Sepsis Induces Extensive Autophagic Vacuolization in Hepatocytes –a clinical and laboratory based study

Abstract

Autophagy is the regulated process cells use to recycle non-essential, redundant, or inefficient components and is an adaptive response during times of stress. In addition to its role in enabling the cell to gain vital nutrients in times of stress, autophagy can also be involved in elimination of intracellular microorganisms, tumor suppression, and antigen presentation. Because of difficulty in diagnosing autophagy, few clinical studies have been performed. This study examined whether autophagy occurs in hepatocytes during sepsis. Electron microscopy (EM) was performed on liver samples obtained from both an observational clinical cohort of 6 septic patients and 4 control patients as well as liver specimens from mice with surgical sepsis (via cecal ligation and puncture (CLP)) or sham operation. EM demonstrated increased autophagic vacuoles in septic versus non-septic patients. Randomly selected fields (3,000 square microns) from control and septic patients contained 1.2 ± 1.5 versus 5.3 ± 3.3 (mean ± SD) complex lysosomal/autophagolysosomal structures per image respectively ( P<0.001). In rare instances, hepatocytes with autophagic vacuoles appeared to be unequivocally committed to death. Membrane alterations (membrane vacuoles, invagination into adjacent organelles and myelin figure-like changes) occur in a subpopulation of mitochondria in sepsis, but other hepatocyte organelles showed no consistent ultrastructural injury. Findings in murine sepsis paralleled those of patients, with 7.2 ± 1.9 versus 38.7 ± 3.9 lysosomal/autophagolysosomal structures in sham and septic mice, respectively ( P =0.002). Quantitative RT-PCR demonstrated that sepsis-induced the upregulation of select apoptosis and cytokine gene expression with minimal changes in the core autophagy genes in liver. In conclusion, hepatocyte autophagic vacuolization increases during sepsis and is associated with mitochondrial injury. However, it is not possible to determine whether the increase in autophagic vacuolization is an adaptive response or a harbinger of cell death.