Transcriptome and proteome profiling reveals TREM2-dependent and -independent glial response and metabolic perturbation in an Alzheimer's mouse model

Elucidating the intricate molecular mechanisms of Alzheimer's disease (AD) requires a multidimensional analysis incorporating various omics data. In this study, we employed transcriptome and proteome profiling of AppNL-G-F, a human APP knock-in model of amyloidosis, at the early and mid-stages of amyloid-beta (Aß) pathology, to delineate the impacts of Aß deposition on brain cells. By contrasting AppNL-G-F mice with TREM2 (Triggering receptor expressed on myeloid cells 2) knockout models, our study further investigates the role of TREM2, a well-known AD risk gene, in influencing microglial responses to Aß pathology. Our results highlight microglial activation as a central feature of Aß pathology, characterized by the significant upregulation of microglia-specific genes related to immune responses such as complement system and antigen presentation, and catabolic pathways such as phagosome formation and lysosome biogenesis. The absence of TREM2 markedly diminishes the induction of these genes, impairs Aß clearance, and exacerbates dystrophic neurite formation. Importantly, TREM2 is required for the microglial engagement with Aß plaques and the formation of compact Aß plaque cores. Furthermore, this study reveals substantial disruptions in energy metabolism and protein synthesis, signaling a shift from anabolism to catabolism in response to Aß deposition. This metabolic alteration, coupled with a decrease in synaptic protein abundance, occurs independently of TREM2, suggesting the direct effects of Aß deposition on synaptic integrity and plasticity. In summary, our findings demonstrate significant microglial activation and metabolic disruption following Aß deposition, offering mechanistic insights into Aß pathology and highlighting the potential of targeting these pathways in AD therapy. Overall design: We performed transcriptome and proteome profiling of single human APP knock-in AppNL-G-F mice at the onset and middle stages of Aß pathology to comprehensively investigate the pathway alterations and molecular mechanisms associated with Aß deposition. AppNL-G-F knock-in mice were selected as they eliminate artifacts related to APP overexpression, such as the mis-localization of APP and the accumulation of APP fragments including CTF-ß (C-terminal fragment of APP) and AICD (APP intracellular domain). Furthermore, we also profiled AppNL-G-F, TREM2 knockout mice to examine how the absence of TREM2 affects the responses of microglia and other glial cells to Aß deposition.