The Role of ERK5 in Dopamine Neuronal Survival

The extracellular signal-regulated kinases (ERKs) 1, 2, and 5 play important physiological roles in neurogenesis, neutrite outgrowth, and neuronal viability in the central nervous system. In this study, ERK1, 2, and 5 expression and activation were examined in the substantia nigra (SN), striatum (STR), and ventral tegmental area (VTA) during postnatal development and normal aging using western blot analysis. An age-related decrease in phosphorylated/activated ERK5 (p-ERK5) was observed in the SN and STR, whereas an increase in total ERK1 was observed in all three regions. Higher expression of total and phosphorylated ERK5 was observed at postnatal day zero (PND0) in all dopaminergic regions, which declined with the postnatal development. However, expression of total ERK1 and ERK2 increased with the postnatal development. An increase in the p-ERK1 and p-ERK2 peak was observed in both dopaminergic cell bodies containing regions, SN and VTA at PND7 as compared to PND0. In contrast, no such peak was observed in the STR with the postnatal development.

In primary DA cultures of the SN and VTA, inhibition of ERK5 but not ERK1 and ERK 2 activation significantly decreased DA neuronal viability. Pretreatment with the glial cell line-derived neurotrophic factor (GDNF) or dopamine neuron stimulating peptide-11 (DNSP-11) did not protect human dopaminergic SH-SY5Y cells against 6-hydroxydopamine (6-OHDA)-induced toxicity at 24 h. However, GDNF or DNSP-11 pretreatment protected against 6-OHDA-induced increase in apoptotic signaling, as measured by caspase-3/7 activity at 6 h; indicating that GDNF and DNSP-11 blocks some, but not all, of the cytotoxic effects of 6-OHDA. Treatment of SH-SY5Y cells with GDNF or DNSP-11 resulted in activation of ERK1, 2, and 5 signaling. Infusion of DNSP-11 into the STR also resulted in modulation of ERK1, 2, and 5 signaling. Increase in tyrosine hydroxylase expression was observed in the STR (42%) and SN (32%), at 7 days and 6 h, respectively, after DNSP-11 infusion.

Together, these data suggest the essential role of ERK1, 2, and 5 kinases in dopamine neuronal survival, especially ERK5. These data raise the possibility that a decline ERK5 signaling may play a role in age-related impairments in dopaminergic function.