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Kazemipour A, Novak O, Flickinger D, Marvin JS, Abdelfattah AS, King J, Borden PM, Kim JJ, Al-Abdullatif SH, Deal PE, Miller EW, Schreiter ER, Druckmann S, Svoboda K, Looger LL, Podgorski K. Author Correction: Kilohertz frame-rate two-photon tomography. Nat Methods 2019; 16:932. [PMID: 31388143 DOI: 10.1038/s41592-019-0545-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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Franke JM, Raliski BK, Boggess SC, Natesan DV, Koretsky ET, Zhang P, Kulkarni RU, Deal PE, Miller EW. BODIPY Fluorophores for Membrane Potential Imaging. J Am Chem Soc 2019; 141:12824-12831. [PMID: 31339313 DOI: 10.1021/jacs.9b05912] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Fluorophores based on the BODIPY scaffold are prized for their tunable excitation and emission profiles, mild syntheses, and biological compatibility. Improving the water-solubility of BODIPY dyes remains an outstanding challenge. The development of water-soluble BODIPY dyes usually involves direct modification of the BODIPY fluorophore core with ionizable groups or substitution at the boron center. While these strategies are effective for the generation of water-soluble fluorophores, they are challenging to implement when developing BODIPY-based indicators: direct modification of BODIPY core can disrupt the electronics of the dye, complicating the design of functional indicators; and substitution at the boron center often renders the resultant BODIPY incompatible with the chemical transformations required to generate fluorescent sensors. In this study, we show that BODIPYs bearing a sulfonated aromatic group at the meso position provide a general solution for water-soluble BODIPYs. We outline the route to a suite of 5 new sulfonated BODIPYs with 2,6-disubstitution patterns spanning a range of electron-donating and -withdrawing propensities. To highlight the utility of these new, sulfonated BODIPYs, we further functionalize them to access 13 new, BODIPY-based, voltage-sensitive fluorophores (VF). The most sensitive of these BODIPY VF dyes displays a 48% ΔF/F per 100 mV in mammalian cells. Two additional BODIPY VFs show good voltage sensitivity (≥24% ΔF/F) and excellent brightness in cells. These compounds can report on action potential dynamics in both mammalian neurons and human stem cell-derived cardiomyocytes. Accessing a range of substituents in the context of a water-soluble BODIPY fluorophore provides opportunities to tune the electronic properties of water-soluble BODIPY dyes for functional indicators.
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Kazemipour A, Novak O, Flickinger D, Marvin JS, Abdelfattah AS, King J, Borden PM, Kim JJ, Al-Abdullatif SH, Deal PE, Miller EW, Schreiter ER, Druckmann S, Svoboda K, Looger LL, Podgorski K. Kilohertz frame-rate two-photon tomography. Nat Methods 2019; 16:778-786. [PMID: 31363222 PMCID: PMC6754705 DOI: 10.1038/s41592-019-0493-9] [Citation(s) in RCA: 73] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Accepted: 06/14/2019] [Indexed: 11/25/2022]
Abstract
Point-scanning two-photon microscopy enables high-resolution imaging within scattering specimens such as the mammalian brain, but sequential acquisition of voxels fundamentally limits its speed. We developed a two-photon imaging technique that scans lines of excitation across a focal plane at multiple angles and computationally recovers high-resolution images, attaining voxel rates of over 1 billion Hz in structured samples. Using a static image as a prior for recording neural activity, we imaged visually evoked and spontaneous glutamate release across hundreds of dendritic spines in mice at depths over 250 µm and frame rates over 1 kHz. Dendritic glutamate transients in anesthetized mice are synchronized within spatially contiguous domains spanning tens of micrometers at frequencies ranging from 1-100 Hz. We demonstrate millisecond-resolved recordings of acetylcholine and voltage indicators, three-dimensional single-particle tracking and imaging in densely labeled cortex. Our method surpasses limits on the speed of raster-scanned imaging imposed by fluorescence lifetime.
