Category Archives: Retinal Disease

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

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. PfeifferJames 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.

Aii Amacrine Cell Connectivity in Degenerating Retina

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

Full resolution version here.

Purpose
Aii amacrine cells (Aii ACs) function in mediating scotopic vision via connection of rod bipolar cells (Rod BCs) to cone bipolar cell pathways. The purpose of this project is to determine the effect of retinal degeneration (RD) on Aii AC networks. We explore this in a pathoconnectome of early RD (RPC1), using a connectome of healthy retina (RC1) as control. Cells in each volume are evaluated by comparison of morphology, synaptic connectivity, and eventually network analysis.

Methods
Tissue for RPC1 was collected from a 10 month old transgenic p347L rabbit model of autosomal dominant retinitis pigmentosa. RC1 was collected from a 13 month old Dutch-Belted rabbit, with no indications of degeneration. Tissue was fixed in a mixed aldehyde solution, before subsequent dehydration, osmication, and resin embedding. Volumes were sectioned at 70nm (RPC1) and 90nm (RC1) and placed on formvar grids. 1 section was reserved from every 30 TEM sections for computational molecular phenotyping where it was placed on a slide and probed for small molecules or proteins. TEM sections were captured at 2.18nm/px using SerialEM software on a JEOL JEM-1400 TEM. The RC1 volume has a diameter of 250µm and RPC1 has a diameter of 90µm. Both volumes were analyzed using the Viking software suite.

Results
In this study, Aii ACs from RPC1 were compared to RC1. Initial results indicate no distinct difference in the morphology other than arbor size, which are likely due to eccentricity differences between volumes. However, in RPC1, we observe multiple instances of Aii AC coupling with Rod BCs in the ON region of the IPL. In contrast, Rod BCs never form gap junctions in healthy retina.

Conclusions
Coupling between Aii ACs and Rod BCs in RPC1 is a unique change in retinal network topology occurring in early RD. Further exploration of network changes as a response to RD is warranted, as many therapeutic interventions currently in development rely upon maintenance of inner retinal circuitry. Prior research demonstrates Rod BCs extend dendrites towards cones and change their receptor expression as rods degenerate. Therefore, knowing the network changes involving Aii ACs and their associations with bipolar cells is crucial to understanding how photoreceptor degeneration affects inner retinal visual processing.

OFF-layer Branches of ON Cone Bipolar Cells in Early Retinal Degeneration

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

Full resolution version here.

Purpose: Cone bipolar cells are customarily classified into superclasses of ON (ON-BCs) and OFF (OFF-BCs). ON or OFF specialization is further segregated by stratification within the inner plexiform layer. Retinal degeneration induces negative plasticity termed remodeling, that includes aberrant neurite extension from multiple cell types (rewiring) and ON-BCs switching their glutamate receptors to match that of OFF-BCs (reprogramming). Previous analysis in healthy retina shows that ON-BCs can make small ribbon synapses in the descending axon or, less frequently, simple single branch projections in the OFF layer. What impact remodeling has on these OFF-layer branches is unknown. In this study, we compare OFF branches from ON-BCs in a connectome of early retinal degeneration (RPC1) to our healthy retinal connectome (RC1).

Methods: Retinal tissues selected for RC1 and RPC1 were collected post-mortem from a 13 month old Dutch-belted healthy female rabbit and a male 10 month old transgenic P347L rabbit model of autosomal dominant retinitis pigmentosa, respectively. RPC1 shows signs of remodeling including rod outer-segment degeneration and aberrant neurite extension. Tissues were fixed in mixed aldehydes and subsequently osmicated, dehydrated, resin embedded, and sectioned at 90 nm (RC1) or 70 nm (RPC1). Sections were placed on formvar grids, stained, and imaged at 2nm/px on a JEOL JEM-1400 TEM using SerialEM software. 1 section was reserved from every 30 for Computational Molecular Phenotyping, and probed for small molecules. Both volumes were evaluated using the Viking software suite.

Results: Ribbons of ON-BCs formed in the OFF layer branches have been previously described to contact glycinergic amacrine cells (ACs), GABAergic ACs, ON ganglion cells, and intrinsically photosensitive ganglion cells. Initial analysis of OFF branches of ON-BCs in RPC1 demonstrate more complex branching than in RC1 and increased number of synapses on these branches. In contrast to the inconsistent OFF layer branch stratification observed in RC1, the OFF branches in RPC1 appear to stratify at a similar level. Evaluation of synaptic partners is ongoing.

