Posttranslational modification of proprotein convertase subtilisin/kexin type 9 is differentially regulated in response to distinct cardiometabolic treatments as revealed by targeted proteomics

Abstract

Background: The proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secreted protein that interacts with the low-density lipoprotein (LDL) receptor at the surface of hepatocytes to regulate circulating LDL cholesterol levels. High circulating PCSK9 levels have been associated with elevated LDL cholesterol. Recently, the Food and Drug Administration of the United States approved new LDL cholesterol–lowering drugs that specifically target the inhibition of PCSK9. Similar to most human proteins, PCSK9 exists in multiple forms as it is the target of posttranslational modifications (PTMs) such as proteolytic cleavage, phosphorylation, and others, which can affect its biological activity. However, commercially available assays, such as enzyme-linked immunosorbent assays, do not discriminate between these forms. Objective: To investigate, in 2 patient cohorts, the relationships between circulating levels of multiple forms of PCSK9 and cardiometabolic interventions or treatments known to reduce LDL cholesterol levels. Methods: PCSK9 forms were measured in plasma: (1) in 20 patients before and 6 months after bariatric surgery and (2) in 132 patients before and 12 months after daily statin treatment. A series of specific peptides used as surrogates for various PCSK9 forms were quantified by a novel semiautomated proteomic assay termed protein affinity capture coupled to quantitative mass spectrometry. Results: Bariatric surgery resulted in a decrease in the plasma level of PCSK9 prodomain (P