Marieke E. Ijsselsteijn, Netherlands
Leiden University Medical Center PathologyAuthor Of 1 Presentation
IRON-LOADING IS A PROMINENT FEATURE OF ACTIVATED MICROGLIA IN ALZHEIMER’S DISEASE PATIENTS
Abstract
Aims
Iron accumulation in Alzheimer’s disease (AD) has been reported to correlate with Aβ and tau spreading, and to accelerate cognitive decline. Additionally, transcriptomic studies identified altered expression of iron-metabolism genes in activated microglia subtypes. Therefore, we aimed to study the prevalence of iron-accumulating microglia in AD and their activation state. Secondly we aimed to study the relation of iron-accumulatingmicroglia with Aβ-plaques.
Methods
We created a multiplex immunofluorescence-panel with markers for P2RY12, TMEM119, Light-Chain Ferritin (FTL), Aβ, Iba1 and DAPI, and stained brain tissue of 12 AD and 9 control patients (Fig. 1A). Cells were automatically segmented, phenotyped, and spatially mapped for further analysis.
Results
Segmentation allowed for identification of 69227 microglia, which were phenotyped into 13 clusters (Fig. 1B). Cluster 1 showed increased FTL and Iba1 expression and decreased TMEM119 and P2RY12 expression, and was significantly more present in AD-patients (P=0.0264; Fig 1C). Further investigation showed this FTL+Iba1+-cluster to be the predominant Aβ-plaque infiltrating microglia-cluster (P<0.0001; Fig. 1D,E). These microglia reflected iron-accumulating microglia (Fig. 1F) and showed advanced dystrophic morphology (Fig. 1G). Finally, these microglia were primarily present in subjects with high Aβ-load and Tau-load (Fig. 1H,I), and were found to be more present in APOE4-carriers (P=0.0667) and to infiltrate Aβ-plaques more (P=0.0381; Fig. 1J,K).
Conclusions
Using multi-marker phenotype evaluation on single cell level, while preserving morphological and spatial information of microglia with relation to Aβ-plaques, we identified activated P2RY12-TMEM119-FTL+Iba1+-microglia, which reflect iron-accumulating microglia in AD and predominantly infiltrate Aβ-plaques. These findings suggest iron to be taken up by microglia and to influence the functional phenotype, especially in conjunction with Aβ.