Transcript expression levels of full-length alpha-synuclein and its three alternatively spliced variants in Parkinson's disease brain regions and in a transgenic mouse model of alpha-synuclein overexpression

Abstract

Alternative splicing is a complex post-transcriptional process that can be regulated by cis-acting elements located within genomic non-coding regions. Recent studies have identified that polymorphic variations in non-coding regions of the α-synuclein gene (SNCA) locus are associated with an increased risk for developing Parkinson’s disease (PD). The underlying mechanism(s) for this susceptibility may involve changes in α-synuclein mRNA expression and alternative splicing. As a first step towards understanding the biology of α-synuclein splice variants in PD, we characterized the levels of the full-length SNCA-140 mRNA transcript and SNCA-126, -112, and -98 alternatively spliced variants in different neuronal regions from PD patients or transgenic mice overexpressing human α-synuclein (ASO). In human post-mortem tissue, α-synuclein spliced transcripts were expressed in a region-specific manner in cortex, substantia nigra, and cerebellum. We observed increased nigral SNCA-140 and SNCA-126 transcript levels in PD patients when compared to neurologically unaffected cases. Human α-synuclein splicing changes were also found to occur in a region-specific manner in ASO mice. Here, SNCA-126, -112, and -98 transcript levels did not increase proportionally with SNCA-140 levels, or parallel the region-specific mouse transcript ratios seen in wild-type (WT) littermates. While most transcripts were elevated in ASO mice when compared to WT mice, the most prominent increase was found in the ventral midbrain of 15-month-old ASO mice. These results demonstrate region-specific human α-synuclein transcript level abnormalities in PD patients and in a transgenic mouse model of α-synucleinopathy. This study is relevant to understanding the normal, adaptive, or pathological role(s) of α-synuclein splice variants.

Synaptoneurosome micromethod for fractionation of mouse and human brain, and primary neuronal cultures

“…As expected, human ␣-synuclein is expressed at elevated levels in both ASOTg SN and Cyt fractions (Rockenstein et al, 2002;Watson et al, 2009). Human ␣-synuclein's expression is similar in both the ASOTg SN and Cyt fraction, but a minor amount of a truncated ␣-synuclein isoform of ∼10-12 kDa size is also evident in the ASOTg SN, possibly due to carboxyl terminal cleavage (Li et al, 2005) and/or alternative RNA splicing (McLean et al, 2012).…”

Alpha-synuclein Post-translational Modifications as Potential Biomarkers for Parkinson Disease and Other Synucleinopathies

“…For example, Alzheimer disease and LB dementia brains seem to be characterized by higher ␣-syn-98 mRNA levels (106) and lower ␣-syn-126 expression (107), whereas an increased level of ␣-syn-112 was reported to be specific for LB dementia patients (108). A recent study suggested a global trend for increased expression of the four ␣-syn splicing variant mRNAs between control and PD patients, but the expression levels were found to vary between different brain regions (109). Surprisingly, clinical studies of ␣-syn isoforms have so far relied only on mRNA analysis, mainly because the levels of expression of the corresponding proteins are very low.…”

Mitochondrial Signaling and Neurodegeneration

“…PD-associated mitochondrial dysfunction induces α-syn [ 71 , 118 , 119 ], which may represent a retrograde signal designed to dampen the bioenergetic burden of synaptic transmission by blocking vesicle exocytosis and neurotransmitter release [ 120 ], to preserve neuronal Ca 2+ homeostasis at MAMs [ 117 ], or to decrease oxidative stress associated with dopamine autoxidation [ 116 ] within the PD brain [ 119 ].…”