Decaffeinated coffee and nicotine-free tobacco provide neuroprotection in Drosophila models of Parkinson's disease through an NRF2-dependent mechanism

Abstract

Epidemiological studies have revealed a significantly reduced risk of Parkinson's disease (PD) among coffee and tobacco users, although it is unclear whether these correlations reflect neuroprotective/symptomatic effects of these agents or preexisting differences in the brains of tobacco and coffee users. Here, we report that coffee and tobacco, but not caffeine or nicotine, are neuroprotective in fly PD models. We further report that decaffeinated coffee and nicotine-free tobacco are as neuroprotective as their caffeine and nicotine-containing counterparts and that the neuroprotective effects of decaffeinated coffee and nicotine-free tobacco are also evident in Drosophila models of Alzheimer's disease and polyglutamine disease. Finally, we report that the neuroprotective effects of decaffeinated coffee and nicotine-free tobacco require the cytoprotective transcription factor Nrf2 and that a known Nrf2 activator in coffee, cafestol, is also able to confer neuroprotection in our fly models of PD. Our findings indicate that coffee and tobacco contain Nrf2-activating compounds that may account for the reduced risk of PD among coffee and tobacco users. These compounds represent attractive candidates for therapeutic intervention in PD and perhaps other neurodegenerative diseases.

Figure 1.

Coffee and tobacco are neuroprotective in both α-synuclein transgenic and parkin null mutant flies. A, The number of DA neurons in the PPL1 cluster of 20-d-old transgenic flies expressing the human α-synuclein protein after exposure to food containing the given concentration of coffee extract. B, The number of DA neurons in the PPL1 cluster of 20-d-old α-synuclein transgenic flies after exposure to food containing the given concentrations of tobacco extract. C, The number of DA neurons in the PPL1 cluster of 20-d-old parkin null flies after exposure to food containing the given concentration of coffee extract or tobacco extract. D, Representative images of PPL1 DA neurons in α-synuclein-expressing flies and parkin mutants after 20 d exposure to the indicated food supplement. Cof, Coffee; Tob, tobacco. Statistical tests were performed using Student's t test (*p < 0.01%; **p < 0.001%). The genotypes were as follows: TH-α-Syn, TH–Gal4 UAS–α-synuclein/TH–Gal4 UAS–α-synuclein; Park^−/−, park²⁵/park²⁵.

Figure 2.

Caffeine and nicotine are not responsible for the neuroprotective properties of coffee and tobacco, respectively. A, The number of DA neurons in the PPL1 cluster of 20-d-old transgenic flies expressing the human α-synuclein protein after exposure to food containing pure caffeine (0.6 μg/ml) or nicotine (0.1 μg/ml) at concentrations that approximate their concentrations in our coffee and tobacco extracts, respectively. B, The number of DA neurons in the PPL1 cluster of 20-d-old parkin null mutants after exposure to food containing pure caffeine (0.6 μg/ml) or nicotine (0.1 μg/ml). C, Representative images of DA neurons in the PPL1 cluster of 20-d-old flies after exposure to food containing the given concentration of caffeine or nicotine. The genotypes were as follows: TH-α-Syn, TH–Gal4 UAS–α-synuclein/TH–Gal4 UAS–α-synuclein; Park^−/−, park²⁵/park²⁵.

Figure 3.

Decaffeinated coffee and nicotine-free tobacco confer neuroprotection in both α-synuclein transgenic and parkin null mutant flies. A, The number of DA neurons in the PPL1 cluster of 20-d-old transgenic flies expressing the human α-synuclein protein after exposure to food containing the given concentrations of decaffeinated coffee or nicotine-free tobacco extract. B, The number of DA neurons in the PPL1 cluster of 20-d-old parkin null mutants after exposure to food containing the given concentration of decaffeinated coffee or nicotine-free tobacco extract. C, Representative images of DA neurons in the PPL1 cluster of 20-d-old flies after exposure to food containing the given concentration of decaffeinated coffee or nicotine-free tobacco extract. Statistical tests were performed using Student's t test (*p < 0.01%; **p < 0.001%). The genotypes were as follows: TH-α-Syn, TH–Gal4 UAS–α-synuclein/TH–Gal4 UAS–α-synuclein; Park^−/−, park²⁵/park²⁵.

Figure 4.

