title: L-BMAA induced ER stress and enhanced caspase 12 cleavage in human neuroblastoma SH-SY5Y cells at low nonexcitotoxic concentrations.
abstract: The cyanobacterial β-N-methylamino-L-alanine (L-BMAA) is described as a low-potency excitotoxin, possibly a factor in the increased incidence of amyotrophic lateral sclerosis (ALS) and Parkinsonism-dementia complex (PDC) in Guam. The latter association is intensively disputed, as L-BMAA concentrations required for toxic effects exceed those assumed to occur via food. The question thus was raised whether L-BMAA leads to neurodegeneration at nonexcitotoxic conditions. Using human SH-SY5Y neuroblastoma cells, L-BMAA-transport, incorporation into proteins, and subsequent impairment of cellular protein homeostasis were investigated. Binding of L-BMAA to intracellular proteins, but no clear protein incorporation was detected in response to (14)C-L-BMAA exposures. Nevertheless, low L-BMAA concentrations (≥ 0.1mM, 48 h) increased protein ubiquitination, 20S proteasomal and caspase 12 activity, expression of the endoplasmic reticulum (ER) stress marker CHOP, and enhanced phosphorylation of elf2α in SH-SY5Y cells. In contrast, high L-BMAA concentrations (≥ 1mM, 48 h) increased reactive oxygen species and protein oxidization, which were partially ameliorated by coincubation with vitamin E. L-BMAA-mediated cytotoxicity was observable 48 h following ≥ 2mM L-BMAA treatment. Consequently, the data presented here suggest that low L-BMAA concentrations result in a dysregulation of the cellular protein homeostasis with ensuing ER stress that is independent from high-concentration effects such as excitotoxicity and oxidative stress. Thus, the latter could be a contributing factor in the onset and slow progression of ALS/PDC in Guam.
authors.affiliation: Department of Human and Environmental Toxicology, University of Konstanz, 78457 Konstanz, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Okle
authors.forename: Kerstin
authors.initials: K
authors.lastname: Stemmer
authors.forename: Ulrich
authors.initials: U
authors.lastname: Deschl
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Dietrich
mesh_terms: D000599:Amino Acids, Diamino / Q000633:toxicity*; D000690:Amyotrophic Lateral Sclerosis / Q000139:chemically induced / Q000453:epidemiology / Q000378:metabolism; D053454:Caspase 12 / Q000378:metabolism*; D018929:Cell Culture Techniques; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D000087522:Cyanobacteria Toxins; D004305:Dose-Response Relationship, Drug; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity*; D006141:Guam / Q000453:epidemiology; D057809:HEK293 Cells; D006801:Humans; D010300:Parkinson Disease / Q000453:epidemiology / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013494:Supranuclear Palsy, Progressive / Q000139:chemically induced / Q000453:epidemiology / Q000378:metabolism; D057149:Ubiquitinated Proteins / Q000378:metabolism
chemical_list: D000599:Amino Acids, Diamino; D000087522:Cyanobacteria Toxins; D018690:Excitatory Amino Acid Agonists; D017382:Reactive Oxygen Species; D057149:Ubiquitinated Proteins; C001824:beta-N-methylamino-L-alanine; C506444:CASP12 protein, human; D053454:Caspase 12