IL-6 induces regionally selective spinal cord injury in patients with the neuroinflammatory disorder transverse myelitis
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
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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Research Article Neuroscience

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 induces regionally specific neural injury in the spinal cord. (A) I...
IL-6 induces regionally specific neural injury in the spinal cord. (A) IL-6 was administered to cortical, hippocampal, and spinal cord organotypic cultures at increasing doses, and cell death was assessed 36 hours later. Data is plotted as the fold induction of death relative to cultures with no IL-6 addition. (B) Adult rats were infused with IL-6 or saline through an intracerebroventricular (IC) cannula at the same rate (0.5 μl/h for 7 days) and concentration (2,000 pg/ml) as that previously administered via a spinal subarachnoid catheter and assessed for weakness. (C) Cortical organotypic cultures were treated with IL-6 and assessed for PARP activity up to 20 hours later. (D) Confocal microscopy of cortex and spinal cord organotypic cultures was performed after the administration of IL-6 to the culture. Scale bars: 50 μm. (E) RT-PCR analysis of iNOS from cortex or spinal cord organotypic cultures was performed at various times after the addition of IL-6. GAPDH serves as a PCR control. (F) Quantitative immunoblot of IL-6R expression from human autopsy tissue lysates. Spinal cord grey and white matter (SCGM and SCWM, respectively) and cortex grey and white matter (CoWM and CoGM, respectively) lysates were generated, subjected to SDS-PAGE, and probed for IL-6R immunoreactivity. (G) Quantitative immunoblot of sIL-6R from the same lysates (shown in chemiluminescent units). (H) Adult rats were infused with either IL-6 or IL-6 plus sIL-6R at a 1:1 molar ratio through a spinal subarachnoid catheter as before. Animals were assessed for hind limb grip strength for the 10-day duration of the experiment. *P < 0.05; **P < 0.04.