Neuronal hyperexcitability in dystrophin-deficient mdx hippocampal neurons: the importance of interleukin-6 and GABAergic regulation

Abstract

Duchenne Muscular Dystrophy (DMD) is a severe neuromuscular disorder arising from loss of the structural protein, dystrophin. It also often presents with cognitive deficits and susceptibility to epilepsy. Expressed in neurons of the hippocampus, dystrophin plays an important role in synapse formation, specifically the post-synaptic organisation of γ-aminobutyric acid A receptors (GABA_ARs). This study explored possible interactions between interleukin (IL)-6, which is elevated in DMD, and GABA_AR signalling in cultured hippocampal neurons of dystrophic mdx mice. Immunofluorescent imaging revealed altered development of network connectivity that displayed similar characteristics to dystrophin-expressing neurons cultured in elevated levels of IL-6. Mdx neurons dependably exhibited spontaneous oscillations. Calcium (Ca²⁺) signalling was further modulated by exposure to agonists and antagonists of GABA_A and GABA_BRs. IL-6-evoked Ca²⁺ responses were enhanced by muscimol, a GABA_AR agonist, in wildtype (WT) and mdx neurons, whilst bicuculline, a GABA_AR antagonist, only suppressed IL-6-evoked Ca²⁺activity in WT neurons. The GABA_BR agonist, baclofen, enhanced IL-6-evoked Ca²⁺ responses only in mdx neurons. Our findings support dysfunctional GABAergic signalling in hippocampal neurons that lack dystrophin, resulting in aberrant neuronal network excitability. The contribution of elevated levels of IL-6 further impact upon Ca²⁺ dyshomeostasis in dystrophic neurons and may underpin cognitive changes reported in dystrophinopathies.

Keywords: Duchenne muscular dystrophy; Dystrophin; GABA; Hippocampus; Learning; Memory.