Figure 5.

Lp(a) Induces Osteogenic Differentiation in VICs

(A to C) VICs in osteogenic media only conditions were used as the baseline comparator, while addition of TGF-β served as a positive calcification control. One week of exposure to Lp(a) (100 mg/dl) induced gene expression of the inflammatory mediator IL-6 and osteoblastic regulators BMP2 and RUNX2. Pre-incubation with the E06 antibody targeting OxPL reduced the transcriptional effect of Lp(a), suggesting that OxPL is intrinsic to the pro-calcific effects of Lp(a). The role of OxPL was further validated using 2 r-apo(a) constructs that differ in their lysine binding sites and consequently their capacity to bind OxPL. (D to F) Three days of exposure to r-apo(a) 17K-WT construct induced increased expression of osteogenic genes. This effect was reduced with the 17KΔLBS10 construct that lacks the ability to bind OxPL. (G and H) Bright-field microscopy images of VICs after stimulation with 17K constructs. 17K-WT induces an activated, rhomboid shape, whereas 17KΔLBS10 was characterized by a quiescent, spindle-shaped morphology. Data represent mean ± SEM for at least n = 3 independent experiments. *p < 0.05; **p < 0.01; ***p < 0.001 compared with OSM only or comparison between 17K-WT and 17KΔLBS10. 17K-WT = 17 kringles wild-type r-apo(a) construct; 17KΔLBS = 17K r-apo(a) construct without lysine binding site; BMP2 = bone morphogenetic protein 2; E06 = E06 monoclonal antibody; IL-6 = interleukin-6; OSM = osteogenic medium; RUNX2 = Runt-related transcription factor 2; TGF-β = transforming growth factor beta. VIC = valvular interstitial cell.