Disease-Associated Microglia (DAM)

Disease-Associated Microglia (DAM)

<table class="infobox infobox-celltype">
<tr>
<th class="infobox-header" colspan="2">Disease-Associated Microglia (DAM)</th>
</tr>
<tr>
<td class="label">Lineage</td>
<td>Glia > Microglia > Disease-Associated</td>
</tr>
<tr>
<td class="label">Markers</td>
<td>TREM2, APOE, CLEC7A/Dectin-1, TYROBP/DAP12, CD68, LPL</td>
</tr>
<tr>
<td class="label">Brain Regions</td>
<td>Brain Parenchyma, Hippocampus, Cortex, Substantia Nigra</td>
</tr>
<tr>
<td class="label">Disease Vulnerability</td>
<td>Alzheimer's Disease, Parkinson's Disease, ALS, MS</td>
</tr>
</table>

Disease-Associated Microglia (DAM)

Introduction

Disease-Associated Microglia (DAM), also known as neurodegenerative-associated microglia (NAM) or MGnD (microglia in neurodegenerative disease), represent a distinct activation state of brain microglia that emerges in response to neurodegenerative pathology. These cells are characterized by a unique transcriptional signature that distinguishes them from the classical pro-inflammatory (M1) or alternative (M2) activation states described in earlier literature[@kerenshaul2017]. DAM are found surrounding amyloid plaques in Alzheimer's disease, dopaminergic neuron loss in Parkinson's disease, and in various other neurodegenerative conditions.

Overview

Disease-Associated Microglia (DAM)

<table class="infobox infobox-celltype">
<tr>
<th class="infobox-header" colspan="2">Disease-Associated Microglia (DAM)</th>
</tr>
<tr>
<td class="label">Lineage</td>
<td>Glia > Microglia > Disease-Associated</td>
</tr>
<tr>
<td class="label">Markers</td>
<td>TREM2, APOE, CLEC7A/Dectin-1, TYROBP/DAP12, CD68, LPL</td>
</tr>
<tr>
<td class="label">Brain Regions</td>
<td>Brain Parenchyma, Hippocampus, Cortex, Substantia Nigra</td>
</tr>
<tr>
<td class="label">Disease Vulnerability</td>
<td>Alzheimer's Disease, Parkinson's Disease, ALS, MS</td>
</tr>
</table>

Disease-Associated Microglia (DAM)

Introduction

Disease-Associated Microglia (DAM), also known as neurodegenerative-associated microglia (NAM) or MGnD (microglia in neurodegenerative disease), represent a distinct activation state of brain microglia that emerges in response to neurodegenerative pathology. These cells are characterized by a unique transcriptional signature that distinguishes them from the classical pro-inflammatory (M1) or alternative (M2) activation states described in earlier literature[@kerenshaul2017]. DAM are found surrounding amyloid plaques in Alzheimer's disease, dopaminergic neuron loss in Parkinson's disease, and in various other neurodegenerative conditions.

Overview

Disease-Associated Microglia represent a paradigm shift in our understanding of microglial function in the brain. Rather than simply being destructive immune effectors, DAM appear to play a dual role—both contributing to pathology through neurotoxic inflammation while simultaneously attempting to contain and clear disease-relevant proteins and debris.

The discovery of DAM was enabled by single-cell RNA sequencing studies that revealed a continuum of microglial states in the aging and diseased brain. These studies identified a specific gene expression program that is induced in microglia in response to amyloid pathology, including upregulation of genes involved in phagocytosis, lipid metabolism, and antigen presentation["@deczkowska2018"].

<!-- taxonomy-enrichment -->

<!-- multi-taxonomy-enrichment -->

Multi-Taxonomy Classification

Taxonomy Database Cross-References

| Taxonomy | ID | Name / Label |
|----------|----|---------------|
| Cell Ontology (CL) | [CL:0000095](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0000095) | neuron associated cell |

Morphology & Electrophysiology

• Morphology: neuron associated cell (source: Cell Ontology)
• Morphology can be inferred from Cell Ontology classification

PanglaoDB Marker Cross-References

• Unknown (PanglaoDB):

External Database Links

• [Cell Ontology (CL:0000095)](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0000095)
• [OBO Foundry (CL:0000095)](http://purl.obolibrary.org/obo/CL_0000095)
• [Allen Brain Cell Atlas](https://portal.brain-map.org/atlases-and-data/bkp/abc-atlas)
• [CellxGene Census](https://cellxgene.cziscience.com/)
• [Human Cell Atlas](https://www.humancellatlas.org/)
• [PanglaoDB](https://panglaodb.se/)

