Nidogen/NID-1 guides regenerating motor axons in the mature nervous system

Abstract

Restoring function to injured axons requires not only regeneration, but also accurate guidance and synapse reformation. Our understanding of how regenerating axons navigate the mature nervous system remains limited, as growth cones confront a cellular and molecular landscape distinct from development. Using Caenorhabditis elegans, we found that the basement membrane protein Nidogen (NID-1) promotes local guidance of regenerating motor axons in the mature nervous system by facilitating their growth alongside neighboring intact neuronal processes. Regenerating cholinergic axons preferentially track the branched dendrites of the PVD mechanosensory neuron or, in the absence of PVD dendrites, are guided alongside GABAergic commissures instead. Loss of nid-1 disrupts this guidance, reducing axon-PVD colocalization, increasing displacement from the pre-injury point of contact with the dorsal nerve cord, and disrupting synapse reformation and functional recovery. Tissue-specific rescue indicates that NID-1 expressed by body wall muscles or the hypodermis is sufficient to guide regenerating axons, whereas muscle-derived NID-1 is required to restore synapse reformation. Genetic data indicate that NID-1 function guides regenerating axons in coordination with laminin and integrin. Although this complex primarily directs cholinergic motor axons, ectopic integrin expression in GABAergic neurons is sufficient to reroute their regenerating axons alongside PVD dendrites in a NID-1-dependent manner. Together, these findings identify a NID-1-dependent post-developmental mechanism for directing regenerating axons and promoting functional repair.