Related Experiment Video
Updated: Aug 13, 2025
Visualizing Lung Cellular Adaptations during Combined Ozone and LPS Induced Murine Acute Lung Injury
Published on: March 21, 2021
Role of Myeloid Cell-Specific TLR9 in Mitochondrial DNA-Induced Lung Inflammation in Mice
Kris Genelyn Dimasuay1, Bruce Berg1, Niccolette Schaunaman1
1Department of Medicine, National Jewish Health, 1400 Jackson Street, Room A639, Denver, CO 80206, USA.
Abstract:
Mitochondrial dysfunction is common in various pathological conditions including obesity. Release of mitochondrial DNA (mtDNA) during mitochondrial dysfunction has been shown to play a role in driving the pro-inflammatory response in leukocytes including macrophages. However, the mechanisms by which mtDNA induces leukocyte inflammatory responses in vivo are still unclear. Moreover, how mtDNA is released in an obese setting has not been well understood. By using a mouse model of TLR9 deficiency in myeloid cells (e.g., macrophages), we found that TLR9 signaling in myeloid cells was critical to mtDNA-mediated pro-inflammatory responses such as neutrophil influx and chemokine production. mtDNA release by lung macrophages was enhanced by exposure to palmitic acid (PA), a major saturated fatty acid related to obesity. Moreover, TLR9 contributed to PA-mediated mtDNA release and inflammatory responses. Pathway analysis of RNA-sequencing data in TLR9-sufficient lung macrophages revealed the up-regulation of axon guidance molecule genes and down-regulation of metabolic pathway genes by PA. However, in TLR9-deficient lung macrophages, PA down-regulated axon guidance molecule genes, but up-regulated metabolic pathway genes. Our results suggest that mtDNA utilizes TLR9 signaling in leukocytes to promote lung inflammatory responses in hosts with increased PA. Moreover, TLR9 signaling is involved in the regulation of axon guidance and metabolic pathways in lung macrophages exposed to PA.
Insights
Mitochondrial DNA (mtDNA) release drives inflammation in obesity via Toll-like receptor 9 (TLR9) signaling in myeloid cells. Palmitic acid enhances mtDNA release and inflammatory responses, impacting axon guidance and metabolic pathways.
Area of Science:
- Immunology
- Cell Biology
- Metabolic Diseases
Background:
- Mitochondrial dysfunction and subsequent mitochondrial DNA (mtDNA) release contribute to inflammation in obesity.
- The precise mechanisms of mtDNA-induced leukocyte inflammation in vivo and its release during obesity remain unclear.
- Toll-like receptor 9 (TLR9) is implicated in innate immune responses to nucleic acids.
Purpose of the Study:
- To elucidate the role of TLR9 signaling in myeloid cells in mediating mtDNA-induced inflammatory responses.
- To investigate the mechanisms of mtDNA release in obese settings, specifically the role of palmitic acid (PA).
- To explore the impact of PA and TLR9 on gene expression pathways in lung macrophages.
Main Methods:
- Utilized a mouse model with TLR9 deficiency in myeloid cells.
- Exposed lung macrophages to palmitic acid (PA) to assess mtDNA release and inflammatory markers.
- Performed RNA sequencing and pathway analysis on TLR9-sufficient and TLR9-deficient lung macrophages treated with PA.
Main Results:
- TLR9 signaling in myeloid cells is critical for mtDNA-mediated pro-inflammatory responses, including neutrophil influx and chemokine production.
- Palmitic acid exposure enhanced mtDNA release from lung macrophages and promoted inflammatory responses, with TLR9 contributing to this effect.
- PA altered gene expression in lung macrophages, up-regulating axon guidance molecules and down-regulating metabolic pathways in a TLR9-dependent manner.
Conclusions:
- Mitochondrial DNA utilizes TLR9 signaling in leukocytes to promote lung inflammation in obesity associated with elevated palmitic acid.
- TLR9 signaling plays a significant role in regulating axon guidance and metabolic pathways in lung macrophages exposed to palmitic acid.
- These findings highlight a novel mechanism linking obesity-associated metabolic changes, mitochondrial dysfunction, and inflammatory responses via TLR9.
