A cullin-RING ubiquitin ligase targets exogenous α-synuclein and inhibits Lewy body-like pathology.

Parkinson's disease (PD) is a neurological disorder characterized by the progressive accumulation of neuronal alpha-synuclein (alpha Syn) inclusions called Lewy bodies. It is believed that Lewy bodies spread throughout the nervous system due to the cell-to-cell propagation of alpha Syn via cycles of secretion and uptake. Here, we investigated the internalization and intracellular accumulation of exogenous alpha Syn, two key steps of Lewy body pathogenesis, amplification and spreading. We found that stable alpha Syn fibrils substantially accumulate in different cell lines upon internalization, whereas alpha Syn monomers, oligomers, and dissociable fibrils do not. Our data indicate that the uptake-mediated accumulation of alpha Syn in a human-derived neuroblastoma cell line triggered an adaptive response that involved proteins linked to ubiquitin ligases of the S-phase kinase-associated protein 1 (SKP1), cullin-1 (Cul1), and F-box domain-containing protein (SCF) family. We found that SKP1, Cul1, and the F-box/LRR repeat protein 5 (FBXL5) colocalized and physically interacted with internalized alpha Syn in cultured cells. Moreover, the SCF containing the F-box protein FBXL5 (SCFFBXL5) catalyzed alpha Syn ubiquitination in reconstitution experiments in vitro using recombinant proteins and in cultured cells. In the human brain, SKP1 and Cull were recruited into Lewy bodies from brainstem and neocortex of patients with PD and related neurological disorders. In both transgenic and nontransgenic mice, intracerebral administration of exogenous alpha Syn fibrils triggered a Lewy body-like pathology, which was amplified by SKP1 or FBXL5 loss of function. Our data thus indicate that SCFFXBL5 regulates alpha Syn in vivo and that SCF ligases may constitute targets for the treatment of PD and other alpha-synucleinopathies.