Matrix metalloproteinase synthesis and expression in isolated LV myocyte preparations

Abstract

In several cardiac disease states, alterations in myocyte and extracellular matrix (ECM) structure occur with left ventricular (LV) remodeling and are associated with changes in matrix metalloproteinase (MMP) activity. Although nonmyocyte cell types have been implicated as sites for synthesis and expression of MMPs within the ECM, whether the LV myocyte itself expresses specific types and active forms of MMPs remains unknown. Accordingly, isolated Ca2+-tolerant LV porcine myocytes (105 cells/ml) in which selective disaggregation and resuspension was performed (13 independent experiments) were plated on basement membrane substrates including Matrigel, collagen IV, laminin, and fibronectin as well as poly-l-lysine. After 24-h incubation, LV myocyte conditioned media were subjected to zymography, a specific MMP-2 proteolytic capture assay, immunoblotting, and ELISA for detection of MMP activity and relative content of the 72-kDa gelatinase MMP-2. Although robust zymographic activity [(pixels ⋅ mm2)/cell] was observed in conditioned media from LV myocytes plated on collagen IV (1,673 ± 297), fibronectin (1,530 ± 281), and poly-l-lysine (2,545 ± 560), proteolytic activity appeared to be lower in conditioned media from LV myocytes plated on Matrigel (842 ± 83) and laminin (1,329 ± 238). MMP-2 proteolytic activity was increased by approximately eightfold in conditioned media taken from LV myocytes plated on poly-l-lysine compared with that of Matrigel. With respect to each of the adhesion substrates, MMP-2 content was at least 50% lower in LV myocyte conditioned media taken from Matrigel and laminin. Immunofluorescent labeling of LV myocytes yielded a strong signal for MMP-2 within the myocyte and along the sarcolemmal surface. In conclusion, this study demonstrated for the first time that adult LV myocytes synthesize and express members of the MMP family and thus may potentially participate in the LV remodeling process through synthesis and secretion of MMPs.