Conclusions: Increased complexity and number of synapses found in the OFF branches of some ON-BCs ultimately may represent ON network corruption. Exploring synaptic partners will reveal potential network alterations in retinal degenerative disease.

Rod Bipolar Cell Networks In A Retinal Pathoconnectome

We presented a poster on Rod Bipolar Cell Networks In A Retinal Pathoconnectome at the 2019 HHMI Connectomics meeting in Berlin today. Downsampled PDF of poster here.

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

Abstract: Ultrastructural connectomics has allowed for precise identification of neural network topologies in retina, exposing synaptic connectivity associated with specific pathways involved in neural retinal processing. In pathological degenerate retina such as retinitis pigmentosa (RP), retinal remodeling emerges as a phenomenon through a series of negative plasticity events originating from neural deafferentation initiated by photoreceptor degeneration. Early stages of remodeling include glial changes, GluR receptor alterations (reprogramming), and rewiring of retinal networks. The connectivities initiated by these processes are currently unknown. To address this problem, we have created an ultrastructural pathoconnnectome of early retinal remodeling in a rabbit model of retinitis pigmentosa, Retinal Pathoconnectome 1 (RPC1).

Rod Bipolar Cell Networks in Early Retinal Remodeling

Rebecca Pfeiffer, a post-doc in the laboratory presented her work on “Rod Bipolar Cell Networks in Early Retinal Remodeling” as a platform presentation at the ISER 2018 meeting in Belfast, Northern Ireland.

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

Abstract: Retinal remodeling is a form of negative plasticity that occurs as a consequence of retinal degenerative diseases. Part of retinal remodeling involves anomalous sprouting of processes, termed neurites. The synaptic structures and partners of the neurites are not yet defined, leading to uncertainty about the consistency of network motifs between healthy and degenerate retina. Our goal is to map out the identities and network relationships of bipolar cell networks using a connectomics strategy. Retinal connectomes or ultrastructural maps of neuronal connectivity have substantially contributed to our understanding of retinal network topology, providing ground truth against which pathological network topologies can be evaluated. We have generated the first pathoconnectome (RPC1), or connectome of pathological tissues, of early retinal remodeling at 2nm/pixel, and are currently investigating the impact of remodeling on network architecture.
The tissue for RPC1 was obtained from a 10mo transgenic P347L rabbit model of autosomal dominant retinitis pigmentosa. Tissue was fixed in mixed aldehydes, osmicated, dehydrated, embedded in epon resin, and sectioned at 70nm. Serial sections were placed on grids, stained, and imaged using a JEOL JEM-1400 TEM using SerialEM software. Every 30th section was reserved for computational molecular phenotyping (CMP), and probed for small molecules: glutamate, glutamine, glycine, GABA, taurine, glutathione; or TEM compatible proteins GFAP and GS. The pathoconnectome volume is explored and annotated using the Viking software suite.
RPC1 was selected as an example of early retinal remodeling, demonstrating Muller cell hypertrophy, metabolic dysregulation, and degeneration of rod outer segments, indicating phase 1 remodeling and neuronal sprouting. We have observed the presence of both cone pedicles and rod spherules within the OPL to be synaptically active with neurites from some rod bipolar cells forming functional synapses with both rod spherules and cone pedicles. These rod bipolar cells also exhibit structurally altered ribbon synapses. We are currently evaluating network motifs and comparing them to networks established from our previous connectome, RC1, generated from a healthy rabbit.
These findings allow us to evaluate and analyze the impact of retinal remodeling on retinal networks which may have important implications for therapeutic interventions being developed which rely on inner retina network integrity.

Pathoconnectome Analysis of Müller Cells in Early Retinal Remodeling

Rebecca Pfeiffer, a post-doc in the laboratory presented her work on “Pathoconnectome Analysis of Müller Cells in Early Retinal Remodeling” as a platform presentation at the RD2018 meeting in Killarney, Ireland.

Authors: Rebecca 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.

Purpose: Glia play important roles in neural system function. These roles include, but are not limited to: amino acid recycling, ion homeostasis, glucose transport, and removal of waste. During retinal degeneration, Muller cells, the primary macroglia of the retina, are one of the first cells to show metabolic and morphological alterations in response to retinal stress. The metabolic alterations observed in Muller cells appear to manifest in regions of photoreceptor degeneration; however, the precise mechanisms that govern these alterations in response to neuronal stress, synapse maintenance, or glia-glia interactions is currently unknown.  This project aims to reconstruct Muller cells from a pathoconnectome of early retinal remodeling at 2nm/pixel with ultrastructural metabolic data to determine the relationship of structural and metabolic phenotypes between neighboring neurons and glia.

