Axonal transport of human α‐synuclein slows with aging but is not affected by familial Parkinson's disease‐linked mutations

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Abstract
Biochemical and genetic abnormalities of α‐synuclein (α‐Syn) are implicated in the pathogenesis of Parkinson's disease (PD) and other α‐synucleinopathies. The abnormal intraneuronal accumulations of α‐Syn in Lewy bodies (LBs) and Lewy neurites (LNs) have implicated defects in axonal transport of α‐Syn in the α‐synucleinopathies. Using human (Hu) α‐Syn transgenic (Tg) mice, we have examined whether familial PD (FPD)‐linked mutations (A30P and A53T) alter axonal transport of Huα‐Syn. Our studies using peripheral nerves show that Huα‐Syn and Moα‐Syn are almost exclusively transported in the slow component (SC) of axonal transport and that the FPD‐linked α‐Syn mutations do not have obvious effects on the axonal transport of α‐Syn. Moreover, older pre‐symptomatic A53T Huα‐Syn Tg mice do not show gross alterations in the axonal transport of α‐Syn and other proteins in the SC, indicating that the early stages of α‐synucleinopathy in A53T α‐Syn Tg mice are not associated with gross alterations in the slow axonal transport. However, the axonal transport of α‐Syn slows significantly with aging. Because the rate of axonal transport affects the stability and accumulation of proteins in axons, age‐dependent‐slowing α‐Syn is a likely contributor to axonal aggregation of α‐Syn in α‐synucleinopathy.