Happy Holidays from The Marclab for Connectomics. It’s been an amazing year, and we look forward to sharing more science with you in 2020.
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.
Authors: Lauren N. Ayton, Nick Barnes, Gislin Dagnelie, Takashi Fujikado, Georges Goetz, Ralf Hornig, Bryan W. Jones, Mahiul M.K. Muqit, Daniel L. Rathbun, Katarina Stingl, James D. Weiland, Matthew A. Petoe.
Abstract: Retinal prostheses are designed to restore a basic sense of sight to people with profound vision loss. They require a relatively intact posterior visual pathway (optic nerve, lateral geniculate nucleus and visual cor- tex). Retinal implants are options for people with severe stages of retinal degenerative disease such as retinitis pigmentosa and age-related macular degeneration.
There have now been three regulatory-approved retinal prostheses. Over five hundred patients have been implanted globally over the past 15 years. Devices generally provide an improved ability to localize high-contrast objects, navigate, and perform basic orientation tasks. Adverse events have included con- junctival erosion, retinal detachment, loss of light perception, and the need for revision surgery, but are rare. There are also specific device risks, including overstimulation (which could cause damage to the retina) or delamination of implanted components, but these are very unlikely.
Current challenges include how to improve visual acuity, enlarge the field-of-view, and reduce a com- plex visual scene to its most salient components through image processing. This review encompasses the work of over 40 individual research groups who have built devices, developed stimulation strategies, or investigated the basic physiology underpinning retinal prostheses. Current technologies are summarized, along with future challenges that face the field.
This is Kevin Rapp, a technician in the lab running some test captures on our original JEOL transmission electron microscope. This microscope is likely the highest use electron microscope on planet Earth, having been run effectively non-stop for over a decade. This microscope, purchased through a generous gift from Martha Ann Dumke Healey made possible our entire connectomics initiatives.
This is Becca Pfeiffer setting up a test capture on our new JEOL electron microscope. We’ve customized this scope, like our previous scope, and it is taking us a little while to track down some variables with a piece of equipment this complex and hammer them down. My thanks to Becca, Jamie and Kevin for working through this together.
Abstract: Standard automated perimetry (SAP), the most common form of perimetry used in clinical practice, is associated with high test variability, impacting clinical decision making and efficiency. Contrast sensitivity isocontours (CSIs) may reduce test variability in SAP by identifying regions of the visual field with statistically similar patterns of change that can be analysed collectively and allow a point (disease)-to-CSI (normal) comparison in disease assessment as opposed to a point (disease)-to-point (normal) comparison. CSIs in the central visual field however have limited applicability as they have only been described using visual field test patterns with low, 6° spatial sampling. In this study, CSIs were determined within the central 20° visual field using the 10-2 test grid paradigm of the Humphrey Field Analyzer which has a high 2° sampling frequency. The number of CSIs detected in the central 20° visual field was greater than previously reported with low spatial sampling and stimulus size dependent: 6 CSIs for GI, 4 CSIs for GII and GIII, and 3 CSIs for GIV and GV. CSI number and distribution were preserved with age. Use of CSIs to assess visual function in age-related macular degeneration (AMD) found CSI guided analysis detected a significantly greater deviation in sensitivity of AMD eyes from normal compared to a standard clinical pointwise comparison (−1.40 ± 0.15 dB vs −0.96 ± 0.15 dB; p < 0.05). This work suggests detection of CSIs within the central 20° is dependent on sampling strategy and stimulus size and normative distribution limits of CSIs can indicate significant functional deficits in diseases affecting the central visual field such as AMD.
This is one of our undergraduates Jeebika Dahal, working to annotate in one of our pathoconnectomics databases. This work is helping us to understand how neural degenerative disease changes wiring, and corrupts processing in neural systems. We work in retina, but the principles apply to all neural systems with implications for Alzheimer’s, Parkinson’s, amyotrophic lateral sclerosis, epilepsy, and more.
Originally posted on Jonesblog.
We have a new manuscript out in Progress In Retinal And Eye Research, Persistent Remodeling And Neurodegeneration In Late-Stage Retinal Degeneration.
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.
This poster was presented today, July 28th at the 2019 International Gap Junction Conference in Victoria, Canada by Crystal L. Sigulinsky, Rebecca L. Pfeiffer, James R. Anderson, Christopher Rapp, Jeebika Dahal, Jessica C Garcia, Jia-Hui Yang, Daniel P. Emrich, Hope Morrison, Kevin D. Rapp, Carl B. Watt, Mineo Kondo, Hiroko Terasaki, Robert E. Marc and Bryan W. Jones.
Almost full resolution version here.
