Cross-talk between macrophages and smooth muscle cells impairs collagen and metalloprotease synthesis and promotes angiogenesis.

Coronary atherosclerosis complicated by plaque disruption and thrombosis is a critical event in myocardial infarction and stroke, the major causes of cardiovascular death. In atherogenesis, macrophages (MAC) and smooth muscle cells (SMC) are key actors; they synthesize matrix components and numerous factors involved in the process. Here, we design experiments to investigate whether SMC-MAC communication induces changes in ECM protein composition and/or neo-angiogenesis. Cell to cell communication was achieved using trans-well chambers, where SMCs were grown in the upper chamber and differentiated MAC in the bottom chamber for 24 or 72h. We found that cross-talk between MAC and SMC during co-culture: (i) significantly decreased the expression of ECM proteins (collagen I, III, elastin) in SMC; (ii) increased the expression and activity of metalloprotease MMP-9 and expression of collagenase MMP-1, in both MAC and SMC; (iii) augmented the secretion of soluble VEGF in the conditioned media of cell co-culture and VEGF gene expression in both cell types, compared with control cells. Moreover, the conditioned media collected from MAC-SMC co-culture promoted endothelial cell tube formation in Matrigel, signifying an increased angiogenic effect. In addition, the MAC-SMC communication led to an increase in inflammatory IL-1β and TLR-2, which could be responsible for cellular signaling. In conclusion, MAC-SMC communication affects factors and molecules that could alter ECM composition and neo-angiogenesis, features that could directly dictate the progression of atheroma towards the vulnerable plaque. Targeting the MAC-SMC cross-talk may represent a novel therapeutic strategy to slow-down or retard the plaque progression.