A novel role for galectin-1 in axonal regeneration in spinal cord

HR QUINTÁ; PASQUINI LA; RABINOVICH GA; PASQUINI JM

Congreso; The 24th Biennial Meeting of ISN-ASN, April 2013. Cancun, México.; 2013

Galectins (Gals) are a family of soluble lectins that form multivalent complexes with glycoconjugates on the cell surface and modulate intracellular signaling pathways for differentiation and survival. Recently, a relationship was described between the ability of Gal-1 to de-activate M1-type microglia in neurodegenerative autoimmune disease (Starossom et al, 2012). However, the effects of this lectin at the neuronal level are poorly understood. Neuropilin-1 (Nrp-1) is a neuronal receptor, which serves as a target of Semaphorin 3A (Sema3A), the latter being an anti-attractant of axonal growth. In the vascular system, Gal-1 has been proposed to act as a ligand for Nrp-1. Our aim was to study the role of Gal-1 in traumatic spinal cord injury (TSCI), since Sema3A expression is turned-on in TSCI and prevents the axonal regeneration via Nrp-1. Gal-1 knockout (Lgals1-/-) mice were used by performing a full TSCI at the thoracic level (T9-T10). These mice were treated with different concentrations of recombinant Gal-1. We demonstrated that Lgals1-/- mice treated with 5 μg of Gal-1 experienced a functional recovery of motricity 6 days post-treatment, structurally associated to neuronal repopulation and high axonal regeneration. In addition, we observed that microglial response was ?turned off? only in Lgals1-/- mice treated with Gal-1 whereas in Lgals1-/- and WT mice treated with vehicle control or WT mice treated with 5 g of Gal-1 this process did not occur. Interestingly, in this last group there was astrocyte hypertrophy in the lesion site. When Gal-1 was increased to 10 g and administered to WT mice, the motor response and axonal regeneration was improved as compared to mice treated with 5 ug of the lectin, whereby Gal-1 has a pro-regenerative isoform-depending action. In this regard, we found a population of cells that co-expressed Nestin and BIII-Neuronal-Tubulin in the lesion. Moreover, exogenous Gal-1 bound the surface of injured motoneurons promoting a spread out of Nrp-1 from a specific point (clustering) to all cellular body, in this point using 3D confocal microscopy reconstruction we could see that Gal-1 and Nrp-1 are linked. Using immunoprecipitation assays we found that only the dimeric form of Gal-1 interacted with Nrp-1. In addition, only the treatment with dimeric form of Gal-1 produced a functional motor recovery. In conclusion, the dimeric form of Gal-1 binds to Nrp-1, (a protein-glycan interaction), and promotes the neuronal regeneration probably by avoiding the binding of Sema3A with Nrp-1 receptor and blocking the inhibitory effect on neuronal regeneration.