The Synucleins and the Astrocyte

SIMPLE SUMMARY: Emerging evidence on synucleins and astrocytes warrants closer inspection of their functional relationship. The expression and release of synucleins from the presynaptic terminal results in synuclein–astrocyte interaction. Notably, astrocytes, along with microglia, remove and degrade excess α-synuclein at the synapse. If astrocytes are impaired, toxic aggregates of α-synuclein can form in disease, and synapse loss and astrocyte dysfunction are early pathological signs of neurodegenerative disease. Less is understood about β-synuclein and γ-synuclein, although evidence indicates astrocytic uptake and expression of both proteins and possible astroprotective functions. Therefore, future research on the interconnection of synucleins and the astrocyte at the synapse will likely shed light on the mechanisms and causes of neurodegenerative disease. ABSTRACT: Synucleins consist of three proteins exclusively expressed in vertebrates. α-Synuclein (αS) has been identified as the main proteinaceous aggregate in Lewy bodies, a pathological hallmark of many neurodegenerative diseases. Less is understood about β-synuclein (βS) and γ-synuclein (γS), although it is known βS can interact with αS in vivo to inhibit aggregation. Likewise, both γS and βS can inhibit αS’s propensity to aggregate in vitro. In the central nervous system, βS and αS, and to a lesser extent γS, are highly expressed in the neural presynaptic terminal, although they are not strictly located there, and emerging data have shown a more complex expression profile. Synapse loss and astrocyte atrophy are early aspects of degenerative diseases of the brain and correlate with disease progression. Synucleins appear to be involved in synaptic transmission, and astrocytes coordinate and organize synaptic function, with excess αS degraded by astrocytes and microglia adjacent to the synapse. βS and γS have also been observed in the astrocyte and may provide beneficial roles. The astrocytic responsibility for degradation of αS as well as emerging evidence on possible astrocytic functions of βS and γS, warrant closer inspection on astrocyte–synuclein interactions at the synapse.