Category Archives: Publications

Store-Operated Calcium Entry In Müller Glia Is Controlled By Synergistic Activation Of TRPC And Orai Channels

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We have a new publication out as collaborators with colleages, Store-Operated Calcium Entry In Müller Glia Is Controlled By Synergistic Activation Of TRPC And Orai Channels authored by Tünde Molnár, Oleg Yarishkin, Peter Barabas, Anthony Iuso, Bryan W. Jones, Robert Marc, Tam Phuong, and David Krizaj.

Bonus, we got the cover!  The image was created by Tam Phuong.

 

Significance: Store-operated Ca2+ signaling represents a major signaling pathway and source of cytosolic Ca2+ in astrocytes. Here, we show that the store-operated response in Müller cells, radial glia that perform key structural, signaling, osmoregulatory and mechanosensory functions within the retina, is mediated through synergistic activation of TRPC and Orai channels. The endfoot disproportionately expresses the depletion sensor STIM1, contains an extraordinarily high density of ER cisternae that shadow neuronal, astrocyte, vascular and axonal structures, interface with mitochondria but also originates SOCE-induced transcellular Ca2+ waves that propagate glial excitation into the proximal retina. These results identify a molecular mechanism that underlies complex interactions between the plasma membrane and calcium stores and contributes to radial glial function, regulation and response to mechanical stress.

Abstract: The endoplasmic reticulum (ER) is at the epicenter of astrocyte Ca2+ signaling. We sought to identify the molecular mechanism underlying store-operated calcium entry (SOCE) that repletes ER Ca2+ stores in mouse Müller cells. Store depletion, induced through blockade of sequestration transporters in Ca2+-free saline, induced synergistic activation of canonical transient receptor potential (TRPC1) and Orai channels. Store-operated TRPC1 channels were identified by their electrophysiological properties, pharmacological blockers and ablation of the Trpc1 gene. ICRAC (Ca2+ release-activated) currents were identified by ion permeability, voltage-dependence and sensitivity to selective Orai antagonists Synta66 and GSK7975A. Depletion-evoked calcium influx was initiated at the Müller endfoot and apical process, triggering centrifugal propagation of Ca2+ waves into the cell body. EM analysis of the endfoot compartment showed high-density ER cisternae that shadow retinal ganglion cell (RGC) somata and axons, protoplasmic astrocytes, vascular endothelial cells and ER-mitochondrial contacts at the vitreal surface of the endfoot. The mouse retina expresses transcripts encoding both Stim and all known Orai genes; Müller glia predominantly express STIM1 whereas STIM2 is mainly confined to the outer plexiform and retinal ganglion cell layers. Elimination of TRPC1 facilitated Müller gliosis induced by the elevation of intraocular pressure (IOP), suggesting that TRPC channels might play a neuroprotective role during mechanical stress. These findings expand the current knowledge about store-operated signaling in astroglia, as well as calcium signaling pathways in Müller astroglia and functional roles these cells play in retinal physiology and pathology.

Seasonal And Post-Trauma Remodeling Of The Ground Squirrel Retina

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We have a new publication out, Seasonal and post-trauma remodeling in cone-dominant ground squirrel retina authored by Dana Merriman, Ben Sajdak, Wei Li and Bryan W. Jones.

Abstract:

With a photoreceptor mosaic containing ∼85% cones, the ground squirrel is one of the richest known mammalian sources of these important retinal cells. It also has a visual ecology much like the human’s. While the ground squirrel retina is understandably prominent in the cone biochemistry, physiology, and circuitry literature, far less is known about the remodeling potential of its retinal pigment epithelium, neurons, macroglia, or microglia. This review aims to summarize the data from ground squirrel retina to this point in time, and to relate them to data from other brain areas where appropriate. We begin with a survey of the ground squirrel visual system, making comparisons with traditional rodent models and with human. Because this animal’s status as a hibernator often goes unnoticed in the vision literature, we then present a brief primer on hibernation biology. Next we review what is known about ground squirrel retinal remodeling concurrent with deep torpor and with rapid recovery upon re-warming. Notable here is rapidly-reversible, temperature-dependent structural plasticity of cone ribbon synapses, as well as pre- and post-synaptic plasticity throughout diverse brain regions. It is not yet clear if retinal cell types other than cones engage in torpor-associated synaptic remodeling. We end with the small but intriguing literature on the ground squirrel retina’s remodeling responses to insult by retinal detachment. Notable for widespread loss of (cone) photoreceptors, there is surprisingly little remodeling of the RPE or Müller cells. Microglial activation appears minimal, and remodeling of surviving second- and third-order neurons seems absent, but both require further study. In contrast, traumatic brain injury in the ground squirrel elicits typical macroglial and microglial responses. Overall, the data to date strongly suggest a heretofore unrecognized, natural checkpoint between retinal deafferentiation and RPE and Müller cell remodeling events. As we continue to discover them, the unique ways by which ground squirrel retina responds to hibernation or injury may be adaptable to therapeutic use.

