Modulation of elastin by monocytes and their secretions

Abstract

Monocytes are functionally diverse cells that have the capacity to secrete several biologically active molecules that modulate the metabolism of other cell types. To determine the influence of monocyte secreted proteins or live monocytes on the metabolism of cultured smooth muscle cells, a sequence of experiments was designed. Monocyte conditioned medium (MCM) or freshly isolated monocytes were added to smooth muscle cell cultures of various ages. The focus of these studies was the extracellular matrix. Treatment of smooth muscle cell culture with MCM drastically decreased the elastin accumulation in the extracellular matrix. The decrease did not appear until the second or third week after the initial exposure of the cultures when compared to untreated smooth muscle cell cultures, was both dose and time dependent. Live monocytes, when freshly plated onto the smooth muscle cells were active in the solubilization of the existing matrix. Conditioned medium reduced the elastin to a greater extent than live cells under several experimental conditions, suggesting labile inhibitors might be closely associated with the phagocytes. These results show that exposure of the smooth muscle cells to monocyte products reduces the amount of elastin accumulation in the matrix. The mechanism responsible for this novel observation is unknown.