Lipid-loaded microglia, also known as foam cells, are a specialized subset of microglia that have accumulated large amounts of intracellular lipid droplets. These cells represent a distinct activation state characterized by metabolic reprogramming and are increasingly recognized as important players in neurodegenerative diseases, particularly Alzheimer's disease (AD)[1]. Foam cells in the brain share morphological and functional similarities with atherosclerotic foam cells, representing a final common pathway for lipid handling in chronic inflammatory conditions[2].
The term "foam cell" derives from the vacuolated, foamy appearance these cells exhibit under microscopy due to accumulated lipid droplets. In the brain, lipid-loaded microglia arise from chronic exposure to amyloid-beta, APOE4-associated lipid dysregulation, and ongoing neuroinflammation[3]. These cells are now recognized as a key therapeutic target, particularly through the TREM2 pathway.
| Taxonomy | ID | Name / Label |
|---|---|---|
| Cell Ontology (CL) | CL:0000129 | microglial cell |
Lipid-droplet-accumulating microglia (LDAM) were first comprehensively characterized by Marschallinger et al. (2020) using single-cell RNA sequencing[4]. This study revealed LDAM as a distinct microglial population with unique transcriptional signature:
Key LDAM Markers (from scRNA-seq):
Single-cell analysis reveals LDAM express a unique gene signature[4:1][5]:
| Gene Category | Upregulated | Function |
|---|---|---|
| Lipid metabolism | Plin2, Lpl, Fabp5 | Lipid droplet formation |
| Phagocytosis receptors | Cd36, Trem2 | Lipid uptake |
| Inflammation | Tnf, Il1b | Pro-inflammatory |
| Metabolism | Hexb, Ctsd | Lysosomal function |
LDAM formation involves several interconnected pathways[6]:
APOE4 isoform significantly promotes LDAM formation[7]:
While both LDAM and Disease-Associated Microglia (DAM) arise in neurodegeneration, they represent distinct states[8]:
| Feature | LDAM | DAM |
|---|---|---|
| Trigger | Lipid dysregulation | Neurodegeneration |
| Key markers | PLIN2+, LPL+ | TREM2+, APOE+ |
| Function | Lipid storage | Phagocytic clearance |
| TREM2 dependence | Partial | Required |
| Phagocytosis | Impaired | Enhanced (Stage 2) |
LDAM are particularly prominent in AD brain[9]:
LDAM increase with normal aging[4:2]:
LDAM-like cells found in:
LDAM exhibit metabolic reprogramming[10]:
Key feature of LDAM[11]:
Marschallinger et al. Lipid-droplet-accumulating microglia represent a dysfunctional and proinflammatory state (2020). 2020. ↩︎ ↩︎ ↩︎
Single-cell analysis of LDAM in aging brain (2021). 2021. ↩︎
LDAM in human AD brain (2021). 2021. ↩︎