Fig. 2

Retinal neurons predominantly express NAD-salvage pathway transcripts. A We examined independent datasets from single cell RNA-sequencing of normal human retina (left) and single nucleus RNA-sequencing of normal human retina (right). Expression of transcripts encoding NAD synthesizing enzyme machinery was compared across cell types of the retina. Retinal neurons demonstrate greater expression levels in a higher proportion of cells for the NAD-salvage pathway (NAMPT, NMNAT1-3) than the Preiss-Handler Pathway (NAPRT, NADSYN1). NAMPT expression is greater than NMRK1-2, suggesting a favoring of nicotinamide as an NAD-salvage pathway substrate over the alternative nicotinamide riboside. Glia and other non-neuronal support cells of the retina also favor the NAD-salvage pathway but have a greater relative expression of Preiss-Handler Pathway and NMRK1 than neurons. B NAMPT, NMNAT1, and NMNAT2 were expressed to a greater extent in RGCs over other retinal neurons. Of the non-neuronal cell types, only microglia/myeloid cells and RPE cells demonstrated strong expression of NAD synthesizing enzyme machinery. C For most cell types, when considering genes with high expression, the distribution of expression within cell types appeared normal, as demonstrated by ridge plots. In the single cell RNA-sequencing (left), distribution of NAMPT and NMNAT2 suggest the possibility of distinct populations, perhaps reflecting different RGC subtypes. This was not observed in the single nucleus sequencing, where distribution of expression appeared more normal for all cell types, with the exception of NMNAT2 in RGCs which had a greater variance, and expression of NAMPT and NMNAT3 in from RPE cells. Retinal neurons: cones, rods, horizontal cells (HCs), bipolar cells (BPs), amacrine cells (ACs), and retinal ganglion cells (RGCs). Non-neuronal retinal cells: myeloid/microglia, Müller glia, astrocytes, vascular cells, and retinal pigment epithelial cells (RPE cells)