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Maneb potentiates paraquat neurotoxicity by inducing key Bcl-2 family members
Qingyan Fei1, Douglas W Ethell
1Division of Biomedical Sciences, University of California Riverside, Riverside, California 92521-0121, USA.
Abstract:
An important feature of Parkinson's disease is the degeneration of dopaminergic neurons in the Substantia Nigra pars compacta. Paraquat (PQ) and MPTP cause the selective degeneration of these neurons in vivo, and combining PQ with maneb exacerbates that pathology. Elucidation of the cell death mechanisms involved is important to understand how multiple environmental toxins may contribute to sporadic Parkinson's disease. We recently reported that PQ induces neuronal apoptosis through Bak activation, in contrast to MPP(+), the toxic metabolite of MPTP, which relies on Bax and p53. Here we show that individually PQ and maneb activate Bak, but together they trigger Bax-dependent cell death. Focusing on mechanisms responsible for this synergy, we found that maneb+PQ increased the expression of three strong Bak inhibitors, Bfl-1, Bcl-xL and Mcl-1, and also induced Bax activators that included Bik and Bim. Those responses favor Bax-dependent MOMP and apoptosis. SiRNA knockdown of Bax and Bak confirmed that individually PQ and maneb induce Bak-dependent cell death, but together they block the Bak pathway and activate apoptosis through Bax.
Insights
Parkinson's disease involves neuron loss. This study reveals that paraquat and maneb toxins, individually activating Bak, synergize to trigger Bax-dependent cell death, offering new insights into Parkinson's pathology.
Area of Science:
- Neuroscience
- Toxicology
- Cell Biology
Background:
- Parkinson's disease (PD) is characterized by dopaminergic neuron degeneration in the Substantia Nigra pars compacta.
- Environmental toxins like paraquat (PQ) and MPTP induce selective dopaminergic neurodegeneration, contributing to sporadic PD.
- Understanding the cell death mechanisms of combined toxins is crucial for PD research.
Purpose of the Study:
- To elucidate the synergistic cell death mechanisms of paraquat (PQ) and maneb in dopaminergic neurons.
- To investigate the roles of Bak and Bax in mediating apoptosis induced by PQ and maneb, individually and in combination.
- To identify the molecular pathways underlying the switch from Bak-dependent to Bax-dependent cell death.
Main Methods:
- Utilized siRNA knockdown of Bax and Bak to confirm their roles in cell death pathways.
- Analyzed the expression of key apoptosis regulators, including Bak inhibitors (Bfl-1, Bcl-xL, Mcl-1) and Bax activators (Bik, Bim).
- Investigated mitochondrial outer membrane permeabilization (MOMP) and apoptosis induction.
Main Results:
- Individually, PQ and maneb induce Bak-dependent apoptosis.
- Concurrently, PQ and maneb trigger Bax-dependent apoptosis, blocking the Bak pathway.
- The combination treatment upregulates Bak inhibitors and increases Bax activators, promoting Bax-dependent MOMP and apoptosis.
Conclusions:
- The combined exposure to PQ and maneb shifts the apoptotic pathway from Bak-dependence to Bax-dependence.
- This synergistic effect involves the modulation of key Bcl-2 family proteins, including Bak inhibitors and Bax activators.
- Findings provide critical insights into how combined environmental insults may contribute to Parkinson's disease pathogenesis.
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