Abstract 622: Active Transport of Molecules From Macrophages Into Smooth Muscle Cells: A New Hypothesis for Smooth Muscle Cell Fate and Plaque Stability
Vascular smooth muscle cells [VSMC], mononuclear cells [MNC] and their local interaction are known to play key roles in atherosclerotic plaque development and destabilization. To study the cellular interactions an in-vitro co-culture model was established. Peripheral blood MNC were isolated by density gradient centrifugation and marked with fluorescence-labeled acetylated low-density lipoprotein [Fl-ac-LDL]. Mitomycin-treated non-proliferating VSMC were seeded semi-confluently and co-cultured with the labeled MNC in a ratio of 1:3. Immuno-cytochemistry revealed that, within 4 weeks of co-culture, >20% of the VSMC cells had acquired Fl-ac-LDL. Transdifferentiation processes of the MNC into VSMC had not taken place but could be excluded by xenogenic cell composure (rat VSMC and human MNC) and subsequent quantitative RT-PCR with human specific primers for VSMC markers. Separation of the cells in a trans-well co-culture system resulted in complete absence of double-labeled cells, too. Moreover, time-lapse microscopy demonstrated that the VSMC acquired the FL-ac-LDL from the MNC by cell-cell-contact beginning within 6 hours of co-culture. When MNC were marked with FL-ac-LDL, which was loaded with fluorescence-labeled cholesterol, lipid droplets accumulated within the VSMC. Cholesterol positive VSMC acquired phagocytotic activity, resembling foam cells. Besides LDL and cholesterol, MNC transported proteins (GFP) and even fluorescence-labeled mitochondria into VSMC. These results demonstrate an exchange of active molecules from MNC to VSMC. They have intriguing implications for plaque pathophysiology. MNC may modulate VSMC behavior and this way determine the fate of VSMC and plaque stability.