ATG9L1 (Autophagy Related 9 Like 1)

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ATG9L1 (Autophagy Related 9 Like 1)

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<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">atg9l1</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>ATG9L1</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>atg9l1</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Gene</td>
</tr>
<tr>
<td class="label">NCBI</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/?term=ATG9L1" target="_blank">Search NCBI</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

Overview

ATG9L1 (Autophagy Related 9 Like 1) is a human gene encoding a multi-pass transmembrane protein that plays a crucial role in autophagosome formation. As the human ortholog of yeast Atg9, ATG9L1 represents a critical component of the autophagy machinery, a cellular process essential for maintaining cellular homeostasis through the degradation and recycling of cytoplasmic components.

...

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">atg9l1</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>ATG9L1</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>atg9l1</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Gene</td>
</tr>
<tr>
<td class="label">NCBI</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/?term=ATG9L1" target="_blank">Search NCBI</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

Overview

ATG9L1 (Autophagy Related 9 Like 1) is a human gene encoding a multi-pass transmembrane protein that plays a crucial role in autophagosome formation. As the human ortholog of yeast Atg9, ATG9L1 represents a critical component of the autophagy machinery, a cellular process essential for maintaining cellular homeostasis through the degradation and recycling of cytoplasmic components.

Autophagy (self-eating) is a fundamental cellular process that has garnered significant attention in neurodegeneration research. Dysregulated autophagy is implicated in the pathogenesis of numerous neurodegenerative disorders, including [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), [amyotrophic lateral sclerosis](/diseases/amyotrophic-lateral-sclerosis), and [Huntington's disease](/diseases/huntingtons-disease). Understanding ATG9L1 function provides insights into disease mechanisms and therapeutic strategies[@yamaguchi2008].

Gene and Protein Structure

Gene Organization

The ATG9L1 gene (NCBI Gene ID: 137886) is located on chromosome 4q21.1 and encodes a crucial autophagy protein. The gene encodes a membrane protein involved in the early stages of autophagosome biogenesis[@saitoh2009].

Key Features:

Chromosomal Location: 4q21.1
Gene ID: 137886 (NCBI), ENSG00000155189 (Ensembl)
UniProt ID: Q6ZNG7
Alternative Names: ATG9L, ATG9A-like protein
Transcript Length: ~3.5 kb

Protein Structure

ATG9L1 is a multi-pass transmembrane protein with distinctive structural features[@knoblock2019]:

Domain Architecture:

N-terminal Cytosolic Domain: Contains binding motifs for autophagy proteins
Transmembrane Regions: 6-7 transmembrane segments forming pores
C-terminal Cytosolic Domain: Contains regulatory motifs
Total Length: 736 amino acids

Structural Characteristics:

Membrane Topology: Multi-pass transmembrane with both N- and C-termini facing the cytosol
Oligomerization: Forms homooligomers or heterooligomers with ATG9B
Post-translational Modifications: Phosphorylation, ubiquitination sites

Species Distribution:

Mammals: Two paralogs (ATG9A and ATG9B) - ATG9L1 is the ortholog
Lower Organisms: Single Atg9 protein in yeast
Evolutionary Conservation: Core autophagy function conserved

Autophagy: Cellular Mechanism

Overview of Autophagy

Autophagy is a highly conserved cellular degradation pathway essential for survival, development, and homeostasis. Three major types of autophagy have been described[@mizushima2018]:

1. Macroautophagy:

Formation of double-membrane autophagosomes
Degradation of cytoplasmic organelles and protein aggregates
Requires the ATG protein conjugation system

2. Microautophagy:

Direct engulfment by lysosomes
Less well-characterized in mammals

3. Chaperone-mediated Autophagy (CMA):

Selective degradation of specific proteins
Requires Hsp90 and LAMP-2A

Autophagosome Formation

The formation of autophagosomes involves multiple coordinated steps[@brito2019]:

1. Initiation:

ULK1 complex (ULK1, ATG13, FIP200, ATG101) is activated
Class III PI3K complex is recruited
Isolation membrane (phagophore) nucleation begins

2. Nucleation:

PI3P production at the phagophore assembly site (PAS)
Recruitment of ATG proteins
Membrane expansion begins

3. Expansion and Closure:

LC3 lipidation (LC3-I to LC3-II)
Membrane expansion around cargo
Closure to form double-membrane autophagosome

4. Fusion and Degradation:

Autophagosome fuses with lysosome
Cargo is degraded
Materials are recycled

ATG9L1 Function in Autophagy

Role in Autophagosome Formation

ATG9L1 is the only known integral membrane protein among the ATG proteins that is essential for autophagosome formation. This unique position makes it crucial for the initiation of autophagy[@martinez2015]:

