Targeting pericytes in the retina: characterization of the inducible NG2-CreERT2 knock-in mouse model.

Pericytes (PCs) are mural cells embedded in a common basement membrane with endothelial cells (ECs) on capillaries. They are key players in the regulation of stability and function of blood vessels and are an essential component of the blood-brain and blood-retinal barrier. In addition, PCs are reported to be involved in wound healing and tissue regeneration and represent a promising target for the modulation of scarring processes. Due to their heterogeneous expression pattern, a single specific molecular marker for PCs remains elusive. Inducible reporter mouse models represent a frequently used tool for tracing the fate of a specific cell type, via the expression of a fluorescence reporter protein in the target cell following tamoxifen (TAM) induction. In a recent study, we characterized the TAM-inducible reporter mouse model NG2-CreERTM-tdTomato and demonstrated specific but marginal PC labeling in the retinal capillary plexuses with mean values ranging from 21.9 to 35.5 %. Since such a low labeling efficiency is not sufficient for reliable cell tracing, we characterized a TAM-inducible Cre mouse model expressing the enhanced estrogen receptor ERT2 in the present work. The NG2-CreERT2 knock-in mouse was crossbred with the tdTomato Ai9 reporter mouse to assess efficiency of PC labeling in the retina. The expression of tdTomato was restricted to mural cells, labeling vascular smooth muscle cells on larger vessels and PCs on capillaries. The use of the CreERT2 mouse resulted in an increased percentage of labeled PCs in the superficial layer of the retina with mean values ranging from 68.5 to 70.2 %.