Category Archives: Retinal Remodeling

Preprint: Neural Circuit Revision in Retinal Remodeling, A Pathoconnectomics Approach

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We have a new preprint out, Neural Circuit Revision in Retinal Remodeling, A Pathoconnectomics Approach.

Authors: Rebecca L Pfeiffer, Jeebika Dahal, Crystal L Sigulinsky, James R Anderson, Isabel A Barrera, Jia-Hui Yang, Olivia Haddadin, Alexis R Houser, Jessica C Garcia, Bryan William Jones

Abstract: The Aii glycinergic amacrine cell (Aii) plays a central role in bridging rod pathways with cone pathways, enabling an increased dynamic range of vision from scotopic to photopic ranges. The Aii integrates scotopic signals via chemical synapses from rod bipolar cells (RodBCs) onto the arboreal processes of Aii ACs, injecting signals into ON-cone bipolar cells (CBbs) via gap junctions with Aiis on the arboreal processes and the waist of the Aii ACs. The CBbs then carry this information to ON and OFF ganglion cell classes. In addition, the Aii is involved in the surround inhibition of OFF cone bipolar cells (CBas) through glycinergic chemical synapses from Aii ACs onto CBas. We have previously shown changes in RodBC connectivity as a consequence of rod photoreceptor degeneration in a pathoconnectome of early retinal degeneration: RPC1. Here, we evaluated the impact of rod photoreceptor degeneration on the connectivity of the Aii to determine the impacts of photoreceptor degeneration on the downstream network of the neural retina and its suitability for integrating therapeutic interventions as rod photoreceptors are lost. Previously, we reported that in early retinal degeneration, prior to photoreceptor cell loss, Rod BCs make pathological gap junctions with Aiis. Here, we further characterize this altered connectivity and additional shifts in both the excitatory drive and gap junctional coupling of Aiis in retinal degeneration, along with discussion of the broader impact of altered connectivity networks. New findings reported here demonstrate that Aiis make additional gap junctions with CBas increasing the number of BC classes that make pathological gap junctional connectivity with Aiis in degenerating retina. In this study, we also report that the Aii, a tertiary retinal neuron alters their synaptic contacts early in photoreceptor degeneration, indicating that rewiring occurs in more distant members of the retinal network earlier in degeneration than was previously predicted. This rewiring impacts retinal processing, presumably acuity, and ultimately its ability to support therapeutics designed to restore image-forming vision. Finally, these Aii alterations may be the cellular network level finding that explains one of the first clinical complaints from human patients with retinal degenerative disease, an inability to adapt back and forth from photopic to scotopic conditions.

Metabolic changes and retinal remodeling in Heterozygous CRX mutant cats (CRXRDY/+)

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We have a new manuscript from the lab in Experimental Eye Research, (PubMed link here). Metabolic changes and retinal remodeling in Heterozygous CRX mutant cats (CRXRDY/+). This manuscript is in collaboration with the Simon Petersen-Jones lab out of Michigan State University.  Authors are: Laurence M. Occelli, Bryan W. Jones @BWJones, Taylor J. Cervantes, and Simon M. Petersen-Jones. The PDF is here.

Abstract: CRX is a transcription factor essential for normal photoreceptor development and survival. The CRXRdy cat has a naturally occurring truncating mutation in CRX and is a large animal model for dominant Leber congenital amaurosis. This study investigated retinal remodeling that occurs as photoreceptors degenerate. CRXRdy/+ cats from 6 weeks to 10 years of age were investigated. In vivo structural changes of retinas were analyzed by fundus examination, confocal scanning laser ophthalmoscopy and spectral domain optical coherence tomography. Histologic analyses including immunohistochemistry for computational molecular phenotyping with macromolecules and small molecules. Affected cats had a cone-led photoreceptor degeneration starting in the area centralis. Initially there was preservation of inner retinal cells such as bipolar, amacrine and horizontal cells but with time migration of the deafferented neurons occurred. Early in the process of degeneration glial activation occurs ultimately resulting in formation of a glial seal. With progression the macula-equivalent area centralis developed severe atrophy including loss of retinal pigmentary epithelium. Microneuroma formation occurs in advanced stages as more marked retinal remodeling occurred. This study indicates that retinal degeneration in the CrxRdy/+ cat retina follows the progressive, phased revision of retina that have been previously described for retinal remodeling. These findings suggest that therapy dependent on targeting inner retinal cells may be useful in young adults with preserved inner retinas prior to advanced stages of retinal remodeling and neuronal cell loss.

