Viewpoint Cite This: Biochemistry XXXX, XXX, XXX−XXX
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Reactive Dopamine Leads to Triple Trouble in Nigral Neurons Markus Riessland, Benjamin Kolisnyk, and Paul Greengard* Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, 1230 York Avenue, New York, New York 10065, United States
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dopamine, underlining the important role of Ca2+ signaling in DA oxidation. It has also been shown that oxidative stress triggers the accumulation of α-synuclein, the core component of Lewy bodies. To test whether oxidized dopamine contributes to the oxidation and accumulation of α-synuclein, Burbulla et al. chemically inhibited tyrosine hydroxylase to block DA synthesis. This lowered the level of α-synuclein accumulation, suggesting that both oxidized dopamine and mitochondrial oxidative stress contribute to the accumulation of α-synuclein in PD. A prevalent issue in the field is that PD mutations produce different phenotypes in mouse models and human dopamine neurons. Burbulla et al. replicated the finding that mice lacking the DJ-1 gene do not show loss of tyrosine hydroxylase positive neurons in the midbrain. In line with this finding, the authors found no change in lysosomal GCase activity or the level of αsynuclein. The researchers generated a mouse model for PD by crossbreeding DJ-1 knockouts with human α-synuclein A53T overexpressing mice. Indeed, the double transgenic mice resembled the features observed in the human DJ-1 mutant iPSC-derived DA neurons, namely, elevated levels of oxidized DA in nigral neurons and decreased lysosomal GCase activity compared to those of controls. Interestingly, the heterozygous expression of DJ-1 was sufficient to ameliorate the pathology, suggesting that a combination of both DJ-1 and α-synuclein accumulation is necessary to cause cellular stress in the nigra. Moreover, the authors were able to prove that high dopamine levels are crucial for triggering cellular pathology in the mouse nigra, by feeding DJ-1 KO mice with L-DOPA. In fact, the researchers observed oxidized dopamine, reduced GCase activity, and an increased level of α-synuclein accumulation in the substantia nigra of these animals. The finding that high levels of DA are an important cause of the increase in the level of oxidized DA, which results in downstream cellular impairments, was additionally confirmed by comparing human and mouse iPSC-derived DA neurons in culture. Only mouse DJ-1 neurons with artificially increased levels of DA showed oxidized DA, decreased GCase enzymatic activity, and decreased rates of survival. Finally, the interspecies differences became even more evident when Burbulla et al. found reduced calcineurin levels and activity in mouse neurons, suggesting that the altered calcium homeostasis has an additional impact on dopamine metabolism in mice. Altogether, Burbulla and colleagues were able to demonstrate a relationship between three well-known pathological features of PD, namely, mitochondrial impairment, lysosomal dysfunc-
utations in a variety of genes encoding either lysosomal or mitochondrial proteins are known to cause the degeneration of dopaminergic neurons in the substantia nigra, eventually leading to Parkinson’s disease (PD).1 In addition, accumulation of α-synuclein results in the formation of Lewy bodies culminating in PD.2 How impairment of any of these three disparate pathways leads to death of the same type of neurons and an indistinguishable clinical presentation has been unclear. Recently, Burbulla et al.3 have identified dopamine oxidation as a common feature in multiple forms of PD. The researchers used induced pluripotent stem cell (iPSC)-derived dopamine neurons from PD patients harboring homozygous c.192G>C mutations in the DJ-1 gene. DJ-1 encodes a C56 family peptidase, which works as a general cellular sensor of oxidative stress. In human DA neurons, this loss-of-function mutation led to an age-dependent accumulation of neuromelanin and an increase in the level of oxidized dopamine. Furthermore, dopamine oxidation in DJ-1 mutant neurons was shown to interfere with mitochondrial function. Using CRISPR/Cas9, the authors could reproduce the same phenotype in healthy control neurons by deleting the DJ-1 gene. Burbulla et al. went on to show that oxidized dopamine was a common feature of neurons harboring mutations in PINK1, PRKN, and LRRK2 and in neurons with SNCA triplications. Moreover, DA neurons derived from idiopathic PD patients presented a similar phenotype but at later time points of differentiation. These findings suggested that dopamine oxidation may be a common mechanism in multiple forms of PD (Figure 1). Neurons with DJ-1 mutations, and neurons derived from patients with idiopathic PD, were found to have drastically weakened lysosomal function. Specifically, the activity of glucocerebrosidase (GCase) was found to be reduced, while the function of another lysosomal enzyme was unaltered. The GCase protein is encoded by the GBA1 gene, which has previously been identified as the most common genetic risk factor for PD.4 Using in-gel near-infrared fluorescence, the authors showed that incubation of purified GCase with dopamine led to posttranslational modifications, which could be blocked by antioxidants. Using tandem mass spectrometry, Burbulla et al. went on to show that incubation of the GCase protein with dopamine caused the modification of key cysteine residues found within the catalytic domain of the enzyme. An increased rate of entry of Ca2+ through Cav1 channels can enhance oxidative stress5 as well as increase the extent of dopamine synthesis via the calcineurin pathway. The authors treated the cells with either the Cav1 blocker isradipine or the calcineurin inhibitor FK506 to test the impact of each on dopamine oxidation. Both treatment strategies resulted in significantly reduced levels of accumulation of oxidized © XXXX American Chemical Society
