[Axonal regeneration in spinal cord injury: key role of galectin-1]

When spinal cord injury (SCI) occurs, a great number of inhibitors of axonal regeneration consecutively invade the injured site. The first protein to reach the lesion is known as semaphorin 3A (Sema3A), which serves as a powerful inhibitor of axonal regeneration. Mechanistically binding of Sem3A to the neuronal receptor complex neuropilin-1 (NRP-1) / PlexinA4 prevents axonal regeneration. In this special article we review the effects of galectin-1 (Gal-1), an endogenous glycan-binding protein, abundantly present at inflammation and injury sites. Notably, Gal1 adheres selectively to the NRP-1/PlexinA4 receptor complex in injured neurons through glycan-dependent mechanisms, interrupts the Sema3A pathway and contributes to axonal regeneration and locomotor recovery after SCI. While both the monomeric and dimeric forms of Gal-1 contribute to "switch-off" classically-activated microglia, only dimeric Gal-1 binds to the NRP-1/PlexinA4 receptor complex and promotes axonal regeneration. Thus, dimeric Gal-1 promotes functional recovery of spinal lesions by interfering with inhibitory signals triggered by Sema3A adhering to the NRP-1/PlexinA4 complex, supporting the use of dimeric Gal-1 for the treatment of SCI patients.