Mitochondrial DAMPs Increase Endothelial Permeability through Neutrophil Dependent and Independent Pathways

Abstract

Trauma and sepsis can cause acute lung injury (ALI) and Acute Respiratory Distress Syndrome (ARDS) in part by triggering neutrophil (PMN)-mediated increases in endothelial cell (EC) permeability. We had shown that mitochondrial (mt) damage-associated molecular patterns (DAMPs) appear in the blood after injury or shock and activate human PMN. So we now hypothesized that mitochondrial DAMPs (MTD) like mitochondrial DNA (mtDNA) and peptides might play a role in increased EC permeability during systemic inflammation and proceeded to evaluate the underlying mechanisms. MtDNA induced changes in EC permeability occurred in two phases: a brief, PMN-independent ‘spike’ in permeability was followed by a prolonged PMN-dependent increase in permeability. Fragmented mitochondria (MTD) caused PMN-independent increase in EC permeability that were abolished with protease treatment. Exposure to mtDNA caused PMN-EC adherence by activating expression of adherence molecule expression in both cell types. Cellular activation was manifested as an increase in PMN calcium flux and EC MAPK phosphorylation. Permeability and PMN adherence were attenuated by endosomal TLR inhibitors. EC lacked formyl peptide receptors but were nonetheless activated by mt-proteins, showing that non-formylated mt-protein DAMPs can activate EC. Mitochondrial DAMPs can be released into the circulation by many processes that cause cell injury and lead to pathologic endothelial permeability. We show here that mitochondria contain multiple DAMP motifs that can act on EC and/or PMN via multiple pathways. This can enhance PMN adherence to EC, activate PMN-EC interactions and subsequently increase systemic endothelial permeability. Mitochondrial DAMPs may be important therapeutic targets in conditions where inflammation pathologically increases endothelial permeability.

Mitochondria in lung disease

“…We have previously shown that mtDNA released from dysfunctional mitochondria in response to stress and/or infection activates the NLRP3 inflammasome (86) and that circulating extracellular mtDNA is associated with mortality in medical intensive care unit (ICU) patients (45). Others have replicated these findings (87,88) and shown that mtDNA also activates the DNA sensor cyclic GMP-AMP synthase (cGAS) (89) intracellularly and activates neutrophils (87), vascular endothelial cells (90), and AMs extracellularly (91). Injection of mitochondrial lysates in the rat causes lung inflammation (87), and mtDNA released as a result of injury in murine models of PF stimulates TGF-β1 release from AECs (92).…”

“…Activates the NLRP3 inflammasome intracellularly (86,88) and activates neutrophils, vascular endothelial cells (90), and AMs extracellularly (40,91) Stimulates TGF-β1 from AECs (92) Activates the NLRP3 inflammasome (86,88) and cGAS (89) Circulating mtDNA as plasma biomarker in medical ICU patients (45) mtDNA increased in a human IPF (61) and murine PQ model of PF (92) mtDNA haplogroups confer susceptibility to COPD (65) mtDNA haplogroups influence atopic diathesis (64) mtDNA abnormalities and asthma (60,62,63) mtDNA mutations and PH (58) mtDNA mutations and lung cancer (59)…”

Extracellular Ribonucleic Acids (RNA) Enter the Stage in Cardiovascular Disease

“…One important function elicited by eRNA is the induction of a robust and immediate rise in intracellular calcium ions in endothelial cells, associated with an increase in vascular permeability. 57,58 Vascular endothelial growth factor (VEGF) serves as a primary multifunctional endothelial permeability and growth factor, promoting several signal transduction pathways to induce angiogenesis, wound repair, and blood vessel regeneration. 59 eRNA can directly interact with VEGF to increase the mobilization and local concentration of this cytokine, thereby provoking VEGF-mediated signal transduction via VEGF receptor-2 and neuropilin-1.…”

The Roles of Mitochondrial Damage-Associated Molecular Patterns in Diseases

“…NLRP3 inflammasome activation (107,142). Adhesion of neutrophils and endothelial cells (153). Activation of TLR9 and NF-jB.…”