Received: October 18, 2017
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DOI: 10.1021/acs.biochem.7b01057 Biochemistry XXXX, XXX, XXX−XXX
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Biochemistry
Figure 1. Model of pathological dopamine oxidation in PD. Ca2+ influx through Cav1 leads to large amounts of intracellular Ca2+, which can trigger mitochondrial membrane uncoupling and calcineurin activation (which increases the rate of dopamine production). An increased level of mitochondrial oxidative stress (by mutation or excess Ca2+) causes an elevation in the level of oxidized dopamine, which in turn can oxidize the mitochondria. Oxidized dopamine has been shown to oxidize α-synuclein, rendering it significantly less soluble and prone to aggregation. The modification of cysteine residues in the catalytic site of glucocerebrosidase (GCase) by oxidized dopamine causes weakened lysosomal function and thereby reduced mitophagy. This results in an accumulation of dysfunctional mitochondria, increasing the level of oxidative stress. Blockage of either Cav1 (by isradipine) or calcineurin (by FK506) has a neuroprotective effect and ameliorates the pathological features described above. Abbreviations: Oxi, oxidation; ROS, reactive oxygen species; α-SYN, α-synuclein. Papapetropoulos, T., Johnson, W. G., Lazzarini, A. M., Duvoisin, R. C., Di Iorio, G., Golbe, L. I., and Nussbaum, R. L. (1997) Mutation in the alpha-synuclein gene identified in families with Parkinson’s disease. Science 276, 2045−2047. (3) Burbulla, L. F., Song, P., Mazzulli, J. R., Zampese, E., Wong, Y. C., Jeon, S., Santos, D. P., Blanz, J., Obermaier, C. D., Strojny, C., Savas, J. N., Kiskinis, E., Zhuang, X., Kruger, R., Surmeier, D. J., and Krainc, D. (2017) Dopamine oxidation mediates mitochondrial and lysosomal dysfunction in Parkinson’s disease. Science 357, 1255−1261. (4) Sidransky, E., Nalls, M. A., Aasly, J. O., Aharon-Peretz, J., Annesi, G., Barbosa, E. R., Bar-Shira, A., Berg, D., Bras, J., Brice, A., Chen, C. M., Clark, L. N., Condroyer, C., De Marco, E. V., Durr, A., Eblan, M. J., Fahn, S., Farrer, M. J., Fung, H. C., Gan-Or, Z., Gasser, T., Gershoni-Baruch, R., Giladi, N., Griffith, A., Gurevich, T., Januario, C., Kropp, P., Lang, A. E., Lee-Chen, G. J., Lesage, S., Marder, K., Mata, I. F., Mirelman, A., Mitsui, J., Mizuta, I., Nicoletti, G., Oliveira, C., Ottman, R., Orr-Urtreger, A., Pereira, L. V., Quattrone, A., Rogaeva, E., Rolfs, A., Rosenbaum, H., Rozenberg, R., Samii, A., Samaddar, T., Schulte, C., Sharma, M., Singleton, A., Spitz, M., Tan, E. K., Tayebi, N., Toda, T., Troiano, A. R., Tsuji, S., Wittstock, M., Wolfsberg, T. G., Wu, Y. R., Zabetian, C. P., Zhao, Y., and Ziegler, S. G. (2009) Multicenter analysis of glucocerebrosidase mutations in Parkinson’s disease. N. Engl. J. Med. 361, 1651−1661. (5) Guzman, J. N., Sanchez-Padilla, J., Wokosin, D., Kondapalli, J., Ilijic, E., Schumacker, P. T., and Surmeier, D. J. (2010) Oxidant stress evoked by pacemaking in dopaminergic neurons is attenuated by DJ-1. Nature 468, 696−700.
tion, and Lewy body formation. This study provides evidence of a common biological cascade in dopaminergic neurons in PD: mitochondrial oxidative stress generates oxidized dopamine that in turn leads to lysosomal dysfunction and α-synuclein accumulation and further mitochondrial dysfunction. This work unravels why the DJ-1 PD mouse model does not show intrinsic TH cell degeneration and proves in vitro and in vivo that the dopamine level itself plays a crucial role in cell typespecific vulnerability. Burbulla’s data confirm that the Ca2+dependent activity and the high level of DA generate cellular stress in nigral neurons that can be ameliorated by manipulation of Ca2+ influx or DA synthesis. These findings open new avenues for future neuroprotective treatment strategies for PD.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Author Contributions
M.R. and B.K. contributed equally to this work. Funding
This work was supported by the U.S. Army Medical Research and Material Command (USAMRMC) via Grants W81XWH12-1-0039 (M.R.) and W81XWH-17-1-0495 (P.G.) and the JPB Foundation via Grant 475 (P.G.). Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Kalia, L. V., and Lang, A. E. (2015) Parkinson’s disease. Lancet 386, 896−912. (2) Polymeropoulos, M. H., Lavedan, C., Leroy, E., Ide, S. E., Dehejia, A., Dutra, A., Pike, B., Root, H., Rubenstein, J., Boyer, R., Stenroos, E. S., Chandrasekharappa, S., Athanassiadou, A., B
DOI: 10.1021/acs.biochem.7b01057 Biochemistry XXXX, XXX, XXX−XXX
