Protein carbamylation renders high-density lipoprotein dysfunctional

Area of Science:

• Cardiovascular Science
• Biochemistry
• Immunology

Background:

• Protein carbamylation, induced by reactive cyanate, is linked to increased cardiovascular risk.
• In vivo, cyanate originates from urea breakdown and inflammation sites via myeloperoxidase (MPO).
• MPO's association with high-density lipoprotein (HDL) in atherosclerotic intima prompted investigation into HDL targeting by cyanate.

Purpose of the Study:

• To determine if cyanate specifically targets HDL in atherosclerotic lesions.
• To investigate the role of MPO-mediated carbamylation in HDL modification within the vessel wall.
• To assess the impact of HDL carbamylation on macrophage foam cell formation.

Main Methods:

• Mass spectrometry was employed to analyze protein carbamylation as a posttranslational modification of HDL.
• Carbamyllysine and 3-chlorotyrosine levels were quantified in lesion-derived HDL, LDL, and total lesion protein.
• Correlation analysis was performed between carbamyllysine content, 3-chlorotyrosine levels, and lesion severity.
• Macrophage cholesterol accumulation and lipid-droplet formation were assessed in response to modified HDL.

Main Results:

• Protein carbamylation was identified as a major posttranslational modification of HDL.
• Lesion-derived HDL exhibited significantly higher carbamyllysine content compared to 3-chlorotyrosine levels and lesion-derived LDL or total protein.
• Carbamyllysine content in HDL increased with lesion severity and correlated with 3-chlorotyrosine levels, suggesting MPO mediation.
• A single carbamyllysine residue on HDL apolipoprotein A-I was sufficient to induce cholesterol accumulation and lipid-droplet formation in macrophages via scavenger receptor class B, type I.

Conclusions:

• HDL carbamylation is a significant posttranslational modification occurring in atherosclerotic lesions, mediated by MPO.
• Carbamylated HDL promotes cholesterol accumulation in macrophages, a key process in foam cell formation.
• HDL carbamylation emerges as a potential contributor to the pathogenesis of atherosclerosis.