DOPAL is transmissible to and oligomerizes alpha-synuclein in human glial cells

• Glial cytoplasmic inclusions (GCIs) containing alpha-synuclein characterize multiple system atrophy (MSA); synuclein oligomers may be pathogenic.
• MSA is also characterized by striatal dopamine (DA) depletion; links between GCIs and DA depletion remain poorly understood.
• This study shows that the autotoxic DA metabolite, 3,4-dihydroxyphenylacetaldehyde (DOPAL), is transmissible to glial cells and that inside glial cells DOPAL enhances the oligomerization of alpha-synuclein.
• The results raise the possibility that DOPAL-synuclein interactions contribute to GCI formation in MSA.

IntroductionGlial cytoplasmic inclusions (GCIs) containing alpha-synuclein (AS) are a neuropathologic hallmark of multiple system atrophy (MSA). Oligomerized AS is thought to be the pathogenic form of the protein. Glial cells normally express little AS, but they can take up AS from the extracellular fluid. 3,4-Dihydroxyphenylacetaldehyde (DOPAL), an obligate intermediate in the intra-neuronal metabolism of dopamine (DA), potently oligomerizes AS. In this study we tested whether DOPAL is taken up by human glial cells and augments intracellular oligomerization of AS.MethodsDOPAL (exogenous or endogenous from co-incubation with PC12 cells) and AS (native or A53T mutant form) were added to the incubation medium of glial cells (glioblastoma or MO3.13 oligodendrocytes). Glial cellular contents of DOPAL and its intracellular metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were measured at up to 180 min of incubation. Glial cellular AS oligomers were quantified by Western blotting.ResultsNeither glioblastoma nor MO3.13 cells contained endogenous catecholamines or AS. Co-incubation of the cells with DA-producing PC12 cells produced time-related increases in DOPAL and DOPAC contents. Similarly, glial cellular DOPAL and DOPAC contents increased rapidly after addition of DOPAL to the medium. After addition of native or A53T-AS, intracellular AS also increased. Incubation of glial cells with both DOPAL and AS enhanced the intracellular oligomerization of native and A53T-AS.ConclusionsDOPAL is transmissible to glial cells and enhances intracellular oligomerization of AS. An interaction of DOPAL with AS might help explain the formation of CGIs in MSA.