Retinal Neurodegeneration in Mice With Streptozotocin-induced Diabetes Mellitus

Abstract

Purpose: We sought to detect the early retinal neurodegeneration by comparing histological changes in the ganglion cell layer to retinal topography in vivo of diabetic mice using the Iowa Reference Algorithm (IRA) for three-dimensional automated layer segmentation of spectral domain optical coherence tomography (OCT).

Methods: C57BL/6 mice (12-week-old) were assigned into streptozotocin-induced diabetes mellitus (DM; n=20) and age-matched control cohorts (n=10). Immunostaining with anti-SNCG antibody was performed on 5-6 cryo-sections of each animal; the density of ganglion cells was quantified by averaging five peripheral regions of each section under light microscopy. Two masked graders were used to manually count the number of ganglion cells. Cell death ELISA was performed to determine retinal cellular apoptosis. OCT imaging (Bioptigen) was performed at baseline, 6 weeks, and 20 weeks after induction of DM. Using the IRA, mathematically enhanced for mouse OCT, average change in thickness of the RNFL-GCL complex was quantified and compared at 0, 6 weeks, and 20 weeks for each group.

Results: The mean number of ganglion cells measured per total cell was reduced at week 20 DM group than age-matched control group (44.1% vs. 50.2%, respectively, p<0.05) but not at week 6 (45.1% vs. 45.4%, p=0.85). Cell death ELISA indicated enhanced apoptosis (1.20mU vs. 0.84mU, respectively, p<0.05) in 20 week DM mice compared with age-matched control but not at week 6 (0.77mU vs. 0.59mU, p=0.07). OCT-based IRA analysis determined that RNFL-GCL thickness in DM mice was thinner compared to age-matched controls at 6 weeks (8.97um vs 10.54um, p<0.05) and 20 weeks (6.45um vs 8.98um, p<0.001).

Conclusions: Inner retinal degeneration is a prominent feature of diabetic retinopathy in this mouse model. Attenuation of the RNFL-GCL complex in mice with 6 weeks of diabetes suggests that OCT may be a more sensitive measure for detecting the earliest retinal changes induced by diabetes.