TREM2 Acts Downstream of CD33 in Modulating Microglial Pathology in Alzheimer's Disease

CD33-/- and/or TREM2-/- mice were crossed with the 5xFAD mouse model of Alzheimer’s disease to generate single and double CD33/TREM2 knock-out mice on 5xFAD background. Transcriptome and gene expression analyses were performed to analyze the impact of CD33 and/or TREM2 knock-out on the transcriptome of microglia in the context of amyloid pathology. The results revealed that CD33 and/or TREM2 knock-out reprogrammed microglial gene expression signatures in 5xFAD mice in an age-dependent manner. Differential gene expression in 5xFAD;CD33-/- microglia depended on the presence of TREM2. These data suggest that TREM2 acts downstream of CD33. Microglia were isolated from brains of WT, 5xFAD, 5xFAD;CD33-/-, 5xFAD;TREM2-/-, and 5xFAD;CD33-/-;TREM2-/- mice at 4 and 8 months of age, using FACS sorting for CD11b and CD45. RNA was extracted using the RNeasy Plus Micro Kit (Qiagen). Libraries were prepared using the TruSeq Stranded mRNA LT Prep Kit (Illumina) and sequenced on an Illumina HiSeq 2500 sequencer using single-end 50. Reads were aligned to mouse genome mm10 using the STAR aligner. Read counts for individual genes were obtained using HTSeq.