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Mitochondrial density contributes to the immune response of macrophages to lipopolysaccharide via the MAPK pathway
Emiko Kasahara1, Atsuo Sekiyama, Mika Hori
1Department of Biochemistry and Molecular Pathology, Osaka City University Graduate School of Medicine, Abeno, Osaka, Japan. kasahara@med.osaka-cu.ac.jp
Abstract:
We investigated the role of mitochondrial reactive oxygen species (ROS) in the response of macrophages to lipopolysaccharide (LPS) using RAW 264.7 cells and their ρ(o) cells lacking mitochondria. Mitochondrial density, respiratory activity and related proteins in ρ(o) cells were significantly lower than those in RAW cells. LPS rapidly stimulated mitochondrial ROS prior to cytokine secretion, such as TNF-α and IL-6, from RAW 264.7 cells by activating the MAPK pathway, while the response was attenuated in ρ(o) cells. Exposure of ρ(o) cells to H(2)O(2) partially restored the secretion of cytokines induced by LPS. These results suggest that mitochondrial density and/or the respiratory state contribute to intracellular oxidative stress, which is responsible for the stimulation of LPS-induced MAPK signaling to enhance cytokine release from macrophages.
Insights
Mitochondria generate reactive oxygen species (ROS) that activate macrophage signaling pathways. This oxidative stress is crucial for lipopolysaccharide (LPS)-induced cytokine release, highlighting mitochondria's role in immune responses.
Area of Science:
- Immunology
- Cell Biology
- Mitochondrial Biology
Background:
- Macrophages are key immune cells that respond to pathogens like lipopolysaccharide (LPS).
- Mitochondria are organelles involved in cellular respiration and energy production.
- Mitochondrial reactive oxygen species (ROS) are implicated in cellular signaling pathways.
Purpose of the Study:
- To investigate the role of mitochondrial ROS in macrophage activation by LPS.
- To determine the contribution of mitochondrial function to LPS-induced inflammatory responses.
Main Methods:
- Utilized RAW 264.7 macrophage cell line and their mitochondrial-deficient ρ(o) counterparts.
- Assessed mitochondrial density, respiratory activity, and protein levels.
- Measured ROS production, MAPK pathway activation, and cytokine (TNF-α, IL-6) secretion following LPS stimulation.
- Administered hydrogen peroxide (H2O2) to ρ(o) cells to assess partial restoration of function.
Main Results:
- ρ(o) cells exhibited significantly lower mitochondrial density and respiratory activity compared to RAW 264.7 cells.
- LPS rapidly induced mitochondrial ROS in RAW 264.7 cells, preceding cytokine secretion via MAPK pathway activation.
- LPS-induced responses, including cytokine secretion, were attenuated in ρ(o) cells.
- H2O2 treatment partially restored LPS-induced cytokine secretion in ρ(o) cells.
Conclusions:
- Mitochondrial density and respiratory state are critical for generating oxidative stress in macrophages.
- This mitochondrial-derived oxidative stress is essential for activating the MAPK pathway in response to LPS.
- Mitochondria play a significant role in regulating LPS-induced inflammatory cytokine release from macrophages.
