ERK1/2 and ERK5 have distinct roles in the regulation of brain‐derived neurotrophic factor expression

Abstract

Neurotrophins play essential roles in the development, differentiation, and survival of neuronal and nonneuronal cells. Alterations in neurotrophin expression have been implicated in a variety of neurodegenerative disorders. Dysregulation of brain-derived neurotrophic factor (BDNF) has been implicated in deficits of long-term potentiation and cognition and may contribute to the development of Alzheimer's disease (AD). In this study, we used complementary pharmacological and molecular approaches to evaluate the role of ERK1/2 and ERK5, two members of the MAPK pathway associated with neuroprotection, in regulating BDNF expression in C6 glial cells and primary astrocytes. Our data revealed that U0126, an inhibitor of both ERK5 and ERK1/2, increased the levels of BDNF mRNA, whereas the MEK1/2-specific inhibitor PD184352 did not, suggesting that ERK5 exerts negative control over BDNF expression. This was supported by experiments in which RNAi-mediated depletion of ERK5 led to an increase in BDNF. In contrast, transfection with constitutively active MEK5 resulted in an inhibition of BDNF expression, confirming the inhibitory role of ERK5 in the regulation of BDNF. Interestingly, transfection with the dominant active mutant of MEK1 (MEKR4F), the upstream activator of ERK1/2, resulted in a modest increase in BDNF levels. Collectively, our data suggest that ERK5 and ERK1/2 exert opposite effects on BDNF expression and support the hypothesis that an imbalance of these two signaling pathways may contribute to the pathology of diseases in which neurotrophin dysregulation is noted.

ERK5/KLF4 signaling as a common mediator of the neuroprotective effects of both nerve growth factor and hydrogen peroxide preconditioning

“…To test this hypothesis further, we used a constitutively active MEK5 construct, (CA-MEK5) (Pi et al 2004), to specifically activate ERK5. We have previously reported that expression of this construct resulted in a significant increase of ERK5 phosphorylation without affecting ERK1/2 phosphorylation (Su et al 2011), demonstrating the specificity of the MEK5 mutant. Consistent with our hypothesis of a protective role of ERK5 on neuronal survival against oxidative stress, we found that transfection with CA-MEK5 led to an increase in cell survival in the face of the H 2 O 2 insult (Fig.…”

“…Given that chemical inhibitors may suffer from specificity issues and further, and comparing different pharmacological agents may be confounded by their relative efficacy against their presumptive targets (i.e., efficacy of U0126 against ERK1/2 vs. ERK5), we elected to employ an RNAi approach to selectively knock down the expression of ERK5, ERK1 or ERK2 in PC12 cells. We previously reported a successful depletion of ERK5 expression in rat primary astrocytes using this method (Su et al 2011). Indeed, transfection of siERK5 significantly inhibited NGF-or PC-induced KLF4 up-regulation, while siERK1/2 had no effect on KLF4 mRNA levels (Fig.…”

“…The beststudied members of this family, ERK1/2, have been considered critical in promoting cell survival against oxidative stress in cultured primary neurons (Hota, Hota et al 2012;Sanchez et al 2012) as well as PC12 cells (Wruck et al 2007;Xiao et al 2011). However, these studies utilized the pharmacological inhibitors U0126 and PD98059, which have been previously used as selective inhibitors of the ERK1/2 signaling pathway but recently reported to effectively inhibit ERK5 signaling pathway as well (Suzaki et al 2004;Su et al 2011). …”

“…b Primary neurons were pre-treated with PC or NGF for 24 h prior to treatment with H 2 O 2 (50 μM) for another 24 h, then cell viability was assessed (n=3). Both PC and NGF rescued neurons from H 2 O 2 (***p<0.001, ****p<0.0001 vs. control, respectively control over BDNF expression, while the ERK1/2 pathway is recruited to preferentially mediate stimulusdriven increases in BDNF expression (Su et al 2011). Therefore, it is critical to delineate the roles of ERK5 versus ERK1/2 when studying a physiological effect.…”

MSK1 regulates environmental enrichment-induced hippocampal plasticity and cognitive enhancement

“…Interestingly, ERK/MAPK signaling plays a key role in the inducible expression of neurotrophins and also serves as a downstream kinase effector of neurotrophin receptor activation (Finkbeiner et al 1997;Kaplan and Miller 2000). For example, the expression of BDNF is mediated by an ERK/MAPK/CREB signaling cassette (Shieh and Ghosh 1999;Su et al 2011), and signaling via BDNF/TrkB affects cellular morphology via actuation of ERK/MAPK/CREB (Alonso et al 2004). Given these findings, one could envision MSK1 functioning within a positivefeedback circuit by which EE drives both neurotrophin expression and, in turn, neurotrophin-dependent enhancement of morphological plasticity.…”