Alpha-synuclein is present in the nucleus in human brain tissue and is pathologically modified in Dementia with Lewy Bodies

Background Dementia with Lewy bodies (DLB) is pathologically-defined by the cytoplasmic accumulation of alpha-synuclein (aSyn) within neuronal cells in the brain. aSyn is predominately pre-synaptic, but has been reported present in various subcellular compartments in cell and animal models. In particular, nuclear aSyn (aSynNuc) is evident in-vitro and in disease models and has been associated with altered DNA integrity, gene transcription, nuclear homeostasis. However, owing to various factors, the presence of aSynNuc in the human brain remains controversial, as does its role in synucleinopathies. Methods Here, we close this gap and provide a unique demonstration confirming the presence of aSynNuc in control (Con) and in DLB post-mortem brain tissue via immunohistochemistry, immunoblot, and label-free mass-spectrometry (MS). Results Discrete intra-nuclear aSyn puncta reactive against phosphorylated serine 129-aSyn (pS129-aSyn) and pan-aSyn antibodies were observed in cortical neurons and non-neuronal cells in fixed brain sections and isolated nuclear preparations from Con and DLB cases. Subsequent biochemical analysis of subcellular fractionated tissue confirmed aSynNuc as present at levels ~10-fold lower than in the cytoplasm. Critically, however, an increase in monomeric pS129-aSyn was observed in DLB cases alongside higher molecular weight pan- and pS129-reactive aSyn species, consistent with the formation of intranuclear phosphorylated aSynNuc oligomers. Furthermore, the occurrence of aSynNuc was confirmed via MS, with 6 unique aSyn derived peptide sequences identified in nuclear fractions (71.4% aSyn sequence coverage). Conclusions Collectively, our data confirm the presence of aSynNuc in human brain tissue and describe DLB-associated nuclear pathology. These findings address a major controversy in the synucleinopathy field by confirming the presence of aSynNuc in autoptic human brain tissue and, for the first time, identify that aSyn is aggregated into novel and potentially pathological assemblies in the nucleus as part of the DLB disease process and thus may contribute to the DLB phenotype.