Role of DNA damage response in Mn-induced neurotoxicity in C. elegans
Food Chemistry
Final Report Abstract
Nowadays it is well accepted that metal ions may play a crucial role in the complex multifactorial mechanisms of neurodegenerative diseases. Exceeding the homeostatic range, the essential trace element manganese (Mn) can cause a neuropathology similar to Parkinson’s disease (PD), which is known as manganism. The underlying mechanisms have yet to be conclusively clarified, but our recent in vitro studies indicate a contribution of Mn-induced oxidative stress, as well as genomic instability by means of a dysregulation of DNA damageinduced poly(ADP-ribosyl)ation (PARylation). The nematode Caenorhabditis elegans (C. elegans) constitutes a distinguished model organism for the essential further investigation of in vivo mechanisms. Mn overload resulted in an increase of various oxidative stress markers, reflective of increased reactive oxygen/nitrogen species (RONS), a shift of the GSH/GSSG- ratio towards GSSG, isoprostane formation, as well as mitochondrial dysfunction. Taking oxidative stress into account, we addressed the question of possibly increasing interactions with macromolecules such as the DNA by means of Mn-induced oxidative DNA damages and induction of the base excision repair (BER) pathway. Analytical and immuno-staining techniques for measurement of 8-oxodG have been established and indicate Mn-induced oxidative DNA damage. This may further trigger an induction or dysregulation of DNA repair pathways. Expression studies of genes involved in the BER, a pathway correcting small base lesions, revealed an induction of the mRNA levels of genes acting in the beginning of the BER. Taking advantage of the easily genetically modifiable nematode we identified, that loss of nth-1, a DNA glycosylase normally removing oxidized purines and pyrimidines, results in hypersensitivity regarding Mn-induced lethality compared to WT worms. As pme-1 (orthologue of PARP1) is a key player in the base excision repair (BER) and in vitro studies pointed out a dysregulation of PARylation following Mn exposure, its role in Mn-induced toxicity and the consequences of pme-1 or pme-2 (orthologue of PARP1 and PARP2) loss were further assessed. While Mn failed to induce PARylation in wildtype worms, short term Mn exposure at the LD50 (lethal dose inducing 50 % worm death) resulted in a PAR-induction in pme-1 deletion mutants due to an increased pme-2 gene expression. This counterregulating mechanisms need to be critically taken into account, using the pme-1 mutant as a model to simulate low PAR levels in order to study for example consequences of PAR inhibition. Altogether, we could clearly point out interactions of Mn, Mn-induced toxicity and DNA repair/DNA damage response. Currently, we are striving to deeper insights in the role of DNA repair in the etiology of manganism.
Publications
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I. Rohn, S. Raschke, M. Aschner, S. Tuck, D. Kuehnelt, A. Kipp, T. Schwerdtle, J. Bornhorst
(See online at https://doi.org/10.1002/mnfr.201801304)