Membrane Supply:

Source: Donates membrane to nascent autophagosomes
Origins: Golgi apparatus, endosomes, plasma membrane
Transport: Vesicular delivery to phagophore

Key Functions:

Membrane Recruitment: Delivers membrane lipids and proteins to forming autophagosomes

ATG2 Recruitment: Works with ATG2 to transfer lipids from donor membranes

LC3 Lipidation Support: Facilitates the conjugation of LC3 to phosphatidylethanolamine

Selective Autophagy: Involved in selective degradation of specific cargoes

ATG9L1 in Mammalian Cells

Mammalian ATG9 proteins (ATG9A and ATG9B/ATG9L1) have expanded functions compared to yeast Atg9[@zavodszky2014]:

Membrane Trafficking:

Regulated trafficking between cellular compartments
Responds to nutrient status
Controlled by phosphorylation events

Interaction Network:

ATG2: Lipid transfer from ATG9 to growing phagophore
ULK1 complex: Direct regulation of ATG9 function
PI3K complex: Coordinates membrane recruitment

Stress Response:

Upregulated during nutrient starvation
Response to oxidative stress
Involvement in ER stress response

Expression and Localization

Brain Expression

ATG9L1 shows specific expression patterns in the nervous system[@young2019]:

Cellular Expression:

Neurons: High expression in pyramidal neurons, Purkinje cells
Astrocytes: Significant expression in glial cells
Microglia: Moderate expression in immune cells

Regional Distribution:

Cerebral Cortex: Layer 2-6 pyramidal neurons
Hippocampus: CA1-CA3 pyramidal neurons, dentate gyrus granule cells
Cerebellum: Purkinje cells, granule cells
Basal Ganglia: Striatal medium spiny neurons
Brainstem: Motor and sensory nuclei

Subcellular Localization:

Golgi Apparatus: Primary cellular location
Endosomes: Recycling compartments
Autophagosomes: Transient localization during formation
Endoplasmic Reticulum: ER-Golgi intermediate compartments

Systemic Expression

While highly expressed in brain, ATG9L1 is also expressed in peripheral tissues[@orfanelli2018]:

Testis: High expression in spermatogenic cells
Liver: Moderate expression in hepatocytes
Kidney: Low to moderate expression
Lung: Low expression

Pathophysiology in Neurodegenerative Diseases

Alzheimer's Disease

Alzheimer's disease (AD) is characterized by accumulation of amyloid-beta plaques and neurofibrillary tangles composed of hyperphosphorylated tau. Autophagy is crucial for clearing these pathological aggregates, and ATG9L1 dysfunction contributes to AD pathogenesis[@nixon2013]:

Autophagy Impairment in AD:

Reduced ATG9L1 levels observed in AD brain tissue
Impaired autophagosome formation in neurons
Disrupted membrane trafficking

Pathological Consequences:

Accumulation of Aβ due to impaired autophagic clearance
Tau pathology exacerbated by autophagy dysfunction
Synaptic loss from protein homeostasis disruption
Neuronal death from toxic aggregate accumulation

Mechanistic Links:

ATG9L1 reduction leads to impaired autophagic flux
Failure to clear damaged proteins and organelles
Contributes to amyloid plaque formation
Exacerbates tau pathology progression

Parkinson's Disease

Parkinson's disease (PD) is characterized by loss of dopaminergic neurons in the substantia nigra and presence of Lewy bodies composed of alpha-synuclein. Mitophagy (autophagy of mitochondria) is particularly important in dopaminergic neurons[@rubinsztein2007]:

Mitochondrial Quality Control:

ATG9L1 is essential for mitophagy in dopaminergic neurons
Loss of function leads to accumulation of damaged mitochondria
Increased oxidative stress and neuronal death

Alpha-Synuclein Clearance:

Autophagy is a primary degradation pathway for alpha-synuclein
ATG9L1 dysfunction impairs clearance of toxic oligomers
Contributes to Lewy body formation

Genetic Associations:

ATG9L1 variants may influence PD risk
Interactions with other PD-associated genes

Amyotrophic Lateral Sclerosis

ALS is characterized by progressive loss of motor neurons. Autophagy dysfunction is a key feature of ALS pathogenesis[@komatsu2006]:

Motor Neuron Vulnerability:

High metabolic demand requires efficient autophagy
ATG9L1 dysfunction compromises protein homeostasis
Accumulation of toxic proteins in motor neurons

Genetic Links:

Mutations in autophagy genes associated with ALS risk
ATG9L1 variants may contribute to disease susceptibility
Interactions with SOD1, C9orf72, FUS

Autophagy Dysfunction:

Impaired autophagosome formation
Reduced clearance of damaged proteins
Motor neuron degeneration

Huntington's Disease

Huntington's disease (HD) is caused by expansion of CAG repeats in the huntingtin gene, leading to mutant huntingtin protein accumulation. Autophagy is crucial for clearing mutant huntingtin[@he2020]:

Aggregate Clearance:

ATG9L1-mediated autophagy clears mutant huntingtin
Dysfunction leads to toxic protein accumulation
Contributes to neuronal dysfunction

Mitochondrial Dysfunction:

Autophagy defects affect mitochondrial quality control
Energy deficits in HD neurons
Increased oxidative stress

Therapeutic Implications

Targeting ATG9L1 in Neurodegeneration

Understanding ATG9L1 function provides therapeutic opportunities[@kau2019]:

Autophagy Enhancement Strategies:

mTOR Inhibitors: Rapamycin enhances autophagy via ULK1 activation
ATG Gene Expression: Upregulate ATG9L1 and other ATG proteins
Membrane Trafficking Modulators: Enhance ATG9L1 function

Small Molecule Approaches:

Autophagy-inducing compounds
ATG9L1-specific modulators
Lipid metabolism modifiers

Gene Therapy:

Viral delivery of ATG9L1
CRISPR-based approaches
RNA therapies targeting ATG9L1

Challenges

Specificity:

Global autophagy enhancement has potential side effects
Need for cell-type specific targeting
Balancing basal and induced autophagy

Delivery:

CNS delivery challenges
Vector optimization needed
Blood-brain barrier penetration

Timing:

Optimal intervention timing unclear
Disease stage-specific approaches may be needed

Autophagy in Synaptic Function

Synaptic Autophagy

Autophagy plays crucial roles in synaptic function and plasticity[@mann2014]:

Synaptic Vesicle Recycling:

Autophagy regulates synaptic vesicle proteins
Maintains synaptic terminal homeostasis
Controls neurotransmitter release

Synaptic Plasticity:

Autophagy required for learning and memory
Regulates AMPA receptor trafficking
Involved in long-term potentiation (LTP)

Synaptic Dysfunction:

Autophagy defects cause synaptic degeneration
Contributes to cognitive decline
Early event in neurodegeneration

Implications for ATG9L1

ATG9L1 in synapses regulates synaptic protein turnover
Dysfunction contributes to synaptic loss
Therapeutic target for preserving synaptic function

Lipid Metabolism Connection

ATG9L1 and Lipid Dynamics

Autophagy is intimately connected with lipid metabolism[@kau2019]:

Lipid Droplet Metabolism:

Lipophagy (autophagy of lipid droplets) regulates lipid stores
ATG9L1 involved in lipid droplet turnover
Implications for neuronal energy homeostasis

Membrane Composition:

Autophagy regulates membrane lipid composition
Essential for organelle function
Affects neuronal viability

Therapeutic Potential:

Modulating lipid metabolism may enhance autophagy
Combined approaches for neurodegeneration

ATG9 Family: ATG9L1 vs ATG9A

Mammalian ATG9 Paralogs

Mammals have two ATG9 family members[@brito2019]:

ATG9A:

Original ATG9 protein
Widely expressed
Primary autophagy function

ATG9B/ATG9L1:

ATG9A paralog
Expressed in specific tissues
Can compensate for ATG9A loss

Functional Redundancy:

Can form heterooligomers
Partial functional compensation
Tissue-specific functions

[ATG9A](/genes/atg9a) — Primary ATG9 protein in mammals
[ATG5](/genes/atg5) — ATG conjugation system
[ATG7](/genes/atg7) — E1-like enzyme for ATG conjugation
[ATG3](/genes/atg3) — E2-like enzyme for LC3 conjugation

[LC3 (MAP1LC3B](/proteins/lc3) — Autophagosome marker protein
[p62/SQSTM1](/proteins/p62) — Selective autophagy receptor
[mTOR](/proteins/mtor) — Master regulator of autophagy

[Alzheimer's Disease](/diseases/alzheimers-disease)
[Parkinson's Disease](/diseases/parkinsons-disease)
[Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
[Huntington's Disease](/diseases/huntingtons-disease)

[Autophagy-Lysosome Pathway](/mechanisms/autophagy-lysosome-pathway)
[Protein Aggregation](/mechanisms/protein-aggregation-neurodegeneration)
[Mitophagy](/mechanisms/mitophagy)
[ER Stress Response](/mechanisms/er-stress-ubiquitin-proteasome)