Methods:  Retinal pathoconnectome 1 (RPC1) is the first connectome to be assembled from pathologic neural tissue (a pathoconnectome). The tissue selected for RPC1 was collected post mortem from a 10 month transgenic P347L rabbit model of autosomal dominant retinitis pigmentosa, fixed in 1% formaldehyde, 2.5% glutaraldehyde, 3% sucrose, and 1mM MgSO4 in cacodylate buffer (pH 7.4). The tissue was subsequently osmicated, dehydrated, resin embedded, and sectioned at 70nm. Sections were placed on formvar grids, stained, and imaged at 2nm/pixel on a JEOL JEM-1400 TEM using SerialEM software. 1 section was reserved from every 30 sections for CMP, where it was placed on a slide and probed for small molecules: glutamate, glutamine, glycine, GABA, taurine, glutathione; or TEM compatible proteins GFAP and GS. The pathoconnectome volume was evaluated and annotated using the Viking software suite.

Results: RPC1 demonstrates hallmarks of early retinal degeneration and remodeling, including the glial phenotypes of hypertrophy and metabolic variation between neighboring Muller cells. Early evaluation of these glia demonstrates variations in osmication in Muller cells as well as apparent encroachment of glial end-feet on one another.  We are currently in the process of reconstructing multiple Muller cells within RPC1 and their neighboring neurons.  Once complete, we will assess the relationship between Muller cell phenotype and the phenotypes of contacted neuronal and glial neighbors.

Conclusions: How neural-glial relationships are affected by retinal remodeling may help us understand why remodeling and neurodegeneration follow photoreceptor degeneration. In addition, determining these relationships during remodeling will be crucial to developing therapeutics with long-term success. RPC1 provides a framework to analyze these relationships in early retinal remodeling through ultrastructural reconstructions of all neurons and glia in an intact retina. These reconstructions, informed by quantitative metabolite labeling, will allow us to evaluate these neural-glial interactions more comprehensively than other techniques have previously allowed.

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

Crystal Sigulinsky, a post-doc in the lab, presented her work on “coupling architecture of the
Aii/ON cone bipolar cell network in the degenerate retina” at the RD2018 meeting in Killarney, Ireland today.  Authors are: Crystal L Sigulinsky, Rebecca L Pfeiffer, James R Anderson, Jeebika Dahal, Hope Morrison, Daniel P. Emrich, Jessica C Garcia, Jia-Hui Yang, Carl B. Watt, Kevin D. Rapp, Mineo Kondo, Hiroko Terasaki, Robert E. Marc, and Bryan W. Jones.

Purpose: Retinal network hyperactivity within degenerative retinal networks is a component of the disease process with implications for therapeutic interventions for blinding diseases that depend upon the surviving retinal network. Connexin36-containing gap junctions centered on the Aii amacrine cell network appear to mediate the aberrant signaling observed in mouse models of retinal degeneration. However, it remains unclear whether this hyperactivity reflects changes in the underlying circuitry or dysfunction/dysregulation of the normative circuitry. Mapping retinal circuitry in the ultrastructural rabbit Retinal Connectome, RC1, has revealed Aii network topologies explicitly involving gap junctions. 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 that extend and dramatically expand the coupled Aii network topologies. Since virtually every gap junction in the inner plexiform layer contains Connexin36, these circuits likely participate in the aberrant signaling of degenerate retinas. This study examines these Aii and ON CBC coupling motifs in Retinal PathoConnectome 1 (RPC1), an ultrastructural pathoconnectome of a rabbit model of retinitis pigmentosa.

Approach: RPC1 is a 2nm/pixel resolution volume of retina from a 10 month old, transgenic P347L rabbit model of autosomal dominant retinitis pigmentosa in early phase 1 retinal remodeling, a time point where cone and rod photoreceptors are still present, albeit going through cell stress. RPC1 spans the vitreous to basal outer nuclear layer and was built by automated transmission electron microscopy and computational assembly. ON CBCs, Aii amacrine cells, and their coupling partners were annotated using the Viking application and explored with 3D rendering and graph visualization of connectivity. Gap junctions were validated by 0.25 nm resolution recapture with goniometric tilt when necessary. Motifs were compared to those discovered in RC1. RC1 is a 2 nm resolution, 0.25 mm diameter volume of a light-adapted adult female Dutch Belted rabbit retina spanning the ganglion cell through inner nuclear layers.

