Laquinimod prevents cuprizone-induced demyelination independent of Toll-like receptor signaling

Abstract

Objective: To test whether Toll-like receptor (TLR) signaling plays a key role for reduced nuclear factor B (NF-κB) activation after laquinimod treatment in the model of cuprizone-induced demyelination, oligodendrocyte apoptosis, inflammation, and axonal damage. Methods: Ten-week-old C57BL/6J, TLR4-/-, and MyD88-/- mice received 0.25% cuprizone for 6 weeks and were treated daily with 25 mg/kg laquinimod or vehicle. After 6 weeks of demyelination, extent of demyelination, oligodendrocyte density, microglia infiltration, and axonal damage were analyzed in the corpus callosum. Additionally, we analyzed primary mouse astrocytes from C57BL/6J, TLR4-/-, MyD88-/-, and TRIF-/- mice for alteration in NF-κB signaling. Results: Vehicle-treated controls from C57BL/6J, TLR4-/-, and MyD88-/- mice displayed extensive callosal demyelination as well as microglial activation. In contrast, mice treated with 25 mg/kg laquinimod showed mainly intact callosal myelin. The demyelination score was significantly higher in all untreated mice compared to mice treated with laquinimod. There were significantly fewer APP-positive axonal spheroids, Mac3-positive macrophages/microglia, and less oligodendrocyte apoptosis in the corpus callosum of laquinimod-treated mice in comparison to untreated controls. Stimulated primary mouse astrocytes from laquinimod-treated groups show reduced NF-kB activation compared to vehicle-treated controls. Conclusions: Our results confirm that laquinimod prevents demyelination in the cuprizone mouse model for multiple sclerosis via downregulation of NF-kB activation. This laquinimod effect, however, does not involve upstream Toll-like receptor signaling.