Comparison of α-synuclein immunoreactivity in the hippocampus between the adult and aged beagle dogs

α-synuclein-lack expression rescues methamphetamine-induced mossy fiber degeneration in dorsal hippocampal CA3

Methamphetamine (METH) - induced cognitive impairments may be related to synaptic degeneration at mossy fiber terminals, critical for spatial memory formation in hippocampal circuits. We have previously found METH-induced neurodegeneration in the striatum by increasing the α-synuclein (α-SYN) level. However, whether and how the METH-induced mossy fiber degeneration is also blamed for the abnormal accumulation of α-SYN remains to be elucidated. Chronic METH exposure decreased mossy fiber density but upregulatedα-SYN and phosphorylated TAU (TAU-pSer396) in hippocampal CA3, associated with glial cell overactivation, axonal neuropathies, and memory impairment. Notably, the knockout of the α-SYN gene significantly alleviated the METH-induced mossy fiber degeneration and memory impairment. Meanwhile, the TAU-pSer396 accumulation and glial activation were ameliorated by α-SYN knockout. Our findings suggest an essential role of α-SYN in mediating METH-induced mossy fiber degeneration, providing promising therapeutic and prophylactic targets for METH-related neurodegenerative diseases.

α-Synuclein aggregation in the olfactory bulb of middle-aged common marmoset

The synaptic protein α-synuclein has been identified as a major component of Lewy bodies, a pathological hallmark of Parkinson's disease (PD). Prior to the formation of Lewy bodies, mislocalization and aggregation of the α-synuclein in brain tissue is frequently observed in various neurodegenerative diseases. Aberrant accumulation and localization of α-synuclein are also observed in the aging human brain, for which reason aging is regarded as a risk factor for neurodegenerative disease. To investigate changes in α-synuclein properties in the aging brain, we compared α-synuclein immunoreactivity in brain tissue of young (2-years-old) and middle-aged (6-years-old) common marmoset (Callithrix jacchus). Our analyses revealed marked changes in α-synuclein immunoreactivity in the olfactory bulb of common marmosets of these age cohorts. Perikaryal α-synuclein aggregations were formed in the olfactory bulb in middle-aged animals. We also observed signals of α-synuclein accumulation in hippocampus in this cohort; however, unlike in the olfactory bulb, hippocampal α-synuclein signals were localized in the synaptic terminals. We did not observe either of these features in younger marmosets, which suggest that aging may play a role in these phenomena. Our results using common marmoset brain corresponded with the observation that the α-synuclein aggregations were first occurred from olfactory bulb in human normal aged and PD brain. Therefore, common marmoset is expected as useful model for α-synuclein pathology.