| Summary: | 碩士 === 高雄醫學大學 === 生理及分子醫學研究所 === 98 === Severe sepsis is associated with overproduction of TNF-α and ROS that leads to energy depletion and cellular damage. Both ROS and damaged organelles are inducers of autophagy, which is a protein quality control system to recycle intracellular nutrients in physiological condition. However, the role of autophagy in the pathophysiological condition under septic insult remains uncertain.
To test the hypothesis that autophagy is beneficial for renal function during sepsis, we evaluated the time course correlation between occurrence of autophagy and organ dysfunction after septic insult using a rat model that simulates human peritonitis by cecal ligation and puncture (CLP). Distribution and localization of autophagy were identified first by immunohistochemistry. Level of autophagy was quantified by Western blot analysis of microtubule-associated protein1 light chain 3-II (LC3-II), a marker for autophagy. The level of autophagy and indicators of renal function such as BUN, Creatinine, CCr and proximal tubular reabsorption rate of Sodium and Lithium (TRNa and TRLi) were compared between rapamycin (an autophagy inducer) treated and non-treated groups to delineate the beneficial or harmful role of autophagy during the progression of sepsis.
Our results showed that most of the LC3 aggregation distributed in the renal cortex. Prominent LC3 aggregation mainly localized in Calbindin D28k (Calcium-binding protein D28K; a marker of distal tubule) negative cells. Protein level of LC3-II was elevated transiently at CLP3h but declined at CLP6h till CLP18h. Indicators of renal function such as BUN, Creatinine, CCr, TRNa and TRLi were significantly decreased at CLP6h and became worse at CLP18h. The level of LC3-II was significantly increased at CLP18h in rapamycin treated group compared to the vehicle-treated group. Accordingly, autophagy is transiently increased in proximal tubule at early sepsis and the loss of autophagy is associated with the dysfunction of proximal tubular reabsorption at late stage of sepsis. Although the level of autophagy was elevated at CLP18h but not CLP9h, no significant improvement of renal dysfunction was observed suggesting the enhancement of autophagy at CLP18h may be too late to rescue the renal function. Before further investigation, the possibility that autophagic cell death triggered by septic insult may play a harmful role in renal dysfunction during sepsis still can’t be ruled out.
These results indicate that, the declination of the recycle function of autophagy in proximal tubules is associated with reabsorption failure at late stage of microbial sepsis. Further understanding the role of autophagy in sepsis may provide important information for developing therapeutic strategy for patients of sepsis.
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