The essential micronutrient manganese is enriched in brain, especially the basal ganglia. We sought to identify neuronal signaling pathways responsive to neurologically relevant manganese levels, as previous data suggested manganese alterations occur in Huntingtons disease (HD). We found that p53 phosphorylation is highly responsive to manganese levels in human and mouse striatal-like neuroprogenitors. The Ataxia Telangiectasia Mutated (ATM) kinase is responsible for this manganese-dependent phosphorylation of p53. Activation of ATM-p53 by manganese was severely blunted by pathogenic alleles of Huntingtin. HD neuroprogenitors exhibited a highly manganese selective deficit in ATM kinase activation, since DNA damage and oxidative injury, canonical activators of ATM, did not show similar deficits. Manganese was previously shown to activate ATM kinase in cell-free assays. We found that human HD neuroprogenitors have reduced intracellular manganese with neurologically relevant manganese exposures. Pharmacological manipulation to equalize manganese between HD and control neuroprogenitors rescued the ATM-p53 signaling deficit. The compound that normalized these levels was the small molecule, KB-R7943, a known inhibitor sodium/calcium exchanger (NCX) inhibitor. However, the mechanism by which KB-R7943 corrects manganese accumulation does not seem to be via direct inhibition of the NCX transporters. We also demonstrated a severe deficit in NCX1 expression in HD cells that may also play a key role in the HD manganese deficiency.
Huntingtons disease cells also show increased genomic instability and DNA damage signaling under basal conditions. Manganese is known to be an important cofactor for several enzymes involved in DNA repair and replication, and we found that the manganese deficiency was most severe in the nucleus compared with other compartments. Manganese supplementation reduced the elevated DNA damage signaling to those found in non-HD cells suggesting that manganese deficiency underlies this phenotype
In short, the ATM-p53 signaling pathway is a manganese responsive signaling pathway. Manganese is an important cofactor with diminished accumulation in HD cell models. These reduced levels may be the reason for observed increases in DNA damage and genomic instability. Further experimentation is needed to elucidate the mechanism of manganese accumulation deficiency mechanism in HD and the KB-R7943 rescue.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-09252014-134959 |
| Date | 29 September 2014 |
| Creators | Tidball, Andrew Martin |
| Contributors | Christopher V. Wright, Michael Aschner, Kevin C. Ess, Aaron B. Bowman |
| Publisher | VANDERBILT |
| Source Sets | Vanderbilt University Theses |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.vanderbilt.edu/available/etd-09252014-134959/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Vanderbilt University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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