Exposure to BMAA mirrors molecular processes linked to neurodegenerative disease

Abstract

The goal of this study is to investigate the molecular pathways perturbed by in-vitro exposure of beta-methylamino-L-alanine (BMAA) to NSC-34 cells via contemporary proteomics. Our analysis of differentially regulated proteins reveals significant enrichment (p<0.01) of pathways related to ER stress, protein ubiquitination, the unfolded protein response, and mitochondrial dysfunction. Upstream regulator analysis indicates that exposure to BMAA induces activation of transcription factors (X-box binding protein 1; nuclear factor 2 erythroid like 2; promyelocytic leukemia) involved in regulation of the UPR, oxidative stress, and cellular senescence. Furthermore, we examine the hypothesis that BMAA causes protein damage via misincorporation in place of L-Serine. We are unable to detect misincorporation of BMAA into protein via analysis of cellular protein, secreted protein, targeted detection of BMAA after protein hydrolysis, or through the use of in-vitro protein translation kits.

Microbial BMAA and the Pathway for Parkinson’s Disease Neurodegeneration

“…Although the molecular mechanisms are still to be explored, Staphylococcus aureus α-toxin and Helicobacter pylori vacuolating cytotoxin (VacA) can promote cytotoxicity through mitochondrial impairment (Arnoult et al, 2009). It should be noted here that BMAA may also have the ability to induce mitochondrial dysfunction (Beri et al, 2017). In vitro studies with NSC-34 cells, a cell line of motor neurons showed that BMAA elicited a pronounced decrease in oxidative phosphorylation, altered calcium homeostasis and exacerbated ROS production.…”

“…While the observation that BMAA interacts very strongly with proteins causing their misfolding has not been disputed, some groups have failed to detect incorporation of BMAA into the primary structure of proteins thus calling into question the role of the misincorporation hypothesis in explaining BMAA's observed neurotoxic effects (Beri et al, 2017;Onselen et al, 2017). Subsequently, alternative mechanisms have been investigated and BMAA has been found to strongly associate with melanin, to selectively inhibit the activity of certain enzymes and to interfere with and disrupt protein refolding in vitro by associating with proteins through electrostatic interactions strong enough to resist TCA precipitation and subsequent washing with SDS or DTT (van Onselen and Downing, 2018).…”

Native Ubiquitin Structural Changes Resulting from Complexation with β-methylamino-L-alanine (BMAA)

“…), 21 and that this substitution could promote misfolding and aggregation; 22 it is important to note that other studies have disputed this theory and were not able to detect similar changes. 23 Still other studies have indicated that BMAA indeed interacts with proteins, but instead through a non-covalent association rather than translational misincorporation. 24 These interactions could lead to BMAA influencing other biochemical pathways including ER stress, protein ubiquitination, the unfolded protein response, and mitochondrial dysfunction.…”

Cellular and Molecular Aspects of the β-N-Methylamino-l-alanine (BMAA) Mode of Action within the Neurodegenerative Pathway: Facts and Controversy

“…These results were confirmed by another proteomic study in NSC-34 cells exposed for 72 h to BMAA (500 µM). Indeed, exposure to BMAA resulted in modification of several molecular pathways known to be implicated in ALS pathogenesis, such as ER stress, eIF2 signalling, protein ubiquitination and misfolded protein response pathways [ 58 ]. Interestingly, the expression of various mitochondrial proteins involved in oxidative phosphorylation, TCA cycle and oxidative stress response was found to be perturbed: BMAA favours activation of transcription factors known to regulate oxidative stress and cellular senescence [ 58 ].…”

“…Indeed, exposure to BMAA resulted in modification of several molecular pathways known to be implicated in ALS pathogenesis, such as ER stress, eIF2 signalling, protein ubiquitination and misfolded protein response pathways [ 58 ]. Interestingly, the expression of various mitochondrial proteins involved in oxidative phosphorylation, TCA cycle and oxidative stress response was found to be perturbed: BMAA favours activation of transcription factors known to regulate oxidative stress and cellular senescence [ 58 ]. Whereas these authors aimed to investigate the hypothesis that BMAA could be misincorporated into cellular protein in place of l -Serine, no evidence of BMAA misincorporation in intracellular or secreted proteins was found.…”