Microglial Phenotyping in Neurodegenerative Disease Brains: Identification of Reactive Microglia with an Antibody to Variant of CD105/Endoglin.

Douglas Walker,Ikuo Tooyama,Thomas Beach,Lih-Fen Lue

doi:10.3390/cells8070766

Abstract

Inflammation is considered a key pathological process in neurodegenerative diseases, including Alzheimer’s disease (AD) and Parkinson’s disease (PD), but there are still mechanisms not understood. In the brain, most microglia are performing essential homeostatic functions, but can also respond to pathogenic stimuli by producing harmful pro-inflammatory cytokines or free radicals. Distinguishing between damaging and homeostatic microglia in human diseased brain tissues is a challenge. This report describes findings using a monoclonal antibody to CD105/Endoglin (R&D Systems MAB1097) that identifies subtypes of activated microglia. CD105/Endoglin is a co-receptor for transforming growth factor beta (TGFβ) receptor that antagonizes TGFβ signaling. CD105/Endoglin is a marker for vascular endothelial cells, but was originally identified as a marker for activated macrophages. This antibody did not identify endothelial cells in brain sections, only microglia-like cells. In this study, we examined with this antibody tissue section from middle temporal gyrus derived from human brains from normal control subjects with low-plaque pathology, high-plaque pathology, and AD cases, and also substantia nigra samples from control and PD cases, in conjunction with antibodies to markers of pathology and microglia. In low-plaque pathology cases, CD105-positive microglia were mostly absent, but noticeably increased with increasing pathology. CD105-positive cells strongly colocalized with amyloid-beta plaques, but not phosphorylated tau positive tangles. In substantia nigra, strong microglial CD105 staining was observed in microglia associated with degenerating dopaminergic neurons and neuromelanin. In PD cases with few surviving dopaminergic neurons, this staining had decreased. By Western blot, this antibody identified polypeptide bands of 70 kDa in brain samples, and samples from microglia, macrophages, and brain endothelial cells. In comparison with other tested CD105 antibodies, this antibody did not recognize the glycosylated forms of CD105 on Western blots. Overall, the data indicate that this antibody and this marker could have utility for subtyping of microglia in pathologically-involved tissue.

Highlights

Neuroinflammation has been considered a prominent feature of Alzheimer’s disease (AD)and Parkinson’s disease (PD) pathology since the identification of strongly immunoreactive major histocompatibility class II (MHCII)-positive microglia associated with AD and PD pathological structures [1,2,3]
The finding of reduced numbers of CD105-positive microglia in PD substantia nigra is contrary to expectations of their being increased numbers of activated microglia in PD; this finding is dependent on the cases being examined, and the ones we examined had severe dopaminergic cell loss
This study demonstrated increased expression of a variant of CD105/endoglin in a class of activated microglia in brains of AD pathology, and those with dopaminergic neuron damage in the substantia nigra

Summary

Introduction

Parkinson’s disease (PD) pathology since the identification of strongly immunoreactive major histocompatibility class II (MHCII)-positive microglia associated with AD and PD pathological structures [1,2,3] These early studies established the hypothesis that microglial inflammatory responses. Cells 2019, 8, 766 to extracellular amyloid-β protein (Aβ) plaques and neurofibrillary tangles, the hallmarks of AD pathology, or to degenerating dopaminergic neurons or α-synuclein structures in PD might be accelerating neurodegeneration through the excessive production of inflammatory cytokines and enzymes. If this was correct, anti-inflammatory agents, such as non-steroidal anti-inflammatory drugs, should be effective in slowing disease progression. The concept that all increased microglial activity could be harmful appears incorrect as microglia are continuing to perform many essential homeostatic and phagocytic functions even in brains affected by AD or PD [5]

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