Activation of TREM2 suppresses laser-induced choroidal neovascularization in mice.

Abstract

Purpose : Mononuclear phagocytes (MPs) contribute to pathological angiogenesis in age-related macular degeneration (AMD), a leading cause of visual impairment in adults. However, the mechanisms that orchestrate the functions of MPs remain poorly understood. The triggering receptor expressed on myeloid cells 2 (TREM2) has been shown to be crucial for the activation of MPs in the context of inflammatory response and phagocytosis. The objective of this study was to investigate the role of TREM2 in pathological angiogenesis in a mouse model for AMD.

Methods : Six to eight-week-old male C57BL/6J (wild-type; WT) and Trem2 knockout (Trem2^-/-) mice were subjected to experimental laser-induced choroidal neovascularization (CNV), a model mimicking neovascular AMD. 20μg purified bovine sulfatide was injected intraperitoneally from day 0 to 6 after laser coagulation to activate TREM2 signaling. At day 7 after laser photocoagulation, mice were euthanized for retinal pigment epithelium/choroid flat-mount preparation and mRNA extraction. CNV lesion area was measured using Image J. The expression of TREM2 or downstream signaling including spleen tyrosine kinase (SYK) and tumor necrosis factor (TNF) were assessed with immunohistochemistry and real-time qPCR. Human retinal microvascular endothelial cells (hRMECs) were treated with 1nM, 10nM or 100nM sulfatide or DMSO control and migration assay and cell viability assay were performed to investigate the direct impact of TREM2 on endothelial cells.

Results : The size of CNV lesions was significantly smaller in sulfatide-treated WT mice (WT-Sulfatide) than control-treated WT mice (WT-CTRL) (n≥27, p<0.001). There was a 2 to 3-fold increase in gene expression of Trem2 in WT-Sulfatide compared with WT-CTRL (n≥5 mice, p<0.05). Upon sulfatide treatment TREM2 and SYK immunosignal was increased and colocalized with IBA1-positive MPs. Tnf mRNA level was decreased in WT-Sulfatide compared with WT-CTRL (n≥5 mice, p<0.05). These changes were completely abolished with the genetic loss of Trem2. Sulfatide did not inhibit endothelial cell proliferation (n≥7 per group) or migration (n=3 per group) in hRMECs.

Conclusions : These findings demonstrated that pharmaceutical activation of TREM2 in MPs led to the impediment of choroidal neovessel formation by suppressing the pro-inflammatory response. Our study provides insight into the critical role of TREM2 in pathological angiogenesis.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.