Fungal-derived semiochemical 1-octen-3-ol disrupts dopamine packaging and causes neurodegeneration

Abstract

Parkinson disease (PD) is the most common movement disorder and, although the exact causes are unknown, recent epidemiological and experimental studies indicate that several environmental agents may be significant risk factors. To date, these suspected environmental risk factors have been man-made chemicals. In this report, we demonstrate via genetic, biochemical, and immunological studies that the common volatile fungal semiochemical 1-octen-3-ol reduces dopamine levels and causes dopamine neuron degeneration in Drosophila melanogaster. Overexpression of the vesicular monoamine transporter (VMAT) rescued the dopamine toxicity and neurodegeneration, whereas mutations decreasing VMAT and tyrosine hydroxylase exacerbated toxicity. Furthermore, 1-octen-3-ol also inhibited uptake of dopamine in human cell lines expressing the human plasma membrane dopamine transporter (DAT) and human VMAT ortholog, VMAT2. These data demonstrate that 1-octen-3-ol exerts toxicity via disruption of dopamine homeostasis and may represent a naturally occurring environmental agent involved in parkinsonism.

Keywords: building-related illness; mold; mushroom alcohol.

Fig. 1.

Common fungal VOC 1-octen-3-ol exposure truncates survival span of wild type and induces mobility defects. The data were collected daily until all of the flies exposed to 1-octen-3-ol were dead, and the percentage mortality of dead flies was calculated. (A) The 50% mortality for wild-type flies is shown (n = 125), and data are from three independent experiments. (B) Forty eight-hour-old wild-type flies were exposed to 0.5 ppm of 1-octen-3-ol, and time to cross a 5-cm distance was recorded after 1 and 7 d of continuous exposure. There was a significant difference in the locomotory activity between wild-type unexposed and exposed flies assessed with a negative geotaxis assay at days 1 and 7. Error bars represent SEM, and the significant difference between wild-type exposed and unexposed flies is indicated; *P < 0.05, **P < 0.005.

Fig. 2.

Effect of 1-octen-3-ol on dopamine pools in head extracts of Drosophila flies. (A) Exposure of TH-GAL4; UAS-GFP to 0.5 ppm of 1-octen-3-ol for 24 h led to a decrease of GFP-expressing TH neurons in adult brains. The PPM1 and PPL1 subgroups of DA neurons are indicated by an arrow and circle, respectively, in unexposed and 1-octen-3-ol–exposed adult brains. (B) Scoring for the average number of subgroups of dopaminergic neurons for control and 0.5-ppm 1-octen-3-ol–exposed TH-GAL4; UAS-GFP adult brains. Except for PPL1, there was a significant decrease in all of the subgroups of dopaminergic neurons in brains exposed to 0.5 ppm of 1-octen-3-ol (n = 10–15). (C) Exposure to 0.5 ppm of 1-octen-3-ol for 24 h caused a decrease in dopamine pools with a subsequent increase in DOPAC levels in head extracts (n = 200 for each group; data represent values from three independent experiments). Error bars represent the SE of the mean, and the significant difference between control and 1-octen-3-ol–exposed brains is indicated; *P < 0.05, **P < 0.005.

Fig. 3.

Radioactive dopamine uptake in transgenic human embryonic HEK-DAT (A) and HEK-DAT/VMAT2 cells (B). Cells were exposed to 10 ppm of 1-octen-3-ol by the airborne exposure method for 2 h. Radioactive dopamine uptake was carried out for 10 min. Uptake was significantly reduced by 95% in HEK-DAT/VMAT2 cells and 90% in HEK-DAT cells as assessed by two-way ANOVA, and the significant difference between unexposed and 1-octen-3-ol–exposed cells is indicated; ****P < 0.0001.

Fig. 4.

Effect of 1-octen-3-ol on transgenic and mutant dVMAT flies. (A) The exposure of two VMAT mutant lines, l(2)SH0459/+ and Delta14/+, to 0.5 ppm of 1-octen-3-ol led to a decrease in the survival duration compared with wild-type flies (n = 60–80). (B) The overexpression of UAS-dVMAT with TH-GAL4 and elav-GAL4 drivers improved the survival duration compared with control flies TH-GAL4/+ and UAS-dVMAT/+ (n = 80–100). (C) When the TH-GAL4;UAS-dVMAT overexpression line was exposed to 0.5ppm 1-octen-3-ol for 24 hr, dopamine and DOPAC pools in head extracts were restored to control levels (n = 160 for each group; data represent values from two independent experiments). NS, nonsignificant. (D) Scoring for the average number of subgroups of dopaminergic neurons for control and 0.5-ppm 1-octen-3-ol–exposed TH-GAL4; UAS-GFP/UAS-dVMAT adult brains. There was no significant decrease in the dopaminergic subgroups except for PPM1 for control and 0.5 ppm of 1-octen-3-ol (n = 8–12 brains for each group). (E) The exposure of 0.5 ppm of 1-octen-3-ol to TH-GAL4; UAS-GFP/UAS-dVMAT adult brains for 24 h failed to cause any detectable morphological changes in GFP-expressing TH neurons. Error bars represent the SE of the mean, and * indicates a significant difference between control and 1-octen-3-ol exposed brains where *P < 0.05 and ***P < 0.001. ##, ΔΔ, and фф represent significant differences between group of flies as shown in B and indicate P < 0.005.

Fig. 5.

Drosophila ple mutants demonstrated sensitivity toward 1-octen-3-ol. (A) Forty eight-hour posteclosed ple mutants ple²/+ and ple⁴/+ exposed to 0.5 ppm of 1-octen-3-ol showed truncation in survival span compared with age-matched wild-type flies exposed to the same concentration of 1-octen-3-ol. Data were collected daily until all of the flies exposed to 1-octen-3-ol were dead, and the percentage mortality of dead flies was calculated. The 50% mortality for wild-type flies is shown (n = 125; data are from three independent experiments). (B) Forty eight-hour-old wild-type and ple mutants ple2 and ple4 were exposed to 0.5 ppm of 1-octen-3-ol, and time to cross a 5-cm distance was recorded. There was no significant difference in the climbing capacity of ple mutants and wild-type flies upon exposure to 1-octen-3-ol for 1 d (n = 60–80 flies), but continuous exposure of 0.5 ppm of 1-octen-3-ol for 7 d led to a significant increase in time to cross a 5-cm distance by ple mutants compared with wild-type flies (n = 30–40). For both assays, two independent experiments were performed. Error bars represent SEM, and the significant difference between wild-type and ple mutants is indicated; *P < 0.05, **P < 0.005.