Identification of a dysfunctional microglial population in human Alzheimer's disease cortex using novel single-cell
Molly E V Swanson1,2,3, Emma L Scotter2,3, Leon C D Smyth2,4,5
1Department of Anatomy and Medical Imaging, Faculty of Medical and Health Science, University of Auckland, Private Bag 92019, Auckland, New Zealand.
Abstract:
In Alzheimer's disease (AD), microglia are affected by disease processes, but may also drive pathogenesis. AD pathology-associated microglial populations have been identified with single-cell RNA-Seq, but have not been validated in human brain tissue with anatomical context. Here, we quantified myeloid cell markers to identify changes in AD pathology-associated microglial populations. We performed fluorescent immunohistochemistry on normal (n = 8) and AD (n = 8) middle temporal gyri, co-labelling the pan-myeloid cell marker, Iba1, with one of 11 markers of interest (MOIs): CD45, HLA-DR, CD14, CD74, CD33, CD206, CD32, CD163, P2RY12, TMEM119, L-Ferritin. Novel image analyses quantified the single-cell abundance of Iba1 and each MOI. Each cell was gated into one Iba1-MOI population (Iba1low MOIhigh, Iba1high MOIhigh, or Iba1high MOIlow) and the abundance of each population was compared between AD and control. Triple-labelling of L-Ferritin and Iba1 with a subset of MOIs was performed to investigate L-Ferritin-MOI co-expression on Iba1low cells. Iba1low MOIhigh myeloid cell populations delineated by MOIs CD45, HLA-DR, CD14, CD74, CD33, CD32, and L-Ferritin were increased in AD. Further investigation of the Iba1low MOIhigh populations revealed that their abundances correlated with tau, but not amyloid beta, load in AD. The Iba1low microglial population highly expressed L-Ferritin, reflecting microglial dysfunction. The L-Ferritinhigh CD74high HLA-DRhigh phenotype of the Iba1low population mirrors that of a human AD pathology-associated microglial subpopulation previously identified using single-cell RNA-Seq. Our high-throughput immunohistochemical data with anatomical context support the microglial dysfunction hypothesis of AD.
Insights
In Alzheimer's disease (AD), specific microglial populations (Iba1low MOIhigh) increase and correlate with tau pathology. This supports the microglial dysfunction hypothesis in AD pathogenesis.
Area of Science:
- Neuroscience
- Immunology
- Pathology
Background:
- Microglia play a dual role in Alzheimer's disease (AD), potentially contributing to pathogenesis.
- Previous single-cell RNA-Seq studies identified AD pathology-associated microglial populations but lacked anatomical context in human tissue.
- Understanding microglial changes in AD is crucial for elucidating disease mechanisms.
Purpose of the Study:
- To validate AD pathology-associated microglial populations in human brain tissue using immunohistochemistry.
- To quantify changes in myeloid cell markers and their association with AD pathology.
- To investigate the microglial dysfunction hypothesis in Alzheimer's disease.
Main Methods:
- Fluorescent immunohistochemistry was performed on middle temporal gyrus tissue from normal and AD individuals (n=8 each).
- Pan-myeloid marker Iba1 was co-labeled with 11 markers of interest (MOIs) including CD45, HLA-DR, CD14, CD74, CD33, CD32, and L-Ferritin.
- Novel image analysis quantified single-cell abundance, gating cells into Iba1-MOI populations (Iba1low MOIhigh, Iba1high MOIhigh, Iba1high MOIlow) for comparison between AD and control groups.
Main Results:
- Increased abundance of Iba1low myeloid cell populations delineated by CD45, HLA-DR, CD14, CD74, CD33, CD32, and L-Ferritin was observed in AD brains.
- The abundance of these Iba1low MOIhigh populations correlated with tau load, but not amyloid beta load, in AD.
- The Iba1low microglial population exhibited high L-Ferritin expression, indicative of microglial dysfunction, and a phenotype mirroring previously identified AD-associated subpopulations.
Conclusions:
- Specific myeloid cell populations (Iba1low MOIhigh) are significantly increased in Alzheimer's disease brains.
- These microglial changes are associated with tau pathology and suggest a state of microglial dysfunction.
- High-throughput immunohistochemistry data supports the microglial dysfunction hypothesis in Alzheimer's disease pathogenesis.
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