In virto model systems for alpha-synuclein

Cell-culture models of a-synuclein provide a valuable route for studying the physiologic and pathologic functions of the protein because they would be potentially amenable to high throughput translation to identify therapeutic compounds. a- Syn can be highly overexpressed in various cell lines and primary neuronal culture systems. Expression of a-syn containing a PD-associated point mutation in PC12 cells leads to loss of dopaminergic release, alteration of the ubiquitin dependent degradation system, and autophagic-dependent cell death. Overexpression of a-syn in H4-glioma cells results in an upregulation of markers associated with toxicity. Delivery of a-syn via HSV-1 transduction in mesencephalic
primary cultures likewise results in enhanced toxicity in infected cells. However, the goal of achieving a robust model of a-syn–dependent cell death in cultured cells amenable to translation to high-throughput screening remains an elusive goal.
Most described a-syn–overexpression systems in mammalian cells result in very mild to no significant changes in markers of toxicity associated with wild-type a-syn expression. Some culture systems demonstrate neuroprotective mechanisms due to a-syn expression. a-Syn expressed in NT-2D1 (human teratocarcinoma cell line) and SK-MC (human neuroblastoma cell line) cells delays cell death induced by serum withdrawal, but the effect is reversed via MPPþ (1-methyl-4-phenylpyridinium) exposure. In lieu of overt changes in cell-death markers associated with a-syn expression, numerous studies have described potential early phenotypes with possible relevance to pathogenesis. A kinetic basis for intracellular accumulation has been demonstrated by
overexpressing Flag- and His-tagged versions of a-syn in PC12 and SH-SY5Y cells. Demonstration of a-syn expression and oligomeric intermediates in living cells through bimolecular fluorescence complementation may also provide insight into a-syn mechanisms. Because overt cell death caused by a-syn expression has been difficult to achieve in mammalian cells, the future of in vitro model systems will likely involve phenotypes outside of toxicity but focused on particular aspects of a-syn conformation, association, or localization. The relevance of data developed in vitro will require confirmation in successful in vivo model systems.