AD-linked R47H-TREM2mutation induces disease-enhancing microglial states via AKT hyperactivation

Dec 1, 2021Science translational medicine

Alzheimer’s-linked R47H-TREM2 mutation may worsen disease by overactivating microglial cells through AKT signaling

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Abstract

The R47H variant of the TREM2 gene is associated with increased risk for late-onset Alzheimer's disease.

Microglial subpopulations carrying the R47H variant exhibit enhanced inflammatory signatures similar to disease-associated microglia.
Activation of the AKT signaling pathway is observed in R47H-associated microglia.
In a tauopathy mouse model, the R47H variant worsens TAU-mediated spatial memory deficits in female mice.
Transcriptomic changes in microglia from R47H mice overlap significantly with those observed in human Alzheimer's brains.
Pharmacological inhibition of AKT with MK-2206 reduces inflammatory signatures in R47H microglia and rescues synapse loss in tauopathy mice.

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The hemizygous R47H variant of triggering receptor expressed on myeloid cells 2 (), a microglia-specific gene in the brain, increases risk for late-onset Alzheimer's disease (AD). Using transcriptomic analysis of single nuclei from brain tissues of patients with AD carrying the R47H mutation or the common variant (CV)–, we found that R47H-associated microglial subpopulations had enhanced inflammatory signatures reminiscent of previously identified disease-associated microglia (DAM) and hyperactivation of AKT, one of the signaling pathways downstream of TREM2. We established a tauopathy mouse model with heterozygous knock-in of the humanwith the R47H mutation or CV and found that R47H induced and exacerbated TAU-mediated spatial memory deficits in female mice. Single-cell transcriptomic analysis of microglia from these mice also revealed transcriptomic changes induced by R47H that had substantial overlaps with R47H microglia in human AD brains, including robust increases in proinflammatory cytokines, activation of AKT signaling, and elevation of a subset of DAM signatures. Pharmacological AKT inhibition with MK-2206 largely reversed the enhanced inflammatory signatures in primary R47H microglia treated with TAU fibrils. In R47H heterozygous tauopathy mice, MK-2206 treatment abolished a tauopathy-dependent microglial subcluster and rescued tauopathy-induced synapse loss. By uncovering disease-enhancing mechanisms of the R47H mutation conserved in human and mouse, our study supports inhibitors of AKT signaling as a microglial modulating strategy to treat AD. TREM2TREM2TREM2

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AD-linked R47H-TREM2mutation induces disease-enhancing microglial states via AKT hyperactivation

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