Inhibition of Retinal Ganglion Cell Axonal Outgrowth Through the Amino-Nogo-A Signaling Pathway

Nogo-A is a myelin-derived inhibitor playing a pivotal role in the prevention of axonal regeneration. A functional domain of Nogo-A, Amino-Nogo, exerts an inhibitory effect on axonal regeneration, although the mechanism is unclear. The present study investigated the role of the Amino-Nogo-integrin signaling pathway in primary retinal ganglion cells (RGCs) with respect to axonal outgrowth, which is required for axonal regeneration. Immunohistochemistry showed that integrin alpha v, integrin alpha 5 and FAK were widely expressed in the visual system. Thy-1 and GAP-43 immunofluorescence showed that axonal outgrowth of RGCs was promoted by Nogo-A siRNA and a peptide antagonist of the Nogo-66 functional domain of Nogo-A (Nep1-40), and inhibited by a recombinant rat Nogo-A-Fc chimeric protein (a-(3)20). Western blotting revealed increased integrin alpha v and p-FAK expression in Nogo-A siRNA group, decreased integrin alpha v expression in a-(3)20 group and decreased p-FAK expression in Nep1-40 group. Integrin alpha 5 expression was not changed in any group. RhoA G-LISA showed that RhoA activation was inhibited by Nogo-A siRNA and a-(3)20, but increased by Nep1-40 treatment. These results suggest that Amino-Nogo inhibits RGC axonal outgrowth primarily through the integrin alpha v signaling pathway.