Characterization and Inhibition of the Interactions of the Alpha-Secretase ADAM17 with the Neuronal-Myelin Signaling Complex Upon Spinal Cord Injury

Upon spinal cord injury, axons attempting to regenerate need to overcome the repulsive actions of myelin- associated inhibitors, including the myelin-associated glycoprotein, Nogo-A, and the oligodendrocyte myelin glycoprotein. These inhibitors bind and signal through a neuronal receptor/co-receptor/transducer complex comprised of NgR1, Lingo-1 and p75. Consequently, p75 is cleaved by alpha-secretase followed by gamma- secretase, triggering downstream signaling that inhibits axonal regrowth. ADAM10 and ADAM17 are both known to function as alpha secretases in neurons. We previously documented that the ganglioside GT1b mediates the assembly of neuronal receptor/co-receptor/transducer complex (NgR1/Lingo-1/p75) and this complex gains the ability to bind to the myelin ligands MAG or Nogo-A (a 5-component neuron-myelin signaling complex). Our preliminary studies also highlighted that that ADAM17, and not ADAM10, is the alpha secretase that recognizes and cleaves p75 when it is a part of a 5-component neuron-myelin signaling complex comprising of NgR1, Lingo- 1, p75, GT1b and a myelin inhibitor. Using a panel of anti-ADAM17 monoclonal antibodies (mAbs) generated in our laboratory, we were able to abrogate the cleavage of p75 in a neuroblastoma-glioma cell line (NG108-15) and to reverse the neurite outgrowth inhibition by the myelin-associated inhibitor MAG. Our studies, however, raise new questions that warrant further investigation. The molecular details of the interactions of the three myelin-based ligands with the neuronal receptor/co-receptor (NgR1/Lingo-1) complex and the specific role of p75 in mediating/stabilizing these interactions, resulting in the initiation downstream signaling, are still elusive. Likewise, the role of the three different myelin-based ligands in the activation of the alpha secretase ADAM17 and in stabilizing the ADAM17 interactions with the 5-component neuron-myelin signaling complex, ensuing regulated intramembrane proteolysis of p75, need to be elucidated. We now propose to carry out multi- disciplinary studies, encompassing biochemical, biophysical, structural and cell biological (using different neuronal cell lines and primary cortical neurons) approaches, that will address these questions and provide new mechanistic understanding of the neuron-myelin interactions and signaling upon spinal cord injury. Our studies will not only provide the first high-resolution structures of neuron-myelin signaling complexes but will also explore a new approach to promote neuronal regenerations via the use of novel, therapeutic alpha secretase-targeting monoclonal antibodies that reverse the myelin-induced neurite outgrowth inhibition. Project Number: 1R21NS144867-01A1 | Fiscal Year: 2026 | NIH Institute/Center: National Institute of Neurological Disorders and Stroke (NINDS) | Principal Investigator: DIMITAR NIKOLOV | Institution: SLOAN-KETTERING INST CAN RESEARCH, NEW YORK, NY | Award Amount: $484,000 | Activity Code: R21 | Study Section: Drug Discovery and Molecular Pharmacology B Study Section[DMPB] View on NIH RePORTER: https://reporter.nih.gov/project-details/11374039