ADAM10, ApoE and TREM2 in the Microglial Response to Aβ Toxicity
Rumana Akhter, Maria Khrestian, Yvonne Shao, Eric Dyne, James Leverenz, Lynn Bekris
Cleveland Clinic Lerner Research Institute
Background: The Late Onset Alzheimer's Disease (LOAD) is strongly associated with a rare variant of Triggering Receptor Expressed on Myeloid cells 2 (TREM2). TREM2 is expressed on the cell surface of microglia, and is a key regulator of inflammatory response including neuro-inflammation. Recent research shows that A Disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) cleaves TREM2 to produce a soluble isoform (sTREM2). It is known that sTREM2 level is elevated in the cerebrospinal fluid of AD patients whereas ADAM10 is low in AD brain. In our preliminary studies we have seen that the human primary microglial cell line HMC3 undergoes a morphological change upon Aβ treatment that corresponds to a upregulation of TREM2 and the sTREM2 isoform. ADAM10 level remains unaltered under the same experimental condition. This apparent ambiguity of unchanged ADAM10 level and high sTREM2 is the focus of this project. Interestingly, apoE, which has been described as a ligand for TREM2, is also elevated upon (Aβ1-42) exposure over time. Therefore, the hypothesis of this study is that cleavage to produce sTREM2 requires a secondary factor, such as apoE. The objective of this study was to determine whether levels of key AD-relevant proteins; ADAM10, apoE, TREM2 and sTREM2, undergo change in human microglial HMC3 cells upon Aβ treatment and how they are associated with each other.
Methods: HMC3 cells were treated with neurotoxic Aβ1-42 oligomers. Differences in protein levels were evaluated using Western blots. Changes in sTREM2 production was evaluated using a Luminex based assay. Changes in TREM2 and the microglial marker IBA1 in Aβ treated HMC3 cells, compared to untreated cells, were analyzed by immunofluorescence.
Results: Dose kinetics confirms that Aβ1-42 (5μM) can induce toxicity in HMC3 cells and is associated with changes in proteins. Changes in levels of some of these key AD-related proteins (apoE,TREM2 and sTREM2, ADAM10), was observed in HMC3 microglia cells upon Aβ1-42 treatment, compared to untreated cells.
Conclusion: Taken together, these results suggest that microglia respond actively to increasing levels of Aβ toxicity in the AD microenvironment by modulating the expression of key immune-related proteins. This study will address the impact of TREM2 as biomarker for neuro-inflammation and AD.