Müller Cell Connectomics In Health And Disease

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This talk was presented today, April 25th at the 2023 Association for Research in Vision and Opthalmology (ARVO) meetings in New Orleans, Louisiana by Rebecca Pfeiffer as part of an ARVO Minisymposium Bryan William Jones organized.

Abstract: Muller cells are a critical component of retinal function and rapidly change metabolically and morphologically in retinal disease. Of Muller cell functions, many require close physical relationships between the Muller cell and the synapses of the neurons they support. Despite this required neuro-glial relationship, little is known about the direct contacts between Muller cells and synapses in healthy or diseased retinas. In order to address this, I use a connectomics/pathoconnectomics approach to reconstruct Muller cells and their neighboring synapses. The retinas evaluated are from a healthy rabbit, retinal connectome 1 (RC1), and from the P347L rabbit model of retinitis pigmentosa, retinal pathoconnectome 1 (RPC1). Preliminary data demonstrate an increase in endfoot entanglement in RPC1 when compared with RC1, and direct synaptic contact analysis of both connectomes is ongoing.

Current Perspective on Retinal Remodeling: Implications for Therapeutics

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We have a new paper out of the lab, a perspectives paper on Retinal Remodeling: Implications for Therapeutics. (pdf here).

Authors are Rebecca L. Pfeiffer @BeccaPfeiffer19, and Bryan W. Jones @BWJones.

Abstract: The retinal degenerative diseases retinitis pigmentosa and age-related macular degeneration are a leading cause of irreversible vision loss. Both present with progressive photoreceptor degeneration that is further complicated by processes of retinal remodeling. In this perspective, we discuss the current state of the field of retinal remodeling and its implications for vision-restoring therapeutics currently in development. Here, we discuss the challenges and pitfalls retinal remodeling poses for each therapeutic strategy under the premise that understanding the features of retinal remodeling in totality will provide a basic framework with which therapeutics can interface. Additionally, we discuss the potential for approaching therapeutics using a combined strategy of using diffusible molecules in tandem with other vision-restoring therapeutics. We end by discussing the potential of the retina and retinal remodeling as a model system for more broadly understanding the progression of neurodegeneration across the central nervous system.

Model-Based Comparison of Current Flow in Rod Bipolar Cells of Healthy and Early-Stage Degenerated Retina

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We have a new manuscript out in Experimental Eye Research, Model-Based Comparison of Current Flow in Rod Bipolar Cells of Healthy and Early-Stage Degenerated Retina. (pdf here)

Authors: Pragya Kosta, Ege Iseri, Kyle Loizos, Javad Paknahad, Rebecca L. Pfeiffer @BeccaPfeiffer19, Crystal L. Sigulinsky @CLSigulinsky, James R. Anderson, Bryan W. Jones @BWJones, and Gianluca Lazzi.

Abstract: Retinal degenerative diseases, such as retinitis pigmentosa, are generally thought to initiate with the loss of photoreceptors, though recent work suggests that plasticity and remodeling occurs prior to photoreceptor cell loss. This degeneration subsequently leads to death of other retinal neurons, creating functional alterations and extensive remodeling of retinal networks. Retinal prosthetic devices stimulate the surviving retinal cells by applying external current using implanted electrodes. Although these devices restore partial vision, the quality of restored vision is limited. Further knowledge about the precise changes in degenerated retina as the disease progresses is essential to understand how current flows in retinas undergoing degenerative disease and to improve the performance of retinal prostheses. We developed computational models that describe current flow from rod photoreceptors to rod bipolar cells

 

Model-based Comparison of Current Flow in Rod Bipolar Cells of Healthy and Early-Stage Degenerated Retina

A pathoconnectome of early neurodegeneration: Network changes in retinal degeneration

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We have a new manuscript out in Experimental Eye Research, A pathoconnectome of early neurodegeneration: Network changes in retinal degeneration. (pdf here)

Authors: Rebecca L. Pfeiffer @BeccaPfeiffer19, James R. Anderson, Jeebika Dahal, Jessica C. Garcia, Jia-Hui Yang, Crystal L. Sigulinsky @CLSigulinsky, Kevin Rapp, Daniel P. Emrich, Carl B. Watt, Hope AB Johnstun, Alexis R. Houser, Robert E. Marc @robertmarc60, and Bryan W. Jones @BWJones.

