Exploring the Role of ADAM17 in Vascular Smooth Muscle Cells and Macrophages Within the Atherosclerotic Plaque
Creators: Kilic, Tolga
Publisher: name: University of Alberta Library
Year: 2024

<p>Atherosclerosis, characterized by arterial fat deposits, is the root cause of many cardiovascular diseases. Plaque deposition results from a series of events initiated by elevated plasma cholesterol, inflammation of the arterial wall, cholesterol uptake, macrophage-derived foam cell formation, and transformation of vascular smooth muscle cells (VSMC) into lipid-laden foam cells. ADAM17 is a membrane-bound protease that can proteolytically process several substrates involved in inflammation, proliferation, lipid metabolism, and cell-cell interactions, thereby regulating cellular events that could lead to plaque deposition. Recent literature suggests that the role of ADAM17 is cell specific. This thesis examines the role of ADAM17 in vascular smooth muscle cells and macrophages, two cell types central to plaque deposition by their ability to form lipid-laden foam cells. We generated mice lacking ADAM17 in vascular smooth muscle cells (VSMC) using the Adam17flox/flox/Myh11cre/ERT2 model. These mice were bred onto an Ldlr-/- (low-density lipoprotein receptor) background, a widely utilized model in atherosclerosis research. This background induces elevated plasma cholesterol and mirrors a genetic predisposition to atherosclerosis, akin to individuals with familial hypercholesterolemia. Mice were fed a high cholesterol diet (48% fat, 1.3%cholesterol) for 5 months to raise plasma lipids and induce atherosclerosis. Plaques were analyzed by oil red O lipid staining of the whole aorta (en face, facing forward) from male animals. Primary cell cultures of aortic VSMC and bone marrow-derived macrophages (BMDM) were employed to analyze cell responses to oxidized LDL (oxLDL) after treatment with a control or Adam17-specific siRNA. Female VSMC were additionally isolated and employed to reinforce the male data. This approach was necessary since Myh11 promoter is located on the Y chromosome, and hence not expressed in females. Mice deficient in ADAM17 within vascular smooth muscle cells (Adam17KD) exhibit a marked increase in plaque area compared to control counterparts. In cell culture investigations, Adam17KD VSMCs and macrophages demonstrated heightened lipid accumulation when exposed to oxLDL as an atherogenic stimulant. Adam17KD VSMCs displayed an elevated propensity to transform into macrophage-like cells. Moreover, these cells exhibited diminished cholesterol efflux in vitro, coupled with attenuated mRNA expression of the cholesterol efflux transporter Abca1 in response to oxLDL. Mice lacking ADAM17 in VSMCs (Adam17KD) have significantly increased plaque area as compared to controls. Cell culture studies revealed that Adam17KD VSMC and BMDM have augmented lipid content when oxidized LDL (oxLDL) is used as an atherogenic stimulant. Adam17KD VSMC leads to elevated transformation into macrophage-like cells. Furthermore, these cells showed reduced cholesterol efflux in vitro, along with blunted Abca1 mRNA expression in response to oxLDL. Efferocytosis, the clearance of dying cells, is another important factor in atherosclerosis to prevent accumulation and further inflammation in the plaque cores. BMDM display elevated efferocytotic capacity (by their ability to bind apoptotic cells) when ADAM17 is deleted, a phenomenon that does not occur in VSMC. This thesis highlights the important cell-specific roles of ADAM17, along with its protective effect in VSMC in atherosclerosis. </p>