Neuregulin-1 receptor tyrosine kinase ErbB4 is upregulated in midbrain dopaminergic neurons in Parkinson disease.

Previously we demonstrated that systemically administered neuregulin-1-ß1, a nerve growth and differentiation factor, passed the blood-brain barrier and accumulated in brain areas with expression of its receptor ErbB4. In substantia nigra (SN), neuregulin-1-ß1 phosphorylated ErbB4 and protected dopaminergic neurons in a toxin-based mouse model of Parkinson disease (PD). We studied ErbB4 in the context of human midbrain dopaminergic degeneration in vivo and in vitro. Post-mortem ventral midbrain tissue sections of neuropsychiatric healthy individuals and PD patients (matched for age, gender and post-mortem delay) were immunostained for ErbB4. Cultured Lund human mesencephalic (LUHMES) post-mitotic dopaminergic neurons were treated with dopaminergic toxins and analyzed for ErbB4 expression. In control individuals, 85.0±5.0% of dopaminergic neurons, containing cytoplasmic neuromelanin, expressed ErbB4 in the SN. In PD cases, the percentage of ErbB4-positive nigral dopaminergic neurons was increased to 94.9±2.5%. The mean ErbB4 immunoreactivity of melanized neurons was higher in PD than controls. LUHMES neurons upregulated ErbB4 when exposed to toxins 1-methyl-4-phenylpyridinium and 6-hydroxydopamine. Increased rate of ErbB4-positive dopaminergic neurons in PD may either reflect a better survival of ErbB4-positive neurons or an increased expression of ErbB4 by remaining neurons to seek trophic support. Enhanced ErbB4 expression in human in vitro toxin-based PD models supports the latter interpretation. Thus, dopaminergic neurons in SN might be susceptible to neuregulin-1 treatment in PD.

Systemic administration of neuregulin-1ß1 protects dopaminergic neurons in a mouse model of Parkinson's disease.

Neuregulin-1 (Nrg1) is genetically linked to schizophrenia, a disease caused by neurodevelopmental imbalance in dopaminergic function. The Nrg1 receptor ErbB4 is abundantly expressed on midbrain dopaminergic neurons. Nrg1 has been shown to penetrate blood-brain barrier, and peripherally administered Nrg1 activates ErbB4 and leads to a persistent hyperdopaminergic state in neonatal mice. These data prompted us to study the effect of peripheral administration of Nrg1 in the context of Parkinson's disease, a neurodegenerative disorder affecting the dopaminergic system in the adult brain. We observed that systemic injections of the extracellular domain of Nrg1ß(1) (Nrg1ß(1)-ECD) increased dopamine levels in the substantia nigra and striatum of adult mice. Nrg1ß(1)-ECD injections also significantly protected the mouse nigrostriatal dopaminergic system morphologically and functionally against 6-hydroxydopamine-induced toxicity in vivo. Moreover, Nrg1ß(1)-ECD also protected human dopaminergic neurons in vitro against 6-hydroxydopamine. In conclusion, we have identified Nrg1ß(1)-ECD as a neurotrophic factor for adult mouse and human midbrain dopaminergic neurons with peripheral administratability, warranting further investigation as therapeutic option for Parkinson's disease patients.