Abstract Body (Do not enter title and authors here): Background: Inflammation and lipid accumulation are major features of atherosclerosis, a leading cause of death and morbidity worldwide. Our previous study recognized ADP-ribosylation, a post-translational modification, as a novel regulator of macrophage activation. We also have established mass spectrometry-based ADP-ribosylation proteomics. Using this technology, we evaluated the completely uncharacterized role of ADP-ribosylation in atherogenesis. We hypothesized that ADP-ribosylated proteins circulate from liver, accumulate in aorta and promote atherogenesis.

Methods and Results: We harvested the aorta, liver, and plasma of LDL receptor-deficient (Ldlr^-/-) mice that were on a regular chow or high-fat diet for 3 or 6 months (n=40/condition). To increase ADP-ribosyl peptide signals in the aorta, we applied our novel recently optimized ion mobility mass spectrometry strategy to generate ADP-ribosylation proteomics data. We analyzed 160 mice aortas and identified 3 APOA1 and 3 APOE ADP-ribosylated peptides in both the aorta and the liver (Fig. A). In addition, these peptides were differentially abundant in the aorta of HFD-fed mice, compared to controls (i.e, APOA1 ARPALEDLR peptide relative abundance (Fig. B)).
Using the same mouse plasma, we then validated the presence of ADP-ribosylated APOA1 and ADP-ribosylated APOE in HDL and chylomicron/VLDL/LDL fractions (Western blot), respectively. This finding indicates that classical apolipoproteins circulate as ADP-ribosylated forms, representing a completely novel class of modified apolipoproteins. Immunohistochemistry confirmed the enrichment of aortic lesions in macrophages and ADP-ribosylation signal (5-fold increase, p=0.0006).

Conclusions: This work provides the first in vivo evidence that ADP-ribosylation occurs in atherosclerotic lesions, which may originate from the liver via circulating blood (Fig. C). Future studies will examine whether ADP-ribosylation of apolipoproteins, specifically APOA1, alters anti-atherogenic functions of HDL.