You might recall research published early last year on TREM2 as a possible regulator of immune cell clearance of amyloid in Alzheimer's disease. Researchers here provide a further update on their investigations of the role of TREM2 in this process. To the degree that the immune system falters in this task of clearing metabolic waste with age, and to the degree that this issue can be reversed or overridden, this may prove to be a useful approach to age-related protein aggregates in the brain, and their contribution to neurodegenerative disease. As is so often the case, however, a treatment cannot be immediately and straightforwardly constructed based on manipulation of TREM2. Its relationship with immune cell activity and the Alzheimer's disease state is complex.
A hallmark of Alzheimer's disease is the formation of toxic deposits in the brain, so-called plaques. Specialized immune cells termed microglia protect the brain by clearing it from these toxic debris. TREM2 is a key factor in activating microglia and thus serves as an important target for novel therapeutic approaches. To further explore these therapeutic options, scientists undertook a detailed analysis of disease development in mice with and without a functional TREM2 gene.
In mice with healthy TREM2, microglia cluster around small emerging plaques early in the disease process and prevent them from enlarging or spreading. Researchers were able to show that microglia are specifically attracted to amyloid plaques. They surround individual plaques and engulf them piece by piece. In contrast, in mice lacking TREM2, microglia were unable to carry out this important task. Therapeutic activation of TREM2 in an early stage of the disease could thus help counteract the formation of toxic amyloid-beta protein aggregates.
However, the study results also call for caution when implementing such a therapy. While TREM2 prevents plaque formation early in disease progression, it may have the opposite effect later on. In more advanced stages of the disease, the plaques grew faster in mice with functional TREM2 than in mice lacking the corresponding gene. The researchers discovered that this could be explained by the fact that TREM2 induces microglia to produce a substance called ApoE, which enhances aggregate formation. "Our study shows that we have to be extremely careful and investigate a new therapeutic approach thoroughly in animal models before testing it on humans. According to our findings, it could have dramatic consequences if we over-activate microglia. In the future, it will be important to treat Alzheimer's disease in a stage-specific manner."