Cytosolic dopamine, calcium and synuclein

The research record

This is the project's file for this landmark, as written and checked. Sources are listed at the end; anything not yet confirmed is marked "Not yet verified".

Who

Eugene Mosharov (first author), David Sulzer (senior, Columbia University Medical Center), David Krantz (UCLA), Kazuto Kobayashi (Fukushima Medical University), Robert Edwards (UCSF) and colleagues. Surmeier, who is linked to the calcium-channel work in landmark 57, is not an author. Support named in the acknowledgments: the Picower Foundation, the Parkinson's Disease Foundation, the National Parkinson Foundation, an NINDS Udall Center and NIDA. Neuron 62(2):218–229, 2009.

What happened

Parkinson's kills neurons in the substantia nigra (SN) but spares the neighbouring ventral tegmental area (VTA). The team used a fine electrode inside single cultured mouse midbrain neurons (some chemical measurements used rat cultures) to measure cytosolic dopamine (dopamine free in the cell fluid, not packed in vesicles).

• Higher cytosolic dopamine and its breakdown products were toxic. Lowering them, by genetic or drug means, protected neurons.
• L-DOPA (100 µM for 1 hour for the dopamine readings; mostly 250 µM for 4 days for the toxicity tests) raised cytosolic dopamine in SN neurons to 2 to 3 times the level in VTA neurons. The rise depended on dihydropyridine-sensitive calcium channels (the L-type channels of landmark 57).
• SN neurons were more easily killed by L-DOPA.
• Deleting alpha-synuclein did not change cytosolic dopamine, but those neurons resisted L-DOPA-induced death.

Why it moved us toward a cure

It tied three separate leads (calcium entry, dopamine storage, synuclein) into one proposed mechanism, and it named several places to intervene. It builds on the storage argument in landmark 268 and the calcium work in landmark 57, and it uses the synuclein finding of landmark 5. The 2017 oxidised-dopamine result in patient neurons (landmark 58) extends the same idea in human cells. The calcium-channel arm was tested in people with isradipine and failed (landmark 57).

Outcome

Open. The work is in cultured mouse neurons, with high L-DOPA doses as the stress. Whether the same ordering holds in living human brains is not shown. A Neuron commentary accompanied the paper (Neuron 62:163–164); Europe PMC lists no correction or retraction.

Sources

• Mosharov et al., Neuron 2009;62:218–229, DOI 10.1016/j.neuron.2009.01.033 (abstract via Europe PMC, PMC2677560)
• Full text, PMC2677560 (affiliations, doses, acknowledgments; the last part of the page was not read)
• Not yet verified: whether the final 36,000 characters of the full text hold a formal funding statement; independent replication in human neurons beyond the patient-neuron work in landmark 58; whether L-DOPA in patients behaves the same (a separate question from disease-causing dopamine).