Abstract
Purpose :
Microglia become activated in parallel with neurodegeneration in the retinas of humans with diabetic retinopathy (DR) and in rodent models but their role in mediating functional vision loss remains unclear. This study tested the hypothesis that chronic ablation of activated retinal microglia can prevent visual function deficits during early-stage DR in the mouse.
Methods :
Male Cx3cr1YFP-CreER/+; Rosa26DTA/+ (TG) mice were given single intraperitoneal (IP) injections of Streptozotocin (STZ; 150mg/kg) delivered in a sodium citrate buffer (pH~4.5) or buffer solution as a control. STZ diabetic (>250mg/dL blood glucose) and non-diabetic mice were transfered to cages containing tamoxifen-infused chow (500mg/kg) or regular chow for 8 weeks to compare control (CTRL), diabetic (STZ), microglia-ablated control (TAM), and microglia-ablated diabetic (TAM+STZ) groups (N=4-5). 9-step scotopic (rod-specific) intensity and 7-step photopic (cone-specific) intensity electroretinography (ERG) assessments were performed on anesthetized mice at 4- and 8-weeks. Retinas were processed post-hoc for immunostaining to assess microglial ablation efficacy. One-way and two-way ANOVA tests were used for statistical analysis.
Results :
Tamoxifen-treated TG mice showed reduced microglial density within one week of treatment (Mean±SEM), corresponding to a >93% decrease (14.4±5.4/mm2 retina; p<.0001) compared to untreated control mice (206.2±6.6) that sustained through 8 weeks of treatment. Comparing STZ to TAM+STZ, the following scotopic measurements showed statistical difference at 4 weeks: (a-wave) 193.9±16.6μV vs. 249.3±14.6 (-4db; p<.0054), 231.0±16.8μV vs. 305.0±15.5 (0db; p<.0001), 307.1±23.3μV vs. 391.0±19.4 (5db; p<.0001); (b-wave) 455.0±48.0μV vs. 589.6±35.8 (0db; p=.0126), 553.6±46.7μV vs. 668.4±32.3 (5db; p=.0499). No significant differences in scotopic measurements were found between TAM+STZ, CTRL, and TAM groups. No significant differences in photopic measurements were found between all groups.
Conclusions :
Our results support our hypothesis that ablation of activated retinal microglia can prevent DR-associated functional vision loss during early-stage DR. Further examination of microglial activation in DR will be needed to understand their unique contribution to neuro-retinal dysfunction.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.