Different uptake of native versus aggregated LDL by aortic valve interstitial cells in normolipidemic-like in-vitro conditions

During atherosclerosis disease, macrophages and vascular smooth muscle cells internalize aggregated low density lipoprotein (agLDL) at much greater extent than native LDL (nLDL). Here, primary cultures of aortic valve interstitial cells (AVICs) were treated for 3 up to 21 days with 50 ug/ml blood-derived nLDL or agLDL, alone or combined with pro-calcific culture media, to ascertain whether (i) agLDL are avidly taken up also by AVICs and (ii) treatment with LDL normolipidemic-like concentration can influence AVIC mineralization. Ultrastructurally, uptake by AVICs resulted to be restricted to agLDL, in accordance with chromatographic estimation of large amounts of intracytoplasmic esterified cholesterol and triglycerides after treatment with agLDL alone. Moreover, LDL were found to exert opposite effects on AVIC mineralization, with pro-calcific cell degeneration being mitigated after treatment with nLDL or exacerbated after treatment with agLDL. Consistently, spectrophotometrical estimations revealed calcium amounts to be decreased in the former cultures and increased in the latter cultures. The calcific process was found to depend on intracellular release of lipidic material and its layering at cell edges and cell debris, acting as major hydroxyapatite nucleator, in the same manner previously found for in-vivo experimental and pathological aortic valve mineralization. These preliminary data suggest that agLDL uptake by AVICs might contribute to lipid accumulation within aortic valves, besides affecting valve mineralization even at normolipidemic concentrations, strengthening the concept that valve stenosis is to be conceived as a valve “atherosclerotic lesion”.