M08 Laquinimod Reduces Neuronal Caspase-6 Activation And Axonal Degeneration In Vitro

Abstract

<h3>Background</h3> Laquinimod is an immunomodulatory compound that reduces relapse rate, brain atrophy and disability progression in multiple sclerosis. It has well-documented effects on inflammation, is widely distributed in the CNS and has been shown to ameliorate axonal damage <i>in vitro</i>and <i>in vivo</i>through an unknown mechanism. We have shown recently that caspase-6 is an important mediator in axonal degeneration, since sympathetic neurons derived from caspase-6 -/- mice do not degenerate when cultured in the absence of neuronal growth factor (NGF). We therefore investigated whether the beneficial effect of Laquinimod on axonal damage is mediated by caspase-6. <h3>Aim</h3> To investigate neuron-specific beneficial effects of Laquinimod. <h3>Methods</h3> Cell-free and cell-based enzymatic activity assays were used to determine whether Laquinimod directly inhibits caspase-6. To investigate an effect on intraneuronal caspase-6 activity, primary cortical neurons were treated with camptothecin in the presence or absence of Laquinimod, and cleavage of the caspase-6 specific substrate lamin A was quantified by ELISA. Axonal degeneration of primary sympathetic neurons from the superior cerebral ganglion was induced by NGF withdrawal in the presence or absence of Laquinimod. <h3>Results</h3> Laquinimod did not directly inhibit caspase-6 activity in cell-free or transfection-based cellular systems. However, the presence of Laquinimod in camptothecin-stressed primary cortical neuron cultures led to a significant decrease in caspase-6 activation. In cultures of primary superior cerebral ganglion neurons, Laquinimod partially protected axons from degeneration after NGF withdrawal, a process that is specifically dependent on caspase-6 activity, in agreement with the reduction of caspase-6 activity observed in stressed cortical neurons. <h3>Conclusions</h3> The beneficial effects of Laquinimod described so far involve neuroprotection through the downregulation of glial activation, whereas our findings represent a novel, purely neuronal mechanism of action for this drug. We propose that by preventing neuronal caspase-6 activation and axonal degeneration, Laquinimod might also provide benefits in other neurodegenerative disorders such as Huntington’s disease that are associated with excessive activation of caspase-6.