Sepsis Induces Extensive Autophagy and Mitochondrial Damage in Human and Mouse Liver
PE Swanson, E Watanabe, JT Muenzer, RS Hotchkiss. University of Washington, Seattle, WA; Washington University, St. Louis, MO
Background: Autophagy is a regulated process by which a cell degrades and recycles its own components; it can be triggered as an adaptive response during times of stress. Incorporation of organelles and cytoplasm into lysosomes (autolysosomes/autophagosomes) constitutes morphologic evidence of this process. The purpose of this study was to determine to what extent organellar damage and autophagy occurs in hepatocytes during sepsis.
Design: Electron microscopy (EM) was performed on post-mortem liver samples from 6 septic patients (obtained within 90 minutes of death) and from 4 control patients who had elective liver resection. Liver specimens were also obtained 24 hours after surgery from 4 sham-operated mice and 4 mice with sepsis surgery (cecal ligation and puncture - CLP). All samples were fixed and processed in a routine fashion. The number of autophagosomes was derived from 2500x magnification survey images (3000 ) to avoid sample bias; counts were performed in a blinded fashion on randomly sequenced images. Patterns of organellar injury were based on higher magnification images (15000-40000x) that were biased in favor of abnormal findings.
Results: Autophagosomes were more numerous in septic patients: 5.3 3.3 vs. 1.2 1.5 (mean SD) autophagosomes per image in sepsis vs. controls, respectively (p<0.001). Mitochondrial membrane abnormalities, including herniation of outer membranes into adjacent organelles, vacuolar change in cristae and myelin figures were seen in sepsis samples, but not controls. Nuclei and other hepatocyte organelles showed no consistent abnormality. Residual bodies were not more common in sepsis. Murine sepsis paralleled human studies, with 38.73.9 and 7.21.9 autophagosomes in septic and sham mice, respectively (p = 0.002). Autophagosomes incorporated lipid droplets in murine, but not human, samples. Neither necrotic nor apoptotic cell death was observed.
Conclusions: Hepatocyte autophagosomes are increased during sepsis in both humans and mice. The reproducible presence of mitochondrial membrane changes suggests both a source of organellar material in sepsis-induced autophagy and an underlying pattern of sepsis-related cell injury. The similarities between human and murine samples emphasizes the value of murine CLP-induced sepsis as a model of human disease.
Monday, March 9, 2009 1:00 PM
Poster Session II # 201, Monday Afternoon