Identifying Hyperreflective Foci in Diabetic Retinopathy via VEGF-Induced Local Self-Renewal of CX3CR1+ Vitreous Resident Macrophages

Abstract

Intraretinal hyperreflective foci (HRF) are significant biomarkers for diabetic macular edema. However, HRF at the vitreoretinal interface (VRI) have not been examined in diabetic retinopathy (DR). A prospective observational clinical study with 162 consecutive eyes using OCT imaging showed significantly increased HRF at the VRI during DR progression (P<0.01), which was reversed by anti-VEGF therapy. F4/80+ macrophages increased significantly at the VRI in Kimba (vegfa+/+) or Akimba (Akita × Kimba) mice (both P<0.01), but not in diabetic Akita (Ins2+/−) mice, indicating macrophage activation was modulated by elevated VEGF rather than the diabetic milieu. Macrophage depletion significantly reduced HRF at the VRI (P<0.01). Furthermore, BrdU administration in Ccr2rfp/+Cx3cr1gfp/+vegfa+/− mice identified a significant contribution of M2-like tissue-resident macrophages (TRMs) at the VRI. Ki-67- and CD11b-positive cells were observed in preretinal tissues of DR patients while exposure of vitreal macrophages to vitreous derived from PDR patients induced a significant proliferation response in vitro (P<0.01). Taken together, the evidence suggests that VEGF drives a local proliferation of vitreous resident macrophages (VRMs) at the VRI during DR. This phenomenon helps to explain the derivation and disease-relevance of the HRF lesions observed through OCT imaging in patients.

Cholesterol crystal formation is a unifying pathogenic mechanism in the development of diabetic retinopathy

“…The presence of CCs is considered a hallmark trait of atherosclerotic plaques [ 44 ], but there is very limited information on CC formation in other tissues. Multiple types of hyper-reflective structures were recently identified by spectral-domain OCT imaging in the retina and choroid in retinal pathologies, including AMD [ 10 – 14 ], Coats’ disease [ 15 ], atheroembolic disease [ 16 ], Bietti crystalline dystrophy and other crystalline retinopathies [ 17 ] and diabetic retinopathy [ 18 , 19 ]. The presence of hyper-reflective structures has also been proposed to be a novel prognostic biomarker in diabetic macular oedema [ 10 – 12 , 22 ].…”

“…The origin and composition of hyper-reflective deposits varied depending on the size, shape, location within the retina and disease status. The hyper-reflective foci in AMD were identified as RPE cell remnants [ 14 , 20 , 21 ], while the hyper-reflective foci at the vitreo-retinal interface in diabetic retinopathy were attributed to activated macrophages [ 19 ]. A particular hyper-reflective structure, hyper-reflective crystalline deposits, are suggested to be comprised of CCs; however, these structures cannot be positively identified as CCs solely by spectral-domain OCT imaging, thus the identity of these crystals remains unknown [ 10 – 13 , 15 , 22 – 24 ].…”

“…With the advancement of spectral-domain optical coherence tomography (OCT) imaging, several types of hyper-reflective deposits have been identified in retinal pathologies, including age-related macular degeneration (AMD) [ 10 – 14 ], Coats’ disease [ 15 ], atheroembolic disease [ 16 ], Bietti crystalline dystrophy and other crystalline retinopathies [ 17 ] and diabetic retinopathy [ 18 , 19 ]. The origin and composition of hyper-reflective deposits varies depending on the size, shape, location within the retina and disease status.…”

Assessment of intraretinal hyperreflective foci using multimodal imaging in eyes with age‐related macular degeneration

“…For example, it is also already established that hyperpigmentation on colour may correspond to thickening of the RPE band without evidence of IHRF, thus hyperpigmentation is clearly not specific for IHRF. On the other hand, this was not the purpose of our study, as we sought to better define the CFP and IR correlates of OCT-IHRF which are a well-established and reliable biomarker of AMD progression risk Third, our study only assessed IHRF in the context of AMD, and thus our findings cannot be extrapolated to many other diseases where IHRF may be observed including Stargardt's disease, retinitis pigmentosa and diabetic retinopathy (Battaglia Parodi et al, 2019;Huang et al, 2022;Midena et al, 2021;Yamaguchi et al, 2022). Finally, we should note that while IHRF may have a uniform appearance on OCT, individual IHRF may reflect different pathological entities and may arise from different pathophysiological processes.…”