Skip to main content

The arterial adventitia: a critical actor in atherosclerotic plaque progression and stability?

Final Report Summary - ADVENTITIA (The arterial adventitia: a critical actor in atherosclerotic plaque progression and stability?)

Cardiovascular disease (CVD), a major cause of morbidity and mortality in the EC, are thought to result at least in part from rupture and subsequent thrombosis of an atherosclerotic plaque. This project aims to demonstrate that arterial perivascular adipose tissue is instrumental in atherosclerotic plaque progression and destabilization. We have addressed the following study objectives:

1) After the preliminary estudies, we considered a major role for NAMPT on plaque development and rupture.Although at present not much is known on its role in atherosclerosis, several reports have demonstrating that serum NAMPT serum levels are increased in inflammatory disorder. To elucidate the influence of adipose-derived cytokines and more specifically the modulatory role of NAMPT in vivo progression and plaque destabilization, we made used of an experimental model in mice and cellular and molecular mechanism involved in the different stages during atherosclerosis development.

LDLr-/- chimeras were generated with lentiviral NAMPT overexpression in the hematopoietic lineage and we determined phenotypic changes on leukocyte differentiation and activation as well as on plaque initiation and progression. In keeping with its presumed anti-apoptotic effect, neutrophils and macrophages from mice with supraphysiological NAMPT expression (+43%) were less apoptotic compared to the control group (-40 % and -15%). Moreover NAMPT overexpression appeared to sensitize myeloid precursors not only to G-CSF (+52%), but also to GM-CSF (+34%). Remarkably, the number of circulating granulocytes LY6Ghigh was unchanged by NAMPT overexpression, while CD11b+ monocyte numbers were even reduced (-51%). Moreover monocytes of mice with NAMPT overexpression were polarized towards a Ly6Clow phenotype and, in keeping, showed decreased CCR2 expression (-39.8%), pointing to a less inflammatory nature of circulating monocytes. This notion was confirmed by in vitro migration assays showing that NAMPT overexpressing macrophages displayed reduced basal and chemokine induced chemokinesis compared to the control group. Despite these profound reduction in inflammatory monocytes, total intima area and plaque cellularity were unchanged upon NAMPT overexpression,. However, reconstitution with NAMPT overexpressing bone marrow resulted in a sharp reduction in necrotic core size (-46%) and in plaque apoptosis (-56%) compared to the control, while plaque macrophage content was also significantly reduced (-60%), consistent with the aforementioned anti-apoptotic and monocytopenic activity of NAMPT. In conclusion, we are the first to demonstrate profound phenotypic effects of hematopoietic NAMPT overexpression on monocytic differentiation, survival and atherosclerosis, identifying this longevity gene as a promising target for therapeutic intervention in inflammation related disorders such as atherosclerosis.

2) A second target that was considered for further studies for its role on plaque development and rupture was MIC/GDF15. Macrophage inhibitory cytokine-1 (MIC-1) which operates in acute phase responses through a currently unknown receptor. Advanced plaques of MIC-1-/- chimeras nevertheless had reduced macrophage infiltrates, increased collagen deposition and decreased necrotic core formation, all features of improved plaque stability. In vitro studies pointed to a prominent,regulatory role of MIC-1 in macrophage cell cycle homeostasis and necrosis but not in apoptosis or apoptotic cell handling. Moreover, our studies establish a direct link between MIC-1 and CCR2 chemotaxis. Conversely MIC-1 induced macrophage chemotaxis in a strictly CCR2 dependent manner by attenuating TGFßRII induced CCR2 desensitization. Collectively, our data indicate that MIC-1 exerts its pro-atherogenic effects by amplifying the MCP-1/CCR2 axis and attenuating TGFßRII signaling. We identified MIC-1 as an acute phase modifier of the CCR2/TGFß-RII dependent inflammatory responses to vascular injury.