Lc3 over-expression improves survival and attenuates lung injury through increasing autophagosomal clearance in septic mice.

OBJECTIVE: To clarify the role of autophagy in sepsis-induced lung injury. BACKGROUND: The role of autophagy as a protective or maladaptive response in lung cells during sepsis has not yet been determined. The lack of specificity of the autophagic process has driven the development of new approaches that assess autophagosomes from formation to fusion with lysosomes. METHODS: Sepsis was induced by cecal ligation and puncture (CLP). The autophagic process was manipulated using the pharmacological inhibitors of the autophagy pathway. Green fluorescent protein (GFP)-microtubule-associated protein 1 light chain 3 (LC3) transgenic mice were further used to determine the role of autophagy. RESULTS: The formation of autophagosomal protein LC3-II progressively accumulated in the lungs over 24 hours after CLP, with the Lc3 gene expression returning to baseline levels at 24 hours. Autophagosome-lysosome fusion, however, gradually decreased from 8 to 24 hours after CLP, suggesting impaired clearance of autophagosomes rather than upregulation of autophagy in the septic lung. In contrast, transgenic mice overexpressing the Lc3 gene exhibited increased clearance of autophagosomes and improved survival after CLP. This protective effect was also seen in decreased cell death, inflammatory responses, neutrophil accumulation, albumin leakage, and edema formation. However, blockade of autophagosome-lysosome fusion with bafilomycin A1 abolished the protective effects in transgenic mice. This indicates that Lc3 transgene attenuates lung injury/inflammation in sepsis, possibly through increasing the clearance of autophagosomes. CONCLUSIONS: Autophagy in the septic lung represents a protective response. However, autophagy, by virtue of excessive autophagosome accumulation, may play a maladaptive role in the late stage of sepsis, leading to acute lung injury.

Complete induction of autophagy is essential for cardioprotection in sepsis.

OBJECTIVE: To investigate the entire process of autophagy in the left ventricle of septic mice, and the functional significance of autophagy by using pharmacological agents. BACKGROUND: Myocardial dysfunction is a common feature in sepsis and contributes to an increased risk of developing multiple organ failure. Autophagy functions predominantly as a prosurvival pathway in the heart during cellular stress. A dynamic process of autophagy that involves the complete activation of autophagy from autophagosome formation to fusion with lysosomes has driven the development of new approaches to detecting autophagy. METHODS: Male mice were subjected to cecal ligation and puncture (CLP) or sham operation. At 1 hour after CLP operation, mice received either rapamycin (induction of autophagy), bafilomycin A1 (inhibition of autophagosomal degradation), or vehicle. RESULTS: The formation of autophagosomes was increased whereas the degradation of autophagosomes was decreased in the left ventricle at 24 hours after CLP. This was consistent with the morphologic finding that septic hearts revealed an increase in autophagosomes but few autolysosomes, indicating incompletion of the autophagic process. Rapamycin, which induced complete activation of autophagy, restored CLP-induced depressed cardiac performances. This cardioprotective effect was also seen in increased ATP levels, and decreased inflammatory responses. Bafiomycin A1, which resulted in incompletion of the autophagic process, did not show any above beneficial effects in CLP mice. CONCLUSIONS: Incompletion of the autophagic process may contribute to sepsis-induced cardiac dysfunction. Treatment with rapamycin may serve a cardioprotective role in sepsis, possibly through the effect of complete induction of autophagy.