Development Of Animal Models Of Local Retinal Degeneration

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Henri Lorach, Jennifer Kung, Corinne Beier, Yossi Mandel, Roopa Dalal, Philip Huie, Jenny Wang, Sengjun Lee, Alexander Sher, Bryan W. Jones, and Daniel Palanker have a new publication, Development of Animal Models of Local Retinal Degeneration (the IOVS direct link is here).

Many of the models of retinal degeneration we explore are genetic.  This project was designed to explore two other alternative approaches to retinal degeneration that are non-genetic and capable of producing highly localized retinal degeneration with precise onset time.

 

Webvision Chapter: Retinal Degeneration, Remodeling and Plasticity

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We have published a new chapter in Webvision, Retinal Degeneration, Remodeling and Plasticity that covers the history of the study of retinal degenerations and some of the implications for vision rescue.  Authors are Bryan W. Jones, Rebecca L. Pfeiffer and Robert E. Marc.  It will, like other Webvision chapters evolve over time, which is the whole point of Webvision, but we hope it will generate some discussion.

The AII Amacrine Cell Connectome: A Dense Network Hub

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AII-connectome

We have a new publication in Frontiers in Neuroscience, The AII Amacrine Cell Connectome: A Dense Network Hub.  Authors are Robert E. Marc, James R. Anderson, Bryan W. Jones, Crystal Sigulinsky and J. Scott Lauritzen.

Abstract:  The mammalian AII retinal amacrine cell is a narrow-field, multistratified glycinergic neuron best known for its role in collecting scotopic signals from rod bipolar cells and distributing them to ON and OFF cone pathways in a crossover network via a combination of inhibitory synapses and heterocellular AII::ON cone bipolar cell gap junctions. Long considered a simple cell, a full connectomics analysis shows that AII cells possess the most complex interaction repertoire of any known vertebrate neuron, contacting at least 28 different cell classes, including every class of retinal bipolar cell. Beyond its basic role in distributing rod signals to cone pathways, the AII cell may also mediate narrow-field feedback and feedforward inhibition for the photopic OFF channel, photopic ON-OFF inhibitory crossover signaling, and serves as a nexus for a collection of inhibitory networks arising from cone pathways that likely negotiate fast switching between cone and rod vision. Further analysis of the complete synaptic counts for five AII cells shows that (1) synaptic sampling is normalized for anatomic target encounter rates; (2) qualitative targeting is specific and apparently errorless; and (3) that AII cells strongly differentiate partner cohorts by synaptic and/or coupling weights. The AII network is a dense hub connecting all primary retinal excitatory channels via precisely weighted drive and specific polarities. Homologs of AII amacrine cells have yet to be identified in non-mammalians, but we propose that such homologs should be narrow-field glycinergic amacrine cells driving photopic ON-OFF crossover via heterocellular coupling with ON cone bipolar cells and glycinergic synapses on OFF cone bipolar cells. The specific evolutionary event creating the mammalian AII scotopic-photopic hub would then simply be the emergence of large numbers of pure rod bipolar cells.

 

A Multi-Scale Computational Model For The Study Of Retinal Prosthetic Stimulation

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Multiscale-model-of-retina

We have a new publication in IEEE, A Multi-Scale Computational Model For The Study Of Retinal Prosthetic Stimulation.  Authors are: Kyle Loizos, Gianluca Lazzi, J. Scott Lauritzen, James R. Anderson, Bryan W. Jones and Robert E. Marc.

Abstract: An implantable retinal prosthesis has been developed to restore vision to patients who have been blinded by degenerative diseases that destroy photoreceptors. By electrically stimulating the surviving retinal cells, the damaged photoreceptors may be bypassed and limited vision can be restored. While this has been shown to restore partial vision, the understanding of how cells react to this systematic electrical stimulation is largely unknown. Better predictive models and a deeper understanding of neural responses to electrical stimulation is necessary for designing a successful prosthesis. In this work, a computational model of an epi-retinal implant was built and simulated, spanning multiple spatial scales, including a large-scale model of the retina and implant electronics, as well as underlying neuronal networks.

 

Retinal Prosthetics, Optogenetics and Photoswitches

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Retinal-Prosthetics-Optogenetics-and-Photoswitches

We have a new publication, Retinal Prosthetics, Optogenetics and Photoswitches in ACS Chemical Neuroscience.  Authors are:  Robert E. Marc, Rebecca L. Pfeiffer, and Bryan W. Jones.

