We have a new Webvision chapter on Retinal Degeneration, Remodeling and Plasticity! Check it out here.
Müller Cell Metabolic Chaos During Degeneration
This abstract was presented today at the 2015 Association for Research in Vision and Opthalmology (ARVO) meetings in Denver, Colorado by Rebecca L. Pfeiffer, Bryan W. Jones and Robert E. Marc.
Purpose: Müller cells (MCs) play a critical role in glutamate (E) metabolism and carbon skeleton cycling in retina. MCs demonstrate changes in metabolism and morphology during retinal degeneration. The timing, extent, regulation, and impacts of these changes are not yet known. We evaluated metabolic phenotypes of MCs and evaluated their capacity to transport glutamate during degeneration.
Methods: Retinas were harvested from wild-type (WT) and rhodopsin Tg P347L rabbits, divided into chips mounted on filters, and incubated in Ames medium with 5 mM D-aspartate (D-Asp), D-glutamate (D-Glu), or D-glutamine (D-Gln) for 10 min at 35 deg to explore transport and metabolism. Chips were fixed in mixed aldehydes and resin embedded for computational molecular phenotyping (CMP) of a range of L- and D-amino acid markers and selected proteins including glutamine synthetase (GS) (J Comp Neurol. 464:1, 2003).
Results: CMP revealed wide variations in metabolite levels across individual MCs from Tg P347L retinas, generating chaotic patterns. GS decreased significantly while glutamine levels (Q) increased, although to varying degrees. Remarkably, E levels were variable and much higher in some MCs than normal, but did not correlate (inversely) with GS levels. Transport experiments using D-Glu, D-Asp, and D-Gln showed that alterations in MC metabolites are not the product of defective transporters, in contrast to previous reports. These results are also inconsistent with conventional models of GS-based E-Q metabolism and microenvironmental regulation of MC phenotypes.
Conclusions: These observations suggest three conclusions. (1) Although degeneration of the retina is certainly the trigger, MC phenotype changes are not a coherent response to the surrounding microenvironment but are, rather, uncoordinated individual MC responses. (2) Although GS is accepted as the primary enzyme responsible for the conversion of E to Q in the normal retina, alternative pathways appear unmasked in the degenerate state. (3) It has been previously hypothesized that MCs in retinal degenerations exhibit deficient E transport. Our experiments show no transport deficiency. This indicates that chaotic metabolite levels emerge from changes in individual MC metabolic processing.
Metabolic Changes Associated With Müller Cells In A Transgenic Rabbit Model Of Retinal Degeneration
This abstract was presented today at the 2014 Association for Research in Vision and Opthalmology (ARVO) meetings in Orlando, Florida by Rebecca L. Pfeiffer, Bryan W. Jones and Robert E. Marc.
Purpose: Müller cells play a central role in retinal metabolism via the glutamate cycle. During retinal degeneration Müller cells are among the first to demonstrate changes, reflected in alterations of metabolic signatures and morphology. The timing, extent and regulation of these changes is not fully characterized. To address this issue, we evaluated Müller cell metabolic phenotypes at multiple stages of retinal remodeling.
Methods: Samples were collected post-mortem from both WT and P347L rabbits. The retinas were then divided into fragments, fixed in buffered aldehydes, and embedded in epoxy resins. Tissues were sectioned at 200nm followed by classification with computational molecular phenotyping (CMP) using an array of small and macromolecular signatures (aspartate (D), glutamate (E), glycine (G), glutamine (Q), glutathione (J), GABA (yy), taurine (T), CRALBP, Glutamine Synthetase (GS), and GFAP). Levels of amino acid or protein were quantified by selecting a region of interest either within the Müller cell population or surrounding neurons and evaluating the intensity of the signal within that region.
Results: CMP reveals overall decreases in GS levels over the course of degeneration. Of notable importance, we saw that in regions of near complete photoreceptor loss neighboring Müller cells may express independent variation in metabolic signatures of E, Q, and GS. Also observed in these Müller cells, ratios of GS:E and GS:Q are not consistent with the ratios seen in WT retina. These results are inconsistent with the current models of both E to Q metabolism and microenvironment regulation of Müller cell phenotypes.
