Aims

Aim 1. Investigating the roles of CD33 isoforms in controlling microglia cell function

Aim 2. Elucidating the roles of CD33 in regulating plaque accumulation

Methods

We are working with both cell culture models as well as mouse models. For cell culture models, we are using U937 cells in which we have deleted the CD33 gene by CRISPR/Cas9 and complemented these cells with different CD33 variants and mutants. These are being tested in phagocytosis assay and cellular signaling assays. We have also developed transgenic mice expressing either the long or short isoform of CD33 in the microglial cell lineage, which have been crossed on 5XFAD mice. Plaque accumulation, scRNAseq, and the distribution of the microglia around the plaques are being assessed.

Results

We find CD33 isoforms differentially control phagocytosis in microglia. We reveal, for the first time, a novel gain-of-function for the short isoform of CD33 that is connected with AD protection. This gain-of-function is dominant and manifests as enhanced phagocytosis and transcriptional skewing. Ongoing findinds with these transgenic mice crossed onto a 5XFAD background will be presented .

Conclusions

Elucidating whether the short isoform of CD33, encoded preferentially by an AD-protective single nucleotide polymorphism, is a loss-of-funciton or gain-of-function variant has been challenging. Our results in two different model systems reveal that there are both loss-of-funciton or gain-of-function phenotypes at play. Which of these phenotypes is responsible for AD protection will be revealed, in part, through ongoing studies with these two isoforms in mouse models of AD.

Aims

Aim 1. Investigating the roles of CD33 isoforms in controlling microglia cell function

Aim 2. Elucidating the roles of CD33 in regulating plaque accumulation

Methods

We are working with both cell culture models as well as mouse models. For cell culture models, we are using U937 cells in which we have deleted the CD33 gene by CRISPR/Cas9 and complemented these cells with different CD33 variants and mutants. These are being tested in phagocytosis assay and cellular signaling assays. We have also developed transgenic mice expressing either the long or short isoform of CD33 in the microglial cell lineage, which have been crossed on 5XFAD mice. Plaque accumulation, scRNAseq, and the distribution of the microglia around the plaques are being assessed.

Results

We find CD33 isoforms differentially control phagocytosis in microglia. We reveal, for the first time, a novel gain-of-function for the short isoform of CD33 that is connected with AD protection. This gain-of-function is dominant and manifests as enhanced phagocytosis and transcriptional skewing. Ongoing findinds with these transgenic mice crossed onto a 5XFAD background will be presented .

Conclusions

Elucidating whether the short isoform of CD33, encoded preferentially by an AD-protective single nucleotide polymorphism, is a loss-of-funciton or gain-of-function variant has been challenging. Our results in two different model systems reveal that there are both loss-of-funciton or gain-of-function phenotypes at play. Which of these phenotypes is responsible for AD protection will be revealed, in part, through ongoing studies with these two isoforms in mouse models of AD.