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Park J, Kuo Y, Li J, Huang YL, Miller EW, Weiss S. Improved Surface Functionalization and Characterization of Membrane-Targeted Semiconductor Voltage Nanosensors. J Phys Chem Lett 2019; 10:3906-3913. [PMID: 31241960 DOI: 10.1021/acs.jpclett.9b01258] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Type-II ZnSe/CdS voltage-sensing seeded nanorods (vsNRs) were functionalized with α-helical peptides and zwitterionic-decorated lipoic acids (zw-LAs). Specific membrane targeting with high loading efficiency and minimal nonspecific binding was achieved. These vsNRs display quantum yield (QY) modulation as a function of membrane potential (MP) changes, as demonstrated at the ensemble level for (i) vesicles treated with valinomycin and (ii) wild-type HEK cells under alternating buffers with different [K+]. ΔF/F of ∼ 1% was achieved.
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Ortiz G, Liu P, Naing SHH, Muller VR, Miller EW. Synthesis of Sulfonated Carbofluoresceins for Voltage Imaging. J Am Chem Soc 2019; 141:6631-6638. [PMID: 30978010 DOI: 10.1021/jacs.9b01261] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We present the design, synthesis, and applications of a new class of voltage-sensitive fluorescent indicators built on a modified carbofluorescein scaffold. Carbofluoresceins are an attractive target for responsive probes because they maintain oxygen substitution patterns at the 3' and 6' positions, similar to fluorescein, while simultaneously possessing excitation and emission profiles red-shifted nearly 50 nm compared to fluorescein. However, the high p Ka of carbofluorescein dyes, coupled with their tendency to cyclize to nonfluorescent configurations, precludes their use in voltage-imaging applications. Here, we overcome the limitations of carbofluoresceins via chlorination to lower the p Ka by 2 units to 5.2 and sulfonation to prevent cyclization to the nonabsorbing form. To achieve this, we devise a synthetic route to halogenated sulfonated carbofluoresceins from readily available, inexpensive starting materials. New, chlorinated sulfone carbofluoresceins have low p Ka values (5.2) and can be incorporated into phenylenevinylene molecular wire scaffolds to create carboVoltage-sensitive fluorophores (carboVF dyes). The best of the new carboVF dyes, carboVF2.1(OMe).Cl, possesses excitation and emission profiles of >560 nm, displays high voltage sensitivity (>30% Δ F/ F per 100 mV), and can be used in the presence of other blue-excited fluorophores such as green fluorescent protein. Because carboVF2.1(OMe).Cl contains a phenolic oxygen, it can be incorporated into fluorogenic labeling strategies. Alkylation with a sterically bulky cyclopropylmethyl-derived acetoxymethyl ether renders carboVF weakly fluorescent; we show that fluorescence can be restored by the action of porcine liver esterase both in vitro and on the surface of living cells and neurons. Together, these results suggest chlorinated sulfone carbofluoresceins can be promising candidates for hybrid chemical-genetic voltage imaging at wavelengths beyond typical fluorescein excitation and emission.
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Boggess SC, Gandhi SS, Siemons BA, Huebsch N, Healy KE, Miller EW. New Molecular Scaffolds for Fluorescent Voltage Indicators. ACS Chem Biol 2019; 14:390-396. [PMID: 30735344 DOI: 10.1021/acschembio.8b00978] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The ability to non-invasively monitor membrane potential dynamics in excitable cells like neurons and cardiomyocytes promises to revolutionize our understanding of the physiology and pathology of the brain and heart. Here, we report the design, synthesis, and application of a new class of fluorescent voltage indicators that make use of a fluorene-based molecular wire as a voltage-sensing domain to provide fast and sensitive measurements of membrane potential in both mammalian neurons and human-derived cardiomyocytes. We show that the best of the new probes, fluorene VoltageFluor 2 (fVF 2), readily reports on action potentials in mammalian neurons, detects perturbations to the cardiac action potential waveform in human induced pluripotent stem cell-derived cardiomyocytes, shows a substantial decrease in phototoxicity compared to existing molecular wire-based indicators, and can monitor cardiac action potentials for extended periods of time. Together, our results demonstrate the generalizability of a molecular wire approach to voltage sensing and highlight the utility of fVF 2 for interrogating membrane potential dynamics.
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Hamzeh H, Alvarez L, Strünker T, Kierzek M, Brenker C, Deal PE, Miller EW, Seifert R, Kaupp UB. Kinetic and photonic techniques to study chemotactic signaling in sea urchin sperm. Methods Cell Biol 2019; 151:487-517. [PMID: 30948028 DOI: 10.1016/bs.mcb.2018.12.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Sperm from sea urchins are attracted by chemical cues released by the egg-a mechanism called chemotaxis. We describe here the signaling pathway and molecular components endowing sperm with single-molecule sensitivity. Chemotactic signaling and behavioral responses occur on a timescale of a few milliseconds to seconds. We describe the techniques and chemical tools used to resolve the signaling events in time. The techniques include rapid-mixing devices, rapid stroboscopic microscopy, and photolysis of caged second messengers and chemoattractants.
