Unveiling a unique microglial phenotype promoting oxidation in the iBRB: insights from single-cell transcriptomics in the NPDR rat model

BACKGROUND: Early diagnosis and targeted treatment of inner blood-retinal barrier (iBRB) impairment in non-proliferative diabetic retinopathy (NPDR) present significant challenges. This study investigates the cellular heterogeneity and early lesions in the iBRB microenvironment. METHODS: We created a single-cell transcriptional atlas of NPDR using retinas from Zucker Diabetic Fatty rats, focusing on the expression of cells within the iBRB microenvironment, particularly microglia. We performed cell-cell gene interaction analyses to investigate intercellular communications among different cell types in the iBRB. Additionally, we conducted differentiation potential and trajectory analysis, transcription factor regulatory network characterization, and enrichment analysis of microglia. We also employed transmission electron microscopy, immunofluorescence, and histological analysis to validate the hypothesis. RESULTS: Based on retinal samples from NPDR rats which had retinal edema and kidney damage, and normal rats, we selected 36,821 cells for subsequent analysis using single-cell sequencing. We identified 669 cells in iBRB and microglia had the highest connectivity value by enrichment analysis. 980 differentially expressed genes related to microglia divide it into 4 subtypes. Among them, Spp1 highly expressed microglia subtype 2 had the highest differentiation potential and was significantly upregulated after NPDR lesions. By integrating histological and biochemical analysis results, the roles of the subtype in the differentiation of microglia in the iBRB microenvironment, such as oxidative stress and apoptosis, were well validated. CONCLUSION: This study identified a novel microglia type in NPDR rats, offering valuable insight into targeted therapeutic strategies for NPDR patients and enhancing our understanding of microglial regulation within the iBRB.