Abstract
Purpose :
To understand the cellular basis of retinal degenerative disease, it is necessary to know the interrelationships among neurons, between neurons and glial cells, and subcellular organelle structure within and outside the areas affected by the disease process. Using a targeted connectomics approach, our goal is to determine the structural changes in organelle structure and glial-neuronal relationships involved in Macular Telangiectasia (MacTel).
Methods :
With an eye from a women with MacTel (age 48) we are examining the macula and perifoveal regions of the retina from one flat-mounted (~3 mm nasal/temporal x 2.5 mm inferior/superior) retinal piece that includes the fovea and extends temporally past the MacTel zone where pathology occurs, a nasal side piece of the MacTel zone oriented radially, and flat & radial pieces from the perifovea. About 10,000, 30 nm serial-sections of the flat-mount block were collected on tape for imaging with either a single-beam or 61-beam SEM. Overview images of every 100th section were used to determine regions of interest in X, Y, and Z planes to examine at a resolution of 4 nm.
Results :
Our analysis of selected regions indicates mitochondrial involvement inside and outside the MacTel zone. Mitochondrial swelling, reduced cristae, and internal densities are observed. This extends recent metabolomics and GWAS studies showing an involvement of de novo L-serine biosynthesis, sphingolipid metabolism, and mitochondrial function in MacTel. The L-serine rate-limiting biosynthetic enzyme PHGDH is only found in retinal glia – Müller cells. In at least some patients, a defect in the gene encoding this enzyme has been identified. We also observe a correlation between macular pigment loss (observed macroscopically) with profound Müller cell loss. Outside the MacTel zone, despite signs of mitochondrial stress, typical retinal circuit motifs are preserved, as is vision.
Conclusions :
Defining the subcellular basis of retinal disease requires a multidisciplinary approach. Using large-scale direct observation at nanometer resolution we have identified specific mitochondrial changes throughout the retina that likely lead to the development of MacTel. The unique role of Müller cells in supporting mitochondrial function in retinal neurons, and themselves, may increase their susceptibility to degeneration in the macula region where metabolic demands are high.
This is a 2020 ARVO Annual Meeting abstract.