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Grenier V, Daws BR, Liu P, Miller EW. Spying on Neuronal Membrane Potential with Genetically Targetable Voltage Indicators. J Am Chem Soc 2019; 141:1349-1358. [PMID: 30628785 DOI: 10.1021/jacs.8b11997] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Methods for optical measurement of voltage dynamics in living cells are attractive because they provide spatial resolution surpassing traditional electrode-based measurements and temporal resolution exceeding that of widely used Ca2+ imaging. Chemically synthesized voltage-sensitive dyes that use photoinduced electron transfer as a voltage-sensing trigger offer high voltage sensitivity and fast-response kinetics, but targeting chemical indicators to specific cells remains an outstanding challenge. Here, we present a new family of readily functionalizable, fluorescein-based voltage-sensitive fluorescent dyes (sarcosine-VoltageFluors) that can be covalently attached to a genetically encoded cell surface receptor to achieve voltage imaging from genetically defined neurons. We synthesized four new VoltageFluor derivatives that possess carboxylic acid functionality for simple conjugation to flexible tethers. The best of this new group of dyes was conjugated via a polyethylene glycol (PEG) linker to a small peptide (SpyTag, 13 amino acids) that directs binding and formation of a covalent bond with its binding partner, SpyCatcher (15 kDa). The new VoltageSpy dyes effectively label cells expressing cell-surface SpyCatcher, display good voltage sensitivity, and maintain fast-response kinetics. In cultured neurons, VoltageSpy dyes enable robust, single-trial optical detection of action potentials at neuronal soma with sensitivity exceeding genetically encoded voltage indicators. Importantly, genetic targeting of chemically synthesized dyes enables VoltageSpy to report on action potentials in axons and dendrites in single trials, tens to hundreds of micrometers away from the cell body. Genetic targeting of synthetic voltage indicators with VoltageSpy enables voltage imaging with low nanomolar dye concentration and offers a promising method for allying the speed and sensitivity of synthetic indicators with the enhanced cellular resolution of genetically encoded probes.
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McNamara HM, Dodson S, Huang YL, Miller EW, Sandstede B, Cohen AE. Geometry-Dependent Arrhythmias in Electrically Excitable Tissues. Cell Syst 2018; 7:359-370.e6. [PMID: 30292705 PMCID: PMC6204347 DOI: 10.1016/j.cels.2018.08.013] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Revised: 07/14/2018] [Accepted: 08/28/2018] [Indexed: 12/12/2022]
Abstract
Little is known about how individual cells sense the macroscopic geometry of their tissue environment. Here, we explore whether long-range electrical signaling can convey information on tissue geometry to individual cells. First, we studied an engineered electrically excitable cell line. Cells grown in patterned islands of different shapes showed remarkably diverse firing patterns under otherwise identical conditions, including regular spiking, period-doubling alternans, and arrhythmic firing. A Hodgkin-Huxley numerical model quantitatively reproduced these effects, showing how the macroscopic geometry affected the single-cell electrophysiology via the influence of gap junction-mediated electrical coupling. Qualitatively similar geometry-dependent dynamics were observed in human induced pluripotent stem cell (iPSC)-derived cardiomyocytes. The cardiac results urge caution in translating observations of arrhythmia in vitro to predictions in vivo, where the tissue geometry is very different. We study how to extrapolate electrophysiological measurements between tissues with different geometries and different gap junction couplings.
