| First Author | Shi Q | Year | 2022 |
| Journal | J Neurosci | Volume | 42 |
| Issue | 27 | Pages | 5294-5313 |
| PubMed ID | 35672148 | Mgi Jnum | J:353416 |
| Mgi Id | MGI:7706260 | Doi | 10.1523/JNEUROSCI.2427-21.2022 |
| Citation | Shi Q, et al. (2022) Microglial mTOR Activation Upregulates Trem2 and Enhances beta-Amyloid Plaque Clearance in the 5XFAD Alzheimer's Disease Model. J Neurosci 42(27):5294-5313 |
| abstractText | The mechanistic target of rapamycin (mTOR) signaling pathway plays a major role in key cellular processes including metabolism and differentiation; however, the role of mTOR in microglia and its importance in Alzheimer's disease (AD) have remained largely uncharacterized. We report that selective loss of Tsc1, a negative regulator of mTOR, in microglia in mice of both sexes, caused mTOR activation and upregulation of Trem2 with enhanced beta-Amyloid (Abeta) clearance, reduced spine loss, and improved cognitive function in the 5XFAD AD mouse model. Combined loss of Tsc1 and Trem2 in microglia led to reduced Abeta clearance and increased Abeta plaque burden revealing that Trem2 functions downstream of mTOR. Tsc1 mutant microglia showed increased phagocytosis with upregulation of CD68 and Lamp1 lysosomal proteins. In vitro studies using Tsc1-deficient microglia revealed enhanced endocytosis of the lysosomal tracker indicator Green DND-26 suggesting increased lysosomal activity. Incubation of Tsc1-deficient microglia with fluorescent-labeled Abeta revealed enhanced Abeta uptake and clearance, which was blunted by rapamycin, an mTOR inhibitor. In vivo treatment of mice of relevant genotypes in the 5XFAD background with rapamycin, affected microglial activity, decreased Trem2 expression and reduced Abeta clearance causing an increase in Abeta plaque burden. Prolonged treatment with rapamycin caused even further reduction of mTOR activity, reduction in Trem2 expression, and increase in Abeta levels. Together, our findings reveal that mTOR signaling in microglia is critically linked to Trem2 regulation and lysosomal biogenesis, and that the upregulation of Trem2 in microglia through mTOR activation could be exploited toward better therapeutic avenues to Abeta-related AD pathologies.SIGNIFICANCE STATEMENT Mechanistic target of rapamycin (mTOR) signaling pathway is a key regulator for major cellular metabolic processes. However, the link between mTOR signaling and Alzheimer's disease (AD) is not well understood. In this study, we provide compelling in vivo evidence that mTOR activation in microglia would benefit beta-Amyloid (Abeta)-related AD pathologies, as it upregulates Trem2, a key receptor for Abeta plaque uptake. Inhibition of mTOR pathway with rapamycin, a well-established immunosuppressant, downregulated Trem2 in microglia and reduced Abeta plaque clearance indicating that mTOR inactivation may be detrimental in Abeta-associated AD patients. This finding will have a significant public health impact and benefit, regarding the usage of rapamycin in AD patients, which we believe will aggravate the Abeta-related AD pathologies. |
