Inhibiting p38 MAPK alpha rescues axonal retrograde transport defects in a mouse model of ALS

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease caused by the degeneration of upper and lower motor neurons. Defects in axonal transport have been observed pre-symptomatically in the SOD1(G93A) mouse model of ALS, and have been proposed to play a role in motor neuron degeneration as well as in other pathologies of the nervous system, such as Alzheimer's disease and hereditary neuropathies. In this study, we screen a library of small-molecule kinase inhibitors towards the identification of pharmacological enhancers of the axonal retrograde transport of signalling endosomes, which might be used to normalise the rate of this process in diseased neurons. Inhibitors of p38 mitogen-activated protein kinases (p38 MAPK) were identified in this screen and were found to correct deficits in axonal retrograde transport of signalling endosomes in cultured primary SOD1(G93A) motor neurons. In vitro knockdown experiments revealed that the alpha isoform of p38 MAPK (p38 MAPK alpha) was the sole isoform responsible for SOD1(G93A)-induced transport deficits. Furthermore, we found that acute treatment with p38 MAPKa inhibitors restored the physiological rate of axonal retrograde transport in vivo in early symptomatic SOD1(G93A) mice. Our findings demonstrate the pathogenic effect of p38 MAPKa on axonal retrograde transport and identify a potential therapeutic strategy for ALS.