Potential pathological roles for oxidized low-density lipoprotein and scavenger receptors SR-AI, CD36, and LOX-1 in aortic valve stenosis

- We studied mechanisms by which OxLDL may contribute to aortic valve stenosis (AVS).
- Scavenger receptors SR-A1, CD36, and LOX-1 are locally expressed in aortic valves.
- Changes in scavenger receptor expression in AVS favor inflammation and angiogenesis.
- Mast cells and TNF alpha induce LOX-1 expression in cultured valvular myofibroblasts.
- Myofibroblasts from AVS patients take up more oxLDL than those from control subjects.

ObjectiveTo clarify the potential mechanisms by which oxidized low-density lipoprotein (oxLDL) could contribute to the progression of aortic valve stenosis (AVS).MethodsWe investigated a total of 46 stenotic and 20 control human aortic valves. The mRNA expression levels of scavenger receptor class A type 1 (SR-A1), CD36, Lectin-like oxidized LDL receptor-1 (LOX-1), and scavenger receptor class B type 1 (SR-B1) were studied using qPCR. Their cellular distribution in the valves was assessed by immunohistochemistry, and the potential effects of oxLDL were studied in cultured myofibroblasts isolated from the aortic valves.ResultsIn AVS, the proinflammatory SR-A1 and the angiogenic LOX-1 were upregulated (p = 0.003 and p = 0.002), whereas the antiangiogenic CD36 was downregulated (p = 0.02). The expression of the atheroprotective SR-B1 remained unchanged. Immunohistochemistry revealed that SR-A1 was expressed by macrophages, whereas the expression of CD36 and LOX-1 was confined to myofibroblasts and endothelial cells in the diseased valves. In cultured valvular myofibroblasts, mast cell-derived components and TNF-α induced LOX-1 expression (p = 0.05 and p < 0.001), whereas oxLDL promoted the expression of proinflammatory cytokines. Furthermore, the expression of osteoprotegerin, an inhibitor of valvular calcification, decreased in response to oxLDL. Finally, myofibroblasts derived from stenotic valves accumulated more DiI-labeled oxLDL than myofibroblasts derived from macroscopically healthy valves (p = 0.035), so revealing enhanced foam cell-forming potential of myofibroblasts in the diseased valves.ConclusionThis study unveils the presence of SR-A1, CD36, and LOX-1 in aortic valves and suggests potential mechanisms by which they may contribute to the pathological angiogenesis, inflammation, calcification, and lipid accumulation in AVS.