The Mitogen-Activated Protein Kinase (MAPK)/Extracellular Signal-Regulated Kinase (ERK) pathway is a central signaling cascade that transduces extracellular signals into cellular responses. Originally characterized in the context of cell proliferation and differentiation, this pathway plays critical roles in neuronal differentiation, synaptic plasticity, learning and memory, and neuronal survival. Dysregulation of MAPK/ERK signaling contributes to the pathogenesis of Alzheimer's disease (AD), Parkinson's disease (PD), and other neurodegenerative disorders. [1]
The MAPK/ERK pathway consists of a three-tier kinase cascade: [2]
Growth Factor → RTK → Ras → Raf → MEK1/2 → ERK1/2 → Nuclear Targets
| Kinase | Alternative Names | Function |
|---|---|---|
| Ras | HRAS, KRAS, NRAS | Small GTPase, molecular switch |
| Raf | ARAF, BRAF, RAF1 | MAPKKK, activates MEK |
| MEK1/2 | MAP2K1, MAP2K2 | MAPKK, activates ERK |
| ERK1/2 | MAPK1 (ERK2), MAPK3 (ERK1) | MAPK, nuclear targets |
Once activated, ERK1/2 translocates to the nucleus and phosphorylates:
ERK signaling is required for long-term potentiation (LTP), the cellular basis of learning and memory. NMDA receptor activation leads to Ras-ERK signaling, which is necessary for AMPA receptor trafficking and synaptic strengthening. In AD, Aβ oligomers impair ERK activation, contributing to synaptic failure. [3]
ERK can phosphorylate tau at multiple sites (Thr181, Ser202, Thr231, Ser396). While ERK-mediated tau phosphorylation may be protective under normal conditions, dysregulated ERK activation in AD contributes to pathological tau hyperphosphorylation and aggregation. [4]
ERK signaling promotes neuronal survival through phosphorylation of pro-survival targets. However, in AD, the pathway is often impaired, reducing neuroprotective signaling. [5]
ERK can regulate amyloid precursor protein (APP) processing and Aβ production. ERK activation may increase BACE1 expression, potentially accelerating Aβ generation. [6]
ERK signaling is required for development and survival of dopaminergic neurons. In PD, impaired ERK signaling contributes to neuronal vulnerability. However, the role is complex—ERK can be protective or detrimental depending on context. [7]
ERK activation is observed in PD brains and model systems. α-Synuclein can both activate and be regulated by MAPK pathways. Sustained ERK activation may contribute to neuronal dysfunction.
ERK can regulate mitochondrial function through phosphorylation of mitochondrial proteins. Impaired ERK signaling contributes to mitochondrial dysfunction in PD.
ERK in microglia drives production of pro-inflammatory cytokines. ERK activation in glia contributes to chronic neuroinflammation in PD.
ERK activation is observed in motor neurons and glia in ALS. The pathway may have dual roles—contributing to inflammation while also promoting survival signaling.
ERK signaling is dysregulated in HD. Both reduced and aberrant ERK activation have been reported, contributing to transcriptional dysfunction and neuronal death. [8]
| Drug | Target | Clinical Use | Status in Neurodegeneration |
|---|---|---|---|
| Selumetinib | MEK1/2 | Approved (cancer) | Preclinical |
| Trametinib | MEK1/2 | Approved (cancer) | Preclinical |
| Cobimetinib | MEK1/2 | Approved (cancer) | Preclinical |
| PD98059 | MEK1 | Research tool | Preclinical |
| U0126 | MEK1/2 | Research tool | Preclinical |
🟡 Moderate Confidence
| Dimension | Score |
|---|---|
| Supporting Studies | 15 references |
| Replication | Multiple studies |
| Effect Sizes | Context-dependent |
| Contradicting Evidence | Some |
| Mechanistic Completeness | 60% |
Overall Confidence: 50%
MAPK cascade signalling and synaptic plasticity. Nat Rev Neurosci. 2004. ↩︎
The role of mitogen-activated protein kinase cascades in signal transduction. Prog Neuropsychopharmacol Biol Psychiatry. 2002. ↩︎
ERK-mediated neuroprotection in Alzheimer's disease: role of autophagy and mitophagy. Front Cell Neurosci. 2023. ↩︎
Tau phosphorylation in Alzheimer's disease: towards a mechanism for tau aggregation. J Alzheimers Dis. 2005. ↩︎
Pathological roles of MAPK signaling pathway in neurodegenerative diseases. Exp Neurobiol. 2010. ↩︎
Role of mitogen-activated protein kinases in the pathogenesis of Alzheimer's disease. Ann NY Acad Sci. 2000. ↩︎
Complex formation and transcriptional activation by MAPKs. Mol Cell Biol. 2001. ↩︎
Dysregulation of the mitogen-activated protein kinase pathway in Huntington's disease. J Huntingtons Dis. 2015. ↩︎