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Kulkarni R, Vandenberghe M, Thunemann M, James F, Andreassen OA, Djurovic S, Devor A, Miller EW. In Vivo Two-Photon Voltage Imaging with Sulfonated Rhodamine Dyes. ACS CENTRAL SCIENCE 2018; 4:1371-1378. [PMID: 30410975 PMCID: PMC6202643 DOI: 10.1021/acscentsci.8b00422] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Indexed: 05/24/2023]
Abstract
Optical methods that rely on fluorescence for mapping changes in neuronal membrane potential in the brains of awake animals provide a powerful way to interrogate the activity of neurons that underlie neural computations ranging from sensation and perception to learning and memory. To achieve this goal, fluorescent indicators should be bright, highly sensitive to small changes in membrane potential, nontoxic, and excitable with infrared light. We report a new class of fluorescent, voltage-sensitive dyes: sulfonated rhodamine voltage reporters (sRhoVR), synthetic fluorophores with high voltage sensitivity, excellent two-photon performance, and compatibility in intact mouse brains. sRhoVR dyes are based on a tetramethyl rhodamine fluorophore coupled to a phenylenevinylene molecular wire/diethyl aniline voltage-sensitive domain. When applied to cells, sRhoVR dyes localize to the plasma membrane and respond to membrane depolarization with a fluorescence increase. The best of the new dyes, sRhoVR 1, displays a 44% ΔF/F increase in fluorescence per 100 mV change, emits at 570 nm, and possesses excellent two-photon absorption of approximately 200 GM at 840 nm. sRhoVR 1 can detect action potentials in cultured rat hippocampal neurons under both single- and two-photon illumination with sufficient speed and sensitivity to report on action potentials in single trials, without perturbing underlying physiology or membrane properties. The combination of speed, sensitivity, and brightness under two-photon illumination makes sRhoVR 1 a promising candidate for in vivo imaging in intact brains. We show sRhoVR powerfully complements electrode-based modes of neuronal activity recording in the mouse brain by recording neuronal transmembrane potentials from the neuropil of layer 2/3 of the mouse barrel cortex in concert with extracellularly recorded local field potentials (LFPs). sRhoVR imaging reveals robust depolarization in response to whisker stimulation; concurrent electrode recordings reveal negative deflections in the LFP recording, consistent with the canonical thalamocortical response. Importantly, sRhoVR 1 can be applied in mice with chronic optical windows, presaging its utility in dissecting and resolving voltage dynamics using two-photon functional imaging in awake, behaving animals.
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Abstract
Ca2+ mediates a host of biochemical and biophysical signaling processes in cells. The development of synthetic, Ca2+-sensitive fluorophores has played an instrumental role in our understanding of the temporal and spatial dynamics of Ca2+. Coupling Ca2+-selective ligands to fluorescent reporters has provided a wealth of excellent indicators that span the visible excitation and emission spectrum and possess Ca2+ affinities suited to a variety of cellular contexts. One underdeveloped area is the use of hybrid rhodamine/fluorescein fluorophores, or rhodols, in the context of Ca2+ sensing. Rhodols are bright and photostable and have good two-photon absorption cross sections (σTPA), making them excellent candidates for incorporation into Ca2+-sensing scaffolds. Here, we present the design, synthesis, and application of rhodol Ca2+ sensor 1 (RCS-1), a chlorinated pyrrolidine-based rhodol. RCS-1 possesses a Ca2+ binding constant of 240 nM and a 10-fold turn response to Ca2+. RCS-1 effectively absorbs infrared light and has a σTPA of 76 GM at 840 nm, 3-fold greater than that of its fluorescein-based counterpart. The acetoxy-methyl ester of RCS-1 stains the cytosol of live cells, enabling observation of Ca2+ fluctuations and cultured neurons using both one- and two-photon illumination. Together, these results demonstrate the utility of rhodol-based scaffolds for Ca2+ sensing using two-photon illumination in neurons.
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Liu P, Grenier V, Hong W, Muller VR, Miller EW. Fluorogenic Targeting of Voltage-Sensitive Dyes to Neurons. J Am Chem Soc 2017; 139:17334-17340. [PMID: 29154543 DOI: 10.1021/jacs.7b07047] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
We present a method to target voltage-sensitive fluorescent dyes to specified cells using an enzyme-catalyzed fluorogenic reaction on cell surfaces. The dye/enzyme hybrids are composed of a photoinduced electron transfer (PeT)-based fluorescent voltage indicator and a complementary enzyme expressed on the cell surface. Action of the exogenous enzyme on the dye results in fluorogenic activation of the dye, enabling fast voltage imaging in defined neurons with sensitivity surpassing those of purely genetically encoded approaches. We employ a bulky methylcyclopropylacetoxymethyl ether to diminish the fluorescence of a PeT-based voltage-sensitive dye, or VoltageFluor. The hydrolytically stable ether can be removed by the action of porcine liver esterase (PLE) to reveal the bright unmodified VoltageFluor. We established that the chemically modified VoltageFluor is a substrate for PLE in vitro and in live cells. When PLE is targeted to the external face of cell membranes, it controls the apparent staining of cells. The use of neuron-specific promoters can direct staining to mammalian neurons to provide clear detection of neuronal action potentials in single trials. All of the new VoltageFluors targeted by esterase expression (VF-EXs) report single spikes in cultured mammalian neurons. The best, VF-EX2, does so with a signal-to-noise ratio nearly double that of comparable genetically encoded voltage reporters. By targeting PLE to neurons, VF-EX2 can interrogate the neuromodulatory effects of serotonin in cultured hippocampal neurons. Taken together, our results show that a combination of synthetic chemistry and biochemistry enables bright and fast voltage imaging from genetically defined neurons in culture.