Crystal L Sigulinsky1, Rebecca L Pfeiffer1, James R. Anderson1, Christopher N. Rapp1, Jeebika Dahal1, Jessica C Garcia1, Jia-Hui Yang1, Daniel P. Emrich1, Hope Morrison1, Kevin D. Rapp1, Carl B. Watt1, Mineo Kondo2, Hiroko Terasaki3, Robert E. Marc1, Bryan W. Jones1
1Moran Eye Center/ Ophthalmology, University of Utah, Salt Lake City, Utah, United States; 2Mie University, Tsu, Japan; 3Nagoya University, Nagoya-shi, Japan;
Background and aim:
Gap junctions are prevalent throughout the neural retina, with expression by every major neuronal class and at every level of signal processing. Yet, the functional roles and expressing cells/participating networks for many remain unknown. Spontaneous network spontaneous hyperactivity observed during retinal degeneration contributes to visual impairment and requires gap junctional coupling in the Aii amacrine cell/ON cone bipolar cell (CBC) network. However, it remains unclear whether this hyperactivity reflects changes in the underlying circuitry or dysfunction of the normative circuitry. Here, we used connectomics-based mapping of retinal circuitry to 1) define the coupling architecture of the Aii/ON CBC network in healthy adult rabbit retina using connectome RC1 and 2) evaluate changes in coupling motifs in RPC1, a pathoconnectome from a rabbit retinal degeneration model.
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. RPC1 is a 0.07 mm diameter volume of degenerate retina from a transgenic P347L model of autosomal dominant retinitis pigmentosa (10-months old, male, New Zealand White background) presenting with ~50% rod loss. 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 network graph visualization. Gap junctions were validated by 0.25 nm resolution recapture with goniometric tilt when necessary.
Complete reconstruction of 37 ON CBCs in RC1 yielded 1339 gap junctions and revealed pervasive in- and cross-class coupling motifs among ON CBCs that produce complex network topologies within the coupled Aii network. Robust rulesets underlie class-specific coupling profiles with specificity defined beyond geometric opportunity. These coupling profiles enabled classification of all 145 ON CBCs contained within RC1 into 7 distinct classes. In RPC1, two ON CBC classes appear to retain their class-specific coupling profiles, accepting and rejecting specific combinations of Aii and ON CBC class partnerships. However, aberrant partnerships exist, including both loss of motifs and acquisition of novel ones.
Gap junctions formed by ON CBCs are prominent network components, with specificity rivaling that of chemical synapses. These gap junctions not only subserve canonical signal transfer for night vision, but also extensive coupling within and across the parallel processing streams. Clearly aberrant morphological and synaptic changes exist in RPC1, including changes in the coupling specificity of both Aii and ON CBCs. Thus, circuit topology is altered prior to complete loss of rods, with substantial implications for therapeutic interventions for blinding diseases that depend upon the surviving retinal network.
We have a new paper out in the Americal Journal of Ophthalmology, Development of a spatial model of age-related change in the macular ganglion cell layer to predict function from structural changes.
Purpose: To develop location specific models of normal, age-related changes in the macular ganglion cell layer (GCL) from optical coherence tomography (OCT). Using these OCT-derived models, we predicted visual field (VF) sensitivity and compared these results to actual VF sensitivities.
Design: Retrospective cohort study
Methods: Single eyes of 254 normal participants were retrospectively enrolled from the Centre for Eye Health (Sydney, Australia). Macular GCL measurements were obtained using Spectralis OCT. Cluster algorithms were performed to identify spatial patterns demonstrating similar age- related change. Quadratic and linear regression models were subsequently utilized to characterize age-related GCL decline. 40 participants underwent additional testing with Humphrey VFs, and 95% prediction intervals were calculated to measure the predictive ability of structure-function models incorporating cluster-based pooling, age-correction and consideration of spatial summation.
Results: Quadratic GCL regression models provided a superior fit (p = <0.0001-0.0066), establishing that GCL decline commences in the late 30’s across the macula. The equivalent linear rates of GCL decline showed eccentricity-dependent variation (0.13μm/year centrally versus 0.06μm/year peripherally), however average, normalized GCL loss per year was consistent across the 64 macular measurement locations at 0.26%. The 95% prediction intervals describing predicted VF sensitivities were significantly narrower across all cluster- based structure-function models (3.79-4.99dB) compared with models without clustering applied (5.66-6.73dB, p <0.0001).
Conclusions: Combining spatial clustering with age-dependent regression allowed the development of robust models describing GCL changes with age. The resultant superior predictive ability of VF sensitivity from ganglion cell measurements may be applied to future models of disease development to improve detection of early macular GCL pathology.