Category Archives: Retinal Disease

Retinal Prosthetics, Optogenetics and Photoswitches

Retinal-Prosthetics-Optogenetics-and-Photoswitches

We have a new publication, Retinal Prosthetics, Optogenetics and Photoswitches in ACS Chemical Neuroscience.  Authors are:  Robert E. MarcRebecca 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.

Metabolic Changes Associated With Müller Cells In A Transgenic Rabbit Model Of Retinal Degeneration

Retina-RLP

This abstract was presented today at the 2014 Association for Research in Vision and Opthalmology (ARVO) meetings in Orlando, Florida by  Rebecca L. PfeifferBryan 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).