Retinal Pericytes: Characterization of Vascular Development-Dependent Induction Time Points in an Inducible NG2 Reporter Mouse Model.

Purpose/aim of the study: In the retina, defects in pericytes (PCs) function/loss are associated with various complications; however, the exact pathological mechanisms are still not fully elucidated. Following the behavior of retina-resident PCs during health and disease will reveal new insights for both the understanding of pathological mechanisms and the development of new regenerative therapies for the treatment of retinopathies. The main goal of this study is to determine whether the NG2-reporter mouse (NG2CreERTM-eGFP) is a suitable model to study the fate of retina-resident PCs. MATERIAL AND METHODS: Vascular development-dependent reporter induction in retinal PCs was evaluated at different time points [(a) > P21, (b) < P21, and (c) P1 to > P21)] and additionally four different modes of application were tested. Reporter expression was evaluated by enhanced green fluorescent protein (eGFP) immunofluorescence by confocal microscopy and induction efficiency was calculated by analyzing NG2-expressing PCs in comparison to eGFP-labeled PCs in the three capillary layers. RESULTS: eGFP-positive PCs were detected in the three retinal capillary layers at all time points and administration routes tested. Multiple tamoxifen (TAM) applications in adult (> P21) NG2CreERTM-eGFP mice resulted in 3.59% eGFP-positive PCs. 2.37% eGFP-labeled PCs were detected after single intraperitoneal TAM injections at early postnatal days (P2/P5); however, just 1.61% PCs revealed reporter expression upon activation via the lactating mother (P4-P7). The highest number of eGFP-labeled PCs (7.09%) was detected following triple TAM administrations (P10-P12). The number of reporter-positive PCs doubled using homozygous animals. CONCLUSION: Despite low recombination efficiency in the used PC-specific fate mapping mouse model, changes in NG2 promoter activity of PCs during vascular development are indicated by single and multiple TAM inductions at different developmental time points. Nevertheless, these findings need further confirmation in up-coming studies by using homozygous NG2CreERTM-eGFP mice and additionally by mating the NG2CreERTM with a different reporter mouse to increase the low recombination efficiency.