Conclusions: RPC1 shows degeneration of rod outer segments, Müller cell hypertrophy and neuronal sprouting, characteristic of early stage retinal degeneration and phase 1 remodeling, when retinal hyperactivity and its reliance on gap junctional coupling has likely already initiated and human patients would still have some vision. All major coupling motifs (Aii-to-Aii, Aii-to-ON CBC, and ON CBC-to-ON CBC) were observed. Preliminary examinations indicate that several ON CBC classes retained their class-specific coupling profiles, accepting and rejecting specific combinations of Aii and ON CBC class partnerships. However, recent findings reveal aberrant partnerships in the coupled network, including both loss of prominent motifs and acquisition of novel ones. Thus, clear aberrant morphological and synaptic changes have been identified in RPC1, including changes in the coupling specificity and gap junction distributions of both Aii amacrine cells and ON CBCs (Figure 6). This suggests that the Aii/ON CBC circuit topology is already altered during early phase 1 remodeling, with substantial implications for therapeutic interventions in human subjects. The full coupling network is actively being examined and progress has begun on RPC2, a second pathoconnectome for examining later, phase 2 remodeling in this same model.

An almost full size poster available here in pdf format.

A Pathoconnectome of Early Retinal Remodeling

This abstract was presented today, Monday, April 30th at the 2018 Association for Research in Vision and Opthalmology (ARVO) meetings in Honolulu, Hawaii by Rebecca Pfeiffer, Robert E. Marc, James R. Anderson, Daniel P. Emrich, Carl B. Watt, Jia-Hui Yang, Kevin D. Rapp, Jeebika Dahal, Mineo Kondo, Hiroko Terasaki, and Bryan W. Jones.

Purpose:
Retinal remodeling is a consequence of retinal degenerative disease, during which neurons sprout new neurites whose synaptic structures and partners are not yet defined. Simultaneously during remodeling, Müller cells (MCs) undergo structural and metabolic changes, whose impact on surrounding neurons is an active area of research. Retinal connectomes have elucidated and validated fundamental networks. These data provide further classification of neuronal types and subtypes and a precise framework for modeling of retinal function, based on ground truth networks. The creation of the first pathoconnectome (RPC1), a connectome from pathological retinal tissue, provides the opportunity to determine connectivites between neurons, while simultaneously evaluating glial remodeling. Computational Molecular Phenotyping (CMP) embedded within the ultrastructure provides metabolic factors of pathologies.

Methods:
RPC1 was collected post-mortem from a 10mo TgP347L rabbit model of adRP, fixed in 1% FA, 2.5% GA, 3% sucrose, and 1mM MgSO4 in cacodylate buffer (pH 7.4). The tissue was osmicated, dehydrated, resin embedded, and sectioned at 70nm. Sections were placed on formvar grids, stained, and imaged on a JEOL JEM-1400 TEM using SerialEM. 1 section was reserved from every 30 section for CMP, where it was probed for small molecules: glutamate, glutamine, glycine, GABA, taurine, glutathione; or proteins GFAP and GS. RPC1 was evaluated using the Viking software suite.

Results:
RPC1 was chosen based on early features of retinal degeneration/remodeling: degeneration of rod OS, MC hypertrophy, and neuronal sprouting. RPC1 consists of 948 serial sections spanning the ONL to the vitreous, with a diameter of 90µm. We find dendrites extending from rod bipolar cells to cone pedicles, originally described in light microscopy, and active synaptic contacts. We also see alterations of synaptic structure in the IPL, and MC morphological changes affecting surface to volume and neuron/glial relationships. Network motifs are being actively investigated.

Conclusions:
We observe many features of remodeling previously described using light microscopy, and confirm active synaptic contact. We also find synaptic structural features, not previously described. In addition, early evaluation of MC morphology demonstrates marked changes in MC shape and associations with nearby neurons and glia, which, combined with CMP, will be instrumental in understanding how MCs affect retinal remodeling.

