A cleaved form of IGF-1, glycine-proline-glutamate (GPE), prevents the death of tyrosine hydroxylase (TH) immunopositive neurons, and restores TH immunoreactivity in the substantia nigra compacta (SNc) and the striatum of a 6-hydroxydopamine (6-OHDA)-induced PD model [100]. Here, IGF1 is linked to Parkinson disease.