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McKeithan WL, Savchenko A, Yu MS, Cerignoli F, Bruyneel AAN, Price JH, Colas AR, Miller EW, Cashman JR, Mercola M. An Automated Platform for Assessment of Congenital and Drug-Induced Arrhythmia with hiPSC-Derived Cardiomyocytes. Front Physiol 2017; 8:766. [PMID: 29075196 PMCID: PMC5641590 DOI: 10.3389/fphys.2017.00766] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2017] [Accepted: 09/19/2017] [Indexed: 12/12/2022] Open
Abstract
The ability to produce unlimited numbers of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) harboring disease and patient-specific gene variants creates a new paradigm for modeling congenital heart diseases (CHDs) and predicting proarrhythmic liabilities of drug candidates. However, a major roadblock to implementing hiPSC-CM technology in drug discovery is that conventional methods for monitoring action potential (AP) kinetics and arrhythmia phenotypes in vitro have been too costly or technically challenging to execute in high throughput. Herein, we describe the first large-scale, fully automated and statistically robust analysis of AP kinetics and drug-induced proarrhythmia in hiPSC-CMs. The platform combines the optical recording of a small molecule fluorescent voltage sensing probe (VoltageFluor2.1.Cl), an automated high throughput microscope and automated image analysis to rapidly generate physiological measurements of cardiomyocytes (CMs). The technique can be readily adapted on any high content imager to study hiPSC-CM physiology and predict the proarrhythmic effects of drug candidates.
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Abstract
Optical methods for interrogating membrane potential changes in neurons promise to revolutionize our ability to dissect the activity of individual cells embedded in neural circuits underlying behavior and sensation. A number of voltage imaging strategies have emerged in the past few years. This Perspective discusses developments in both small-molecule and genetically encoded fluorescent indicators of membrane potential. We survey recent advances in small-molecule fluorescent indicators that rely on photoinduced electron transfer to sense voltage as well as refinements of voltage-sensitive fluorescent proteins and new opsin-based strategies for monitoring voltage changes. We compare the requirements of fluorescent voltage indicators to those for more canonical Ca2+ sensing as a way to illuminate the particular challenges associated with voltage imaging.
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Rodrigues GMC, Gaj T, Adil MM, Wahba J, Rao AT, Lorbeer FK, Kulkarni RU, Diogo MM, Cabral JMS, Miller EW, Hockemeyer D, Schaffer DV. Defined and Scalable Differentiation of Human Oligodendrocyte Precursors from Pluripotent Stem Cells in a 3D Culture System. Stem Cell Reports 2017; 8:1770-1783. [PMID: 28552605 PMCID: PMC5470111 DOI: 10.1016/j.stemcr.2017.04.027] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 04/22/2017] [Accepted: 04/24/2017] [Indexed: 12/22/2022] Open
Abstract
Oligodendrocyte precursor cells (OPCs) offer considerable potential for the treatment of demyelinating diseases and injuries of the CNS. However, generating large quantities of high-quality OPCs remains a substantial challenge that impedes their therapeutic application. Here, we show that OPCs can be generated from human pluripotent stem cells (hPSCs) in a three-dimensional (3D), scalable, and fully defined thermoresponsive biomaterial system. We used CRISPR/Cas9 to create a NKX2.2-EGFP human embryonic stem cell reporter line that enabled fine-tuning of early OPC specification and identification of conditions that markedly increased the number of OLIG2+ and NKX2.2+ cells generated from hPSCs. Transplantation of 50-day-old OPCs into the brains of NOD/SCID mice revealed that progenitors generated in 3D without cell selection or purification subsequently engrafted, migrated, and matured into myelinating oligodendrocytes in vivo. These results demonstrate the potential of harnessing lineage reporter lines to develop 3D platforms for rapid and large-scale production of OPCs. A defined and scalable 3D system accelerates the differentiation of OPCs from hPSCs A NKX2.2-EGFP hESC reporter line enables optimization of OPC differentiation 3D-derived OPCs engraft, migrate, and mature after implantation into NOD/SCID mice
