Experimental Hindlimb Ischemia Increases Neutrophil-Mediated Matrix Metalloproteinase Activity: A Potential Mechanism for Lung Injury After Limb Ischemia

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Abstract
Background Acute limb ischemia initiates a systemic inflammatory response, including pulmonary polymorphonuclear leukocyte (PMN) sequestration and acute lung injury. Lung injury is partly attributed to release by PMN’s of extracellular matrix (ECM) modifying metalloproteinases (MMPs). We hypothesized that acute hindlimb ischemia (HI) would increase MMP activity in the lung and other organs and that systemic neutrophil depletion before HI would block this effect. Study design Seventeen FVB/N Tie2/LacZ-182 SATO female mice were randomly divided into four groups: HI + PBS (Group 1), HI + antineutrophil antibody (Group 2), HI + isotype matched control antibody (Group 3), and no HI + PBS (Group 4). HI was achieved by unilateral femoral artery ligation. Neutrophil depletion was confirmed. Three days postligation, lung, liver, and kidney were harvested. MMP-2 and -9 expression and activation (gelatin zymography) and membrane type-1 MMP (MT1-MMP, western blotting) were quantified by densitometry and NIH Image Analysis software. Statistical significance was determined with an analysis of variance. Results Zymograms revealed a 46% increase in pulmonary proMMP-9 in Group 1 versus Group 4 (6,107 ± 472 [mean ± SEM] densitometry units [DU] versus 3,287 ± 675 DU, p < 0.05). A similar trend was observed for active MMP-9 (3,189 ± 541 DU versus 1,417 ± 927 DU, p = 0.16). Neutrophil depletion (Group 2) decreased proMMP-9 levels by 51% (2,996 ± 314 DU versus 6,107 ± 472 DU, p < 0.05) and active MMP-9 by 75% (810 ± 444 DU versus 3,189 ± 541 DU, p < 0.05) compared with Group 1. Active MMP-2 increased 51% after HI (Group 1, 3,230 ± 86 DU versus Group 4, 1,599 ± 327 DU, p < 0.05). Neutrophil depletion decreased the HI-induced activation of MMP-2 by 43% (Group 2, 1,829 ± 471 DU versus Group 1, 3,230 ± 86 DU, p < 0.05). Conclusions HI increases pulmonary proMMP-9, active MMP-9, and active MMP-2 levels. Neutrophil depletion blocks this effect. These data suggest that acute limb ischemia leads to PMN-mediated changes in MMP activity.