Novel Cell-Based Parkinson's Model Shows Promise

A new in-vitro model of Parkinson's disease, induced by the pesticide rotenone, appears to recapitulate much of the cellular pathology that marks the neurodegenerative disease. The important difference from previous similar studies, say the authors of the Journal of Neuroscience article, was the use of chronic, low-level exposure to the toxin.

Rotenone is one of several toxins that can produce a parkinsonian condition in vivo, including both selective destruction of substantia nigra dopaminergic (DA) neurons and accumulation of insoluble α-synuclein inclusions (Lewy bodies) in DA neurons. The mechanism for this effect is not clear, but one of the well-known effects of rotenone is to interfere with complex I of the mitochondrial electron transfer chain, and complex I activity is known to be decreased in PD.

In their new model of rotenone exposure, -Timothy Greenamyre, Todd Sherer and colleagues at Emory University in Atlanta, Georgia, and the U.S. National Institute on Aging in Bethesda, Maryland, maintained human neuroblastoma cells in culture with 5 nM rotenone. At four weeks, the cells appeared normal, but about 5 percent had begun to undergo apoptosis. In addition, levels of insoluble α-synuclein and ubiquitin (another component of Lewy bodies) increased. The cells also showed evidence of oxidative stress, including decreased glutathione and signs of oxidative damage to DNA and proteins.

Even more dramatic was the manner in which the chronic treatment appeared to weaken the cells to further oxidative damage. The researchers challenged the cells with H2O 2, an oxidative species that is abundant in dopaminergic cells as a byproduct of dopamine metabolism. The rotenone-sensitized cells released more cytochrome C from mitochondria, activated caspase-3, and increased apoptosis relative to untreated cells.

The authors point out one significant limitation of the study, namely that the cells used were not dopaminergic neurons, which are notoriously difficult to keep alive for chronic in-vitro study. Nevertheless, the authors believe that further experiments in this model will allow them to define the sequence of cellular responses to chronic complex I inhibition, probe for links to the pathology of PD, and screen potential therapeutics.—Hakon Heimer

Comments

  1. Interesting study to link rotenone's inhibition of complex I with PD pathology, i.e. alpha-synuclein and ubiquitin abnormalities and cell death.

    View all comments by Edward Koo

  2. Developing adequate cell culture models of synuclein aggregation has proved challenging, and this paper makes a significant step forward. It is curious that the process is so slow, given that the cells divide and likely don't exist in the same state (as one non-dividing cell) for 4 weeks. However, the slow kinetics of rotenone toxicity is consistent with prior studies with compound.

    View all comments by Benjamin Wolozin

  3. The work by Tim Greenamyre, Todd Sherer, and colleagues provides a novel cellular model of chronic environmental toxin exposure that may well be relevant to Parkinson’s disease (PD). Although the authors did not use dopaminergic neurons (which they discuss in their paper) the data are nonetheless intriguing. Chronic low-dose rotenone treatment of a dividing neuronal cell line, SKN-MC, induced accumulation of endogenous α-synuclein protein in parallel with ubiquitin accumulation. Both soluble and insoluble α-synuclein protein levels increased, while α-synuclein mRNA did not. The data infer that rotenone contributes to α-synuclein protein stability. These findings are similar to studies by Dino Di Monte and colleagues (Manning-Bog et. al, 2002 ) in which non-transgenic mice expressing endogeonous levels of α-synuclein developed α-synuclein aggregates in substantia nigra neurons after treatment with the herbicide paraquat.

    The relevance of both studies, in cells and animals expressing endogenous wild-type α-synuclein, is that they begin to model what may occur in the more prevalent non-familial forms of PD. SKN-MC cells also exhibited reduced glutathione levels and had increased DNA and protein damage after chronic low-dose rotenone. Remarkably, the cells exhibited almost no apoptosis even after 4 weeks of rotenone treatment unless they were further stressed by H2O2 treatment. However, that endogenous levels of wild-type α-synuclein can be stimulated to aggregate secondary to environmental toxins in a manner to make neuronal cells more vulnerable is an important observation. In addition, these models are in line with anecdotal reports from patients with idiopathic PD, who attribute the onset of their parkinsonian symptoms to the use of herbicides. It will now be important to elucidate the mechanism(s) contributing to altered α-synuclein stability, and to determine how such changes impact neuronal viability.

    References:

    Manning-Bog AB, McCormack AL, Li J, Uversky VN, Fink AL, Di Monte DA. The herbicide paraquat causes up-regulation and aggregation of alpha-synuclein in mice: paraquat and alpha-synuclein. J Biol Chem. 2002 Jan 18;277(3):1641-4. PubMed.

    View all comments by Ruth Perez

  4. Very interesting study to link environmental toxins like rotenone with the development of PD. The development of cellular model of alpha-synuclein aggregation is important to understand the molecular mechanism of alpha-synuclein toxicity and screening for inhibitors of alpha-synuclein aggregation and toxicity.

    View all comments by Omar El-Agnaf

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Further Reading

Primary Papers

  1. Sherer TB, Betarbet R, Stout AK, Lund S, Baptista M, Panov AV, Cookson MR, Greenamyre JT. An in vitro model of Parkinson's disease: linking mitochondrial impairment to altered alpha-synuclein metabolism and oxidative damage. J Neurosci. 2002 Aug 15;22(16):7006-15. PubMed.

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