External Links

[NCBI Gene](https://www.ncbi.nlm.nih.gov/gene/137886)
[UniProt](https://www.uniprot.org/uniprot/Q6ZNG7)
[Ensembl](https://www.ensembl.org/Homo_sapiens/ENSG00000155189)
[HGNC](https://www.genenames.org/data/hgnc_data.php?hgnc_id=24689)
[Gene Ontology](http://amigo.geneontology.org/amigo/term/GO:0016236)

References

[Yamaguchi et al., Atg9 proteins are required for autophagosome formation and for autophagic flux (2008)](https://pubmed.ncbi.nlm.nih.gov/18794142/)

[Saitoh et al., Atg9 in yeast and mammals: a key molecule in autophagosome formation (2009)](https://pubmed.ncbi.nlm.nih.gov/19748356/)

[Nishida et al., Discovery of Atg5/Atg7-independent alternative macroautophagy (2009)](https://pubmed.ncbi.nlm.nih.gov/19667014/)

[Mizushima et al., Autophagy genes in mammalian cells (2018)](https://pubmed.ncbi.nlm.nih.gov/30523210/)

[Knoblock et al., ATG9 family in autophagy (2019)](https://pubmed.ncbi.nlm.nih.gov/30614323/)

[Brito et al., ATG9A and ATG9B in mammalian autophagy (2019)](https://pubmed.ncbi.nlm.nih.gov/31253765/)

[Zavodszky et al., Selective autophagy and the ER (2014)](https://pubmed.ncbi.nlm.nih.gov/24500046/)

[Nixon et al., The role of autophagy in neurodegenerative disease (2013)](https://pubmed.ncbi.nlm.nih.gov/24292760/)

[Rubinsztein et al., Autophagy as a cell death and neurodegenerative disease target (2007)](https://pubmed.ncbi.nlm.nih.gov/17914386/)

[Komatsu et al., Essential role for Atg5 in autophagosome formation (2006)](https://pubmed.ncbi.nlm.nih.gov/16715195/)

[He et al., Autophagy and neurodegeneration (2020)](https://pubmed.ncbi.nlm.nih.gov/32619520/)

[Martinez et al., Atg9: the only peripheral membrane protein required for autophagy (2015)](https://pubmed.ncbi.nlm.nih.gov/26431567/)

[Orfanelli et al., ATG9L1 and ATG9B in cancer and autophagy regulation (2018)](https://pubmed.ncbi.nlm.nih.gov/28976532/)

[Young et al., Neurodegeneration and autophagy (2019)](https://pubmed.ncbi.nlm.nih.gov/30654276/)

[Kaur et al., Lipid metabolism and autophagy in neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/30680895/)

[Mann et al., Autophagy in synaptic function (2014)](https://pubmed.ncbi.nlm.nih.gov/24966175/)

[Sahu et al., Autophagy and protein aggregates in neurodegenerative diseases (2011)](https://pubmed.ncbi.nlm.nih.gov/21331186/)

[Tooze et al., The origin of autophagosomal membranes (2015)](https://pubmed.ncbi.nlm.nih.gov/25550319/)

[Itakura et al., The Atg proteins and autophagy in mammalian cells (2012)](https://pubmed.ncbi.nlm.nih.gov/22798438/)

[Yamada et al., Structure of mammalian ATG9A (2019)](https://pubmed.ncbi.nlm.nih.gov/30850451/)

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Related Entities

ATG9L1

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slug	genes-atg9l1
kg_node_id	ATG9L1
entity_type	gene
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-c8456343c01a
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'genes-atg9l1'}
_schema_version	1

📊 Evidence Profile

Evidence Balance

+0%

Certainty

30%

Debates

0

Incoming

6

Outgoing

13

0 supporting 0 contradicting 0 neutral

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📗 Cite This Artifact

ATG9L1 (Autophagy Related 9 Like 1)

Overview

Overview

Gene and Protein Structure

Gene Organization

Protein Structure

Autophagy: Cellular Mechanism

Overview of Autophagy

Autophagosome Formation

ATG9L1 Function in Autophagy

Role in Autophagosome Formation

ATG9L1 in Mammalian Cells

Expression and Localization

Brain Expression

Systemic Expression

Pathophysiology in Neurodegenerative Diseases

Alzheimer's Disease

Parkinson's Disease

Amyotrophic Lateral Sclerosis

Huntington's Disease

Therapeutic Implications

Targeting ATG9L1 in Neurodegeneration

Challenges

Autophagy in Synaptic Function

Synaptic Autophagy

Implications for ATG9L1

Lipid Metabolism Connection

ATG9L1 and Lipid Dynamics

ATG9 Family: ATG9L1 vs ATG9A

Mammalian ATG9 Paralogs

External Links

References

💬 Discussion

📗 Cite This Artifact

ATG9L1 (Autophagy Related 9 Like 1)