Impact of Glaucoma On Retinal Ganglion Cell Subtypes: A Single-Cell RNA-seq Analysis of the DBA/2J Mouse

This abstract was presented today, May 1st at the 2018 Association for Research in Vision and Opthalmology (ARVO) meetings in Honolulu, Hawaii by Siamak Yousefi, Hao Chen, Jesse Ingels, Sumana R. Chintalapudi, Megan Mulligan, Bryan W. Jones, Vanessa Marie Morales-Tirado, Pete Williams, Simon W. John, Felix Struebing, Eldon E. Geisert, Monica Jablonski, Lu Lu, Robert Williams

Purpose
We are developing methods to define molecular signatures of cellular stress during early stages of glaucoma for major subtypes of retinal ganglion cells (RGCs). Our first aim is to develop reliable mRNA biomarkers for RGC subtypes in the DBA/2J (D2) mouse model prior to disease onset. Our second objective is to quantify cellular stress in RGC subtypes at early stages of disease using known sets of stress-responsive transcripts (e.g. Struebing et al, 2016 PMID:27733864; Williams et al. 2017, PMID:28209901; Lu et al, ARVO 2018).

Methods
Whole retinas from D2 or D2.Cg-Tg(Thy1-CFP)23Jrs/SjJ at 130 to 150 days-of-age were dissociated gently and size selected (>10 µm). RGCs were enriched using THY1 antibody-coated beads. Fluidigm HT microfluidics plates were used to isolate and generate scRNA-seq libraries of full length polyA-positive mRNAs using SMART-Seq v4. Libraries were sequenced using HiSeq3000, PE151. Following alignment using STAR, expression was normalized to log2(FPKM+1) across ~25,000 unique transcript models. Cells with fewer than 1000 detected genes and genes expressed in fewer than 1% of RGCs were excluded. Sets of genes with high variance and/or high expression were used for principal component analysis (PCA). Twenty PCs were used for graph-based unsupervised clustering and visualized using t-distributed stochastic neighbor embedding (tSNE). Gene specificity was computed for all transcripts across all clusters. The top transcripts per cluster with expression >1 in 1% or more of cells, were used to diagnose cellular identify of clusters. The top 30 genes per cluster were searched in PubMed against a panel of cell and tissue specific terms using Chilibot.

Results
The scRNA-seq protocol generates 150,000 – 200,000 uniquely mapped mRNA reads/cell and ~5000 genes/cells. We currently have 1600 cells, of which over half are RGCs. Around 75% of cells are positive for two or more of the following RGC markers: Thy1, Rbpms, Rbpms2, Jam2, G3bp1, and Ywhaz. This set of cells and different subsets of genes are now being used for RGC clustering. We have identified at least 17 clusters in initial datasets using these protocols and are now linking clusters to major classes of RGCs.

Conclusions
Molecular signatures of cellular stress and RGC subtypes in early stage of glaucoma should now be identifiable using unsupervised learning techniques.

Circuit Remodeling In Retinal Degeneration

This abstract was presented yesterday, April 29th at the 2018 Association for Research in Vision and Opthalmology (ARVO) meetings in Honolulu, Hawaii by Bryan W. Jones.

Abstract:

The retina is a complex, heterocellular tissue with most/all retinal cell classes becoming impacted or altered in retinitis pigmentosa (RP) and age-related macular degeneration (AMD) in a process called retinal remodeling. Defining disease and the stage-specific cytoarchitectural and metabolic responses in RP and AMD is critical for highlighting targets for intervention. We now know that negative plasticity and neural retinal remodeling occurs regardless of retinal insult in models of retinal degeneration as well as in human RP and in human AMD, revealing that no retinal disease fails to trigger remodeling and reprogramming.

Evidence in the literature over the past decade has improved our understanding into mechanisms of initial retinal degeneration and informed our understanding of the subsequent remodeling events in the neural retina that occur post-photoreceptor degeneration. Remodeling associated with retinal degeneration is intimately linked with insults that cause photoreceptor stress and eventually photoreceptor cell death. These phenomena result in reprogramming of cell types in retina followed by progressive neural degeneration akin to CNS neural degenerations involving both neuronal and glial classes. No cell class in the retina is spared from the effects of remodeling. The earliest cell classes involved in remodeling are horizontal, bipolar and Müller cells and the Müller glia are the last cell class left in the remodeling retina.

Our efforts are now focused on elucidating the precise wiring changes in retina, through the creation of pathological connectomes, or “patho-connectomes” to study precisely what the circuit topologies are, compared to normal topologies derived from Retinal Connectome 1 (RC1).  Also, because temporal windows are critical to understanding when interventions may be possible, we are exploring when circuit topology revisions occur to understand their impact on information flow in the retina and their impact on rescues of vision loss.  Precise circuit topologies in early retinal degenerative events is our first area of exploration with ultrastructural reconstructions of outer retinal neurons, bipolar cells and horizontal cells.  Müller glia are also of intense interest as we are tracking the earliest metabolic and morphological changes in glia in response to retinal degenerations.