The mammalian target of rapamycin (mTOR) pathway integrates nutrient availability, growth factor signaling, lysosomal status, and cellular energy balance to regulate protein synthesis, autophagy, and stress adaptation.[@saxton2017][@tramutola2017] In neurodegeneration, abnormal mTOR signaling is critical because it shapes proteostasis, synaptic plasticity, lysosomal function, and inflammatory responses across [neurons](/entities/neurons) and glia.[@tramutola2017][@caccamo2013]
mTOR Signaling Pathway Diagram
```mermaid flowchart TB subgraph Inputs["Upstream Inputs to mTORC1"] A["Growth factors<br/>IGF-1, BDNF"] --> B["PI3K"] B --> C["AKT"] C -->|"inhibits"| D["TSC1/2"] D -->|"inhibits"| E["RHEB-GTP"]
I["Energy stress<br/>low ATP"] --> J["AMPK"] J -->|"activates"| K["TSC2"] K --> D J -->|"phosphorylates Raptor"| L["Raptor"] L -->|"inhibits"| M["mTORC1"] E --> M H --> M end
subgraph Active["mTORC1 Active Complex"] O["mTOR + Raptor + mLST8 + PRAS40"] end
M --> O
...
mTOR Signaling Pathway in Neurodegeneration
Overview
The mammalian target of rapamycin (mTOR) pathway integrates nutrient availability, growth factor signaling, lysosomal status, and cellular energy balance to regulate protein synthesis, autophagy, and stress adaptation.[@saxton2017][@tramutola2017] In neurodegeneration, abnormal mTOR signaling is critical because it shapes proteostasis, synaptic plasticity, lysosomal function, and inflammatory responses across [neurons](/entities/neurons) and glia.[@tramutola2017][@caccamo2013]
mTOR Signaling Pathway Diagram
Mermaid diagram (expand to render)
mTOR Complexes
mTORC1 Structure and Function
The mTOR complex 1 (mTORC1) consists of:
mTOR — the catalytic core serine/threonine kinase[@saxton2017]
Raptor (regulatory-associated protein of mTOR) — scaffolds substrate recruitment[@saxton2017]
mLST8 — supports kinase activity[@saxton2017]
PRAS40 and Deptor — regulatory subunits that inhibit activity under certain conditions[@saxton2017]
mTORC1 functions as a nutrient/energy sensor and promotes anabolic processes:
Protein synthesis via [p70S6K](/proteins/p70s6k-protein) and [4E-BP1](/proteins/4ebp1-protein) phosphorylation[@saxton2017]
Lipid synthesis through SREBP activation[@saxton2017]
Ribosome biogenesis[@saxton2017]
Autophagy suppression via [ULK1](/proteins/ulk1) phosphorylation and [TFEB](/proteins/tfeb-protein) inhibition[@saxton2017][@mizushima2020]
mTORC2 Structure and Function
The mTOR complex 2 (mTORC2) consists of:
mTOR — the catalytic core[@saxton2017]
Rictor (rapamycin-insensitive companion of mTOR) — defining subunit[@saxton2017]
mLST8 — shared with mTORC1[@saxton2017]
Protor1/2 and Deptor — regulatory subunits[@saxton2017]
mTORC2 regulates:
AKT full activation through Ser473 phosphorylation[@saxton2017][@huang2013]
PKCα phosphorylation and cytoskeletal organization[@saxton2017]
SGK1 activation for ion transport and cell survival[@saxton2017]
Role in Autophagy
mTORC1 is a central negative regulator of autophagy. When active:
ULK1 phosphorylation: mTORC1 phosphorylates [ULK1](/proteins/ulk1) at Ser757, disrupting the ULK1-AMPK interaction and inhibiting autophagy initiation[@mizushima2020]
TFEB inhibition: mTORC1 phosphorylates [TFEB](/proteins/tfeb-protein), retaining it in the cytoplasm and preventing transcription of lysosomal and autophagy genes[@mizushima2020]
ATG proteins: mTORC1 signaling modulates the activity of ATG proteins involved in autophagosome formation[@mizushima2020]
In neurodegeneration, mTORC1 hyperactivation contributes to:
Dysregulated protein synthesis contributes to synaptic dysfunction in [Alzheimer's disease](/diseases/alzheimers-disease) and [Parkinson's disease](/diseases/parkinsons-disease).
Role in Synaptic Plasticity
mTOR signaling is essential for synaptic plasticity through:
Local translation at synapses: mTORC1 activity in dendritic spines regulates synthesis of synaptic proteins[@hoeffer2009]
Long-term potentiation (LTP): Required for the protein synthesis-dependent late phase of LTP[@hoeffer2009]
Memory consolidation: mTOR-dependent translation in the hippocampus is necessary for memory formation[@hoeffer2009]
However, excessive mTOR activity can impair synaptic function by:
Promoting abnormal protein synthesis[@tramutola2017]
Inhibiting autophagy needed for synaptic vesicle recycling[@mizushima2020]
Contributing to dendritic spine abnormalities observed in AD[@tramutola2017]
Relevance to Alzheimer's Disease
In Alzheimer's disease, mTOR dysregulation manifests as:
Hyperactivity: mTOR signaling is elevated in AD brains, contributing to amyloid accumulation and impaired autophagy[@tramutola2017]
Tau pathology: mTOR phosphorylates tau at multiple sites; hyperactivation promotes tau aggregation and impairs tau clearance[@tramutola2017][@caccamo2013]
Synaptic failure: Abnormal translation regulation contributes to synaptic protein loss[@tramutola2017]
Therapeutic targeting: mTOR inhibitors show promise in preclinical AD models but must balance benefits against potential cognitive side effects[@tramutola2017]
Relevance to Parkinson's Disease
In Parkinson's disease and related synucleinopathies:
α-Synuclein clearance: mTORC1 inhibition enhances autophagic clearance of [α-synuclein](/proteins/alpha-synuclein)[@caccamo2013]
Lysosomal function: mTOR regulates lysosomal biogenesis; dysregulation contributes to impaired protein clearance[@caccamo2013]
Mitochondrial quality control: mTOR affects mitophagy through ULK1 regulation[@mizushima2020]
[Saxton RA, Sabatini DM, mTOR signaling in growth, metabolism, and disease (2017)](https://doi.org/10.1016/j.cell.2017.02.004)
[Tramutola A, Lanzillotta C, Di Domenico F, Targeting mTOR to reduce Alzheimer-related cognitive decline: from current hits to future therapies (2017)](https://doi.org/10.3389/fphar.2017.00799)
[Caccamo A, Magri A, Medina DX, Wisely EV, Lopez-Aranda MF, Silva AJ, Oddo S, mTOR regulates tau phosphorylation and degradation: implications for Alzheimer's disease and other tauopathies (2013)](https://doi.org/10.18632/aging.100590)
[Mizushima N, The role of the Atg1/ULK1 complex in autophagy regulation (2020)](https://doi.org/10.1016/j.tcb.2020.10.004)
[Huang W, Zhu PJ, Zhang S, et al, mTORC2 controls actin polymerization required for consolidation of long-term memory (2013)](https://doi.org/10.1038/nn.3453)
[Hoeffer CA, Klann E, mTOR signaling: at the crossroads of plasticity, memory and disease (2009)](https://doi.org/10.1016/j.tins.2009.12.003)
[Manzoni C, Mamais A, Dihanich S, et al, Pathogenic mutations in LRRK2 modulate mTOR signaling and ULK1 activity in neurons (2022)](https://doi.org/10.1093/brain/awab099)