Synaptic Changes in Mice Lacking Alpha- and Gamma-Synucleins

Background: Alpha-synuclein is a key protein involved in the pathogenesis of Parkinson disease (PD). Its intermediate aggregated forms disturb the normal function of dopaminergic (DA) neurons. Furthermore, the loss of intraneuronal connections may precede nerve cell death in PD. Disturbance of presynaptic functions of alpha-synuclein and its family members, beta- and gamma-synuclein, can apparently be the first step in nigrostriatal system dysfunction. Based on their structure homology and subcellular localization, the three synuclein proteins could have overlapping functions. This also indicates necessitates to study each protein in isolation. Methods: We have established a unique mouse line with conditional knockout (KO) of alpha-synuclein inactivation on the background of gamma-synuclein KO. Results: During the early phase of alpha-synuclein loss of function, mice demonstrate reduced explorer activity, decreased gene expression of Mao-B in the midbrain, and transiently increased levels of beta-synuclein protein in the striatum after alpha-synuclein inactivation, as results, metabolism of dopamine stays unscathed. These changes can be caused by specific regulation of Mao-B by alpha-synuclein or can be a physiological reaction aimed at restoring alpha-synuclein levels. No significant changes in gene expression patterns of dopamine-related enzymes in the midbrain or protein levels in the striatum and midbrain were observed. Conclusions: Our data suggest that sudden alpha-synuclein depletion leads to an increase in beta-synuclein levels, likely as functional replacement. This result supports that beta-synuclein can compensate the loss of alpha-synuclein. In general, this process may characterize synapse reconstruction in early alpha-synuclein dysfunction with gamma-synuclein absence and form the basis for replacement therapeutic strategies in PD.