Abstract
Purpose :
Diabetic Retinopathy (DR) is a leading cause of visual impairment in working age adults. Loss of retinal ganglion cells (RGCs) –the output neurons of the neural retina lining the back of the eye – contributes to visual impairment in this disease. Vascular changes occur with diabetes and these contribute to RGC death (Feit-Leichman et al., IOVS, 2005; Kern and Barber, The Journal of Physiology, 2008). However, little is known about the sequence of morphological and connectivity alterations in RGCs preceding their loss. Knowledge of these alterations would reveal the early impact of diabetes on RGC structure and connectivity. There are four well characterized ‘alpha’ RGC types in the mammalian murine retina with stereotypic lamination and functional profiles: ON-Sustained (ON-SUS), ON-Transient (ON-T), OFF-Transient (OFF-T), and OFF-Sustained (OFF-SUS) RGCs (Krieger et al., PLoS one, 2017). Using a mouse model of diabetes, we aimed to investigate the early effects of diabetes on the morphology and synaptic connectivity of these four RGC types.
Methods :
Male Ins2 Akita/+ mice (Jackson labs) and littermate controls were collected at a 6-week timepoint: 2 weeks after initiation of hyperglycemia in this strain. Alpha RGCs were biolistically labeled with tdTomato as a cell-fill and fluorescently conjugated PSD-95 as a marker for excitatory synapses (Morgan et al., Neural Development, 2008). RGCs were imaged using a Leica SP8 confocal microscope and image stacks were visualized in Amira (Thermo Fisher Scientific). RGC types were determined by lamination of RGC dendrites in the retinal synaptic layer. Dendritic branching was analyzed by Sholl analyses (Fiji/Image J, NIH). PSD-95 density and asymmetric index were calculated by custom-written Matlab codes. Immunohistochemistry for RGC markers was performed at the 8-week timepoint to determine the density of RGCs across genotypes.
Results :
Average asymmetric index of RGC types was not different between genotypes. At the 8-week timepoint, RGC cell density was not affected across genotypes. RGC branching pattern and synaptic density was selectively altered in retinas from diabetic mice in a subtype-specific manner.
Conclusions :
The morphology and connectivity of RGCs is altered in a subtype-specific manner, within a short duration of diabetes before the onset of RGC loss.
This is a 2021 ARVO Annual Meeting abstract.