IGFBPL1 Ameliorates Angiogenesis in a Choroidal Neovascularization Mouse Model through Modulation of Microglia Activation

Abstract

Purpose : Choroidal neovascularization (CNV) is a key feature of wet age-related macular degeneration (AMD), characterized by microglia activation and abnormal angiogenesis. Insulin-like growth factor-binding protein 1 (IGFBPL1) has been found to alleviate neuroinflammation by restoring activated microglia to homeostasis in an Igf1r-dependent manner. However, its impact on angiogenesis in the eye is unknown.

Methods : Laser CNV was induced in adult mice carrying an inducible microglia-specific deletion of Igf1r, driven by Cx3cr1^CreERT (Cx3cr1^CreERTIGF1r^flox/flox or △Igf1r^-/-). Thirty days after tamoxifen injection, IGF1r^flox/flox, and △Igf1r^-/- mice were subjected to retinal laser injury and intravitreal injection of IGFBPL1 (100 ng). Igf1r^fl/fl mice treated with PBS served as a control. Seven days post-CNV, Optical coherence tomography (OCT) was used to assess the lesion size. Retinal pigment epithelia (RPE)-choroidal complexes (RCSC) were immunostained for lectin, IBA-1, and VEGFa. The tube formation assay using primary mouse choroidal endothelial cells (CECs) was performed to study the direct effects of IGFBPL1 (400 ng/ml) on CEC angiogenesis. To determine the effect of microglial secretory signals on CEC tube formation, conditioned media (CM) was collected from primary mouse microglia treated with lipopolysaccharide (LPS), LPS+IGFBPL1 (400 ng/ml), and PBS control.

Results : IGFBPL1 attenuated laser-induced lesion measured by OCT in Igf1r^fl/fl mice compared to PBS treatment (p<0.01) but failed to do so in △Igf1r^-/- mice. Immunolabeling in RCSC demonstrated decreases in the number of IBA-1 positive cells (p<0.01), VEGFa-positive area (p<0.01), and lectin-positive area (p<0.05) induced by IGFBPL1 when compared to PBS. CEC treated with IGFBPL1 revealed no differences in tube formation compared to PBS-treated control (p>0.05). CM collected from LPS-treated cultures showed a proangiogenic effect on EC tube formation, an increased number of junctions (p<0.01), number of nodes (p<0.05), and total tubule length (p<0.0001) compared with CM from PBS-treated microglia. The CM from LPS+IGFBPL1-treated microglia cultures displayed no increased angiogenesis compared to PBS controls (p>0.05).

Conclusions : IGFBPL1 is a promising therapeutic agent that reduces pathological angiogenesis in the eye without directly affecting the EC by modulating microglial activation and pro-angiogenic secretome.

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