In addition, as in the early phase of the RVO mouse model, BI-X inhibited the decrease in blood flow in the late phase. In the late phase, aflibercept monotherapy exacerbated blood flow reduction, whereas BI-X monotherapy suppressed the reduction. As the retina (like other tissues) is nourished through systemic blood flow, neuroprotection is potentially achieved by the amelioration of retinal blood flow. At 8 days after occlusion in the retina of the RVO mouse model, TNF-α, Nrp-1, and plexin A1 levels in the retina were notably increased and hardly changed by aflibercept monotherapy; however, all were markedly reduced by BI-X monotherapy (see
Fig. 5). Aflibercept reduced the retinal expression of TNF-α in the early phase of the RVO mouse model (see
Fig. 3B) but had no effect on the retinal expression of TNF-α in the late phase of the RVO mouse model (see
Fig. 5B). Interestingly, the Sema3A neutralizing antibody BI-X reduced the retinal expression of Sema3A and TNF-α in both the early and late phases of the RVO mouse model (see
Fig. 3A,
Fig. 5A). The biphasic reduction of TNF-α expression in the retina observed with BI-X is consistent with the report that TNF-α initiates not only inflammation and response to injury, but also subsequent epidermal repair.
37 These complex effects have also been determined from the involvement of multiple second-messenger pathways of TNF-α signaling.
38 The most commonly reported role of TNF-α in the eye is to induce cell death.
39 In other words, the results of this study indicate that Sema3A neutralizing antibodies may inhibit retinal cell death at any time point during RVO pathology. Direct interactions between Nrp-1 and Fer kinase, which is selectively associated with the NRP1 cytoplasmic domain, have been reported to be important for Sema3A-induced neuronal death,
34 supporting our data on the induction of neuronal cell death through Nrp-1. These results suggest that neutralizing Sema3A could inhibit retinal thinning in the RVO mouse model through inactivation of Sema3A-induced, plexin A1-mediated signaling, and reduce the retinal inflammation.