Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB252

Poster Communications

Synaptic expression of interleukin-6 receptors and dystrophin may indicate a role in cognitive deficits associated with loss of dystrophin.

K. A. Stephenson1, C. Shanahan1, M. G. Rae1, D. O'Malley1

1. Physiology, University College Cork, Cork, Cork, Ireland.

The symptoms of Duchenne Muscular Dystrophy (DMD), a heritable X-linked recessive disorder which affects approximately 1 in 3500 live male births, are due to loss of the cytoskeletal protein, dystrophin. Dystrophin has a crucial role in protecting skeletal muscle from contraction-induced damage but is also expressed in neurons of some brain regions, such as the hippocampus. An absence of dystrophin can result in dysfunctional synapses in both DMD boys and the dystrophin-deficient mdx mouse, and DMD patients exhibit significant deficits in cognitive function (1). Chronic inflammation in DMD is associated with elevated circulating levels of the pro-inflammatory cytokine, interleukin-6. Although typically found at low levels in the healthy brain, IL-6 can be elevated in diseased brains where cognitive function is also impaired (2, 3). The aim of this study was therefore to determine if IL-6 receptors (IL-6Rs) are co-expressed with dystrophin at hippocampal synapses. If so, this may indicate a role for IL-6 in dysregulated synaptic transmission associated with loss of dystrophin. Dissociated hippocampal neurons (3-5 day old) from dystrophin-expressing C57BL/6 mice were cultured for 10-12 days in culture medium with or without supplemental recombinant IL-6 (1nM). Immunofluorescence and confocal microscopy were used to visualise fixed hippocampal neurons labelled with antibodies against IL-6 receptors, synaptophysin and dystrophin (n=3 cultures). RT- qPCR was used to compare gene expression of IL-6 and IL-6R in WT and mdx hippocampal tissue (n=10 per group). IL-6R expression was present in cell bodies and processes of cultured hippocampal neurons and was co-localised with the pre-synaptic marker, synaptophysin. Incubation with supplemental IL-6 resulted in clustering of IL-6Rs, particularly within neuronal somata. Dystrophin expression was also evident in synaptophysin-expressing clusters but was unaffected by incubation with IL-6. Although peripheral IL-6 is elevated in both DMD patients and mdx mice, we did not find any differences in the gene expression of IL-6 (p>0.05) or IL-6R (p>0.05) between our WT or mdx hippocampal tissue. These findings indicate that pre-synaptic IL-6Rs may interact with dystrophin and contribute to synaptic transmission in hippocampal neurons. Although we did not detect differences in overall hippocampal IL-6Rs in WT and mdx tissue using RT-qPCR, further studies examining synaptic expression of IL-6Rs in dystrophin-deficient mdx mouse hippocampal neurons may help to elucidate the possible role of this cytokine in dystrophin-deficient associated cognitive dysfunction.

Where applicable, experiments conform with Society ethical requirements