Methamphetamine and terminal oxidant stress in dopaminergic neurons

Project: Research project

Project Details

Description

Methamphetamine is a potent and addictive psychostimulant abused by 12 million people in the US at least
once (NSDUH, 2012) but also FDA-approved to treat ADHD and obesity. Parkinson’s disease (PD) is a
neurodegenerative movement disorder affecting ~4 million people;1 risk for developing PD is increased 2-3 fold
by methamphetamine use.2-4 This correlation suggests that methamphetamine use promotes the loss or
dysfunction of dopaminergic neurons in the substantia nigra pars compacta (SNc). Loss of these neurons is
responsible for the core motor symptoms of PD.5,6 That said, methamphetamine use could trigger dysfunction
in other neuronal populations as well.
How methamphetamine might promote neurodegeneration is not clear. Two major obstacles to gaining this
understanding are 1) the lack of optical probes that allow key physiological parameters to be assessed in
relevant subcellular regions and 2) the inability to selectively express probes in relevant neuronal populations.
The P30 is addressing the second obstacle by generating transgenic BAC-Cre mice. But to fully take advantage
of these mice, the first obstacle needs to be addressed. The proposed project will do that by generating Credependent,
genetically encoded optical probes for cytosolic and mitochondrial redox status.
Why a redox probe? DA metabolism has long been thought to increase oxidant stress, but the evidence for this
has largely been indirect.7-12 Under normal conditions, DA metabolism is likely quite low due to sequestration
of DA into vesicles; however, methamphetamine
administration dramatically elevates extracellular and
intracellular DA.13-18 We hypothesize that
methamphetamine-induced elevation of cytosolic DA
leads to mitochondrial – but not cytosolic – oxidant
stress in dopaminergic terminals (Fig. 1). We think that
elevated mitochondrial oxidant stress is driven by
monoamine oxidase B (MAO-B) metabolism of
cytosolic DA; MAO-B is hypothesized to increase
mitochondrial oxidant stress by shuttling electrons to
the electron transport chain. This hypothesis runs
completely counter to current theories of how DA
causes oxidant stress, which posit (without relevant
data) that DA metabolism either increases cytosolic
quinones or increases cytosolic hydrogen peroxide
production by MAO-B. Both these models predict an
elevation in cytosolic oxidant stress, not mitochondrial
oxidant stress.
As outlined above, the lack of clarity in the field is a
consequence of our poor tools. In the last 5 years, we
have characterized a ratiometric, reversible redox
probe that is suitable for two-photon laser microscopy
in ex vivo brain slices. This probe – roGFP – can be
target to the cytosol or to the mitochondrial matrix.
Using this probe, we have generated strong preliminary
data in favor of our hypothesis (see below). But what
we need to do is to generate Cre-dependent expression
constructs that can be packaged into an
adenoassociated virus vector. These constructs could
then be used in appropriate BAC-Cre mice being
generated by the P30 to interrogate relevant
populations of neuron before and after
methamphetamine treatment. Having these tools
will advance the mission of the P30 and NIDA.
StatusFinished
Effective start/end date7/1/152/28/17

Funding

  • Rockefeller University (5P30DA035756-03)
  • National Institute on Drug Abuse (5P30DA035756-03)

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