Lysosomal pathology associated with alpha-synuclein accumulation in transgenic models using an eGFP fusion protein

Disorders with Lewy body (LB) formation, such as Parkinson's disease (PD) and dementia with Lewy bodies (DLB), are characterized by alpha-synuclein accumulation in the neuronal cell body. Recent studies have suggested that in addition to LBs, alpha-synuclein might accumulate more widely throughout the neurons and their processes, leading to neurodegeneration and functional impairment. The precise patterns of alpha-synuclein accumulation in vivo, however, and its relationship with subcellular neuronal alterations such as lysosomal pathology are not completely clear. To this end, we developed transgenic (tg) in vivo and in vitro models expressing a stable enhanced green fluorescent protein (eGFP) tagged in the C-terminal site of a human (h)alpha-synuclein construct under the regulatory control of the platelet-derived growth factor-beta (PDGFbeta) promoter and carried out confocal, ultrastructural, and biochemical studies. In tg mice, confocal studies demonstrated a wide distribution of halpha-synuclein-eGFP in the neuronal cell bodies, axons, and presynaptic terminals. In several neuronal cell bodies and their neurites, halpha-synuclein-eGFP was found not only as inclusions but also as discrete granular structures that in double-labeling studies colocalized with antibodies against halpha-synuclein and the lysosomal marker cathepsin D. Consistent with these findings, ultrastructural analysis showed that halpha-synuclein-eGFP overexpression resulted in the accumulation of electrodense inclusions and laminated bodies suggestive of lysosomal pathology, and that the halpha-synuclein-eGFP protein was more abundant in the lysosomal fractions of the tg animals. Taken together, these findings support the notion that enhanced visualization of alpha-synuclein utilizing a hybrid eGFP molecule reveals a more widespread accumulation of this molecule in several neuronal compartments, promoting lysosomal dysfunction. Furthermore, the PDGFbeta-halpha-synuclein-eGFP tg model might be a valuable tool in testing new treatments for LBD in a fast and reliable manner.