Age-dependent retinal abnormalities and neurodegeneration in the small kinky tail mutant

Abstract

Purpose : The purpose of this study is to investigate the link between aging and age-dependent diseases at the molecular level. We study mouse mutants with accelerated aging to identify novel factors involved in these processes. The small kinky tail (skt) mutation leads to a kinked tail and small body size in mice. We have identified age-dependent retinal abnormalities and hippocampal neurodegeneration in skt mice. This study aims to further characterize the skt phenotypes and identify the causative gene.

Methods : Immunohistochemical analysis of retinal sections from 4, 8, and 16-week old skt mutants and heterozygous controls was performed to examine age-dependent phenotypes, including inflammation, stress response, and synaptic abnormalities. Retinal sections were stained with hematoxylin and eosin (H&E) to measure the outer nuclear layer thickness (ONLT). Brains of 2-year old mice were perfused with 4% PFA and used for H&E and immunohistochemical analysis. Genetic mapping of the skt mutation was performed using an F₂ intercross (B6/LT-skt/skt x C3Sn.BLiA-Pde6b⁺/DnJ). The resulting 2.5Mbp region was sequenced on the Illumina HiSeq platform.

Results : We observe an increase in microglia in skt retina at 4 weeks, which persists past 8 weeks. Specifically, we observe a large increase in activated microglia in the ONL and retinal pigment epithelium (RPE) at 4 and 8 weeks of age. By 8 weeks of age, there is significant damage to the skt retina and a decrease in ONLT. Age-related abnormalities are also present in the synaptic layers of the retina at 8 weeks. The skt brain exhibits abnormalities in the hippocampal neurons, including an increase in a stress marker, glial fibrillary acidic protein (GFAP), a decrease in the axon number, and an increase in cell death. Additionally, skt mice exhibit a reduced lifespan compared to heterozygous controls. Via positional cloning, we have identified the causative mutation within chondroitin sulfate synthase 1 (Chsy1).

Conclusions : Our study has identified a novel function for Chsy1 in aging within the brain and retina. The causative mutation in Chsy1 induces a large increase in inflammatory cells that precedes retinal degeneration. These data suggest that inflammation could be the primary defect causing the neurodegeneration and reduced lifespan in skt mice.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.