Effects of Mesenchymal Stem Cell Therapy on the Time Course of Pulmonary Remodeling Depend on the Etiology of Lung Injury in Mice

Objective: Recent evidence suggests that mesenchymal stem cells may attenuate lung inflammation and fibrosis in acute lung injury. However, so far, no study has investigated the effects of mesenchymal stem cell therapy on the time course of the structural, mechanical, and remodeling properties in pulmonary or extrapulmonary acute lung injury. Design: Prospective randomized controlled experimental study. Setting: University research laboratory. Subjects: One hundred forty-three females and 24 male C57BL/6 mice. Interventions: Control mice received saline solution intratracheally (0.05 mL, pulmonary control) or intraperitoneally (0.5 mL, extrapulmonary control). Acute lung injury mice received Escherichia coli lipopolysaccharide intratracheally (2 mg/kg in 0.05 mL of saline/mouse, pulmonary acute lung injury) or intraperitoneally (20 mg/kg in 0.5 mL of saline/mouse, extrapulmonary acute lung injury). Mesenchymal stem cells were intravenously injected (IV, 1 x 10(5) cells in 0.05 mL of saline/mouse) 1 day after lipopolysaccharide administration. Measurements and Main Results: At days 1, 2, and 7, static lung elastance and the amount of alveolar collapse were similar in pulmonary and extrapulmonary acute lung injury groups. Inflammation was markedly increased at day 2 in both acute lung injury groups as evidenced by neutrophil infiltration and levels of cytokines in bronchoalveolar lavage fluid and lung tissue. Conversely, collagen deposition was only documented in pulmonary acute lung injury. Mesenchymal stem cell mitigated changes in elastance, alveolar collapse, and inflammation at days 2 and 7. Compared with extrapulmonary acute lung injury, mesenchymal stem cell decreased collagen deposition only in pulmonary acute lung injury. Furthermore, mesenchymal stem cell increased metalloproteinase-8 expression and decreased expression of tissue inhibitor of metalloproteinase-1 in pulmonary acute lung injury, suggesting that mesenchymal stem cells may have an effect on the remodeling process. This change may be related to a shift in macrophage phenotype from M1 (inflammatory and antimicrobial) to M2 (wound repair and inflammation resolution) phenotype. Conclusions: Mesenchymal stem cell therapy improves lung function through modulation of the inflammatory and remodeling processes. In pulmonary acute lung injury, a reduction in collagen fiber content was observed associated with a balance between metalloproteinase-8 and tissue inhibitor of metalloproteinase-1 expressions.