Manganese Health Research Program: Phase 2, Core 14
|Research Core Project Number:|
|Research Core Project:||Molecular Mechanisms Underlying Mn Neurotoxicity|
|Core Principal Investigator (CPI):||BethAnn McLaughlin, Ph.D.
Department of Neurology, 465 21st Avenue South,
MRB III Room 8110, Nashville TN 37232-8548
Jane Wu, M.D.
Michael Aschner, Ph.D.
- Surveying the molecular damages caused by Mn exposure in primary neuronal cultures and in animal model.
- Evaluate the mechanism of Mn induced cell death, effects of Mn on cellular redox status and the role of apoptotic pathways.
- Assess global alterations in gene expression evoked by Mn exposure in vitro and in vivo.
- Assess global alterations in protein expression and modification evoked by Mn exposure in vitro and in vivo.
- Validate the changes in candidate genes and gene products caused by Mn intoxication using biochemical, molecular and cellular assays.
- Develop a comprehensive model by identifying factors rendering cells vulnerable to Mn exposure.
Accumulating evidence supports that cell death associated with a host of neurological disorders including Alzheimer's and Parkinson's diseases is potentiated by exposure to Mn (Saydam et al, 2003; for recent reviews see Leonard et al., 2004; Kurosaki et al., 2004; Aschner & Dorman, 2004). Manganese (Mn) is an essential nutrient, integral to proper metabolism of amino acids, proteins, lipids, and carbohydrates. It plays many roles in proper cortical functioning as a cofactor for enzymes, but high occupational exposure to the compound has been linked to basal ganglia dysfunction. Symptoms of Mn-related neurotoxicity are similar to those seen in patients with Parkinson's disease (PD), including rigidity, tremor, bradykinesia, and dystonia. An increase in brain Mn levels has been associated with Parkinsonian symptoms, and occupational exposure to Mn is common especially in welders (Condamine et al, 1998, Witholt et al., 2000). Recent studies suggest that welding may be a risk factor for PD and that the clinical and pathophysiological features of manganese-associated Parkinsonism may overlap with that of PD (Racette et al 2001; 2005). The economic, social and emotional toll of Mn toxicity has only recently come to light (for recent reviews see Leonard et al., 2004; Kurosaki et al., 2004; Aschner & Dorman, 2004). Although recent studies have provided insights into the genetic mechanisms of neurodegeneration, the data on the interaction between genetics and environmental factors has lagged far behind. In particular, very little is known about molecular mechanisms underlying Mn neurotoxicity. In this application, we seek to use cutting edge microarray and proteomic technologies to identify early changes in gene expression and protein products following Mn exposure. The goal of our study is to understand molecular mechanisms underlying Mn neurotoxicity and to help establish early detection methods for Mn neurotoxicity. Such studies will facilitate the identification of individuals that may be predisposed to the adverse effects of Mn.
We have developed both an in vivo and an in vitro model to understand the contribution of manganese to Parkinsonian symptoms. The principle goal of the in vivo studies was to determine if the behavioral phenotype of manganese exposure is due to selective loss of dopaminergic cells. To this end, Dr. Michael Aschner's laboratory prepared C57BL/6 mice animals that were given intraperitoneal injections of MnCl2 (5 mg/kg/day) or saline daily for 30 days. These animals were used to determine if manganese induced alterations in protein expression in the basal ganglia circuit, which would be consistent with a specific loss of dopaminergic neurons. The McLaughlin and Aschner labs collaboratively developed immunohistochemical analyses and cell counting techniques in which we determined there was a 17% reduction in neurons expressing tyrosine hydroxylase, an enzyme required for the production of dopamine, in the substantia nigra (SN) of Mn-treated animals. Quantification of Nissl bodies through cresyl-violet staining revealed a widespread reduction total neuronal number throughout the SN. One of the consequences of loss of dopaminergic cells would be a loss of GAD67, the rate-limiting enzyme in GABA production in the striatum, which receives projections from the substantia nigra. We observed decreases in numbers of GAD67 expressing interneurons within the STR and the GP of Mn-treated mice. This decrease was 39.4% in the STR and 14% in the GP. While we did not observe changes in the activated form of the cell death protein caspase 3 in the substantia nigra, striatum or other regions, we hypothesize that this was likely due to the fact that cleavage of this protease is an earlier event in the chronic exposure paradigm. The results of these studies suggest that Mn exposure can produce neurochemical dysfunction in key areas of the basal ganglia, including the striatum and globus pallidus. Ongoing experiments using primary cultures of ventral midbrain neurons are elucidating the cell signaling mechanism responsible for the selective vulnerability observed with Mn exposure.
|Project started: Funding not received yet|
|Scheduled completion date:|
|Anticipated completion date: This is 24month program|
Stankowski J., Leitch D., Aschner M., McLaughlin B. and Stanwood G. D. (2008) Selective vulnerability of dopaminergic systems to Manganese: Relevance to occupational exposure. Neurotoxicology And Teratology 30, 259.
Key research accomplishments:
Publications/Presentations arising from project:
Last updated: January 31, 2006