Conclusions: These observations indicate two conclusions. First, although the degenerate state of the retina is the likely trigger inducing Müller cells to express altered metabolic signatures, the rate at which the metabolic state changes is not purely a product of the surrounding environment, but also a stochastic change within individual Müller cells. Second, although it is commonly accepted that GS is the primary enzyme which converts Q to E as part of the glutamate cycle, in degenerate retina alternative pathways may be utilized following decrease in GS.
Support: NIH EY02576 (RM), NIH EY015128 (RM), NSF 0941717 (RM), NIH EY014800 Vision Core (RM), RPB CDA (BWJ), Thome AMD Grant (BWJ).
Interesting Paper: Gene Expression Changes Within Müller Glial Cells in Retinitis Pigmentosa
Retinal degenerations are accompanied by retinal remodeling events. These events alter the structure and function of the retina and involve to a large extent, Müller cells which seem to serve as pathways for neuronal migration. This paper by Karin Roesch, Michael B. Stadler and Constance L. Cepko looks at gene expression changes in the Müller cells, one of the glial cells of the retina as the rd1 mouse retina degenerates.
While the paper is not terribly conclusive in its definition of genes or pathways involved, (partially I suspect because of the limited time points examined and the late point in the examinations), this paper does however point in a direction that is useful to the retinal degeneration community. Specifically, Müller cells are fundamentally involved in the remodeling process. Intervening there is an opportunity to arrest or slow down the retinal remodeling process to allow for interventions and understanding which genes are involved is a good first step.
Notable Paper: Receptor interacting protein kinase mediates necrotic cone but not rod cell death in a mouse model of inherited degeneration
How photoreceptor cells go through the process of cell death has been an outstanding question. The authors of this paper by Yusuke Murakami, Hidetaka Matsumoto, Miin Roh, Jun Suzuki, Toshio Hisatomi, Yasuhiro Ikeda, Joan W. Miller, and Demetrios G. Vavvas have further defined the process and identified the receptor interacting protein kinase (RIP) pathway as a possible target for intervention in patients with retinitis pigmentosa (RP). The authors used the rd10 mouse model, a mouse model of retinitis pigmentosa to examine the cell death process. They defined RIP kinase as a mediator of necrotic cell death in cones. RIP3, has been defined as they key regulator of programmed necrosis and its expression was elevated in rd10 retinas during cone photoreceptor death and not rod photoreceptor death. Furthermore, the cone photoreceptor cell death was rescued by RIP3 deficiency and by pharmacological treatment with RIPkinase inhibitors. Continue reading “Notable Paper: Receptor interacting protein kinase mediates necrotic cone but not rod cell death in a mouse model of inherited degeneration”
The Rd8 mutation of the Crb1 gene is present in vendor lines of C57BL/6N mice and embryonic stem cells
This is an important issue for anyone involved in using murine models of retinal degeneration. It turns out that contamination of Rd8 mutation in the B6 mice is more wide spread than the C57BL/6N mice. Labs worldwide are going to have to reassess their data due to this mutation and all reviewers will ask about this in the immediate future. The genotyping analysis of a variety of vendor lines is described in this paper by Mary J. Mattapallil, Eric F. Wawrousek, Chi-Chao Chan, Hui Zhao, Jayeeta Roychoudhury, Thomas A. Ferguson, and Rachel R. Caspi. The take home message is that the rd8 mutation is in the C57BL/6N strain which is used worldwide to produce transgenic and knockout models. The implications for non-vision labs are not as clear, but for vision labs, substantial disease can be present unrelated to another specific disease gene and will need to be accounted for.
