Serum neurofilament light reveals the contraction from widespread to lesion-bound neuroaxonal injury during autoimmune neuroinflammation
Blood-based neurofilament light (sNfL) indicates neuroaxonal injury in multiple sclerosis and is on the cusp of being implemented into clinical routine. However, anatomical origins and pathophysiological mechanisms of NfL release during acute relapses and later chronic disease stages are still poorly understood. Here, we applied immunohistochemistry, single molecule array, spatial transcriptomics and microglia/axon co-cultures to gain insight into spatio-temporal NfL release in experimental autoimmune encephalomyelitis (EAE). Results: Association of spinal cord white matter lesions and sNfL levels revealed a distinct, stage-dependent anatomical pattern of neuroaxonal damage: In chronic EAE, sNfL levels were predominately associated with anterolateral lumbar lesions, whereas in early EAE sNfL showed no correlation with lesions in any anatomical location. Furthermore, neuroaxonal damage in late EAE was largely confined to white matter lesions, but showed a widespread distribution in early EAE. Followingthis spatio-temporal pattern of neuroaxonal damage, spatial transcriptomics revealed a widespread cyto- and chemokine response at early disease stages, whereas late EAE was characterized by a prominent glial cell accumulation in white matter lesions. These findings were corroborated by immunohistochemistry and micro-glia/axon co-cultures, which further revealed a strong association between CNS myeloid cell activation and neuroaxonal damage both in vivo and in vitro. Interpretation: Our data demonstrate that sNfL release in EAE driven by CNS myeloid cells exhibits progress in a disease stage-dependent centripetal manner from normal-appearing white matter to focal white matter lesions. These findings may further aid the interpretation of elevated sNfL levels in multiple sclerosis patients at different disease stages. Overall design: 3 animals for each disease stage, 2 for healthy control