Abstract
Purpose :
Metabolic syndrome (MetS) is a combination of impairments including hyperlipidemia, hyperglycemia, and obesity. Patients displaying MetS have greater risk for glaucoma, diabetic retinopathy, and Alzheimer’s disease. Mounting evidence suggests that microglial perturbations contribute to the pathogenesis of neurological disorders. It is unclear if metabolic stress modulates microglial responses, despite MetS being a risk factor for neurodegenerative diseases. Furthermore, direct comparisons between retinal and brain microglia are lacking. We characterized brain and retinal microglial transcriptional responses to metabolic stress using single cell RNA-sequencing (scRNA-seq).
Methods :
We performed scRNA-seq comparing retinal and brain CD11B+ cells from high-fat diet (HFD) fed or standard diet fed C57BL/6J mice and New Zealand Obese mice, a mouse strain that exhibits hallmarks of MetS. Animals were fed either a standard diet or HFD from 2-9mo of age. We sequenced microglia from n=3 mice per mouse strain per sex per diet at 9mo and n=3 mice per strain per sex at 2mo. We performed integration and clustering using Seurat. Differential expression analyses were performed on pseudobulked counts and subjected to standard RNA-seq analysis methods including limma and EdgeR.
Results :
Many retinal, but few brain, microglia were within a cluster noted by Klf2 expression. This cluster displayed increased expression of genes associated TNF signaling, angiogenesis and phagosome formation relative to homeostatic microglia. Previously defined microglial transcriptional states that are modulated in response to neurodegeneration including disease-associated microglia, did not expand in response to prolonged metabolic stress in either retina or brain. However, homeostatic microglia altered expression of genes involved in vessel development and health, and cellular senescence in response to metabolic stress or HFD.
Conclusions :
scRNA-seq of brain and retinal microglial identified transcriptional differences between retinal and brain microglia relevant to retinal pathologies. Metabolic stress, unexpectedly, did not alter the abundance of microglial states but rather altered genes associated with vascular integrity and cellular stress. Collectively, this work provides the foundation to unveil roles for microglia in the context of obesity and MetS in the retina and brain.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.