The implications of this mTOR-inhibiting activity, as they relate neovascular retinal disorders, were examined via fluorescein angiography (
Fig. 2A). In rat OIR models, returning the pups to normoxia after vaso-obliteration has occurred during the hyperoxic phase should result in the sprouting of new capillaries. However, abnormal vessels may arise in the form of neovascular tufting, called pathological angiogenesis.
25 As can be seen (
Fig. 2B), neovascularization was least extensive in rats treated with rAAV2-shmTOR-GFP (4.28 ± 2.86,
P = 0.00103), whereas untreated, mock-treated, and rAAV2-shCon-GFP-injected animals had neovascularization present in 20.95 ± 6.85, 14.50 ± 2.47, and 16.64 ± 4.92 percent of their total retinal areas, respectively. During vaso-obliteration in the first part of OIR model generation, the creation of a capillary-free region in the rat retina results in an increased amount of avascular areas,
26 and as vessels are regenerated in the second phase, an inverse relationship is found to exist between neovascular tufting and healthy vascular regeneration.
25 As such, a reduction of neovascularization correlates to increased normal revascularization, resulting in decreased avascularity. This was observed in the rat OIR model (
Fig. 2C), in which untreated (26.31 ± 7.06), mock-treated (26.15 ± 4.30), and rAAV2-shCon-GFP-treated (27.96 ± 3.04) rats had greater percentages of avascular areas in their retinas compared with those injected with rAAV2-shmTOR-GFP (12.29 ± 2.57,
P = 0.00310). Hyperoxia only affects retinal capillaries, leaving larger arteries and veins intact. Whereas vascular sprouting from the latter and any unaffected capillaries are responsible for regenerating the capillary network, with neovascular tufting being a dysfunction of this process, retinal arties become tortuous, which is found in a number of retinopathic conditions.
25 Vessel tortuosity was least severe in rats treated with rAAV2-shmTOR-GFP (0.098 ± 0.022,
P = 0.00040), whereas ratios of 0.181 ± 0.040, 0.204 ± 0.074, and 0.201 ± 0.043 were observed in untreated, mock-treated, and rAAV2-shCon-GFP-treated animals, respectively (
Fig. 2D).