Post-translational modifications of apolipoproteins in diabetes and cardiovascular risk prediction – POTOMAC

Type 2 diabetes is a major health burden worldwide. The disease is primarily characterized by chronic hyperglycemia and lipoprotein metabolism disorders, reducing both the quality of life and life expectancy, especially by promoting cardiovascular complications. Therefore, patients with type 2 diabetes display an increased risk of cardiovascular diseases compared with the general population. Since traditional clinical markers cannot fully explain this phenomenon, the identification of new relevant biomarkers is essential for a better stratification and a better care of the most at-risk diabetic patients.

In that context, post-translational modifications of proteins are promising as such structural changes are varied and sensitive to environmental factors associated with diabetes. Besides, post-translational modifications modify the structure of proteins, change the affinity of proteins for biological partners or targets, and act directly on their functionalities. Interestingly, apolipoproteins constitute the structural and regulatory protein component of lipoproteins, responsible for the transport of hydrophobic lipids in the bloodstream. Abnormal apolipoprotein concentrations have been associated with many metabolic and cardiovascular disorders, and plasma apolipoproteins can predict cardiovascular diseases better than plasma lipids.

As abnormalities in lipoprotein metabolism are important in type 2 diabetes, we hypothesize that the hyperglycemic environment associated with diabetes overexposes apolipoproteins to post-translational modifications. These structural changes might contribute to critical modifications in lipoprotein functions and turnovers leading to the residual cardiovascular disease risk observed in patients with type 2 diabetes. Due to their involvement in lipid metabolism and atherogenesis, circulating apolipoproteins appear are of interest for the identification of new relevant biomarkers relating to such modifications. In addition, targeted mass spectrometry-based approaches are very efficient for high-throughput analysis of apolipoproteins in biological fluids. However, methodological challenges exist for the study of post-translational modifications because of their low stoichiometric levels and their diverse chemical natures.

POTOMAC aims to identify relevant apolipoprotein post-translational modifications via the fundamental approaches of targeted proteomics to functional experiments of biochemistry and cell biology in order to propose a set of new peptide biomarkers related to major apolipoprotein post-translational modifications that will be reliable for large-scale profiling in humans and better stratification of cardiovascular disease risk in patients with type 2 diabetes. Our objectives are:
1) to select relevant apolipoprotein post-translational modifications associated with type 2 diabetes and to perform mass spectrometry characterization of novel specific peptide biomarkers reflecting these modifications,
2) to select the best candidates based on their associations with lipoprotein metabolism dysfunctions determined in vivo, ex vivo, and in vitro,
3) to validate peptide candidates in clinical settings including human cohorts and interventional clinical trials, and
4) to determine their clinical relevance in comparison with the large-scale evaluation of metabolism dysregulation (oxidative stress, inflammation) obtained by complementary approaches.

Ultimately, we believe that the combination of the information, namely the concentrations of apolipoproteins and their post-translational modification levels, will help to better understand the mechanisms associated with the disease development and will open new therapeutic avenues.