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Adil MM, Vazin T, Ananthanarayanan B, Rodrigues GMC, Rao AT, Kulkarni RU, Miller EW, Kumar S, Schaffer DV. Engineered hydrogels increase the post-transplantation survival of encapsulated hESC-derived midbrain dopaminergic neurons. Biomaterials 2017; 136:1-11. [PMID: 28505596 DOI: 10.1016/j.biomaterials.2017.05.008] [Citation(s) in RCA: 77] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Revised: 04/26/2017] [Accepted: 05/04/2017] [Indexed: 01/21/2023]
Abstract
Cell replacement therapies have broad biomedical potential; however, low cell survival and poor functional integration post-transplantation are major hurdles that hamper clinical benefit. For example, following striatal transplantation of midbrain dopaminergic (mDA) neurons for the treatment of Parkinson's disease (PD), only 1-5% of the neurons typically survive in preclinical models and in clinical trials. In general, resource-intensive generation and implantation of larger numbers of cells are used to compensate for the low post-transplantation cell-survival. Poor graft survival is often attributed to adverse biochemical, mechanical, and/or immunological stress that cells experience during and after implantation. To address these challenges, we developed a functionalized hyaluronic acid (HA)-based hydrogel for in vitro maturation and central nervous system (CNS) transplantation of human pluripotent stem cell (hPSC)-derived neural progenitors. Specifically, we functionalized the HA hydrogel with RGD and heparin (hep) via click-chemistry and tailored its stiffness to encourage neuronal maturation, survival, and long-term maintenance of the desired mDA phenotype. Importantly, ∼5 times more hydrogel-encapsulated mDA neurons survived after transplantation in the rat striatum, compared to unencapsulated neurons harvested from commonly used 2D surfaces. This engineered biomaterial may therefore increase the therapeutic potential and reduce the manufacturing burden for successful neuronal implantation.
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Miller EW. (Near-Infra) Red Means STOP: Shutting Down Cancer with NIR Light. ACS CENTRAL SCIENCE 2017; 3:266-268. [PMID: 28470040 PMCID: PMC5408336 DOI: 10.1021/acscentsci.7b00102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
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Kulkarni RU, Kramer DJ, Pourmandi N, Karbasi K, Bateup HS, Miller EW. Voltage-sensitive rhodol with enhanced two-photon brightness. Proc Natl Acad Sci U S A 2017; 114:2813-2818. [PMID: 28242676 PMCID: PMC5358379 DOI: 10.1073/pnas.1610791114] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have designed, synthesized, and applied a rhodol-based chromophore to a molecular wire-based platform for voltage sensing to achieve fast, sensitive, and bright voltage sensing using two-photon (2P) illumination. Rhodol VoltageFluor-5 (RVF5) is a voltage-sensitive dye with improved 2P cross-section for use in thick tissue or brain samples. RVF5 features a dichlororhodol core with pyrrolidyl substitution at the nitrogen center. In mammalian cells under one-photon (1P) illumination, RVF5 demonstrates high voltage sensitivity (28% ΔF/F per 100 mV) and improved photostability relative to first-generation voltage sensors. This photostability enables multisite optical recordings from neurons lacking tuberous sclerosis complex 1, Tsc1, in a mouse model of genetic epilepsy. Using RVF5, we show that Tsc1 KO neurons exhibit increased activity relative to wild-type neurons and additionally show that the proportion of active neurons in the network increases with the loss of Tsc1. The high photostability and voltage sensitivity of RVF5 is recapitulated under 2P illumination. Finally, the ability to chemically tune the 2P absorption profile through the use of rhodol scaffolds affords the unique opportunity to image neuronal voltage changes in acutely prepared mouse brain slices using 2P illumination. Stimulation of the mouse hippocampus evoked spiking activity that was readily discerned with bath-applied RVF5, demonstrating the utility of RVF5 and molecular wire-based voltage sensors with 2P-optimized fluorophores for imaging voltage in intact brain tissue.
