CCR2⁺ monocytes infiltrate atrophic lesions in age‐related macular disease and mediate photoreceptor degeneration in experimental subretinal inflammation in Cx3cr1 deficient mice

Abstract

Atrophic age-related macular degeneration (AMD) is associated with the subretinal accumulation of mononuclear phagocytes (MPs). Their role in promoting or inhibiting retinal degeneration is unknown. We here show that atrophic AMD is associated with increased intraocular CCL2 levels and subretinal CCR2+ inflammatory monocyte infiltration in patients. Using age- and light-induced subretinal inflammation and photoreceptor degeneration in Cx3cr1 knockout mice, we show that subretinal Cx3cr1 deficient MPs overexpress CCL2 and that both the genetic deletion of CCL2 or CCR2 and the pharmacological inhibition of CCR2 prevent inflammatory monocyte recruitment, MP accumulation and photoreceptor degeneration in vivo. Our study shows that contrary to CCR2 and CCL2, CX3CR1 is constitutively expressed in the retina where it represses the expression of CCL2 and the recruitment of neurotoxic inflammatory CCR2+ monocytes. CCL2/CCR2 inhibition might represent a powerful tool for controlling inflammation and neurodegeneration in AMD.

Comprehensive analysis of mouse retinal mononuclear phagocytes

“…The number of subretinal EdU+ cells can then be compared in mice with and without clodronateliposome-induced monocyte depletion. Local EdU administration failed to mark subretinal cells, suggesting that ocular proliferation does not play a significant role in the light-induced accumulation of subretinal macrophages 14 . This technique can only be used for short-term experiments and is not adapted for the evaluation of chronic inflammation.…”

“…AMWAP transcription is rapidly induced in microglia from different retinal disease mouse models, including inherited photoreceptor dystrophies and different light challenge paradigms 7,32,33,39 . Another good marker to detect microglia reactivity is CCchemokine ligand 2 (CCL2, alias monocyte chemoattractant protein 1, MCP-1), which has a key role in pro-inflammatory mononuclear phagocyte chemotaxis and migration in the retina 14,40 .…”

“…However, the use of bone marrow transplantation to generate GFP+ leukocyte chimeras is problematic as it necessitates total body irradiation which may alter microglia function and cranial sparing resulting in incomplete bone marrow engraftment. To better evaluate the extent of inflammatory monocytes in subretinal mononuclear phagocyte accumulation, we previously used a simpler method 14 . We permanently marked the circulating monocytes with repeated EdU injections, a traceable nucleotide that is integrated in the DNA of dividing cells, prior to and during lightinduced subretinal inflammation in Cx3cr1 -/-mice.…”

Neuropilin-1 mediates myeloid cell chemoattraction and influences retinal neuroimmune crosstalk

“…This is evident in the retina, in which an intensified, largely microglial/macrophage-based immune response is associated with the progression of several sight-threatening diseases, such as diabetic retinopathy (DR) (3)(4)(5), age-related macular degeneration (AMD) (6)(7)(8), and retinopathy of prematurity (ROP) (9,10). Together, these retinal diseases account for the principal causes of loss of sight in industrialized countries (6,11,12).…”

High-resolution contrast-enhanced optical coherence tomography in mice retinae

“…We envision that the methods described herein may be used in the future to shed light on the roles of immune cells [25][26][27][28] and biomarkers, such as amyloid beta, 29 VEGFR1, 30 and α v β 3 31 in atrophic age-related macular degeneration and other retinal disorders. These results will help us better understand the cellular and molecular basis of disease progression via longitudinal studies.…”