In Vivo Optogenetic Manipulation of Transgene Expression in Retinal Neurovasculature.

The retina is prone to developing pathological neovascularization, a leading cause of blindness in humans. Because excess neovascularization does not affect the entire retina, global inhibition treatment of angiogenesis critically interferes with healthy, unaffected retinal tissue. We therefore established an in vivo photoactivated gene expression paradigm which would allow light-mediated targeting of antiangiogenic genetic treatment only to affected retinal regions. We synthesized a "caged" (i.e., reversibly inhibited) photosensitive 4-hydroxytamoxifen analog. Molecular docking analyses validated its reduced transcriptional activity. Caged 4-hydroxytamoxifen was intravitreally injected into mice harboring the inducible Cre/lox system, with CreERT2 being expressed via the Tie2 promoter in the neurovasculature. Subsequent in vivo irradiation of eyes significantly induced retinal expression of a Cre-dependent transgene in retinal blood vessels. Using GFAP-CreERT2 mice, successful photoactivation was also achieved in eyes and also in ex vivo brain slices for validation of the approach. This highlights the possibility of light-mediated gene therapies specific for the retina, a key first step in personalized medicine.