The chaperone-like protein 14-3-3h interacts with human a-synuclein aggregation intermediates rerouting the amyloidogenic pathway and reducing a-synuclein cellular toxicity

Abstract

Familial and idiopathic Parkinson's disease (PD) is associated with the abnormal neuronal accumulation of a-synuclein (aS) leading to b-sheet-rich aggregates called Lewy Bodies (LBs). Moreover, single point mutation in aS gene and gene multiplication lead to autosomal dominant forms of PD. A connection between PD and the 14-3-3 chaperone-like proteins was recently proposed, based on the fact that some of the 14-3-3 isoforms can interact with genetic PD-associated proteins such as parkin, LRRK2 and aS and were found as components of LBs in human PD. In particular, a direct interaction between 14-3-3h and aS was reported when probed by coimmunoprecipitation from cell models, from parkinsonian brains and by surface plasmon resonance in vitro. However, the mechanisms through which 14-3-3h and aS interact in PD brains remain unclear. Herein, we show that while 14-3-3h is unable to bind monomeric aS, it interacts with aS oligomers which occur during the early stagesofaSaggregation. This interaction diverts the aggregation processevenwhen14-3-3his present in sub-stoichiometric amounts relative to aS. When aS level is overwhelmingly higher than that of 14-3-3h, the fibrillation process becomes a sequestration mechanism for 14-3-3h, undermining all processes governed by this protein. Using a panel of complementary techniques, we single out the stage of aggregation at which the aS/14-3-3h interaction occurs, characterize the products of the resulting processes, and show how the processes elucidated in vitro are relevant in cell models. Our findings constitute a first step in elucidating the molecular mechanism of aS/14-3-3h interaction and in understanding the critical aggregation step at which 14-3-3h has the potential to rescue aS-induced cellular toxicity.