γ-Enolase C-terminal peptide promotes cell survival and neurite outgrowth by activation of the PI3K/Akt and MAPK/ERK signalling pathways

Abstract

γ-Enolase, a glycolytic enzyme, is expressed specifically in neurons. It exerts neurotrophic activity and has been suggested to regulate growth, differentiation, survival and regeneration of neurons. In the present study, we investigated the involvement of γ-enolase in PI3K (phosphoinositide 3-kinase)/Akt and MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) signalling, the two pathways triggered predominantly by neurotrophic factors. Whereas the PI3K/Akt pathway, rather than the MAPK/ERK pathway, is involved in γ-enolase-enhanced cell survival, γ-enolase-stimulated neurite outgrowth requires both pathways, i.e. the activation of both PI3K and ERK1/2, leading to subsequent expression of the growth-cone-specific protein GAP-43 (growth-associated protein of 43 kDa). MEK (MAPK/ERK kinase) and PI3K inhibition blocked or attenuated the neurite outgrowth associated with dynamic remodelling of the actin-based cytoskeleton. We show that γ-enolase-mediated PI3K activation regulates RhoA kinase, a key regulator of actin cytoskeleton organization. Moreover, the inhibition of RhoA downstream effector ROCK (Rho-associated kinase) results in enhanced γ-enolase-induced neurite outgrowth, accompanied by actin polymerization and its redistribution to growth cones. Our results show that γ-enolase controls neuronal survival, differentiation and neurite regeneration by activating the PI3K/Akt and MAPK/ERK signalling pathways, resulting in downstream regulation of the molecular and cellular processes of cytoskeleton reorganization and cell remodelling, activation of transcriptional factors and regulation of the cell cycle.

Neuroprotective role of γ‐enolase in microglia in a mouse model of Alzheimer's disease is regulated by cathepsin X

“…This result confirms the role of cathepsin X, which specifically cleaves the C-terminal dipeptide of c-enolase, in diminishing c-enolase neurotrophic activity. The protective effect of c-enolase was observed also in the test for overall neurite outgrowth (Hafner et al, 2012), as followed by the levels of GAP-43, a recognized marker for axon growth zones (Van Hooff et al, 1989). Differentiated PC12 cells treated by Ab showed a significant reduction in GAP-43 expression (Fig.…”

“…In brains with AD pathology, extensive neuritic dystrophy is accompanied by a dramatic remodelling of actin filaments (Heredia et al, 2006;Braithwaite et al, 2010). c-Enolase is involved in cytoskeleton remodelling by activating PI 3-K and MAPK signalling pathways (Hafner et al, 2012); therefore, it could also have a beneficial effect on neuronal functions by promoting neurite outgrowth.…”

“…To analyse protein secretion of c-enolase in microglial culture medium, protein determination and western blot analyses were performed as described (Hafner et al, 2012). In western blot, the following primary antibodies were applied: monoclonal mouse anti-C-terminal of c-enolase, suitable for detection of its active form (1:500) (Santa Cruz Biotechnology) and monoclonal mouse antiinternal region of c-enolase, suitable for detecting active and cleaved forms of c-enolase (1:500) (Santa Cruz Biotechnology) and the following secondary HRP-coupled anti-mouse antibodies…”

“…Further, gamma-enolase is considered to be a neuronal marker (Herrmann & Ehrenreich, 2003) as well as a marker for morphological status in AD (Chaves et al, 2010) and possesses a neurotrophic activity (Hattori et al, 1995). It controls neuronal survival, differentiation and neurite regeneration by activating phosphatidylinositol 3-kinase (PI 3-k) and mitogen-activated protein kinase (MAPK) signal transduction pathways (Hafner et al, 2012), as do other neurotrophic factors, such as NGF (Kaplan & Miller, 1997). c-Enolase neurotrophic activity is associated with the ability to be translocated towards the plasma membrane and with its intact C-terminal end, which is cleaved by cysteine protease cathepsin X (Obermajer et al, 2009;Hafner et al, 2010).…”

Transcriptional and Epigenetic Regulation in Injury-Mediated Neuronal Dendritic Plasticity

“…Transcription factors are essential for the initiation of target gene transcription for the further production of transcription factors or the translation of other genes that play roles in the retraction, regrowth, and reorganization of dendritic branches [4][5][6]. Much of what we know about the roles transcription factors play in these processes stem from limited studies on the actions of a handful of key factors.…”