L-serine reduces spinal cord pathology in a vervet model of preclinical ALS/MND

The early neuropathological features of amyotrophic lateral sclerosis/motor neuron disease (ALS/MND) are protein aggregates in motor neurons and microglial activation. Similar pathology characterizes Guamanian ALS/Parkinsonism dementia complex, which may be triggered by the cyanotoxin b-N-methylamino-L-alanine (BMAA). We report here the occurrence of ALS/MND-type pathological changes in vervets (Chlorocebus sabaeus; n ¼ 8) fed oral doses of a dry powder of BMAA HCl salt (210 mg/kg/day) for 140 days. Spinal cords and brains from toxin-exposed vervets were compared to controls fed rice flour (210 mg/kg/day) and to vervets coadministered equal amounts of BMAA and L-serine (210 mg/kg/ day). Immunohistochemistry and quantitative image analysis were used to examine markers of ALS/MND and glial activation. UHPLC-MS/MS was used to confirm BMAA exposures in dosed vervets. Motor neuron degeneration was demonstrated in BMAA-dosed vervets by TDP-43^þ proteinopathy in anterior horn cells, by reactive astrogliosis, by activated microglia, and by damage to myelinated axons in the lateral corticospinal tracts. Vervets dosed with BMAA þ L-serine displayed reduced neuropathological changes. This study demonstrates that chronic dietary exposure to BMAA causes ALS/MND-type pathological changes in the vervet and coadministration of L-serine reduces the amount of reactive gliosis and the number of protein inclusions in motor neurons.