TIMP-1 associates with myelin membrane and preserves myelin in injured peripheral nerve

Myelin enables rapid impulse propagation in axons across long distances. Following peripheral nerve injury, Schwann cells provide trophic, metabolic, and immune support to damaged neurons. To facilitate myelin repair, Schwann cells activate a robust transcriptional program, including the tissue inhibitor of metalloproteinase (TIMP)-1 gene. TIMP-1 is a potent protease inhibitor and neurotrophic factor, traditionally known as a secreted protein. This study presents the first evidence of a myelin/membrane lipid raft-associated (mm)TIMP-1 protein fraction in the nervous system. Specifically, we identified mmTIMP-1 in the rat sciatic nerve after chronic constriction injury (CCI) using multiple complementary approaches. Dual-immunofluorescence revealed TIMP-1 co-localization with myelin protein in the myelin sheath of CCI nerve. Immunoblotting and mass-spectrometry of sucrose gradient-fractionated nerves further confirmed presence of TIMP-1 in myelin/membrane lipid rafts. Both TIMP-1 and (mm)TIMP-1 levels increased in the nerves during the early phase (day 1) and declined in the late phase (day 28) of CCI. Recombinant (r)TIMP-1 replacement therapy during the late phase CCI, administered by intraneural injection, led to improved myelin neuropathology and accumulation of myelin protein. This study identifies a novel subcellular TIMP-1 fraction associated with the myelin sheath and highlights TIMP-1's reparative activity in peripheral nerve myelin in vivo, opening new avenues for exploring functional activities of TIMP-1 isoforms in the nervous system.