ApoE Citrullination: A bona fide posttranslational modification (RPA Pilot/Seed Project)

"Post-translational modifications (PTMs) are thought to play important mechanistic roles in biological decision nodes. A growing recognition of under-studied PTMs continue to introduce new biology to the field and pathological or therapeutic entry points. Our group recently uncovered a novel PTM of ApoE, named citrullination (citR), caused by the enzymes peptidyl-arginine deiminase (PADs). PAD- induce citrullination irreversibly converts arginine residues within proteins/ peptides to citrulline. We identified several findings indicating that: 1) ApoE4 is a client of PAD2/ 4 (PAD2 citrullinates to a greater extent); 2) ApoE4 is citrullinated at 70% of its arginine residues including the polymorphic allele (R158); 3) ApoE4 reciprocally stimulates PAD2 activity; and 4) PAD2 is significantly increased in AD.
Central Hypothesis: We posit that citrullination of ApoE by PAD2 alters ApoE4’s function through its polymorphic allele (citR158, receptor binding domain, and lipid binding domain. The proposed aims establish the necessary framework to determine the bi-directional relationship between PAD2 activity, citrullination of ApoE, and disease phenotypes associated with dementia. This application is designed to address fundamental questions that test our hypotheses, develop premise, provide mechanistic directionality, and establish methodology and critical tools for larger extramural applications."