Neurodegeneration-Associated Microglia (NAM)

Neurodegeneration-Associated Microglia (NAM)
Taxonomy	ID
Cell Ontology (CL)	[CL:0000095](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0000095)
Database	ID
Cell Ontology	[CL:0000095](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0000095)
Cell Ontology	[CL:0000129](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0000129)
Gene	Function
TREM2	Triggering receptor on myeloid cells 2
TYROBP	TYROBP signaling adaptor
CD33	Siglec-3 receptor
APOE	Apolipoprotein E
SPP1	Osteopontin
ITGAX	CD11c
Feature	DAM (Stage 1-2)
TREM2	Intermediate
APOE	Moderate
Type I IFN genes	Present
Proliferation genes	High
Disease duration	Early
Strategy	Compound
TREM2 agonist	AL002
TREM2 bispecific	TREM2xCD3
Anti-APOE antibody	Aprinocarsen

Introduction

Neurodegeneration-Associated Microglia (NAM) are a specialized microglial phenotype identified through single-cell transcriptomics that emerges in response to chronic neurodegeneration. Unlike disease-associated microglia (DAM) or activated microglia, NAM represents a distinct cell state characterized by a specific gene expression signature associated with late-stage neurodegenerative processes^{1(2017). A Unique Microglia Type Associated with Alzheimer's Disease. Cell, 170(7), 1276-12902017 · DOI 10.1016/j.cell.2017.11.018Open reference}.

Overview

Microglia are the resident immune cells of the central nervous system, derived from yolk sac progenitors early in embryogenesis. In the healthy brain, microglia perform essential homeostatic functions including synaptic pruning, debris clearance, and immune surveillance.

Under neurodegenerative conditions, microglia adopt multiple activation states. The NAM phenotype represents one of these states, characterized by a gene expression profile distinct from both homeostatic microglia and the DAM response seen in early Alzheimer’s disease.

Multi-Taxonomy Classification

Taxonomy Database Cross-References

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)

• OBO Foundry (CL:0000095)

• Allen Brain Cell Atlas

• CellxGene Census

• Human Cell Atlas

• PanglaoDB

Taxonomy & Classification

PanglaoDB Marker Cross-References

• Unknown (PanglaoDB):

External Database Links

• Cell Ontology (CL:0000095)

• OBO Foundry (CL:0000095)

• Allen Brain Cell Atlas

• CellxGene Census

• PanglaoDB

Molecular Signature

Marker Genes

NAM cells are characterized by elevated expression of:

Distinguishing from DAM

Role in Neurodegeneration

Alzheimer’s Disease

NAM microglia are prominently found in:

1. Amyloid plaque vicinity - Surrounding dense-core plaques

2. Tau pathology regions - Areas with neurofibrillary tangles

3. Atrophic regions - Areas showing neuronal loss

Pathogenic Functions

• Failed phagocytosis - Impaired clearance of amyloid and debris

• Synaptic loss - May contribute to synapse elimination

• Pro-inflammatory cytokine production - Chronic neuroinflammation

• Iron accumulation - Ferrostatin-sensitive cell death

Protective Functions

• Plaque containment - May limit amyloid spread

• Phagocytic activity - Removal of dead cells

• Trophic support - Limited neurotrophic factor release

TREM2 and NAM Biology

TREM2 Variants

TREM2 genetic variants significantly influence NAM function:

• R47H (AD risk) - Impaired lipid sensing, reduced phagocytosis

• R62H - Intermediate risk

• Q33X (PLOSL) - Loss-of-function, Nasu-Hakola disease

TREM2 Signaling

Aβ/Lipid → TREM2 → TYROBP (DAP12) → SYK → PI3K → Phagocytosis
                                            ↓
                                      Inflammation

Therapeutic Targeting

Disease Associations

Alzheimer’s Disease

• NAM density correlates with cognitive decline

• TREM2 variant carriers show altered NAM response

• Appears in later disease stages

Parkinson’s Disease

• NAM-like cells in substantia nigra

• Associated with α-synuclein pathology

• May contribute to dopaminergic neuron loss

ALS

• Upregulation of NAM markers in motor cortex

• Linked to TDP-43 pathology

• Microglial activation correlates with progression

Frontotemporal Dementia

• NAM cells in affected cortical regions

• Associated with tau and TDP-43 pathology

Therapeutic Implications

Modulating NAM Activity

1. TREM2 modulation - Agonists to enhance phagocytosis

2. Anti-inflammatory approaches - Reduce chronic neuroinflammation

3. Lipid metabolism targeting - APOE-directed therapies

4. CSF1R inhibition - Reduce microglial proliferation

Biomarker Potential

• TREM2 in CSF - Reflects microglial activation

• sTREM2 - Soluble TREM2 as disease marker

• NAM gene signature - Blood-based RNA signatures

Research Methods

Identification

• Single-nucleus RNA sequencing

• Spatial transcriptomics

• Flow cytometry with surface markers

Animal Models

• 5xFAD mice (amyloid model)

• P301S tau model

• α-synuclein overexpression models

• TREM2 knock-in/knock-out crosses

See Also

• Microglia

• TREM2

• Alzheimer’s Disease

• Parkinson’s Disease

• Amyotrophic Lateral Sclerosis

• Dementia with Lewy Bodies

• Neuroinflammation

Background

The study of Neurodegeneration Associated Microglia (Nam) 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.

External Links

• Alzheimer’s Disease Neuroimaging Initiative

• AMP-AD Consortium

• Allen Brain Atlas - Microglia