Matrix metalloproteinase synthesis and expression in isolated LV myocyte preparations

In several cardiac disease states, alterations in myocyte and extracellular matrix (ECM:) structure occur with left ventricular (LV) remodeling and ar e associated with changes in matrix metalloproteinase (MMP) activity. Altho ugh nonmyocyte cell types have been implicated as sites for synthesis and e xpression of MMPs within the ECM, whether the LV myocyte itself expresses s pecific types and active forms of MMPs remains unknown. Accordingly, isolat ed Ca2+-tolerant LV porcine myocytes (10(5) cells/ml) in which selective di saggregation and resuspension was performed (13 independent experiments) we re plated on basement membrane substrates including Matrigel, collagen TV, laminin, and fibronectin as well as poly-L-lysine. After 24-h incubation, L V myocyte conditioned media were subjected to zymography, a specific MMP-2 proteolytic capture assay, immunoblotting, and ELISA for detection of MMP a ctivity and relative content of the 72-kDa gelatinase MMP-2. Although robus t zymographic activity [(pixels.mm(2))/cell] was observed in conditioned me dia from LV myocytes plated on collagen IV (1,673 +/- 297), fibronectin (1, 530 +/- 281), and poly-L-lysine (2,545 +/- 560), proteolytic activity appea red to be lower in conditioned media from LV myocytes plated on Matrigel (8 42 +/- 83) and laminin (1,329 +/- 238). MMP-8 proteolytic activity was incr eased by approximately eightfold in conditioned media taken from LV myocyte s plated on poly-L-lysine compared with that of Matrigel. With respect to e ach of the adhesion substrates, MMP-2 content was at least 50% lower in LV myocyte conditioned media taken from Matrigel and laminin. Immunofluorescen t labeling of LV myocytes yielded a strong signal for MMP-2 within the myoc yte and along the sarcolemmal surface. In conclusion, this study demonstrat ed for the first time that adult LV myocytes synthesize and express members of the MMP family and thus may potentially participate in the LV remodelin g process through synthesis and secretion of MMPs.