| The current treatment for Parkinson's disease (PD) only addresses the symptoms of the disease, not the underlying death of dopaminergic neurons that produce the movement disorder. Glial cell line-derived neurotrophic factor (GDNF) has been investigated as a therapeutic target for PD, as it is a potent neurotrophic factor for dopamine neurons in vitro and in vivo. However, this protein-based therapy was abruptly halted from clinical trials. Meanwhile, small molecules are desirable therapeutic agents due to effective penetration of the blood brain barrier, stability, and specificity. Toward this end, three small peptides of varying lengths (5, 11, and 17 amino acids) are proposed to be released with the proteolytic processing of GDNF. It is our hypothesis that these peptides are produced in vivo, and that they will exert neurotrophic actions on dopaminergic neurons. The peptides were tested in primary cultures harvested from the ventral mesencephalon of F14 Sprague Dawley rat fetuses. GDNF served as the gold standard by which to measure the peptide performance. All of the small molecules exhibited some degree of neurotrophism in culture. The 11-mer peptide, however, compared to GDNF in its effects on cell survival and morphological differentiation. This peptide has been named dopamine neuron stimulating peptide (DNSP-11). Immnuofluorescent labeling was used to determine the cellular location of DNSP-11 in vitro and across developmental time points in vivo. DNSP-11 localized to the nucleus and cytoplasm of dopaminergic neurons. Moreover, DNSP-11 was present in the striatum and substantia nigra of early embryonic and postnatal time points, including E14, E16, E19, postnatal day (PND) 0, and PND 10. DNSP-11 did in fact colocalize with GDNF in dopaminergic neurons at PND 10, suggesting the peptide precursor is actually produced in vivo. These experiments provide evidence that peptide derivatives of GDNF have biological activity, and that DNSP-11, in particular, is present in vivo during developmental time points that are highly influenced by neurotrophic signaling. Furthermore, DNSP-11 may prove a promising therapeutic agent for treatment of PD.;KEYWORDS: GDNF, peptide derivatives, DNSP-11, neurotrophism, therapeutic agent. |