Abstract: Connectomics has demonstrated that synaptic networks and their topologies are precise and directly correlate with physiology and behavior. The next extension of connectomics is pathoconnectomics: to map neural network synaptology and circuit topologies corrupted by neurological disease in order to identify robust targets for therapeutics. In this report, we characterize a pathoconnectome of early retinal degeneration. This pathoconnectome was generated using serial section transmission electron microscopy to achieve an ultrastructural connectome with 2.18nm/px resolution for accurate identification of all chemical and gap junctional synapses. We observe aberrant connectivity in the rod-network pathway and novel synaptic connections deriving from neurite sprouting. These observations reveal principles of neuron responses to the loss of network components and can be extended to other neurodegenerative diseases.

 

Müller Cell Metabolic Signatures: Evolutionary Conservation and Disruption in Disease

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We have a new manuscript out in Trends in Endocrinology & Metabolism, Müller Cell Metabolic Signatures: Evolutionary Conservation and Disruption in Disease.

Authors: Rebecca L. Pfeiffer @BeccaPfeiffer19, Robert E. Marc @robertmarc60, and Bryan William Jones @BWJones.

This manuscript functions as both a review and presents some exciting new data demonstrating how the glutamate cycle is disrupted during retinal degenerative disease.

Abstract: Müller cells are glia that play important regulatory roles in retinal metabolism. These roles have been evolutionarily conserved across at least 300 million years. Müller cells have a tightly locked metabolic signature in the healthy retina, which rapidly degrades in response to insult and disease. This variation in metabolic signature occurs in a chaotic fashion, involving some central metabolic pathways. The cause of this divergence of Müller cells, from a single class with a unique metabolic signature to numerous separable metabolic classes, is currently unknown and illuminates potential alternative metabolic pathways that may be revealed in disease. Understanding the impacts of this heterogeneity on degenerate retinas and the implications for the metabolic support of surrounding neurons will be critical to long-term integration of retinal therapeutics for the restoration of visual perception following photoreceptor degeneration.

Pathoconnectome Analysis of Müller Cells in Early Retinal Remodeling

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We have a new manuscript out in Clinical Neurophysiology, An Update on Retinal Prostheses. PubMedDirect Link PDF here.

Authors: Rebecca L Pfeiffer, James R Anderson, Daniel P Emrich, Jeebika Dahal, Crystal L Sigulinsky, Hope AB Morrison, Jia-Hui Yang, Carl B Watt, Kevin D Rapp, Mineo Kondo, Hiroko Terasaki, Jessica C Garcia, Robert E Marc, and Bryan W Jones.

Abstract: Glia play important roles in neural function, including but not limited to amino acid recycling, ion homeostasis, glucose metabolism, and waste removal. During retinal degeneration and subsequent retinal remodeling, Müller cells (MCs) are the first cells to show metabolic and morphological alterations in response to stress. Metabolic alterations in MCs chaotically progress in retina undergoing photoreceptor degeneration; however, what relationship these alterations have with neuronal stress, synapse maintenance, or glia-glia interactions is currently unknown. The work described here reconstructs a MC from a pathoconnectome of early retinalremodeling retinalpathoconnectome 1 (RPC1) and explores relationships between MC structural and metabolic phenotypes in the context of neighboring neurons and glia. Here we find variations in intensity of osmication inter- and intracellularly, variation in small molecule metabolic content of MCs, as well as morphological alterations of glial endfeet. RPC1 provides a framework to analyze these relationships in early retinal remodeling through ultrastructural reconstructions of both neurons and glia. These reconstructions, informed by quantitative metabolite labeling via computational molecular phenotyping (CMP), allow us to evaluate neural-glial interactions in early retinal degeneration with unprecedented resolution and sensitivity.

 

 

Persistent Remodeling And Neurodegeneration In Late-Stage Retinal Degeneration

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We have a new manuscript out in Progress In Retinal And Eye Research, Persistent Remodeling And Neurodegeneration In Late-Stage Retinal Degeneration.

Authors: Rebecca L. Pfeiffer, Robert E. Marc, and Bryan William Jones.

