Torsin-mediated protection from cellular stress in the dopaminergic neurons of Caenorhabditis elegans

Parkinson's disease (PD) is linked genetically to proteins that function in the management of cellular stress resulting from protein misfolding and oxidative damage. Overexpression or mutation of alpha-synuclein results in the formation of Lewy bodies and neurodegeneration of dopaminergic (DA) neurons. Human torsinA, mutations in which cause another movement disorder termed early-onset torsion dystonia, is highly expressed in DA neurons and is also a component of Lewy bodies. Previous work has established torsins as having molecular chaperone activity. Thus, we examined the ability of torsinA to manage cellular stress within DA neurons of the nematode Caenorhabditis elegans. Worm DA neurons undergo a reproducible pattern of neurodegeneration after treatment with 6-hydroxydopamine (6-OHDA), a neurotoxin commonly used to model PD. Overexpression of torsins in C. elegans DA neurons results in dramatic suppression of neurodegeneration after 6-OHDA treatment. In contrast, expression of either dystonia-associated mutant torsinA or combined overexpression of wild-type and mutant torsinA yielded greatly diminished neuroprotection against 6-OHDA. We further demonstrated that torsins seem to protect DA neurons from 6-OHDA through downregulating protein levels of the dopamine transporter (DAT-1) in vivo. Additionally, we determined that torsins protect robustly against DA neurodegeneration caused by overexpression of alpha-synuclein. Using mutant nematodes lacking DAT-1 function, we also showed that torsin neuroprotection from alpha-synuclein-induced degeneration occurs in a manner independent of this transporter. Together, these data have mechanistic implications for movement disorders, because our results demonstrate that torsin proteins have the capacity to manage sources of cellular stress within DA neurons.