抄録
Dopaminergic neurons in the substantia nigra project to the striatum. In humans, a selective loss of the nigrostriatal projection is a pathological hallmark of Parkinson disease (PD). The regeneration of this pathway shows great promise as a therapy for PD. Although several factors are known to direct dopaminergic axons into the striatum, it remains unclear how the axons extend in the striatum in order to innervate their targets. To address this issue, we reconstructed the dopaminergic innervation of striatal cells using primary cultured cells derived from rat embryos. When mesencephalic cells containing dopaminergic neurons were adjacently paired-cultured with striatal cells, dopaminergic neurites extended from the mesencephalic cell region to the striatal cell region. The neurites were mainly axons and extended along the striatal neuronal clusters. In addition, this paired-cultivation enabled the quantitative evaluation of dopaminergic neurite outgrowth to the striatal cell region. Integrin family is one of intercellular adhesion molecules forming αβ heterodimers, and to date, 8 β subunits have been reported to assemble with 18 α subunits to form 24 distinct integrins. The extension of dopaminergic neurites was suppressed by the pharmacological inhibition of integrin α5β1. Knockdown of integrin α5 in dopaminergic neurons suppressed the neurite outgrowth to the striatal cell region. In contrast, the knockdown of integrin α5 in non-dopaminergic mesencephalic and striatal cells had no effect. Integrin α5 assembles only with integrin β1. These results indicate that integrin α5β1 expression on dopaminergic neurons is involved in the dopaminergic neurite outgrowth on striatal neurons. Pluripotent stem cells are promising candidates of cell transplantation therapy for PD. Mouse embryonic stem cells were transfected with integrin α5 gene. They were differentiated into dopaminergic neurons, and replated on striatal cultures. Overexpression of integrin α5 in dopaminergic neurons enhanced their neurite outgrowth on striatal cells. This finding suggests that integrin α5 overexpression in dopaminergic neurons promote the innervation of striatal neurons. In summary, we established the evaluation system for dopaminergic innervation of striatal neurons and proposed that integrin α5β1 plays a key role in the innervation.
