Loss of Sarm1 reduces retinal ganglion cell loss in chronic glaucoma

Glaucoma is one of the leading causes of irreversible blindness worldwide and vision loss in the disease results from the deterioration of retinal ganglion cells (RGC) and their axons. Metabolic dysfunction of RGC plays a significant role in the onset and progression of the disease in both human patients and rodent models, highlighting the need to better define the mechanisms regulating cellular energy metabolism in glaucoma. This study sought to determine if Sarm1, a gene involved in axonal degeneration and NAD+ metabolism, contributes to glaucomatous RGC loss in a mouse model with chronic elevated intraocular pressure (IOP). Our data demonstrate that after 16 weeks of elevated IOP, Sarm1 knockout (KO) mice retain significantly more RGC than control animals. Sarm1 KO mice also performed significantly better when compared to control mice during optomotor testing, indicating that visual function is preserved in this group. Our findings also indicate that Sarm1 KO mice display mild ocular developmental abnormalities, including reduced optic nerve axon diameter and lower visual acuity than controls. Finally, we present data to indicate that SARM1 expression in the optic nerve is most prominently associated with oligodendrocytes. Taken together, these data suggest that attenuating Sarm1 activity through gene therapy, pharmacologic inhibition, or NAD+ supplementation, may be a novel therapeutic approach for patients with glaucoma.

Circumferential trabecular meshwork cell density in the human eye

The cells residing in the trabecular meshwork (TM) fulfill important roles in the maintenance of the tissue and the regulation of intraocular pressure (IOP). Here we examine (i) TM cell distribution along the circumference of the human eye, (ii) differences in TM cell density between regions of high and low outflow, and (iii) whether TM cell distribution in eyes from donors with primary open angle glaucoma (POAG) differs from that of normal eyes. Toward this end, the TM cell density from 12 radial segments around the circumference of the TM of human donor eyes (n = 6) with and without POAG was determined using histochemical methods. Areas of high, median, and low outflow were mapped in a different set of human donor eyes that were perfused in organ culture, and TM cell densities in these areas were determined in normal (n = 11) and POAG eyes (n = 6). Our analysis of 1380 tissue sections taken from the first set of six eyes shows that the average TM cell density of these six eyes ranges from 15.5 to 23.7 cells/100 μm and is negatively correlated to the maximum IOP recorded for each donor eye (R² = 0.91). Considerable differences in TM cell density exist among sections taken from the same segment of an individual eye (average standard deviation = 2.35 cells/100 μm). Less variability is observed among the segment averages across the eye's circumference (average standard deviation = 1.03 cells/100 μm). Variations in cell density are similar between normal and POAG eyes and are not correlated with the anatomic position of examined segments (p = 0.745). The analysis of the second set of eyes shows that TM regions of high outflow display a TM cell density similar to regions of median or low outflow in both normal and POAG eyes. Together these findings demonstrate that (i) statistically significant differences in TM cell density exist along the circumference of each eye (ii) TM cellularity is not correlated with segmental flow and (iii) eyes with POAG, while displaying reduced TM cellularity, do not exhibit higher TM cell variability than normal eyes. Finally, statistical analysis of sections and segments indicates that measurements from 12 sections taken from 2 segments provide a reliable and cost-effective estimate of a human eye's TM cell density.