Decaffeinated coffee and nicotine-free tobacco rescue the climbing and lifespan defects of parkin mutants. A, The climbing ability of 1-d-old parkin null mutants after exposure to food containing the given concentrations of decaffeinated coffee or nicotine-free tobacco extract. B, The survival rate of park^Z472/Z472 hypomorphic mutants on food containing the given concentrations of decaffeinated coffee or nicotine-free tobacco extract. Statistical tests were performed using Student's t test (*p < 0.05%). The genotype in A was Park^−/− (park²⁵/park²⁵). The genotype in B was Park^−/− (park^Z472/park^Z472).

Figure 5.

Coffee and tobacco confer neuroprotection in a cell culture model of PD. A, B, The number of DA neurons in primary embryonic neuronal cultures prepared from transgenic flies expressing α-synuclein after 3 d exposure to coffee or decaffeinated coffee (A), or tobacco or nicotine-free tobacco extracts (B). C, Representative images of primary embryonic DA neurons expressing human α-synuclein after treatment with the indicated extract. Coffee and tobacco extracts were added to cell culture media at a 1:2000 dilution. Statistical tests were performed using Student's t test (**p < 0.001%).

Figure 6.

Decaffeinated coffee and nicotine-free tobacco are protective in an Alzheimer's disease fly model and in a polyglutamine disease fly model. A, The climbing ability of 1-, 10-, and 20-d-old transgenic flies expressing the human β-amyloid peptide after exposure to food containing the given concentrations of decaffeinated coffee or nicotine-free tobacco extract. B, The survival rate of transgenic flies expressing the human β-amyloid peptide on food containing the given concentrations of decaffeinated coffee or nicotine-free tobacco extract. C, The relative number of transgenic flies expressing a human polyglutamine protein that survive to the adult stage of development after exposure to food containing the given concentrations of decaffeinated coffee or nicotine-free tobacco extract. D, The survival rate of transgenic flies expressing a human polyglutamine protein on food containing the given concentrations of decaffeinated coffee or nicotine-free tobacco extract. Statistical tests were performed using Student's t test (*p < 0.05%). The genotypes were as follows: Elav-Aβ42, Elav–Gal4/+; UAS–Αβ₄₂/+; Elav-Q78, Elav–Gal4/+; UAS–polyQ78/+.

Figure 7.

Decaffeinated coffee and nicotine-free tobacco confer neuroprotection through an Nrf2-dependent mechanism. A, The glutathione abundance of WT animals raised on food supplemented with coffee, tobacco, decaffeinated coffee, or nicotine-free tobacco. B, The expression of GFP, relative to actin in transgenic flies bearing the Nrf2 reporter construct gstD1–GFP after exposure to food supplemented with coffee, tobacco, decaffeinated coffee, or nicotine-free tobacco. C, The abundance of the Cnc (the Drosophila Nrf2 homolog) transcript relative to ferritin in WT flies and in transgenic flies expressing a CncRNAi construct. D, The number of DA neurons in the PPL1 cluster of 20-d-old transgenic flies expressing the human α-synuclein protein and an RNAi construct targeting the Cnc transcript, after exposure to food containing coffee, tobacco, decaffeinated coffee, or nicotine-free tobacco extracts. Statistical tests were performed using Student's t test (*p < 0.05%). The genotypes were as follows: WT, W1118; gstD1-GFP, gstD1–GFP/gstD1–GFP; Elav-G, Elav–Gal4/+; Elav-CncRNAi, Elav–Gal4/+; UAS–CncRNAi/+; TH-CncRNAi, TH–Gal4/UAS–CncRNAi; TH-α-Syn; CncRNAi, TH–Gal4, UAS–α-synuclein/TH–Gal4, UAS–α-synuclein; UAS–CncRNAi/+.

Figure 8.

The Nrf2 activator cafestol confers neuroprotection in Drosophila models of PD. A, The expression of GFP, relative to actin in transgenic flies bearing the Nrf2 reporter construct gstD1–GFP, after exposure to food supplemented with 0.2 μg/ml cafestol. B, The number of DA neurons in the PPL1 cluster of 20-d-old α-synuclein transgenic flies after exposure to food containing 0.2 μg/ml cafestol. C, The number of DA neurons in the PPL1 cluster of 20-d-old parkin null flies after exposure to food containing 0.2 μg/ml cafestol. Statistical tests were performed using Student's t test (*p < 0.05%). The genotypes were as follows: gstD1-GFP, gstD1–GFP/gstD1–GFP; TH-α-Syn, TH–Gal4 UAS–α-synuclein/TH–Gal4 UAS–α-synuclein; Park^−/−, park^25/25.