HDL-associated phosphatidylserine modulates the myeloid compartment and protects from atherosclerosis
A Bernal, C Grao Roldan, I Sanchez, J A Nicolas Avila, L Pena Couso, A Hidalgo, W J M Mulder, C Perez MedinaAbstract
Background
Atherosclerosis is a lipid-driven, chronic inflammatory disease of the arteries that frequently precedes myocardial infarction and stroke. High-density lipoprotein (HDL) plays a central role in lipid metabolism and mediates key natural atheroprotective processes. HDL-raising therapies thus sparked great enthusiasm but failed to deliver the anticipated outcomes in clinical trials.
Purpose
In this study, we sought to investigate the anti-atherosclerotic properties of an HDL-like formulation incorporating phosphatidylserine (PS), a negatively charged phospholipid that is involved in efferocytosis.
Methods
We developed a reconstituted HDL formulation enriched in PS, henceforth PS@rHDL. Its effect on cholesterol efflux and efferocytosis was determined in vitro using murine bone marrow-derived macrophages (BMDMs). Its biodistribution was characterized through radioactive methods, and for its cell tropism by flow cytometry. To evaluate the formulation’s therapeutic efficacy, in vivo experiments including histopathological and immunophenotyping were carried out in Apoe-/- mice with atherosclerosis. We also evaluated its impact in phagocytic activity. Finally, treated mice underwent a Staphylococcus aureus infection challenge and their response was monitored to assess potential immunosuppressive effects.
Results
In vitro, PS@rHDL enhanced cholesterol efflux capacity and efferocytotic activity in BMDMs. Besides the liver, PS@rHDL accumulated in myeloid tissues such as bone marrow and spleen, but also in the aorta as shown by biodistribution studies. In these tissues, the formulation exhibited high affinity for myeloid cells, especially for macrophages in aorta (Fig. 1). In vivo, our in-depth experiments provided evidence of the formulation’s potent plaque-stabilizing and anti-inflammatory action in Apoe-/- mice (Fig. 2A and 2B). These effects were mediated by a shift in the monocyte/macrophage compartment toward homeostatic/repairing phenotypes, as confirmed by flow cytometry and histology (Fig. 2C and 2D). Additionally, PS@rHDL boosted phagocytic activity in aorta (Fig. 2E). Importantly, PS@rHDL did not compromise the ability of treated mice to fight a Staphylococcus aureus infection (Fig. 2F).
Conclusions
Collectively, our results demonstrate that phosphatidylserine formulation into an HDL-like composition leads to potent atheroprotective effects and holds promise as a viable approach to improve immunomodulatory therapies.