I’m really proud of the work that Becca did on this manuscript.  It does a couple of important things including summarizing the field of retinal remodeling, but also introducing some new data that plants a flag to define retinal degeneration and retinal remodeling as the first steps in what becomes progressive neurodegeneration.  We view the retina as an excellent model to begin exploring diseases like Alzheimer’s, Parkinson’s, and other progressive neurodegenerative diseases.  In addition, Becca also demonstrates a new potential mechanism for misfolded proteins, that may point the way for how proteinopathies spread.

Abstract: Retinal remodeling is a progressive series of negative plasticity revisions that arise from retinal degeneration, and are seen in retinitis pigmentosa, age-related macular degeneration and other forms of retinal disease. These processes occur regardless of the precipitating event leading to degeneration. Retinal remodeling then culminates in a late-stage neurodegeneration that is indistinguishable from progressive central nervous system (CNS) proteinopathies. Following long-term deafferentation from photoreceptor cell death in humans, and long-lived animal models of retinal degeneration, most retinal neurons reprogram, then die. Glial cells reprogram into multiple anomalous metabolic phenotypes. At the same time, survivor neurons display degenerative inclusions that appear identical to progressive CNS neurodegenerative disease, and contain aberrant α-synuclein (α-syn) and phosphorylated α-syn. In addition, ultrastructural analysis indicates a novel potential mechanism for misfolded protein transfer that may explain how proteinopathies spread. While neurodegeneration poses a barrier to prospective retinal interventions that target primary photoreceptor loss, understanding the progression and time-course of retinal remodeling will be essential for the establishment of windows of therapeutic intervention and appropriate tuning and design of interventions. Finally, the development of protein aggregates and widespread neurodegeneration in numerous retinal degenerative diseases positions the retina as a ideal platform for the study of proteinopathies, and mechanisms of neurodegeneration that drive devastating CNS diseases.

Coupling Architecture Of The AII/ON Cone Bipolar Cell Network In Degenerate Retina

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This abstract was presented today, April 8th at the 2019 Association for Research in Vision and Opthalmology (ARVO) meetings in Vancouver, Canada as a platform presentation by Crystal L. Sigulinsky, Rebecca L. Pfeiffer, James R. Anderson, Daniel P. Emrich, Christopher Rapp, Jeebika Dahal, Jessica Garcia, Hope Morrison, Kevin D. Rapp, Jia-Hui Yang, Carl B. Watt, Robert E. Marc and Bryan W. Jones.

Purpose
In mouse models of retinal degeneration, connexin36-containing gap junctions in the Aii amacrine cell network appear to mediate aberrant hyperactivity within the retina. However, it remains unclear whether this hyperactivity reflects changes in the underlying circuitry or dysfunction of the normative circuitry. Our connectomics-based mapping of retinal circuitry in rabbit Retinal Connectome 1 (RC1) has dramatically expanded the coupled Aii network. In addition to canonical Aii-to-Aii and Aii-to-ON cone bipolar cell (CBC) coupling, we describe pervasive in- and cross-class coupling motifs among ON CBCs. This study examines the changes in these coupling motifs in RPC1, an ultrastructural retinal pathoconnectome from a rabbit model of retinitis pigmentosa.

Methods
RC1 and RPC1 are connectomes built by automated transmission electron microscopy at ultrastructural (2 nm/pixel) resolution. RC1 is a 0.25 mm diameter volume of retina from a 13 month old, light-adapted female Dutch Belted rabbit and serves as the healthy reference connectome. RPC1 is a 0.09 mm diameter volume of pathological retina from a 10 month old, male transgenic P347L model of autosomal dominant retinitis pigmentosa showing early phase 1 retinal remodeling, when rod photoreceptors are still present, but stressed. ON CBCs, Aii amacrine cells, and their coupling partners were annotated using the Viking application. Coupling motifs and features were explored with 3D rendering and graph visualization of connectivity. Gap junctions were validated by 0.25 nm resolution recapture with goniometric tilt when necessary.

Results
All major coupling motifs were observed. Several ON CBC classes retained their class-specific coupling profiles, accepting and rejecting specific combinations of Aii and ON CBC class partnerships. However, aberrant partnerships exist in the coupled network, including both loss of prominent motifs and acquisition of novel ones.

Conclusions
Clearly aberrant morphological and synaptic changes exist in RPC1, including changes in the coupling specificity and gap junction distributions of both Aii amacrine cells and ON CBCs. This indicates that the Aii/ON CBC circuit topology is already altered during early phase 1 remodeling, with substantial implications for therapeutic interventions for blinding diseases that depend upon the surviving retinal network in human patients.