The cyanobacterial toxins BMAA and 2,4-DAB perturb the l-serine biosynthesis pathway and induce systemic changes in energy metabolism in human neuroblastoma cells: A proteomic study

Blue-green algae (cyanobacteria), an ancient phylum of bacteria, produce a wide array of secondary metabolites that are toxic to humans. Rapid growth of cyanobacteria in an aquatic environment can result in algal blooms capable of turning waterways green and increasing toxin levels in the environment. Cyanobacterial toxins were first linked to the high incidence of a complex neurodegenerative disorder reported on the island of Guam in the 1940s but more recently have been linked to clusters of sporadic amyotrophic lateral sclerosis (sALS) worldwide. The non-protein amino acid β-N-methylamino-L-alanine (BMAA) and its isomer L-2,4-diaminobutyric acid (2,4-DAB) are produced concurrently by most cyanobacterial species. We carried out proteomic analysis on human neuroblastoma cells treated with BMAA and 2,4-DAB to determine the underlying mechanisms of toxicity resulting from exposure to these cyanotoxins and identified significant changes in the l-serine biosynthesis pathway as well as pathways associated with energy production in the cell such as fatty acid ß-oxidation and glycolysis. The impact on the serine biosynthetic pathway was supported by demonstrating a significant decrease in both mRNA and protein levels of the enzyme 3-phosphoglycerate dehydrogenase (PHGDH) the first committed step in serine biosynthesis. PHGDH uses 3-phospho-D-glycerate (3PG) an intermediate in the glycolytic pathway as a substrate, and co-incubation of cells with l-serine restored expression levels of PHGDH as did cell pre-treatment with the glycolytic product pyruvate. This is the first study to link exposure to BMAA and 2,4-DAB to impairments in the l-serine biosynthesis pathway and broad disturbances in energy metabolism.