Post-translational guanidinylation of the HDL protein ApoA-1

Post-translational guanidinylation of the HDL protein ApoA-1

High-density lipoproteins (HDL) are well-known cardioprotective mediators. Dysfunctional HDL strongly contributes to increased cardiovascular mortality in chronic kidney disease (CKD) patients. Post-translational modifications (PTMs) of HDL proteins can lead to functional impairments of HDL. However, there is a lack of conclusive molecular data on the occurrence of PTMs in HDL from CKD patients compared to HDL isolated from healthy controls. Therefore, this study aimed to analyze PTMs major HDL protein apolipoprotein A-I (apo A-I) in these cohorts’.

The prevalence of PTMs of apol A-1 from CKD patients at KDIGO stages 1-5, as well as from healthy controls, were analyzed by mass spectrometry. The plasma proteins were purified, desalted by chromatography and analyzed by MALDI-TOF-MS following MS/MS analyses. The resulting mass-spectrometric data were compared with the MASCOT database (Matrix Science, UK). In addition, authentic human apolipoprotein A-1 (Sigma Aldrich, Germany) was invitro modified by incubation with urea and analyzed by the identical mass-spectrometric approach.

This mass-spectrometric approach identified post-translational guanidinylations of apolipoprotein A-1. The number of post-translational guanidinylations of apolipoprotein A-1 in plasma from CKD patients increased in advanced CKD stages. The identification of post-translational guanidinylations of apolipoprotein A-1 was validated by incubating apolipoprotein A-1 with urea and mass-spectrometric analyses. The degree of post-translational guanidinylations of apolipoprotein A-1 depended on urea concentration, suggesting a urea-dependent mechanism of protein guanidinylations in uremic patients.

In an ongoing clinical study, the pathophysiological consequences of guanidinylated apo A-I are analyzed.