Abstract:

Three technologies have emerged as therapies to restore light sensing to profoundly blind patients suffering from late-stage retinal degenerations: (1) retinal prosthetics, (2) optogenetics, and (3) chemical photoswitches. Prosthetics are the most mature and the only approach in clinical practice. Prosthetic implants require complex surgical intervention and provide only limited visual resolution but can potentially restore navigational ability to many blind patients. Optogenetics uses viral delivery of type 1 opsin genes from prokaryotes or eukaryote algae to restore light responses in survivor neurons. Targeting and expression remain major problems, but are potentially soluble. Importantly, optogenetics could provide the ultimate in high-resolution vision due to the long persistence of gene expression achieved in animal models. Nevertheless, optogenetics remains challenging to implement in human eyes with large volumes, complex disease progression, and physical barriers to viral penetration. Now, a new generation of photochromic ligands or chemical photoswitches (azobenzene-quaternary ammonium derivatives) can be injected into a degenerated mouse eye and, in minutes to hours, activate light responses in neurons. These photoswitches offer the potential for rapidly and reversibly screening the vision restoration expected in an individual patient. Chemical photoswitch variants that persist in the cell membrane could make them a simple therapy of choice, with resolution and sensitivity equivalent to optogenetics approaches. A major complexity in treating retinal degenerations is retinal remodeling: pathologic network rewiring, molecular reprogramming, and cell death that compromise signaling in the surviving retina. Remodeling forces a choice between upstream and downstream targeting, each engaging different benefits and defects. Prosthetics and optogenetics can be implemented in either mode, but the use of chemical photoswitches is currently limited to downstream implementations. Even so, given the high density of human foveal ganglion cells, the ultimate chemical photoswitch treatment could deliver cost-effective, high-resolution vision for the blind.

Synapse Classification And Localization In Electron Micrographs

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Synapse-classification_

We have a new publication, Synapse Classification And Localization In Electron Micrographs in Pattern Recognition Letters.  Authors are: Vignesh Jagadeesh, James Anderson, Bryan W. Jones, Robert Marc, Steven Fisher and B.S. Manjunath.

Abstract:  Classification and detection of biological structures in Electron Micrographs (EM) is a relatively new large scale image analysis problem. The primary challenges are in modeling diverse visual characteristics and development of scalable techniques. In this paper we propose novel methods for synapse detection and localization, an important problem in connectomics. We first propose an attribute based descriptor for characterizing synaptic junctions. These descriptors are task specific, low dimensional and can be scaled across large image sizes. Subsequently, techniques for fast localization of these junctions are proposed. Experimental results on images acquired from a mammalian retinal tissue compare favorably with state of the art descriptors used for object detection.

Retinal connectomics: A New Era For Connectivity Analysis in The New Visual Neurosciences

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New-Visual-Neurosciences

We have a new publication, this one a chapter titled: Retinal connectomics: A New Era For Connectivity Analysis in The New Visual Neurosciences (A little cheaper on Amazon here) textbook.  Authors are Robert E. Marc, Bryan W. Jones, James S. Lauritzen, Carl B. Watt and James R. Anderson.

Retinal Connectomics: Toward Complete, Accurate Networks

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Retinal Connectomics_600

We have a new publication, Retinal connectomics: Toward complete, accurate networks in Progress in Retinal and Eye Research.  Authors are:  Robert E. Marc, Bryan W. Jones, Carl B. Watt, Crystal Sigulinsky, James R. Anderson and J. Scott Lauritzen.

Abstract:
Connectomics is a strategy for mapping complex neural networks based on high-speed automated electron optical imaging, computational assembly of neural data volumes, web-based navigational tools to explore 1012-1015 byte (terabyte to petabyte) image volumes, and annotation and markup tools to convert images into rich networks with cellular metadata. These collections of network data and associated metadata, analyzed using tools from graph theory and classification theory, can be merged with classical systems theory, giving a more completely parameterized view of how biologic information processing systems are implemented in retina and brain. Networks have two separable features: topology and connection attributes. The first findings from connectomics strongly validate the idea that the topologies complete retinal networks are far more complex than the simple schematics that emerged from classical anatomy. In particular, connectomics has permitted an aggressive refactoring of the retinal inner plexiform layer, demonstrating that network function cannot be simply inferred from stratification; exposing the complex geometric rules for inserting different cells into a shared network; revealing unexpected bidirectional signaling pathways between mammalian rod and cone systems; documenting selective feedforward systems, novel candidate signaling architectures, new coupling motifs, and the highly complex architecture of the mammalian AII amacrine cell. This is but the beginning, as the underlying principles of connectomics are readily transferrable to non-neural cell complexes and provide new contexts for assessing intercellular communication.