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Knight AS, Kulkarni RU, Zhou EY, Franke JM, Miller EW, Francis MB. A modular platform to develop peptoid-based selective fluorescent metal sensors. Chem Commun (Camb) 2017; 53:3477-3480. [PMID: 28272633 DOI: 10.1039/c7cc00931c] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Despite the reduction in industrial use of toxic heavy metals, there remain contaminated natural water sources across the world. Herein we present a modular platform for developing selective sensors for toxic metal ions using N-substituted glycine, or peptoid, oligomers coupled to a fluorophore. As a preliminary evaluation of this strategy, structures based on previously identified metal-binding peptoids were synthesized with terminal pyrene moieties. Both derivatives of this initial design demonstrated a turn-off response in the presence of various metal ions. A colorimetric screen was designed to identify a peptoid ligand that chelates Hg(ii). Multiple ligands were identified that were able to deplete Hg(ii) from a solution selectively in the presence of an excess of competing ions. The C-terminal fluoropeptoid derivatives demonstrated similar selectivity to their label-free counterparts. This strategy could be applied to develop sensors for many different metal ions of interest using a variety of fluorophores, leading to a panel of sensors for identifying various water source contaminants.
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Kulkarni RU, Yin H, Pourmandi N, James F, Adil MM, Schaffer DV, Wang Y, Miller EW. A Rationally Designed, General Strategy for Membrane Orientation of Photoinduced Electron Transfer-Based Voltage-Sensitive Dyes. ACS Chem Biol 2017; 12:407-413. [PMID: 28004909 DOI: 10.1021/acschembio.6b00981] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Voltage imaging with fluorescent dyes offers promise for interrogating the complex roles of membrane potential in coordinating the activity of neurons in the brain. Yet, low sensitivity often limits the broad applicability of optical voltage indicators. In this paper, we use molecular dynamics (MD) simulations to guide the design of new, ultrasensitive fluorescent voltage indicators that use photoinduced electron transfer (PeT) as a voltage-sensing switch. MD simulations predict an approximately 16% increase in voltage sensitivity resulting purely from improved alignment of dye with the membrane. We confirm this theoretical finding by synthesizing 9 new voltage-sensitive (VoltageFluor, or VF) dyes and establishing that all of them display the expected improvement of approximately 19%. This synergistic outworking of theory and experiment enabled computational and theoretical estimation of VF dye orientation in lipid bilayers and has yielded the most sensitive PeT-based VF dye to date. We use this new voltage indicator to monitor voltage spikes in neurons from rat hippocampus and human pluripotent-stem-cell-derived dopaminergic neurons.
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Adil MM, Rodrigues GMC, Kulkarni RU, Rao AT, Chernavsky NE, Miller EW, Schaffer DV. Efficient generation of hPSC-derived midbrain dopaminergic neurons in a fully defined, scalable, 3D biomaterial platform. Sci Rep 2017; 7:40573. [PMID: 28091566 PMCID: PMC5238378 DOI: 10.1038/srep40573] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Accepted: 12/08/2016] [Indexed: 01/01/2023] Open
Abstract
Pluripotent stem cells (PSCs) have major potential as an unlimited source of functional cells for many biomedical applications; however, the development of cell manufacturing systems to enable this promise faces many challenges. For example, there have been major recent advances in the generation of midbrain dopaminergic (mDA) neurons from stem cells for Parkinson's Disease (PD) therapy; however, production of these cells typically involves undefined components and difficult to scale 2D culture formats. Here, we used a fully defined, 3D, thermoresponsive biomaterial platform to rapidly generate large numbers of action-potential firing mDA neurons after 25 days of differentiation (~40% tyrosine hydroxylase (TH) positive, maturing into 25% cells exhibiting mDA neuron-like spiking behavior). Importantly, mDA neurons generated in 3D exhibited a 30-fold increase in viability upon implantation into rat striatum compared to neurons generated on 2D, consistent with the elevated expression of survival markers FOXA2 and EN1 in 3D. A defined, scalable, and resource-efficient cell culture platform can thus rapidly generate high quality differentiated cells, both neurons and potentially other cell types, with strong potential to accelerate both basic and translational research.
