Abstract
Purpose :
Mutations in TULP1 are causative of retinal degenerations including retinitis pigmentosa and Leber congenital amaurosis. The retina of Tulp1-/- mice is characterized by rapid loss of photoreceptors while the inner retina is reportedly maintained at the initial stage of degeneration. Using histology analysis we tested whether cellular alterations extend to the inner retina in Tulp1-/- mice before postnatal day (p) 14.
Methods :
Immunocytochemistry using various markers was undertaken in retinal cryosections from Tulp1-/- and Tulp1+/+ control mice (both on C57 background) at p5, 8 and 14; n=3-5 per group. Qualitative and quantitative morphological analysis on microscope images from these samples was performed.
Results :
We assessed the structure of the Tulp1-/- retina before the onset of major photoreceptor degeneration. In agreement with previous work, we detected minor alterations in thickness of the retinal layers between p5-14. The greatest difference observed was shortened photoreceptor segments in Tulp1-/- mice at p14; 11.2±0.7 vs 19.8±0.3 um, p<0.001. Using different retinal markers we identified significant cellular and subcellular alterations. In the outer plexiform layer, the photoreceptor synapses were compromised, while the horizontal cell processes invaded the photoreceptor layer in Tulp1-/- mice but not in controls. In the inner nuclear layer, the number of amacrine cells was significantly reduced in Tulp-/- mice at p14; 232.0±36.5 vs 318.1±45.9 um, p<0.01. Additionally, the morphology of both cell bodies and processes of Muller glia was altered. Apart from the large number of TUNEL+ cells in the outer nuclear layer in Tulp1-/-, TUNEL+ cells were also detected in the inner nuclear layer in Tulp-/- but not in Tulp1+/+ retinas at p14; 4.08±0.5 vs 0.0±0.0 (per section), p<0.01. Distinct stratification of the neuropil in the inner plexiform layer was evident by p14 in Tulp+/+ retinas. On the contrary, Tulp1-/- dendrites arborized more diffusely in the inner plexiform layer at p14.
Conclusions :
Our data suggest compromised synaptic development/function and altered cellular morphology and composition in the inner retina in Tulp-/- mice by p14. These deviations precede the major photoreceptor cell loss, which emerges from ~p16 and indicate early involvement of the inner retina in retinal degeneration in Tulp-/- mice.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.