Calcium: Alpha-Synuclein Interactions in Alpha-Synucleinopathies

Aggregation of the pre-synaptic protein, alpha-synuclein (alpha-syn), is the key etiological factor in Parkinson's disease (PD) and other alpha-synucleinopathies, such as multiple system atrophy (MSA) and Dementia with Lewy bodies (DLB). Various triggers for pathological alpha-syn aggregation have been elucidated, including post-translational modifications, oxidative stress, and binding of metal ions, such as calcium. Raised neuronal calcium levels in PD may occur due to mitochondria' dysfunction and/or may relate to calcium channel dysregulation or the reduced expression of the neuronal calcium buffering protein, calbindin-D28k. Recent results on human tissue and a mouse oxidative stress model show that neuronal calbindin-D28k expression excludes alpha-syn inclusion bodies. Previously, cell culture model studies have shown that transient increases of intracellular free Ca(II), such as by opening of the voltage-gated plasma calcium channels, could induce cytoplasmic aggregates of a-syn. Raised intracellular free calcium and oxidative stress also act cooperatively to promote alpha-syn aggregation. The association between raised neuronal calcium, alpha-syn aggregation, oxidative stress, and neurotoxicity is reviewed in the context of neurodegenerative alpha-syn disease and potential mechanism based therapies.