Undersized Dendritic Arborizations in Retinal Ganglion Cells of the rd1 Mutant Mouse: A Paradigm of Early Onset Photoreceptor Degeneration
This paper by Devid Damiani, Elena Novelli, Francesca Mazzoni and Enrica Strettoi documents continued negative plasticity in retina by examining ganglion cells in the rd1 mouse. The rd1 mouse is one of many models of retinal degenerative disease, in this case as an autosomal recessive retinal degenerative disease. This work gets at the remodeling issue in retinal degenerative diseaseby examining the last cells in the chain of retinal cells that process information before sending it out to the brain and other CNS centers for further processing. Continue reading “Undersized Dendritic Arborizations in Retinal Ganglion Cells of the rd1 Mutant Mouse: A Paradigm of Early Onset Photoreceptor Degeneration”
Review: Defective Trafficking of Rhodopsin and Its Role In Retinal Degenerations
This is a great review paper on the role of rhodopsin trafficking and its influence on retinal degenerative disease by TJ Hollingsworth and Alecia Gross. Rhodopsin delocalization in rod photoreceptors has been recognized for some time as one of the first indications of retinal photoreceptor cell stress in retinal degenerative diseases, so I was intrigued when seeing this paper come up in PubMed. Continue reading “Review: Defective Trafficking of Rhodopsin and Its Role In Retinal Degenerations”
Dysmorphic Photoreceptors in a P23H Mutant Rhodopsin Model of Retinitis Pigmentosa Are Metabolically Active and Capable of Regenerating to Reverse Retinal Degeneration
This paper (and the cover article) is the result of a collaborative effort between Damian C. Lee, Felix R. Vazquez-Chona, W. Drew Ferrell, Beatrice M. Tam, Bryan W. Jones, Robert E. Marc, and Orson L. Moritz.
Notable Paper: Gene Therapy Rescues Photoreceptor Blindness in Dogs and Paves The Way for Treating Human X-linked Retinitis Pigmentosa
This paper in PNAS by William A. Beltran, Artur V. Cideciyan, Alfred S. Lewin, Simone Iwabe, Hemant Khanna, Alexander Sumaroka, Vince A. Chiodo, Diego S. Fajardo, Alejandro J. Román, Wen-Tao Deng, Malgorzata Swider, Tomas S. Alemán, Sanford L. Boye, Sem Genini, Anand Swaroop, William W. Hauswirth, Samuel G. Jacobson and Gustavo D. Aguirre is a continuation of their work in retinal degeneration, this form of retinal degeneration, X-linked retinitis pigmentosa (RP).
Metabolic Profiling of Activated Retinal Glia
Presented at the Society for Neuroscience meetings in Washington, D.C. by Felix Vazquez-Chona, William Drew Ferrell, Ed Levine, Bryan William Jones and Robert E. Marc. Full size poster can be seen here. Continue reading “Metabolic Profiling of Activated Retinal Glia”
Retinoid Receptors Trigger Neuritogenesis in Retinal Degenerations
This paper by Y Lin, BW Jones, A Liu, JF Tucker, K Rapp, L Luo, W Baehr, PS Bernstein, CB Watt, JH Yang, MV Shaw and RE Marc examines the neuronal sprouting or neuritogenesis components of retinal remodeling found in retinal degenerative disease and describes a control process for retinoid X receptors (RXRs) in neuritogenesis. Continue reading “Retinoid Receptors Trigger Neuritogenesis in Retinal Degenerations”
Notable Paper: Retinal Remodeling in the Tg P347L Rabbit, a Large-Eye Model of Retinal Degeneration
This paper is the result of a collaborative effort between Bryan William Jones, Mineo Kondo and Hiroko Terasaki, Carl Watt, Kevin Rapp, James Anderson, Yanhua Lin, Maggie Shaw, Jia-Hui Yang and Robert Marc.
This work presents a substantial advance in models of Retinitis pigmentosa (RP), an set of inherited blinding diseases characterized by progressive loss of retinal photoreceptors. Continue reading “Notable Paper: Retinal Remodeling in the Tg P347L Rabbit, a Large-Eye Model of Retinal Degeneration”
Cone Opsin Determines The Time Course of Cone Photoreceptor Degeneration in Leber Congenital Amaurosis
It is been long known that ventral and central cones degenerate more rapidly than dorsal cones in retinoid-deprived LCA (Leber’s Congenital Amaurosis) models. This paper in PNAS by Tao Zhang, Wolfgang Baehr…
