Induction of proinflammatory molecules in mice with amyotrophic lateral sclerosis: No requirement for proapoptotic interleukin‐1β in neurodegeneration

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Abstract
Recent studies have demonstrated the activation of caspase-1 and caspase-3 in mice expressing mutant superoxide dismutase 1 (SOD1), models of amyotrophic lateral sclerosis. Caspase-1 converts the prointerleukin-1β into a potent proinflammatory molecule involved in the innate immune response and in neurodegenerative diseases. We report on the chronic expression of interleukin-1β mRNA in the spinal cord of SOD1G37R mice, together with robust mRNA expression for the nuclear factor-κB (NF-κB) inhibitor IκBα, for other proinflammatory cytokines and chemokines (interleukin-6, tumor necrosis factor-α, monocyte chemoattractant protein-1) and for the toll-like receptor TLR2 involved in innate immunity. To further assess the interleukin-1β contribution to neurodegeneration, we generated mice expressing SOD1G37R in a context of interleukin-1β gene knockout. Surprisingly, the absence of interleukin-1β had no effect on the life span of SOD1G37R mice, nor on the extent of motor axon degeneration at age 7 and 10 months. Whereas neither compensatory induction of the interleukin-1α mRNA nor increases in mRNA levels for IκBα, tumor necrosis factor-α and macrophage chemoattractant protein-1 occurred as a result of interleukin-1β gene disruption, enhanced levels of TLR2 mRNA were detected in SOD1G37R mice lacking interleukin-1β. We conclude that interleukin-1β does not directly contribute to motor neuron degeneration in SOD1G37R mice, but it may act as a modulator of the innate immune response.