Background: Neurodegenerative diseases such as Parkinson’s disease and motor neurone disease are characterised by protein misfolding and deposition of protein aggregates in the nervous system. In 90% of cases these diseases are sporadic with no known cause. It is essential therefore that we identify the environmental factors involved. Non-protein amino acids (NPAAs) present in the environment have been implicated as causative factors in neurological disorders since they can be mis-incorporated into proteins in place of protein amino acids modifying native-protein structure generating misfolded aggregate-prone proteins.
Methods: We use quantitative proteomic approaches to examine the expression of proteins in human neuroblastoma cells (SH-SY5Y) after exposure to NPAAs to determine the mechanisms underlying their toxicity.
Results: Quantitative TMT labelling of proteins from human neuroblastoma cells treated with BMAA, a NPAA produced by cyanobacteria (blue-green algae), generated a comprehensive data set of differentially expressed proteins. Analysis revealed a proteotoxic stress response consistent with protein misfolding as well as changes to many pathways known to be involved in neurodegenerative diseases. Incorporation of certain NPAAs into proteins also resulted in a loss of solubility of specific proteins such as histone H4. In order to detect NPAAs in proteins with a greater sensitivity and specificity we developed a new method that allows NPAAs to be detected in peptides using mass spectrometry. This novel approach overcomes many limitations associated with protein hydrolysis which is currently the only method available.
Conclusions: The data presented supports the hypothesis that NPAAs can be misincorporated into proteins, cause protein misfolding and can impact on pathways implicated in neurodegenerative diseases.