Critical Role for the CXCL10/CXCR3 Axis in Leukocyte Recruitment and Neuronal Injury in Traumatic Optic Neuropathy

Abstract

Purpose: Traumatic optic neuropathy (TON) is an acute injury of the optic nerve secondary to trauma that usually occurs during motor vehicle and bicycle accidents, falls, assaults, war, and natural disaster. Loss of retinal ganglion cells (RGC) is an essential pathological process in TON, yet mechanisms responsible for RGC death remain unclear. In this study, we determined the involvement of leukocytes, which are the major inflammatory cells in this process, and investigated potential mechanisms underlying leukocyte recruitment.

Methods: Mouse model of TON was induced by a transient crush of optic nerve (ON) behind the eye globe. Real-time in vivo leukocyte trafficking along retinal vessels was determined using the Spectralis HRA+OCT imaging system in wild type (WT) mice transplanted with bone marrow from WT-GFP or CXCR3 knockout (KO)-GFP mice. Retinas were collected from 1 hour to 7 days after ON crush for quantitative PCR and histological studies. In vitro studies were performed using primary RGCs and leukocytes isolated from mice.

Results: Analysis of real-time leukocyte trafficking revealed a dramatic increase in leukocyte adhesion and rolling in veins near the optic nerve head 12 hours after ON injury. At 24 hours after injury, massive leukocyte infiltration was observed in superficial retina and these cells were identified as T-cells, microglia/monocytes, and neutrophils but not B-cells. In contrast, RGC loss was not noticeable even at 24 hours after ON injury. CXCL10 is a chemokine that induces recruitment and activation of inflammatory cells after binding to its receptor CXCR3. Levels of CXCL10 and CXCR3 mRNA were markedly elevated in TON with a peak increase (9.9 fold and 2.6 fold respectively) at 3 hours after ON crush. Deleting CXCR3 in bone marrow cells significantly reduced leukocyte recruitment and prevented RGC death after ON injury. Co-culture of RGCs with leukocytes resulted in 3.2 fold increase in RGC apoptosis.

Conclusions: These results indicate that leukocyte recruitment in retinal vessels near optic nerve head is an early event in TON. CXCL10 released from retinal cells has an essential role in recruiting leukocytes in a CXCR3-dependent manner and inducing RGC death.