MMP9 and acute lung injury: Previous studies have demonstrated that high tidal volume (VT) mechanical ventilation may upregulate Src, Smads, and the production of inflammatory cytokines, including tumor necrosis factor-α (TNF-α), macrophage inflammatory protein-2 (MIP-2), and matrix metalloproteinase-9 (MMP-9) in acute lung injury (ALI) [4, 7–13].