Background: Resistin, an adipokine with inflammatory properties, has been associated with plaque vulnerability. Vascular smooth muscle cells and macrophages are the major cellular components in advanced atherosclerotic plaques and interdependently affect plaque stability. The purpose of this study was to examine the effects of resistin on the interactions of vascular smooth muscle cells and macrophages using co-culture systems. Methods: Human monocytes were differentiated into macrophages. Vascular smooth muscle cells were grown and starved prior to co-culture condition. Indirect co-culture was performed by treating macrophages with resistin at 10 ng/mL for 24 hours with/without εV1-2, a selective protein kinase C epsilon inhibitor. Macrophages supernatants were then used to treat vascular smooth muscle cells for 24 hours. Direct co-culture was performed by culturing macrophages and vascular smooth muscle cells together for 24 to 48 hours. Cultures were evaluated for changes in proliferation, apoptosis, and gene expression of apoptosis, proliferation, and inflammation-associated genes. Results: Macrophages induced vascular smooth muscle cells proliferation, which was further exaggerated in resistin-treated macrophages in the indirect co-culture model. Resistin also upregulated cyclin D1 and proliferating cell nuclear antigen via protein kinase C epsilon in the indirect co-culture. Augmented proliferation was further confirmed in the direct co-culture model, particularly at increased macrophage ratios. However, resistin treatment induced apoptosis in the presence of direct cell to cell interactions. Along with the shift to apoptosis, expressions of caspase 3 and caspase 8 were upregulated. The expression of kappa-light-chain-enhancer of activated B cells 1 and 2 was similar in direct and indirect co-cultures. Conclusion: Resistin promotes a shift from proliferation to apoptosis in vascular smooth muscle cells and macrophage co-culture systems with cellular composition similar to that found in vulnerable regions of plaques. Protein kinase C epsilon mediates the effects of resistin, suggesting that protein kinase C epsilon may represent a therapeutic strategy in resistin-associated atherosclerotic complications.
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