A novel peptide inhibitor targeted to caspase-3 cleavage site of a proapoptotic kinase protein kinase C delta (PKCδ) protects against dopaminergic neuronal degeneration in Parkinson’s disease models

Oxidative stress and apoptosis are considered common mediators of many neurodegenerative disorders including Parkinson’s disease (PD). Recently, we identified that PKCδ, a member of the novel PKC isoform family, is proteolytically activated by caspase-3 to induce apoptosis in experimental models of PD [Eur. J. Neurosci. 18 (6):1387–1401, 2003; Antioxid. Redox Signal. 5 (5):609–620, 2003]. Since caspase-3 cleaves PKCδ between proline and aspartate residues at the cleavage site 324DIPD327 to activate the kinase, we developed an irreversible and competitive peptide inhibitor, Z-Asp(OMe)-Ile-Pro-Asp(OMe)-FMK (z-DIPD-fmk), to mimic the caspase-3 cleavage site of PKCδ and tested its efficacy against oxidative stress-induced cell death in PD models. Cotreatment of z-DIPD-fmk with the parkinsonian toxins MPP+ and 6-OHDA dose dependently attenuated cytotoxicity, caspase-3 activation, and DNA fragmentation in a mesencephalic dopaminergic neuronal cell model (N27 cells). However, z-DIPD-fmk treatment did not block MPP+-induced increases in caspase-9 enzyme activity. The z-DIPD-fmk peptide was much more potent (IC50 6 μM) than the most widely used and commercially available caspase-3 inhibitor z-DEVD-fmk (IC50 18 μM). Additionally, z-DIPD-fmk more effectively blocked PKCδ cleavage and proteolytic activation than the cleavage of another caspase-3 substrate, poly(ADP-ribose) polymerase (PARP). Importantly, the peptide inhibitor z-DIPD-fmk completely rescued TH+ neurons from MPP+- and 6-OHDA-induced toxicity in mouse primary mesencephalic cultures. Collectively, these results demonstrate that the PKCδ cleavage site is a novel target for development of a neuroprotective therapeutic strategy for PD.