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Deal PE, Kulkarni RU, Al-Abdullatif SH, Miller EW. Isomerically Pure Tetramethylrhodamine Voltage Reporters. J Am Chem Soc 2016; 138:9085-8. [PMID: 27428174 PMCID: PMC5222532 DOI: 10.1021/jacs.6b05672] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
We present the design, synthesis, and application of a new family of fluorescent voltage indicators based on isomerically pure tetramethylrhodamines. These new Rhodamine Voltage Reporters, or RhoVRs, use photoinduced electron transfer (PeT) as a trigger for voltage sensing, display excitation and emission profiles in the green to orange region of the visible spectrum, demonstrate high sensitivity to membrane potential changes (up to 47% ΔF/F per 100 mV), and employ a tertiary amide derived from sarcosine, which aids in membrane localization and simultaneously simplifies the synthetic route to the voltage sensors. The most sensitive of the RhoVR dyes, RhoVR 1, features a methoxy-substituted diethylaniline donor and phenylenevinylene molecular wire at the 5'-position of the rhodamine aryl ring, exhibits the highest voltage sensitivity to date for red-shifted PeT-based voltage sensors, and is compatible with simultaneous imaging alongside green fluorescent protein-based indicators. The discoveries that sarcosine-based tertiary amides in the context of molecular-wire voltage indicators prevent dye internalization and 5'-substituted voltage indicators exhibit improved voltage sensitivity should be broadly applicable to other types of PeT-based voltage-sensitive fluorophores.
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Miller EW. Small molecule fluorescent voltage indicators for studying membrane potential. Curr Opin Chem Biol 2016; 33:74-80. [PMID: 27318561 DOI: 10.1016/j.cbpa.2016.06.003] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 05/31/2016] [Accepted: 06/01/2016] [Indexed: 11/18/2022]
Abstract
Voltage imaging has the potential to unravel the contributions that rapid changes in membrane voltage make to cellular physiology, especially in the context of neuroscience. In particular, small molecule fluorophores are especially attractive because they can, in theory, provide fast and sensitive measurements of membrane potential dynamics. A number of classes of small molecule voltage indicators will be discussed, including dyes with improved two-photon voltage sensing, near infrared optical profiles for use in in vivo applications, and newly developed electron-transfer based indicators, or VoltageFluors, that can be tuned across a range of wavelengths to enable all-optical voltage manipulation and measurement. Limitations and a 'wish-list' for voltage indicators will also be discussed.
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Rubinstein N, Liu P, Miller EW, Weinstain R. meso-Methylhydroxy BODIPY: a scaffold for photo-labile protecting groups. Chem Commun (Camb) 2015; 51:6369-72. [PMID: 25761909 DOI: 10.1039/c5cc00550g] [Citation(s) in RCA: 95] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Here, we show that by installing a meso-methylhydroxy moiety, the boron dipyrromethene (BODIPY) scaffold can be converted into an efficient caging group, removable by green light. We describe caging and uncaging of important chemical functionalities and demonstrate green light mediated control over biological processes in cultured cell lines and neurons.
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Grenier V, Walker AS, Miller EW. A Small-Molecule Photoactivatable Optical Sensor of Transmembrane Potential. J Am Chem Soc 2015; 137:10894-7. [PMID: 26247778 DOI: 10.1021/jacs.5b05538] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This paper discloses the design, synthesis, and imaging applications of the first member of a new class of SPOTs, small-molecule photoactivatable optical sensors of transmembrane potential. SPOT2.1.Cl features an established voltage-sensitive dye, VoltageFluor2.1.Cl--or VF--capped with a dimethoxy-o-nitrobenzyl (DMNB) caging group to effectively diminish fluorescence of the VF dye prior to uncaging. SPOT2.1.Cl localizes to cell membranes and displays weak fluorescence until photoactivated. Illumination generates the parent VF dye which then optically reports on changes in the membrane voltage. After photoactivation with spatially restricted light, SPOT2.1.Cl-loaded cells display bright, voltage-sensitive fluorescence associated with the plasma membrane, while neighboring cells remain dark. Activated SPOT reports on action potentials in single trials. SPOT can be activated in neuron cell bodies or uncaged in dendrites to enable structural tracing via "backfilling" of the dye to the soma, followed by functional imaging in the labeled cell. The combination of cellular specificity achieved through spatially defined patterns of illumination, coupled with the fast, sensitive, and noncapacitive voltage sensing characteristics of VF dyes makes SPOT2.1.Cl a useful tool for interrogating both structure and function of neuronal systems.
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