Taxonomy & Classification

| Database | ID | Name | Confidence |
|----------|----|------|------------|
| Cell Ontology | [CL:0000095](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0000095) | neuron associated cell | Medium |
| Cell Ontology | [CL:0000129](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0000129) | microglial cell | Medium |

PanglaoDB Marker Cross-References

• Unknown (PanglaoDB):

External Database Links

• [Cell Ontology (CL:0000095)](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0000095)
• [OBO Foundry (CL:0000095)](http://purl.obolibrary.org/obo/CL_0000095)
• [Allen Brain Cell Atlas](https://portal.brain-map.org/atlases-and-data/bkp/abc-atlas)
• [CellxGene Census](https://cellxgene.cziscience.com/)
• [PanglaoDB](https://panglaodb.se/)

Markers and Identification

Core DAM Markers

• TREM2 (Triggering Receptor Expressed on Myeloid Cells 2): The key signaling receptor driving DAM activation
• APOE (Apolipoprotein E): Lipid transport protein highly upregulated in DAM
• CLEC7A (Dectin-1): C-type lectin receptor involved in phagocytosis
• TYROBP (DAP12): Adaptor protein that partners with TREM2
• CD68: Lysosomal/endosomal marker
• LPL (Lipoprotein Lipase): Lipid metabolism enzyme

Stage-Specific Markers

DAM activation occurs in a staged manner:

Stage 1 DAM (pre-DAM):

• Upregulation of APOE, CLEC7A
• TREM2-independent
• Metabolic changes

• TREM2-dependent
• Enhanced phagocytic activity
• Neuroprotective functions

Role in Alzheimer's Disease

Amyloid Clearance

DAM are found in close association with amyloid plaques in AD brain tissue, where they appear to form a protective barrier. Their functions include:

• Phagocytosis of Aβ: DAM show enhanced uptake of amyloid-beta peptides
• Plaque compaction: DAM can engulf and compact Aβ, potentially reducing diffuse plaque burden
• Secretion of Aβ-clearing enzymes: Production of matrix metalloproteinases and other proteases

Tau Pathology

Microglial involvement in tau pathology is more complex:

• TREM2 signaling influences tau propagation and seeding
• Chronic DAM activation may exacerbate tau pathology through secreted factors
• Microglial dystrophy in advanced disease may reduce effective clearance

TREM2 and AD Risk

Genetic variants in TREM2 significantly modify AD risk:

• R47H variant: Increases AD risk ~3-fold (similar to APOE ε4)
• R62H variant: Moderate risk increase
• Loss-of-function variants: Protective effects observed in some studies

Role in Parkinson's Disease

Alpha-Synuclein Clearance

In PD, DAM are involved in the response to alpha-synuclein pathology:

• Phagocytosis of α-syn: DAM can engulf extracellular α-syn aggregates
• Inflammatory responses: DAM secrete cytokines that may influence disease progression
• TREM2 involvement: TREM2 variants modify PD risk, similar to AD

Dopaminergic Neuron Vulnerability

Microglial activation in the substantia nigra correlates with dopaminergic neuron loss:

• Pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) are elevated in PD substantia nigra
• Reactive oxygen species from activated microglia contribute to oxidative stress
• Neuroinflammation is thought to accelerate disease progression

Therapeutic Implications

Targeting DAM for Treatment

• Antibody-based TREM2 activation
• Small molecule TREM2 modulators
• Currently in clinical development for AD

• Microglial inhibition (e.g., colony-stimulating factor 1 receptor inhibitors)
• Selective cytokine blockade
• Pro-resolving lipid mediators

• Enhancing Aβ clearance without overactivation
• Promoting efficient debris removal

• Mitochondrial function support
• Lipid metabolism normalization

Clinical Trials

Several approaches targeting microglial pathways are in clinical trials:

• Anti-TREM2 antibodies (gantenerumab, etc.)
• CSF1R antagonists (peunacimod)
• Tyrphostin inhibitors (BL-9450)

See Also

• [Microglia](/cell-types/microglia)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [TREM2](/genes/trem2)
• [APOE](/proteins/apoe)
• [Neuroinflammation](/mechanisms/neuroinflammation-pathway)
• [Neurodegeneration-Associated Microglia

• [Alzheimer's Association - microglia research](https://www.alz.org/) - Research updates
• [Michael J. Fox Foundation - inflammation in PD](https://www.michaeljfox.org/) - Research information
• [PubMed - TREM2 microglia](https://pubmed.ncbi.nlm.nih.gov/?term=TREM2+microglia+Alzheimer) - Literature search

Background

The study of Disease Associated Microglia (Dam) has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.