Abstract
Purpose :
The success of cell-based therapies for photoreceptor degenerations depends on transplanted photoreceptors forming synaptic connections with the host retina. Although the impact of photoreceptor loss on the inner retina has been well-characterized in lower mammals, the impact on the cone-dominated primate macula is not well understood. Here, we used a laser ablation model of acute photoreceptor degeneration to determine the impact of deafferentation on the survival and synaptic integrity of inner retinal neurons.
Methods :
We studied 4 laser lesions from 3 adult macaque eyes (2 M. fascicularis, 8-15 years, 1 M. Mulatta 19 years). To create focal regions of photoreceptor ablation, we used a femtosecond-pulsed laser (730 nm, 27-33 J/cm2) focused on the photoreceptor layer using an adaptive optics scanning light ophthalmoscope. Lesions were made ~1-15 degrees from the foveal center and eyes were harvested for histology at 3 weeks, 4, 8 & 12 months post-ablation. The integrity of horizontal cells (HCs) and different bipolar cell types (BCs) was assessed using cell-type specific and synaptic markers. Deafferented regions were identified with antibodies for VGLUT1. Cell densities were compared between lesioned and neighboring unlesioned regions by one-sample t-test.
Results :
Deafferentation was associated with focal loss of H1 and H2 HCs as early as 3 weeks post-ablation (p<0.0001). This result was confirmed with three HC markers (ONECUT1, PVALB, CALB1), suggesting neuronal loss rather than down-regulation of marker proteins. In contrast, the densities of rod BC (PKCα, p = 0.52), On-BCs (Islet 1, p =0.19) and Off midget BCs (recoverin, p=0.23) were unchanged at all timepoints. Deafferented On-BCs showed marked loss of dendritic mGluR6 and TRPM1 as early as 3 weeks post-lesion but expression of somatic TRPM1 remained (n = 3 lesions, 2 retinas). In the central fovea, the observed changes in post-receptoral neurons were laterally offset from the laser lesions consistent with deafferentation, rather than direct laser damage, underlying the changes.
Conclusions :
Acute photoreceptor ablation in primate leads to loss of HCs and On-BC-associated synaptic proteins as early as 3 weeks post-deafferentation. The long-term survival of rod and cone BCs in lesioned regions holds promise for cell-based therapies.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.