IL-6 induces regionally selective spinal cord injury in patients with the neuroinflammatory disorder transverse myelitis
Adam I. Kaplin, … , Peter A. Calabresi, Douglas A. Kerr
Adam I. Kaplin, … , Peter A. Calabresi, Douglas A. Kerr
Published October 3, 2005
Citation Information: J Clin Invest. 2005;115(10):2731-2741. https://doi.org/10.1172/JCI25141.
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IL-6 induces regionally selective spinal cord injury in patients with the neuroinflammatory disorder transverse myelitis

Abstract

Transverse myelitis (TM) is an immune-mediated spinal cord disorder associated with inflammation, demyelination, and axonal damage. We investigated the soluble immune derangements present in TM patients and found that IL-6 levels were selectively and dramatically elevated in the cerebrospinal fluid and directly correlated with markers of tissue injury and sustained clinical disability. IL-6 was necessary and sufficient to mediate cellular injury in spinal cord organotypic tissue culture sections through activation of the JAK/STAT pathway, resulting in increased activity of iNOS and poly(ADP-ribose) polymerase (PARP). Rats intrathecally infused with IL-6 developed progressive weakness and spinal cord inflammation, demyelination, and axonal damage, which were blocked by PARP inhibition. Addition of IL-6 to brain organotypic cultures or into the cerebral ventricles of adult rats did not activate the JAK/STAT pathway, which is potentially due to increased expression of soluble IL-6 receptor in the brain relative to the spinal cord that may antagonize IL-6 signaling in this context. The spatially distinct responses to IL-6 may underlie regional vulnerability of different parts of the CNS to inflammatory injury. The elucidation of this pathway identifies specific therapeutic targets in the management of CNS autoimmune conditions.

Authors

Adam I. Kaplin, Deepa M. Deshpande, Erick Scott, Chitra Krishnan, Jessica S. Carmen, Irina Shats, Tara Martinez, Jennifer Drummond, Sonny Dike, Mikhail Pletnikov, Sanjay C. Keswani, Timothy H. Moran, Carlos A. Pardo, Peter A. Calabresi, Douglas A. Kerr

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IL-6 is necessary and sufficient to induce injury of oligodendrocytes an...
IL-6 is necessary and sufficient to induce injury of oligodendrocytes and axons in spinal cord organotypic cultures by generating NO. (A) CSF (100 μl) from a TM or control patient was added to culture media of spinal cord organotypic cultures, and cellular injury was assessed by ethidium homodimer uptake with Hoechst counterstain (inset). IL-6 was immunodepleted by preincubating TM CSF with an IL-6 antibody and clearing the IL-6 antibody complex with protein A sepharose. Magnification, ×20. (B) Tissue lysates from spinal cord organotypics were generated at various times after the administration of IL-6 and subjected to SDS-PAGE followed by immunoblot analysis. (C) Quantification of the data shown in B by chemiluminescent signal intensity of 3 independent experiments. (D) RT-PCR analysis of RNA derived from spinal cord organotypic cultures at the indicated times after addition of IL-6 at 2,000 pg/ml. (E) Dual-color confocal microscopy was carried out with spinal cord organotypic cultures treated with IL-6 for 24 hours. Microglia were identified by incubating live cultures with DiI-Ac-LDL, which is endocytosed by phagocytosing cells. After fixation, iNOS immunohistochemistry was carried out, revealing the expression of iNOS within microglia. Scale bar: 50 μm. (F) NT and iNOS preferentially accumulated within the exterior white matter of spinal cord organotypic cultures. Scale bar: 200 μm. (G) Addition of IL-6 to a final concentration of 2,000 pg/ml to spinal cord organotypic cultures in the presence or absence of the iNOS inhibitor 1400W. *P < 0.05. (H) WT and iNOS-heterozygous and -KO spinal cord organotypic cultures were exposed to IL-6 and assessed for cellular death.