Real-time imaging of leukocyte trafficking as a biomarker for retinal neuronal injury

Abstract

Purpose : Retinal neuronal death is a common pathological feature of retinopathy as well as Alzheimer’s disease. Vascular inflammation plays a critical role in the pathogenesis of these diseases. However, it is unclear whether vascular inflammation during the early stage of disease predicts retinal neuronal loss which occurs at a relative late stage. This study is to develop an approach to non-invasively examine retinal vascular inflammation in vivo in real time and evaluate its value in predicting retinal ganglion cell (RGC) loss

Methods : C57BL/6 mice were injected with lipopolysaccharide (LPS 4 mg/kg, i.p.) to induce retinal vascular inflammation and used to develop a protocol to examine leukocyte trafficking in real time. A mouse model of optic nerve crush (ONC) was used to study RGC death after axonal injury. Two methods were employed to label leukocytes in vivo: 1) Acradine orange (AO) was injected via tail vein (1 mg/kg); 2) Bone marrow from mice expressing green fluorescent protein (EGFP) was transplanted into wild type mice to generate chimeric mice (BM-EGFP) expressing GFP in leukocytes. Leukocyte trafficking along retinal vessels was examined by scanning laser ophthalmoscopy (SLO) and RGC injury was determined by optical coherence tomography (OCT) and immunohistochemistry

Results : The fluorescence signal of leukocytes labeled with AO was weak and transient. In contrast, BM-EGFP mice exhibited high and stable fluorescence intensity of leukocytes, and produced high-quality, sustained and repeatable imaging of leukocyte trafficking. Therefore BM-EGFP mice were selected to study leukocyte trafficking in the ONC model. At 9 hours after ONC injury when RGC loss is absent, dramatic increases in leukocyte rolling, attachment and infiltration were observed in veins around the optic nerve head. At 7 days after ONC, analysis of retinal structure by non-invasive OCT revealed a significant reduction in the thicknesses of total retina and the ganglion cell complex (GCC) layer, which was associated with significant RGC loss seen in retinal flatmount preparations. Linear regression analyses indicate that the extent of leukocyte attachment to vessels at 9 hours after ONC was linearly correlated with GCC thickness reduction and RGC loss at 7 days after ONC

Conclusions : Real-time imaging of leukocyte trafficking, an early event after retinal injury, could be used as a biomarker to predict retinal neuronal degeneration

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.