Matrix metalloproteinase 9/neutrophil gelatinase associated lipocalin/tissue inhibitor of metalloproteinasess type 1 complexes are localized within cardiomyocytes and serve as a reservoir of active metalloproteinase in porcine female myocardium.

Matrix metalloproteinase 9 (MMP-9) is crucial for physiological tissue repair and pathophysiological myocardial remodeling. The regulation of its functioning has been shown to be mediated by formation of complexes with tissue inhibitor of metalloproteinases 1 (TIMP-1) and neutrophil gelatinase associated lipocalin (NGAL). We investigated the mRNA and protein expression of MMP-9, TIMP-1 and NGAL, the formation of complexes, their gelatinolytic activity and cellular localization in left ventricle (LV) from 10 female pigs with induced systolic heart failure (HF), 5 control pigs, and a woman with severe HF. The MMP-9, TIMP-1 and NGAL mRNA in LV did not differ between diseased and healthy pigs. In all pigs MMP-9, TIMP-1 and NGAL proteins were present in LV as high molecular weight (HMW) complexes (115, 130, 170 and 220 kDa), and no monomers were found. A 80 and 115 kDa gelatinolytically active bands were present in all LV homogenates. A 130-kDa active band was seen only in LV from pigs with severe HF. Similar results were found in the explanted heart of a female patient with severe HF. The incubation of the homogenates of porcine LV at 37°C resulted in appearance of 88 kDa active band, which was accompanied by a decreased intensity of HMW bands. The incubation of the homogenates of porcine LV (depleted of active MMP-9) with trypsin generated 80 and 115 kDa active bands. Immunohistochemistry revealed the presence of MMP-9 in the cytoplasm of porcine cardiomyocytes, but not in cardiofibroblasts. Our data suggest that MMP-9 originates from cardiomyocytes, forms the gelatinolytically inactive complexes with TIMP-1 and NGAL, present in normal and failing myocardium, likely serving as a reservoir of active MMP-9. Further studies are needed to elucidate the role of these HMW complexes in the extracellular matrix remodeling during the progression of HF, which presence should be considered when developing efficient strategies inhibiting myocardial matrix metalloproteinases.