Abnormal mitochondrial fusion–fission balance contributes to the progression of experimental sepsis

Abstract

Sepsis-associated multiple organ failure is a major cause of mortality characterized by a massive increase of reactive oxygen and nitrogen species (ROS/RNS) and mitochondrial dysfunction. Despite intensive research, determining events in the progression or reversal of the disease are incompletely understood. Herein, we studied two prototype sepsis models: endotoxemia and cecal ligation and puncture (CLP)—which showed very different lethality rates (2.5% and 67%, respectively)—, evaluated iNOS, ROS and respiratory chain activity, and investigated mitochondrial biogenesis and dynamics, as possible processes involved in sepsis outcome. Endotoxemia and CLP showed different iNOS, ROS/RNS, and complex activities time-courses. Moreover, these alterations reverted after 24-h endotoxemia but not after CLP. Mitochondrial biogenesis was not elicited during the first 24 h in either model but instead, 50% mtDNA depletion was observed. Mitochondrial fusion and fission were evaluated using real-time PCR of mitofusin-2 (Mfn2), dynamin-related protein-1 (Drp1), and using electron microscopy. During endotoxemia, we observed a decrease of Mfn2-mRNA levels at 4–6 h, and an increase of mitochondrial fragmentation at 6 h. These parameters reverted at 24 h. In contrast, CLP showed not only decreased Mfn2-mRNA levels at 12–18 h but also increased Drp1-mRNA levels at 4 h, and enhanced and sustained mitochondrial fragmentation. The in vivo pretreatment with mdivi-1 (Drp1 inhibitor) significantly attenuated mitochondrial dysfunction and apoptosis in CLP. Therefore, abnormal fusion-to-fission balance, probably evoked by ROS/RNS secondary to iNOS induction, contributes to the progression of sepsis. Pharmacological targeting of Drp1 may be a potential novel therapeutic tool for sepsis.

Keywords::

• nitric oxide
• mitochondria
• lipopolysaccharide
• reactive oxygen species
• iNOS

Acknowledgments

The authors thank Prof Norberto Sanjuan and Margarita López for electron microphotographs.

Declaration of interest

The authors report no declarations of interest. The authors alone are responsible for the content and writing of the paper.

This work was supported by the Agencia Nacional de Promoción Científica y Tecnológica (FONCyT) grant PICT 01625 (to M.C.C.), University of Buenos Aires grant UBACyT M058 and W443 (to J.J.P. and M.C.C.), CONICET grant PIP 0422 (to M.C.C.), and Fundación Pérez Companc, Buenos Aires, Argentina.