to consensus amongst measurements as well as critical insights into the underlying mechanisms of mechanotransduction.

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