Mesenchymal Stromal Cells Deficient in Autophagy Proteins Are Susceptible to Oxidative Injury and Mitochondrial Dysfunction.

Oxidative stress resulting from inflammatory responses that occur during acute lung injury and sepsis can initiate changes in mitochondrial function. Autophagy regulates cellular processes in the setting of acute lung injury, sepsis, and oxidative stress by modulating the immune response and facilitating turnover of damaged cellular components. We have shown that mesenchymal stromal cells (MSCs) improve survival in murine models of sepsis by also regulating the immune response. However, the effect of autophagy on MSCs and MSC mitochondrial function during oxidative stress is unknown. This study investigated the effect of depletion of autophagic protein microtubule-associated protein 1 light chain 3B (LC3B) and beclin 1 (BECN1) on the response of MSCs to oxidative stress. MSCs were isolated from wild-type (WT) and LC3B-/- or Becn1+/- mice. MSCs from the LC3B-/- and Becn1+/- animals had increased susceptibility to oxidative stress-induced cell death as compared with WT MSCs. The MSCs depleted of autophagic proteins also had impaired mitochondrial function (decreased intracellular ATP, reduced mitochondrial membrane potential, and increased mitochondrial reactive oxygen species production) under oxidative stress as compared with WT MSCs. In WT MSCs, carbon monoxide (CO) preconditioning enhanced autophagy and mitophagy, and rescued the cells from oxidative stress-induced death. CO preconditioning was not able to rescue the decreased survival of MSCs from the LC3B-/- and Becn1+/- animals, further supporting the tenet that CO exerts its cytoprotective effects via the autophagy pathway.

Carbon monoxide confers protection in sepsis by enhancing beclin 1-dependent autophagy and phagocytosis.

AIMS: Sepsis, a systemic inflammatory response to infection, represents the leading cause of death in critically ill patients. However, the pathogenesis of sepsis remains incompletely understood. Carbon monoxide (CO), when administered at low physiologic doses, can modulate cell proliferation, apoptosis, and inflammation in pre-clinical tissue injury models, though its mechanism of action in sepsis remains unclear. RESULTS: CO (250 ppm) inhalation increased the survival of C57BL/6J mice injured by cecal ligation and puncture (CLP) through the induction of autophagy, the down-regulation of pro-inflammatory cytokines, and by decreasing the levels of bacteria in blood and vital organs, such as the lung and liver. Mice deficient in the autophagic protein, Beclin 1 (Becn1(+/-)) were more susceptible to CLP-induced sepsis, and unresponsive to CO therapy, relative to their corresponding wild-type (Becn1(+/+)) littermate mice. In contrast, mice deficient in autophagic protein microtubule-associated protein-1 light chain 3B (LC3B) (Map1lc3b(-/-)) and their corresponding wild-type (Map1lc3b(+/+)) mice showed no differences in survival or response to CO, during CLP-induced sepsis. CO enhanced bacterial phagocytosis in Becn1(+/+) but not Becn1(+/-) mice in vivo and in corresponding cultured macrophages. CO also enhanced Beclin 1-dependent induction of macrophage protein signaling lymphocyte-activation molecule, a regulator of phagocytosis. INNOVATION: Our findings demonstrate a novel protective effect of CO in sepsis, dependent on autophagy protein Beclin 1, in a murine model of CLP-induced polymicrobial sepsis. CONCLUSION: CO increases the survival of mice injured by CLP through systemic enhancement of autophagy and phagocytosis. Taken together, we suggest that CO gas may represent a novel therapy for patients with sepsis.