Transcriptional Comparison of Human and Murine Retinal Neovascularization
Background: Retinal neovascularization (RNV) as a result of retinal ischemia, such as in proliferative diabetic retinopathy (PDR) and retinopathy of prematurity (ROP), can lead to vitreous hemorrhage, tractional retinal detachment, and irreversible loss of vision if left untreated. Although panretinal laser photocoagulation and anti-vascular endothelial growth factor (VEGF) injections are efficient treatment modalities, a significant number of patients do not respond to either treatment. This clinical finding suggests that other, previously unrecognized mediators and signaling pathways may contribute to RNV development and could represent valuable targets for future treatments.  Methods: In search of phylogenetically conserved angiogenic mediators, we examined the transcriptional profile of murine RNV from C57BL/6J mice (n=14) in the oxygen-induced retinopathy (OIR) model as well as human RNV membranes from PDR patients (n=7), who had undergone vitrectomy and compared them with corresponding control tissues (n=13, 10 respectively). Genes that were differentially expressed (DEGs) between RNV and control samples were identified for human and murine samples and their associated gene ontology (GO) clusters analyzed. Lastly, human and murine DEGs were compared to identify phylogenetically conserved factors.  Findings: Transcriptional profiles of murine RNV showed that DEGs linked to the activation of the innate immune system (Msn, Cd34), extracellular matrix organisation (Col4a1, Gfap), and regulation of angiogenesis (Col4a2, Fgf2) were significantly upregulated both at the ischemic, preproliferative stage of the disease (OIR p14) as well as at the proliferative stage (OIR p17). While similar GO terms were upregulated in human RNV, only a small overlap in DEGs between both species was detected. Phylogenetically conserved mediators upregulated in both murine and human RNV included ANGPT2, S100A8, MCAM, EDNRA, MRC1, and CCR7.  Interpretation: This study identifies phylogenetically conserved inflammatory and pro-angiogenic mediators that are significantly upregulated in both murine and human RNV. Among them, MCAM, ENDRA and MRC1 emerged as the most upregulated, phylogenetically conserved DEGs not yet implicated in human RNV, thus representing potential new treatment targets for ischemic retinal diseases. Overall design: Retinal tissue from the OIR mouse model from the following groups: nonOIR p14 (n=7), nonOIR p17 (n=6), OIR p14 (n=6), and OIR p17 (n=8).